The severe dependence of oxygen reduction reaction (ORR) in fuel cells on platinum (Pt)-based catalysts greatly limits the process of their commercialization. Therefore, developing cost-reasonable non-precious-metal catalysts to replace Pt-based catalysts for ORR is an urgent task. Here, we use the composite of inexpensive polyaniline and superfine polytetrafluoroethylene powder as precursor to synthesize a metal-free N,F-codoped porous carbon catalyst (N,F-Carbon). Results indicate that the N,F-Carbon catalyst obtained at the optimized temperature 1000 °C exhibits almost the same onset (0.97 V vs RHE) and half-wave potential (0.84 V vs RHE) and better durability and higher crossover resistance in alkaline medium compared to commercial 20% Pt/C, which is attributed to the good dispersion of fluorine and nitrogen atoms in the carbon matrix, high specific surface area, and the synergistic effects of fluorine and nitrogen on the polarization of adjacent carbon atoms. This work provides a new strategy for in situ synthesis of N,F-codoped porous carbon as highly efficient metal-free electrocatalyst for ORR in fuel cells.Keywords: metal-free electrocatalysts; N,F-codoped porous carbon; oxygen reduction reaction; polyaniline-based composite; polytetrafluoroethylene;

The donor–acceptor codoping is an effective approach to tune the photoelectrochemical properties of TiO2. Here, we systematically investigate the effects of (I+N) codoping on the electronic structures and H2O splitting reactions of anatase TiO2 by using density functional theory. It is found that the codoping of the stable charge-compensated (I+N) donor–acceptor pair in anatase TiO2 not only can prevent the recombination of photogenerated electron–hole pairs but also can effectively reduce the band gap to 2.251 eV by forming an intermediate band within the band gap. The band edge alignment of (I+N) codoped TiO2 is desirable for H2O splitting, and the calculated optical absorption curve of (I+N) codoped TiO2 verifies that (I+N) codoping can significantly improve visible-light absorption. Moreover, we also calculate the chemical reaction pathways of H2 generation via H2O splitting on (I+N) codoped TiO2 surfaces by using the climbing nudged elastic band (cNEB) method and find that the (I+N) codoping in TiO2 can efficiently reduce the energy barrier of H2 production by about 1.0 eV. These findings imply that the (I+N) codoped anatase TiO2 is a promising visible-light photocatalyst for H2O splitting.

Efficient carbon capture is an essential step in many energy-related processes. Here, we use molecular dynamics simulations and free energy analysis to investigate the inherent implication of the ZIF-8/glycol slurry based adsorption and absorption hybrid technique for carbon capture. Our results reveal that the formation of two-layer ordered hydrogen bond (HB) networks of glycol molecules on the ZIF-8 surface is the physical origin of the high efficiency of using ZIF-8/glycol slurry for carbon capture. It is found that the film composed of two-layer HB networks acts as a selective gatekeeper, allowing the penetration of CO2 molecules but efficiently blocking CH4. The interaction between the HB-forming solvent and ZIF-8 is the key to the formation of the semipermeable film, while the solute–solvent interaction is essential for film crossing. Finally, we discuss the basis for the design of highly efficient nanopore/slurry system for filtering and separation technologies. The uncovered mechanism for the hybrid technique opens up an exciting strategy for highly efficient CO2 separation.

It is still a challenge to find high-efficiency adsorbents for the separation of noble gases. In this work, we combine the grand canonical Monte Carlo (GCMC) simulation and adsorption integral equation to theoretically characterize the pore size distribution (PSD) of experimentally synthesized nitrogen-doped nanoporous carbon (Carbon-ZX) and further predict the selectivity of Carbon-ZX for Xe/Kr, Xe/Ar, and Rn/N2 mixtures. Results indicate that the selectivities of Carbon-ZX for Xe/Kr and Xe/Ar apparently are greater than that of other MOFs in the same conditions, which also is further confirmed by Henry’s constant and isosteric adsorption heat. Moreover, the Carbon-ZX for the Rn/N2 binary mixture shows the extremely high selectivity (about 800–1200) in the molar fraction XRn < 0.001, which means that Carbon-ZX is a promising candidate for indoor Rn capture. In short, this work provides a useful method to characterize the experimentally synthesized nanoporous materials and further explores their applications in adsorption and separation.

Development of an efficient photocatalyst with both strong visible light absorption and high charge mobility is highly desirable but still remains a great challenge. In this work, we use density functional theory (DFT) calculations to investigate the electronic structure and the surface activity of M-doped (M = transition metals V, Cr, Mn, Zr, Nb and Mo) and M–N-codoped (N = nitrogen) SrTiO3(001) perovskite surfaces in order to obtain the optimal photocatalytic material with both strong visible light absorption and high charge mobility. Results indicate that the N–Nb codoped SrTiO3(001) surface possesses not only a suitable band gap of 1.90 eV, but also desirable strong visible light absorption and high charge mobility. In addition, by exploring the adsorption and decomposition behavior of water on these modified surfaces, we found that the N–Nb codoped SrTiO3(001) surface not only has band alignments well positioned for the feasibility of photooxidation and photo-reduction of water, but also significantly reduces the activation energy of the water decomposition reaction. Therefore, the N–Nb codoped SrTiO3(001) surface designed here is a very promising candidate for water splitting in the visible light region, which provides a theoretical basis for designing new photocatalytic materials.

In this study, we synthesize a luminescent porous organic polymer nanotube (PNT-1) through copolymerization of the monomers 1,3,5-tris-(3-bromo-phenyl)-[1,3,5]triazine (TBT) and 2,6-dibromopyridine (2,6-DP) by Ni-catalyzed Yamamoto reaction. Results indicate that PNT-1 exhibits high luminescence intensity, stability and reusability, and it can be used as an efficient luminescent probe for sensitively and selectively sensing H2S. Furthermore, we also use UV-absorption as well as EDS and XPS spectra to further explore the luminescence quenching mechanism of PNT-1 as a luminescent probe for sensing H2S. All the results reveal that the formation of N–S bond between PNT-1 and H2S makes the electron in PNT-1 more stable and therefore leads to the luminescence quenching effect of PNT-1 for sensing H2S. Moreover, we also find that PNT-1 as a luminescent probe is still applicable for sensing H2S in vitro assay system simulated using PBS buffer solution.

•Flexible conductive polydimethylsiloxane metacomposites were prepared.•Negative permittivity was observed in the nanocomposites.•Induced electric dipoles attributed to the negative permittivity.Metacomposites with negative electromagnetic parameters can be promising substitute for periodic metamaterials. In this paper, we devoted to fabricating flexible metacomposite films, which have great potential applications in the field of wearable cloaks, sensing, perfect absorption and stretchable electronic devices. The conductivity and the complex permittivity were investigated in flexible polydimethylsiloxane (PDMS)/multi-walled carbon nanotubes (MWCNTs) membranous nanocomposites, which were fabricated via in-situ polymerization process. With the increase of conductive one-dimension carbon nanotubes concentration, there was a percolation transition observed in conduction due to the formation of continuous networks. The dielectric dispersion behavior was also analyzed in the spectra of complex permittivity. It is indicated that the conduction and polarization make a combined effect on the dielectric loss in flexible PDMS/MWCNTs composites. The negative permittivity with a dielectric resonance was obtained, and was attributed to the induced electric dipoles.Download high-res image (226KB)Download full-size image

•We use ZIF as a template to synthesize three nitrogen-doped porous carbons.•The as-synthesized Carbon-ZD can almost completely remove the methylene blue (MB) pollutant from wastewater.•The as-synthesized Carbon-ZD also shows extremely high adsorption capacity (1148 mg/g) of MB.•The Carbon-ZD possesses excellent regeneration and reusability.Dyes as one of organic pollutants have received increasing attention due to its harmful effects on many forms of life, in which methylene blue (MB) is often considered as a model organic pollutant for experimental measurement. In this work, we synthesize three ZIF-derived N-doped porous carbon adsorbents and further investigate their performance of removing MB from wastewater. Results indicate that MB saturated adsorption capacities of Carbon-ZD, Carbon-ZS, Carbon-Z are 1148.2, 791.3 and 505.3 mg/g, respectively, which means that Carbon-ZD is a better MB adsorbent, compared to the other two. Moreover, when the excessive adsorbents are used to treat wastewater containing MB pollutant, Carbon-ZD can almost completely remove the MB pollutant, because the removal percent of Carbon-ZD is almost 100%, which means that Carbon-ZD is an excellent candidate for MB removal from wastewater. Further experiments indicate that Carbon-ZD also possesses excellent regeneration and reusability, as well as anti-interference ability when MO and MB pollutants coexist in wastewater. To explore adsorption kinetic and thermodynamics, we also found that the pseudo-second order model can satisfyingly describe MB adsorption kinetics and the Langmuir model can well describe MB adsorption isotherm. The excellent performance of Carbon-ZD for MB removal from wastewater is mainly attributed to the high BET specific surface area, suitable pore size distribution and nitrogen-doping. It is expected that the strategy of rationally designing ZIF or MOF template to prepare nitrogen-doped porous carbon adsorbents can open a new way to develop highly efficient adsorbents for removing pollutants in wastewater.Download high-res image (119KB)Download full-size image

Two porous organic polymer nanotubes (PNT-2 and PNT-3) were synthesized via Ni-catalyzed Yamamoto reaction, using 2,4,6-tris-(4-bromo-phenyl)-[1,3,5]-triazine (TBT) as one monomer, and 2,7-dibromopyrene (DBP) or 1,3,6,8-tetrabromopyrene (TBP) as another monomer. The scanning electron microscope (SEM) images show that both PNT-2 and PNT-3 possess clear hollow tube structures. Luminescent measurements indicate that both PNT-2 and PNT-3 can serve as luminescent probe for highly selective and sensitive detection of Fe3+ by luminescent quenching effect. Absorption competition quenching (ACQ) mechanism is also proposed to explain luminescent quenching behavior, i.e., the overlap of the UV-spectra between Fe3+ and PNTs causes the energy competition, and therefore leads to luminescent quenching. Moreover, both PNT-2 and PNT-3 still show high selectivity and sensitivity for sensing Fe3+ in 10% ethanol aqueous solution, which means that the two porous PNTs are promising candidates as luminescent probes for detecting Fe3+ in practical applications.

It remains a huge challenge to develop nonprecious electrocatalysts with high activity to substitute commercial Pt catalysts for oxygen reduction reactions (ORR). Here, the Cu,N-codoped hierarchical porous carbon (Cu–N–C) with a high content of pyridinic N was synthesized by carbonizing Cu-containing ZIF-8. Results indicate that Cu–N–C shows excellent ORR electrocatalyst properties. First of all, it nearly follows the four-electron route, and its electron transfer number reaches 3.92 at −0.4 V. Second, both the onset potential and limited current density of Cu–N–C are almost equal to those of a commercial Pt/C catalyst. Third, it exhibits a better half-wave potential (∼16 mV) than a commercial Pt/C catalyst. More importantly, the Cu–N–C displays better stability and methanol tolerance than the Pt/C catalyst. All of these good properties are attributed to hierarchical structure, high pyridinic N content, and the synergism of Cu and N dopants. The metal–N codoping strategy can significantly enhance the activity of electrocatalysts, and it will provide reference for the design of novel N-doped porous carbon ORR catalysts.Keywords: Cu; hierarchical pores; N-codoped porous carbon; ORR; pyridinic N

Shale oil is an important unconventional resource gathered in shales with nanoscale pores. In this work molecular dynamics simulations were performed to investigate the diffusion of shale oil in the clay-rich shale. The montmorillonite model was used to represent the clay-rich shale, and octane was used as a shale oil model. Results show that the diffusion coefficient of shale oils is extremely small in the basal spacing of 2.8 nm, and with the increase of basal spacing, the diffusion coefficient increases by several orders of magnitude. This observation indicates that once the shale oils flow from microscopic pores into the mesoscopic pores, it would be accompanied by the decrease of oil density and extreme increase of diffusion coefficient, which is very beneficial for exploitation of shale oils. However, it is still difficult to exploit the oil molecules adsorbed in the microscopic pore. Besides, by exploring the effect of chain length of the oil molecule on the diffusion, we found that the shorter chain oils are beneficial for exploitation. It is expected that these simulation results provide useful reference and important fundamentality for the investigation of shale oils.

A seires of functional group decorated porous covalent organic polymers (COPs) have been synthesized, and the effects of founctional groups on the luminescent property of these materials were investigated. Results indicate that both the carboxyl (COOH) and sulfuryl chloride (SO2Cl) functional groups can significantly enhance the luminescent intensity of matrix COP-401, while other groups (i.e., NH2; NO2; OH; CHO) cannot. Further studies show that the carboxyl and sulfuryl chloride functionalized COPs (i.e., COP-401-COOH and COP-401-SO2Cl) as luminescent probes can high selectively and sensitively sense Fe3+ ion, while unmodificated maxtrix COP-401 cannot. In addition, when COP-401-SO2Cl is dissolved in chloroform, it shows an obvious luminescence changing from blue to yellow, which indicates that it is a very promising luminescent probe for selectively sensing chloroform. In short, the COOH and SO2Cl functional groups are two excellent modifiers for developing new luminescent porous organic polymer materials.

Porous covalent polymers are attracting increasing interest in the fields of gas adsorption, gas separation, and catalysis due to their fertile synthetic polymer chemistry, large internal surface areas, and ultrahigh hydrothermal stabilities. While precisely manipulating the porosities of porous organic materials for targeted applications remains challenging, we show how a large degree of diversity can be achieved in covalent organic polymers by incorporating multiple functionalities into a single framework, as is done for crystalline porous materials. Here, we synthesized 17 novel porous covalent organic polymers (COPs) with finely tuned porosities, a wide range of Brunauer–Emmett–Teller (BET) specific surface areas of 430–3624 m2 g–1, and a broad range of pore volumes of 0.24–3.50 cm3 g–1, all achieved by tailoring the length and geometry of building blocks. Furthermore, we are the first to successfully incorporate more than three distinct functional groups into one phase for porous organic materials, which has been previously demonstrated in crystalline metal–organic frameworks (MOFs). COPs decorated with multiple functional groups in one phase can lead to enhanced properties that are not simply linear combinations of the pure component properties. For instance, in the dibromobenzene-lined frameworks, the bi- and multifunctionalized COPs exhibit selectivities for carbon dioxide over nitrogen twice as large as any of the singly functionalized COPs. These multifunctionalized frameworks also exhibit a lower parasitic energy cost for carbon capture at typical flue gas conditions than any of the singly functionalized frameworks. Despite the significant improvement, these frameworks do not yet outperform the current state-of-art technology for carbon capture. Nonetheless, the tuning strategy presented here opens up avenues for the design of novel catalysts, the synthesis of functional sensors from these materials, and the improvement in the performance of existing covalent organic polymers by multifunctionalization.

Rapid and sensitive detection of nitroaromatic explosives has attracted considerable attention due to their serious harm to our world. In this work, two porous luminescent covalent-organic polymers (COP-401 and COP-301) have been synthesized through copolymerization of double ligands. The results indicate that the two COPs with high thermal stability show significant luminescence quenching effects for nitroaromatic explosives. In particular, the two COPs exhibit not only a high sensitivity (about 1 ppm) for nitoraromatic explosives, but also an extremely high selectivity for 2,4,6-trinitrophenol (PA), which suggests that they are promising luminescent probes for highly sensitive and selective detection of nitroaromatic explosives, especially for PA.

We adopt 1,3,6,8-tetrabromopyrene (TBP) and 1,3,5-tris(4-bromophenyl)benzene (TBB) as double monomers to synthesize a series of porous covalent organic polymers (COPs) using the Ni-catalyzed Yamamoto reaction. By manipulating the reactive ratios of two monomers, we successfully achieve the color tailoring of the resultant COP samples. Interestingly, the emission peaks of these porous COP samples cover a wide color range from 533 up to 815 nm, which is the first near-infrared luminescent porous organic material. Further study indicates that these porous COPs can serve as luminescent sensors for highly sensitive and selective sensing of nitroaromatic explosives and metal ions. These materials might also find more applications in photocatalysis, organic electronics and medical imaging.

Nanoparticle (NP)-based drug delivery systems offer fundamental advantages over current therapeutic agents that commonly display a longer circulation time, lower toxicity, specific targeted release, and greater bioavailability. For successful NP-based drug delivery it is essential that the drug-carrying nanocarriers can be internalized by the target cells and transported to specific sites, and the inefficient internalization of nanocarriers is often one of the major sources for drug resistance. In this work, we use the dissipative particle dynamics simulation to investigate the effect of NP hardness on their internalization efficiency. Three simplified models of NP platforms for drug delivery, including polymeric NP, liposome and solid NP, are designed here to represent increasing nanocarrier hardness. Simulation results indicate that NP hardness controls the internalization pathway for drug delivery. Rigid NPs can enter the cell by a pathway of endocytosis, whereas for soft NPs the endocytosis process can be inhibited or frustrated due to wrapping-induced shape deformation and non-uniform ligand distribution. Instead, soft NPs tend to find one of three penetration pathways to enter the cell membrane via rearranging their hydrophobic and hydrophilic segments. Finally, we show that the interaction between nanocarriers and drug molecules is also essential for effective drug delivery.

A series of nitrogen-doped porous carbons are prepared from nitrogen-containing zeolitic imidazolate framework (ZIF) and additional carbon sources (including melamin, urea, xylitol and sucrose) via co-carbonization at T = 950 °C. Results indicate that macromolecular carbon sources, say, sucrose, can effectively protect the nitrogen loss from ZIF backbone owing to the pre-melting and polymerization of the sucrose adsorbed on the ZIF surface in the carbonization process, which makes the corresponding ZIF-derived porous Carbon-ZS have high nitrogen content and excellent capacitive performance. The specific capacitance of Carbon-ZS in 6 M KOH solution reaches 285.8 F g−1 at a current density of 0.1 A g−1 owing to its relatively high nitrogen content and proper hierarchical pore structure. In particular, the capacitance of Carbon-ZS is higher than previously reported IRMOF-derived carbon, ZIF-67-derived carbon and ZIF-8/furfuryl alcohol co-derived carbon. Besides high capacitance, moreover, Carbon-ZS also shows excellent cycling stability and good electric conductivity as electrode materials for electric double-layer capacitors.

Based on an experimentally synthesized dye D5 (also named d01 in this work), we designed and screened a series of dyes d02–d06 with different electron donors, such as diphenyl ethylene benzene, phenothiazine and perylene and d07–d12, by modifying the donor of d06 using different electron-donating groups. The results indicate that the donor in d12 is a promising electron donor. Therefore, we further designed six novel D–π–A structures of BUCT7–BUCT12 by using the electron donor in d12 as a donor, any two of 3,4-ethylenedioxy thiophene (EDOT), thienothiophene and dithieno[3,2-b:2′,3′-d] thiophene (s-DTT) groups as a π-conjugated bridge, and dicyanovinyl carboxylic acid and dicyanovinyl sulfonic acid as the acceptors. The calculated results indicate that BUCT7–BUCT12 dyes show smaller HOMO–LUMO energy gaps, higher molar extinction coefficients and obvious redshifts compared to the experimentally synthesized d01 dye. In particular, the newly designed BUCT8 dye not only exhibits a redshift of 134 nm and a higher molar extinction coefficient with an increment of 74.1% compared to d01 dye, but also has an extremely broad absorption spectrum covering the entire visible range up to the near-IR region of 1000 nm. In addition, we also found that the dyes with dicyanovinyl sulfonic acid as the electron acceptor are superior to the ones with dicyanovinyl carboxylic acid.

Developing high-capacity gas storage materials is still an important issue, because it is closely related to carbon dioxide capture and hydrogen storage. This work proposes a “from inorganic to organic” strategy, that is, using tetrakis(4-bromophenyl)methane (TBM) to replace silicon in zeolites, to design porous aromatic frameworks (PAF_XXXs) with extremely high pore volume and accessible surface area, because the silicon atom in the silicon-based zeolites and the TBM ligand have the same coordination manner. Through the adoption of this strategy, 115 organic PAF_XXXs based on the inorganic zeolite structures were designed. These designed PAF_XXXs have the same topology with the corresponding matrix zeolites but possess significantly higher porosity than matrix zeolites. In general, the surface area, pore volume, and pore size of PAF_XXX are in the ranges of 4600–6000 m2/g, 2.0–7.9 g/cm3, and 10–55 Å, respectively. In particular, the hydrogen uptake of PAF_RWY reaches 5.9 wt % at 100 bar and 298 K, exceeding the DOE 2015 target (5.5 wt %) for hydrogen storage. Moreover, PAF_RWY is also a promising candidate for methane storage and CO2 capture, owing to its extremely high pore volume and accessible surface area.

We investigated the electronic structures of N-, F-, and I-doped anatase TiO2 to explore the enhancement mechanism of incident photon-to-current conversion efficiency (IPCE) in dye-sensitized solar cells (DSSCs) based on N-, F-, and I-doped anatase TiO2 photoanodes. The hybrid density functional calculation results indicate that n-type F and I doping is better than p-type N doping. The incorporation of I dopant is very favorable to improve the conductivity, the open-circuit voltage, and the visible-light absorption of anatase TiO2. Moreover, the I doping can facilitate the electron injection from the dye molecule to the TiO2 substrate by analyzing the calculated electronic properties of adsorbed dye/TiO2 complexes. As a result, the I doping can significantly enhance the IPCE of DSSCs. In addition, it is found that the metallic n-type doping on the Ti site of the TiO2 photoanode can be an effective approach to improve the performance of DSSCs. It is expected that this work can provide valuable information for the development of TiO2-based DSSCs.

We use grand canonical Monte Carlo and molecular dynamics simulations to systematically investigate the membrane-based separation performance of four diamond-like frameworks (PAF-1, Diamondyne, TND-1, and TND-2) for CO2/H2, CO2/N2, CO2/CH4 and CH4/H2 mixtures. Diamondyne (also named D-Carbon) shows high membrane selectivity for gas mixtures of CO2/H2, CO2/N2, CO2/CH4, and CH4/H2 compared to MOF and COF membranes. Comprehensively considering the permeation selectivity and permeability, we find that diamondyne and TND-2 are promising candidates for CO2/H2 and CO2/N2 separation. Moreover, diamondyne and TND-2 exceed the Robeson’s upper line for CO2/N2 mixtures. The separation performance of diamondyne for CO2/CH4 mixtures also exceeds the Robeson’s upper limitation, indicating that diamondyne is also a promising candidate for separation of the CO2/CH4 mixtures. It is expected that this work can provide guidance and reference for development and design of high selectivity membranes for gas mixtures.

We have successfully prepared nanoporous Carbon-L and -S materials by using ZIF-7 as a precursor and glucose as an additional carbon source. Results indicate that Carbon-L and -S show an appropriate nitrogen content, high surface area, robust pore structure and excellent graphitization degree. The addition of an environmentally friendly carbon source – glucose – not only improves the graphitization degree of samples, but also plays a key role in removing residual Zn metal and zinc compound impurities, which makes the resulting materials metal-free in situ nitrogen-doped porous carbons. By further investigating the electrocatalytic performance of these nitrogen-doped porous carbons for oxygen reduction reaction (ORR), we find that Carbon-L, as a metal-free electrocatalyst, shows excellent electrocatalytic activity (the onset and half-wave potentials are 0.86 and 0.70 V vs. RHE, respectively) and nearly four electron selectivity (the electron transfer number is 3.68 at 0.3 V), which is close to commercial 20% Pt/C. Moreover, when methanol was added, the Pt/C catalyst would be poisoned while the Carbon-L and -S would be unaffected. By exploring the current-time chronoamperometric response in 25000 s, we found that the duration stability of Carbon-L is much better than the commercial 20% Pt/C. Thus, both Carbon-L and -S exhibit excellent ability to avoid methanol crossover effects, and long-term operation stability superior to the Pt/C catalyst. This work provides a new strategy for in situ synthesis of N-doped porous carbons as metal-free electrocatalysts for ORR in fuel cells.

In this work, metal–organic framework (MOF) UMCM-1 and amino functionalized MOF (i.e., UMCM-1-NH2) were synthesized and their performances as luminescent probes were investigated. It is found that both unmodified and amino functionalized MOFs exhibit a luminescence quenching effect on metal ions. In particular, the amino functionalized MOF (UMCM-1-NH2) possesses high sensitivity and selectivity for Fe3+ ions and the luminescence is completely quenched in 10−3 M DMF solution of Fe3+. Moreover, the regenerated UMCM-1-NH2 still has high selectivity for Fe3+ ions, which suggests that the functionalized UMCM-1-NH2 is a promising luminescent probe for selectively sensing iron ions.

We develop a new S(DIH) equation based on the difference of isosteric heats (DIH) to calculate the selectivity for CO2 over CH4 in metal–organic frameworks (MOFs) and covalent–organic materials. Using the S(DIH) equation to predict the selectivity requires only the adsorption isotherms of pure components and the DIH of the two components. By comprehensive comparison with the GCMC data in different types of porous materials, including MOFs, ZIFs, COFs and PAFs, it is found that the new S(DIH) equation can predict with high accuracy the selectivity of different types of porous materials for CO2 over CH4 at the low pressure of p = 0–1 bar. Therefore, the new S(DIH) can serve as an efficient tool for the selectivity predictions of porous materials for CO2 over CH4 at p = 0–1 bar, especially for the cases in which experiments can measure the adsorption isotherms and adsorption heats of pure components (such as CO2, CH4, N2 and H2) because the new S(DIH) requires only the adsorption isotherms and adsorption heats of pure components as inputs. In short, the new S(DIH) equation can be considered as a valuable screening tool for obtaining an estimation about the selectivity of a porous material for a certain component of the gas mixture.

A series of ZIF-derived porous carbon materials are prepared via co-carbonization of ZIF-7 and additional carbon sources, such as glucose, ethylene glycol, glycerol and furfuryl alcohol. Results indicate that ZIF-7/glucose composite-derived Carbon-L-950 as an electrode for the electrochemical capacitor exhibits a high specific capacitance of 228 F g−1 in 6 M KOH at a current density of 0.1 A g−1, even 178 F g−1 at a high current of 10 A g−1 and good stability over 5000 cycles. Moreover, the conductive agent (like acetylene black) is not required in the preparation process of the working electrode, which not only lowers the preparation costs but also is favorable for stability and performance. This facile fabrication of ZIF-derived porous carbon materials may open up a new avenue for producing a new family of porous carbon materials for advanced energy storage devices, such as fuel cells, supercapacitors and lithium batteries.

The recently reported diamondyne is a fascinating new carbon allotrope with multifunctional applications (J. Mater. Chem. A, 2013, 1, 3851; ibid 2013, 1, 9433). Here we theoretically predict two new tetrahedral node diamondyne (TND) frameworks by replacing the carbon nodes of diamondyne and diamond with the acetylenic linkage (C–CC–C)-formed tetrahedron node. The two resulting theoretical materials (marked as TND-1 and TND-2) exhibit extremely high specific surface areas (SSA) of 6250 and 2992 m2 g−1, respectively. Interestingly, the SSA of TND-1 is calculated to be the highest among all porous carbon materials. By further studying the CO2 capture performance of TND-1 and TND-2, it is found that the CO2 uptake of TND-1 reaches 2461 mg g−1 at 298 K and 50 bar, which outperforms all MOFs, COFs and ZIFs, while the selectivity of TND-2 for CO2/H2 reaches 104 at 35 bar, which is superior to most of the porous materials. In short, the hypothetical TND frameworks are promising candidates for CO2 capture in practical industry.

As potential third generation photovoltaic cells, dye-sensitized solar cells (DSSCs) have attracted extensive research interests and have become one of the hot topics in current research. In this work, a series of DSSCs based on TiO2 photoanodes modified by graphene oxide (GO) and nitrogen-reduced graphene oxide (N-rGO) were fabricated. Results indicate that N-rGO is a better TiO2 photoanode modifier of DSSCs compared to GO. With an increase in the amount of N-rGO, the open circuit voltage increases, while both the short circuit current and power conversion efficiency (PCE) of the DSSCs exhibit a maximum at the content of 0.2 wt % N-rGO. In particular, the maximum PCE of the DSSCs reaches 7.19% in this work, which gains a 13.23% enhancement compared to the PCE of 6.42% of conventional TiO2 DSSCs. The enhancement of the PCE of the DSSCs with N-rGO was mainly attributed to the reduction in electron recombination and the increase in electron transfer efficiency after incorporating N-rGO into TiO2 photoanodes.Keywords: Dye-sensitized solar cells; Nitrogen-doped graphene; Open circuit voltage; Photovoltaic cells; Short circuit current

A coarse-grained molecular dynamics simulation was used to investigate the stress–strain behavior of nanorod-filled polymer composites. The effects of the interfacial interaction, aspect ratio of fillers, filler functionalization, chemical couplings between the polymer and the filler and the filler loading on the mechanical reinforcement were explored. The results indicate that there exists an optimal nanorod volume fraction for elastomer reinforcement. The strong polymer–nanorod interaction enhances the reinforcement of polymer nanocomposites. Meanwhile, it is found that nanorods with longer length and smaller diameter, and the chemical functionalization of nanorods can help realize the efficient interfacial stress transfer. And excessive chemical couplings between polymers and nanorods are harmful to mechanical properties. An upturn in the modulus at large deformation is observed in the Mooney–Rivlin plot, attributed to the limited chain extensibility. Particularly, the medium polymer–nanorod interfacial strength and low nanorod volume loading will lead to better dispersion of nanorods. It is suggested that the reinforcement mechanism comes from the nanorod alignment and bond orientation, as well as from the limited extensibility of chain bridges at large deformation. In addition, an optimal nanorod volume fraction can also be explained by the strong polymer–nanorod network. Compared to glassy systems, the mechanism for the significantly enhanced reinforcement of rubbery systems is also demonstrated. In short, our simulation study of nanorod-induced mechanical reinforcement will provide a basic understanding of polymer reinforcement.

Recent experimental studies have shown the ability of tailoring the nanoparticle (NP)–cell interaction via the engineering of NP surfaces. Although the considerable progress has been made in design of patterned NPs for drug delivery, the effect of surface pattern on the NP–cell interaction is not fully understood yet. In this work, we used a dissipative particle dynamics method to systematically investigate the effects of NP surface pattern on its penetration across a membrane. For stripy NPs or patchy NPs having a large stripe width or patch size, an “insertion–rotation” penetration mechanism is found. Results indicate that stripy NPs and patchy NPs coated with narrow stripes or small patches can directly penetrate the cell membrane with a less constrained rotation. By considering the spontaneous penetration of many NPs into a vesicle, we found that NP aggregation would lead to the shape change of the vesicle, and therefore cause the leakage of encapsulated solvent or membrane rupture, implying the possible cytotoxicity. In short, this work gives a fundamental understanding for the penetration mechanism of the ligand patterned NPs, which provides useful reference for the design of NPs for controllable cell penetrability and targeted delivery of drugs.

Owing to the wide application of polymeric materials, understanding the fracture mechanism of amorphous polymers at strain fields is a fundamentally important challenge. In this work, we use molecular dynamics simulations to investigate the uniaxial deformation of amorphous polyethylene and further monitor the polyethylene fracture process induced by stretching. Results indicate that the polyethylene systems with chain lengths of 600–800 united atoms exhibit the fracture behavior at a temperature T < 200 K and the strain of 1.0. Further study shows that in the stretching process, the disentanglement and orientation of chains lead to the formation of small cavities in the middle region of the system, and the small cavities subsequently form a large hole, causing the fracture of the whole system. Definitely, the fracture is determined by the two factors of mobility and entanglement of chains. The polyethylene systems with a high chain mobility or a high chain entanglement do not fracture. Finally, a schematic diagram is put forward to illustrate the fracture behavior.

Designing highly efficient sensitizers for dye-sensitized solar cells (DSSCs) is an urgent task because it is closely related to the practical application of DSSCs. In this work, we designed and screened a series of triphenylamine derivative dyes with donor–π–acceptor (D–π–A) structure using different electron donors, π bridges and electron acceptors, and further used density functional theory (DFT) and time-dependent DFT (TDDFT) approaches to investigate the molecular orbital energy levels, absorption spectra, and light harvesting efficiency of these newly designed dyes. Results indicate that the donor group in D2, π bridges in Pi10–Pi12 and the acceptor group in A7 are promising functional groups for D–π–A structure. Using the above screened functional groups as donors, π bridges and acceptors, we designed six novel D–π–A structures of BUCT1–BUCT6. The results indicate that BUCT1–BUCT6 dyes show smaller HOMO–LUMO energy gaps, higher molar extinction coefficients and obvious redshifts compared to the experimentally synthesized P0 dye. In particular, the newly designed BUCT2 dye exhibits not only a 215 nm redshift and a higher molar extinction coefficient with an increment of 32.4% compared to P0 dye, but also has an extremely broad absorption spectrum covering the entire visible range up to the near-IR region of 1100 nm. Therefore, the BUCT2 dye is a very promising candidate for highly effective DSSCs with near-infrared light harvesting up to 1100 nm. We also found that the dyes with two –CN groups and a sulfonic acid group as the electron acceptor are more efficient than dyes with one –CN group and a sulfonic acid group.

The rising worldwide energy demands and the difficulty in developing novel clean energies have greatly stimulated the exploitation of shale gas. Understanding adsorption and diffusion of shale gas under different geological depths is an important issue. In this work, we use grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to investigate adsorption and diffusion behavior of shale gas (main component is methane) in a modeled shale in different burial depths up to 6 km. To examine the diffusion of shale gas, the equilibrium configuration of GCMC simulation is used as initial inputs for further MD simulations. The results indicate that the capacity of shale gas increases slightly with the depth, while the diffusion coefficient of shale gas in the shale matrix decreases with the increase of the pressure. Interestingly, a maximum diffusion coefficient of methane appears in a burial depth of 5 km. By cooperatively considering adsorption and diffusion results, we propose that the optimum operating condition is under a depth of 3–5 km. Moreover, we find that, when the basal spacing increases to 100 Å, the diffusion coefficients obtain an improvement of 80 times compared to the case with basal spacing of 8 Å, which provides useful guidance for exploitation of shale gas.

The electronic properties of monolayer transition-metal dichalcogenide MX2 (M = Mo and W; X = S and Se) interfaced TiO2(110) composites were investigated by hybrid density functional theory. In the MX2/TiO2(110) composites, MX2 serves as an efficient photosensitizer, and the electron–hole pair can, therefore, be easily generated by visible-light irradiation and be effectively separated by the electron injection from MX2 to TiO2. This mechanism is quite different from the one of the foreign elements doped TiO2, in which the electron is directly excited from the midgap impurity states into the CB of TiO2, leading to an optical absorption edge extending to the visible-light region. Moreover, we reveal that the prerequisite of designing the highly efficient semiconductor–TiO2 photocatalytic composites is to select the proper semiconductor, which holds the band gap of ∼2.0 eV and generates a built-in potential of 0.3–0.5 eV in the composite, as a photosensitizer, which can be also considered as a fundamental criteria to screen the suitable semiconductor and further to design the TiO2-based heterojunction composites for improving visible-light photocatalysis.

We use grand canonical Monte Carlo simulations to investigate adsorption and separation of metal–organic frameworks and covalent–organic materials for the noble gas Xe. Results indicate that PAF-302 among these materials studied shows not only the highest gravimetric excess uptake of 4009 mg/g but also the largest volumetric uptake of 216 V(STP)/V, due to its large pore size and high accessible surface area. The gravimetric excess uptake of Xe at intermediate pressure follows the order of PAF-302 > UMCM-1 > IRMOF-1 > Cu-BTC > COP-4 > ZIF-8, which is entirely consistent with the accessible surface areas. Moreover, the maximum gravimetric excess uptakes of Xe in different materials exhibit an entirely linear correlation with the accessible surface area. However, at low pressure of p < 1 bar, the Cu-BTC shows the highest Xe uptake of 500 mg/g, owing to its exposed metal sites and small side pockets. For the binary mixtures, the selectivity of Xe/N2 follows the order of Cu-BTC > ZIF-8 > COP-4 > IRMOF-1 > UMCM-1 > PAF-302, which is actually the same with the order of difference of isosteric heats (DIH), and is in excellent agreement with our previous conclusion (i.e., the selectivity of a material is closely related to the DIH). In particular, the selectivity of Cu-BTC for Xe over N2 reaches 80, which is an excellent candidate for Xe separation. In short, this work indicates that PAF-302 is an excellent candidate for Xe storage at intermediate pressure, whereas Cu-BTC is an excellent material for Xe separation.

The wide band gap of titanium dioxide (TiO2) limits its photoactivity only in the ultraviolet-light region and greatly blocks application of TiO2 in solar energy. Finding a pure TiO2 phase with a band gap around 2.0 eV is a very important issue for solar energy applications. We use the first-principles calculations to predict a fluorite TiO2(111) surface phase formed on the reconstructed high-energy rutile TiO2(011) surface. The band gap of the fluorite TiO2(111) surface phase is about 2.1 eV. We propose that engineering the high-energy surfaces of common TiO2 to obtain the fluorite TiO2(111) surface phase at room conditions is a promising method for the preparation of pure TiO2 materials with visible-light activity.

The toxic gases, such as CO and NO, are highly dangerous to human health and even cause the death of person and animals in a tiny amount. Therefore, it is very necessary to develop the toxic gas sensors that can instantly monitor these gases. In this work, we have used the first-principles calculations to investigate adsorption of gases on defective graphene nanosheets to seek a suitable material for CO sensing. Result indicates that the vancancy graphene can not selectivly sense CO from air, because O2 in air would disturb the sensing signals of graphene for CO, while the nitrogen-doped graphene is an excellent candidate for selectivly sensing CO from air, because only CO can be chemisorbed on the pyridinic-like N-doped graphene accompanying with a large charge transfer, which can serve as a useful electronic signal for CO sensing. Even in the environment with NO, the N-doped graphene can also detect CO selectively. Therefore, the N-doped graphene is an excellent material for selectively sensing CO, which provides useful information for the design and fabrication of the CO sensors.

Nowadays, achieving a uniform dispersion of rod-like molecules (like carbon nanotube) in a polymer matrix is still a complicated and unsettled issue in polymer physics and chemical physics. It is very significant to fully understand the effects of deterministic factors on dispersion and aggregation processes of nanorods in the polymer matrix. Here, we adopt a coarse-grained molecular dynamics simulation to investigate the nanorod- filled polymer nanocomposites. It is found that the characteristic relaxation time of the end-to-end vector correlation exhibits an Arrhenius-like temperature-dependent behavior and both the rotational and translational diffusion coefficients have a linear relationship with temperature. By tuning the polymer–nanorod interaction in a wide range, we obtain the spatial organization of nanorods and the best dispersion state at the intermediate interfacial interaction. Meanwhile, we observe that grafting polymer chains on the nanorod surface could promote the dispersion. Moreover, a lower or higher temperature than glassy transition temperature can prevent the nanorod aggregation. The aggregation of nanorods can be significantly accelerated by nanorod–nanorod attraction, while inhibited by cross-linking of polymer chains and external shear fields. In short, by tailoring the deterministic factors above, we can effectively control the dispersion or even spatial organization of one-dimensional nanorods in polymer nanocomposites.

Since the C60 and graphene were discovered, carbon allotropes have attracted an increasing attention. Here we designed a porous diamond-like carbon framework (named as D-carbon) by inserting –CC– linkers into all the C–C bonds in a diamond, which is a new carbon allotrope formed by sp3–sp hybridized carbon atoms. Interestingly, the porous D-carbon exhibits a high bulk modulus of 91.7 GPa, which is one order of magnitude larger than other porous MOF and COF materials. Moreover, the D-carbon also shows an extremely high excess volumetric methane uptake of 255 v(STP)/v at 298 K and 35 bar, largely exceeding the target (180 v(STP)/v) of US DOE and all other porous materials.

Porous covalent–organic materials (COMs) are a fascinating class of nanoporous material with high surface area and diverse pore dimensions, topologies and chemical functionalities. These materials have attracted ever-increasing attention from different field scientists, owing to their potential applications in gas storage, adsorptive separation and photovoltaic devices. The versatile networks are constructed from covalent bonds (B–O, C–C, C–H, C–N, etc.) between the organic linkers by homo- or hetero-polymerizations. To design and synthesize novel porous COMs, we first summarize their synthesis methods, mainly including five kinds of coupling reaction, i.e. boronic acid, amino, alkynyl, bromine and cyan group-based coupling reactions. Then, we review the progress of porous COMs in clean energy applications in the past decade, including hydrogen and methane storage, carbon dioxide capture, and photovoltaic applications. Finally, to improve their gas adsorptive properties, four possible strategies are proposed, and high-capacity COMs for gas storage are designed by a multiscale simulation approach.

Olefin–paraffin separation is one of the most significant processes in the petrochemical industry. An energy efficient method such as adsorption is considered to be a promising alternative to the traditional cryogenic distillation for the purification of olefins or paraffins. In this work, the grand canonical Monte Carlo (GCMC) method was used to study the adsorption and separation of light hydrocarbons (including ethylene, ethane, propylene and propane) by two diamond-like frameworks: diamondyne (originally named D-carbon in J. Mater. Chem. A, 2013, 1, 3851) and PAF-302, and further explore the mechanism for the adsorptive separation of olefins and paraffins. It is found that both diamondyne and PAF-302 show high uptake of hydrocarbons under ambient conditions, which greatly exceed those of MOFs and ZIFs. The saturation adsorption amounts of ethylene, ethane, propylene and propane on diamondyne are 14.5, 12.3, 10.3 and 8.9 mmol g−1, while they are 31.8, 28.0, 32.0, 30.3 mmol g−1 for PAF-302, which indicates that PAF-302 is an excellent candidate for hydrocarbon adsorption. In addition, it is also found that diamondyne shows preferential adsorption of olefins in the olefin–paraffin mixtures, like most commonly reported MOFs and ZIFs. However, interestingly, PAF-302 exhibits favorable adsorption for paraffins over olefins, which is an entirely different behavior to diamondyne, even though they have similar diamond-like structures.

Covalent organic polymer-4 (COP-4) supported palladium (Pd) catalysts were prepared for the first time. The Pd particles are highly dispersed into pores of COP-4 with electron reduction and the use of N,N-dimethylformamide (DMF) as the solvent. The catalysts show high activity for CO oxidation.

The layered polymer nanocomposites have attracted great interest from scientists due to their unique properties. However, the formation mechanism of these nanocomposites in the intercalation process is not fully understood yet. In this work, we simulate the intercalation processing of polymer chains into two layered sheets. By systematically tuning the polymer–sheet interaction, temperature, chain length, organic surfactant modification and interlayer distance, we found that the intermediate polymer–sheet interaction, low polymer molecular weight and large interlayer distance would enhance the intercalation kinetics. However, the presence of surfactants promotes the intercalation process of chains into layered sheets only when the interaction between polymer and surfactants is strong enough. In the intercalation process, the polymer chain first elongates and then contracts. To uncover the mechanism of aggregation and formation of layered sheets–polymer network, we examine the formation of bridge chains between layered sheets. Generally, the polymer chain does not adsorb totally on one single layer, but crosses over from one layer to another. Moreover, the number of bridge chains monotonically decreases with the increase of the polymer–sheet interaction and interlayer distance, but increases with the polymer chain length. It is expected that the structural and dynamic behavior of polymer chains intercalated into the layered sheets could deepen our understanding of polymer nanocomposites filled with layered sheets.

In this study, hybrid density functional theory calculations have been used to investigate the electronic structures of (Mg, S), (2Al, S), (Ca, S), and (2Ga, S) codoped anatase TiO2, aiming at improving their photoelectochemical performance for water splitting. It is found that the acceptor metals (Mg, Al, Ca, and Ga), assisting the coupling of the incorporated S with the neighboring O in TiO2, lead to the fully occupied energy levels in the forbidden band of TiO2, which is driven by the antibonding state π* of the S–O bond. It is also found that the metal-assisted S–O coupling can prevent the recombination of the photo-generated electron–hole pairs and effectively reduce the band gap of TiO2. Among these systems, the (Mg, S) codoped anatase TiO2 has the narrowest band gap of 2.206 eV, and its band edges match well with the redox potentials of water. We propose that this metal-assisted S–O coupling could improve the visible light photoelectrochemical activity of anatase TiO2.Highlights► Hybrid density functional theory calculations of codoped anatase TiO2. ► Metal-assisted S–O coupling can effectively reduce the band gap of TiO2. ► Band edges of codoped TiO2 match well with the redox potentials of water. ► (Mg, S) codoped TiO2 has the band gap of 2.206 eV.

Nanoparticle-assisted drug delivery has been emerging as an active research area. Achieving high drug loading is only one facet of drug delivery issues; it is also important to investigate the effect of surface charge distribution on self-assembly of nanoparticles on cellular membranes. By considering the electrostatic distribution of patterned nanoparticles, we used dissipative particle dynamics simulations to investigate the self-assembly of pattern charged nanoparticles with five different surface charged patterns. It is found that both surface charged pattern and nanoparticle size significantly affect the self-assembly of nanoparticles on cellular membranes. Results indicate that 1/2 pattern charged small nanoparticles can self-assemble into dendritic structures, while those with a 1/4 pattern self-assemble into clusters. As the nanoparticle size increases, 1/2 pattern charged medium nanoparticles can self-assemble into linear structures, while those with a 1/4 pattern self-assemble into clusters. For very large nanoparticles, both 1/2 pattern and 1/4 pattern charged nanoparticles self-assemble into flaky structures with different connections. By considering the effects of surface charged pattern and nanoparticle size on self-assembly, we found that nanoparticle self-assembly requires a minimum effective charged area. When the local charged area of nanoparticles is less than the threshold, surface charge cannot induce nanoparticle self-assembly; that is, the surface charged pattern of a nanoparticle would determine effectively the self-assembly structure. It is expected that this work will provide guidance for nanoparticle-assisted drug delivery.

Understanding the band gap narrowing of anatase TiO2 induced by B–N codoping is attractive and significant for their potential applications in renewable energy by converting sunlight to electricity or fuels. In this work, we use hybrid density functional calculations to investigate the electronic structures of B–N codoped TiO2 and further explore the mechanism of band gap narrowing of anatase TiO2 induced by B–N codoping. It is found the band gap narrowing of anatase TiO2 induced by the B-assisted N–O coupling effect (i.e., the substitution of Ti by B and the substitution of O by N, marked as (B[sub], N) codoping) is more effective than the compensation effect between the interstitial B donor and the substitutional N acceptors on O site (marked as (B[int], 3N) codoping). Results indicate that the (B[sub], N) codoped anatase TiO2 is an intrinsic semiconductor with a band gap of 1.762 eV, exhibiting a figure-of-merit for photoelectrochemical (PEC) catalysis in the visible light region. By considering the formation energy, we suggest adopting the strong O-rich environment to synthesize the (B[sub], N) codoped anatase TiO2. Actually, the B-assisted N–O coupling effect could significantly improve the visible light PEC performance of anatase TiO2. It is expected that this work can provide valuable information for design of new TiO2-based photocatalysts.

We have systematically investigated the CO2 storage and separation in a new class of porous aromatic frameworks (PAFs) with diamond-like structure by molecular simulations. Because of the small pore size of 5.2 Å, PAF-301 exhibits not only much higher CO2 uptakes at low pressure (275 mg/g at 298 K and 1 bar) but also much higher selectivities for the CO2/H2, CO2/N2, CO2/CH4, and CH4/H2 mixtures than the other three PAFs. The uptakes of CO2 in PAF-303 and PAF-304 reach 3432 and 3124 mg/g at 298 K and 50 bar, respectively, which are larger than MOF-200 (2437 mg/g) and MOF-210 (2396 mg/g), suggesting the two PAFs are promising candidates for high-capacity CO2 storage. Interestingly, the selectivity of PAFs is closely related to the difference of isosteric heats (DIH) of two components and is independent with the molar fraction at zero pressure. Therefore, we proposed an efficient DIH approach to screen porous materials for separation of mixture gases and derived the relation between the selectivity and the difference of isosteric heats based on Langmuir adsorption theory. The derived DIH equation can quickly screen out promising porous materials (including PAFs, COFs, MOFs, etc.) for separation of mixture gases.

Owing to the importance of drug delivery in cancer or other diseases’ therapy, the targeted drug delivery (TDD) system has been attracting enormous interest. Herein, we model the TDD system and design a novel rod-like nanocarrier by using the coarse grained model-based density functional theory, which combines a modified fundamental measure theory for the excluded-volume effects, Wertheim’s first-order thermodynamics perturbation theory for the chain connectivity and the mean field approximation for van der Waals attraction. For comparison, the monomer nanocarrier TDD system and the no nanocarrier one are also investigated. The results indicate that the drug delivery capacity of rod-like nanocarriers is about 62 times that of the no nanocarrier one, and about 6 times that of the monomer nanocarriers. The reason is that the rod-like nanocarriers would self-assemble into the smectic phase perpendicular to the membrane surface. It is the self-assembly of the rod-like nanocarriers that yields the driving force for the targeted delivery of drugs inside the cell membrane. By contrast, the conventional monomer nanocarrier drug delivery system lacks the driving force to deliver the drugs into the cell membrane. In short, the novel rod-like nanocarrier TDD system may improve the drug delivery efficiency. Although the model in this work is simple, it is expected that the system may provide a new perspective for cancer targeted therapy.

A group of polygonal carbon nanotubes (P-CNTs) have been designed and their mechanical behavior was investigated by classical molecular dynamics simulations. The research aimed at exploring the effects of structure, temperature, and strain rate on the mechanical properties. The results indicate that the Young's modulus of P-CNTs is lower than those of circumcircle carbon nanotubes (C-CNT). Moreover, with an increase in the number of sides to the polygons, the Young's modulus increases and is much closer to that of C-CNT. The effects of temperature and strain rate on the mechanical properties of P-CNTs show that the higher temperature and slower strain rate result in a lower critical strain and weaker tensile strength. In addition, it was found that the critical strains of P-CNTs are dependent on the tube size. Finally, we used the transition-state theory model to predict the critical strain of P-CNTs at given experimental conditions. It is expected that this work could provide feasible means to manipulate the mechanical properties of novel P-CNTs and facilitate the mechanical application of nanostructures as potential electronic devices.

Reducing anthropogenic carbon dioxide emission has become an urgent environmental and climate issue of our age. Here, a series of covalent-organic polymers (COPs) are synthesized, and the adsorption properties of these COPs for H2, CO2, CH4, N2 and O2 are studied. The H2 uptake of COP-2 reaches 1.74 wt% at 77 K and 1 bar, which is among the highest reported uptakes in the field of microporous organic polymers under similar conditions, and CO2 and CH4 adsorption capacities are 594 mg g−1 and 78 mg g−1, respectively, at 298 K and 18 bar. Then, based on the single component isotherm, the dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is used to predict the selectivity of the COP materials for post-combustion (CO2–N2) and pre-combustion (O2–N2) gas mixtures. The IAST predicted results indicate that COP-1 exhibits significantly higher selectivity compared to COP-2, 3 and 4, due to its smaller pore size. In particular, the adsorption selectivity of COP-1 for the CO2–N2 mixture reaches 91 at a CO2:N2 ratio of 15:85 at 298 K and 1 bar, and 2.38 for the 21:79 O2–N2 mixture at 298 K and 1 bar. Furthermore, these COPs also show robust properties for the removal of CO2 from natural gas. The adsorption selectivity of COP-1 for CO2–CH4 is in the range of 4.1–5.0 at a CO2:CH4 ratio of 15:85 at 0 < P < 40 bar.

First-principles calculations are performed to investigate the effects of the electron-deficiency of N-doped graphenes on their application in lithium ion batteries (LIBs), where three different defect models, graphitic, pyridinic, and pyrrolic graphenes are used. First, we investigate adsorption of a single Li atom on various graphenes and explore the change of the electronic properties in order to understand the adsorption mechanism. Then, adsorption of multiple Li atoms is also performed to consider the lithium storage properties of N-doped graphene nanosheets. The results show that the pyridinic graphene is the most suitable for Li storage with a high storage capacity, while the graphitic structure is the weakest of the three types. Moreover, the average potential of Li intercalation in the graphene materials was also calculated, and results indicate that the reversible capacity of the pyridinic structure can reach 1262 mAh g−1, which is higher than the experimental data (1043 mAh g−1). Therefore, we recommend pyridinic graphene in the N-doped structures as anode materials of lithium ion batteries and the corresponding reversible capacity of LIBs would be improved significantly. It is expected that this work could provide helpful information for the design and fabrication of anode materials of LIBs.

Recent experiment and simulation show that introduction of lithium in the frameworks can enhance the gas-storage capacities of framework materials. Here a covalent-organic polymer-1 (COP-1) has been synthesized through the self-polymerization of monomer 1,3,5-tris((4-bromophenyl)ethynyl) benzene (TBEB) by the nickel(0)-catalyzed Yamomoto reaction. To enhance gas adsorption properties of the COP-1 material, we have proposed a novel lithium-decorating approach in which the alkynyl functionalities in COP-1 are postsynthetically converted to lithium carboxylate groups with the aid of dry ultrapure CO2. In particular, the H2 uptake of lithium-modified COP material is 1.67 wt % at T = 77 K and ∼1 bar, which is increased by ∼70.4%, compared with the unmodified compounds. Besides, the enhancement effects of lithium modification on CO2 and CH4 adsorption have also been observed. It is expected that this approach proposed here would provide a new direction for lithium modification of MOFs and COFs for clean energy and environmental applications.

We systematically investigate the diffusion and separation behavior of hydrogen and methane in covalent organic frameworks (COFs) and Li-doped counterparts. The results indicate that the self-diffusivities of hydrogen and methane in COFs decrease monotonically with the increase of pressure. Interestingly, after Li doping into COFs, the self-diffusivities first increase at low pressure, and then reach a plateau, and finally decrease slightly at high pressure. This phenomenon stems from the fact that the Li atom has a strong affinity to the gas molecules. In addition, it is also found that the COFs show a larger self-diffusivity than most of the metal–organic frameworks (MOFs), and the permselectivities of the COFs for H2/CH4 are 1 order of magnitude higher than the Li-doped COFs. In particular, the adsorption selectivity of Li-doped COFs for CH4/H2 gets a significant improvement, compared to undoped ones. To further understand the effect of Li doping on diffusion and separation of gases, the isosurface and the contour plots of the center of mass and radial distribution functions of gases are also explored. In short, the Li doping into COFs can increase the adsorption selectivity of COF materials significantly, while for a kinetic separation process, the undoped COF-based membranes might be a very promising material.

Reducing the anthropogenic emission of CO2is currently a top priority due to its global warming effect. Capturing CO2 by porous materials is a promising approach due to its energetic efficiency and technical feasibility. A promising adsorbent for capturing CO2 should possess not only large BET specific surface areas (SSAs) but also high heat of adsorption. Since the intrinsic quadrupole moment of the CO2 molecule exists, introduction of a polar functional group in the framework of porous materials could enhance CO2 uptake. In this work, we adopt the postsynthetic modification approach to synthesize UMCM-1-NH2-MA (MA = maleic anhydride) material on the basis of UMCM-1-NH2 with an extremely high BET SSA of 4064 m2 g–1 and further explore the effects of free acid functionalities and aromatic amino groups on CO2 capture. The experimental and theoretical results show that, besides amino groups, the polar acidic functionalities also exhibit excellent capability for CO2 capture. Moreover, our first-principles calculations indicate that the aromatic imino group loses affinity toward CO2 significantly, compared with the aromatic amino group. In short, we believe that incorporating polar acidic functionalities into the porous materials could be an alternatively suitable approach for enhancing CO2 capture.

Our recently developed improved united atom force field shows a good quality to reproduce both the static and transport properties of neat ionic liquids (ILs). Combined with the TIP4P-Ew water model, the force field is used to simulate the mixture of 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) and water without further optimization to adjust any cross parameters. Liquid densities of the mixture are well predicted over the entire concentration range at temperatures from 298.15 to 353.15 K. Simulations also reproduce the positive values of excess volumes and excess enthalpies, as well as their increase with temperature. The simulated viscosities are in good agreement with experimental values, especially in the water-rich region. We found three distinct regions by analyzing the concentration dependent self-diffusion coefficients via Stokes–Einstein (SE) relation, indicating the mixture experiences significant microheterogeneity with the adding of water. This observation is well connected to the structure features obtained in simulations, such as radial distribution functions (RDFs), spatial distribution functions (SDFs) and water clustering analysis. At the water mole fraction (x2) less than 0.2, most of the water molecules are isolated in the polar cation–anion network in ionic liquids. With the increase of x2 from 0.2 to 0.8, large water cluster forms and eventually percolates the whole system. When x2 > 0.8, ionic liquids show a moderate degree of aggregation (with maximum around 0.9 to 0.95) before the cations and anions are fully dissolved in water.

We present a rare example of Zeolitic Imidazolate Framework-8 (ZIF-8), Zn(MeIM)2•(DMF)•(H2O)3, as luminescent probes with multi-function sensitivity to detect metal ions and small molecules. Our results show that the luminescence intensity of ZIF-8 is strongly sensitive to Cu2+ and Cd2+ ions and small molecules such as acetone. In particular, the luminescence intensity of desolvated ZIF-8 proportionally decreases to the concentration of Cu2+, while increases to the concentration of Cd2+ owing to the recognition of element-imidazole nitrogen sites. The luminescence intensity increases gradually with the increase of amounts of acetone in the standard desolvated ZIF-8-emulsions. These results reveal that the ZIFs might be a good luminescent sensor for metal ions and small molecules.

The adsorption of pure N2/H2/CH4/CO2 along with the adsorption and separation of mixtures thereof in two metal organic frameworks (MOFs) of UMCM-1 and UMCM-2 have been extensively studied using a hybrid method of computer simulation and adsorption theory. It is found that the excess adsorption isotherms from grand canonical Monte Carlo (GCMC) simulations basically agree with the available experimental data of pure gases, except for H2 adsorption in UMCM-1 at 298 K. Moreover, the GCMC results show that both MOF materials exhibit an excellent storage capacity for pure CH4 and CO2 at room temperature. The excess uptakes of CH4 by UMCM-1 and UMCM-2 for at 5000 kPa are 12.53 and 15.06 mmol g−1, while those of CO2 at 4500 kPa are 30.13 and 36.04 mmol g−1, respectively, which approaches and even exceeds the 30.82 mmol g−1 of MOF-177. In addition, dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is also used to correlate the simulated adsorption isotherms of pure gases and further predict the separation of equimolar mixtures. IAST shows a good agreement with the GCMC results in most cases studied here. The selectivities of both MOF materials in CH4/H2 and CH4/N2 are insensitive to the pressure. The selectivities of both MOF materials for CH4/H2 are almost the same having a value of 4, while they are 2 for CH4/N2. By contrast, the selectivities for CO2/H2, CO2/N2 and CO2/CH4 apparently rely on the pressure, showing 16.4 and 26.9, 5.4 and 7.8, and 2.9 and 4.7 at 4000 kPa for UMCM-1 and UMCM-2, respectively. Compared with other MOFs materials, their separation ability is not prominent, but they are suitable for gas storage.

Adsorption of H2S and SO2 pure gases and their selective capture from the H2S-CH4, H2S-CO2, SO2-N2, and SO2-CO2 binary mixtures by the single-walled carbon nanotubes (SWNT) are investigated via using the grand canonical Monte Carlo (GCMC) method. It is found that the (20, 20) SWNT with larger diameter shows larger capacity for H2S and SO2 pure gases at T = 303 K, in which the uptakes reach 16.31 and 16.03 mmol/g, respectively. However, the (6,6) SWNT with small diameter exhibits the largest selectivity for binary mixtures containing trace sulfur gases at T = 303 K and P = 100 kPa. By investigating the effect of pore size on the separation of gas mixtures, we found that the optimized pore size is 0.81 nm for separation of H2S-CH4, H2S-CO2, and SO2-N2 binary mixtures, while it is 1.09 nm for the SO2-CO2 mixture. The effects of concentration and temperature on the selectivity of sulfide are also studied at the optimal pore size. It is found that the concentration (ppm) of sulfur components has little effect on selectivity of SWNTs for these binary mixtures. However, the selectivity decreases obviously with the increase of temperature. To improve the adsorption capacities, we further modify the surface of SWNTs with the functional groups. The selectivities of H2S-CO2 and SO2-CO2 mixtures are basically uninfluenced by the site density, while the increase of site density can improve the selectivity of H2S-CH4 mixture doubly. It is expected that this work could provide useful information for sulfur gas capture.

By employing an idealized model of a polymer network and filler, we have investigated the stress-strain behavior by tuning the filler loading and polymer–filler interaction in a broad range. The simulated results indicate that there actually exists an optimal filler volume fraction (between 23% and 32%) for elastomer reinforcement with attractive polymer–filler interaction. To realize this reinforcement, the rubber–filler interaction should be slightly stronger than the rubber–rubber interaction, while excessive chemical couplings are harmful to mechanical properties. Meanwhile, our simulated results qualitatively reproduce the experimental data of Bokobza. By introducing enough chemical coupling between the rubber and the filler, an upturn in the modulus at large deformation is observed in the Mooney-Rivlin plot, attributed to the limited chain extensibility at large deformation. Particularly, the filler dispersion state in the polymer networks is also characterized in detail. It is the first demonstration via simulation that the reinforcement mechanism stems from the nanoparticle-induced chain alignment and orientation, as well as the limited extensibility of chain bridges formed between neighboring nanoparticles at large deformation. The former is influenced by the filler amount, filler size and filler–rubber interaction, and the latter becomes more obvious by strengthening the physical and chemical interactions between the rubber and the filler. Remarkably, the reason for no obvious reinforcing effect in filled glassy or semi-crystalline matrices is also demonstrated. It is expected that this preliminary study of nanoparticle-induced mechanical reinforcement will provide a solid basis for further insightful investigation of polymer reinforcement.

Owing to the important roles of chemical gates in biological systems, the biomimetic design of artificial switchable nanodevices has been attracting tremendous interest. Here, we design a cylindrical thermo-sensitive channel, in which nanofliudic transport properties can be controlled by manipulating environmental temperature. The switchable channel is formed by a polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-PAA-PS)-like triblock copolymer brush whose conformation and phase behavior are dependent on temperature. With the increase of temperature, the designed channel exhibits “close→open→close” behavior, which can serve as a kind of excellent switchable nanodevice for nanofluidic controllable transportation.Keywords (keywords): controllable transport; copolymer brushes; nanofluid; thermo-switchable channel

A cost-effective, classical united-atom (UA) force field for ionic liquids (ILs) was proposed, which can be used in simulations of ILs composed by 1-alkyl-3-methyl-imidazolium cations ([Cnmim]+) and seven kinds of anions, including tetrafluoroborate ([BF4]−), hexafluorophosphate ([PF6]−), methylsulfate ([CH3SO4]−), trifluoromethylsulfonate ([CF3SO3]−), acetate ([CH3CO2]−), trifluoroacetate ([CF3CO2]−), and bis(trifluoromethylsulfonyl)amide ([NTf2]−). The same strategy in our previous work (J. Phys. Chem. B2010, 114, 4572) was used to parametrize the force field, in which the effective atom partial charges are fitted by the electrostatic potential surface (ESP) of ion pair dimers to account for the overall effects of polarization in ILs. The total charges (absolute values) on the cation/anion are in the range of 0.64–0.75, which are rescaled to 0.8 for all kinds of ions by a compromise between transferability and accuracy. Extensive molecular dynamics (MD) simulations were performed over a wide range of temperatures to validate the force field, especially on the enthalpies of vaporization (ΔHvap) and transport properties, including the self-diffusion coefficient and shear viscosity. The liquid densities were predicted very well for all of the ILs studied in this work with typical deviations of less than 1%. The simulated ΔHvap at 298 and 500 K are also in good agreement with the measured values by different experimental methods, with a slight overestimation of about 5 kJ/mol. The influence of ΔCp (the difference between the molar heat capacity at constant pressure of the gas and that of liquid) on the calculation of ΔHvap is also discussed. The transport coefficients were estimated by the equilibrium MD method using 20–60 ns trajectories to improve the sampling. The proposed force field gives a good description of the self-diffusion coefficients and shear viscosities, which is comparable to the recently developed polarizable force field. Although slightly lower dynamics is found in simulations by our force field, the order of magnitude of the self-diffusion coefficient and viscosity are reproduced for all the ILs very well over a wide temperature range. The largest underestimation of the self-diffusion coefficient is about one-third of the experimental values, while the largest overestimation of the viscosity is about two times the experimental values.

It is a great challenge to fully understand the microscopic dispersion and aggregation of nanoparticles (NPs) in polymer nanocomposites (PNCs) through experimental techniques. Here, coarse-grained molecular dynamics is adopted to study the dispersion and aggregation mechanisms of spherical NPs in polymer melts. By tuning the polymer–filler interaction in a wide range at both low and high filler loadings, we qualitatively sketch the phase behavior of the PNCs and structural spatial organization of the fillers mediated by the polymers, which emphasize that a homogeneous filler dispersion exists just at the intermediate interfacial interaction, in contrast with traditional viewpoints. The conclusion is in good agreement with the theoretically predicted results from Schweizer et al. Besides, to mimick the experimental coarsening process of NPs in polymer matrixes (ACS Nano2008, 2, 1305), by grafting polymer chains on the filler surface, we obtain a good filler dispersion with a large interparticle distance. Considering the PNC system without the presence of chemical bonding between the NPs and the grafted polymer chains, the resulting good dispersion state is further used to investigate the effects of the temperature, polymer–filler interaction, and filler size on the filler aggregation process. It is found that the coarsening or aggregation process of the NPs is sensitive to the temperature, and the aggregation extent reaches the minimum in the case of moderate polymer–filler interaction, because in this case a good dispersion is obtained. That is to say, once the filler achieves a good dispersion in a polymer matrix, the properties of the PNCs will be improved significantly, because the coarsening process of the NPs will be delayed and the aging of the PNCs will be slowed.

Using the first-principles calculation, we investigate the adsorption of CO and NO on (8, 0) silicon nanotubes (SiNTs). The detailed analysis of the structural and electronical properties of various optimized configurations is performed. The results show that CO molecule can be chemisorbed on SiNT with the C atom bonding with the Si atom of the tubular surface when CO is located on the top site, accompanying with the binding energy of 1.559 eV and charge transfer of 0.658|e|, which are larger than the results of other configurations. For the SiNT-NO systems, there exist four strong chemical adsorption configurations. The most stable configuration is the N atom bonding with two Si atoms on the bridge site. The binding energy is 2.135 eV and charge transfer is 2.064|e|. In addition, it is found that both the C–O and N–O bonds are elongated when CO and NO are chemisorbed on SiNT. Compared to carbon nanotubes (CNTs) or silicon carbon nanotubes (SiCNTs), the SiNTs have stronger interaction with the CO and NO and can provide more sensitive signal for CO and NO sensing. In particular, the semiconducting (16, 0) SiNT would become metallic after adsorption CO, and the SiNTs after adsorption of NO would be magnetic, which can serve as a sensitive signal for CO or NO sensing. In short, the SiNTs with the semconducting structure are a very promising candidate for CO and NO sensing and detection.

Effectively separating CO2 from the natural gas, which is one of alternative “friendly” fuels, is a very important issue. A hybrid material CNT@Cu3(BTC)2 has been prepared to separate CO2 from the CO2/CH4 mixture. For comparison of separation efficiency, a series of representative metal–organic frameworks (MOF-177, UMCM-1, ZIF-8, MIL-53 (Al), and Cu3(BTC)2) have also been synthesized by the solvothermal method. Adsorption isotherms of CO2 and CH4 pure gases are measured by Hiden Isochema Intelligent Gravimetric Analyzer (IGA-003). The dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is used to predict adsorption of each component in the CO2/CH4 mixture. The IAST-predicted results show that the hybrid material CNT@Cu3(BTC)2 exhibits the greatest selectivity among the six materials, and its selectivity keeps in the range of 5.5 to 7.0 for equimolar CO2/CH4 mixture at 1 < p < 20 bar, which is higher than activated carbons. Moreover, the selectivity of CNT@Cu3(BTC)2 for the CO2/CH4 mixture keeps almost no change with the composition of CH4, which is one of the excellent properties as a promising separation material. In short, this hybrid material CNT@Cu3(BTC)2 shows great potential in separation and purification of CO2 from various CO2/CH4 mixtures by adsorptive processes in important industrial systems.

Separation of carbon dioxide and methane in cylindrical geometries materials (including MCM-41 and single-walled carbon nanotube (SWNT)) is investigated systematically using grand canonical Monte Carlo (GCMC) simulations. The selectivities of carbon dioxide with respect to methane (CO2/CH4) in MCM-41 and SWNT at different temperatures and mole fractions are obtained. Simulation results indicate that the selectivity of MCM-41 for CO2/CH4 is insensitive to the bulk mole fraction, while that of the SWNT varies significantly with the bulk mole fraction, although both the MCM-41 and SWNT are described using the cylindrical pore model. By exploring the effects of temperature, pore size and pressure on the selectivity of CO2/CH4, it is found that, to separate CO2 and CH4 efficiently, high pressure, low temperature and small pore size are preferred. In particular, the selectivity of CO2/CH4 in the SWNT can reach 11 at low temperature T = 233 K, high pressure of p = 20 bar and small pore size of 1.52 nm. Compared to the slit-like pores, the cylindrical pores are more efficient for separation of CO2/CH4 at the same temperature and pore size. It is expected that this work can provide useful information for practical application to the separation of CO2/CH4, especially for the determination of operating conditions and geometrical features of porous adsorptive materials.Figure optionsDownload full-size imageDownload as PowerPoint slide

Poly(styrene-b-N-isopropylacrylamide) (PSt-b-PNIPAM) with a narrow molecular weight distribution is prepared by reversible addition−fragmentation transfer radical polymerization. The dithioester group at the chain end of PSt-b-PNIPAM is converted into thiol terminal group by LiB(C2H5)3H. Gold nanoparticles and the PSt-b-PNIPAM interact via the terminal thiol group (-SH). The size of the gold nanoparticles coated with copolymers can be easily manipulated by adjusting the molar ratio of HAuCl4/PSt-b-PNIPAM. Interestingly, the thermosensitive gold nanoparticles exhibit a sharp and reversible transparent−opaque transition between 25 and 40 °C. Moreover, the transition change is sensitive to the size of the gold nanoparticles and the macromolecular weight of the copolymer. The maximum wavelength of the surface plasmon band and the hydrodynamic size of the PSt-b-PNIPAM-Au micelles are sensitive to temperature, pH, and salt concentration. A considerable red shift from 524 to 534 nm in the plasmon band is observed in 0.9% NaCl aqueous solution, but no appreciable change in the band is observed in pure water when the temperature increases from 25 to 40 °C. With a decrease of the pH of the solution, the maximum wavelength of the surface plasmon band exhibits a red shift (from 520 to 534 nm). In addition, dynamic light scatting (DLS) reveals that the hydrodynamic size of coated gold nanoparticles exhibits a small change under alkaline and neutral (pH = 7) conditions, but it gives a pronounced change in the acidic condition (from 350 to 280 nm) when the temperature increases from 25 to 40 °C. Furthermore, the UV−vis absorption spectrum clearly shows that the red shift of the thermosensitive gold nanoparticles is reversible.

Self-assembly is a versatile approach for the preparation of polymer nanocomposites with prescribed morphologies in the high-technology applications. Here, we use a Brownian dynamics (BD) method to explore the self-assembly of star-polymer-attached nanospheres and propose that a star polymer attached to the nanosphere brings anisotropy and induces the formation of polymer nanocomposites with different morphologies. These morphologies include hollow sphere, porous structure, lamella, perforated lamella with star polymer through nanosphere, and cylinder-like nanosphere, core−shell micelle, gyroid-like network, and star-polymer-formed cylindrical structure, depending on temperature, concentration, and nanosphere size. To give a framework of these mesostructures, a temperature versus concentration phase diagram is presented for each case of nanospheres. In order to better understand the self-assembly of star-polymer-attached nanospheres, we also explore the mechanism of the formation of these morphologies by examining the packing details of star polymers. It is expected that this work would provide useful information for engineering novel polymer nanocomposite materials by means of the mesophase self-assembly.

A multiscale theoretical method, which combines the first-principles calculation and grand canonical Monte Carlo (GCMC) simulation, is used to investigate the adsorption capacities of hydrogen in nondoped and Li-doped covalent organic borosilicate frameworks (COF-202). Our simulations indicate that the total gravimetric and volumetric hydrogen uptakes of COF-202 reach 7.83 wt % and 44.37 g/L at T = 77 K and p = 100 bar, respectively. To enhance the hydrogen storage capacity of COF-202, the doping of Li atoms in COF-202 is studied systematically. First, the first-principles calculations are performed to investigate the possible adsorption sites and the quantity of Li atoms doped in COF-202. Our results prove that, for a single Li atom, the top of the phenyl groups in COF-202 is the most favorable adsorption site; for coadsorption of two Li atoms, with one adsorbed at the top site of a phenyl group and the other at its neighboring interstitial site between the phenyl group and the B−O−Si linkage is the most favorable adsorption mode. Our GCMC simulations predict that the total gravimetric and volumetric uptakes of hydrogen in the Li-doped COF-202 reach 4.39 wt % and 25.86 g/L at T = 298 K and p = 100 bar, respectively, where the weight percent of Li equals to 7.90 wt %. This suggests that the Li-doped COF-202 is one of the most promising candidates for hydrogen storage at room temperature.

We use the multiscale simulation approach, which combines the first-principles calculations and grand canonical Monte Carlo simulations, to comprehensively study the doping of a series of alkali (Li, Na, and K), alkaline-earth (Be, Mg, and Ca), and transition (Sc and Ti) metals in nanoporous covalent organic frameworks (COFs), and the effects of the doped metals on CO2 capture. The results indicate that, among all the metals studied, Li, Sc, and Ti can bind with COFs stably, while Be, Mg, and Ca cannot, because the binding of Be, Mg, and Ca with COFs is very weak. Furthermore, Li, Sc, and Ti can improve the uptakes of CO2 in COFs significantly. However, the binding energy of a CO2 molecule with Sc and Ti exceeds the lower limit of chemisorptions and, thus, suffers from the difficulty of desorption. By the comparative studies above, it is found that Li is the best surface modifier of COFs for CO2 capture among all the metals studied. Therefore, we further investigate the uptakes of CO2 in the Li-doped COFs. Our simulation results show that at 298 K and 1 bar, the excess CO2 uptakes of the Li-doped COF-102 and COF-105 reach 409 and 344 mg/g, which are about eight and four times those in the nondoped ones, respectively. As the pressure increases to 40 bar, the CO2 uptakes of the Li-doped COF-102 and COF-105 reach 1349 and 2266 mg/g at 298 K, respectively, which are among the reported highest scores to date. In summary, doping of metals in porous COFs provides an efficient approach for enhancing CO2 capture.Keywords: CO2 capture; covalent organic frameworks; first-principles calculations; grand canonical Monte Carlo simulation; metal-doping

By using a multiscale theoretical method, which combines the first-principles calculation and grand canonical Monte Carlo (GCMC) simulation, we studied storage capacities of methane in 3D covalent organic frameworks (COFs) and their Li-doped compounds at T = 243 and 298 K. Our results predicted that, at T = 298 K and 35 bar, the excess gravimetric capacities of COF-102 and COF-103 reach 17.72 and 16.61 wt % (corresponding to 302 and 285 cm3 (STP)/g)), which are in good agreement with experimental data, while the excess volumetric capacities of COF-102 and COF-103 reach 127 and 108 v (STP)/v, respectively. The high methane storage capacity of the COFs can be attributed to their ultrahigh surface areas and low densities. To further enhance the methane capacity, we investigated the impact of Li-doping on the methane storage performance of the COFs. Our first-principles calculations show that the Li cation doped in the COFs can enhance the binding of methane to the substrate significantly because of the London dispersion and the induced dipole interaction, due to the strong affinity of Li cation to methane molecules. At T = 298 K and relatively low pressures (p < 50 bar), the Li-doping method nearly doubles the methane uptakes of the COFs, compared to the nondoped materials. In particular, at T = 298 K and p = 35 bar, the methane volumetric uptakes of Li-doped COF-102 and COF-103 reach 303 and 290 v (STP)/v, respectively, which is more than 2 times those in the nondoped (127 and 108 v (STP)/v). To the best of our knowledge, the Li-doped 3D COFs show the largest methane storage uptakes at room temperature to date.

We have used the multiscale simulation method to evaluate the hydrogen storage performance of a recently designed new class of porous materials, PAF-30X (X = 1−4), with diamond-like structure. Our simulation results show that the hydrogen uptakes of PAFs mainly depend on their densities and free volumes. Among the four frameworks, PAF-304 and PAF-303 possess significantly higher gravimetric hydrogen uptakes than the recently reported covalent organic framework-102 (COF-102) and belong to the most promising candidates for hydrogen storage so far. In particular, at T = 298 K and 100 bar, the gravimetric hydrogen uptake of PAF-304 reaches 6.53 wt %, which is the highest among all of the present porous materials without modification.Keywords (keywords): covalent organic frameworks; diamond-like structure; hydrogen storage; multiscale simulation method; porous aromatic frameworks;

The effects of structure, temperature, and strain rate on mechanical properties of all the SiGe nanotubes in armchair and zigzag structures (n = 4−13) in two atomic arrangement types are investigated by classical molecular dynamics simulation. During the extending tests, we observe three structural transformations from initial structure, tensile structure, to critical structure deformation. The simulation results indicate that the Young’s modulus of nanotubes is closely dependent on their diameter, chirality, and arrangement structure. The type 1 (alternating atom arrangement type) armchair SiGe nanotube exhibits the largest Young’s modulus, compared with other nanotubes with the same index n. By exploring the effects of temperature and strain rate on mechanical properties of SiGe nanotubes, it is found that the higher temperature and lower strain rate lead to the lower critical strain and tensile strength. Furthermore, it is also found that the critical strains for both armchair and zigzag nanotubes in two arrangement types are significantly dependent on the tube diameter and chirality. The armchair type 1 nanotube exhibits the highest mechanical critical strain and tensile strength among all these nanotubes with the same index n. On the basis of the transition-state theory model, we predict that the critical strain of the SiGe (6,6) type 1 nanotube at 300 K, stretched with a strain rate of 5%/h, is about 3.38%, which is in good agreement with the recent experimental results. Our results might provide potential applications in manipulating mechanical and electromechanical properties of the nanostructures suitable for electronic devices.

A theoretical method, which combines the first-principle calculations and a canonical Monte Carlo (CMC) simulation, was used to study the structures of Au clusters with sizes of 25–54 atoms supported on the MgO(1 0 0) surface. Based on a potential energy surface (PES) fitted to the first-principle calculations, an effective approach was derived to model the Au–MgO(1 0 0) interaction. The second moment approximation to the tight-binding potential (TB-SMA) was used to model the Au–Au interactions in the CMC simulation. It is found that the Au clusters with sizes of 25–54 atoms supported on the MgO(1 0 0) surface possess an ordered layered fcc epitaxial structure.

On the basis of the coarse grained model, we investigated the adsorption of nonuniformly charged fullerene-like nanoparticles on planar polyelectrolyte brushes (PEBs) in aqueous solution by using Brownian dynamics simulation. It is found that the electroneutral nanoparticles can be adsorbed by the PEB, which is attributed to the asymmetrical electrostatic interactions of the PEB with the positively charged sites and negatively charged sites of the fullerene-like nanoparticles. The simulation results indicated that the adsorption amount exhibits non-monotonic behavior with the dipole moment of nanoparticles. First, the adsorption amount increases with the dipole moment and then reaches the maximum at the dipole moment of μ = 10.45. Finally, the adsorption falls at the dipole moment of μ = 14.39. The reason may be that, at the extremely large dipole moment of μ = 14.39, the fullerene-like nanoparticles aggregate together to form a big cluster in the bulk phase, which can be confirmed by the extremely high peak in the radial distribution function between nanoparticles. Accordingly, it is difficult for nanoparticles to enter into the PEB at the dipole moment of μ = 14.39. In addition, it is also found that the brush grafting density is an important factor affecting the brush thickness.

A general synthesis strategy to prepare metal nanostructures by self-assembly was proposed by molecular dynamics (MD) simulation. In this simulating synthesis strategy, the metal nanostructures were generated by the self-assembly of the amorphous nanoparticles with the attractive forces of the nanoparticle−nanoparticle interactions by the annealing MD method at high temperatures, and finally, the resulting amorphous metal nanostructures were cooled to 10 K, which could resemble the nanoparticle self-assembly in experiment. By using the simulating synthesis, we obtained the full atomistic models of the shape-controlled metal nanostructures, including Au, Ag−Au, and beaded Ag−Cu nanorods, triangular and hexagonal Ag nanoplates, triangular Ag−Au and hexagonal Au, cubic hollow Fe, and Ag−Au nanoframes. It is found that these models are in good agreement with the experimental results. Moreover, we predicted a new metal nanostructure, Au nanoporous framework architecture, which has not been reported in experiment, by self-assembly of the Au nanoparticles. The predicted architecture possesses three-dimensional periodic inner-connecting channels and cavities. It is believed that our simulating synthesis approach will help facilitate the preparation and design of novel metal nanostructures in experiment.

By using the first-principles DFT calculations, we design a novel hydrogen storage material, Li12Si60H60 composite, and validate its geometric stability. It is found that the adsorbed Li atoms do not cluster on the Si60H60 fullerene unlike other metals such as Ti, owing to the relatively low Li−Li binding energy and the inhibition of Si−H bonds. Our results show that the Li-doping enhances the hydrogen adsorption ability of Si60H60 significantly, owing to the charge transfer from the doped Li atoms to the host material and the polarization of the adsorbed H2 molecules. By combining the first-principles calculation and grand canonical Monte Carlo simulation, we further investigate the hydrogen storage capacity of the simulation-synthesized exohedral Li12Si60H60 composite at T = 77 K. As the vdW gap (i.e., the separation between the surfaces of two Li12Si60H60 fullerenes) is equal to 8.2 Å, the total hydrogen uptake of the square-arranged Li12Si60H60 array reaches 12.83 wt % at p = 10 MPa, while the excess hydrogen uptake shows a maximum of 7.46 wt % at p = 6 MPa. Impressively, at T = 298 K and p = 10 MPa, the Li12Si60H60 array still exhibits a total hydrogen uptake of 3.88 wt % at the vdW gap of 8.2 Å. These results clearly indicate that the composite, Li12Si60H60 fullerene, is a promising candidate for hydrogen storage.Keywords: first-principles calculation; grand canonical Monte Carlo simulation; hydrogen storage; Li-doped silicon-fullerene; simulating synthesis of materials

A porous coordination framework material, Zn4O(BDC)(BTB)4/3 (labeled 1 for simplification), has been prepared and applied to hydrogen storage. Its storage capacity has been measured, and the absolute and excess H2 adsorption uptakes reach 6.23 and 5.43 wt % at 77 K and 20 bar, respectively. Moreover, a multiscale simulation method, which combines first-principles calculation and grand canonical Monte Carlo simulation, has been used to evaluate H2 adsorption in this material. The simulation results successfully reproduce the experimentally determined hydrogen uptake in 1 at T = 77 K and in the pressure range 0−20 bar. Furthermore, the simulation predicts that the hydrogen capacity in 1 reaches 9.5 wt % at 77 K and 100 bar, which is among the highest reported in the literature to date. Clearly, this material is a promising adsorbent for hydrogen storage.

A Brownian dynamics (BD) simulation is performed to investigate the effect of counterion valence on the properties of polyelectrolyte (PE) brushes grafted on two apposing walls. By increasing the counterion valence from monovalence to divalence and further to trivalence, the PE brushes on two separate walls begin to shrink to produce a tunnel in the center of the confinement, which provides a path for the nanoparticle to pass the PE brushes in this system. That is to say, the added counterions can act as a switch-controller of the opening−closing behavior of the PE chains grafted on the two walls. By exploring the dynamic properties of nanoparticles, it is found that the mobility of nanoparticles increases with the addition of the higher valent counterions; i.e., the nanoparticle can diffuse along the tunnel induced by high valent counterions. In addition, we also investigate dependences of the thickness and distribution of the PE brushes on the grafting density, concentration, and valence of counterions. It is expected that this work can provide a good insight into the design of formation of a tunnel for nanoparticle access in the PE brushes controlled by the counterion valences.

We systematically investigated the structural and dynamic properties of nanofilled elastomer on the basis of the idealized model of elastomer and nanoparticle. The simulated results indicate that the introduced nanoparticles induce more efficient chain packing. Meanwhile, a mobility gradient of polymer chains is found to exist approaching the nanoparticles. For the dynamic properties, we find for the first time that both the time−concentration and time−temperature superposition principles (TCSP and TTSP) are applicable at the chain length scale, while both break down at the segmental length scale for the filled system. However, the TTSP still holds at the segmental length scale for the pure system. Furthermore, the time−temperature−concentration superposition principle (TTCSP) applies well for the terminal relaxation of polymer nanocomposites. This scaling behavior has the underlying implication that the rheological properties (i.e., steady-state shear viscosity) of polymer nanocomposites possess thermorheological simplicity. In addition, interestingly, the characteristic relaxation time as a function of filler concentration exhibits an Arrhenius temperature dependence, if the concentration variation is regarded as an inverse of temperature variation. We suggest the introduced nanoparticles exert the similar effect to the thermodynamic variables (e.g., pressure and temperature) on the polymer dynamics. Lastly the stress relaxation of the model system is also examined. The decay of the bond orientation of polymer chains during the relaxation process is studied by changing the draw ratio, the filler loadings and the affinity between the nanoparticle and polymer. In order to equivalently investigate the stress relxation, we propose a new approach named conformational relaxation. It is observed that the conformational relaxation can be approximately fitted well by an exponential function for the pure and filled systems, similar to the stress relaxation. The TTSP is also applicable for the conformational relaxation of the pure system, while breaks down for that of the filled system. The relaxation time extracted by fitting the conformational relaxation curves with an exponential function at different temperatures, exhibits an Arrhenius relationship with the temperature for the pure and filled systems. Moreover, contrary to the isotropic dynamics during the creep process of the polymer from the simulated results of de Pablo, our simulated result shows an anistropic polymer dynamics with an accelerated relxation in the predeformed direction during the stress relaxation process.

Brownian dynamics simulations were carried out to explore the self-assembly of amphiphilic copolymers composed of a linear hydrophilic head and a hydrophobic tail with different architectures. In order to investigate the effect of architecture of hydrophobic tail on self-assembling behavior, these architectures of linear, branched, starlike, and dendritic tails were selected for comparison, and the branching parameter of the tail was employed to characterize the tail architectures. The critical micelle concentration (cmc), dynamics of aggregation, aggregate distribution, gyration radius distribution, density profiles of micelle, shape anisotropy, and thermal stability were examined for the four typical types of copolymers. The calculated results reveal that the self-assembly of linear tail copolymer has the lowest cmc, and the consequently formed polymeric micelles have narrow dispersion and greater aggregate size, and the micelle is closer to spherical shape. It was found that the cmc is inversely proportional to the branching parameter. Linear tail aggregates in solution to form polymeric micelles with higher physical stability, compared to other architectures of tail. The size of polymeric micelle increases with the increase of the branching parameter of the tail, and it exhibits an exponential relationship with the branching parameter. In addition, the micelles formed from copolymers with a high branching parameter of the tail were found to have higher thermal stability. This work provides useful information on designing self-assembling systems for preparing polymeric micelles applied to drug delivery.

We performed grand canonical Monte Carlo (GCMC) simulations to characterize the hexagonally ordered carbon nanopipes CMK-5 and further investigated the adsorptive properties of this material for H2. The geometrical model from Solovyov et al. was used to characterize the hexagonal structure of the CMK-5 adsorbent. The interactions between a fluid molecule inside and outside the nanopipe and a single layer were calculated by the potential models proposed by Tjatjopoulos et al. and Gordon et al. When the calculated results were fitted to the experimental isotherm of N2 adsorption at 77 K, the structural parameters of the CMK-5-S material were obtained. To improve H2 adsorption, we also optimized the structural parameters of CMK-5 material. The maximum excess gravimetric and volumetric uptakes of H2 in the CMK-5 material with the optimized structural parameters at T = 77 K are 5.8 wt % and 41.27 kg/m3, which suggest that the CMK-5 material with an optimized structure is a promising adsorbent for gas adsorption.

A Brownian dynamics (BD) simulation is performed to investigate the effect of the bridging conformation of a polyelectrolyte (PE) with two charged heads (two-heads PE) on the radial distribution function (RDF) and diffusion behavior of macroions on the basis of the coarse grained model. For comparison, the system containing macroions and the PE with only one charged head (one-head PE) is also investigated. The simulation results indicate that, at low concentrations, the bridging effect of the two-heads PE chain leads to correlation of macroions. The reason is that at low concentration the gyration radius of the PE chain is less than the average distance between two macroions. When the two-heads PE chains are adsorbed on different macroions, the bridging effect of the PE chain dominates the RDF and diffusion behavior of the macroions. With the increase of the concentration of the system, when the gyration radius of the PE chain is greater than the average distance between two macroions, the bridging effect of the PE chain becomes trivial. By investigating the mechanism of the two-heads PE chain affecting the static and dynamic properties of the macroions, we can provide useful information for the synthesis of stabilizers and destabilizers of colloidal particles.

On basis of a coarse-grained model, we investigate the conformational behavior of a spherical polyelectrolyte brush (SPB) in a solution containing oppositely charged linear polyelectrolytes. Our results obtained from Brownian dynamics (BD) simulations show that with increasing amount of linear polyelectrolytes the SPB undergoes the process of swelling → collapse → reswelling. The collapse of the SPB is due to the replacement of confined counterions by linear polyelectrolytes and is well described within a theoretical mean field approach. This replacement and a strong correlation between linear chains and SPB chains lead to a drop in the osmotic pressure inside the SPB. The reswelling is caused by further adsorption of linear chains and counterions. This in turn results in an enhanced excluded volume effect within SPB. A weak charge inversion of the SPB complex is observed. With increasing length of linear polyelectrolytes the collapse of the SPB and its reswelling is shifted toward lower concentrations of linear chains at which both effects occur. An increasing grafting density induces a multilayer structure of adsorbed linear chains and SPB chain segments. The packing process in turn increases the thickness of the SPB. We find that adsorbed linear polyelectrolytes are significantly denatured compared to the free ones in the solution.

Grand-canonical Monte Carlo (GCMC) simulations were performed to investigate the adsorption behavior of methane and hydrogen on a highly ordered carbon molecular sieve CMK-1 material. The rod-aligned slitlike pore (RSP) model was used to emphasize the grooved structure of the material, and the pore size distribution (PSD) was introduced to characterize the geometrical heterogeneity of the materials quantitatively. The PSD determined from adsorption isotherms of N2 at 77 K indicates that the CMK-1 adsorbent is a mesoporous material. By combining the GCMC and PSD techniques, adsorption isotherms of CH4 at 303 K and H2 at 303 and 77 K in the CMK-1 materials were obtained. The simulated isotherms are in an excellent agreement with experimental data, suggesting that it is necessary and efficient to use the PSD to characterize the materials. The GCMC predictions demonstrate that gravimetric uptakes of CH4 and H2 in the CMK-1 material at 30 MPa and 303 K are 31.23 and 1.19 wt %, respectively. Although a greater loading of 4.58 wt % for H2 is favored at 77 K and the same pressure, it does not reach the U.S. Department of Energy target of 6.5 wt %. By analyzing isosteric heats, we found that the adsorptions of CH4 at 303 K and H2 at 77 K exhibit an evidently energetic heterogeneous behavior in CMK-1 materials, with a broad range of isosteric heats of 10−27 kJ/mol for CH4 and 2.73−9.9 kJ/mol for H2. However, the adsorption behavior tends to be energetically homogeneous for H2 at 303 K, because the isosteric heat mainly centers on the range 4.82−6.65 kJ/mol. In addition, by exploring the relationship between the pore width and the surface excess, we found that, for CH4 at 303 K, the optimal operating conditions corresponding to the maximum surface excess are w = 1.2422 nm and P = 6 MPa, whereas for H2 at 77 K, they are w = 1.0647 nm and P = 3 MPa.

On the basis of the coarse-grained model, we performed Brownian dynamics simulations to investigate behavior of the polyelectrolyte (PE)−macroion complexations in 1:1 and 3:1 salt contents. Our simulation results show that in 3:1 salt content there exists a critical salt concentration (CSC), which is determined by the charge stoichiometry, for the breakup of the PE−macroion complexations. Beyond the CSC concentration, an obvious depletion appears in the macroion−macroion and macroion−PE interactions, which is absent in 1:1 salt content. Both the mobilities of macroions and PEs increase monotonically with increasing the salt concentration in 1:1 and 3:1 salt contents. And the mobility in 3:1 salt content is always larger than that in corresponding 1:1 salt content, which is due to the fact that in 3:1 salt content the PE−macroion complexations are looser than those in 1:1 salt content. Moreover, we observed the collapse and re-expansion of PE chains with the increase of the salt concentration in the PEs−macroions systems of 3:1 salt content, which is due to the charge inversion of PE chains induced by the adsorption of trivalent cations. In addition, we also explored the effects of salt concentration and the length and charge density of PE chains. Our simulation results show that the effects of the length and charge density of PE chains in both salt contents on the radial distribution functions (RDFs) between macroions and between a macroion and a PE segment are similar to these in salt free solution basically. However, we observed an interesting phenomenon that the gyration radius of PE chains in the system of 3:1 salt content is not affected significantly by its charge density, while that in 1:1 salt content increases monotonically.

A common computational method for the characterization of porous materials is to calculate the adsorption isotherm of fluids in the materials from the preassumed wall–fluid potential. If the wall–fluid potential is unknown, the common computational method becomes invalid. In a realistic experiment, however, it is common to know the experimental adsorption isotherm of nitrogen and not to know the wall–fluid potential. Here we propose a stepwise approximation for modeling wall–fluid potential under conditions where only the adsorption isotherm of nitrogen is measured experimentally. Based on the modeled wall–fluid potential, we can characterize the porous materials and predict the adsorption of other adsorbates on the materials. It is expected that the approach would provide a powerful means for the characterization of novel materials under conditions where only the experimental adsorption isotherm is available.We propose a stepwise approximation for modeling wall–fluid potential. On the basis of the modeled wall–fluid potential, we can characterize the porous materials and predict adsorption of other adsorbates on the materials.

Newly designed fluorine-doped magnetic carbon (F-MC) was synthesized in situ though a facile one-step pyrolysis-carbonization method. Poly(vinylidene fluoride) (PVDF) served as the precursor for both carbon and fluorine. 2.5% F content with core-shell structure was obtained over F-MC, which was used as a adsorbent for the Cr(VI) removal. To our best knowledge, this is the first time to report that the fluorine doped material was applied for the Cr(VI) removal, demonstrating very high removal capacity (1423.4 mg g−1), higher than most reported adsorbents. The unexpected performance of F-MC can be attributed to the configuration of F dopants on the surface. The observed pseudo-second-order kinetic study indicated the dominance of chemical adsorption for this process. High stability of F-MC after 5 recycling test for the Cr(VI) removal was also observed, indicating that F-MC could be used as an excellent adsorbent for the toxic heavy metal removal from the wastewater.

•A series of functional group rich organic (FGRO) shale models were constructed on base of the experimental results.•Adsorption and selectivity of CH4/CO2 in FGRO shales were studied by molecular simulation.•The epoxy rich organic shale is beneficial for sequestration of CO2.•1 km depth was recommended as optimal condition for exploitation of shale gas or sequestration of CO2.The exploration of shale gas resources has been increasing rapidly in the past decades owing to the growing demands for resources and environmental protection. In this work, we construct a series of functional group rich organic (FGRO) shale models. The shale gas capacity, sequestration amount of CO2 and selectivity of CO2/CH4 in these organic-rich shales are explored by molecular simulation. It is found that the shale gas capacities in the FGRO shale models are smaller than that in pristine pillared shale model owing to the excluded volume effect of organic matter. However, the FGRO organic matter shows a significant effect on the selectivity of CO2/CH4. In particular, the selectivity of CO2/CH4 in the epoxy group rich organic (EGRO) shale model reaches 8.36, which is 3.73 times of that in pristine model without organic matter. Therefore, the EGRO shale may be a potential reservoir for sequestration of CO2. Meantime, by exploring the effects of geological depth on exploitation of shale gas or sequestration of CO2, an optimum depth of 1 km is recommended. It is expected that this work provides useful guidance for exploitation of shale gas and sequestration of CO2.Download high-res image (120KB)Download full-size image

Separation of carbon dioxide and methane in cylindrical geometries materials (including MCM-41 and single-walled carbon nanotube (SWNT)) is investigated systematically using grand canonical Monte Carlo (GCMC) simulations. The selectivities of carbon dioxide with respect to methane (CO2/CH4) in MCM-41 and SWNT at different temperatures and mole fractions are obtained. Simulation results indicate that the selectivity of MCM-41 for CO2/CH4 is insensitive to the bulk mole fraction, while that of the SWNT varies significantly with the bulk mole fraction, although both the MCM-41 and SWNT are described using the cylindrical pore model. By exploring the effects of temperature, pore size and pressure on the selectivity of CO2/CH4, it is found that, to separate CO2 and CH4 efficiently, high pressure, low temperature and small pore size are preferred. In particular, the selectivity of CO2/CH4 in the SWNT can reach 11 at low temperature T = 233 K, high pressure of p = 20 bar and small pore size of 1.52 nm. Compared to the slit-like pores, the cylindrical pores are more efficient for separation of CO2/CH4 at the same temperature and pore size. It is expected that this work can provide useful information for practical application to the separation of CO2/CH4, especially for the determination of operating conditions and geometrical features of porous adsorptive materials.Download full-size image

We present a rare example of Zeolitic Imidazolate Framework-8 (ZIF-8), Zn(MeIM)2•(DMF)•(H2O)3, as luminescent probes with multi-function sensitivity to detect metal ions and small molecules. Our results show that the luminescence intensity of ZIF-8 is strongly sensitive to Cu2+ and Cd2+ ions and small molecules such as acetone. In particular, the luminescence intensity of desolvated ZIF-8 proportionally decreases to the concentration of Cu2+, while increases to the concentration of Cd2+ owing to the recognition of element-imidazole nitrogen sites. The luminescence intensity increases gradually with the increase of amounts of acetone in the standard desolvated ZIF-8-emulsions. These results reveal that the ZIFs might be a good luminescent sensor for metal ions and small molecules.

Covalent organic polymer-4 (COP-4) supported palladium (Pd) catalysts were prepared for the first time. The Pd particles are highly dispersed into pores of COP-4 with electron reduction and the use of N,N-dimethylformamide (DMF) as the solvent. The catalysts show high activity for CO oxidation.

In this work, metal–organic framework (MOF) UMCM-1 and amino functionalized MOF (i.e., UMCM-1-NH2) were synthesized and their performances as luminescent probes were investigated. It is found that both unmodified and amino functionalized MOFs exhibit a luminescence quenching effect on metal ions. In particular, the amino functionalized MOF (UMCM-1-NH2) possesses high sensitivity and selectivity for Fe3+ ions and the luminescence is completely quenched in 10−3 M DMF solution of Fe3+. Moreover, the regenerated UMCM-1-NH2 still has high selectivity for Fe3+ ions, which suggests that the functionalized UMCM-1-NH2 is a promising luminescent probe for selectively sensing iron ions.

The recently reported diamondyne is a fascinating new carbon allotrope with multifunctional applications (J. Mater. Chem. A, 2013, 1, 3851; ibid 2013, 1, 9433). Here we theoretically predict two new tetrahedral node diamondyne (TND) frameworks by replacing the carbon nodes of diamondyne and diamond with the acetylenic linkage (C–CC–C)-formed tetrahedron node. The two resulting theoretical materials (marked as TND-1 and TND-2) exhibit extremely high specific surface areas (SSA) of 6250 and 2992 m2 g−1, respectively. Interestingly, the SSA of TND-1 is calculated to be the highest among all porous carbon materials. By further studying the CO2 capture performance of TND-1 and TND-2, it is found that the CO2 uptake of TND-1 reaches 2461 mg g−1 at 298 K and 50 bar, which outperforms all MOFs, COFs and ZIFs, while the selectivity of TND-2 for CO2/H2 reaches 104 at 35 bar, which is superior to most of the porous materials. In short, the hypothetical TND frameworks are promising candidates for CO2 capture in practical industry.

Reducing anthropogenic carbon dioxide emission has become an urgent environmental and climate issue of our age. Here, a series of covalent-organic polymers (COPs) are synthesized, and the adsorption properties of these COPs for H2, CO2, CH4, N2 and O2 are studied. The H2 uptake of COP-2 reaches 1.74 wt% at 77 K and 1 bar, which is among the highest reported uptakes in the field of microporous organic polymers under similar conditions, and CO2 and CH4 adsorption capacities are 594 mg g−1 and 78 mg g−1, respectively, at 298 K and 18 bar. Then, based on the single component isotherm, the dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is used to predict the selectivity of the COP materials for post-combustion (CO2–N2) and pre-combustion (O2–N2) gas mixtures. The IAST predicted results indicate that COP-1 exhibits significantly higher selectivity compared to COP-2, 3 and 4, due to its smaller pore size. In particular, the adsorption selectivity of COP-1 for the CO2–N2 mixture reaches 91 at a CO2:N2 ratio of 15:85 at 298 K and 1 bar, and 2.38 for the 21:79 O2–N2 mixture at 298 K and 1 bar. Furthermore, these COPs also show robust properties for the removal of CO2 from natural gas. The adsorption selectivity of COP-1 for CO2–CH4 is in the range of 4.1–5.0 at a CO2:CH4 ratio of 15:85 at 0 < P < 40 bar.

We adopt 1,3,6,8-tetrabromopyrene (TBP) and 1,3,5-tris(4-bromophenyl)benzene (TBB) as double monomers to synthesize a series of porous covalent organic polymers (COPs) using the Ni-catalyzed Yamamoto reaction. By manipulating the reactive ratios of two monomers, we successfully achieve the color tailoring of the resultant COP samples. Interestingly, the emission peaks of these porous COP samples cover a wide color range from 533 up to 815 nm, which is the first near-infrared luminescent porous organic material. Further study indicates that these porous COPs can serve as luminescent sensors for highly sensitive and selective sensing of nitroaromatic explosives and metal ions. These materials might also find more applications in photocatalysis, organic electronics and medical imaging.

We develop a new S(DIH) equation based on the difference of isosteric heats (DIH) to calculate the selectivity for CO2 over CH4 in metal–organic frameworks (MOFs) and covalent–organic materials. Using the S(DIH) equation to predict the selectivity requires only the adsorption isotherms of pure components and the DIH of the two components. By comprehensive comparison with the GCMC data in different types of porous materials, including MOFs, ZIFs, COFs and PAFs, it is found that the new S(DIH) equation can predict with high accuracy the selectivity of different types of porous materials for CO2 over CH4 at the low pressure of p = 0–1 bar. Therefore, the new S(DIH) can serve as an efficient tool for the selectivity predictions of porous materials for CO2 over CH4 at p = 0–1 bar, especially for the cases in which experiments can measure the adsorption isotherms and adsorption heats of pure components (such as CO2, CH4, N2 and H2) because the new S(DIH) requires only the adsorption isotherms and adsorption heats of pure components as inputs. In short, the new S(DIH) equation can be considered as a valuable screening tool for obtaining an estimation about the selectivity of a porous material for a certain component of the gas mixture.

The adsorption of pure N2/H2/CH4/CO2 along with the adsorption and separation of mixtures thereof in two metal organic frameworks (MOFs) of UMCM-1 and UMCM-2 have been extensively studied using a hybrid method of computer simulation and adsorption theory. It is found that the excess adsorption isotherms from grand canonical Monte Carlo (GCMC) simulations basically agree with the available experimental data of pure gases, except for H2 adsorption in UMCM-1 at 298 K. Moreover, the GCMC results show that both MOF materials exhibit an excellent storage capacity for pure CH4 and CO2 at room temperature. The excess uptakes of CH4 by UMCM-1 and UMCM-2 for at 5000 kPa are 12.53 and 15.06 mmol g−1, while those of CO2 at 4500 kPa are 30.13 and 36.04 mmol g−1, respectively, which approaches and even exceeds the 30.82 mmol g−1 of MOF-177. In addition, dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is also used to correlate the simulated adsorption isotherms of pure gases and further predict the separation of equimolar mixtures. IAST shows a good agreement with the GCMC results in most cases studied here. The selectivities of both MOF materials in CH4/H2 and CH4/N2 are insensitive to the pressure. The selectivities of both MOF materials for CH4/H2 are almost the same having a value of 4, while they are 2 for CH4/N2. By contrast, the selectivities for CO2/H2, CO2/N2 and CO2/CH4 apparently rely on the pressure, showing 16.4 and 26.9, 5.4 and 7.8, and 2.9 and 4.7 at 4000 kPa for UMCM-1 and UMCM-2, respectively. Compared with other MOFs materials, their separation ability is not prominent, but they are suitable for gas storage.

Since the C60 and graphene were discovered, carbon allotropes have attracted an increasing attention. Here we designed a porous diamond-like carbon framework (named as D-carbon) by inserting –CC– linkers into all the C–C bonds in a diamond, which is a new carbon allotrope formed by sp3–sp hybridized carbon atoms. Interestingly, the porous D-carbon exhibits a high bulk modulus of 91.7 GPa, which is one order of magnitude larger than other porous MOF and COF materials. Moreover, the D-carbon also shows an extremely high excess volumetric methane uptake of 255 v(STP)/v at 298 K and 35 bar, largely exceeding the target (180 v(STP)/v) of US DOE and all other porous materials.

Olefin–paraffin separation is one of the most significant processes in the petrochemical industry. An energy efficient method such as adsorption is considered to be a promising alternative to the traditional cryogenic distillation for the purification of olefins or paraffins. In this work, the grand canonical Monte Carlo (GCMC) method was used to study the adsorption and separation of light hydrocarbons (including ethylene, ethane, propylene and propane) by two diamond-like frameworks: diamondyne (originally named D-carbon in J. Mater. Chem. A, 2013, 1, 3851) and PAF-302, and further explore the mechanism for the adsorptive separation of olefins and paraffins. It is found that both diamondyne and PAF-302 show high uptake of hydrocarbons under ambient conditions, which greatly exceed those of MOFs and ZIFs. The saturation adsorption amounts of ethylene, ethane, propylene and propane on diamondyne are 14.5, 12.3, 10.3 and 8.9 mmol g−1, while they are 31.8, 28.0, 32.0, 30.3 mmol g−1 for PAF-302, which indicates that PAF-302 is an excellent candidate for hydrocarbon adsorption. In addition, it is also found that diamondyne shows preferential adsorption of olefins in the olefin–paraffin mixtures, like most commonly reported MOFs and ZIFs. However, interestingly, PAF-302 exhibits favorable adsorption for paraffins over olefins, which is an entirely different behavior to diamondyne, even though they have similar diamond-like structures.

A coarse-grained molecular dynamics simulation was used to investigate the stress–strain behavior of nanorod-filled polymer composites. The effects of the interfacial interaction, aspect ratio of fillers, filler functionalization, chemical couplings between the polymer and the filler and the filler loading on the mechanical reinforcement were explored. The results indicate that there exists an optimal nanorod volume fraction for elastomer reinforcement. The strong polymer–nanorod interaction enhances the reinforcement of polymer nanocomposites. Meanwhile, it is found that nanorods with longer length and smaller diameter, and the chemical functionalization of nanorods can help realize the efficient interfacial stress transfer. And excessive chemical couplings between polymers and nanorods are harmful to mechanical properties. An upturn in the modulus at large deformation is observed in the Mooney–Rivlin plot, attributed to the limited chain extensibility. Particularly, the medium polymer–nanorod interfacial strength and low nanorod volume loading will lead to better dispersion of nanorods. It is suggested that the reinforcement mechanism comes from the nanorod alignment and bond orientation, as well as from the limited extensibility of chain bridges at large deformation. In addition, an optimal nanorod volume fraction can also be explained by the strong polymer–nanorod network. Compared to glassy systems, the mechanism for the significantly enhanced reinforcement of rubbery systems is also demonstrated. In short, our simulation study of nanorod-induced mechanical reinforcement will provide a basic understanding of polymer reinforcement.

By employing an idealized model of a polymer network and filler, we have investigated the stress-strain behavior by tuning the filler loading and polymer–filler interaction in a broad range. The simulated results indicate that there actually exists an optimal filler volume fraction (between 23% and 32%) for elastomer reinforcement with attractive polymer–filler interaction. To realize this reinforcement, the rubber–filler interaction should be slightly stronger than the rubber–rubber interaction, while excessive chemical couplings are harmful to mechanical properties. Meanwhile, our simulated results qualitatively reproduce the experimental data of Bokobza. By introducing enough chemical coupling between the rubber and the filler, an upturn in the modulus at large deformation is observed in the Mooney-Rivlin plot, attributed to the limited chain extensibility at large deformation. Particularly, the filler dispersion state in the polymer networks is also characterized in detail. It is the first demonstration via simulation that the reinforcement mechanism stems from the nanoparticle-induced chain alignment and orientation, as well as the limited extensibility of chain bridges formed between neighboring nanoparticles at large deformation. The former is influenced by the filler amount, filler size and filler–rubber interaction, and the latter becomes more obvious by strengthening the physical and chemical interactions between the rubber and the filler. Remarkably, the reason for no obvious reinforcing effect in filled glassy or semi-crystalline matrices is also demonstrated. It is expected that this preliminary study of nanoparticle-induced mechanical reinforcement will provide a solid basis for further insightful investigation of polymer reinforcement.

Porous covalent–organic materials (COMs) are a fascinating class of nanoporous material with high surface area and diverse pore dimensions, topologies and chemical functionalities. These materials have attracted ever-increasing attention from different field scientists, owing to their potential applications in gas storage, adsorptive separation and photovoltaic devices. The versatile networks are constructed from covalent bonds (B–O, C–C, C–H, C–N, etc.) between the organic linkers by homo- or hetero-polymerizations. To design and synthesize novel porous COMs, we first summarize their synthesis methods, mainly including five kinds of coupling reaction, i.e. boronic acid, amino, alkynyl, bromine and cyan group-based coupling reactions. Then, we review the progress of porous COMs in clean energy applications in the past decade, including hydrogen and methane storage, carbon dioxide capture, and photovoltaic applications. Finally, to improve their gas adsorptive properties, four possible strategies are proposed, and high-capacity COMs for gas storage are designed by a multiscale simulation approach.

A series of ZIF-derived porous carbon materials are prepared via co-carbonization of ZIF-7 and additional carbon sources, such as glucose, ethylene glycol, glycerol and furfuryl alcohol. Results indicate that ZIF-7/glucose composite-derived Carbon-L-950 as an electrode for the electrochemical capacitor exhibits a high specific capacitance of 228 F g−1 in 6 M KOH at a current density of 0.1 A g−1, even 178 F g−1 at a high current of 10 A g−1 and good stability over 5000 cycles. Moreover, the conductive agent (like acetylene black) is not required in the preparation process of the working electrode, which not only lowers the preparation costs but also is favorable for stability and performance. This facile fabrication of ZIF-derived porous carbon materials may open up a new avenue for producing a new family of porous carbon materials for advanced energy storage devices, such as fuel cells, supercapacitors and lithium batteries.

Rapid and sensitive detection of nitroaromatic explosives has attracted considerable attention due to their serious harm to our world. In this work, two porous luminescent covalent-organic polymers (COP-401 and COP-301) have been synthesized through copolymerization of double ligands. The results indicate that the two COPs with high thermal stability show significant luminescence quenching effects for nitroaromatic explosives. In particular, the two COPs exhibit not only a high sensitivity (about 1 ppm) for nitoraromatic explosives, but also an extremely high selectivity for 2,4,6-trinitrophenol (PA), which suggests that they are promising luminescent probes for highly sensitive and selective detection of nitroaromatic explosives, especially for PA.