Co-reporter:Guoyu Yang and Kechen Wu
The Journal of Physical Chemistry C December 7, 2017 Volume 121(Issue 48) pp:27139-27139
Publication Date(Web):November 14, 2017
DOI:10.1021/acs.jpcc.7b08810
Developing nonlinear optical nanodevices compatible for the current silicon chip industry is of great interest. Modified silicene, with its single atomic silicon thickness, has become a rising material. Here, on the basis of first-principle calculations, two-dimensional halogen and hydrogen saturated silicene are proposed to be competing candidates for strong second-harmonic generation (SHG) material workings in the mid-IR range. The SHG coefficient is more than 10 times larger than KH2PO4 (KDP) with high electron cloud deformability around halogen atoms. Also the Si–H absorption peak is within the range of 2102–2140 cm–1 (4673–4757 nm), red-shifted compared to 3300 cm–1 (3030 nm) of C–H in graphane. In addition, the two-dimensional material construction method can be extended to other novel two-dimensional single-element materials, including borophene, phosphorene, germanene, arsenene, antimonene, and bismuthene.
Co-reporter:Jun Li;Zuju Ma;Kechen Wu
RSC Advances (2011-Present) 2017 vol. 7(Issue 14) pp:8460-8466
Publication Date(Web):2017/01/23
DOI:10.1039/C6RA28304G
The improvement of the thermoelectric performance (determined by the ZT value) of materials is limited by the inter-correlation of the transport coefficients. By performing first principle calculations combined with semi-classical Boltzmann theory, we have systematically investigated the geometric, electronic and thermoelectric properties of AgTaO3 under external strain. It is demonstrated that the electronic structure and phonon transport can be modified independently. Compressive strain along the c-axis decreases the energy separation between the light and heavy valence bands and generates multiple valence band valleys near the Fermi level. Such band structure modification greatly enhances the Seebeck coefficient for the p-type doped compound, which is increased from 600 μV K−1 (δc = 0%) to 690 μV K−1 (δc = −5%). Similarly, tensile strain softens the chemical bonding, favoring the reduction of thermal conductivity. Therefore, the improvement in the thermoelectric performance of AgTaO3 under strain suggests that strain engineering is a generally applicable route to enhancing the Seebeck coefficient and ZT in thermoelectric materials.
Co-reporter:Zuju Ma;Jinyu Hu;Rongjian Sa;Qiaohong Li;Yongfan Zhang;Kechen Wu
Journal of Materials Chemistry C 2017 vol. 5(Issue 8) pp:1963-1972
Publication Date(Web):2017/02/23
DOI:10.1039/C6TC05510A
Although numerous superior nonlinear optical (NLO) crystals for the UV-vis to the near-infrared (IR) region have been established, the development of an efficient NLO material capable of broadband second harmonic generation (SHG) in the mid-IR region is still a big challenge. In this work, we performed hybrid functional calculations to accurately assess the mid-IR NLO capabilities of a group of I3–V–VI4 compounds (with I = Ag or Cu, V = P or As, and VI = S or Se). The linear and nonlinear optical properties of these crystals were predicted and analyzed. This group of compounds display moderate optical anisotropy of refraction (0.1 > Δn > 0.03) to fulfill the phase-matching conditions. In particular, the static SHG coefficients of Cu3AsS4, Ag3PSe4 and Cu3PSe4 are predicted to be about twice that of the benchmark AgGaSe2. A detailed analysis of their precise electronic structures and local dipole moments suggests that it is the coupling of the large dipole moment vector of the constituent asymmetry [I–VI4] tetrahedron and the strong covalent character between V and VI ions that contributes to the large SHG response. These candidates would promote the development of the mid-IR NLO functional materials.
Co-reporter:Qiaohong Li;Zuju Ma;Rongjian Sa;Hertanto Adidharma;Khaled A. M. Gasem;Armistead G. Russell;Maohong Fan;Kechen Wu
Journal of Materials Chemistry A 2017 vol. 5(Issue 28) pp:14658-14672
Publication Date(Web):2017/07/18
DOI:10.1039/C7TA03115G
The finding that transition metals on Mo2C-supported nanocatalysts are promising for water-gas shift (WGS) reactions at room temperature has generated much excitement. However, the progress achieved with computational chemistry in this area is far behind that of experimental studies. Accordingly, density functional theory (DFT) calculations have been used to design the catalytic activity center structure and study the stabilities and catalytic performances of transition metals doped on β-Mo2C(001) surfaces. A new catalyst that comprises atomically dispersed Pt over Mo2C was designed using DFT. The bimetallic Mo2C surfaces doped with single metal Pt exhibit catalytic activities similar to those of the Pt systems for WGS, while demonstrating the advantages of lower costs and higher thermal stabilities. Importantly, the Pt@Mo2C catalyst is more efficient than the pure Pt catalyst for H2 production under the same reaction conditions. Meanwhile, the density of active sites of Pt@Mo2C(001) for H2 production is considerably increased due to its highly dispersed Pt structure. Therefore, Mo and Pt can synergistically increase H2 production. These findings are significantly beneficial for establishing the relationship between the structure and characteristics of the catalyst, understanding the catalytic activities of single-atom catalysts, and gaining insight into the feasibility of developing substitutes for expensive noble metal catalysts.
Co-reporter:Jinyu Hu;Zuju Ma;Rongjian Sa;Yongfan Zhang;Kechen Wu
Dalton Transactions 2017 vol. 46(Issue 8) pp:2635-2642
Publication Date(Web):2017/02/21
DOI:10.1039/C6DT04196E
In recent years, a series of fluoride carbonate crystals, as second harmonic generation (SHG) materials, have been considerably developed; however the lead in these materials is a potential threat to the environment. In this study, the structure, mechanical and optical properties of ABCO3F (A = Rb, Cs; B = Ge, Sn) were systematically investigated to find alternatives to APbCO3F. We found that the RbSnCO3F crystal displays substantial stability and remarkable linear optical properties compared with those of the lead fluoride carbonate SHG materials. In particular, RbSnCO3F exhibits unexpected anisotropy of refractive indices, a key feature to satisfy the phase matching condition in the ultraviolet spectral region. In addition, RbSnCO3F shows a large SHG response, about 21 times that of KH2PO4 (KDP) with the coefficient of 8.21 pm V−1. Our results highlight that RbSnCO3F should be a candidate for a lead-free fluoride carbonate SHG material for achieving coherent light output in laser fields. This investigation also unravels the structure–property relationship of fluoride carbonates, contributing to explore more excellent SHG materials in future.
Co-reporter:Jun Li;Zuju Ma;Rongjian Sa;Kechen Wu
RSC Advances (2011-Present) 2017 vol. 7(Issue 52) pp:32703-32709
Publication Date(Web):2017/06/23
DOI:10.1039/C7RA05193J
In the pursuit of high thermoelectric conversion efficiency, both high operating temperature and high figure of merit ZT are desirable. Thermoelectric materials used in high-temperature power generation are still in great demand. Here we demonstrate the n-type doped barium stannate (BaSnO3) behaves as a robust candidate, as a high-temperature thermoelectric material, due to its ultrahigh power factor and excellent structural and chemical stability. A systematic calculation focused on the geometric, electronic and thermoelectric transport properties of BaSnO3 is performed by using density functional theory combined with Boltzmann transport theory. It can be noticed that the electrical conductivity of BaSnO3 is improved dramatically when it is n-type doped, resulting from the small effective mass and extraordinary high mobility. The power factor maximum reaches 1.5 × 10−3 W m−1 K−2 at 1200 K with the optimal carrier concentration 1.6 × 1019 cm−3, which suggests the great potential of BaSnO3 as an n-type high temperature thermoelectric material.
Co-reporter:Yuman Peng;Zuju Ma;Junjie Hu;Kechen Wu
RSC Advances (2011-Present) 2017 vol. 7(Issue 65) pp:40922-40928
Publication Date(Web):2017/08/18
DOI:10.1039/C7RA07113B
In order to effectively utilize the visible solar light to catalyze and decompose water into hydrogen and oxygen, the ultraviolet light responsive photocatalyst Sr2Ta2O7 is engineered via co-doping of the anionic (S) and cationic (V/Nb) to shift the VBM (valence band maximum) upward and CBM (conduction band minimum) downward by approximately 1 eV, respectively. By first principles study (GGA-PBE), it is discovered that the VBM of (S, V) co-doped Sr2Ta2O7 is shifted upward by 1.14 eV while the CBM of this system is shifted downward by 0.68 eV, which is due to the appearance of impurity states near the VBM and CBM, respectively. For (S, Nb) co-doped Sr2Ta2O7, the VBM is shifted upward by 0.74 eV and the CBM is shifted downward by 0.63 eV. No impurity states of Nd are created, neither near the CBM nor in the band gap for (S, Nb) co-doped case, probably because the Sr2Ta2O7 is essentially isostructural with Sr2Nb2O7. For these two systems mentioned above, it could be a feasible way for Sr2Ta2O7 photocatalyst on water splitting under UV irradiation to convert into the visible light-utilizing material without introducing extra electrons or holes.
Co-reporter:Zuju Ma;Sen Lin;Rongjian Sa;Qiaohong Li;Kechen Wu
RSC Advances (2011-Present) 2017 vol. 7(Issue 39) pp:23994-24003
Publication Date(Web):2017/05/03
DOI:10.1039/C7RA02853A
The oxygen evolution reaction (OER) is known to be the bottleneck of water-splitting. Ag3PO4 is a highly efficient visible light photocatalyst for dye degradation and water oxidation to O2, with a higher OER rate than BiVO4 and WO3. Despite extensive studies on Ag3PO4, the surface properties including surface electronic states, reaction sites and mechanisms of OER on Ag3PO4 surfaces are not clear at present. Herein, we reported a comparative first-principles density functional theory study of the bulk, surface properties and the mechanism of OER on the three primary low index facets of Ag3PO4: (100), (110) and (111). We revealed for the first time that the rate-limiting step of the OER on Ag3PO4 (100), (110) and (111) surfaces is the dehydrogenation of HO* (HO* → O* + H+ + e−), which is different from most reported metal oxides and nitrides like TiO2 and g-C3N4. The OER process on the (100) surface tends to proceed by following a different mechanism as that on the (110) and (111) surfaces. The illumination of the Ag3PO4 (100), (110), and (111) surfaces with solar light provides enough overpotential for the OER to proceed spontaneously. In particular, the free energy change of removal of the first proton from water on the Ag3PO4 (111) surface is much lower than that on (100) and (110) surfaces, giving an explanation for the experimentally observed higher catalytic activity of the (111) surface. The exposed phosphorus atoms on the Ag3PO4 (111) surface promote the dehydrogenation of H2O and suppress the formation of mid-gap states. Our results are profound for understanding the underlying mechanism of the photocatalytic water oxidation process occurring on Ag3PO4 surfaces, and serve as a foundation for developing new high-performance Ag3PO4 based photocatalysts for water splitting and organic contaminant decomposition.
Co-reporter:Jinyu Hu;Zuju Ma;Rongjian Sa;Yongfan Zhang;Kechen Wu
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 23) pp:15120-15128
Publication Date(Web):2017/06/14
DOI:10.1039/C7CP01946G
It is still a challenge to design and synthesize high performance broader ultraviolet non-linear optical (NLO) materials. Two new transition-metal silicates have recently attracted a lot of attention due to their strong phase-matched second harmonic generation (SHG) responses (about 4.5 times higher than KDP). However, the electronic and optical properties underlying the high performance of these materials and consequently, the possibility of designing more efficient silicates for NLO applications are not presently clear. In this study, the geometrical structure and bonding character, electronic structure and optical properties of Li2M4[(TiO)Si4O12] (M = K+, Rb+) crystals have been systematically determined based on the density functional theory. Satisfactory agreement between the experimental and theoretical results indicates that the method and conditions used herein are favorable. A detailed analysis of the precise electronic structure and dipole moments of the two compounds suggests that it is the strong covalent character between Ti(Si) and O and the same orientation alignment of the dipole moment vector of the constituent asymmetric [TiO5]6− square pyramid anion units that result in the large SHG responses for the two compounds. In addition, the unavailable linear and non-linear optical experimental parameters, including dielectric function, optical absorption and birefringence, and all the components of the SHG coefficients are reported for the first time. This investigation unravels the structure–property relationships of titanosilicates and may be significant in terms of providing an efficient strategy towards designing more potential and competitive NLO materials.
Co-reporter:Zhen Wu, Jun Li, Xin Li, Min Zhu, Ke-chen Wu, Xu-tang Tao, Bai-Biao Huang, and Sheng-qing Xia
Chemistry of Materials 2016 Volume 28(Issue 19) pp:6917
Publication Date(Web):September 19, 2016
DOI:10.1021/acs.chemmater.6b02498
The complex Zintl phase Ca9Zn4.5Sb9 is a promising thermoelectric material due to its low thermal conductivity. Initial studies revealed that undoped Ca9Zn4.5Sb9 has a maximum zT value of 0.37 at 823 K. Hall effect measurements on Ca9Zn4.5–xAl2x/3Sb9 (x = 0, 0.5, 1), which nominally feature identical carrier concentration, suggested that control of the interstitial chemistry is critical in affecting the mobility of this system. Removal of the interstitial atoms results in rapid decrease in the carrier mobility, which has negative effects on the overall thermoelectric performance. Further material optimization was successfully carried out via Cu-doping in Ca9Zn4.5Sb9, with the aid of theoretical predictions. This resulted in high concentration of interstitial atoms as in Ca9Zn4.5–xCuxSb9 (x = 0.05, 0.1, 0.15, 0.2). For the optimized composition Ca9Zn4.35Cu0.15Sb9, a maximum of the figure of merit (zT = 0.72) was obtained at 873 K, which is increased by more than twice compared to the undoped material Ca9Zn4.5Sb9.
Co-reporter:Jun Li, Zuju Ma, Chao He, Qiaohong Li and Kechen Wu
Journal of Materials Chemistry A 2016 vol. 4(Issue 10) pp:1926-1934
Publication Date(Web):25 Jan 2016
DOI:10.1039/C5TC03814F
LiB3O5 (LBO), although with high nonlinearity, is angular non-phase matched in deep ultraviolet second harmonic generation (SHG) processes due to its small birefringence. The structural configuration distortion is a promising way to improve the birefringence. By means of first principles computations, the effect of strain along the a, b and c-axes on the birefringence of LBO is systematically predicted in this work. We find that the birefringence can be effectively and considerably enhanced (to 0.075 at 266 nm) by applying a rather weak strain (0.42 GPa) along the c-axis. Such a strain-induced increase in the birefringence of LBO is favourable for extending the shortest wavelength that can be produced by means of the SHG process. The results indicate that strain-engineering is an effective strategy for enhancing birefringence, which behaves like a switch to control the generation of deeper coherent light output for some nonlinear optical crystals.
Co-reporter:Qiaohong Li, Luyang Qiao, Ruiping Chen, Zuju Ma, Rui Si, Yuangen Yao and Kechen Wu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 4) pp:2784-2791
Publication Date(Web):15 Dec 2015
DOI:10.1039/C5CP07309J
We examined the potential catalytic role of the palladium chloride catalyst in CO oxidation using density functional theory and experimental investigations. The active plane of the palladium chloride catalyst is identified as (140). We found that the defective PdCl2(140) surface is able to facilitate the activation of O2 and subsequently promote the oxidation of CO. The most significant reaction channel, the Eley–Rideal mechanism (MER1), proceeds first by a peroxo-type (OOCO) intermediate formation, second by O adsorption with the first CO2 release, then by the second CO attraction and the second CO2 formation, and finally by the second CO2 desorption and restoration of the defective PdCl2(140) surface. The rate-determining step is the formation of the second CO2 in the whole catalytic cycle. Compared to the previously reported catalytic systems, the reaction activation barrier (0.54 eV) of CO oxidation in the PdCl2 catalyst is low, indicating PdCl2 as a potential high-performance catalyst for CO oxidation. The present results enrich our understanding of CO oxidation of Pd-based catalysts and provide a basis for fabricating Pd-based catalysts with high activity.
Co-reporter:Zuju Ma, Rongjian Sa, Qiaohong Li and Kechen Wu
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 2) pp:1050-1058
Publication Date(Web):26 Nov 2015
DOI:10.1039/C5CP05847C
New metal-free carbon nanodot/carbon nitride (C3N4) nanocomposites have shown to exhibit high efficiency for photocatalytic solar water splitting. (J. Liu, et al., Science, 2015, 347, 970) However, the mechanism underlying the ultrahigh performance of these nanocomposites and consequently the possibilities for further improvements are not at present clear. In this work, we performed hybrid functional calculations and included long-range dispersion corrections to accurately characterize the interfacial electron coupling of the graphene quantum dot–graphitic carbon nitride composites (Gdot/g-C3N4). The results revealed that the band gap of Gdot/g-C3N4 could be engineered by changing the lateral size of Gdots. In particular, the C24H12/g-C3N4 composites present an ideal band gap of 1.92 eV to harvest a large part of solar light. More interestingly, a type-II heterojunction is formed at the interface of the Gdot/g-C3N4 composites, a desirable feature for enhanced photocatalytic activity. The charge redistribution at the interface leads to strong electron depletion above the Gdot sheet and electron accumulation below the g-C3N4 monolayer, potentially facilitating the separation of H2O oxidation and reduction reactions. Furthermore, we suggested that the photocatalytic performance of the Gdot/g-C3N4 nanocomposites can be further improved by decreasing the thickness of Gdots and tuning the size of Gdots.
Co-reporter:Gaoji Wang, Yongqin Wei and Kechen Wu
Dalton Transactions 2016 vol. 45(Issue 32) pp:12734-12738
Publication Date(Web):18 Jul 2016
DOI:10.1039/C6DT02062C
Two coordination compounds with the formula Ln5(H2O)(OH)4(NO3)3(BZA)4L (Ln = Tb3+ (1), Dy3+ (2)) have been assembled in a one-pot synthesis from the tetrasubstituted cyclen derivative ligand N,N′,N′′,N′′′-tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane (H4L), Ln(NO3)3·xH2O (Ln = Tb3+ (x = 6), Dy3+ (x = 5)) and the auxiliary ligand benzoic acid (HBZA). Single-crystal X-ray diffraction studies reveal that both compounds feature a novel homometallic appended cubane geometry. The magnetic study on 1 suggests the presence of anti-ferromagnetic interactions, whereas 2 exhibits weak ferromagnetic coupling. Under an applied dc field, 1 shows no out-of-phase alternating current (ac) signal whereas 2 shows slow-relaxation processes that correspond to an energy gap (Ea/kB) of 4.11 K and a pre-exponential factor (τ0) of 3.45 × 10−5 s.
Co-reporter:Gaoji Wang;Yongqin Wei;Kechen Wu
European Journal of Inorganic Chemistry 2016 Volume 2016( Issue 24) pp:3927-3931
Publication Date(Web):
DOI:10.1002/ejic.201600509
Two coordination complexes EuII2EuIII4(OH)4(bza)4L2 (1) and EuIII5(H2O)(OH)4(NO3)3(bza)4L (2) have been assembled with the tetrasubstituted cyclen ligand N,N′,N′′,N′′′-tetrakis(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane (H4L) and the auxiliary ligand benzoic acid (Hbza). Complex 2 is a pentanuclear EuIII cluster whereas complex 1 is a huge heterovalent 2EuII/4EuIII cluster in which two divalent europium ions are trapped within the macrocyclic cavities of the designed ligands L and are further isolated from the environment by peripheral phenyl rings and the tetrahedral 4EuIII cluster, which results in the enhanced oxidative stability of Eu2+. The luminescence of complex 1 was investigated and is discussed in comparison with the luminescence of ligand H4L and complex 2. Owing to the protection of Eu2+ by the macrocyclic ligands L, the heterovalent complex exhibits a strong broad emission band with a maximum at 533 nm as well as the characteristic sharp emissions of Eu3+. The broad emission is redshifted compared with that of ligand H4L and has been attributed to the Laporte-allowed 4f65d1 4f7 transition of Eu2+.
Co-reporter:Zuju Ma, Kechen Wu, Baozhen Sun and Chao He
Journal of Materials Chemistry A 2015 vol. 3(Issue 16) pp:8466-8474
Publication Date(Web):10 Mar 2015
DOI:10.1039/C5TA01020A
Ag-based oxides, particularly AgSbO3, have attracted attention in photocatalytic O2 evolution from water splitting. Employing state-of-the-art DFT calculations and a statistical mechanical approach, we investigated the incorporation of Bi into AgSbO3 to form a AgSb1−xBixO3 solid-solution for tuning the band gap to the optimum (around 2.0 eV) for the photocatalysis of water splitting under sunlight. A phase transition from the pyrochlore to ilmenite phase was predicted at x ≈ 0.21. The band gap decreases almost linearly with increasing Bi concentration for each phase. The decreased band gap is attributed to the lower energy of the Bi s–O p antibonding orbitals than that of the Sb s–O p antibonding orbitals in the conduction bands. Excitingly, a band gap of around 2.0 eV was obtained at x = 0.1875. The combination of a strong oxidizing potential and an optimal band gap for solar light absorption makes the pyrochlore AgSb0.8125Bi0.1875O3 solid-solution a promising candidate for the production of oxygen in a Z-scheme water-splitting system.
Co-reporter:Ming-yan Pan, Zu-ju Ma, Xiao-cun Liu, Sheng-qing Xia, Xu-tang Tao and Ke-chen Wu
Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:9695-9700
Publication Date(Web):25 Aug 2015
DOI:10.1039/C5TC01887K
Two new quaternary pnictide-based multinary compounds, Ba4AgGa5P8 and Ba4AgGa5As8, were synthesized from Pb-flux reactions. By using the single crystal X-ray diffraction technique the structures were determined to crystallize with the noncentrosymmetric (NCS) space group Iba2 (No. 45) (cell parameters: a = 7.294(9)/7.4769(8) Å, b = 18.03(2)/18.5766(19) Å, c = 6.557(8)/6.7590(7) Å for the P- and As-containing compounds, respectively). Theoretical calculations indicate strong SHG responses for both compounds, which are approximately two times larger than that of AgGaSe2. Based on the calculated cutoff-energy-dependent static SHG coefficients, the large NLO coefficients of these compounds should originate from the distorted GaPn4 tetrahedra, which construct various layers and chains giving rise to a large polarization. Both compounds have moderate birefringence (Δn), 0.157 and 0.206 for Ba4AgGa5P8 and Ba4AgGa5As8, respectively, suitable to meet the phase-matching condition in the SHG process.
Co-reporter:Yongqin Wei, Rongjian Sa, Qiaohong Li and Kechen Wu
Dalton Transactions 2015 vol. 44(Issue 7) pp:3067-3074
Publication Date(Web):15 Dec 2014
DOI:10.1039/C4DT03421J
The mixed-lanthanide metal–organic frameworks (M'LnMOFs) applied for accurate, non-invasive and self-reference temperature measurements have been only recently recognized. It is a great challenge for chemists to fulfil the requirements of a thermostable structure, intense luminescence and high temperature sensitivity on one LnMOF ratiometric thermometer for thermometric applications. By choosing 2,4-(2,2′:6′,2′′-terpyridin-4′-yl)-benzenedisulfonic acid (H2DSTP) as the first ligand and changing the ancillary ligand to oxalic acid (OA) or 1,4-benzene dicarboxylic acid (BDC), we have successfully developed two types of highly stable and sensitive thermometers [Tb1−xEux(OA)0.5(DSTP)]·3H2O and [Tb1−xEux(BDC)0.5(DSTP)]·2H2O (x = 0.01, 0.02) that in addition exhibit brilliant luminescence over a wide temperature range, providing a new strategy to explore luminescence-based M'LnMOF thermometers.
Co-reporter:Yongqin Wei, Gaoji Wang, and Kechen Wu
Crystal Growth & Design 2015 Volume 15(Issue 11) pp:5288
Publication Date(Web):October 5, 2015
DOI:10.1021/acs.cgd.5b00804
Due to the instability of divalent europium ions, the heterometallic Eu(II)/Ln(III) complex has not yet been reported. By utilizing coordination chemistry principles, a macrocyclic ligand, N,N′,N″,N‴-tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecae (H4L), has been rationally designed to encapsulate Eu2+ and to enable direct formation of the first mixed Eu(II)/Ln(III) complexes, namely, EuII2LnIII4(OH)4(NIC)4L2 (Ln = Sm, Eu, Tb; HNIC = nicotinic acid). Two divalent europium ions are trapped within the macrocyclic cavities of designed ligands L and are further isolated from the environment by outside phenyl rings and the tetrahedral 4Ln(III) cluster, resulting in the enhanced stability of Eu2+. Cyclic voltammetry experiments showed that the oxidation potential of Eu2+ in the heterovalent 2Eu(II)/4Ln(III) cluster is larger than that for the ferrocene/ferrocenium redox couple, which has never been reported previously for Eu2+-containing complexes. Further development of Eu(II) complexes has been limited because Eu2+ could be easily oxidized to Eu3+. The dramatic oxidative stability of as-synthesized complexes not only verifies the synthetic feasibility but also highlights the prospective applications of mixed Eu(II)/Ln(III) coordination complexes.
Co-reporter:Qiaohong Li, Yongqin Wei, Rongjian Sa, Zuju Ma and Kechen Wu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 48) pp:32140-32148
Publication Date(Web):07 Aug 2015
DOI:10.1039/C5CP03740A
Considering the importance of palladium-based and doped metal-oxide catalysts in CO oxidation, we design a new Pd3O9@α-Al2O3 catalyst and simulate its efficiency under a hydroxylated effect. The structure, electronic structure and oxidation activity of the hydroxylated Pd3O9@α-Al2O3(0001) surface are investigated by density functional theory. Under the O-rich growth conditions, Pd preferentially replaces Al. The lowest formation energy of the Pd-doped α-Al2O3(0001) surface is 0.21 eV under conditions wherein the coverage of the Pd-doped α-Al2O3 is 0.75 on a pre-hydroxylated surface and the water coverage is 0.25, which leads to formation of a Pd3O9 cluster embedded in the Al2O3(0001) surface. The reaction mechanisms of CO oxidization have been elucidated first by CO adsorption and migration, second by Ov formation with the first CO2 release, then by the first foreign O2 filling and CO co-adsorption, and finally by the second CO2 desorption and restoration of the hydroxylated Pd3O9@α-Al2O3(0001) surface. The rate-determining step is the formation of the first CO2 in the whole catalytic cycle. The results also indicate that the energy barrier for CO oxidization is obviously reduced compared to that of the undoped surface, which implies that the introduction of Pd can efficiently improve the oxidation reactivity of the α-Al2O3(0001) surface. Compared to the synthesized Ir1/FeOx (1.41 eV) and Pt1/FeOx (0.79 eV) catalysts, the reaction activation barrier of CO oxidation is lowered by 0.65 eV and 0.03 eV, respectively. Therefore, the Pd3O9@α-Al2O3 catalyst shows superior catalytic activity in CO oxidation. The present results enrich the understanding of the catalytic oxidation of CO by palladium-based catalysts and provide a clue for fabricating palladium-based catalysts with low cost and high activity.
Co-reporter:Bao-Zhen Sun, Zuju Ma, Chao He and Kechen Wu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 44) pp:29844-29853
Publication Date(Web):16 Oct 2015
DOI:10.1039/C5CP03700J
Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 μW cm−1 K−2 along the a direction, while a relatively low value (11.72 μW cm−1 K−2) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (κmin) along the a direction is estimated to be about 0.67 and 0.55 W m−1 K−1 for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m−1 K−1 at 300 K). The reasonable PF and κmin suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 1019 (SnSe2) vs. 2.87 × 1019 cm−3 (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials.
Co-reporter:Qiaohong Li, Zhangfeng Zhou, Ruiping Chen, Baozhen Sun, Luyang Qiao, Yuangen Yao and Kechen Wu
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 14) pp:9126-9134
Publication Date(Web):23 Feb 2015
DOI:10.1039/C4CP05738D
Oxidative coupling of toxic pollutant CO to form the platform raw chemical material dimethyl oxalate (DMO) has been industrialized however the catalytic mechanism has been unknown so far. The reaction mechanism of CO oxidative coupling to form DMO on a Pd(111) surface has been investigated using density functional theory (DFT) and in situ diffuse reflectance infrared (DRIR) spectroscopy. DFT calculations and in situ DRIRS measurements indicate that two co-adsorbed intermediates COOMe and OCCO, initiate the reaction. C–C coupling occurs earlier due to a low coupling barrier and small steric hindrance. The results also suggest that Pd(111) is selective towards DMO over DMC, and that CO pre-adsorption and CO in excess effectively enhance the yield of DMO. The microscopic elucidation of this important reaction suggests improvements in coal-to-EG (CTEG) production which can be applied in practice to effectively enhance the yield and reduce the cost. The results may help with further fine-tuning and designing of high-efficient noble metal catalysts.
Co-reporter:Bao-Zhen Sun, Zuju Ma, Chao He and Kechen Wu
RSC Advances 2015 vol. 5(Issue 69) pp:56382-56390
Publication Date(Web):23 Jun 2015
DOI:10.1039/C5RA06134B
We present a detailed theoretical study of the SnS compound, which has not been investigated in depth to date, concerning its crystal structure, electronic structure and thermoelectric property. The results of this study show that pure SnS is not a good thermoelectric material but that its ZT can be increased by adjusting both the temperature and carrier concentration. Further, the optimal temperatures and carrier concentrations for producing the peak ZT are identified. The peak ZT is always below unity in the low-temperature Pnma phase; conversely, when the crystal undergoes a displacive phase transition at 878 K, the peak ZT is enhanced to 1.61 ± 0.02 at 1080 K. Additionally, the average ZT in the Cmcm phase (e.g., approximately 1.3) is significantly higher than that in the Pnma phase (e.g., 0.31 ± 0.05). Therefore, the optimally doped SnS material may be highly efficient in its thermal-to-electrical energy conversion at high temperatures. We attribute the remarkable high ZT of doped SnS to the high sensitivity of the electrical conductivity to the carrier concentration. The results of this study describe a simple and viable strategy to optimize the ZT value of the SnS compound using the synergetic tuning of temperature and carrier concentration.
Co-reporter:Chao He, Zu-Ju Ma, Bao-Zhen Sun, Rong-Jian Sa, Kechen Wu
Journal of Alloys and Compounds 2015 Volume 623() pp:393-400
Publication Date(Web):25 February 2015
DOI:10.1016/j.jallcom.2014.11.062
•The nonlinear optical response of BiFeO3 changes nonlinearly with polarization.•Nonlinear optical response could be used as criteria for the polarization reversal.•Analyzed the origin of the change of nonlinear optical response.•The hybridization of Bi 6s and O 2p leads to the ferroelectric displacement.Rhombohedral BiFeO3 which has a large spontaneous polarization is a candidate material for ferroelectric random access memory (FeRAM). And the polarization reversal is the key factor for the application of FeRAM. Here, the electronic, linear and nonlinear optical properties, structure and its stability of BiFeO3 during the continuous polarization reversal from reference cubic phase to ferroelectric R3c phase were systematically investigated by LSDA + U (local spin density approximation plus Hubbard U) and DFPT (density functional perturbation theory) method. We proposed that the nonlinear optical second order coefficients could be indicators to check the polarization reversal of BiFeO3 and our result showed that the coefficient reach its maximum between 20% distortion and 40% distortion during the half path of the reversal. The relationship between the nonlinear optical second order coefficient and the Bader charge was also compared and we found the coefficient is also dependent on the Bader charge. In addition, the linear optical absorption coefficient was calculated; the obvious change in absorption peaks was observed during the transition. By comparing the crystal orbital of the reference cubic phase and distorted R3c phase we found that the hybridized Bi 6s and O 2p is the main reason that causes the structure distortion. The local phonon density of states proves that the Bi and O interaction is the origin of the instability of cubic phase BiFeO3. The factor group analysis showed the change of Raman and IR modes during the transition.
Co-reporter:Zuju Ma, Kechen Wu, Rongjian Sa, Qiaohong Li, Chao He, Zhiguo Yi
International Journal of Hydrogen Energy 2015 Volume 40(Issue 2) pp:980-989
Publication Date(Web):12 January 2015
DOI:10.1016/j.ijhydene.2014.11.088
•The structural origin of the enhancement in the visible and UV light photocatalytic activities of N-doped La2Ti2O7.•The effects of substantial and interstitial N atoms on the band gap engineering and photocatalytic activities.•The predicted band gap value of 2.46 eV agrees well with the experimental value of 2.51 eV.Recently, a wide-band-gap layered perovskite compound La2Ti2O7 (LTO) has been reported to show a significant enhancement of both the visible and UV light photocatalytic activities after doping with N atoms. It is known that the doping sites often act as recombination centers of the photo-exited carriers and block the redox reactions. In this work, we investigated the origin of the enhancement in photocatalytic activity of N-doped LTO by using density functional theory (DFT) calculations. More than 40 models were constructed by considering ionic state of dopants, distance between dopants, doping concentrations, and formation of oxygen vacancy. The structure-properties relation of N-doped LTO was established. We found that the model of Sub3N–3Odv (with three dispersed substitutional N atoms at O sites and one oxygen vacancy in 87-atom LTO supercell) well explains both the shift-up of the valence bands and the narrowed band gap observed in experiment. The obtained band gap of 2.46 eV agrees well with the experimental value of 2.51 eV. For the models with interstitial N atoms, the impurity states are mainly localized at the higher-energy region of the band gap, which may trap the photo-excited carriers and decrease the photocatalytic activity. The work provides a potential implication for effective band-gap narrowing of wide-gap photocatalysts.
Co-reporter:Jing Ren, Zuju Ma, Chao He, Rongjian Sa, Qiaohong Li, Kechen Wu
Computational Materials Science 2015 Volume 106() pp:1-4
Publication Date(Web):August 2015
DOI:10.1016/j.commatsci.2015.04.031
•Ga3AsO7 is predicted as a best piezoelectric candidate with high Curie temperature among these crystals.•We predict three new structures and they meet the mechanical stability rule.•The relationship between the bridging angle θ and piezoelectric constant is discussed.A first-principles study of the structure, elastic and piezoelectric properties of A3BO7 (A = Ga, Al; B = P, As) using the density functional perturbation theory (DFPT) has been performed. The structure-properties relation was established. We found that the piezoelectric constant is highly sensitive to the distortion of crystal structures. The larger A–O–B bridging angle θ is, the smaller piezoelectric stress coefficient e15 will be. The obtained piezoelectric tensor d15 of Ga3AsO7 is −23.9 pC/N, which is more than ten times larger than the d11 of SiO2. The new finding will be useful in the applications of Ga3AsO7 in the piezoelectric devices with high Curie temperature.Three structures of our compounds were simulated by substituting the corresponding elements, based on the structure of Ga3PO7. Then we calculated the elastic and piezoelectric constants and predicted the Ga3AsO7 is the most promising piezoelectric material of them. The structure of A3BO7 compounds. Atoms showed in (a) with A, B and O colored blue, green and red respectively as well as the bridging angle θ. Polyhedral structures were represent in (b) with BO4 tetrahedrons in blue and three AO5 trigonal bipyramids in dark gray. Besides, the direction of lattice was (a) x, (b) y and (c) z.
Co-reporter:Chao He, Zuju Ma, Bao-Zhen Sun, Qiaohong Li, Kechen Wu
Computational Materials Science 2015 Volume 105() pp:11-17
Publication Date(Web):July 2015
DOI:10.1016/j.commatsci.2015.04.016
•The ground state of perfect LiOsO3 is G-type antiferromagnetic insulating state by LSDA + U and HSE.•Li-defects could lead to the shift of Fermi level towards valence bands.•The defects could destroy the magnetic order, leading to a metallic state.•Perfect LiOsO3 has a large value of spontaneous polarization and nonlinear optical coefficient.A comprehensive investigation has been made on the ground state, magnetic, ferroelectric and optical properties of the recently synthesized ferroelectric-like LiOsO3 by first-principle calculations. It is found that the ground state of perfect LiOsO3 is G type antiferromagnetic (G-AFM) order by both LSDA + U with Ueff > 0 eV and HSE. For the G-AFM order, when Ueff > 1.75 eV the charge gap opens for LiOsO3 while the gap is about 0.60 eV by HSE. So the perfect LiOsO3 should be a G-AFM semiconductor. As for the Li-defected Li0.94OsO3, the Fermi level shifts to the valence bands. On the other hand the translational periodicity is destroyed by various defects, leading to the disappearance of magnetic order which is responsible for the ferroelectric metal state observed in experiment. This is proved by the decrease of the Os average magnetic moments of Li-defected LiOsO3. The calculated spontaneous polarization of perfect LiOsO3 is about 22.23 μC/cm2 and the largest component of second order nonlinear optical coefficient is 80.795 pm/V, which indicate that it should be a potential ferroelectric and nonlinear optical material.The crystal structure, Os magnetic moment and band gap of perfect G-AFM LiOsO3 obtained by both calculated and fitted method as a function of Ueff within LSDA + U.
Co-reporter:Chao-Yong Mang, Cai-Ping Liu, Guang-Ming Liu, Bei Jiang, Hai Lan, Ke-Chen Wu, Ya Yan, Hai-Fei Li, Ming-Hui Yang, Yu Zhao
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2015 Volume 136(Part C) pp:1401-1408
Publication Date(Web):5 February 2015
DOI:10.1016/j.saa.2014.10.028
•The conformational stability is influenced by the intramolecular hydrogen bonds.•Only the preferred conformation of 3S screw configuration can display the negative optical rotation.•The preferred conformation of 3S screw configuration has the positive lowest energy band of the electronic CD spectrum.A cyclic dipeptide often has the multiple configurations and the abundant conformations. The density functional theory (DFT) method is used to search the preferred conformation of the most probable configuration for cordycedipeptide A isolated from the culture liquid of Cordyceps sinensis. The time-dependent DFT approach is exploited to describe the profile of electronic circular dichroism (CD). The calculated results show that the most probable configuration is 3S6R7S, whose preferred conformation has a negative optical rotation and a positive lowest energy electronic CD band.On the basis of the DFT and time-dependent DFT computations, as the global minimum, the preferred conformation of 3S6R7S configuration for cordycedipeptide A has a negative optical rotation and a positive lowest energy band of electronic CD.
Co-reporter:Jian Lin, Rongjian Sa, Mingxing Zhang, and Kechen Wu
The Journal of Physical Chemistry A 2015 Volume 119(Issue 29) pp:8174-8181
Publication Date(Web):June 24, 2015
DOI:10.1021/acs.jpca.5b03456
The second-order nonlinear optical (NLO) properties of a series of dithienylethene- (DTE-) containing Pt(II) complexes have been investigated by density functional theory calculations. The first hyperpolarizabilities β of studied systems can be greatly enhanced by simple ligand substitutions. Because of the nature of DTE units, the β values also can be varied by the use of lights in the studied systems. The highest β difference between photoisomers can over 1000 × 10–30 esu, with the contrast around five times. Thus, the studied systems can act as effective photoswitchable second-order NLO materials. The time-dependent density functional theory calculations revealed that the charge transfer patterns of studied systems have special characters compared to other reported DTE-containing NLO switched chromogens, the DTE units mainly act as electron-donors in studied systems, and the variation of β can be viewed as alternation of donor abilities of DTE units; thus, our work also proposed a new mechanism for designing photoswitched NLO multifunctional materials.
Co-reporter:Yongqin Wei, Qiaohong Li, Rongjian Sa and Kechen Wu
Chemical Communications 2014 vol. 50(Issue 15) pp:1820-1823
Publication Date(Web):06 Dec 2013
DOI:10.1039/C3CC48344D
The intrinsic white-light-emitting properties of a lanthanide metal–organic framework that approach requirements for solid-state lighting are easily improved by incorporating minute quantities of red-emitting Eu3+ into the host framework by virtue of the isostructural character of the La3+ and Eu3+ compounds and efficient sensitization of ligands toward Eu3+ ions.
Co-reporter:Xuemei Shi, Zuju Ma, Chao He, Kechen Wu
Chemical Physics Letters 2014 Volume 608() pp:219-223
Publication Date(Web):21 July 2014
DOI:10.1016/j.cplett.2014.06.017
Highlights
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DFT computations are performed on the optical properties of metal halides.
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HgI2 exhibits large second-order nonlinear optical coefficient.
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HgI2 exhibits suitable IR transparency and optical birefringence.
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HgI2 is predicted to be a promising mid-to-far IR nonlinear optical crystal.
Co-reporter:Rongjian Sa, Liang Fang, Mingdong Huang, Qiaohong Li, Yongqin Wei, and Kechen Wu
The Journal of Physical Chemistry A 2014 Volume 118(Issue 39) pp:9113-9119
Publication Date(Web):July 1, 2014
DOI:10.1021/jp5064319
The binding modes of urokinase-type plasminogen activator (uPA) with five inhibitors (1-(7-sulfonamidoisoquinolinyl) guanidine derivatives) were predicted based on molecular dynamic simulations. MM/PBSA free-energy calculations and MM/GBSA free-energy decomposition analyses were performed on the studied complexes. The calculated binding free energies are reasonably consistent with the experimental results. The free-energy decomposition analyses elucidate the different contributions of the energy of some favorable residues in the interactions between protein and ligand of each complex. The results indicate that the inhibitors mainly interact with the S1 pocket of uPA, wherein the hydrogen bonds and the interactions between guanidines and the corresponding residues play an important role. Moreover, hydrogen bond analyses show the water-mediated hydrogen-bond network near the S1 pocket between uPA, and the ligand probably leads to excellent selectivity of these inhibitors on uPA.
Co-reporter:Zuju Ma, Kechen Wu, Rongjian Sa, Qiaohong Li, Yongfan Zhang
Journal of Alloys and Compounds 2013 Volume 568() pp:16-20
Publication Date(Web):15 August 2013
DOI:10.1016/j.jallcom.2013.03.082
•The elasticity of γ-NaAsSe2 was calculated for the first time.•The strong nonlinear optical response was well reproduced theoretically.•γ-NaAsSe2 possesses large piezoelectric and linear electro-optical effect.•The microscopic origins of these properties were discussed.•The potential applications in acousto-optical and nonlinear optical devices.Monoclinic NaAsSe2 (γ-NaAsSe2) has been reported to be a potential IR nonlinear optical material due to the very strong second harmonic generation (SHG). Here, we present a systematic density functional theory (DFT) study on the elasticity, SHG response, linear electro-optical (EO) effect, and piezoelectricity of this compound and analyze the microscopic origins of these properties. We find that γ-NaAsSe2 has smaller values of elastic moduli than those of AgGaSe2, and behaves in a ductile manner. The strong SHG response observed experimentally is well predicted by the 2n + 1 theorem and the “sum over states” expressions based on the DFT. As with the strong SHG response, γ-NaAsSe2 also presents large linear EO coefficient (r11 = 32.7 pm/V, as large as that of LiNbO3), and piezoelectric coefficient (e11 = 1.27 C/m2, about seven times larger than that of α-quartz). The highly distorted structure and the strong hybridizations between As and Se sp orbitals are identified as the chief sources of these unique properties. Our results demonstrate the potential applications of γ-NaAsSe2 in piezoelectric, electro-optical, and nonlinear optical devices.
Co-reporter:Wenxu Zheng, Yongqin Wei, Chong-bin Tian, Xueying Xiao and Kechen Wu
CrystEngComm 2012 vol. 14(Issue 10) pp:3347-3350
Publication Date(Web):02 Mar 2012
DOI:10.1039/C2CE25108F
A chirally helical coordination polymer [Ni4(H2O)7L4·H2O]n (H2222L = 2-(pyridin-2-yl)-1H-imidazole-4,5-dicarboxylic acid) constructed from a Ni4L4 building block exhibits spontaneous chiral resolution and the enantiomers of 1M and 1P have been confirmed by single-crystal analysis and solid-state circular dichroism spectra. The magnetic properties of compound 1 are also discussed.
Co-reporter:Wenxu Zheng, Yongqin Wei, Xueying Xiao and Kechen Wu
Dalton Transactions 2012 vol. 41(Issue 11) pp:3138-3140
Publication Date(Web):03 Feb 2012
DOI:10.1039/C2DT12238C
An enantioenriched three-dimensional quartz-type framework {[Ni1.5(tzdc)(H2O)3]·3H2O}n (H3tzdc = 4H-1,2,4-triazole-3,5-dicarboxylic acid) possessing chiral channels is obtained through spontaneous asymmetric crystallization without any enantiopure additive.
Co-reporter:Wentao Wu, Kechen Wu, Zuju Ma, Rongjian Sa
Chemical Physics Letters 2012 Volume 537() pp:62-64
Publication Date(Web):1 June 2012
DOI:10.1016/j.cplett.2012.04.025
Abstract
The thermoelectric properties of p-type doped AgGaTe2 with chalcopyrite structure have been investigated within DFT theoretical framework. The electrical transportations of AgGaTe2 strongly depend on the doping level as well as the temperature. The Seebeck coefficients at various temperatures corresponding to the optimal doping level are all about 270 μV/K. Thus the optimal doped AgGaTe2 could be obtained by adjusting the Seebeck coefficient to 270 μV/K in the future experiment. The figure of merit of AgGaTe2 at 900 K reaches 1.19 under optimal doping level indicating AgGaTe2 is a very promising thermoelectric material.
Co-reporter:Chaoyong Mang, Caiping Liu, Kechen Wu
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2012 Volume 98() pp:444-452
Publication Date(Web):December 2012
DOI:10.1016/j.saa.2012.08.075
Stereo-chemistry and chiroptics of several alkynyl cyclophanes with multiple binaphthyls are investigated using density functional calculations. It is revealed that the lower-energy Cotton effects of tetragon-shape cyclophanes originate from electronic transitions on two long sides while the higher-energy Cotton effects have important origin in electronic transitions on two short sides. According to spectral characteristic and relative energy, we deduce that two low-energy conformers of S5 with two meta-position-substituted benzene rings are likely to coexist. For S6 as a macrocyclic molecule including eight binaphthyls, we infer that only one conformer as S6c is populated. This conformer is of a groove-shape structure with the αβαβ orientation of four meta-position-substituted benzene rings.Graphical abstractStereo-chemistry and chiroptics of several alkynyl cyclophanes with multiple binaphthyls are investigated using density functional calculations.Highlights► The ECD spectra depend on the rotational dihedral angle between two naphthyl planes. ► The ECD spectra come from electronic transitions of long edges or short edges. ► For S5, the two lowest-energy conformers are likely to coexist. ► For S6, only one conformer is likely to be populated.
Co-reporter:Zuju Ma ; Zhiguo Yi ; Jing Sun ;Kechen Wu
The Journal of Physical Chemistry C 2012 Volume 116(Issue 47) pp:25074-25080
Publication Date(Web):November 6, 2012
DOI:10.1021/jp3093447
Recently developed photoelectrode Ag3PO4 exhibits extremely high quantum yield (up to 90% at 420 nm) of O2 generation from water oxidation, but it can only absorb part of visible light and cannot reduce water to release H2. It is still a challenge to develop the high performance water splitting photocatalysts toward broader solar spectrum response. We theoretically investigated the electronic and photocatalytic properties of Ag3PC4VI (C = O, S, Se) by the hybrid density functional method. The experimental band gap of Ag3PO4 (2.45 eV) was well reproduced by this level of theory (2.49 eV). We found that orthorhombic Ag3PSe4 presents not only an ideal direct band gap (2.09 eV) to harvest a large part of solar light in the visible range but also suitable reduction potential (−0.275 V vs normal hydrogen electrode, NHE) for water reduction. Ag3PS4 has a relatively larger band gap of 2.88 eV, but it has a rather negative reduction potential (−0.53 V vs NHE). The analysis of the density of states and the single-state charge densities suggested that the weakened P–CVI bonds and the disappearance of Ag–Ag interaction from Ag3PO4 to Ag3PC4VI(C = S, Se) result in the great change of the conduction band minimum from the highly delocalized Ag s orbitals to the strong mixing of P–Se(S) orbitals. The potential problems of stability and photocorrosion for Ag3PC4VI(C = S, Se) were also discussed. Our theoretical results demonstrated that Ag3PC4VI(C = S, Se) both are potential candidates for the photocatalytic hydrogen generation from water.
Co-reporter:Yongqin Wei, Kechen Wu, Jiangang He, Wengxu Zheng and Xueying Xiao
CrystEngComm 2011 vol. 13(Issue 1) pp:52-54
Publication Date(Web):28 Oct 2010
DOI:10.1039/C0CE00547A
A chirally helical coordination polymer [Zn(H2O)(ONCP)Cl]n self-assembled with ligand 2-(2-carboxyphenyl)imidazo(4,5-f)(1,10)phenanthroline displays second harmonic generation efficiency, which is approximately two times as much as that of potassium dihydrogen phosphate (KDP), and tunable photoluminescence images form yellow-green to white based on the variation of excitation light.
Co-reporter:Qiaohong Li;Kechen Wu;Rongjian Sa;Yongqin Wei
Journal of Cluster Science 2011 Volume 22( Issue 3) pp:365-380
Publication Date(Web):2011 September
DOI:10.1007/s10876-011-0391-5
We present the first-principle calculations on the electronic excitations and second-order properties in solution phase of two typical inorganic trinuclear anionic clusters, [MoCu2S4(SPh)2]2− and [Mo2CuS4]1−(edt)2(PPh3) (edt=1,2-ethanedithiolato) in the framework of density functional theory (DFT). The computed excitation energies are in good agreement with the outcome of the measurements. The predicted values of the molecular quadratic hyperpolarizabilities are of the comparable order of those of the typical organometallic chromophores. We demonstrate the significant contributions to the second-order responses from the charge transfers between the metal centers (MMCT) which are ascribed to the direct metal–metal bonding interactions in these two charged clusters. This meaningful ligand-independent mechanism for the second-order response largely relates to metal–metal bonding strength, and the understanding will benefit to the future design of the new-generation molecular based nonlinear optical materials and optoelectronic devices by means of the conscious tuning of metal–metal interactions and metal-core structures of inorganic polynuclear clusters.
Co-reporter:Fei Lin, Kechen Wu, Jiangang He, Rongjian Sa, Qiaohong Li, Yongqin Wei
Chemical Physics Letters 2010 Volume 494(1–3) pp:31-36
Publication Date(Web):9 July 2010
DOI:10.1016/j.cplett.2010.05.067
Abstract
Mixed-metal borides are promising superhard materials (Kaner et al. (2005) [1]). In this Letter, density functional computations have been applied to the structural, electronic and elastic properties of mixed-metal diborides Re0.5Ir0.5B2, Re0.5Tc0.5B2, Os0.5W0.5B2 and Os0.5Ru0.5B2. The elastic moduli decrease from pure metal diboride ReB2 to Re0.5Ir0.5B2 and on the contrary increase from OsB2 to Os0.5W0.5B2 because boron–metal interactions are contaminated by the occupied anti-bonding orbitals. Alloying ReB2 (OsB2) with Tc (Ru) decreases the elastic moduli owing to the relativistic effects. Mixed-metal effects on elastic deformations focus on bonding strengths, which effectively tune the elastic properties of metal diborides.
Co-reporter:Jiangang He, Kechen Wu, Rongjian Sa, Qiaohong Li, Yongqin Wei
Chemical Physics Letters 2010 490(4–6) pp: 132-137
Publication Date(Web):
DOI:10.1016/j.cplett.2010.03.038
Co-reporter:Qiaohong Li, Kechen Wu, Yongqin Wei, Rongjian Sa, Yiping Cui, Canggui Lu, Jing Zhu and Jiangang He
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 22) pp:4490-4497
Publication Date(Web):24 Apr 2009
DOI:10.1039/B903582F
We present in this paper the second-order nonlinear optical properties of a series of penta-nuclear metal clusters [MS4Cu4X2Py6] (M = Mo, W; X = Br, I) on the basis of the hyper-Rayleigh scattering experiments and the first-principle calculations (TDDFT). The measurements obtain the notably large dynamic quadratic hyperpolarizabilities at 1064 nm [β(−2ω, ω, ω) values are around 200 × 10−30 esu] and, by extrapolation, a large static values around 60 × 10−30 esu. The computational results of the electronic excitation energies and quadratic hyperpolarizabilities by TDDFT method are in good agreement with the experimental values and by careful examination they are both dependent on the nature of the metals. The in-depth analysis of the mechanism for the second-order response unambiguously shows the evidence of the contribution of direct metal–metal interaction charge transfers. This provides a new tool to tune nonlinear optical properties in exploiting metal cluster materials and molecular devices.
Co-reporter:Yongqin Wei, Yunfang Yu, Rongjian Sa, Qiaohong Li and Kechen Wu
CrystEngComm 2009 vol. 11(Issue 6) pp:1054-1060
Publication Date(Web):09 Feb 2009
DOI:10.1039/B815464C
Two novel cobalt(II) coordination polymers [Co2(H2O)4(Hbidc)2]n (1) and [Co(Hbidc)]n (2), (Hbidc = 1H-benzimidazole-5,6-dicarboxylate) were synthesized hydrothermally by treating CoSO4 and H3bidc at 160 or 220 °C, respectively. X-Ray diffraction analyses showed that compound 1 is a 1-D chain polymer with dimer units [Co2(H2O)4(Hbidc)2] and the infinite chains of compound 1 array uniformly towards the crystallographic a-axis in a 3-D supramolecular framework which possesses abundant hydrogen-bonding interactions between uncoordinated carboxylo-oxygen atoms and coordinated water molecules or N–H groups in imidazole rings. Compound 2 is a novel five-coordinated cobalt(II) chain compound exhibiting a 2-D polymeric network with parallel zip-like cobalt–carboxylate chains along the crystallographic b-axis and the 2-D polymeric networks of compound 2 exhibit a layered arrangement, in which the strong hydrogen-bonding interaction between uncoordinated carboxylo-oxygen atoms and N–H groups in the imidazole rings play a key role in the final 3-D supramolecular architectures. Magnetic studies revealed that compound 1 shows a ferromagnetic coupling between two CoII ions in the dimer unit and compound 2 exhibits an antiferromagnetic property.
Co-reporter:Jiangang He, Kechen Wu, Caiping Liu, Rongjian Sa
Chemical Physics Letters 2009 Volume 483(1–3) pp:30-34
Publication Date(Web):24 November 2009
DOI:10.1016/j.cplett.2009.10.052
The geometries, electronic structures, and stabilities of MSi14 clusters (M = Sc–Ni) have been studied by using density functional theory. The results demonstrate that the cage composed of fourteen Si atoms can completely encapsulate a 3d transition-metal atom. The binding forces of MSi14 clusters mainly origin from the electrostatic and orbital interactions. In binding (or embedding) energy calculation, the Wigner–Witmer spin conservation rule is needed in the cases of CrSi14 and MnSi14. Among MSi14 clusters, only CrSi14 shows the highest stability and chemical inertness simultaneously, indicating that only 20-electron rule can be applied to MSi14 species.The minimum polarizability principle (MPP) is helpful to determine the stabilities of 3d transition-metal doped Si14 clusters. The pronounced stability of CrSi14 among these clusters shows only 20-electron counting rule can be applied to them.
Co-reporter:Jiangang He, Kechen Wu, Rongjian Sa, Qiaohong Li, Yongqin Wei
Chemical Physics Letters 2009 Volume 475(1–3) pp:73-77
Publication Date(Web):16 June 2009
DOI:10.1016/j.cplett.2009.05.010
The electronic structures and static dipole polarizabilities of M3N@C2n fullerenes (M = Sc and Y; 2n = 68–98) were studied by using density functional theory. Unlike nonmetal endohedral fullerenes, M3N@C2n show smaller static dipole polarizabilities than the corresponding C2n ones do. It is because the induced electric field of carbon cages is reduced by inserting M3N cluster. The mean dipole polarizabilities of M3N@C2n fullerenes were found to correlate closely to their chemical hardness and electron delocalization volume. The refractive indexes of the face-centered-cubic crystals assembled by M3N@C2n fullerenes were also estimated.Under weak external electric field, the M3N cluster encapsulated in C2n fullerene reduces the field induced by the carbon cage and, consequently, the M3N@C2n fullerenes show smaller dipole polarizability than the corresponding C2n cage.
Co-reporter:Yan Wu, Rongjian Sa, Qiaohong Li, Yongqin Wei, Kechen Wu
Chemical Physics Letters 2009 Volume 467(4–6) pp:387-392
Publication Date(Web):5 January 2009
DOI:10.1016/j.cplett.2008.11.073
The influence of Cd2+ on nucleobases and base pairing has been studied systematically using high-level DFT method. Cd2+ strongly interacts with adenine (A), changing tautomer structures and affecting the tautomer equilibrium whereas the Cd2+-thymine (T) interaction barely shifts the equilibrium of T tautomers. The isoenergy of metal-bridged A–Cd2+–T base pair complexes in the same binding pattern reveals the absence of interaction between A and T. The effects of Cd2+ in H-bond base pairing have also been discussed to further understand the possible schemes in cadmium induced DNA mutations.Interaction of Cd2+ with adenine and thymine and influence of metalation in base pairing are studied with high level DFT methods. Cd2+ binding to adenine nucleobases changes the equilibrium of tautomers and preferably supports the imino form rare tautomer.
Co-reporter:Qiaohong Li, Kechen Wu, Rongjian Sa, Yongqin Wei
Chemical Physics Letters 2009 Volume 471(4–6) pp:229-233
Publication Date(Web):26 March 2009
DOI:10.1016/j.cplett.2009.02.052
Abstract
The quadratic hyperpolarizability (β) of 4-(dimethylamino-4′-stilbazole)tungsten pentacarbonyl (W(CO)5DAS) organometallic chromophore has been studied by DFT/TDDFT methods. The intrinsical mechanism for the second-order response has been ascribed to the contribution from metal-to-ligand charge transfer. The consideration of the solvent effect quantitatively improves the consistency of the calculated data with the experimental data, and switches the βvec sign. The βvec value is remarkably sensitive to the polarized solvent and even exhibits the different mechanisms for the second-order response in gas and solution phases. The possibilities of using this intriguing effect in the perspective of a molecular switch device are evaluated.
Co-reporter:Yunfang Yu, Yongqin Wei, Ria Broer, Rongjian Sa, Kechen Wu
Journal of Solid State Chemistry 2008 Volume 181(Issue 3) pp:539-551
Publication Date(Web):March 2008
DOI:10.1016/j.jssc.2007.12.028
Novel mononuclear, trinuclear, and hetero-trinuclear supermolecular complexes, [Co(phen)2(H2O)(HTST)]·2H2O (1), [Co3(phen)6(H2O)2(TST)2]·7H2O (2), and [Co2Cu(phen)6(H2O)2(TST)2]·10H2O (3), have been synthesized by the reactions of a new tri-sulfonate ligand (2,4,6-tris(4-sulfophenylamino)-1,3,5-triazine, H3TST) with the M2+ (M=Co, Cu) and the second ligand 1,10-phenanthroline (phen). Complex 1 contains a cis-Co(II)(phen)2 building block and an HTST as monodentate ligand; complex 2 consists of two TST as bidentate ligands connecting one trans- and two cis-Co(II)(phen)2 building blocks; complex 3 is formed by replacing the trans-Co(II)(phen)2 in 2 with a trans-Cu(II)(phen)2, which is the first reported hetero-trinuclear supramolecular complex containing both the Co(II)(phen)2 and Cu(II)(phen)2 as building blocks. The study shows the flexible multifunctional self-assembly capability of the H3TST ligands presenting in these supramolecular complexes through coordinative, H-bonding and even π–π stacking interactions. The photoluminescent optical properties of these complexes are also investigated and discussed as well as the second-order nonlinear optical properties of 1.Novel mononuclear, trinuclear, and hetero-trinuclear supermolecular complexes, [Co(phen)2(H2O)(HTST)]·2H2O (1), [Co3(phen)6(H2O)2(TST)2]·7H2O (2), and [Co2Cu(phen)6(H2O)2(TST)2]·10H2O (3), have been synthesized by the reactions of a new tri-sulfonate ligand (2,4,6-tris(4-sulfophenylamino)-1,3,5-triazine, H3TST) with the M2+ (M=Co, Cu) and the second ligand 1,10-phenanthroline (phen). The study shows the flexible multifunctional self-assembly capability of H3TST ligand presenting in these supramolecular complexes.
Co-reporter:Qiaohong Li, Rongjian Sa, Yongqin Wei and Kechen Wu
The Journal of Physical Chemistry A 2008 Volume 112(Issue 22) pp:4965-4972
Publication Date(Web):May 8, 2008
DOI:10.1021/jp712156t
We present a comparative study of the metal−metal interaction effect on the static quadratic hyperpolarizabilities of two typical dinuclear rhenium clusters. The electronic structures, excitation spectra, dipolar moments, static polarizabilities, and quadratic hyperpolarizabilities of the two complexes with direct metal−metal interactions have been computed and analyzed with the use of high-level DFT/TDDFT methods. The geometries and the first intense excitations agree with the relevant reported measurements. The orbital decomposition scheme (J. Phys. Chem. A 2006, 110, 1014−1021) has been applied to analyze the relationship between the electronic structures and nonlinear optical (NLO) properties of these two complexes. We propose an unprecedented NLO response mechanism featuring the contribution of the direct metal−metal interaction transition process in these dinuclear rhenium complexes. This contribution positively enhances the quadratic hyperpolarizability and relates to the intensity of the metal−metal interactions of the complexes. The results are helpful to the development of NLO chromophores in polynuclear metal clusters through the molecular design technique.
Co-reporter:Kechen Wu, Caiping Liu, Chaoyong Mang
Optical Materials 2007 Volume 29(Issue 9) pp:1129-1137
Publication Date(Web):May 2007
DOI:10.1016/j.optmat.2006.05.005
Linear and nonlinear optical properties of the organic–inorganic hybrid crystal, l-arginine phosphate monohydrate crystal have been investigated by the first-principles calculation as well as the electronic and vibrational properties. The calculated nonlinear optical coefficients agreed well to the experimental data. The results showed both organic and inorganic structural building blocks contribute to the large nonlinear optical activities of this crystal and the significant contribution of the intermolecular hydrogen bonds. The absorption-edges on both IR and UV sides of LAP crystal have been estimated and the structure–property relationship has been discussed. The study is helpful to the further development of l-arginine phosphate monohydrate crystal analogs with improved nonlinear optical properties.
Co-reporter:Jinyu Hu, Zuju Ma, Rongjian Sa, Yongfan Zhang and Kechen Wu
Dalton Transactions 2017 - vol. 46(Issue 8) pp:NaN2642-2642
Publication Date(Web):2017/01/19
DOI:10.1039/C6DT04196E
In recent years, a series of fluoride carbonate crystals, as second harmonic generation (SHG) materials, have been considerably developed; however the lead in these materials is a potential threat to the environment. In this study, the structure, mechanical and optical properties of ABCO3F (A = Rb, Cs; B = Ge, Sn) were systematically investigated to find alternatives to APbCO3F. We found that the RbSnCO3F crystal displays substantial stability and remarkable linear optical properties compared with those of the lead fluoride carbonate SHG materials. In particular, RbSnCO3F exhibits unexpected anisotropy of refractive indices, a key feature to satisfy the phase matching condition in the ultraviolet spectral region. In addition, RbSnCO3F shows a large SHG response, about 21 times that of KH2PO4 (KDP) with the coefficient of 8.21 pm V−1. Our results highlight that RbSnCO3F should be a candidate for a lead-free fluoride carbonate SHG material for achieving coherent light output in laser fields. This investigation also unravels the structure–property relationship of fluoride carbonates, contributing to explore more excellent SHG materials in future.
Co-reporter:Yongqin Wei, Rongjian Sa and Kechen Wu
Dalton Transactions 2016 - vol. 45(Issue 46) pp:NaN18667-18667
Publication Date(Web):2016/10/26
DOI:10.1039/C6DT03655D
A long π-conjugated organic ligand 2-(2,4-disulfophenyl)imidazo(4,5-f)(1,10)-phenanthroline (H3sfpip) featuring blue-green emission was used to construct Eu(III) MOFs to obtain a target white-light-emitting LnMOF with no dopant atom in its structure. Two complexes, [Eu(H2O)2(OH)(Hsfpip)]·H2O (1) and [Eu(H2O)(oa)0.5(Hsfpip)]·2H2O (2), were successfully synthesized under similar hydrothermal reaction conditions. The absence or presence of an ancillary ligand such as oxalic acid (oa) showed direct influence on the coordination mode of the Hsfpip linker and in the final topology of the polymeric structure. Complex 1 displays an unstable 2D polymeric structure and weak red luminescence from Eu3+ due to the quenching effect of high-energy O–H oscillators around the inner coordination sphere of the metal center, whereas the introduction of an ancillary ligand such as oxalic acid results in a tight-bonding 3D polymeric structure and an intense white light emission from complex 2. Moreover, due to the skeleton rigidity and robustness of complex 2, the white light emission can be improved via a heating process.
Co-reporter:Yongqin Wei, Qiaohong Li, Rongjian Sa and Kechen Wu
Chemical Communications 2014 - vol. 50(Issue 15) pp:NaN1823-1823
Publication Date(Web):2013/12/06
DOI:10.1039/C3CC48344D
The intrinsic white-light-emitting properties of a lanthanide metal–organic framework that approach requirements for solid-state lighting are easily improved by incorporating minute quantities of red-emitting Eu3+ into the host framework by virtue of the isostructural character of the La3+ and Eu3+ compounds and efficient sensitization of ligands toward Eu3+ ions.
Co-reporter:Ming-yan Pan, Zu-ju Ma, Xiao-cun Liu, Sheng-qing Xia, Xu-tang Tao and Ke-chen Wu
Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN9700-9700
Publication Date(Web):2015/08/25
DOI:10.1039/C5TC01887K
Two new quaternary pnictide-based multinary compounds, Ba4AgGa5P8 and Ba4AgGa5As8, were synthesized from Pb-flux reactions. By using the single crystal X-ray diffraction technique the structures were determined to crystallize with the noncentrosymmetric (NCS) space group Iba2 (No. 45) (cell parameters: a = 7.294(9)/7.4769(8) Å, b = 18.03(2)/18.5766(19) Å, c = 6.557(8)/6.7590(7) Å for the P- and As-containing compounds, respectively). Theoretical calculations indicate strong SHG responses for both compounds, which are approximately two times larger than that of AgGaSe2. Based on the calculated cutoff-energy-dependent static SHG coefficients, the large NLO coefficients of these compounds should originate from the distorted GaPn4 tetrahedra, which construct various layers and chains giving rise to a large polarization. Both compounds have moderate birefringence (Δn), 0.157 and 0.206 for Ba4AgGa5P8 and Ba4AgGa5As8, respectively, suitable to meet the phase-matching condition in the SHG process.
Co-reporter:Qiaohong Li, Kechen Wu, Yongqin Wei, Rongjian Sa, Yiping Cui, Canggui Lu, Jing Zhu and Jiangang He
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 22) pp:NaN4497-4497
Publication Date(Web):2009/04/24
DOI:10.1039/B903582F
We present in this paper the second-order nonlinear optical properties of a series of penta-nuclear metal clusters [MS4Cu4X2Py6] (M = Mo, W; X = Br, I) on the basis of the hyper-Rayleigh scattering experiments and the first-principle calculations (TDDFT). The measurements obtain the notably large dynamic quadratic hyperpolarizabilities at 1064 nm [β(−2ω, ω, ω) values are around 200 × 10−30 esu] and, by extrapolation, a large static values around 60 × 10−30 esu. The computational results of the electronic excitation energies and quadratic hyperpolarizabilities by TDDFT method are in good agreement with the experimental values and by careful examination they are both dependent on the nature of the metals. The in-depth analysis of the mechanism for the second-order response unambiguously shows the evidence of the contribution of direct metal–metal interaction charge transfers. This provides a new tool to tune nonlinear optical properties in exploiting metal cluster materials and molecular devices.
Co-reporter:Qiaohong Li, Yongqin Wei, Rongjian Sa, Zuju Ma and Kechen Wu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 48) pp:NaN32148-32148
Publication Date(Web):2015/08/07
DOI:10.1039/C5CP03740A
Considering the importance of palladium-based and doped metal-oxide catalysts in CO oxidation, we design a new Pd3O9@α-Al2O3 catalyst and simulate its efficiency under a hydroxylated effect. The structure, electronic structure and oxidation activity of the hydroxylated Pd3O9@α-Al2O3(0001) surface are investigated by density functional theory. Under the O-rich growth conditions, Pd preferentially replaces Al. The lowest formation energy of the Pd-doped α-Al2O3(0001) surface is 0.21 eV under conditions wherein the coverage of the Pd-doped α-Al2O3 is 0.75 on a pre-hydroxylated surface and the water coverage is 0.25, which leads to formation of a Pd3O9 cluster embedded in the Al2O3(0001) surface. The reaction mechanisms of CO oxidization have been elucidated first by CO adsorption and migration, second by Ov formation with the first CO2 release, then by the first foreign O2 filling and CO co-adsorption, and finally by the second CO2 desorption and restoration of the hydroxylated Pd3O9@α-Al2O3(0001) surface. The rate-determining step is the formation of the first CO2 in the whole catalytic cycle. The results also indicate that the energy barrier for CO oxidization is obviously reduced compared to that of the undoped surface, which implies that the introduction of Pd can efficiently improve the oxidation reactivity of the α-Al2O3(0001) surface. Compared to the synthesized Ir1/FeOx (1.41 eV) and Pt1/FeOx (0.79 eV) catalysts, the reaction activation barrier of CO oxidation is lowered by 0.65 eV and 0.03 eV, respectively. Therefore, the Pd3O9@α-Al2O3 catalyst shows superior catalytic activity in CO oxidation. The present results enrich the understanding of the catalytic oxidation of CO by palladium-based catalysts and provide a clue for fabricating palladium-based catalysts with low cost and high activity.
Co-reporter:Bao-Zhen Sun, Zuju Ma, Chao He and Kechen Wu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 44) pp:NaN29853-29853
Publication Date(Web):2015/10/16
DOI:10.1039/C5CP03700J
Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 μW cm−1 K−2 along the a direction, while a relatively low value (11.72 μW cm−1 K−2) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (κmin) along the a direction is estimated to be about 0.67 and 0.55 W m−1 K−1 for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m−1 K−1 at 300 K). The reasonable PF and κmin suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 1019 (SnSe2) vs. 2.87 × 1019 cm−3 (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials.
Co-reporter:Qiaohong Li, Zhangfeng Zhou, Ruiping Chen, Baozhen Sun, Luyang Qiao, Yuangen Yao and Kechen Wu
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 14) pp:NaN9134-9134
Publication Date(Web):2015/02/23
DOI:10.1039/C4CP05738D
Oxidative coupling of toxic pollutant CO to form the platform raw chemical material dimethyl oxalate (DMO) has been industrialized however the catalytic mechanism has been unknown so far. The reaction mechanism of CO oxidative coupling to form DMO on a Pd(111) surface has been investigated using density functional theory (DFT) and in situ diffuse reflectance infrared (DRIR) spectroscopy. DFT calculations and in situ DRIRS measurements indicate that two co-adsorbed intermediates COOMe and OCCO, initiate the reaction. C–C coupling occurs earlier due to a low coupling barrier and small steric hindrance. The results also suggest that Pd(111) is selective towards DMO over DMC, and that CO pre-adsorption and CO in excess effectively enhance the yield of DMO. The microscopic elucidation of this important reaction suggests improvements in coal-to-EG (CTEG) production which can be applied in practice to effectively enhance the yield and reduce the cost. The results may help with further fine-tuning and designing of high-efficient noble metal catalysts.
Co-reporter:Zuju Ma, Rongjian Sa, Qiaohong Li and Kechen Wu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 2) pp:NaN1058-1058
Publication Date(Web):2015/11/26
DOI:10.1039/C5CP05847C
New metal-free carbon nanodot/carbon nitride (C3N4) nanocomposites have shown to exhibit high efficiency for photocatalytic solar water splitting. (J. Liu, et al., Science, 2015, 347, 970) However, the mechanism underlying the ultrahigh performance of these nanocomposites and consequently the possibilities for further improvements are not at present clear. In this work, we performed hybrid functional calculations and included long-range dispersion corrections to accurately characterize the interfacial electron coupling of the graphene quantum dot–graphitic carbon nitride composites (Gdot/g-C3N4). The results revealed that the band gap of Gdot/g-C3N4 could be engineered by changing the lateral size of Gdots. In particular, the C24H12/g-C3N4 composites present an ideal band gap of 1.92 eV to harvest a large part of solar light. More interestingly, a type-II heterojunction is formed at the interface of the Gdot/g-C3N4 composites, a desirable feature for enhanced photocatalytic activity. The charge redistribution at the interface leads to strong electron depletion above the Gdot sheet and electron accumulation below the g-C3N4 monolayer, potentially facilitating the separation of H2O oxidation and reduction reactions. Furthermore, we suggested that the photocatalytic performance of the Gdot/g-C3N4 nanocomposites can be further improved by decreasing the thickness of Gdots and tuning the size of Gdots.
Co-reporter:Qiaohong Li, Luyang Qiao, Ruiping Chen, Zuju Ma, Rui Si, Yuangen Yao and Kechen Wu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 4) pp:NaN2791-2791
Publication Date(Web):2015/12/15
DOI:10.1039/C5CP07309J
We examined the potential catalytic role of the palladium chloride catalyst in CO oxidation using density functional theory and experimental investigations. The active plane of the palladium chloride catalyst is identified as (140). We found that the defective PdCl2(140) surface is able to facilitate the activation of O2 and subsequently promote the oxidation of CO. The most significant reaction channel, the Eley–Rideal mechanism (MER1), proceeds first by a peroxo-type (OOCO) intermediate formation, second by O adsorption with the first CO2 release, then by the second CO attraction and the second CO2 formation, and finally by the second CO2 desorption and restoration of the defective PdCl2(140) surface. The rate-determining step is the formation of the second CO2 in the whole catalytic cycle. Compared to the previously reported catalytic systems, the reaction activation barrier (0.54 eV) of CO oxidation in the PdCl2 catalyst is low, indicating PdCl2 as a potential high-performance catalyst for CO oxidation. The present results enrich our understanding of CO oxidation of Pd-based catalysts and provide a basis for fabricating Pd-based catalysts with high activity.
Co-reporter:Jun Li, Zuju Ma, Chao He, Qiaohong Li and Kechen Wu
Journal of Materials Chemistry A 2016 - vol. 4(Issue 10) pp:NaN1934-1934
Publication Date(Web):2016/01/25
DOI:10.1039/C5TC03814F
LiB3O5 (LBO), although with high nonlinearity, is angular non-phase matched in deep ultraviolet second harmonic generation (SHG) processes due to its small birefringence. The structural configuration distortion is a promising way to improve the birefringence. By means of first principles computations, the effect of strain along the a, b and c-axes on the birefringence of LBO is systematically predicted in this work. We find that the birefringence can be effectively and considerably enhanced (to 0.075 at 266 nm) by applying a rather weak strain (0.42 GPa) along the c-axis. Such a strain-induced increase in the birefringence of LBO is favourable for extending the shortest wavelength that can be produced by means of the SHG process. The results indicate that strain-engineering is an effective strategy for enhancing birefringence, which behaves like a switch to control the generation of deeper coherent light output for some nonlinear optical crystals.
Co-reporter:Zuju Ma, Kechen Wu, Baozhen Sun and Chao He
Journal of Materials Chemistry A 2015 - vol. 3(Issue 16) pp:NaN8474-8474
Publication Date(Web):2015/03/10
DOI:10.1039/C5TA01020A
Ag-based oxides, particularly AgSbO3, have attracted attention in photocatalytic O2 evolution from water splitting. Employing state-of-the-art DFT calculations and a statistical mechanical approach, we investigated the incorporation of Bi into AgSbO3 to form a AgSb1−xBixO3 solid-solution for tuning the band gap to the optimum (around 2.0 eV) for the photocatalysis of water splitting under sunlight. A phase transition from the pyrochlore to ilmenite phase was predicted at x ≈ 0.21. The band gap decreases almost linearly with increasing Bi concentration for each phase. The decreased band gap is attributed to the lower energy of the Bi s–O p antibonding orbitals than that of the Sb s–O p antibonding orbitals in the conduction bands. Excitingly, a band gap of around 2.0 eV was obtained at x = 0.1875. The combination of a strong oxidizing potential and an optimal band gap for solar light absorption makes the pyrochlore AgSb0.8125Bi0.1875O3 solid-solution a promising candidate for the production of oxygen in a Z-scheme water-splitting system.
Co-reporter:Wenxu Zheng, Yongqin Wei, Xueying Xiao and Kechen Wu
Dalton Transactions 2012 - vol. 41(Issue 11) pp:NaN3140-3140
Publication Date(Web):2012/02/03
DOI:10.1039/C2DT12238C
An enantioenriched three-dimensional quartz-type framework {[Ni1.5(tzdc)(H2O)3]·3H2O}n (H3tzdc = 4H-1,2,4-triazole-3,5-dicarboxylic acid) possessing chiral channels is obtained through spontaneous asymmetric crystallization without any enantiopure additive.
Co-reporter:Yongqin Wei, Rongjian Sa, Qiaohong Li and Kechen Wu
Dalton Transactions 2015 - vol. 44(Issue 7) pp:NaN3074-3074
Publication Date(Web):2014/12/15
DOI:10.1039/C4DT03421J
The mixed-lanthanide metal–organic frameworks (M'LnMOFs) applied for accurate, non-invasive and self-reference temperature measurements have been only recently recognized. It is a great challenge for chemists to fulfil the requirements of a thermostable structure, intense luminescence and high temperature sensitivity on one LnMOF ratiometric thermometer for thermometric applications. By choosing 2,4-(2,2′:6′,2′′-terpyridin-4′-yl)-benzenedisulfonic acid (H2DSTP) as the first ligand and changing the ancillary ligand to oxalic acid (OA) or 1,4-benzene dicarboxylic acid (BDC), we have successfully developed two types of highly stable and sensitive thermometers [Tb1−xEux(OA)0.5(DSTP)]·3H2O and [Tb1−xEux(BDC)0.5(DSTP)]·2H2O (x = 0.01, 0.02) that in addition exhibit brilliant luminescence over a wide temperature range, providing a new strategy to explore luminescence-based M'LnMOF thermometers.
Co-reporter:Gaoji Wang, Yongqin Wei and Kechen Wu
Dalton Transactions 2016 - vol. 45(Issue 32) pp:NaN12738-12738
Publication Date(Web):2016/07/18
DOI:10.1039/C6DT02062C
Two coordination compounds with the formula Ln5(H2O)(OH)4(NO3)3(BZA)4L (Ln = Tb3+ (1), Dy3+ (2)) have been assembled in a one-pot synthesis from the tetrasubstituted cyclen derivative ligand N,N′,N′′,N′′′-tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane (H4L), Ln(NO3)3·xH2O (Ln = Tb3+ (x = 6), Dy3+ (x = 5)) and the auxiliary ligand benzoic acid (HBZA). Single-crystal X-ray diffraction studies reveal that both compounds feature a novel homometallic appended cubane geometry. The magnetic study on 1 suggests the presence of anti-ferromagnetic interactions, whereas 2 exhibits weak ferromagnetic coupling. Under an applied dc field, 1 shows no out-of-phase alternating current (ac) signal whereas 2 shows slow-relaxation processes that correspond to an energy gap (Ea/kB) of 4.11 K and a pre-exponential factor (τ0) of 3.45 × 10−5 s.
Co-reporter:Jinyu Hu, Zuju Ma, Rongjian Sa, Yongfan Zhang and Kechen Wu
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 23) pp:NaN15128-15128
Publication Date(Web):2017/05/17
DOI:10.1039/C7CP01946G
It is still a challenge to design and synthesize high performance broader ultraviolet non-linear optical (NLO) materials. Two new transition-metal silicates have recently attracted a lot of attention due to their strong phase-matched second harmonic generation (SHG) responses (about 4.5 times higher than KDP). However, the electronic and optical properties underlying the high performance of these materials and consequently, the possibility of designing more efficient silicates for NLO applications are not presently clear. In this study, the geometrical structure and bonding character, electronic structure and optical properties of Li2M4[(TiO)Si4O12] (M = K+, Rb+) crystals have been systematically determined based on the density functional theory. Satisfactory agreement between the experimental and theoretical results indicates that the method and conditions used herein are favorable. A detailed analysis of the precise electronic structure and dipole moments of the two compounds suggests that it is the strong covalent character between Ti(Si) and O and the same orientation alignment of the dipole moment vector of the constituent asymmetric [TiO5]6− square pyramid anion units that result in the large SHG responses for the two compounds. In addition, the unavailable linear and non-linear optical experimental parameters, including dielectric function, optical absorption and birefringence, and all the components of the SHG coefficients are reported for the first time. This investigation unravels the structure–property relationships of titanosilicates and may be significant in terms of providing an efficient strategy towards designing more potential and competitive NLO materials.
Co-reporter:Zuju Ma, Jinyu Hu, Rongjian Sa, Qiaohong Li, Yongfan Zhang and Kechen Wu
Journal of Materials Chemistry A 2017 - vol. 5(Issue 8) pp:NaN1972-1972
Publication Date(Web):2017/01/23
DOI:10.1039/C6TC05510A
Although numerous superior nonlinear optical (NLO) crystals for the UV-vis to the near-infrared (IR) region have been established, the development of an efficient NLO material capable of broadband second harmonic generation (SHG) in the mid-IR region is still a big challenge. In this work, we performed hybrid functional calculations to accurately assess the mid-IR NLO capabilities of a group of I3–V–VI4 compounds (with I = Ag or Cu, V = P or As, and VI = S or Se). The linear and nonlinear optical properties of these crystals were predicted and analyzed. This group of compounds display moderate optical anisotropy of refraction (0.1 > Δn > 0.03) to fulfill the phase-matching conditions. In particular, the static SHG coefficients of Cu3AsS4, Ag3PSe4 and Cu3PSe4 are predicted to be about twice that of the benchmark AgGaSe2. A detailed analysis of their precise electronic structures and local dipole moments suggests that it is the coupling of the large dipole moment vector of the constituent asymmetry [I–VI4] tetrahedron and the strong covalent character between V and VI ions that contributes to the large SHG response. These candidates would promote the development of the mid-IR NLO functional materials.
Co-reporter:Qiaohong Li, Zuju Ma, Rongjian Sa, Hertanto Adidharma, Khaled A. M. Gasem, Armistead G. Russell, Maohong Fan and Kechen Wu
Journal of Materials Chemistry A 2017 - vol. 5(Issue 28) pp:NaN14672-14672
Publication Date(Web):2017/06/12
DOI:10.1039/C7TA03115G
The finding that transition metals on Mo2C-supported nanocatalysts are promising for water-gas shift (WGS) reactions at room temperature has generated much excitement. However, the progress achieved with computational chemistry in this area is far behind that of experimental studies. Accordingly, density functional theory (DFT) calculations have been used to design the catalytic activity center structure and study the stabilities and catalytic performances of transition metals doped on β-Mo2C(001) surfaces. A new catalyst that comprises atomically dispersed Pt over Mo2C was designed using DFT. The bimetallic Mo2C surfaces doped with single metal Pt exhibit catalytic activities similar to those of the Pt systems for WGS, while demonstrating the advantages of lower costs and higher thermal stabilities. Importantly, the Pt@Mo2C catalyst is more efficient than the pure Pt catalyst for H2 production under the same reaction conditions. Meanwhile, the density of active sites of Pt@Mo2C(001) for H2 production is considerably increased due to its highly dispersed Pt structure. Therefore, Mo and Pt can synergistically increase H2 production. These findings are significantly beneficial for establishing the relationship between the structure and characteristics of the catalyst, understanding the catalytic activities of single-atom catalysts, and gaining insight into the feasibility of developing substitutes for expensive noble metal catalysts.
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![4-[4,6-BIS[4-(DIETHYLAMINO)PHENYL]-1,3,5-TRIAZIN-2-YL]-N,N-DIETHYLANILINE](http://img.cochemist.com/ccimg/201600/201544-02-7.png)
![4-[4,6-BIS[4-(DIETHYLAMINO)PHENYL]-1,3,5-TRIAZIN-2-YL]-N,N-DIETHYLANILINE](http://img.cochemist.com/ccimg/201600/201544-02-7_b.png)
