•A bio-gel template natural lotus roots was used to synthesize CoFe2O4 nano-catalysts.•Samples with porous structure and of large specific area (∼95.6 m2/g) were obtained.•The annealed CoFe2O4 were proven to be highly efficient in catalyzing aerobic oxidation of cyclohexane.•Optimum parameters were found as O2 pressure 1.6 MPa, reaction time 6.0 h and temperature 150 °C.•Self-catalysis of cyclohexanone was discovered which makes the strategy more positive in applications.Magnetic cobalt ferrite (CoFe2O4) particles were synthesized via a solvothermal pathway by using the gel of natural lotus roots as bio-gel template. Samples with porous structure and of large specific area (∼95.6 m2/g) were prepared, which were assembled by CoFe2O4 particles of uniform sizes (ca. 15.0 nm). The annealed CoFe2O4 nanoparticles were proven to be highly efficient catalysts for aerobic oxidation of cyclohexane. Factors such as oxygen pressure, temperature, reaction time and self-catalysis by adding cyclohexanone have been studied in view of improving the conversion of cyclohexane as well as the selectivity of KA oil (cyclohexanone and cyclohexanol). Optimum parameters were found at an initial O2 pressure of 1.6 MPa when the reaction was conducted for 6.0 h at the temperature of 150 °C. The maximum conversion of cyclohexane oxidation reaches 16.43%, and the selectivity 90.3% for KA oil was obtained. This research provides a facile way of developing green catalysts in the aerobic oxidation of cyclohexane.A bio-template synthetic strategy was proposed to prepare porous CoFe2O4 nano-catalyst with the aid of supercritical CO2 drying. The catalyst show good performance towards the aerobic oxidation of cyclohexane in a solvent-free system.Download high-res image (229KB)Download full-size image

A new method is developed to immobilize silver (Ag) nanocrystals (NCs) on carbon nanotubes (CNTs) by using the pre-coated MoS2 as sacrificial layers, and a type of composite materials consisting with CNTs, Ag NCs and MoS2 have been prepared. In this method the ultral-thin layers of MoS2 are coaxially pre-coated on the CNTs to prepare the hybrid of CNTs-MoS2. The CNTs-MoS2 is used as substrates to immobilize Ag NCs in a hydrothermal solution. During the hydrothermal reaction the MoS2 is oxidized by [Ag(NH3)2]+, and parts of the MoS2 layers are removed in the form of (NH4)2MoO4. The Ag NCs are found to be uniformly dispersed on the CNTs-MoS2. The fabricated composites (CNTs-MoS2–Ag) exhibit excellent catalytic performances in the antibacterial tests under illumination by visible lights. The antibacterial performance is contributed by the ultra-small Ag NCs and the brilliant photo-absorption afforded by the synergistic effects between the CNTs-MoS2 and Ag NCs.

Studies on the configuration of dye molecules are of great importance in revealing origins of the electronic bands as well as understanding their transitions. In this work, we utilized dye molecules named Nile blue A, which are a type of oxazine dyes, to study the molecular configurations when they are transferred from solutions to a solid surface. The Langmuir–Blodgett (LB) technique was employed to construct such an interface where the interaction between the dye molecules and solid supports can be pursued. Hybrid films were prepared via the LB depositions, and the dye molecules were assembled on the elementary clay sheets (laponite, saponite). The configuration of Nb reflected by the molecular orientation, packing density, phase behavior, and variances of the surface tension has been derived. The ex situ spectroscopy characterizations such as UV–vis absorption, fluorescence emission, and excitation spectra were carried out on these LB films to reveal the fact that the adsorbed Nb molecules are mainly assembled in two types of configurations. Adsorbed state I was found to be achieved at high concentrations (1–10 ppm) of clay dispersions and low surface pressure (∼5 mN/m). In this state the anionic oxazine rings of Nb are adsorbed on clay sheets sharing a large lift-off area. This configuration gives allowable fluorescence (λ = 550 nm). Lower clay concentration (<1 ppm) and high surface pressure (10–30 mN/m) yield the adsorbed state II in which the oxazine chromophores were arranged in a side-by-side style, and the dye molecules stand perpendicularly to the clay sheets. This conformation exhibits no photoluminescence.

In this work, the band-emissions of both the magic-sized clusters (MSCs) and nanosized quantum dots (QDs) of cadmium arsenide (Cd3As2) are studied versus time during the hot-bubbling synthesis. The syntheses are performed by introducing the ex-situ produced H3As into the hot-surfactant solutions dissolved with cadmium oleate and ligand molecules. It is found that the MSCs are produced within 4.0 min because of the color change of the solution. However, these clusters are not stable, and the peak of the photoabsorption shifts from 528 to 540 nm with the growth time. Across a shallow energy barrier, the MSCs grow into nanosized quantum dots whose photoluminescence wavelengths are found to extend into the NIR region (λ > 1480 nm) after a growth period of ∼45.0 min. The quantum yield of the band emissions ranges 2.5–8.0% during the growth of Cd3As2 QDs. Analyses from the time-resolved fluorescence decay profiles suggest that the ultrafast exciton radiative decays are the dominant recombination in the Cd3As2 MSCs, and the lifetime is about 0.69 ns. Longer lifetime emissions (200–300 ns) are found in the nanosized QDs, which is ascribed to the delocalized excitons in the lowest QD state after thermalization. This research highlights the origin and evolution of band-emissions in Cd3As2 QDs, which gives an in-depth understanding of the electronic structures of Cd3As2 QDs, and thus lending them wider potential applicability.

•A polyethylene glycol-assisted strategy was developed.•The homogeneous composite of CNTs-MoS2-carbon was prepared.•The composite was used as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs).•The CNTs-MoS2-carbon CEs possess low Rct of 1.73 Ω cm2.•DSSCs based on CNTs-MoS2-carbon CEs achieve a power conversion efficiency of 7.23%.Carbon nanotubes-MoS2-carbon (CNTs-MoS2-carbon) was synthesized via a method of wet impregnation and calcination with the assistance of surface-active polyethylene glycol 400 (PEG400). Characterizations of TEM, Raman spectra, XRD, XPS, BET and TG-DSC revealed that CNTs were homogenously coated with ultra-thin layers of MoS2. It was demonstrated that the unique structure is attributed to the wetting and emulsification capacity of PEG400. The CNTs-MoS2-carbon was used as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Analyses of electrochemistry indicate that the CEs modified by CNTs-MoS2-carbon have high activity and stability in the electro-reduction from I3− to I− due to the low charge transfer resistance. DSSCs based on CNTs-MoS2-carbon CEs were demonstrated to have a power conversion efficiency of 7.23%, which is higher than Pt CEs (6.19%).We developed a polyethylene glycol-assisted strategy to improve the coating of ultra-thin MoS2 on carbon nanotubes (CNTs). The composite was used as counter electrodes (CEs) for dye-sensitized solar cells to give a higher photo-to-electron efficiency than that of Pt CEs.

•Axle-sleeve structured MWCNT/PANI composite was prepared.•The optimum mass ratio of MWCNT/ANIranges between 1:3 and 1:1.•The π-π drive force was confirmed by spectroscopicmeans.•The polymerization time of 12∼24 hrs affords the highest conversion efficiency.•The DSSCs assembled with the MWCNTs/PANI CEs exhibit a comparable η(7.21%) as that with Pt CE (7.59%).Axle-sleeve structured composite materials made with multi-walled carbon nanotubes (MWCNTs) and polyaniline (PANI) were prepared, characterized, and employed as cost-effective counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The composite was synthesized by co-polymerization of aniline with carboxylated MWCNTs by using ammonium persulfate in the acidic medium. Thin films of MWCNTs/PANI were prepared via a spin coating technique followed by thermal treatment in N2 atmosphere. The micro-structure of the composite was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) linked with energy dispersive spectroscopy (EDS). The coating layer of PANI on the MWCNTs and new-formed chemical bonds between MWCNTs and PANI was studied by UV-Vis absorption, X-ray photoelectron spectroscopy (XPS), Raman and FT-IR spectroscopic means. The effect of the multiple-level porosity or the axle-sleeve structures in the composite of MWCNTs/PANI on the electro-catalytic activity was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopic (EIS) analysis. The DSSCs assembled with MWCNTs/PANI as CEs exhibit a comparable energy conversion efficiency (η) of 7.21% as compared to that of a DSSC consisting of a screen-printed Pt CE (η = 7.59%). These promising results propose a potential application of MWCNTs/PANI in cost-effective DSSCs.Axle-sleeve structured composite materials made with carbon nanotubes and polyaniline were prepared via a co-polymerization strategy. The composite materials were employed as cost-effective counter electrode modifier in dye-sensitized solar cells which demonstrate a comparable photo-to-electron conversion efficiency as the Pt catalyst.

Cd3P2 quantum dots (QDs) have been synthesized in both aqueous and high boiling point surfactant solutions via a gas-bubbling method. The synthesized QDs exhibit photoluminescent wavelengths spanning across the visible red to the near-infrared (NIR) spectral region. Two types of shell materials, SiO2 nano-beads and PS micro-spheres, have been employed to encapsulate the Cd3P2 QDs which provide protecting layers against physiological solutions. The coating layers are proven to enhance the optical and chemical stability of Cd3P2 QDs, and make the fluorescent particles capable of sustaining long-term photo-oxidation. To demonstrate the applicability of the bio-labelling, the fluorescent composite particles (PS@QDs, SiO2@QDs) were injected into a culture medium of colorectal carcinoma (LoVo) cells. The results demonstrated that the PS@QDs exhibited a brighter fluorescence, but the SiO2@QDs provided a better photo-stability which consequently led to long-term cancer cell detection as well as a much lower release of toxic Cd2+ into the PBS solutions.

•The H2SiO3 exfoliation was used to synthesize MoS2 nanosheets.•The MoS2 nanosheets present excellent visible light absorbance properties.•Methyl orange can be degraded by MoS2 nanosheets under visible light.•H+ adsorbed by MoS2 facilitates producing free radicals of OH.MoS2 nanosheets were for the first time prepared by H2SiO3 exfoliation, i.e., the precursors ((NH4)6Mo7O24·4H2O and thiourea) were embedded inside the hydrogel of H2SiO3 which provides steric hindrance for MoS2 growth. After removal of H2SiO3, MoS2 nanosheets were obtained. The appropriate dosage of hydrogel of silicic acid is the determining factor in preparing homogeneous nanosheets of MoS2. The prepared MoS2 nanosheets possess a high specific surface area of 37.8 m2/g, and present excellent UV–visible-NIR absorbance properties, and the absorption peaks of visible region are much higher than that of ultraviolet region. Therefore, they can be used as excellent catalysts for visible-light-driven degradation of methyl orange (MO). The effect of photo-degradation parameters of MO including pH value, dosage of catalyst and initial concentration was studied. The strongly acidic solution of MO facilitates producing free radicals of OH in this catalytic system. The MoS2 nanosheets can be reused 10 times with little change of degradation rate, indicating that they are stable under visible-light irradiation.

Surface chemical and electrochemical techniques were applied to reveal the unfolding of bovine serum albumin (BSA) molecules induced by concentrations in aqueous solution. Real-time surface pressures vs time (π–t) kinetic curves were recorded over an aqueous subphase (190 mL) by spreading BSA solutions of different concentrations but of the same amount (8.0 × 10–4 mg) at the air/water (A/W) interface. A critical concentration (∼1.0 ppm) was discovered below which the surface pressure declines with time and the BSA is totally solubilized in the water subphase. Above this critical concentration (e.g., 8.0 ppm), the surface pressure goes up and the protein molecules assemble into a Langmuir monolayer at the A/W interface. These findings demonstrate that the BSA molecules have different conformations in the spreading protein solutions. The conformational transition in BSA molecules induced by concentrations was also confirmed by spectroscopy means and the catalytic hydrogen evolution reaction on a silver amalgam electrode by using constant current chronopotentiometric stripping. This discovery fills in gaps of Foster’s N (normal) → F (fast) model, in which the unfolding of BSA molecules occurs at neutral pH values (8.0–4.3).

We demonstrated an environmentally friendly photoanode composed of nano-flower structured hematite (α-Fe2O3) and a photocathode composite made of reduced graphene oxide–polyaniline (PANI-RGO) for efficient dye-sensitized solar cells (DSSCs). The porous petals–root structure of the α-Fe2O3 film characterized by different structural means (XRD, SEM, HRTEM, SAED and N2 adsorption–desorption) was demonstrated to provide an efficient pathway for the charge carrier transfer of DSSCs. The incident photon-to-electron conversion efficiency (IPCE) profiles suggested a broad photo-response spectral region of up to 700 nm in the presence of nano-flower α-Fe2O3 in the photoanode. The PANI-RGO composite coated on the counter electrode was proven to have a higher photon-to-electron conversion efficiency than the conventional Pt, which is attributed to the improved electro-catalytic activity and conductivity of PANI-RGO. It was found that the energy conversion efficiency (1.24%) achieved from PANI-RGO as photocathode material is increased by a factor of 1.3 compared with Pt. The better electro-catalytic activity of PANI-RGO CE is brought about by a synergistic effect between PANI and RGO, which was verified by micro-Raman spectroscopy and electrochemical characterizations (CV, EIS).

The Langmuir–Blodgett (LB) technique has been employed for the construction of a model of interfacial supported ionic liquids (ILs) catalyst. In this model a hybrid LB film consists of three components: ionic liquids (imidazolium chloride with different length of substituent alkyl chain), catalyst carrier (saponite and laponite), and catalyst species (platinum nanocrystals). It was found imidazolium ILs with carbon number more than six in the alkyl substituents can form stable Langmuir monolayer over diluted clay dispersions. By recording surface pressure versus time (π–t) kinetic curves, we found that the adsorption of imidazolium ILs or platinum nanocrystals by clay elementary layers reaches equilibrium within 200 s, and the molar Gibbs free energy change −dG (kJ mol–1) for the adsorption lies in the range 0.34–5.6 kJ mol–1. Surface pressure versus area (π–A) isotherms revealed that platinum nanocrystals are adsorbed by the IL–clay Langmuir films at the air–water interface, and there are two phase transition points in the π–A isotherms during the compression of IL–clay–Pt. We utilized two methods, i.e., interfacial chemical methods (π–t, π–A) and spectroscopic measurements (UV–vis absorption, atomic absorption spectroscopy (AAS)) to quantify the amount of imidazolium IL and Pt that are presented in the LB films. Results showed that the amount of adsorbed 1-hexadecyl-3-methylimidazolium chloride (C16MIM) in the hybrid film C16MIM–saponite–Pt at the first deposition layer is around 0.65 ng mm–2. Laponite gives a higher adsorption capacity for loading IL and Pt nanocrystals. Attenuated total reflectance (ATR)–Fourier transform infrared spectra (FTIR) confirmed the presence of IL in the LB film which shares ordered vibrational conformation, and the degree order of C16MIM molecules becomes worse after incorporation of Pt nanocrystals. Transmission electron microscopy (TEM) verified that Pt nanoparticles with size of ∼5.0 nm tend to be adsorbed on the edges of clay layers, and the surface coverage of Pt particles can be tuned by the compression pressure. The Pt-containing LB films were deposited on a glass carbon electrode (GCE), and the electrocatalytic performance toward methanol electro-oxidation and synergistic effects between the three components have been studied by means of cyclic voltammetry (CV) and chronoamperometry (CA). The results indicated that the film IL–clay–Pt exhibits a remarkable enhancement in catalytic activity and stability compared to clay–Pt in terms of the onset potential for methanol oxidation, the specific mass current density based on the amount of Pt catalyst, and the slower decay of steady-state current in the CA profile.

The present paper describes a new type of composite photo-anode of SiO2/TiO2 that was prepared by adding nano-sized SiO2 into the TiO2 (P25) paste during the fabrication of dye-sensitized solar cells (DSSCs). The effects of the added SiO2 on the performance of DSSCs were investigated and the preparative procedures of DSSCs were optimized. It was found that certain amount of SiO2 added in the P25 powder was crucial to reduce the agglomeration and enhance the dispersion of P25 powders, which helps to achieve a better connection and thus higher electron transfer efficiency not only between the TiO2 particles but also between the TiO2 particles and the FTO substrate. Under the same standard air mass 1.5 illumination (100 mW cm−2), the DSSCs constructed by SiO2/P25 composite photo-anodes show higher solar energy-to-electricity conversion efficiency (e.g., η = 8.4%) compared to those by bare P25 electrodes (typically η = 5.8%). The higher η mainly results from its higher short-circuit photocurrent density (Jsc = 18.7 mA cm−2) while the open-circuit voltage (Voc) remains unchanged and was found to be ∼780 mV. The fill factor (FF) was 0.57. The great enhancement in Jsc of DSSCs is ascribed to the SiO2 energy barrier layer which increases the separation of injected electrons and oxidized dyes/redox couple as well as retards the recombination reactions in the resulting DSSCs.Highlights► A new composite photo-anode consisting of SiO2/TiO2 was prepared and employed in dye-sensitized solar cells (DSSCs). ► The SiO2 incorporated in the composite film was found to affect the performance of DSSCs in three aspects. ► The three aspects are: decreasing the agglomerations, acting as a partial barrier layer and increasing the adhesion. ► The DSSCs constructed by SiO2/P25 (7.5 wt%) show a higher solar energy-to-electricity conversion efficiency (8.4%).

The synthesis of nanoparticles using a gas–liquid interfacial reaction, which for the first time is shown to result in highly monodisperse materials across a range of sizes, is presented. We demonstrate, using cadmium phosphide as the paradigm that this synthesis method can provide colloidal nanocrystals or quantum dots monodisperse enough so that for the first time multiple transitions in their absorbance spectra can be observed. Clear evidence is given that the resulting cadmium material is Cd6P7 and not Cd3P2, and a thorough investigation into the role of temperature and growth time and their effects on the optical properties has been conducted. This strategy can be extended to synthesize other relevant members of the binary component pnictide semiconducting family, and the chemistry of the pnictide compound formation using this synthetic methodology has been explained using the redox potential of the metals. The suitability of the resulting cadmium phosphide quantum dots for applications in light-emitting diodes (LEDs) has further been demonstrated.Keywords: cadmium phosphide; gas−liquid interface reaction; light-emitting diode; quantum dot synthesis