Yangang Wang

Facile One-Step Synthesis of Hybrid Graphitic Carbon Nitride and Carbon Composites as High-Performance Catalysts for CO2 Photocatalytic Conversion

Utilizing and reducing carbon dioxide is a key target in the fight against global warming. The photocatalytic performance of bulk graphitic carbon nitride (g-C3N4) is usually limited by its low surface area and rapid charge carrier recombination. To develop g-C3N4 more suitable for photocatalysis, researchers have to enlarge its surface area and accelerate the charge carrier separation. In this work, novel hybrid graphitic carbon nitride and carbon (H-g-C3N4/C) composites with various carbon contents have been developed for the first time by a facile one-step pyrolysis method using melamine and natural soybean oil as precursors. The effect of carbon content on the structure of H-g-C3N4/C composites and the catalytic activity for the photoreduction of CO2 with H2O were investigated. The results indicated that the introduction of carbon component can effectively improve the textural properties and electronic conductivity of the composites, which exhibited imporved photocatalytic activity for the reduction of CO2 with H2O in comparison with bulk g-C3N4. The highest CO and CH4 yield of 22.60 μmol/g-cat. and 12.5 μmol/g-cat., respectively, were acquired on the H-g-C3N4/C-6 catalyst with the carbon content of 3.77 wt % under 9 h simulated solar irradiation, which were more than twice as high as that of bulk g-C3N4. The remarkably increased photocatalytic performance arises from the synergistic effect of hybrid carbon and g-C3N4.

Effect of support calcination temperature on Ag structure and catalytic activity for CO oxidation

SiO2 with different nanostructures, namely hexagonal mesoporous silica(HMS), and three unordered commercial silica, were used as supports to fabricate silver catalysts using an incipient wetness impregnation method. It was found that Ag/HMS catalyst showed a high catalytic activity. Next, the HMS support was calcined at different temperatures before impregnation of AgNO3. The effect of calcination temperature of HMS support was investigated in terms of structure and catalytic activity of Ag catalysts. The support and catalysts were characterized by N2 adsorption-desorption isotherms, Thermogravimetric-differential thermal analyzer, X-ray diffraction, H2-temperature program reduction and transmission electron microscopy. The results showed that calcination of HMS at an appropriate temperature(750 °C) before catalyst preparation would benefit the formation of highly dispersive small sized Ag particles on the HMS support and markedly enhance the catalytic activity of Ag/HMS catalyst toward CO oxidation.

Hierarchically mesostructured TiO2/graphitic carbon composite as a new efficient photocatalyst for the reduction of CO2 under simulated solar irradiation

A hierarchically mesostructured TiO2/graphitic carbon composite photocatalyst with a high content of nanocrystalline TiO2 was prepared using a simple one-step nanocasting route. X-ray diffraction, thermogravimetric analysis, nitrogen adsorption–desorption, transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize this photocatalyst. It was observed that the coexistence of silica and graphitic carbon during the high temperature treatment stabilized the crystalline phase and the size of the anatase TiO2 nanocrystals (5–7 nm in diameter), which were uniformly dispersed in the graphitic carbon matrix after silica removal. The obtained hierarchically mesostructured TiO2/graphitic carbon composite photocatalyst with a high specific surface area and a high surface concentration of hydroxyl groups exhibited considerably higher activity in the photocatalytic reduction of CO2 with H2O under simulated solar irradiation compared to mesostructured anatase TiO2 prepared using a sol–gel method.

Efficient Photocatalytic Bilirubin Removal over the Biocompatible Core/Shell P25/g-C 3 N 4 Heterojunctions with Metal-free Exposed Surfaces under Moderate Green Light Irradiation

Highly-monodispersed g-C3N4/TiO2 hybrids with a core/shell structure were synthesized from a simple room temperature impregnation method, in which g-C3N4 was coated through self-assembly on the commercially available Degussa P25 TiO2 nanoparticles. Structural and surface characterizations showed that the presence of g-C3N4 notably affected the light absorption characteristics of TiO2. The g-C3N4/TiO2 heterojunctions with metal-free exposed surfaces were directly used as biocompatible photocatalysts for simulated jaundice phototherapy under low-power green-light irradiation. The photocatalytic activity and stability of g-C3N4/TiO2 were enhanced relative to pure P25 or g-C3N4, which could be ascribed to the effective Z-scheme separation of photo-induced charge carriers in g-C3N4/TiO2 heterojunction. The photoactivity was maximized in the 4 wt.% g-C3N4-coated P25, as the bilirubin removal rate under green light irradiation was more than 5-fold higher than that under the clinically-used blue light without any photocatalyst. This study approves the future applications of the photocatalyst-assisted bilirubin removal in jaundice treatment under moderate green light which is more tolerable by humans.

Surfactant-assisted Nanocasting Route for Synthesis of Highly Ordered Mesoporous Graphitic Carbon and Its Application in CO2 Adsorption

Highly ordered mesoporous graphitic carbon was synthesized from a simple surfactant-assisted nanocasting route, in which ordered mesoporous silica SBA-15 maintaining its triblock copolymer surfactant was used as a hard template and natural soybean oil (SBO) as a carbon precursor. The hydrophobic domain of the surfactant assisted SBO in infiltration into the template’s mesoporous channels. After the silica template was carbonized and removed, a higher yield of highly-ordered graphitic mesoporous carbon with rod-like morphology was obtained. Because of the improved structural ordering, the mesoporous carbon after amine modification could adsorb more CO2 compared with the amine-functionalized carbon prepared without the assistance of surfactant.

Nanocasting synthesis of chromium doped mesoporous CeO 2 with enhanced visible-light photocatalytic CO 2 reduction performance

Chromium doped mesoporous CeO2 catalysts were synthesized via a simple nanocasting route by using silica SBA-15 as the template and metal nitrates as precursors. The effect of Cr doping concentration (5%, 10%, 15% and 20% of the initial Cr/(Cr+Ce) molar percentage) on the structures of these catalysts and their photocatalytic performances in reduction of CO2 with H2O were investigated. The results indicated that the introduction of Cr species could effectively extend the spectral response range from UV to visible light region (400-700nm) and improve the electronic conductivity for the mesoporous CeO2 catalysts which exhibited an enhanced photocatalytic activity in the reduction of CO2 with H2O when compared with the non-doped counterpart. The highest CO and CH4 yield of 16.2μmol/g-cat. and 10.1μmol/g-cat., respectively, were acquired on the optimal chromium doped CeO2 catalyst with the initial Cr(Cr+Ce) molar percentage of 15% under 8h visible-light irradiation, which were more than twice as high as that of bare CeO2. The remarkably increased photocatalytic performance should be attributed to the advantageous structural and compositional features of the chromium doped mesoporous CeO2.

Constructing Highly Uniform Onion-Ring-like Graphitic Carbon Nitride for Efficient Visible-Light-Driven Photocatalytic Hydrogen Evolution

The introduction of microstructure to the metal-free graphitic carbon nitride (g-C3N4) photocatalyst holds promise in enhancing its catalytic performance. However, producing such microstructured g-C3N4 remains technically challenging due to a complicated synthetic process and high cost. In this study, we develop a facile and in-air chemical vapor deposition (CVD) method that produces onion-ring-like g-C3N4 microstructures in a simple, reliable, and economical manner. This method involves the use of randomly packed 350 nm SiO2 microspheres as a hard template and melamine as a CVD precursor for the deposition of a thin layer of g-C3N4 in the narrow space between the SiO2 microspheres. After dissolution of the microsphere template, the resultant g-C3N4 exhibits uniquely uniform onion-ring-like microstructures. Unlike previously reported g-C3N4 powder morphologies that show various degrees of agglomeration and irregularity, the onion-ring-like g-C3N4 is highly dispersed and uniform. The calculated band gap for onion-ring-like g-C3N4 is 2.58 eV, which is significantly narrower than that of bulk g-C3N4 at 2.70 eV. Experimental characterization and testing suggest that, in comparison with bulk g-C3N4, onion-ring-like g-C3N4 facilitates charge separation, extends the lifetime of photoinduced carriers, exhibits 5-fold higher photocatalytic hydrogen evolution, and shows great potential for photocatalytic applications.

Simple solid-state method for synthesis of Li[Li0.20Mn0.534Ni0.133Co0.133]O2 cathode material with improved electrochemical performance in lithium-ion batteries

Layered Li[Li0.20Mn0.534Ni0.133Co0.133]O2 cathode materials for Li-ion battery were successfully prepared by a novel simple solid-state method using acetate or carbonate as a precursor under high temperature, and were then surface-modified with nanostructured alumina (Al2O3). The prepared cathode materials were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM), transmission electron microscope (TEM), and electrochemical measurements. The XRD results show that all the cathode materials possess an α-NaFeO2 structure type with high crystallinity. SEM and TEM images reveal that the cathode materials have a monodisperse nonspherical morphology and the surface became rough but their morphology did not change very much after Al2O3 coating. XRF test proved the presence of Al2O3 in the samples after coating treatment. The electrochemical measurements exhibit that the Al2O3-coated cathode materials have a higher capability and cycling performance in lithium-ion battery than that of uncoated samples. Further, electrochemical impedance spectra (EIS) measurement shows that the Al2O3 nanoparticles on the surface of the cathode materials reduced side reactions during cycling electrode/electrolyte interface and provided a balanced electronic and Li-ion conductivity. This promising technology for making high performance electrodes would inspire the design and development of a wide range of other battery-related materials in a more eco-friendly way.