Solar Light Responsive Photocatalytic Activity of Reduced Graphene Oxide–Zinc Selenide Nanocomposite

Solution processable reduced graphene oxide–zinc selenide (RGO–ZnSe) nanocomposite has been successfully synthesized by an easy one-pot single-step solvothermal reaction. The RGO–ZnSe composite was characterized structurally and morphologically by the study of XRD analysis, SEM and TEM imaging. Reduction in graphene oxide was confirmed by FTIR spectroscopy analysis. Photocatalytic efficiency of RGO–ZnSe composite was investigated toward the degradation of Rhodamine B under solar light irradiation. Our study indicates that the RGO–ZnSe composite is catalytically more active compared to the controlled-ZnSe under the solar light illumination. Here, RGO plays an important role for photoinduced charge separation and subsequently hinders the electron–hole recombination probability that consequently enhances photocatalytic degradation efficiency. We expect that this type of RGO-based optoelectronics materials opens up a new avenue in the field of photocatalytic degradation of different organic water pollutants.     

石墨相碳化氮复合材料的制备及其可见光光催化性能的研究

目的提高半导体石墨相氮化碳(g-C_3N_4)的光催化性能。方法通过Hummers法和半封闭一步热裂解法制备了氧化石墨烯(GO)和g-C_3N_4,再分别利用溶剂热法、热缩聚法和浸渍化学还原法制得相应的TiO_2/g-C_3N_4、ZnO/g-C_3N_4、RGO/g-C_3N_4复合材料。采用X-射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、紫外-可见漫反射吸收光谱(UV-Vis DRS)和傅里叶变换红外光谱(FT-IR)等手段对复合材料进行表征,并以降解罗丹明B(Rh B)来评价其在可见光下的光催化性能。结果以尿素与三聚氰胺的混合物为原料通过热裂解法制备的g-C_3N_4,比使用纯尿素制备的g-C_3N_4具有更优的催化效果。TiO_2、ZnO、RGO的引入提高了g-C_3N_4的光催化活性,Rh B的降解率分别为95.6%、95.0%、78.1%。RGO质量分数为2.0%时,RGO/g-C_3N_4复合材料的催化效率最高。结论通过g-C_3N_4特殊的能带调控优势与TiO_2、ZnO、RGO的协同作用,提高了复合材料在可见光区的吸收强度和电子传导能力,进而提高了在可见光下的光催化性能。     

One-pot hydrothermal synthesis of ruthenium oxide nanodots on reduced graphene oxide sheets for supercapacitors

Ruthenium oxide nanodots have been deposited on reduced graphene oxide (RGO) sheets homogeneously by hydrothermal and annealing methods. Adding NaOH solution in GO colloids prevents the restack and agglomeration of GO sheets when mixed with ruthenium chloride solution. Local crystallization of RuO₂ in the composites is revealed by X-ray diffraction and transmission electron microscopy. The element mapping image demonstrates the uniform distribution of Ru on RGO sheets. Unlike the pure crystalline RuO₂ exhibiting poor electrochemical performance, the composites present superior capacitive properties. The hydrothermal time is optimized and a maximum of 471 F g⁻¹ is measured in the composites at 0.5 A g⁻¹ when loaded with 45 wt% of RuO₂. After 3000 cycles, its specific capacitance remains 92% of the maximum capacitance. Our results suggest potential application of the reduced graphene oxide/ruthenium oxide composites to supercapacitors.     

Solvothermal synthesis and characterization of tungsten oxides with controllable morphology and crystal phase

Tungsten oxides with various morphologies and crystal phases were synthesized by solvothermal reactions at 200 °C for 7-12 h using different solvents. The morphology and crystal phase of tungsten oxides changed depending on the solvents, i.e., spherical particles of ca. 1 μm in diameter consisting of nanowires, spindle shaped bundles of ca. 1 μm in length consisting of nanowires and accumulations consisting of micrometer sized plates and/or rods of tungsten oxides were obtained using ethanol, 1-propanol and water-ethanol mixed solution, respectively. When water-ethanol mixed solution was used, the crystallinity of tungsten oxide increased but the specific surface area greatly decreased. Crystallinity of tungsten oxides had more important effects on the NO degradation under light irradiation. The product using 42.9 vol.% water-ethanol mixed solvent consisted of the mixture of anhydrous tungsten oxide and hydrous tungsten oxide with preferential orientation of (0 0 2) plane and small band gap energy (2.43 eV), and showed higher photocatalytic degradation of NO even though it had a much smaller specific surface area than those prepared using ethanol and 1-propanol.     

A strategy for single-step elaboration of V2O5-grafted TiO2 nanostructured photocatalysts with evenly distributed pores

V₂O₅-TiO₂ nanostructured porous layers were grown through micro arc oxidation of titanium in vanadate containing electrolytes. This study sheds light on the effect of the electric current type on the photocatalytic performance of the layers. Surface morphology of the layers was investigated by SEM. The results revealed a porous structure with a pores size of 30-180 nm depending on the frequency and the duty cycle. A uniform porous structure was obtained under the pulse-DC regime. Topographical investigations revealed a rough surface which is favorable for catalytic applications. Our XRD and XPS results showed that the layers consisted of anatase, rutile, and vanadium oxide phases whose fraction was observed to change depending on the electric variables. Finally, methylene blue was selected as a model material in order to evaluate the photocatalytic performance of the grown layers. The layers which were fabricated under pulse current, especially those synthesized at the frequency of 500 Hz and duty cycle of 5%, exhibited higher photocatalytic efficiency under ultraviolet and visible illuminations on account of their higher surface area and anatase/rutile fraction.     

Cu and CuO nanoparticles immobilized by silica thin films as antibacterial materials and photocatalysts

CuO nanoparticles with average diameter of about 20 nm were accumulated on surface of sol-gel silica thin films heat treated at 300 °C in air. Heat treatment of the CuO nanoparticles at 600 °C in a reducing environment resulted in effective reduction of the nanoparticles and penetration of them into the film. While the thin films heat treated at 300 °C exhibited a strong antibacterial activity against Escherichia coli bacteria, the reducing process decreased their antibacterial activity. However, by definition of normalized antibacterial activity (antibacterial activity/surface concentration of coppers) it was found that Cu nanoparticles were more toxic to the bacteria than the CuO nanoparticles (by a factor of ∼ 2.1). Thus, the lower antibacterial activity of the reduced thin films was assigned to diffusion of the initially accumulated copper-based nanoparticles into the film. The CuO nanoparticles also exhibited a slight photocatalytic activity for inactivation of the bacteria (∼ 22% improvement in their antibacterial activity). Instead, the normalized antibacterial activity of the Cu nanoparticles covered by a thin oxide layer highly increased (∼ 63% improvement) in the photocatalytic process. A mechanism was also proposed to describe the better antibacterial activity of the Cu than CuO nanoparticles in dark and under light irradiation.     

Enhanced visible-light-response photocatalytic activity of bismuth ferrite nanoparticles

Multiferroic BiFeO₃ nanoparticles were prepared by a sol-gel rapid calcination technique with average diameter of 35 nm with narrow size distribution. The band gap was determined to be 2.06 eV, indicating their potential application as visible-light-response photocatalyst. The photocatalytic behaviors of BiFeO₃ nanoparticles were estimated by the degradation of Rhodamine B (RhB) under visible light irradiation. And the photocatalytic activities under different pH values were further studied for the first time. The result shows that the BiFeO₃ nanoparticles exhibit the highest photocatalytic activity in the solution with the lowest pH value, almost 100 times higher than that of the bulk.     

Preparation of large scale photocatalytic TiO2 films by the sol-gel process

Nanocrystalline titanium dioxide films were formed on frosted and clear borosilicate glass with a large surface area (12 × 22 cm) using doctor blade and spray coating techniques. The films were subjected to a high temperature treatment at 550 °C. X-ray diffraction (XRD) analysis indicated that the TiO₂ films contain only the anatase phase. Optical microscopy was used to determine the morphology changes after the deposition of each layer. Scanning electron microscopy (SEM) was used to study the films surface morphology. The large scale TiO₂ films produced showed a high photocatalytic activity which was evaluated by the degradation of methyl orange (MO) in aqueous solution (10 mg L^− 1) under illumination of a UV light source with an overall irradiance of 0.9 mW cm^− 2. UV-visible spectrophotometry was used to monitor the degradation of MO through the decrease of the main absorbance peak at 464 nm. The results demonstrated that a complete decomposition of MO could be achieved after 2 h of UV irradiation.     

Suspension plasma sprayed TiO2 coatings using different injectors and their photocatalytic properties

Stable water- and water/ethanol suspensions of TiO₂ were plasma sprayed on stainless steel substrates. The suspensions were injected using two different systems: external, using an atomizing injector, and internal, performed with a continuous-stream injector inside the plasma torch anode. In order to find the optimal spray parameters, seven experimental runs were performed and the resulted deposits were mainly characterized by means of scanning electron microscopy and X-ray diffraction analysis. The microstructural examinations revealed that the coatings obtained by internal injection of the suspension show two principal characteristics: dense zones with well molten big lamellae and porous zones containing fine nanometric and submicrometric grains. When applying the internal continuous-stream injector, the amount of anatase varied from about 1.6 vol.% to 8.8 vol.%. The amount was with 9.4 vol.% to 15.4 vol.% considerably lower when an external atomizing injector was used. The photocatalytic activity of selected coatings was determined by measuring the degradation of an aqueous solution of dye methylene blue. The photon efficiency of titania deposits, which is a measure of the photocatalytic performance, varied from 0.022% up to 0.032% and did not seem to depend on the amount of anatase phase.     

A novel photocatalyst and improvement of photocatalytic properties by Cu doping

A new series of photocatalysts, Bi₂Zn_2/3−xCu_xTa_4/3O₇ (Cu-β-BZT) crystals with pyrochlore structure were synthesized by the method of solid-state reaction (SSR). With small amount of Cu doped (0.01 ≤ x ≤ 0.04), the phase structure was kept to be monoclinic pyrochlore as pure β-BZT. The diffuse reflectance spectrum of Cu-β-BZT samples showed a red shift. The method of Cu doping enhanced the photocatalytic activity, and when the value of x is 0.03, the sample showed the highest activity, which is about 10 times higher than that of pure β-BZT under UV light. Especially, the samples of Cu-β-BZT showed photocatalytic activities under visible light irradiation (λ > 400 nm). Effects of the Cu doped on the photocatalytic activities of the catalysts were also discussed.