Photo-electrochemistry of metallic titanium/mixed phase titanium oxide

In this study, the effect of potassium hydroxide concentration in anodization bath, anodization time, and calcination temperature on the photo-electrochemical behavior of metallic titanium/mixed phase titanium oxide is investigated. Further, the phase structure of a titanium oxide photocatalyst prepared on a titanium electrode through a high-voltage anodization method is examined. The study exploits photo-electrochemical, Fourier transform infrared spectroscopy attenuated total reflectance (FTIR–ATR), X-ray diffraction, and Raman spectroscopic methods to obtain better insights into the mechanism of mixed-phase titanium oxide formation. In this regard, the photo-electrochemical properties of the photocatalysts prepared in single excitation energy, violet light (410 nm), were investigated. The anodization time and the potassium hydroxide concentration in the anodization bath have significant effects on the photo-electrochemical properties of the photocatalysts. The experiments show that the effect of potassium hydroxide concentration is a function of the anodization potential applied, demonstrating different patterns as the anodization potential changes. Furthermore, FTIR-ATR, X-ray diffraction, and Raman spectroscopic studies reveal that the extended anodization times decrease the population of OH-containing groups, leading to lower photo-electrochemical performance. On the other hand, the formation of anatase phases becomes more favorable only in the extended anodization times before application of the calcination process. Additionally, the calcination temperature has a significant impact on the anatase to rutile ratio. Finally, increasing potassium hydroxide concentration leads to the formation of an amorphous titanium oxide layer. It can be concluded that the obtained information might have a significant impact on the preparation of titanium oxide and other metal oxide photocatalysts through the high voltage anodization process.     

0D/3D ZnIn2S4/Ag6Si2O7 nanocomposite with direct Z-scheme heterojunction for efficient photocatalytic H2 evolution under visible light

Constructing heterojunction structure is a feasible way to realize an efficient and durable photocatalysts. Herein, a novel Z-scheme zero/three dimensional (0D/3D) ZnIn₂S₄/Ag₆Si₂O₇ (ZIS/ASO) composite was rationally designed, synthesized and analyzed. ZIS/ASO composite possesses a layer structure for increasing light response, a special 0D/3D structure for reducing the photo-induce carriers migration path, and numerous active sites for absorbing H₂O and producing H₂. This composite retains the high oxidation and reduction ability by facilitating separation and migration as well as limiting recombination of photo-induced carriers via the intimate interface between ZIS and ASO. Undoubtedly, the synthesized ZIS/ASO photocatalyst achieved a high photocatalytic H₂ activity, and the optimum sample shows a satisfactory H₂ evolution rate of 590.56 μmol g⁻¹ h⁻¹, distinctly better than that of pure ZIS. More importantly, this composite exhibits high stability and recyclability and is expected to be applied in practical application. Based on the H₂ evolution experimental results and electrochemical tests, the Z-scheme heterostructure construction of the composite was confirmed. This work expects to inspire a unique protocol for synthesizing Z-scheme photocatalysts for water splitting under visible light irradiation.     

Preparation of transparent ts-1 zeolite film and its photocatalytic isomerization under uv irradiation

TS-1 zeolite film has been prepared by using nano sized TS-1 zeolite particles for the photocatalytic isomerization of cis-2-butene. TS-1 zeolite film showed optical transparent property and the thickness of film was 0.7 μm. UV irradiation of TS-1 zeolite film in the presence ofcis-2-butene leads to the photocatalytic isomerization ofcis-2-butene intotrans-2-butene at the temperature of 275 K. The yield oftrans- 2-butene was linearly increased with UV-irradiation time.     

聚焦单模微波辐射法制备Pr-TiO_2纳米簇及其光学性能的研究

以钛酸丁酯和硝酸镨为原料,将溶胶-凝胶法制备的纳米Pr-TiO_2颗粒采用Discover聚焦单模微波进行微波处理。采用XRD、SEM、TEM考察了微波辐射温度、时间及功率对其晶型结构、表观形貌及光催化性能的影响。结果表明:当微波辐射温度为120℃,功率为100 W,辐射20 min时得到晶型结构比较完善的锐钛矿纳米Pr-TiO_2,并且在此条件下对甲基橙的降解率最高,光催化性能最强。对其形貌进行分析可知,所制备的纳米Pr-TiO_2为花球状的纳米簇,并且此结构是由片层结构组装而成,所制备的Pr-TiO_2纳米簇为多晶结构。利用聚焦单模微波法拓宽了TiO_2的光响应范围,提高了可见光的利用率。。     

Photocatalytic hydrogen production by flower-like graphene supported ZnS composite photocatalysts

Flower-like graphene (FG) prepared by a transformer coupled plasma enhanced chemical vapor deposition method was used as support for the preparation of composite photocatalysts. Small ZnS particles were formed on the surface of FG by a hydrothermal process with ZnCl₂ and Na₂S precursors. The surface morphology, surface area, surface chemistry, crystalline property, optical properties, photogenerated current and photocatalytic hydrogen production activity of the FG-ZnS photocatalysts were investigated by using the X-ray diffraction, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectra, photocurrent response, photoluminescence spectra, electrochemical impedance spectra and photocatalytic hydrogen production tests. The maximum hydrogen production rate of FG-ZnS composite photocatalyst ZS-G0.02 was 11600 μmol g^?1h^?1 under UV light irradiation at a graphene/ZnCl₂ precursor weight ratio of 0.02. The flower-like structure of FG may help the light absorption, adsorption of sacrificing agents in the solution, and separation of photogenerated carriers. In comparison with pristine ZnS photocatalyst, the FG-ZnS nanocomposites exhibits enhanced photocatalytic hydrogen production activity.     

Ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag2CrO4 nanocomposites as visible-light-driven photocatalysts with excellent activity

This work reports ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag₂CrO₄ nanocomposites as excellent visible-light-driven photocatalysts. The ZnO/AgI/Ag₂CrO₄ nanocomposite with 20% of Ag₂CrO₄ has the superior activity in degradation of rhodamine B. Activity of this nanocomposite is nearly 167, 6.5, and 45-fold higher than those of the ZnO, ZnO/AgI, and ZnO/Ag₂CrO₄ samples, respectively. The ternary nanocomposite also showed enhanced activity relative to its counterparts for degradation of methylene blue and methyl orange as two dye pollutants under visible-light irradiation. The UV–vis DRS and PL spectra confirmed that the excellent photocatalytic activities are due to more visible-light absorption ability and efficiently separation of the charge carriers. Based on the effects of different scavengers, it was found that superoxide ions are the primary reactive species to cause the degradation reaction. Furthermore, the highly enhanced activity of the ternary nanocomposite was described using a proposed mechanism.     

Synthesis and photocatalytic performance of Ag-loaded β-Bi2O3 microspheres under visible light irradiation

The visible-light-driven photocatalyst Ag/β-Bi₂O₃ microspheres were synthesized by a simple chemical method. First, β-Bi₂O₃ microspheres were obtained by a thermal treatment of sphere-like Bi₂O₂CO₃ precursor at 360 °C for 3 h in air and then Ag nanoparticles were in situ incorporated into β-Bi₂O₃ microspheres by impregnation method. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and photoluminescence measurements. The experimental results demonstrated that the visible light absorption of β-Bi₂O₃ photocatalyst is greatly enhanced with the incorporation of Ag nanoparticles. The SEM and TEM observations revealed that the Ag nanoparticles can be homogenously incorporated in the β-Bi₂O₃ microspheres. The photocatalytic activity of Ag/β-Bi₂O₃ sample was evaluated by the photodegradation of the Rhodamine-B under visible light irradiation as a function of Ag content. It is found that the photocatalytic efficiency of β-Bi₂O₃ can be significantly improved with the incorporation of Ag nanoparticles up to 2.0 wt% Ag. The mechanism for the enhanced photocatalytic activity is also presented.     

Hydrothermal synthesis, characterization, and photocatalytic performances of Cr incorporated, and Cr and Ti co-incorporated MCM-41 as visible light photocatalysts for water splitting

A series of Cr incorporated, and Cr and Ti co-incorporated MCM-41 photocatalysts were synthesized by hydrothermal method. X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (UV–vis), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence analysis (XRF), N₂ adsorption–desorption isotherms and Raman spectra were used to investigate the effects of the incorporated elements on the structure of MCM-41. The experimental results for photocatalytic water splitting under visible light irradiation (λ > 430 nm) demonstrated that the photocatalytic activities of Cr-MCM-41 and Cr-Ti-MCM-41 catalysts for hydrogen production decreased with an increase in the amount of Cr incorporated. Compared with the Cr-MCM-41 which had the same amount of incorporated Cr, the Cr-Ti-MCM-41 exhibited much higher hydrogen evolution activities.