Facile construction Z-scheme anatase/rutile TiO2/g-C3N4 hybrid for efficient photocatalytic H2 evolution under visible-light irradiation

Z-scheme anatase/rutile TiO₂/g-C₃N₄ hybrids (denoted as LTARCN-x, x represents calcination temperature) were designed and synthesized by growing TiO₂ nanorods on the surface of g-C₃N₄ utilizing impregnation-calcination method. Furthermore, through the etched effect of hydrochloric acid and calcination treatment, the as-prepared LTARCN-x possessed abundant pore structure and larger surface area, and the surface area of LTARCN-425 was 8.5 times than that of bulk g-C₃N₄. Meanwhile, the g-C₃N₄ would play a role of carrier to prevent from the aggregation of TiO₂ nanorods. In addition, under visible light irradiation, the Z-scheme heterostructure would be constructed between the rutile TiO₂ nanorod and g-C₃N₄ nanosheet, respectively. The optimized photocatalyst LTARCN-425 exhibited a preferable activity, the photocatalytic hydrogen production rate of LTARCN-425 was about 1031 μmol g^?1 h^?1, and it was about 6.3 and 13.6 times than that of g-C₃N₄ and TiO₂, respectively. Moreover, the photocatalytic mechanism of the hydrogen production was studied intensively via designing fluorescent probe, Pt and PbO₂ deposition experiment, and the characterizations of EPR, TEM, HRTEM and XPS.     

Design of TiO2 nanocrystals with enhanced sunlight photocatalytic activity by exploring calcining conditions

As a promising inorganic semiconductor photocatalyst, TiO₂ has been widespread concerned since 1972. However, its practical application is limited due to its low efficiency for utilizing solar light and rapid recombination of photo-generated charges. Here, we report a way to solve these problems by calcining TiO₂ samples under different conditions. It was found that the catalytic performance of TiO₂ catalysts was closely related to calcination temperature and calcination atmosphere. The XRD, Raman spectra, BET, UV–vis spectra, SEM and TG-DTA investigations of the catalysts revealed that the crystal structure of TiO₂, the specific surface area, and abundant oxygen vacancies were the primary factors influencing the performance of TiO₂ catalysts. Consequently, the TiO₂ nanocrystal calcined in a nitrogen/hydrogen mixed atmosphere at 300 °C for 3 h exhibited higher catalytic activity than others. These results demonstrated that annealing conditions can play an important role in catalyst activity.     

Facile fabrication of ordered assembled TiO2/g-C3N4 nanosheets with enhanced photocatalytic activity

A series of assembled porous TiO₂/g-C₃N₄ (TC) powders composed of spherical nanoparticles were synthesized by controlling the molar ratio of urea to tetrabutyl titanate (TBOT) in a facile hydrothermal process. A nanosheets-constructed hierarchical structure was obtained at the molar ratio of urea to TBOT of 10:1, which possessed uniform mesopores with bimodal distribution (0.5–1.5 nm and 2–20 nm) and interconnected macropores between TC nanosheets. The specific surface area achieved 98.4 m² g^?1. X-ray diffraction (XRD) patterns and high resolution transmission electron microscope (HRTEM) analysis proved that the nanosheets are made of overlapping TC nanocomposite. Photoluminescence (PL) spectra results illustrated that a well-defined hierarchical porous structure is particularly desired for the low recombination rate of carriers. Further, the TC-decorated carbon fiber (CF) cloth was obtained based on the nanosheets assembled hierarchical structure, which showed more outstanding photocatalytic behavior with high degradation capability for Rhodamine B (RhB) (99.9%) and tetracycline hydrochloride (89.8%) at 60 min by 500 W Xe lamp irradiation. After five consecutive cycles, the degradation efficiencies of TC/CF cloth for both RhB and tetracycline hydrochloride all remained above 90% of the initial value.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Manifestation of enhanced and durable photocatalytic H2 production using hierarchically structured Pt@Co3O4/TiO2 ternary nanocomposite

A hierarchical structure composed of Pt@Co₃O₄/TiO₂ (CTP) ternary nanocomposite was synthesized and demonstrated for its enhanced and durable production of hydrogen from glycerol under simulated solar light irradiation. The rate of hydrogen production over the optimized composition was found to be 19.2 mmol h^?1 g^?1_cat. The obtained XRD and XPS results revealed the facile formation of the composite. The heterojunction formed in the ternary system remarkably enhanced the visible light absorption properties and charge separation in CTP as evidenced from their UV–visible absorption and PL spectra, respectively. The optimized union of the materials with specific properties and their intimate physical contacts might be the origin for the manifested, improved and durable photocatalytic efficiency towards hydrogen production.     

Facile synthesis of TiO2-supported Al2O3 ceramic hollow fiber substrates with extremely high photocatalytic activity and reusability

TiO₂ oxide was deposited on a microstructured α-Al₂O₃ ceramic hollow fiber substrate by a simple one-step solution-immersion process with tetraethyl orthosilicate (TEOS) as a binder. The effects of the starting coating solution's composition on the photocatalytic properties of TiO₂ powders deposited on a substrate was determined by using TiO₂-supported Al₂O₃ ceramic hollow fiber substrates fabricated from coating solutions with different compositions and examining the substrates' effect on the methylene blue (MetB) degradation reaction under ultraviolet light. A strong correlation was observed between the initial coating solution compositions and the final photocatalytic characteristics of the TiO₂-supported Al₂O₃ ceramic hollow fiber substrates. Under optimal conditions, the MetB removal efficiency reached about 91% in a few minutes. To the best of our knowledge, this is the highest and most rapidly attained MetB removal efficiency reported for TiO₂-supported Al₂O₃ ceramic hollow fiber substrates. Furthermore, apart from attaining an extremely high photocatalytic activity within minutes, the fabricated TiO₂-supported Al₂O₃ ceramic hollow fiber substrates exhibited high photocatalytic stability even after several cycles.     

Simple fabrication of N-doped mesoporous TiO2 nanorods with the enhanced visible light photocatalytic activity

N-doped mesoporous TiO₂ nanorods were fabricated by a modified and facile sol–gel approach without any templates. Ammonium nitrate was used as a raw source of N dopants, which could produce a lot of gasses such as N₂, NO₂, and H₂O in the process of heating samples. These gasses were proved to be vitally important to form the special mesoporous structure. The samples were characterized by the powder X-ray diffraction, X-ray photoelectron spectrometer, nitrogen adsorption isotherms, scanning electron microscopy, transmission electron microscopy, and UV-visible absorption spectra. The average length and the cross section diameter of the as-prepared samples were ca. 1.5 μm and ca. 80 nm, respectively. The photocatalytic activity was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The N-doped mesoporous TiO₂ nanorods showed an excellent photocatalytic activity, which may be attributed to the enlarged surface area (106.4 m² g^-1) and the narrowed band gap (2.05 eV). Besides, the rod-like photocatalyst was found to be easy to recycle.     

Synthesis of Fe3O4 nanowire@CeO2/Ag nanocomposites with enhanced photocatalytic activity under sunlight exposure

Ternary magnetic Fe₃O₄ nanowire@CeO₂/Ag nanocomposites have been firstly synthesized by means of hydrothermal and co–precipitation techniques, and their ability to adsorb, photocatalytic degradation organic pollutants, methylene blue present in water, and separate, has been demonstrated. The results show that CeO₂ and Ag nanoparticles are uniformly deposited on the surface of Fe₃O₄ nanowires. The photocatalytic experiments demonstrate that the Fe₃O₄@CeO₂/Ag nanocomposites exhibit remarkably enhanced photocatalytic properties and stability compared to CeO₂, CeO₂/Ag, Fe₃O₄@CeO₂, Fe₃O₄ under natural sunlight exposure. Moreover, excellent photocatalytic degradation efficiency for phenol and MO are also observed. The enhanced photocatalytic performance may be attributed to the synergetic effect of Fe₃O₄ nanowire, CeO₂ and Ag nanoparticles, which lead to the enhanced light harvesting, the promoted charge separation and enhanced adsorption capacity. In addition, the Fe₃O₄@CeO₂/Ag photocatalyst can be easily collected and separated by an external magnet. These results suggest that the nanocomposites could be exploited as potential candidates for solar photocatalysis.     

Thickness effect in the photocatalytic activity of TiO2 thin films derived from sol-gel process

TiO₂ films in various thicknesses were prepared by sol-gel method, and their photocatalytic activities in the decomposition of gaseous 2-propanol were evaluated. It was found that the photocatalytic activities of transparent TiO₂ films increase with the increase of film thickness: The photocatalytic activity of TiO₂ films in 670 nm-thickness was 3.7 times that of films in 70 nm-thickness. We proposed that the higher photocatalytic activities for the thicker TiO₂ films originate from the greater amount of photogenerated electron and hole pairs, which are transferred from the inside to the surface of TiO₂ films. We also provided some experimental evidences supporting this mechanism.     

Fabrication of heterogeneous photocatalysts for insight role of carbon nanofibre in hierarchical WO3/ MoSe2 composite for enhanced photocatalytic hydrogen generation

Mimicking the natural photosynthesis system, artificial photocatalysis facilitates effective utilization of solar energy for environmental sustainability and hydrogen energy production. In this work, the robust and efficient carbon fiber has been successfully incorporated into the interface between WO₃ nanodots and MoSe₂ needles using the facile hydrothermal and solvothermal method. The suitable interfacial contact of heterogeneous photocatalysts plays a significant role in the separation/transfer of interfacial photogenerated electron-hole pairs and hetero-junction. It seems an efficient approach for enhanced photocatalytic performance since the greater area of contact could improve the interfacial rate of charge transfer. The phase structure of prepared WO₃ nanodots changed from the monoclinic to hexagonal phase by the addition of co-catalyst. The experimental results exhibited that carbon fiber played a tri-functional role to boost up the photocatalytic activity over MoSe₂ nanostructures. It's not only act as operative co-catalyst but could also serve as the conductive electron bridges, rather than general cocatalyst, to accumulate electrons and encourage the hydrogen generation kinetics over the WO₃ photocatalysts. More interestingly, the WO₃?1% MoSe₂?1.5% carbon fiber and WO₃?1%MoSe₂ nanocomposites demonstrated the excellent rates of hydrogen evolution 438.7 and 356.2?mmol/g.h, which were 7.6 and 6.17 times higher when compared to that of pure MoSe₂, respectively. Under the visible light excitation, the atomically junction encourages fast electron transfer from nanofibers to MoSe₂ to suppress the rapid recombination kinetics within WO₃ nanodots and extend the lifetime of WO₃ charge carrier's, thereby releasing more photogenerated electrons with higher reducing power for hydrogen evolution. The current work can contribute with new perspectives and mechanistic insight for the design and development of heterogeneous photocatalysts WO₃ based nanostructures using the combination of MoSe₂ and trifunctional carbon nanofibers for environment and energy harvesting applications.     

Characterization of Ti/Si binary oxides prepared by the sol-gel method and their photocatalytic properties: The hydrogenation and hydrogenolysis of CH3CCH with H2O

Titanium-silicon (Ti/Si) binary oxides having different Ti content were prepared by the sol-gel method and utilized as photocatalysts for the hydrogenation and hydrogenolysis of CH₂CCH with H₂O. The photocatalytic reactivity and selectivity of these catalysts were investigated as a function of the Ti content and it was found that the hydrogenolysis reaction (C₂H₆ formation) was predominant in regions of low Ti content, while the hydrogenation reaction (C₃H₆ formation) proceeded in regions of high Ti content. The in situ photoluminescence, diffuse reflectance absorption, FT-IR, XAFS (XANES and EXAFS), and XPS spectroscopic investigations of these Ti/Si binary oxides indicated that the titanium oxide species are highly dispersed in the SiO₂ matrices and exist in a tetrahedral coordination exhibiting a characteristic photoluminescence spectrum. The charge transfer excited state of the tetrahedrally coordinated titanium oxide species plays a significant role in the efficient photoreaction with a high selectivity for the hydrogenolysis of CH₃CCH to produces mainly C₂H₆ and CH₄, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity for the hydrogenation of CH₃CCH to produce C₃H₆, being similar to reactions of the powdered TiO₂ catalysts. The good parallel relationship between the yield of the photoluminescence and the specific photocatalytic reactivity of the Ti/Si binary oxides as a function of the Ti content clearly indicates that the high photocatalytic reactivity of the Ti/Si binary oxides having low Ti content is associated with the high reactivity of the charge transfer excited state of the isolated titanium oxide species in tetrahedral coordination, [Ti³⁺-O⁻]*.     

H6P2W18O62/TiO2-SiO2光催化降解有机染料的研究

采用浸渍法制备了H6P2W18/TiO2-SiO2光催化剂,并采用傅里叶变换红外光谱(FT-IR)、X射线粉末衍射(XRD) 、扫描电子显微镜(SEM)对其进行了表征,通过光催化剂H6P2W18O62/TiO2-SiO2对甲基橙的研究,得出催化剂制备适宜条件为：H6P2W18O62的负载量为30%,催化剂活化温度为200 ℃,煅烧时间为3 h。以光催化降解染料废水甲基橙为探针反应, 探讨了甲基橙初始浓度,催化剂用量、溶液pH值对光催化降解效果的影响以及催化剂的重复使用性能. 结果表明,H6P2W18/TiO2-SiO2光催化剂表现出较高的光催化性能,在催化剂的用量为1.39 g/L,甲基橙溶液初始浓度为5 mg/L, 初始pH=3.5时, 反应时间为2.5 h优化条件下,甲基橙的降解率可达99.2%,且产生了协同效应. H6P2W18O62/TiO2-SiO2光催化剂对亚甲基蓝、罗丹明B和甲基红均具有较高的光催化性能,降解率达84.0%~100.0%. 光催化剂还表现出较好的重复使用性能,第5次降解率仍为94.4%.     

H_6P_2W_(18)O_(62)/TiO_2-SiO_2光催化降解有机染料

采用浸渍法制备了H6P2W18O62/Ti O2-Si O2光催化剂,并采用傅里叶变换红外光谱(FTIR)、X射线粉末衍射(XRD)、扫描电子显微镜(SEM)对其进行了表征。通过光催化剂H6P2W18O62/Ti O2-Si O2对含甲基橙模拟废水进行处理,结果表明,H6P2W18O62/Ti O2-Si O2光催化剂表现出较高的光催化性能,在催化剂用量为1.39 g/L,甲基橙溶液质量浓度为5 mg/L,初始p H=3.5,反应时间2.5 h的条件下,甲基橙的降解率可达99.2%,且产生了协同效应。H6P2W18O62/Ti O2-Si O2光催化剂对罗丹明B、亚甲基蓝和甲基红均具有较高的光催化性能,降解率达84.0%~100.0%。光催化剂还表现出较好的重复使用性能,第5次降解率仍为94.4%。     

H_3PW_(12)O_(40)/TiO_2-SiO_2催化合成环己酮1,2-丙二醇缩酮

采用H3PW12O40/TiO2-SiO2为催化剂,以1,2-丙二醇、环己酮为原料合成环己酮1,2-丙二醇缩酮。探讨H3PW12O40/TiO2-SiO2对该反应的催化活性。实验表明:H3PW12O40/TiO2-SiO2是合成环己酮1,2-丙二醇缩酮的良好催化剂;在n(环己酮)∶n(1,2-丙二醇)=1∶1.6,反应时间为60min,环己烷用量为6mL,催化剂的用量占反应物料总质量的0.8%的适宜条件下,其收率可达81.9%。     

Reversible redox behavior of Fe2O3/TiO2 composites in the gaseous photodegradation process

The use of photocatalytic technology in VOCs pollutants removal has caused great attention. Fe₂O₃ possesses some unique advantages among diverse visible-light driven photocatalysts due to its narrow bandgap, abundant reserves and favorable biosafety. In this work, Fe₂O₃/TiO₂ composites was fabricated by a facile impregnation method and their photocatalytic performance towards acetaldehyde and o-xylene was detected. TEM, EDS, photoluminescence spectra and UV-Vis were used to characterize the morphology and properties of the Fe₂O₃/TiO₂ composites. It was proved that the photocatalytic ability of TiO₂ was greatly improved by coupling with Fe₂O₃. Interestingly, the Fe₂O₃/TiO₂ composites showed deactivation in the degradation of acetaldehyde while no such phenomenon in the o-xylene case. The reason could be that Fe³⁺ accepted the photo-induced electrons of TiO₂ and was reduced to Fe²⁺, which can easily combine with the intermediate product of acetaldehyde and generated Fe(CH₃COO)₂. Moreover, the deactivated photocatalyst can be regenerated by heat treatment, since Fe(CH₃COO)₂ can be decomposed into Fe₂O₃ in air. ESR was further used to demonstrate this mechanism. This work reveals the coupled redox reactions in the photocatalytic process, which is benefit for the design of new photocatalysts.     

Surfactant-free synthesis of a novel octahedral ZnFe2O4/graphene composite with high adsorption and good photocatalytic activity for efficient treatment of dye wastewater

Recently, significant effort has been made toward the development of graphene-based visible-ligh-responsive photocatalysts and their application to dye wastewater treatment. Herein, a series of octahedral ZnFe₂O₄/graphene (ZnFe₂O₄-G) nanocomposites were synthesized using a one-pot solvothermal reaction without the need of a surfactant as novel bifunctional materials exhibiting both high adsorption and good visible-light-responsive photocatalyst properties. The crystal structure, morphology and photocatalytic degradation properties, as well as adsorption behavior, of the octahedral ZnFe₂O₄/graphene composites were investigated in detail. The adsorption capacity and UV–vis spectrometry results indicate that the dye removal efficiency over the samples followed the order of: methylene blue (MB) > rhodamine B (RhB) > methyl orange (MO). The ZnFe₂O₄-G materials exhited enhanced photocatalytic degradation properties for cationic dyes (MB and RhB) compared to those for the anionic dye (MO). In addition, the experimental results indicate that the ZnFe₂O₄-G materials can decompose H₂O₂ in the visible-light photocatalytic process to form hydroxyl radicals (•OH), which are mainly responsible for the photodegradation of the organic contaminants.     

Facile one-pot synthesis of a BiOBr/Bi2WO6 heterojunction with enhanced visible-light photocatalytic activity for tetracycline degradation

Photocatalytic removal of tetracycline (TC) from the wastewater is of great value in the chemical and environmental engineering field. Here, we introduced a facile one-step method for the synthesis of BiOBr/Bi₂WO₆ heterojunctions by using cheap CTAB as the Br source. We showed the possibility of our method to fine-tune the content of BiOBr in the produced BiOBr/Bi₂WO₆ by simply changing the dosage of cetyltrimethylammonium bromide (CTAB), providing a platform for the delicate tuning of the visible-light absorbance ability of the composites. With a suitable heterojunction structure of BiOBr/Bi₂WO₆-0.2, it exhibited an ultrarapid photocatalytic activity towards TC (20 mg·L^-1), with a competitive removal efficiency of 88.1% within 60 min and an ultrahigh removal rate of 0.0349 min^-1. It could also be robustly recycled for at least 5 cycles with slight removal efficiency loss. We demonstrated that this exciting photocatalytic performance was due to the highly decreased recombination of photoinduced electrons and holes on our composites by constructing this heterojunction structure, and the resulting OH and contributed to the effective degradation of TC to CO₂.     

H4SiW12O40改性TiO2的制备及光催化性能研究

通过超声分散法制备了H4SiW12O40掺杂TiO2光催化剂,采用XRD、红外光谱进行表征。考察了H4SiW12O40的掺杂比例、催化剂的煅烧温度、催化剂的投加量、反应物的初始浓度对光催化降解碱性品红溶液的影响,并利用TOC测定和紫外-可见吸收光谱进一步研究了光催化降解过程。研究结果表明：H4SiW12O40掺杂后,TiO2的粒径减小,比表面积增大,光谱响应范围发生红移;硅钨酸掺杂TiO2的最佳比例为3.20%wt.;催化剂的最佳煅烧温度为400℃;催化剂的最佳用量为0.4g/L;当碱性品红溶液的初始浓度为14mg/L时,光催化效果较好;此外,光催化降解碱性品红溶液的过程可能是分步进行的。     

Fabrication of Al2O3/AlN composite ceramics with enhanced performance via a heterogeneous precipitation coating process

To improve the thermal and mechanical properties of Al₂O₃/AlN composite ceramics, a novel heterogeneous precipitation coating (HPC) approach was introduced into the fabrication of Al₂O₃/AlN ceramics. For this approach, Al₂O₃ and AlN powders were coated with a layer of amorphous Y₂O₃, with the coated Al₂O₃ and AlN powders found to favor the formation of an interconnected YAG second phase along the grain boundaries. The interconnected YAG phase was designed to act as a diffusion barrier layer to minimize the detrimental interdiffusion between Al₂O₃ and AlN particles. Compared with samples prepared by a conventional ball-milling method, the HPC Al₂O₃/AlN composites exhibited less AlON formation, a higher relative density, a smaller grain size and a more homogeneous microstructure. The thermal conductivity, bending strength, fracture toughness and Weibull modulus of the HPC Al₂O₃/AlN composite ceramics were found to reach 34.21 ± 0.34 W m⁻¹ K⁻¹, 475.61 ± 21.56 MPa, 5.53 ± 0.29 MPa m^1/2 and 25.61, respectively, which are much higher than those for the Al₂O₃ and Al₂O₃/AlN samples prepared by the conventional ball-milling method. These results suggest that HPC is a more effective technique for preparing Al₂O₃/AlN composites with enhanced thermal and mechanical properties, and is probably applicable to other composite material systems as well.