Study of adsorption and degradation of acid orange 7 on the surface of CeO2 under visible light irradiation

Cerium dioxide was prepared by the precipitation method and found to be an efficient photocatalyst to degrade azodyes under visible light irradiation. Nonbiodegradable azodyes acid orange 7 (AO7) was selected as modal target to examine the photocatalytic activity of CeO₂. AO7 could be efficiently degraded in aqueous suspension of CeO₂ under visible light illumination. The catalyst was characterized by X-ray diffraction (XRD), N₂ sorption, transmission electron microscopic image (TEM) and UV/vis absorption spectrum techniques. AO7 solution was quickly decolorized and partly mineralized under visible light irradiation with existing CeO₂. The photodegradation rate of this azodye catalyzed by CeO₂ is much faster than those occurring on commercial titania (Degussa P25) under otherwise identical conditions of visible light irradiation. Experiments were conducted to examine the adsorption mode of acid orange 7 on CeO₂ and adsorption capacity at different pH values. The possible degradation pathway has been proposed for the photocatalytic degradations by using certain radical scavengers and gas chromatography–mass spectrometry (GC–MS) to determine intermediates. The enhanced photoactivity of the lanthanide oxide CeO₂ was attributed to the superior adsorption capacity and special 4f electron configuration.     

Efficient decomposition of organic compounds with FeTiO3/TiO2 heterojunction under visible light irradiation

FeTiO₃/TiO₂, a new heterojunction-type photocatalyst working at visible light, was prepared by a simple sol–gel method. Not only did FeTiO₃/TiO₂ exhibit greatly enhanced photocatalytic activity in decomposing 2-propanol in gas phase and 4-chlorophenol in aqueous solution, but also it induced efficient mineralization of 2-propanol under visible light irradiation (λ ≥ 420 nm). Furthermore, it showed a good photochemical stability in repeated photocatalytic applications. FeTiO₃ showed a profound absorption over the entire visible range, and its valence band (VB) position is close to that of TiO₂. The unusually high photocatalytic efficiency of the FeTiO₃/TiO₂ composite was therefore deduced to be caused by hole transfer between the VB of FeTiO₃ and TiO₂.     

Preparation of novel nanometer TiO2 catalyst doped with upconversion luminescence agent and investigation on degradation of acid red B dye using visible light

An unreported nanometer TiO₂ photocatalyst doped with upconversion luminescence agent (40CdF₂ · 60BaF₂ · 0.8Er₂O₃) utilizing visible light was prepared. Its photocatalytic activity was checked through the photocatalytic degradation of acid red B as a model compound under visible light irradiation. Results show that the upconversion luminescence agent prepared as dopant can effectively turn visible lights to ultraviolet lights, which can be absorbed by nanometer TiO₂ particles to produce the electron-cavity pairs. Therefore, the photocatalytic ability of this novel TiO₂ photocatalyst has greatly been enhanced compared with undoped and common TiO₂ photocatalyst.     

Photocatalytic properties of a novel layered photocatalyst CsLaSrNb2NiO9

A new visible-light-driven photocatalyst CsLaSrNb₂NiO₉ based on the 2-D layered perovskite crystal structure was prepared by using the solid-state method. Photocatalytic H₂ evolution from the aqueous CH₃OH solution was achieved on the photocatalysts CsLaSrNb₂NiO₉ under UV or visible light irradiation. A possible electronic band structure of CsLaSrNb₂NiO₉ was proposed in regard to the complicated photocatalytic and photophysic properties.     

Nb/N Co-Doped Layered Perovskite Sr2TiO4: Preparation and Enhanced Photocatalytic Degradation Tetracycline under Visible Light

Sr₂TiO₄ is a promising photocatalyst for antibiotic degradation in wastewater. The photocatalytic performance of pristine Sr₂TiO₄ is limited to its wide bandgap, especially under visible light. Doping is an effective strategy to enhance photocatalytic performance. In this work, Nb/N co-doped layered perovskite Sr₂TiO₄ (Sr₂TiO₄:N,Nb) with varying percentages (0–5 at%) of Nb were synthesized by sol-gel and calcination. Nb/N co-doping slightly expanded the unit cell of Sr₂TiO₄. Their photocatalytic performance towards antibiotic (tetracycline) was studied under visible light (λ > 420 nm). When Nb/(Nb + Ti) was 2 at%, Sr₂TiO₄:N,Nb(2%) shows optimal photocatalytic performance with the 99% degradation after 60 min visible light irradiation, which is higher than pristine Sr₂TiO₄ (40%). The enhancement in photocatalytic performance is attributed to improving light absorption, and photo-generated charges separation derived from Nb/N co-doping. Sr₂TiO₄:N,Nb(2%) shows good stability after five cycles photocatalytic degradation reaction. The capture experiments confirm that superoxide radical is the leading active species during the photocatalytic degradation process. Therefore, the Nb/N co-doping in this work could be used as an efficient strategy for perovskite-type semiconductor to realize visible light driving for wastewater treatment.     

Effect of Surface Treatment on the Selective Photocatalytic Oxidation of Benzyl Alcohol into Benzaldehyde by O2 on TiO2 Under Visible Light

The photocatalytic oxidation of benzyl alcohol into benzaldehyde proceeded with high conversion and selectivity on a TiO₂ photocatalyst by O₂ under visible light irradiation. Surface complex formed by the interaction of benzyl alcohol with the Ti sites and/or surface OH groups of TiO₂ play an important role in the absorption of visible light and unique selective photocatalytic reaction.     

Photocatalytic activity of TiO2 supported on multi-walled carbon nanotubes under simulated solar irradiation

TiO₂ particles supported on multi-walled carbon nanotubes (MWCNTs) were prepared using a sol–gel method to investigate their photocatalytic activity under simulated solar irradiation for the degradation of methyl orange (MO) in aqueous solution. The prepared composites were analyzed using XRD, SEM, EDS and UV–vis absorption spectroscopy. The results of this study indicated that there was little difference in the shape and structure of MWCNTs/TiO₂ composite and pure TiO₂ particles. The composite exhibited enhanced absorption properties in the visible light range compared to pure TiO₂. The degradation of MO by MWCNTs/TiO₂ composite photocatalysts was investigated under irradiation with simulated solar light. The results of this study indicated that MWCNTs played a significant role in improving photocatalytic performance. Different amounts of MWCNTs had different effects on photodegradation efficiency, and the most efficient MO photodegradation was observed for a 2% MWCNT/TiO₂ mass ratio. Photocatalytic reaction kinetics were described using the Langmuir–Hinshelwood (L–H) model. The photocatalyst was reused for eight cycles, and it retained over 95.2% photocatalytic degradation efficiency. Possible decomposition mechanisms were also discussed. The results of this study indicated that photocatalytic reactions with TiO₂ particles supported on MWCNTs under simulated solar light irradiation are feasible and effective for degrading organic dye pollutants.     

Enhanced photocatalytic activity of TiO2/SiO2 by the influence of Cu-doping under reducing calcination atmosphere

Cu-doped titania photocatalyst supported on silica beads (Cu-TiO₂/SiO₂) were prepared under different Cu-ion concentration and under different calcination atmosphere. The properties and performance of Cu-TiO₂/SiO₂ were compared with undoped TiO₂/SiO₂ photocatalyst. The effect of Cu-doping and calcination atmosphere on photocatalytic degradation of phenol under both black light and visible light irradiation were investigated, where in both cases the degradation rate of phenol by Cu-doped catalyst prepared under reducing calcination atmosphere was found to be higher than the undoped catalyst or Cu-doped catalyst prepared under air atmosphere. This may be attributed to increase in visible light absorption and lengthening of photogenerated electron–hole pair recombination time. The photocatalytic beads were characterized by X-ray diffraction (XRD), UV-Vis absorption spectroscopy and SEM/EDAX analysis.     

Preparation and photocatalytic properties of a novel kind of loaded photocatalyst of TiO2/SiO2/γ‐Fe2O3

A novel kind of loaded photocatalyst of TiO₂/SiO₂/γ‐Fe₂O₃ (TSF) that can photodegrade effectively organic pollutants in the dispersion system and can be recycled easily by a magnetic field is reported in this paper. The γ‐Fe₂O₃ cores in TiO₂/γ‐Fe₂O₃ are found to reduce the activity of the TiO₂ photocatalyst in the photodegradation of dyes under either UV or visible light irradiation. Addition of a SiO₂ membrane between the γ‐Fe₂O₃ core and the TiO₂ shell weakens efficiently the influence of the γ‐Fe₂O₃ cores on the TiO₂ photocatalytic activity and leads to a highly active and magnetically separable photocatalyst on TSF. Comparison of the photodegradation processes of dyes under UV and visible irradiation is also carried out. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhanced visible‐light‐driven photocatalytic activities of LiInO2 by Mo6+‐doping strategy

A novel visible‐light‐driven photocatalyst of Mo‐doped LiInO₂ nanocomposite was successfully synthesized through a sol‐gel method. The effect of Mo‐doping concentrations on the microstructures and properties of LiInO₂ was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy, photoluminescence, and ultraviolet‐visible absorption spectra. The photocatalytic properties of the as‐prepared samples were evaluated by the photocatalytic degradation of methylene blue (MB) dye under visible‐light irradiation. The results demonstrated that the photocatalytic activity of 6% Mo‐LiInO₂ reached to 98.6%, which was much higher than that of the undoped photocatalyst LiInO₂ (only 46.8%). The enhanced photocatalytic activity is ascribed to Mo‐doping strategy. The holes play an important role in the process of the photodegradation of MB. The superior photocatalytic activity of the as‐prepared Mo‐LiInO₂ nanocomposites suggests a potential application for organic dye degradation of wastewater remediation. This work provides a further understanding on tailoring the band structure of semiconductor photocatalyst for enhancing visible‐light absorption and promoting electron‐hole separation by Mo‐doping strategy.     

Photoreduction of Carbondioxide on Surface Functionalized Nanoporous Catalysts

Nanoporous photocatalysts have been designed to exhibit unique photocatalytic activities through framework substitution of titanium species or surface immobilization of rhenium complex onto mesoporous silica. This article summarizes recent work on the synthesis, characterization and photocatalytic activities of the designed porous photocatalysts performed by the present authors. Various spectroscopic investigations revealed that the photo-excited states of these catalysts play a vital role in the photocatalytic reactions and their photocatalytic reactivities are strongly dependent on structures of active sites, which are confined and immobilized in the restricted framework structure of the mesoporous silica. Highly dispersed titanium oxide species incorporated in the framework of mesoporous silica exhibited high and unique photocatalytic reactivity for the reduction of CO₂ with H₂O to produce CH₄ and CH₃OH under UV irradiation, its reactivity being much higher than bulk TiO₂. The cationic rhenium(I) complex was encapsulated into a mesoporous AlMCM-41 material by ion-exchange method, yielding a visible light photocatalyst to be active for photocatalytic reduction of CO₂.     

Highly visible light responsive metal loaded N/TiO2 nanoparticles for photocatalytic conversion of CO2 into methane

Photocatalytic reduction of carbon dioxide (CO₂) into valuable hydrocarbon such as methane (CH₄) using water as reducing agent is a good strategy for environment and energy applications. In this study, a facile and simple sol-gel method was employed for the synthesis of metal (Cu and Ag) loaded nanosized N/TiO₂ photocatalyst. The prepared photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, BET Surface area analyzer, X-ray photoelectron spectroscopy and UV–vis diffuses reflectance spectroscopy. The photocatalytic conversion of CO₂ into methane was carried out under visible light irradiation (λ≥420 nm) by prepared photocatalysts in order to evaluate the photocatalytic efficiency. The results demonstrate that Ag loaded N/TiO₂ showed enhanced photocatalytic performance for methane production from CO₂ compared to other Cu–N/TiO₂, N/TiO₂ and TiO₂ photocatalysts. The improvement in the photocatalytic activity could be attributed to high specific surface area, extended visible light absorption and suppressed recombination of electron – hole pair due to synergistic effects of silver and nitrogen in the Ag–N/TiO₂ photocatalyst. This study demonstrates that Ag–N/TiO₂ is a promising photocatalytic material for photocatalytic reduction of CO₂ into hydrocarbons under visible light irradiation.     

Ag nanoparticles loaded TiO2/MWCNT ternary nanocomposite: A visible-light-driven photocatalyst with enhanced photocatalytic performance and stability

A visible light active photocatalyst, Ag/TiO₂/MWCNT was synthesized by loading of Ag nanoparticles onto TiO₂/MWCNT nanocomposite. The photocatalytic activity of Ag/TiO₂/MWCNT ternary nanocomposite was evaluated for the degradation of methylene blue dye under UV and visible light irradiation. Ag/TiO₂/MWCNT ternary nanocomposite exhibits (~9 times) higher photocatalytic activity than TiO₂/MWCNT and (~2 times) higher than Ag/TiO₂ binary nanocomposites under visible light irradiation. The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir. Effect of different scavengers on the degradation of methylene blue dye in the presence of catalyst has been investigated to find the role of photogenerated electrons and holes. Simultaneously, the Ag/TiO₂/MWCNT shows excellent photocatalytic stability. This work highlights the importance of Ag/TiO₂/MWCNT ternary nanocomposite as highly efficient and stable visible-light-driven photocatalyst for the degradation of organic dyes.     

Hydrothermal synthesis and visible-light photocatalytic activity of porous peanut-like BiVO4 and BiVO4/Fe3O4 submicron structures

Porous peanut-like BiVO₄ and BiVO₄/Fe₃O₄ submicron structures were synthesized by a template-free hydrothermal process at 160 °C for 24 h. 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), vibrating sample magnetometer (VSM) and UV–vis spectroscopy. The photocatalytic activity of BiVO₄ and BiVO₄/Fe₃O₄ submicron structures were evaluated for the degradation of Rhodamine B (RhB) and methylene blue (MB) under visible light irradiation with and without the assistance of H₂O₂. According to the experimental results obtained, porous peanut-like BiVO₄/Fe₃O₄ composite photocatalyst shows higher photocatalytic activity in the H₂O₂-assisted system under visible light irradiation compared to BiVO₄. Recycling test on the BiVO₄/Fe₃O₄ composite photocatalyst for the degradation of RhB under visible light irradiation indicates that the composite photocatalyst is stable in the H₂O₂-assisted system in five cycles. Therefore, this composite photocatalyst will be beneficial for efficient degradation of organic pollutants present in water and air under solar light.     

Photocatalytic degradation of rhodamine B and phenol by solution combustion synthesized BiVO4 photocatalyst

Visible-light-induced BiVO₄ photocatalyst has been successfully synthesized via a solution combustion synthesis (SCS) method. The photocatalytic activities of the as-synthesized sample were evaluated by the photodegradation of rhodamine B (RhB) and phenol under visible-light irradiation (λ > 420 nm). The decolorization of high-concentrated RhB (10^− 4 M) and the variation of the chemical oxygen demand (COD), demonstrated that the BiVO₄ photocatalyst was efficient in aromatic organic compounds degradation. The reduction of total organic carbon (TOC) (about 22.0% after 4.5 h of irradiation) showed that the mineralization of RhB over the BiVO₄ photocatalyst is realized. Additionally, much enhanced photocatalytic performance for phenol degradation was also realized with the assistance of appropriate amount of H₂O₂.     

Development of an S-doped titania nanotube (TNT) site-selectively loaded with iron(III) oxide and its photocatalytic activities

We investigated an S-doped titania nanotube (TNT) loaded with Fe₂O₃ nanoparticles in order to improve photocatalytic activity of S-doped TNT under visible light irradiation. S-doped TNT was successfully prepared using the solid-phase method at 350 °C under aerated conditions. S-doped TNT showed photoabsorption in the 400–500 nm visible light region and showed photocatalytic activity for oxidation of acetaldehyde under visible light irradiation. Loading of Fe₂O₃ on S-doped TNT remarkably improved the photocatalytic activity of S-doped TNT. PA spectra measurement, which was performed in order to elucidate the mechanism of activity improvement, showed that the efficiency of charge separation between photoexcited electrons and holes was improved because the electrons were trapped by Fe₂O₃. Enhancement of photocatalytic activity was strongly dependent on the site of Fe₂O₃ nanoparticles loaded on TNT. PA spectra measurement showed that the photoexcited electrons transferred to Fe₂O₃ from S-doped TNT under UV light irradiation or to S-doped TNT from Fe₂O₃ under visible light irradiation.     

Iridium,carbon and nitrogen multiple-doped TiO2 Nanoparticles with enhanced photocatalytic activity

The aim of this research is to enhance the photocatalytic activity of TiO₂ nanoparticles for the UV–visible light by multiple-doping with Iridium, carbon and nitrogen. The tridoped TiO₂ photocatalyst were prepared by wet chemical method, and characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible light diffuse reflection spectroscopy and room temperature photoluminescence spectroscopy. Besides, the photocatalytic H₂ evolution performance of Ir-C-N tridoped TiO₂ under UV–visible light irradiation was evaluated. It was found that Ir existed as Ir⁴⁺ by substituting Ti in the lattice of TiO₂; meanwhile, C and N were also incorporated into the surface of TiO₂ nanoparticles in interstitial mode. Meanwhile, Ir-C-N tridoping extended the absorption of TiO₂ into the visible light region and narrowed its band gap to ~3.0 eV, resulting in enhanced photocatalytic H₂ evolution under UV–visible light irradiation. This could be attributed to narrow band gap and proper electronic structure of TiO₂ after Ir-C-N tridoping.     

Microwave fabrication of Cu2ZnSnS4 nanoparticle and its visible light photocatalytic properties

Cu₂ZnSnS₄ nanoparticle with an average diameter of approximately 31 nm has been successfully synthesized by a time effective microwave fabrication method. The crystal structure, surface morphology, and microstructure of the Cu₂ZnSnS₄ nanoparticle were characterized. Moreover, the visible light photocatalytic ability of the Cu₂ZnSnS₄ nanoparticle toward degradation of methylene blue (MB) was also studied. About 30% of MB was degraded after 240 min irradiation when employing Cu₂ZnSnS₄ nanoparticle as a photocatalyst. However, almost all MB was decomposed after 90 min irradiation when introducing a small amount of H₂O₂ as a co-photocatalyst. The enhancement of the photocatalytic performance was attributed to the synergetic effect between the Cu₂ZnSnS₄ nanoparticle and H₂O₂. The detailed photocatalytic degradation mechanism of MB by the Cu₂ZnSnS₄ was further proposed.     

Photocatalytic degradation of formic acid with simultaneous production of hydrogen over Pt and Ru-loaded CdS/Al-HMS photocatalysts

The CdS/Al-HMS, Pt- and Ru-loaded CdS/Al-HMS photocatalysts were prepared by template, ion exchange and precipitation reaction, and were characterized by N₂ adsorption/desorption measurements, X-ray diffraction (XRD), UV-Visible diffuse reflectance spectra (UVDRS), X-ray fluorescence (XRF), transmission electron microscopy (TEM) and fluorescence emission spectra (FES). The result showed that CdS in the form of clusters was highly dispersed inside the channels of Al-HMS. The reaction activities of photocatalysts were examined by photocatalytic degradation of formic acid under visible light irradiation (λ ≥ 420 nm). The photocatalyst, CdS/Al-HMS loaded 0.34 wt.% Pt, showed the highest H₂ evolution at a rate of 7.63 mL h^− 1 with an apparent quantum yield of 2%.     

Efficient photocatalytic degradation of organic dyes over titanium dioxide coating upconversion luminescence agent under visible and sunlight irradiation

In order to use the sunlight efficiently, a new titanium dioxide (TiO₂) photocatalyst with high catalytic activity under visible light irradiation was prepared with sol–gel technique. In this work, an upconversion luminescence agent, crystallized Er³⁺:Y₃Al₅O₁₂, was synthesized and its characters were determined. It is found that this crystallized Er³⁺:Y₃Al₅O₁₂ can emit three upconversion fluorescent peaks below 387 nm under the excitation of 488 nm visible light. Hence, this upconversion luminescence agent could transform visible light into ultraviolet light, which could satisfy the genuine requirement of TiO₂ photocatalyst. Additionally, the upconverison mechanisms were also discussed. Meanwhile, the prepared TiO₂ photocatalysts coating upconversion luminescence agent were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photocatalytic activity of prepared TiO₂ powder was tested through the degradation of congo red in aqueous solution as a model compound under visible and sunlight irradiation. To affirm the complete mineralization, the ion chromatography and total organic carbon (TOC) were used to observe the mineralized anions and organic residues. The experimental results proved that the prepared TiO₂ photocatalyst coating crystallized Er³⁺:Y₃Al₅O₁₂ behaved much higher photocatalytic activity under visible light and sunlight irradiation, and was able to decompose the congo red in aqueous solution efficiently. Therefore, this method may be envisaged as a novel technology for treating dyes wastewater using solar energy, especially for textile industries in developing countries.