Visible Light Catalytic Activity Research Articles

Binary-phase TiO2 modified Bi2MoO6 crystal for effective removal of antibiotics under visible light illumination

A series of binary-phase TiO2 modified Bi2MoO6 nanocrystals have been prepared via a solvothermal-calcination process. Trace TiO2 modification can effectively enhance the visible light catalytic activity of Bi2MoO6 to remove the antibiotics in aqueous solution. The obtained TiO2/Bi2MoO6 composites were investigated by some physicochemical techniques like XRD, N2 adsorption, SEM, TEM, UV–vis DRS, Raman, XPS, PL and Photo-electrochemical measurement. The presence of TiO2 nanoparticles (NPs) influenced the crystal growth of Bi2MoO6, decreasing the crystal size of Bi2MoO6 and effectively promoting its specific surface area. Moreover, the conduction band of TiO2 can serve as the electron transfer platform, which largely boosts the effective separation of photocarriers at TiO2/Bi2MoO6 heterojunction interface. With optimal TiO2 content (0.41 wt%), TiO2/Bi2MoO6 exhibited the best photocatalytic performance for different antibiotics degradation, e.g. ciprofloxacin, tetracycline and oxytetracyline hydrochloride under visible light irradiation. Moreover, the mechanism for enhanced photocatalytic performance in ciprofloxacin degradation was illuminated.

Unveiling the Role of Defects on Oxygen Activation and Photodegradation of Organic Pollutants.

The status of defects of TiO2 are of fundamental importance in determining its physicochemical properties. Here we report a simple chemical deposition method for controllable synthesis of defective anatase TiO2 nanocrystals under various calcination atmospheres. XPS and ESR analysis reveals that both the oxygen vacancies ( VO) and the trivalent titanium (Ti3+) defects exist in TiO2 after N2 treatment (N-TiO2). Meanwhile, mainly VO defects can be obtained in TiO2 with air calcination (A-TiO2). ESR spectra for reactive oxygen species determination, clearly show that the visible light catalytic activity is mainly caused by the efficient activation of oxygen molecules to •O2- species for A-TiO2, which play an important role in hindering the accumulation of intermediates during p-chlorophenol (4-CP) photodegradation process. However, the oxygen molecules cannot be activated for N-TiO2 even with superior visible light absorption and thus the photogenerated electron are reductant, which participated in the transformation of BQ to HQ via electron shuttle mechanism. Moreover, A-TiO2 exhibits higher separation efficiency of photogenerated carriers than that of N-TiO2, showing the critical role of VO with a suitable concentration in transferring photogenerated charges.

Improved visible-light catalytic activities of novel Au/P-doped g-C3N4 photocatalyst for solar fuel production and mechanism

The noble metal decorated photocatalytic materials have received marvelous attention in recent decade owing to their exceptional applications in energy conversion and environmental remediation. Herein, we have successfully fabricated Au decorated phosphorus doped graphitic carbon nitride (Au/P-CN) photocatalyst for the first time via ionic liquid and in situ photo-reduction methods. The resultant photocatalyst exhibits significant visible-light activities for water splitting to evolve H2 and CO2 conversion to CH4. The amount of H2 evolved over Au/P-CN photocatalyst is 97 μmol, ∼12-fold enhanced compared to that of the bare CN (8 μmol). Similarly, the amount of CH4 produced over Au/P-CN photocatalyst is 24 μmol, about 6-fold enhanced compared to that of the bare CN (4 μmol). The calculated quantum efficiencies for H2 evolution and CH4 production are ∼3.60% and ∼2.83%, respectively at λ = 420 nm. The exceptional photocatalytic activities are attributed to the extended visible-light absorption and improved charge carriers separation via the dopant induced surface states and the well decorated Au nanoparticles. This work demonstrate that the Au decorated CN-based photocatalysts show promising applications in photocatalysis for water splitting to evolve H2 and CO2 conversion to CH4 under visible-light irradiation.

Novel one-step fabrication of highly ordered Mo-doped TiO2 nanotubes arrays with enhanced visible light catalytic activity

Doping with transition metals has been established as a promising approach for extending the absorption spectrum of TiO2 to the visible light region for enhancing its photocatalytic (PC) activity under visible light illumination. In this work, highly ordered Mo-doped TiO2 nanotubes arrays (Mo-TNTs) were fabricated by a facile in situ anodization of Ti in ethylene glycol/fluoride electrolyte using sodium molybdate as the molybdenum source. The doping levels (0.13–1.51 at.%) of Mo were conveniently adjusted by varying the initial concentrations of sodium molybdate and ammonium fluoride in the electrolyte. Various characterizations were performed to investigate the morphologies, crystal phases, elements’ valence states of the as-prepared samples. Results indicated that Mo6+ ions were successfully introduced into the lattice of anatase TiO2, forming isostructural substitution of Ti4+. Compared with undoped TNTs, the Mo-TNTs exhibited the obvious extension of absorption spectra to the visible light region, higher photoelectric conversion efficiency and lower recombination of photogenerated carriers. Meanwhile, their photoelectrochemical properties were also significantly affected by the doping level of Mo. Of all samples, 6Mo-TNTs (0.82 at.% Mo) showed the best photoelectrochemical performance and highest PC activity under visible light. This was mainly attributed to the synergetic contributions of the enhanced visible light absorption and suppressed recombination.

Fabrication of three-dimensional porous La-doped SrTiO3 microspheres with enhanced visible light catalytic activity for Cr(VI) reduction

In recent years, much effort has been focused on the development of the photocatalysts with high performance under visible light irradiation. In this paper, three-dimensional porous La-doped SrTiO3 (LST) microspheres were prepared by a modified sol–gel method, in which the agarose gel/SrCO3 microsphere and La2O3 were employed as the template and the La resource, respectively. The as-prepared LST microspheres exhibit a porous structure with a diameter of about 10 μm and a surface pore size of about 100 nm. The La element was doped into the crystal lattice of SrTiO3 by the substitution of La3+ for Sr2+. Therefore, the absorption edge of LST samples shifts toward the visible light region, and their photocatalytic activity for the Cr(VI) reduction is enhanced under visible light. Among all LST samples, LST-0.5 (the La3+ doping content is 0.5 wt-%) exhibited the highest visible-light photocatalytic activity, which can reduce 84% Cr(VI) within 100 min. This LST materials may become a promising photocatalyst for the facile treatment of wastewater containing poisonous heavy metal ions.

Flower-like Cu2ZnSnS4 architectures synthetize and their visible-light catalytic properties

Cu2ZnSnS4 (CZTS) as a typical p-type semiconductor, has attracted much more attention because of its many potential applications. Its nanoparticles were prepared successfully with a solvothermal method, Cu(II), Zn(II) and Sn(IV) inorganic salts and thiourea as precursors, and deionized water, ethylene alcohol and N, N-dimethylformamide as solvents. The degradation of Rhodamine B (RhB) aqueous solution was carried out to investigate the visible-light catalytic activity under metal halide lamp. The results indicated that different morphology of CZTS had photocatalytic activity to RhB under visible light, and flower-like CZTS with deionized water displayed higher photodegradation efficiency than other samples, with degradation rate of 99.8% within 100 min.

Synthesis of S-Doped porous g-C3N4 by using ionic liquids and subsequently coupled with Au-TiO2 for exceptional cocatalyst-free visible-light catalytic activities

The development of new technologies for carbon dioxide reduction, water splitting, and pollutant degradation has been a demanding challenge in the globe due to critical energy and environmental issues. Herein, we have successfully synthesized sulfur doped porous g-C3N4 (S-PCN) using ionic liquid, and then coupled nanocrystalline anatase TiO2 and Au-modified TiO2 to obtain nanocomposites. The amount-optimized 1 Au-6 T/6S-PCN nanocomposite exhibits exceptional visible-light activities for CO2 conversion to CH4, H2 evolution, and 2,4-dichlorophenol degradation, respectively by ∼32-time (365 μmol g−1h−1), ∼41-time (330 μmol g−1h−1) and ∼24-time (95% 10 mg h−1L−1) enhancement compared to the porous g-C3N4 (PCN). The calculated quantum efficiencies for CH4 production and H2 evolution are ∼4.67% and ∼3.34% at 420 nm wavelength. Based on these results, it is suggested that the exceptional photoactivities are attributed to the large surface area (100.5 m2g−1), extended visible-light response and enhanced charge separation via dopant induced surface-states and subsequently coupled Au-TiO2. Furthermore, the CO2 and H as active radicals would be dominant to respectively initiate CO2 and H2O reduction, and the produced OH plays a vital role in 2,4-dichlorophenol degradation. This work demonstrates that the designed PCN-based nanocomposites show promising applications in CO2 photo-reduction, water splitting, and pollutant degradation.

Preparation and characterization of fullerene (C60)-modified BiVO4/Fe3O4 nanocomposite by hydrothermal method and study of its visible light photocatalytic and catalytic activity

ABSTRACTIn this study, BiVO4/Fe3O4/C60 nanocomposite has been synthesized for the first time using a facile and feasible hydrothermal method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), vibrating sample magnetometer (VSM), and N2 adsorption-desorption analysis were utilized to analyze the structure, morphology, size, and the magnetic property of the synthesized nanocomposite. The photocatalytic activity of the magnetic BiVO4/Fe3O4/C60 nanocomposite was investigated for the degradation of methylene blue. The results showed that 84% degradation of methylene blue (MB) (25 mg/L) solution within 5 h with a rate constant equal to 0.0049 min−1 in the presence of BiVO4/Fe3O4/C60 nanocomposite and H2O2 (1 mL, 30%) under visible light irradiation. The effects of BiVO4/Fe3O4/C60 dosage, H2O2 amount dye initial concentration and C60 amount on the efficiency of degradation process were investigated. Furthermore, the catalytic activity of the magnetic BiVO4/Fe3O4/C60 nanocomposite was investigated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using sodium borohydride (NaBH4) in the aqueous solution and at room temperature. The results showed that BiVO4/Fe3O4/C60 nanocomposite exhibited an excellent performance for the reduction of 4-NP with 97% conversion into its corresponding amino derivative within 38 min with a constant rate equal to 0.0775 min−1. As indicated by the results, the magnetic BiVO4/Fe3O4/C60 nanocomposite exhibited much higher photocatalytic and catalytic activity than BiVO4/ C60, BiVO4/Fe3O4, and pure BiVO4. Moreover, the BiVO4/Fe3O4/C60 nanocomposite could be magnetically separated from the reaction mixture due to the presence of the Fe3O4 and reused without any change in structure.

Enhanced visible light catalytic activity of MoS2/TiO2/Ti photocathode by hybrid-junction

In photoelectrochemical (PEC) water splitting systems, crucial obstacles limiting their performance are poor charge carrier dynamics and high recombination rate of photoexcited electron-hole pairs. Here, we report that this issue can be alleviated by engineering a hybrid-junction that is composed of homo- and hetero- junctions. This strategy is performed by facile hand-spraying MoS2 over the surface of anatase/rutile homo-junction TiO2 film on the Ti substrate to further form a hybrid-junction photocathode. By applying this photocathode into PEC reactor, enhanced catalytic activity is achieved under visible light (AM1.5 illumination of 300 W/m2) with hydrogen evolution reaction (HER) potential of −114 mV versus reversible hydrogen electrode (RHE) at 10 mA/cm2 and long-term stability of more than 10 times improvement comparing to ordinary electrode without the introduction of hybrid-junction. The hybrid-junction that effectively regulates charge separation and transfer pathways is proven to be responsible for the enhanced activity. As a novel exploration, this hybrid-junction system comprising of low-cost, efficient charge separation and transfer, and visible light responsivity offers a new path for relative materials to boost their PEC performance.

SnO2 as co-catalyst for enhanced visible light photocatalytic activity of Bi2MoO6

Exploring visible light active semiconductor photocatalysts is one of greatly significant issues. We show herewith the Bi2MoO6/SnO2 hybrid photocatalysts meet the requirement for degradation of organic contaminant. The Bi2MoO6/SnO2 displays better visible light catalytic activity than that of Bi2MoO6. SnO2 as co-catalyst can provide more active sites as well as transfer and restrain the charge recombination, leading to the enhancement of catalytic activity. 30 wt.% SnO2 emersions can degrade 90% for nitrobenzene and 97% for Rhodamine under visible light irradiation.

Silver-attached reduced graphene oxide nanocomposite as an eco-friendly photocatalyst for organic dye degradation

Dye effluents play a major role in polluting water bodies, and various treatment technologies are being used for their removal. Among these methods, green photocatalysis involving solar radiation has achieved tremendous momentum because of its economically viable and environmentally friendly nature. Noble metals, especially silver, shows visible light catalytic activity and this makes it a suitable candidate for photodegradation of organic dyes. Here, we report the synthesis of silver nanoparticles supported on graphene oxide sheets by a hydrothermal method. We have grown silver nanoparticles on highly conducting reduced graphene oxide sheets, thereby preventing electron–hole pair recombination. The as-prepared silver-decorated reduced graphene oxide nanocomposite was characterized by UV–Vis spectroscopy, X-ray diffraction, Raman spectroscopy, photoluminescence technique, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and BET measurements. The photocatalytic ability of the prepared composite was evaluated against two dyes—indigo carmine and methylene blue—in the presence of sodium borohydride as an inducer. The calculated apparent rate constants and the measured TOC values indicate the enhanced catalytic efficiency of the sample as compared to pure silver nanoparticles. A possible pathway and mechanism for photocatalytic dye degradation under solar radiation is also included in this work.

In-Situ Synthesis of Hydrogen Titanate Nanotube/Graphene Composites with a Chemically Bonded Interface and Enhanced Visible Photocatalytic Activity.

Hydrogen titanate nanotube (HTT)/graphene nanocomposites are synthesized by hydrothermal reduction of graphene oxide (GO) and simultaneous preparation of nanotubular HTT via an alkaline hydrothermal process. By using this facile in-situ compositing strategy, HTT are densely supported upon the surface of graphene sheets with close interface contacts. The as-prepared HTT/graphene nanocomposites possess significantly enhanced visible light catalytic activity for the partial oxidation of benzylic alcohols. The amount of graphene has significant influence on catalytic activity and the optimal content of graphene is 1.0 wt %, giving a normalized rate constant k of 1.71 × 10−3 g/m2·h, which exceeds that of pure HTT and HTT/graphene-1.0% mixed by a factor of 7.1 or 5.2. Other than the general role of graphene as a high-performance electron acceptor or transporter, the observed enhancement in photocatalytic activity over HTT/graphene can be ascribed to the improved interfacial charge migration from enhanced chemical bonding (Ti–C bonds) during the in-situ compositing process. The formation of Ti–C bonds is confirmed by XPS analysis and the resulting enhanced separation of photoinduced charge carriers is demonstrated by electrochemical impedance spectra and transient photocurrent response.

Synergism of 3D g-C3N4 decorated Bi2WO6 microspheres with efficient visible light catalytic activity

g-C3N4 decorated Bi2WO6 microspheres with scales of 2.0∼3.0 μm were prepared via a hydrothermal method. The matching of energy band between g-C3N4 and Bi2WO6 facilitate the absorption visible light and the separation of electron-carrier. The morphology, constitute and optical properties of the as-prepared samples is confirmed by different characterization techniques, such as, XRD, XPS, EDS, SEM, UV–vis, and N2 adsorption-desorption. The photocatalytic activities were assessed by the photodegradation of Methyl orange (MO) and phenol under visible light irradiation. The results indicated that the decoration of g-C3N4 evidently improves the photocatalytic activity of Bi2WO6, and the content of g-C3N4 has significantly effect on the catalytic activity of Bi2WO6. By comparison of other samples, 3 wt% g-C3N4/Bi2WO6 composites present an extraordinary enhanced photocatalytic activity for the photodegradation of MO and phenol under visible light. On the basis of the result and discussion, the possible mechanism of enhanced photocatalytic activity of g-C3N4/Bi2WO6 composites is proposed. It implies that the combination of g-C3N4 and Bi2WO6 provided synergistic photocatalytic activity via an efficient electron transfer process. Furthermore, the photocatalytic degradation of MO over g-C3N4/Bi2WO6 is promoted mainly by h+, and the same time •OH also plays a positive role in this degradation process.

Solvothermal Synthesis of Sphere-Like ZnS Microparticles and Its Visible-Light Catalytic Properties.

The cauliflower-like ZnS microspheres consisting of the nanospheres were prepared via one step template-free approach employing a solvothermal process using Zn(NO3)2·6H2O and CH4N2S as precursors in the mixture solution. The morphology, structure characterization, and crystal structure of the as-prepared ZnS were performed by X-ray diffraction, scanning electron microscopy, UV-visible absorption, and X-ray photoelectron spectroscopy. The results showed that cauliflowerlike ZnS microspheres were prepared under this condition and the size of the particles were about 3~5 μm. In addition, the excellent photocatalytic activity and degradation mechanism of ZnS microspheres have been investigated and discussed in detail. The degradation of Rhodamine B (RhB) aqueous solution was carried out to investigate the visible-light catalytic activity under metal halide lamp. The results indicated that different size of ZnS had photocatalytic activity to RhB under visible light, and sphere-like ZnS displayed high photodegradation efficiency with degradation rate of 98% within 140 min.

A facile strategy for the synthesis of ferroferric oxide/titanium dioxide/molybdenum disulfide heterostructures as a magnetically separable photocatalyst under visible-light

Semiconductor photocatalysts is a promising approach to combat both environmental pollution and global energy shortage despite the challenges of recycling and stability. In this paper, magnetic Fe3O4 particle is introduced in the system and Fe3O4/TiO2/MoS2 heterostructures can be formed in a facile strategy. The morphology and structure of Fe3O4/TiO2/MoS2 can be controlled by adjusting the hydrolysis rate of the titanium source. MoS2 is designed to fill in the mesoporous of TiO2 core, forming heterojunction on the surface and near-surface of TiO2 under solvothermal conditions. With respect to the decomposition of a rhodamine B (RhB) solution under visible light, the Fe3O4/TiO2/MoS2 heterostructures display highly photocatalytic activities in aqueous solutions, and they can be easily recovered to realize cyclic utilization by applying an external magnetic field. Thus, the effective magnetic recycle of the catalyst is achieved, and high visible light catalytic activity is ensured simultaneously. Since the current method is simple and flexible to create recyclable catalysts with high stability in this way, it could promote the practicability of semiconductor photocatalysts in water treatment, degradation of dye pollutants, and environmental cleaning.

Research on modified silicone compound photocatalyst by doping N

In order to improve the visible light response and reaction efficiency of nitrogen-doped TiO2 set urea as nitrogen source, and silica gel as the load reagent adopt sol-gel method to prepare powder of nitrogen-doped TiO2 supported on SiO2 , use equal volume impregnation method to load MnO2 on catalyst, and then obtain the composite photocatalyst after drying, and roasting .The prepared composite catalysts were characterized by XPS, TEM, SEM, XRD and other methods. Moreover, the photo-catalytic activity of the composite catalysts under visible-light region was tested, and the influences of nitrogen content and calcinations temperature on the photo-catalytic activity were investigated. The results show that:(1) the range of light response of modified composite catalyst was expanded from ultraviolet region to visible-light region, which results in high visible-light catalytic activity in the degradation of methyl orange.(2) Through the mechanism of photo-catalytic reaction and the treatment effect analysis, MnO2 as catalytic resulting O2 can be served as a good electronic capture agent and improve the reaction efficiency.(3)With the reduction of nitrogen content,and the increase of calcination temperature, the visible-light catalytic activity was weakened.(4) The activity of catalyst was reused six times, without significant reduction and had excellent efficiency and stability.

Synthesis and photocatalytic properties of visible-light-responsive, three-dimensional, flower-like La-TiO2/g-C3N4 heterojunction composites.

We prepared a new three-dimensional, flower-like La–TiO2/g-C3N4 (LaTiCN) heterojunction photocatalyst using a solvothermal method. Analysis and characterization were performed by conducting scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform-infrared spectroscopy, ultraviolet-visible spectrophotometry, and nitrogen adsorption and desorption. The prepared g-C3N4 nanosheets could reach 100 nm in size and covered the TiO2 surface. A tightly bound interface formed between the g-C3N4 and TiO2, speeding up the effective transfer of photo-induced electrons. In addition, the incorporation of La3+ reduced the electron–hole recombination efficiency. Consequently, the prepared La–TiO2/g-C3N4 composite material exhibited better visible-light catalytic activity than pure TiO2.

Preparation of Novel Mesoporous Photocatalyst Bi<sub>4</sub>O<sub>5</sub>Br<sub>2</sub>/SBA-15 with Enhanced Visible-Light Catalytic Activity

Photocatalysis is one of the most promising methods owing to its great potential to relieve environmental issue. To construct efficient photocatalyst with low energy consumption, mild catalytic conditions, and stable chemical properties are highly desired. In this work, a novel, highly active and environmental friendly mesoporous photocatalyst Bi4O5Br2/SBA-15 was synthesized by hydrothermal method, and its characteristics and visible-light catalytic activity were investigated. The synthesized photocatalyst consisted of Langmuir type IV hysteresis loops, which was confirmed to be a composite material with mesoporous structure. It exhibited a high visible-light absorption intensity and a low recombination rate of photo-generated electrons and holes. When the mass ratio of Bi/SiO2 was 30/100 during the synthesis, the obtained photocatalyst (Bi30/SBA-15) reflected the fastest Rhodamine B (RhB) removal rate and achieved 100% decolorization of RhB by both adsorption and degradation process. This high decolorization efficiency can also be maintained and realized by recycling the used composite in practice. The enhanced visible-light photocatalytic activity of novel Bi4O5Br2/SBA-15 photocatalyst can be ascribed to the existing active sites both inside and outside SBA-15 which enhanced the separation of photo-generated electrons and holes.

Structure and excellent visible light catalysis of Prussian blue analogues BiFe(CN)6·4H2O

BiFe(CN)6·4H2O, which exhibited a layered structure of FeC6 and BiN6 coordination polyhedra, was synthesised and exhibited excellent visible light catalytic activity.

Lantern-like bismuth oxyiodide embedded typha-based carbon via in situ self-template and ion exchange-recrystallization for high-performance photocatalysis.

Efficient photocatalysts induced by visible light (e.g. BiOI) have attracted wide attention for energy storage and environmental pollutant rehabilitation. In this work, N-doped bamboo tube-like carbon (NTC) was derived directly from the carbonization of bio-waste (withered typha grass) under an ammonia atmosphere. During fabrication, the BiOI/NTC material was used as a self-sacrificing template and I- ions were gradually replaced by OH- ions from NH3·H2O solution. Then Bi7O9I3/NTC was formed with micro-/nanohierarchical structures, which could exactly be explained by the in situ ion exchange-recrystallization mechanism. Thereinto, the well-defined hierarchical lantern-like Bi7O9I3 composed of interconnecting ultrathin nanosheets firmly embedded the "bamboo tubes" of NTC, which endow sufficient interface and high specific surface area (40 m2 g-1). The multiple synergistic effects of the lantern-like structure with ultrathin nanosheets, low iodine content and well-contacted interface endow the synthesized Bi7O9I3/NTC with outstanding visible-light catalytic activity. The results show that the obtained Bi7O9I3/NTC degraded 93.5% of methyl orange and 97.6% of rhodamine B within 2 hours, showing superior performance as compared to the pure BiOI. Therefore, our work demonstrates a controllable approach that can provide guidelines for designing optimized bismuth oxyiodide-based photocatalyst materials and has the potential for application in environmental remediation.