Showing papers on "Photocatalysis published in 2012"

A review on the visible light active titanium dioxide photocatalysts for environmental applications

Abstract: Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.

Graphene-Like Carbon Nitride Nanosheets for Improved Photocatalytic Activities

Abstract: Graphitic (g)-C3N4 with a layered structure has the potential of forming graphene-like nanosheets with unusual physicochemical properties due to weak van der Waals forces between layers. Herein is shown that g-C3N4 nanosheets with a thickness of around 2 nm can be easily obtained by a simple top-down strategy, namely, thermal oxidation etching of bulk g-C3N4 in air. Compared to the bulk g-C3N4, the highly anisotropic 2D-nanosheets possess a high specific surface area of 306 m2 g-1, a larger bandgap (by 0.2 eV), improved electron transport ability along the in-plane direction, and increased lifetime of photoexcited charge carriers because of the quantum confinement effect. As a consequence, the photocatalytic activities of g-C3N4 nanosheets have been remarkably improved in terms of OH radical generation and photocatalytic hydrogen evolution.

TiO2 photocatalysis: Design and applications

Abstract: TiO 2 photocatalysis is widely used in a variety of applications and products in the environmental and energy fields, including self-cleaning surfaces, air and water purification systems, sterilization, hydrogen evolution, and photoelectrochemical conversion. The development of new materials, however, is strongly required to provide enhanced performances with respect to the photocatalytic properties and to find new uses for TiO 2 photocatalysis. In this review, recent developments in the area of TiO 2 photocatalysis research, in terms of new materials from a structural design perspective, have been summarized. The dimensionality associated with the structure of a TiO 2 material can affect its properties and functions, including its photocatalytic performance, and also more specifically its surface area, adsorption, reflectance, adhesion, and carrier transportation properties. We provide a brief introduction to the current situation in TiO 2 photocatalysis, and describe structurally controlled TiO 2 photocatalysts which can be classified into zero-, one-, two-, and three-dimensional structures. Furthermore, novel applications of TiO 2 surfaces for the fabrication of wettability patterns and for printing are discussed.

Synergetic Effect of MoS2 and Graphene as Cocatalysts for Enhanced Photocatalytic H2 Production Activity of TiO2 Nanoparticles

Abstract: The production of H2 by photocatalytic water splitting has attracted a lot attention as a clean and renewable solar H2 generation system. Despite tremendous efforts, the present great challenge in materials science is to develop highly active photocatalysts for splitting of water at low cost. Here we report a new composite material consisting of TiO2 nanocrystals grown in the presence of a layered MoS2/graphene hybrid as a high-performance photocatalyst for H2 evolution. This composite material was prepared by a two-step simple hydrothermal process using sodium molybdate, thiourea, and graphene oxide as precursors of the MoS2/graphene hybrid and tetrabutylorthotitanate as the titanium precursor. Even without a noble-metal cocatalyst, the TiO2/MoS2/graphene composite reaches a high H2 production rate of 165.3 μmol h–1 when the content of the MoS2/graphene cocatalyst is 0.5 wt % and the content of graphene in this cocatalyst is 5.0 wt %, and the apparent quantum efficiency reaches 9.7% at 365 nm. This unusu...

Polymeric Graphitic Carbon Nitride for Heterogeneous Photocatalysis

Abstract: Polymeric graphitic carbon nitride (for simplicity, g-C3N4) is a layered material similar to graphene, being composed of only C, N, and some impurity H. Contrary to graphenes, g-C3N4 is a medium band gap semiconductor and an effective photocatalyst for a broad variety of reactions, and it possesses a high thermal and chemical stability In this Perspective, we describe the polycondensation of this structure, how to modify band positions and band gap by doping and copolymerization, and how to texture the organic solid to make it an effective photocatalyst. We then describe the photochemical splitting of water and some mild and selective photooxidation reactions catalyzed by g-C3N4.

An amine-functionalized titanium metal-organic framework photocatalyst with visible-light-induced activity for CO2 reduction.

Abstract: Let your light shine: the photocatalytic reduction of carbon dioxide to the formate anion under visible light irradiation is for the first time realized over a photoactive Ti-containing metal-organic framework, NH(2)-MIL-125(Ti), which is fabricated by a facile substitution of ligands in the UV-responsive MIL-125(Ti) material.

Advanced Oxidation Processes for Wastewater Treatment: Formation of Hydroxyl Radical and Application

Abstract: Advanced oxidation processes (AOPs), defined as those technologies that utilize the hydroxyl radical (·OH) for oxidation, have received increasing attention in the research and development of wastewater treatment technologies in the last decades. These processes have been applied successfully for the removal or degradation of toxic pollutants or used as pretreatment to convert recalcitrant pollutants into biodegradable compounds that can then be treated by conventional biological methods. The efficacy of AOPs depends on the generation of reactive free radicals, the most important of which is the hydroxyl radical (·OH). The authors summarize the formation reactions of ·OH and the mechanisms of pollutants degradation. They cover six types of advanced oxidation processes, including radiation, photolysis and photocatalysis, sonolysis, electrochemical oxidation technologies, Fenton-based reactions, and ozone-based processes. Controversial issues in pollutants degradation mechanism were discussed. They review t...

Photo-catalyzed degradation of hazardous dye methyl orange by use of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide.

Abstract: The high rate of electron/hole pair recombination reduces the quantum yield of the processes with TiO2 and represents its major drawback. Adding a co-adsorbent increases the photocatalytic efficiency of TiO2. In order to hybridize the photocatalytic activity of TiO2 with the adsorptivity of carbon nanotube, a composite of multi-walled carbon nanotubes and titanium dioxide (MWCNT/TiO2) has been synthesized. The composite was characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared absorption spectroscopy (FTIR), and diffuse reflectance UV–vis spectroscopy. The catalytic activity of this composite material was investigated by application of the composite for the degradation of methyl orange. It was observed that the composite exhibits enhanced photocatalytic activity compared with TiO2. The enhancement in photocatalytic performance of the MWCNT/TiO2 composite is explained in terms of recombination of photogenerated electron–hole pairs. In addition, MWCNT acts as a dispersing agent preventing TiO2 from agglomerating activity during the catalytic process, providing a high catalytically active surface area. This work adds to the global discussion of how CNTs can enhance the efficiency of catalysts.

Hydrothermal synthesis of graphene-TiO 2 nanotube composites with enhanced photocatalytic activity

Abstract: In this study, TiO2 nanotube (TNT)/reduced graphene oxide (hGO) composites were prepared by an alkaline hydrothermal process. This was achieved by decorating graphene oxide (GO) layers with commercially available TiO2 nanoparticles (P90) followed by hydrothermal synthesis, which converts the TiO2 nanoparticles to small diameter (∼9 nm) TNTs on the hGO surface. The alkaline medium used to synthesize the TNTs simultaneously converts GO to deoxygenated graphene oxide (hGO). Compared to GO, the hGO has a ∼70% reduction of oxygenated species after alkaline hydrothermal treatment. The graphene nature of hGO in the composites was confirmed by X-ray diffraction (XRD), Raman, FTIR, and X-ray photoelectron spectroscopy (XPS) analysis. The photocatalytic performance of the hGO-TNT composites was evaluated for the photodegradation of malachite green. It was found that the ratio of hGO to TNT in the composites significantly affects the photocatalytic activity. Higher amounts of hGO in hGO-TNT composites showed lower p...

Polycondensation of thiourea into carbon nitride semiconductors as visible light photocatalysts

Abstract: Converting solar energy into hydrogen gas by water splitting is considered as a long-term solution to address global energy and environmental problems. Great effort has been devoted to the search for abundant systems for the purpose of efficient capture, conversion, and storage of solar energy in a cost-effective manner. To further advance the recently-developed carbon nitride photocatalysis for solar hydrogen generation, thiourea, a sulfur-containing compound, was used as a cheap and easily-available starting material for the synthesis of graphitic carbon nitride semiconductors. The as-prepared photocatalysts were subjected to several characterizations, and the results showed that the heating temperature and the presence of sulfur motifs offer a facile chemical pathway for the control of the condensation/polymerization of carbon nitride, and thus adjusting their textural and electronic properties. Photocatalytic activity experiments demonstrated that the g-C3N4 synthesized from thiourea exhibited a much higher H2 production rate than that of g-C3N4 prepared from dicyanamide or urea, and this activity can be further enhanced by increasing the condensation temperature.

Dramatic Activity of C3N4/BiPO4 Photocatalyst with Core/Shell Structure Formed by Self-Assembly

Abstract: Core/shell structured C3N4/BiPO4 photocatalyst is fabricated via a facile ultrasonic dispersion method. The thickness of the shell may be controlled by tuning the amount of C3N4 in the dispersion, which determines the enhanced level of photocatalytic activity. The optimum photocatalytic activity of C3N4/BiPO4 at a weight ratio of 4% (C3N4/BiPO4) under UV irradiation is almost 4.5 times as high as that of reference P25 (TiO2) and 2.5 times of BiPO4. More attractively, the dramatic visible light photocatalytic activity is generated due to the C3N4 loaded. The enhancement in performance is demonstrated to be the match of lattice and energy level between the C3N4 and BiPO4. This match facilitates the separation and transfer of photogenerated electron–hole pairs at the heterojunction interfaces and may be important for other core/shell structured materials. In addition, this method is expected to be extended for other C3N4 loaded materials.

Graphene oxide modified g-C3N4 hybrid with enhanced photocatalytic capability under visible light irradiation

Abstract: Graphene oxide modified g-C3N4 (GO/g-C3N4) with efficient photocatalytic capability under visible light irradiation was fabricated by sonochemical approach. Transmission electron microscopy images demonstrated that GO was two-dimensional sheets with chiffon-like ripples and the g-C3N4 possessed a layered structure. GO was overlaid on the surface of g-C3N4 in the GO/g-C3N4 hybrids. The UV–vis diffuse reflectance spectra showed that the GO/g-C3N4 hybrid had intense optical absorption in the visible light region. Photoluminescence spectra confirmed that the separation efficiency of photogenerated charge in GO/g-C3N4 was more intensive than pristine g-C3N4, indicating the GO acts as a separation centre and electron acceptor in the GO/g-C3N4 hybrid. The effective photogenerated charge separation efficiency lead to a remarkable improvement in the visible light photocatalysis. The pseudo-first-order kinetic constants of photocatalytic degradation of rhodamine B and 2, 4-dichlorophenol under visible light irradiation with GO/g-C3N4 were 3.80 and 2.08 times as large as that with pristine g-C3N4, respectively. This work indicates that the metal-free GO/g-C3N4 hybrid photocatalyst is a promising material in waste control, and GO could be an excellent material to combine with other semiconductors to make composites.

Large scale electrochemical synthesis of high quality carbon nanodots and their photocatalytic property

Abstract: High quality carbon nanodots (C-dots) with high purity were synthesized through a mild, one-step electrochemical approach, without the assistance of any chemicals but only pure water. This high productivity method makes the synthetic process of C-dots synthesis both economical as well as environment-friendly. The as prepared C-dots are predominantly multi-layer graphene oxide, with luminescence and high up-conversion photoluminescence (emission of light at shorter wavelengths than the excitation wavelength). Meanwhile, C-dots showed peroxidise mimetic function and visible-light-sensitive photocatalytic activity for methyl orange degradation. In addition, a novel photocatalyst (TiO2/C-dots) was obtained by combining C-dots with TiO2 through an easy hydrothermal method. Remarkably, TiO2/C-dots exhibited an excellent visible-light photocatalytic activity.

Hydrogen-treated WO3 nanoflakes show enhanced photostability

Abstract: Here we report that photostability and photoactivity of WO3 for water oxidation can be simultaneously enhanced by controlled introduction of oxygen vacancies into WO3 in hydrogen atmosphere at elevated temperatures. In comparison to pristine WO3, the hydrogen-treated WO3 nanoflakes show an order of magnitude enhanced photocurrent, and more importantly, exhibit extraordinary stability for water oxidation without loss of photoactivity for at least seven hours. The enhanced photostability is attributed to the formation of substoichiometric WO3−x after hydrogen treatment, which is highly resistive to the re-oxidation and peroxo-species induced dissolution. This work constitutes the first example where WO3 can be stabilized for water oxidation in neutral medium without the need for oxygen evolution catalysts. The demonstration of electrochemically stable WO3 could open up new opportunities for WO3 based photoelectrochemical and photocatalytic applications.

Synthesis and Efficient Visible Light Photocatalytic Hydrogen Evolution of Polymeric g-C3N4 Coupled with CdS Quantum Dots

Abstract: Novel CdS quantum dot (QD)-coupled graphitic carbon nitride (g-C3N4) photocatalysts were synthesized via a chemical impregnation method and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. The effect of CdS content on the rate of visible light photocatalytic hydrogen evolution was investigated for different CdS loadings using platinum as a cocatalyst in methanol aqueous solutions. The synergistic effect of g-C3N4 and CdS QDs leads to efficient separation of the photogenerated charge carriers and, consequently, enhances the visible light photocatalytic H2 production activity of the materials. The optimal CdS QD content is determined to be 30 wt %, and the corresponding H2 evolution rate was 17.27 μmol·h–1 under visible light irradiation, ∼9 times that of pure g-C3N4. A possible photocatalytic mechanism of the CdS/g-C3N4 comp...

Graphene Transforms Wide Band Gap ZnS to a Visible Light Photocatalyst. The New Role of Graphene as a Macromolecular Photosensitizer

Abstract: We report the assembly of nanosized ZnS particles on the 2D platform of a graphene oxide (GO) sheet by a facile two-step wet chemistry process, during which the reduced graphene oxide (RGO, also called GR) and the intimate interfacial contact between ZnS nanoparticles and the GR sheet are achieved simultaneously. The ZnS–GR nanocomposites exhibit visible light photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure–photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS–GR nanocomposites acts as an organic dye-like macromolecular “photosensitizer” for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR–semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from the semiconductor. This new concept ...

A Water‐Stable Porphyrin‐Based Metal–Organic Framework Active for Visible‐Light Photocatalysis

Abstract: Metal–organic frameworks (MOFs) permit the combination of high internal surface area with chemical and physical functionality conferred by the molecular linker. Porphyrins are versatile functional molecules in catalysis, light harvesting, and molecular sensing. Porphyrins have been used as building blocks for MOFs, affording catalysts, light harvesting and selective sorption in liquid and gas phases. MOFs based on Alcarboxylate coordination chemistry are amongst the most thermally and chemically stable of such systems reported to date. Here we report a waterstable porous porphyrin MOF with a BET surface area of 1400 m g 1 which performs visible-lightdriven hydrogen generation from water. The freebase porphyrin can be metalated within the rigid host structure. The reaction of AlCl3·6 H2O with the free-base meso-tetra(4-carboxyl-phenyl) porphyrin H2TCPP (Figure 1b) in water under hydrothermal conditions at 180 8C followed by washing with dimethyl formamide (DMF) to remove unreacted ligand leads to the formation of the microcrystalline porous red compound H2TCPP[AlOH]2(DMF3(H2O)2) 1 (referred to as Al-PMOF, experimental details are given in section 1.1 in the Supporting Information). The linker consists of four benzoate groups around the central porphyrin core. The analyzed composition reveals that no aluminium is coordinated within the porphyrin ring, consistent with the need to use reactive trialkylaluminium reagents for metalation of the porphyrin in solution. The reaction temperature is required to solubilize the porphyrin linker. The crystal structure of 1 was solved and refined from synchrotron powder Xray diffraction collected at 100 K. Indexing and Pawley refinement revealed an orthorhombic cell (a = 31.978(3) , b = 6.5812(4) , c = 16.862(2) , V= 3548.7(6) ) consistent with the C222, Cmm2, and Cmmm space groups. Each of these candidate space groups was evaluated by simulated annealing using a semi-rigid body to describe the TCPP unit (Figure S1 in the Supporting Information) with eight refined parameters describing distances and angles within the porphyrin. The best results were obtained for the benzoic acid group perpendicular to the central porphyrin ring, which can be best described in Cmmm symmetry, and zero occupancy for Al at the center of the porphyrin. This model was used in the final Rietveld analysis (Figure 1a). Fourier mapping revealed a single guest atom in the channels attributed to oxygen from water, which was included in the final refinement (Figure S2 in the Supporting Information). Each porphyrin linker in 1 is coordinated to eight aluminium centers (Figure 1c–e) through the four carboxylate groups which each bridge two aluminium units. There is Figure 1. a) Final Rietveld refinement of 1 (100 K) showing observed (gray crosses), calculated (line a), and difference (line b) plots (Q = 2p/d). Bragg peak positions are indicated. b) TCPP porphyrinic linker in 1. c–e) Crystal structure of 1 viewed down [001], [100], and [010] directions, respectively.

Mesoporous carbon nitride with in situ sulfur doping for enhanced photocatalytic hydrogen evolution from water under visible light

Abstract: In situ sulfur-doped mesoporous g-C3N4 (mpgCNS) was synthesized from a simple organosulfur compound, thiourea, using SiO2 nanoparticles as the hard template. The resultant product has a high surface area of 128 m2 g−1 and mesopores in the range of 10–20 nm. Based on X-ray photoelectron spectroscopy analysis, the doped sulfur was proposed to substitute carbon in mpgCNS and a downshift of 0.25 eV was resulted in its conduction band. Optical studies indicated that mpgCNS exhibits enhanced and extended light absorbance in the visible light region and a much lower density of defects compared to the native g-C3N4. As a result, mpgCNS has been found to be 30 times more active than the native g-C3N4 for hydrogen evolution from photocatalytic water splitting. A high quantum efficiency of 5.8% at 440 nm was obtained which is among the highest for carbon nitride photocatalysts.

Gold Nanoparticles Located at the Interface of Anatase/Rutile TiO2 Particles as Active Plasmonic Photocatalysts for Aerobic Oxidation

Abstract: Visible-light irradiation (λ > 450 nm) of gold nanoparticles loaded on a mixture of anatase/rutile TiO2 particles (Degussa, P25) promotes efficient aerobic oxidation at room temperature. The photocatalytic activity critically depends on the catalyst architecture: Au particles with <5 nm diameter located at the interface of anatase/rutile TiO2 particles behave as the active sites for reaction. This photocatalysis is promoted via plasmon activation of the Au particles by visible light followed by consecutive electron transfer in the Au/rutile/anatase contact site. The activated Au particles transfer their conduction electrons to rutile and then to adjacent anatase TiO2. This catalyzes the oxidation of substrates by the positively charged Au particles along with reduction of O2 by the conduction band electrons on the surface of anatase TiO2. This plasmonic photocatalysis is successfully promoted by sunlight exposure and enables efficient and selective aerobic oxidation of alcohols at ambient temperature.

Nitrogen Vacancy-Promoted Photocatalytic Activity of Graphitic Carbon Nitride

Abstract: Vacancy defects can play an important role in modifying the electronic structure and the properties of photoexcited charge carriers and consequently the photocatalytic activity of semiconductor photocatalysts. By controlling the polycondensation temperature of a dicyandiamide precursor in the preparation of graphitic carbon nitride (g-C3N4), we introduced nitrogen vacancies in the framework of g-C3N4. These vacancies exert remarkable effects on modifying the electronic structure of g-C3N4 as shown in UV-visible absorption spectra and valence band spectra. Steady and time-resolved fluorescence emission spectra show that, due to the existence of abundant nitrogen vacancies, the intrinsic radiative recombination of electrons and holes in g-C3N4 is greatly restrained, and the population of short-lived and long-lived charge carriers is decreased and increased, respectively. As a consequence, the overall photocatalytic activity of the g-C3N4, characterized by the ability to generate center dot OH radicals, photodecomposition of Rhodamine B, and photocatalytic hydrogen evolution under both UV-visible and visible light, was remarkably improved.

Fabrication of composite photocatalyst g-C3N4–ZnO and enhancement of photocatalytic activity under visible light

Abstract: The g-C3N4–ZnO composite photocatalysts with various weight percents of ZnO were synthsized by a simple calcination process The photocatalysts were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), UV-vis diffuse reflection spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) The PXRD and HR-TEM results show that the composite materials consist of hexagonal wurzite phase ZnO and g-C3N4 The solid-state UV-vis diffuse reflection spectra show that the absorption edge of the composite materials shifts toward the lower energy region and to longer wavelengths in comparison with pure ZnO and g-C3N4 Remarkably, the photocatalytic activity of g-C3N4–ZnO composites has been demonstrated, via photodegradation of Methyl Orange (MO) and p-nitrophenol experiments The photocatalytic activity of g-C3N4–ZnO for photodegradation of Methyl Orange and p-nitrophenol under visible light irradiation was increased by over 3 and 6 times, respectively, to be much higher than that of single-phase g-C3N4, clearly demonstrating a synergistic effect between ZnO and g-C3N4 The concentrations of Zn2+ in g-C3N4–ZnO system after a photocatalytic reaction at various reaction times were found to be much lower than those for a ZnO system under the same reaction conditions, indicating that the g-C3N4–ZnO composite possesses excellent long-term stability for a photocatalytic reaction in aqueous solutions Furthermore, a synergistic photocatalysis mechanism between ZnO and g-C3N4 was proposed based on the photodegradation results Such obviously improved performance of g-C3N4–ZnO can be ascribed mainly to the enhancement of electron–hole separations at the interface of ZnO and g-C3N4

Visible-Light-Promoted Photocatalytic Hydrogen Production by Using an Amino-Functionalized Ti(IV) Metal–Organic Framework

Abstract: The present article describes the hydrogen production from an aqueous medium over amino-functionalized Ti(IV) metal–organic framework (Ti-MOF-NH2) under visible-light irradiation. Ti-MOF-NH2, which employs 2-amino-benzenedicarboxylic acid as an organic linker, has been synthesized by a facile solvothermal method. Pt nanoparticles as cocatalysts are then deposited onto Ti-MOF-NH2 via a photodeposition process (Pt/Ti-MOF-NH2). The XRD and N2 adsorption measurements reveal the successful formation of a MOF framework structure and its remaining structure after deposition of Pt nanoparticles. The observable visible-light absorption up to ∼500 nm can be seen in the DRUV–vis spectrum of Ti-MOF-NH2, which is associated with the chromophore in the organic linker. Ti-MOF-NH2 and Pt/Ti-MOF-NH2 exhibit efficient photocatalytic activities for hydrogen production from an aqueous solution containing triethanolamine as a sacrificial electron donor under visible-light irradiation. The longest wavelength available for the ...

Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates

Abstract: Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO.

Synthesis of MWNTs/g-C3N4 composite photocatalysts with efficient visible light photocatalytic hydrogen evolution activity

Abstract: Novel multi-walled carbon nanotubes (MWNTs) and graphitic carbon nitride (g-C3N4) composite photocatalysts were synthesized via a facile heating method. The resulting MWNTs/g-C3N4 composite photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The photoelectrochemical I–t curves were tested using several on–off cycles of visible light irradiation. The visible light photocatalytic hydrogen evolution was investigated for MWNTs/g-C3N4 in methanol aqueous solutions. The optimal MWNTs content is determined to be 2.0 wt%; and corresponding H2 evolution rate is 7.58 μmol h−1, about 3.7 folds that of pure g-C3N4. A possible mechanism of MWNTs on the enhancement of visible light performance is proposed. It suggests that MWNTs play key roles, which may lead to efficiently separation of the photo-generated charge carriers and, consequently, enhance the visible light photocatalytic H2 production activity.

Nanostructured SnO2–ZnO Heterojunction Photocatalysts Showing Enhanced Photocatalytic Activity for the Degradation of Organic Dyes

Abstract: Nanoporous SnO2–ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO2 particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO2 particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption–desorption analyses, transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy. The SnO2–ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO2 nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV–visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO2–ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO2, that is, 3.7 eV, and Z...

WO3 nanorods/graphene nanocomposites for high-efficiency visible-light-driven photocatalysis and NO2 gas sensing

Abstract: One-dimensional (1-D) nanostructures are of great importance due to their superior charge transport properties. Anchoring 1-D semiconductor nanomaterials on graphene offers potential advantages in photoelectrochemical and sensing applications. This paper presents a systematic investigation on the incorporation of WO3 nanorods and graphene for high-efficiency visible-light-driven photocatalysis and NO2 gas sensing. This novel composite shows remarkably enhanced performance compared to pure WO3 nanorods for these applications. The high photocatalytic activity of the WO3/graphene nanocomposite is found to be related to the increased adsorption toward chemical species, enhanced light absorption and efficient charge separation and transfer. Meanwhile, the improved conductivity, specific electron transfer and increased gas adsorption also contribute to their superior sensitivity and selectivity to NO2 gas.

Graphitic carbon nitride (g-C3N4)–Pt-TiO2 nanocomposite as an efficient photocatalyst for hydrogen production under visible light irradiation

Abstract: Porous graphitic carbon nitride (g-C3N4) was prepared by a simple pyrolysis of urea, and then a g-C3N4–Pt-TiO2 nanocomposite was fabricated via a facile chemical adsorption followed by a calcination process. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance absorption spectra, and electron microscopy. It is found that the visible-light-induced photocatalytic hydrogen evolution rate can be remarkably enhanced by coupling TiO2 with the above g-C3N4, and the g-C3N4–Pt-TiO2 composite with a mass ratio of 70 : 30 has the maximum photoactivity and excellent photostability for hydrogen production under visible-light irradiation, and the stable photocurrent of g-C3N4–TiO2 is about 1.5 times higher than that of the bare g-C3N4. The above experimental results show that the photogenerated electrons of g-C3N4 can directionally migrate to Pt-TiO2 due to the close interfacial connections and the synergistic effect existing between Pt-TiO2 and g-C3N4 where photogenerated electrons and holes are efficiently separated in space, which is beneficial for retarding the charge recombination and improving the photoactivity.