Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

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.

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

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

In this paper, visible light assisted degradation of various pollutants using different methods has been briefly reviewed. These methods have been broadly divided into two main categories. In the first category, the use of TiO2 semiconductor facilitating the photooxidative degradation of organic pollutants has been presented. This semiconductor has been treated in several ways. A major aim of these treatments is to maximize the range of wavelength in the visible light region for wastewater treatment. In the second category, various ways of degrading organic pollutants without the use of TiO2 semiconductor have been briefly outlined. The role of Fe(II)/Fe(III), etc., species in the sensitization process of various substrates helping it in the process to photocatalytic degradation reactions of organic pollutants has been highlighted. Also, the usage of semiconductors other than TiO2 has been critically analyzed.

Visible light induced photocatalytic degradation of organic pollutants

Photodegradation of organic pollutants, viz. phenol, chlorophenol, 1,2-dichloroethane and trichloroethylene in water has been achieved on the surface of TiO2 semiconductor modified with thionine and eosin Y by using visible light. After 5 h of irradiation with a 50 W tungsten lamp, over 55–72% degradation of pollutants is achieved. A working mechanism involving excitation of surface bound dye, followed by charge injection into the TiO2 conduction band is proposed.

Demineralization of organic pollutants on the dye modified TiO2 semiconductor particulate system using visible light

Visible light assisted degradation of aromatics, viz phenol, chlorophenol, 1,2-dichloroethane, trichloroethylene and surfactants, viz cetyl pyridinium chloride (CPC; cationic), sodium dodecylbenzene sulfonate (DBS; anionic) and neutral Triton-X 100 in air-equilibrated aqueous mixtures has been achieved on the surface of TiO2 semiconductor modified with methylene blue (MB) and rhodamine B (RB). Under 5 h of irradiation with a 150 W xenon lamp, over 40–75% degradation of pollutants has been observed. The failure of pollutants to degrade on non-conducting Al2O3 surface essentially suggests the role of semiconducting TiO2 photocatalyst in the photochemical process. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO2 conduction band and formation of reactive O2−/ HO2 radicals is proposed for the degradation of organics to carbon dioxide.

Visible light induced photodegradation of organic pollutants on dye adsorbed TiO2 surface

Asymmetric epoxidation of unsaturated hydrocarbons catalyzed by ruthenium complexes

M(salen) complexes (M=Mn(III), Ni(II); salen=bis-(salicyldene)ethylenediamine) have been encapsulated in zeolite Y and characterised. Mn(salen)+ complex was also anchored in montmorillonite clay and characterised. Epoxidation of olefins, viz. cyclohexene, cyclooctene and 1-hexene with terminal oxidants (NaOCl, KHSO5) was carried out with the anchored catalyst complexes and found that the epoxidation of linear olefin (1-hexene) is selectively facile than cyclic olefins. Experimental results are compared with those reported for M(salen) complexes catalysed olefin epoxidation in homogeneous and heterogenised-homogeneous catalytic conditions.

Debabrata Chatterjee

Papers

Visible light induced photocatalytic degradation of organic pollutants

Demineralization of organic pollutants on the dye modified TiO2 semiconductor particulate system using visible light

Visible light induced photodegradation of organic pollutants on dye adsorbed TiO2 surface

Asymmetric epoxidation of unsaturated hydrocarbons catalyzed by ruthenium complexes

Olefin epoxidation catalysed by Schiff-base complexes of Mn and Ni in heterogenised-homogeneous systems