This paper reviews recent studies on the semiconductor photocatalysis based on surface-modified TiO2 of which application is mainly focused on environmental remediation. TiO2 photocatalysis that is based on the photoinduced interfacial charge transfer has been extensively studied over the past four decades. A great number of modification methods of semiconductor photocatalysts have been developed and investigated to accelerate the photoconversion, to enable the absorption of visible light, or to alter the reaction mechanism to control the products and intermediates. In this regard, various modification methods of TiO2 are classified according to the kind of surface modifiers (metal-loading, impurity doping, inorganic adsorbates, polymer coating, dye-sensitization, charge transfer complexation) and their effects on photocatalytic reaction mechanism and kinetics are discussed in detail. Modifying TiO2 in various ways not only changes the mechanism and kinetics under UV irradiation but also introduces visible light activity that is absent with pure TiO2. Each modification method influences the photocatalytic activity and mechanism in a way different from others and the observed modification effects are often different depending on the test substrates and conditions even for the same modification method. Better understanding of the modification effects on TiO2 photocatalysis is necessary to obtain reliable results, to assess the photoconversion efficiency more quantitatively, and to further improve the modification methods.

Surface modification of TiO2 photocatalyst for environmental applications

Application of doped photocatalysts for organic pollutant degradation - A review

The reduction of nitro compounds to the corresponding amines is one of the most utilized catalytic processes in the fine and bulk chemical industry. The latest development of catalysts with cheap metals like Fe, Co, Ni, and Cu has led to their tremendous achievements over the last years prompting their greater application as “standard” catalysts. In this review, we will comprehensively discuss the use of homogeneous and heterogeneous catalysts based on non-noble 3d-metals for the reduction of nitro compounds using various reductants. The different systems will be revised considering both the catalytic performances and synthetic aspects highlighting also their advantages and disadvantages.

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Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

SnS2/SnO2 nanocomposites with tunable SnO2 contents were prepared via in situ hydrothermal oxidation of SnS2 nanoparticles in 0.375–4.5 mass% H2O2 aqueous solutions at 180 °C for 0–12 h. The structure, composition and optical properties of the as-prepared SnS2/SnO2 nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Brunauer–Emmett–Teller (BET) surface area analysis, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. Furthermore, their photocatalytic properties were tested for the degradation of methyl orange in water under visible light (λ > 420 nm) irradiation. It was found that the as-prepared SnS2/SnO2 nanocomposites with suitable SnO2 content not only demonstrated superior photocatalytic activity to both SnS2 nanoparticles and physically mixed SnS2/SnO2 composite nanoparticles, but also had remarkable photocatalytic stability. The tight attachment of SnO...

High-Performance Visible-Light-Driven SnS2/SnO2 Nanocomposite Photocatalyst Prepared via In situ Hydrothermal Oxidation of SnS2 Nanoparticles

Synthesis of magnetic CoFe2O4/g-C3N4 composite and its enhancement of photocatalytic ability under visible-light

The effect of calcination on P25 titania at different temperatures has been studied by XRD, nitrogen adsorptiondesorption isotherm, BET-surface area, pore volume, pore size, particle size and crystallite size in order to understand the conversion of anatase phase to rutile phase. The fraction of anatase and rutile has been determined using XRD. Although the crystallinity remains the same, the phase change of anatase to rutile is inevitable with temperature. The isotherms show the nonporous characteristics of the P25 samples. In addition, nitrogen adsoption by the samples decreased appreciably with crystallinity. The pore volume and BET surface area show a large decrease at 900 o C. The particle size, crystallite size, and pore size show an increasing trend with increase in temperature. Analysis of the physical characteristics indicates that P25 titania samples can be used for catalytic applications at less than 500 o C.

http://nopr.niscair.res.in/bitstream/123456789/6124/1/IJCA%2048A%2810%29%201378-1382.pdf

Effect of surface area, pore volume and particle size of P25 titania on the phase transformation of anatase to rutile

Sulfated Fe2O3–TiO2 synthesized from ilmenite ore: A visible light active photocatalyst

The structures of phosphated titania and sulphated titania are studied with a combined approach using DFTB3LYP/Lan12DZ and experimental studies such as XRD, XPS, and DRIFT spectra. The infrared absorptions, Mulliken charges, bond lengths, and dipole moments are investigated for the phosphated and sulphated titania structures optimized by DFT calculations. The XRD patterns obtained for both the modified titania show that the as-synthesized materials are amorphous in nature. The DRIFT spectra show the presence of bidentate complex in both sulphated and phosphated titania. The XPS data show the presence of Ti-O-S and Ti-O-P linkages in sulphated and phosphated titania respectively. The evaluation of IR absorptions obtained by DFT and DRIFT spectra reveal the most favorable structure of bridged bidentate for sulphated titania and a combination of monodentate and chelating bidentate for phosphated titania.

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XPS and IR spectral studies on the structure of phosphate and sulphate modified titania: A combined DFT and experimental study

An environmentally benign route for the single-step synthesis of mesoporous sulfated titania is described by a seeding method using titanium oxysulfate as the titania source. The hydrolysis was performed in the presence of NaOH and seed under constant-volume conditions around 98 °C. The XPS and DRIFT spectra show the existence of a bridged bidentate sulfate complex on the surface of titania. The elimination of sulfur on heat treatment showed a characteristic change in mesoporosity, specific surface area, and crystallinity of the material. The transformation of sulfated titania to anatase was incomplete at 900 °C, showing a delay in crystallization due to the presence of sulfur. Studies on the thermal stability of the sulfated titania showed that the material obtained can be used for various applications at temperatures below 300 °C. The ammonia-TPD and catalytic performance studies of the sulfated titania samples showed the presence of strong acid sites.

Single-Step Synthesis and Structural Study of Mesoporous Sulfated Titania Nanopowder by a Controlled Hydrolysis Process

The liquid phase selective hydrogenation of cinnamaldehyde has been investigated on cobalt (15 wt%) impregnated on alumina, silica and various phases of titania supports. The multiple reduction stages observed in the TPR studies suggest the presence of cobalt aluminate/silicate/titanate species, and DRIFT spectra results seem to corroborate this observation. An optimum level of conversion and selectivity to cinnamyl alcohol was observed at 120 °C and 10 kg/cm2 hydrogen pressure. Co/TiO2 exhibited a greater conversion (47.4%) and selectivity to cinnamyl alcohol (58%) than Co/Al2O3 and Co/SiO2, which may be attributed to the presence of TiO
 x
 (x   Co/SiO2 > Co/Al2O3. The hydrogenation of CMA is believed to preferentially proceed via adsorption of C=O on the surface of Co/TiO2.

K. Joseph Antony Raj

Papers

Effect of surface area, pore volume and particle size of P25 titania on the phase transformation of anatase to rutile

Sulfated Fe2O3–TiO2 synthesized from ilmenite ore: A visible light active photocatalyst

XPS and IR spectral studies on the structure of phosphate and sulphate modified titania: A combined DFT and experimental study

Single-Step Synthesis and Structural Study of Mesoporous Sulfated Titania Nanopowder by a Controlled Hydrolysis Process

Selective Hydrogenation of Cinnamaldehyde over Cobalt Supported on Alumina, Silica and Titania