Mechanochemical synthesis of ternary heterojunctions TiO2(A)/TiO2(R)/ZnO and TiO2(A)/TiO2(R)/SnO2 for effective charge separation in semiconductor photocatalysis: A comparative study.

TiO2, ZnO, and SnO2 metal oxides were synthesized by the sol-gel method and heterojunctions were fabricated by combining TiO2 with either ZnO or SnO2 in a 1:1 ratio using mechanochemical ball milling process. The ball milling process promotes phase transition of TiO2 from anatase to rutile and yields ternary heterojunction of the type TiO2(A)/TiO2(R)/ZnO and TiO2(A)/TiO2(R)/SnO2 (A-anatase and R-rutile). These ternary heterojunctions were characterized by various analytical techniques and its photocatalytic efficiency is evaluated using 4-Chloro Phenol as a model compound under UV and solar light. The enhanced catalytic activity of TiO2(A)/TiO2(R)/ZnO heterojunction is attributed to the formation of Ti3+-Vo defect states which leads to the efficient charge carrier separation. During the ball milling process severe crystal deformation takes place in TiO2 and ZnO lattices by creating crystal lattice distortion which leads to the formation of defects due to valency mismatch between Ti4+ and Zn2+. A mechanistic pathway is proposed for the enhanced photocatalytic activity of the ternary heterojunctions.

Review on modified TiO2 photocatalysis under UV/visible light: selected results and related mechanisms on interfacial charge carrier transfer dynamics.

Titania is one of the most widely used benchmark standard photocatalysts in the field of environmental applications. However, the large band gap of titania and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. The former can be overcome by modifying the electronic band structure of titania including various strategies like coupling with a narrow band gap semiconductor, metal ion/nonmetal ion doping, codoping with two or more foreign ions, surface sensitization by organic dyes or metal complexes, and noble metal deposition. The latter can be corrected by changing the surface properties of titania by fluorination or sulfation or by the addition of suitable electron acceptors besides molecular oxygen in the reaction medium. This review encompasses several advancements made in these aspects, and also some of the new physical insights related to the charge transfer events like charge carrier generation, trapping, detrapping, and their transfer to surface are discussed for each strategy of the modified titania to support the conclusions derived. The synergistic effects in the mixed polymorphs of titania and also the theories proposed for their enhanced activity are reported. A recent venture on the synthesis and applications of anatase titania with a large percentage of reactive {001} facets and their band gap extension to the visible region via nonmetal ion doping which is a current hot topic is briefly outlined.

Crystal structure of nonadentate tricompartmental ligand derived from pyridine-2,6-dicarboxylic acid: Spectroscopic, electrochemical and thermal investigations of its transition metal(II) complexes.

The coordinating behavior of a new dihydrazone ligand, 2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine towards manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been described. The metal complexes were characterized by magnetic moments, conductivity measurements, spectral (IR, NMR, UV-Vis, FAB-Mass and EPR) and thermal studies. The ligand crystallizes in triclinic system, space group P-1, with α=98.491(10)°, ß=110.820(10)° and γ=92.228(10)°. The cell dimensions are a=10.196(7)Å, b=10.814(7)Å, c=10.017(7)Å, Z=2 and V=1117.4(12). IR spectral studies reveal the nonadentate behavior of the ligand. All the complexes are neutral in nature and possess six-coordinate geometry around each metal center. The X-band EPR spectra of copper(II) complex at both room temperature and liquid nitrogen temperature showed unresolved broad signals with g(iso)=2.106. Cyclic voltametric studies of copper(II) complex at different scan rates reveal that all the reaction occurring are irreversible.

Photodegradation of methyl red by advanced and homogeneous photo-Fenton's processes: a comparative study and kinetic approach.

The degradation of methyl red (MR), an azo dye, was carried out by the homogeneous photo-Fenton's process (HPFP) and the advanced photo-Fenton's process (APFP) using symmetrical peroxides such as hydrogen peroxide and ammonium persulfate (APS) as oxidants. The APFP showed higher efficiency than their homogeneous counterparts even at high dye concentrations due to the faster reduction of Fe3+ to Fe2+ ions on the iron surface. H2O2 proved to be a better oxidant for both the processes. However, APS efficiently inhibited the precipitation of iron oxy hydroxides at higher dosage of iron powder compared to H2O2 by providing excess acidity to the reaction medium. The rate constant for the kinetics of decolorisation by various oxidation processes is of the order: Fe0/H2O2/UV>Fe0/H2O2/dark>Fe0/APS/UV>Fe2+/H2O2/UV>Fe0/UV>Fe0/APS/dark>Fe0/dark approximately H2O2/UV>Fe2+/APS/UV>APS/UV>Fe2+/H2O2/dark>Fe2+/APS/dark approximately Fe2+/UV. The degradation reaction was followed by UV-visible and GC-MS spectroscopic techniques. Based on the intermediates obtained, probable degradation mechanisms have been proposed. It was found that the initial mechanism in the APFP involves the reduction of azo groups to amines while in the case of HPFP it leads to the formation of hydroxylated products due to the oxidation of azo groups.