M.R. Pai

Antibacterial activities of Nd doped and Ag coated TiO2 nanoparticles under solar light irradiation

Nanosized (8-9 nm) Nd doped and Ag coated TiO(2) nanoparticles have been synthesized by sol-gel method. The physicochemical properties of these particles were investigated by X-ray diffraction (XRD), diffuse reflectance UV-visible (DRUV) spectra and Brunauer-Emmett-Teller (BET) surface area analysis. The antibacterial activities of the samples were studied for Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) both, under the light and dark conditions. The results reveal that the extent of activity shows the order as undoped TiO(2)<Nd doped TiO(2)<Ag coated TiO(2). The mechanism of bactericidal action of the nanoparticles, in presence of sunlight has been explained with the help of microscopic analyses. The bacterial damage is observed to proceed through initial perforation of the cell, damage of cell wall and finally the bacterial death.

Photocatalytic H2 generation over In2TiO5, Ni substituted In2TiO5 and NiTiO3 – a combined theoretical and experimental study

We report here the role of Ni substitution in modifying the crystal structure, optical absorption properties and electronic properties of indium titanate, In2(1−x)Ni2xTiO5−δ (0.0 ≤ 2x ≤ 0.4) and its consequent effect on the photocatalytic properties for H2 generation. Rietveld refinement of observed XRD patterns of the titanates revealed that Ni2+ substitution has led to a decrease in lattice cell parameters and cell volume, contraction of InO6 octahedra and consequently improved charge carrier properties. Furthermore, the conduction band maximum (CBM) was found to be a hybrid state between Ni, Ti and In orbitals in 10% Ni-doped sample, which suggests that the photo-induced charges can be better transported in the substituted samples from zigzag chains of [·Ni–O–Ti⋯In–O–Ti----]. The UV-visible diffuse reflectance spectra exhibited that the band gap of the indium titanate phase decreased sequentially with an increase in the extent of Ni substitution. The underlying cause for band gap narrowing on Ni substitution was evaluated from plane wave based DFT calculations using the GGA + U approach. The decreasing order of photocatalytic activity (as a percentage of Ni substitution) for hydrogen generation from water–methanol mixture is as follows: 10% > 5% > indium titanate > 15% > 20%. The fall in activity below indium titanate coincided with the appearance of ilmenite NiTiO3 phase. Plane wave based DFT calculations performed on NiTiO3 revealed that strong intermixing of Ni-3d with O-2p orbitals occurred in the valence band of NiTiO3 and resulted in generation of a pseudo band gap of 0.3 eV at 1.4 eV below the Fermi level. This pseudo band gap might act as a hindrance and may contribute to weakening the intensity of the electronic transition due to Ni2+ → Ti4+ charge transfer. We propose here that an optimal concentration of 10% Ni substitution in indium titanate modifies the structural and electronic properties favorably leading to better photocatalytic activity by reducing the band gap, enhancing of the electron–hole separation and improving charge carrier properties.

Hydrothermal synthesis of Ag@TiO2–Fe3O4 nanocomposites using sonochemically activated precursors: magnetic, photocatalytic and antibacterial properties

Fe3O4–TiO2 nanocomposites have been synthesized by hydrothermal method using sonochemically activated precursors. X-ray diffraction analysis of the samples reveals the formation of pure phase composites. The optical properties of the composites are superior to TiO2 as noted from the red shift in the diffused reflectance spectra of the composites. The presence of nanocubes of Fe3O4, nanospheres of TiO2 and heterojunctions of the two in the composite samples have been observed in transmission electron micrographs. The magnetic properties of the samples were determined with the help of vibrating sample magnetometry (VSM) and magnetic force microscopy (MFM). The photocatalytic activity of the samples was investigated in terms of degradation of methyl orange (MO) dye. The composites could be easily separated from the reaction mixture after photocatalysis due to their magnetic behaviour. However, the photocatalytic activity of the composites was observed to be lower compared to bare TiO2. The composite (15% Fe3O4–TiO2) when modified by coating it with Ag showed enhanced photocatalytic activity. Further, the antibacterial activities of the samples were also examined using E. coli as a model organism. Positive results were obtained only for the Ag coated composite with lower MIC (minimum inhibition concentration) values.

Mechanism of CO + N2O Reaction via Transient CO32−Species over Crystalline Fe-Substituted Lanthanum Titanates

Some newer mechanistic aspects investigated by in situ Fourier transform infrared (FTIR) in conjunction with catalytic activity under similar conditions over crystalline lanthanum titanates as a function of Fe substitution at the B-site for the CO + N(2)O reaction are reported for the first time in the present communication. La(2)Ti(2(1-x))Fe(2x)O(7-delta) (0.0 < or = x < or = 1.0) was synthesized by gel combustion where Fe(3+) substitution effectively enhanced the conversion rates for N(2)O reduction as compared to the pristine La(2)Ti(2)O(7) (LTOGC). Among all samples, maximum conversion over La(2)Ti(0.8)Fe(1.2)O(7-delta) [LF(0.6)GC] catalyst was observed. In situ FTIR results reveal that substitution-induced anionic vacancies/defects provide additional sites on the surface of LF(0.6)GC for CO chemisorptions, whereas a perfect stoichiometric lattice like LTOGC is devoid of such sites. Surface-adsorbed CO reacts with surface lattice oxygen in the case of nonstoichiometric LF(0.6)GC to produce carbonates (M-CO(3)(2-)) at a much lower temperature. The reaction proceeds via carbonate formation, leaving the catalytic surface oxygen deficient in LF(0.6)GC, and therefore facilitates the reduction of preadsorbed, N(2)O [N(2)O(g) + * --> N(2) + *-O) by easily adsorbing the oxygen species (*-O) generated in N(2)O reduction, which is subsequently driven away by adsorbed/gas phase CO, whereas in the case of LTOGC, progress of the reaction was sluggish in the absence of transient carbonate species. Dissociative chemisorptions of N(2)O are not facilitated on stoichiometric oxygen excess titanate, as there is no vacancy in the surface to accommodate another oxygen atom. The redox mechanism via CO(3)(2-) species is proposed for CO + N(2)O reaction over La(2)Ti(2(1-x))Fe(2x)O(7-delta), as against the associative mechanism observed in the unsubstituted sample, La(2)Ti(2)O(7), as suggested by in situ FTIR in conjunction with catalytic activity results.

Fundamentals and Applications of the Photocatalytic Water Splitting Reaction

Catalysis under light irradiation, called photocatalysis, is attracting a great deal of attention from the viewpoint of fundamental science and for practical use. The topic of photocatalytic water splitting becomes increasingly important owing to its essential role in solving today’s environment- and energy-related problems. This chapter gives a comprehensive treatment to all important aspects of oxide materials for photocatalytic hydrogen production from water. First, we discuss the principles and processes involved in photocatalytic water splitting, followed by the experimental methods, and finally the different oxide semiconductor materials used as photocatalysts for these reactions and compare their performance.

The structure - activity relationship in catalytic behavior of ThMnVO oxides

Abstract With an objective to elucidate the influence of structural changes on catalytic properties, the oxygen content, reducibility and chemical stability of substituted metavanadates of thorium, viz., Th(MnxV1-xO3-)4 with 0 × 1, were monitored using temperature programmed reduction / oxidation (TPR/TPO), powder XRD and FTIR techniques in conjunction with thermogravimetry. Catalytic activity was evaluated for oxidation of CO as a function of Mn content. The formation of new phases ThMn2(VO4)2O2 and ThMn4O8 was established and indexed on the basis of tetragonal unit cell with a0 = 7.124 A and c0 = 6.348 A and the hexagonal unit cell with a0 = 6.468 A and c0 = 11.188 A , respectively. The mixed oxide compositions generally exhibited better stability towards the repeated cycles of reduction and reoxidation compared to MnO2 or un-substituted vanadates or manganates. The reduction of an individual component in a mixed oxide depended on the extent of substitution and the catalytic activity of the mixed oxides was found to be very sensitive to resultant structural changes and to the oxygen non-stoichiometry. The compositions with the oxygen rich VO4 groups in general showed poorer activity for CO oxidation reaction compared to those comprising of VO3 groups.

Corundum type indium oxide nanostructures: ambient pressure synthesis from InOOH, and optical and photocatalytic properties

A simple, cost effective, surfactant free and scalable synthesis of rhombohedral In2O3 (rh-In2O3) nanostructures with controllable size and shape has been developed under ambient pressure by thermal dehydration of InOOH nanostructures. The InOOH nanostructures have been prepared by solvothermal reaction between indium nitrate hydrate with tetramethylammonium hydroxide (TMAH) in anhydrous methanol at 140 °C without any surfactant. The structure and morphology of the nanostructures have been characterized in detail by X-ray powder diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The studies reveal that highly crystalline nanostructures of InOOH and rh-In2O3 with rice-grain type morphology are formed. The optical properties of the InOOH and rh-In2O3 nanostructures have been explored by UV-visible diffuse reflectance spectroscopy (UV-DRS) and room-temperature photoluminescence (PL) studies. The direct band gap of as-synthesized InOOH and rh-In2O3 nanostructures was estimated to be 3.75 and 2.95 eV, respectively, from the diffuse reflectance absorbance spectra. Both InOOH and rh-In2O3 nanostructures show intense blue emission under UV excitation which is attributed to the presence of oxygen vacancies. The thermal stability of the rh-In2O3 phase has been studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA) and dilatometry of the as prepared sample. The potential of InOOH and rh-In2O3 nanostructures as photocatalytic materials for hydrogen generation from water/methanol (2 : 1) mixtures under UV/vis irradiation has also been evaluated for the first time.

Synergistic enhancement of microbubble formation in ultrasound irradiated H2O–CH3OH mixtures probed by dynamic light scattering

This report investigates the formation of microbubbles in water–methanol mixtures upon ultrasound irradiation and its correlation with the yield of H2 obtained as a result of sonochemical splitting of water. The yield of hydrogen produced by sonochemical reaction is monitored at different compositions of water–methanol mixtures. The evidence for the formation of microbubbles upon ultrasound irradiation is obtained by the dynamic light scattering technique. Microbubble formation during ultrasound irradiation of water–methanol mixtures, their stability and size distribution, has been quantitatively estimated. The effect of composition of the water–methanol mixture and duration of irradiation on the extent of bubble formation has been inferred from the changes in the light scattering intensity and its time correlation function. Exceptional stability of microbubbles without any additives is observed at a certain composition of the water–methanol mixture (4 : 3, v/v). The extent of microbubbles formed in the mixture correlates well with the yield of hydrogen detected.