Sambandam Anandan

PHOTOCATALYTIC ACTIVITIES OF THE NANO-SIZED TIO2-SUPPORTED Y-ZEOLITES

Abstract Scientific studies of TiO 2 as photocatalyst started more than two and half decades ago. High efficiency in the photocatalytic reactions was achieved by increasing the surface area of the photocatalyst by supporting fine TiO 2 particles on porous materials. Among various supports, zeolites seem to be an attractive candidate. So, the present review focuses on the photocatalytic reactivities and their mechanisms of various Ti-based photocatalysts for various different types of reactions in order to achieve as highly efficient photocatalytic reactivities as possible.

Dye sensitized hydrogen evolution from water

Abstract Photochemically stable catalysts for continuous production of dihydrogen from water in the presence of visible light are yet to be developed. Most of the proposed systems suffer from loss of activity with use, at varying extent. In the present investigation, the photoactivity of Pt/TiO 2 system in the visible region is improved by the addition of the sensitizer ([Ru(dcbpy) 2 (dpq)] 2+ ) [where dcbpy=4,4′-dicarboxy 2,2′-bipyridine and dpq=2,3-bis-(2′-pyridyl)-quinoxaline] leading to efficient water reduction. This system is relatively inexpensive, reproducible, extremely stable and efficient in conversion of light into dihydrogen in aqueous solution. In order to obtain maximum information about the performance of TiO 2 –Pt catalysts, we varied the components and conditions of the system for water reduction. The dependence of the dihydrogen evolution rate on the amount of catalysts, concentration of the sensitizer and percentage of platinum on TiO 2 has been studied. In addition to the above, a comparative study on the photocatalytic activities of Pt/TiO 2 and Pt/ZnO in the presence of the above sensitizer for the production of hydrogen was also made.

Ultrasound assisted photocatalytic degradation of diclofenac in an aqueous environment.

Diclofenac (DF) is an anti-inflammatory drug found in aqueous environments as a pollutant due to its widespread use. The sonolytic, photocatalytic and sonophotocatalytic degradation of DF using three photocatalysts (TiO(2), ZnO and Fe-ZnO) were studied. The degradation of DF followed first-order like kinetics. The sonophotocatalytic degradation using TiO(2) under UV-vis radiation showed a slight synergistic enhancement in the degradation of the parent compound, whereas a detrimental effect was observed for the mineralization process. In the case of Fe-ZnO, both degradation and mineralization showed near additive effects. A number of degradation products were identified.

Photocatalytic degradation of Acid Red 88 using Au–TiO2 nanoparticles in aqueous solutions☆

Metal loaded semiconductors in general possess greater photocatalytic activity than pure semiconductors. Hence, with an attempt to achieve higher photocatalytic activity, Au-TiO(2) photocatalysts were prepared by deposition-precipitation method and used for the photocatalytic degradation of an azo dye (Acid Red 88; AR88). The materials were characterized by different analytical techniques. A possible mechanism for the photocatalytic degradation of AR88 by Au-TiO(2) in the absence and presence of other oxidizing agents (peroxomonosulfate (PMS), peroxodisulfate (PDS) & hydrogen peroxide (H(2)O(2))) has been proposed. The extent of mineralization of the target pollutant was also evaluated using Total Organic Carbon (TOC) analysis.

Performance of dye-sensitized solar cells fabricated with extracts from fruits of ivy gourd and flowers of red frangipani as sensitizers

Natural dyes extracted from fruits of ivy gourd and flowers of red frangipani were used as sensitizers to fabricate dye sensitized solar cells (DSSCs). The UV-Vis absorption spectroscopy, Fourier transform infrared (FTIR), Fourier transform Raman (FT-Raman) and liquid chromatography-mass spectrometry (LC-MS) studies indicated the presence of β-carotene in the fruits of ivy gourd and anthocyanins in the flowers of red frangipani. The extract of the flowers of red frangipani exhibits higher photosensitized performance compared to the fruits of ivy gourd and this is due to the better charge transfer between the dyes of flowers of red frangipani and the TiO(2) photoanode surface.

The interaction of sonochemically synthesized gold nanoparticles with serum albumins

Spherical gold nanoparticles of approximately 16nm were synthesized using a sonochemical reduction method and characterized using UV-vis spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM). The binding of these gold nanoparticles with bovine serum albumin (BSA) and human serum albumin (HSA) was investigated using UV-vis absorption and fluorescence spectroscopic techniques. A strong quenching of the fluorescence from serum albumins was observed due to the formation of a ground state complex with gold nanoparticles (static quenching). The fluorescence quenching constants, number of binding sites and binding constants were determined using Stern-Volmer and Benesi-Hildebrand plots. Using Forster Resonance Energy Transfer (FRET) theory, the distance between the donor (serum albumins) and acceptor (gold nanoparticles) was obtained, which showed that HSA has more affinity towards sonochemically synthesized gold nanoparticles compared to gold nanoparticles synthesized using other methods.

Colorimetric and fluorescence sensing of fluoride anions with potential salicylaldimine based schiff base receptors.

Salicylaldimine based schiff base receptors with different substituents showing fluorescent enhancement in the presence of fluoride anion was visualized through naked eye as well as by change in spectral properties (UV-vis and fluorescent techniques). The reason for such fluorescence enhancement may be due to hydrogen bond interaction between receptor recognition site and fluoride anion. Such a hydrogen bond interaction creates a six-membered transition state, which avoids quenching processes. To support this, fluorescence enhancement factor (FEF) was calculated and it was found to be more (FEF=652) for -NO(2) substituted receptor compared to other receptors.

Sonochemical synthesis of CuO nanostructures with different morphology.

This paper describes a highly efficient and rapid approach of synthesizing different CuO nanostructures in aqueous solutions using ultrasound irradiation of copper(II) acetate with urea/sodium hydroxide in the presence of polyvinylpyrrolidone (PVP), as stabilizing polymer. Field emission scanning electron microscope images clearly indicate the formation of CuO quasi-spherical microarchitectures and long-straw like structure in the presence of urea and sodium hydroxide. Other characterization techniques such as TEM, XRD and XPS are also provided to support the formation of such structures. One of the reasons for the formation of such CuO nanostructures may be due to the formation of a polymer-metal complex with the stabilizing polymer (PVP).

High surface area Ag-TiO2 nanotubes for solar/visible-light photocatalytic degradation of ceftiofur sodium

Titanium dioxide nanotubes (TiO2 NTs) with very high surface area (469 m(2)/g) have been synthesized through a simple hydrothermal method and their surface has been modified using silver nanoparticles (Ag NPs). The Ag NPs deposited TiO2 NTs (Ag-TiO2 NTs) show an extended optical response from UV to visible region coupled with a surface plasmon resonance band and thus can be utilized as a plasmonic photocatalyst. The photoluminescence intensity of TiO2 NTs is lower than that of TiO2 nanoparticles due to the delocalization of photogenerated electrons along the one dimensional nanotubes which reduces the rate of charge recombination. The Langmuir adsorption constant of Ag-TiO2 NTs (for ceftiofur sodium adsorption) is twice that of P25 TiO2. The Ag-TiO2 NTs exhibit excellent photocatalytic activity toward the degradation of ceftiofur sodium (CFS) due to high surface area and mesoporosity of TiO2 NTs. The addition of peroxomonosulfate in the photocatalytic system greatly amplifies the CFS degradation owing to the simultaneous generation of both OH and SO4(-). The catalyst retains its photocatalytic activity at least up to four consecutive cycles.

Sonophotocatalytic degradation of monocrotophos using TiO2 and Fe3

Monocrotophos (MCP) is an organophosphate insecticide that has been found as a pollutant in aqueous environments. The sonolytic, photocatalytic and sonophotocatalytic degradation of MCP in the presence of homogeneous (Fe(3+)) and heterogeneous photocatalysts (TiO(2)) were studied. The photocatalytic degradation rate using TiO(2) was found to be lower than that of sonolysis alone due to the interference of phosphate ions formed as an intermediate product. On the other hand, a 15 fold enhancement in the degradation rate was found when photolysis was carried out in the presence of Fe(3+) compared to the rate observed with photolysis alone. The combination of sonolysis and photocatalysis (using either TiO(2) or Fe(3+)) showed a detrimental effect. Synergy indices of 0.62 and 0.87 were found for the sonophotocatalytic degradation of MCP in the presence of TiO(2) and Fe(3+), respectively. Total organic carbon (TOC) analysis was carried out to study the extent of mineralization of MCP. It was found that the mineralization process was additive for both TiO(2) and Fe(3+) sonophotocatalysis. HPLC and electrospray mass spectrometry (ESMS) techniques were employed for the identification of the degradation intermediates. The sonication of MCP led to the formation of dimethyl phosphate, dimethylphosphonate, 3-hydroxy 2-buteneamide and N-methyl 3-oxobutanamide as the intermediate products.