Shivatharsiny Rasalingam

Versatility of heterogeneous photocatalysis: synthetic methodologies epitomizing the role of silica support in TiO2 based mixed oxides

Heterogeneous photocatalysis continues to be an active area of research with focus on developing catalytic systems that can degrade toxic pollutants in the gas and aqueous phase, and split water to generate hydrogen and oxygen. In this review, the incorporation of silica phases in titanium dioxide based photocatalysts is reviewed.

Modulation of pore sizes of titanium dioxide photocatalysts by a facile template free hydrothermal synthesis method: implications for photocatalytic degradation of rhodamine B.

Mesoporous TiO2 photocatalysts were prepared in ethanol media by using relatively green, template free sol-gel technique. A mild hydrothermal treatment procedure was employed to tune the pore sizes of the materials. Comprehensive techniques that include powder X-ray diffraction, diffuse reflectance spectroscopy, specific surface area analysis, electron microscopy, FT-IR, TGA, and ζ-potential measurements were used to characterize the titania materials. Porosity (pore size and pore volume) of the materials were found to be key factors for the variation in the rate of photocatalytic degradation of rhodamine B; in addition to specific surface area, and surface hydroxyl groups. An increase in porosity permits effective transport of the dye molecules resulting in an increase in the rate of the degradation in materials having larger pores. A detailed electrospray ionization-mass spectrometric (ESI-MS) study was carried out for selected materials to identify photodegraded intermediates and products formed during the degradation of rhodamine B. In addition, experiments were also carried out to understand the role of reactive oxygen species (ROS). In summary, this work provides a simple way to tune pore sizes without the use of any template and an insight into the influence of pore size for the photocatalytic degradation of rhodamine B.

Removal of hazardous pollutants from wastewaters: applications of TiO 2 -SiO 2 mixed oxide materials

The direct release of untreated wastewaters from various industries and households results in the release of toxic pollutants to the aquatic environment. Advanced oxidation processes (AOP) have gained wide attention owing to the prospect of complete mineralization of nonbiodegradable organic substances to environmentally innocuous products by chemical oxidation. In particular, heterogeneous photocatalysis has been demonstrated to have tremendous promise in water purification and treatment of several pollutant materials that include naturally occurring toxins, pesticides, and other deleterious contaminants. In this work, we have reviewed the different removal techniques that have been employed for water purification. In particular, the application of TiO2-SiO2 binary mixed oxide materials for wastewater treatment is explained herein, and it is evident from the literature survey that these mixed oxide materials have enhanced abilities to remove a wide variety of pollutants.

An investigation into the effect of porosities on the adsorption of rhodamine B using titania-silica mixed oxide xerogels.

Aperiodic mesoporous titania-silica (TiO2·SiO2) xerogels with varying silica contents were synthesized under ambient conditions. The physico-chemical properties of the xerogels were examined by a variety of techniques that include powder X-Ray Diffraction (XRD), nitrogen adsorption, Fourier Transform-Infra-Red spectroscopy (FT-IR), Scanning and Transmission Electron Microscopies (SEM and TEM), Thermo Gravimetric Analysis (TGA), zeta potential, and Diffuse Reflectance Spectroscopic (DRS) studies. The adsorption of a model dye molecule, rhodamine B (RhB) was studied over the titania-silica xerogels and compared with titania and silica. It was determined that the pore volume of the xerogels mainly influences the adsorption of RhB. The xerogels exhibited good adsorption capacity with more than 90% dye removal at low dye concentrations. Our results suggest that low cost approaches to the synthesis of xerogels with tailored properties such as large pore volume could provide cost-effective solutions to mitigate environmental problems related to removal of water based toxic pollutants such as dyes by simple adsorption processes.

Nanocasting of Periodic Mesoporous Materials as an Effective Strategy to Prepare Mixed Phases of Titania

Mesoporous titanium dioxide materials were prepared using a nanocasting technique involving silica SBA-15 as the hard-template. At an optimal loading of titanium precursor, the hexagonal periodic array of pores in SBA-15 was retained. The phases of titanium dioxide could be easily varied by the number of impregnation cycles and the nature of titanium alkoxide employed. Low number of impregnation cycles produced mixed phases of anatase and TiO2(B). The mesoporous TiO2 materials were tested for solar hydrogen production, and the material consisting of 98% anatase and 2% TiO2(B) exhibited the highest yield of hydrogen from the photocatalytic splitting of water. The periodicity of the pores was an important factor that influenced the photocatalytic activity. This study indicates that mixed phases of titania containing ordered array of pores can be prepared by using the nanocasting strategy.