Ranjit T. Koodali

Size-Dependent Bacterial Growth Inhibition and Mechanism of Antibacterial Activity of Zinc Oxide Nanoparticles

The antibacterial properties of zinc oxide nanoparticles were investigated using both gram-positive and gram-negative microorganisms. These studies demonstrate that ZnO nanoparticles have a wide range of antibacterial activities toward various microorganisms that are commonly found in environmental settings. The antibacterial activity of the ZnO nanoparticles was inversely proportional to the size of the nanoparticles in S. aureus. Surprisingly, the antibacterial activity did not require specific UV activation using artificial lamps, rather activation was achieved under ambient lighting conditions. Northern analyses of various reactive oxygen species (ROS) specific genes and confocal microscopy suggest that the antibacterial activity of ZnO nanoparticles might involve both the production of reactive oxygen species and the accumulation of nanoparticles in the cytoplasm or on the outer membranes. Overall, the experimental results suggest that ZnO nanoparticles could be developed as antibacterial agents against a wide range of microorganisms to control and prevent the spreading and persistence of bacterial infections.

Lanthanide modified semiconductor photocatalysts

Lanthanide ion modified semiconductor photocatalysts have been explored for photocatalytic degradation of organic pollutants, dye molecules, for photo-splitting of water under both ultra-violet (UV) and visible light conditions. This review provides an in-depth analysis of lanthanide ion semiconductor photocatalysts with focus on titania based photocatalysts. The emphasis is on delineating the underlying factors responsible for the enhanced activities observed by several research groups and in providing guidance to researchers in this area.

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.

Visible light driven photocatalytic evolution of hydrogen from water over CdS encapsulated MCM-48 materials

CdS encapsulated cubic MCM-48 mesoporous photocatalysts were prepared by a post-impregnation method. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption isotherm, UV-visible diffuse reflectance spectroscopy (DRS), FT-IR spectrometry, X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), and photoluminescence (PL) spectroscopy were employed for the characterization of the CdS incorporated MCM-48 siliceous materials. MCM-48 was loaded with different amounts of CdS. In the current study, all the samples showed photocatalytic activity under visible light (λ > 400 nm) irradiation for production of hydrogen from splitting of water in the absence of Pt, which is usually used in photocatalytic splitting of water. The photocatalytic activity of the CdS incorporated MCM-48 mesoporous photocatalysts was found to be dependent on the CdS loading and the pore size of MCM-48 siliceous support. The highest solar hydrogen evolution rate by visible light irradiation from the splitting of water was determined to be 1.81 mmol h−1 gCdS−1 and the apparent quantum yield was estimated to be 16.6%.

Versatility of Evaporation-Induced Self-Assembly (EISA) Method for Preparation of Mesoporous TiO2 for Energy and Environmental Applications

Evaporation-Induced Self-Assembly (EISA) method for the preparation of mesoporous titanium dioxide materials is reviewed. The versatility of EISA method for the rapid and facile synthesis of TiO2 thin films and powders is highlighted. Non-ionic surfactants such as Pluronic P123, F127 and cationic surfactants such as cetyltrimethylammonium bromide have been extensively employed for the preparation of mesoporous TiO2. In particular, EISA method allows for fabrication of highly uniform, robust, crack-free films with controllable thickness. Eleven characterization techniques for elucidating the structure of the EISA prepared mesoporous TiO2 are discussed in this paper. These many characterization methods provide a holistic picture of the structure of mesoporous TiO2. Mesoporous titanium dioxide materials have been employed in several applications that include Dye Sensitized Solar Cells (DSSCs), photocatalytic degradation of organics and splitting of water, and batteries.

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.

Photocatalytic degradation of aqueous organic pollutants using titania supported periodic mesoporous silica

Periodic mesoporous materials are extensively employed as supports for dispersing photocatalytically active species since they possess very high surface areas, large pore volumes and can be easily synthesized.

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.

Mesoporous coupled ZnO/TiO2 photocatalyst nanocomposites for hydrogen generation

The present work investigates mesoporous coupled ZnO-TiO2 based nanocomposites towards photocatalytic hydrogen generation. The effect of Zn2+ loadings was examined on the photocatalytic activities of the sol-gel derived ZnO-TiO2 nanocomposites employing a structure-directing template. ZnO-TiO2 nanocomposites were characterized by powder X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, nitrogen isotherm, Raman, and electrochemical impedance spectroscopy (EIS) methods. The photocatalytic H2 evolution of the ZnO-TiO2 suspensions was evaluated in an aqueous methanol medium under UV illumination. The Zn2+ concentrations utilized to prepare ZnO-TiO2 nanocomposites were found to have significant effect on the specific surface area, pore volume, and photocatalytic activity. The H2 evolution results obtained with ZnO-TiO2 nanocomposites were compared with H2 generation using commercial TiO2 P25 and individual ZnO nanoparticles. The photocatalytic activity of ZnO-TiO2 co...