P. Mohapatra

Pillared clay as an effective catalyst for low temperature VOCs decomposition

Volatile organic compounds (VOCs) are organic chemicals mostly emitted from different sources like industrial or domestic having high vapor pressure at room-temperature conditions. Some of these are also anthropogenic in nature and also these are the major contributor for the photochemical ozone. The different methods available for the abatement of VOCs are thermal oxidation, catalytic oxidation, photocatalytic oxidation, adsorption etc. Due to the stringent regulation of VOCs emission in different countries there is a need of efficient abatement technology to preserve the environment. In this context catalytic combustion of organic pollutants offers considerable advantages over the industrially operated thermal combustion process. Generally, oxidative destruction is possible at low temperature in presence of a catalyst. In addition catalytic process is more energy efficient and can operate with very dilute pollutants. A number of catalysts have been used for the complete oxidation of VOCs, among these Pillared clays type porous materials are also useful for the purpose. Pillared clays have high surface area, pore volume, thermal stability and can be tailor made for particular catalytic application compared with the parent clays. In the present review we will summarize the latest developments on the clay based materials including the effect of different controlling parameters for the synthesis of pillared clay based porous materials and its specific application for the low temperature VOCs decomposition. In particular the effect of transition metals like iron and manganese oxide pillared clay on the VOC decomposition is discussed.

Phase transformation of ZrO2 nanoparticles produced from zircon

This article focuses on the phase transformation of zirconia (ZrO2) nanoparticles produced from zircon using a bottom-up approach. The influence of mechanical milling and thermal annealing on crystalline phase transformation of ZrO2 nanoparticles was explored. It was found that the iron oxide, as an inherent impurity present in ZrO2 nanoparticles, produced from zircon stabilises the cubic phase after calcination at 600°C. The stabilised cubic phase of ZrO2 nanoparticles was disappeared and transformed into partial tetragonal and monoclinic phases after mechanical milling. The phase transformation occurred on account of the crystal defect induced by high-energy mechanical milling. The destabilisation of cubic phase into monoclinic phase was observed after the thermal annealing of ZrO2 nanoparticles at 1000°C. The phase transitions observed are correlated to the exclusion of iron oxide from the zirconia crystal structure.