P.V.R.K. Ramacharyulu

Synthesis, characterization and photocatalytic activity of Ag–TiO2 nanoparticulate film

Ag–TiO2 nanoparticulate film was synthesized by dip coating followed by adsorption and photoreduction in UVA light, characterized by transmission electron microscopy, scanning electron microscopy, energy dispersive analysis of X-rays, glancing angle X-ray diffractometry and UV-Vis absorption spectrophotometry techniques. The data indicated the presence of TiO2 particles of anatase phase of size varying from 5–15 nm, Ag nanoparticles of size varying from 10–20 nm, and also indicated the added visible light activity in Ag–TiO2 nanoparticle films. Photocatalytic degradation of methyl parathion (O,O-dimethyl O-(4-nitrophenyl) phosphorothioate), a well known pesticide in aqueous solution was studied using Ag–TiO2 nanoparticulate film and the data was compared with TiO2 nanoparticulate film. Photocatalytic degradation reactions demonstrated pseudo first order behaviour. Methyl parathion was found to be degraded initially to paraoxon which further was degraded to p-nitrophenol, trimethyl ester of phosphoric acid, trimethyl ester of phosphothioic acid, and finally to phosphate ion. Minute amounts of carbon dioxide and acetaldehyde were also detected.

Breakthrough behaviour of activated charcoal cloth samples against oxygen analogue of sulphur mustard

Abstract The breakthrough behaviour of activated charcoal cloth samples against an oxygen analogue (OA) of sulphur mustard has been studied using the modified Wheeler equation. Activated charcoal cloth samples having different surface area values in the range of 481 to 1290 m 2 /g were used for this purpose. Breakthrough behaviour was found to depend on the properties of the activated charcoal cloth, properties of the OA and the adsorption conditions. Activated charcoal cloth with a high surface area of 1290 m 2 /g, relatively large surface density of 160 g/m 2 and coarser fiber structure exhibited better kinetic saturation capacity value, 0.19 g/g, against OA vapours when compared to others, thus confirming its potential use in foldable masks for protection against chemical warfare agents. Key words: chemical warfare agents, sulphur mustard, oxygen analogue, breakthrough time, activated charcoal cloth 1. Introduction Achieving respiratory protection is a challenging task when air is contaminated with deadly persistent chemical warfare agents (CWA) such as sulphur mustard (HD). HD is a toxic CWA which causes blisters on exposure. It causes damage to skin, eyes and respiratory system. It is highly persistent, has a high boiling point and low volatility, and it remains in the environment for long intervals of time [1]. Adsorption systems containing granular activated carbon (GAC) have been employed for the purpose of purifying air contaminated with CWA for respiratory protection [2-6]. Breakthrough characteristics (BC) of the GAC bed depend upon the nature of adsorbate, nature of the adsorbent, surface functional groups, surface area, pore size distribution, bed geometry, granular size, air flow rate, concentration of contaminant, etc. [7,8]. From this viewpoint, Jonas et al. have studied the BC of GAC beds against nerve agents like dimethyl methyl phosphonate (DMMP) and isopropyl methyl phosphonofluoridate [9,10]. Later, Prasad et al. [11-13] studied the BC of a GAC bed, and a bed of Whetlerite carbon granules, against deadly vapours of HD. In both studies the modi-fied Wheeler equation was used to analyze the adsorption parameters. HD and DMMP were found to be strongly adsorbed on GAC due to low volatility and high affinity towards solid surfaces. The relative humidity (RH) of the contaminant air stream also affects the BC of carbon beds [14]. In spite of that fact, while many researchers have studied the effect of RH on BC of GAC beds against various organic vapours, reports on the effect of RH on the BC of GAC beds or activated charcoal cloth (ACC) beds against CWA are scanty. Kaplan et al. [14] have studied the BC of GAC beds against DMMP. Ad-sorption capacity value was found to be reduced with an increase in RH. To our knowledge, there have been no reports available on the effect of RH on the BC of HD or its surrogates on either GAC or ACC.Filtration systems containing GAC beds have a rigid shape and more weight. Consequent-ly, while they offer durable protection without any doubt, they are not suitable for incorpora -