The combined use of ozone and activated carbon has recently started to be developed for the treatment of toxic effluents. However, the effect of ozone on the properties of activated carbon is not fully elucidated. A study was undertaken of modifications in the surface properties of a commercial activated carbon produced by its ozonation during different time periods. Surface chemistry of the activated carbon samples was characterized by selective neutralization, temperature-programmed desorption, X-ray photoelectron spectroscopy, and pH of the point of zero charge. Surface area and volume of micropores and mesopores were obtained from nitrogen adsorption isotherms at 77 K. Adsorption properties were determined by methylene blue adsorption index. Results show that the higher the ozone dose, the higher is the oxidation of the carbon and the greater is the number of acid groups present on the carbon surface, especially carboxylic groups, whereas the pH of the point of zero charge decreases. The surface area, micropore volume, and methylene blue adsorption all reduce with higher doses. These results are explained by the ozone attack on the carbon and the fixation of oxygen groups on its surface.
OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 9735 We report the role played by acidic surface sites of ZSM-5 on ozone removal. Ozone removal is mainly due to ozone decomposition on mild/strong Lewis acid sites. Adsorbed oxygen species appear on ZSM-5 surface because of ozone decomposition.
Keywords:Acidic sites Chemical surface properties Lewis acid sites Ozone Synthetic zeolites ZSM-5 zeolite a b s t r a c t In this work, chemical interactions between ozone and zeolite surface active sites are studied in order to propose a process for gaseous ozone removal. Synthetic ZSM-5 zeolites with three different Si/Al 2 ratios and similar specific surface areas and microporous volumes were used in this study. Zeolite samples were characterised using Fourier Transform InfraRed spectroscopy (FTIR) and pyridine sorption IR studies in order to determine acidic site concentrations and strength. Ozone removal experiments were conducted in a quartz fixed-bed flow reactor, at 20°C and 101 kPa. Experiments using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) were conducted in order to identify adsorbed ozone and/or adsorbed oxygen species on zeolite surface. Pyridine IR measurements evidence two kinds of Lewis acid sites induced by extra-framework aluminium species and electronic aluminium defaults inside zeolite structure. Results obtained here evidence the important role of acidic surface sites of ZSM-5 zeolite on gaseous ozone removal. The total amount of removed ozone is found to be directly proportional to the total content of Lewis acid sites. DRIFTS experiments exhibit two bands around 800 and 1400 cm À1 that could correspond to adsorbed oxygen species linked to zeolite surface. DRIFTS experiments also exhibit a band around 1100 cm À1 that correspond to adsorbed ozone on the zeolite surface. Gaseous ozone removal using ZSM-5 zeolite could be largely attributed to ozone decomposition on Lewis acid sites and also to ozone adsorption on the surface of the zeolites.
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