Alumina and nickel-alumina aerogels for anionic azo-dyes adsorption -

Abstract

Azo-dyes are being discharged nowadays in water from various industries without any prior treatment which could lead to serious environmental problems. Different physical, chemical, and biological processes are used to remove these toxic azo-dyes. However, the physical adsorption of these dyes is considered to be the most efficient and economic technique. In this thesis, alumina and nickel-alumina aerogels with different nickel content were synthesized using a straightforward and fast epoxide-initiated gelation sol-gel method. These aerogels were later calcined at different temperatures and the effect of calcination on the chemical, structural, and surface properties of the aerogels was evaluated. In addition, alumina and nickel-alumina aerogels were tested for adsorption of three anionic azo-dyes and the effect of nickel content, pH, temperature, calcination, and initial dye concentration on the adsorption were investigated. Nickel-alumina aerogels showed a higher adsorption capacity than alumina aerogels, however the adsorption capacities of both aerogels were higher than the one reported in literature. The adsorption kinetics followed a pseudo-second order representative of a coexistence of chemisorption and physisorption processes and the adsorption process was found to be exothermic. The calculated activation energy revealed that the adsorption of orange II and methyl orange was facilitated by physical adsorption processes while the adsorption of congo red was facilitated by physical and chemical processes.