Evolution of adsorption kinetics and isotherms of gallic acid on an activated carbon oxidized by ozone: Comparison to the raw material

The evolutions of both adsorption kinetics and isotherms of gallic acid on a commercial activated carbon (AC), initially submitted to ozone in water for 4 h were studied. The microporous properties were investigated by N2 physisorption at 77 K and the surface oxygen groups created on the surface of the carbon by oxidation were characterized by Fourier Transform Infrared Spectroscopy (FTIR). The studies of the adsorption kinetics and the isotherms of gallic acid on the ozonated and non ozonated AC were carried out at several temperatures (between 5 °C and 50 °C). Four models (pseudo-first order, pseudo-second order, Elovich and the intraparticle model) were used in order to determine kinetic parameters of adsorption. The best results were obtained with the pseudo-second order model. Moreover, a decrease in both the rate constant and the activation energy of adsorption with the ozone exposure time of AC was evidenced. However, no modification appeared in the adsorption mechanism rate limited by the intraparticle diffusion both for ozonated and for non ozonated AC. Two models (Langmuir and Dubinin–Radushkevich) were tested from experimental isotherms and compared. The Langmuir model provided the best correlation under all the temperatures. Results showed that ozonation of AC for 4 and 8 h led to an increase in surface oxygen groups, which can be considered as acid groups, without microporous modification. The adsorption capacity of the oxidized material was increased by a value up to 28% under all the experiments. The Langmuir and the DR models showed that the surface occupied increases and the process of micropores filling proves to be favoured when the AC is oxidized by ozone.