Adsorption characteristics of benzene carboxylic acids from aqueous solution by Zr(IV)-loaded collagen fiber

A novel adsorbent, Zr(IV)-loaded collagen fiber (ZLCF), was prepared and its adsorption characteristics to benzoic acid (BA), o-phthalic acid (o-PA), p-phthalic acid (p-PA) and m-phthalic acid (m-PA) from aqueous solution were investigated. It was found that the adsorption equilibrium data of these benzene carboxylic acids can be well fitted by both Langmuir and Freundlich models. But the adsorption capacity of the benzene carboxylic acids changes with the number and position of carboxyl groups on benzene ring. In general, ZLCF has high adsorption capacity to all benzene carboxylic acids investigated. The adsorption capacity of BA, o-PA, m-PA and p-PA was 0.4616, 0.5892, 0.4912 and 0.3138 mmol/g, respectively, when 10 ml of 6 mmol/L benzene carboxylic acid solution was adsorbed by 0.05 g ZLCF at 293 K. Furthermore, the studies of the adsorption kinetics indicated that the adsorption kinetics of BA was close to the pseudo-first-order rate model and thus the boundary diffusion would be the rate-controlling step. In contrast, the adsorption kinetics of o-PA, m-PA and p-PA can be well described by the pseudo-second-order rate model, which implies that the chemical adsorption should be the rate-controlling step.