Using basic parameters to evaluate adsorption potential of alternative materials: example of amoxicillin adsorption by activated carbon produced from termite bio-waste

Abstract

The minimum set of parameters that can be used to assess the adsorption capacity of activated carbon (AC) produced from termite bio-waste was determined. Three types of AC were prepared: AC600 at 600 °C, MAC600 at the same temperature and impregnated with FeCl3, and AC800 at 800 °C. The influence of the solution pH on the adsorption, adsorption kinetics, isotherms and thermodynamic parameters was considered to characterize the amoxicillin (AMX) adsorption process. The AC materials had surface areas (m2 g−1) of approximately 248.8 for AC600, 501.6 for AC800 and 269.5 for MAC600, with point of zero charge (pHPZC) values of 8.3, 7.5 and 1.7, respectively. A time period of 30 min was chosen for the adsorption kinetics, which was best represented by the pseudo-first-order model for AC600, the intraparticle diffusion model for AC800 and the pseudo-second-order model for MAC600. Regarding the isotherms, a maximum adsorption of 23.4 mg g−1 was found for AC800. In general, the thermodynamic parameters demonstrated a non-spontaneous process. It seems that the medium conditions, the adsorbate and adsorbent characteristics, and the Gibbs free energy are the most important parameters to be considered in a preliminary assessment of the adsorption efficiency of specific adsorbent/adsorbate pairs.