Functionalized adsorbents prepared from fruit peels: Equilibrium, kinetic and thermodynamic studies for copper adsorption in aqueous solution

Abstract

Biosorbent preparation of agro-industrial wastes (orange and pineapple peels) was studied in order to improve the adsorption capacity for Cu(II). The maximum adsorption capacity (163 mg g−1) was obtained with the biosorbent prepared from orange peels by a physical-chemical process: a vacuum drying process (DIC: Instant Controlled Pressure Drop) followed by a citric acid chemical treatment; these results signify an increase in the order to 4.19 times of adsorption capacity (300%) comparing with the peels without modification. DIC treatment increases the porosity and active sites on the peels surface; FTIR studies after chemical treatment showed only signals attributed to ROH and RCOOH functional groups, present on the biosorbents surface. Characterization of the biosorbents from fruit peels was carried out before and after adsorption of Cu(II), in order to describe the adsorption mechanism. As a result, Cu(II) adsorption on the modified fruit peels could be associated with the interaction between Cu(II) and R-COO- groups on their surface due to physisorption phenomena with an associated heat of adsorption in the order of −13.78 ± 2.10 kJ mol−1. Thus, the proposed process enhance the adsorbent properties of the fruit peels; these biosorbents can be prepared in order to be selective for pollutant removal in water treatment processes.