Low-cost agricultural wastes (orange peels) for the synthesis and characterization of activated carbon biosorbents in the removal of pharmaceuticals in multi-component mixtures from aqueous matrices

Abstract

In recent years, bio-based carbons derived from environmentally friendly biomass materials have received considerable attention because of their abundance, easy processability, tunable surface properties and relatively low cost. Herein, a simple, less hazardous and low-cost method for the synthesis of ultrahigh surface area activated carbon material was proposed using orange peels as a carbon source. Within this context, three different biosorbents were synthesized: activated carbon samples derived from orange peels after activation with (i) phosphoric acid by pyrolysis at 450 °C (ORPs-H3PO4(450)) and (ii) at 650 °C (ORPs-H3PO4(650)), as well as (iii) after activation with potassium hydroxide at 450 °C (ORPs-KOH(450)). Characterisation and morphology of all materials has been conducted using various characterization techniques as FTIR, BET and SEM. The adsorption capacity was evaluated in a multi-component fashion for a mixture of five NSAIDs, namely diclofenac (DCF), ibuprofen (IBF), ketoprofen (KPF), salicylic acid (SAL) and paracetamol (PAR). The evaluation of the adsorption was achieved by investigating several variables like the effect of the solution’s pH, of contact time (kinetic modelling) and of the initial pharmaceuticals’ concentration. Acidic pH (pH = 2) appeared to be the optimal pH value while the pseudo-second order kinetic model and the Langmuir model demonstrate better fitting to the adsorption kinetics and isotherms respectively. Increase of temperature from 25 to 35 °C appears to have a positive effect on the adsorption capacity and the negative values of ΔG0 indicated that all target pharmaceuticals were adsorbed spontaneously to the synthesized biosorbents. Aqueous eluents with different pH values were used to accomplish desorption while pH = 6 appears to the optimum pH value for the desorption of the target pollutants.