Assessment of adsorptive competition of two antibiotics removal from aqueous media onto activated watermelon seeds: experimental and theoretical study using DFT method

Activated Watermelon seeds (AC-WmS) were successfully used as adsorbent for the competition removal of two antibiotics Sulphamethazine (SMT) and Sulfamethoxazole (SMX) from aqueous media in single and binary systems. The effects of various parameters influencing the adsorptive competition of SMT and SMT, such as contact time, adorbent dose and pH on the adsorption extent were investigated and examined in a batch mode. The pH zero-pointcharge of AC-WmS-500 is pH(ZPC) = 5.8. The adsorption capacities are 97.8 mg/g and 109.25 mg/g for SMT and SMX, respectively. Equilibrium data were well represented by the Freundlich model for SMT and SMX in binary system. The q(max) of SMX in the single system was decreased from 97.8 to 35.16 mg/g. Theoretical study was made for the determination of the charge density on the sites of the reagents, the prediction of the electrophilic/nucleophilic character of the reagents, the prediction of the local reactivity of the reagents, the indices of local electrophily and of nucleophily, by the method of the density functional theory DFT/B3LYP, with the base 6-311 G (d, p) shows that the competitive adsorption between the two antibiotics were observed and it was noticed that SMT was favoured as well as being more electrophilic than SMX, and greater interaction with surface sites in the single and binary system with an removal efficiency forSMT and SMX of 94% and 85%, respectively. The theoretical results are in good accordance with the experimental data reported.