A novel metal-free perylene-functionalized graphite adsorbent for efficient antibiotic removal from wastewater

Adsorption remains a widely utilized and effective technique for removing chemical contaminants from polluted water, and novel adsorbents are currently in the process of being developed. The presence of antibiotics residues in aqueous effluents is a potential concern due to their potential adverse effects on living organisms. In this work, perylene tetracarboxylic acid-functionalized expanded graphite (PTCA-EG) was synthesized as a metal-free adsorbent and its potential for efficient treatment of contaminated wastewater with cefalexin (CLX) antibiotic was studied. The experimental variables were modeled and optimized using central composite design (CCD) and response surface methodology (RSM) to maximize adsorption efficiency. In this regard, the contact time of 20 min, solution pH of 7.0, adsorbent dosage of 18 mg, and initial CLX concentration of 45 mg L^-1 were found to be the optimum conditions for adsorptive removal of CLX with a maximum efficiency of 99 ± 1.21%. In addition, the adsorption equilibrium data were well analyzed with isotherm, kinetic, and thermodynamic studies. The isotherm results revealed the adsorption process was favorable and took place on the heterogeneous surface. Moreover, the Langmuir maximum adsorption capacity (Q_max) was determined as 220.7 mg g^-1. Also, thermodynamic parameters revealed the spontaneity and endothermic nature of the adsorption process. The reusability studies demonstrated that the spent PTCA-EG can be easily regenerated through NaOH solution (0.01 mol L^-1) and reused for six cycles without any significant decrease in its adsorption efficiency. Also, the PTCA-EG showed excellent behavior in adsorptive removal of CLX in real water samples including river water (96.61 ± 1.82%) and hospital effluents (91.91 ± 3.41-93.69 ± 3.06%).