Modified and unmodified Banana Peel biochars for simultaneous and efficient adsorption of Procaine penicillin from wastewater. Isotherm studies

Abstract

The widespread presence of antibiotics in wastewater poses serious environmental and public health risks due to their persistence and contribution to antimicrobial resistance. This study evaluates the adsorption performance of unmodified banana peel biochar (BPB) and aluminum/zinc oxide–modified banana peel biochar nanocomposite (AZB) for the removal of procaine penicillin (PP) from aqueous solutions. The adsorbents were synthesized via controlled pyrolysis and metal-oxide modification, and characterized using FTIR, SEM–EDX, and TEM to elucidate their surface chemistry, morphology, elemental composition, and nanoscale features. SEM revealed that BPB possesses a relatively smooth and compact carbonaceous surface with isolated pores, whereas AZB exhibits a highly roughened, fibrous, and tubular Al₂O₃-decorated architecture, enhancing surface area and adsorption site accessibility. EDX confirmed successful Al₂O₃ incorporation (5.84 wt% Al) alongside diverse metallic (Fe, Ag, Ca, K, Na) and non-metallic (C, O, Si, S) elements, supporting multiple adsorption mechanisms. TEM analysis showed nanosized particles ranging from 7–98 nm, with an average particle size of ~9 nm, indicating a high surface-to-volume ratio favorable for adsorption. Batch adsorption studies examined the effects of solution pH (2–9), adsorbent dosage (0.005–0.15 g), and initial PP concentration (10–200 mg L⁻¹) at 303 K. Maximum adsorption occurred at pH 9, with capacities of 222.22 mg g⁻¹ for BPB and 1428.57 mg g⁻¹ for AZB, demonstrating the superior performance of AZB across all conditions. Equilibrium data best fitted the Langmuir isotherm model (R² > 0.86), indicating monolayer adsorption on energetically favorable sites. FTIR analysis confirmed that adsorption involved electrostatic attraction, ion exchange, hydrogen bonding, and surface complexation. The markedly enhanced performance of AZB is attributed to its structurally complex surface, nanoscale particle distribution, and chemically diverse functional groups, including Al–O sites. Overall, metal-oxide-modified banana peel biochar represents a low-cost, sustainable, and highly effective adsorbent for pharmaceutical contaminants, with strong potential for practical wastewater remediation applications.