Adsorption of cadmium and ciprofloxacin from aqueous solution by pretreated Bryophyllum pinnatum: equilibrium, kinetics and thermodynamic studies

Abstract

Several water bodies have been affected by potentially toxic elements and pharmaceutical derivatives. To eliminate these contaminants from the aquatic environment, wastewater treatment techniques must be developed. In this study, low cost Bryophyllum pinnatum (BP) was pretreated with acid and used as a promising adsorbent for cadmium ion (Cd²⁺) and ciprofloxacin (CIP) uptake from aqueous solution. The adsorption factors (pH, dosage and initial adsorbate concentration) were estimated after characterization of pretreated BP using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, N₂ adsorption/desorption and zeta potential analyses. Optimum adsorption was achieved at pH 11 using an adsorbent dosage of 0.25 g, with monolayer uptake capacities of 18.51 and 11.66 mg g⁻¹ for Cd²⁺ and CIP, respectively. The Freundlich and Temkin isotherms provided the best fit for Cd²⁺ and CIP uptake, respectively, with low error values. The uptake of Cd²⁺ and CIP on the surface of pretreated BP is best explained by pseudo-second order kinetics, signifying that chemisorption and intra-particle diffusion of the adsorbates on the surface sites occurred in three stages. The adsorption process occurred spontaneously in an endothermic manner based on thermodynamic evaluation. The extent of the reusability of pretreated BP was tested after five consecutive cycles, which further proved economic viability. The characterization and adsorption analysis demonstrated the dominant role of electrostatic attraction during Cd²⁺ and CIP removal, accompanied by pore filling, hydrogen bonding and hydrophobic interactions. The present work affirms that pretreated BP is promising for application in Cd²⁺ and CIP removal from aqueous media.