Hydroxyapatite@cellulose@nZVI composite: Fabrication and adsorptive removal of doxycycline, Cr(VI) and As(III) from wastewater

Abstract

In this study, a biogenic nanocomposite (HAP@CL@nZVI) was successfully developed using hydroxyapatite derived from eggshell waste, cellulose, and green-synthesized nano zero-valent iron for the removal of doxycycline (DOX), Cr(VI), and As(III) from aqueous solutions. Under optimized conditions, HAP@CL@nZVI demonstrated high adsorption capacity, with pH playing a critical role in the process with peak adsorption occurring at pH 8 for DOX, pH 2 for Cr(VI), and pH 7 for As(III). Mechanisms involved electrostatic attraction, hydrogen bonding, and π-π interactions for DOX, while electrostatic interactions and surface complexation governed Cr(VI) and As(III) adsorption. The Langmuir isotherm model indicated monolayer adsorption processes, with maximum adsorption capacities of 74.07, 111.11 and 79.37 mg/g for DOX, Cr(VI), and As(III) respectively. Kinetic studies unveiled pseudo-first-order kinetics for DOX and pseudo-second-order kinetics for Cr(VI) and As(III). The study highlights strong regeneration potential of HAP@CL@nZVI, rendering it a sustainable, eco-friendly adsorbent for pharmaceutical wastewater treatment and toxic metal ion remediation.