Development and application of coffee husk-based polyaniline composite (CF@PANi) for enhanced ammonium removal from aqueous solutions

Abstract

This study focuses on the development and evaluation of a novel composite material, designated as CF@PANi, which integrates coffee husk and polyaniline for the purpose of ammonium adsorption from aqueous solutions. The composite was synthesized under optimized conditions and characterized using various analytical techniques. The results from SEM and EDS indicated significant structural and compositional changes following the adsorption process, including an increase in porosity and a notable rise in nitrogen content from 6.35% to 17.24%, thereby confirming effective ammonium uptake. BET analysis revealed that the synthesized composite possesses a mesoporous structure with a surface area of 7.0642 m² g⁻¹. FTIR spectroscopy identified active functional groups, such as amine (–NH, –NH₂) and hydroxyl (–OH), critical for adsorption. Batch adsorption experiments were conducted to assess the effects of various parameters, including pH, adsorbent dosage, contact time and initial ammonium concentration, on adsorption performance. The optimal conditions for ammonium adsorption were determined to be at a pH of 7, with a PANi : CF ratio of 1 : 2 and a contact time of 40 min, achieving a maximum adsorption capacity (q_e) of 25.05 mg g⁻¹, as predicted by the Langmuir isotherm model. Kinetic studies indicated that the adsorption process follows a pseudo-second-order model. The mechanistic analysis highlighted key processes involved in ammonium adsorption, including electrostatic attraction, cation exchange, surface complexation, physical adsorption, and cation–π interactions.