Valorization of Tea Dust and Coffee Grounds for Efficient Removal of -Malachite Green from Aqueous Media.

The textile industry ranks among the most water- and dye-intensive sectors, contributing significantly to global water pollution. Textile effluents are rich in persistent synthetic dyes that are non-biodegradable and hazardous to aquatic ecosystems. Among these, malachite green (MG), a widely used cationic dye, poses severe eco-friendly and health risks due to its harmfulness, mutagenicity, and long-term stability. Addressing its removal using low-cost, sustainable materials has become a pressing environmental challenge. This study presents a novel approach by valorizing agro-industrial wastes—namely tea dust (TD) and coffee grounds (CG)—as eco-friendly, magnetically separable adsorbents used for the efficient adsorption of MG dye. The raw materials were modified through two activation techniques (oven and microwave heating), followed by magnetization, yielding eight engineered sorbents: TD-O, TD-M, CG-O, CG-M, and their magnetic counterpart’s m-TD-O, m-TD-M, m-CG-O, and m-CG-M. Comprehensive characterization was performed using DLS, FTIR, TGA, and XRD, while morphological and topographical changes were monitored via SEM and AFM before and after adsorption. Batch adsorption studies assessed the influence of pH, contact time, adsorbent dose, initial dye concentration, and temperature. Results revealed superior dye removal efficiency by magnetic composites, with adsorption capabilities extending from 52.19 to 75.80 mg/g and removal efficiencies of 91.2% to 98.2% under optimal conditions (pH 2, 50 ppm, 0.08 g dose, 120 min). Kinetic data followed the pseudo-first-order model, and equilibrium behaviour aligned with the Freundlich isotherm, indicating multilayer adsorption. The composites also demonstrated potent antibacterial activity against Staphylococcus aureus and Escherichia coli, and maintained high performance over five reuse cycles. These findings underscore the practical potential of green, magnetized sorbents for cost-effective wastewater treatment and support their integration into circular economy strategies.