Caffeine removal from synthetic wastewater using magnetic fruit peel composites: Material characterization, isotherm and kinetic studies

Abstract This work investigated the adsorption capacity of banana and orange peels, magnetite and their corresponding magnetic composites in the removal of caffeine from synthetic wastewater. The characteristics of the adsorbents were studied using proximal analysis, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Brunauer, Emmett and Teller (BET) analysis and X-ray diffraction. Batch adsorption tests were conducted to determine the influence of the adsorbent dose (0.5 and 10.0 g/L), contact time (5 – 180 min) and initial caffeine concentration (10 – 50 mg/L) in the caffeine removal. The fittings of the experimental data to the pseudo first order, pseudo second order, Elovich, and diffusion kinetic models, as well as to the Langmuir, Freundlich and Sips isotherm models were also studied. The use of magnetic peels improved around 1.7 times the adsorption capacity of peels. The effective doses were 3.5 g/L of orange peel, 9.5 g/L of banana peel, 2.5 g/L of orange peel composite, 5.5 g/L of banana peel composite, and 5 g/L of magnetite, achieving caffeine removal efficiencies of 95.5 ± 0.3%, 90.5 ± 0.5%, 93.6 ± 0.2%, 89.2 ± 0.01% and 54.8 ± 0.8%, respectively. The adsorption using the peels, magnetite, and their magnetic composites better fitted the pseudo first order kinetic model and the Langmuir and Sips isotherm models.