Removal of Cr (VI) from synthetic effluents using hydrochar from waste açaí (Euterpe precatoria Mart.) seeds as a low-cost biosorbent

ABSTRACT Chromium (Cr) is a common contaminant in aquatic ecosystems, and in its hexavalent form (Cr (VI)) can cause serious risks to human health. This study utilized açaí waste to prepare a novel hydrochar (AWR) for Cr (VI) removal. AWR was characterized by Boehm titration, point of zero charge, infrared spectroscopy, thermogravimetric analysis, specific surface area measurement, scanning electron microscopy, and elemental analysis. A 23 factorial design examined the influence of key factors (pH, hydrochar mass, and Cr (VI) concentration). Results showed that acidic functional groups predominate on the surface of AWR. Under optimal conditions (pH = 2, hydrochar mass = 0.150 mg, and solution concentration = 150 mg L−1), Cr (VI) removal exceeded 96% with maximum adsorption capacity (Qmax) = 20.60 mg g−1 at 35°C. Adsorption kinetics followed a pseudo-second-order model, and the Tenkin isotherm best described the data. Thermodynamic analysis indicated that Cr (VI) adsorption is spontaneous and endothermic. This study demonstrated that AWR is a novel, effective, and cost-effective adsorbent for removing Cr (VI) from water environments.