Biocarvão de borra de café pelo processo hidrotermico com níquel (ii) ou cobre (ii) como precursor de carvão ativado

Abstract

Brazil, the world's largest coffee producer, generates large volumes of coffee grounds as waste, approximately 450 kg of dry grounds per ton of coffee processed. This work proposes the reuse of this byproduct as a carbonaceous precursor for the production of hydrochars by hydrothermal carbonization (HTC) catalyzed by metal ions (Ni2+ and Cu2+) and, subsequently, of activated carbon by physicochemical activation. The HTC process was conducted in the absence and presence of metal ions (Cu2+ and Ni2+), with the aim of evaluating their catalytic influence. The results demonstrated that HTC promoted the formation of carbonaceous and polyaromatic structures, with higher yields in hydrochars prepared with metal ions (Cu2+ and Ni2+), highlighting the catalytic effect of these ions in the hydrolysis, dehydration, and repolymerization reactions of the biomass. After physicochemical activation, the carbons presented estimated surface areas of 801 m2·g−1 (AC-Cu) and 729 m2·g−1 (AC-Ni), while the reference carbon Alpha-W810, evaluated by the same method, exhibited an area of 502 m2·g−1. In the methylene blue isotherms, the AC-Cu and AC-Ni carbons exhibited maximum adsorption capacities of 415 mg·g−1 and 378 mg·g−1, respectively, values higher than those obtained for the Alpha-W810 carbon (260 mg·g−1) under the same conditions. The isotherms were best fitted by the Langmuir model, confirming adsorption onto homogeneous monolayers, while the kinetics followed the pseudo-second-order model, suggesting a predominance of chemisorption. In summary, metal ion-catalyzed HTC proved to be an efficient strategy and, when combined with physicochemical activation, demonstrated the potential to produce activated carbons with high adsorptive performance, suitable for applications as adsorbents in the treatment of aqueous effluents and environmental remediation.