Biocarvão modificado com beta-ciclodextrina para remoção de surfactantes de meio aquoso

Abstract

Coffee husks constitute the primary residue of coffee production in Brazil, accounting for approximately 50% of the dry fruit mass. The utilization of coffee husks can be done through the production of biochar, which serves as an adsorbent material for the removal of environmental contaminants. Surfactants are a class of substances with unique properties found in almost all cleaning and self-care products. Due to their wide application, surfactants are present in large quantities in urban and industrial wastewater. If not properly treated, these wastewaters can have a negative impact on aquatic ecosystems. In this work, biochars were produced from coffee husks (either in their natural state or pre-treated with citric acid or NaOH) through pyrolysis at 400 °C for 1 hour, with a heating rate of 10 °C/min. The biochars were then functionalized with β-cyclodextrin using glutaraldehyde and epichlorohydrin as crosslink agents. The materials were characterized through infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), conductometric titration, and determination of the point of zero charge (PZC). Adsorption studies of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) were performed on the produced materials. FTIR and Raman results indicated that the materials exhibit low crystallinity levels and few surface functional groups. SEM analyses revealed that biochars produced from NaOH-treated coffee husks have enhanced porosity. Adsorption assays demonstrated that surfactant adsorption is pH-influenced and reaches equilibrium after a 24-hour contact period. Additionally, an increase in the adsorptive capacity of CPC for the functionalized biochars was observed, with a maximum experimental qe of 113 mg g-1 at pH = 7 and 25 °C. CPC adsorption was favored at high temperatures, suggesting an entropy-driven process. However, SDBS adsorption was ineffective in all evaluated materials.