Adsorption activity of spent coffee ground biochar for the removal of Vivizole Red 3BS dye from aqueous solution

Abstract

Abstract Spent coffee ground (SCG) is rich in carbon, and slow pyrolysis can convert biomass into biochar that can be used as an adsorbent to remove dyes. In one-step carbonization and activation of SCG, iron (III) chloride and K2CO3 were used as a catalyst and solid-state activator, respectively. The predictive model for the removal of the dye by the activated SCG biochar was evaluated through response surface methodology- central composite design (RSM-CCD). ANOVA result analysis showed that among the model terms, the effect of pH was the most significant in removing the Vivizole Red 3 BS 150 % (VR 3BS) dye. The optimum values suggested by the CCD were an initial dye concentration of 20 mg/L, pH 3, an adsorbent dose of 0.5 g per 100 mL, and a contact time of 60 min, where the optimum removal of the dye was 94 %. The optimum conditions were validated using synthetic and textile wastewater, and the percent removals of the VR 3BS dye by the activated SCG were 96% and 90 %, respectively. The dye removal efficiency of activated SCG biochar was more significant than that of commercial activated carbon. The Langmuir model best described the adsorption isotherm. Adsorption kinetic data fitted well to the pseudo-second-order model. Both intraparticle and film diffusions affected the dye's adsorption rate. The thermodynamics study has shown that the adsorption process was a spontaneous, less random, exothermic process governed by a physical sorption mechanism. Thermal regeneration of the exhausted biochar improved VR 3BS dye removal efficiency.