Spent coffee activated carbon via microwave-induced H3PO4 activation for brilliant green dye removal: statistical parametric optimization

Herein, spent coffee (SPC) was converted to activated carbon (SPCAC) via microwave-assisted H₃PO₄ activation. The microwave power was set at 600 W and irradiation time 15 min with an impregnation ratio of precursor/chemical activator (1-g SPC:2-mL H₃PO₄). The surface property and functionality of SPCAC was investigated by several analytical techniques that include gas adsorption (BET), SEM, XRD, FTIR, and pH_pzc. The applicability of the SPCAC adsorbent was evaluated for the removal of cationic brilliant green (BG) dye from aqueous solution. Thus, the adsorptive removal process was optimized using the Box-Benken design (BBD) to assess key adsorption parameters that include SPCAC dosage (0.05–0.15 g/100 mL) coded as (A), solution pH (4–9) coded as (B) and contact time (30 to 360 min) coded as (C). The analysis of variance (ANOVA) test shows the significant interaction between the key adsorption parameters (AB, AC, and BC). From BBD results, optimal BG dye removal (99.6%) was recorded at 0.15 g of SPCAC dose, pH 6.5, and a 30-min contact time. The adsorption mechanism of BG dye onto SPCAC was assigned to various factors that include pore filling, electrostatic forces, π-π stacking, and H-bonding. Thus, the finding of this research shows the potential benefits of converting spent coffee into active carbon by using a convenient thermochemical method with practical application for the removal of toxic cationic dyes from aqueous media.