Adsorption of Acid Red 35 (AR35) dye onto Mandarin Biochar-TETA (MBT) derived from Mandarin peels

Abstract In this study, a new biochar was produced from mandarin peel residues by dehydration with 50% sulfuric acid followed by decoration with oxidation then reaction with TETA. The effect of the obtained new biochar on the ability to remove AR35 dye from the aqueous solution was investigated. The prepared Mandarin Biochar-TETA (MBT) was characterized by FT-IR, BJH, BET, SEM, DSC, TGA, XRD and EDX analyses. The optimum pH value for AR35 dye adsorption was determined as 1.5. The highest removal percentage of AR35 dye was 97.50% using 300 mg L−1 AR35 dye initial concentration and 2.5 g L−1 MBT dose. The MBT had a maximum adsorption capacity (Qm) of 476.19 mg g−1. The data obtained were analyzed with Langmuir, Freundlich, Tempkin, Dubinin-Radushkevich and Jovanovic isotherm models. In addition, the data obtained from these isotherm models were tested using different error functions (hybrid error function (HYBRID), average percent errors (APE), the sum of the absolute errors (EABS), Chi-square error (X2), the root mean square errors (RMS) and Marquardt's percent standard deviation (MPSD)) equations. The Dubinin-Radushkevich isotherm model was best fitted to the experimental data of MBT. Kinetic data were evaluated by pseudo-first-order (PFO), pseudo-second-order (PSO), elovich, intraparticle diffusion and film diffusion models. The adsorption rate was primarily controlled by a pseudo-second-order rate model with a good correlation (R2 > 0.99). The adsorption mechanism process of AR35 dye by MBT mainly involves the adsorption of anions via the electrostatic attraction forces that develop with the increase in the number of positively charged regions at acidic pH values. The results indicate that MBT is promising for the removal of AR35 dye from water and could be repeatedly used without significant loss of adsorption efficiency.