Isotherm, Kinetics, and Optimization Modeling of Cr(VI) Ions and Methylene Blue Dye Adsorption from Water by an Aminobiochar Hydrogel

Abstract This work presents a novel hydrogel produced from a newly manufactured aminobiochar with a high adsorption capacity for the removal of various pollutants from water. This study investigates the adsorption of Cr (VI) ions and methylene blue (MB) dye using a fabricated aminobiochar hydrogel (ABHG) synthesized from orange peels via microwave-assisted sulfuric acid activation, followed by oxidation, amination, and hydrogel formation. The ABHG exhibited a high surface area and diverse functional groups, confirmed by BET, SEM, FTIR, and TGA analyses. The FTIR analysis shows the presence of C–H, C≡C, C=C, C=O, and SO3 groups on the surface of the prepared hydrogel adsorbent. Under optimal conditions (initial concentration of 25 mg/L for both MB dye and Cr (VI) ions, contact time of 90 min for MB dye and 180 min for Cr (VI), pH 7.2 for MB dye and 1.04 for Cr (VI), and temperature 25 °C), maximum removal efficiency of both contaminants was achieved. Optimal adsorption experiments demonstrated maximum capacities of 476.19 mg/g for MB dye and 1250.00 mg/g for Cr (VI) ions based on the Langmuir isotherm model. Kinetic analysis showed MB dye adsorption followed a pseudo-second-order model, whereas Cr (VI) adsorption fitted a pseudo-first-order model. Using response surface methodology (RSM), the highest removal efficiencies were achieved with 0.958 g ABHG for 59.78 mg/L Cr (VI) and 1.91 g ABHG for 27.41 mg/L MB dye. Artificial neural network (ANN) modeling further validated these findings, confirming the potential of ABHG as an effective adsorbent for wastewater treatment.