Sustainable high-efficiency removal of cationic and anionic dyes using new super adsorbent biochar: performance, isotherm, kinetic and thermodynamic evaluation

Abstract

In the age of modernity, biochar deserves special attention as an environmentally friendly material in the field of adsorption owing to its innocuous nature, longevity, convenience, pH-dependent active surface, and non-toxicity. In this study, a super porous, non-toxic, green adsorbent was developed using a Borassus flabellifer raw seed hydrogel as a prospective natural sorbent for cationic and anionic dye elimination. The impact of carbonization temperature (350 and 700 °C) on chemical composition, crystallinity, and morphology was assessed employing a series characterization of methods. Furthermore, the effects of key parameters including preliminary dye concentration, pH, adsorbent dosage, and time were analyzed and optimized. The crude biochar exhibits an 80.34 m² g⁻¹ specific surface area and astonishing adsorption efficiency of 10 596 (pH ∼10) and 7095.43 (pH ∼6) mg g⁻¹ for malachite green (MG) and Congo red (CR) removal respectively. The highest removal efficiency of 100% and 92% was obtained for MG and CR removal at the lowest concentration of 10 mg L⁻¹. Six isotherms including Langmuir, Freundlich, Elovich, Halsey, Harkins–Jura, and Temkin were engaged to probe the equilibrium dynamics of MG and CR dye adsorption and the characteristic parameters. The Langmuir model yielded the finest fit to empirical results with R² ≈ 0.999. Other isotherm models fit the adsorption data in the following order Halsey = Freundlich (R² > 0.98) > Elovich (R² > 0.97) > Temkin (R² > 0.95) > Harkins–Jura (R² ≈ 0.6). The kinetic data were analyzed using the pseudo-first order, pseudo-second order, Elovich, and Bangham models. The adsorption kinetic data were discovered to be in good agreement with the pseudo-second-order model (R² = 0.999) and the rate of the adsorption process is predominantly controlled by pore and liquid film diffusion. The newly synthesized virgin biochar in this study could be perceived as a low-cost and promising eco-friendly bio-sorbent without any secondary by-product for the elimination of MG and CR from industrial wastewater.