Removal of methylene blue from wastewater by maize cob-derived functionalized biochar adsorbents: synthesis, characterization, and batch adsorption studies for the evaluation of modelling and mechanism

Abstract

Wastewater treatment using low-cost adsorbents developed from indigenous agro-waste materials via eco-friendly and economical methods has garnered significant attention to protect the environment from pollution. Due to the rapid industrialization and urbanization, a huge amount of wastewater is discharged from several large-, small-, and medium-scale industries, which is loaded with several hazardous toxicants, resulting in severe damage to the ecosystem and public safety. This work investigated the adsorptive elimination of MB dye from wastewater by developing a maize cob-derived functionalized biochar and applying a batch adsorption study. Meanwhile, multifunctional biosorbents, i.e., functionalized biochar (FBC) adsorbents, were produced using pyrolysis and the EIPS technique from an innovative and beneficial source, namely, maize (Zea mays) cob, after harvesting the edible parts of the plant. The influential parameters, like the initial concentration and pH of wastewater, the dosage of adsorbents, operational time, and temperature, were properly optimized during the real-time experiments. Additionally, the considered samples were characterized by FESEM, EDX, FTIR-ATR spectroscopy, XRD, and UV-vis-NIR analysis. The experimental adsorption data were evaluated and interpreted by applying several well-established mathematical models. For adsorption isotherm analysis, the Langmuir, Temkin, and Freundlich models were applied, whereas the pseudo-first-order and pseudo-second-order models were applied for the evaluation of the reaction kinetics. Moreover, to determine the thermodynamic nature, the Gibbs energy (ΔG), entropy (ΔS), and enthalpy (ΔH) of the experimental adsorption were calculated and analyzed for a better understanding of the actual sorption behavior of the applied FBC regarding the selective separation of MB dye from wastewater. It is noteworthy that the maximum adsorption efficiency and removal percentage were found to be around 126.91 mg g−1 and around 99.99%, respectively. The maximum R2 value was found to be around 0.999 for the Temkin and pseudo-second-order models. The negative ΔG value around −9.224 kJ mol−1 and ΔH around −75.034 kJ mol−1 indicated that the reaction was spontaneous and exothermic in nature.