Zn-Al layered double hydroxide supported on waste cow dung-derived biochar as a highly efficient adsorbent for anionic dye removal from contaminated water.

In this study, Zn-Al-SO LDH-functionalized biochar was fabricated using the co-precipitation method. The biochar was synthesized from waste cow dung using a low-temperature pyrolysis process (300 °C). The materials were fully characterized by TGA, FTIR, EDS, SEM, and XRD analysis. Then, a comparative study was performed to investigate the adsorption capacity of the materials against an anionic dye (i.e., methyl orange (MO)). The LDH-functionalized biochar demonstrated high adsorption capacity (400 mg/g in 120 min, at pH 5) compared to the raw biochar (212 mg/g in 120 min, at pH 5). The effect of various adsorption parameters (e.g., pH of the dye solution, temperature, initial concentration, adsorbent dosage, and contact time) was investigated. The adsorption of MO on LDH-functionalized biochar followed the Freundlich isotherm and pseudo-second-order kinetics, while the raw biochar followed the Langmuir isotherm and pseudo-second-order kinetics. The thermodynamic data indicated the endothermic nature of adsorption and an increase in the degree of randomness during adsorption. The enhanced adsorption capacity of the Zn-Al LDH-functionalized char was attributed to the synergistic effect of the surface adsorption into the porous biochar matrix, interlayer adsorption, and ion exchange capacity of the LDHs. Therefore, modification of waste cow dung-derived biochar with Zn-Al LDH can be a promising approach to fabricate a highly efficient adsorbent for toxic dyes from wastewater.