Maize stalk-derived biochar modified with CuAl-layered double hydroxide for rapid methyl orange adsorption: parametric optimization, isotherm, kinetic and desorption studies

Concern over toxic dye contamination of water bodies has grown in recent times, threatening both the environment and public health. Herein, CuAl-layered double hydroxide (CuAl-LDH) loaded maize stalk biochar (CuAl-LDH@MSB) was synthesized through coprecipitation-impregnation at different Cu 2+ /Al 3+ molar ratios (2:1, 3:1 and 4:1) followed by pyrolysis at 600 o C for 1.5 h to facilitate the CuAl-LDH layers crystallization on biochar. The prepared adsorbents were characterized using SEM-EDX, BET, FTIR, XRD and pH pzc techniques. The CuAl-LDH@MSB composites’ adsorption behaviour was investigated using methyl orange (MO) as the target contaminant. The CuAl-LDH@MSB sample prepared at a 3:1 Cu 2+ : Al 3+ molar ratio (CuAl-LDH@MSB3:1) exhibited higher methyl orange (MO) adsorption efficiency than the composites prepared at Cu 2+ : Al 3+ molar ratio of 2:1 and 4:1. Optimization of MO adsorption onto CuAl-LDH@MSB3:1 using the Taguchi method determined optimum conditions (20 mg/L initial MO concentration, pH 6, adsorption time of 90 min and 0.75 g/50 mL adsorbent dosage), under which the composite removed 99.3% of MO from aqueous solution. Equilibrium adsorption data best fitted the Sips isotherm ( mg/g), suggesting heterogeneous-multilayer adsorption process. Kinetic data were effectively described by pseudo-first-order kinetic model ( ), indicating that the MO adsorption onto CuAl-LDH@MSB3:1 was mainly controlled by surface and physisorption mechanisms. Moreover, dye molecules were desorbed from MO-laden CuAl-LDH@MSB3:1 using H 2 SO 4 and NaOH as regenerants, and it was observed that aqueous NaOH desorbed nearly 70% of dye molecules from the spent adsorbent after the 4 th cycle, as compared to H 2 SO 4 solution that desorbed 57% of the adsorbed MO molecules from the spent adsorbent. The results demonstrated that CuAl-LDH@MSB3:1 possessed great potential as a cheap, sustainable and efficient adsorbent for removal of anionic dye from aqueous solution.