Synthesis and Characterization of Biochar and Nano-Biochar Composites Derived from Biomass (Colutea cilicica) for the Removal of Cationic Dyes from Aqueous Solutions

Abstract

In this study, the removal of Methylene blue (MB) and Malachite green (MG) dyestuffs from aqueous solutions was investigated using biochar and iron-modified biochar derived from biomass (Colutea cilicica). Biochar was prepared by pyrolyzing biomass at 500 °C with a heating rate of 10 °C/min, and further modified with nanoscale zero-valent iron (nZVI) to obtain nZVI-biochar. The adsorption performance of both biochar and nZVI-biochar was systematically evaluated under varying experimental conditions, including solution pH, contact time, adsorbent dosage, and initial dye concentration. Equilibrium and kinetic studies were performed, along with thermodynamic analyses at different temperatures. The optimum pH for dye removal was determined as 7.0. Adsorption equilibrium was reached within 120 min, and the kinetic data were best described by the pseudo-second-order model. Equilibrium data fitted well to the Langmuir isotherm model. The maximum adsorption capacities were 70.67 mg/g (biochar) and 81.17 mg/g (nZVI-biochar) for MB, and 61.43 mg/g (biochar) and 83.13 mg/g (nZVI-biochar) for MG. Overall, the modified nZVI-biochar composite exhibited significantly enhanced adsorption capacity compared to unmodified biochar. The synthesized nano-biochar composite can be proposed as a potential alternative adsorbent for the removal of cationic dyes from wastewater.