Cd(II) adsorption from aqueous solution using pristine and activated Melocanna baccifera biochar: isotherm and kinetics studies

Bamboo biochar is effective at adsorbing a wide range of heavy metals and is relatively stable under environmental conditions. Cadmium contamination in aquatic systems poses a significant risk to environmental and human health, creating a need for efficient, low-cost adsorbents for water treatment. In this study, pristine and chemically activated biochars derived from M. baccifera bamboo were evaluated for Cd(II) removal from aqueous solution. The objective was to investigate the effect of chemical activation on adsorption performance and to elucidate the adsorption mechanisms using equilibrium and kinetic analyses. Biochar was activated using various concentrations of potassium hydroxide (KOH) and phosphoric acid (H 3 PO 4 ). Among the tested methods, activation with 60% KOH demonstrated the highest adsorption efficiency, leading to its selection for further characterization and adsorption studies. Batch experiments revealed that the adsorption process is significantly influenced by pH, with optimal removal observed at pH 5. The equilibrium data were best represented by the Langmuir isotherm, indicating maximum adsorption capacities of 15.15 mg/g for pristine biochar and 24.39 mg/g for activated biochar. Kinetic analysis indicated that the adsorption kinetics conform to the Pseudo-second-order model, with Intraparticle diffusion and liquid-film diffusion identified as contributing factors in the rate-controlling steps. Fourier-transform infrared (FTIR) spectroscopy analysis showed shifts in the O-H, C=O, and C-O functional groups. These changes suggest that surface complexation and ion exchange are the primary mechanisms involved in the binding of cadmium ions. The results of this study demonstrate that KOH activation significantly improves the physicochemical properties and adsorption performance of bamboo biochar. This research highlights the potential of activated biochar derived from Melocanna baccifera as a sustainable and locally available adsorbent for the removal of cadmium from contaminated water. This also supports its potential application in cost-effective water purification systems.