Efficient cadmium sequestration from water using cotton husk biochar and copper oxide nanocomposite: adsorption...

Water contamination with hazardous heavy metals, particularly cadmium (Cd) poses significant environmental and health risks due to its toxicity, persistence, and carcinogenic potential. This study evaluates the efficacy of cotton husk-derived adsorbents: natural cotton husk (CHN), cotton husk biochar (CHB), and a copper oxide nanocomposite (CHNC) for Cd removal from aqueous solutions. The adsorbents were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analysis, revealing distinct functional groups, surface morphologies, and porosity profiles. Batch adsorption experiments examined the effects of initial Cd concentration (1.25-20 mg/L), adsorbent dosage (0.5-1.5 g/100 mL), and contact time (15-120 min) under controlled pH (6.0) and temperature (26 ± 1°C). Results demonstrated that CHNC exhibited superior Cd removal efficiency (> 90%) due to enhanced surface area (21.174 m²/g) and multifunctional adsorption mechanisms, including electrostatic attraction and chemisorption. CHB showed intermediate performance (80-90%), while CHN exhibited the lowest efficiency (60-75%). Kinetic studies revealed that adsorption followed pseudo-second-order kinetics (R² > 0.99), indicating chemisorption as the dominant mechanism. Equilibrium data were well-described by the Freundlich isotherm (R² = 0.99), suggesting heterogeneous multilayer adsorption. Comparative analysis with previous studies highlights the cost-effectiveness and high adsorption capacity of cotton husk-based materials, particularly CHNC as compared with conventional adsorbents. This study underscores the potential of agricultural waste utilization for sustainable water treatment, offering a viable solution for Cd remediation in contaminated water systems.