Fabrication of Dimensionally Stable Rice Husk Biochar Composites and Their Mechanistic Insights into Cu 2+ Adsorption

To address the challenges of dust emission and poor recoverability associated with conventional powdered biochar, a dimensionally stable and recyclable biochar composite (PCL–CMC@RHB) was fabricated using rice husk biochar (RHB) as the carbon matrix, polycaprolactone (PCL) as a binding polymer, and sodium carboxymethyl cellulose (CMC) as a pore-forming and co-binding agent. The structural morphology and adsorption mechanisms were systematically examined through scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The PCL–CMC coating significantly improved the mechanical integrity and interfacial compactness of RHB while preserving its intrinsic porosity and reactive surface chemistry. Kinetic analysis revealed that the Cu²⁺ adsorption process followed a pseudo-second-order model (R² ≈ 0.999), indicating chemisorption as the dominant mechanism. The optimized composite achieved a maximum Cu²⁺ adsorption capacity of 34.4 mg g⁻¹ and a removal efficiency exceeding 96 %, comparable to that of pristine RHB (35.8 mg g⁻¹, ≈ 97 %). These results confirm that polymer incorporation enhanced structural stability without compromising adsorption performance. Moderate PCL–CMC loadings optimized both accessible surface area and reactive site density, maximizing Cu²⁺ uptake and recyclability. FTIR spectra further demonstrated the formation of stable Cu–O coordination complexes through surface complexation and ion-exchange reactions. This study establishes a scalable strategy for engineering dimensionally stable biochar composites that combine high adsorption efficiency, mechanical durability, and environmental reusability—offering a sustainable platform for heavy-metal remediation in water and soil systems..