Development of Coconut Shell Derived Nanobiochar as High-Efficient Adsorbent for Removal of Congo Red and Malachite Green from Wastewater

This study presents an innovative approach for the efficient removal of Congo red (CR) and malachite green (MG) dyes from wastewater using coconut shell-derived nanobiochar (NBC). The NBC was synthesised via a two-step process involving controlled pyrolysis, KOH activation and ball milling to achieve nanoscale dimensions, thereby enhancing its adsorption performance. The resulting NBC demonstrated exceptional dye removal capabilities, with maximum adsorption capacities of 220 mg g-1 for MG and 140 mg g–1 for CR under optimal conditions. Comprehensive characterisation using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS) confirmed the high surface area (400 m2 g–1), negative zeta potential (-30.8 mV) and superior dispersion stability of NBC material, which are essential for efficient dye adsorption. The adsorption kinetics were well-described by the pseudo-second-order model suggesting that chemisorption is the predominant adsorption mechanism. Thermodynamic analysis indicated that the adsorption process is both spontaneous and endothermic. These findings highlight the potential of NBC as a cost-effective, scalable and sustainable adsorbent for dye-laden wastewater treatment. The study also demonstrates the feasibility of utilizing coconut shell waste as a renewable biomass resource, contributing to environmental remediation while promoting circular economy practices.