Efficient removal of cadmium ions from wastewater using metal oxide-doped sunflower stem-generated biochar: sorption mechanism and performance

Cadmium (Cd) contamination poses severe environmental and public health risks, necessitating effective and sustainable remediation strategies. This study investigates the potential of sunflower stem-derived biochar, functionalized with nickel oxide (NiO) and cobalt oxide (CoO) nanoparticles, as an advanced sorbent for Cd(II) removal from aqueous solutions. The biochar was synthesized via pyrolysis at 300 degrees C, and it was then modified through dispersion of two metal oxide nanoparticles individually using an ultrasound-assisted method, enhancing its surface functionality and structural integrity. Characterization techniques, including X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy fitted with energy-dispersive X-ray spectroscopy (SEM-EDX), confirmed the formation of highly porous, mesoporous structures with well-dispersed metal oxide nanoparticles. Sorption experiments demonstrated optimal Cd(II) removal under pH 6.0, contact time 120 min, and a sorbent dose of 4.0 g/L, yielding maximum sorption capacities of 5.7, 11.0, and 16.3 mg/g for blank biochar, NiO-doped biochar, and CoO-doped biochar, respectively. Sorption process followed pseudo-second-order kinetics, the Langmuir isotherm model, and spontaneous exothermic removal as detected via thermodynamic analysis. Notably, CoO-doped biochar retained 89.8% efficiency over five regeneration cycles, highlighting its recyclability and potential for long-term application. Compared to previously reported sorbents, the developed metal oxide-doped biochars exhibited superior selectivity, stability, and regeneration capacity, making them promising candidates for scalable industrial wastewater treatment. This study contributes to advancing biochar-based sorbents as cost-effective, environmentally sustainable solutions for heavy metal remediation.