Co3O4/activated carbon nanocomposite derived from Hura crepitans biomass for enhanced adsorptive removal of some heavy metals from dyeing wastewater

In this study, a sustainable nanocomposite adsorbent was developed by integrating activated carbon (AC) derived from Hura crepitans biomass with green-synthesized Co 3 O 4 nanoparticles for the efficient removal of heavy metals from dyeing wastewater. The activated carbon was produced via carbonization at 600 °C followed by HNO 3 activation, while Co 3 O 4 nanoparticles were synthesized using Hura crepitans extract and subsequently immobilized onto the carbon matrix through a wet impregnation approach. The characterization using XRD, HRSEM, EDX, HRTEM, and SAED confirmed the successful formation of a porous Co 3 O 4 /AC nanocomposite with uniformly distributed nanoparticles and well-developed surface morphology. Batch adsorption studies were conducted to evaluate the removal performance of Cr, Cu, Cd, and Fe ions under varying contact times (0–30 min), adsorbent dosages (0.2–0.7 g), and temperatures (30–80 °C). The Co 3 O 4 /AC nanocomposite exhibited markedly superior adsorption efficiency compared with pristine activated carbon and Co₃O₄, achieving complete removal (100%) of Cr at an optimal adsorbent dosage of 0.6 g. The maximum adsorption capacities were 78.52, 69.54, 64.37, and 72.18 mg g −1 for Cr, Cu, Cd, and Fe, respectively. Kinetic modeling indicated that the adsorption process followed the pseudo-second-order model, while equilibrium data were best described by the Langmuir isotherm model (R 2 > 0.98), suggesting that chemisorption and monolayer adsorption dominated the uptake mechanism. Thermodynamic analysis further revealed negative Gibbs free energy values, confirming the spontaneous and thermodynamically favorable nature of the process. In addition, the nanocomposite maintained appreciable performance over multiple adsorption–desorption cycles, demonstrating good reusability. Unlike previous studies that predominantly focused on single-metal systems or dye degradation, the present Co 3 O 4 /AC nanocomposite demonstrated efficient simultaneous removal of multiple heavy metals from real dyeing wastewater. This enhanced performance is attributed to the synergistic interaction between the high surface area and functional groups of activated carbon and the redox-active Co 3 O 4 nanoparticles, which collectively provide multiple adsorption pathways and binding sites for metal ion sequestration.