Biosynthesis, characterization, and utilization of rice husk nanosilica in the adsorption of heavy metals from simulated wastewater

With the rapidly rising industrial development around the world, the need for nanoparticles and wastewater treatment methods remains a significant issue for the preservation of the environment. Silica nanoparticles (SN) have recently been identified as potential nano-sized water treatment adsorbents. In this study, we employed silica nanoparticles (SN) as adsorbents to purify water. Rice husks (RH), a biomass agricultural solid waste resource, were used to create silica nanoparticles (SN). The produced silica nanoparticle was characterized using SEM, XRD, FTIR, TGA, TEM, zeta potential analysis, and nitrogen gas adsorption. Silica nanoparticles were presented with a crystallite size of 23.5 nm, with an XRD pattern, and a BET surface area of 529.2 m.2g−1. Additionally, the FTIR spectra were studied, and it was discovered that the presence of surface complexes, reaction, ion exchange, and electrostatic attraction mechanisms. Furthermore, silica nanoparticles were studied for wastewater treatment from Cd2+ and Pb2+ under various adsorption conditions. The Cd2+ and Pb2+ adsorption was investigated under various application settings, including dose adsorbent, pH, temperature, initial concentration of heavy metals, and shaking time. Cd2+ and Pb2+ adsorption onto SN matched PSO kinetic models and were suitably matched by the Elovich model. The Temkin and Langmuir isotherm models can accurately predict the equilibrium values for Cd2+ and Pb2+ adsorption on the SN. The Langmuir isotherm model indicated that silica nanoparticles exhibited maximum adsorption capacities of 37.91 mg/g for Cd²⁺ and 44.93 mg/g for Pb²⁺ ions, respectively. The adsorption process is both spontaneous and endothermic according to its thermodynamic properties. Reusability and desorption tests indicated that HNO3 is the most effective desorbing agent for Cd2+ and Pb2+, with 99 and 98 % efficiency, respectively. Whereas solid adsorbent can be recycled after seven adsorption/desorption cycles, Cd²⁺ and Pb²⁺ adsorption capacities decreased by only 7 % and 6 %, respectively.