Adsorption of heavy metal ions and organic pollutants from refining wastewater by magnetically synthesized silver nanoparticles coated with graphene oxide

The release of heavy metals and organic pollutants from industrial, agricultural, and domestic sources presents a serious threat to water bodies and ecosystems. Removing contaminants from refinery wastewater is essential for protecting water quality and the environment. This study developed silver nanoparticles using Saccharomyces cerevisiae in a magnetic field, which were subsequently coated with graphene oxide (GO) to create an effective adsorbent. The beads have been tested for their effectiveness in removing heavy metals such as lead, mercury, and cadmium, as well as organic contaminants like naphthalene, phenol, and fluorene from wastewater. At an optimal pH of 7, a contact time of 6 h, and a temperature of 298 K, the as-developed Ag-GONA beads exhibited maximum adsorption capacities of 326.77 mg/g for lead Pb, 300.37 mg/g for mercury Hg, 219.13 mg/g for cadmium Cd, 71.93 mg/g for naphthalene, 67.77 mg/g for fluorene, and 58.11 mg/g for phenol. Kinetic analysis suggested that the process involved chemisorption following a pseudo-second order (PSO) mechanism, while equilibrium data were well described by the Langmuir isotherm. Adsorption took place via hydrogen bonding, pore filling, and electrostatic attraction. The Ag-GONA beads showed remarkable reusability, with the removal rate of Pb(II) decreasing from 99.9% to 78% after six cycles. In contrast, the removal rates for Hg(II) and Cd(II) remained consistent, staying between 75% and 80%. The removal of naphthalene, phenol, and fluorene demonstrated a reduction of about 20% over six consecutive adsorption and desorption cycles. This novel adsorbent presents a promising, sustainable approach for refinery wastewater treatment, advancing environmental conservation strategies.