Water contamination by heavy metals is of dire concern considering its harmful effect on humans, plants, and animals. Thus, it justifies the scientific attention and resources to removing metal ions from water sources. While different technologies have been employed to reduce or eliminate metals from an aqueous solution, recent studies have focused on metal ion adsorption given its high efficiency, simplicity, and economic advantages over technologies such as reverse osmosis, filtration, membrane separation, and chemical precipitation. Efficient metal pollutants removal from water requires an adsorbent with numerous adsorption sites, biocompatibility, large surface area, and functionalization ability. The search for these specifics in adsorbents has informed the development of activated carbon, chitosan, functionalized polymers, and other adsorbents; however, these absorbents are still limited by poor diffusion ability in wastewater, separation difficulties, and low active site capacity. Magnetic nanoparticles (MNPs), particularly magnetite (Fe3O4) nanoparticles, offer an advantageous alternative due to their high surface area and active sites, increased biocompatibility, magnetically controlled separation ability, and reusability. However, to ensure adequate adsorption of heavy metal ions from an aqueous solution, MNPs require surface functionalization to enhance adsorption-desorption kinetics while increasing adsorption sites and reusability. Small molecule compounds including citric acid (CA), thiols, nitrilotriacetic acid (NTA), 3-aminopropyl) triethoxysilane (APTES), 3-mercaptopropyl trimethoxysilane and glutaraldehyde (GA) can be used to functionalize MNPs as to prevent secondary aggregation in solution and to increase specific metal ion- particle interactions and binding.
In this work, MNPs surface functionalized with APTES, APTES-GA, CA, and Thiols were synthesized and characterized for their physicochemical properties using scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential measurements (ZP) and Fourier Transform Infrared Spectroscopy (FTIR). The MNPs were then evaluated for their metal-ion removal efficiency through batch adsorption experiments to optimize contact time, adsorbent dose, initial metal ion concentration, and pH. These parameters are particularly important for determining the relationship between the type and concentration of free adsorptive sites on the functionalized adsorbents and the concentrations of the heavy metals in contaminated water. Adsorption isotherm models were applied to experimental data to explore the mechanism of adsorption and surface properties. The findings from the study inform the choice and optimal usage of MNPs for removing metal ions in water and will inform the design of future MNP based water treatment technologies.
