Novel Magnetic Nanoparticle Adsorbents for Organic and Inorganic Contaminants

Water is not only a resource, but a life source. However, water pollution is one of the most challenging global issues that seriously threatened to people's life and sustainable development. With the continual concern over the presence of naturally-occurring and anthropogenic organic and inorganic contaminants in the aquatic environment, there is a growing need for the implementation of innovative treatment methods for the elimination of these contaminants from natural waters and wastewater effluents. Featuring high adsorption capacity, good regenerability, and surface area accessibility, magnetic nanoparticles (MNPs) have emerged as a new generation of sorbent materials for environmental decontamination in the past few years. Due to their superparamagnetic property that can be attracted to a magnetic field, it is easy to separate these MNPs adhered with contaminants from aqueous solution or complicated matrices by simply applying an external magnetic field; no filtration, centrifugation or gravitational separation is needed, making them a much more sustainable option than more traditional approaches for removing organic and inorganic contaminants. In this doctoral research, 4 different novel magnetic-core composite nanoparticle sorbents were developed for organic and metal contaminants remediation in aquatic systems. These sorbents have a core-shell structure with a magnetite core and a silica porous layer that permanently confines surfactant micelles (namely as Mag-PCMAs, targeting organic contaminants removal) or are functionalized with metal-binding organic ligands (namely as Mag-Ligands, targeting metal contaminants removal). The physicochemical properties of these magnetic nanoparticle sorbent was fully characterized via transmission electron microscopy, scanning electron microscopy, thermogravimetric analyses, fourier transform infrared spectroscopy, superconducting quantum interference device magnetometer, X-ray diffraction and BET porosimeter. The removal efficiencies of organic contaminants such as PAHs, emerging organic contaminants (EOCs, including pharmaceuticals, industrial additives) onto Mag-PCMAs and metal contaminants such as cadmium, lead, mercury, chromium and etc. onto Mag-Ligand were evaluated across a wide range of environmental conditions (e.g. pH, water hardness). The adsorption isotherms and kinetics of various contaminants onto the magnetic nanoparticle sorbents were determined respectively. Competitive sorption studies were conducted to determine the selectivity sequence among multiple metal ions onto Mag-Ligands. Isothermal titration microcalorimetry (ITC) was used to obtain key quantitative thermodynamic binding data of the interactions between Mag-Ligand and metal ions, providing the enthalpy, entropy and free energy of binding values as well as binding constants. Micelle swelling agent was used to optimize Mag-PCMAs’ porous structure for increasing pore volume and surface area to achieve higher removal efficiency and sorption kinetics. In addition, study was investigated on simultaneous removal of metal contaminants and PAHs across a variety of environmental conditions. The regenerability and reusability of these magnetic nanoparticle sorbents were also studied; both Mag-PCMAs and Mag-Ligand can be regenerated via rinsing with methanol or dilute acid, and can be reused for several treatment cycles without significant decrease on efficiency. This study has provided a rapid, effective and more sustainable approach for organic and metal contaminants remediation from aquatic systems