Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

Highlights: • Environmental impact of engineered MNPs. • MNPs and their hybrids explored for use in energy, analytical chemistry, and catalysis. • Surface modification to MNPs allow biocompatible applications. • Adsorptive and separative removal of a wide range of contaminants from aquatic environments. • Active remediation and natural attenuation of contaminants in soil and groundwater using MNPs. - Abstract: This review focuses on environmental implications and applications of engineered magnetite (Fe₃O₄) nanoparticles (MNPs) as a single phase or a component of a hybrid nanocomposite that exhibits superparamagnetism and high surface area. MNPs are synthesized via co-precipitation, thermal decomposition and combustion, hydrothermal process, emulsion, microbial process, and green approaches. Aggregation/sedimentation and transport of MNPs depend on surface charge of MNPs and geochemical parameters such as pH, ionic strength, and organic matter. MNPs generally have low toxicity to humans and ecosystem. MNPs are used for constructing chemical/biosensors and for catalyzing a variety of chemical reactions. MNPs are used for air cleanup and carbon sequestration. MNP nanocomposites are designed as antimicrobial agents for water disinfection and flocculants for water treatment. Conjugated MNPs are widely used for adsorptive/separative removal of organics, dyes, oil, arsenic, phosphate, molybdate, fluoride, selenium, Cr(VI), heavy metal cations, radionuclides, and rare earth elements. MNPs can degrade organic/inorganic contaminants via chemical reduction or catalyze chemical oxidation in water, sediment, and soil. Future studies should further explore mechanisms of MNP interactions with other nanomaterials and contaminants, economic and green approaches of MNP synthesis, and field scale demonstration of MNP utilization.