Recent developments in engineered nanomaterials for water treatment and environmental remediation

Engineered nanomaterials (ENMs) have been widely used not only to remove contaminants from surface water but also to remediate soil and groundwater contaminated with organic/inorganic pollutants via advanced oxidation and chemical reduction, sorption, complexation, (co)precipitation, or membrane filtration. The characteristics of ENMs cannot be extrapolated from their bulk counterparts because the properties fundamentally change when bulk materials are downsized to the nanoscale range (1-100 nm). ENMs are efficient for decontamination due to the large specific surface area, high surface reactivity (e.g., catalytic activity), and increased multifunctionality [e.g., nanohybrids (NHs)]. Nevertheless, the application of bare NMs for water purification or contaminated site remediation is often restricted due to their vulnerability to aggregation, surface passivation, and thus limited mobility to the target pollutants in contaminated sites. Consequently, over the last few decades, NMs have been modified or hybridized with one or more NM conjugates to counteract the negative effects associated with the use of bare NMs and to achieve multifunctionality by tailoring NMs’ size, morphology, dimensionality, surface properties, etc. This chapter primarily focuses on the recent developments of ENMs during the past 10 years and their applications for water treatment and contaminant cleanup. Methods for functionalization or conjugation of NMs are categorized into five broad classes (doping, immobilization, surface functionalization, NHs, and green synthesis). In-depth reaction mechanisms in water treatment technologies (adsorption, catalysis, membrane filtration, antibacterial activity) and in situ soil and groundwater remediation using ENMs are discussed in details. Moreover, the potential challenges in application of modified or multifunctional hybrid NMs are identified to guide for future research.