Modifying engineered nanomaterials to produce next generation agents for environmental remediation.

The application of pristine nanomaterials (PNMs) for environment remediation remains challenging due to inherently high potential for aggregation, low stability, sub-optimum efficiency, and non-uniformity in size and toxicity. Conversely, modified nanomaterials (MNMs) approaches have shown significant potential to enhance the technical and economic efficiency of conventional nanoscale remediation strategies by decreasing aggregation of nanomaterials by imparting electrostatic, electrosteric or steric repulsion between particles. Furthermore, the solubility enhancing agents in MNMs have been shown to increase metal bioavailability and accelerate the breakdown of pollutants. As such, it is imperative to modify nanomaterials for unlocking their full potential and expanding their range of applications. However, there is no comprehensive review in the literature that evaluates the efficacy and environmental impact of MNMs against PNMs in the environment. This critical review identifies major barriers preventing the widescale application of nano-enabled remediation and discusses strategies to increase the stability and activity of nanomaterials at reaction sites. The higher reactivity and versatility of MNMs, along with novel properties and functionalities, enable effective removal of a range of chemical pollutants from complex environmental matrices. Additionally, MNMs show significant improvement in mobility, reactivity, and controlled and targeted release of active ingredients for in situ remediation. However, the uncertainties associated with the adverse effects of some modification agents of MNMs are not well-understood, and require further in-depth investigations. Overall, our findings show that MNMs are potentially more efficient, cost-effective, and resilient for remediation of soil and sediment, water, and air pollution than PNMs. The possible action mechanisms of MNMs have been demonstrated for different environmental compartments. Conclusively, this work provides a path forward for developing effective nano-enabled remediation technologies with MNMs, which are widely applicable to a range of environmental contamination scenarios.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.