Review of Advances in Engineering Nanomaterial Adsorbents for Metal Removal and Recovery from Water: Synthesis and Microstructure Impacts

Adsorption is widely applied in both potable and municipal or industrial wastewater treatments process. Nanomaterial adsorbents (NAs) have emerged as efficient candidates to remove toxic metals from water. However, scalable application of NAs beyond bench-scale material discovery and translation to full scale deployment has been limited but essential to realize the potential NAs offer for environmental remediation. In this critical review, we summarize, discuss, and compare various NA synthesis methods and assess their scalability to supply materials for full-scale applications. Moreover, as the importance of the microstructure of nanomaterial itself has been recognized in recent years, we also scrutinize the effect of NAs structures including crystal facets, phases, and tunability of active sites (e.g., functional groups) on metal adsorption. The review concludes with prioritizing research needs that balance large-scale production costs and feasibility to produce desired properties of NAs at commercial scale quantities. Meanwhile, an NAs evaluation protocol (e.g., life cycle costing (LCC) and life cycle assessment (LCA)) should be established to test NAs at the material discovery stage that considers both adsorption capacity and mass transfer kinetics and perform long-term testing (e.g., recovery) of NA real applications.