Best practices for evaluating new materials as adsorbents for water treatment

Water pollution is becoming a major concern, because of the increasing numbers and concentrations of persistent, bioaccumulative, and toxic anthropogenic pollutants in fresh water resources. Many recent studies have considered new adsorbents to remove these emerging contaminants from water resources, including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), porous organic polymers (POPs), porous aromatic frameworks (PAFs), porous cyclodextrin-based polymers, and many others. These materials systems incorporate elements of molecular design to target specific pollutants, and many have porosity and high surface areas that provide rapid uptake and high capacity. Although they represent timely and important advances in materials design and synthesis, the characterization of their adsorption performance is sometimes not relevant for water treatment, insufficient, or implemented in ways that prevent comparison to the state-of-the-art materials. This Perspective scrutinizes common practices in the recent literature and provides guidance for designing conclusive and effective adsorption experiments with novel adsorbents. Efforts to adhere to these best practices will allow researchers to evaluate novel adsorbents effectively and will facilitate the emergence of general design criteria for the removal of emerging contaminants from water. Proper experimental design can give crucial insights for understanding adsorption mechanisms, as well as enabling comparisons among different studies, which will better contribute to solving current and future water quality problems.