A review on the design and application of bi-functionalized adsorbents to remove different pollutants from water.

Abstract

This review provides a bibliometric analysis of chemically bi-functionalized materials that have been employed as advanced adsorbents to remove various types of organic and/or inorganic (cationic and/or anionic) pollutants from water and wastewater. The relevance of regeneration and reuse experiments for bi-functionalized adsorbents is discussed, since they have been shown to be fundamental in advancing the technology readiness level (TRL) and for assessing technical, economic, and environmental feasibility. Only 56% of the studies compiled in this review carried out regeneration and reuse experiments, and few studies have proposed and discussed waste management of adsorbents after depletion of their adsorption capacity. The aim of the present critical analysis is to inform and encourage researchers in this field, given the lack of in-depth information in the literature concerning advanced materials especially designed for the simultaneous removal of different types of pollutants coexisting in complex aqueous matrices in various environments, which slows transfer of the technology to the market. Among the compiled support materials, the most investigated were silica-based (~46%), followed by polymers (~15%) and biomass (~11%), with the adsorption capacity (Qmax) of bi-functionalized adsorbents outperforming mono-functionalized adsorbents, in most cases. For inorganic pollutants, the highest and lowest Qmax values of 4.67 and 1.51 mmol g− 1 for Cr(VI) were reported for polymer- and silica-based adsorbents, respectively. Biomass- and xerogel-based adsorbents were the most efficient for organic compounds, with Qmax values of 39.2 and 2.61 mmol g− 1 for trichloroacetic acid and methylene blue, respectively. In summary, the results were promising, but advances are still needed, since most of the developed technologies presented low TRL of ≤4, representing a challenge for transition of the technologies to the pilot scale (TRL ≥ 6) or for transfer to the market.