Recent advancements in graphene adsorbents for wastewater treatment: Current status and challenges

From emerging pollutants to emerged threat, researchers are continuously looking for promising technologies for wastewater treatment. Adsorption has been identified as the most convenient approach for treating wastewater at low-cost and with high-efficiency. Recently, graphene and its derivatives have gained heightened attention as novel adsorbents because of their unique molecular structure and outstanding physicochemical properties. Heavy metals, dyes, polycyclic aromatic hydrocarbons (PAHs) and other pollutants, which are widely concerned recently, all show different adsorption behaviors. Numerous functional groups, resonating and delocalized pi-electron system of graphene derivatives lead to the formation of various adsorptive interactions i.e., pi-pi interactions, electrostatic interactions, H-bonding, etc. with these venomous pollutants, and quarantine them in solution. The pristine form of graphene subsidiaries tends to exhibit low sorption efficiency due to high propensity of agglomeration, lack of selectivity, hydrophobicity and difficulty in phase separation after treatment. Therefore, designing of efficient graphene composites through the surface modification with numerous functional groups, polymers or nanoparticles is an ongoing challenge. Complex graphene composites are increasingly reported, but the fate of pollutants and adsorption mechanisms are still far to be fully clarified. This review summarizes the recent progresses in the application of graphene-based adsorbents for eliminating a wide range of organic and inorganic pollutants from wastewater. A critical explanation is provided on the synthesis of graphene adsorbents, systematic adsorption and desorption mechanisms along with their pollutant removal performances under different experimental conditions. A brief perspective on upcoming research needs and challenges involved in the designing of high-quality graphene-based adsorbents are highlighted. (C) 2020 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.