Construction of adsorbents with graphene and its derivatives for wastewater treatment: a review

Graphene and its derivatives have captured enormous attention in the design and fabrication of graphene-based adsorbents to handle various water pollutants due to their huge specific surface area, unique two-dimensional structure, intriguing surface properties, tailorable microstructure, ease of being functionalized/modified, and good processibility for integration with other organic and inorganic species. However, many challenges remain for this topic that are undergoing intense study. For example, the specific role of the graphene component in the adsorption process is not evidenced in many existing reports, although there have been some speculations. Moreover, the high cost and environmental safety issues of graphene materials derived from graphite by the popular modified Hummers' method are not well addressed. These challenges bring about an ambiguous development trend in using graphene and its derivatives to construct next-generation adsorbents. Herein, we present a timely, up-to-date overview and perspectives to summarize the recent development of adsorbents constructed with graphene and its derivatives. We first discuss different kinds of graphene-based adsorbents (e.g., intrinsic, doped, modified/functionalized, composited, and a combination thereof). We then categorize the adsorbates, compliant to graphene-based adsorbents, into contaminants with various charge states, different water solubilities and complexity, emerging contaminants, and others. Further, multifunctional applications, trace contaminant treatment, and adsorption mechanism analysis are sequentially presented for graphene-based adsorbents. Finally, after summarizing the development of graphene-based adsorbents using graphene oxide as a typical starting material, we provide the current challenges and future perspectives for the rational design and fabrication of active, durable, and economical adsorbents constructed with graphene and its derivatives.