Removal of toxic metals from wastewater environment by graphene-based composites: A review on isotherm and kinetic models, recent trends, challenges and future directions

Access to clean water has reduced in recent years due to pollution and man-made activities. Wastewater treatment regimens are many such as electrocoagulation, adsorption, ozonation, membrane and advanced oxidation processes. Owing to economical, resource availability and ease of operation adsorption has upper hand over all other methods employed in wastewater treatment. Graphene based adsorbents attracted researchers due to their ability to play dual role as adsorbent and photo-catalysts. When it comes to removal of heavy metals and dyes graphene-based aerogels are successful. Graphene composites were predominantly synthesized by top-down and bottom-up approach methods. Graphene composites are mesoporous and have microporous structure on surface. Graphene has copper desorption efficiency of 90 % upon 10th consecutive cycle. Graphene based adsorbents have adsorption efficiency of 367, 246 and 106.3 mg-1 for lead, zinc and cadmium respectively. Though graphene possesses numerous applications, this review was devoted towards heavy metals removal from aqueous environment. In detail, the synthesis routes and interaction mechanism were explained and also the adsorption isotherms, kinetics were added. This review will serve as support for future research directions on removal of wastewater contaminants (heavy metals).