Heavy metal and organic pollutants removal from water using bilayered polydopamine composite of sandwiched graphene Nanosheets: One solution for two obstacles

Abstract

The swift and unprogrammed industrial development has engendered several human hazards, including water contamination by heavy metals (Pb2+ and Hg2+) and organic pollutants largely added by agricultural operations (pesticide sprays). The deleterious effects of these contaminants have been extensively studied, highlighting the need for an efficient, quick, and targeted water treatment process. We built a cellulose graphene material sandwiched between double layered polydopamine (PDM) metal–organic framework (MOF). The composite material efficiently removed two water contaminants, i.e., heavy metals (Pb2+, and Hg2+), and persistent organic pollutants-POPs (PCB44 (2,2′,3,5′-tetrachlorobiphenyl), and gamma-HCH (1,2,3,4,5,6-Hexachlorocyclohexane)). The material was proved a highly stable metal–organic MOF composite (FeBT-PDM21/CG20) under dynamic physical conditions (pH 2–12 and temperature 4–65 °C). The extrinsic porosity in the bilayered MOF was due to internally pinned PDM, porous for water, and binds 1758 mg of Hg2+, 488 mg Pb2+, 673 mg PCB 44, and 596 mg gamma-HCH per gram of the composite material. Water samples with a one ppm standard concentration of each contaminant were cleaned up to the drinking level after just one adsorption cycle with the MOF. The material effectively adsorbed persistent organic pollutants (POPs), leaving no detectable graphene traces in water. The novelty of the material lies in the quick water filtration process (1 mL/min by 1 cm2 of material area) up to the drinking water quality. Furthermore, the cleaning property remained persistent at different physical conditions, including pH. Moreover, the material proved stable and robust during lab assays.