Reversible photoregulation of morphological structure for porous coumarin-graphene composite and the removal of heavy metal ions

Abstract In this study, a photoreversible graphene oxide (GO) - coumarin (GC) composite is fabricated by electrostatic self-assembly of positively charged nitrogenous coumarin surfactant and negatively charged GO. It is found that the introduction of coumarin not only results in a large amount of micropores and mesopores on the surface of GO, but photo-regulates its structure transformation between close-packed structure and 3D pleat-like structure, solves the separation problem, improves and reversibly controls its adsorption capacity, under 365/254 nm light irradiation. The maximum adsorption capacity of the GC composite and the Irradiated GC composite (the GC composite irradiated by 365 nm light for 30 min) for Pb2+ are 403.97 and 492.51 mg/g, respectively, under room temperature at pH 6. The adsorption kinetic processes of these two composites are described by pseudo-second-order kinetic model, and the equilibrium data are well fitted with the Langmuir isotherm model. Furthermore, adsorption-desorption experiments show that these two composites have effective reusability, and display desirable adsorption capacities toward Cd2+, Cu2+ and Zn2+ heavy metal ions. The results indicate that the GC composite provide theoretical and experimental basis for structurally photocontrollable materials, and can be served as photoreversible adsorbents for effective removal of heavy metal ions from wastewater.