Highly efficient adsorption of Congo red in single and binary water with cationic dyes by reduced graphene oxide decorated NH2-MIL-68(Al)

Abstract

The reduced graphene oxide decorated NH2-MIL-68(Al) (RGO/NMA) is synthesized via one-pot solvothermal process and systematically characterized for the congo red (CR) removal from single and binary water with cationic dyes. The characterization results show that the surface area of negatively charged RGO/NMA is significantly enhanced by the introduction of reduced graphene oxide (RGO). The CR adsorption is investigated as a function of contact time, initial CR concentration, temperature, pH and ionic strength. It shows that the maximum CR adsorption capacity of RGO/NMA (473.93mg/g) is 121% and 1337% higher than NH2-MIL-68(Al) (NMA) and RGO, respectively. The adsorption dynamic analysis shows that the Pseudo-second-order model presents the best fitting to CR adsorption compared with Pseudo-first-order and Elovich model. The adsorption rate-limited step is successively controlled by film-diffusion and intra-particle diffusion according to the applicability measurement of intra-particle diffusion, boyd's film-diffusion models and external mass transfer plots. Based on the suitability of isotherm models, the CR adsorption process can be described in order of Langmuir>Temkin>Freundlich>Hill. The adsorption mechanism involved the electrostatic attraction, π–π dispersion interaction and hydrogen bonds for the spontaneously exothermic adsorption process are indentified using the three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectrum The synergistic effect occurs in the simultaneous removal CR and cationic from water. The RGO/NMA has the excellent reusability and the resource utilization of CR loaded RGO/NMA as photocatalyst for Cr(VI) reduction under visible light irradiation is highly feasible.