One-pot Synthesis Of Mn-doped TiO₂ Grown On Graphene And The Mechanism For Removal Of Cr???and Cr???

In order to control the pollution of aqueous Cr solution effectively,the study prepared a visible light response of reduced graphene oxide?rGO?loaded Mn doped TiO₂ composite photocatalyst to investigate the efficiency and mechanism of light photocatalytic removal of aqueous Cr ions.The main contents were:Firstly,graphene oxide was prepared by the method of improved Hummers',then composite materials were prepared by one-pot solvent thermal method.GO was reduced to rGO through the solvent thermal process,rGO and TiO₂ were firmly bonded together by the covalent bonds.The materials were characterized using SEM,TEM,XRD,TGA,UV-Vis DRS,PL and EIS techniques to determine the micro morphology,physical and chemical properties.SEM and TEM analyses showed that the Mn-TiO₂ particles are uniformly grown in situ on graphene nanosheet,TEM images and XRD analyses confirmed that Mn-TiO₂ particles were anatase,the particle size was 7⁸ nm.TGA analyses showed that the actual rGO load of rGO-Mn-TiO₂ composite materials were close to the theoretical load.UV-Vis DRS analyses showed that Mn doped TiO₂ had improved visible light response property and decreased band gap.In addition,PL and EIS analyses showed that rGO-Mn-TiO₂ composite materials had decreased electron-hole recombination and the low charge transfer resistance made the charge carriers easy to separate and the electron could transfer effectively.Secondly,the as-prepared Mn-TiO₂ and rGO-Mn-TiO₂ materials were used in the adsorption-photocatalytic removal of Cr?VI?under the visible light,respectively.In this paper,the adsorption equilibrium experiments of the materials were carried out,and then the influences of Mn doping amount,rGO loading capacity and pH value to the removal of Cr were investigated with 20 mg/L initial Cr concentration.The results showed that the Cr removal efficiency of rGO-Mn-TiO₂ reached 97.32% in 30 min and 99.02% in 60 min under the optimum conditions.rGO-Mn-TiO₂ materials also demonstrated good recyclability and strong stability in the reusability experiment.Finally,the mechanisms of efficient removal of Cr ions from solution by Mn-TiO₂ and rGO-Mn-TiO₂ materials were explored.The adsorption of Mn-TiO₂ was mainly carried out by the hydroxyl groups,while that of rGO-Mn-TiO₂ was mainly carried out by rGO.The efficient removal of Cr?VI?by rGO and Mn-TiO₂ was achieved by the synergistic effect of adsorption and photocatalysis.The generated Cr?III?continued to be adsorbed by rGO helped to the release of abundant photocatalytic sites of Mn-TiO₂,so as to make the process of Cr removal always maintain a high efficiency.