Facile Hydrothermal Synthesis Of 2D-layers/TiO₂ And Its Photoreduction For Cr??? Removal

At present,the environmental problems have been significantly improved with the improvement of domestic environmental governance policies.However,the serious threat of heavy metals to human beings and the environment still exists,which is still one of the most serious topics of global concerns.Among these heavy metals,Cr???is known for its highly toxicity,which can cause vomiting,diarrhea,kidney damage,liver disease,even lung cancer and other symptoms.In this work,a new type of composite photocatalysis material with two-dimensional layered structure,such as 2D-RGO/TiO₂,2D-WS₂/TiO₂ and RGO/WS₂/TiO₂,were prepared,which were used for removing heavy metal Cr???in water.The removal performance and mechanism of Cr???were studied by photocatalysis method.The specific research contents are as follows:TiO₂/RGO composite photocatalyst was synthesized by a facile hydrothermal method,which was used for photocatalytic reduction of Cr???under visible light irradiation.The product was characterized by X-ray powder diffraction?XRD?,Scanning electron microscope?SEM?,Nitrogen adsorption-desorption isotherms,UV-visible diffuse-reflection spectra?DRS?,Photoluminescence?PL?,Electrochemical impedance spectroscopy?EIS?and X-ray photoelectron spectroscopy?XPS?,respectively.The regular cubic shaped anatase TiO₂ particles were uniformly anchored on the wrinkles surface of the reduce graphene oxide?RGO?,which owned excellent electron transfer.Additionally,the band energy gap of TiO₂/RGO was 3.06 eV.It indicated that electron transferred from TiO₂ to RGO more easily under visible irradiation and migrated to the surface of TiO₂/RGO.Theoretical DFT calculation,PL and EIS evaluation reconfirmed that RGO served as the electron acceptor to trap the photoinduced electrons from TiO₂,which exhibited the separation efficiency of electrons and holes.The specific surface area of the P-25 and the prepared TiO₂/RGO samples were 68.5 and 185.3 m²?g^-1,respectively.It might expose more surface active site to contact with metal ions,which directly led to an obvious photocatalytic property enhancement.TiO₂/RGO showed superior photocatalytic performance for Cr???reduction at lower pH.The maximum photocatalytic removal capacity of Cr???could reach 99.81mg?g^-1 in no more than 100min.Excited by light,electrons transfer from TiO₂ to RGO and migrated to its surface.Cr???adsorbed on the protonated surface of photocatalysts accepted electrons was reduced to Cr?III?,in which both e^-and?O^2-played important role.The positive charged photocatalyst facilitated Cr???adsorption and the desorption of Cr?III?during the process of photocatalytic reduction of Cr???.This study not only provided a facile way to fabricate TiO₂/RGO photocatalyst but also showed outstanding photoreduction ability and provided insights into the mechanism of photocatalytic reduction of toxic Cr???by theoretical calculations and experiment.g-C₃N₄ was prepared by solvothermal method,then compounded the Ti O₂precursor on the surface of g-C₃N₄ to obtain g-C₃N₄/TiO₂ photocatalytic material under hydrothermal condition.The materials were characterized and analyzed by SEM,DRS,PL and electrochemistry.Compared with g-C₃N₄,TiO₂ and P-25 materials,g-C₃N₄/TiO₂have better photocatalytic performance and optical stability under visible light irradiation.The experimental results shown that photogenerated electrons?e^-?and superoxide radicals??O₂^-?are important active substances for photocatalytic reduction of Cr???,and e^-play a major role.2D-WS₂/TiO₂ composite photocatalyst was prepared by one-step sol-gel hydrothermal method using sodium tungstate,cysteine and four butyl titanate as raw materials.The properties of TiO₂ were characterized by SEM,mapping,PL,UV Vis and electrochemistry.It shows that TiO₂ particles with uniform size and shape are evenly distributed on the surface of 2D-WS₂.Compared with the standard P-25 material,it has more excellent optical and electrochemical properties.The theoretical results showed that 2D-WS₂/TiO₂ material can be used for photocatalytic reduction to remove Cr???pollution in water.The photocatalytic reduction of Cr???was carried out under visible light.The experimental results showed that the 2D-WS₂/TiO₂ has better photocatalytic performance than P-25,which is consistent with the characterization results.The optimal photocatalytic experimental conditions were:pH=2 of 20 mg/L Cr???solution;with this condition,the photocatalytic reduction efficiency of Cr???can reach 99.47%;adding interference ions Cu²⁺,Zn²⁺,SO₄^2-and CH₃OH to explore the photocatalytic performance,the addition of Cu²⁺and Zn²⁺can reduce the photocatalytic reaction rate but have no affection on the final reduction efficiency;the addition of SO₄^2-can enhance the photocatalytic efficiency;the addition of organic matter CH₃OH can accelerate the photocatalytic reaction process.The new 2D-WS₂/TiO₂ composite photocatalyst was easy to obtain and has potential application in the photocatalytic reduction of Cr???pollution in wastewater.In this work,three kinds of two-dimension layered structure and TiO₂ nanoparticle composite materials were prepared by means of one step hydrothermal method and sol-gel method,and the photocatalytic reduction of Cr???in water was carried out.At the same time,the materials were characterized by electrochemical methods and the combination of theoretical calculation and experiment.The mechanism of Cr???reduction was proved theoretically.It has potential application value for the removal of Cr???from industrial wastewater.