Study On Controllable Synthesis Of Cuprous Oxide Based Photocatalytic Materials And The Degradation For Organic Pollutants In Water

Exploring efficient strategies for the degradation of organic pollutions in water has importantly practical value to ensure the high-quality development of the social economy.As a promising technology for the degradation of organic pollution,photocatalysis has attracted extensive attention in the field of water treatment due to its low cost,mild reaction conditions and no secondary pollution.Photocatalyst is significantly critical in photocatalysis technology.Among a series of alternative photocatalysts,Cu2O based photocatalyst is one of the most promising photocatalytic materials with visible-light-responsive.However,its large-scale application has been seriously restricted by its low quantum efficiency and poor stability.In view of the defects of Cu2O photocatalyst,this paper intends to modify Cu2O by doping and constructing heterojunction,reducing the recombination of Cu2O photogenerated charge and improving its photocatalytic efficiency and stability.This paper aims to explore the efficient preparation methods of Cu2O based photocatalytic materials for water treatment by doping with metal Cr and non-metallic Cl and constructing the TiO2/Cu2O and α-Fe2O3/Cu2O heterojunction.Furthermore,the inherent mechanism for enhancing photocatalytic activity and the degradation kinetic of organic pollutants in water have been investigated.The antibiotics levofloxacin and Rhodamine B were selected as simulated organic pollutants.Based on liquid chromatography/mass spectrometry and frontier orbital theory,the reaction mechanism and degradation path of photocatalytic degradation of simulated organic compounds were explored.The response surface optimization method was used to optimize the process conditions of photocatalytic degradation of organic pollutants.At the same time,the change characteristics of energy band structure of Cu2O based photocatalytic materials were revealed by density functional theory.The innovative achievements of specific research mainly include the following aspects:(1)Controllable synthesis of Cr-Cu2O microcrystals and mechanism of photocatalytic oxidation for antibiotics in water.Cr-Cu2O was prepared by the hydrothermal method.The structural characterization and photocatalytic test showed that the XRD diffraction peak of Cr-Cu2O microcrystals moved to a higher diffraction angle with the increase of Cr doping.The lattice defects promoted the absorption efficiency of Cu2O in the visible spectrum range and significantly improved the photocatalytic activity of Cu2O.Cr-Cu2O microcrystals showed more obvious mesoporous structure and larger specific surface area than pure Cu2O.The micro morphology of Cr-Cu2O gradually evolved from spherical to polyhedron,octahedron and cube.Compared with pure Cu2O microcrystals,the prepared Cr-Cu2O microcrystals exhibited a wider band gap and higher separation efficiency of photogenerated carries with oxygen vacancies The optimum conditions for photocatalytic degradation of LVX by Cr-Cu2O microcrystals has been demonstrated to be that the pH of the solution was 8.0,the initial concentration of LVX was 52.0 mg/L,and the reaction temperature was 51.0℃.Under the optimal reaction conditions,the measured photocatalytic degradation rate of Cr-Cu2O microcrystals for LVX can reach 79.6%,revealing an excellent photocatalytic degradation performance and stability for LVX in water.-OH was the key active species for photocatalytic degradation of LVX.At the same time,the dopant of Cr increased the band gap of Cu2O and introduced the Cr 3d hybrid orbit into the Cu2O,resulting in a blue shift of the absorption edge and promoting the formation of oxygen vacancy defects.Oxidative ring-opening of piperazine and carboxyl along with decarboxylation of quinolones were the main reaction pathways of Cr-Cu2O photocatalytic degradation for LVX in water.(2)Study on the enhancement mechanism of Cl doped Cu2O and photocatalytic removal for LVX in water.Cl-Cu2O microcrystals were prepared by the hydrothermal method.The characterization and test results showed that the diffraction peak of Cu2O(111)crystal surface first increased and then decreased with the increase of Cl doping,which enhanced the photocatalytic activity of Cu2O.Cl-Cu2O microcrystals contained a large number of lattice defects of oxygen vacancies.The unpaired electrons effectively inhibited the recombination of photogenerated electron-hole pairs and improved the charge transfer.In the visible spectrum range of 400～500 nm,the absorbance of Cl-Cu2O was significantly higher than that of pure Cu2O microcrystals.The band gap of Cl-Cu2O microcrystals decreased with the dopant of the Cl.The morphology of Cl-Cu2O microcrystals gradually evolved from cube to polyhedron,regular octahedron and octahedron with concave surface.The optimum conditions for photocatalytic degradation of LVX by Cl-Cu2O microcrystals were as follows:the pH of the solution was 7.5,the initial concentration of LVX was 27.5 mg/L,and the reaction temperature was 40.0℃.Under the optimal reaction conditions,the measured photocatalytic degradation rate of LVX by Cl-Cu2O microcrystal can reach 85.8%,suggesting an excellent photocatalytic degradation performance and stability for LVX in water.The bottom of the conduction band and the top of the valence band of Cl-Cu2O energy band structure gradually moved to the low energy end,and the Fermi level moved to the high energy end to the bottom of the conduction band and passed through the first energy level of the conduction band with the increase of Cl doping,resulting in the decrease of the band gap and the red shift of the absorption edge.·OH was the key active species of Cl-Cu2O microcrystal photocatalytic degradation of LVX.The ring-opening and decarboxylation of quinolones were the main reaction paths of Cl-Cu2O photocatalytic degradation for LVX in water.(3)Construction of TiO2/Cu2O heterostructure exposed(111)crystal plane and study on photocatalytic performance for the organic wastewater.The p-n type TiO2/Cu2O heterojunction was prepared by the hydrothermal method.The structural characterization and photocatalytic test results showed that the prepared p-n type TiO2/Cu2O heterojunction exhibited high crystallite purity and exposed the preferred orientation of high-energy(111)crystal plane,which enhanced the photocatalytic activity of Cu2O.The absorbance of p-n type TiO2/Cu2O heterojunction in the visible spectrum range was significantly improved and the band gap width increased by constructing heterojunction compared with Cu2O microcrystals,which can provide facilitated photogenerated carrier transfer and improved photoelectric conversion efficiency.TiO2 microcrystals can be uniformly loaded on the surface of p-n type TiO2/Cu2O heterojunction microcrystals with higher specific surface area and octahedral crystal morphology.The optimum process conditions for RhB degradation were as follows:photocatalytic time was 3.0 h,catalyst dosage was 40.0 mg/L and solution pH was 3.0.Under the optimum degradation conditions,the measured photocatalytic degradation rate of RhB can reach 91.8%.After 9 times of recycling,the degradation rate of RHB can reach 85.6%,showing excellent photocatalytic activity and stability.The construction of p-n type TiO2/Cu2O heterojunction can promote the transition of electrons from the conduction band of Cu2O to the conduction band of TiO2,and the transfer of holes from the valence band of TiO2 to the valence band of Cu2O,inhibiting the recombination of photogenerated electron-hole pairs and improving the performance of photocatalytic degradation of RhB in water.(4)Construction of magnetic-α-Fe2O3/Cu2O heterojunction water treatment materials and photocatalytic reaction mechanism.The p-n type-α-Fe2O3/Cu2O heterojunction was prepared by the hydrothermal method.The structural characterization and photocatalytic test results revealed that the prepared p-n type-α-Fe2O3/Cu2O heterojunction had the preferred growth orientation of exposing(111)crystal plane and the strain induced effect of diffraction peak was caused by α-Fe2O3 compounding into Cu2O microcrystals.The p-n type α-Fe2O3/Cu2O heterojunction had internal electric field and interface Schottky barrier,which can effectively inhibit the recombination of photogenerated electron-hole pairs.Compared with pure Cu2O microcrystals,the p-n type α-Fe2O3/Cu2O heterostructures exhibited more efficient visible light absorption efficiency and higher separation efficiency of photogenerated carries.The micromorphology of the p-n type α-Fe2O3/Cu2O heterojunction crystallites gradually evolved from cube to irregular polyhedron and approximate sphere with smooth edge with the increase of α-Fe2O3 content.The optimum process conditions for degradation of LVX were as follows:the reaction temperature was 50.0℃,the initial concentration of LVX was 31.0 mg/L,and the pH of the solution was 6.8.Under the optimum degradation conditions,the measured photocatalytic degradation rate of LVX was 79.4%.The paramagnetic α-Fe2O3/Cu2O exhibited a excellent photocatalytic degradation efficiency and stability for LVX in water The energy band structure of α-Fe2O3/Cu2O heterojunction became dense and gradually moved to the low-energy end,resulting in the increase of the band gap width of the heterojunction and the blue shift of the absorption edge.·O2-was the main active species of p-n type α-Fe2O3/Cu2O heterojunction photocatalytic oxidation of LVX.Piperazine group oxidation,ring-opening and decarboxylation of quinolones were the main reaction pathways of the photocatalytic water treatment process.