Construction Of Cu₂O And Its Composites For Degrading Organic Dyes

Organic dyes discharged from the textile industry are one of the largest sources of dye wastewater.Removing these dyes not only purifies and protects the water environment,but also maintains aquatic flora and fauna as well as human health.Sunlight-driven heterogeneous photocatalytic oxidation is an ideal technique for the elimination of organic dyes in wastewater.So far,about 200 kinds of visible light photocatalysts have been developed and applied in the field of sewage treatment.Among kinds of visible light photocatalytic materials,Cu₂O has attracted much attention due to its high chemical activity,non-toxicity,low cost,and easy preparation.However,the photocatalytic degradation efficiency of single Cu₂O is not high,due to its narrow band gap and fast electron-hole recombination.In order to improve the photocatalytic performance of Cu₂O,strategies such as doping,semiconductor compounding,and constructing heterojunctions can be used to precipitate the separation and migration of photogenerated carriers,thereby improving the photocatalytic degradation efficiency.In this thesis,Cu₂O was first synthesized by a one-step hydrothermal method using different sulfur sources.Next,Cu₂O was coupled with Cu₂S and CeO₂ to form p-n type Cu₂O-Cu₂S and n-n type Cu₂O-CeO₂heterojunctions,respectively,which were applied to the dye sewage treatment.The results showed that the formed heterojunction composite had higher removal rate of dyes and enhanced stability compared to the single material.The main contents of the dissertation are as follows:1.Using nano-CuO and CuSO₄ as copper sources,Na₂S·9H₂O and thioacetamide as sulfur sources as well as reducing agent,Cu₂O materials was prepared without any template and surfactant.And Cu₂O materials synthesized from different feedstocks were applied in the photocatalytic degradation of methyl orange in water.The study showed that Cu₂O synthesized from different feedstocks had different degradation efficiencies of methyl orange（MO）in water with 43%degradation rate by the Cu₂O synthesized from CuO and thioacetamide,63%from Cu SO₄ and Na₂S·9H₂O,80%from CuO and Na₂S·9H₂O,while the degradation rate of commercial Cu₂O was 30%.The higher degradation efficiency of the cubic Cu₂O material synthesized from CuO and Na₂S·9H₂O over MO was ascribed to its smaller particle size and better dispersibility.2.A series of p-n type heterojunction Cu₂O-Cu₂S composites(S_8:1.5,S_8:2,S_8:2.5 and S_8:3)were successfully synthesized by adjusting the molar ratio of CuO and Na₂S·9H₂O.The S_8:2.5 sample had the best photocatalytic degradation efficiency in 20 mg/L MO dye with 94%the degradation efficiency within 2 h,and the photocatalyst presented good stability.This was due to the formation of the p-n type heterojunction facilitated the separation of photogenerated electrons and holes,and further improved the photocatalytic degradation efficiency of the Cu₂O-Cu₂S sample.In additon,the S_8:2.5sample was illuminated under visible light for 2 h,and then placed in a MO solution in a dark environment.It was found that the removal rate of MO of the S_8:2.5 sample after illumination reached 85.4%.Compared with single Cu₂O,the removal rate of MO was increased by 57.5%for the S_8:2.5 sample.It showed that the S_8:2.5 sample still had photocatalytic degradation efficiency in the dark,and there was a certain post-irradiation catalytic"memory"effect.3.Using cubic Cu₂O,cubic CeO₂ and porous CeO₂ as templates,respectively,cubic Cu₂O-CeO₂,cubic CeO₂-Cu₂O and porous CeO₂-Cu₂O composites with n-n type heterojunctions were constructed via chemical reduction method.The photocatalytic degradation efficiencies of the three composite materials for different organic dyes were also investigated,and the results showed that the composite materials had superior photocatalytic degradation efficiency compared to the single materials,which were attributed to the formation of n-n type heterojunction.The enhanced absorption of visible light further improved the photocatalytic degradation efficiency the composites over dyes.