Study On The Fabrication And Photocatalytic Performance Of LDHs-based Heterojunction Composites

Under the severe situation of global energy crisis and environmental problems,more use of renewable energy has become an urgent matter of the moment.Due to the characteristics of low energy consumption,high processing efficiency and no secondary pollution,photocatalytic technology has great development prospects in solving the problems of energy shortage and environmental pollution in nowadays society.In recent years,researchers have made great progress in the research of various semiconductors,but the current single photocatalyst still has the problems of low activity,low light utilization rate and poor stability.Therefore,two or more kinds of semiconductors are often coupled together in some form on the micro and nano scale to form composites to solve the above problems.Layered double hydroxides（LDHs）,also known as hydrotalcite,has a unique layered structure,low cost and simple preparation method.In this paper,LDHs were used as the basis materials to establish heterojunction structures through coupling with other semiconductors,trying to develop photocatalysts with high activity,light utilization efficiency and stability.This work was mainly carried out in three points:（1）Firstly,Zn Fe-LDH was prepared by a co-precipitation method,and then Sn WO₄and Zn Fe-LDH were coupled by a hydrothermal synthesis method to obtain Sn WO₄/Zn Fe-LDH heterojunction composites.Methyl orange（MO）was used as the simulated pollutant to investigate the photocatalytic performance of the prepared samples.When the mass fraction of Zn Fe-LDH was 5%,the photodegradation efficiency of Sn WO₄/Zn Fe-LDH composites for MO reached 95.14%within 40 min under visible light irradiation after dark reaction.Under the experimental conditions,the photocatalytic efficiency of Sn WO₄/Zn Fe-LDH composites increased with the increase of catalyst dosage or the decrease of substrate concentration.After 5 cycles,the degradation efficiency of the composite remained at 92.4%,indicating the remarkable stability and reusability.（2）In order to improve the photocatalytic activity of LDHs,Zn Al-LDH prepared by co-precipitation method was calcined to obtain calcined layered double hydroxides（CLDHs）,then Zn Al-CLDH/ZIF-8heterojunction composites were further obtained by loading ZIF-8 onto Zn Al-CLDH by co-precipitation method.Compared with LDHs,CLDHs have higher photocatalytic activity,which may be due to the formation of spinel phase structure and thus have more catalytic active sites.Methylene blue（MB）was used as the simulated pollutant to investigate the photocatalytic performance of the prepared samples.The composite with 5%mass fraction of ZIF-8 showed the best catalytic activity among all the samples.The photodegradation efficiency of the optimal compositefor MB reached 97.35%within 105 min of irradiation after dark reaction.After 5 cycles,the photodegradation efficiency of the composite remained at 92.59%,indicating that it had high stability and reusability.（3）In order to improve the photocarrier separation and migration efficiency of photocatalyst,the Z-scheme heterojunction could be construct to improve the band structure.（Bi O）₂CO₃/Zn Fe-LDH heterojunction composites with excellent photocatalytic performance were synthesized by a hydrothermal method.Tetracycline（TC）aqueous solution was used as simulated antibiotic wastewater to investigated the photocatalytic performance of the as prepared samples.By measuring the values of absorbance,it was found that the composite with 5%mass fraction of Zn Fe-LDH showed the optimal photocatalytic activity,and the degradation efficiency reached 98.09%after adsorption for 30 min and lighting for 90 min.After 5 cycles,the photodegradation efficiency of the composite remained at 85.0%,indicating the high stability and reusability of the composite.