Preparation And Application Of Cu-Al Layered Double Hydroxide

Copper-aluminum layered double hydroxide（CuAl-LDH）has been widely investigated by researchers.By introducing the transition-metal copper ions into the layer,CuAl-LDH exhibited excellent structure and performance.In this paper,CuAl-LDH was chosen as the research object.The preparation process of CuAl-LDH,the degradation behavior of methyl orange by means of CuAl-LDH as catalyst,and the catalysis for the dechlorination and carbonization of PVC were studied respectively.The main research findings are depicted as follows:CuAl-LDH was prepared by hydrothermal method using water and dimethylsulfoxide as a mixed solvent.The addition of dimethyl sulfoxide inhibits the hydrolysis of urea leading to the p H of the solution to grow slowly which reduces the influences of the Jahn-Teller effect on the materials.Copper and aluminum are distributed evenly over the layers of nanosheets,and these nanosheets form a unique flower-like structure by self-assembly.Fenton oxidation technology was carried out to treat methyl orange dye wastewater.CuAl-LDH was used as a heterogeneous catalyst to catalyze the decomposition of hydrogen peroxide to generate hydroxyl radicals with strong oxidizing ability,which can convert methyl orange into biodegradable intermediate or water,carbon dioxide and inorganic salts.The effects of CuAl-LDH dosage,hydrogen peroxide dosage and reaction temperature on degradation efficiency were investigated.The results show that rising the temperature and increasing the dosage of CuAl-LDH and hydrogen peroxide are beneficial to the degradation efficiency of methyl orange when the reaction conditions are as follows:CuAl-LDH 20mg,hydrogen peroxide0.5m L,temperature 40℃,methyl orange can degrade completely within 10min.However,due to the large amount of intermediates adsorbed on the surface of CuAl-LDH during the catalyst recycling process,the contact of active sites with hydrogen peroxide was hindered,resulting in a significant decrease in the degradation rate of methyl orange.The catalytic effect of CuAl-LDH on the thermal degradation and combustion of PVC was studied.The results show that the addition of CuAl-LDH can effectively accelerate the dehydrochlorination of PVC and promote the carbon-forming reaction of PVC at high temperature.The catalytic mechanism can be explained as follows:HCl is firstly absorbed by CuAl-LDH to form Cu Cl₂/Al Cl₃ containing a large amount of Lewis acidic sites,which can combine with electrons and radicals to accelerate the dehydrochlorination reaction of PVC to form carbenium ion and conjugated unsaturated structure.These conjugated olefin segments undergo the isomerization,cyclization,aromatization,rearrangement and cross-linking reactions to form polycyclic aromatic hydrocarbon structures,which carbonize to form char under high temperature.