Synthesis And Photocatalytic Properties Of Calcined Zinc Aluminum Hydrotalcite And Its Composites

Photocatalysis technology has been applied to water pollution due to its friendly environment,complete degradation of pollutants and low cost.Calcination product of hydrotalcite is a common photocatalyst.That have a series of advantages,such as adjustable structure composition,large specific surface area and good thermal stability.The calcination of Zn Al-LDH is a common photocatalyst which Zinc Oxide(Zn O)play an important role in photocatalysis,however,the band gap of Zn O is so large that can not fully utilization the sunlight.This paper is based on the precursor of Zn Al-LDH.Through changing calcination temperature and introducing other materials to narrow the band gap of photocatalyst to sufficiently utilization the sunlight.The details are as follows:1.The metal oxide Zinc Oxide and zinc aluminate(Zn O/Zn Al2O4)with heterostructure were obtained via calcining Zn Al-LDH at high temperature(low temperature300?,500? were prepared as reference).Cr(VI)as the target pollutant,the results revealed that,the samples calcined at high temperature with heterostructure performs best which contributed to the special structer can translate photoelectrons to avoid recombination of the photogenerated electron and hole.The different conditions of photocatalytic Cr(VI)were discussed.It is found that p H plays an important role on photocatalysis.In a certain range,the catalyst performed better at lower p H value.As a hole capture agent,citric acid(CA)can not only capture holes,but also acidity modulators,which can effectively improve the efficiency of Cr(VI)reduction.The precousor calcined at High temperature can form spinel compact structure Zn Al2O4 that can inhibit the hydrotalcite shape memory effect,so it has high photochemical stability.2.The low-temperature calcination products of hydrotalcite were added to ultrasonic dissection solution of graphene oxide,and the hydrotalcite lamellar oxide graphene oxide film layer nanocomposite with sandwich structure was synthesized via hydration process of hydrotalcite(the "shape memory effect" of the hydrotalcite),then,The heated reduced graphene oxide composites with excellent visible light photocatalytic properties can be prepared through calcinated at high temperature.The composites can give full play to the graphene oxide andhydrotalcite.Based on this principle,the nanocomposites with sandwich structure were synthesised by adding the Zn Al-MMO which was calcined at 500? to ultrasonic stripping of graphene oxide.the characterization analysis of XRD,SEM,HRTEM and XPS proved that the GO was successfully intercalated to the interlamination of Zn Al-LDH and the presence of graphene oxide increases the crystallinity of the crystals after hydration.the calcined products were characterized by UV-vis-DRS and PL spectra,the results denoted that the band gap of thermal reduction of graphene oxide(RGO)/Zn Al-MMO(RGO-Zn Al-MMO)nanocomposites had a greatly decreasescompared to that of the pure Zn Al-MMO,the absorption of the visible region is greatly enhanced,the band gap of the 4.33% content of RGO nanocomposite is only 2.45 e V which was attributed to the electroconductivity of RGO.Methyl orange(MO)was used as the target pollutant,the photocatalytic performance of RGO-Zn Al-MMO was tested.The results show that the nanocomposites RGO-Zn Al-MMO exhibits excellent photocatalytic activity under visible light.Changing the reaction conditions of photodegradation of MO,we found that the p H of initial solution has a great impact on photocatalytic activity,when the p H value of the initial solution was ranged from 3 to7.43,the photocatalyst performs best.After four cycles,the phoyodegration rate of the catalyst has no signicantly decreased;the hydroxyl radical(.OH)was found to play a leading role in the photocatalytic oxidation of MO by adding the active capture agent.