Study Of ZnAl-LDHs And Its Modified Materials Adsorption And Photocatalytic Degradation Of Cr(?) Wastewater

Chromium and its compounds are widely used in metallurgy,electroplating,printing and dyeing,processing hides,metal manufacture and so on in the actual industrial manufacture which form are Cr?III?and Cr?VI?.Cr?VI?has extreme toxic and its toxicity is 100 times than Cr?III?.China regards Cr?VI?as one of the indicators for carrying out the total quantity control.Therefore,it is of great practical significance to study the separation disposal technology and method of wastewater treatment.Photocatalytic reaction is an effective method to dispose chromium pollution as a new way of synthesis and environmental protection,which is a kind of green clean,high efficiency and economy.Layered double hydrotalcite possess unique interlaminar anions exchangeability,main laminate cation collocation and structural recombination ability,widely apply to catalysis,adsorption and other fields.Silver carbonate can be applied to visible light catalytic technology because of its narrow forbidden band and sensitive visible light response.However,due to sensitive visible light response and instability of silver carbonate,it leads to the occurence of light corrosion.This subject combines the above two,the zinc-aluminum layered double hydroxides was ordered to be the substrate,decorating with silver carbonate,and the performance of them in the adsorption and photocatalytic degradation of chromium pollution was studied.1?The preparation and characterization of ZnAl-LDHs and its modified materials.This article used co-precipitation method to prepare ZnAl-LDHs and Ag₂CO₃/ZnAl-LDHs.Applied XRD,FTIR,SEM,EDS,TG-DTA and BET measuring method to analysize and characterize the property of crystal structure,surfacial morphology and molecular structure.The XRD measured materials possessed the pure phase of layered double hydroxides and good crystallinity.Ag₂CO₃ on the ZnAl-LDHs has no influence to the crystal structure,Ag/LDHs sample has high purity.The BET analysis of ZnAl-LDHs and Ag/LDHs demonstrates IV isothermal curve and H₃ retention loop which shows there is gap between particles with properties of sheet.The specific surface area of ZnAl-LDHs is 62.598m²/g and Ag/LDHs is38.896m²/g.Combining other FTIR,SEM,EDS and TG-DTA show ZnAl-LDHs has typical hydrotalcite-like compounds features and the EDS analysis of Ag/LDHs demonstrate that Ag₂CO₃ effectively decorate to ZnAl-LDHs.2?Study and compare the removal chromium adsorption property of Ag/LDHs and ZnAl-LDHs.Study and compare the removal chromium adsorption property of Ag/LDHs and ZnAl-LDHs.Study the catalysts'adding dosage,different initial concentration?calculated by K₂Cr₂O₇?,reaction temperature and pH value of the concentration to influence the Ag/LDHs and ZnAl-LDHs removal chromium.And through the kinetic to study the removal chromium of Ag/LDHs.Temperature has little influence to Ag/LDHs and ZnAl-LDHs.PH value has big effect on Ag/LDHs.And the removal rate of Ag/LDHs is much better than that of ZnAl-LDHs,which is higher about 40%⁵0%in the same condition.Ag/LDHs'adsorption of Cr?VI?is more suitable to describe pseudo-second-order kinetics model and it indicates the key of controlling reaction rate is chemical adsorption.The value of k₂ is lower which indicates the reaction rate is quick.Ea is 83.17 kJ/mol which shows the reaction is controlled by the reaction rate.3?Study and compare the removal chromium photocatalytic property of Ag/LDHs and ZnAl-LDHs.Study the catalysts'adding dosage,photocatalytic reaction time,different initial concentration?calculated by K₂Cr₂O₇?,reaction pH value and reaction temperature of the concentration to influence the Ag/LDHs and ZnAl-LDHs removal chromium.The kinetic law of photocatalytic reduction of Cr?VI?under visible light condition is studied and discuss photocatalytic theory.The reaction is corresponding to the Langmuir-Hinshelwood first-order-kinetic equation.Due to the exsistence of silver carbonate,it makes elcctron hole in the visible light and reduct Cr???to Cr???.And then convert Cr???to Cr?OH?_3.Finally separate it from the solution.