Preparation,Modification And Application Of LDHs Films In Wastewater Treatment

Layered double hydroxides(LDHs)have great applications in the field of photocatalysis owing to their excellent structural characters,such as various metal ions in laminates,flexible and exchangeable interlayer anions.However,the application of LDHs is limited due to the high recombination rate of photogenerated charges and the difficulty of recycling.In order to solve the above problems,LDHs films and powders were prepared by hydrothermal method.By changing the composition of metal ions in the laminate,doping iron ions,and the modification of LDHs using layered materials BiOX(X=Cl,Br,I),the separation and transmission of photogenerated electron-hole pairs are promoted,which improves the efficiency of photocatalytic degradation of pollutants.Meanwhile,the recycling of photocatalyst is realized,which can broaden the application of LDHs in wastewater treatment.1.LDHs films and powders with different metal ions(Ni,Al,Fe)were prepared by hydrothermal method,and modified by iron ion doping.The effects of iron ion doping and metal ions on the photocatalytic degradation of single wastewater(methyl orange,MO)and simulated mixed wastewater(coexistence solution of MO and silver ion)by LDHs films were studied.The experimental results show that when treating the single wastewater,iron ion acts as the trap for electron-hole pairs,which accelerates the recombination of photogenerated electron-hole pairs.As a result,Fe doped LDHs films show a worse photocatalytic degradation effect on MO.For the treatment of mixed wastewater containing MO and silver ion,iron ion and silver ion show synergistic enhancement effect,which is conducive to the separation of photogenerated electron-hole pairs.Among them,Fe doped NiAl-LDH films show the best degradation effect on MO and the degradation rate reached 11.92%·mg^-1.2.NiAl-LDHs growth film,NiAl-LDHs deposition film and NiAl-LDHs composite film were prepared by hydrothermal method.The degradation effect of three kinds of NiAl-LDHs films on MO was studied.Using NiAl-LDHs composite film as the photocatalyst,the photocatalytic degradation of mixed wastewater containing MO and metal ions was studied.The effects of Fermi energy level(E_F)on the photocatalytic degradation of organic pollutants and the photocatalytic reduction of heavy metal ions by NiAl-LDHs composite film were investigated.The Experimental results show that the photocatalytic activity of NiAl-LDHs composite film increases with the increase of E_F(from 79.71%to 82.55%).When MO coexists with various metal ions,the reduction ability of NiAl-LDHs composite film for heavy metal ions(more than 95%)and the photocatalytic degradation efficiency of MO(84.5%)are improved.3.BiOX(X=Cl,Br,I)/NiAl-LDHs composites were prepared by mechanical mixing method.The effects of the ratio of BiOX(X=Cl,Br,I)to NiAl-LDHs and the types of BiOX on the photocatalytic activity of BiOX/NiAl-LDHs composites were investigated by using anionic dye(MO)and cationic dye(methylene blue,MB)as the degradation objects.Experimental results show that when the ratio of NiAl-LDHs to BiOX is 1:1,BiOX(X=Cl,Br,I)/NiAl-LDHs composites exhibit the best photocatalytic degradation effect on MO and MB.Among them,using BiOCl/NiAl-LDHs composites as the photocatalyst,MO and MB had been completely decolorized by photocatalytic reaction for 90 min and 60 min,respectively.The types of BiOX(X=Cl,Br,I)affect the photocatalytic activity of BiOX(X=Cl,Br,I)/NiAl-LDHs composites.Due to the synergistic effect of adsorption and photocatalysis,the photocatalytic activity of BiOCl/NiAl-LDHs was improved.In addition,BiOX(X=Cl,Br,I)/NiAl-LDHs films were prepared by a coating method.The removal effect of dye by the composite films was studied,and the influence of the adhesion between the film and the substrate on the photocatalytic activity was discussed.