Preparation And Properties Research Of Exfoliated Bentonite-Based Ag₃PQ₄

The organic pollutants such as esters and phenols cause serious pollution to water.Based on the photocatalytic technology has the advantages of high environmental efficiency,no secondary pollution,high mineralization degree,and Ag₃PO₄has the advantages of high quantum yield and high photocatalytic activity,but Ag₃PO₄is prone to photocorrosion,slightly soluble in water,and agglomerates,resulting in poor stability.We synthesized novel visible-light response exfoliated bentonite-based Ag₃PO₄photocatalyst.The specific research contents of this paper are as follows:Firstly,the Na-bentonite was exfoliated by high-speed centrifugation at10000 r/min to obtain the exfoliated bentonite（EB）;EB/Ag₃PO₄and EB/Ag₃PO₄/Ag Br were synthesized by deposition and ion-exchange methods.XRD,SEM,TEM,XPS,BET,UV-vis and other characterization showed that in the EB/Ag₃PO₄/Ag Br,Ag Br with an average particle size of about 5-10 nm was loaded on the surface of relatively large spherical Ag₃PO₄with an average particle size of about 10-30 nm,and they were uniformly dispersed on the single layer of exfoliated bentonite;the light absorption range of EB/Ag₃PO₄/Ag Br was widened to 400-800 nm.The above results show that EB/Ag₃PO₄/Ag Br has higher photocatalytic oxidation degradation performance and stability due to nano size effect and enhanced light absorption intensity,and the contact interface with a large number of active sites is formed by exfoliated bentonite as support.Secondly,the degradation of methylparaben（MPB）by EB/Ag₃PO₄/Ag Br was used as the template reaction.It was found that the best ratio of EB/Ag₃PO₄/Ag Br when Ag Br:Ag₃PO₄was 3:7,and 20 mg/L 100 m L of MPB could be achieved completely degradation in the system with p H=8,and when illumination for 60 min the degradation rates of ethylparaben（EPB）,propylparaben（PPB）,and butylparaben（Bu PB）were 97.97%,95.6%and93.93%,respectively.The degradation rate of EB/Ag₃PO₄/Ag Br was 91%after five cycles.At the same time,it was found that the adsorption rates of Ag₃PO₄,EB/Ag₃PO₄and EB/Ag₃PO₄/Ag Br（30%）were 1.88%,33.57%and 29.45%respectively in the dark reaction stage,which indicated that the adsorption and photocatalytic oxidation had synergistic effect;the kinetic study showed that the degradation of MPB followed the first-order kinetic model,and the kinetic constant of EB/Ag₃PO₄/Ag Br(K₃=0.0358 min^-1)was 4 times and 2.75 times than that of Ag₃PO₄(K₁=0.011 min^-1)and EB/Ag₃PO₄(K₂=0.013 min^-1).The results of free radical capture and LC-MS showed that the contribution rate of h⁺and·OH to the degradation of MPB was 74.41%and 30.88%respectively,which indicated that the degradation of MPB was realized by gradually attacking the intermediate products of benzoic acid,3-hydroxybenzoic acid,4-hydroxybenzoic acid and azelaic acid,thus MPB can be degraded into CO₂and H₂O.Thirdly,the magnetic La Fe O₃was synthesized by citric acid method,and the magnetic properties of La Fe O₃were used to make up for the defects that EB/Ag₃PO₄/Ag Br material was not easy to recover and could not completely degrade the organic pollutant phenol;EB/Ag₃PO₄/La Fe O₃was synthesized by deposition precipitation method.It was found by XRD,TEM,BET and UV-vis that there are two kinds of lattice fringes in EB/Ag₃PO₄/La Fe O₃,which were La Fe O₃（201）face corresponding 0.24 nm and Ag₃PO₄（210）face corresponding0.27 nm.It can be inferred that the heterojunction structure is formed between La Fe O₃and Ag₃PO₄,and there is no Ag^o.The surface composition of the composite are Ag₃PO₄and La Fe O₃.There are O_OHand O_O2which can produce a lot of·OH and H₂O₂in the material,which makes the absorption range of EB/Ag₃PO₄/La Fe O₃broaden to the whole near infrared region.Fourth,EB/Ag₃PO₄/La Fe O₃was applied to the photocatalytic degradation of phenol.The results showed that the heterojunction structure formed between Ag₃PO₄and La Fe O₃semiconductor played the best role in photocatalytic degradation（the degradation rate of phenol was 93.37%）when doped with 40%La Fe O₃,and the degradation rate of EB/Ag₃PO₄/La Fe O₃to 20 mg/L 50 m L phenol was 98%when p H=7.It was found that the stability of EB/Ag₃PO₄/La Fe O₃（81.62%）was significantly higher than that of Ag₃PO₄/La Fe O₃（40.95%）due to the presence of exfoliated bentonite.This shows that the synergistic effect among EB,Ag₃PO₄and La Fe O₃in EB/Ag₃PO₄/La Fe O₃broadens the scope of light absorption,promotes the separation of electron hole pairs,enhances the adsorption performance and the stability of the material.When La Fe O₃was deposited on the surface of Ag₃PO₄particles and loaded on the exfoliated bentonite,the P-N heterojunction resulted in the high-speed transport of photocarriers on the catalyst interface,which reached a new energy balance and further enhanced the photocatalytic activity and stability of the material.