Preparation And Studies On Photocatalytic Activities Of Ag₃PO₄ Catalysts With Morphology Controlled Or Modified By Methods Of Ba Dosing Or Heterojunction Building

Photocatalytic phenomenon has become a research hotspot since its discovery.Perfect photocatalysts are expected to be in response to visible light,with high photocatalytic activities,with good stabilities and with low cost.So developing desirable photocatalysts is the priority of photocatalytic research.Ag3PO4 serves as an efficient photocatalyst and has obtained much attention.In this paper,we have synthesized some new photocatalysts by methods of morphology controlling,element doping and heterojunction building.As for the newly synthesized catalysts,we will study their structural,physical and optical properties as well as their photocatalytic properties and stabilities.Furthermore,possible photocatalytic degradation schemes will be proposed.Primary research results are as follows:1.The sodium carboxymethylcellulose(CMC)morphology controlled experimental samples were prepared by ion-exchange method.The characterized results were as follows:the dosed CMC affected the morphology of Ag3PO4 when synthesized and triangle package-likewise morphology appeared in the experimental Ag3PO4 sample when the mass ratio of dosed CMC and Ag3PO4 was 1:500.The band gaps of three experimental samples were 2.26 eV,2.34 eV and 2.31 eV,respectively.In the degradation experiment of RhB and MO under visible light,all morphology controlled experimental samples exhibited better photocatalytic activities than control Ag3PO4.When the mass ratio of dosed CMC and Ag3PO4 was 1:500,the experimental Ag3PO4 sample promoted the photocatalytic activities most,this could attribute to its triangle package-likewise morphology.2.Ba element doped Ag3PO4 experimental samples were synthesized by ion-exchange method.The characterized results were as follows:the dosed Ba affected the crystal structure,new substance was even found in 4wt%Ba-Ag3PO4 sample.The band gaps of four Ba-Ag3PO4 samples were 2.39 eV,2.31 eV,2.30 eV and 2.28 eV,respectively.In the degradation experiment of RhB and MO under visible light,the lwt%Ba-Ag3PO4 sample exhibited the most excellent photocatalytic activities,compared with pure Ag3PO4,when exposed to visible light for 12 minutes,the removal rate of RhB was improved by 9.3%and when exposed to visible light for 24 minutes,the removal rate of RhB was improved by 41.9%.Moreover,we deduced from the total organic carbon(TOC)test results that lwt%Ba-Ag3PO4 photocatalst could realize continual mineralization of MO.In addition,lwt%Ba-Ag3PO4 manifested better stabilities than pure Ag3PO4 in four-run repeated photocatalytic degradation experiments.At last,as the experimental results shown about active species verification,the dominant active species in photocatalytic degradation were holes(h+)followed by superoxide anions(O2·-).3.BaGd2MoO7 and BaIn2MoO7 photocatalysts were first synthesized by high temperature solid phase sintering method.The characterized results were as follows:the as-obtained experimental samples presented irregularly spherical morphology and were all nearly nanoparticles with high purity.They both crystallized with a cubic structure by space group Fd3m.The band gaps of two catalysts were 2.49 eV and 2.62 eV,respectively,which implied that they could realize visible-light response.In the degradation experiment of MO under visible light,the removal rates of MO for BaGd2MoO7,BaIn2MoO7 and N-doped TiO2 photocatalysts were nearly 100%,83.6%and 61.6%after irradiation for 240 minutes,respectively.So BaGd2MoO7 and BaIn2MoO7 exhibited much more excellent photocatalytic activities than N-TiO2,of which BaGd2MoO7 was the most outstanding photocatalyst.4.The Ag3PO4/BaGd2MoO7 heterojunction experimental samples were prepared by ion-exchange method,the mass percentages of BaGd2MoO7 and Ag3PO4 were 10wt%,25wt%and 50wt%,respectively.The characterized results were as follows:the Ag3PO4/BaGd2MoO7 heterojunction experimental samples all contained the crystal structures of BaGd2MoO7 and Ag3PO4.The band gaps of three heterojunction experimental samples were 2.38 eV,2.35 eV and 2.30 eV,respectively.In the degradation experiment of RhB under visible light,the photocatalytic activities of heterojunction catalysts with low content of BaGd2MoO7 were nearly equal to pure Ag3PO4,with which as photocatalysts RhB were both almost completely removed under irradiation for 18 minutes,but declined fiercely in the degradation experiment of MO under visible light.As TOC test results shown,Ag3PO4/25wt%BaGd2MoO7 photocatalyst displayed higher mineralization than pure Ag3PO4 for the removal of RhB.Moreover,the stabilities of heterojunction experimental samples with Ba doped displayed satisfactory outcomes.According to this,we might as well think that using two methods including element dosing and heterojunction building could not only remain high photocatalytic activities but improve the stabilities of Ag3PO4,and hence saved the cost of photocatalysts.According to theoretical estimation,the valence band and conduction band positions of BaGd2MoO7(ECB=-0.37 eV,EVB=2.09 eV)were both negative than lwt%Ba-Ag3PO4(ECB=0.31 eV,EVB=2.62 eV)which was favorable for the separation of photo-generated electrons and holes and hence improved the photocatalytic activities of photocatalysts.As the experimental results shown about active species verification,the dominant active species in photocatalytic degradation were hydroxyl radicals(·OH)and superoxide anions(O2·-).At last,one possible photocatalytic degradation scheme of lwt%Ba-Ag3PO4/25wt%BaGd2MoO7 catalyst was proposed.