Silver-based Z-scheme Composite Photocatalysts:Synthesis,Properties And Photocatalytic Mechanisms

Since the photocatalytic technique become a significant way for environmental remedy,semiconductor-based photocatalytic materials have developed rapidly in recent years.single-component semiconductors show some disadvantages in practical photocatalytic application.Such as high recombination rate of photo-induced hole-electron pairs and low utilization of sunlight.In order to avoiding these shortcomings,in recent years,combination of two semiconductors to form a heterostructure is an efficient way.Two semiconductors with appropriate energy level difference could effectively promote the carrier separation and transfer.On the other hand,the combination of narrow/wide bandgap semiconductors could widen spectral response.Both these two photocatalytic systems are beneficial for enhancing photocatalytic performances.In addition,a ternary composite heterostructure could be established by introducing a noble metal into a semiconductor/semiconductor-based composite photocatalyst.By compared with binary semiconductor photocatalyst,these ternary composite heterostructures show the better photocatalytic activities.Because a Z-scheme photocatalytic system could be formed betweem these semiconductors and noble metals.Z-scheme photocatalytic system is facilitated for separation of carriers.Particularly,metal Ag,as a good conductor,is a noble metal with good LSPR absorption,and it is widely used in construction of composite photocatalytic systems.Based on the above background,this article is devoted to design and prepare various of Ag-based composite photocatalysts.The photocatalytic performances and Z-scheme photocatalytic mechanisms of these composite photocatalysts are also investigated.The specific works are presented as following:?1?A p-n heterostructure is synthesized by coupling p-type semiconductor Ag₆Si₂O₇ and n-type semiconductor ?-Fe₂O₃ short nanotubes?SNTs?at the first time.The morphologies,crystal structures,photocatalytic performances and photocurrent properties of as-synthesized ?-Fe₂O₃/Ag₆Si₂O₇ heterostructures are investigated.The photocatalytic performance of ?-Fe₂O₃/Ag₆Si₂O₇ heterostructures could be tailored by adjusting the ratio of ?-Fe₂O₃ and Ag₆Si₂O₇.When the ratio of ?-Fe₂O₃ and Ag₆Si₂O₇ is 12.5:4,this heterostructure show the best photocatalytic performance for degradation of various organic pollutants,which is better than prure ?-Fe₂O₃,Ag₆Si₂O₇ and commercial TiO2.Furthermore,comparing with pure ?-Fe₂O₃ SNTs,the photocurrent intensity of ?-Fe₂O₃/Ag₆Si₂O₇ heterostructures is improved 62 times.The enhanced significant photocatalytic performance of ?-Fe₂O₃/Ag₆Si₂O₇ heterostructures could be attributed to the Z-scheme charge separation system between Ag₆Si₂O₇ NPs,Ag and ?-Fe₂O₃ SNTs.?2?The Ag nanoparticles are coated on the surface of ?-Fe₂O₃ SNTs by classic silver mirror reaction after surface modification.After partial oxidation of Ag nanoparticles,the final ?-Fe₂O₃/Ag/AgCl heterostructure are obtained.The photocatalytic performances of these V/Ag/AgCl heterostructures are tailored by adjusting the ratio of Ag and AgCl.The photocatalytic activities are tested by the degradation of organic dye Rhodamine B?RhB?under the UV-Visible mixed light,visible light??>450 nm?and UV light??<420 nm?irradiation.The V/Ag/AgCl heterostructure show the best photocatalytic performance among all the ?-Fe₂O₃,?-Fe₂O₃/Ag,commercial TiO2 and ?-Fe₂O₃/Ag/AgCl samples.The enhanced photocatalytic performance is attributed to the LSPR associated Z-scheme photocatalytic system.Specifically,the broad spectral response and efficient charge transfers among Ag,?-Fe₂O₃ and AgCl in this Z-scheme system are the main reasons for improving photocatalytic performance.?3?Novel g-C₃N₄ polymer photocatalyst is induced to the Ag/Ag3PO4 composite photocatalysts.The influence of Ag content and ratio of each component on the photocatalytic performance of g-C₃N₄/Ag/Ag3PO4 are closely considered.During the photocatalytic test?carried out by the degradation of organic dye acid orange 7 under visible light??>450 nm?and UV-Visible mixed light.?,it is found that the sample with g-C₃N₄,Ag3PO4 and Ag ratio of 1:2.52:0.12 show the best photocatalytic performance.The photocatalytic performance of this sample is better than g-C₃N₄,g-C₃N₄/Ag3PO4,commercial TiO2 and other g-C₃N₄/Ag/Ag3PO4 samples.It indicates that Ag content in this composite heterostructure play a crucial rule in tailoring the photocatalytic performances.Moreover,the g-C₃N₄/Ag/Ag3PO4 also show the excellent photocatalytic stability.The stable and significant superior photocatalytic performance of g-C₃N₄/Ag/Ag3PO4 could be attributed to the fast charge separation among g-C₃N₄,Ag and Ag3PO4 during the Z-scheme charge transfer and recombination process.?4?After investigation of these Ag-based Z-scheme photocatalytic system,the Au/Ag bimetal is induced into AgCl semiconductor.The Ag/Au/AgCl hollow heterostructure is synthesized by using Ag nanowires as raw materials during the galvanic replacement reaction?GRR?.The photocatalytic performances of these Ag/Au/AgCl hollow heterostructures are adjusted by the ratio of Au,Ag and AgCl.The photocatalytic tests are carried out by degradation of A07 under UV-Visible mixed light illumination.When the ratio of Au,Ag and AgCl is 8:2:6,the Ag/Au/AgCl hollow heterostructure show the best photocatalytic activity.The reaction rate of this Ag/Au/AgCl hollow heterostructure is more than 80 times better than it of Ag nanowires.It is also 6 times better than commercial TiO2.The superior photocatalytic performance of Ag/Au/AgCl could be attributed to the fast charge separation,the localized surface plasmon resonance?LSPR?and plasmon resonance energy transfer?PRET?of noble metals.