Construction And Photocatalytic Properties Of 2D Layered Photocatalysts With MXene As Electron Mediator

With the rapid development of human society and the rapid advancement of industrialization,environmental security and energy security have become two major problems that humans must face.Photocatalysis technology is considered to be an effective way to solve the above problems at the same time.Therefore,it is very necessary to develop an environmentally friendly and efficient photocatalytic technology.Recently,MXenes,a graphene-like two-dimensional（2D）layered material,have attracted extensive attention of researchers due to their superior physical and chemical properties,such as excellent electrical conductivity,high mechanical strength,and outstanding optical properties.In this paper,2D Ti₃C₂MXene is used as the research object to construct a two-dimensional layered photocatalytic material with Ti₃C₂MXene as an electron mediator.2D/2D Ti₃C₂/SnS₂Schottky heterojunction photocatalysts and 2D/2D/2D PCN（Protonated g-C₃N₄）/Ti₃C₂/Bi₂MoO₆ternary Z-type heterojunction photocatalysts were prepared,respectively.The catalytic performance of the prepared photocatalysts was evaluated by degrading tetracycline hydrochloride（TC-HCL）.The specific contents and results are as follows:（1）MAX titanium aluminum carbide（Ti₃Al C₂）was used as the precursor to prepare multi-layer MXene（Ti₃C₂）samples by fluoride salt/strong acid etching method.Then,the multi-layer Ti₃C₂MXenes were then intercalated using organic reagents（DMSO）as intercalating agents.Finally,the multilayer Ti₃C₂MXene was exfoliated into ultrathin 2D Ti₃C₂nanosheets by ultrasonic exfoliation.The crystal structure,microscopic morphology,elemental composition and chemical valence state of 2D Ti₃C₂nanosheets were explored by XRD,TEM and AFM characterizations before etching and after etching and ultrasonic stripping.（2）2D/2D Ti₃C₂/SnS₂heterojunction photocatalytic materials were constructed in situ by a simple hydrothermal method.The effects of 2D Ti₃C₂nanosheets on the structure and properties of 2D/2D Ti₃C₂/SnS₂heterojunction photocatalytic materials were investigated.The performance of the prepared photocatalysts was evaluated by photocatalytic degradation of TC-HCL under visible light irradiation.Compared with pure SnS₂,the 3%Ti₃C₂/SnS₂composite photocatalyst exhibits excellent photocatalytic activity,the TC-HCL degradation efficiency reaches 87.7%,and the first-order kinetic rate constant k value is 2.7 times higher than that of the pure SnS₂sample.The enhanced photocatalytic performance benefits from the formation of2D/2D Schottky heterojunctions,which are beneficial to facilitate photogenerated carrier transfer and separation,and also provide more active sites for photodegradation reactions.Furthermore,the photoresponse ability of the composite photocatalyst is greatly enhanced due to the addition of Ti₃C₂with excellent optical properties.（3）A novel 2D/2D/2D PCN/Ti₃C₂/Bi₂MoO₆ternary Z-type heterojunction was successfully fabricated by a simple hydrothermal method and electrostatic self-assembly method.The photocatalytic performance of ternary PCN/Ti₃C₂/Bi₂MoO₆composites was evaluated by degrading TC-HCL under visible light irradiation.Compared with pure Bi₂MoO₆,PCN,Ti₃C₂/Bi₂MoO₆and 5%PCN/Bi₂MoO₆,the 5%PCN/Ti₃C₂/Bi₂MoO₆composite exhibited higher photocatalytic activity,and the degradation efficiency of TC-HCL reached 81.3%.In addition,the kinetic rate constant k of the 5%PCN/Ti₃C₂/Bi₂MoO₆sample reaches 0.0155 min^-1,which is 3.6 times of pure Bi₂MoO₆(0.0043 min^-1),1.7 times of pure PCN(0.0089 min^-1)and 1.3 times of the 5%PCN/BMO sample(0.0118 min^-1),respectively.The enhanced photocatalytic performance benefits from the surface-to-surface contact 2D layered structure,which not only shortens the charge transfer distance but also provides a large number of charge transfer channels.In addition,Ti₃C₂MXene was used as an electron transfer mediator to accelerate the separation and transfer of photogenerated carriers between Bi₂MoO₆and PCN,thereby enhancing the photocatalytic efficiency.Based on the band structure of the composites and radical trapping experiments,a possible Z-type charge transfer mechanism is proposed.