| TiO2-based nanomaterials are well-known as an efficient photocatalyst owing to their great advantages containing low cost,strong oxidizing power,physicochemical stability and environmental friendliness.The TiO2-based titanate nanosheets(TNSs)are synthesized by one-step hydrothermal method.Compared with other TiO2-based nanomaterials,the as-prepared TNSs obviously exhibit porous flake-like structure with large grain size and specific surface area(300-400 m2/g)and small thickness,which is expected that more reactive sites are exposed and more reactants can contact with TNSs.In addition,more photo-generated electrons can fast transfer and reach the surface easily to involve in the photocatalytic reactions.Hence,these advantages of TNSs result in a higher adsorption-photocatalytic performance.However,like TiO2-based nanomaterials,it’s difficult to utilize visible light due to its wide band gap of about 3.2 eV and the recombination of photo-induced electron and hole pairs is too fast in TNSs.For this reason,based on the structural peculiarities and physicochemical properties of TNSs,here we realize the modification of TNSs surface and interface via different methods containing the loading of transition metal oxides,deposition of noble metal and coupling suitable semiconductors.And the microstructure,photoelectrical properties and visible-light photocatalytic activity of the modified TNSs are also studied.1、The visible-light-sensitive titanate nanosheets were synthesized with Cr2O3 successfully loaded and well dispersed on(Cr-TNSs)by one-step hydrothermal method for enhanced photocatalytic activity.As our previous reports,the as-prepared samples obviously exhibited porous flake-like structure with large specific surface area(300-400 m2/g).Accompanied with the hydrothermal growth of TNSs,loaded Cr2O3 not only influenced the layered structure of TNSs,but also brought about remarkable enhancement on the visible-light response and the separation of photogenerated carriers.The XPS fitting results indicated that Cr3+ mainly existed in trivalent forms and caused the change in binding states toward Ti and O.Based on the evaluation of photocatalytic activity,it was found that Cr-TNSs obtained an significantly improvement for RhB and K2Cr2O7(Cr(VI))degradation under visible-light irradiation,which was attributed to the retarding of charge recombination and the effective electron transfer from Cr2O3 to TNSs.The better photocatalytic activity was obtained with an optimal content(0.5 at.%)of Cr3+,and the degradation rate(Kapp)was 2.9-fold and 4.1-fold,respectively,as compared to TNSs.The cyclic tests demonstrated the nice stability and recycling performance of samples.The alternative mechanisms for the visible-light-sensitive photocatalytic activity were also proposed.2、The quantitative Pt deposited(0.25 wt.%)Cr2O3-loaded TNSs(Pt/Cr-TNSs)with different proportions of Cr3+ was prepared via in situ photoreduction method.Pt was uniformly dispersed on the surface of TNSs,which had no obvious impact on its morphology and structure.XPS analysis results showed that the deposition of Pt hardly affected the surfacial chemical states of TNSs and Cr-TNSs.In addition to the elemental Pt(Pt0),there were a few Pt species existing as Pt-Oads form.After Pt loading on TNSs,it caused the distinct absorption in the visible-light region due to the surface localized plasmon resonance(LSPR).Besides,the Cr-TNSs still had obviously characteristic absorption in the visible region.After Pt deposited,the photogenerated carriers interfacial transfer and separation efficiency of Cr-TNSs further improved.The visible-light photocatalytic H2 production activity was evaluated using the samples with Pt nanoparticles as cocatalyst.The results showed that the H2 production rate of Pt/Cr-TNSs(0.25 wt.%of Pt)was observably enhanced,giving a relatively high H2 generation rate of 473 μmol h-1 g-1 for Pt/0.5%Cr-TNSs.Driven by visible light,Cr2O3/TNSs nano-heterostructure could produce good synergistic effect with Pt cocatalyst as electron sink,which greatly enhanced the photocatalytic H2 evolution efficiency.The cyclic tests demonstrated the nice stability and recycling performance of samples,and Pt could firmly exist on TNSs surface.3、The compound of Cr-TNSs coupled with MoS2 nanoflowers was prepared via solvothermal method.Under the same proportion of MoS2,the MoS2@Cr-TNFs(Cr-TM)samples with different amounts of Cr2O3 were obtained.Cr-TNFs could fully contact with MoS2 active edges,forming nanoflocs layered structure.XPS analysis results showed that the compound Cr-TNFs with MoS2 almost didn’t affect their surface chemical states.The coupled electron orbit between them might exist at the interface as Ti-O-Mo bonding forms,and the loaded Cr2O3 could stablize on the TNFs.In addition,the as-prepared Cr-TM composites exhibited both the overall enhancement in visible-light response and Cr2O3 characteristic absorption.As the support of electron transport and migration,MoS2 could play the role of cocatalyst,improving the interfacial transfer efficiency of photo generated electrons,and accelerating the in-layered transport and separation with holes.The visible-light photocatalytic H2 production test results indicated that the H2 production rate of Cr-TM(20 wt.%of MoS2)was observably enhanced,giving a relatively high H2 generation rate of 217 μmol h-1 g-1.for 0.5%Cr-TM.Driven by visible light,Cr2O3/TNFs nano-heterostructure could bring about good synergistic effect with MoS2 cocatalyst,in which the photo-induced electrons could pass through MoS2 basal planes and reach the active edge sites,participating in the proton-reduction reaction.The cyclic tests demonstrated the nice stability and recycling performance of samples,and MoS2 could well contact with TNFs surface. |
PDF Full Text Request