Preparation Of Y₂SiO₅:Pr³⁺,Li-NaNb_xTa_1-xO₃ And Na₂Nb_xTa_2-xO₆-cocatalysts Composites And Study On Visible Light Photocatalytic Hydrogen Production

Photocatalytic hydrogen production from water splitting,as one of the most promising technique to convert inexhaustible solar energy into high calorific value hydrogen energy,has attracted more and more attention.In recent years,sodium tantalate compounds?NaTaO3,Na₂Ta₂O₆?as active photocatalysts have come into the front stage and become the focus of concern owing to its comparatively wide band gap and superior photocataytic properties.Photocatalytic hydrogen production capability is closely associated with the band energy levels of semiconductor materials.The wide band-gap of NaTa O3?Eg = 4.00 eV?and Na₂Ta₂O₆?Eg = 4.87 eV?can provide enough driving force for oxidation-reduction reaction in photocatalytic hydrogen production.However,the NaTaO3 and Na₂Ta₂O₆ can only utilize less than 4 % ultraviolet-light of solar spectrum due to its wide band-gap.Thus,it handicaps the practical application of NaTaO3 and Na₂Ta₂O₆ as a photocatalyst for maximum sunlight harvesting.To remedy this drawback,an efficient strategy was proposed,that is,the wide band gap photocatalyst is combined with up-conversion luminescence agent,which allows the use of visible and near infrared lights to activate NaTaO3 and Na₂Ta₂O₆.These up-conversion luminescence agents possess the ability to convert the visible or near infrared lights into the ultraviolet-light,which satisfies the genuine absorption requirement of wide band gap photocatalysts.Particularly,Y₂SiO₅:Pr³⁺,Li+ as up-conversion luminescence agents have wide ultraviolet emission bandwidth?230-310 nm?.Unfortunately,pure NaTaO3 and Na₂Ta₂O₆ can only absorb a small portion of ultraviolet-light that is obtained by Y₂SiO₅:Pr³⁺,Li.To absorb all the up-conversion ultraviolet-light emission of Y₂SiO₅:Pr³⁺,Li,it is necessary to properly the extend light respond range of NaTaO3 and Na₂Ta₂O₆ in the ultraviolet region.Therefore,appropriately adjusting the band gap of NaTaO3 and Na₂Ta₂O₆ can be achieved by introducing isovalent Nb?V?at Ta?V?sites to extend light respond ranges of Na₂Ta₂O₆,which can better match with the up-conversion emissions of Y₂SiO₅:Pr³⁺,Li.The increase in the amount of Nb?V?will yield small red shift for NaNb_xTa_1-xO₃ and Na Nb_x Ta2-xO6,thus creating a optimum Ta/Nb ratio to exactly absorb overall the ultraviolet-light emitted by Y₂SiO₅:Pr³⁺,Li.In addition,the charge carrier recombination rate and photo-e-transport rate are also crucial for photocatalytic hydrogen production activity.Pt as conduction band co-catalyst and Au nanoparticles decorated reduced graphene oxide?RGO?as synergetic co-catalyst can quickly and effectively separate photo-generated electrons and holes.So,the activity of Y₂SiO₅:Pr³⁺,Li/Pt-NaNb_xTa_1-xO₃ and Y₂SiO₅:Pr³⁺,Li/Na₂Nb_xTa_2-xO₆/?Au/RGO?achieved significant enhancement in photocatalytic hydrogen production.Herein,the excellent and visible-light-driven photocatalyst,Y₂SiO₅:Pr³⁺,Li/Pt-NaNb_xTa_1-xO₃ and Y₂SiO₅:Pr³⁺,Li/Na₂Nb_xTa_2-xO₆/?Au/RGO?,was successful synthesized via sol-gel and hydrothermal methods.Furthermore,it was applied to photocatalytic hydrogen production from aqueous methanol solution for the first time under visible-light irradiation.It is noteworthy that the photocatalytic activity of NaTaO3/Na₂Ta₂O₆ was significantly enhanced by loading Y₂SiO₅:Pr³⁺,Li,Pt/?Au/RGO?and doping Nb.The enhanced photocatalytic activity is because the photocatalytic system can more utilize visible-light and efficiently separate electron-hole pairs.Besides,when the mass ratio of Y₂SiO₅:Pr³⁺,Li and NaNb0.5Ta0.5O3/Na2Nb0.5Ta1.5O6 is 0.4:1.0,the Y₂SiO₅:Pr³⁺,Li/Pt-NaNb0.5Ta0.5O3/Y₂SiO₅:Pr³⁺,Li/Na2Nb0.5Ta1.5O6/?Au/RGO?shows the highest visible-light photocatalytic activity of hydrogen production.