Preparation Of High Proportion Of Z-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/Pt/In₂O₃ Photocatalyst And Study On Visible-light Hydrogen Production From Water Splitting

With the rapid development of society and the acceleration of urbanization,issues such as energy crisis and environmental pollution have become increasingly prominent.Exploring green,efficient and sustainable alternatives to new energy carriers is a hot topic for most researchers today.The application of semiconductor photocatalytic technology to the decomposition of water to produce hydrogen,the production clean energy and renewable energy has a wide application prospect.At present,many semiconductor photocatalyst are used in research of photocatalytic decomposition of water to produce hydrogen.However,most of the excellent semiconductor photocatalyst have a wide band gap and can only exhibit photocatalytic activity under ultraviolet light irradiation,resulting in inefficient use of solar energy.In addition,photo-generated electron-hole pairs are easily recombined,weak redox ability and poor stability,resulting in low activity of these photocatalysts,which have not yet reached the level of industrial production.In order to improve the activity of photocatalytic hydrogen production,we first selected Nb₂O₅ and In₂O₃ semiconductor photocatalysts with different band gaps to form a Z-scheme Nb₂O₅/In₂O₃ photocatalytic system.The formed Z-scheme photocatalytic system has three advantages:?1?The recombination of photo-generated electron-hole pairs in the respective components can be effectively suppressed.?2?The composition of the Z-scheme photocatalytic system retained the valence band potential with strong oxidation ability and the conduction band potential with strong reduction ability in the two semiconductor photocatalysts,so that the whole system has strong redox capacity.?3?Semiconductor photocatalysts with different different band gaps,which allow them to absorb light in different wavelength ranges,making full use of the solar spectrum.Although the Z-scheme Nb₂O₅/In₂O₃ photocatalytic system formed has these advantages,there are still some shortcomings.Since the Nb₂O₅ semiconductor photocatalyst has a wide band gap,it exhibits high photocatalytic activity only under ultraviolet light irradiation.In fact,ultraviolet light only accounts for 4%of the solar spectrum,making most of the visible light difficult to use by photocatalysts,which limits the application of Nb₂O₅.In order to make the Z-scheme Nb₂O₅/In₂O₃ photocatalytic system operate normally,we use the up conversion illuminant agent Er³⁺:Y₃Al₅O₁₂ in combination with the Nb₂O₅ semiconductor photocatalyst.Er³⁺:Y₃Al₅O₁₂ can absorb visible light and converts them into ultraviolet light to excite the wide band gap Nb₂O₅.Such improvements have greatly improved the range of utilization of the solar spectrum.Thirdly,when constructing a Z-scheme Nb₂O₅/In₂O₃ photocatalyst,in order to avoid rapid recombination of photogenerated electron-hole pairs in Nb₂O₅ and In₂O₃,the addition of a conductive channel between the two semiconductors accelerates the transfer of electrons on the Nb₂O₅ conduction band to the In₂O₃ valence band and binds to the holes on the In₂O₃ valence band.Finally,in order to obtain a high proportion of Z-scheme photocatalyst,we propose a new preparation method,that is,Coating-Demoulding?C-D?method,for obtaining a high proportion of Z-scheme photocatalyst particles.Through this mandatory method,different catalyst particles can effectively be combined together,greatly enhancing the proportion of Z-scheme photocatalyst composite particles and reduce the number of non-Z-scheme composite particles as by-products.The experimental results prove that this new preparation method is beneficial to improve the activity of the Z-scheme photocatalyst.In this paper,Z-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/In₂O₃ photocatalyst can be prepared by Mechanical-Mixing?M-M?method.High proportion of Z-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/In₂O₃ and Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/Pt/In₂O₃ photocatalysts can be prepared by Coating-Demoulding?C-D?method.In Coating-Demoulding?C-D?Z-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/Pt/In₂O₃ photocatalyst,Pt nanoparticles as conductive channels are fixed between Er³⁺:Y₃Al₅O₁₂@Nb₂O₅ and In₂O₃.Er³⁺:Y₃Al₅O₁₂ as up-conversion luminescence agent can provide enough ultraviolet-lights to activate wide band-gap Nb₂O₅.The as-prepared samples are characterized by X-ray diffractometer?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,energy dispersive X-ray?EDX?spectroscopy,X-ray photoelectron spectroscopy?XPS?,UV-vis diffuse reflectance spectra?UV-VisDRS?,fouriertransforminfraredspectra?FT-IR?,photoluminescence?PL?spectra and related electrochemical tests.Further,the effects of heat-treated temperature,heat-treated time and used times on the photocatalytic hydrogen production activity of Mechanical-Mixing?M-M?Z-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/In₂O₃,Coating-Demoulding?C-D?Z-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/In₂O₃andCoating-Demoulding?C-D?Z-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/Pt/In₂O₃ composite are studied in detail.The experimental resultsshowedthatthephotocatalyticactivityofZ-scheme Er³⁺:Y₃Al₅O₁₂@Nb₂O₅/Pt/In₂O₃ composite is the highest in photocatalytic hydrogen production when heat-treated temperature and time are 500°C and 1.0 h,respectively,and that the high photocatalytic activity can be maintained within four cycles.It can be confirmed that the Coating-Demoulding?C-D?method can effectively combine different photocatalyst particles in predicted order,greatly enhancing the proportion of highly active Z-scheme photocatalyst particles.In summary,this study successfully designed an effective visible light-driven photocatalyst for photocatalytic hydrogen production.It is of great significance to improve the preparation method of Z-scheme photocatalyst and large-scale hydrogen production.