The Preparations Of K₂La₂Ti₃O₁₀ Catalyst And The Study Of Its Photocatalytic Activity For Water Splitting

Hydrogen energy,as a secondary energy souece, is an ideal green energy because of its nonpollution and renewablity.The hydrogen production by water photocatalytic splitting using photocatalysts has been known as an economic and clean technology and a promising process for solar conversion and storage.The development of highly photoresponsible catalysts is the core of water photo splitting.The progress in research of photocatalytic water splitting for hydrogen production was reviewed involving photocatalysts species,photoreaction system and effective visible light harvest for water photolysis.This paper focuses on the research such as preparation and modification of efficient photocatalysts sensitive to visible light.Conclusions were made as follows:An ion-exchangeable layered perovskite type oxide,K₂La₂Ti₃O₁₀,was prepared by polymerized complex method and sol-gel method and characterized by XRD,DRS,SEM and XPS,et al.The influence of preparation method on the photocatalytic reactivity of K₂La₂Ti₃O₁₀ for hydrogen production was studied while I^- was used as electron donor.It was found that the sol-gel method showed a superiority compared with the polymerized complex method.When K₂La₂Ti₃O₁₀ prepared by sol-gel method was used as photocatalyst for water splitting,the hydrogen production rate was twice than that prepared by polymerized complex.The preparation condition was temperate.It was easy to get single phase K₂La₂Ti₃O₁₀ photocatalyst with sol-gel method.The optimum water splitting conditions was obtained when K₂La₂Ti₃O₁₀ was used as photocatalyst and I^- as electron donor as follows:pH 11.5 and the amount of loading RuO₂ on the K₂La₂Ti₃O₁₀ photocatalyst was 0.2-0.3%(Wt).The hydrogen production rate was 57μmol.l^-1h^-1 under ultraviolet radiation and was 16.5μmol.l^-1h^-1 under visible light radiation.The influence of calcination atmosphere on the photocatalytic reactivity of K₂La₂Ti₃O₁₀ for hydrogen production was investigated.The photocatalytic reactivity of K₂La₂Ti₃O₁₀ prepared under air,Ar and H₂ atmosphere was compared under ultraviolet and visible light radiation with I^- as electron donor.The results showed that K₂La₂Ti₃O₁₀ had higher photocatalytic activity for hydrogen production prepared under Ar and H₂ atmosphere than that prepared under air atmosphere.The hydrogen production rates under ultraviolet irradiation were 127.5,81.3 and 57μmol.l^-1h^-1 respectively when K₂La₂Ti₃O₁₀ was prepared underAr,H₂ and air atmosphere as photocatalyst.The hydrogen production rates under visible light irradiation were 40.2,30.2 and 16.5μmol.l^-1h^-1 respectively when K₂La₂Ti₃O₁₀ was prepared under Ar,H₂ and air atmosphere as photocatalyst.The fourth periodic transition metals were firstly used to modify the wide band gap K₂La₂Ti₃O₁₀ photocatalyst to improve the photocatalytic activity and visible light responses of K₂La₂Ti₃O₁₀.Effects of doping elements and doping concentrations on the photocatalytic activity of K₂La₂Ti₃O₁₀ for hydrogen production under ultraviolet light and visible light irradiation were investigated.The results showed that K₂La₂Ti₃O₁₀ doped with Cr,Zn and V exhibited higher photocatalytic reactivity of hydrogen production.K₂La₂Ti₃O₁₀ doped with Cr exhibited highest photocatalytic reactivity of hydrogen production.Owing to the red shift of light absorption when doped with Cr,Zn and V,doping K₂La₂Ti₃O₁₀ showed photocatalytic activity under visible light irradiation.The optimum doping concentration of Cr,Zn and V was found when K₂La₂Ti₃O₁₀ as photocatalyst and I^- as electron donor.(1)The optimum doping concentration of Cr was 2.0%.The hydrogen production rate was 1500μmol.l^-1h^-1 under ultraviolet irradiation and 83.6μmol.l^-1h^-1 under visible light irradiation.(2)The optimum doping concentration of Zn was 1.5%.The hydrogen production rate was 131.9μmol.l^-1h^-1 under ultraviolet irradiation and 57.8μmol.l^-1h^-1 under visible light irradiation.(3)The optimum doping concentration of V was 1-1.5%.The hydrogen production rate was 100μmol.l^-1h^-1 under ultraviolet irradiation and 44μmol.l^-1h^-1 under visible light irradiation.The hydrogen production rate under visible light irradiation was higher than that reported in the literatures and patents when I^- was used as electron donor.The boron family elements were used to modify the wide band gap K₂La₂Ti₃O₁₀ photocatalyst to improve the photocatalytic activity and visible light responses of K₂La₂Ti₃O₁₀.Effects of doping elements and doping concentrations on the photocatalytic activity of K₂La₂Ti₃O₁₀ for hydrogen production under ultraviolet and visible light irradiation were investigated.Owing to the red shift of light absorption when doped with boron family elements,K₂La₂Ti₃O₁₀ showed photocatalytic activity under visible light irradiation.The optimum doping concentration of boron family elements was found when K₂La₂Ti₃O₁₀ as photocatalyst and I^- as electron donor. (1)The concentration of B was 1.0%,the hydrogen production rate was 151.7μmol.l^-1h^-1 under ultraviolet irradiation.The concentration of B was 2.0%,the hydrogen production rate was 83.6μmol.l^-1h^-1 visible light irradiation.(2)The optimum concentration of Al was 2.0%.The hydrogen production rate was 138μmol.l^-1h^-1 UNDER ultraviolet irradiation and 78.1μmol.l^-1h^-1 under visible light irradiation.(3)The concentration of Ga was 3.0%,the hydrogen production rate was 192.4μmol.l^-1h^-1 under ultraviolet irradiation.The concentration of Ga was 1.5%,the hydrogen production rate was 97.3μmol.l^-1h^-1 under visible light irradiation.(4)The optimum concentration of In was 1.0%-2.0%.The hydrogen production rate was 115μmol.l^-1h^-1 or so under ultraviolet irradiation and 48μmol.l^-1h^-1 or so under visible light irradiation.The hydrogen production rate under visible light irradiation was higher than that reported in the literatures and patents when I^-was used as electron donor.Base on the crystal characterization of K₂La₂Ti₃O₁₀ photocatalyst,the electronic structures of K₂La₂Ti₃O₁₀ doped with the fourth periodic transition metals and the boron family elements have been analyzed by the first principles calculations with the density functional theory.The the calculations results reveals the photo responses in the visible region and improvement of photocatalytic activity.(1)The fermi energy level of K₂La₂Ti₃O₁₀ moved to the conduction bands when doped with Cr and V and new levels occurred between the conduction and valence bands.The E_g of K₂La₂Ti₃O₁₀ was reduced and photoproduced electrons and holes were easily excited with lower energy compare with the undoped K₂La₂Ti₃O₁₀.The top of K₂La₂Ti₃O₁₀ valence bands doped with Zn moved towards higher energy and conduction bands bottom moved towards lower energy,the K₂La₂Ti₃O₁₀ was reduced and photoproduced electrons and holes were easily excited with lower energy compare with the undoped K₂La₂Ti₃O₁₀.(2)The fermi energy level of K₂La₂Ti₃O₁₀ moved to the conduction bands when doped with B and new levels occurred between the conduction and valence bands.The top of K₂La₂Ti₃O₁₀ valence bands doped with Al,Ga,In moved towards higher energy and conduction bands bottom moved towards lower energy,the E_g of K₂La₂Ti₃O₁₀ was reduced and photoproduced electrons and holes were easily excited with lower energy compare with the undoped K₂La₂Ti₃O₁₀.