The Promotion Of SrTiO₃ And TiO₂ Photocatalysts For Visible Light Activity,and The Exploration Of Fluorescein Visible Light Photocatalyst

Photocatalytic water splitting is one of the most attractive routes to use and store solar energy.In 1972,Fujishima and Honda were first reported that TiO₂ electrode can produce hydrogen under UV irradiation.Many wide bandgap semiconductors,such as TiO₂ and SrTiO₃ have advantages of acid and alkali corrosion resistance,good stability,low cost and non-toxic,and are most widely used.The main problems are that the photocatalysts only utilize UV light which accounts the 3%⁴% of the sunlight,the recombination of photogenerated carriers is too fast.Therefore,expanding the semiconductor absorption range and promoting the charge separation are effective ways to improve the photocatalytic activity of hydrogen production.Our detailed works and acquired results are as follows:1 A novel SrTiO₃-Ba₂FeNbO₆ solid solutions for visible light hydrogen production.BaTiO₂ is a common perovskite materials and not able to photocatalytic hydrogen production due to the lower position of the conduction band?0.08 V versus NHE?than the standard of hydrogen?0 V?.Substituting Ti for Fe and Nb atoms in perovskite type of BaTiO₂ can effectively regulate the valence band and conduction band position of perovskite materials.We prepared SrTiO₃-Ba2FeNbO6 solid solutions to enhance the charge separation efficiency of Ba2FeNbO6.This novel STO-BFNO perovskite solid solution has a good hydrogen production activity under visible light?7.15 mmol/h?.2 Constructing bulk defective perovskite SrTiO₃ nanocubes for high performance photocatalysts.The current study suggests that the oxygen vacancies with appropriate concentration not only can expand the absorption range of semiconductor,but also improve the separation efficiency of photogenerated carriers,so as to enhance the photocatalytic activity and the utilization efficiency of sunlight.Oxygen vacancies are usually constructed by chemical reduction under high temperature,such as using hydrogen,aluminum vapor and sodium borate to reduce semiconductor.SrTiO₃ nanocubes are synthesized by using TiO₂ as Ti source,SrCO₃ as Sr source,NaCl and KCl as mixed molten salts.We also prepare SrTiO₃ nanocubes with oxygen vacancies both in bulk and surface area by using Ti powders as a second Ti source.When the molar ratio of Ti/TiO₂ is 5:7,the bset activity of SrTiO₃ nanocubes is obtained and the hydrogen production rate is 8.48 mmol/h under visible light?l > 420 nm,50 mg?.IPCE tests show that SrTiO₃?5:7?with oxygen vacancies has the obvious improvement of photoelectric separation efficiency in the UV region and the photoelectric response also extendeds to 430 nm?SrTiO₃ without oxygen vacancies only active until 400 nm?.Surface photovoltage spectroscopy?SPS?shows that SrTiO₃ gradually shifts from the n type to the p type with the increase of oxygen vacancies.3 Hierarchical TiO₂ spheres decorated with Au nanoparticles for visible light hydrogen production.We have prepared the TiO₂ nano microspheres with high specific surface areas?97 cm2/g?by solvothermal method,as the larger specific surface areas than commercial P25 TiO₂? 50 cm2/g?,the TiO₂ nano microspheres have a better hydrogen production activity?335 mmol/h,10 mg?.Thioglycolic acid?TGA?molecules have both carboxyl?-COOH?and sulfhydryl?-SH?,-COOH group can be adsorbed on the surface of TiO₂,while-SH group has a very strong force with Au ions.Finally,by adding sodium borohydride solution and reducing HAuCl4 fastly,the Au nanoparticles of 5 nm with a good dispersion are obtained.SEM,TEM,EDAX and DRS results demonstrate that the Au nanoparticles are loaded on the surface of TiO₂ nano microspheres.The photocatalytic tests show that Au nanoparticles have different effects under UV and visible light,respectively.TiO₂ is inspired under UV light,while the generated electrons transfer to Au nanoparticles and produce hydrogen on the surface of Au nanoparticles.The Au nanoparticles are inspired due to surface plasma resonance?SPR?absorption under visible light,while the generated electrons transfer to TiO₂ microspheres and produce hydrogen on the surface of TiO₂.4 The formation process of TiO₂@CdS composite structure.TiO₂ photocatalyst have an ultraviolet response and no visible light activity,while CdS is a narrow bandgap semiconductor photocatalytic materials?Eg = 2.4 eV?and has the high visible light photocatalytic activity.But CdS is less stable due to light corrosion.Building TiO₂/CdS composite materials not only can enhance the visible light activity of TiO₂,but also reduce the light corrosion of CdS.We prepared the 250 nm TiO₂/CdO composite nanofibers via electrostatic spinning and treated by sodium sulfide solution,finally the CdS nanosheets coated TiO₂ hollow nanotubes composite materials are formed.We speculate that the formation process of TiO₂@CdS composite structure.First of all,the CdO is dissolved under high temperature hydrothermal treatment,the nanofiber of TiO₂ nanoparticles are transformed into a loose structure.Then,the dissolved CdO are transformed into CdS nanosheets coated on the outside of TiO₂ hollow nanotubes.When the Ti/Cd is 1:1 and 2:1,CdS nanosheets coated TiO₂ hollow nanotubes are formed due to the formation of more CdS;when Ti/Cd is 4:1 and 8:1,CdS nanosheets are not sufficient to coat TiO₂ hollow nanotubes.The TiO₂@CdS?1:1?nanocomposites have the best H2 production rate of 19.7?UV-Vis?and 3.4 mmol/h?l > 420 nm?for 50 mg samples.5 A novel fluorescein supramolecular nanosheets for visible light hydrogen production and novel molecular hydrogen system which uses fluorescein as the photosensitizer.The fluorescein supramolecular nanosheets are synthesized according to a simple dissolution-recrystallization reaction by adding methanol to dissolve original fluorescein purchased from Aladdin Reagent Company and evaporating methanol at 250 °C.SEM and TEM images show the morphology is nanosheets.The optimal mass fraction of Pt is about 1% and H2 production rate is 21.01 mmol/h?l > 420 nm?for 50 mg when 0.5 M oxalic acid serves as holes scavenger and one times than C3N4 prepared from urea.The corresponding apparent QE at 420 ± 10 nm reaches 1.2%.The active wavelength only reaches 520 nm,although UV-Vis DRS shows a strong light absorption after 520 nm.Surface photovoltage spectrum presents an active visible light photovoltage response reaching 529.6 nm,which is accord with the active wavelength of H2 production.Photocatalytic H2 production tests indicate the fluorescein supramolecular nanosheets are a Visible-Light-Active and unstable photocatalyst.We also report a novel molecular hydrogen system which uses a noble metal free fluorescein as the photosensitizer,Pt nanoparticle as the cocatalyst and triethanolamine?TEOA?as the hole scavenger.The highest H2 production rate is 163.81 mmol/h?l > 420 nm?and quantum efficiencies of our system are among the highest reported for the molecular hydrogen systems in the visible light range.Our system exhibits relative durability and the H2 production rate is still as high as 55.94 mmol/h even after molecular hydrogen reaction 120 h.