Study On Improving The Performance Of Photo-thermal Synergistic Catalytic Hydrogen Production By TiO₂ With Non-noble Metal Auxiliary Catalyst

Photocatalytic hydrogen production technology is an effective way to make use of abundant renewable solar energy to produce clean energy and alleviate energy and environmental problems.As a semiconductor material,titanium dioxide(TiO₂)is widely used in photocatalytic hydrogen production due to its abundant reserves,non-toxic and stable physical and chemical properties.However,the practical application of pure TiO₂(P25)is limited due to its low ability to capture light and high recombination rate of photogenerated e-/h+pairs.To achieve high efficiency of photocatalytic hydrogen production,rational design and development of a novel TiO₂-based photocatalysts is necessary.A series of new photocatalytic materials are constructed via the way of adjusting the structure and optimizing the surface reaction active sites.The new materials were synthesized with P25 as matrix material and histidine(His),copper,nickel as the cocatalysts.Different photocatalysts of P25 modified with His,Cu and Ni are constructed by the methods of complexation and in-situ photodeposition.Taking the prepared system materials as the research object,the morphology and structure of the materials are characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD)and ultraviolet visible absorption spectroscopy(UV-vis);the valence and binding mode of surface chemical elements are characterized by X-ray photoelectron spectroscopy(XPS),fourier transform infrared spectroscopy(IR);the mechanism of the improvement of photocatalytic hydrogen production performance is analyzed by transient photocurrent response(I-t curve),impedance spectroscopy(EIS)and electron paramagnetic resonance(EPR).A series of His modified titanium dioxide photocatalysts are prepared by dipping method to improve the photocatalytic hydrogen production performance.TEM and XRD analysis show that TiO₂-His and pure TiO₂ have similar morphology,particle size and crystal phase composition.In the liquid phase reaction system,photocatalytic hydrogen evolution by splitting water is carried out under 300 W Xe lamp irradiation and the reaction temperature of 15?.The results show that TiO₂-His-3 shows the highest photocatalytic H2 evolution activity(4.77 ?mol/(g·h·m2g-1)),which is 3.77 times higher than that of pure TiO₂.The photocatalytic activity of TiO₂-His-3 catalyst has no significantly decline over 30 h,indicating that the catalyst has good hydrogen production stability.The results of IR and XPS analysis show that the fast interface charge transfer channel is formed between His and the oxygen atoms in TiO₂.The photogenerated holes migrate from the valence band of TiO₂ to the highest occupied molecular orbital of His,which reduces the recombination rate of photogenerated charges,moreover improves the efficiency of hydrogen production.The use of cocatalysts is an effective way to improve the separation and transfer of interfacial charges.After the introduction of copper species into TiO₂-His system,the xCu-His-P25 photocatalysts are constructed by the method of histidine complexation and in-situ photodeposition.TEM,UV-vis and Mapping results show that Cu-His-P25 has the similar morphology and phase composition as pure P25,and copper is uniformly dispersed on P25 surface.The results of photocatalytic experiments show that Cu-His-P25 exhibits excellent photocatalytic activity for hydrogen producction in the reaction system at 5?,the reaction rate is as high as 0.718 mmol/(g·h),which is 512.9,239.3 and 1.37 times of pure P25,His-P25 and Cu-P25,respectively.XPS,I-t,EIS and other characterization methods are used to analyze the mechanism of improving photocatalytic performance.The introduction of copper further improves the separation efficiency of photoinduced electrons and holes,and improves the H2-evolution performance.It provides a new way for the preparation of high-efficiency photocatalysts.Apart from introducing copper species as cocatalyst,the photocatalytic activity for hydrogen production is further enhanced by adding thermal assistance.xCu/His/P25 photocatalysts are synthesized and used for photocatalytic hydrogen production via steam reforming of methanol.The analysis results of TEM,XRD,XPS,I-t and PL show that Cu+species uniformly dispersed on P25 support;the morphology,structure and phase composition of pure P25 are not changed after introduction of histidine and Cu+;N-Cu species on the xCu/His/P25 surface contributes to the scattering and stabilization of Cu+species;after introduction of Cu,the absorption edge of P25 has a slight red-shift and the absorption range is extended to the visible region.The photocatalytic hydrogen production experiments show that Cu/His/P25 photocatalyst exhibits excellent high apparent quantum efficiency(AQE)(79.87%),which is almost 19.01 and 2.11 times of pristine P25 and 0.58Cu/P25,under the irradiation of 365 nm single-wavelength light with light intensity 12.26 mW/cm2.Cu/His/P25 also has shown the higher active and stable H2-evolution via MSR compared with precious metal catalyst(Pt/P25,Au/P25).The mechanism of enhanced photocatalytic performance is attributed to the fact that the imidazole ring in histidine,which is beneficial to the transfer of protons and electrons.The rapid separation and migration of photogenerated carriers accelerate the photocatalytic reaction.In addition,the photocatalytic reaction rate is greatly improved under the thermal assistance,the hydrogen production rate is 6.08 times higher than that of single photocatalysis,which indicates that thremal and photo in the catalytic process is synergistic rather than simply superimposed.This method is more effective and economical than traditional photocatalysis.According to the calculation,the hydrogen yield per photon is as high as 0.891,which is higher than the theoretical value(below 0.5)of traditional reaction yield.Therefore,methanol as hydrogen source participates in the photocatalytic hydrogen production reaction under the photo-thermal synergistic effect.The Ni-modified P25 nanoparticles are prepared by photodeposition method and applied to the photothermal catalytic hydrogen production reaction.The results of photocatalytic activity experiments show that the 2.0Ni/His/P25 catalyst has the best H2-evolution rate(61.5 mmol/(g·h))under the irradiation of 365 nm single-wavelength light with light intensity 34.7 mW/cm2,and the apparent quantum efficiency is 0.92,which is 4.69 times and 123 times that of single methanol reforming and single decomposed water,respectively.Under lower light intensity(12.26 and 23.8 mW/cm2)radiation,the apparent quantum efficiency can be as high as 1.20 and 1.19,respectively.Combined with the H2-production activity experiment results,there is a thermal reaction.While the reaction temperature is 100? and no light irradiation,the methanol steam reforming reaction does not occur.The reason for the increasement in hydrogen production rate and the apparent quantum yield over 1 may be that the introduction of nickel improves the photo responsive ability of the catalyst,and the synergistic effect of heat further promotes the steam reforming of methanol to produce hydrogen.This research provides a design idea and experimental basis for the synthesis of high-efficiency photocatalysts to achieve efficient utilization of solar energy in the photocatalytic reaction process.