Large Specific Surface Area Anatase TiO₂ For Photocatalytic Hydrogen Production From Lignocellulose

Lignocellulosic biomass is the most abundant renewable resources in nature,and it is also one of the ideal energy materials for the sustainable development of human society.However,due to the lack of some ways to convert lignocellulosic biomass into energy source,lignocellulosic biomass is difficult to be widely used as energy source.Photocatalytic H₂productiuon from lignocellulosic biomass is one of the ideal ways to realize the conversion of lignocellulosic biomass to hydrogen energy driven by solar energy under mild conditions.However,the photocatalytic H₂production performance is still low due to the lack of effective photocatalysts,the design and development of highly-efficient photocatalysts is a key scientific problem for photocatalytic H₂production from lignocellulosic biomass.Aiming at this key problem,we design low-cost,non-toxic and highly stable TiO₂-based photocatalysts through the morphology,crystal surface regulation and co-catalyst modification strategies,the improved photogenerated charge separation efficiency,accelerated^·OH and H₂generation rate result in the enhanced photocatalytic H₂production activities of TiO₂-based photocatalysts.The main research content of this paper is as follows:（1）An ultra-thin anatase TiO₂ nanosheets photocatalyst with a thickness of about 2.1 nm and a（001）exposed surface of 94.5%was prepared by hydrothermal method by using tetrabutyltitanate as the titanium source.The specific surface area of TiO₂nanosheets achieves 123 m²·g^-1.The photocurrent measurement shows that the ultra-thin structure of TiO₂nanosheets is advantageous for the photogenerated charge to migrate to the surface of photocatalyst,improving the photogenerated charge separation efficiency.At the same time,the large specific surface area of the ultra-thin TiO₂nanosheets photocatalyst provides abundant active sites for^·OH generation.Theoretical calculation also shows that the（001）surface of TiO₂has a low^·OH generation energy barrier,which is conducive to^·OH generation.Because^·OH is a key species for the oxidation of lignocellulose,the rasied^·OH generation rate accelerates the oxidative decomposition of lignocellulose.Under 300 W Xe light irradiation,the ultra-thin TiO₂nanosheets photocatalyst loaded with 1%Pt shows enhanced photocatalytic hydrogen production activity with the a H₂generation rate of 275 and 26μmol·h^-1·g^-1inα-cellulose and polar wood chip aqueous solution,respectively,which is 2.4 and 2.1 times higher than the reference TiO₂nanosheets photocatalyst.The apparent quantum efficiency of ultra-thin TiO₂nanosheets photocatalyst inα-cellulose aqueous solution reaches 1.89%under 380nm.The mechanism for the decomposition of lignocellulose during photocatalytic H₂production reaction was studied by high performance liquid chromatography,and the results shows that the decomposition products of lignocellulose contains glucose,glucuronic acid,lactic acid,CO₂,and the corresponding mechanism for the decomposition of lignocellulose was discussed.（2）The use of Pt as a co-catalyst can improve the photocatalytic H₂production performance of TiO₂photocatalyst,but the high cost of Pt limits its application in the field of photocatalytic H₂production from lignocellulosic biomass.In order to develop low cost co-catalyst for photocatalytic H₂production from lignocellulosic biomass,we designed and prepared Mo S₂modified nitrogen-doped graphite carbon nanocages（NGC）as co-catalyst to improve photocatalytic H₂production performance of TiO₂photocatalyst.Because NGC is a good substrate for the growth of Mo S₂and TiO₂,a ternary Mo S₂@NGC/TiO₂photocatalyst is formed.Although the bare TiO₂nanoparticles with a high specific surface area of 160.2 m²·g^-1,the potocatalytic H₂production performance of TiO₂nanoparticles photocatalyst was low.When TiO₂nanoparticles were combined with Mo S₂@NGC cocatalyst,the photocatalytic H₂production performance from lignocellulosic biomass was significantly improved.The photocurrent mearsument shows that NGC can be used as an excellent charge transfer medium to achieve rapid charge transfer of photogenerated electrons from TiO₂photocatalyst to Mo S₂.When the loading amount of Mo S₂@NGC catalyst was 3%,the Mo S₂@NGC/TiO₂photocatalyst shows the highest phoptocatalytic H₂production performance with a H₂generation rate of 131.4μmol·h^-1·g^-1in cellulose solution under 300W Xe irradiation,and the apparent quantum efficiency reaches 0.73%at 380 nn.Furthermore,the H₂generation rate of 3%Mo S₂@NGC/TiO₂photocatalyst under 300 W Xe irradiation in wheat straw,corncob,polar wood chip,bamboo,rice hull,corn straw and rice straw achieves 4.9,6.7,11.7,14.5,8.4,7.3 and 6.2μmol·h^-1·g^-1,respectively.