Materials Design And Synthesis For Photocatalytic H₂ Production Facilitated By Organic Oxidation Half Reaction

Photocatalytic hydrogen production has been recognized as a clean and green method of acquiring energy,which can effectively mitigate the severe situation that environmental pollution and energy depletion are triggered by the drastic consumption of fossil fuel.While using semiconductors as photocatalysts for splitting pure water into hydrogen and oxygen,the oxygen evolution reaction?OER?always plays a key role of rate-determing step and greatly limits the overall efficiency of hydrogen production.In addition,oxidation products always have little utilization value.In view of the aforementioned problems,herein we propose two strategies:“lowering financial cost of organics”and“promoting values of organic products”.Specifically,hydrogen were produced by photocatalysts via reforming cellulose and selectively oxidizing benzyl alcohol.Meanwhile we explored the effective optimization measures to further enhance the catalysts'activities,and afford some valuable experience for designing efficient catalytic systems.The specific research contents are follows:?1?Solid acid photocatalysts reformed cellulose into H₂.Cellulose is a typical kind of rich and cheap biomass,but owns complex structure and limited solubility which greatly bring down the photocatalytic hydrogen yield.By modifying Ni_xS_y and SO₄^2-on TiO₂ surface via“one-pot”approach,the photocatalytic activity was significantly enhanced and valued as 3.02 mmol g^-11 h^-1,which was 76-fold higher than P25,and comparable to Pt-TiO₂.Specifically,the sulfate species binding with titanium dioxide can serve as solid acid for accelerating the dissolution and hydrolyzation processes of cellulose,and getting more biomass molecules available to trap the photogenerated holes.As an efficient HER cocatalyst,Ni_xS_y works on driving the protons reduction process and yielding more H₂.Further investigations suggested that the accumulated formate intermediate performed a harm effect on catalyst's activity,making HER rate brought down as reaction time extended.While introducing alkali into system would inhibit the strong adsorption of catalyst for formate,and corresponding deactivation phenomenon.?2?Dually functional units?HER/dehydrogenation?promoted photocatalytic H₂production and selective oxidation of benzyl alcohol.Using benzyl alcohol as organic reactant,we investigated the photocatalytic hydrogen production coupled with the selective oxidation of benzyl alcohol.We loaded Ni_xS_y nanoparticles on ZnS nanorods surface,and the composite was granted with the ternary augments in H2 yield,alcohol conversion and more strikingly,benzaldehyde selectivity?from 8.1%to 90.5%?,compared with ZnS alone.After a series of characterization and radicals trapping experiments,we found a transformation of reaction mechanism resulted from Ni_xS_y:as for ZnS,holes are major oxidative species for selective oxidation;but in composite,Ni_xS_y and photogenerated electrons simultaneously boost the activation and dehydrogenation processes of benzyl alcohol,and the formed intermediate is further oxidized to benzaldehyde by holes,which can be swiftly desorbed away from catalyst and therefore avoid overoxidation.The work indicates the dual roles of NixSy nanoparticles as both hydrogen evolution unit and dehydrogenation unit.