Facile Modification of Titania with Nickel Sulfide and Sulfate Species for the Photoreformation of Cellulose into Hydrogen.

Photocatalytic cellulose reformation is regarded as a potential and affordable route for sustainable H2 evolution. However, direct photoreformation still suffers from challenges such as the limited solubility of cellulose and the dependence on the catalytic activity of noble metals. Herein, we report a new photoreformation of cellulose into H2 over TiO2 that is modified with nickel sulfide (Nix Sy ) and chemisorbed sulfate species (SO42- ) by a one-pot approach. A significant elevation in the photocatalytic hydrogen evolution rate is achieved with a maximal value of 3.02 mmol g-1  h-1 during the first 3 h, which is almost 76-fold higher than that of P25 and comparable to that of Pt-P25. Aided by systematic investigation, it is proposed that nickel sulfide and sulfate modification contribute synergistically to the remarkably increased efficiency of biomass transformation. Specifically, Nix Sy acts as a cocatalyst for photocatalytic H2 production, and we infer that SO42- ions promote cellulose hydrolysis and the consequent accessibility of the biomass to catalysts. Further, the accumulated formate intermediates have a poisoning effect on the catalysts, the desorption of which can be controlled by tuning the aqueous alkalinity. Overall, our strategy for the modification of TiO2 with SO42- and Nix Sy provides a new perspective for the concurrent acceleration of cellulose hydrolysis and increase of the number of hydrogen evolution sites for the efficient photocatalytic reformation of cellulose into H2 .