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 H-2 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 H-2 over TiO2 that is modified with nickel sulfide (NixSy) 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 3.02mmolg(-1)h(-1) during the first 3h, 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, NixSy acts as a cocatalyst for photocatalytic H-2 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 NixSy 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 H-2.