Efficient photocatalytic hydrogen production by bacteriochlorophyll-a derivatives with different esterifying side chains.

TiCT MXene, a new family of 2D materials, has been successfully used as an ideal co-catalyst for enhancing photocatalytic activity due to its excellent physicochemical properties. Bacteriochlorophyll (BChl), one of the most abundant photosynthetically active pigments, has been studied in the field of artificial photosynthesis due to its constant and efficient absorption of solar energy and conversion of the excitation energy into chemical energy. In this work, five BChl-a derivatives with a range of different side chain groups in the C17 substituent were prepared and deposited on the TiCT MXene surface by a solvent evaporation process to form BChl-n@TiCT (n = 1∼5) composite photocatalysts, which were used for the visible light-driven photocatalytic hydrogen evolution reaction (HER) in an aqueous solution. Among the five BChls investigated, BChl-5 possessing a quaternary ammonium terminal showed the best performance and BChl-5@TiCT composite exhibited an excellent hydrogen production activity of as high as 51 μmol/h/g. This is primarily attributed to the excellent photophysical and photochemical properties provided by the self-aggregation of BChl-5 in the BChl-5@TiCT composite and the outstanding charge transport capability of the 2D TiCT MXene. At the same time, the fast carrier separation and transfer capability between BChl-5 and TiCT provides reliable charge transport for photocatalytic HER.