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[Display omitted] Ti 3 C 2 T x 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 Ti 3 C 2 T x MXene surface by a solvent evaporation process to form BChl-n@Ti 3 C 2 T x (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@Ti 3 C 2 T x composite exhibited an excellent hydrogen production activity of as high as 51 μmol/h/g cat. This is primarily attributed to the excellent photophysical and photochemical properties provided by the self-aggregation of BChl-5 in the BChl-5@Ti 3 C 2 T x composite and the outstanding charge transport capability of the 2D Ti 3 C 2 T x MXene. At the same time, the fast carrier separation and transfer capability between BChl-5 and Ti 3 C 2 T x provides reliable charge transport for photocatalytic HER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Organic heterojunction of Chl–g-C 3 N 4 was constructed for visible-light driven H 2 evolution. • Highly efficient electron-hole separation occurred through the organic heterojunction structure. • Chl@g-C 3 N 4 /MXene-based photocatalytic system were developed for noble metal-free HER. • This work provides directions for preparation of organic heterojunction structures suitable for HER. Sustainable conversion of solar energy to hydrogen energy by photocatalytic splitting of water through the use of semiconductor photocatalytic materials is considered to be a promising and sustainable alternative proposal to replace conventional fossil fuels. However, efficient solar-driven photocatalytic hydrogen production has remained a great challenge due to the prevailing problems of existing semiconductor photocatalytic materials. It is shown that constructing heterostructures is a very powerful way to improve the photocatalytic hydrogen production capacity of composites under visible light. Therefore, in this work, an organic heterojunction structure based on chlorophyll (Chl) molecules and graphitic carbon nitride (g-C 3 N 4) is reported and exploited for efficient solar energy-driven photocatalytic hydrogen evolution reaction (HER). Meanwhile, noble metal-free photocatalysts were successfully constructed with Ti 3 C 2 T x MXene nanosheets through a simple stepwise complexation process of Chl, g-C 3 N 4 , and Ti 3 C 2 T x for the achievement of HER for the photocatalytic decomposition of water. The results show that the optimal Chl@g-C 3 N 4 /Ti 3 C 2 T x organic heterojunction composite has a remarkably advanced HER performance of 131 μmol/h/g cat , as compared with the traditional Chl@Ti 3 C 2 T x and g-C 3 N 4 /Ti 3 C 2 T x composites. The results provide new ideas for exploring MXene based catalysts for highly efficient conversion of solar energy. [ABSTRACT FROM AUTHOR]