Photocatalytic Hydrogen Evolution Based On Bacteriochlorin Derivative/Ti₃C₂T_x MXene Complexes

In the past decades,with the excessive consumption of fossil fuels and the rapidly increasing of global greenhouse gases,the exploration of new sustainable energy sources has become a constant goal pursued by all mankind.As a new energy source characterized by high energy storage and environmental friendliness,hydrogen energy is considered the most promising future energy source to replace traditional fossil fuels in the future,which has attracted the increasing attention of researchers.The most readily available and abundant renewable resource on our planet is solar energy,providing our planet with more energy per hour than the total energy consumed by human activities in a year,so direct conversion of solar energy into chemical fuels is indeed the best way to address the sustainable growth of global energy demand.Among the many areas of research,solar-driven photocatalytic hydrogen evolution（HER）is one of the most promising methods for converting solar energy into chemical energy.However,how to develop low-cost and high-efficiency photocatalysts has become the focus.After many years of research,traditional photocatalysts still suffer from poor visible light absorption,insufficient active sites for hydrogen production,and low efficiency of photogenerated electron-hole pair separation,etc.Compared with traditional photocatalysts,chlorophyll is widely distributed in nature,environmentally friendly,and has good light capture and energy transfer properties,while carotenoids can further broaden the light absorption range for chlorophyll.In addition,conventional co-catalysts usually consist of noble metals.Ti₃C₂T_x MXene is a novel two-dimensional transition metal material that is an effective alternative to noble metal co-catalysts due to its low cost,easy modification and excellent electronic properties.In this paper,natural bacteriochlorin is linked with a series of dyes with and without the ability to absorb light to prepare new panchromatic sensitizers,and the two-dimensional transition metal material Ti₃C₂T_x MXene is used as a co-catalyst to construct a bacteriochlorin based noble metal-free photocatalytic system Dyes/Ti₃C₂T_x to carry out a series of studies.The main works are as follows:In this work,bacteriochlorophyll-a（BChl-a）derivatives combined with a series of carotenoids were synthesized and deposited on the surface of Ti₃C₂T_x MXene to prepare organic-inorganic composites as noble metal-free photocatalysts for HER.The optical properties of six kinds of dye-sensitizers,namely,methyl bacteriopyropheophorbide-a（Dye-1）,four bacteriochlorin-carotenoid dyads（Dyes-2-5）,and a triad（Dye-6）were investigated both in solutions and in the solid thin films,and the composites（Dye@Ti₃C₂T_x）were used as photocatalysts for HER under the white light irradiation（λ>420 nm）in aqueous suspension system in the presence of ascorbic acid at p H=2.8.Among the Dyes-1-6 possessing a different side chain at the C17-propionate terminal of bacteriochlorin chromophore,the Ti₃C₂T_x hybrid photocatalyst composed of Dye-4 with siphonaxanthin analog unit showed the highest hydrogen evolution efficiency,and its best value was 5 times larger compared to Dye-1@MXene without a conjugated carotenoid chromophore.Other Dye@Ti₃C₂T_x composites showed enhanced H₂evolution abilities over Dye-1@MXene,depending on the structural characteristics of dye-sensitizers composed of bacteriochlorin and different kinds of carotenoids.The observed high activity of Dye-4@MXene for HER is attributed to the panchromatic light absorption ability of Dye-4 through visible to near-infrared range as well as the desirable charge separation at the Dye-4@Ti₃C₂T_x interface.This study provides new insights for utilizing photosynthetic dyes to construct MXene hybrid structures suitable for photocatalytic water-splitting H₂ production.We synthesized bacteriochlorophyll a（BChl-a）derivatives with a series of carotenoids to prepare（Dye@Ti₃C₂T_x）organic-inorganic composites for photocatalytic hydrogen evolution,and in this chapter we continue to use bacteriochlorophyll a（BChl-a）derivatives with different peripheral substituents attached at 17 substituents to synthesize new dyes as photocatalysts for hydrogen evolution.The formation of Dye-a-e@Ti₃C₂T_x complexes of photocatalytic hydrogen evolution were carried out,which showed that Ti₃C₂T_x MXene without the addition of dye sensitizer could generate 1μmol h^-1 g^-1 of hydrogen,while Dye-a-e@Ti₃C₂T_x composites showed improved photocatalytic hydrogen evolution performance.The Dye-e@Ti₃C₂T_x composites were found to exhibit the best hydrogen evolution efficiency by optimizing the mass ratio of each dye to Ti₃C₂T_x MXene.But hydrogen evolution is less than that of light-absorbing dyes.Finally,we also performed EIS and TPC measurements on the complexes with excellent hydrogen evolution performance,and the introduction of C17 site substituents resulted in good hydrogen evolution of Dye-e@Ti₃C₂T_x,which is its higher efficiency due to light absorption capacity,electron transfer capacity,and efficient charge separation at the interface,resulting in efficient hydrogen evolution.