Hydrogen bond driven assembly for Langmuir-Blodgett films of multiporphyrin-sensitized carbon nitrides as both photosensitizers and catalysts for hydrogen evolution

Photocatalytic hydrogen evolution with the use of semiconductors as the light-harvesting units is an attractive route for the clean and renewable energy development. Here, we report interfacial self-assembly of Pd(II)directed multiporphyrin arrays sensitized oxidized graphitic carbon nitride (O-g-C3N4) nanocomposites and their Langmuir-Blodgett (LB) films. The nanocomposites and LB films can act as both the light-harvesting unit and catalyst for the hydrogen evolution under irradiation. Monolayer behaviors and spectroscopic features indicate that EDTA and polyacrylic acid (PAA) in the subphases can stabilize the monolayer stability and facilitate the LB film deposition, attributed to the hydrogen bonding between EDTA/PAA and tetraaminoporphyrin (TAPP). The multiporphyrin arrays-sensitized O-g-C3N4@(Pd-TAPP)3 nanocomposites display improved hydrogen evolution efficiency, because of the expanded light absorption region as well as enhanced separation and transport efficiency of the photoinduced charge carriers. Particularly, when the LB films of O-g-C3N4@(PdTAPP)3-EDTA or -PAA are used as the light-harvesting unit and catalyst, the hydrogen evolution rate is about 5-10 times higher than that of the solid powders of similar nanocomposites. Mechanism investigation suggest that EDTA and PAA can not only improve the monolayers and LB films' stability, but also act as the bridged species between the carbon nitride, multiporphyrin arrays and electron donors, hence enhanced charged transfer and hydrogen evolution efficiency.