The synthesis of interface-modulated ultrathin Ni(ii) MOF/g-C3N4 heterojunctions as efficient photocatalysts for CO2 reduction.

It is highly desirable to improve charge separation and to provide catalytic functions for the efficient photocatalytic CO2 reduction reaction (CO2RR) on g-C3N4 (CN). Here, dimension-matched ultrathin NiMOF/CN heterojunctions have been successfully constructed by the in situ growth of NiMOF nanosheets on hydroxylated and 1,4-aminobenzoic acid (AA) functionalized CN nanosheets, respectively, with ultrasonic assistance. The resultant NiMOF/CN heterojunctions exhibited excellent photocatalytic activities for the CO2RR to produce CO and CH4, especially NiMOF/CN-AA, which had photoactivity 18 times higher than that of bare CN. Based on the surface photovoltage responses, wavelength-dependent photocurrent action spectra, electrochemical impedance spectra, and CO2 electrochemical reduction data, it is clearly confirmed that the exceptional photoactivity mainly resulted from the favorable charge transport properties of ultrathin CN and coupled NiMOF, and from the greatly enhanced charge separation via excited high-level electron transfer from CN to NiMOF in the resultant intimately contacted heterojunction caused by the induction effect of AA, and also from the provided catalytic functionality of the central Ni(ii) for CO2 activation. This work provides a feasible synthetic protocol to fabricate MOF-containing dimension-matched heterojunctions with good charge separation for efficient photocatalysis.