MOF-Derived Defective Co 3 O 4 Nanosheets in Carbon Nitride Nanocomposites for CO 2 Photoreduction and H 2 Production.

In photocatalysis, especially in CO 2 reduction and H 2 production, the development of multicomponent nanomaterials provides great opportunities to tune many critical parameters toward increased activity. This work reports the development of tunable organic/inorganic heterojunctions comprised of cobalt oxides (Co 3 O 4 ) of varying morphology and modified carbon nitride (CN), targeting on optimizing their response under UV-visible irradiation. MOF structures were used as precursors for the synthesis of Co 3 O 4 . A facile solvothermal approach allowed the development of ultrathin two-dimensional (2D) Co 3 O 4 nanosheets (Co 3 O 4 -NS). The optimized CN and Co 3 O 4 structures were coupled forming heterojunctions, and the content of each part was optimized. Activity was significantly improved in the nanocomposites bearing Co 3 O 4 -NS compared with the corresponding bulk Co 3 O 4 /CN composites. Transient absorption spectroscopy revealed a 100-fold increase in charge carrier lifetime on Co 3 O 4 -NS sites in the composite compared with the bare Co 3 O 4 -NS. The improved photocatalytic activity in H 2 production and CO 2 reduction is linked with (a) the larger interface imposed from the matching 2D structure of Co 3 O 4 -NS and the planar surface of CN, (b) improvements in charge carrier lifetime, and (c) the enhanced CO 2 adsorption. The study highlights the importance of MOF structures used as precursors in forming advanced materials and the stepwise functionalization of the individual parts in nanocomposites for the development of materials with superior activity.