Here we report a 2D-2D heterostructure of g-C3N4/UMOFNs photocatalysts via mechanical grinding two kinds of two-dimensional nanosheets of g-C3N4 nanosheets and UMOFNs, which exhibits enhanced H2 evolution from water with simulated solar irradiation. g-C3N4 nanosheets are in close contact with UMOFNs, and there is a certain interaction between them, showing the effect of superimposition on the two-dimensional layer. The 2D-2D heterostructure offers a maximal photocatalytic hydrogen production activity of 1909.02 mu mol g(-1) h(-1) with 3 wt% of UMOFNs, which is 3-fold higher than that of g-C3N4 nanosheets (628.76 mu mol g(-1) h(-1)) and 15-flod higher than that of bulk g-C3N4 (124.30 mu mol g(-1)) The significant increasement of photocatalysis is due to 2D-2D heterostructure possessing a short charge transfer distance and large contact area between g-C3N4 and UMOFNs. The highly dispersed Ni-O, Co-O and pi-pi bonds in UMOFNs of 2D-2D structure also promote charge transfer and enhance the photocatalytic activity. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.