Rational design of 3D carbon nitrides assemblies with tunable nano-building blocks for efficient visible-light photocatalytic CO2 conversion

g-C3N4 is an appealing non-metal photocatalyst for CO2 reduction, while it shows unsatisfactory performance due to poor CO2 adsorption ability and deficient collection of photo-excited charges, but its efficiency greatly relies on the effective bulk and surface separation of photoexcited charge carriers. To address the challenges, we elaborately design Ag nanoparticles decorated 3D ordered g-C3N4 assemblies based on a synergistic route of Ag-induced supramolecular tailoring and assembling followed by thermal polymerization. The 3D structural topology of the nano-units for g-C3N4 can be altered from 2D orderly stacked nanosheets to 1D twisty g-C3N4 nanotubes by varying the amount of Ag(I). Moreover, the band structures and nitrogen vacancies can also be well-regulated. As supported by experimental and DFT calculation results, ACNNT-2 demonstrates excellent CO2 adsorption capacity, superior light harvesting ability, efficient charge separation and more localized charge density distribution, which can effectively decrease the energy barrier for COOH* intermediate and boost the CO* desorption, resulting in a superior photocatalytic selectivity. Consequently, in sharp contrast to BCN, the ACNNT-2 manifests a markedly improved CO generation rate of 145.5 μmol g−1h−1 under visible-light irradiation, reflecting an 18-fold enhancement together with a CO selectivity of 89%. This strategy provides a profound insight into the multiscale modulation of g-C3N4 photocatalysts with enhanced efficiency.