Engineering 0D/2D Architecture of Ni(OH)2 Nanoparticles on Covalent Organic Framework Nanosheets for Selective Visible-Light-Driven CO2 Reduction

Abstract

Low-dimensional materials serving as photocatalysts favor providing abundant unsaturated active sites and shortening the charge transport distance, but the high surface energy readily causes the aggregation that limits their application. Herein, it is demonstrated that 2D covalent organic framework (COF) TpBD nanosheets are effective in the dispersion and stabilization of 0D Ni(OH)₂ . The COF precursor TpBD is synthesized from the Schiff base condensation of 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) and exfoliated into 2D nanosheets named BDNs via ultrasonication. The formation of highly dispersive 0D Ni(OH)₂ on BDNs is reached under a mild weak basic condition, enabling robust active sites for CO₂ adsorption/activation and rapid interface cascaded electron transport channels for the accumulation of long-lived photo-generated charges. The champion catalyst 30%Ni-BDNs effectively catalyze the CO₂ to CO conversion under visible-light irradiation, offering a high CO evolution rate of 158.4 mmol g^-1 h^-1 and turnover frequency of 51 h^-1 . By contrast, the counterpart photocatalyst, the bulk TpBD stabilized Ni(OH)₂ , affords a much lower CO evolution rate and selectivity. This work demonstrates a new avenue to simultaneously construct efficient active sites and electron transport channels by coupling 0D metal hydroxides and 2D COF nanosheets for CO₂ photoreduction.

Keywords: CO2 reduction; composite material; covalent organic frameworks; nanosheets; photocatalysis.