All-organic ultrathin ionic-pyridine-COF/boron-doped-g-C3N4 heterojunction for CO2 photoconversion integrated with alcohol oxidation

Charge separation and the redox catalytic efficiencies critically affect the photocatalytic performances for CO2 reduction integrated with selective organic oxidation. Herein, ionic pyridine-covalent organic framework (COF) nanosheets were synthesized by precisely attaching imidazolium bromide (ImBr) ionic liquid pair to the pyridine acceptor via covalent bonding. The resultant ionic ImBr-TPpy COF was further assembled with boron-doped carbon nitride (BCN) nanosheets through pi-pi induced assembly, obtaining all-organic two-dimensional nanoheterojunctions. The best ImBr-TPpy/BCN heterojunction photocatalyst can simultaneously enable the CO2 conversion rate of 1.59 mmol g-1 h-1 (100 % CO2 reduction selectivity) and the benzyl alcohol conversion rate of 0.81 mmol g-1 h-1 (90.0 % benzyl aldehyde selectivity) in pure water at room temperature under the UV-vis light irradiation. Notably, the apparent quantum yield reaches 12.7 % (420 nm), superior to those of reported analogous systems for CO2 conversion coupled with organic transformation. Combined space/time-resolved technologies and quasi in situ X-ray photoelectron spectroscopy confirm the efficient Z-scheme charge transfer from BCN to ImBr-TPpy, specifically to ImBr. Moreover, the electron kinetics of ImBr-TPpy/BCN investigated using transient absorption spectroscopy (TAS). The electron transfer rate within the heterojunction and the electron transfer efficiency under reaction conditions were quantified to be of 7.2 x 108 s-1 and 78 % by fs-TAS and in situ mu s-TAS, respectively. In situ Fourier-transform infrared spectra and theoretical simulations uncover that ImBr and B--N pair sites catalyze selective CO2 reduction and alcohol dehydrogenation to produce aldehyde. This work offers a promising route for valorizing solar-driven carbon neutral conversion.