Interfacial electric field–regulated all-organic heterojunction for highly selective photocatalytic CO2 reduction

Electron-rich CNNS and electron-deficient COFV induce a built-in electric field via Fermi-level equilibration. • PEI improves interfacial contact and strengthens charge transfer. • A metal-free Type-II heterojunction enables efficient directional charge migration. • Exceptional CO 2 photoreduction is achieved in pure water without sacrificial agents or metals. The development of efficient metal-free photocatalysts is of great importance for advancing solar-driven CO 2 conversion. Graphitic carbon nitride (g-C 3 N 4 ) has attracted extensive attention due to its unique electronic structure and excellent stability; however, its photocatalytic efficiency is severely limited by rapid photogenerated charge carrier recombination. Herein, we construct a metal-free COFV/CNNS heterojunction by exploiting the electronic disparity between electron-rich carbon nitride nanosheets (CNNS) and an electron-deficient π-conjugated covalent organic framework (COFV). A polyethyleneimine (PEI)-mediated surface modification strategy is employed to regulate interfacial assembly and enhance interfacial contact between the two components. The intimate heterointerface induces interfacial charge redistribution driven by the intrinsic electronic disparity between CNNS and COFV, leading to the formation of a built-in electric field at the interface through Fermi-level equilibration and electronic coupling. This internal electric field, together with the strong interfacial interaction, promotes efficient separation and directional migration of photogenerated charge carriers, thereby suppressing recombination and significantly enhancing photocatalytic performance. The optimized COFV/CNNS-60 composite exhibits a CO evolution rate of 14.8 times that of pristine CNNS and 3.9 times that of COFV under visible-light irradiation (λ ≥ 420 nm) in pure water without any sacrificial agents. This work provides a general strategy for constructing high-performance metal-free photocatalysts via interfacial electronic regulation and interface engineering, offering new insights into sustainable solar-to-fuel conversion. Download: Download high-res image (407KB) Download: Download full-size image