Novel benzimidazole-linked microporous conjugated polymers for highly selective adsorption and photocatalytic reduction of diluted CO₂

Integrated capture and photoreduction of diluted CO₂ into energy-rich fuels represents an important challenge in renewable energy research and is attracting remarkable attention. In this study, two new benzimidazole-linked conjugated microporous polymers (CMPs), namely TFPA-DAB and TFPT-DAB, have been constructed by the condensation of 3,3′-diaminobenzidine (DAB) with tris(4-formylphenyl)amine (TFPA) and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (TFPT), respectively. The abundant basic N sites within the polymer network endow both TFPA-DAB (44.82 cm³ g⁻¹) and TFPT-DAB (53.21 cm³ g⁻¹) with high CO₂ uptake at 273 K and 1 bar. Initial slope selectivity calculations demonstrated that TFPT-DAB possessed excellent CO₂/N₂ selectivity of 103 in comparison with TPFA-DAB (85) at 273 K as a result of changing the polymer core from 2,4,6-triphenyl-1,3,5-triazine to triphenylamine. Moreover, TFPT-DAB showed a narrower band gap down to 2.35 eV and better interface charge transfer than TFPA-DAB. Accordingly, under a 1% CO₂/N₂ atmosphere with water vapor as the electron donor, TFPT-DAB without a cocatalyst exhibited a superior CO production rate (CPR) of up to 178.45 μmol h⁻¹ g⁻¹ with almost 100% reaction selectivity (>420 nm), which is 5 times that of TFPA-DAB (35.31 μmol h⁻¹ g⁻¹) and ranks among the highest of known photocatalysts for gas-solid-phase CO₂ reduction to date. This contribution indicates the bright prospect of benzimidazole-linked CMPs for highly efficient photoreduction of low-content CO₂ in industrial exhaust.