In-situ synthesized porphyrin polymer/TiO₂ composites as high-performance Z-scheme photocatalysts for CO₂ conversion

The promising photocatalytic conversion of CO₂ into valuable fuel promotes the development of photocatalyst through various methods. In this work, TiO₂ nanoparticle was composited with covalent porphyrin polymers (COP-Ps) to fabricate composite photocatalysts. The resultant COP-Ps/TiO₂ composites by in situ hydrothermal method exhibit much improved photocatalytic activity for the conversion of CO₂ into CO relative to two components, and it is attributable to improved charge transfer between two moieties led by strong interaction. Especially, TiO₂ is composited more evenly with the sulfonated hollow COP-P (sh-COP-P). The resultant composite sh-COP-P/TiO₂ performs best with a CO production rate of 5.70 μmol·g⁻¹·h⁻¹, which is approximately 20.4 times as high as that of pure TiO₂ and 2.3 times of sh-COP-P polymer. For comparison, the simple physical mixture of sh-COP-P and TiO₂ (sm-sh-COP-P/TiO₂) was fabricated, and it performs more badly due to poor mixing uniformity. A Z-scheme photocatalytic mechanism was proposed for sh-COP-P/TiO₂ composite on the basis of energy band analysis and hydroxyl radical test. This study provides a new in situ strategy to fabricate organic polymer/metal oxide composites of high photocatalytic activity for CO₂ reduction.