In situ fabrication of TiO2 nanoparticles/2D porphyrin metal–organic frameworks for enhancing the photoreduction of CO2 to CO

Abstract

Developing photocatalysts for CO₂ reduction with high efficiency and selectivity in a photocatalytic system remains urgent yet challenging. Herein, we report the highly selective photocatalyzed reduction of CO₂ to CO by in situ grown ultrafine TiO₂ nanoparticles on an ultrathin two-dimensional (2D) porphyrin metal–organic framework (Al-MOF@TiO₂). Al-MOF and TiO₂ nanoparticles are connected by 4,4-bipyridine (BPY): the nitrogen atom of BPY coordinates with the metal aluminum in Al-MOF and with TiO₂ to form the Ti–O–N bond. The ultrathin 2D Al-MOF improved the dispersibility and stability of TiO₂ under prolonged light illumination. Additionally, the interfacial Ti–O–N covalent bond promoted charge carrier transfer and separation along with the rapid migration of charge carriers to the surface for the selective reduction of CO₂ to CO. The hybrid photocatalyst demonstrated excellent capability in reducing CO₂ to CO with a selectivity of 94.1%, producing 1901 μmol g⁻¹ of CO, which is eight times higher than that obtained using pure Al-MOF. Furthermore, the Al-MOF@TiO₂ photocatalyst exhibited superior stability, maintaining its structural integrity in an aqueous reaction system. This work provides an effective strategy for improving the stability and charge separation property of metallic oxide-modified photocatalysts for efficient photocatalytic CO₂ reduction.