Co-ZIF-9/TiO2 nanostructure for superior CO2 photoreduction activity

Abstract

Cobalt-containing zeolitic imidazolate frameworks (Co-ZIF-9) have recently emerged as efficient imidazolate motifs for CO₂ adsorption and activation. Herein, we adopt an imidazolate motif as a cocatalyst for TiO₂ based CO₂ photoreduction. Co-ZIF-9/TiO₂ (denoted as ZIF_x/T) composite materials were firstly synthesized via an in situ synthetic procedure, and this endowed the fabricated ZIF_x/T composites with a well-designed nanostructure in which TiO₂ and Co-ZIF-9 were closely bound with each other, thus leading to better charge separation compared to the previously reported physical mixture of ZIF with other semiconductors. Via optimization of the concentration of Co-ZIF-9 in the ZIF_x/T composites, 8.79 μmol of CO, 0.99 μmol of CH₄, and 1.30 μmol of H₂ with a total utilized photoelectron number (UPN) of 28.17 μmol could be obtained over ZIF_0.03/T after 10 h of CO₂ photoreduction, which is about 2.1 times that of pure TiO₂. Linear sweep voltammetry at the pseudo stationary state in a CO₂ saturated solution further revealed that Co-ZIF-9 can effectively activate the CO₂ molecule and positively shift the onset potential of CO₂ reduction for ZIF_x/T (x ≤ 0.10). Moreover, photoluminescence spectra suggest that the ZIF_x/T composites prepared via the in situ synthetic procedure have better charge separation efficiency with less Co-ZIF-9 content. Accordingly, both better CO₂ activation and charge separation contribute to the high activity of the well-designed ZIF_x/T nanostructure.