Enhancing CO2to Alcohol Conversion: Powerful Photocatalysts Based on TiO2–Cu(I)-Iodine-Pyridine One-Dimensional Coordination Polymers

Abstract

Coordination polymers (CPs) are promising materials for environmental applications, particularly in catalysis, due to their flexible structures, tunable electronic properties, and adaptable surface chemistry. This study reports the one-step, room-temperature synthesis of five 1D Cu(I)-iodide-pyridine based CPs with the general formula [CuI(L)]n, where L represents different pyridine derivatives: pyridine (CP1), 3-methylpyridine (CP2), 4-methylpyridine (CP3), 2-amino-4-methylpyridine (CP4), and 2-chloro-4-methylpyridine (CP5). All of the compounds exhibit band gap energies around 3 eV, making them suitable candidates for photocatalytic applications. Indeed, the study investigates the photoreduction of CO2to alcohols using a heterogeneous photocatalytic system consisting of TiO2and varying proportions of CPs. The reactor design enables the rapid removal of produced alcohols, preventing them from being oxidized by TiO2as sacrificial materials and thus achieving near-zero net alcohol production. The optimal TiO2@CP mixture, TiO2@5%CP4, demonstrated higher chemical stability due to the amine substituent on the pyridine, which facilitates hydrogen bonding between CP chains, and an enhanced ability to interact with CO2, as confirmed by adsorption experiments and DFT calculations. The optimized mixture achieved selective methanol production of 894 μg·g cat–1·h–1, significantly surpassing the benchmark photocatalytic system TiO2@3%CuO (318 μg·g cat–1·h–1). Furthermore, TiO2@5%CP4 maintained stable photocatalytic performance over 10 h without noticeable degradation.