Photocatalytic reduction of carbon dioxide using sol-gel derived titania-supported CoPc catalysts

Abstract

CoPc loaded titania was synthesized by an improved sol–gel method using a homogeneous hydrolysis technique. The grain size of TiO₂ and CoPc–TiO₂ was uniform and average diameters were less than 20 nm. Both catalysts had two crystal phases, of which rutile accounted for about 28%. When they were used for the photoreduction of CO₂ in NaOH solution under ambient conditions, the formate yield was significantly higher than that of the others, such as formaldehyde, methanol and so on. In order to increase the activity of the photocatalysts some factors were optimized, including the quantity of CoPc–TiO₂ catalyst, concentration of Na₂SO₃ hole scavenger, concentration of the NaOH solution and irradiation time. Under the optimal conditions, the gross photocatalytic reduction of CO₂ was 1032 µmol (g cat)^–1. Furthermore, the yield of CH₄ did not increase in the presence of CH₃OH or HCHO, showing that the generation of CH₄ from CO₂ did not proceed viamethanol as an intermediate under these conditions.