Highly improved photoreduction of carbon dioxide to methanol using cobalt phthalocyanine grafted to graphitic carbon nitride as photocatalyst under visible light irradiation

A substantially improved methanol yield was achieved from the photoreduction of carbon dioxide under visible light by using a hybrid photocatalyst consisting of molecular cobalt phthalocyanine tetracarboxylic acid (CoPc-COOH) complex immobilized to the organic semiconductor graphitic carbon nitride (g-C3N4) and triethylamine as sacrificial electron donor. The structural and morphological features of the hybrid photocatalyst determined by various techniques like FTIR, UV–Vis, Raman, XPS, TGA, BET etc. After 24 h of light irradiation, the methanol yield by using g-C3N4/CoPc-COOH photocatalyst (50 mg) was found to be 646.5 µmol g−1cat or 12.9 mmol g−1cat with conversion rate 538.75 µmol h−1 g−1cat. However, the use of homogeneous CoPc-COOH (6.5 µmol Co, equivalent to g-C3N4/CoPc-COOH) and g-C3N4 (50 mg) provided 88.5 μmol (1770 μmol g−1cat) and 59.2 μmol (1184 μmol g−1cat) yield of methanol, respectively under identical conditions. The improved photocatalytic efficiency of the hybrid was attributed to the binding ability of CoPc-COOH to CO2 that provided the higher CO2 concentration on the support. Further, the semiconductor support provided better electron mobility and charge separation with the integrated benefit of facile recovery and recycling of the material at the end of the reduction process.