Photo-catalytic CO2 reduction using sol–gel derived titania-supported zinc-phthalocyanine

Carbon dioxide was photo-catalytically reduced to produce formic acid in an aqueous solution using visible light irradiation. Titania and zinc-phthalocyanine (ZnPc)-loaded titania were synthesized by a sol–gel method and in situ chemical synthesis technique. The photo-catalytic reactions were conducted in a Pyrex reactor with a visible light irradiating. XRD and DRS revealed that ZnPc was on the TiO2 surface. The optimum technique was in situ chemical synthesis and the optimum amount of ZnPc loading was 1.0 wt.% for the highest dispersion among catalysts. The formic acid yield of 1.0 wt.% in situ ZnPc/TiO2 was 978.6 μmol/g catalyst following 10 h of visible light illumination and the conversion was 0.37%. The yield was higher than those of sol–gel TiO2 and ZnPc/BH-1, whose yields were 321.0 and 756.2 μmol/g catalyst, respectively. Experimental results indicated that the formic acid yield was significantly increased by loading ZnPc. ZnPc has a higher selectivity than metal catalysts for the reduction of CO2. The photo-catalytic efficiency of ZnPc/TiO2 was markedly increased because of the lowering re-combination probability for hole–electron pairs.