Pure g-C3N4 sample was prepared by thermal treatment of melamine at 520 °C, and iron-modified samples (0.1, 0.3 and 1.1 wt.%) were prepared by mixing g-C3N4 with iron nitrate and calcination at 520 °C. The photocatalytic activity of the prepared materials was investigated based on the photocatalytic reduction of CO2, which was conducted in a homemade batch reactor that had been irradiated from the top using a 365 nm Hg lamp. The photocatalyst with the lowest amount of iron ions exhibited an extraordinary methane and hydrogen evolution in comparison with the pure g-C3N4 and g-C3N4 with higher iron amounts. A higher amount of iron ions was not a beneficial for CO2 photoreduction because the iron ions consumed too many photogenerated electrons and generated hydroxyl radicals, which oxidized organic products from the CO2 reduction. It is clear that there are numerous reactions that occur simultaneously during the photocatalytic process, with several of them competing with CO2 reduction.
Formal quantum efficiencies for the photocatalytic reduction of CO2 in a gas phase batch reactor
