To improve the CO2 adsorption on the photocatalyst, which is an essential step for CO2 photoreduction, solid solutions were fabricated using a facile calcination treatment at 900 °C. Using various alkalis, namely NaOH, Na2CO3, KOH, K2CO3, the resulted samples presented a much higher CO2 adsorption capacity, which was measured with the pulse injection of CO2 on the temperature programmed desorption workstation, compared to the pristine Evonik P25. As a result, all of the fabricated solid solutions produced higer yield of CO under UV light irradiation due to the increased basicity of the solid solutions even though they possessed only the rutile polymorph of TiO2. The highest CO2 adsorption capacity under UV irradiation was observed in the sample treated with NaOH, which contained the highest amount of isolated hydroxyls, as shown in the FTIR studies.
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