Photoelectrocatalytic characterization of carbon-doped NaTaO3 applied in the photoreduction of CO2 towards the formaldehyde production

A carbon-doped NaTaO3 perovskite (NaTaO3-C) was synthesized by the chemical solvo-combustion method. The as-prepared material NaTaO3-C was annealed at temperatures of 500, 550, 600, 650, and 700 degrees C in an air atmosphere, in order to study the crystalline phases present in these samples, and to relate the morphological, physical and chemical properties of the carbon-doped perovskites to the photocatalytic activity to perform the CO2 reduction in aqueous medium. The formation of a composite between the carbon and the perovskite, and the presence of a second phase, Na2Ta4O11, was confirmed through XRD measurements. While it is true that both formations improved the photocatalytic activity of the NaTaO3-C, an optimal carbon amount is a key parameter to reduce the band gap value and diminish the charge transference resistance by an improvement in the electrical conductivity of the sample. It is worth to mention that the optimal ratio between the surface area and crystallinity of the sample was achieved by the NaTaO3-C annealed al 650 degrees C. These parameters play an important role to explain an improved photocatalytic activity caused by a higher reactive surface and lower recombination of the charges photogenerated onto larger crystals. The photoelectrochemical tests revealed that the material annealed a 650 degrees C is the only sample with a conduction band value more negative than the potential required to perform the generation of formaldehyde from the photocatalytic reduction of CO2. The photocatalytic activity was evaluated in neutral aqueous medium, NaTaO3-C 650 degrees C presented the highest formaldehyde production (39 mu mol g( -1)).