Photoreduction Of Carbon Dioxide Over The Strongly Oxidative Sodium Peroxide

"Artificial photocatalysis"using semiconductor and solar light has been dreamed of an ideal green chemical technology to convert greenhouse gas CO₂ into renewable hydrocarbon fuels.It is widely regarded as one of the most promising technologies in dealing with the global energy crisis and environmental issues,and thus has been attracting more and more attention from both academy and industry.However,the low solar-to-chemical conversion efficiency has long been the“bottle-neck”that prevents"artificial photocatalysis"from practical applications.It is well known that,in an ideal artificial photocatalytic reaction involved by H₂O,the photocatalyst plays an important role in catalyzing both the hydrogenation of CO₂ and the oxidation of H₂O.Mainly limited by the semiconducting characteristics,however,almost of photocatalysts and their derivatives developed so far are only able to reduce protons but unable to oxidize H₂O according to the electrochemical potential determination.As a result,the activity of CO₂ conversion with H₂O as reductant is usually low and the reaction can only last a short time.To some extent,the oxidation of H₂O on photocatalysts is a critical challenging step towards CO₂ photoreduction.In addition,how to get sufficient adsorption and activation of CO₂ molecules on photocatalysts is another challenge,because oxygen accumulation on the surface of photocatalysts blocks further H₂O oxidation and CO₂ reduction,thus leading to decreased efficiency of CO₂ photoreduction.In the context as mentioned above,we propose for the first time a study on CO₂photoreduction with the strong oxide Na₂O₂ under ultraviolet light irradiation.Theoretical calculation and experimental results have demonstrated that with oxygen-enriched structure,Na₂O₂ is intrinsically a semiconductor with a bang gap of3.4 eV.Meanwhile,Na₂O₂ has the dual properties favorable for both oxidizing of H₂O and adsorbing of CO₂.It has shown that CO₂ conversion into CO could be realized under UV light irradiation in a vaporized H₂O environment.The evolution of CO gas increased almost linearly at a rate of 1.2?mol/h in 12 hours when the molar ratio of H₂O and Na₂O₂ was 1:1.FT-IR spectrometry study revealed that the formation of carbonates is a crucial intermediate process.Additionally,the mechanism of CO₂photoreduction into CO over Na₂O₂ was also proposed in this thesis.