Photocatalytic CO₂ Reduction By A Ruthenium Complex Sensitizing G-C₃N₄ Combing With Cobalt-based Catalyst

The massive burning of fossil fuels not only consumes the limited environmental resources,but also emits a large amount of CO₂,which makes the environmental situation even worse.CO₂ leads to the global warming.Therefore,it is essential to look for renewable energy sources to replace fossil fuels.Solar energy is the most abundant and inexhaustible in the available renewable energy.So it is realizable to utilize artificial simulation of photosynthesis to convert CO₂ into usable organic small molecule fuels.However,due to the high stability of CO₂,reducing CO₂ requires high energy.Therefore,the development of high-efficiency photocatalysts is an effective choice to reduce thermodynamic and kinetic barriers of CO₂reduction.g-C₃N₄ has attracted much attention because of its narrow band gap,easy preparation,non-toxicity and low cost.In contrast,the defects of its low utilization rate of visible light,small specific surface area and easy recombination of photogenerated electron-hole pairs restrict it’s application.Therefore,this article aims to modify g-C₃N₄ for the above shortcomings.Firstly,g-C₃N₄was exploited to increase its active sites,and the photosensitizer ruthenium-based complex was fixed on g-C₃N₄ with carboxyl groups to improve the utilization of visible light.Then,a series of Ru L₂L’@x C₃N₄/MOF（x,usage amounts of g-C₃N₄:100,200,400 mg）photocatalysts were prepared by combining with the Co-MOF-74.The photocatalytic CO₂ reduction reaction shows that Ru L₂L’@200C₃N₄/MOF exhibits excellent catalytic efficiency.Within 3 h irradiation,4688μmol/g of CO and 727μmol/g of H₂ were detected,the selectivity of CO was up to 86.6%.And through photoelectrochemistry experiment,UV–Vis DRS and PL spectroscopy,it is confirmed that Ru@200C₃N₄/MOF has better electron-hole separation ability and fast electronic transmission capability than Ru L₂L’@100C₃N₄/MOF and Ru L₂L’@400C₃N₄/MOF.In addition,on the basis of the ruthenium complex sensitizing g-C₃N₄,the molecular catalyst cobalt dipyridine and ruthenium terpyridine co-adsorbed on g-C₃N₄ with carboxyl group.When Ru²⁺:Co²⁺=10:1,within 4 h irradiation,233μmol/g of CO and 68.1μmol/g of H₂ were detected,the selectivity of CO was up to 77.4%.And through experiments speculated that the charge transfer of photocatalytic CO₂.