Design And Research Of CO 2 Photocatalytic Reduction Materials

The combustion of fossil fuels can release large amount of CO₂ leading to an imbalance in the carbon cycle of the ecosystem and global warming,while global warming is the one of the most urgent environmental issues.Compared with other greenhouse gases,carbon dioxide,as a greenhouse gase,contributes more than 65%to global climate change.As the temperature rises,the glaciers melt is melting,the natural disasters occur frequently and global rainfall increases.How to reduce the concentration of carbon dioxide in the air is one of the urgent problems to be solved.Solar energy which is known as a clean renewable energy source is endless.Inspired by photosynthesis in nature,useing semiconductor photocatalysts to reduce CO₂ and water to fuel under the drive of light is a promising strategy currently.According to the current situation,most of the reactions in the photocatalytic reduction of CO₂ are carried out in a pure CO₂ system?high concentration?.Although this has given some significance for CO₂ reduction studies,it is still necessary for photocatalytic research under atmospheric CO₂ concentration?low concentration?.As a clean energy and industrial chemical,methane shows strong demand in production and life,but the technology for methane extraction needs further research and development.Therefore,it would be of great significance finding suitable photocatalysts for the photoreduction of CO₂ to produce methane.For these reasons,we chose the Bi₂WO₆ and cobalt-based catalysts to increase methane production and achieve the reduction of the low-concentration CO₂ by modification.We also studied the mechanism of the reduction of CO₂.The main content is divided into two parts:First:we synthesized ultrathin Bi₂WO₆ nanosheets with a thickness of about 5nm by a hydrothermal method.The structure of ultrathin nanosheets,which could provide more active sites,is beneficial to the adsorption of CO₂.It can also reduce the distance of electron transportation and improve the separation efficiency of carriers.We found that the Bi₂WO₆ nanosheets can split water to produce oxygen and provide protons for the CO₂ reduction process.We loaded Pt on the Bi₂WO₆ nanosheets.The introduction of Pt nanoparticles not only increased the adsorption of CO₂,but also captured electrons to increase the carrier separation efficiency thus accelerate the hydrogenation of CO₂ reduction.The loading of Pt greatly enhanced the ability of Bi₂WO₆ to photocatalytically reduce CO₂ to methane.Comparing Bi₂WO₆ nanosheets with different Pt loadings,it was found that 0.5%Pt loaded Bi₂WO₆ nanosheets exhibited the best performance.This study reveals that the photodeposition of Pt changes the structure and optical properties of Bi₂WO₆ nanosheets and these changes synergistically increase the efficiency of photocatalytic reduction of CO₂ to CH₄.It is provided a new idea to find catalysts for photocatalytic reduction of CO₂ to produce CH₄.Second:we successfully designed the partially oxidized cobalt nanoparticles coated by the nitrogen-doped carbon layer?Co@NC?via high-temperature calcination.Based on the previous study,we introduced Pt on Co@NC surface by microwave method.The nitrogen in the carbon layer not only facilitates electron transport,but also provides dispersing and anchoring sites for Pt deposition.It is worth noting that the system was carried out under low-concentration CO₂?400 ppm?circumstance without any sacrificial agent.Co@NC with different Pt loadings showed different catalytic reduction performance of CO₂.The Co@NC decorated with 1 wt%Pt exhibited the best ability for CO₂ reduction to CH₄(14.4?mol·g^-1·h^-1).This study is meaningful for the design and modification of catalysts for low-concentration CO₂ reduction.