Preparation Of Three-dimensional Nitrogen-doped Graphitic Carbon-based Composites For Photocatalytic CO₂ Reduction

With the rapid development of industrial technology,there have been significant advancements in production capacity and economic growth.However,this progress has also led to increased environmental pressures and heightened consumption of fossil fuels.Industrial emissions and excessive burning of fossil fuels have resulted in a gradual rise in atmospheric CO₂ concentrations.It is well-known that excessive CO₂emissions contribute to global warming.Therefore,in order to mitigate global climate change and address the issue of energy scarcity,there has been a significant focus on the utilization of CO₂.Inspired by photosynthesis in nature,photocatalysts can be used to convert CO₂ into valuable chemical fuels such as hydrocarbons,which is a very environmentally friendly technology.This approach reduces the harm caused by climate warming and provides a viable solution for future energy storage and supply.The 3D nitrogen-doped graphitic carbon（N-GC）has good chemical stability,tunable band structure,and excellent visible light responsiveness.However,pure N-GC has a smaller dielectric constant and weaker screening effects,which results in a significant coulomb interaction between electrons and holes（e^--h⁺）,leading to the formation of numerous neutral bound e^--h⁺pairs that strongly affect the excitonic effects involved in the photoexcitation process.Therefore,this paper focuses on optimizing the electronic structure and controlling the morphology of 3D N-GC catalysts using different transition metal（Cu,Co,Fe,Ni）,metal oxide（Co₃O₄,Cu₂O,NiO）,and alloy（CoFe）materials.The goal is to enhance the adsorption of CO₂ on the catalyst surface and facilitate the separation of e^--h⁺pairs,thereby improving the performance and long-term stability of 3D N-GC photocatalysts for CO₂ reduction.The main research contents are presented as follows:（1）With copper nitrate and polyvinylpyrrolidone（PVP）as raw materials,a facile polymer thermal treatment strategy has been employed to fabricate 3D honeycomb-like N-GC with embedded core-shell Cu@Cu₂O NPs.Under visible light irradiation,the Cu@Cu₂O/N-GC-600 catalyst has the highest yields of CH₄ and CO at 5.56μmol·（h·g）^-1 and 3.97μmol·（h·g）^-1,respectively.The excellent photocatalytic activity is attributed to the synergistic effects between the unique N-GC framework and core–shell Cu@Cu₂O NPs,which accelerates the transfer of charge carriers and promotes the accumulation of photogenerated electrons on core-shell Cu@Cu₂O NPs.（2）Based on cobalt nitrate and PVP as raw materials,a facile polymer thermal treatment strategy has been employed to fabricate 3D porous N-GC frameworks with embedded Co O,which are employed as catalysts.The experimental results showed that the Co O@N-GC-500 catalyst showed excellent photocatalytic performance and stability.Under visible light irradiation,the maximum yields for CH₄ and CO are 10.03μmol·（h·g）^-1 and CO is 5.16μmol·（h·g）^-1,respectively.The high photocatalytic performance of Co O@N-GC-500 catalyst is attributed to the efficient separation of the photogenerated electron-hole pairs,large specific surface area,and strong visible light absorption capacity.（3）The composites of CoFe alloy NPs encapsulated in a 3D honeycomb N-GC framework were also successfully prepared by a simple polymer thermal treatment strategy using cobalt nitrate,iron nitrate and PVP as raw materials.Under visible light irradiation,the maximum yields of the CoFe/N-GC-800 catalyst are 10.87μmol·（h·g）^-1and 10.04μmol·（h·g）-1 for CH4 and CO,respectively.In the photocatalytic CO2reduction,CoFe alloy NPs act as active sites and efficiently catalyze the reduction of CO₂.This composite not only possesses excellent photocatalytic performance but also exhibits remarkable light absorption capacity and efficient separation of e^--h⁺pairs.（4）The 3D palm frond-like S-scheme heterojunction structure of Co₃O₄@NiO/graphitic carbon（Co@Ni/GC）composites was prepared using a simple polymer thermal treatment strategy.Under visible light irradiation,the Co@Ni/GC-700catalyst achieves maximum yields of 9.79μmol·（h·g）^-1 for CH₄ and 4.89μmol·（h·g）^-1for CO.The 3D palm frondlike S-scheme heterojunction catalyst exhibits high catalytic performance,stability,sustainability,and environmental friendliness,making it a promising catalyst for applications in the field of photocatalysis...