Preparation Of Transition Metal Clusters Modified Carbon Nitride Catalysts And The Catalytic Properties Study

Chemical industry is the basic and pillar industry of a country,which plays a pivotal role in the national economy.The chemical industry provides abundant chemicals for people’s production and life,but the production,use and disposal of chemicals also cause more and more environmental pollution.Therefore,it is of far-reaching practical significance to use green chemical technology to produce chemicals and to solve the pollution problems caused by chemical industry production to environment.Fenton reaction is an important method for organic synthesis and degradation of organic pollutants in water,and is considered as one of the most promising advanced oxidation processes.As an important chemical raw material for the synthesis of phenolic resins,caprolactam and adipic acid,phenol is widely used in the industrial production of dyestuffs,pharmaceuticals,pesticides,fragrances and plastics.However,90%of phenol is produced by the traditional three-step isopropyl benzene process,but this process has high energy consumption and serious environmental problems.To overcome these disadvantages,Fenton reaction is widely used in the oxidation of benzene to phenol reaction.The one-step oxidation of benzene to phenol is achieved by using H₂O₂ as the oxidant.This green synthesis process can stop the environmental pollution caused by the production process from the source,and is the most promising alternative route to the isopropyl benzene route.Meanwhile,Fenton reaction is also widely used for the degradation of organic pollutants in water.The activation of H₂O₂ by catalysts generates a large amount of highly active·OH,which eventually converts organic pollutants into H₂O,CO₂ and other small molecules,which is one of the most promising technologies in the field of environmental water pollution.The key to the industrial application of this Fenton catalytic oxidation technology lies in the development of highly efficient catalysts.Graphite-like carbon nitride（g-C₃N₄）,a non-metallic polymer semiconductor with a graphite-like layered structure,has a moderate forbidden band width,visible light response,easy modification,and cheap availability.It can be used as an excellent Fenton reaction catalyst carrier,which has received increasing attention in recent years.However,the specific surface area of bulk phase carbon nitride is very small,the crystallinity is low,and the photogenerated electron pairs are easily compounded,resulting in poor catalytic performance.Therefore,to address the above problems,this paper will improve the catalytic oxidation performance of g-C₃N₄ from the aspects of preparation process optimization,morphology modulation,and metal cluster modification.The main research contents include the following aspects:（1）Three-dimensional porous carbon nitride（3DCN）was synthesized by a bottom-up supramolecular self-assembly method.The material has a three-dimensional interconnected open skeleton structure composed of ultra-thin nanosheet units,which effectively avoids stacking of carbon nitride nanosheets and provides a way for faster carrier transport.On the other hand,the material has a three-dimensional porous structure and abundant N-containing anchoring sites,making it an ideal carrier for ultra-small metal clusters.（2）High-density Fe cluster-modified porous carbon nitride catalysts（denoted as Fe N_x/CCN）were successfully prepared by a combination of mechanochemical reaction and one-step pyrolysis.The structure-activity relationship between the structure of carbon nitride modified by metal clusters and the catalytic activity and selectivity of benzene hydroxylation was investigated by series characterization.The results show that Fe clusters are evenly distributed in porous carbon nitride with a load rate of up to 32%,and Fe sites may be coordinated to the carbon nitride through Fe²⁺-C≡N-Fe³⁺and Fe-N_x bonds.The high-density Fe clusters provide abundant active sites,porous structure and ultra-thin nanosheets are conducive to the transfer of reactants and carriers,thus promoting the benzene hydroxylation reaction.The new green catalytic material exhibited high activity and selectivity in phenol synthesis,and the synthesis efficiency of phenol was further improved by combining with the polyphase photocatalysis technology.The maximum yield of phenol under visible light could reach 28.1%.The reaction mechanism of Fe based catalysts catalyzing the synthesis of phenol from benzene under visible light was explored in conjunction with the Fenton reaction,in which the·OH radical plays a major role in the photocatalytic oxidation process of benzene to phenol.This work will provide valuable information for the design of metal nanocluster catalysts and the application of organic synthesis.（3）Hollow tubular Cu cluster-modified carbon nitride material（denoted as Cu N_x/CCN）with large specific surface area were prepared by a simple green mechanochemical reaction and thermal polymerization.The internal structure evolution of the catalyst was studied at different thermal polymerization temperatures.TEM showed that,with the increase of holding time,the small-sized hollow tubes were pyrolyzed and curled into large-sized hollow tubes with a length of 1～8μm and a width of 200～1000 nm,and the pores on the wall of the hollow tubes gradually became more and larger.The porous hollow tube structure not only provides abundant active sites,but also can be used as micro-nano reactor to accelerate the catalytic reaction.The abundant N atoms in the carbon nitride can anchor the Cu atoms,which are uniformly distributed in the carbon nitride through the coordination of Cu⁺-C≡N-Cu²⁺and Cu-N_x bonds.The catalytic performance of Cu N_x/CCN activation of H₂O₂ to degrade methylene blue dyes was investigated.The results showed that the porous hollow structure accelerated the transfer of reactants and activated H₂O₂,which promoted the catalytic degradation reaction and improved the catalytic degradation efficiency.It showed good catalytic activity against methylene blue and other dyes in the absence of light.The degradation efficiency of MB could reach99.9%in 30 min.Meanwhile,the catalyst has good cycling stability,the degradation efficiency of MB remained 95.8%after 5 cycles.The mechanism study revealed that¹O₂,·O^2-and·OH active radicals worked together during the catalytic degradation process.The catalyst can achieve rapid degradation of organic dyes in water with efficient activation of H₂O₂.