Synthesis And Photocatalytic Performances Of Carbon Nitride-based Photocatalytic Materials

How to use carbon nitrides to efficiently convert solar energy has drew wide attention,which helps solve the long-standing issues,such as energy shortages and environmental pollution control and prevention.Carbon nitrides materials is inexpensive and easily available,it`s unique two-dimensional structure and the band gap narrower than the classical wide bandgap semiconductor TiO₂,with more negative conduction band positions,with more positive valence band positions and etc.However,the bulk carbon nitrides prepared by the high temperature polycondensation of organic compounds,suffering from drawbacks such as rapid recombination of photoelectron-hole pairs,small specific surface area,and narrow photoresponse range.Based on the above issues,this article aims to design and synthesize some photocatalytic materials based on carbon nitrides,and intends to enhance its photocatalytic performance and explain the inherent reasons.The main contents are as followings:1?Synthesis of heterojunction photocatalyst Co@NC/g-C₃N₄ that Co@NC nanotubes and ultrathin g-C₃N₄ were assembled by ultrasonic.It exhibits higher performance in photocatalytic water splitting systems at rates up to 1208?molg^-1h^-1,which is comparable to some Pt@catalyst systems.The intrinsic reason is that the nano-tubes with metal nanoparticles encapsulated that obtained by heat-condensation of cobalt salt and melamine.Not only provide a large light scattering reflection channel,enhance light absorption,but also has a good electron transfer effect,effectively transfer photoelectron of g-C₃N₄ nano-sheets stimulated by light.At the same time,the Co nanoparticles act as an electron clustering center,with triethanolamine act as a sacrificial agent to hole.Co@NC/g-C₃N₄ heterojunction photocatalyst activates water to generate a large amount of hydrogen.2?The"bottom-up"self-assembling synthesize Ti₃C₂T_x/g-C₃N₄ two-dimensional heterojunction can completely degrade RhodamineB within 60 minutes under visible light.Ti₃C₂ was etched and exfliated,which is enriched in·OH terminations and imparted semiconducting properties,giving it both a high carrier mobility with metallic properties and a more negative conduction band potential than g-C₃N₄.When g-C₃N₄ is excited by visible light to generate electron-hole separation and the electrons transition to the conduction band,the holes in its valence band migrate to Ti₃C₂T_x to form a multi-hole two-dimensional structure,forming Mott-Schottky barrier,prevents backflow of holes.This two-dimensional heterojunction facilitates the efficient separation of electron-holes and increases the lifetime of photogenerated carriers.Holes and electrons activate adsorb-oxygen and water to produce radicals with stronger oxidizing power such as·O₂^-and·OH,making organic pollutants degrade faster.3?Mechanical mixing with Ti₃C₂T_x and melamine,one-step calcination to obtain TiO₂@C/g-C₃N₄.Among them,two-dimensional?2D?TiO₂@C riched Ti³⁺and plane carbon nanosheets are derived from Ti₃C₂Tx.and combined with in-situ formed g-C₃N₄nanosheets to form a two-dimensional heterojunction.The resulting TiO₂@C/g-C₃N₄has NH₃ productivity of 250.6?mol g^-1h^-1 in visible light,which is superior to the nitrogen-ammonia conversion reported previously.Because this two-dimensional structure has abundant surface defects,high electron donating capability,suitable light absorption range,excellent charge transport and nitrogen activation ability,it has proved to be a photocatalyst that can be used for nitrogen reduction?NRR?.