Design Synthesis,structural Regulation,and Photocatalytic Performance Of Supramolecular Assembled C₃N₄

As an additional compelling approach to solar energy development alongside photovoltaic and photothermal methods,photocatalysis can effectively convert light energy into chemical energy that is more convenient for transportation,storage,and utilization.In the process of photocatalysis,the reduction of photogenerated electrons and the oxidation of holes to the substrate occur in series and in parallel,working together to manage charge consumption and substance exchange.Through the thoughtful design of photocatalyst structures and catalytic reaction systems,it is possible to efficiently utilize photogenerated electrons and holes for the synthesis of high-value-added chemicals.Graphitic carbon nitride（C₃N₄）,as an organic semiconductor photocatalyst,offers advantages such as non-toxicity,ease of preparation,low density,high stability,and excellent biocompatibility.The energy band position meets the requirements of both water decomposition thermodynamics and most organic oxidation reactions.Bulk C₃N₄（BCN）contains noticeable defects in key aspects of photocatalysis,such as light absorption,photogenerated charge separation and transfer,surface charge transfer,and mass transfer.Among various synthesis methods,the supramolecular strategy stands out as the most effective approach to designing and synthesizing the C₃N₄ structure due to its convenient structural adjustability.The diversity of precursor molecules,synthesis conditions,and assembly modes empowers this strategy to precisely control the chemical structure of C₃N₄ at the molecular level,thereby achieving a collaborative optimization of product morphology,electronic structure,and surface properties.This,in turn,enhances the photocatalytic efficiency of C₃N₄.The primary research contents of this paper are as follows:（1）Supramolecular assembly synthesis of anemone-like ultra-thin porous carbon nitride towards photocatalytic water splitting and benzyl alcohol oxidation.An asymmetric multilevel precursor（L-Arg Mx）was synthesized by amidation and hydrogen bonding between melamine and L-arginine under hydrothermal conditions.After thermal polymerization,fascicular anemone-like carbon nitride（ACNx）with ultra-thin porous tubes,and aldehyde modification on conjugated skeleton was synthesized.The element composition,morphology and energy band structures of ACNx can be precisely regulated by adjusting the precursors ratio.In the coupling reaction between water decomposition and benzyl alcohol oxidation at room temperature under simulated sunlight,the H₂ evolution efficiency of ACNx and the conversion and selectivity of benzyl alcohol oxidation are much higher than that of BCN.ACNx has enhanced visible light absorption,efficient photogenerated charge separation and transport,and suitable band location.Deuterium（²D）isotope labeling results proved that the direct proton source of the photocatalytic product H₂ was H₂O rather than benzyl alcohol.EPR under simulated reaction conditions showed that the dehydrogenation of benzyl alcohol was driven by reactive oxygen species produced by water oxidation.This provides an important inspiration for the coupling of aqueous phase photocatalytic H₂ evolution with organic oxidation.（2）Room-temperature photocatalytic methanol-water reforming with a multistage symmetry-broken carbon nitride.As the extension of the above work,a series of amino acid-melamine precursors（AMx）with different forms were synthesized by self-assembly of different amino acids（L-methionine,L-asparagine,L-tryptophan,and L-cystine）and melamine respectively.The chirality of amino acids breaks the precursors symmetry through hydrogen bond networks.And the symmetry-broken property was inherited by the polymerization products（ACNs）.L-methionine-carbon nitride（MetCNx）,as the main research object,has a multistage symmetry-broken structure.Under simulated sunlight irradiation,MetCNx finally achieved an ultra-high efficiency of 3:1 molar ratio of H₂ and CO₂ and higher CO₂ selectivity compared to BCN from room-temperature photocatalytic methanol-water reforming.These are attributed to the abundant micro-nano scale structural distortions in MetCNx that provide transfer and release sites for internal charges,and the anisotropic distribution of carbon vacancies and carboxyl that promote charge separation.In addition,the surface carboxyls promote the adsorption and activation of methanol and water molecules.Then the efficient photocatalic water splitting can generate abundant oxygen-containing radicals,which ultimately inhibits the formation of CO.（3）Ultrathin porous carbon nitride nanosheets were synthesized by interfacial self-assembly for room-temperature photocatalic alcohol-water reforming.Based on the improvement of the self-assembly synthesis strategy,the interface self-assembly strategy was adopted to make melamine and cyanuric acid self-assembly at the liquids interface,and the nanoprecursor with ultra-thin thickness and regular shape was prepared.After hot polymerization,the ultra-thin,porous hexagonal laminate carbon nitride（LCN）were synthesized.This method can achieve simple and gentle preparation of ultra-thin C₃N₄ nanosheets.Thanks to the large specific surface area and the high efficiency of photogenerated charge separation and transport,LCN has achieved much higher efficiencies than BCN in the room temperature photocatalytic reactions of methanol/ethanol/glycerin-water reforming.