Study On The Morphology Control Of G-C₃N₄ And The Improvement Of Photocatalytic Hydrogen Production Performance By Amorphous Carbon Modification

The shortage of fossil fuels caused by energy shortages and environmental pollution has severely restricted the sustainable development of human society.The development of new technologies to solve these problems has become a research hotspot in the world today.Among them,semiconductor photocatalysis technology is regarded as one of the most ideal ways to control environmental pollution and solve the shortage problem.After long-term efforts by researchers,semiconductor photocatalytic technology has made great progress in the field of photocatalytic decomposition of hydrogen and degradation of pollutants.In particular,the non-metal polymer semiconductor g-C3N4 has been widely studied for its advantages such as low cost,simple preparation method,good thermal stability and chemical stability.However,insufficient utilization of light（λ>460 nm）,the high recombination rate of photogenerated electrons and holes,and triplet–triplet annihilation of intrinsic characteristics lead to extremely low photon efficiency,which severely limits the application of g-C3N4 in actual production.In this paper,the morphological regulation is used to suppress the tri-three quenching and the introduction of carbon materials to promote the separation of photogenerated electrons and holes.The utilization efficiency of photon is improved,and the photocatalytic decomposition of hydrogen production activity is improved.The research content is mainly divided into two parts:（1）In the first part of the work,g-C₃N₄ was modified mainly for the purpose of simplifying cumbersome operation steps,shortening the experimental period,and promoting the separation of photogenerated electrons and holes to improve the utilization efficiency of photons.Glucose and MCA were used as precursors of amorphous carbon and g-C3N4,respectively,and a time-saving and energy-saving microwave oven was used as a heating source to prepare amorphous carbon-modified g-C₃N₄.In the TEM image,it can be seen that the g-C₃N₄ nanosheet synthesized by this strategy is only 11.2 nm thick,which is significantly thinner than the pure phase g-C3N4 nanosheet（23.4 nm）.Because of the thermal polycondensation,steric hindrance occurs due to the formation of amorphous carbon by glucose,which inhibits the layer accumulation of g-C3N4 during the thermal polycondensation process.Under visible light irradiation,the photocatalytic decomposition rate of sample CCN-50 reached 746.95μmol·h^-1·g^-1,which is 2.1 times of the photocatalytic activity of pure g-C₃N₄.The increase in photocatalytic activity is mainly due to the fact that thin g-C₃N₄ inhibits the intersystem crossing in the photocatalytic process,thereby weakening the triplet–triplet annihilation and improving the utilization of photon.At the same time,the introduction of amorphous carbon promotes the separation of photogenerated electrons and holes,further improving the photocatalytic activity.（2）In the second part of the work,the modification of g-C₃N₄ was studied mainly by regulating the morphology of g-C3N4 to suppress the photon utilization of the catalyst by suppressing the triplet–triplet annihilation.Using melamine as a precursor,PVP as a templating agent and ammonium chloride as a foaming agent,an amorphous carbon-modified g-C3N4 nanosheet was obtained by calcination in a muffle furnace.It can be clearly seen from the SEM and TEM images that after the introduction of PVP,the calcined g-C3N4 is changed from a solid block to a small piece of nanosheet structure.The change of its structure is mainly due to the hydrogen bond formed by PVP and melamine during the thermal polycondensation process.The presence of hydrogen bond can fix the melamine molecule on the long chain of PVP molecule,and then disperse the melamine molecule.Significantly reduce the thermal stability of melamine.At the same time,it can also inhibit the interlayer deposition of g-C₃N₄ in the thermal polycondensation process,and then obtain a thinner g-C₃N₄ nanosheet.Under visible light irradiation,the photocatalytic decomposition rate of water by sample PCNH-0.02 reached 769.89μmol·h^-1·g^-1,which was 9.3 times of the activity of g-C₃N₄ in bulk phase.The increase of photocatalytic activity is mainly due to the fact that the thin g-C₃N₄ inhibits the triad annihilation of the intersystem between the catalysts in the photocatalytic process and improves the utilization of photon.At the same time,the amorphous carbon remaining after calcined PVP is introduced into the surface of g-C₃N₄ promotes the separation of photogenerated electrons and holes,and further enhances the photocatalytic decomposition of hydrogen production activity.