The Application Of Metal-free G-C₃N₄-based Semiconductor Nanomaterials For Photoelectrochemical Sensing And Photocatalysis

As the cornerstone of photoelectrochemical sensing and photocatalysis,semiconductor photoactive nanomaterials fundamentally determine the level of photoelectrochemical performance and photocatalytic performance.Traditional metal-based semiconductor nanomaterials face problems of stability,biocompatibility,and environmental pollution,which hinder their practical applications in biosensors and environmental governance.Metal-free semiconductor nanomaterials composed of carbon,nitrogen,oxygen,phosphorus,sulfur and other non-metallic elements show excellent photoactivity,biocompatibility and stability.Therefore,the shortcomings of metal-based semiconductor nanomaterials can be effectively overcome by using stable,efficient,and cost-effective metal-free semiconductor nanomaterials.In organic polymers consisting only of C and N,Graphite-like carbon nitride(g-C₃N₄),an n-type polymer semiconductor nanomaterial,has a certain visble light response.However,due to the still large band gap,the recombination of charge,and the inferior carrier transfer efficiency,the performance still needs to be further improved.The electronic structure and optical properties of g-C₃N₄ can be improved through morphological control,structural engineering,and formation of heterostructures,to achieve the purpose of improving performance.In this paper,based on the n-type semiconductor material g-C₃N₄,which is simple to prepare,high stability,good biocompatibility and environmentally friendly,a photoelectrochemical biosensor for the specific detection of H₂O₂ and a metal-free photocatalyst for synthesis of H₂O₂ under visible light were constructed respectively.The emergence of p-n heterogenous junction and element doping regulate the optical physical properties and electronic structural of semiconductor materials.Finally,the capability of g-C₃N₄ pronouncedly ameliorated,realizing the highly sensitive and selective photoelectrochemical sensing and photocatalytic synthesis of H₂O₂.This paper mainly contains the following three parts:Chapter 1:IntroductionThis chapter mainly gives a brief introduction to g-C₃N₄,summarizes the common strategies for improving the performance of g-C₃N₄,and clarifies the current development status and research progress of g-C₃N₄ in the field of photoelectrochemical sensing and photocatalysis.Chapter 2:The photocathode sensing analysis of H₂O₂ by composite nanomaterial g-C₃N₄/P3HT with p-n heterostructureAs one of the most stable reactive oxygen species,H₂O₂ is involved in many important life activities in organisms.Abnormal levels of H₂O₂ in the body also reflect the occurrence of many diseases,thus the sensitive and selective detection of H₂O₂ is very important in the early diagnosis of diseases.Photoelectrochemical bioanalysis inherits the advantages of optical and electrochemical methods.Under the"light excitation,electrical detection" mode,the influence of background signals is reduced,and the sensitivity of detection is significantly improved.In this chapter,a composite nanostructure of g-C₃N₄ and conjugated organic p-type semiconductor poly(3-hexylthiophene)(P3HT)is constructed,to realize a visible light-responsive photocathode H₂O₂ biosensing.Due to the fit of band position and electronic structure characteristics,g-C₃N₄ can be well combined with P3HT,improving the utilization efficiency of visible light,promoting charge separation,and ameliorating carrier mobility,which significantly enhancing photoelectrochemical performance.Chapter 3:Phosphorus-doped defect-engineered g-C₃N₄ to achieve visible light-driven catalytic synthesis of H₂O₂H₂O₂ is widely used in the fields of chemical industry,environmental restoration,sustainable energy conver si on/storage,and medical treatment.At present,the production of H₂O₂ on the market has always relied on the anthraquinone method,which has many problems such as environmental pollution and safety hazards.Photocatalytic synthesis driven by solar energy is one of the effective ways to directly and efficiently synthesize H₂O₂.Studies have shown that g-C₃N₄ has suitable optical properties and electronic structure,which can promote the reduction oxygen to generate H₂O₂ through two electrons under visible light irradiation.In addition,due to the generation of intermediate 1,4-endoperoxide,g-C₃N₄ has high selectivity for the generattion H₂O₂.However,due to limited visible light utilization,low charge separation efficiency and catalyst poisoning,the overall light conversion efficiency is low.In this paper,phosphorus-doped g-C₃N₄ was prepared by chemical vapor deposition.After the doping,the visible light absorption capability of the semiconductor catalyst was ameliorated,and the reduction capability of photo-induced electrons was increased.In addition,the doping of phosphorus also introduces more defects into the semiconductor,which will capture photo-induced electrons,relieving the recombination of photo-induced carriers,and greatly heightening the catalytic property of the semiconductor nanomaterial.Eventually,the capability of photocatalytic synthesis of H₂O₂ was nearly improved by 10 times,which realized the efficient,stable and pollution-free synthesis strategy of H₂O₂.