Construction Of Broad-Spectral Responded Graphitic Phase Carbon Nitride For Photoelectrochemical Detection

The photoelectrochemical(PEC)sensing platform combines the characteristics of mild optical signals and sensitive electrical signals,which has a wider linear range and a lower limitation of detection and thus has broad application prospects.The key factor that determines PEC sensing performance is the photoactive material.Graphitic carbon nitride(g-C₃N₄)is a two-dimensional layered semiconductor with a morphology similar to graphite,which has excellent chemical stability and unique electronic band structure.Because of its abundant and low-cost raw materials,simple and efficient preparation process,and excellent PEC performance,it has received widespread attention in the field of PEC sensing,but the high photo-generated carrier recombination rate and low light utilization rate of bulk g-C₃N₄ limit its application.This thesis aims to accelerate the surface charge transfer rate in the in-plane and its external interface of the g-C₃N₄ structure,therefore,to improve its PEC performances.The materials effectively alleviate the inherent problems of low photoelectric conversion efficiency and low light utilization efficiency of bulk g-C₃N₄,and successfully constructed the PEC sensing platforms to evaluate the detection performance of environmental pollutants.The specific research contents are as follows:(1)Using the strategy of metal ion doping to improve the in-plane charge transfer performance of g-C₃N₄ and construct a PEC aptamer sensing platform.Copper(I)/g-C₃N₄(Cu⁺/g-C₃N₄)photoactive material was prepared by solvothermal reaction using ionic liquid bis(1-hexadecyl-3-methylimidazole)copper tetrachlorocuprate(II)([C₁₆MIm]₂Cu Cl₄)as Cu source.The introduction of Cu⁺changed the internal surface charge distribution of g-C₃N₄.The results of the study showed that its photo-induced carrier generation rate and transfer capacity was significantly enhanced,the carrier recombination rate was greatly reduced,and the visible light absorption capacity was broadened from?460 nm to?520 nm.The PEC aptamer sensing platform based on Cu⁺/g-C₃N₄ realizes the high-efficiency detection of bisphenol A in a water environment with a detection range of 0.05 to 5.0×10⁴ pg·m L^-1,and the limitation of detection is0.016 pg·m L^-1(at S/N=3).(2)The use of microscopic construction of semiconductor energy band potential difference can realize the spontaneous transport of photo-generated carriers,improve the photoelectric conversion efficiency,and obtain higher detection sensitivity.By constructing nickel oxide nanocrystals/g-C₃N₄(Ni O NCs/g-C₃N₄)heterostructure to improve its external interface charge transfer performance and constructing a PEC sensing platform.Using the ionic liquid1-hydroxyethyl-3-methylimidazole chloride salt([HOEt MIm]Cl)as a dispersant,the well-dispersed Ni O nanocrystals(with the average particle size of 10 nm)were prepared on the g-C₃N₄ sheet.The self-built electric field at the heterogeneous interface effectively promotes the separation of the electron-hole pairs of the g-C₃N₄ material,thereby improving its photoelectric conversion ability and the utilization ability of light.Moreover,due to the introduction of Ni O,its light absorption range is broadened to the entire visible light,significantly improving the utilization of the solar light for g-C₃N₄.The PEC aptamer sensing platform constructed based on Ni O NCs/g-C₃N₄ successfully realized the quantitative detection of oxytetracycline in water,with a detection range of 4.60 to 4.60×10⁴ pg·m L^-1,and a detection limit of 1.83 pg·m L^-1(S/N=3).(3)By improving the photo absorption ability of photoelectroactive materials and the separation and transmission efficiency of photogenerated carriers,the sensitivity,and detection range of the PEC sensing platform can be improved synergistically.The surface plasmon resonance(SPR)effect of precious metals is used to construct silver/g-C₃N₄/carbon sphere(Ag/g-C₃N₄/CS)to improve the charge transfer performance of the external interface,and to construct a PEC sensing platform.Ascorbic acid is used as a reducing agent to reduce the silver ions in silver nitrate to silver,it also acts as a carbon source to generate carbon spheres at the same time.The research results show that the synergy effect between the SPR effect of Ag nanoparticles and the electron acceleration effect of carbon spheres makes the PEC properties of the composite material significantly improved,and the use of monochromatic light irradiation reveals the photoelectric performance enhancement mechanism of the composite material under different excitation wavebands and simultaneously achieves the construction of the PEC sensing platform.The PEC sensing platform based on Ag/g-C₃N₄/CS successfully realized the quantitative detection of 4-chlorophenol in water.The detection range is 16 to 1.10×10³ ng·m L^-1,and the limitation of detection is 5.33 ng·m L^-1(S/N=3).