Construction Of Carbon Nitride-based Photoelectrochemical Sensors And Their Applications For Antibiotic Detection

The abuse of antibiotics has caused their residues to enter the ecological cycle and food chain,which has posed a major threat to ecological balance and human health.Therefore,it is urgent to develop accurate,sensitive,and effective analytical methods for antibiotic detection.Photoelectrochemical?PEC?sensors have attracted attention in the field of antibiotic detection because of their advantages of rapid analysis,simple equipment,and low background signal.While the design and preparation of photosensitive materials with high PEC activity is one of the key links in the development of high-performance PEC sensors.Carbon nitride materials can effectively improve the photoelectric conversion efficiency and PEC response after reasonable modification and coupling.Given this,this thesis has designed and prepared a series of carbon nitride-based functional nanomaterials with excellent PEC properties by using strategies such as heterojunction formation,defect engineering,and metal doping,and explored and revealed the mechanisms which enhanced their PEC performance;further using aptamer as biometric identification element,three PEC sensors with high analytical performance were constructed for antibiotic detection successfully.The main research contents are as follows:1.A simple one-step method was used to prepare the composite of LaFeO₃ wrapped with graphite-phase carbon nitride?g-C₃N₄?shell.It was confirmed by characterizations that the composite was a core-shell p-n heterojunction functional nanomaterial,denoted as LaFeO₃@g-C₃N₄.The photoelectric performance study shows that the visible light response and PEC stability of LaFeO₃@g-C₃N₄ are better than pure LaFeO₃ and pure g-C₃N₄,as well as the composite of LaFeO₃ loaded on g-C₃N₄?LaFeO₃/g-C₃N₄?reported in the literature;its photocurrent intensity is4.3,3.4 and 2.3 times of them in turn.The improvement of LaFeO₃@g-C₃N₄'s visible light utilization efficiency is due to the formation of the core-shell structure and the synergistic effect of p-n heterojunction on strengthening the interface interaction.Using LaFeO₃@g-C₃N₄ as the photoactive interface,combined with the streptomycin?STR?aptamer,a PEC sensor for sensitive and specific recognition STR was constructed.The PEC sensor displays a wide linear range?0.01-10000 nM?and low detection limit?0.0033 nM,S/N=3?,and can be used for the detection of STR in actual milk samples.2.First,using 2 g of melamine and different contents of 2,4,6-triaminopyrimidine?TAP?as precursors,a series of ultrathin polymeric carbon nitride?PCN?were prepared by supramolecular aggregation and ionic melt polycondensation methods.Then,a one-pot hydrothermal method was used to prepare Bi-doped ultrathin PCN functional nanomaterials with carbon vacancies?CV?,denoted as Bi/CV-PCN.The photoelectric performance study indicates that 0.2 g TAP doping amount of PCN and Bi/CV-PCN with 25%Bi content have the best photoelectric performance;the PEC signal of Bi/CV-PCN is not only 24,6 and 2 times that of pristine Bi,g-C₃N₄ obtained by melamine and PCN in turn,but also more stable.The mechanism study reveals that the surface plasmon resonance?SPR?effect of Bi promotes the ability to capture visible light,the intermediate energy level generated by carbon vacancies accelerates the separation of charge carriers,and synergistically improve the PEC performance.Bi/CV-PCN was used as the photosensitive material,and the enrofloxacin?ENR?aptamer was modified by covalent bonding to develop a PEC sensor for rapid and sensitive determination of ENR.Its linear range is 1.0×10^-5-1.0×10³ ng mL^-1,the detection limit is 3.3×10^-6 ng mL^-1?S/N=3?,and can be used to detect ENR in milk and chicken samples.3.First,BiVO₄/g-C₃N₄ was prepared,and then the BiVO₄/g-C₃N₄ was partially reduced in-situ by NaBH₄,thereby successfully preparing ternary Z-scheme heterojunction functional nanomaterials of Bi SPR-promoted BiVO₄/g-C₃N₄,denoted as Bi/BiVO₄/g-C₃N₄.The photoelectric performance study shows that BiVO₄/g-C₃N₄ with 70%BiVO₄ content and Bi/BiVO₄/g-C₃N₄ with NaBH₄ concentration of 50 nM have the best photoelectric performance;compared with the single and binary systems?such as g-C₃N₄,BiVO₄,Bi/BiVO₄,and BiVO₄/g-C₃N₄?,Bi/BiVO₄/g-C₃N₄ exhibits the lowest bandgap?1.85 eV?and excellent PEC properties,such as its photocurrent response is 10.4 and 3.4 times of Bi/BiVO₄ and BiVO₄/g-C₃N₄.The mechanism study reveals that plasmonic Bi acts as an electron conduction bridge to form the Z-scheme structure,remarkably boosting the separation of electron-hole pairs;the synergistic effect of Z-scheme heterojunction and the SPR effect of Bi effectively accelerate the charge carrier migration and enhance the PEC response.Using Bi/BiVO₄/g-C₃N₄ as photoactive material,covalently bonded oxytetracycline?OTC?aptamer,and fabricated an efficient PEC sensor to achieve the detection of OTC.Its detection range is 0.01-1000 nM,with the detection limit as low as 0.0033nM?S/N=3?,and can be successfully applied for the determination of OTC in milk samples.