Research On Sensor Based On G-C₃N₄ Nanosheets

Graphite phase nitrogen carbide(g-C₃N₄)is a novel carbon-based two-dimensional sheet-structured nanomaterial,composed of highly ordered triazine ring units.As a typical metal-free semiconductor material,g-C₃N₄ has the advantages of high specific surface area,good physical and chemical stability,unique electronic energy band structure and good photoelectric response.The large specific surface area of g-C₃N₄ nanosheets can provide more surface active sites,which is conducive to the deposition of other nanoparticles on the surface.These advantages make it widely used in sensor.The hazards of food safety issues and drug abuse to people's health cannot be ignored.It is still a challenge to detect the harmful substances using the sensitive and simple.With the rapid development of nanotechnology,sensors based on nanomaterials,as a convenient and sensitive analysis method,can quickly quantitatively detect harmful substances in food safety issues and widely used drugs.In this thesis,based on the advantages of the large specific surface area and the metal coordination points of g-C₃N₄,a fluorescence colorimetric dual response sensor and an electrochemical sensor were constructed to detect organophosphorus pesticides and acetaminophen,respectively.Part one:Detection of organophosphorus pesticides based on Cu²⁺ modified g-C₃N₄ nanosheets with fluorescence and colorimetric dual response sensorsObjective:Based on Cu²⁺modified g-C₃N₄(Cu²⁺-g-C₃N₄)nanosheets,a fast and sensitive fluorescence and colorimetric dual-response sensor was designed to detect organophosphorus pesticides.The designed sensor was used to detect organophosphorus pesticides in actual samples of vegetables and tap water,providing a solution for the sensitive and rapid detection of pesticide residues in food.Methods:Cu²⁺-g-C₃N₄ nanocomposite was synthesized according to the method reported in the reference.The as-prepared nanocomposite was characterized by transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD)and energy dispersive X-ray analysis(EDS).Firstly,the fluorescence properties and peroxidase activity of Cu²⁺-g-C₃N₄ were verified,the reaction conditions of p H,concentration of H₂O₂ and acetylcholinesterase(ACh E)were optimized.Then,the malathion was detected under the optimal conditions and the detection limit was calculated.Finally,the add sample recovery method was used to detect the malathion in celery and tap water,respectively.Results:Both g-C₃N₄ and Cu²⁺-g-C₃N₄ are lamellar structures,and the FT-IR,XRD and EDS results prove the successful synthesis of Cu²⁺-g-C₃N₄composites.In the fluorescence method,Cu²⁺can effectively quench the fluorescence of g-C₃N₄.The optimal reaction concentration of ACh E is 2000m U/m L,and the detection range and detection limit of malathion are 70?800n M and 6.798 n M,respectively.In the colorimetric method,Cu²⁺-g-C₃N₄ has excellent peroxidase activity.Optimization experiments show that the optimal p H is 4.5 and the optimal reaction concentrations of H₂O₂ and ACh E are 10m M and 125 m U/m L.The detection range and detection limit of malathion are2.5?25 n M and 1.204 n M,respectively.Fluorescence and colorimetric methods acheive better recovery rates of malathion in celery and tap water.Conclusion:The fluorescence and colorimetric dual response sensor based on Cu²⁺-g-C₃N₄ nanosheets realizes the sensitive detection of malathion.Compared with other literatures,it broadens the linear range,reduces the detection limit,and can sensitively detect malathion added to celery and tap water.This method provides a reference for the design and application of similar sensors,and provides a solution strategy for the rapid and sensitive detection of pesticide residues in food.Part two:Electrochemical sensor based on Cu X(CuO,Cu₂O and CuS) composite g-C₃N₄ nanosheets to detect acetaminophenObjective:Based on Cu X(CuO,Cu₂O and CuS)composite g-C₃N₄nanosheets(referred to CuO/g-C₃N₄,Cu₂O/g-C₃N₄ and CuS/g-C₃N₄),the electrochemical sensors were constructed to detect the widely used drug acetaminophen.The differences of the detection range,sensitivity and mechanism of the three composite materials were evaluated.The designed electrochemical sensors provided a new idea for the rapid and sensitive detection of acetaminophen.Methods:The methods reported in the references were used to synthesize CuO/g-C₃N₄,Cu₂O/g-C₃N₄ and CuS/g-C₃N₄ nanocomposites.The as-prepared nanocomposite were characterized using TEM,high resolution transmission electron microscope(HRTEM),FT-IR,XRD,X-ray photoelectron spectroscopy(XPS)and EDS.The p H and deposition volume were optimized.Acetaminophen was detected under optimal conditions.In order to explore the differences in the detection sensitivity of the three materials,a kinetic study was carried out and the electrocatalytic rate constants of the three composite materials were calculated.The selectivity,repeatability and stability of the sensor were evaluated.Finally,the actual sample acetaminophen tablets were tested.Results:The XRD and XPS characterizations prove the successful synthesis of Cu X/g-C₃N₄.The electrocatalytic activity of the three composite materials in descending order is CuS/g-C₃N₄>CuO/g-C₃N₄>Cu₂O/g-C₃N₄.The optimum p H and deposition volume of CuO/g-C₃N₄,Cu₂O/g-C₃N₄ and CuS/g-C₃N₄ modified electrode for acetaminophen detection are p H 7,9,6and 8,6,6?L,respectively.The detection range and detection limit of CuO/g-C₃N₄,Cu₂O/g-C₃N₄ and CuS/g-C₃N₄ modified electrodes for acetaminophen detection by it curve are 5?300,5?250,5?500?M and 0.319,0.469,0.259?M,respectively.The order of detection limit from low to high is CuS/g-C₃N₄<CuO/g-C₃N₄<Cu₂O/g-C₃N₄,which is consistent with the electrocatalytic activity results.The electrocatalytic rate constant from high to low is CuS/g-C₃N₄(1.9332)>CuO/g-C₃N₄(0.4939)>Cu₂O/g-C₃N₄(0.0679),which confirm the results of detection ranges and limits.The electrochemical sensor has good selectivity,repeatability and stability for detecting acetaminophen,and can sensitively detect acetaminophen tablets.Conclusion:The electrochemical sensor based on Cu X/g-C₃N₄nanocomposites realizes the sensitive detection of acetaminophen.Compared with other documents,it has a wider linear range and lower detection limit,and has good selectivity,repeatability and stability,which is expected to be an effective method for on-site detection of acetaminophen.