| Silver(Ag)-based materials have superior physical and chemical properties.However,they are prone to agglomerate during the synthesis and application,resulting in the increase in size,decrease in specific surface area,reduction of reaction sites and decline in reactivity.Now,Ag-based functional composites are prepared by in situ growth or fixation with the carriers,which are expected to have the excellent performances of the functional complementation between Ag-based materials and carriers,and advantages of the components.However,when they are used in electrochemical sensing analysis,background interference is often a serious problem caused by the high application potential.Based on the above background and problems,two typical Ag-based materials,Ag nanoparticles(Ag NPs)and Ag-based metal-organic frameworks(Ag-MOF)were selected as the research objects,and four kinds of Ag-based functional composites were prepared combined with zinc oxide(ZnO)nanorods arrays,nitrogen-doped porous carbon(N-PC)and ferroferric oxide(Fe3O4)magnetic particles as the carrier,taking advantage of the large surface area and strong load capacity of ZnO arrays and N-PC,as well as the unique magnetic response of Fe3O4.The intrinsic structure-activity relationship between the morphology,composition of each material,and its conductivity,electrochemical sensing properties were systematically explored.Furthermore,the electrochemical sensing mechanisms of Ag-based functional composites were discussed,and the specific and sensitive electrical analyses of sulfur-containing pesticides(SPs),hydrogen sulfide(H2S),cysteine(Cys)and chloride ions(Cl-)were successfully achieved at near zero potentials based on the change of electrochemical signals of solid-state AgX(X:Cl or Br).1.(Chapter 2)Ag/ZnO nanorods arrays were prepared and their properties were investigated for electrical sensing analysis of SPs.Ag NPs-doped ZnO nanorods(Ag/ZnO)arrays were in-situ grown on tin indium oxide(ITO)electrodes by hydrothermal method,and an electrochemical sensing platform was constructed.By adjusting Cl-concentration,the concentration ratio of Ag+to Zn2+,pH value and response time,the electrical sensing response to SPs was investigated.Under the optimal conditions,after the addition of Cl-ions,the Ag/ZnO arrays-based sensor generated significant oxidation signals of solid-state AgCl at a low potential(i.e.,0.12 V).Importantly,when phoxim(Phox)as a model of SPs was introduced,AgCl was triggered and transformed into non-electroactive Ag-Phox due to the Ag-S bond with strong stability between Ag+and Phox.Therefore,the oxidation peak currents of solid-state AgCl decreased dramatically,and SPs could be electrochemical analyzed at a low potential.Meanwhile,the photocatalytic degradation of Phox by Ag/ZnO nanorods was investigated.The Ag/ZnO arrays-based sensor presented a linear range from 0.050 to 700.0 μM for the detection of Phox,with a limit of detection down to 0.010 μM.The developed electroanalysis method was employed to detect the residual Phox in the samples of tap water and vegetable.In addition,with the photocatalytic degradation performance of Ag/ZnO nanorods,the Phox adsorbed on the electrode surface could be removed by photocatalytic degradation after each detection,thus realizing the regeneration of the sensor.2,(Chapter 3)Fe3O4@Ag-MOF magnetic composites were developed and their electrical sensing properties for H2S in aquaculture water were investigated.Magnetic particles Fe3O4 were prepared by solvothermal method to support Ag-MOF and contruct Fe3O4@Ag-MOF magnetic composites.Ag-MOF have received considerable interests in recent years due to the outstanding properties such as high porosity,large specific surface area and numerous Ag+active sites.Fe3O4 particles were prepared by solvothermal method and then used to support Ag-MOF to prepare Fe3O4@Ag-MOF magnetic composites.Because of the the strong chemical bond formed between-COOH of Ag-MOF and-OH of Fe3O4,Ag-MOF could uniformly attach to Fe3O4 particles.Fe3O4@Ag-MOF magnetic composites were attached onto the magnetic electrodes owing to the strong magnetic response.By adjusting Cl-ions concentration,the concentration ratio of Fe3O4 to Ag,pH value and response time,the electrical sensing response to H2S was investigated.It was discovered that the Fe3O4@Ag-MOF-based electrochemical sensors could exhibit the excellent electrochemistry signals of solid-state AgCl at a potential approaching zero(i.c.,0.12 V)after the adding of Cl-ions under the optimal conditions.After the introduction of H2S,since Ag+ and S2-could form a more stable Ag-S bond,AgCl was transformed into Ag2S without the electrochemical activiey.The oxidation peak currents of solid-state AgCl rationally reduced,which could realize the detection of H2S at a low potential.The developed electroanalytical method could facilitate the detection of H2S in the linear range from 4.0 to 1400 nM,with a limit of detection down to 2.0 nM.Besides,it was employed to detect H2S in the aquaculture freshwater samples with the satisfactory results.Importantly,after each of the electrochemical detection,Fe3O4@Ag-MOF on the electrode surface could be removed and refixed by introducing an external magnetic field to achieve the electrode renewal.3.(Chapter 4)Ag-MOF coated nitrogen-doped porous carbon(N-PC)composites were developed and their electrochemical sensing properties for the detection of Cys were investigated.In order to further improve the conductivity of Ag-MOF,carbon-based materials were selected as the carrier,and Ag-MOF coated N-PC(N-PC@Ag-MOF)composites were prepared by solvothermal method.It was discovered that N-PC could significantly improve the conductivity of N-PC@Ag-MOF composites.And N-PC@Ag-MOF composites could present the high electrochemical stability because N atom of N-PC might form coordination bond with Ag+ions of Ag-MOF.By adjusting Br-concentration,the amount of N-PC,pH value and response time,the response to Cys was systematically studied by the electrochemical sensing analysis.Especially,N-PC@Ag-MOF-based sensors could display the stable and sharp electrochemical signals of the solid-state AgBr at a considerably low potential approaching zero(i.e.,0.02 V)after adding of Br-ions under the optimal conditions.More importantly,once the target analyte Cys was added,mercapto group(-SH)in Cys molecule could interact with Ag+to form a strong Ag-S bond,which could transfer AgBr into non-electroactive Ag-Cys.This method was utilized to detect Cys in the range of 0.10-100 μM and 100-1300 μM with a detection limit of 0.050 μM,which could be carried out to analyze Cys in milk samples.4.(Chapter 5)Based on conducting polymer polypyrrole(PPy)and Ag-MOF coated N-PC(N-PC@Ag-MOF),N-PC@Ag-MOF-PPy composites were prepared and successfully used for the electrochemical sensing analysis of Cl-ions.In order to further improve the conductivity of N-PC@Ag-MOF composites,N-PC@Ag-MOF were synthesized by solvothermal method using N-PC as the carrier,and then PPy particles were uniformly deposited on the surface of N-PC@Ag-MOF by chemical polymerization method to fabricate N-PC@Ag-MOF-PPy composites.It was found that the N-PC@Ag-MOF-PPy composites could exhibit the high peak current and the low peak potential during the oxidation of Ag.By adjusting the volume of pyrrole,pH value and response time,the response performances of Cl-ions were systematically studied by electrochemical sensing.More importantly,the introduction of PPy could significantly improve the conductivity of composites.In the present of Cl-ions,the oxidation peak currents of solid-state AgCl increased,while the oxidation peak potentials gradually approached zero,which could realize the highly sensitive sensing analysis of Cl-ions.This developed electroanalysis strategy could facilitate the detection of Cl-ions in a broad linear range of 0.15 μM-250 mM,with a detection limit down to 0.10 μM,which had been successfully used for the highly sensitive sensing analysis of Cl-ions in the actual samples of human serum and urine. |
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