| The design and fabrication of the sensitive interface plays a crucial role in the electrochemical sensing field.In this dissertation,the defective two-dimensional nanomaterials are used as the research object to construct electrochemically sensitive interfaces.The nano-structure of materials and electrochemical sensing performance are studied with the help of modern advanced technologies,such as X-ray photoelectron spectroscopy(XPS)and X-ray absorption fine structure(XAFS).The structure-activity relationship between the active sites of defective nanomaterials and electrochemical sensing mechanisms was establish.In addition,the interaction between heavy metal ions and different atomic planes,including the chemical valence,the coordination structure around the atom,etc.,was investigated.This paper explores the issue of electrochemical detection interference that has plagued people and fully demonstrates the electron-induced-interference effect.Based on this,the main research content of this paper contains the following aspects:(1)A defective(001)crystal surface-exposed TiO2 nanosheet was designed and prepared for high-sensitivity electrochemical detection of heavy Hg(?).Studies have shown that oxygen vacancies and trivalent Ti3+ regulate the electronic states and electrochemical sensing properties of TiO2 nanosheets.We demonstrated the presence of surface oxygen vacancies and trivalent Ti3+ by X-ray photoelectron spectroscopy,Raman spectroscopy,electron paramagnetic resonance,and infrared spectroscopy.EXAFS results demonstrated that oxygen vacancies participated in the catalyzed electrochemical detection process:oxygen vacancies adsorb O2 molecules,while Ti3+provides one electron to form O·-,serving as adsorption and electron transfer active sites for heavy metal ions..These findings prove that the concept of surface-electronic-state-modulation can make nanomaterials with poor conductivity directly be used for electrochemical detection without modifying other active materials to solve the problem of low conductivity,nor do they need to consider adsorption-desorption equilibrium of heavy metal ions on the surface of materials.(2)We present a high electrochemical sensitivity of?237.1 ?A cm-2 ?M-1 toward copper(?)[Cu(?)]based on oxygen-deficient titanium dioxide(TiO2-x)nanosheets.We fully demonstrated an atomic-level relationship between electrochemical behaviors and the key factors,including the high-energy(001)facet percentage,oxygen vacancy concentration,surface-OH content,and charge carrier density,is fully demonstrated.These four factors were quantified using Raman,electron spin resonance,X-ray photoelectron spectroscopy spectra,and Mott-Schottky plots.In the mutual interference investigation,we selected cadmium(?)[Cd(?)]as the target ion because of the significant difference in its stripping potential(?700 mV).The results show that the Cd(?)can enhance the sensitivity of TiO2-x nanosheets toward Cu(?),exhibiting an electron-induced mutual interference effect as demonstrated by X-ray absorption fine structure spectra.These findings support the promising opportunity for developing highly sensitive materials and for demonstrating the mutual interference mechanism among ions during the electrochemical analysis.(3)Metal-atom doping strategy is employed to mediate the defects and crystal phase and consequently improve the electrochemical activity of intrinsically inert MoS2 for sensitive detection of HMIs.As an example,Mn-mediated MoS2(Mn-MoS2)exhibited a high electrochemical sensitivity of 82.18 ?A ?M-1 toward Pb(?),which was almost five times that of pure MoS2.S vacancy defects and phase structure change were achieved after Mn-mediating process,which were characterized by high-angle annular dark-field scanning transmission electron microscopy,electron spin resonance,Raman,and X-ray photoelectron spectroscopy spectra.The good electronic property of Mn-MoS2 caused by defect-and phase-engineering was investigated by Mott-Schottky and electrochemical impedance spectra plots.Because of the tailored active sites,1T-phase imbedding,and improved electronic states in Mn-MoS2,very surprisedly,chemical interaction between Pb(?)and S atoms was observed.The formation of chemical bond facilitates the electron transfer and in-situ catalytic redox reactions,and consequently enhances the electrochemical sensitivity.Additionally,Fe,Co,Ni,and Cu elements were also selected as dopants to investigate their sensing performance.These findings stimulate new opportunities for enhancing the electrochemical sensitivity and for investigating the atom-level electrochemical behavior by defect-and phase-engineering. |
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