Analysis And Application Of Luminol Electroluminescence In The Characterization Of Hydrogen Bonding And Oxygen Vacancy

Electrochemical luminescence(ECL)has been successfully applied in the field of analysis and detection due to its high sensitivity and selectivity.In the O2-luminol ECL system,the formation and conversion of various free radicals such as hydroperoxy radicals(HOO·)and superoxide anions(O2·-)are involved the luminol ECL process.HOO' is widely exist in the atmosphere and radical-molecule complexes formed via hydrogen bonding between HOO· and other different species have drawn significant attention because of their importance in atmospheric chemistry.Many conventional techniques,including IR,NMR and Raman spectroscopy,cannot characterize the existence of hydrogen bonds formed between HOO' and other molecules due to the short lifetime of radicals.In addition,the oxygen vacancies in the oxides promote the adsorption and reduction of O2 to produce O2·-,which has an important influence on the catalytic performance of the oxides.Commonly used methods for characterizing oxygen vacancies,such as ESR,Raman,XPS,etc.,have the disadvantages of complicated operation,expensive cost,and low selectivity.Recently,ECL has been successfully applied in the field of characterization due to its high sensitivity and selectivity,ease of operation,and low cost.In this study,we use ECL as a new characterization method to characterize the hydrogen bond formed by HOO· and other molecules and detect the oxygen vacancy concentrations in the oxides.The specific research contents are as follows:1.The formation of HOO' is involved in the luminol ECL process.Luminol ECL intensity is inversely proportional to the hydrogen bond strength formed between amides and HOO· in the presence of amides.Thus,a luminol ECL probe is established to screen the hydrogen bond strength between amide and HOO·.The related mechanism is that the increase in the electron-donating ability of the electron-donating group in the amide increases the hydrogen bonding strength,which prevents the reversible formation of HOO·.The amount of O2·-generated by HOO·decreases and the intensity of lumino ECL decreases.In addition,the hydrogen bond strength results obtained by the ECL probe have a good correspondence with the theoretically calculated results.Finally,the universality of the probe was verified by measuring the strength of the hydrogen bond formed between HOO· and the carboxylic acid.2.The formation of O2·-is involved in the luminol ECL process,and the concentration of oxygen vacancies in TiO2 is proportional to the content of O2·-.TiO2 with different oxygen vacancy concentrations was modified on the surface of the working electrode,and the intensity of luminol ECL is used as a probe to screen the oxygen vacancy concentration in TiO2.The oxygen vacancy concentration of TiO2 was adjusted by Cu2+doped into the lattice of TiO2,and the oxygen vacancy concentration in doped TiO2 was determined by XPS.Luminol ECL signal on TiO2 modified gold electrode is proportional to the concentration of oxygen vacancies in TiO2.The amount of O2·-production depends on the concentration of oxygen vacancies.The oxygen vacancies serve as the adsorption and reaction sites of O2 and promote the production of O2·-.In addition,the reliability of the ECL probe was verified by studying the oxygen vacancy concentrations in Cu/Fe/Co/Cr-doped TiO2 samples with the same doping concentration and N-doped TiO2 samples with different doping concentrations.The oxygen vacancy concentration obtained by the ECL probe closely matches the oxygen vacancy concentration measured by XPS.Therefore,ECL opens a new way for screening oxygen vacancies in oxide materials.