Application Of Operando NMR Technique On The Mechanism Study For Photocatalytic Degradation Of Pollutants

At present,the presence of tetracycline organic pollutants and heavy metal ions such as Cr（Ⅵ）in water bodies have threatened the ecosystem.Photocatalytic technology has received extensive attention from researchers due to its non-polluting and sustainable development advantages,and its ability to effectively degrade tetracycline（TC）and reduce hexavalent chromium Cr（Ⅵ）.At present,among many methods for evaluating the degradation of tetracycline（TC）and the reduction efficiency of Cr（Ⅵ）,ultraviolet-visible spectrophotometry（UV-vis）is usually used to analyze the degree of degradation.However,for some colorless heavy metal ions and colorless toxic groups,UV-vis cannot accurately analyze them,and the influence of the dispersion of the catalyst on the reduction effect cannot be considered.Therefore,the development of a fast,simple,accurate and l reaches the highest ayer selection measurement method will be of great value for evaluating the degradation efficiency.In this research,two operando NMR techniques have been developed in this paper,and they have been applied to the study of the degradation process mechanism of pollutants TC and Cr（Ⅵ）.The specific content is as follows:1.The operando high-field nuclear magnetic resonance technology was applied to the study of the mechanism of pollutant TC degradation process.Experiments have found that operando NMR technology can detect colorless and toxic products（the benzene ring internal structure）that UV-vis cannot detect,so that it can accurately reflect the true degree of degradation.Taking a series of titanium dioxide（Vo-TiO₂） with different concentrations of oxygen vacancies as the research object,the degradation efficiency is detected by operando nuclear magnetic resonance technology.By comparing with the results of UV-vis,it can be concluded that,when the UV-Vis spectrophotometry results indicate that TC can be fully degraded,the ¹H NMR spectroscopy results clearly indicate that the benzene rings still exist in high concentration at that time.This study improves the usability,reliability and accuracy of the test methods used in TC degradation studies,and provides an experimental reference for the design of high-efficiency catalysts.2.The operando low-field nuclear magnetic resonance technology was applied to the study of the photocatalytic reduction of Cr（Ⅵ）,and the concentration in the reaction solution was measured by layer selection.Materials such as Ag₉NCs/g-CN supported by silver nanoclusters were prepared,and the process of photoreduction of Cr（Ⅵ）was detected by operating operando low-field nuclear magnetic resonance technology.In addition,for the first time,the layer selection NMR technology was combined with low-field NMR and applied to the measurement of Cr（Ⅵ）reduction process.The experimental results show that the reduction efficiency of Cr（Ⅵ）solution is different in each area of the Cr（Ⅵ） solution under different catalyst dispersion states,when the catalyst is uniformly dispersed after ultrasound,the overall catalytic efficiency is the highest.