Adsorption Characteristics and Mechanism of Hydrochloric Acid Modified Okara Insoluble Dietary Fiber to Nitrite

In order to study the adsorption characteristics and mechanism of HCl modified soybean residue to nitrite, the insoluble dietary fiber（HPIDF）, HCl-HPIDF was prepared by modifying HPIDF with nitrite as the target pollutant.The morphology and structure of HCl-HPIDF were characterized by particle size analysis, scanning electron microscopy（SEM）, Fourier Transform infrared spectroscopy（FT-IR）, X-ray diffraction（XRD）, and thermogravimetric analysis. Meanwhile, the basic composition of HCl-HPIDF was determined, and its influence on NO^-₂ adsorption effect under different conditions, adsorption kinetics and adsorption thermodynamics were studied. The results showed that the removal rate of NO^-₂ by HCl-HPIDF was increased by 20.87% compared with that before modification and the content of protein and ash decreased to varying degrees, while the content of total dietary fiber increased relatively. The specific surface area of HCl-HPIDF particles increased. The surface of HCl-HPIDF particles changed from folds to honeycomb holes, exposed more oxygen-containing functional groups, and increased crystallinity and thermal stability. The adsorption kinetics of HCl-HPIDF for NO^-₂ accords with the quasi-second-order kinetic model. Freundlich isothermal adsorption model can describe the adsorption process of NO^-₂ by HCl-HPIDF, and the adsorption thermodynamics showed that the adsorption process was endothermic and non-spontaneous. After HCl modification of HPIDF, the adsorption removal rate of NO^-₂ was significantly improved, which provided a theoretical basis for the subsequent adsorption of nitrite in the human body by soybean residue insoluble dietary fiber as a natural adsorbent.