氯化十六烷基吡啶改性蒙脱石对赭曲霉毒素A的吸附效果及机理

Adsorption Effect and Mechanism of Cetylpyridine Chloride Modified Montmorillonite on Ochratoxin A

赭曲霉毒素A (OTA)常见于霉变饲料中,动物食用后会严重损害其身体机能;蒙脱石具有良好的吸附性能,常用作吸附剂,具有保护动物胃肠粘膜的作用。使用氯化十六烷基吡啶(CPC)改性蒙脱石,通过X射线衍射、红外光谱、润湿接触角等揭示改性前后蒙脱石的层间距、官能团和亲疏水性的变化规律,并对比蒙脱石改性前后对OTA的吸附效果。结果表明:CPC成功进入蒙脱石层间且疏水性提升;改性后的蒙脱石(CPC-Mt)对OTA的吸附率高于未改性的蒙脱石。CPC-Mt对OTA的吸附动力学和等温线表明:CPC-Mt吸附OTA符合准二级动力学吸附模型和Linear等温线模型,说明CPC-Mt对OTA以化学吸附为主,且满足吸附/分配模型。根据等温线结果提出吸附机理,CPC-Mt与OTA主要以疏水和静电作用相结合。

Introduction Mycotoxins are secondary metabolites with a high toxicity produced by fungi and widely exist in feeding,thus reducing feed quality and affecting human-being and animal health.Montmorillonite as a feed additive can effectively reduce the risk of mycotoxin absorption by organisms,but its surface is highly hydrophilic,and the binding rate with weak/non-polar mycotoxins(such as OTA)is low.In this paper,OTA/montmorillonite composite adsorption material(i.e.,CPC-MT)was prepared with pyridine salt CPC as a modifier.Its structure before and after montmorillonite modification was analyzed.The OTA adsorption behavior of modified montmorillonite was investigated through batch adsorption experiments combined with kinetic and isothermal adsorption models,so as to provide a technical scheme for effective adsorption of mycotoxins in feed.Methods Cetylpyridine chloride(CPC)modified montmorillonite was prepared in water bath under stirring.The modified product was obtained by centrifugal washing,drying,grinding and sieving.The layer spacing,functional groups and hydrophilicity(i.e.,contact angle)of montmorillonite before and after modification were determined by X-ray diffraction(XRD),Fourior tranform infrared spectroscopy(FTIR)and contact angle measurement.In a simulated body fluid environment at different pH values,the adsorption effect of montmorillonite on OTA before and after modification was analyzed,and the adsorption mechanism was further discussed through adsorption kinetics and adsorption isotherm.Results and discussion The XRD analysis shows that the crystal surface spacing of montmorillonite after CPC modification gradually increases from 1.25 nm to 1.52 nm with the increase of the amount of modifie.The layer spacing of montmorillonite at 1.5 CEC is the maximum,and gradually shifts to a lower angle as the amount of modifier increases.These results indicate that the long carbon chains entering the interlayer or CPC of CP+after ion exchange with the interlayer cations of montmorillonite are combined with montmorillonite due to the electrostatic interaction.According to the organic cation chain length,the angle between the layers of montmorillonite and the layer spacing,the CPC is arranged in the interlayer of montmorillonite at an angle of 13.6°.From the FT-IR analysis,the antisymmetric and symmetric tensile vibration and shear vibration of-CH2 in CPC and the C-H stretching vibration on CPC benzene ring appear in organic modified montmorillonite,and the intensity of the-CH2/C-H absorption peak of CPC gradually increases,resulting in a certain degree of change in the lattice of montmorillonite.This indicates that CPC and montmorillonite are combined. From the contact angle analysis, the surface of montmorillonite changes from hydrophilic tohydrophobic, and CP+ between montmorillonite layers basically reaches a saturation value at 1.5CEC. The TGA analysis shows thatCPC-Mt has a mass loss peak with increased decomposition of organic matter, decreased surface adsorbed water, and increasedorganic carbon content, which is conducive to the OTA adsorption.The results of batch adsorption experiment show that as the amount of modifier increases the adsorption rate of X-NMt to OTA is36.0%, and the adsorption rate of 0.5-2.0 CPC-Mt to OTA is 51.3%, 70.0%, 77.1% and 77.5%, respectively. In addition, theadsorption effect of CPC-Mt on OTA at a certain pH value of a simulated intestinal fluid is slightly better than that of gastric fluid,indicating that no OTA desorption occurs during the whole process of a simulated body fluid.Conclusions CPC entered the interlayer of montmorillonite, and the montmorillonite changed from hydrophilic to hydrophobicwhen using CPC modified montmorillonite. When CPC-Mt was used to adsorb OTA in simulated animal body fluids, the adsorptionrate of CPC-Mt increased from 36.0% to 77.5%, compared with that of X-NMt. The adsorption behavior of OTA by CPC-Mt followedthe quasi-second-order kinetic adsorption model, indicating that OTA adsorption was controlled by chemical reaction. The adsorptionprocess followed the adsorption/distribution model, and the transformation of CPC-Mt from hydrophilic to hydrophobic played a keyrole in the adsorption of weak polar OTA. According to the adsorption mechanism analysis, the organic carbon chain of CP+ was usedas a distribution medium, and the organic part of OTA was absorbed into the modified montmorillonite through hydrophobicdistribution when CP+ was inserted into montmorillonite. OTA and CP+ could adsorb each other due to the electrostatic interaction.