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.

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.

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 to hydrophobic, and CP⁺ between montmorillonite layers basically reaches a saturation value at 1.5CEC. The TGA analysis shows that CPC-Mt has a mass loss peak with increased decomposition of organic matter, decreased surface adsorbed water, and increased organic 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 is 36.0%, 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, the adsorption 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.

CPC entered the interlayer of montmorillonite, and the montmorillonite changed from hydrophilic to hydrophobic when using CPC modified montmorillonite. When CPC-Mt was used to adsorb OTA in simulated animal body fluids, the adsorption rate of CPC-Mt increased from 36.0% to 77.5%, compared with that of X-NMt. The adsorption behavior of OTA by CPC-Mt followed the quasi-second-order kinetic adsorption model, indicating that OTA adsorption was controlled by chemical reaction. The adsorption process followed the adsorption/distribution model, and the transformation of CPC-Mt from hydrophilic to hydrophobic played a key role in the adsorption of weak polar OTA. According to the adsorption mechanism analysis, the organic carbon chain of CP⁺ was used as a distribution medium, and the organic part of OTA was absorbed into the modified montmorillonite through hydrophobic distribution when CP⁺ was inserted into montmorillonite. OTA and CP⁺ could adsorb each other due to the electrostatic interaction.