Cationic surfactants modified kaolin – Efficient adsorbents for mycotoxins

Abstract

The natural kaolin from a plant for the production of quartz sand in Rgotina, Serbia (KR) was modified with two cationic surfactants - octadecyl dimethyl benzyl ammonium chloride (O) and hexadecyltrimethylammonium bromide (H). Both surfactants were added in amounts equal to 90% of kaolin cation exchange capacity (CEC). The obtained materials were denoted as OKR and HKR. Characterizations of KR, OKR, and HKR were done by Fourier transform infrared spectroscopy (FTIR) spectroscopy and zeta potential measurements. FTIR spectra and zeta potential measurements confirmed the presence of both surfactants at the kaolin surface. Adsorption of mycotoxins – zearalenone (ZEN) and ochratoxin A (OCHRA) was studied by the natural kaolin and organokaolines under in vitro conditions. The effects of the amount of the adsorbent, the initial ZEN and OCHRA concentrations, and pH, on adsorption of mycotoxins, were investigated. Preliminary results of adsorption of ZEN and OCHRA by KR showed that natural kaolin had no affinity to adsorb these mycotoxins. However, the presence of both organic cations in the kaolin structure significantly increased adsorption of ZEN and OCHRA. Adsorption of the mycotoxins by OKR and HKR increased with increasing the amount of each adsorbent in suspension. Slightly higher adsorption of ZEN than OCHRA by both adsorbents was observed at both pHs. ZEN and OCHRA adsorption increased for both OKR and HKR as the concentration of the initial toxins increased at pH 3 and 7. OCHRA and ZEN are hydrophobic molecules that possess different functional groups and may exist in various forms at different pH values. OCHRA adsorption by OKR and HKR followed nonlinear isotherms at pH 3 and 7, and higher adsorption capacity was obtained for OKR. Also, OCHRA adsorption capacity for OKR and HKR was much higher at pH 3. The obtained results suggest that adsorption of OCHRA was dependent on the form of OCHRA in solution and that type of surfactant had an influence on OCHRA adsorption. Adsorption of ZEN by organokaolines also showed nonlinear isotherms at pH 3 and 7 and similar amounts were adsorbed at both adsorbents at both pH values. The obtained adsorption capacities suggest that adsorption of ZEN was practically independent of the form of the toxin in solution and also on the type of the organic cations in the kaolin structure. Based on the obtained results, kaolin modified with surfactants may be effective materials for adsorption of ZEN and OCHRA.