离子液体表面活性剂改性凹凸棒石去除玉米赤霉烯酮

Adsorption Properties of Ionic Liquid Surfactants Modified Attapulgite Toward Zearalenone

玉米赤霉烯酮(ZEN)由于强生殖毒性、致癌等毒害作用,严重危害动物和人体健康,吸附法是去除ZEN的有效方法之一。采用咪唑类离子液体表面活性剂(C_nmimBr,n=12、14、16、18)改性凹凸棒石(APT)制备了ZEN吸附剂(C_nmimBr-APT)。通过Fourier红外光谱(FT-IR)、X射线衍射(XRD)、氮气吸附-脱附分析等表征方法结合烧失量、吸湿率测定,探讨了C_nmimBr-APT的微观结构及表界面性质,系统考察了改性参数(C_nmimBr用量及碳链长度)和吸附条件(吸附剂用量、吸附时间、初始浓度、pH值、共存营养物质)对C_nmimBr-APT吸附性能的影响。结果表明:C_nmimBr改性过程未改变APT的晶体结构,改性后吸附剂的表面疏水性增强。吸附驱动力主要为C_nmimBr中碳链与ZEN分子间的疏水作用,吸附性能与C_nmimBr用量和碳链长度呈正相关。C_(16)mimBr-APT对ZEN的吸附过程符合准二级动力学模型和Langmuir等温模型,当C_(16)mimBr用量为5.0%(质量分数)时,C_(16)min Br-APT对ZEN的最大吸附量为7.45 mg·g^(-1)。吸附体系的pH值及共存氨基酸、维生素和矿物质(L-赖氨酸、维生素B1、Ca^(2+)、Cu^(2+)、Fe^(3+)等)对ZEN吸附性能无显著影响。因此,C_nmimBr-APT在吸附去除ZEN方面具有潜在的应用价值。

Introduction Zearalenone(ZEN)as an estrogenic fungal toxin produced by Fusarium graminearum widely presents in grains,corn,wheat and their by-products.The presence of ZEN seriously endangers the health of animal and humanbeing due to the reproductive toxicity,immunotoxicity,genotoxicity,carcinogenic and teratogenic effects.The adsorption method is the most effective way to remove ZEN,and the commonly used adsorbents are silicate minerals.Attapulgite is an advantageous resource in China,which is used as a feed material to enhance immune function and antioxidant capacity,promote intestinal health,and improve animal production performance and product quality.However,it is difficult to realize the efficient removal of low polarity and hydrophobic ZEN using hydrophilic and negatively charged attapulgite.It is thus indispensable to modify attapulgite with cationic surfactants to enhance their surface hydrophobicity and adsorption property toward ZEN.Imidazole ionic liquid surfactant CnmimBr has lower critical micelle concentration,higher adsorption efficiency and better surface properties than conventional surfactants with the same carbon chain length.In this paper,attapulgite was modified with ionic liquid surfactant CnmimBr for the efficient adsorption of ZEN.Methods APT(25.0 g)was dispersed in 250 mL distilled water at a stirring rate of 540 r/min to form a uniform suspension,and different types of CnmimBr(i.e.,C12mimBr,C14mimBr,C_(16)mimBr,and C18mimBr)were added into the suspension with different concentrations(i.e.,0.5%,1.0%,2.5%,3.0%,and 5.0%),respectively.The mixtures of CnmimBr and APT were stirred at room temperature for 4 h,and then the solid products labeled as CnmimBr-APT nanocomposites were centrifuged,washed with deionized water until no bromine ions,dried at 105°C for 4 h,and ground to the fine particles below 75μm.The removal ratio of CnmimBr-APT nanocomposites toward ZEN was determined via batch experiments.The influences of CnmimBr amounts and carbon chain length on the adsorption performance for ZEN were investigated.1.0%C_(16)mmBr-APT,2.5%C_(16)mmBr-APT,and 5.0%C_(16)mmBr-APT were selected as adsorbents to investigate the effect of adsorption condition(i.e.,adsorbent dosage,contact time,pH value,initial concentration,and coexisting nutrients)on the adsorption performance of ZEN.The adsorption process was analyzed using kinetic and thermodynamic models.Results and discussion According to the Fourier transform infrared spectra, the relative intensity of C―H bonds at 2 930 cm^(-1) and2 865 cm^(-1), and C=N at 1 630 cm^(-1) gradually increases with the increase in the carbon chain length and added amount of CnmimBr,indicating that CnmimBr is anchored on the APT surface to realize the organic modification. Meanwhile, the organicization degreealso increases with the increase in the carbon chain length and CnmimBr dosage. Furthermore, the modification process does notchange the crystal structure of APT, but the specific surface area reduces with the increase in the hydrophobicity, which is beneficialto the efficient removal of ZEN through hydrophobic interaction.The in-vitro adsorption experiments indicate that the adsorption performance of CnmimBr-APT nanocomposites is positivelyassociated with CnmimBr dosage and carbon chain length. The adsorption process follows the pseudo second order kinetic model andLangmuir isotherm. When the modified amount of C_(16)mimBr is 5.0%, the maximum adsorption capacity of C_(16)minBr-APTnanocomposites to ZEN is 7.45 mg·g^(-1). Furthermore, pH value and co-existed nutrients (e.g., amino acids, vitamins and minerals)have little effect on the adsorption performance of ZEN.Conclusions The novel ZEN adsorbents were prepared based on the organic modification of APT using CnmimBr with differentcarbon chain lengths. The results indicated that CnmimBr modification did not change the crystal structure of APT, while the surfacehydrophobicity increased with the increase in the carbon chain length of CnmimBr. Meanwhile, the adsorption capacity ofCnmimBr-APT nanocomposites toward ZEN increased with the increase in the CnmimBr dosage, carbon chain length, adsorbentdosage, and initial solution concentration. The adsorption mechanism was mainly due to the hydrophobic interaction between the longorganic carbon chains of CnmimBr and ZEN molecules, and CnmimBr-APT nanocomposites presented a considerable applicationpotential for the removal of ZEN adsorbents due to the good selective adsorption in the presence multiple nutrients.