Surface Functionalization of Montmorillonite with Chitosan and the Role of Surface Properties on Its Adsorptive Performance: A Comparative Study on Mycotoxins Adsorption
壳聚糖蒙脱土表面功能化及其表面性质对其吸附性能的影响：霉菌毒素吸附的比较研究

Gaofeng Wang, Jie Xu, Zhiming Sun,* and Shuilin Zheng
Gaofeng Wang、Jie Xu、Zhiming Sun* 和 Shuilin Zheng

Cite This: Langmuir 2020, 36, 2601-2611
引用此：朗缪尔 2020， 36， 2601-2611

Read Online 在线阅读

ACCESS I 访问 I

Lull Metrics & Mo

国 Article Recommendations
国文章推荐

(0) Supporting Information
（0）支持信息

Abstract 抽象

Understanding surface and interfacial information, which has a close relationship to the structures and properties of materials, helps guide the design of materials for specific applications. This study focuses on the surface functionalization of montmorillonite (Mt) with chitosan (CTS) and exploring the role of surface properties on its adsorptive performance. Two prototypical products, namely, $180 - Htc @ Mt$ and $250 - Htc @ Mt$ , were fabricated via the hydrothermal method at 180 and $250^{\circ} C$ , respectively. Field emission scanning electron microscopy revealed that hydrothermal carbon (Htc) derived from CTS anchored on the surface of Mt uniformly with a spherical morphology. The introduction of Htc endowed the surface of Mt with abundant hydroxy, amine, and amide groups; organic carbon; developed porosity; and hydrophobic interfacial property. Hydrothermal temperature has huge impacts on the surface system, and smaller particles (average size of 27 vs 53 nm ) with deeper carbonization, higher content of carbonaceous and nitrogenous functional groups, more developed porosity ( 66.149 vs $39.434 m^{2} / g$ of specific surface area, $0.115 vs 0.090 {cm}^{3} / g$ of pore volume), and slightly decreased hydrophobicity can be readily achieved at a higher temperature. The incoming surface protonated amine and amide functional groups show an ion-dipolar interaction to polar aflatoxin $B_{1} ({AFB}_{1})$ , and the increased organic carbon content as well as interfacial hydrophobicity generate a hydrophobic interaction to weak polar zearalenone (ZER). Consequently, the surface functionalization affords Mt enhanced adsorption capacity for ${AFB}_{1}$ , approximately two times compared with Mt, and superior adsorption ability for ZER ( $10 mg / g$ ). The present work provides sufficient evidence of “surface directs application” of Mt, which encourages researchers to focus on studies of the surface science of clay minerals.
了解表面和界面信息与材料的结构和特性密切相关，有助于指导特定应用的材料设计。本研究重点介绍蒙脱土（Mt）与壳聚糖（CTS）的表面功能化，并探索表面特性对其吸附性能的影响。两个原型产物，即 $180 - Htc @ Mt$ 和 $250 - Htc @ Mt$ ，分别在 180 和 $250^{\circ} C$ 下通过水热法制备。场发射扫描电子显微镜显示，来自 CTS 的水热碳（Htc）均匀地锚定在 Mt 表面，呈球形形态。Htc 的引入赋予了 Mt 表面丰富的羟基、胺基和酰胺基团;有机碳;发展的孔隙率;和疏水界面特性。热液温度对表面系统有巨大影响，在较高温度下可以很容易地实现碳化更深、碳质和含氮官能团含量更高的较小颗粒（平均尺寸为 27 和 53 nm）、孔隙率更发达（比表面积 $0.115 vs 0.090 {cm}^{3} / g$ 、孔体积 66.149 vs $39.434 m^{2} / g$ ）和略微降低的疏水性。进入的表面质子化胺和酰胺官能团与极性黄曲霉毒素 $B_{1} ({AFB}_{1})$ 发生离子-偶极相互作用，增加的有机碳含量以及界面疏水性与弱极性玉米赤霉烯酮（ZER）产生疏水相互作用。因此，表面功能化使 Mt 的吸附能力增强，约为 ${AFB}_{1}$ Mt 的两倍，并且对 ZER 具有优异的吸附能力（ $10 mg / g$ ）。目前的工作为 Mt 的“表面指导应用”提供了足够的证据，这鼓励研究人员专注于粘土矿物的表面科学研究。

INTRODUCTION 介绍

Montmorillonite (Mt), an ubiquitous clay mineral in soils and sediments, participates in diverse geochemical processes and dominates numerous chemical reactions.

^{1 - 3}

It has presented excellent performances in extensive applications, such as adsorption,

^{4, 5}

catalysis

^{6 - 8}

and drug carrier.

^{9, 10}

Surface and interlayer properties of Mt were observed to play vital roles during these applications of Mt-based materials.

^{11 - 13} Mt

is composed of two

Si - O

tetrahedral ( T ) sheets and one

Al - O

octahedral (O) sheet, resulting in a typical 2:1 TOT layer structure. The isomorphous substitutions of

{Al}^{3 +}

{Mg}^{2 +}

in the O sheet as well as the substitutions of

{Si}^{4 +}

{Al}^{3 +}

in the T sheets lead to the permanent negative charges of Mt , which are balanced by exchangeable cations, such as

{Ca}^{2 +}, {Na}^{+}, K^{+}

, and

{Mg}^{2 +}

, in the interlayer of Mt . The unique layer structure, permanent negative charges, high cations exchangeable capacity (CEC), and large specific surface area afford distinct surface and interlayer properties for Mt. In the last few decades, plenty of studies in regard to the applications and
蒙脱石（Mt）是土壤和沉积物中无处不在的粘土矿物，参与多种地球化学过程，并主导着许多化学反应。

^{1 - 3}

它在吸附、

^{4, 5}

催化

^{6 - 8}

和药物载体等广泛应用中表现出优异的性能。

^{9, 10}

观察到 Mt 的表面和层间特性在 Mt 基材料的这些应用中起着至关重要的作用。

^{11 - 13} Mt

由两个

Si - O

四面体（T）片和一个

Al - O

八面体（O）片组成，形成典型的 2：1 TOT 层结构。O 片中 by 的

{Al}^{3 +}

同构取代以及

{Si}^{4 +}

T 片中 by

{Al}^{3 +}

的取代导致 Mt 的永久负电荷，这些负电荷被 Mt 夹层中的可交换阳离子（如

{Ca}^{2 +}, {Na}^{+}, K^{+}

、和

{Mg}^{2 +}

）

{Mg}^{2 +}

平衡。独特的层结构、永久负电荷、高阳离子交换容量（CEC）和大比表面积为 Mt 提供了独特的表面和层间特性。在过去的几十年里，关于应用和
modification strategies of Mt have attracted increasing research interests at both academic and industrial scales.

^{14, 15}

However, major researches focused on modifications of the interlayer of Mt , such as organic Mts modified with cationic, nonionic, and zwitterionic surfactants

^{16 - 19}

and pillared Mts intercalated with polycations

Al, Ti, Zr

, and

{Fe}^{20 - 22}

The role of surface properties on the applications of Mt and research interests on the surface science of Mt have received few attentions.
Mt 的修饰策略在学术和工业层面吸引了越来越多的研究兴趣。

^{14, 15}

然而，主要研究集中在 Mt 夹层的改性上，如阳离子、非离子和两性离子表面活性剂

^{16 - 19}

修饰的有机 Mts 和聚阳离子插层的柱状 Mt

Al, Ti, Zr

，以及

{Fe}^{20 - 22}

表面性质对 Mt 应用的作用和对 Mt 表面科学的研究兴趣较少。

As a matter of fact, Mt has an especially large specific surface area due to the layer structure and negatively charged surface resulting from the broken edge of the

Si - O

tetrahedron, which
事实上，由于四面体的断边

Si - O

导致的层结构和带负电的表面，Mt 具有特别大的比表面积，这

Table 1. Main Chemical Compositions of Raw Mt (wt %)
表 1.Raw Mt 的主要化学成分（wt %）

sample 样本	${SiO}_{2}$	${Al}_{2} O_{3}$	${Fe}_{2} O_{3}$	CaO	MgO 氧化镁	$K_{2} O$	${Na}_{2} O$	${TiO}_{2}$	LOI	total 总
Mt 山	67.21	15.60	1.08	1.55	1.70	0.26	0.42	0.08	12.65	100.55

may trigger very intriguing performances on the surface of

Mt^{23}

Christianah

^{24}

investigated the point of zero charge (PZC), point of zero net proton charge (PZNPC), and surface charge density of Mt , in relation to its sorption characteristics for nickel and copper removal, and found that the sorption of metal ions by Mt was pH dependent, implying the decisive roles of PZC, PZNPC, and surface charge density of Mt on its adsorption performance. Marisa

^{25}

studied the surface chemistry of K-montmorillonite and pointed out that ionic strength influenced the PZNPC, but temperature has a very small effect on the surface. Maria

^{26}

compared the surface acidity of Mt on its catalytic performance of the formation of 1,5 -benzodiazepine from 1,2 -phenylenediamine and acetone and revealed that the type (Brønsted and Lewis type) and amount of acid sties played a critical role in the cyclocondensation process. Wen

^{27}

also studied the surface acidity of Mt on the catalytic oxidation effect of toluene and obtained that

{Al}_{30}

-PILM showed a higher catalytic activity under lower temperature than

{Al}_{13}

-PILM. Consequently, surface properties of Mt , such as PZC, PZNPC, and acidity, do have great influences on its application performances, and factors like ion strength, pH , chemical compositions, and functional groups can affect the surface properties of Mt.
可能会在表面

Mt^{23}

引发非常有趣的表现Christianah

^{24}

研究了零电荷点（PZC）、零净质子电荷点（PZNPC）和 Mt 的表面电荷密度，与其去除镍和铜的吸附特性有关，发现 Mt 对金属离子的吸附与 pH 值有关，这意味着 PZC 的决定性作用， PZNPC，以及 Mt 的表面电荷密度对其吸附性能的影响。Marisa

^{25}

研究了 K-蒙脱石的表面化学，并指出离子强度会影响 PZNPC，但温度对表面的影响非常小。Maria

^{26}

比较了 Mt 的表面酸度与其从 1,2-苯二胺和丙酮形成 1,5-苯二氮卓类药物的催化性能，并揭示了酸攸的类型（Brønsted 和 Lewis 型）和数量在环缩合过程中起着关键作用。温

^{27}

还研究了Mt的表面酸性对甲苯催化氧化作用的影响，

{Al}_{30}

得到-PILM在较低温度下表现出比

{Al}_{13}

-PILM更高的催化活性。因此，Mt 的表面性质，如 PZC、PZNPC 和酸度，确实对其应用性能有很大影响，离子强度、pH 值、化学成分和官能团等因素会影响 Mt 的表面性质。

As a naturally abundant adsorbent, the adsorption performance of Mt for multifarious chemical contaminants, including dyes, heavy metals, organic matter, and gas molecules, has been extensively studied.

^{23, 28, 29}

However, the adsorption capacities and affinities of raw Mt for many contaminants are particularly weak due to the low reactivity of Mt surface. For example, Mt is considered as the most feasible material to solve the mycotoxins contamination issue, which poses serious threats to human health and food security, due to its low price and nontoxicity.

^{16 - 18}

However, raw Mt has low adsorption efficiency and nearly no adsorption affinity for apolar mycotoxins. In fact, the simultaneous presence of polar and apolar mycotoxins in food products have been a long-standing challenge. Based on the theoretical analysis, several techniques have been proposed to activate the surface of Mt , such as loading metal nanoparticles

^{30, 31}

or carbon nanoparticles (CNPs)

^{32 - 34}

on the surface of Mt . CNPs with porous structures, high specific surface area, and abundant functional groups have exhibited an outstanding performance in various fields.

^{35}

They have prominent advantages of being environmentally benign, cost efficient, and resource rich.

^{24, 36, 37}

The method of loading CNPs on Mt has merit for reducing the agglomeration of a single CNP and then enhancing their adsorption efficiencies. However, to the best of our knowledge, deep insights into the binding mechanism between Mt and CNPs, the way Mt prevents agglomeration of CNPs, and the factors that affect the carbonization of CNPs on Mt have not been illuminated clearly so far. Additionally, CNPs were generally derived from carbohydrates, such as glucose, amylopectin, cellulose, and biomass. Biopolymer chitosan (CTS), a kind of nontoxic, renewable, biocompatible, and biodegradable carbohydrate with more abundant hydroxyl, amine, and amide functional groups, has never been considered as the carbon source for the surface modification of

Mt .^{38, 39}

Recently, pioneering studies have demonstrated that CTS
作为一种天然丰富的吸附剂，Mt 对多种化学污染物（包括染料、重金属、有机物和气体分子）的吸附性能已得到广泛研究。

^{23, 28, 29}

然而，由于 Mt 表面的反应性低，原始 Mt 对许多污染物的吸附能力和亲和力特别弱。例如，Mt 被认为是解决霉菌毒素污染问题的最可行材料，由于其价格低廉且无毒，霉菌毒素污染问题对人类健康和食品安全构成严重威胁。

^{16 - 18}

然而，raw Mt 的吸附效率低，对非极性霉菌毒素几乎没有吸附亲和力。事实上，食品中同时存在极性和非极性霉菌毒素一直是一个长期的挑战。基于理论分析，已经提出了几种活化 Mt 表面的技术，例如在 Mt 表面加载金属纳米颗粒

^{30, 31}

或碳纳米颗粒（CNP）。

^{32 - 34}

CNPs 具有多孔结构、高比表面积和丰富的官能团，在各个领域都表现出优异的性能。

^{35}

它们具有环境友好、成本效益高和资源丰富的突出优势。

^{24, 36, 37}

在 Mt 上加载 CNP 的方法具有减少单个 CNP 的团聚并提高其吸附效率的优点。然而，据我们所知，对 Mt 和 CNPs 之间的结合机制、Mt 阻止 CNP 聚集的方式以及影响 CNPs 在 Mt 上碳化的因素的深入了解到目前为止还没有得到明确阐明。此外，CNP 通常来自碳水化合物，例如葡萄糖、支链淀粉、纤维素和生物质。生物高分子壳聚糖（CTS）是一种无毒、可再生、生物相容、可生物降解的碳水化合物，具有更丰富的羟基、胺和酰胺官能团，从未被视为表面改性的

Mt .^{38, 39}

碳源最近，开创性的研究表明，CTS
showed superior effects in areas of adsorption and degradation.

^{40, 41}

The abundant functional groups of CTS, if they can be successfully loaded on the surface of Mt , were expected to dramatically improve the adsorptive performance of Mt.
在吸附和降解区域显示出优异的效果。

^{40, 41}

CTS 丰富的官能团，如果能够成功负载在 Mt 表面，有望显着提高 Mt 的吸附性能。

In this study, two prototypical surface-functionalized Mt by hydrothermal carbon (Htc) derived from CTS, namely, 180Htc@Mt and 250-Htc@Mt, were fabricated via the hydrothermal carbonization method. The effect of hydrothermal temperature on the carbonization process and surface systems of Mt , including morphologies, functional groups, chemical compositions, interfacial hydrophobicity, and surface areas, was systematically investigated with field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) specific area. The binding mechanism between Mt and Htc as well as the way Mt prevents the agglomeration of a single Htc was profoundly expounded. The influences of these surface properties on the adsorptive performance of Mt were explored by a comparative study on mycotoxin adsorption for both aflatoxin

B_{1} ({AFB}_{1})

and zearalenone (ZER) (Figure S1), which are typical representations of polar and weak-polar mycotoxins and the most common contaminations in food products, through simulating gastrointestinal conditions in vitro. The adsorption mechanisms for

{AFB}_{1}

and ZER were investigated thoroughly in order to explain the role of the surface functionalization of Mt on its enhanced adsorptive performance.
在本研究中，通过水热碳化法制备了两种由 CTS 衍生的热液碳（Htc）的原型表面功能化 Mt，即 180Htc@Mt 和 250-Htc@Mt。采用场发射扫描电子显微镜（FESEM）、傅里叶变换红外光谱（FTIR）、X 射线衍射（XRD）、X 射线光电子能谱（XPS）和 Brunauer-Emmett-Teller （BET）比面积系统研究了水热温度对 Mt 碳化过程和表面体系的影响，包括形貌、官能团、化学成分、界面疏水性和表面积。Mt 和 Htc 之间的结合机制以及 Mt 阻止单个 Htc 聚集的方式得到了深刻的阐述。通过对黄曲霉毒素

B_{1} ({AFB}_{1})

和玉米赤霉烯酮（ZER）的霉菌毒素吸附进行比较研究，探讨了这些表面特性对 Mt 吸附性能的影响（图 S1），它们是极性和弱极性霉菌毒素的典型代表，也是食品中最常见的污染，通过模拟体外胃肠道条件。为了解释 Mt 的表面功能化对其增强吸附性能的作用，对 Zer 的

{AFB}_{1}

吸附机理进行了深入研究。

EXPERIMENTAL SECTION 实验部分

Materials. Ca-Mt, containing very little quartz with high purity (

\geq 90 wt %

) and a cation exchange capacity (CEC) of 68.29 meq/ 100 g , was obtained from a mineral company in Inner Mongolia, China. The main chemical compositions of raw Mt are listed in Table 1. Low-viscosity CTS (<200 mPa•s) with

80 %

deacetylation, acetic acid

({CH}_{3} COOH, \geq 99 wt %)

, and sodium hydroxide (

NaOH, \geq 98 wt %

) were purchased from Aladdin Industrial Co., China.

{AFB}_{1} (\geq 99.5 wt

%)

and ZER (

\geq 99.5 wt %

) were purchased from Fermentek Co. Ltd, Israel. Phosphoric acid solution

(H_{3} {PO}_{4}, \geq 85 wt %)

, disodium phosphate

({Na}_{2} {HPO}_{4}, \geq 98

wt %), sodium phosphate monobasic

({NaH}_{2} {PO}_{4}, \geq 98

wt %), methyl alcohol (

{CH}_{3} OH, \geq 99.9

wt %), and acetonitrile

(C_{2} H_{3} N, \geq 99.8

wt %) were purchased from Beijing Reagent Co., China.
材料。Ca-Mt 含有极少的石英，纯度高（

\geq 90 wt %

），阳离子交换容量（CEC）为 68.29 meq/100 g，是从中国内蒙古的一家矿业公司获得的。生 Mt 的主要化学成分列于表 1 中。低

80 %

粘度 CTS （<200 mPa•s）含脱乙酰、乙酸

({CH}_{3} COOH, \geq 99 wt %)

和氢氧化钠（

NaOH, \geq 98 wt %

）购自中国阿拉丁工业有限公司。

{AFB}_{1} (\geq 99.5 wt

%)

和 ZER （

\geq 99.5 wt %

）购自以色列 Fermentek Co. Ltd。磷酸溶液

(H_{3} {PO}_{4}, \geq 85 wt %)

、磷酸二钠

({Na}_{2} {HPO}_{4}, \geq 98

wt %）、磷酸二氢

({NaH}_{2} {PO}_{4}, \geq 98

钠 wt %）、甲醇（

{CH}_{3} OH, \geq 99.9

wt %）和乙腈

(C_{2} H_{3} N, \geq 99.8

wt % 购自中国北京试剂有限公司。

Surface Functionalization Method. The surface modification procedures are illustrated in Figure S2. Initially, 4 g of Mt powder was dispersed in 300 mL of deionized water to form suspension A, and 0.6 g of CTS (the type and loading amount of CTS was determined preliminarily and are presented in Figures S3 and S4) was dissolved in 100 mL of acetic acid solution

(1 % v / v)

to form solution B. Solution B was introduced slowly into suspension A using a peristaltic pump. The CTS was allowed to adsorb on Mt for 6 h at

60^{\circ} C

under continuous stirring by a magnetic stirrer. Afterward, the excess CTS that did not adsorb on Mt was separated and discarded by centrifugation at 4000 rpm for 10 min . The purpose of this step was to prevent the formation of single carbon particles and promote the effective fabrication of the Htc@Mt composite. The residual solid was re-dispersed with 72 mL deionized water and transferred to a 100 mL Teflon autoclave, which was maintained at a controllable temperature for 24 h . Finally, the product was collected by filtration, washed with ethanol/water solution (

50 %, v / v

), and dried at

60^{\circ} C

for 24 h . Samples obtained at

180^{\circ} C

and

250^{\circ} C

were denoted as
表面功能化方法。表面改性程序如图 S2 所示。最初，将 4 g Mt 粉末分散在 300 mL 去离子水中形成悬浮液 A，将 0.6 g CTS（CTS 的类型和负载量初步确定，如图 S3 和 S4 所示）溶解在 100 mL 乙酸溶液

(1 % v / v)

中，形成溶液 B。使用蠕动泵将溶液 B 缓慢引入悬浮液 A 中。CTS 在磁力搅拌器的持续搅拌

60^{\circ} C

下在 Mt 上吸附 6 h。之后，将未吸附在 Mt 上的过量 CTS 分离出来，并以 4000 rpm 离心 10 分钟丢弃。此步骤的目的是防止单碳颗粒的形成并促进Htc@Mt复合材料的有效制备。用 72 mL 去离子水重新分散残留固体并转移到 100 mL 特氟龙高压灭菌器中，在可控温度下保持 24 h。最后，过滤收集产物，用乙醇/水溶液（

50 %, v / v

）洗涤，并在 24 h 下

60^{\circ} C

干燥。获得的

180^{\circ} C

样本和

250^{\circ} C

表示为

180-Htc@Mt and 250-Htc@Mt, respectively. Pristine CTS without the partition of Mt was also treated at

250^{\circ} C

for comparison and was denoted as

250 - Htc

.
分别为 180-Htc@Mt 和 250-Htc@Mt。没有 Mt 分区的原始 CTS 也被处理

250^{\circ} C

以进行比较，并表示为

250 - Htc

。

Analytical Methods. The main chemical composition of Mt was determined by X-ray fluorescence spectrometer (XRF, 1800, Shimadzu, Japan). The surface morphologies of samples were observed with a FESEM (SU8000, Hitachi, Japan). Samples were coated with gold and observed under an SE2 model. The size distribution of carbon particles on the surface of Mt was determined by a statistical method using a software called Nano Measure version 1.2 according to 9 SEM images. The functional groups on the surface of Mt were recorded by FTIR (Nicolet IS10, Thermo Fisher Scientific, USA). Samples were prepared by mixing KBr and sample powder and then pressing them into pellets. The surface chemical compositions were determined by XPS (250Xi, Thermo ESCALAB, USA). The binding energies were calibrated with C

1 s (285.0 eV)

as a reference. The peak-differentiating and imitating for the high resolution of Si

2 p, Al 2 p, C 1 s

, and N 1 s were performed on an XPSPEAK software using the least square method employing Gaussian-Lorentzian functions and the Shirley-type background. The atom contents of various carbonaceous and nitrogenous species were calculated on the basis of eq 1 .
分析方法。Mt 的主要化学成分由 X 射线荧光光谱仪（XRF， 1800， Shimadzu， Japan）测定。用 FESEM （SU8000， Hitachi， Japan）观察样品的表面形态。样品涂有金，并在 SE2 模型下观察。根据 9 张 SEM 图像，使用称为 Nano Measure 1.2 版的软件通过统计方法确定 Mt 表面碳颗粒的尺寸分布。Mt 表面的官能团通过 FTIR （Nicolet IS10，Thermo Fisher Scientific，美国）记录。通过将 KBr 和样品粉末混合，然后将其压制成颗粒来制备样品。表面化学成分由 XPS （250Xi， Thermo ESCALAB， USA）测定。以 C

1 s (285.0 eV)

作为参考校准结合能。在 XPSPEAK 软件上使用采用高斯-洛伦兹函数和 Shirley 型背景的最小二乘法对高分辨率 Si

2 p, Al 2 p, C 1 s

和 N 1 s 进行峰区分和模拟。根据方程 1 计算各种碳质和含氮物质的原子含量。

{atom}_{i} = A \times \frac{{area}_{i}}{{area}_{t}}

where atom

_{i}

represents the atom percentage of specie

i

in a sample,

A

represents the atom concentration of element C or N in a sample, and area

_{i}

and area

_{t}

represent the peak fit areas of specie

i

and total areas of various species determined from XPS. The BET specific surface area and Barrett-Joyner-Halenda (BJH) size distribution were obtained based on the measurement of

N_{2}

adsorption-desorption isotherms at 77 K (ASAP 2020, Micromeritics, USA). Because of the existence of carbonaceous species derived from CTS, the samples were initially degassed under

60^{\circ} C

for 12 h or overnight using a degassing system to remove the physically adsorbed water; a higher temperature will influence the chemistry of resultant samples.

^{42}

And the weight of the guest-free samples was recorded upon degassing. Then, the sample tubes were mounted on the measurement station, the adsorptive gas was introduced slowly, and the total weight of samples plus the adsorbed gas was recorded. The interfacial hydrophobicity of samples was deduced from moisture-adsorption capacities ( Ma ) under relative humidity of

33 %

and ambient temperature

(25^{\circ} C)

carried out in a constant climate chamber (GDW-300, China). 1 g of each sample was allowed to adsorb moisture until the equilibrium of mass. The adsorbed moisture amounts at different time intervals were recorded and calculated using eq 2 . We used the reciprocal of Ma to evaluate the relative hydrophobicity of samples. The structural information was characterized by powder XRD (D8, Bruker, Germany) with

Cu K α

radiation (

λ = 0.15406 nm

) operating at 40 kV and 40 mA .
其中 atom

_{i}

表示样品

i

中物种的原子百分比，

A

表示样品中元素 C 或 N 的原子浓度，面积

_{i}

和面积

_{t}

表示物种的峰拟合面积

i

和由 XPS 确定的各种物质的总面积。BET 比表面积和 Barrett-Joyner-Halenda （BJH）尺寸分布是根据 77 K 下吸附-脱附等温线的测量

N_{2}

获得的（ASAP 2020， Micromeritics， USA）。由于存在源自 CTS 的碳质物质，最初使用脱气系统对样品进行脱气

60^{\circ} C

12 小时或过夜，以去除物理吸附的水;较高的温度会影响所得样品的化学性质。

^{42}

并在脱气时记录无客体样品的重量。然后，将样品管安装在测量站上，缓慢引入吸附气体，记录样品的总重量加上吸附气体。样品的界面疏水性是通过在恒温恒湿室（GDW-300， China）中相对湿度

33 %

和环境温度下

(25^{\circ} C)

的水分吸附能力（马）推导出来的。每个样品中允许 1 g 吸附水分直至质量平衡。记录不同时间间隔的吸附水分量，并使用方程 2 计算。我们使用马的倒数来评估样品的相对疏水性。结构信息通过粉末 XRD （D8， Bruker， Germany）和 40 kV 和 40 mA 的

Cu K α

辐射（

λ = 0.15406 nm

）进行表征。

Ma = \frac{m_{t} - m_{0}}{m_{0}} \times 100 %

where Ma is the adsorbed moisture amount (%),

m_{t}

is the mass of the sample plus the adsorbed moisture (unit/g) at time

t

, and

m_{0}

is the initial mass of the dried sample (unit/g).
其中马是吸附的水分量（%），

m_{t}

是样品的质量加上当时

t

的吸附水分（单位/g），

m_{0}

是干燥样品的初始质量（单位/g）。

In Vitro Adsorption Experiments. The adsorption performance was evaluated on the basis of adsorption isotherms of mycotoxins in vitro, which was performed at pH values of 3.5 (simulated gastric fluid) or 6.5 (simulated intestinal fluid) and temperature of

37^{\circ} C

(close to body temperatures of most mammals). In vitro study is a fast and convenient method to obtain the basic information about mycotoxin adsorbents before a time-consuming bioassay. In a typical batch model, 3 mg of each sample was added into 5 mL mycotoxin working solution. The initial concentrations of

{AFB}_{1}

and ZER working solutions were kept in the range

0.2 - 1.0

and

5.0 - 10.0 mg / L

, respectively. After a complete adsorption for

120 \min, 1 mL

of the supernatant was separated from the system with a

0.22 μ m

membrane filter. The concentrations of mycotoxins prior to and after adsorption were determined by the high performance liquid chromatography
体外吸附实验。根据霉菌毒素的体外吸附等温线评估吸附性能，该吸附性能在 pH 值为 3.5（模拟胃液）或 6.5（模拟肠液）和温度

37^{\circ} C

（接近大多数哺乳动物的体温）下进行。体外研究是一种快速便捷的方法，可在耗时的生物测定之前获取有关霉菌毒素吸附剂的基本信息。在典型的批次模型中，将每个样品 3 mg 添加到 5 mL 霉菌毒素工作溶液中。和 ZER 工作溶液的初始浓度

{AFB}_{1}

分别保持在和

0.2 - 1.0

5.0 - 10.0 mg / L

范围内。完全吸附

120 \min, 1 mL

后，用

0.22 μ m

膜过滤器将上清液与系统分离。采用高效液相色谱法测定吸附前后霉菌毒素的浓度
(HPLC) analysis. pH effects on the adsorption process of

{AFB}_{1}

or ZER were performed at

1.000 mg / L

{AFB}_{1}

8.000 mg / L

of ZER. All adsorption experiments were repeated in triplicates, and the mean values and standard deviations of three triplicates were presented.
（HPLC）分析。pH 值对 ZER 或

{AFB}_{1}

ZER 的吸附过程的影响

1.000 mg / L

{AFB}_{1}

8.000 mg / L

是在 ZER 或 ZER 下进行的。所有吸附实验一式三份重复，并给出一式三份的平均值和标准差。

RESULTS AND DISCUSSION 结果与讨论

Surface Characterizations. Figure 1 displays the surface morphologies of the two Htc@Mt products as well as of Mt
表面表征。图 1 显示了两种 Htc@Mt 产物以及 Mt 的表面形态

Figure 1. FESEM images of (a) raw Mt, (b) 180-Htc@Mt, © 250Htc@Mt, and (d) 250-Htc.
图 1.（a）原始 Mt、（b） 180-Htc@Mt、© 250Htc@Mt 和（d） 250-HTC 的 FESEM 图像。
and

250 - Htc

. Raw Mt exhibits a unique sheet-like structure with a smooth surface, which can provide sufficient surface sites for the loading of Htc (Figure 1a). After hydrothermal treatment, a mass of spherical particles distribute on the surface of Mt uniformly, indicating that the biopolymer CTS converts from fibriform to spherical Htc due to the lowest surface energy of the sphere (Figure

1 b, c

). In order to investigate the effect of temperature on the particle size of Htc , the particle size distributions of Htc on the surface of Mt were obtained by a statistical analysis. Notably, the average particle size of Htc on

250 - Htc @ Mt (27 nm)

is smaller than that on

180 - Htc @ Mt

( 53 nm ), demonstrating the deeper carbonization of Htc at a higher temperature (Figure S5). In comparison, a single

250 - Htc

without the partition of Mt also generates spheres but shows an obvious agglomeration (Figure 2d), reflecting the significant role of Mt as a carrier to prevent the agglomeration of

Htc .^{43}

Moreover, the introduction of Mt also has an inhibiting effect on the size of Htc particles since the mean size of Htc on the surface of

250 - Htc @ Mt

is evidently smaller than that on

250 - Htc

(Figure S5). Several literatures also disclosed the inhibiting effect of a carrier on the particle size.

^{37, 43}

The reason that a single

250 - Htc

tends to aggregate may be the simultaneous presence of both negatively charged (oxygen) and positively charged (protonated hydroxyl and amine) functional groups in

250 - Htc

derived from CTS, leading to the electrostatic interactions between

250 - Htc

particles themselves. As is well known, Mt has a negatively charged surface, which can attract positively charged species of Htc, resulting in the uniform dispersion of Htc particles on the surface of Mt. Thus, the introduction of Mt prevents the agglomeration of a single Htc and promotes the formation of smaller particles on the surface of Mt compared to

250 - Htc

. Smaller particle sizes were expected to expose higher surface areas and more surface functional groups, which would improve the adsorption performance of products. Therefore, the surface immobilization of Mt with Htc not only functionalizes the surface of Mt , but also promotes the dispersibility of Htc in return.
和

250 - Htc

.Raw Mt 表现出独特的片状结构，表面光滑，可以为 Htc 的负载提供足够的表面位置（图 1a）。水热处理后，大量球形颗粒均匀分布在 Mt 表面，表明由于球体表面能最低，生物聚合物 CTS 从纤维状转化为球形 Htc（图

1 b, c

）。为研究温度对 Htc 粒径的影响，通过统计分析得到 Htc 在 Mt 表面的粒径分布。值得注意的是，Htc 的平均

250 - Htc @ Mt (27 nm)

粒径小于 on

180 - Htc @ Mt

（ 53 nm），表明 Htc 在较高温度下碳化程度更高（图 S5）。相比之下，没有 Mt 分区的单个

250 - Htc

也会产生球体，但表现出明显的团聚（图 2d），反映了 Mt 作为载体在防止团聚方面的重要作用

Htc .^{43}

。此外，Mt 的引入对 Htc 颗粒的大小也有抑制作用，因为 Htc 在表面

250 - Htc @ Mt

的平均大小明显小于

250 - Htc

（图 S5）。一些文献还披露了载体对粒径的抑制作用。

^{37, 43}

单个

250 - Htc

倾向于聚集的原因可能是 CTS 衍生的

250 - Htc

中同时存在带负电（氧）和带正电（质子化羟基和胺）的官能团，从而导致颗粒本身之间的

250 - Htc

静电相互作用。众所周知，Mt 具有带负电的表面，可以吸引带正电的 Htc 物种，导致 Htc 颗粒在 Mt 表面均匀分散。因此，与

250 - Htc

相比，Mt 的引入可以防止单个 Htc 的团聚，并促进在 Mt 表面形成更小的颗粒。预计较小的粒径会暴露出更高的表面积和更多的表面官能团，这将提高产品的吸附性能。因此，Htc 对 Mt 的表面固定不仅使 Mt 表面功能化，而且反过来也促进了 Htc 的分散性。

Received: November 28, 2019
收稿日期： 2019-11-28
Revised: February 15, 2020
修订日期：2020 年 2 月 15 日
Published: February 21, 2020
发布时间：2020 年 2 月 21 日

Surface Functionalization of Montmorillonite with Chitosan and the Role of Surface Properties on Its Adsorptive Performance: A Comparative Study on Mycotoxins Adsorption 壳聚糖蒙脱土表面功能化及其表面性质对其吸附性能的影响：霉菌毒素吸附的比较研究

Abstract 抽象

INTRODUCTION 介绍

EXPERIMENTAL SECTION 实验部分

RESULTS AND DISCUSSION 结果与讨论

Surface Functionalization of Montmorillonite with Chitosan and the Role of Surface Properties on Its Adsorptive Performance: A Comparative Study on Mycotoxins Adsorption
壳聚糖蒙脱土表面功能化及其表面性质对其吸附性能的影响：霉菌毒素吸附的比较研究