【作者】 张海真；

【导师】 孙小梅； 李步海；

【作者基本信息】 中南民族大学 ， 分析化学， 2008， 硕士

【摘要】 壳聚糖分子中含有大量氨基,容易结合溶液中的H+而被质子化,它对许多无机酸、有机酸及酸性化合物有良好的吸附性能,但是壳聚糖易溶于酸性溶液,作为吸附剂的应用受到了限制。本文对壳聚糖的结构特性、改性研究现状以及实际应用进行了充分的文献调研,在此基础上,选用乳化交联法,以戊二醛为交联剂,壳聚糖为单体包埋磁性纳米颗粒,合成了磁性壳聚糖微球(MCTS),研究了它对三种酸性植物激素的吸附行为;在异丙醇介质中以高氯酸为催化剂,用环氧氯丙烷活化,在磁性微球表面引入羟丙基氯基团,制备成羟丙基氯磁性微球(ECH-MCTS),再将乙二胺接枝到微球表面,合成了胺化磁性壳聚糖微球(EN-MCTS);研究对比了改性前后三种磁性壳聚糖微球对阴离子染料酸性桃红B(AR)、活性艳蓝X-BR(RBB)及酸性品红(FA)的吸附性能,并对吸附过程的热力学和动力学以及吸附机理进行了讨论。将壳聚糖粉末制备成磁性壳聚糖树脂,在外加磁力的作用下,易实现介质分离,大大拓展了壳聚糖的应用范围。主要研究工作和结果如下:1.磁性壳聚糖微球的合成与表征。考察了交联剂戊二醛的用量对微球形貌的影响。光学显微镜表明,交联剂加入量增加,微球成球率提高,但是随交联剂浓度的提高,形成的微球粘结状况加剧,并且对植物激素脱落酸的吸附效果也随之变差。说明过多的交联剂占据了壳聚糖表面的活性位点-NH2,导致吸附量下降。当壳聚糖用量为0.5g,戊二醛浓度为7%时,合成的磁性微球分散性能较好,粒径分布较均匀。用扫描电子显微镜(SEM)及透射电镜(TEM)观察微球的形貌和粒径,球形规则,表面光滑,微球粒径3~5μm;用傅立叶红外光谱仪(FT-IR)、X射线粉末衍射仪(XRD)、差示扫描量热仪(DSC)及热重法(TG)研究了其物质结构及性质的变化,解析结果表明,反尖晶石型晶体结构的Fe3O4纳米粒子被包裹在微球内,含量为10.9%;合成的磁性壳聚糖微球较壳聚糖本体的热稳定性有所降低,但是225℃以前热稳定性高。2.磁性壳聚糖微球对酸性植物激素的吸附行为及作用机理将磁性壳聚糖微球用于吸附植物激素脱落酸(ABA)、赤霉酸(GA3)、吲哚乙酸(IAA)。用静态吸附法研究了吸附剂用量、溶液酸度、离子强度、吸附时间以及三种植物激素初始浓度对吸附率的影响,优化了吸附条件。将实验数据用动力学的准一级方程和准二级方程,以及吸附等温方程Langmuir和Freundlich模型拟合,探讨了MCTS对三种植物激素的吸附机理。实验结果表明,吸附剂用量为1.25 g L-1比较适宜。该吸附剂在20min内对ABA(c0 = 32.28mg L-1)、IAA(c0 = 43.80mg L-1)、GA3(c0 = 200.0mg L-1)的吸附率达到最高,最大吸附率分别为89%、93%、81%。而且,该磁性微球的吸附性能受溶液酸度,溶液离子强度的影响较大,这是因为吸附起主要作用的是―NH2,pH低时,氨基质子化,与ABA、IAA、GA3离解生成的酸根离子发生正负离子的结合,完成吸附过程。pH升高,不利于―NH2质子化,pH太低不利于ABA、IAA、GA3的离解,都会导致吸附性能下降;而溶液离子强度的增加,使ABA、IAA、GA3处于更多的离子氛围,与活性位点结合的空间阻碍和静电斥力作用增加,盐离子也阻碍氨基与植物激素的结合使吸附率下降。上述方程拟合结果显示,三种植物激素的吸附过程更符合准二级动力学方程,表明此吸附过程主要受化学吸附控制。对ABA、GA3的吸附倾向于Langmuir等温模型,证明此类吸附主要是单分子层吸附。并且0.1 mol L-1 NaCl可将吸附剂再生,用Tris-HCl平衡后循环使用五次的吸附率仅下降5%,说明该磁性壳聚糖微球可重复使用。3.改性磁性壳聚糖微球的制备与表征壳聚糖的碱性与其吸附效果密切相关,交联后的壳聚糖微球碱性变弱,吸附容量降低,因此制备了两种改性微球:①用环氧氯丙烷活化磁性壳聚糖微球制得ECH-MCTS,②用乙二胺接枝于微球表面得到了新型胺化磁性壳聚糖微球EN-MCTS。滴定法测定了产物表面的氨基含量,用FT-IR、XRD和TG研究了ECH-MCTS及EN-MCTS结构及性质的变化。结果表明,ECH-MCTS的氨基含量明显下降,表明环氧氯丙烷可能同时与壳聚糖上的氨基和羟基反应;而EN-MCTS的氨基含量比MCTS高一倍多,并且EN-MCTS的碱性增强,有效提高了它的吸附能力;两种改性磁性微球也是以无定形体存在的非晶态材料,其内包裹的Fe3O4晶体结构未变,含量也无显著变化,并保持了良好的磁性相分离性能。4.三种磁性壳聚糖微球对阴离子染料的吸附行为及作用机理研究了MCTS、ECH-MCTS、EN-MCTS对AR、RBB、FA三种阴离子染料的吸附行为。考察了吸附时间、溶液酸度和温度对吸附的影响。实验结果表明,当AR和FA浓度分别为0.50和0.80 mmol L-1,吸附剂用量分别为0.5g L-1和0.8g L-1时,EN-MCTS在60min内对二者的吸附率达95%以上;当RBB初始浓度为0.30 mmol L-1,三种吸附剂用量为0.8g L-1时,4h内达吸附平衡,MCTS对RBB的吸附率达98%以上,吸附时间以5 h为宜。随着染料浓度的增加,三种吸附剂对染料的吸附容量增大,三种染料的吸附,随着溶液pH的增大,吸附率均呈下降趋势,但MCTS比ECH-MCTS、EN-MCTS受到酸度的影响要大。实验数据用动力学方程和吸附等温模型拟合,结果表明,三种磁性微球对于阴离子染料的吸附符合准二级动力学方程和Langmuir吸附等温模型,表明它们对三种阴离子染料的吸附是单分子层形式的化学吸附过程。用0.5mol L-1 NaOH+ 2 mol L-1NaCl(体积比1:1)再生处理吸附剂,再次最高吸附率均>95%。更多还原

【Abstract】 The molecule of chitosan contains high contents of amino groups, which can be protonated by integrating H+ in solution. So it has favorable adsorbability to some inorganic acid, organic acid, acor compound. Chitosan can be dissolved in acid solution. It limits its application as absorbent.The references about the chitosan structure characteristics, properties and modification research actualities and its practical application had been investigated sufficiently. On the basis of this, using glutaradehyde as the cross-linker, magnetic chitosan microspheres (MCTS) were prepared by the suspension cross-linking technique.The experiments had been carried out to study the adsorption behavior of MCTS for three kinds of phytohormone. In the medium of isopropanol, using perchloric acid as catalyst, hydroxypropyl chloride magnetic chitosan microspheres (ECH-MCTS) were prepared. Furthermore, aminated magnetic chitosan microspheres (EN-MCTS) were prepared by grafting ethylenediamine on the microsphere surface. The adsorption efficiency of aminated magnetic chitosan microspheres were investigated in removal of anoinic dyes acid rhodamine B(AR)、fuchsin acid (FA) and reactive brilliant blue X-BR (RBB) compared with MCTS and ECH-MCTS. The adsorption thermodynamics, kinetics and mechanism were discussed. Chitosan powder had been prepared to be magnetic resin. To the contribution of magnetic field, the chitosan and the resin can be easily isolated. This expanded the application of chitosan consumedly. The major study works and results were as follows:1. The preparation and characterization of magnetic chitosan microspheres.The effects of the dosage of crosslinker glutaraldehyde on microspheres morphology and yield had been observed intensively. The modality observed by optical microscope show that, the yield of microsphere increased, but the aggregation of the microspheres became more serious as the quantity of crosslinker increasing and the adsorption values to abscisic acid decreased correspondingly. The reason was that the amino groups on the surface of the microspheres had been occupied by overmany crosslinker. Therefore, when the crosslinker concentration was 7% and the qantity of the chitosan was 0.5 g, the magnetic microspheres with good dispersion property and uniformity the particle size diffusion were obtained.Scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to investigate the morphology and size of the microspheres. The results indicated that the microspheres had well shaped spherical form with smooth surface and the particle size was 3~5μm. The fourier transfor IR (FT-IR) spectrameter , X-ray diffraction (XRD) , differential scanning calorimetry (DSC) and thermogravinetry (TG) were used to analyze the molecular structure and the alteration of the microspheres’thermal character. The results showed that Fe3O4 nanoparticles remained its spinel structure, which packed in the microspheres to form core-shell structure, and the weight percentage of Fe3O4 nanoparticles was estimated to be about 10.9 wt%. The thermal stability of MCTS was lower than chitosan, but was as high as chitosan before 225℃, and also can be easily separated from aqueous solution under the magnetic field.2. The studies of adsorption behaviour and mechanism for acidic phytohormone onto magnetic chitosan mocrospheresMCTS was utilized to adsorb abscisic acid (ABA), gibberellin (GA3) ,3-indoleacetic acid (IAA) by static adsorption. The effects of adsorbent dosage, contact time, pH and the original concentration of ABA, GA3, IAA on the adsorption rate were investigated and optimized. In order to explore the adsorption mechanism of the modified microspheres, the experimental data were fitting by dynamics model including pseudo-second-order equation and pseudo-first-order equation, and isotherms Langmuir and Freundlich isotherms. The results showed that the adsorbent dosage was appropriated at 1.25 g L-1. In 20 minutes ,the adsorption rate to ABA(c0 = 32.28mg L-1),IAA(c0 = 43.80mg L-1),GA3(c0 = 200.0mg L-1)raised up to maximum, and the one step adsorption rate was 89%,93% and 81% respectively. Furthermore, the adsorption efficiencies were greatly influenced by the acidity and ionic strength of solution. A possible explanation for pH effect on adsorption may be related to the surface charge of magnetic microspheres and phytohormone. Amino groups on the surface of microspheres played a major role in adsorption proces. It could be protoned in low pH, combining with acid radical ion dissociated by ABA, IAA or GA3 to complete the adsorption process. So when the pH is too low, amino group couldn’t be protonated easily, but the high acidity impeded the dissociation of ABA, IAA and GA3. And aslo as the increase of ionic strength, high concentrations of NaCl ions could cover the particle surface and form an ion shield, which can decrease the diffusivity of phytohormone and enlarge the absorbed molecules, and therefore reduce the adsorption rate.The results for the experimental data applying pseudo-first-order equation and pseudo-second-order equation showed that the adsorption for phytohormone conformed to the pseudo-second-order equation. It confirmed that the adsorption rate was controlled by chemical sorption. The isotherms model of ABA and GA3 of the modified microspheres indicated that Langmuir isotherm equation gave better fit than the Freundlich isotherm. It confirmed that the adsorption on microspheres was in a monolayer form. The regeneration of the adsorbents could be implemented by 0.1 mol L-1 sodium chloride , only the 5% decrease of adsorption rate could be obtained after regenerating absorbents for five times. These results indicated that the magnetic chitosan microspheres can be recycled.3. The preparation and characterization of modified magnetic chitosan microspheres.The adsorption efficiency of chitosan closely related to its alkalinity. Cross-linking reaction weakened the alkalinity of absorbent and reduced the adsorption efficiency of absorbent. Thus, two kinds of modified microspheres were prepared in order to increase the adsorption efficiency.①Preparation of hydroxypropyl chloride magnetic chitosan microspheres (ECH-MCTS) by using epichlorohydrin modified magnetic chitosan microspheres②Preparation of a new adsobent aminated magnetic chitosan microspheres (EN-MCTS) by using ethylenediamine grafted on the surface of microspheres.The content of amino groups on microspheres were determined by titrimetric method. IR , XRD ,DSC and TG were used to analyze the alteration of ECH-MCTS and EN-MCTS’molecular structure and characte. The results showed that the amino group content of ECH-MCTS decreased obviously. It indicated that both amino groups and hydroxy groups participated in the reaction with ethylenediamine. However, the amino group content of EN-MCTS was twice than that of MCTS. So the alkalinity of EN-MCTS had been strengthened and the adsorbability had been enhanced .4. The studies on adsorption behaviour and mechanism for anionic dye onto MCTS, ECH-MCTS and EN-MCTSThe adsorption behaviour for the three anionic dyes acid rhodamine B, fuchsin acid and reactive brilliant blue X-BR were studied, the experimental factors contact time, pH and temperature had also been explored and optimized. The results showed that within 60 minutes, the adsorption rate for AR and FA on EN-MCTS can reach to 95%, when the original concentrations of AR were chosen at 0.50 mmol L-1, FA were at 0.80 mmol L-1, and the adsorbent dosage was at 0.5 g L-1 and 0.8 g L-1 respectively. However, within 4 hours, the adsorption rate for RBB can reach to 98% on EN-MCTS when the original concentrations were chosen at 0.30 mmol L-1 and the adsorbent dosage was at 0.8 g L-1. The adsorption capability could be enhanced as the concentration of dyes increasing, while the adsorption rate decreased as the acidity increasing on the three magnetic microspheres. But the adsorption on MCTS was affected greatly by the solution acidity compared with ECH-MCTS and EN-MCTS. The results indicated that the adsorption for anionic dyes were affected by the structure of dyes and the steric hindrance of amino groups on microspheres .The results for the experimental data applying dynamics equations and isotherm equations showed that the adsorption for anionic dyes conformed to the pseudo-second-order equation and Langmuir isotherm equation. It confirmed that the adsorption process was in monolayer controlled by chemical sorption. The regeneration of the adsorbents could be implemented by 0.5 mol L-1 NaOH + 2 mol L-1NaCl (V/V=1:1) , the second-regenerated ratios were all > 95%.更多还原