【作者】 黄健花；

【导师】 王兴国；

【作者基本信息】 江南大学 ， 食品科学， 2008， 博士

【摘要】 本论文以凹凸棒石粘土(简称“凹凸棒土”)为原料,对其结构进行系统分析,根据其结构特征,研究制备了两种具有重要应用前景的新型材料——用于吸附的十八烷基三甲基氯化铵改性凹凸棒土、用于脂肪酶固载的硅烷偶联剂KH550改性凹凸棒土。采用FTIR、XRD、TG-DTG-DSC、比表面积与孔径分布、AFM等分析方法比较凹凸棒土改性前后的结构变化,研究其改性机理。纳米聚合效应和相对较低的离子交换容量使凹凸棒土在十八烷基三甲基氯化铵改性过程中不破坏凹凸棒石的晶体结构,通过表面接枝实现其改性的目的。通过比较发现十八烷基三甲基氯化铵较其它的季铵盐阳离子表面活性剂在凹凸棒土上的接枝率高。借助超声波手段,可大大提高其改性效率,十八烷基三甲基氯化铵的接枝率44.66%。十八烷基三甲基氯化铵改性凹凸棒土的比表面积由酸处理凹凸棒土的152.85m2/g下降为63.96m2/g,孔径则分布未发生明显变化。凹凸棒石含有丰富的吸附水、结合水、结构水和结构羟基,有利于硅烷偶联剂KH550发生水解反应,形成大量硅羟基结构,这些硅羟基结构与凹凸棒石的羟基进一步缩合,或KH550的硅羟基自身缩合,覆盖于凹凸棒石表面,改变其表面形态和性质,形成新的网络结构,丰富了凹凸石的孔道,1.3-3.5nm之间的孔径明显增加;改性后凹凸棒土的比表面积由酸处理凹凸棒土的152.85m2/g增加为182.09m2/g。与常规酸活化凹凸棒土、凹凸棒土原矿、商业化脱色用凹凸棒土吸附剂相比,十八烷基三甲基氯化铵改性凹凸棒土,对苯酚和活性染料的吸附性能更加理想。该凹凸棒土吸附剂对苯酚的吸附是物理吸附过程,其相互作用力较弱,吸附放热较少,苯酚浓度为100mg/L时,放热约12kJ/mol;吸附速率由表面扩散控制,吸附过程符合拟二级速率方程,吸附速率常数k为1.367g/(mg min),初始吸附速率为0.8534mg/(g min)。十八烷基三甲基氯化铵改性凹凸棒土对活性染料的吸附是化学吸附-物理吸附共同作用的过程,化学吸附占优势;染料浓度越低,吸附热越大,浓度小于150mg/L时,吸附焓变几乎不随浓度变化而变化,吸附热约为40kJ/mol,以化学吸附为主,同时存在表面扩散控制的物理吸附;随着浓度的逐渐增加,吸附热逐渐减少,体系发生物理吸附的比例增加。体系在前15min主要是化学吸附,在30℃、50℃、70℃下的吸附初始速率均很大,达250mg/(g min)以上,化学吸附极易发生;随着吸附的进行,吸附速率急剧下降,20min后,以表面扩散控制的物理吸附主。十八烷基三甲基氯化铵改性凹凸棒土对大豆异黄酮-单宁酸混合溶液、葛根素-单宁酸混合稀溶液中的单宁酸具有很好的选择性吸附性能。十八烷基三甲基氯化铵改性凹凸棒土对茶多酚-单宁酸混合稀溶液体系中的吸附试验表明,单宁酸基本被完全除去,吸附剂对茶多酚各组分具有不同的吸附性能,对茶多酚中各组分的吸附能力如下:儿茶素棓酸酯CG(表儿茶素棓酸酯ECG)>棓儿茶素棓酸酯GCG(表棓儿茶素棓酸酯EGCG)>儿茶素C(表儿茶素EC)>棓儿茶素GC(表棓儿茶素EGC)。在疏水作用力、静电作用力和氢键作用力的共同作用下,十八烷基三甲基氯化铵改性凹凸棒土实现对单宁酸的有效吸附。十八烷基三甲基氯化铵改性凹凸棒土对单宁酸的吸附平衡符合Freundlich方程。吸附放热,约为20kJ/mol,是物理吸附。动力学研究表明,吸附剂对单宁酸的吸附速率很快,一定范围内,温度升高有利于提高吸附速率,单宁酸浓度越低,则吸附速率越大;吸附剂对单宁酸有较大的吸附容量。KH550改性凹凸棒土,经戊二醛交联进行脂肪酶固定化。确定其固载工艺条件为:40mL浓度为1mg/mL的脂肪酶磷酸缓冲液(pH7.0)溶液,加入0.400g经0.5%的戊二醛处理的KH550改性凹凸棒土,温度控制在25-30℃之间,固定化6h,得到固定化脂肪酶产品。原子力显微镜和扫描电镜分析证实,脂肪酶已经在KH550改性凹凸棒土载体上成功实现固载。所得到产品的酶活为3100-3300U/g,酶活回收率可达50%。经固定化的脂肪酶,其最适pH和最适温度均发生变改变,耐酸碱性能和耐热性能较原酶有明显提高,固定化脂肪酶具有较好的重复使用性能,重复使用八次后,酶活仍可保持85%左右。更多还原

【Abstract】 Palygorskite was characterized and then organo-modified to prepare two novel materials. Octodecyl trimethyl ammonium chloride (OTMAC) modified palygorskite was used as an adsorbent, and 3-aminopropyltriethoxysilane modified palygorskite was used as a support for lipase immobilization.An extensive study was performed on the mineral characteristics and modification mechanism of palygorskite in terms of thermal properties (TG-DTG-DSC), chemical composition (FT-IR spectroscopy), morphology (AFM), specific surface area (BET method), pore size distribution (gas adsorption method), basal spacing (XRD).Cation surfactant was mainly grafted on the surface of palygorskite without changing its crystal structure, because of its nano aggregation and low cation exchange capacity. OTMAC was grafted on the surface of palygorskite because it is electronegative. And ultrasonic treating improved the efficiency. The grafting ratio was 44.66%. The OTMAC modified palygorskite had a surface area of 63.96 m2/g, a large reduction from that of acid activated palygorskite (152.85 m2/g). The pore size distributions of the palygorskite had no significant change after OTMAC modification.There were lots of water and hydroxy groups in the palygorskite, with which 3-aminopropyltriethoxysilane was hydrolyzed to become silanol group. The 3-amino- propyltriethoxysilane was then grafted or covered on the palygorskite through dehydration condensation of the silanol group and hydroxyl group of palygorskite. The pores were formed and the surface areas were improved during the modification process. The 3-aminopropyltriethoxysilane modified palygorskite had more pores with the size from 1.3 to 3.5 nm than the acid activated palygorskite. The 3-aminopropyltriethoxysilane modified palygorskite had a surface area of 182.09 m2/g, a large increasing from that of acid activated palygorskite (152.85 m2/g).The OTMAC modified palygorskite adsorbed phenol and active dyes more effectively than the acid activated palygorskite, natural palygorskite and commercial palygorskite adsorbent. Adsorption of phenol on OTMAC modified palygorskite was a physical adsorption. Heat for the adsorption was low because of the small force between them. Heat was 12 kJ/mol when the concentration of phenol was 100mg/L. The adsorption mechanism of phenol was controlled by the surface diffusion. Second-order adsorption kinetics was observed in the case, the rate constant was 1.367 g/(mg min) and the initial adsorption raet was 0.8534 mg/(g min). Adsorption of active dyes on the OTMAC modified palygorskite was a chemical-physical process, and the chemical adsorption was the main one. The heat was about 40 kJ/mol at lower concentration (<150mg/L). All of the initial adsorption rates were larger than 250 mg/(g min) at three different temperatures (30℃、50℃、70℃). Chemical interaction was the main force for the adsorption at low concentration. And the physical adsorption also happened with the increasing of the concentration.Tannin was selectively removed by OTMAC modified palygorskite from model tannin/soybean isoflavones and tannin/puerarin mixtures. Adsorption of tannin/tea polyphenols on OTMAC modified palygorskite was also detected. And the results showed that tannin was removed thoroughly. The adsorption capacity of adsorbent for different components in tea polyphenols was as follows: CG(ECG)>GCG(EGCG)>C(EC)>GC (EGC). The selective adsorption of tannin on OTMAC modified palygorskite was driven by the collaboration of hydrogen bonding, electrostatic force and hydrophobic interactions of tannin molecular with adsorbent.Adsorption of tannin on OTMAC modified palygorskite was a physical process. In adsorption isotherm experiments of tannin adsorption on OTMAC modified palygorskite, obtained data fitted well to the Freundlich model. The enthalpy value of adsorption of tannin on OTMAC modified palygorskite was about 20 kJ/mol. Studies found the high velocity and large capacity for the adsorption of tannin on OTMAC modified palygorskite. The velocity of adsorption was increased with the increasing of temperature and the decreasing of concentration of tannin in a certain range. The tannin molecular contacting with the adsorbent was increased with the decreasing of the concentration of tannin.Lipase from Candida lipolytica was covalently immobilized on 3-aminopro- pyltriethoxysilane modified palygorskite support through glutaraldehyde. The optimized immobilization protocol was as follows: 0.4 g of glutaraldehyde-activated 3-amino- propyltriethoxysilane modified palygorskite supports were added to 40 mL enzyme solution in phosphate buffer pH 7.0, with a protein content of 1 mg/mL. The covalently bond process was performed over 6 h at 25-30℃. Scanning electron micrographs and atomic force micrographs proved the covalently immobilization of lipase on the palygorskite support through glutaraldehyde. The activity of 3,100-3,300 U/g per gram immobilized lipase was obtained. Immobilized lipase retained activity over wider ranges of temperature and pH than those of the free enzyme. The optimum pH and temperature of the immobilized lipase was different from those of free lipase. The immobilized enzyme retained high activity after 8 cycles.更多还原