摘要：
采用一步法,通过控制 AB2单体和三羟甲基丙烷的摩尔量,利用 Michael 加成反应制备得到一种端羟基超支化聚(胺酯)[Hyperbranched poly(amine-ester),HPAE],在此基础上研究了 HPAE 对茶多酚(tea polyphenols, TPs)的吸附特性及其反应时间和不同 pH 对该吸附行为的影响.结果表明：在298 K 条件下,pH 7,m(TPs)∶m (HPAE)=14∶1时,吸附量随时间的增加而增大,吸附6 h 后达到平衡,其实验所得平衡吸附量 Qe(experiment, Exp)为279.69 mg/g.吸附动力学模拟结果显示其准一级动力学模型、准二级动力学模型和 Weber-Morris 颗粒内扩散模型的 R 2分别为0.6148,0.9977,0.7445.准二级动力学模型拟合计算所得平衡吸附量 Qe,2(calculation, Cal)为302.11 mg/g,与 Qe(Exp)更为接近,因此该吸附过程符合准二级动力学方程,并且可能是物理吸附为主. HPAE 对茶多酚的吸附量主要受介质 pH 影响.在298 K 条件下,m(TPs)∶m(HPAE)=5∶1时吸附量随 pH 升高而增加,当 pH=4时,平衡吸附量 Qe 为72.56 mg/g；当 pH=7时,平衡吸附量 Qe 为194.90 mg/g.利用 pH 对吸附的效应特性,可通过调节 pH 方法方便洗脱吸附茶多酚.结果也显示该吸附剂对茶多酚的吸附能力远远大于相同吸附条件下大孔树脂的吸附能力.%Summary Tea polyphenols (TPs),as one kind of effective components in tea,are composed of catechins, anthocyanins,flavonoids,etc.Catechins take up 70% 80% of TPs.The epigallocatechin gallate (EGCG) is the most abundant and important bioactivity among TPs.Various studies have demonstrated that EGCG possesses a higher efficient bioactivity compared with other components of tea polyphenols, especially in inhibiting carcinogenesis and preventing metastasis in established tumors.Therefore,it was studied widely to develop new methods or techniques to enhance the efficiency of extraction and purification of TPs (including EGCG). Now column chromatography is the main method in purification industry of TPs.However,this technique involves of organic solvents and complex operational processes,which leads to an environmental pollution and increases the additional costs virtually.The demand for an environment-friendly and cheaper technique in TPs industry is growing rapidly while more people become to pay attention to ambient bio-environment,so seeking for some new methods or new materials is of great significance.The hyperbranched poly (amine-ester)(HPAE) is a new sort of materials,having internal cellular structure and a large amount of hydroxyl terminals.HPAE has been widely used as surface modifiers,drug carriers and adsorbents for heavy metal ions on account of its high adsorption properties and complex ability.To date,there is no research on the adsorption of tea polyphenols by HPAE.The objective of this study is to investigate the characteristics of HPAE as a new environment-friendly and low-energy adsorbent for the adsorption of tea polyphenols from aqueous solutions. The adsorbent HPAE was prepared by one step method with 1-(bis(2-hydroxyethyl)amino) pentan-3-one(as a AB2 monomer) and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (as a core molecule) in our laboratory.The kinetic experiments of adsorption were done with 10 mL HPAE(1%,w/w)and 40 mL 98% TPs solution(3.5 g/L) under the condition of 298 K and pH 7.0.The TPs contents in supernatant were determined by HPLC methods. The experiments about effects of different pH values (from 4.0 to 8.0) on adsorption also were done with similar steps with 40 mL TPs solution (1.25 g/L).Finally,the comparison of the adsorption capacity was made among HPAE and 1 6 kinds of traditional macroporous resins under the same condition of 298 K,pH=7. The results indicated that the adsorption of tea polyphenols by HPAE increased with time and reached equilibrium time in six hours of contact.The experimental value of the equilibrium adsorption capacity Q e(Exp)was 279.69 mg/g.The R 2 values were 0.614 8,0.997 7 and 0.744 5 for the pseudo-first-order kinetic model,pseudo-second-order kinetic model and intraparticle diffusion kinetic model,respectively.The pseudo-second-order kinetic model due to its higher R 2 value and closest Q e,2(Cal),was considered to be the best choice to describe the adsorption behavior of tea polyphenols by HPAE,suggesting that the adsorption mechanism might be a physical adsorption process. The increase in pH from 4 to 8 resulted in the increase in the TPs adsorption capacity,indicating that pH had an obvious effect on the TPs adsorption capacity onto HPAE and adsorbed tea polyphenols could be desorbed by controlling pH value in acid medium.The maximum adsorption capacity of HPAE was 194.90 mg/g at the present experiment condition,and far greater than the adsorption capacity of macroporous resins studied widely in TPs industry,such as LSA-8,LSA-20, XDA-1,HPD600,NKA,AB-8,D3520,D4020,PVPP and PA,etc. In conclusion,the new adsorbent HPAE has excellent adsorption and desorption properties for tea polyphenols. Its adsorption capacity could achieve 1 94.90 mg/g,and adsorption of TPs could be desorbed easily by adjusting pH instead of using organic solvents.HPAE shows a great potential as an environment-friendly and high efficiency substitute materials for tea comprehensive processing.
