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高强度、多孔海藻酸钠/粘土复合水凝胶和水凝胶膜的制备及其对铅离子的吸附性能研究
毛辛有
Subtype硕士
Thesis Advisor王传义
2018-05-25
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline材料工程
Keyword重金属 吸附 水凝胶 水凝胶膜 粘土
Abstract

重金属污染严重威胁到人类的健康。特别是水体中的重金属污染物更容易经由食物链在人体内富集。当人体内的重金属含量超过人体可承受的范围时就会危害到人体的健康。水凝胶因表面富含羧基、羟基、氨基等对重金属离子具有化学吸附作用的官能团而被认为是一种有潜力的重金属吸附剂。本论文针对水凝胶作为重金属吸附剂存在的强度限制和尺寸限制,通过构建半互穿聚合物网络、粘土复合、制膜等方法,合成了高强度、多孔的海藻酸钠/粘土复合水凝胶和水凝胶膜,具体如下:(1)水凝胶作为一种重金属吸附剂,因其易于分离而备受关注,但其力学性能较差,限制了水凝胶的应用。我们通过将天然的凹凸棒引入海藻酸钠-聚(丙烯酸)半互穿聚合物网络水凝胶中来解决这一问题。结果显示,10%凹凸棒复合水凝胶的压应力为1.230 MPa,比纯水凝胶的压应力0.299MPa高4.1倍。10%凹凸棒复合水凝胶具有较高的的吸附容量,对铜离子的吸附量为272.8 mg/g,对铅离子的吸附容量为391.7 mg/g。经五次循环后,10%凹凸棒复合水凝胶对铜离子和铅离子仍然分别能保持261.7 mg/g和368.1 mg/g的吸附容量。我们的研究结果表明,具有网络结构的海藻酸钠-聚(丙烯酸)/凹凸棒复合水凝胶是一种极具潜力地高效的、可回收的重金属吸附剂。(2)在之前的研究中,粘土的致孔作用被报道过,但据我们所知,关于其致孔机理却还没有任何报道。在这个工作中我们提出了一种合理的凹凸棒致孔的机制,这种机制被总结为非牺牲性的类淀粉致孔机制。我们进一步地研究了凹凸棒复合水凝胶的多孔结构对吸附动力学、吸附等温线和吸附热力学的影响,并提出一种合理的吸附吸附机理。我们认为:普通水凝胶和凹凸棒复合水凝胶吸附行为的不同主要是由凹凸棒诱导形成的多孔结构导致的,一方面凹凸棒占据了表面活性位点的空间导致表面吸附作用减弱,另一方面多孔结构使铅离子可以进入水凝胶内部被吸附,提高了水凝胶内部空间的利用率。(3)水凝胶作为重金属吸附剂,因其块体的形状而具有操作简单、易于固液分离的优点,但吸附大部分只发生在表面,导致内部利用率低。虽然引入多孔的结构也能在一定程度上提高水凝胶内部利用率,但过慢的扩散速率导致响应速度变慢。为此我们选用可降解的海藻酸钠、羧甲基纤维素钠和膨润土作为膜的原材料,通过简单的钙交联,设计并合成了一种易于合成的、环境友好的水凝胶膜。该水凝胶吸附膜具有良好的拉伸性能,可伸长超过自身长度的一倍以上,且能恢复自身形状,最大拉伸强度为0.565 MPa。在保证机械强度的前提下,该水凝胶膜对铅离子具有较高的吸附容量,在样品用量为25 mg/25mL,初始浓度为100 mg/L时,对铅离子的最大吸附容量为93.28 mg/g。最后为了解决水凝胶膜在循环过程中机械性能下降的缺点,我们提出了一种再生膜的技术,再生膜的拉伸强度为0.601 MPa,五次循环后吸附容量为92.52 mg/g。

Other Abstract

Human health is threatened by heavy metal pollution. In particular, heavy metal pollutants in water environment are more easier to enrich in the human body via the food chain. When the content of heavy metals in the human body exceeds the unbearable range of human body, it will endanger human health. Hydrogel is considered to be a potential heavy metal adsorbent because its surface is rich in the functional groups (carboxyl, hydroxyl, and amino groups) which have a strong chemical adsorption effect on heavy metal ions. This paper aim to the limitations strength and size of hydrogels as heavy metals adsorbents. The high strength and porous sodium alginate/clay composite hydrogel and hydrogel film are synthesized via constructing a semi interpenetrating polymer network, clay composite and film preparation. The work is as follows:(1) Hydrogels are gaining interest as heavy metal adsorbents because of their easy separation, but hydrogel applications are limited due to their poor mechanical property. Here we solve this problem by introducing natural attapulgite into the sodium alginate–poly(acrylic acid) semi-interpenetrating polymer network of the hydrogel. Results show that the compressive stress of the hydrogel with 10% attapulgite, of 1.230 MPa, was 4.1 times higher than that of pure hydrogel, of 0.299 MPa. The adsorption capacity of hydrogel with 10% attapulgite was high, of 272.8 mg/g for Cu2+ and 391.7 mg/g for Pb2+. Even after five cycles of adsorption, the hydrogel with 10% attapulgite still adsorbs 261.7 mg/g Cu2+ and 368.1 mg/g Pb2+. Our findings thus reveal that network-structured sodium alginate–poly(acrylic acid)/attapulgite hydrogel holds great potential as an efficient and recyclable adsorbent for heavy metal removal.(2) In previous study, the clay–induced porous effect has been reported but as we know, the mechanism of clay–induced porous effect has not been reported. In this work, a reasonable mechanism of attapulgite–induced porous effect, which is described as non–sacrificial starch-like pore forming mechanism, is proposed. Further, the influence of the porous structure of the attapulgite composite hydrogel on the adsorption kinetics, the adsorption isotherm and the adsorption thermodynamics were studied, and a reasonable adsorption mechanism is proposed. Our researches show that the difference in adsorption behavior between ordinary hydrogel and attapulgite composite hydrogel is due to the porous structure induced by the attapulgite. On the one hand, the introduction of attapulgite reduced the surface active sites of hydrogels, resulting in the reduction of chemisorption on the surface. On the other hand, attapulgite–induced porous structure provides more opportunities for heavy metal ions to enter the interior of the hydrogel, resulting in increasing of internal utilization of the hydrogel.(3) Hydrogel as a heavy metal adsorbent is usually bulk. The bulk hydrogel is easily separated after adsorption and it is beneficial to reuse, but most of the adsorption only occurs on the adsorbent surface result in low internal utilization. The introduction of a porous structure can increase the internal utilization of the hydrogel, but the slow diffusion rate results in a slower response. To overcome size limits, an environment-friendly hydrogel film is designed and easily synthesized. The degradable sodium alginate, carboxymethyl cellulose and bentonite are selected as the raw materials, and the hydrogel film is obtained through a simple calcium crosslinking. The hydrogel film can be stretched more than double and recover quickly, whose tensile stress is as high as 0.565 MPa. The maximum adsorption capacity for lead ions is 93.28 mg/g when the sample dose is 25 mg/25 mL and the initial concentration is 100 mg/L. Finally, a regenerative hydrogel film technology is proposed to overcome the strength decline due to cycling. Results showed that the tensile strength of the regenerated film was 0.601 MPa, and the adsorption capacity was 92.52 mg/g after five cycles.

Pages64
Document Type学位论文
Identifierhttp://ir.xjipc.cas.cn/handle/365002/5418
Collection环境科学与技术研究室
Recommended Citation
GB/T 7714
毛辛有. 高强度、多孔海藻酸钠/粘土复合水凝胶和水凝胶膜的制备及其对铅离子的吸附性能研究[D]. 北京. 中国科学院大学,2018.
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