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磷是生命活动中必不可少的重要营养物质,但水体磷浓度超标,会导致藻类过度生长,从而大量消耗水中的溶解氧,影响水质[1],引起水体富营养化,是农业生产中环境影响较大的问题[2]。根据2020年中国生态环境状况公报数据显示,我国近30%地表水呈现富营养化状态。磷为不可再生资源,从废水中分离与回收含磷化合物,不仅能解决水体富营养化问题,保护生态环境,还能有效回收利用磷资源,具有很大的经济价值和社会效应,也是一项迫在眉睫的艰巨任务[3]。
近年来,多种解决水体磷污染的方法取得重要的进展。例如化学沉淀法、生物法、吸附法、离子交换法、结晶法以及电渗析等。其中,吸附法具有简单、高效的优势受到人们的普遍关注,合成经济有效的吸附剂,在水体磷污染治理领域应用潜力很大[4]。对固体载体材料进行固载化,使其具备吸附磷酸盐的特征又可循环利用,具有重要的研究意义。以沸石[5]、碳材料[6]、二氧化硅[7]、生物炭[8]、纤维素等生物质[9]作为载体制备除磷材料的研究有了显著的进展,但它们在应用上也存在一些不足。例如,天然矿石如沸石材料热稳定性不高;多孔材料孔内修饰困难,而且水相目标分子难以进入孔径之中限制其应用;碳材料如石墨烯价格昂贵;此外,粉末载体材料回收不便,易导致二次污染。因此,制备高效稳定、绿色环保可循环利用的新型磷酸盐吸附材料吸附和回收水体磷酸盐具有重要研究价值。
腈纶纤维,作为一种成熟的合成纤维,通常应用于衣织物和室内装饰纺织品的加工[10]。具有柔软蓬松、强度高、弹性好、耐热和耐光[11]等特点,其表面含有的丰富的氰基,可以通过化学改性的方法使其转化为酰胺、羧基、偕肟胺等基团[12],是理想的载体材料,并广泛应用于固载有机小分子催化有机反应[13],吸附重金属离子[14]或有机污染物[15]。本课题组已制备了许多不同结构和性质的功能性纤维,如载铁离子负载胺功能化纤维[16]净化水体磷酸盐,研究发现,腈纶纤维改性的铁离子负载胺功能化纤维,有利于提高对磷酸盐的吸附能力(24 mg·g−1 P),是一种环保、高效的磷酸盐吸附剂,且可重复使用5次以上[16]。因此,通过化学修饰引入新的官能团,制备功能化纤维具有较高的可行性,对提高废水中磷酸盐的去除和回收具有重要的研究意义。
作为先前功能化纤维的合成及其对水体磷酸盐去除方面工作[16-17]的延伸。本文以腈纶纤维为载体,将与水体磷具有交换作用的阴离子修饰到纤维表层,通过改变卤代烃烷基链的长度调控纤维表面亲疏水性,制备系列极性可调的季铵盐功能化纤维(图1),通过红外光谱、扫描电镜、X-射线粉末衍射等技术进行表征,以证明纤维的成功修饰。系统研究了不同极性修饰得季铵盐功能化纤维对水体磷的净化与回收,探究了 pH、吸附时间、磷酸盐初始浓度等对磷酸盐的影响,旨在为水体磷污染防控及纺织纤维资源化利用提供新思路。
极性可调功能化纤维的构建及其对废水磷酸盐的去除
The construction of polarity regulable functionalized fibers and its removal of phosphate in wastewater
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摘要: 本文利用腈纶纤维(PANF)便于回收、易于修饰、价格低廉等优点,通过不同链长卤代烃的季铵化反应,构建系列极性可调的功能化腈纶纤维,通过红外光谱、扫描电镜、X-射线衍射等技术进行表征,并研究纤维表层极性调控对水体磷酸盐的吸附性能的影响。结果表明,正溴丁烷修饰的季铵化纤维(PANT-C4F)对磷的吸附能力(25 mg·g−1 P)优于正溴己烷和正溴辛烷修饰的季铵盐功能化纤维(PANT-C6F、PANT-C8F)。改性纤维材料的吸附动力学更符合准二级动力学模型,吸附等温线采用Langmuir模型拟合更优,说明功能化纤维对磷的去除主要为单分子层化学吸附。PANT-C4F在pH 7左右时,对磷的吸附效果最好,且3 min达到平衡,因此具有较高的吸附效率。此外,PANT-C4F吸附的磷酸盐可以在NaCl溶液中解吸附,至少可以循环5次以上,实现功能化纤维的循环利用和磷的有效回收。研究表明,PANT-C4F是一种高效的水体磷酸盐吸附材料,具有较高的实际应用价值。Abstract: This study utilized the characteristic of polyacrylonitrile fiber (PANF) which can be easily recycled and modified with low price, we constructed a series of polarity regulable functional polyacrylonitrile fibers by the quaternary ammonium reaction with halogenated hydrocarbons of different chain lengths, which was characterized by FTIR, SEM and XRS, the adsorption ability effect of polar regulation on water phosphate was also be investigated. The results showed that phosphorus adsorption capacity (25 mg·g−1 P) of n-brombutane modified quaternary ammonium fibers (PANT-C4F) was better than quaternary ammonium fibers modified with n-bromhexane and n-bromocane (PANT-C6F、PANT-C8F). The second-order plot for modified polyacrylonitrile fiber materials are more suitable to describe the adsorption kinetics, and the Langmuir model are better to fit the adsorption isotherms, which indicate the phosphorus adsorption by functional fibers is mainly occurred through single molecular layer chemisorption. When the pH was about 7, the functional fibers had the best adsorption effect on phosphorus, and reached the balance of suction in 3 min which proved it has high adsorption efficiency. In addition, those phosphate adsorbed by PANT-C4F can be desorbed in NaCl solution to realize the recycling of functionalized fibers and the effective recovery of phosphorus at least 5 times, the results showed the PANT-C4F is a kind of high efficient material for phosphorus adsorption in wastewater with high practical application value.
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Key words:
- polyacrylonitrile fibers /
- polarity /
- quaternization /
- adsorption /
- phosphate
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表 1 纤维的增重和官能团
Table 1. The weight gain and functionality of the fibers
纤维
Fiber增重/%
Weight官能度/(mmol·g−1)
FunctionalityPANTF 28.9 2.18 PANT-C4F-a 5.9 0.41 PANT-C4F-b 20.8 1.26 PANT-C4F-c 35.4 1.91 PANT-C6F 27.7 1.31 PANT-C8F 37.8 1.42 注:PANT-C4F(a-c)分别为0.5、3、5 h时间下,制备的不同增重正溴丁烷修饰的季铵盐功能化纤维. 表 2 功能化纤维对磷的吸附性能比较
Table 2. Comparison of quaternary ammonium fibers
季铵化功能纤维
Quaternary ammonium functional fibersm/mg C1/(mg·L−1 P) C2/(mg·L−1 P) Q/(mg·g−1 P) PANT-C4F 11.0 5.30 20 13.36 PANT-C6F 11.0 6.15 20 12.59 PANT-C8F 11.0 6.97 20 11.85 表 3 元素分析数据
Table 3. Elemental analysis data of different fibers
条目Entry 纤维类型Sample C/% N/% H/% 1 PANF 66.25±0.12 25.49±0.07 5.12±0.02 2 PANTF 59.68±0.01 22.02±0.03 6.85±0.07 3 PANT-C4F 53.87±0.30 18.25±0.01 6.58±0.07 4 PANT-C4F-P 53.51±0.07 17.77±0.12 6.50±0.01 5 PANT-C4F-1 53.39±0.01 17.50±0.08 6.56±0.01 表 4 改性腈纶纤维吸附磷的动力学及等温线拟合方程参数
Table 4. Kinetic and isotherm parameters for phosphorus adsorption onto modified polyacrylonitrile fibers
模型Model 参数 R2 准一级 k1=0.8020 qe=24.7634 mg·g−1 P 0.9956 准二级 k2=0.0519 qe=26.1712 mg·g−1 P 0.9967 Langmuir k=0.0784 qmax=37.3552 mg·g−1 P 0.9273 Freundlich kf=3.8498 n=1.6486 0.9113 -
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