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四环素(TC)是一种典型的广谱抗生素,广泛应用于人类疾病的防治和畜牧养殖业病害的预防,其在世界范围被大量使用,导致环境中残留的四环素越来越多[1-2],这些积累的四环素对人体健康和生态安全造成了严重危害[3-5]。因此水体中的TC污染去除受到人们越来越多的关注。
吸附法由于操作简单、吸附效率高等特点而备受关注,是一种去除水体中TC常用的方法[6-8]。吸附材料的孔道结构对分子尺寸大的污染物的吸附具有重要的影响,如孔道尺寸排斥效应的存在导致分子尺寸大的污染物极低的吸附[9,10]。通过扩孔或者调变孔径结构能增强分子尺寸大的有机物吸附性能,研究表明CO2活化制备的多孔炭,具有高孔隙体积和丰富的中孔,显著提高了对TC的吸附去除[11]。共价三嗪多孔聚合材料(CTFs)具有高的比表面积、有序的孔结构、良好的热稳定性和化学稳定性等特点[12-14],在气体储存和催化方面备受关注[15-17]。根据之前研究发现,CTFs对水体中有机污染如芳香族化合物苯、苯酚、苯胺和硝基苯等[18],以及双酚A[19]、腐殖酸[20]、染料等[21-24]具有很高的吸附性能,其具有大孔道能有效的避免尺寸排斥效应。因此,CTFs是一种吸附去除水体中TC潜在的吸附剂,但目前对于TC在CTFs的吸附机理,与CTFs孔结构作用关系的研究尚不清楚。
本研究采用离子热共聚法制备了两种孔径大小不同的CTFs材料,通过X射线衍射、红外光谱和N2吸附/脱附等方法对其结构和表面性质进行了表征。选取抗生素四环素(TC)作为模拟污染物,系统研究了CTFs对TC的吸附行为,包含等温线、动力学、pH值和离子强度的影响,揭示TC在CTFs上的吸附机理以及CTFs孔结构在吸附中的重要作用。
共价三嗪多孔聚合材料对水中四环素的吸附行为及其机理
Adsorption behavior and mechanism of the porous covalent triazine-based framework for tetracycline in water
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摘要: 采用离子热共聚法制备了两种共价三嗪多孔材料(CTFs),采用BET、XRD、FTIR表征手段研究了CTFs结构和理化性质,并研究了其对四环素(TC)的吸附性能和机理。表征结果表明,CTF-1仅具有微孔结构,CTFDCBP含有中孔结构,CTFDCBP的孔道结构是无定形的,两种CTFs均存在三嗪结构振动峰。吸附实验结果表明,CTFs对TC的吸附过程符合Freundlich等温吸附模型和准二级动力学模型。孔道尺寸排斥效应的存在,使得CTFDCBP对TC的吸附亲和力比CTF-1高1—2个数量级,吸附TC后,CTF-1比表面积和孔隙总体积变化不大,而CTFDCBP比表面积从1745 m2·g−1下降至220.5 m2·g−1,孔隙总体积从1.420 cm3·g−1减小至0.2280 cm3·g−1。中孔孔道作用存在导致TC在两种CTFs表现了不同的pH影响趋势。电子屏蔽作用导致阳离子降低了TC在CTFs上的吸附。CTFs材料对TC附机理包括静电作用力、阳离子-π 键作用、π-π 电子交互作用和孔道作用。研究结果表明,CTFDCBP是一种高效吸附去除水体中TC潜在的吸附剂。Abstract: Two kinds of covalent triazine frameworks (CTFs) with different pore structures were synthesized by ionothermal method. The crystal structure and physicochemical properties of CTFs were studied using BET, XRD, and FTIR. Batch adsorption experiments were carried out to investigate the adsorption behavior and adsorption mechanism of tetracycline (TC). Characterization results illustrated that only microporous structure was contained in CTF-1 and amorphous mesoporous structure was contained in CTFDCBP. In addition, triazine structure vibration peaks have been detected in both two kinds of CTFs. The adsorption process accorded with the Freundlich isothermal adsorption model and pseudo-secondary kinetic model. The adsorption experiment indicated that the adsorption affinity for TC in CTFDCBP is 1—2 orders of magnitude higher than that in CTF-1. The specific surface area and total pore volume of CTF-1 changed slightly after adsorption of tetracycline, while the specific surface area of CTFDCBP decreased vigorously from 1745 m2·g−1 to 220.5 m2·g−1, and total pore volume decreased from 1.420 cm3·g−1 to 0.2280 cm3·g−1. The effects of pH for TC adsorption on two kinds of CTFs were different due to the mesoporous mechanism. Adsorption of TC on CTFs was reduced because of the electronic shielding. Adsorption mechanisms were proposed including electrostatic interactions, cation-π, π-π electron-donor-acceptor interaction, and pore size interaction with the triazine structure of CTFs. Finding in this study demonstrated that the mesoporous CTFDCBP exhibited great potential as an effective adsorbent for TC removal from water.
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Key words:
- covalent triazine-based framework /
- tetracycline /
- adsorption mechanism
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表 1 CTF-1和CTFDCBP的比表面积和孔体积参数
Table 1. Specific surface area, and pore volume parameters for CTF-1and CTFDCBP
吸附剂Adsorbent 比表面积/(m2·g−1)
Surface areaaVmicb/(cm3·g−1) Vmesc/(cm3·g−1) Vtd/(cm3·g−1) CTF-1 782.4 0.3500 0.0500 0.4000 CTFDCBP 1745 0.7000 0.7200 1.420 a Brunauer-Emmett-Teller (BET) 方法计算得到;b 微孔体积,由Dubinin-Astakhov 方法计算得到;c 中孔体积,由Vt-Vmic 得到;d 总孔体积,由P/P0 = 0.976 得到.
a Determined by N2 adsorption using the Brunauer–Emmett–Teller (BET) method; b Micropore volume, calculated using the Dubinin–Astakhov method; c Mesopore volume, calculated by Vt-Vmic; d Total pore volume, determined at P/P 0 = 0.976.表 2 TC在CTF-1和CTFDCBP吸附的Freundlich 模型拟合参数
Table 2. Freundlich model fitting parameters for tetracycline (TC) adsorption on CTF-1 and CTFDCBP
TC/Adsorbent KF/(mmol1-n ·Ln·kg-1) n R2 Kd/(L·kg-1) TC/CTF-1 80.00±4.00 0.1400±0.0100 0.9660 103-105 TC/CTFDCBP 2300±90 0.1600±0.0100 0.9800 104-106 表 3 拟一级动力学和拟二级动力学拟合参数
Table 3. Fitting parameters for adsorption kinetics by pseudo-first order and pseudo-second order models.
C0/
(mmol·L−1)qexpa/
(mmol·kg−1)拟一级动力学方程b 拟二级动力学方程c k1/
(min−1)qcald/
(mmol·kg−1)R2 k2/
(kg· mmol−1·min−1)qcald/
(mmol·kg−1)R2 0.2250 1068 2.710×10−4 250.9 0.9110 4.730×10−5 1063 0.9990 a qexp 为平衡吸附量的实验值。b lg(qe-qt) = lg(qe)-k1t/2.303。qe平衡吸附量的拟合值,qt是t时吸附量,k1为拟一级动力学速率常数。c t/qt = 1/(k2qe2)+t/qe。qe平衡吸附量的拟合值,qt是t时吸附量,k2为拟二级动力学速率常数。d 从吸附动力学模型计算得到吸附量.
a qexp is the experimental equilibrium adsorption capacity。b lg(qe-qt) = lg(qe)-k1t/2.303. qe is the equilibrium adsorbed concentration, qt is the adsorbed concentration at time t, k1 is the pseudo-first order rate constant.。c t/qt = 1/(k2qe2)+t/qe. qe is the equilibrium adsorbed concentration, qt is the adsorbed concentration at time t, k1 is the pseudo- second order rate constant.。d The adsorption capacity is calculated from the adsorption kinetic model. -
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