-
氯酚(chlorophenols,CPs)是一类重要的有机化工原料,广泛应用于杀虫剂、除草剂和木材防腐剂的生产. 由于氯酚具有高毒性、持久性和“三致效应”(致癌、致畸、致突变)而被我国以及美国、欧盟等国家和地区列入优先控制污染物名单[1 − 2]. 氯酚污染物的毒性主要源于自身的芳环结构和氯原子取代基,而氯原子取代基是其主要毒性位点,氯原子数目越多毒性越高[3]. 此外,氯酚因氯原子的p轨道电子及苯环上的π电子易形成稳定的共轭体系而具有较强的化学稳定性. 高电负性的氯原子使苯环表现出难氧化的疏水性,抑制了苯环裂解酶的活性,提高了其抗生物降解能力,使其比普通的酚类污染物更难降解[4 − 5]. 因此,高效处理氯酚污染物的关键在于高毒性氯位点的精准去除. 目前, 去除氯酚污染物的主要处理方法有生物法、物理法和化学法等[6 − 8]. 生物法周期长且微生物受制于氯酚类污染物的高毒性难以发挥效用,物理法、化学法均存在使用成本高且能够引起二次污染等问题.
近年来,光催化技术因具有高效、环保、经济等优势在水污染控制领域显现出广阔的应用前景[9]. 有研究成果表明,光催化技术能够通过调控自由基与非自由基路径实现氯酚类污染物的深度处理[10],但自由基与非自由基反应的引发均需以过氧化物(过一硫酸盐、过二硫酸盐)为媒介,在面临复杂反应体系中由过氧化物引发的自由基与非自由基路径极易受反应体系中杂质污染物的干扰,且对氯酚污染物脱氯的靶向性较差及生成的中间副产物容易造成二次污染的问题. Chen等[11]构建了一种基于缓释碳耦合生物电化学系统,精准促进氯代烃的次序脱氯为乙烯,有效解决氯代烃降解不彻底导致的有毒有害中间产物积累的问题,实现了氯代烃的高效完全脱氯和脱毒. 因此,通过构建合适的光催化体系来实现氯酚污染物的精准脱氯,可减少次生风险及二次污染,将具有重要的环境意义,其中选择具有靶向性脱氯的光催化剂即成为了解决问题的关键.
共价三嗪框架(Covalent triazine-based frameworks,CTFs)是一类由芳香环和富氮三嗪环作为连接单元组成的二维层状聚合物[12]. 因高比表面积、可调的孔结构、合适的带隙和高化学稳定性,CTFs在吸附和光催化方面具有可开发的潜力[13]. 由于CTFs的特殊结构使其具有吸附剂的显著特征,引入的富电子三嗪环单元结构使其具有光催化反应能力,从而兼具吸附和光催化双功能的CTFs成为了去除水中有机污染物的理想催化剂[14 − 15].
本文采用1,4-苯二甲腈经离子热三聚合成具有共价三嗪框架的光催化剂CTF-1,测定其对4-氯酚(4-CP)、2,4-二氯酚(2,4-DCP)、2,4,6-三氯酚(2,4,6-TCP)和五氯酚(PCP)4种氯酚类污染物的光催化反应速率常数及脱氯效率,分析氯酚分子结构与脱氯降解效率的关系,并初步探索光催化脱氯降解机制,为光催化技术应用于卤代酚类废水的脱卤去除提供理论依据.
共价三嗪有机框架材料对水中氯酚类污染物的光催化脱氯降解
Photocatalytic dechlorination of chlorophenol pollutants in aqueous solution by covalent triazine organic framework material
-
摘要: 利用共价三嗪有机框架材料(CTF-1)对4-氯酚(4-CP)、2,4-二氯酚(2,4-DCP)、2,4,6-三氯酚(2,4,6-TCP)和五氯酚(PCP)等4种不同氯原子取代数目的氯酚类污染物进行光催化降解研究,探讨了底物结构对氯酚脱氯降解效率的影响及机制. 结果表明,氯酚脱氯降解过程明显受苯环氯原子取代数目的影响,氯原子数目越多,脱氯降解效率越高,氯原子数目与表观速率常数呈显著正相关,氯酚降解及脱氯速率均为:PCP >2,4,6-TCP >2,4-DCP >4-CP. 对CTF-1光催化降解氯酚机制研究表明,活性物种在反应中不起作用,体系反应机制为针对氯酚上取代氯位点进行水解脱氯过程. 本研究结果为深入揭示氯酚脱氯降解机制提供了理论依据,也为光催化技术处理卤代酚类废水提供了技术参考.Abstract: In this study, covalent triazine organic framework material (CTF-1) was applied to degrade four chlorophenols (CPs) with different chlorine atoms, including 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP). The effect and mechanism of substrate structure on the dechlorination degradation efficiency of chlorophenols were explored. The dechlorination degradation process of CPs were significantly influenced by the purpose of selecting the number of chlorine atoms in the benzene ring. The more chlorine there was, the higher the dechlorination degradation efficiency. The number of chlorine atoms was significantly positively correlated with the apparent rate constant. The results showed that the degradation rate and dechlorination rate of CPs were as follows: PCP > 2,4,6-TCP > 2,4-DCP > 4-CP. The study on the mechanism of CTF-1 photocatalytic degradation of CPs showed that the active species do not play a role in the reaction, and the system reaction mechanism was the hydrolysis dechlorination process targeting the substituted chlorine sites on CPs. This study provided a theoretical basis for further revealing the degradation mechanism of CPs, as well as a technical reference for the treatment of halogenated phenol wastewater using photocatalytic technology.
-
Key words:
- CTF-1 /
- chlorophenols /
- photocatalytic degradation /
- dechlorination /
- chlorine atom numbers.
-
图 1 (a)CTF-1沿x轴方向的结构视图;CTF-1的SEM图(b)、XRD衍射图(c)、红外光谱图(d)、固体核磁13C NMR谱图(e)和N2吸附-脱附等温线图(插图:Barrett-Joyner-Halenda孔径分布)(f)
Figure 1. (a) The view of the structure of CTF-1 along the x axis; (b) SEM image, (c) XRD pattern, (d) FTIR pattern, (f) Solid state MAS-13C-NMR spectra and N2 adsorption-desorption isotherm (inset: BJH pore size distribution) of CTF-1
表 1 氯酚类污染物的液相检测方法
Table 1. Liquid phase detection methods for chlorophenol pollutants
污染物
Pollutants流动相
Mobile phase (V:V)流速/(mL·min−1)
Flow rate检测波长/nm
Detection wavelength柱温/℃
Column temperature4-CP 乙腈:水=50:50 1 280 35 2,4-DCP 甲醇:水=70:30 1 285 35 2,4,6-TCP 甲醇:水=70:30 1 290 35 PCP 甲醇:2%乙酸=80:20 0.8 300 35 -
[1] KEITH L, TELLIARD W. ES&T special report: Priority pollutants: I-a perspective view[J]. Environmental Science & Technology, 1979, 13(4): 416-423. [2] USEPA. Water quality criteria summary. Ecological risk assessment branch (WH-585) and human risk assessment branch (WH-550D) [R]. Washington DC, USA: Health and Ecological Criteria Division, 1991. [3] PAPAZI A, KARAMANLI M, KOTZABASIS K. Comparative biodegradation of all chlorinated phenols by the microalga Scenedesmus obliquus-the biodegradation strategy of microalgae[J]. Journal of Biotechnology, 2019, 296: 61-68. doi: 10.1016/j.jbiotec.2019.03.010 [4] PERA-TITUS M, GARCı́A-MOLINA V, BAÑOS M A, et al. Degradation of chlorophenols by means of advanced oxidation processes: A general review[J]. Applied Catalysis B: Environmental, 2004, 47(4): 219-256. doi: 10.1016/j.apcatb.2003.09.010 [5] AHLBORG U G, THUNBERG T M. Chlorinated phenols: Occurrence, toxicity, metabolism, and environmental impact[J]. Critical Reviews in Toxicology, 1980, 7(1): 1-35. doi: 10.3109/10408448009017934 [6] OLANIRAN A O, IGBINOSA E O. Chlorophenols and other related derivatives of environmental concern: Properties, distribution and microbial degradation processes[J]. Chemosphere, 2011, 83(10): 1297-1306. doi: 10.1016/j.chemosphere.2011.04.009 [7] de OLIVEIRA J C A, RODRIGUES P R M, de LUCENA S M P. Prediction of chlorophenols adsorption on activated carbons by representative pores method[J]. Environmental Science and Pollution Research, 2022, 29(53): 79866-79874. doi: 10.1007/s11356-022-18571-x [8] CHO Y C, HSU C C, LIN Y P. Integration of in situ chemical oxidation and permeable reactive barrier for the removal of chlorophenols by copper oxide activated peroxydisulfate[J]. Journal of Hazardous Materials, 2022, 432: 128726. doi: 10.1016/j.jhazmat.2022.128726 [9] SARAVANAN A, KUMAR P S, VO D V N, et al. Photocatalysis for removal of environmental pollutants and fuel production: A review[J]. Environmental Chemistry Letters, 2021, 19(1): 441-463. doi: 10.1007/s10311-020-01077-8 [10] ZADA A, KHAN M, KHAN M A, et al. Review on the hazardous applications and photodegradation mechanisms of chlorophenols over different photocatalysts[J]. Environmental Research, 2021, 195: 110742. doi: 10.1016/j.envres.2021.110742 [11] CHEN X Q, BAI C H, LI Z L, et al. Directional bioelectrochemical dechlorination of trichloroethene to valuable ethylene by introduction poly-3-hydroxybutyrate as a slow release carbon source[J]. Chemical Engineering Journal, 2023, 455: 140737. doi: 10.1016/j.cej.2022.140737 [12] SHEN Y, ZHU C, SONG S, et al. Defect-abundant covalent triazine frameworks as sunlight-driven self-cleaning adsorbents for volatile aromatic pollutants in water[J]. Environmental Science & Technology, 2019, 53(15): 9091-9101. [13] QIAN Z F, WANG Z J, ZHANG K A I. Covalent triazine frameworks as emerging heterogeneous photocatalysts[J]. Chemistry of Materials, 2021, 33(6): 1909-1926. doi: 10.1021/acs.chemmater.0c04348 [14] SUN M, HAN S, FENG J J, et al. Recent advances of triazine-based materials for adsorbent based extraction techniques[J]. Topics in Current Chemistry, 2021, 379(4): 24. doi: 10.1007/s41061-021-00336-8 [15] ZENG T, JIN S J, LI S Q, et al. Covalent triazine frameworks with defective accumulation sites: Exceptionally modulated electronic structure for solar-driven oxidative activation of peroxymonosulfate[J]. Environmental Science & Technology, 2022, 56(13): 9474-9485. [16] KUECKEN S, ACHARJYA A, ZHI L J, et al. Fast tuning of covalent triazine frameworks for photocatalytic hydrogen evolution[J]. Chemical Communications, 2017, 53(43): 5854-5857. doi: 10.1039/C7CC01827D [17] ZHU C, FANG Q L, LIU R L, et al. Insights into the crucial role of electron and spin structures in heteroatom-doped covalent triazine frameworks for removing organic micropollutants[J]. Environmental Science & Technology, 2022, 56(10): 6699-6709. [18] HUANG L M, WANG D K, ZENG H H, et al. Synergistically interactive P-Co-N bonding states in cobalt phosphide-decorated covalent organic frameworks for enhanced photocatalytic hydrogen evolution[J]. Nanoscale, 2022, 14(48): 18209-18216. doi: 10.1039/D2NR05076E [19] GARBA Z N, ZHOU W M, LAWAN I, et al. An overview of chlorophenols as contaminants and their removal from wastewater by adsorption: A review[J]. Journal of Environmental Management, 2019, 241: 59-75. [20] SAPUTRA E, PRAWIRANEGARA B A, SUGESTI H, et al. Covalent triazine framework: Water treatment application[J]. Journal of Water Process Engineering, 2022, 48: 102874. doi: 10.1016/j.jwpe.2022.102874 [21] 李鸿渐, 季秋忆, 朱诺亚, 等. 可见光下竹叶生物炭掺杂BiOBrxCl1-x光催化降解罗丹明B[J]. 环境化学, 2022, 41(10): 3390-3398. doi: 10.7524/j.issn.0254-6108.2021060801 LI H J, JI Q Y, ZHU N Y, et al. Photocatalytic degradation of rhodamine B by bamboo leaf biochar doped with BiOBrxCl1-x under visible light[J]. Environmental Chemistry, 2022, 41(10): 3390-3398 (in Chinese). doi: 10.7524/j.issn.0254-6108.2021060801
[22] CABEZUELO O, MARTINEZ-HAYA R, MONTES N, et al. Heterogeneous riboflavin-based photocatalyst for pollutant oxidation through electron transfer processes[J]. Applied Catalysis B: Environmental, 2021, 298: 120497. doi: 10.1016/j.apcatb.2021.120497