催化功能纤维降解染料等有机污染物的研究

【作者】 吕汪洋；

【导师】 陈文兴；

【作者基本信息】 浙江理工大学 ， 纺织工程， 2010， 博士

【摘要】 当前,水环境污染已成为当今世界各国都面临的重大课题,而纺织印染工业所排放的染料等有机污染物废水是其中一个重要的污染源。工业上普遍采用吸附和生物法处理染料等有机污染物,吸附法只是将染料等有机物从液相转移到固相,并没有完全消除有机污染物,生物法处理周期长、设备占用面积大,会因染料等有机物对生物的毒性作用而不能有效的去除。与之相比,高级氧化技术通过产生强氧化性的活性种能直接将染料等有机物有效降解,甚至彻底矿化,引起人们的广泛关注,但这些高级氧化技术也有一定的局限,如易带来二次污染、处理成本高、不适合大流量废水处理等。因此,开发高效、对环境无危害的染料等有机污染物处理方法是化学研究的一个重要课题。金属酞菁及其衍生物与细胞色素P-450的活性中心金属卟啉结构相似,是由亚胺桥键连接四个对称的异吲哚单元构成的共轭π电子大环体系,具有良好的化学稳定性,在催化氧化方面的研究已成为金属酞菁应用研究的一个重要领域。我们注意到,染料在纺织业中主要是用于纤维染色的,而染色的机理就是染料在很短时间内从染液富集或固着到纤维上的过程。在这种思想的指导下,本文提出了“纤维相转移原位催化降解染料等有机污染物”的思想,将金属酞菁负载到纤维材料上制备得到“催化功能纤维”,利用其直接降解废水中染料等有机污染物,巧妙地利用染料等有机物与纤维的亲和性,即纤维吸附富集废水中的染料等有机物,同时将其在纤维介质中原位催化降解。该方法结合了传统吸附法和高级氧化法的优势,不仅能凭借纤维对染料等有机物的亲和力进行有效富集,而且能在纤维中对其进行快速有效地降解,解决了传统吸附法存在的吸附饱和问题,还可以改善高级氧化法的环境适应性,同时催化功能纤维降解废水中的染料等有机污染物是一个多相催化反应,纤维载体的选择使金属酞菁的重复使用成为可能,避免了小分子金属酞菁使用时带来的二次污染。论文取得了一些具有重要学术价值和应用前景的研究成果。1.采用苯酐-尿素路线制备了四硝基钴酞菁,然后将其还原成四氨基钴酞菁（CoTAPc）,通过三聚氯氰对CoTAPc环上的氨基进行修饰,首次制备了水溶性、且具有较高反应活性的钴酞菁衍生物——四（2,4-二氯-1,3,5-三嗪基）氨基钴酞菁（Co-TDTAPc）,使用UV/Vis、FTIR和TGA等方法对其进行表征。然后将其负载到纤维素纤维上,制备得到纤维素纤维负载钴酞菁催化剂（Co-TDTAPc-F）。2.根据“纤维相转移原位催化降解染料等有机污染物”的思想,采用对环境友好的H2O2作为氧化剂,Co-TDTAPc-F能对多种结构较稳定的染料进行催化氧化降解,其中包括:酸性红G、活性艳红X-3B、活性艳红K-2BP、活性艳红M-3BE、活性黄M-3RE、活性艳蓝M-BRE和直接桃红12B等染料。相对于Co-TDTAPc/H₂O₂均相体系,采用Co-TDTAPc-F/H₂O₂异相体系对染料进行催化氧化降解能大大提高染料的降解效率。该催化反应在酸性条件下速率最快,与Fenton试剂不同的是,该体系在碱性条件下也有较好的催化效率,且经多次循环使用后Co-TDTAPc-F的催化活性并没有明显下降。在向该反应体系中加入NaCl后,染料的降解速率会大大提高,由于印染废水中含有大量的这类电解质,因此,这一结果将有利于其在印染废水处理中的应用。通过对染料催化氧化降解过程中产生的中间产物进行分析发现:染料降解过程中首先生成含苯环和萘环的化合物,然后它们继续发生氧化降解而开环,最后生成一些可以生物降解的小分子脂肪酸类化合物,如乙二酸、丙二酸和顺丁烯二酸等,也有部分中间体被直接矿化为CO2和H2O。在整个催化氧化过程中,纤维素纤维本身起到至关重要的作用:快速富集浓缩染料,进而提高染料氧化降解的速率;阻止酞菁类催化剂因聚集而失活;有利于克服一些不利因素的影响,如乙醇和异丙醇等,相反,当这些物质存在时,反而提高了染料的催化降解速率。另外,Co-TDTAPc-F/H₂O₂体系还能有效地催化降解邻氯苯酚（2-CP）、对氯苯酚（4-CP）、2,4-二氯苯酚（2,4-DCP）和2,4,6-三氯苯酚（2,4,6-TCP）等酚类化合物,催化中间产物也是一些脂肪酸类化合物,研究还表明Co-TDTAPc-F不仅能使酚类化合物发生开环反应,而且还能将生成的脂肪酸类化合物继续深度氧化。3.分别将CoTAPc负载到氧化处理后的碳纤维（CF）、碳纳米纤维（CNF）和多壁碳纳米管（MWNTs）上,制得CoTAPc-CF、CoTAPc-CNF和CoTAPc-MWNTs催化剂。以CoTAPc-MWNTs为例,使用IR、XPS、UV/Vis和EPR等对其进行了表征。以罗丹明6G（Rh6G）为研究对象,分别研究了在H₂O₂存在下CoTAPc-CF和CoTAPc-CNF对Rh6G的氧化情况,结果表明它们均能在常温、pH中性条件下快速有效地催化氧化Rh6G,发现这些碳纤维材料的引入大大提高钴酞菁的催化活性。为了更深入地研究碳纤维材料对金属酞菁催化性能的影响,选择结构更加规整且表面缺陷更少的MWNTs作为载体,重点研究了CoTAPc-MWNTs对Rh6G的催化氧化性能及其催化机理。采用电子顺磁共振技术对CoTAPc-MWNTs/H₂O₂催化体系进行分析,结果表明该催化氧化过程是非自由基反应。原位电化学实验的测试结果表明反应过程中CoTAPc-MWNTs中的MWNTs上产生了大量的空穴,空穴的形成会使MWNTs上产生一些局部高电势的活性位,能快速地将吸附在CoTAPc-MWNTs上的Rh6G进行氧化,MWNTs在反应过程中为催化反应提供了一个新的电子转移通道。另外,还研究了CoTAPc-MWNTs/再生纤维素复合纤维对染料的催化氧化性能,发现其在酸性、中性和碱性条件下均能有效地催化氧化染料,进一步改善钴酞菁所处的反应环境,从而大大拓宽了钴酞菁在催化氧化领域的应用范围。因此,选用具有π电子共轭结构的碳纤维材料能大大提高钴酞菁的催化活性,这为金属酞菁催化活性的增强提供了一个新的途径,为设计更加高效的金属酞菁相转移催化体系奠定了基础。4.为了进一步提高“纤维相转移原位催化降解染料等有机污染物”的应用范围,本文选择了具有优良吸附特性和较高化学稳定性的活性碳纤维（ACF）作为金属酞菁的载体,将Co-TDTAPc负载到ACF制备得到Co-TDTAPc-ACF催化剂。Co-TDTAPc-ACF/H₂O₂体系能在较宽pH和温度范围内快速有效地催化氧化对硝基苯酚（4-NP）等酚类化合物,与小分子钴酞菁相比,ACF的引入大大提高了钴酞菁的催化活性,而且Co-TDTAPc-ACF具有很好的重复使用性能。通过GC/MS对酚类化合物降解产物进行分析可知,这些酚类化合物首先脱去取代基生成芳香类物质,芳香物质继续氧化开环,生成可生物降解的小分子有机酸,如顺丁烯二酸、丁二酸、己二酸和羟基丁二酸等。该体系与CoTAPc-MWNTs/H₂O₂体系的反应过程类似,均属于非自由基反应,能克服其它高级氧化法因自由基捕获剂的存在而终止反应的缺陷,使Co-TDTAPc-ACF/H₂O₂催化体系具有广阔的应用前景。Co-TDTAPc-ACF/H₂O₂催化体系结合了金属酞菁的催化作用和活性碳纤维的吸附作用,其中活性碳纤维的主要作用有:特殊的π电子共轭多孔结构使钴酞菁的催化活性大大提高,而且使钴酞菁便于重复循环使用;活性碳纤维的多微孔结构和巨大的比表面积有助于缩小反应空间,减小了传质过程中的阻碍,降低了反应的活化能,从而大大提高了反应速率;可富集低浓度的有机污染物达到对其浓缩的目的,这有利于加快催化氧化反应。因此,Co-TDTAPc-ACF/H₂O₂体系可对酚类化合物实现边吸附边催化氧化,达到快速有效地去除酚类化合物的目的。更多还原

【Abstract】 At present, water pollution has become a major issue in many countries, particularly in developing countries. Dye pollutant from dyestuffs and textile industry is a dangerous source of environment contamination. The conventional treatment technologies widely used in industry for eliminating dyes include adsorption and biological treatment. However, adsorption treatments simply transfer dyes from solution to adsorbents, and cannot completely eliminate them. Biological treatments are limited to some extent due to the long treatment period, the larger occupied area of equipments and the biological toxicity of various dyes. Recently, advanced oxidation processes （AOPs）, which have high degradation rates, have received increasing attention as a promising technology for the efficient destruction of dyes and other organic pollutants, while some oxidation processes need energylight sources, like ultraviolet light, and may bring secondary pollution. Therefore, there is a clear need for more efficient and eco-friendly approaches to removing dyes and other organic pollutants from wastewater.Metallophthalocyanine derivatives （MPcs）, having analogous structure to the active center of cytochrome P-450, are highly conjugated macrocyclic compounds and have been extensively studied as catalysts for a variety of applications in organic synthesis, green chemistry and environmental treatment. Recently, MPcs have received increasing attention in some catalytic oxidation systems using H₂O₂ as oxidant. We note that dyes in the textile industry is mainly used for fiber dyeing, and the mechanism of dyeing is the enrichment and fixation processes of dyes from solution to fiber in a very short time. In light of the above considerations, we demonstrated that a new method,“phase transfer in situ catalytic oxidation,”which is based on fiber supported MPcs （catalytic functional fiber）, can be applied to eliminate various dyes. Because fibers have a high natural affinity to dyes by physical and chemical interaction, dyes can be enriched or adsorbed onto the fiber, and be oxidized rapidly and effectively in situ at the surface and interior of fiber. This method combines common adsorption and AOPs together. The advantage of this method is that dyes can be transferred quickly from aqueous phase to adsorbent material （fiber） and be decomposed in situ immediately in the presence of oxidant and on-site catalyst. This method resolves the problem of adsorption saturation and improves the environmental adaptability of AOPs. The oxidative process of dyes in the presence of catalytic functional fiber is a heterogeneous catalytic reaction. Catalytic functional fiber is recuperated easily from dyes solution for the reuse, and causes no secondary pollution. The phase transfer in situ catalytic oxidation has proven itself to be a feasible approach, which may be potentially applied to the elimination of widely existing pollutants. This dissertation has gained some valuable results both in academic disciplines and practical applications.1. The phthalic anhydride-urea route was employed to synthesize cobalt tetranitrophthalocyanine, which was then reduced into cobalt tetraaminophthalocyanine （CoTAPc）. A novel aqueous soluble and highly reactive metallophthalocyanine derivative, cobalt tetra（2,4-dichloro-1,3,5-triazine）aminophthalocyanine （Co-TDTAPc）, was prepared by modification of CoTAPc with cyanuric chloride and characterized by UV/Vis, FTIR, TGA, and so on. Because of the high reactive groups in the side chains, Co-TDTAPc was immobilized on the cellulosic fiber by covalent bond to obtain a novel cellulosic fiber supported MPcs catalysts （Co-TDTAPc-F）.2. Based on“phase transfer in situ catalytic oxidation”, we choose the inexpensive and eco-friendly H₂O₂ as the sole oxidant in our reaction system. The Co-TDTAPc-F/H₂O₂ system can efficiently decompose various dyes, including C. I. Acid Red 1 （AR1）, C. I. Reactive Red 2, C. I. Reactive Red 24, C. I. Reactive Red 195, C. I. Reactive Yellow 145, C. I. Reactive Blue 221 and C. I. Direct Red 31. The catalytic activity of Co-TDTAPc-F in the heterogeneous system is evidently higher than that of Co-TDTAPc in the homogeneous system. This catalytic reaction can proceed at a wide pH range from acidic to alkaline in the Co-TDTAPc-F/H₂O₂ catalytic system, although lower pH resulted in higher oxidation rate. This result is distinct from the traditional Fenton system where the oxidation can only take place at the pH lower than 3. Co-TDTAPc-F is stable, causes no secondary pollution and remains efficient in repetitive test cycles with no obvious degradation of catalytic activity. This system has no negative effect caused by NaCl as encountered in other systems; instead, NaCl is an accelerant for the current catalytic oxidation. Therefore, it is an additional advantage for our system to be used practically. The intermediates and by-products formed in the catalytic oxidation of dyes were examined by HPLC, TOC, FTIR and GC/MS. The results show that the intermediates include phenol and naphthol analogy complexes. Then the opening of the phenyl-ring and naphthyl-ring occur to form small molecular biodegradable aliphatic carboxylic compounds such as oxalic acid, malonic acid and maleic acid etc. Some of the intermediates can be mineralized into CO2 and H2O. The fiber phase plays an important role in the whole catalytic oxidation process, improves the decomposition rate of dyes by concentrating dyes and catalytic active sites in the reaction system, prevents the formation of dimeric phthalocyanine and provides a microenvironment that is prosperous to the catalytic reaction. Importantly, the Co-TDTAPc-F/H₂O₂ system can overcome the effect of negative factors, such as ethanol and isopropanol. By contraries, these additives can accelerate the degradation of dyes. In addition, Co-TDTAPc-F has a high catalytic ability to degrade chlorophenols （CPs） such as 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol in the presence of H₂O₂. The process of decomposition of CPs in the Co-TDTAPc-F/H₂O₂ system includes the dechlorination of CPs and the opening of benzene rings. The main intermediates are oxalic acid, maleic acid and succinic acid, which can also be further degraded in this system. Therefore, the catalytic oxidation in the Co-TDTAPc-F/H₂O₂ system leads to a deeper oxidation.3. Carbon fiber （CF）, carbon nanofiber （CNF） and multiwalled carbon nanotubes （MWNTs） used to support MPcs catalysts （CoTAPc-CF, CoTAPc-CNF and CoTAPc-MWNTs） were prepared using covalent immobilization of CoTAPc on them, and characterized by X-ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectra and thermogravimetric analysis. The oxidative removal of rhodamine 6G （Rh6G） in the presence of CoTAPc-CF or CoTAPc-CNF was investigated by examination of UV/Vis absorption spectra. The results showed that Rh6G was oxidized efficiently in the CoTAPc-CF/H₂O₂ or CoTAPc-CF/H₂O₂ system at neutral pH and room temperature. The introduction of CF and CNF resulted in a marked enhanced catalytic activity that CoTAPc does not have. In order to further investigate the effect of carbon fiber materials on the catalytic performance of MPcs, the more structured MWNTs with less surface defects were chosen as the support. Electron paramagnetic resonance spin-trap experiments indicated that CoTAPc-MWNTs have a novel non-radical pathway, which is different from common CoTAPc catalytic systems. On the basis of the online electrochemical measurements in the CoTAPc-MWNTs/H₂O₂ system, we inferred that MWNTs participated directly in the electron transfer during the catalytic oxidation process and generated abundant holes, which provided local high electric potential at active sites for the oxidation of the adsorbed Rh6G. In this catalytic system, MWNTs provide strong adsorption to conjugated Rh6G due to their special sp2 hybridized surface, and are able to rapidly oxidize the conjugated dye by a special electron transfer pathway. In addition, CoTAPc-MWNTs/regenerated cellulose composite fiber （CoTAPc-MWNTs-F） was prepared by solution spinning and was used to catalyze the oxidation of Rh6G. The results indicated that CoTAPc-MWNTs-F/H₂O₂ system could efficiently oxidize Rh6G in acidic, neutral and alkaline conditions, thereby improving the reaction environment of cobalt phthalocyanine and greatly broadening the scope of application of cobalt phthalocyanine in catalytic oxidation fields. The enhanced catalytic performance of cobalt phthalocyanine by inducing theπ-conjugated carbon fiber materials may provide a new strategy for the design of highly efficient oxidation catalysts.4. In order to further develop“phase transfer in situ catalytic oxidation”for removing other organic pollutants, activated carbon fiber （ACF） was chosen as the support for the MPcs due to its extremely high adsorption capacity and unusual chemical stability. We immobilized Co-TDTAPc covalently on ACF to obtain a novel heterogeneous catalyst, Co-TDTAPc-ACF. The Co-TDTAPc-ACF/H₂O₂ system can efficiently remove phenols such as 4-nitrophenol （4-NP） across a wide pH and temperature range. Importantly, compared with homogeneous Co-TDTAPc used alone, the introduction of ACF contributed specifically to the activity enhancement of Co-TDTAPc. This might be attributed to the fact that ACF provides a predominant enrichment of catalytic active sites and improves catalytic oxidation efficiency by concentrating substrates from solution dozens, and even hundreds, of times. Gas chromatography/mass spectrometry analysis demonstrated that most of the phenols was oxidized into less-toxic and more-biodegradable compounds, such as maleic acid, succinic acid, malic acid and adipic acid, etc. Controlled experiments showed that the presence of 2-propanol, as hydroxyl radicals scavenger, has little influence on 4-NP oxidation. The result of electron paramagnetic resonance spin-trap experiments indicated that ACF result in a different reaction pathway from free radicals pathway to non-radical mechanism, and open up a new channel to specifically enhance the catalytic activity of cobalt phthalocyanine. Repetitive tests showed that Co-TDTAPc-ACF can maintain high catalytic activity over several cycles, and it has a better regeneration capability under mild conditions. Furthermore, as an improved phase transfer catalytic oxidation system, Co-TDTAPc-ACF/H₂O₂ may be identified as a potential conventional approach to treat wastewater by combining enrichment and catalytic oxidation together. Depend on the self-reliance regeneration capability of Co-TDTAPc-ACF in the presence of H₂O₂, it is expected to provide a technology capable of being operated in a continuous and efficient mode to treat organic pollutants.更多还原