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高级氧化技术(AOP)被认为是利用高活性的自由基团对有毒有害有机污染物质进行非选择性强氧化的过程。其中,催化臭氧氧化由于氧化还原电位高、污染物去除速率快、无二次污染风险等优点被认为是极具前景的水处理技术[1-3]。理想的催化臭氧氧化催化剂需要满足以下几方面要求:1)具有高自由基产生率的催化材料; 2)具有高活性位点的催化材料; 3)催化剂的制备简单及制备成本低[4]。多种负载型金属及其氧化物被应用于催化臭氧氧化,其在非均相催化臭氧氧化中表现出优异的性能。然而,催化过程中催化剂内部金属离子的流失不可避免地带来潜在的二次污染问题,因此,寻找可催化臭氧氧化的非金属催化剂对于该技术的实际应用具有重要意义。
目前已有研究对活性炭、碳纳米管、还原氧化石墨烯等碳材料在催化臭氧氧化中的应用进行了探索[5-7]。ZHANG等[5]用碳纳米管作为臭氧催化剂提高了臭氧的降解效率,延长了活性自由基寿命,并且催化剂具有很好的稳定性。WANG等[7]采用活性炭负载还原氧化石墨烯对废水TOC去除率达到60%。CHEN等[8]以多孔结构的活性炭对四氯苯酚为目标降解物进行催化臭氧降解,在1 h后四氯苯酚的去除率达到68%。与这些低维材料相比,具有三维多孔网状结构的碳材料不仅可以为污染物降解提供足够的表面活性位点,还可以提供多孔通道提高物质传输,因此,其有望作为新型催化剂用于催化臭氧高效降解污染物[9-10]。
目前,三聚氰胺碳海绵目前主要被用于做超级电容器、油水分离、光热膜蒸馏等方面。SONG等[11]利用三聚氰胺碳海绵超强疏水性对各种油类和有机溶剂具有良好的选择性吸附。CHEN等[12]以三聚氰胺碳海绵作为电极,电容可达到250 F·g-1。ZHU等[13]将三聚氰胺海绵表现出的超强光吸收特性,将其应用在光热辅助膜蒸馏中,获得2.5倍提高的蒸馏浓缩效率,远远优于单一的膜蒸馏过程。但三聚氰胺泡沫作为一种多孔碳骨架材料催化臭氧氧化催化剂的研究尚未见报道。
本研究以三聚氰胺泡沫为前驱体,通过高温碳化制备三维多孔碳海绵,对其进行一系列表征分析,并考察催化臭氧氧化有机染料和实际印染废水中的应用进行,考察碳化温度对微观结构和催化性能的影响,同时测试碳海绵重复利用效果,并进一步对催化机理进行讨论。
三维多孔碳海绵催化臭氧氧化有机染料
Three-dimensional porous carbon sponge for catalytic ozonation of organic dyes
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摘要: 针对目前催化臭氧氧化催化剂效率较低、易损失等缺点,通过高温煅烧制备了三聚氰胺碳海绵,以廉价易得的三聚氰胺泡沫直接碳化制备出柔性碳海绵,探讨其在催化臭氧氧化降解印染废水反应中的应用潜力;采用SEM观察、比表面积测定、傅里叶红外光谱和X-射线光电子能谱对碳化前后泡沫进行了表征,探讨了碳化前后泡沫微观结构的变化与催化降解印染废水性能与机理。结果表明:氮气氛围下高温煅烧获得了兼具微孔/介孔结构的三维碳骨架,为催化反应提供充分暴露的活性位点和高效的传质通道;在催化臭氧氧化染料的过程中,973 K下制备的碳泡沫呈现出最为优异的催化活性,显著高于均相臭氧氧化和常规活性炭催化臭氧氧化;自由基捕获实验表明催化过程由羟基自由基(·OH)所主导,超氧自由基(·O2-)则发挥了次要作用;富含多孔结构的碳海绵对于活性自由基的生成起到了积极贡献,从而在实际印染废水处理中具有良好的降解性能。研究为开发低成本的三维碳材料用于催化臭氧降解有机污染废水提供了新思路。Abstract: With interconnected network architecture, 3-D porous carbon is a promising material for energy conversion, catalysis and environmental applications. In view of the disadvantages of low efficiency and easy loss for the current catalytic ozonation catalyst, melamine carbon sponge, a type of the elastic carbon sponge, was prepared through high temperature calcination: the direct carbonization of inexpensive melamine foam. Then its potential application in catalytic ozonation of printing and dying wastewater was investigated. SEM, BET, FT-IR and XPS were used to characterize the foam before and after carbonization. Furthermore, the change in the foam microstructure before and after carbonization, and the performance and mechanisms of its catalytic degradation of printing and dyeing wastewater were discussed. The results showed that the high-temperature calcination of the foam under nitrogen atmosphere resulted in the formation of 3-D carbon skeleton with micro/mesoporous structures, which provided active sites and high effective mass transport channels for catalytic reactions. During catalytic ozonation of dyes, the catalyst from carbon sponge fabricated at 973 K presented the best activity, which was higher than homogeneous ozonation and conventional activated carbon catalyzed ozonation. Free radical capture experiments proved that·OH was the dominant reactive species for catalytic ozonation, while·O2- played a minor role. Due to the significant contribution of porous and conductive skeleton to the generation of reactive radicals, carbon sponge exhibited good performance for treating actual wastewater. This work provides a facile method to explore the low-cost 3-D catalyzed system for advanced oxidation of organic pollutants in wastewater.
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Key words:
- melamine foam /
- carbon sponge /
- advanced oxidation process /
- catalytic ozonation /
- wastewater treatment
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表 1 实际废水水质参数
Table 1. Quality parameters of actually wastewater
统计数据 COD/(mg·L-1) UV254 浊度/NTU pH 数值 600 1.2 0.6 7.5 偏差 ±20 ±0.1 ±0.02 ±0.2 -
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