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大量研究表明,高级催化氧化法的复合水处理方法经常表现出协同效应,如光/芬顿催化、光催化/臭氧,电催化/紫外光等[1-5]。同样,光电耦合催化体系也存在着明显的协同效应。安太成等[6]发现光电耦合系统中有机物的降解速率远远大于单一的光降解和电降解;XIAO等[7]发现光电耦合系统可以将垃圾渗滤液的COD和氨氮去除率分别提高22.2%和33.4%;HURWITZ等[4]发现在光电同步降解苯酚中,TOC降解率明显大于单一的光催化和电催化;PIRES等[8]发现光电耦合催化对于污水中微生物的破坏也具有一定协同性。这说明光电耦合催化的协同性体现在很多方面,并可以大大提高有机物的降解效率。掌握了协同效应的产生原因,便可通过人为控制其影响因素来直接或者间接控制协同效应的大小。这样,不仅可以节约成本,还可以提高降解效率,故其意义重大。
针对协同效应的产生机理问题,HURWITZ等[4]认为光电耦合体系中紫外光照促进了电催化子系统中的HClO的分解,产生了强氧化性物质Cl·,进而促进了有机物的降解;有研究[9]认为在光助电芬顿体系中,当电芬顿反应将60%的TOC去除后,剩下的小分子物质就极易被紫外灯直接照射分解,很快达到100%的矿化,由此产生协同作用;JAAFARZADEH等[10]认为在光电臭氧体系中,紫外光的存在激活了溶液中的活性物质,产生了更多的 · OH进而产生较强的协同效应。
3,4-二甲基苯胺(3,4-DMA)是一种难降解有机污染物[11-12],并广泛存在于制药和印染废水中。此类废水具有极强的毒性和致癌性[11-14],且此类废水具有高盐、难降解和可生化性差的特点,使得传统的生物法处理效果较差,效率较低[15-16]。因此,本研究以3,4-DMA废水为研究对象,建立一种量化协同效应大小的评判标准,通过不同体系下对其降解速率的研究和羟基自由基的检测,以探讨不同影响因素下的协同效应及协同效应的产生原因。
光电耦合技术处理3,4-二甲基苯胺废水的协同效应
Synergistic effects of hybrid photo-electrocatalytic degradation of 3,4-dimethylaniline wastewater
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摘要: 高级催化氧化法的复合水处理工艺经常出现协同效应,但对于协同效应的产生机理仍不清楚。因此,针对光电耦合催化氧化体系,采用协同度为量化指标,研究了不同光照、电流密度、曝气强度、初始pH等条件对光电耦合催化体系降解3, 4-二甲基苯胺(3,4-DMA)的协同效应的影响;并通过光助电催化实验、电助光催化实验和羟基自由基检测实验,探讨了协同效应存在的原因。结果表明,光电耦合催化氧化系统存在协同效应,且协同度受外部条件的影响。协同效应产生的原因主要包括:外加电场促进体系产生了更多的羟基自由基;紫外光照使得3,4-DMA及其降解中间产物受到激发而提高了对羟基自由基等活性氧物种的利用率;电催化过程中的析氧副反应为光催化提供了电子受体,从而提高了系统的总体降解效率。这为深入研究和人为调控协同效应提供了新的方法。Abstract: The synergistic effects often occur in many advanced oxidation processes, while its mechanisms are still unclear. Hence, in this study, the synergetic level was taken as an indicator, and the effects of illumination, current intensity, aeration intensity and initial pH on the synergistic effects of hybrid photo-electrocatalytic degradation of 3,4-dimethylaniline (3,4-DMA) were determined. Furthermore, photo-assisted electrocatalytic, electro-assisted photocatalytic and hydroxyl radicals detection experiments were carried out to explore the degradation mechanism. The results indicated that the synergistic effects occurred in the hybrid photo-electrocatalysis system, and the synergetic level was affected by external conditions. The reasons for the synergetic effects were ascribed to the following items. The applied electric fields promoted the yield of hydroxyl radicals. The ultraviolet radiation improved the utilization of active oxides such as hydroxyl radicals by stimulating 3,4-DMA and its intermediates. The oxygen evolution side reaction in electrocatalysis provided electron acceptors for photocatalysis, which could enhance the degradation efficiency of the whole treatment system. This research provided a new method for further study and regulation of the synergetic effects.
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表 1 不同外加电场下的光催化的 · OH产率和R2
Table 1. · OH yield and R2 under different applied electric fields in photocatalytic system
场强/(V·cm−1) 产率/(mg·(L·min)−1) R2 0 0.082 0.999 1.0 0.083 0.998 1.5 0.099 0.996 2.0 0.086 0.996 2.5 0.085 0.992 表 2 不同光照强度下的协同作用
Table 2. Synergistic effects under different light intensities
反应类型 k/min−1 R2 光照强度/W f /% 光催化1) 0.013 0.998 6 — 电催化2) 0.219 0.996 6 — 光电耦合催化3) 0.295 0.994 6 21.35 光催化1) 0.023 0.998 12 — 电催化2) 0.219 0.996 12 — 光电耦合催化3) 0.333 0.996 12 27.32 光催化1) 0.030 0.993 18 — 电催化2) 0.219 0.996 18 — 光电耦合催化3) 0.373 0.999 18 33.24 注:1)光照强度为6 W;2) 电流密度为2.5 mA·cm−2;3) 电流密度为2.5 mA·cm−2、光照强度为6 W。所有实验3,4-DMA的浓度5 mg·L−1,室温,氯化钠浓度为6 000 mg·L−1,初始pH均为6.4,搅拌转速300 r·min−1。 表 3 光助电催化时3,4-DMA降解速率常数
Table 3. Degradation rate constant of 3,4-DMA by photo-assisted electrocatalytic systems
光照强度/W k/min−1 R2 增效作用/% 0 0.219 0.996 0 6 0.232 0.998 5.97 12 0.312 0.990 42.29 18 0.267 0.993 22.14 表 4 初始pH对光电耦合催化系统协同度的影响
Table 4. Effect of initial pH on synergetic level of hybrid photo-electrocatalytic oxidation
反应类型 k/min−1 R2 pH f/% 光催化1) 0.008 0.993 3 — 电催化2) 0.447 0.973 3 — 光电耦合催化3) 0.465 0.986 3 2.15 光催化1) 0.013 0.998 6.4 — 电催化2) 0.219 0.996 6.4 — 光电耦合催化3) 0.295 0.994 6.4 17.96 光催化1) 0.021 0.992 9 — 电催化2) 0.160 0.978 9 — 光电耦合催化3) 0.255 0.987 9 29.02 注:1) 光照强度为6 W;2) 电流密度为2.5 mA·cm−2;3) 电流密度为2.5 mA·cm−2、光照强度为6 W。所有实验3,4-DMA的浓度5.0 mg·L−1,室温,氯化钠浓度为6 000 mg·L−1,搅拌速度300 r·min−1,初始pH分别为3、6.4、9。 -
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