AMC Advances in Material Chemistry 2331-012X Scientific Research Publishing 10.12677/amc.2024.122013 AMC-84860 AMC20240200000_21759583.pdf 化学与材料 Ti/RuO 2电极高效降解RB19染料废水的研究 Study on Efficient Degradation of RB19 Dye Wastewater by Ti/RuO 2Electrode 2 1 2 1 心睿 2 1 2 1 2 1 银安 2 1 营茹 2 1 武汉工程大学化学与环境工程学院,湖北 武汉 null 12 04 2024 12 02 95 102 © Copyright 2014 by authors and Scientific Research Publishing Inc. 2014 This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

蒽醌染料产量大,用途广泛,结构中含有毒性较大的基团,一旦流入水环境中,对动植物的生长发育和人类的器官功能造成不可逆转的伤害。本文采用循环伏安法研究了活性蓝19 (RB19)在Ti/RuO2电极上的电化学氧化行为。此外,探究了以Ti/RuO2电极作为阳极电化学降解RB19模拟废水的最佳工艺参数。实验结果表明,在最佳条件下,RB19脱色率为80.8%,CODCr去除率为31.2%。Ti/RuO2电极对RB19的电化学降解效率较高,是一种理想的电极材料。 Anthraquinone dye has large yield, widely used, and contains more toxic groups in its structure. Once it flows into the water environment, it causes irreversible damage to the growth and development of plants and animals and people’s organ functions. The electrochemical oxidation behavior of reactive blue 19 (RB19) on Ti/RuO2electrode was studied by cyclic voltammetry. In addition, the optimum process parameters of electrochemical degradation of RB19 simulated wastewater using Ti/RuO2electrode as anode were investigated. The results showed that the decolorization rate of RB19 was 80.8% and the removal rate of CODCrwas 31.2%. Ti/RuO2electrode had high electrochemical degradation efficiency for RB19 and was an ideal electrode material.

蒽醌染料,活性蓝19,电化学降解,Ti/RuO 2电极, Anthraquinone Dye Reactive Blue 19 Electrochemical Degradation Ti/RuO 2Electrode
摘要

蒽醌染料产量大,用途广泛,结构中含有毒性较大的基团,一旦流入水环境中,对动植物的生长发育和人类的器官功能造成不可逆转的伤害。本文采用循环伏安法研究了活性蓝19 (RB19)在Ti/RuO2电极上的电化学氧化行为。此外,探究了以Ti/RuO2电极作为阳极电化学降解RB19模拟废水的最佳工艺参数。实验结果表明,在最佳条件下,RB19脱色率为80.8%,CODCr去除率为31.2%。Ti/RuO2电极对RB19的电化学降解效率较高,是一种理想的电极材料。

关键词

蒽醌染料,活性蓝19,电化学降解,Ti/RuO2电极

Study on Efficient Degradation of RB19 Dye Wastewater by Ti/RuO<sub>2</sub> Electrode<sup> </sup>

Lin Chen, Yang Li, Xinrui Huang, Ge Zhang, Jing Gao, Yin’an Ming, Yingru Wang*

School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan Hubei

Received: Mar. 15th, 2024; accepted: Apr. 12th, 2024; published: Apr. 19th, 2024

ABSTRACT

Anthraquinone dye has large yield, widely used, and contains more toxic groups in its structure. Once it flows into the water environment, it causes irreversible damage to the growth and development of plants and animals and people’s organ functions. The electrochemical oxidation behavior of reactive blue 19 (RB19) on Ti/RuO2electrode was studied by cyclic voltammetry. In addition, the optimum process parameters of electrochemical degradation of RB19 simulated wastewater using Ti/RuO2electrode as anode were investigated. The results showed that the decolorization rate of RB19 was 80.8% and the removal rate of CODCrwas 31.2%. Ti/RuO2electrode had high electrochemical degradation efficiency for RB19 and was an ideal electrode material.

Keywords:Anthraquinone Dye, Reactive Blue 19, Electrochemical Degradation, Ti/RuO2Electrode

Copyright © 2024 by author(s) and beplay安卓登录

This work is licensed under the Creative Commons Attribution International License (CC BY 4.0).

http://creativecommons.org/licenses/by/4.0/

1. 引言

染料是一种能够吸收可见光的发色基团或芳香结构组成的有机化合物,广泛应用于皮革制造、造纸、食品技术、化妆品和农业活动等 [ 1 ] 。目前产量位居第二的染料是蒽醌染料,每年约有84,000吨染料流失到水中,这使得20%的水污染来自染料工业 [ 2 ] 。蒽醌染料由于其结构特点,难以自然降解,这不仅对生态环境造成不可修复的破坏,而且对人体健康带来了严重的威胁。因此,寻找一种有效的去除废水中蒽醌染料的方法迫在眉睫。

目前,染料废水的处理方法有吸附法 [ 3 ] [ 4 ] [ 5 ] 、光催化氧化法 [ 6 ] [ 7 ] [ 8 ] 、生物法 [ 9 ] [ 10 ] 和电化学氧化法 [ 11 ] [ 12 ] 等。电化学氧化法可在较短时间内快速、高效地去除染料残留物,且不需要外部试剂的干预,在处理难降解废水等领域已经获得一定的研究成果且广泛应用。该方法是在外加电场的作用下,通过特制的电化学反应器产生强氧化性物质,使废水中的污染物通过氧化还原反应被去除,这些强氧化性物质一般是羟基自由基(•OH)、H2O2和氯气(Cl2)等 [ 13 ] [ 14 ] 。

影响电化学处理效率的因素有很多,如反应器类型、电极材料、外加电压、电解质浓度等,其中电极材料是最重要的因素之一。电极材料不仅决定了活性物质的类型,而且影响了电化学氧化的过程和污染物的处理效率 [ 15 ] [ 16 ] ,因此选择合适的电极材料是电化学氧化法处理染料废水的关键。目前,电化学氧化法降解染料废水使用的电极材料主要包括石墨电极 [ 17 ] 、铂电极 [ 18 ] 、Ti/RuO2电极 [ 19 ] 、PbO2电极 [ 20 ] 和Ti/SnO2-Pb电极 [ 21 ] 等。尺寸形状稳定型(DSA)电极克服了贵金属电极价格昂贵、不锈钢电极自身容易溶解导致金属离子溶出以及石墨电极机械强度低的缺点,是一种良好的阳极材料。Elumalai [ 22 ] 以DSA电极作为阳极,以不锈钢电极作为阴极,研究了活性黄186 (RY186)染料的电化学降解,实验结果表明,在pH值、RY186浓度、Fe2+浓度、H2O2投加量和电流密度分别为3、0.15 g/L、0.015 g/L、0.2 g/L和0.1 mA/cm2的条件下,反应15分钟后,RY186去除率可达99%,COD去除率高达94.82%。

本文以Ti/RuO2电极作为阳极,研究了RB19的电化学降解情况。首先,采用循环伏安法研究了Ti/RuO2电极在RB19模拟废水中的电化学氧化行为。其次,通过条件实验确定了电化学降解RB19的最佳操作参数。最后,通过CODCr研究了RB19在最佳条件下的矿化情况。

2. 实验材料与方法 2.1. 实验材料

RB19 (AR)购于上海鼎芬化学科技有限公司,无水硫酸钠(Na2SO4)购于国药集团化学试剂有限公司。本实验使用的仪器有:紫外可见分光光度计(UV2900,上海舜宇恒平科学仪器有限公司),多组输出直流电源供应器(GPS-4303C,固纬电子(苏州)有限公司),电化学工作站(CHI660E,上海辰华仪器有限公司)。

2.2. 电化学降解实验

实验室制备了RB19模拟废水,电化学降解实验装置与文献 [ 23 ] 相同。在250 mL的烧杯中加入200 mL RB19模拟废水,阳极为Ti/RuO2电极,阴极为不锈钢电极,反应时间为60分钟。采用紫外可见分光光度法测定RB19的浓度,RB19脱色率N如式(1)所示。

N = C 0 − C t C 0 × 100 % (1)

其中C0和Ct分别为RB19初始和给定时间t的浓度,mg/L。

2.3. 分析方法

CODCr的测定方法采用重铬酸盐法(HJ 828-2017),CODCr去除率的计算公式 [ 24 ] 如式(2)所示。

COD Cr 去 除 率     =     ( COD Cr ) 0 − ( COD Cr ) t ( COD Cr ) 0 × 100 % (2)

式中(CODCr)0和(CODCr)t为反应前和反应后的CODCr(mg/L)。

3. 结果与讨论 3.1. 循环伏安(CV)曲线分析

为了确定RB19在Ti/RuO2电极上的电化学氧化行为,本小节构建并使用了三电极体系,如图1所示。本装置以铂片电极为辅助电极,饱和甘汞电极为参比电极,Ti/RuO2电极为工作电极,在0.025 mol/LNa2SO4+ 100 mg/LRB19溶液中进行了CV曲线测试,实验结果如图2所示。

图1. 三电极体系原理图;1) 工作电极;2) 铂片电极;3) 饱和甘汞电极;4) 电化学工作站

图2. Ti/RuO2电极的CV曲线

如图2所示,在空白体系中未出现氧化还原峰,当在溶液中加入RB19后,CV曲线仍然没有出现新的峰值,且峰形也没有产生很大的变化。测试结果表明,RB19的电化学降解可能并不是直接发生在阳极表面,而是由阳极表面产生的活性物质引起的二次过程 [ 25 ] ,该过程如式(3)和(4)所示 [ 26 ] :

M ( H 2 O ) → M ( · OH ) + H + + e − (3)

M ( · OH ) + R → M ( ) + RO + H + + e + (4)

其中M(•OH)为电极的电活性位点,RO为有机氧化产物,在电解过程中,H2O在Ti/RuO2电极表面放电形成吸附的•OH,与RB19发生氧化还原反应,这些反应加速了电极上的电子传递,促进了RB19的电化学降解 [ 27 ] 。

3.2. 影响电化学降解RB19模拟废水的因素

在3.1小节中初步研究了RB19在Ti/RuO2电极上是一个间接氧化的过程,在电化学测试的基础上,本小节以Ti/RuO2电极作为阳极,以不锈钢电极作为阴极,在二维电极反应器中电化学降解RB19模拟废水,考察了外加电压、极板间距、电解质浓度和RB19初始浓度对降解效果的影响,探究最佳工艺参数。

3.2.1. 外加电压

图3. Ti/RuO2电极处理RB19模拟废水的降解效果;(a) 外加电压;(b) 极板间距;(c) 电解质浓度;(d) RB19初始浓度

在图3(a)中,采用不同的外加电压(5~11 V)来研究降解效率,随着施加电压的增加,RB19脱色率也相应增加。然而随着外加电压的增大,RB19脱色率并没有明显程度地增加,在外加电压为7 V的条件下RB19去除率为69.1%,与在外加电压为11 V的条件下RB19去除率仅相差6%,同时在较高的电压下可以观察到Ti/RuO2电极与不锈钢电极表面均产生大量的气泡,气泡逐渐上升覆盖了原有的电极面积,导致Ti/RuO2电极与不锈钢电极的有效反应面积减小,所以RB19的降解效果并没有大范围提高。因此,综合考虑选择7 V作为最佳外加电压。

3.2.2. 极板间距

图3(b)研究了电极间距(10~25 mm)对RB19脱色率的影响,RB19脱色率随着极板间距的增加而降低。较小的电极间距改善了电解反应的传质过程,有效地增加了•OH与RB19染料分子之间的碰撞概率,从而加速了电解反应。然而极板间距并不是越小越好,随着降解反应的进行,副反应也同时产生,伴随着转子的搅拌作用溶液中产生了许多气泡,使RB19染料分子和阴阳离子的传质过程受到限制,从而影响了RB19的降解效果。因此,综合考虑选择15 mm作为最佳极板间距。

3.2.3. 电解质浓度

从图3(c)可以看出,电解质浓度对Ti/RuO2电极的降解效果有较大的影响,在电解质浓度为0.02~0.05 mol/L的范围内,RB19去除率均在60%以上。高浓度电解质的加入,加快降解RB19,但是高浓度的电解质容易增加副反应的产生,未参加电解反应的阴阳离子会附着在Ti/RuO2电极与不锈钢电极的表面,阻碍电极发生氧化还原过程,降低反应所需要的活性物质的生成量,同时减少Ti/RuO2电极与不锈钢电极的使用寿命。随着电解质浓度的增加,RB19去除率并没有明显程度地增大,在电解质浓度为0.04 mol/L的条件下RB19去除率为79.7%,与在电解质浓度为0.05 mol/L的条件下RB19去除率仅相差1.7%。因此,综合考虑选择0.04 mol/L作为最佳电解质浓度。

3.2.4. RB19初始浓度

如图3(d)所示,在RB19初始浓度为100~400 mg/L的范围内,考察了RB19初始浓度对RB19去除率的影响,当改变RB19初始浓度时,Ti/RuO2电极对RB19的去除率均在70%以上。随着RB19初始浓度的增加,溶液中RB19染料分子总数也在增加,而Ti/RuO2电极与不锈钢电极在反应过程中产生的活性物质是有限度的,可能不足以完全氧化降解RB19,另外RB19在脱色过程中形成的中间产物与RB19染料分子本身可能存在竞争关系,都需要被活性物质氧化降解,所以导致RB19去除率降低。RB19在初始浓度为200 mg/L时的脱色率为80.8%,与初始浓度为100 mg/L时的脱色率仅相差1.6%。RB19的脱色率差异不大,但是在RB19初始浓度为200 mg/L时,单位时间内对RB19的去除率更高。因此,从电极降解效率的角度出发,综合考虑选择200 mg/L作为最佳RB19初始浓度。

上述实验结果表明,以Ti/RuO2电极作为阳极处理RB19模拟废水的最佳工艺参数为:外加电压7 V,极板间距15 mm,电解质浓度0.04 mol/L,RB19初始浓度200 mg/L,在此条件下,电化学降解RB19模拟废水60分钟后RB19脱色率为80.8%。该结果说明Ti/RuO2电极作为阳极对RB19模拟废水的电化学降解具有较高的降解效率。

3.3. RB19的矿化率

紫外可见分光光度法可以测定反应过程中RB19的浓度,但是RB19的矿化情况尚不清楚,RB19的矿化程度可以通过CODCr去除率来确定。为了研究Ti/RuO2电极降解RB19模拟废水的矿化率,在最佳条件下检测了降解后的CODCr。如图4所示,电解60 min后,RB19的脱色率为80.8%,CODCr去除率为31.2%。结果表明,RB19的电化学脱色效果较好,但不能完全矿化。从CODCr的变化可以看出,只有一部分RB19被氧化为H2O和CO2,而另一部分的副产物以有机物和可溶性盐的形式存在 [ 28 ] 。

图4. RB19的脱色率和矿化率

4. 结论

本文通过对Ti/RuO2电极进行电化学测试,表明RB19的电化学氧化行为是一个间接氧化的过程。采用Ti/RuO2电极作为阳极电化学降解RB19模拟废水,实验结果表明,在外加电压为7 V、极板间距为15 mm、电解质浓度为0.04 mol/L和RB19初始浓度为200 mg/L的条件下,电解60分钟后,RB19脱色率为80.8%,CODCr去除率为31.2%。Ti/RuO2电极对RB19模拟废水的脱色效果较高,是一种较为理想的电极材料。

致谢

感谢武汉工程大学第十四届研究生教育创新基金项目(CX2022434)的基金支持。

文章引用

陈 琳,李 阳,黄心睿,张 歌,高 晶,明银安,王营茹. Ti/RuO2电极高效降解RB19染料废水的研究Study on Efficient Degradation of RB19 Dye Wastewater by Ti/RuO2Electrode[J]. 材料化学前沿, 2024, 12(02): 95-102. https://doi.org/10.12677/amc.2024.122013

参考文献 References Collivignarelli, M.C., Abba, A., Miino, M.C., et al. (2019) Treatments for Color Removal from Wastewater: State of the Art. Journal of Environmental Management, 236, 727-745.
https://doi.org/10.1016/j.jenvman.2018.11.094
Routoula, E. and Patwardhan, S.V. (2020) Degradation of Anthraquinone Dyes from Effluents: A Review Focusing on Enzymatic Dye Degradation with Industrial Potential. Environmental Science & Technology, 54, 647-664.
https://doi.org/10.1021/acs.est.9b03737
Jawad, A.H., Abdulhameed, A.S., Surip, S.N., et al. (2023) Hybrid Multifunctional Biocomposite of Chitosan Grafted Benzaldehyde/Montmorillonite/Algae for Effective Removal of Brilliant Green and Reactive Blue 19 Dyes: Optimization and Adsorption Mechanism. Journal of Cleaner Production, 393, Article ID: 136334.
https://doi.org/10.1016/j.jclepro.2023.136334
Cheng, S., Zhang, L., Xia, H., et al. (2017) Characterization and Adsorption Properties of La and Fe Modified Activated Carbon for Dye Wastewater Treatment. Green Processing and Synthesis, 6, 487-498.
https://doi.org/10.1515/gps-2016-0120
Li, C.J., Zhang, Y.J., Chen, H., et al. (2022) Development of Porous and Reusable Geopolymer Adsorbents for Dye Wastewater Treatment. Journal of Cleaner Production, 348, Article ID: 131278.
https://doi.org/10.1016/j.jclepro.2022.131278
Bilal, M., Rasheed, T., Iqbal, H.M.N., et al. (2018) Photocatalytic Degradation, Toxicological Assessment and Degradation Pathway of CI Reactive Blue 19 Dye. Chemical Engineering Research & Design, 129, 384-390.
https://doi.org/10.1016/j.cherd.2017.11.040
Mahmoodi, N.M., Keshavarzi, S. and Ghezelbash, M. (2017) Synthesis of Nanoparticle and Modelling of Its Photocatalytic Dye Degradation Ability from Colored Wastewater. Journal of Environmental Chemical Engineering, 5, 3684-3689.
https://doi.org/10.1016/j.jece.2017.07.010
Zhang, J., Yu, H., Quan, X., et al. (2016) Ceramic Membrane Separation Coupled with Catalytic Ozonation for Tertiary Treatment of Dyestuff Wastewater in a Pilot-Scale Study. Chemical Engineering Journal, 301, 19-26.
https://doi.org/10.1016/j.cej.2016.04.148
Xie, X., Zheng, X., Yu, C., et al. (2019) Highly Efficient Biodegradation of Reactive Blue 19 under the Activation of Tea Residue by a Newly Screened Mixed Bacterial Flora DDMY2. RSC Advances, 9, 24791-24801.
https://doi.org/10.1039/C9RA04507D
Srinivasan, S. and Sadasivam, S.K. (2021) Biodegradation of Textile Azo Dyes by Textile Effluent Non-Adapted and Adapted Aeromonas Hydrophila. Environmental Research, 194, Article ID: 110643.
https://doi.org/10.1016/j.envres.2020.110643
Lyu, J., Han, H., Wu, Q., et al. (2019) Enhancement of the Electrocatalytic Oxidation of Dyeing Wastewater (Reactive Brilliant Blue KN-R) over the Ce-Modified Ti-PbO2 Electrode with Surface Hydrophobicity. Journal of Solid State Electrochemistry, 23, 847-859.
https://doi.org/10.1007/s10008-018-04170-9
Mei, R.Q., Wei, Q.P., Zhu, C.W., et al. (2019) 3D Macroporous Boron-Doped Diamond Electrode with Interconnected Liquid Flow Channels: A High-Efficiency Electrochemical Degradation of RB-19 Dye Wastewater under Low Current. Applied Catalysis B: Environmental, 245, 420-427.
https://doi.org/10.1016/j.apcatb.2018.12.074
Irikura, K., Bocchi, N., Rocha-Filho, R.C., et al. (2016) Electrodegradation of the Acid Green 28 Dye Using Ti/Beta-PbO2 and Ti-Pt/Beta-PbO2 Anodes. Journal of Environmental Management, 183, 306-313.
https://doi.org/10.1016/j.jenvman.2016.08.061
Umukoro, E.H., Peleyeju, M.G., Ngila, J.C., et al. (2017) Towards Wastewater Treatment: Photo-Assisted Electrochemical Degradation of 2-Nitrophenol and Orange II Dye at a Tungsten Trioxide Exfoliated Graphite Composite Electrode. Chemical Engineering Journal, 317, 290-301.
https://doi.org/10.1016/j.cej.2017.02.084
Orts, F., Del Rio, A.I., Molina, J., et al. (2018) Electrochemical Treatment of Real Textile Wastewater: Trichromy Procion HEXL (R). Journal of Electroanalytical Chemistry, 808, 387-394.
https://doi.org/10.1016/j.jelechem.2017.06.051
Rodríguez-Narváez, O.M., Picos, A.R., Bravo-Yumi, N., et al. (2021) Electrochemical Oxidation Technology to Treat Textile Wastewaters. Current Opinion in Electrochemistry, 29, Article ID: 100806.
https://doi.org/10.1016/j.coelec.2021.100806
Goren, A.Y., Recepoglu, Y.K., Edebali, O., et al. (2022) Electrochemical Degradation of Methylene Blue by a Flexible Graphite Electrode: Techno-Economic Evaluation. Acs Omega, 7, 32640-32652.
https://doi.org/10.1021/acsomega.2c04304
Bezerra Rocha, J.H., Soares Gomes, M.M., Vieira Dos Santos, E., et al. (2014) Electrochemical Degradation of Novacron Yellow C-RG Using Boron-Doped Diamond and Platinum Anodes: Direct and Indirect Oxidation. Electrochimica Acta, 140, 419-426.
https://doi.org/10.1016/j.electacta.2014.06.030
Degaki, A.H., Pereira, G.F., Rocha, R.C., et al. (2014) Effect of Specific Active Chlorine Species and Temperature on the Electrochemical Degradation of the Reactive Blue 19 Dye Using a Boron-Doped Diamond or DSA Anode in a Flow Reactor. Electrocatalysis, 5, 8-15.
https://doi.org/10.1007/s12678-013-0156-z
Abu Ghalwa, N.M. and Zaggout, F.R. (2006) Electrodegradation of Methylene Blue Dye in Water and Wastewater Using Lead Oxide/Titanium Modified Electrode. Journal of Environmental Science and Health Part A, Toxic/Hazardous Substances & Environmental Engineering, 41, 2271-2282.
https://doi.org/10.1080/10934520600872888
Hu, Z., Guo, C., Wang, P., et al. (2022) Electrochemical Degradation of Methylene Blue by Pb Modified Porous SnO2 Anode. Chemosphere, 305, Article ID: 135447.
https://doi.org/10.1016/j.chemosphere.2022.135447
Elumalai, G., Sowmya, B., Rajan, R.K., et al. (2023) Experimental Study of Photo Electro-Fenton Method for the Removal of Reactive Yellow 186: Influence of Operational Parameters. Environmental Progress & Sustainable Energy, 42, e14061.
https://doi.org/10.1002/ep.14061
Cheng, N., Huang, J. and Wang, Y. (2022) Establishment of Electrochemical Treatment Method to Dye Wastewater and Its Application to Real Samples. Main Group Chemistry, 21, 523-537.
https://doi.org/10.3233/MGC-210148
Wang, Q., Tu, S.Q., Wang, W.Y., et al. (2021) Fabrication of In2O3 Doped PbO2 Anode and Its Application for Electrochemical Degradation of Norfloxacin in Aqueous Solutions. Journal of Environmental Chemical Engineering, 9, Article ID: 106462.
https://doi.org/10.1016/j.jece.2021.106462
Britschgi, J., Bilke, M., Schuhmann, W., et al. (2022) Indirect Electrooxidation of Methane to Methyl Bisulfate on a Boron-Doped Diamond Electrode. Chemelectrochem, 9, e202101253.
https://doi.org/10.1002/celc.202101253
Roth, H., Gendel, Y., Buzatu, P., et al. (2016) Tubular Carbon Nanotube-Based Gas Diffusion Electrode Removes Persistent Organic Pollutants by a Cyclic Adsorption—Electro-Fenton Process. Journal of Hazardous Materials, 307, 1-6.
https://doi.org/10.1016/j.jhazmat.2015.12.066
Alaoui, A., El Kacemi, K., El Ass, K., et al. (2015) Activity of Pt/MnO2 Electrode in the Electrochemical Degradation of Methylene Blue in Aqueous Solution. Separation and Purification Technology, 154, 281-289.
https://doi.org/10.1016/j.seppur.2015.09.049
Belal, R.M., Zayed, M.A., El-Sherif, R.M., et al. (2022) Electrochemical Degradation and Degree of Mineralization of the BY28 Dye in a Supporting Electrolyte Mixture Using an Expanded Dimensionally Stable Anode. Electrocatalysis, 13, 26-36.
https://doi.org/10.1007/s12678-021-00680-9
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