Discoloration of aqueous reactive dye solutions in the UV/Fe0 system

A remoção do corante reativo Reactive Blue 4 (RB4) por redução eletroquímica em solução aquosa foi investigada sobre eletrodo de carbono vítreo reticulado. O grupo antraquinona presente no corante RB4 é reduzido em pH < 8,0 em uma única etapa a hidroquinona, segundo um processo reversível de dois elétrons e reação de pré-protonação, via geração de um radical semiquinona detectado espectrotométricamente. Em pH > 8,0, ambas as formas não e pré-protonada da antraquinona são reduzidas em duas etapas reversíveis de dois elétrons. Após 3 horas de eletrólise em meio ácido e neutro o corante perde 60% de sua coloração, enquanto que em meio alcalino perde apenas 37%. Simultaneamente, 64% de remoção de carbono orgânico total foi obtida após eletrólise em meio ácido de pH 2,0.The electrochemistry reduction for the removal of Reactive Blue 4 (RB4) dye from aqueous solution using reticulated glassy carbon electrode is investigated. At pH < 8.0 the anthraquinone group of the RB4 dye are reduced in one cathodic step to hidroquinone after a reversible two-electron process involving a precedent two protons reaction. A stable semiquinone is detected by spectrophotometric technique. At pH > 8.0 the reduction process involves two reversible 2-electron steps, whose species are generated by a protonation equilibrium of anthraquinone group. The results shows that 60% of color removal was obtained after 3 hours of RB4 dye electrolysis at acidic and neutral conditions and only 37% at alkaline conditions. Simultaneously 64% of total organic carbon was removed after electrolysis at pH 2.0.Keywords: reactive dyes, electrochemical reduction, dye treatment, reactive blue 4 IntroductionReactive dyes are the main group of dyes used in the textile industry.1 They are very effective in fabric dyeing due to the reactive groups capable of forming covalent bonds with a hydroxyl or amino group on the fiber. Inefficiencies in the dyeing process results in 10-15% of all dyestuff being lost directly to wastewater.2 Therefore, their crescent world consumption has attracted the critical attention of the public and the authorities with respect to the toxicological and environmental aspects of the reactive dyes. 3,4 Dye wastewater is usually treated by physical or chemical treatment process. They include physicalchemical flocculation, electroflotation, membranefiltration, electrokinetic coagulation, ion-exchange, irradiation, precipitation and other treatment using activated carbon. 5 Over the past few years, alternative methods 6-10 for dye treatment have been investigated, including chemical oxidation with reagents such as: ozone, hydrogen peroxide, ozone/UV, hydrogen peroxide/UV and Fenton's reagent [hydrogen peroxide + Fe (II)]. The application of electrochemical oxidation with or without UV light as method for dye degradation have also been investigated, [11][12][13][14][15] but no mechanisms of the reduction were discussed. [16][17][18][19] Most of the electrochemical studies involving reduction of reactive dyes are based on mercury electrode [16][17...

Section: Introductionmentioning

confidence: 99%

Decolourization of anthraquinone reactive dye by electrochemical reduction on reticulated glassy carbon electrode

Carneiro

Boralle

Stradiotto

et al. 2004

“…[7][8][9][10][11] Dyes are another category of complex chemicals that are labile to reduction, as already shown for several dyes. [12][13][14][15][16][17][18] Several metals (such as Zn, Sn, Pt) can be used as reduction agents, but iron has received the foremost emphasis due to its high efficiency in addition to its low cost and toxicity. [19][20][21][22][23][24][25][26][27][28][29] Mass spectrometry (MS) has been used for a long time for the measurement of isotopes and to determine the structure of organic molecules.…”

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confidence: 99%

Degradation of food dyes by zero-valent metals exposed to ultrasonic irradiation in water medium: optimization and electrospray ionization mass spectrometry monitoring

Pavanelli¹,

Bispo²,

Nascentes³

et al. 2011

A degradação redutiva de quatro corantes típicos (Azul Brilhante, Amaranto, Amarelo Crepúsculo e Vermelho 40), largamente empregados pela indústria alimentícia, por metais de valência zero (Fe e Sn), sob irradiação ultrassônica (US) em meio aquoso ácido (pH 3,0), foi estudada. As reações foram monitoradas por ESI(-)-MS (espectrometria de massas com ionização electrospray no modo negativo), além de espectrofotometria UV-Vis e carbono orgânico total (TOC). A influência de parâmetros preponderantes (tempo de exposição à radiação ultrassônica e massa do metal) nas taxas de degradação foi seguramente estabelecida por meio da construção de planejamentos fatoriais e superfícies de resposta. Deste modo, observou-se que, sob as condições experimentais otimizadas, ferro metálico (Fe) degradou eficientemente todos os corantes (com taxas de degradação superiores a 90% após 30 min de reação), enquanto que estanho metálico (Sn) apresentou um desempenho notavelmente inferior. As baixas taxas de mineralização obtidas foram consequência, provavelmente, do caráter essencialmente redutivo de tais processos. Baseado nos resultados do monitoramento por ESI(-)MS, uma rota de degradação plausível para o corante Azul Brilhante em meio aquoso, pelo sistema Fe/US, foi proposta e envolve, como etapas iniciais, a hidrogenação da ligação dupla exocíclica carbono-carbono, seguida pela inserção de hidreto no grupamento imino da molécula.The reductive degradation of four prototype dyes largely employed by the food industry (Brilliant Blue, Amaranth, Sunset Yellow and Red 40), by zero-valent metals (Fe and Sn) under ultrasonic irradiation in acidic aqueous solution (pH 3.0), was studied. The reactions were monitored by direct infusion ESI(-)-MS (electrospray ionization mass spectrometry in the negative ion mode) as well as by UV-Vis and total organic carbon (TOC). The influence of major parameters (time of exposure to ultrasonic irradiation and mass of metal) on the degradation rates was firmly established by means of factorial design and surface response approaches. Hence, it was noticed that, under the optimized experimental conditions, metallic iron (Fe) was able to efficiently degrade all the dyes (with rates higher than 90% after 30 min reaction time), whereas metallic tin (Sn) exhibited a noticeably lower performance. Low mineralization rates were achieved probably due to the essentially reductive character of such process. Based on the results from the ESI(-)-MS monitoring, a plausible degradation route for the Brilliant Blue dye in aqueous medium by the Fe/US system was proposed. Hence, this route involves, as initial pathways, the hydrogenation of the exocyclic carbon-carbon double bond of the dye followed by the insertion of hydride at its imino moiety. Keywords: electrospray ionization mass spectrometry, monitoring, food dyes, zero-valent metals IntroductionColor is by far the most important sensorial property of foods. In this way, dyes have been widely used to accentuate their original colors, or to provide different ones.While bei...

“…This material showed a degradation efficiency similar to those exhibited by several with different commercial Fe 0 sources. [31][32][33] RBB degradation by RWZVIP could be carried out through reductive or oxidizing pathways, depending on the oxygen level and pH. The former seems to be the preferential mechanism for azo dye chromophore degradation; the latter, which is due to in situ Fentonreactions, promotes effective mineralization of the dye.…”

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confidence: 99%

Azo dye degradation by recycled waste zero-valent iron powder

Pereira¹,

Freire²

2006

Neste trabalho é apresentado um método eficiente para a degradação de corantes, usando uma fonte de pó de ferro zero ambientalmente amigável (resíduo de um processo industrial). A influência de vários fatores experimentais (tais como: pH, massa de ferro, tamanho de partícula, concentração do substrato, atmosfera inerte ou oxidante) sobre a eficiência do ferro zero em reduzir o grupo cromóforo e o teor de carbono orgânico total de um azocorante (Preto Remazol B) foi avaliada. O processo de degradação do corante apresentou uma cinética de primeira ordem com uma constante de 0,153 min -1 . Nas condições otimizadas (pH=3, [Fe] = 5 g L -1 , tamanho de partícula ≤ 250 μm), este processo promoveu uma descoloração de 95% e redução de 70% na concentração de carbono orgânico total de uma solução 100 mg L -1 do corante. Este processo também foi empregado na degradação de um efluente industrial têxtil apresentando bons resultados e demonstrando capacidade para ser uma alternativa para a remediação de sistemas aquáticos poluídos.In this paper an efficient method for azo dye degradation using an environmentally friendly zero-valent iron powder source is presented (iron particles discarded from a manufacturing process). The influence of several experimental parameters (such as pH, iron mass, particle size, substrate concentration, oxidizing and inert atmospheres) on the ability of zero-valent iron to reduce the chromophoric groups and total organic carbon content of the azo dye Remazol Black B was evaluated. Kinetic studies revealed that the azo degradation by Fe 0 appeared to be first-order with respect to substrate, with an observed rate constant (k obs ) of 0.153 min -1 . Under the optimized operational conditions (pH 3, [Fe] = 5 g L -1 , iron particle size ≤ 250 μm), the iron-based process produced net a reduction in color and total organic carbon of about 95% and 70%, respectively. The process was also evaluated for the degradation of textile effluent. The studied process showed good characteristics, which can make it an effective alternative for polluted aquatic system remediation.Keywords: reductive degradation process, dye degradation, effluent treatment, Fenton´s reagent IntroductionOver the last decades, the increasing demand for dyes by the textile industry has shown a high pollutant potential. It is estimated that around 10 -15% of the dyes are lost in the effluent during the dyeing processes. 1,2 The discharge of highly colored synthetic dye effluents can be very damaging to the receiving water bodies, since these dyes in the water strongly absorb sunlight, which decreases the intensity of light absorbed by water plants and phytoplankton, reducing photosynthesis and the oxygenation of water reservoirs. 3 Also, public perception of water quality is greatly influenced by its color. The presence of unnatural colors is esthetically unpleasant and tends to be associated with contamination. 4 In addition, dyes used in the textile industry may be toxic to aquatic organisms and can be resistant to natural biological deg...