Decolorization Reaction Research Articles

A rapid azo dye decolorization of methyl orange by the foam zero‐valent nickel

In this article, foam zero‐valent nickel (FZVN) was put forward as a promising zero‐valent metal for the pretreatment of azo dye wastewater (MO as a model contaminant). The characteristics of FZVN were evaluated by methods of Barrett‐Emmett‐Teller, scanning electron microscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy. Moreover, influence of key experimental parameters, including oxygen concentration, presence of different acid, pH, and temperature on the MO decolorization were systematically ascertained. Furthermore, possible mechanism of MO removal by FZVN was investigated by using Liquid chromatography‐mass spectrometry (LC‐MS). Results showed that FZVN was a three‐dimensional pore material with a specific surface area of 3 m2 g−1. Moreover, anoxic condition, presence of acetic acid, higher temperatures and acid conditions were beneficial to decolorize MO by FZVN while the decolorization process obeyed the first order kinetic model with an apparent rate constant (kapp) of 0.162 min−1 at pH value of 4 (25°C). The activation energy Ea obtained from the decolorization reaction was 83.1 kJ mol−1. Based on LC‐MS results, the role of FZVN in the decolorization reaction process was suggested as follows: strong reductive, catalysis, and adsorption. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 686–694, 2018

Photochromism of Dihydroindolizines. Part XXI: Multiaddressable Photochromic Performances based on Pyrrolo[1,2 -b ]pyridazine photochromes: Kinetics, Substituent Effect and Solvatochromism

Abstract In the present study, the thermal 1,5-electrocyclization back reaction from betaines (colored forms) to dihydroindolizines (DHIs, colorless) was studied in seven organic solvents with different polarities at various temperatures. The spectroscopic, thermodynamic and photochromic properties of such photo- and solvatochromic material based on betaines/DHIs is investigated. It is obvious that the rate of the thermal back reaction depend on solvent polarity. Exploration of the activation parameters unravel an underlying compensation between ΔH ≠ and ΔS ≠ . The 1,5-electrocylization decoloration reaction is found to follow two-step mechanism, the first step corresponds to the transoid-cisoid isomerization and the second one is the ring closure from the cisoid intermediate and formation of the carbon-carbon bond to form the initial spiro isomer. The special solvent effects were discussed based on the linear free energy relationship. The solvatochromism of the dihydroindolizines (DHIs) was studied and analyzed by means of the empirical Kamlet–Taft and Catalan solvent parameter set. The obtained results suggest that the change of polarizability within the solvents is the major factor for the observed solvent dependence.

Electrochemical decolorization of C.I. Acid Orange 3 in the presence of sodium chloride at iridium oxide electrode

The electrocatalytic degradation of C.I. Acid Orange 3 from simulated wastewater by indirect electrochemical oxidation using an IrOx electrode was investigated. The effects of different operating parameters on the rate of dye decolorization were studied. The influences of mixing, electrolyte concentration, applied current, and initial dye concentration were examined. The change in dye concentration was followed by ultraviolet–visible spectroscopy, while the formation of reaction intermediates was established using high-performance liquid chromatography–mass spectrometry analysis. Ultraviolet–visible spectroscopy showed a decrease of the absorption peak at 374 nm during the electrolysis and the appearance of a new absorption maximum at 460 nm. The decolorization reaction can be followed only at 460 nm. Four intermediate products (two mono- and two dichlorinated) were detected. At the end of the study, a phytotoxicity assay was performed to determine the effectiveness of the applied method. The results showed that the applied electrochemical treatment of C.I. Acid Orange 3 leads to a decrease in phytotoxicity from 53 to 28%.

Irreversible Bleaching of Donor–Acceptor Stenhouse Adducts on the Surfaces of Magnetite Nanoparticles

AbstractTwo novel donor–acceptor Stenhouse adducts (DASAs) featuring the catechol moiety were synthesized and characterized. Both compounds bind strongly to the surfaces of magnetite nanoparticles. An adrenaline‐derived DASA renders the particles insoluble in all common solvents, likely because of poor solvation of the zwitterionic isomer generated on the nanoparticle surfaces. Well‐soluble nanoparticles were successfully obtained using dopamine‐derived DASA equipped with a long alkyl chain. Upon its attachment to nanoparticles, this DASA undergoes an irreversible decoloration reaction owing to the formation of the zwitterionic form. The reaction follows first‐order kinetics and proceeds more rapidly on large nanoparticles. Interestingly, decoloration can be suppressed in the presence of free DASA molecules in solution or at high nanoparticle concentrations.

Synthesis of a Fe/AC Fenton‐like catalyst and heterogeneous catalysis in decolorization of Sunset Yellow by pulsed high‐voltage discharge

AbstractBACKGROUNDA new Fe/AC heterogeneous Fenton‐like catalyst was prepared using a dipping–sintering method. The prepared catalyst was characterized by X‐ray diffraction and scanning electron microscopy. The decolorization of Sunset Yellow was conducted in a self‐designed pulsed high‐voltage discharge system by the catalysis of the prepared heterogeneous catalyst. Effects of preparation conditions of catalyst (carrier material, sintering temperature and dipping time) and operating conditions (catalyst dosage, pH and treatment method) on decolorization efficiency were investigated.RESULTSSpherical activated carbon (AC) was selected as the carrier material and the optimal dipping time and sintering temperature were 8 h and 350 °C, respectively. The efficiency of decolorization of Sunset Yellow was above 90% after 30 min of a pulsed high‐voltage discharge process with 5 g heterogeneous catalyst and at pH 2.00. The utilization of copper mesh not only enhanced the decolorization of Sunset Yellow but also facilitated the reusability of the prepared heterogeneous catalyst. The efficiency of decolorization of Sunset Yellow with prepared Fe/AC heterogeneous Fenton‐like catalyst (5 g) was even a little higher than that with homogeneous catalyst (1.635 mmol L−1 Fe2+). The decolorization efficiency remained above 90% after ten recycles of the catalyst, indicating that the prepared heterogeneous catalyst has good stability and reusability. In addition, a possible catalytic mechanism for the decolorization reaction in a pulsed high‐voltage discharge system with prepared Fe/AC heterogeneous Fenton‐like catalyst was proposed by determination of H2O2 and ·OH concentrations in deionized water.CONCLUSIONSThe prepared Fe/AC heterogeneous Fenton‐like catalyst efficiently degrades Sunset Yellow wastewater in a pulsed high‐voltage discharge system. © 2016 Society of Chemical Industry

Photocatalytic decolorization of azo dyes on TiO2: Prediction of mechanism via conceptual DFT

The aim of this study is to develop a shortcut method to predict the intermediates and the mechanism of decolorization reactions of azo dyes. To this purpose, Reactive Red 195 (RR195) was chosen as the representative member of azo dyes and photocatalytic decolorization reaction of RR195 in the presence of TiO2 under UV-A light irradiation was investigated. TiO2 was synthesized by an acid-catalyzed sol-gel method from an alkoxide precursor and characterized by XRD, XPS, ESEM-EDX and BET measurements. The decolorization reaction was monitored by UV–vis, FTIR, GC–MS and ESEM-EDX techniques. Conceptual Density Functional Theory was applied to the degradation reaction of the target molecule and reactivity descriptors were calculated by means of DFT/B3LYP/6-31G* level of theory. Eventually, the reactive sites of the molecule for OH radical attack were determined and the reaction mechanism was predicted by combining the results of the DFT calculations with the experimental FTIR and GC–MS analyses. The predicted mechanism was confirmed by comparison with the experimental results on simple structures reported in the literature. The results of the study suggest that TiO2/UV photocatalysis may be used as a method for treatment of diluted wastewaters in textile industries, adsorption on TiO2 surface occurs through sulfo and carbonyl groups of the dye molecule, while decolorization by the breaking of the NN double bond of the chromophore group.

Light-Activated Sensitive Probes for Amine Detection.

Our new, simple, and accurate colorimetric method is based on diarylethenes (DAEs) for the rapid detection of a wide range of primary and secondary amines. The probes consist of aldehyde- or ketone-substituted diarylethenes, which undergo an amine-induced decoloration reaction, selectively to give the ring-closed isomer. Thus, these probes can be activated at the desired moment by light irradiation, with a sensitivity that allows the detection of amines at concentrations as low as 10-6 m in solution. In addition, the practical immobilization of DAEs on paper makes it possible to detect biogenic amines, such as cadaverine, in the gas phase above a threshold of 12 ppbv within 30 seconds.

Mechanism and kinetics of treatment of acid orange II by aged Fe-Si-B metallic glass powders

The mechanism and kinetics of acid orange II (AOII) treated by aged gas-atomized Fe-Si-B metallic glass (MG) powders were investigated in this study. The decolorization reaction is shown to obey the pseudo-first-order kinetic model, and the treatment processes could be divided into two stages: a slow step followed by a rapid one. This observation is in accordance with the following results, the azo dye is simply adsorbed onto the Fe-based MG powders in the initial stage, because the oxide layer coated on the powder surface depresses the degradation reaction by covering the activity sites, and then the degradation occurs with the desquamation of the powders. The AOII could be degraded with a rapid reaction rate when the Fe-based MG powders are applied to the treatment process again, because of the consumption of the oxide layer and the unchanged core of the Fe-based MGs. These findings will promote the practical application of MGs in degrading azo dyes.

Decolorization of reactive orange 16 azo dye in wastewater using CAT/ IrCl3/HClO4 redox system: Delineation of kinetic modeling and mechanistic approaches

Reactive orange 16 (RO16) is a reactive azo dye, which is chiefly used in textile industry. In the present research, a simple and expeditious decolorization technique has been developed for the removal of this dye present in the wastewater. Kinetics and oxidative decolorization of RO16 dye with chloramine-T (CAT) in HClO4 medium catalyzed by iridium (III) chloride (IrCl3) have been investigated spectrophotometrically (λmax = 496 nm) at 303 K. The reaction exhibited a first-order dependence of rate on [CAT]o and [RO16]o respectively. The rate of the reaction was retarded with increase in [H+] and shows an order less than unity. The order with respect to [IrCl3] was fractional. Oxidation products were identified as 6-acetamido-3,4-dioxo-3,4-dihydro naphthalene-2-sulfonic acid and 2-(phenyl sulfonyl)-ethyl hydrogen sulphate by mass spectral analysis. IrCl3 catalyzed decolorization reaction is about six times faster than the uncatalyzed reaction. Activation parameters have been computed. The kinetic modelings and mechanistic pathway have been worked out. The oxidative decolorization process has significantly reduced the COD. Phytotoxicity studies demonstrated that the treated dye was less toxic than untreated dye sample. Economic analysis was performed. Notably, the developed oxidative decolorization technique is expected to be helpful for treating RO16 dye present in industrial wastewater with suitable modifications.

Efficient coloration and decoloration reactions of fast photochromic 3H–naphthopyrans in PMMA-b-PBA block copolymer

Fast photochromic molecules have attractive potential to apply to the ophthalmic lenses and real-time dynamic holography. However, the thermal decoloration reaction rate and the photoconversion efficiency of the photochromic molecules largely depend on their surrounding medium. Herein, we investigated the thermal decoloration behavior of fast photochromic 3H–naphthopyrans in poly(methyl methacrylate)-b-poly(n-butylacrylate) (PMMA-b-PBA) block copolymer. The rapid photoswitching properties of the fast photochromic molecules were achieved by using the block copolymer as a host polymer matrix.

Photochromism of dihydroindolizines Part XIX. Efficient one-pot solid-state synthesis, kinetic, and computational studies based on dihydroindolizine photochromes

For the first time, one-pot solid-state synthesis of 12 photochromic materials based on photochromic dihydroindolizine system substituted in both fluorene part (region A) and the heterocyclic part (region C) has been established. This method has immense advantages, which are short-time reaction, high-yield and low-yield by-products, and easily purification and separation processes. In addition, this method will help in getting over the tremendously purification and low-yield problems faced since the worth-finding of this family of photochromic materials. The absorption maxima (λmax) and the half-lives (t1/2) of the colored betaines were detected in all cases using multichannel UV/Vis spectrophotometric measurements. The rate constants of the thermal back reaction of the betaines were determined at constant temperature by measuring the decrease in the maximum absorption intensity (λmax) with time. The half-lives (t1/2) and rate constants (k) of betaines under examination were calculated by plotting lnA against time (t). The kinetic measurements could be detected by both spectra scan and time-dependent decay measurements. Examination of the Arrhenius parameters reveals an underlying compensation between Ea and log A, whereby an increase in Ea is opposed by an increase in log A. The compensation appears in the corresponding Eyring parameters, ΔH≠ and ΔS≠; betaine structural changes that lead to lower, more favorable enthalpies of activation engender opposing entropic changes. At the isokinetic temperature Tiso = β, structural changes do not affect the rate constant of a reaction series because the changes of ΔH≠ are counterbalanced by changes of ΔS≠. The existence of an isokinetic relationship indicates a common structure of the transition state of all thermal back reaction of betaine under investigation. The computational results suggest that the decoloration reaction is a two-step mechanism. The first step corresponds to the transoid–cisoid isomerization with an activation barrier of 10.3 kJ mol−1, and the second step is the ring closure from the cisoid intermediate with a barrier 71.3 kJ mol−1, which represent the rate determining step for thermal decoloration. The photochemical ring opening of DHIs to betaines is a disrotatory 1,5-electrocyclic reaction, whereas the thermal ring-closing occurs in the conrotatory mode. Copyright © 2016 John Wiley & Sons, Ltd.

Decolorization of Selected Synthetic Textile Dyes by Yeasts from Leaves and Fruit Peels.

Discharge of textile dyes into the environment poses a significant threat. They are poorly biodegradable and toxic due to their complex composition and aromatic structures. In the search for alternatives to physical and chemical treatments, biodegradation of synthetic dyes by various microbes is emerging as an effective and promising approach. The decolorization of synthetic dyes by yeast co-cultures and consortia from leaves and fruit peels was assessed at a 50 μg/mL dye concentration. Yeasts isolates from leaves and fruit peels were screened for potential decolorization of synthetic dyes at 25-50 μg/mL. Decolorization parameters were optimized for synergistic properties and development of yeast co-cultures and consortium. Possible decolorization reactions were initially assessed by cell immobilization, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and Fourier transform infrared spectroscopy (FTIR) analysis. A total of 16 organisms were isolated from rose, mango, and pineapple leaves and pineapple fruit peels. Only 4 organisms showed high decolorization of four synthetic dyes: Direct Pink B, Disperse Yellow 5G, Direct Fast Orange S, and Reactive Turquoise Blue G. The optimum condition for best decolorizers of selected dyes at 50 μg/mL were Candida guilliermondii (Y011) for Direct Pink B at pH 9, 37°C; C. dubliniensis (Y014) for Disperse Yellow 5G at pH 4, 25°C; C. guilliermondii (Y004) for Direct Fast Orange S at pH 7, 25°C, and C. famata (Y003) for Reactive Turquoise Blue G at pH 4, 35°C. None of the 4 yeast isolates showed any antagonistic activity when subjected to the lawn-spotting method for the formation of co-cultures and consortium. The best co-cultures obtained 61% decolorization of Direct Pink B, 65% decolorization of Disperse Yellow 5G, 41% decolorization of Direct Fast Orange S, and 50-51% decolorization of Reactive Turquoise Blue G. Immobilized yeast cells were active in decolorizing the dyes and SDS-PAGE analysis confirmed the presence of an extracellular protein. The results of FTIR also showed changes in the functional group of Direct Pink B, but minimal changes in the functional groups of Reactive Turquoise Blue G, indicating a different decolorization pathway. Yeasts in co-cultures and consortia can decolorize toxic synthetic dyes through different decolorization pathways such as enzyme degradation and bioaccumulation. This technique may have a use in the treatment of wastewater systems.

PEI-based hydrogels with different morphology and sizes: Bulkgel, microgel, and cryogel for catalytic energy and environmental catalytic applications

Polyethyleneimine (PEI)-based hydrogels with different morphologies as bulkgel, microgel, and a cryogel form were synthesized, and used as templates for in situ Co, Ni, and Cu metal nanoparticles preparation. Because of the size, porosity and morphological differences of the prepared PEI-based hydrogels (bulkgel, microgel and cryogel), interesting and versatile applications were shown. The prepared PEI-M (M: Co, Ni) hydrogel composite systems were used as catalysts for the hydrolysis of NaBH4 for H2 production, in the reduction reaction of 4-, and 2- nitrophenols (4-NP, and 2-NP) to their corresponding amino forms, 4-AP and 2-AP, respectively, and in the decolorization reaction of methylene blue (MB) and Eosin Y (EY) dyes (EY) (M: Cu). It was shown that without a metal catalyst, bare NaBH4 is not good source of H2 sources e.g., in the hydrolysis of NaBH4 for H2 production, the self-hydrolysis of NaBH4 can only produce 152±2.5mL H2 in 280min whereas the same amount of NaBH4 can produce 250mL for under 60min in the presence of Co nanoparticles within PEI matrices. It was found that the reduction reactions of 4-, and 2-nitrophenols to 4-, and 2- aminophenols, and the decolorization of dyes also required metal nanoparticles catalysts within PEI hydrogel. The hydrogen generation rate (HGR, ml H2/(g of cat)(min)), and turnover frequency (TOF, mol H2/(molcat)(min)) values were calculated and compared for PEI hydrogels with different sizes and morphologies. Higher HGR and TOF values were observed in H2 production using PEI-Co microgel composite catalyst systems than PEI-Co bulk hydrogel and cryogel composite catalyst systems with 424ml H2/(g of cat)(min) and 0.98mol H2/(mol cat)(min) respectively. The higher TOF value was observed for the reduction reaction of 4-, and 2-NPs to their corresponding amino forms as 0.881, and 1.323mol H2/(mol cat)(min), respectively catalyzed by PEI-Ni cryogel composite systems than PEI-Ni microgel and bulkgel composite catalyst system. Better Ea value for H2 production was calculated for PEI-Ni microgel composite systems with 38.3J/molK. And the activation energy values for reduction of 4-NP to 4-AP by PEI-Cu composite cryogel system, and for reduction of 2-NP to 2-AP by PEI-Ni composite cryogel system were calculated as 15.2 and 29.6J/molK, respectively. The catalytic performances of PEI-Cu hydrogel composite system for decolorization of MB and EY in different media such as sea water, creek water, tap water, and distilled water were compared and the PEI-Cu cryogel composite provided the fastest decolorization capabilities for both dyes. Interestingly, amongst all the media, MB and EY decolorization in seawater by PEI-Cu cryogel was accomplished in 2 and 9min with 96.3% and 97.3% decolorization, respectively, with the same catalyst system.

Immobilization of horseradish peroxidase onto kaolin.

Kaolin showed as a very perspective carrier for the enzyme immobilization and it was used for the adsorption of horseradish peroxidase (HRP). The effects of the enzyme concentration and pH on the immobilization efficiency were studied in the reaction with pyrogallol and anthraquinone dye C.I. Acid Violet 109 (AV 109). In addition, Fourier transform infrared spectroscopy, scanning electron microscopy and analysis by Brunauer-Emmett-Teller were performed for kaolin, thermally activated kaolin and the immobilized enzyme. It has been shown that 0.1 IU of HRP-kaolin decolorized 87 % of dye solution, under the optimal conditions (pH 5.0, temperature 24 °C, dye concentration 40 mg/L and 0.2 mM of H2O2) within 40 min. The immobilized HRP decolorization follows the Ping Pong Bi-Bi mechanism with dead-end inhibition by the dye. The biocatalyst retained 35 ± 0.9 % of the initial activity after seven cycles of reuse in the decolorization reaction of AV 109 under optimal conditions in a batch reactor. The obtained kinetic parameters and reusability study confirmed improvement in performances of k-HRP compared to free, indicating that k-HRP has a great potential for environmental purposes.

Development of Three-Dimensional Electrodes of PbO2Electrodeposited on Reticulated Vitreous Carbon for Organic Eletrooxidation

The application of electrochemical technology for the degradation of organic pollutants often faces two main problems, related to the anode material and mass transport limitations. Although PbO2 electrode is inexpensive and provides satisfactory electrooxidation kinetics, in the form of plane electrodes it is unable to resolve the mass transfer problem that arises at low concentrations of organics. In this work, an electrochemical flow reactor was developed for the preparation of three-dimensional electrodes consisting of PbO2 films electrodeposited onto reticulated vitreous carbon. The electrodes were characterized in terms of the substrate coating, morphology, structure, and electrocatalytic activity in the decoloration reaction of Reactive Blue 19 dye. The results showed that it was possible to deposit a uniform film of PbO2 on the surface of the substrate after optimization of the current density and deposition time (0.7 mA cm-2 for 30 min). Comparison of the plane and three-dimensional electrodes revealed that the turbulence generated by the porous matrix significantly accelerated the dye decoloration kinetics, increasing 3.3-fold the first order kinetic constant (from 0.010 min-1 for VC/PbO2 to 0.033 min-1 for RVC/PbO2).

A sensitive kinetic spectrophotometric determination of traces of tungsten in solution based on its inhibitory effect on the decolorization reaction of potassium permanganate

The present work describes a rapid and sensitive method for the determination of ultra micro amounts of tungsten (VI) based on its inhibitory effect on the oxidation of 4-hidroxycoumarine by potassium permanganate in the presence of hydrochloric acid. The sensitivity of the method is 20 ng/cm3. The probable relative error is -4.8-13 % for the W(VI) concentration range 250 to 20 ng/cm3, respectively. Kinetic equations for the investigated process which determine the order of the reactions regarding to each reaction parameter under certain experimental conditions were proposed, and they allowed quantification of the unknown concentrations W(VI) in solution. The detection and quantification limit of the method are 4.5 and 15.1 ng/cm3. The effects of certain foreign ions upon the reaction rate were determined for the assessing the selectivity of the method.

Synthesis and characterization of [Zn–Al] LDH: Study of the effect of calcination on the photocatalytic activity

The photocatalytic decolorization of methylene blue (MB) was performed using [Zn–Al] layered double hydroxides (LDH) either as such or calcined. The prepared photocatalysts were characterized by XRD, ICP, TEM, nitrogen physisorption at −196°C and DRS. Photocatalytic study showed that [Zn–Al] LDH without any treatment presented the best photocatalytic activity which was even better than that of commercial ZnO nanoparticles. It provided a decolorization percentage of 90% after 1h irradiation time.The influence of dye concentration, solution pH, photocatalyst dose and some inorganic anions on the photodecolorization of MB was investigated. Results showed that an acidic pH reduced the effectiveness of the photocatalytic process however an alkaline pH slightly improved the reaction. The presence of Cl−, NO3− and CO32− leads to a decrease in the decolorization rate of the dye contrary to SO42− which improved the reaction. The optimum mass of photocatalyst corresponded to 0.49mmol of Zn.The decolorization reaction followed a Langmuir–Hinshelwood model only at low concentrations of MB.

Biodegradation of dye-containing wastewater by fusant strains using a sequential anaerobic–aerobic process

A fusant strain T1, which was constructed by protoplast fusion between Acinetobacter sp. SRL8, Escherichia sp. XBR68 and Acinetobacter sp. RC10, could simultaneously decolorize three different dyes, namely reactive brilliant blue XBR, disperse orange SRL, and red base RC. Maximum decolorization of initial 30 mg L−1 was achieved at pH 7.0, 35°C and 3% inoculum (v/v) under anaerobic condition during 24 h incubation. The decolorization ratio for XBR, SRL, and RC by the strain T1 could reach 91.5, 87.6, and 65.7%, respectively. Supplementation with appropriate concentration of glucose (0.2%, w/v) in the decolorization reaction system could further enhance decolorization percent. The strain T1 was highly tolerant to three different dyes up to 400 mg L−1. Biological decolorization of the three different dyes by the strain T1 was investigated in a sequential anaerobic/aerobic process. The reaction system was operated at room temperature. The results indicated that over 95% color removal was obtained in anaerobic process and 97.6% COD removal occurred in the aerobic process.

Sulfur K-edge XANES for methylene blue in photocatalytic reaction over WO3 nanomaterials

We investigated the photocatalysis of dendritic nanostructured WO3/W composite materials fabricated by He plasma irradiation to tungsten plates, followed by the surface oxidation. The samples promoted the decolorization reaction of methylene blue (MB) aqueous solution under near infrared (NIR) light irradiation. To verify the MB molecule is actually decomposed by the photocatalysis of the samples, reaction products were analyzed by S K-edge XANES measurements for the MB solution kept with the samples under the light irradiation or in the dark.By the light irradiation, the σ*(S–C) peak in the XANES spectra reduced and a new peak originated from SO42− species was clearly observed, suggesting that S–C bonds in a MB molecule are broken by the NIR light irradiation and finally the sulfur species exists in the solution in the state of SO42− ion. After the adsorption reaction in the dark, the XANES spectra of the sample surfaces showed a sharp π*(S–C) peaks, indicating that MB molecules are adsorbed on the sample surfaces and stacked each other by the π–π interaction. These results demonstrate that the photocatalytic decomposition of MB molecules really proceeds over WO3/W composite materials even under NIR light irradiation.

Effect of biological mediator, 3-hydroxyanthranilic acid, in dye decolorization by Fenton processes

The fungal metabolite 3-hydroxyanthranilic acid (3-HAA), commonly produced by the white-rot fungus Picnoporus cinnabarinus, presents Fe3+-reducing activity and was used as redox mediator to increase the degradation of dyes by classical Fenton (Fe2+/H2O2) and Fenton-like reactions (Fe3+/H2O2) in solution. The experimental results were estimated in terms of decolorization to examine the treatment efficiency. 3-HAA displayed prooxidant properties in the decolorization of methylene blue, chromotrope 2R, methyl orange, phenol red, safranin T, and a mixture of dyes, and its use resulted in a more intense and continuous dye decolorization. For example, Fe2+/H2O2 decolorized 27% of safranin T, whereas Fe2+/H2O2/3-HAA decolorized 63% of the same dye after 60 min of reaction. The dyes were not decolorized in the presence of 1% (v/v) tert-butanol, which is an OH scavenger, confirming the involvement of this radical in the decolorization reactions. Assays concerning the influence of the concentration of 3-HAA showed that maximum decolorization of phenol red was reached at 30 μmol L−1 of this mediator. On the other hand, antioxidant property was observed at high concentration of this compound (above 90 μmol L−1). Generally, the consumption of H2O2 was increased in the reactions containing 3-HAA.