Exploiting stored TiO2 electrons for multi-electron reduction of an azo dye methyl orange in aqueous suspension

The mechanism of multi-electron reduction of methyl orange (MO) azo dye on TiO₂ nanoparticles has been studied performing stopped flow technique. A multi-electron reduction of azo dye has been investigated. It was found that a multistep reduction of the dye takes place: the stored electrons reduce the conjugative system of the azo group resulting in the decolorization of the dye and leading to the formation of hydrazine derivative followed by further 2 electron transfer step leading to the cleavage of the N–N bond and the formation of aromatic amines. The FTIR analysis of the products confirms the proposed mechanism of the dye reduction. The kinetic parameters and of the multi-electrons reduction of the MO have been determined. The rate of MO reduction was found to be dependent on both the TiO₂ electrons and the dye concentrations.     

Efficient peroxide decoloration of azo dye catalyzed by polyethylene glycol-linked manganese chlorin derivative

We reported here that polyethylene glycol (PEG)-linked manganese pyrochlorophyllide a (PEG-MnPChlide a) possesses remarkable catalytic activity comparable to horseradish peroxidase (HRP). The PEG-MnPChlide a catalyzed the oxidation decoloration reaction of C.I. Acid Orange 7 by hydrogen peroxide under a mild aqueous condition, pH 8.0 at 25 °C. The manganese pyrochlorophyride a methylester (MnPChlide a ME) dissolved in a Triton X-100 micellar solution also exhibited the catalytic activity, indicating the micellar environment plays an important role in the catalytic reaction. The reaction rate was accelerated by addition of imidazole. The catalytic reactions were analyzed by Michaelis–Menten kinetics, revealing that the higher reactivity of catalyst–substrate complex is responsible for the present catalytic reaction system.     

Analytical control of photocatalytic treatments: degradation of a sulfonated azo dye

The degradation of Methyl Orange (C₁₄H₁₄N₃SO₃Na), chosen as a model sulfonated azo dye, was investigated in aqueous solutions containing suspended polycrystalline TiO₂ particles under irradiation with simulated sunlight. The dye disappearance and the formation of the mineralization end products were monitored; the formation of the main transient intermediates was also examined in detail. Particular attention was devoted to the identification and to the evolution of fragments retaining the chromophoric group. The comparison of data coming from various analytical techniques led to a possible reaction mechanism for the degradation process, giving insight into an aspect of the treatment which has not been considered in previous studies.     

Metal complexes of azo compounds derived from 4-acetamidophenol and substituted aniline

The Ni(II) and Cu(II) complexes of four azo compounds (H₂L^1–4), namely, 2-(p-X-phenylazo)-4-acetamidophenol (X = OCH₃, NO₂, Br, and H for H₂L¹, H₂L², H₂L³, and H₂L⁴, respectively) were prepared and characterized on the basis of their analytical, spectroscopic, magnetic, and conductance data. The isolated complexes are found to have the general formulae [M(HL^1–4)Cl(H₂O)₃] (M = Ni(II) and Cu(II)). The chelates are found to have octahedral structure. The infrared spectra show that H₂L^1–4 ligands are coordinated to the metal ions in a uninegative bidentate manner, with NO donor sites of the azo N and the deprotonated phenolic O. The ligands and their chelates are subjected to thermal analysis. The biological activity of the synthesized ligands and their metal complexes also are screened against the adult Tribolium confusum mortality. They showed remarkable biological activity.     

Synthesis, NMR and X-ray characterisation of 6-substituted 4-amino-5-aryldiazenyl-1-arylpyridazinium salts

A new simple method has been used to prepare 6-substituted 4-(subst. amino)-5-aryldiazenyl-1-arylpyridazinium salts from N-methyl- or N-aryl-3-amino-1-phenylbut-2-en-1-ones and 4-aminopent-3-en-2-ones and substituted benzenediazonium tetrafluoroborates or hexafluorophosphates. The structure of selected derivatives was studied by means of ¹⁵N NMR spectra and X-ray.     

Simple route to a novel class of pyrazolidine-3,5-dione based azo dyes

We report an easiest synthesis strategy of a new class of synthetic dyes by coupling of functionalized pyrazolidine-3,5-dione derivatives via diazotization reaction with aromatic diamine for the azoic dyes or via dimerization reaction to synthesize the H chromophore dyes. Electron delocalization between the two coupled components has been studied using UV-vis spectroscopy, infrared, and NMR spectroscopy. In addition, the formation mechanism of such compounds has been discussed.     

Synthesis and dyeing performance of a novel polycarboxylic acid azo dye

A novel reactive polycarboxylic acid dye was synthesized by the reaction of polymaleic anhydride（PMA） with 3-methyl-1-（4- sulfonylphenyl）-4-（4-aminophenylazo）-2-pyrazoline-5-one.The structure of the novel dye was characterized by FTIR,UV-vis and ¹³C NMR spectra.The dyeing properties of dye on cotton were tested,and the novel dye possessed high fixation and good fastness.     

Triorganotin(IV) esters of 2-{[ N -(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoic acid,instability of the cyclohexyl derivative

Three triorganotin(IV) esters of 2-{[N-(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoic acid were prepared and studied by IR and NMR spectroscopy and X-ray crystallography for the tributyl- and triethyltin(IV)-2-{[N-(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoates (2, 3). These compounds are monomeric in solution with four-coordinate tin. The hydrazo tautomeric forms are present in chloroform solution as well as in the solid state. The coordination geometries of tin in 2 and 3 are trigonal bipyramidal with all three carbons in equatorial positions, one carboxylic oxygen and the quinone-type oxygen from adjacent molecules are in axial positions forming centrosymmetric dimers with the ring containing 20 members. The yield of the tricyclohexyltin(IV) derivative (4) is much lower than 2 or 3, with instability towards moisture in solution. The product of the reaction with water is the bis(µ²-hydroxo)-bis{2-{[N-(2-oxo-2H-naphthalene-1-yliden)hydrazo]}benzoato}tetracyclohexylditin (4a) dimer. The tin is five-coordinate in the solid state by two cyclohexyl and two hydroxy groups, the last coordination site is occupied by a monodentate carboxy group. The dimeric form of this compound remains in chloroform solution.     

Thermal decomposition of the magnesium, zinc, lead and niobium chelates derived from 8-quinolinol

Solid M-Ox compounds, whereM represents Mg(II), Zn(II), Pb(II) and NbO(III), and Ox is 8-quinolinol, have been prepared. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and infrared absorption spectra (IR) have been used to characterize and to study the thermal stability and thermal decomposition of these compounds.The authors acknowledge the FAPESP (Proc. 90/2932-4), CAPES and CNPq for financial support.     

5-amino-2-methylpyridinium hydrogen fumarate: An XRD and NMR crystallography analysis

Single-crystal X-ray diffraction structures of the 5-amino-2-methylpyridinium hydrogen fumarate salt have been solved at 150 and 300 K (CCDC 1952142 and 1952143). A base–acid–base–acid ring is formed through pyridinium-carboxylate and amine-carboxylate hydrogen bonds that hold together chains formed from hydrogen-bonded hydrogen fumarate ions. ¹H and ¹³C chemical shifts as well as ¹⁴N shifts that additionally depend on the quadrupolar interaction are determined by experimental magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) and gauge-including projector-augmented wave (GIPAW) calculation. Two-dimensional homonuclear ¹H-¹H double-quantum (DQ) MAS and heteronuclear ¹H-¹³C and ¹⁴N-¹H spectra are presented. Only small differences of up to 0.1 and 0.6 ppm for ¹H and ¹³C are observed between GIPAW calculations starting with the two structures solved at 150 and 300 K (after geometry optimisation of atomic positions, but not unit cell parameters). A comparison of GIPAW-calculated ¹H chemical shifts for isolated molecules and the full crystal structures is indicative of hydrogen bonding strength.     

Enhanced visible-light-driven photodegradation of Acid Orange 7 azo dye in aqueous solution using Fe-N co-doped TiO2

FeN -co-doped TiO₂ photocatalysts are prepared by sol–gel method using titanium tetraisopropoxide, urea and iron(II) acetylacetonate as precursors of titania, nitrogen and iron, respectively. The prepared samples are analysed from chemical-physical point of view by X-ray diffraction (XRD), Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), specific surface area measurements and scanning electron microscopy (FESEM). UV–Vis DRS spectra evidence that the co-doping of TiO₂ with N and Fe leads to the narrowing of the band gap value (2.7 eV) with respect to Fe-doped TiO₂ (2.8 eV) and N-doped TiO₂ (2.9–3 eV). XRD patterns show that photocatalysts are mainly in anatase phase and Fe and N ions are successfully incorporated into the TiO₂ lattice. The average crystallite size of Fe-N co-doped TiO₂ is slightly lower than the other samples and equal to about 7 nm and the specific surface area of the co-doped sample results to be 117 m² g⁻¹. Photocatalytic performances of all prepared samples are evaluated by analysing the degradation of Acid Orange 7 azo dye under visible light irradiation. Photocatalytic efficiency obtained using FeN co-doped TiO₂ strongly increases compared to undoped TiO₂, N-doped TiO₂ and Fe-doped TiO₂ photocatalysts. In detail, using the co-doped photocatalyst, dye discoloration and mineralization result equal to about 90 and 83% after 60 min of LEDs visible light irradiation, underlining the best performances of the FeN co-doped TiO₂ photocatalyst both in terms of treatment time and electric energy consumption.     

Facile synthesis and properties of alkali-clearable azo disperse dye containing a carboxylic ester moiety

A yellow, alkali-clearable azo disperse dye containing a carboxylic ester moiety was readily synthesized from the reactant p-aminobenzoic acid by successive diazotization, coupling reaction, chlorination and esterification with ethanol. Then its molecular structure was characterized by FTIR,1H NMR,13 C NMR,mass spectrometry and elemental analysis. The synthesized dye and a similar control dye containing the acylamide moiety（I） were applied to dyeing poly（ethylene terephthalate） fabric and their washing and rubbing fastness properties with different post-treatment methods（reduction clearing and alkali clearing） were examined and compared. It is found that the ester-containing disperse dye shows good alkali-clear ability on poly（ethylene terephthalate） fabric and contaminates little to environment due to the absence of reductants, as well as low toxicity and easy recycling of the hydrolysates.     

染发剂中2-氨基-4-硝基苯酚和2-氨基-5-硝基苯酚的液相色谱-质谱法测定方法研究

2-氨基-4-硝基苯酚和2-氨基-5-硝基苯酚在染发剂中同时可用做氧化染发剂.在市场上氧化型染发剂占有70%～80%,是广泛使用的染发剂.     

UV/H2O2/草酸铁络合物光降解偶氮蓝染料的研究

光氧化法是近年来日益受人们重视的一种治理染料废水的新方法,而现有方法光量子效率低、光能耗大、处理费用高。已有研究表明草酸铁络合物有较高的光降解效率。而在到达地面的太阳辐射中,紫外辐射只占4％左右,所以研究弱紫外辐射下光降解染料废水意义重要。本文用6W低压汞灯光源,过氧化氢．草酸铁络合物光降解水溶液中的偶氮蓝染料,考察pH值、H2O2浓度、染料浓度及光强等因素对降解结果的影响,探讨以自然光为光源催化降解偶氮蓝染料的可行性。     

Synthesis,characterization and biological activities of some azo derivatives of aminothiadiazole derived from nicotinic and isonicotinic acids

In this study we synthesized the new compounds containing bis-1,3,4-thiadiazole 3(A–D)_n from many reaction steps (cyclization, diazotization and etherification respectively). The compounds have been characterized by melting point, FT-IR and ¹H NMR data. All the synthesized compounds have been evaluated in vitro for their antimicrobial activities against several microbes like: Escherichia coli, Klebsiellia pneumonia, Pseudomonas aeruginosa, Serratia marscens and Staphylococcus aureus and show that some of these compounds have very good antibacterial activity.     

Polyelectrolyte complexes. V. Solid‐state properties of some polycation/azo dye complexes controlled by the dye structure

The solid‐state properties of some polycation/azo dye complexes according to the dye structure were studied in this work. One polycation contained about 95 mol % N,N‐dimethyl‐2‐hydroxypropyleneammonium chloride units in the backbone (PCA₅), and eight azo dyes, different in either the number of sulfonic groups or their distribution, were used as opposite components. The selected azo dyes were as Crystal Scarlet, Congo Red, Crocein Scarlet MOO, Ponceau SS, Amaranth, Ponceau S, Direct Blue 1, and Direct Red 80. Information on the compensation degree of the oppositely charges was obtained by the elemental analysis of the solid‐state polycation/dye complexes (the experimental contents of chlorine, nitrogen, and sulfur were compared with the calculated values). Differential scanning calorimetry was employed to probe the strength of the intermolecular interactions in the PCA₅/dye complexes. Wide‐angle X‐ray diffraction was used to assess the supramolecular order of the solid‐state complexes. The physical properties of the PCA₅/azo dye complexes (the complex stoichiometry, glass‐transition temperature, decomposition temperature, and degree of supramolecular order) were influenced mainly by the dye structure but also by the polycation concentration and the presence of NaCl. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 264–272, 2003     

Synthesis and characterization of azo dyestuff based on bis(2-hydroxyethyl) terephthalate derived from depolymerized waste poly(ethylene terephthalate) fibers

This work aimed at effectively utilizing the chemically depolymerized waste poly(ethylene terephthalate)(PET) fibers into useful products for the textile industry.PET fibers were glycolytically degraded by excess ethylene glycol as depolymerizing agent and zinc acetate dihydrate as catalyst.The glycolysis product,bis(2-hydroxyethyl) terephthalate(BHET),was purified through repeated crystallization to get an average yield above 80%.Then,BHET was nitrated,reduced,and azotized to get diazonium salt.Finally,the produced diazonium salt was coupled with 1-(4-sulfophenyl)-3-methyl-5-pyrazolone to get azo dyestuff.The structures of BHET and azo dyestuff were identified by FT1 R and ~1H NMR spectra and elemental analysis.Nylon filaments dyed by the synthesized azo dyestuff with the dye bath pH from 4.14 to 5.88 showed bright yellow color.The performances of the dyestuff were described with dye uptake,color fastness,K/S,L~*,a~*,b~*.and △E~* values.     

Synthesis of new 2-amino-5-hydroxymethyl-2-thiazolines

A simple and convenient method is proposed for the synthesis of 2-amino-5-hydroxymethylthiazolines with various substituents in the amino group, which is based on hydrolysis of the corresponding 5-halomethyl derivatives of thiazoline in the presence of divalent lead oxide. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 456–463, 2007.     

Anaerobic reduction of a sulfonated azo dye, Congo Red, by sulfate-reducing bacteria

The capacity for anaerobic decolorization of a sulfonated azo dye, Congo Red, by a strain of a sulfate-reducing bacterium was evaluated. After optimizing the growth rate of the bacteria on a simple carbon source and terminal electron acceptor pair, lactate and sulfate, respectively, the effect of the dye concentration on their growth rate was analyzed. The decolorization rate was affected by the dye concentration in the growth medium. The azo-bond cleavage mechanism of reductive decolorization with the formation of benzidine was consistent with the results, as this metabolite was identified by high-performance liquid chromatography. Several fractions of the culture medium, including lysed cell extracts, were examined for the capacity to reduce the azo dye. This reduction capacity was found in the culture medium in which the cells had previously grown. The results showed that the mechanism of reductive decolorization of this sulfonated azo dye was extracellular and nonenzymatic, consistent with the production of sulfide anion by the microorganisms while growing on lactate and sulfate. The sulfide anions were the cause of the reduction leading to the disappearance of color in the medium. To increase the rate of decolorization, the presence of ferrous ion was also necessary together with the lactate and sulfate substrates.     

Effect of solvent on absorption and fluorescence spectra of a typical fluorinated azo dye for its acidic and basic structures

The effect of 15 polar solvents on absorption and fluorescence energies of a typical fluorinated azo dye, 4-(2,3,5,6-tetrafluoro-pyridin-4-yl azo)-phenol, was reported for its acidic, MH, and basic, M, structures.For MH, the absorption energy is described on the basis of multi-linear equation with Taft's π* (solvent polarity) and β (hydrogen bond acceptor) parameters while the fluorescence energy varies rectilinearly with free energy of transferring the proton to the surrounding solvent, ΔG_t°.For M, the hydrogen bonding donor ability of protic solvent, α, is a predominant factor which affects the absorption energy while in aprotic solvents, the absorption energy correlates linearly with Kirkwood function. As the ability of the solvent for hydrogen bonding increases, the absorption band width will increase in parallel with the transition energy.