Azo Dye In Aqueous Solution Research Articles

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.

Functionalized Cellulose for the Controlled Synthesis of Novel Carbon-Ti Nanocomposites: Physicochemical and Photocatalytic Properties.

Carbon–Ti nanocomposites were prepared by a controlled two-step method using microcrystalline cellulose as a raw material. The synthesis procedure involves the solubilization of cellulose by an acid treatment (H3PO4 or HNO3) and the impregnation with the Ti precursor followed of a carbonization step at 500 or 800 °C. The type of acid treatment leads to a different functionalization of cellulose with phosphorus- or oxygen-containing surface groups, which are able to control the load, dispersion and crystalline phase of Ti during the composite preparation. Thus, phosphorus functionalities lead to amorphous carbon–Ti composites at 500 °C, while TiP2O7 crystals are formed when prepared at 800 °C. On the contrary, oxygenated groups induce the formation of TiO2 rutile at an unusually low temperature (500 °C), while an increase of carbonization temperature promotes a progressive crystal growth. The removal of Orange G (OG) azo dye in aqueous solution, as target pollutant, was used to determine the adsorptive and photocatalytic efficiencies, with all composites being more active than the benchmark TiO2 material (Degussa P25). Carbon–Ti nanocomposites with a developed micro-mesoporosity, reduced band gap and TiO2 rutile phase were the most active in the photodegradation of OG under ultraviolet irradiation.

A green synthesis of nanocatalysts based on reduced graphene oxide/magnetic nanoparticles for the degradation of Acid Red 1.

The increasing amount of organic dye-polluted wastewater from the textile industry makes the development of techniques for the efficient purification and reuse of wastewater an urgent issue. Accordingly, solid adsorbents based on three-dimensional (3D) reduced graphene oxide (rGO) aerogels combined with magnetic nanoparticles (rGO@Fe3O4) appear to be potential materials, which offer fast and efficient discoloration of dye solutions by dye adsorption, simultaneously acting as Fenton reaction nanocatalysts, and thus may eliminate organic dyes. In this work, 3D rGO@Fe3O4 aerogel nanocatalysts were synthesized via a low-energy, simple, one-step in situ method, in which GO and FeSO4·7H2O were simultaneously reduced. Consequently, monolithic porous nanocatalyst 3D structures were obtained, with a specific surface area of 241 m2 g−1 and pore volume 0.39 cm3 g−1. The nanocatalysts were applied for the degradation of Acid Red 1 azo-dye in aqueous solution in the presence of hydrogen peroxide, without the need for external energy. The effect of the adsorbent dose, and concentration of dye and peroxide on the dye removal was studied. The degradation of the dye was monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. It was found that an increase in the amount of peroxide allowed complete degradation of the dye together with high molar mass side-products with a conjugated aromatic structure. The good nanocatalyst performance was explained based on the charge-transfer complex established between rGO and the magnetic nanoparticles, allowing the regeneration of ferrous ions during the Fenton process.

Evaluation performance of Fe–Mn–Ce–O mixed metal oxides and Fe–Mn–Ce–O/Montmorillonite for adsorption of azo dyes in aqueous solution and oxidation reaction

The present study focused on synthesis of A–Fe–Mn–Ce–O, B–Fe–Mn–Ce–O and B–Fe–Ce–Mn–O/montmorillonite (B–Fe–Ce–Mn–O/MMT), (A and B differ in the method of preparation). The structure and morphology of the as-synthesized nanocomposites were characterized by FTIR, FESEM, XRD and EDX. The adsorption behavior of the prepared samples was tested through elimination of MB and RhB from aqueous solution. The effect of different parameters namely amount of adsorbent, pH, contact time, temperature, thermodynamics and equilibrium of adsorption were investigated. Based on the results, for A–Fe–Mn–Ce–O and B–Fe–Mn–Ce–O/MMT the adsorption process is endothermic, spontaneous and langmuier isotherm model best fitted the data. Comparison of the maximum adsorption capacity obtained for the adsorption of MB on synthetic adsorbents is as follows: B–Fe–Mn–Ce–O/MMT > A–Fe–Mn–Ce–O > B–Fe–Mn–Ce–O. In the next step, A–Fe–Mn–Ce–O, B–Fe–Mn–Ce–O and B–Fe–Ce–Mn–O/MMT were applied as catalysts in oxidation reaction. The investigation revealed that A–Fe–Mn–Ce–O catalyzed oxidation of benzyl alcohol with H2O2 as green oxidant yielded benzaldehyde (<99% selectivity) with 99% conversion. It was found that with B–Fe–Mn–Ce–O as catalyst, <99% conversion was achieved to <99% selectivity for 1-Phenyl-1,2-ethanediol. Comparison of the catalytic activity of the nanoparticles obtained in the oxidation reaction is as follows: A–Fe–Mn–Ce–O > B–Fe–Mn–Ce–O > B–Fe–Mn–Ce–O/MMT.

Degradation of azo dye under visible light irradiation over nanographene oxide–zinc oxide nanocomposite as catalyst

Nanographene oxide (NGO) was prepared from natural graphite flakes via modified Hummer’s method. Nanocomposite of NGO and zinc oxide (NGO–ZnO) in the ratio of 1:1 was prepared by sol–gel method. Structural and physiochemical properties of the synthesized NGO and NGO–ZnO nanocomposite were investigated with the help of powder X ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope coupled with energy-dispersive X ray analysis (SEM/EDX), thermal gravimetric analysis and differential scanning calorimetry (TGA/DSC) and atomic force microscopy (AFM). The PXRD results showed the conversion of graphite to nanographene oxide. It was observed from the FTIR spectra that graphite oxidized by strong oxidant KMnO4 showed the presence of oxygen atoms on the graphite layer. Thus, certifies the presence of oxygen-containing functional groups COOH, C=O, C–O–C in GO films. SEM image indicated the morphology of NGO and inclusion of nano-zinc oxide in graphene layer. EDS analyzed the components in the material. Percentage of oxygen in NGO shows extensive oxidation of graphene layer and percentage of zinc calculated by EDS agreed with theoretical ratio. TGA/DSC analyzer indicated the thermal stability of the material. AFM indicated exfoliation of graphite to graphene. Photocatalytic activities of the prepared samples were evaluated by degradation of rhodamine 6B (Rh 6B) azo dye in aqueous solution. From the measured absorbance values, the photocatalytic activity of NGO–ZnO nanocomposite was found to be excellent than pure NGO.

Photoelectro-peroxone process for the degradation of reactive azo dye in aqueous solution

ABSTRACT This study evaluated the degradation of reactive yellow F3R (RY F3R) dye by photoelectro-peroxone (PEP) process. The study showed that the PEP gave 97.66% colour and 84.64% TOC removals at 1.176 h−1 which were 14 and 1.4 times greater than photolysis and electro-peroxone processes, respectively. Quenching experiment showed that hydroxyl radical and singlet oxygen were predominant oxidizing species in RY F3R degradation. In addition, results of the colour and TOC removal by the application of PEP to real field textile wastewater showed that PEP offer an efficient and propitious technology for organic pollutant degradation.

Comparison of performances of hydrodynamic cavitation in combined treatments based on hybrid induced advanced Fenton process for degradation of azo-dyes

In the present work, the degradation of azo-dyes in aqueous solutions by using hydrodynamic cavitation is performed. Methyl orange was chosen as colorant model pollutant. During the experimental tests, the effect of various operating parameters on the decolourization efficiency was investigated. In the first series of experiments, the hydrodynamic cavitation was optimized in terms of operating inlet pressure and cavitation number to get the maximum decolorization yields of the dye, at the constant temperature of 20 °C and with an initial methyl orange concentration equal to 5 ppm. It was observed that there was an optimum inlet pressure value (4 bar) to get the best decolourization efficiency (about 32%). For the optimal configuration, in correspondence of 4 bar, a first order kinetic equal to 0.0054 min −1 and a value of electrical energy per order EEO of 3793.81 kW h m-3 were calculated. Subsequently, the combined effect of hydrodynamic cavitation and hydrogen peroxide on dye degradation has been studied. The efficiency of the HC-H2O2 system, under optimal conditions, was more than 50% in terms of dye decolourization. Finally, a series of experiments have been performed by combining hydrodynamic cavitation with the addition of hydrogen peroxide and metal ions (iron and nickel) in solution. The dye degradation became greater than 90%; this increase was explained by supposing that an induced advanced Fenton process has been generate thus improving the performance of the entire cavitation system.

Catalytic degradation of real-textile azo-dyes in aqueous solutions by using Cu–Co/halloysite

Catalytic degradation of textile dyes in diluted aqueous solutions with minimal consumption of energy is a great challenge for wastewater treatment and environmental protection. Efficient heterogeneous catalysts are needed to completely oxidize azo-dyes under soft conditions. In this work, catalysts of Cu–Co oxide (1:2 molar ratio) supported on halloysite (Ha) nanotubes (CuCo(5%)/Ha and CuCo(10%)/Ha) were synthesized and used in the catalytic wet peroxide oxidation of reactive yellow 145 (RY-145) and basic red 46 (BR-46). The catalysts were characterized by chemical analysis, X-ray diffraction, Raman spectroscopy, \(\hbox {N}_{2}\) adsorption isotherms, scanning electron microscopy and transmission electron microscopy. The results showed that the synthesized catalysts possess nanotubular structure with good mesoporosity, and the spinel structure \(\hbox {CuCo}_{2}\hbox {O}_{4}\) was identified as the active phase deposited on Ha. The catalysts degraded these azo-dyes in diluted solutions (\(22\, \hbox {mg l}^{-1}\) of RY-145 and \(35\, \hbox {mg l}^{-1}\) of BR-46) under mild reaction conditions (\(25^{\circ }\hbox {C}\), atmospheric pressure, pH 4 and minimum amounts of both catalyst and \(\hbox {H}_{2}\hbox {O}_{2})\). Significant levels of dye conversion (\(93.1\pm 2.2\%\) for RY-145 and \(54.4 \pm 2.0\%\) for BR-46) were achieved in a relatively short time. In addition, significant values of total organic carbon removal (\(59.5 \pm 1.8\%\) for RY-145 and \(33.9 \pm 1.4\%\) for BR-46) were obtained, indicating the total oxidation of a significant fraction of these dyes to \(\hbox {CO}_{2}\) and \(\hbox {H}_{2}\hbox {O}\).

Cu doped TiO2-Bi2O3 nanocomposite for degradation of azo dye in aqueous solution: Process modeling and optimization using central composite design

Cu doped TiO2-Bi2O3 hybrid as a visible active photocatalyst was syhthesized by a sol-gel method and the weight fraction of Cu (1–5 wt. %), and Bi2O3 (3–8 wt. %) was optimized using response surface methodology. The photodegradation of methyl orange (MO) was carried out to evaluate photoactivity properties of the prepared samples under visible light irradiation. The Cu-TiO2-Bi2O3 nanocomposite with a weight fraction of 1 and 8% for Cu and Bi2O3 has the best photocatalytic activity for MO degradation. The characteristics of photocatalyst with optimum composite (1 wt. % of Cu and 8 wt. % Bi2O3) were also investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance spectra (DRS). The DRS spectra approved that the adsorption wavelength of Cu doped TiO2-Bi2O3 is in the visible light range (470 nm).The influence of amount of catalyst (0.8–1.2 g L−1), MO concentration (10–20 mg L−1)and initial pH of the solution(4–6) in on MO photodegradation was modeled and optimized using central composite designe based on response surface methodology.The value of MO removal decreases by about 15% when MO concentration increases from 10 to 20 mg L−1. Maximum dye removal was achieved about 74% at 10 mg L−1 of MO, 1.2 g L−1 catalyst loading and pH of 4.

Polyaniline/attapulgite-supported nanoscale zero-valent iron for the rival removal of azo dyes in aqueous solution

In this paper, polyaniline/attapulgite (PANI/APT)-supported nanoscale zero-valent iron (nZVI) composites were synthesized by liquid-phase chemical reduction method and used for the removal of two kinds of dyes. The structure of as-prepared nZVI/PANI/APT was characterized by various test methods. The removal property and degradation mechanism for azo (alizarin yellow R, methyl red, chrome black T, methyl orange) and non-azo (methylene blue, rhodamine B) dyes in aqueous solution were investigated. The presence of PANI/APT can decrease the aggregation of nZVI particles with maintenance of reactivity and improving adsorption capacity for degradation azo dye. The experiment results showed that the removal property of the composite materials on azo dyes is obviously better than that on non-azo dyes. The varying removal efficiencies of dyes depend on the different degradation mechanisms. Azo dyes removal by nZVI/PANI/APT was mainly due to the reductive cleavage of the N = N of nZVI, while non-azo dyes removal mainly contributes to the adsorption of PANI/APT. The study demonstrated that nZVI/PANI/APT has potential applications for the removal of azo dyes from wastewaters.

SrSnO3 perovskite obtained by the modified Pechini method—Insights about its photocatalytic activity

The use of SrSnO3 as a photocatalyst in different applications has been growing in recent years, particularly for degradation of organic dyes. In the present work, SrSnO3 catalyst was synthesized by the modified Pechini method and applied in the photocatalytic degradation of a textile azo-dye in aqueous solution under ultraviolet irradiation. The dominant photocatalytic species for this system were evaluated, determined from terephthalic acid photohydroxylation and from different scavengers. Moreover, electrochemical data were used to evaluate charge transfer between SrSnO3 and the species involved in the photocatalysis – O2, H2O and the scavengers. The irradiation time required to achieve 98% decolorization of a Remazol Golden Yellow (RNL) solution was 10 h. The catalyst simultaneously reduced all the absorption bands in the UV–vis spectrum of RNL, suggesting pollutant degradation. Isopropanol, silver and formic acid were all employed to test the importance of different photocatalytic processes and the photohydroxylation of terephthalic acid confirmed the generation of OH. A comparison of the SrSnO3 band positions and the potential of relevant redox couples suggests possible mechanisms for OH generation from both photogenerated carrier types (electrons and holes), in agreement with the results obtained using the hole/electron scavengers.

Experimental evaluation of Reactive Yellow 17 degradation using UV light and iron ions activated peroxydisulfate: Efficiency and kinetic model

In the present study, the degradation of Reactive Yellow 17 (RY17) azo dye in aqueous solution was performed using UV light and iron ions as activators of peroxydisulfate (S2O82− or PDS). The effect of several parameters affecting the degradation process was studied and the optimum conditions are found to be: [RY17] = 10 mg/L, [Fe2+] = 0.05 mM, [S2O82−] = 1 mM and the pH = 3. The obtained results showed that the removal degrees of RY17 using different processes such as S2O82−/Fe2+, S2O82−/UV and S2O82−/Fe2+/UV was 63.3%, 81.0% and 95.4% respectively within 20 min of the degradation. Based on theses removal degrees, the degradation efficiency of the RY17 increases in the order: S2O82−/Fe2+/UV > S2O82−/UV > S2O82−/Fe2+ > UV > S2O82−. The experimental data were analyzed using the first-order, second-order and Behnajady-Modirshahla-Ghanbery (BMG) kinetic models, and the kinetic data were in good agreement with the BMG model. Under the optimal conditions, the comparative study of the RY17 degradation using two salts Na2S2O8 and K2S2O8 showed a strong similarity. The total mineralization was monitored using COD and TOC techniques. The results showed that the peroxydisulfate activated by UV and Fe2+/UV system is efficient for the degradation and mineralization of RY17; it could also be an alternative for the treatment of the real wastewater contaminated by azo dyes.

Study on the Reduction Properties of Thiourea Dioxide and Its Application in Discharge Printing of Polyester Fabrics

The thiourea dioxide (TDO) was tentatively applied as a reductive discharging agent onto the discharge printing of polyester fabrics. The effect of aqueous solution temperature on the reducing capacity of TDO was thoroughly investigated by measuring oxidation-reduction potentials and hydrolysis kinetic curves. The effects of TDO on disperse dyes in aqueous solution and disperse dyes printed on the surfaces of glass substrates or polyester fabrics were investigated by analyzing the color changes before and after TDO discharge treatment. It was confirmed that TDO reduction became stronger with increasing aqueous solution temperature. TDO could destroy the chromogenic groups of the selected azo-dyes in aqueous solution and on the surfaces of glass substrates. Different from cotton and silk fabrics, the discharge effect of TDO directly depended on the compact structure of the polyester fibers. When a discharge accelerant was added into white discharge pastes with TDO, the compact structure of polyester fibers was opened up to achieve a good discharge effect. This study provides a new method for TDO development and a new strategy for the discharge printing of polyester fabrics.

Degradation of orange II dye under dark ambient conditions by MeSrCuO (Me = Mg and Ce) metal oxides

Abstract This work investigates the catalytic performance and materials property of ternary metal oxides as Me0.25Sr0.25Cu0.5O (Me = Mg and Ce). The catalysts were tested for the heterogeneous degradation of orange II (OII) azo dye in aqueous solution in the dark at room temperature without any other reagents or energy/light irradiation. The MeSrCuO degraded more than 97% OII in the first 30 min, higher than that of binary metal oxides SrCuO (90.5%) or single metal oxides CeO2 (23.6%) and MgO (23.3%). The degradation pathway predominantly occurred by OII contacting the catalyst surface and resulting in the breakdown of azo bonds and the generation of electrons. Partial mineralization of OII dye occurred thus confirming the generation of radical species. Hence, electrons reacted with dissolved O2 in the OII aqueous solution, leading to the consecutive formation of reactive radical species (e.g., O2 −, HO2 , H2O2, OH). Radical trapping experiment confirmed the presence of radical species. XPS analysis revealed part of Cu2+ underwent irreversible reduction after reaction due to the electron donation from OII with the accompanied increase in Cu+ species in the spent samples. Cycling tests confirmed the reduction of the catalytic activity, clearly indicating that Cu2+ was the active phase in MeSrCuO for the degradation of OII dye.

&lt;b&gt;Influence of pH and concentration on the decolorization and degradation of BR red azo dye by ozonization

Ozone application has been generally reported based only on the oxidation of textile dyes. In this study, a central composite design and surface response methodology were applied to optimize operational parameters pH and concentration of the dye in the decolorization process. The oxidation of Corafix BR Red Azo dye in aqueous solutions was carried out in a semi-batch bubble column reactor with ozone production at 0.702 g hour -1 . Tests were performed at pH 4, 7 e 10 and initial dye concentration of 50, 100 and 150 mg L -1 . The maximum removal efficiency was 98% for pH 10 and initial dye concentration of 50 mg L -1 with pseudo-first order constant rate (k 1 ) of 0.0595 min -1 . Statistical analysis determined the influence of pH and dye concentration in the decolorization process. The pH presented a positive effect on the decolorization while the variation in dye concentration had a negative effect on the same variable, indicating the higher the pH and the lower the initial concentration of dye, the higher the efficiency. Toxicity tests performed before and after ozonization showed acute toxicity for the test organism Daphnia similis with higher percentage of mortality after ozonization.

Ozonation of Reactive Orange 4 dye aqueous solution using mesoporous Cu/SBA-15 catalytic material

The catalytic ozonation using mesoporous SBA-15 supported copper catalyst (Cu/SBA-15) was employed for the degradation of reactive orange 4 (RO4) azo dye in aqueous solution. The catalyst was synthesized and characterized using BET, SEM, TEM and EDX techniques. The characteristic results revealed highly ordered mesoporous structure, uniform pore sizes, parallel arranged channels and large surface area for the catalyst. The effects of copper loading on SBA-15, initial solution pH and ozone dose on the degradation of RO4 dye were studied. The complete colour removal from RO4 azo dye aqueous solution was obtained after 21 min of ozonation. The maximum TOC removal efficiency of 86% was obtained at optimum operational conditions of 2% copper loadings, initial solution pH 9 and ozone dose of 5 g/m3 after 60 min reaction time. The degradation pathway of catalytic ozonation reaction was studied by adding t-butanol as radical scavenger and it was found that the presence of radical scavenger had no effect on colour removal efficiency suggesting direct ozone molecular type mechanism. However, TOC removal efficiency was significantly reduced with the addition of t-butanol, thereby, indicating a hydroxyl radical based mechanism. The catalytic ozonation reaction followed pseudo-first order kinetics with respect to RO4 dye concentration. The reusability study for the catalyst suggested a negligible loss in the degradation efficiency after five runs of experiments. The stability of the catalyst was studied by performing leaching experiments which suggested that the catalyst has the potential to be utilized for the degradation of aqueous dye solution.

Physicochemical Study of Gamma-irradiated mono azo dye in aqueous Solutions as liquid dosimeter

AQUEOUS solutions of pH indicator (mono azo dye) Amacid Yellow M (AYM) dye were titrated by different concentrations of (H+) resulting from irradiation decomposition of trichloroethylene (ClHC=CCl2) (TCE) solution for possible use as an monitoring device (label) for gamma radiation. The titrated solutions were readout spectrophotometrically. These solutions can be used qualitatively as routine indicators in the 0.5–5 kGy range because they have stable change in color for (AYM) from yellow to red at 540 nm depending on irradiated trichloroethylene [H+]. The effective dose range exceeds in this technique due to avoiding direct exposure of dye to gamma radiation, utilizing back titration technique followed by color measurements using spectrophotometer. Moreover, the useful measuring range was found to be 5kGy. The solutions can be used qualitatively as routine indicators in the range of 0.5 to 2kGy. Further calculations such as rate of reaction (r) and kinetic constant (k) have been assigned.

Easy preparation of gold nanostructures supported on a thiolated silica-gel for catalysis and latent fingerprint detection

Herein, we report an extremely simple, fast and controllable method for preparing gold nanoclusters (GNC) and gold nanospheres (GNS) in situ onto a thiol-organofunctionalized silica gel (MPS) for catalysis and detection of latent fingerprints (LFPs). The silica gel surface was suitably modified with thiol groups by a silylation reaction method using 3-(mercaptopropyl)trimethoxysilane (MPTS). Spectroscopic data (UV-visible-NIR and PL) have shown that the as-prepared thiol-modified silica is able to reduce Au3+ ions in situ, producing orange-red light emitting GNCs. For preparing GNS, on the other hand, it was necessary an adsorption step followed by a reduction with NaBH4. Various experimental conditions for the preparation of GNS were studied, such as the gold precursor and reducing agent concentrations and the reaction time. TEM, XRD and UV-visible-NIR analyses showed, respectively, the presence of approximately spherical particles with a face-centered cubic structure and a plasmon resonance band, which is controllable by changing those synthesis parameters. The as-prepared samples have shown high catalytic activity for the reduction of an AZO dye in aqueous solution, being able to decolorize 92% of the dye content within only 40 min. GNS/MPS and bare MPS have also shown enhanced activity for detecting LFPs deposited over porous and non-porous surfaces, including glass, polymer, paper, metal, leather, ceramic and wood. Our method has shown to be a suitable alternative for conventional techniques, it is easier to apply, fast-responsive, reusable, durable and thermally stable.

Acid–Base Properties of Azo Dyes in Solution Studied Using Spectrophotometry and Colorimetry

Colorimetry and spectrophotometry with chemometric data processing were used to study the acid–base properties of azo dyes in aqueous solution. The capabilities of both methods were compared. Ionization constants of all the functional groups of the azo compounds studied could be determined relative to the change in the specific color difference depending on the acidity of the medium. The colorimetric functions of ion-molecular forms of azo compounds used as an analytical signal allow us to obtain complete information on the acid–base equilibrium in a wide acidity range.

Mechanism studies on methyl orange dye degradation by perovskite-type LaNiO3-δ under dark ambient conditions

Perovskite materials have attracted much attention in heterogeneous catalysis. Here, we report a perovskite type material LaNiO3-δ (LNO) for degradation of methyl orange (MO) azo dye in aqueous solutions under dark ambient conditions (room temperature, atmospheric pressure) without additional lights or chemical stimulants. The high degradation percentage of 5ppm MO with 1.5g/L LNO was 94.3% after 4h with a stirring speed of 500rpm. Reactions under nitrogen, oxygen and carbon dioxide conditions were performed with efficiencies of 19.6%, 7.1%, and 96.8% respectively after 6h to understand the mechanism. MO was shown to degrade under dark ambient condition via main intermediates, sulfanilic acid anion and N,N-dimethyl-p-phenylenediamine (DPD), by electrospray ionization mass spectrometry (ESI/MS) and high performance liquid chromatography (HPLC). Degradation of MO under such a mild condition is due to two synergic effects proposed by means of XRD, FTIR, TGA, SEM, and XPS. Nickel is oxidized during MO degradation; lanthanum carbonate (La-analog calkinsite) is formed on the LNO surface due to the aqueous solution environment and speeds up azo bond cleavage. This work unravels the mechanism behind MO degradation by LNO under dark ambient conditions for the first time. It is a fundamental information on perovskite for dye degradation, especially for lanthanum series of perovskite. Excellent perovskite materials should be tailorable for water remediation applications considering the large variety of perovskites in terms of constituents and composition.