Model Azo Dye Research Articles

Investigating the efficacy of Palladium Doped Ceria for the Photodegradation of Azo Dyes

Ceria (CeO2) was prepared by microwave assisted precipitation method while sonothermal method was utilized for the synthesis of palladium doped ceria (Pd-CeO2) photocatalyst. HR-TEM analysis confirms the face centered cubic geometry (FCC) of CeO2. The particle size of Pd-CeO2 calculated from HR-TEM analysis (7.6±2.18 nm) is in close relation with XRD (8.25±0.25 nm). The SAED pattern of Pd-CeO2 shows the poly crystallinity where the d-spacing was 0.31 and 0.30 nm which corresponds to CeO2 and Pd crystal facets 111 and 100 respectively. The amount of dopant and existence of Pd, Ce and O was confirmed from EDX spectra and elemental mapping. BET surface area analysis of CeO2 (64.45 m2/g), Pd-CeO2 (60.20 m²/g) revealed that the decrease in the surface area of CeO2 due to Pd loading which is confirmed by pore volume (0.079 cm³/g) for CeO2 and pore volume for Pd-CeO2 (0.073 cm³/g). The photocatalytic activity of Pd-CeO2 was screened against a model azo dye Acid red-4 (AR-4). The fluctuation of the rate of photodegradation (PD) of AR-4 was observed under different reaction conditions. Therefore, the reaction parameters were optimized to achieve best catalytic activity up to PD; 98%. The kinetic study suggests that the PD of AR-4 follows 1st order kinetics with regression coefficient (R2=0.973) and rate constant (k=0.024/min). Recycling study revealed the prolong use of catalyst without significant loss of activity. DFT study and experiments revealed the synergism of Pd on the photo response of CeO2. Perhaps this synergistic effect due to metal support interaction, causes redistribution of charges and Fermi energy levels. The synthesized catalyst showed potential application for the treatment of textile industrial effluents.

New insights into the mechanism of azo dye biodegradation by Lactococcus lactis

Azo dye reduction by syntrophic microbial communities is still unclear, with conflicting observations reported in the literature. In this study, the biodegradation mechanism of a model azo dye by Lactococcus lactis strain LLSP-01 isolated from an acidogenic reactor system was investigated. Proteomics and RT-PCR analysis results showed that LLSP-01 azoreductase (AzoL) was not expressed by the isolate during exposure to Direct Black 22. In contrast, the mechanism appears to involve biosorption by glycoconjugates, particularly exopolysaccharides (EPS) and rhamnolipids, as proteins from the LPS O-antigen metabolism were statistically higher expressed in cells challenged with the target compound. Based on the proteomic observations, it is hypothesized that Direct Black 22 is adsorbed into the biofilm matrix and indirectly reduced by an SDR family oxidoreductase, in a mechanism mediated by riboflavin carriers. Induction of a ring-cleaving dioxygenase in the presence of azo dye indicates further degradation of the resulting aromatic amines. The collected results show that azo dye reduction by L. lactis is mediated by enzymes with broad range specificity, and not the typical azoreductases. This information can assist in the design of new strategies for the bioremediation of textile azo dyes.

UV light assisted degradation of acid orange azo dye by ZVI-ZnS and effluent toxicity effects

Azo dyes, the most common synthetic dyes used in the textile industry, are known xenobiotic compounds and recalcitrant to conventional degradation treatments. As consequence, such contaminants are often discharged into the effluents, treating aquatic ecosystems. Among several processes, the use of zero valent iron (ZVI) represents a suitable alternative to degrade organic molecules containing azo bonds. However, its applications are limited by corrosion and loss of reactivity over the time. To overcome these constraints, ZVI has been coupled to a suitable semiconductor (ZnS) to get a catalytic composite (ZVI-ZnS) active under UV light. The present work deals with the degradation of acid orange (AO7), used as model azo dye, by UV/ZVI-ZnS, as one step treatment and in combination with an adsorption process by biochar. The influence of ZVI-ZnS concentration (0.25, 0.5, 1 and 2 g/L) and reaction time (0–160 min) on degradation of AO7 were investigated. Intermediates formation was monitored by ESI-FT-ICR-MS analysis and the effluent toxicity was assessed by using Artemia franciscana. The experimental results showed that the UV/ZVI-ZnS process at 1 g/L of catalyst allowed to achieve a removal of AO7 up to 97% after 10 min. An increase of the dye relative concentrations as well as the toxicity related to intermediates formations has been observed for treatment time higher than 10 min. The total removal of AO7 together with effluent toxicity reduction was obtained only after the combined treatment (UV/ZVI-ZnS + biochar).

Improved Laccase Encapsulation in Copper-Doped Zeolitic Imidazolate Framework-8 for Reactive Black 5 Decolorization

As the largest group of synthetic dyes, azo dyes can pose various health and environmental risks due to their widespread use and challenging degradation. Laccases are efficient green biocatalysts for the degradation of organic pollutants. Herein, we report the in situ packaging of laccase in copper-doped zeolitic imidazolate framework-8 (ZIF-8) for the decolorization of reactive black 5, which is a model azo dye. The immobilization support (Cu5/mZIF-8) was obtained via lowering the precursor ratio of ZIF-8 and incorporating copper ions during the synthesis process. Cu5/mZIF-8 were found to be nanospheres with an average diameter of around 150 nm. Laccase encapsulated in Cu5/mZIF-8 showed an activity recovery of 75.6%, which was 2.2 times higher than that of the laccase embedded in ZIF-8. Meanwhile, the immobilized laccase (Lac@Cu5/mZIF-8) showed a higher catalytic activity in organic solvents than that of the free enzyme. In the presence of a mediator, Lac@Cu5/mZIF-8 could remove 95.7% of reactive black 5 in 40 min. After four consecutive cycles, the dye decolorization efficiency declined to 28%. About four transformation products of reactive black 5 were identified via LC-MS analysis, and the potential decolorization mechanism was proposed. The results indicated that the immobilized laccase could be used as an efficient biocatalyst in dye decolorization.

Assessment of the superior photocatalytic properties of Sn2+-containing SnO2 microrods on the photodegradation of methyl orange

A microporous Sn2+-containing SnO2 material presenting microrod morphology and a surface area of 93.0 m2 g–1 was synthesized via a simple hydrothermal route. Sn2+ ions were detected in the interior of the material (15.8 at.%) after the corrosion of a sample through sputtering. The material’s optical properties have demonstrated the absorption of a considerable fraction of visible light up to wavelengths of 671 nm, due to the presence of Sn2+ states in the material’s band structure. The analysis of the internal crystalline structure of a single microrod was carried out with the aid of a focused ion beam microscope and indicated that the material is mesocrystalline down to nanoscale level. It was proposed that the Sn2+ ions occupy intergranular sites in the highly defective crystalline structure of the material and that Sn2+ states, as well as its relatively large surface area, are responsible for the material’s superior photoactivity. The synthesized material was tested as a photocatalyst to decompose hazardous contaminants in water. The photocatalytic performance of the material was much higher than those of commercial TiO2 and SnO2 materials, decomposing nearly all methyl orange (an azo-dye model) content in water (10 mg L–1) in 6 min under UV irradiation for a photocatalyst dose of 5.33 g L–1. The photodegradation of methyl orange was also verified under visible light.

Exploring the functionality of an active ZrF-laccase biocatalyst towards tartrazine decolorization

This work describes the design and fabrication of zirconia-fucoidan (ZrF) using the modified sol–gel method as the substrate for laccase immobilization (ZrF-laccase). Based on Bradford analysis, the amount of immobilized laccase and the immobilization efficiency were determined at 130 mglaccase/gsupport and 87%, respectively. The immobilization efficiency was also confirmed by determining physicochemical parameters (such as spectroscopic, thermal stability, electrokinetic, surface area and pore volume) of the prepared zirconia-fucoidan materials with and without laccase immobilization. The decrease in the value of the isoelectric point (from 6.4 to 4.0), the specific surface area (from 366 to 108 m2/g) and the pore volume (from 0.33 to 0.18 mL/g) after the immobilization process indicates effective immobilization of the laccase on the zirconia-fucoidan material. The relative activity of immobilized laccase was determined using the 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) oxidation reaction. The ZrF-laccase biocatalytic system exhibits higher enzymatic activity than free laccase under a range of pH and temperature conditions (above 40% of initial activity) and can be reused in ten reaction cycles, retaining approximately 80% of its initial activity. The ZrF-laccase biocatalytic system was evaluated for the degradation of tartrazine as a model azo dye. The ZrF-laccase biocatalytic system could achieve 95% tartrazine decolorization in five repetitive cycles. Based on mass spectroscopy analysis, the pathway of tartrazine degradation was also proposed. Proposed methodology as well combination of zirconia, fucoidan and laccase appear to be a promising approach and open new pathways for production of highly effective biocatalyst for various applications focused on removal of emerging pollutants from the environment.

Behavior of N-Doped TiO2 and N-Doped ZnO in Photocatalytic Azo Dye Degradation under UV and Visible Light Irradiation: A Preliminary Investigation

N-doped TiO2 (N-TiO2) and N-doped ZnO (N-ZnO) were synthesized utilizing ammonia as a dopant source. The chemico-physical characteristics of synthesized samples were studied by Raman spectroscopy, X-ray diffraction, SEM analysis, N2 adsorption–desorption at −196 °C, and diffuse reflectance spectroscopy. Compared to undoped samples, the introduction of nitrogen in the semiconductor lattice resulted in a shift of band-gap energy to a lower value: 3.0 eV for N-ZnO and 2.35 eV for N-TiO2. The photocatalysts were tested for the degradation of Eriochrome Black T (EBT), which was selected as a model azo dye. Both N-doped semiconductors evidenced an improvement in photocatalytic activity under visible light irradiation (62% and 20% EBT discoloration for N-TiO2 and N-ZnO, respectively) in comparison with the undoped samples, which were inactive in the presence of visible light. Different behavior was observed under UV irradiation. Whereas N-TiO2 was more photoactive than commercial undoped TiO2, the introduction of nitrogen in ZnO wurtzite resulted in a drastic reduction in photocatalytic activity, with only 45% EBT discoloration compared to total color removal obtained with the commercial ZnO sample, suggesting intrinsic limitations for doping of this class of semiconductors.

Electrodeposited Fe on Cu foam as advanced fenton reagent for catalytic mineralization of methyl orange.

In many countries, the textile industry remains the major contributor to environmental pollution. Untreated textile dyes discharged into water negatively impact the performance of aquatic organisms and may cause a variety of serious problems to their predators. Effective wastewater treatment is a key to reducing environmental and human health risks. In this work, the Fe/Cu catalysts were used in heterogeneous Fenton’s reaction for the degradation of high concentrations of methyl orange (model azo dye) in aqueous solutions. For the first time, the catalysts were prepared onto commercial copper foams by potentiostatic electrodeposition of iron using an environmentally friendly electrolyte. The influence of electrodeposition conditions, H2O2 concentration, dye concentration and temperature on the model dye degradation was investigated. It was revealed that both the surface area and the catalyst loading play the major role in the effective dye degradation. The experimental results involving spectrophotometric measurements coupled with total carbon and nitrogen quantification suggest that a solution containing up to 100 mg/L of methyl orange can be successfully decolorized within 90 s at 50°C using porous Fe/Cu catalyst in the presence of hydrogen peroxide that largely surpasses the current state-of-the-art performance. Already within the first 10°min, ∼ 30% of total methyl orange concentration is fully mineralized. The described process represents a cost-efficient and environmentally friendly way to treat azo dyes in aqueous solutions.

Consideration of Photoactivity of TiO2 Pigments via the Photodegration of Methyl Orange under UV Irradiation.

Developing a rapid and reliable method for measuring the photoreactivity of TiO2 pigments is of great importance for industrial application. The photoactivity of industrial TiO2 pigments were evaluated via the photodegradation of a model azo dye, methyl orange (MO), in the present work. The TiO2 pigments were characterized by Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–vis) spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The photoactivity test results showed that the anatase TiO2 pigment was responsible for accelerating MO degradation, while the rutile pigment acted as a stabilizer, and effective UV absorber retarded the photodegradation of MO. It was found that the photodegradation of MO was driven mainly by photoholes (h+) and hydroxyl radicals (•OH), in the presence of TiO2 pigment with high photoactivity. With the help of the degradation intermediates during the photodegradation process and the calculated data, the preliminary degradation mechanism including azo bond cleaving, h+ oxidation, and hydroxylated products’ generation for MO was also elucidated. The photoactivity of TiO2 pigments can be rapidly evaluated in this work, which would be an efficient approach for assessing the product quality control and the end-use performance of TiO2 pigments.

Synthesis, Characterization, and Solar Photo-Activation of Chitosan-Modified Nickel Magnetite Bio-Composite for Degradation of Recalcitrant Organic Pollutants in Water

Photocatalysis is a promising process for decomposing harmful organic pollutants in water. In this study, solar/photocatalytic degradation of two model azo dyes, i.e., methylene blue (MB) and methyl red (MR), in water usinga nanostructured chitosan-modified nickel magnetite (CS-NM) bio-composite was investigated. The CS-NM bio-composite was synthesized through a co-precipitation method and characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), thermogravimetry (TGA), and UV-Vis spectroscopy. FTIR analysis showed the uniform incorporation and conjugation of nickel magnetite (NM) into the chitosan (CS) polymer matrix. SEM showed that the average particle size was 0.5 μm. The TGA results revealed the good thermal stability of the prepared bio-composite at 300 °C. The point of zero charge was calculated as 7.5. The effect of water quality and process parameters, such as concentration of dyes, catalyst dose, solution pH, and temperatures, was investigated, for application purposes. The solar/CS-NM photocatalysis resulted in 99 and 96% degradation of individual MB and MR (C0 = 50 ppm), respectively, in 90 min. The degradation of MB and MR by solar/CS-NM photocatalysis followed pseudo-first-order kinetics, with observed rate constants (k) of 0.077 and 0.072 min−1, respectively. The CS-NM photocatalyst showed high recyclability, represented by only a 4–6% loss in the photocatalytic efficiency, after four cycles. The results showed that solar/CS-NM photocatalysis is an efficient technique for degrading recalcitrant organic pollutants, such as azo dyes, in water environments.

Decolorization of Reactive Black 5 by Immobilized Bacterial Cells

Azo dyes are xenobiotic contaminants that pose a substantial risk to environmental and human health. The study investigates biodecolorization potential of immobilized bacterial cells. Newly isolated bacterial cells were immobilized with two support matrices viz. sodium alginate and magnetite nanoparticles for the decolorization of model azo dye - reactive black 5. The bacterial cells coated with magnetic nanoparticles displayed complete decolorization of dye (100 ppm) in 16 h, while cells immobilized in sodium alginate beads required more time for complete removal of dye (24 h). Coated bacterial cells exhibited stable decolorization with repeated use for 12 cycles. However, due to destabilization of sodium alginate beads and subsequent cell leaching, stable decolorization was observed until 3rd cycle only. Nanoparticles coated bacterial cells offer the advantage of easy separation, allowing the cells to be reused for multiple cycles. Biodecolorized medium was analyzed by UV-Vis spectroscopy and FTIR techniques. The magnetic nanoparticles and coated bacterial cells were characterized through XRD and SEM, respectively. Overall results indicate that magnetite nanoparticles coated bacterial cells could be an effective tool for the decolorization of azo dyes.

Novel biologically synthesized metal nanopowder from wastewater for dye removal application.

A novel adsorbent based on metal sulfide nanoparticles (MeSNPs) was biologically synthesized from metallic wastewater and examined for azo dyes removal from aqueous solution in batch and continuous systems. The size of the MeSNPs was in the range of 8-10nm, with an average specific surface area of 120.4 m2/g. Batch adsorption study was then carried out using Direct Red 80 (DR 80) and Mordant Blue 9 (MB 9) as the model azo dyes by varying MeSNPs dosage, contact time, pH, and initial dye concentration. More than 99% removal efficiency of both the dyes was achieved by using MeSNPs at the following optimum conditions: 200mg dosage, pH 2, 6min contact time, and 100mg L-1 initial dye concentration. The batch sorption isotherm results were described using the Sips model, with the maximum predicted capacity values of 143.7 and 198.3mg of dye per gram of adsorbent for DR 80 and MB 9, respectively. Besides, the sorption kinetic data for both the dyes followed the pseudo-second-order rate. Furthermore, maximum desorption efficiency values of 93% for DR 80 and 97% for MB 9 were achieved using an aqueous solution of pH 12, thus indicating that the adsorbent can be regenerated and reused further. Dynamic adsorption of the dyes was studied using a fixed-bed column with the MeSNPs as a function of liquid flow rates. The results showed an increase in breakthrough time with a decline in the flow rates for both DR 80 and MB 9 and the breakthrough behavior was explained using Thomas, Clark, and Yoon-Nelson models.

Tuning donor-acceptor strength through preferential binding in mesoporous ZrO2-TiO2 nanocomposite as mechanistic approach for enhanced photocatalytic degradation of Alizarin Yellow GG dye

A comparative study on the structure and photocatalytic activity of halo-aggregated and differently connected ZrO2@TiO2 and TiO2@ZrO2 nanocomposites was investigated here towards photodegradation of Alizarin yellow GG model azo dye. The nanocomposites were synthesized by two-step sol-gel method with predominant monoclinic phase for ZrO2, anatase phase for TiO2, and characterized through different structural and spectroscopy tools. The photocatalysts with high adsorption capability were however differing in their photodegradation efficiency attributed to varying preferential binding at their interfaces and Zr4+ substitution in the TiO2 lattice. Between the two nanocomposites, superior photocatalytic property was shown by ZrO2@TiO2 exhibiting 90–93% degradation efficiency with reproducibility. The growth of titania over zirconia in ZrO2@TiO2 reduced the surface states and defects of the core nanocrystal (NC) through strong Zr-O-Ti binding, besides providing shallow traps in smaller TiO2 NCs that enhanced the separation of photogenerated carriers. The process was also assisted through trapping of holes by surface OH groups on ZrO2 reducing the carrier migration to TiO2. The type I heterojunction had favorable positive and negative potentials for valence and conduction bands in ZrO2 and TiO2 compared to intermediate superoxide anion and hydroxyl radical generation potentials that catapulted the dye degradation. The interfacial contact in TiO2@ZrO2 nanocomposite on the other hand, has been very weak as understood from their absorption and photoluminescence spectra resulting in poorer degradation efficiency. Alizarin yellow GG being a prominent textile azo dye and there are not many reports on its photodegradation, the study also assumes significance in the context of sunlight driven photocatalysis and environmental remediation.

Biogenic sulfide for azo dye decolorization from textile dyeing wastewater

Azo dye is the most versatile class of dyes used in the textile industry. Although the sulfidogenic process shows superiority in the removal of azo dye, the role of biogenic sulfide produced by sulfate-reducing bacteria (SRB) in the decolorization of azo dye is unclear. This study explored the mechanism of biogenic sulfide for removal of a model azo dye (Direct Red 81 (DR 81)) through biotic and abiotic batch tests with analysis of intermediates of the azo dye degradation. The results showed that biogenic sulfide produced from sulfate reduction directly cleaved two groups of azo bond (-NN-), thereby achieving decolorization. Moreover, the decolorization rate was enhanced by nearly 3-fold (up to 42 ± 1 mg/L-hr; removal efficiency > 99%) by adding an external carbon source or elevating the initial azo dye concentration. This study showed that biogenic sulfide plays an essential role in azo dye decolorization and provides a new avenue for the potential application of biogenic sulfide from the sulfidogenic system for the treatment of azo dye-laden wastewater.

Degradation and Detoxification of Congo Red azo dye by Immobilized Laccase of Streptomyces sviceus

The discharge of textile effluents enriched with reactive azo dyes is of critical importance owing to inability of the dyes to degrade in waste water and their carcinogenic, mutagenic effects to various organisms. This study initiated based on the need to gaze into molecular mechanism of marine bacterial bioremediation process to develop strategies for the decolorization and detoxification of the synthetic azo dyes. The experimental work carried out to explore decolorization and degradation efficacy of laccase derived from marine actinobacteria, Streptomyces sviceus by choosing Congo red-21 as model azo dye. The extracellular production of laccase was confirmed with plate assay in medium supplemented with ABTS as substrate. Laccase was purified to homogeneity from 72hrs culture of Streptomyces sviceus by Fast performance liquid chromatography and the molecular size of laccase was noticed as 60 kDa. The purified laccase was immobilized with an efficiency of 82% by Calcium alginate method. The crude, purified and immobilized forms of the laccase enzyme was used to decolorize the Congo red-21. Crude laccase enzyme showed 69% of decolorization of Congo red-21 after 48h where as purified and immobilized laccase represented 78% and 92% of colour removal after 24 h respectively. Fourier-transform infrared spectroscopy, High Performance Liquid Chromatography and Gas chromatography–mass spectrometry were used to unravel the molecular mechanism of dye detoxification and also identify nontoxic products released from Congo Red-21 upon administration with immobilized laccase. Based on GC-MS data, it may deduce that immobilized laccase of Streptomyces sviceus cleaves the Congo red-21 dye followed by oxidative cleavage, desulfonation, deamination, demethylation process.

Photocatalytic Decolorization of Methyl Red on Nanoporous Anodic ZrO2 of Different Crystal Structures

High surface area, self-organized nanoporous ZrO2 arrays with perfect adhesion to the Zr substrate were synthesized by anodization in an aqueous electrolyte containing (NH4)2SO4 and NH4F. The obtained semiconductor materials were tested as photocatalysts for decolorization of the methyl red (MR) as a model azo dye pollutant. It was demonstrated that as-synthesized anodic ZrO2 anodic layers are already crystalline and, therefore, do not require further thermal treatment to provide a high photocatalytic performance. However, photocatalytic efficiency could be improved by annealing at a relatively low-temperature of 350 °C. Higher annealing temperatures caused a gradual drop of photocatalytic activity. The photocatalytic behavior was correlated with the crystal phase transformation in anodic ZrO2. It was found that higher photocatalytic activity was observed for the tetragonal phase over the monoclinic phase (predominant at elevated temperatures). It results from the optimal and complex electronic structure of annealed ZrO2 with three different energy states having absorption edges at 2.0, 4.01 and 5.28 eV.

Synthesis of environmentally benign ultra-small copper nanoclusters-halloysite composites and their catalytic performance on contrasting azo dyes

Supported metal nanoclusters (NCs) are an ideal catalytic system from their ultra-small size (<3 nm), reactivity and confinement on support materials. Whether synthesis of such composite is feasible using copper (Cu) as catalyst on nontoxic and inexpensive support material but without using any toxic reducing agent is yet to be explored. Here, synthesis of CuNCs using only biocompatible glutathione and localised them on halloysite nanotubes (HNTs) would be a sustainable catalyst composite. Following hydrothermal reaction, composites CuNCs@HNT and CuNCs@HNT-PS were synthesised by one-step and post-synthesis methods, respectively. State-of-the-art tools, including high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy revealed NCs formation, chemical states, and confinement and stability as composite, while catalysis reaction was monitored by spectrophotometer. Both composites exhibited faster catalytic performance than did bare NCs for the degradation of contrasting model azo dyes, methylene blue (MB) and methyl orange (MO). CuNCs, CuNCs@HNT and CuNCs@HNT-PS required only 93 ± 1.0, 17.5 ± 2.5 and 27 ± 2.5 s, respectively for 100% degradation of MB whereas >90% degradation of MO occurred by 120 ± 5.21, 75 ± 3.15 and 90 ± 3.61 min, respectively. Composites showed excellent catalytic reusability and environmental nontoxicity. Therefore, as effective and safe catalysts, they can shed light on exploring further usage in the environment and industrial set-ups.

Development of a free radical-based kinetics model for the oxidative degradation of chlorazol black in aqueous solution using periodate photoactivated process

This paper presents the first modeling study on UV/periodate (IO4–) advanced oxidation process. A reaction mechanism consisting in 45 chemical reactions including a number of radicals (IO3•, IO4•, •OH, O•–, HO2•, O2•–, O3•–) and non-radical intermediates/products (O(3 P), O3, IO3–, H2O2, HO2–, I2O6 and I2O8) has been developed to assess the reactive species generation, use and distribution during the oxidation of one model azo dye, chlorazol black (CB), by the periodate photoactivated process. The model fitted excellently the CB degradation data over a wide range of solution pH and initial IO4– concentration. Unavailable second-order rate constants of several important reactions were optimized using the genetic algorithm. Those include O3 + IO3• → IO4• + O2 (k = 1 × 108 M−1s−1), 2IO4• → I2O8 (k = 4.68 × 108 M−1s−1), reaction of CB with •OH (k = 1 × 109 M−1s−1), IO3• (k = 2.63 × 108 M−1s−1), IO4• (k = 0 M−1s−1), O(3 P) (k = 0 M−1s−1) and O3 (k = 0.574 M−1s−1). Besides, the first order kinetic constant of periodate photolysis, IO4– + hv → IO3• + O•– and IO4– + hv → IO3– + O(3 P), were respectively (0.5–4.16)×10-3 s−1 and ∼2 × 10-4 s−1, indicating that the radical pathway for IO4– photolysis is predominately the IO3–-releasing path. OH and IO3 were found to play the key role in the CB degradation. The concentration of radicals increased with pH decrease and initial periodate concentration rise, favoring higher degradation rate at acidic conditions and higher IO4– dosages. The selectivity analysis showed that the contribution of these species is ∼ 79 % for •OH and ∼ 21 % for IO3•, under various conditions of pH and [IO4–]0. This study would helpfully provide some practical indications for the application of UV/periodate AOP

Tautomerism of azo dyes in the solid state studied by 15N, 14N, 13C and 1H NMR spectroscopy, X-ray diffraction and quantum-chemical calculations

The azo–hydrazo tautomerism of four model azo dyes in the solid state is investigated by multinuclear solid-state nuclear magnetic resonance (SS-NMR) spectroscopy, X-ray diffraction and quantum-chemical calculations. The measurement of 15N SS-NMR spectra is the most straightforward way to determine the tautomeric state of solid azo compounds. Unfortunately, the sensitivity of these nuclei for SS-NMR is very low and the acquisition of 15N spectra in a reasonable time may be challenging. It is demonstrated that a natural abundance of almost 100% of another nitrogen isotope, 14N, can be exploited for the investigation of the tautomerism. Indirect detection of 14N nuclei via protons is an elegant approach for the rapid and unequivocal determination of the tautomeric form. Furthermore, a comparison of experimental carbon SS-NMR chemical shifts with those obtained in solution or by quantum-chemical computations can be used for the same purpose.

Bio-synthesized palladium nanoparticles using alginate for catalytic degradation of azo-dyes

Abstract Palladium nanoparticles (PdNPs) were synthesized in a green way using sodium alginate functioning as both reductant and stabilizer. The formation of as-synthesized PdNPs was supervised by Ultraviolet–visible (UV–Vis) spectroscopy and confirmed by the surface plasmon resonance (SPR) band. The effect of several synthesis factors such as precursor ratio, solution pH, reaction time, and temperature were investigated by the factorial design of experiments in order to optimize the experimental conditions. The optimal synthesis parameters were achieved by heating 1.0 ml of 1.0% sodium alginate (SA), 3.0 ml of 10−2 mol·L−1 H2PdCl4 at 80 °C for a period of 30 min in a neutral reaction medium (pH = 6). High-resolution transmission electron microscope (HRTEM), energy dispersive X-ray (EDX) spectroscopy, selected area electron diffraction (SAED) pattern, X-ray powder diffraction (XRD), and dynamic light scattering (DLS) were used to confirm the uniform spherical shapes and high crystallinity of PdNPs with average particle size of (2.12 ± 1.42) nm. The SEM images show the distribution of PdNPs presented among the SA. FTIR spectra indicate that SA is a good capping agent to stabilize PdNPs for a long time. The catalytic degradation of model azo-dyes such as mono-azo (Cibacron Yellow FN–2R) and di-azo (Cibacron Deep Red S–B) were confirmed the catalytic activity of PdNPs. The PdNPs can accelerate the degradation rate by more than 80 and 10 times respectively as confirmed by kinetics constant (k) values.