Decolorization Mechanism Research Articles

Adsorption Removal of Safranin Dye Contaminants from Water Using Various Types of Natural Zeolite

The presented study involved detail investigation for the adsorption properties of three types of natural zeolite (heulandite, clinoptilolite, and phillipsite). The studied zeolite samples were described based on the structural features from the XRD patterns and the surficial morphologies from SEM images. The selected zeolite minerals were applied as adsorbents in the decolorization of safranin-T dye from water. The estimated uptake capacities for safranin revealed the higher capacity of heulandite than clinoptilolite and Phillipsite (heulandite>clinoptilolite>phillipsite). As per the kinetic studies, 240min was detected as the decolorization equilibrium of safranin by heulandite and clinoptilolite; and 480min for phillipsite zeolite. The decolorization mechanisms were classified as chemical processes and represented strongly by Lagergren assumption and Elovich model. Monolayer adsorption form was suggested for the uptake by heulandite and clinoptilolite (Langmuir); and multilayer form was predicted for phillipsite (Freundlich). Neutral to alkaline environment was detected to be the best medium for considerable removal of safranin. Natural zeolite minerals also were applied effectively in safarnin decontamination from raw water and showed effective values in the decolorization of other types of dyes.

Combined intra- and extracellular reduction involved in the anaerobic biodecolorization of cationic azo dye by Shewanella oneidensis MR-1

Microbial reduction decolorization is a promising strategy for cationic azo dye pollution remediation, but the reduction mechanism is unclear yet. In this work, the anaerobic reduction decolorization mechanism of cationic red X-GRL (X-GRL) by Shewanella oneidensis MR-1 (MR-1) was investigated from both intracellular and extracellular aspects. The exogenous additional riboflavin treatment test was used to analyze the extracellular reduction mechanism of X-GRL, and the actual role of riboflavin during the reduction of X-GRL was identified by three-dimensional fluorescence analysis for the first time. The proteinase K and the electron competitor treatment tests were used to analyze the intracellular reduction mechanism of X-GRL. Moreover, the effect of external environment on the reduction mechanism of X-GRL was elucidated by the decolorization performance of MR-1 wild type and its mutants, ΔomcA/mtrC, ΔmtrA, ΔmtrB and ΔcymA, under different external pH conditions. The results indicated that X-GRL could be decolorized by MR-1 in both extracellular and intracellular spaces. The extracellular decolorization of X-GRL could be caused by Mtr respiratory pathway or the indirect reduction of riboflavin, while the intracellular decolorization might occur due to the intracellular reduction depending on CymA pathway and a NADH-dependent reduction catalyzed by intracellular azoreductases. Furthermore, the proportion of extracellular decolorization decreased, whereas that of intracellular decolorization increased as the environmental pH rose.

Kinetics and mechanism of the oxidative decolorization of direct violet 31 in the presence of peroxodisulfate-silver(I) as a redox system

The redox decolorization of direct violet 31 [DV-31]− by Ag(I)/S2O82− under conditions similar to the Fenton process was studied kinetically in aqueous solution over a range of different concentrations of dye and redox system. The oxidation rate increases with decreasing pH. The reaction is catalyzed by Ag(I) through the formation of Ag(II) which is a very strong oxidizing agent. A tentative mechanism for silver(I) catalyzed oxidation of [DV-31]− by peroxydisulfate is proposed. Pseudo-order conditions were maintained in all experiments by using an excess of S2O82− (> 10-fold). The reaction obeys the following rate law: $$ {\text{Rate}} = \left( {K_{1} K_{2} k_{5} \left[ {H^{ + } } \right] + K_{3} k_{6} } \right)\left[ {{\text{Ag}}^{ + } } \right]\left[ {{\text{S}}_{2} {\text{O}}_{8}^{2 - } } \right] $$ The magnitudes of the thermodynamic activation parameters suggest that electron transfer proceeds through an outer-sphere mechanism. Sodium dodecylsulfate (SDS) was found to decrease the rate of reaction due to attraction of the Ag(I) ion into the SDS pseudo-phase, leaving other reactants in the bulk solution. Additionally, 1H NMR spectra of [DV-31]− before and after degradation confirmed almost complete mineralization of the dye.

One-step fabrication of cobalt-embedded carbon nitride as a magnetic and efficient heterogeneous catalyst for activating oxone to degrade pollutants in water

Abstract Cobalt nanoparticles (NPs) immobilized on N-doped carbonaceous substrates are attractive heterogeneous catalysts for activating Oxone to degrade pollutants. However, conventional preparation of Co NPs/N-doped carbon composites involves multi-step syntheses of N-doped carbon substrates, and then immobilization of Co NPs on substrates, which are complicated and time-consuming. In this study, a convenient one-step fabrication technique is developed for preparing a composite of Co/N-doped carbon via carbonization of a mixture of melamine and cobalt acetate. The resulting Co@CN is comprised of Co NPs evenly distributed over a carbon nitride (CN) matrix. Co@CN could exhibit porous structures and magnetic controllability, making it an appealing catalyst for Oxone activation. Catalytic activities for Oxone activation by Co@CN are investigated via batch-type decolorization experiments of amaranth (AMR) dye. Co@CN shows much higher catalytic activities than C3N4 and Co3O4, the benchmark catalyst, for Oxone activation to decolorize AMR. In comparison to the other reported catalysts, Co@CN demonstrates the much lower activation energy for AMR decolorization. The mechanism of AMR decolorization by Co@CN-activated Oxone is also determined by investigating Electron paramagnetic resonance (EPR) analysis and effects of radical inhibitors on AMR decolorization. These comparisons indicate the promising features of Co@CN as a heterogeneous catalyst for activating Oxone. The fabrication technique proposed here can be also adopted to develop similar composites of metallic NPs distributed over CN matrices for various catalytic applications.

ELECTROCHEMICAL OXIDATION OF SYNTHETIC ORGANIC DYES BY FERRATE (VI), USING COMMERCIAL STEEL WOOL ELECTRODES

This paper deals with the in-situ electrochemical oxidation of Reactive Black 5 (RB-5), Reactive Blue 19 (RB-19) and Allura Red AC (AR-AC), using commercial steel wool as electrodes. At the optimal conditions (18 V and NaOH 0.33M), the decolorization of RB-19 (anthraquinone-type dye) is much more rapid than those of azo dyes RB-5 and AR-AC. The reaction rates based on a first order reaction model were 0.134 min -1 for RB-19, 0.043 min -1 for RB-5 and 0.028 min -1 for AR-AC. Color removal efficiencies were higher than 95% achieved in 120 min. The analyses of spectra of the three dyes in the visible region indicate a complete cleavage of both azo and quinoid chromophores. In the case of RB-19 no new absorption peaks occurred in the UV region, showing a partial oxidation of aromatic groups without the generation of intermediates. In case of both azo-type dyes RB-5 and AR-AC, formation/accumulation of intermediates followed by their partial oxidation may have occurred. All these observations indicate that the predominant mechanism for decolorization was the oxidation of the three dyes. We conclude that that the electrochemical oxidation by ferrate (VI), under low voltages and low NaOH concentrations, using commercial steel wool as electrodes is an efficient and cost-effective alternative for the decolorization of azo and anthraquinone type dyes. For future studies a COD analysis should be made in order to correlate the decolorization and the elimination of the organic load in the dye solutions.

Effective destaining of methylene blue with low concentrations under visible light irradiation in the presence of Mg(OH)2

In this work, three types of Mg(OH)2 nanomaterials with different morphologies (flower-like, plate-like and disk-like) were synthesized and used for the decolorization of methylene blue (MB) with low concentrations. It turned out that the MB solution (10 mg/L) could be completely discolored within 2 h in the presence of flower-like Mg(OH)2 under visible light irradiation. Further investigation showed that it was mainly the interface interaction between MB molecules and hydroxyl groups on Mg(OH)2 surface that caused the decolorization of MB solution. The possible decolorization mechanism can be concluded to two steps. First, the MB molecules undergone a demethylation or methyl substitution process and converted into intermediate products owing to the existence of hydroxyl groups on the surface of Mg(OH)2. Then, the intermediates were converted into other small molecule products via ring-opening reaction under visible light irradiation. This work provides a green, efficient and applicable method for treating MB wastewater with low concentrations.

Degradation of toluidine red, an oil soluble azo dye by Halomonas strain IP8 at alkaline condition

A salt tolerant bacteria, Halomonas strain IP8, was used for the degradation of an oil soluble azo dye, Toluidine Red (C.I. no. 12120). The effect of different culture conditions such as initial dye concentration, pH, NaCl percent (w/v) and temperature were studied at static condition using the one-factor-at-a-time method (OFAT) method as optimization technique. According to the results, the optimized conditions were 25 mg/l dye concentration, pH 9.5, 5% (w/v) NaCl, and temperature 35 °C. The decolorization mechanism was analyzed through UV–vis spectrophotometric method, high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometer (GC-MS) analyses. UV–vis scan of supernatants before and after treatment suggested that decolorization was accrued under degradation mechanism rather than inactive surface adsorption. HPLC analysis confirmed this conclusion. The identified metabolite from GC-MS results was 1-diazo 2-naphtol at m/z 170 ± 1. A pathway was proposed for dye degradation based on the identified fragment by GC-MS analysis.

Reductive decolorization of azo dyes via in situ generation of green tea extract-iron chelate.

In this study, rapid decolorization of azo dyes was achieved by in situ-generated green tea extract-iron (GTE-Fe) chelate for the first time. When changing reaction conditions from the aerobic condition to the anaerobic condition, the decolorization efficiencies of two azo dyes, i.e., acid orange 7 (AO7) and acid black 1 (AB1), increased from 46.38 and 83.17 to 90.13 and 95.37%, respectively. The recalcitrant AO7 was then selected as the targeting pollutant in subsequent optimization and mechanism studies. Experimental evidences showed that the initial concentrations of AO7, Fe(III), and GTE are the key factors to optimize the decolorization efficiency. Further characterization studies by spectroscopic analysis, including FESEM, FTIR, and XPS, suggested that the major mechanism of AO7 decolorization is the nucleophilic attack of the oxygen in green tea polyphenols (GTP), and this attack could be facilitated by the organometal chelation. This study provided an efficient and environmental friendly strategy to decolorize azo dyes via in situ generation of the GTE-Fe chelate, as well as its mechanistic insights, shedding lights on in situ remediation of azo dye pollution. Graphical abstract ᅟ.

The Effect of Decolorizing Agent on the Optical Properties of High Iron Contents Soda-Lime Silicate Glass

The aim of this study is to decolorize the high iron content (more than 0.1 %wt Fe2O3) glass. The contained 0.13 wt% iron oxide (Fe2O3) soda-lime silicate is prepared by high iron content sand with 0.17 wt% of Fe2O3. Iron oxide in soda-lime glass presents in two forms, Fe2+(green) « Fe3+(yellow). In principle, high iron content sand is not suitable to produce tableware. Therefore, the glass manufactures require high purity of sand because they want to control the amount of iron oxide as low as possible, which usually tableware glass contains only small amount of iron oxide (0.01 - 0.04 wt% Fe2O3) to avoid iron effect (green color). The soda-lime silicate glasses is decolorized by three different agents, Neodymium oxide (Nd2O3), Manganese oxide (MnO2), and Tin oxide (SnO2) 0.125 0.25 0.50 1.00 and 2.00 %wt respectively. The glasses are melted twice in the platinum crucible and investigated of the optical properties by UV-Vis spectrophotometer. The results of the color in CIE L*a*b* system are found that glass containing MnO2and SnO2slightly changes to white shade, but still presents in green. However, the result of contained 1.00 and 2.00 %wt SnO2glasses is nearly cleared, the result of contained Nd2O3glasses are satisfied, and the contained 0.25 %wt Nd2O3glass is showed very clear. Anywise the color of glasses containing 1.00 and 2.00 %wt Nd2O3turned to blue. The reaction of glasses containing Mn and Sn occur according to the mechanism of chemical decolorization. The reactions was described by the following equation, Fe2++ Mn3+g Fe3++ Mn2+and Fe2++ Sn5+f Fe3++ Sn4+, but the reactions are limited and strongly depending on the redox equilibrium. For Nd2O3,the reaction presents according to physical decolorization, because the color of Nd2O3is stable in melted glass and it can dismissed the color of Fe2O3directly. Therefore, this method can apply for the tableware glass production with high iron content sand.

The application of an efficient modified decolorizer in coagulation treatment of high color reclaimed water.

High color concentrations in inflows at reclaimed water treatment plants are typically considered as emergency situations, which must be solved using an appropriate decolorizing process. Using the decoloration mechanism of a modified dicyandiamide-formaldehyde polymer (DFP), a urea-formaldehyde polymer and a melamine-formaldehyde polymer (MFP) were prepared with ammonium chloride and ammonium sulfate as the modifiers. An orthogonal experiment indicated that a modified urea-formaldehyde polymer had no effect on decolorization; however, the MFP modified by ammonium chloride in number 16 (MMFP-C16), the DFP modified by ammonium chloride in number 9 (MDFP-C9) and modified by ammonium sulfate in number 6 (MDFP-S6) were successful. The removal rates were above 50% in acidic and reactive dye reclaimed water. Fourier transform infrared spectroscopy was used to microscopically analyze the differences in decolorization effect among the polymers. The effect of pH on decolorization was analyzed. Compared to the MDFP-C9 and MDFP-S6, the MMFP-C16 was not sensitive to changes in conditions. The pilot plant test proved that the three optimal decolorizers also had a good decolorizing effect, and MMFP-C16 was better both at decolorizing and floc sedimentation. Thus, the latter can be considered as an efficient modified decolorizer for rapid treatment of high color reclaimed water.

Study on decolorization of dyeing wastewater by electrochemical treatment

In view of the decolorization of dyeing wastewater, three different kinds of simulated dyeing wastewater were treated by electrochemical method. The effects of current density, initial pH, electrolyte concentration and initial concentration of dye on the treatment effect were investigated, and the decolorization mechanism and color reversion were studied. The experimental results show that the decolorization rate of the three kinds of dyeing wastewater is more than 90% after 60min treatment. And the decolorization process is mainly chromogenic groups gradually destroyed, the dye molecules are gradually degraded. Moreover, in the natural conditions, aeration conditions, heating conditions, almost no phenomenon of color reversion occured.

Synthesis, photoelectrochemical properties and solar light-induced photocatalytic activity of bismuth ferrite nanoparticles

Bismuth ferrite (BFO) nanoparticles prepared by solid state reaction route were characterized by various characterization techniques such as XRD, FESEM, HRTEM, UV–Vis DRS, PL etc., and their photocatalytic activities were evaluated by decolorization of aqueous solution of Congo red (CR) under solar light. The photocatalytic activity of BFO was increased by increasing the preparation temperature from 350 to 500 °C and then decreased with rise in temperature. The results of electrochemical measurements such as linear sweep voltammetry (LSV), electrochemical impedence (EIS), and Mott–Schottky analysis of BFO nanoparticles corroborated the findings of their photocatalytic activity. The enhanced photocatalytic response of the sample prepared at 500 °C is attributed to its smallest band gap, minimum crystallite size (30 nm), efficient separation, and lowest possible recombination of photo-generated charge carriers. The effects of amount of nano-BFO, irradiation time, initial CR concentration, and BFO calcination temperature on the decolorization of CR were examined. It was observed that 1 g/L nano-BFO calcined at 500 °C can decolorize up to 77% a 10-ppm CR dye solution under solar irradiation for 60 min. The studies included scavenger tests for identification of reactive species and a possible mechanism of dye decolorization.

Enhanced UV/H2O2 process by expanded graphite: an effective method for rhodamine B dye decolorization

In the present work, the decolorization of rhodamine B (RhB) dye was studied using a UV/H2O2 process enhanced by expanded graphite (EG). The effects of initial solution pH, EG/H2O2 dosage, and reaction temperature on decolorization were investigated. The decolorization effectiveness increased with increasing EG and H2O2 doses but reached optima with 1.0 g/L and 1.0 mL/L, respectively. The UV/H2O2 process enhanced by EG for RhB dye decolorization followed the pseudo-first-order kinetics model and exhibited an enhancement effect with the rate constant (k) of 0.05268 min−1 (k = 0.01972 min−1 for the UV/H2O2 process). The improved decolorization efficiency of RhB may be ascribed to the cooperation effect in the UV/H2O2 process enhanced by EG. Furthermore, the possible mechanism of RhB decolorization was discussed. EG not only acts as an absorbent of RhB dye and H2O2 molecules, but also acts as a catalyst to decompose H2O2.

Whitening Sulfonated Alkali Lignin via H2O2/UV Radiation and Its Application As Dye Dispersant

Sulfonated alkali lignin (SAL) can be used as dye dispersants, but its dark color may lead to a severe staining problem, thus hindering its application. Here, a UV/H2O2 whitening process was applied to decolorize SAL and the color was faded by 50%. The structural changes of SAL before and after whitening were characterized by GPC, UV–vis, FTIR, fluorescence, and potentiometric titration, and the mechanism of decolorization was deduced. The results show that the contents of aromatic ring, methoxyl, and phenolic hydroxyl groups in SAL decreased by 37%, 64%, and 78%, respectively, while the content of carboxylic groups increased by 187% after being radiated in H2O2 for 20 h. The changes in chromophoric group and the contribution of each chromophoric group to the overall color before and after whitening were also investigated. Due to the removal of chromophores, the staining phenomenon of light-colored SAL (LSAL) was reduced effectively when it was used as a dye dispersant.

A quasi-homogeneous catalysis and electron transfer chain for biodecolorization of azo dye by immobilized phenazine redox mediator

The anaerobic bio-reduction rate of many different contaminants is slow due to the limitations and efficiencies of electron transfer. In this study, the phenazine immobilized in hydrophilic material was tested as a redox mediator (RM) and quasi-homogeneous catalysis to reduce the mass transfer limitation and increase the decolorization efficiency. Neutral red (NR) was immobilized to polyacrylic acid (PAA) hydrogel by chemical reaction and obtained a content of NR as high as 3.58 mmol cm−3 of PAA. The novel functional material (PAA-NR), with three-dimensional polymeric network with high porosity and water contents (92–98%, w/v) achieved 13.5 fold higher in the anaerobic decolorization efficiency compared to the control. The optimal conditions for decolorization with PAA-NR hydrogel were 40 °C and pH 8.0. Additionally, the electron transfer mechanism of decolorization was investigated by testing with six inhibitors. NADH and FAD chains were involved in the decolorization process. PAA-NR acted as an insoluble redox mediator to accelerate Reactive Brilliant Red K-2BP (K-2BP) reduction through mediating electron transfer between the azoreductase and K-2BP, resulting in higher electron transfer and decolotization efficiency. This immobilizing technology extended the RM application and demonstrated high catalytic activity on pollutant anaerobic transformation.

Photocatalytic effect of (TiO2/CeO2) with support of β-cyclodextrin for enhanced performance under solar light

In this study, we have reported the interaction of binary metal oxides (TiO2/CeO2) with β-CD towards enhancement in the photocatalytic performance under solar light irradiation. The interactions of (TiO2/CeO2) with β-CD characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis diffuse reflectance spectroscopy (DRS). XRD analysis shows that the fluorite structure of CeO2 and anatase structure of TiO2 have not been changed after the addition of β-CD. The structure morphology of (TiO2/CeO2), not changed by the addition of β-CD, is also confirmed by SEM analysis. Addition of CeO2 and β-CD with TiO2 is found to be significantly extended the absorption edge towards the visible region which is confirmed by UV-DRS spectral data. The photocatalytic activity of the modified (TiO2/CeO2)-β-CD system was evaluated by decolorization of Rhodamine B (RhB) dye taken as a model pollutant under solar light irradiation. The formation of an inclusion complex of RhB with β-CD is confirmed by UV–Vis analysis. Various experimental parameters like (TiO2:CeO2) ratio, initial concentration of RhB dye, dose of the catalyst, irradiation time and pH have been investigated. Kinetic results show that decolorization reaction follows pseudo-first-order kinetics. The mineralization of RhB dye was also confirmed by COD measurements. The modified (TiO2/CeO2)-β-CD system exhibits higher photocatalytic activity than (TiO2/CeO2), TiO2 and CeO2. A suitable reaction mechanism for the effective decolorization of RhB dye by (TiO2/CeO2)-β-CD system has also been proposed.

Purification of Dye-stuff Contained Wastewater by a Hybrid Adsorption-Periphyton Reactor (HAPR): Performance and Mechanisms

sThe aim of this study was to develop an environmental-benign bio-measure that could be used to purify dye-contaminated wastewater. Herein, a hybrid adsorption-periphyton reactor (HAPR), combining a bioadsorbent based adsorption unit and a periphyton-based photo-bioreactor (PPBR), was built and applied for the first time. Firstly, an efficient bioadsorbent, i.e, microwave-activated swede rape hull (MSRH), was produced, characterized and applied in an adsorption column, to pretreat methylene blue (MB) wastewater with high concentration (~100 mg L−1 or higher). Thereafter, the effluent of adsorption column, with lower dye concentration (~0.5 mg L−1), was collected and further purified by PPBR. Results showed that dye removal efficiency by HAPR was 99.95% (from 200 mg L−1 to 0.1 mg L−1 or lower). Decolorization mechanisms by PPBR, included adsorption process by extracellular polymeric substances (EPS) on the surface of periphyton and degradation process. The study showed that HAPR was a novel, environmental friendly, efficient and promising dye-purification method and deserved further attention in future investigation.

Effects of the addition of Co, Ni or Cr on the decolorization properties of Fe-Si-B amorphous alloys

Fe-based amorphous alloys show great potential in degrading azo dyes and other organic pollutants, and are widely investigated as a kind of environmental-friendly materials for wastewater remediation. In this paper, the effects of Co, Ni or Cr addition on the decolorization properties of Fe-Si-B amorphous alloys were studied, and the mechanism of their different effects was analyzed. Co addition could lower the activation energy of Fe-Si-B amorphous alloys in decolorizing azo dyes, and had no weakening effect on the decolorization capability of Fe-Si-B amorphous alloys. Ni addition led to partial crystallization of Fe-Si-B amorphous alloys, and the decolorization mechanism at low temperatures changed from chemical degradation to physical adsorption. Cr addition could enhance the corrosion resistance of Fe-Si-B amorphous alloys, but the amorphous alloys completely lost the decolorization capability no matter at lower or higher temperatures. The results of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that the addition of Co, Ni or Cr could generate different surface structures that had significant influences on the decolorization process. Our work demonstrated that the effiecient decolorization of azo dyes by Fe-based alloys could be realized only when amorphous nature and incompact surface structure were simultaneously achieved for the alloys.

Fabrication of a novel hierarchical flower-like hollow structure Ag2WO4/WO3 photocatalyst and its enhanced visible-light photocatalytic activity

A series of hierarchical flower-like hollow structure Ag2WO4/WO3 photocatalysts was synthesized and characterized by XRD, SEM, Raman spectroscopy, XPS, photoluminescence (PL) spectra, and BET. The obtained results indicated the growth of finely distribution of Ag2WO4 on the surface of the WO3 hollow sphere. UV–vis diffuse reflectance spectroscopy (DRS) was used to investigate the absorption range and band gap of photocatalysts. The photocatalytic activities of the photocatalysts were evaluated by the decolorization of Rhodamine B (RhB) under visible-light irradiation. The results showed that the highest activity could be reached up to 94%. It was also found that the heterojunction structure photocatalyst exhibited excellent stability. The kinetic reaction rate of heterojunction structure photocatalyst was nearly 17.0 and 7.5 times higher than those of pure WO3 and Ag2WO4. A possible photocatalytic mechanism for decolorization of Rhodamine B was proposed.

Annealing-induced different decolorization performances of Fe-Mo-Si-B amorphous alloys

In this paper, as-spun Fe77.2Mo0.8Si9B13 amorphous ribbons were annealed in a vacuum furnace at different temperatures firstly, and then the decolorization performances of as-spun ribbons and annealed ribbons were investigated. It was found that all ribbons could decolorize acid orange II dye solutions efficiently. The as-spun ribbons showed a much faster decolorization rate than the annealed ribbons, and the ribbons annealed at lower temperatures exhibited better decolorization performances than those annealed at higher temperatures. The decolorization mechanism of those ribbons was analyzed, and thermodynamic stabilization and surface state changes caused by annealing treatment were considered responsible for the differences in their decolorization performances.