Methylene Blue Oxidation Research Articles

E-beam evaporated TiO2 and Cu-TiO2 on glass: Performance in the discoloration of methylene blue and 2-propanol oxidation

TiO2 and Cu-TiO2 thin films were deposited by e-beam evaporation and then annealed at 350 and 500°C. Their structure, surface morphology and optical properties were studied by X-ray diffraction, scanning electron microscopy, cross-sectional TEM, UV–vis, FT-IR spectroscopy and X-ray absorption spectroscopy. A single-phase source material was used for the first time in the deposition process, thus avoiding preferential evaporation of Cu with respect to TiO2, and resulting in an even concentration of Cu in the doped films. The photocatalytic activity was evaluated by degradation of pre-adsorbed methylene blue (MB) in dry conditions and gaseous 2-propanol in oxygen atmosphere under visible and simulated solar light, respectively. Results suggested that high surface hydroxylation of the as-deposited films is an important factor for MB oxidation occurring through a dye-sensitized mechanism activated by visible light absorption. Conversely, the rate of photodegradation of 2-propanol is enhanced in annealed samples due to the greater crystallinity and less electron-hole recombination, with the TiO2 annealed at 500°C being the most efficient photocatalyst. However, Cu-doped samples resulted the most active samples during the degradation of MB under visible radiation. Finally, the performance at increasing thickness (250, 500, 1000, up to 2000nm) was tested for the most reactive films revealing a marked rise in photocatalytic activity up to 1000nm.

Copper-doped akaganeite: Application in catalytic Cupro-Fenton reactions for oxidation of methylene blue

In this work an iron oxide – akaganeite – was obtained and used as a Fenton catalyst for the oxidation of methylene blue. The ability of dye oxidation was evaluated after incorporating copper into the structure of akaganeite to improve the catalytic properties of the material. EDS spectroscopy shows the presence of copper in iron oxide whereas XRD, XANES and EXAFS reveal that copper is indeed incorporated into akaganeite’s structure. Color removal of methylene blue (MB) was monitored by UV–vis Spectroscopy. The results obtained by this technique showed that akaganeite doped with a higher percentage of copper presented better MB removal capacity, reaching 65.7% at 180min. The study by ESI–MS showed the formation of the intermediates during the degradation of this dye. Moreover, this material presented a significant mineralization of MB with removal of 45.5% of the organic carbon. The synergistic effect between iron and copper ions into the akaganeite structure favored formation of hydroxyl radicals, promoting the oxidation of the methylene blue dye.

Highly Sensitive Detection of Silver Ions Enabled by RecJf Exonuclease Cleavage and Reductant‐Mediated Electrochemical Amplification

AbstractA novel electrochemical approach for a silver ion (Ag+) assay is proposed based on Ag+‐induced DNA structure transformation for target recognition, RecJf exonuclease mediated cleavage for background signal decline, and a specific reductant‐assisted reaction for electrochemical amplification. Generally, in the presence of Ag+, cytosine–Ag+–cytosine with high stability forms and the single‐stranded DNA probe on the electrode transforms into a hairpin structure, which resists degradation by RecJf exonuclease. A DNA probe is labeled with methylene blue (MB), which supplies an intense electrochemical signal. Moreover, the employment of a reductant can assist the oxidation of MB, which amplifies the signal in situ. High sensitivity is thus achieved and the calculated detection limit for Ag+ detection is 3 pm. This method also demonstrates excellent selectivity in the presence of interfering ions. Moreover, it can be successfully applied to the voltammetric determination of Ag+ in drinking and lake water.

Treatment of Methylene Blue water solution by submerged pulse arc in multi-electrode reactor

Pulsed submerged arc (SA) treatment of aqueous methylene blue (MB) solutions was studied in the reactor with multiple mobile iron (Fe) based electrodes. The discharges were carried out between these electrodes, which are repetitively brought into collision contact with fixed electrodes, connected to the power supply. The new reactor allows electrical discharges and MB decomposition in a large (600ml) volume of liquid. The effects of alternating filtration, electrode type, arcing energy, vibration, aging of the solutions after arcing and the added H2O2 concentration on MB decomposition were studied. The ratio between the number of milliliters of the treated solution that reached complete removal of MB to the time required for this is greater by factor of 7.5 than this ratio for two electrode system obtained for the same SA conditions. The treatment efficiency in multi electrode reactor is explained by the numerous collisions of multiple electrodes leading to the formation of eroded nano-particles with the surface catalytically active towards MB oxidation.

Optimization of Ti/Ta2O5–SnO2 electrodes and reaction parameters for electrocatalytic oxidation of methylene blue

Among existing water treatment methods for organic-containing wastewaters, advanced oxidation process, particularly electrocatalytic oxidation, is a technique allowing to reach high degradation and mineralization efficiencies. Electrodes tested for use in electrocatalytic oxidation processes contain either expensive or platinum/group metals such as Pt-, Ru-, Ir-, Pd-, or boron-doped diamond and Sb and Pb compounds which are toxic for the environment. Thereby, there is a need for environmentally friendly and less expensive electrodes. The objectives of this research were to optimize annealing temperature of Ti/Ta2O5–SnO2 electrodes, establish the working media for organic compound oxidation processes as well as check degradation, mineralization and current efficiencies for methylene blue dye oxidation. Decolorisation efficiency of 95 % was achieved in 2 h at pH = 6.5. Neutral media showed also higher efficiency towards COD decrease which was equal to 85 % after 2 h of electrolysis. The lowest energy consumption of 7.7 kWh m−3 required for 100 % decolorisation was observed for the electrodes annealed at 550 °C at pH = 2. The highest current efficiency of 10.1 % attributed to 80 % of COD reduction was obtained for the electrode annealed at 550 °C at pH = 6.5. The optimization data allow further extrapolating of electrocatalytic oxidation process on Ti/Ta2O5–SnO2 electrodes to pilot scale.

Modified Zeolite with Transition Metals Cu and Fe for Removal of Methylene Blue from Aqueous Medium: Mass Spectrometry Study

Textile industries are one of the main sources of water pollution. Wastewater containing dyes present a serious environmental problem because of its high toxicity and possible accumulation in the environ- ment. In this work were explored the characteristics of removal of methylene blue dye employing zeo- lites modified with transition metals (Cu, Fe). The zeolites with iron or copper were prepared by using NaY and Naβ zeolites as precursors, replacing part of ion sodium for copper or iron ions through the ion exchange method. All materials were characterized by several analytical techniques, in order to gain information about the structure and catalytic activity. Modified zeolites showed a remarkable ac- tivity in H2O2 decomposition and in the discoloration an organic dye in aqueous medium. ESI-MS stud- ies of the methylene blue oxidation showed that the oxidation of the dye occurs via a Fenton type sys- tem in which *OH radicals are formed in situ and added to the ring structure of the organic substrate. In addition, modification of the zeolite with transition metal proved to be an interesting pathway to produce efficient catalysts for the oxidation of organic molecules, i.e. dyes in aqueous media. Copyright © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Catalytic oxidation of methylene blue by dendrimer encapsulated silver and gold nanoparticles

The catalytic oxidation of methylene blue was investigated in the presence of dendrimer generation five terminated NH2 encapsulated silver (AgDENs), and gold (AuDENs) nanoparticles as catalyst. The synthesis process of encapsulated metal nanoparticles were monitored by UV/vis spectrophotometry and their average diameters determined by transmission electron microscopy analysis, respectively. The kinetics was monitored using UV/vis spectrophotometry, under pseudo-first order conditions, resulting in observed rate constants kobs. Langmuir–Hinshelwood approach was applied to model the kinetic process. The adsorption of methylene blue on the catalyst surface is related to the type of metal nanoparticle present, and presents the rate-determining step.

Influence of hydrogen peroxide on the simultaneous removal of Cr(VI) and methylene blue from aqueous medium under atmospheric pressure plasma jet

An efficient reduction of Cr(VI) to Cr(III) was carried out under argon plasma jet operating in aqueous medium. The effect of gas flow, pH and addition of a buffer were examined. Typical results indicated that argon plasma favored the formation of the highest amount of hydrogen peroxide that reduces Cr(VI) to Cr(III), especially under acidic medium. Quantification of hydroxyl radicals and the effect of various hydroxyl scavengers were studied. It was observed that simultaneous mitigation of Cr(VI) and methylene blue is more beneficial than removal of the individual pollutant. Methylene blue promoted the Cr(VI) reduction, whereas addition of catalytic amounts of iron(II) salt favored methylene blue oxidation via Fenton reactions. During the present study, a maximum energy yield of around 24g/kWh was obtained at 16kV and 50ppm of Cr(VI) concentration.

Synthesis of magnetically recoverable ferrite (MFe2O4, M [dbnd] Co, Ni and Fe)-supported TiO2 photocatalysts for decolorization of methylene blue

Effects of ferrite materials as supports (CoFe2O4, NiFe2O4, and Fe3O4) on nano-TiO2 were elucidated by their use in the oxidation of methylene blue. These photocatalysts, which were synthesized by co-precipitation, were characterized by XRD, SEM, EDS and VSM. The crystalline phase of TiO2 onto magnetic MFe2O4 was formed by anatase and rutile. TiO2/CoFe2O4 exhibited the strongest magnetic property of the prepared catalysts, and the photocatalytic efficiencies followed the order TiO2/CoFe2O4>TiO2/NiFe2O4>TiO2/Fe3O4. MB decolorization was enhanced with the amount of TiO2 on the photocatalyst, and was moderately affected by the extent of structural distortion of ferrite supports.

Maghemite nanosorbcats for methylene blue adsorption and subsequent catalytic thermo-oxidative decomposition: Computational modeling and thermodynamics studies

In this study methylene blue (MB) has been investigated for its adsorption and subsequent catalytic thermo-oxidative decomposition on surface of maghemite (γ-Fe2O3) nanoparticles. The experimental adsorption isotherm fit well to the Freundlich model, indicating multi-sites adsorption. Computational modeling of the interaction between the MB molecule and γ-Fe2O3 nanoparticle surface was carried out to get more insights into its adsorption behavior. Adsorption energies of MB molecules on the surface indicated that there are different adsorption sites on the surface of γ-Fe2O3 confirming the findings regarding the adsorption isotherm. The catalytic activity of the γ-Fe2O3 nanoparticles toward MB thermo-oxidative decomposition has been confirmed by subjecting the adsorbed MB to a thermo oxidation process up to 600°C in a thermogravimetric analyzer. The experimental results showed a catalytic activity for post adsorption oxidation. The oxidation kinetics were studied using the Ozawa–Flyn–Wall (OFW) corrected method. The most probable mechanism functions were fifth and third orders for virgin MB and MB adsorbed onto γ-Fe2O3 nanoparticles, respectively. Moreover, the results of thermodynamic transition state parameters, namely changes in Gibbs free energy of activation (ΔG‡), enthalpy of activation (ΔH‡), and entropy of activation (ΔS‡), emphasized the catalytic activity of γ-Fe2O3 nanoparticles toward MB oxidation.

Photoinduced Crystallization and Activation of Amorphous Titanium Dioxide

Titanium dioxide (TiO2) is one of the most common photosensitive materials used in photocatalysis, solar cells, self-cleaning coatings, and sunscreens. Although the crystalline TiO2 phases such as anatase and rutile are well-known to be photoactive, whether amorphous TiO2 is active in photocatalytic reactions is still controversial. Here we show that amorphous TiO2 prepared by the commonly used sol–gel method of tetrabutyl titanate hydrolysis is active in photocatalytic water reduction and methylene blue oxidation under the irradiation of a xenon lamp. The amorphous TiO2 gains photoactivity after an induction period of approximately an hour, suggesting that phase transition is involved. Using an extensive series of microscopic and spectroscopic analyses, we further show that the photoinduced crystallization by amorphous TiO2 forms a nanometer-thin layer of rutile nanocrystallites under the irradiation in the middle ultraviolet range. The resulting core–shell nanoparticles have a bandgap of 3.3 eV and are enriched with surface-active sites including reduced titanium and oxygen vacancies. The revelation of photoinduced crystallization raises the possibility of preparing photosensitive TiO2 using low-temperature radiation techniques that can not only save energy but also incorporate heat-sensitive components into manufacturing.

Simple preparation of tungsten supported carbon nanoreactors for specific applications: Adsorption, catalysis and electrochemical activity

Porous carbon supported tungsten carbide nanoreactors, two sizes (∼25 and 170nm), were designed using economical petroleum pitch residue followed by tungsten (W) doping. X-ray diffractions showed both carbon tungsten composites (CTC-25 and CTC-170) contained tungsten subcarbide (W2C) and monocarbide (WC) as the major and minor crystalline phases, respectively. The present study provides a multiple perspective of carbon tungsten composites (CTCs) for methanol oxidation (as an electrode), adsorption (as an adsorbent) and degradation (as a solid catalyst) of methylene blue (MB). The operational electrodes were designed from both CTCs and used as a catalyst in an electrocatalysis process. The electrocatalysts exhibited high and stable catalytic performance (CTCE-25>CTCE-170) in methanol electro-oxidation. The newly synthesized W-doped carbon nanoreactors were used successfully as an adsorbent for MB and a heterogeneous catalyst for MB oxidation. Ordered CTC-25 and CTC-170 exhibited dynamic MB adsorption within 15min and complete oxidation of MB in 25–40min. A synergetic effect between tungsten carbide and the carbon cage framework was noted.

Radical-Initiated Decoloration of Methylene Blue in a Gas–Liquid Multiphase System Via DC Corona Plasma

The mechanism of methylene blue (MB) oxidation initiated by hydroxyl radicals (·OH) in a gas–liquid multiphase plasma reactor was investigated. Direct current corona plasma was applied to produce ·OH. The effects of liquid solution pH and plasma-forming gas components (air, N2, He, CO2) were evaluated. The removal of MB exceeded 90 % after 3 h of treatment under an air atmosphere at neutral pH, and it was shown to be mainly through the function of ·OH. Further experiments demonstrated that ·OH was mainly produced through electron-molecule collision processes. The energy efficiency of the process was assessed to be as high as 3.8 × 10−3 mol/kWh when the removal of MB reached 95.7 %. This high value was due to the countless liquid droplets greatly increasing the contact surface area. The results using CO2 as the forming gas indicated that the carbonate in solution has a negative effect on the generation of ·OH.

Manganese oxide – an excellent microwave absorbent for the oxidation of methylene blue

The enhanced degradation of methylene blue in the presence of manganese oxide under microwave was mainly attributed to the magnetic moment of center Mn and the charge transfer.

Ordered mesoporous hematite promoted by magnesium selective leaching as a highly efficient heterogeneous Fenton-like catalyst

Selective leaching of Mg in Mg modified mesoporous hematite promotes highly efficient wet peroxide oxidation of methylene blue.

Band Gap Engineering of ZnO using Core/Shell Morphology with Environmentally Benign Ag2S Sensitizer for Efficient Light Harvesting and Enhanced Visible-Light Photocatalysis

Band gap engineering offers tunable optical and electronic properties of semiconductors in the development of efficient photovoltaic cells and photocatalysts. Our study demonstrates the band gap engineering of ZnO nanorods to develop a highly efficient visible-light photocatalyst. We engineered the band gap of ZnO nanorods by introducing the core/shell geometry with Ag2S sensitizer as the shell. Introduction of the core/shell geometry evinces great promise for expanding the light-harvesting range and substantial suppression of charge carrier recombination, which are of supreme importance in the realm of photocatalysis. To unveil the superiority of Ag2S as a sensitizer in engineering the band gap of ZnO in comparison to the Cd-based sensitizers, we also designed ZnO/CdS core/shell nanostructures having the same shell thickness. The photocatalytic performance of the resultant core/shell nanostructures toward methylene blue (MB) dye degradation has been studied. The results imply that the ZnO/Ag2S core/shell nanostructures reveal 40- and 2-fold enhancement in degradation constant in comparison to the pure ZnO and ZnO/CdS core/shell nanostructures, respectively. This high efficiency is elucidated in terms of (i) efficient light harvesting owing to the incorporation of Ag2S and (ii) smaller conduction band offset between ZnO and Ag2S, promoting more efficient charge separation at the core/shell interface. A credible photodegradation mechanism for the MB dye deploying ZnO/Ag2S core/shell nanostructures is proposed from the analysis of involved active species such as hydroxyl radicals (OH(•)), electrons (e(-)(CB)), holes (h(+)(VB)), and superoxide radical anions (O2(•-)) in the photodegradation process utilizing various active species scavengers and EPR spectroscopy. The findings show that the MB oxidation is directed mainly by the assistance of hydroxyl radicals (OH(•)). The results presented here provide new insights for developing band gap engineered semiconductor nanostructures for energy-harvesting applications and demonstrate Ag2S to be a potential sensitizer to supersede Cd-based sensitizers for eco-friendly applications.

Application of full factorial design for methylene blue dye removal using heat-activated persulfate oxidation

In this study, a thermally activated persulfate oxidation process was investigated to treat aqueous methylene blue (MB) dye. Effects of temperature (55–80°C), initial pH (2.3–9.3), and potassium persulfate concentration (500–2000 (mg/L)) on MB color removal were examined. Results showed that acidic and neutral pH values were more favorable for MB oxidation than basic pH values. Based on experimental results, increasing the temperature from 55 to 80 (°C), and oxidant dose from 500 to 2000 (mg/L) enhanced the color removal efficiency (CR%) from 36% to 99.5% and from 55% to 98%, respectively. Kinetic study indicated that MB dye removal was a pseudo first-order reaction with respect to the various concentrations of MB and persulfate. Activation energy for the hot persulfate oxidation of MB was obtained as 112.3 (kJ/mol). To analyze the experimental data, an experimental design was applied by considering four operating parameters, including initial dye concentration, oxidant dosage, temperature and reaction time as input variables. A model was proposed for the statistical analysis of color removal prediction. Model predictions were found to be in good agreement (R2=0.96, adjusted R2=95.6%) with experimental data.

Modeling methylene blue oxidation by means of Fenton chemistry enhanced by UV irradiation at mild conditions

Taking into account that Fenton chemistry can be enhanced under UV radiation, a systematic activation of different H2O2 concentrations (7–50 mM) in 0.05M Na2SO4 (pH 2 adjusted with H2O4) was carried out, in the presence of UV/Fe2+ in a photochemical reactor. From the experimental results, a simple empirical correlation between the H2O2 activation velocity (AV) and its concentration was derived, as a result, a chemical model for the OH⋅ production was obtained. Considering that the attractiveness of the Fenton chemistry is its near-stoichiometric generation of a strong oxidant, it is possible to model the oxidation of organic matter under mild conditions. In this way, the fraction of H2O2 produced/consumed provides a measure of the efficiency of the oxidation process. The chemical model was tested in the photochemical reactor with several methylene blue (MB) concentrations (0.1–0.3 mM). Experimentally and theoretically, it was found that 0.1, 0.2, and 0.3mM MB can be oxidized in 85, 90, and 100 min, respectively. The predictions of the theoretical model are based on 90% of Chemical Oxygen Demand (COD) abatement. Thus, the theoretical results (time for achieving 90% of COD removal, and the stoichiometric amount of H2O2 required for such COD achievement) obtained from the chemical model, agree within a range of 5–15% of relative error against the experimental results. Although Fenton chemistry is very complex, under this approach it is possible to predict the oxidation of the organic matter contained in synthetic industrial effluents by means of a simple chemical model.

Three-Dimensional Electro-Fenton Degradation of Methyleneblue Based on the Composite Particle Electrodes of Carbon Nanotubes and Nano-Fe3O4

Carbon nanotubes/magnetic nano-Fe3O4 composite (CNTs/Fe3O4NPs) were prepared by chemical co-precipitation. Ti/SnO2electrode was used as the anode, the CNTs/Fe3O4 composite as particle electrodes, and graphite electrode as cathode respectively. Four different systems for degradation of methylene blue (MB) in neutral medium were investigated: Ti/SnO2 anode (A), Ti/SnO2 anode with CNTs particle electrodes (B), Ti/SnO2anode with Fe3O4NPs particle electrodes (C), and Ti/SnO2anode with CNTs/Fe3O4NPs particle electrodes (D). It was found that D system exhibited much higher MB degradation efficiency than others, attaining 82 % in 30 min. The enhanced efficiency was attributed to Ti/SnO2 anodic direct oxidation of MB and CNTs/Fe3O4 NPs composite particle electrodes which could activate molecule oxygen to produce more H2O2 and ·OH. CNTs/Fe3O4 NPs particle electrodes could achieve magnetic separation easily for reuse and exhibited good degradation efficiency to MB.

Fenton-like processes and adsorption using iron oxide-pillared clay with magnetic properties for organic compound mitigation.

In this work, a new step was added to the classic route of iron-pillared clay obtention, resulting in a material with both magnetic and oxidative properties. The saturation of the material surface intercalated with trinuclear acetate-hydroxo iron (III) nitrate in glacial acetic acid atmosphere before heat treatment promoted magnetic phase formation (FePMAG). The material was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS), and X-ray photoelectron spectroscopy (XPS). FePMAG showed an increase of 0.57 nm in basal spacing which contributed to the specific surface area increase from 39.1 to 139.2 m(2)/g. The iron phase identified by XRD and XPS was maghemite, with a little presence of hematite formed by the trinuclear acetate-hydroxo iron (III) nitrate decomposition during heat treatment. In the adsorption tests, FePMAG displayed a good capacity for organic dye methylene blue (MB) removal, reaching 41 % at 150 min. Under photo-Fenton conditions, the material showed an excellent MB oxidation capacity, completely removing the color of the solution within 90 min. Identification of the oxidation products with lower molecular (m/z = 160, 220, and 369) mass was performed by electrospray ionization mass spectroscopy (ESI-MS).