Phenol Removal through Chemical Oxidation using Fenton Reagent

In this study, phenol, aromatic, and non‐biodegradable organic matter were investigated and found to be removed from the model solution through chemical oxidation using Fenton reagent. The effects of the initial phenol concentration, hydrogen peroxide, and ferrous sulfate concentrations on the removal efficiency were investigated. Performance of the chemical oxidation process was monitored with phenol and COD (Chemical Oxygen Demand) analyses. In the experimental studies, phenol removal of over 98 % and COD removal of nearly 70 % were achieved. The optimum conditions for Fenton reaction both for initial phenol concentrations of 200 and 500 mg/L were found at a ratio [Fe²⁺]/[H₂O₂] (mol/mol) equal to 0.11. According to the results, chemical oxidation using Fenton reagent was found to be too effective, especially for phenol removal. However, this method has limited removal efficiency for COD.     

Electrocatalytic production of OH radicals and their oxidative addition to benzene

The feasibility of the electrochemical generation of Fenton's reagent is demonstrated and the subsequent reaction of produced OH radical with benzene studied. Under the proposed working conditions, phenol is obtained as the main product, with current yield as high as 60% (on the basis of 3 F/mole of phenol) and with only traces of other higher oxidized compounds. At fixed H₂SO₄ concentration and with suitable [Fe³⁺]/[O₂] ratio, a maximum in current yield is obtained; this yield may presumably be increased if continuous removal of phenol is employed during the electrolysis.     

Hydroxylation of phenol with H2O2 over transition metal containing nano-sized hollow core mesoporous shell carbon catalyst

The catalytic performance of transition metal (Fe²⁺ or Cu²⁺) containing nano-sized hol low core mesoporous shell carbon (HCMSC) heterogeneous catalysts for the hydroxylation of phenol with hydrogen peroxide (H₂O₂) in water was investigated in a batch reactor. The metal-containing HCMSC catalyst showed higher activity than the same metal ion-exchanged zeolites. The nature of the metal and its content in the HCMSC had remarkable influence on the reaction results under the typical reaction conditions (PhOH/H₂O₂=3, reaction temperature=60 ‡C). Fe²⁺ containing HCMSC catalyst showed high catalytic activity with phenol conversion of 29%, selectivity to catechol (CAT) and hydroquinone (HQ) about 85%, H₂O₂ effective conversion about 70% and selectivity to benzoquinone (BQ) below 1% in the batch system.     

Oxidative desulfurization of Gas oil by polyoxometalates catalysts

Several polyoxometalates: Na₂HPM₁₂O₄₀, H₃PM₁₂O₄₀, Na₂HPM₁₂O₄₀, (VO)H[PM₁₂O₄₀] and (n-Bu₄N)₃[PM₁₂O₄₀] (M = Mo and W) as well as (n-Bu₄N)_3 + x[PW_12−xV_xO₄₀] (x = 0–3) were synthesized and characterized. Benzothiophene, dibenzothiophene and 4,6-dimethyl-dibenzothiophene were used as model sulfur compounds in gas oil. The oxidation reaction was performed using different polyoxometalates as catalyst and H₂O₂/acetic acid. The experimental results show that the W-based polyoxometalate catalysts are more active than the Mo catalysts. The oxidation reactivity of the catalysts depends on the type of countercation: Na⁺ > H⁺ > (VO)⁺ > (n-Bu₄N)⁺. In a series of (n-Bu₄N)_3 + x [PW_12−xV_xO₄₀] (x = 0–3) the order of catalytic activity is V₃ > V₂ > V₁ > V₀. The reactivity order of the sulfur compounds is: dibenzothiophene > 4,6-dimethyldibenzo-thiophene > benzothiophene. The catalytic system in this work was used for the oxidation of gas oil combined with solvent extraction to remove sulfur content in gas oil. Under mild reaction condition, high sulfur removal up to 98% can be achieved with high oil recovery (90%).     

Synthesis and characterization of nano-crystalline strontium hexaferrite using the co-precipitation and microemulsion methods with nitrate precursors

Nano-crystalline strontium hexaferrite (SrFe₁₂O₁₉) powder was synthesized using the classical co-precipitation and microemulsion methods. The precursors were obtained by precipitating Sr²⁺ and Fe²⁺ ions using tetramethylammonium hydroxide and calcinating at different temperatures ranging from 400 °C to 1000 °C in air. The influence of the Sr²⁺/Fe³⁺ mol ratio and the calcination temperature on the product formation and magnetic properties were studied. The formation of nanosized particles of SrFe₁₂O₁₉ with a relatively high saturation magnetization M_s = 64 Am²/kg, remanent magnetization of M_r = 39 Am²/kg and a coercitivity of H_c = 5.5 kOe was achieved at a Sr²⁺/Fe³⁺ mol ratio of 1:8 calcined at 900 °C. The formation of the SrFe₁₂O₁₉ was inspected using XRD analysis, thermogravimetric analysis (TGA), differential thermal analysis (DTA), TEM, and magnetic measurements.     

Preparation, characterization and bifunctional electrocatalysis of an inorganic-organic complex with a vanadium-substituted polyoxometalate

An inorganic-organic complex with a vanadium-substituted polyoxometalate 1, formulated as [Cu(phen)₂]₂PVW₁₁O₄₀ was hydrothermally synthesized. Complex 1 crystallizes in the monoclinic P2(1)/c space group with a = 25.9932(12) Å, b = 11.9889(6) Å, c = 23.2672(11) Å, β = 113.6750(10)°, V = 6640.5(6) Å³, R = 0.0312, and Z = 4. Complex 1 is constructed from a Keggin-type anion PVW₁₁O₄₀⁴⁻ coordinated to two [Cu(phen)₂]²⁺ units. One [Cu(phen)₂]²⁺ unit is coordinated to a terminal oxygen and the other [Cu(phen)₂]²⁺ unit is coordinated to a bridging oxygen of the polyoxoanion. Redox activities for both the tungsten and vanadium centers have been observed using cyclic voltammetry performed on 1-bulk modified carbon paste electrode (CPE). It was found that 1 presents good electrocatalytic activities not only for the reduction of IO₃⁻, NO₂⁻, and H₂O₂ but also the oxidation of l-cysteine. Complex 1 also shows intense luminescent properties arising from ligand-to-copper charge transfer and oxygen-to-vanadium charge transfer at room temperature in the solid state.     

Amperometric flow injection analysis as a new approach for studying disperse systems

Fast and simple quantitative determination in dispersed systems (layered double hydroxides - LDHs - suspensions in aqueous solutions) was performed by a procedure that couples flow injection and amperometric detection (FI-AM). LDH dispersions are injected in a continuous flow (1 mL min⁻¹) of 0.05 mol L⁻¹ KNO₃ solution and [Cu(H₂O)₆]²⁺, used as a probe, is detected at a glassy carbon electrode housed in a flat electrochemical cell. The current intensity, recorded at the selected working potential (−0.25 V vs Ag/AgCl/NaCl (3 mol L⁻¹)), presents a linear relationship with [Cu(H₂O)₆]²⁺ concentration and the procedure offers high sensitivity (slope = 0.036 μA/(μmol L⁻¹)), a low detection limit (=0.7 μmol L⁻¹) and a wide quantification range (4-200 μmol L⁻¹).The method was applied to [Cu(H₂O)₆]²⁺ determination in two particular LDH-aqueous solution dispersed systems: (1) [Cu(H₂O)₆]²⁺ scavenging by etilendiammintetraacetic acid (EDTA) modified Zn-Al-LDHs, and (2) [Cu(H₂O)₆]²⁺ release from a copper doped Mg-Al-LDHs. The results obtained are comparable to those reported in previous works using different quantification techniques. FI-AM determination is applied without sample pretreatment (solid-supernatant separation) providing a high sampling rate (above 120 samples h⁻¹) that allows a better comprehension of the processes, particularly at the initial stages.     

Hydrothermal synthesis of NaNbO3 with low NaOH concentration

NaNbO₃ fine powders were prepared by reacting niobium pentoxide with low NaOH concentration solution under hydrothermal conditions at 160 °C. The reaction ruptured the corner-sharing of NbO₆ octahedra in the reactant Nb₂O₅, yielding various niobates, and the structure and composition of the niobates depended on the [OH⁻] and reaction time. The fine Nb₂O₅ powder first aggregated to large particles and then turned to metastable intermediates with multifarious morphology. The reaction was fast for the situation of [OH⁻] = 2 M. The [OH⁻] determined the structure of final products, and three types of NaNbO₃ powder with the orthorhombic, tetragonal and cubic symmetries were obtained, respectively, depending on the [OH⁻]. The low [OH⁻] was propitious to yield orthorhombic NaNbO₃. The present work demonstrated that higher [OH⁻] was not favored to synthesize NaNbO₃ powders and the conversion speed in this reaction was not in proportion to the [OH⁻].     

Carbonate and sulphate green rusts—Mechanisms of oxidation and reduction

The oxidation and reduction of carbonate, GR(CO₃), and sulphate, GR(SO₄), green rusts (GR) have been studied through electrochemical techniques, electrochemical quartz crystal microbalance (EQCM), FTIR, XRD and SEM. The used samples were made of thin films electrodeposited on gold substrate. The results from the present work, from our previous studies and from literature were compiled in order to establish a general scheme for the formation and transformation pathways involving carbonate or sulphate green rusts. Depending on experimental conditions, two routes of redox transformations occur. The first one corresponds to reaction via solution and leads to the formation of ferric products such as goethite or lepidocrocite (oxidation) or to the release of Fe^II ions into the solution (reduction) with soluble Fe^II-Fe^III complexes acting as intermediate species. The second way is solid-state reaction that involve conversion of lattice Fe²⁺ into Fe³⁺ and deprotonation of OH groups in octahedra sheets (solid-state oxidation) or conversion of lattice Fe³⁺ into Fe²⁺ and protonation of OH groups (solid-state reduction). The solid-state oxidation implies the complete transformation of GR(CO₃) or GR(SO₄) to ferric oxyhydroxycarbonate exGRc-Fe(III) or ferric oxyhydroxysulphate exGRs-Fe(III), for which the following formulas can be proposed, Fe^III₆(OH)_(12−2y)(O)_(2+y)(H₂O)_(y)(CO₃) or Fe^III₆(OH)_(12−2z)(O)_(2+z)(H₂O)_(6+z)(SO₄) with 0 ≤ y or z ≤ 2. The solid-state reduction gives ferrous hydroxycarbonate exGRc-Fe(II) or ferrous hydroxysulphate exGRs-Fe(II), which may have the following chemical formulas, [Fe^II₆(OH)₁₀(H₂O)₂]·[CO₃, 2H₂O] or [Fe^II₆(OH)₁₀(H₂O)₂]·[SO₄, 8H₂O].     

Degradation of an Anthraquinone Dye by Ozone/Fenton: Response Surface Approach and Degradation Pathway

A coupled O₃/Fenton process is applied to study the degradation ef?ciency of organic pollutants. The C.I. Acid Blue 80 (AB80), a kind of anthraquinone dye, is used as target contaminant. The results show that the combination of ozonation and Fenton process is a highly effective way of removing color from wastewater. Response surface methodology is applied to optimize the working conditions and the effects and interactions among initial pH (X₁), mole ratio of H₂O₂/Fe²⁺ (X₂) and ozone flux (X₃) are investigated. Regression equations determines that the best condition is that initial pH = 2.85, [H₂O₂]/[Fe²⁺] = 18.10 and ozone flux = 55.70 L.h^?1. It turns out the relative error of 1.32% with the predicted model when the actual value which is 88.76% in the best condition, compared to the predictive value of 88.95% under same condition. UV-Vis and FT-IR analysis are used as an assisted technique to study degradation mechanism during the oxidation process. The intermediate products are determined by gas chromatography/mass spectrometry (GC/MS) analysis and the plausible degradation pathway is proposed.     

Electrocatalyst materials for fuel cells based on the polyoxometalates—K7 or H7[(P2W17O61)Fe(H2O)] and Na12 or H12[(P2W15O56)2Fe4(H2O)2]

Free acids of the iron substituted heteropoly acids (HPA), H₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (HFe1) and H₁₈[(P₂W₁₅O₅₆)₂Fe^III₂(H₂O)₂] (HFe2) were prepared from the salts K₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (KFe1) and Na₁₂[(P₂W₁₅O₅₆)₂Fe^III₄(H₂O)₂] (NaFe4), respectively. The iron-substituted HPA were adsorbed on to XC-72 carbon based GDLs to form HPA doped GDEs after water washing with HPA loadings of ca. 1 μmol. The HPA was detected throughout the GDL by EDX. Solution electrochemistry of the free acids are reported for the first time in sulfate buffer, pH 1-3. The hydrogen oxidation reaction was catalyzed by KFe1 at 0.33 V, with an exchange current density of 38 mA/cm². Moderate activity for the oxygen reduction reaction was observed for the iron substituted HPA, which was dramatically improved by selectively removing oxygen atoms from the HPA by cycling the fuel cell cathode under N₂ followed by reoxidation to give a restructured oxide catalyst. The nanostructured oxide achieved an OCV of 0.7 V with a Tafel slope of 115 mV/decade. Cycling the same catalysts in oxygen resulted in an improved catalyst/ionomer/carbon configuration with a slightly higher Tafel slope, 128 mV/decade but a respectable current density of 100 mA/cm² at 0.2 V.     

Phenol methylation over nanoparticulate CoFe2O4 inverse spinel catalysts: The effect of morphology on catalytic performance

A series of CoFe₂O₄ nanoparticles have been prepared via co-precipitation and controlled thermal sintering, with tunable diameters spanning 7–50 nm. XRD confirms that the inverse spinel structure is adopted by all samples, while XPS shows their surface compositions depend on calcination temperature and associated particle size. Small (<20 nm) particles expose Fe³⁺ enriched surfaces, whereas larger (50 nm) particles formed at higher temperatures possess Co:Fe surface compositions close to the expected 1:2 bulk ratio. A model is proposed in which smaller crystallites expose predominately (1 1 1) facets, preferentially terminated in tetrahedral Fe³⁺ surface sites, while sintering favours (1 1 0) and (1 0 0) facets and Co:Fe surface compositions closer to the bulk inverse spinel phase. All materials were active towards the gas-phase methylation of phenol to o-cresol at temperatures as low as 300 °C. Under these conditions, materials calcined at 450 and 750 °C exhibit o-cresol selectivities of 90% and 80%, respectively. Increasing either particle size or reaction temperature promotes methanol decomposition and the evolution of gaseous reductants (principally CO and H₂), which may play a role in CoFe₂O₄ reduction and the concomitant respective dehydroxylation of phenol to benzene. The degree of methanol decomposition, and consequent H₂ or CO evolution, appears to correlate with surface Co²⁺ content: larger CoFe₂O₄ nanoparticles have more Co rich surfaces and are more active towards methanol decomposition than their smaller counterparts. Reduction of the inverse spinel surface thus switches catalysis from the regio- and chemo-selective methylation of phenol to o-cresol, towards methanol decomposition and phenol dehydroxylation to benzene. At 300 °C sub-20 nm CoFe₂O₄ nanoparticles are less active for methanol decomposition and become less susceptible to reduction than their 50 nm counterparts, favouring a high selectivity towards methylation.     

Gaseous Elemental Mercury Removal Using Combined Metal Ions and Heat Activated Peroxymonosulfate/H2O2 Solutions

Several novel oxidation removal processes of elemental mercury (Hg⁰) from flue gas using combined Fe²⁺/Mn²⁺ and heat activated peroxymonosulfate (PMS)/H₂O₂ solutions in a bubbling reactor were proposed. The operating parameters (e.g., PMS/H₂O₂ concentration, Fe²⁺/Mn²⁺ concentration, solution pH, activation temperature, and Hg⁰/NO/SO₂/O₂/CO₂ concentration), mechanism and mass transfer-reaction kinetics of Hg⁰ removal were investigated. The results show that heat and Fe²⁺/Mn²⁺ have significant synergistic effect for activating PMS and PMS/H₂O₂ to produce free radicals to oxidize Hg⁰. Hg⁰ removal is strongly affected by PMS/H₂O₂ concentration, Fe²⁺/Mn²⁺ concentration, activation temperature, and solution pH. · and ·OH produced from combined heat and Fe²⁺/Mn²⁺ activated PMS/H₂O₂ play a leading role in Hg⁰ removal. Under optimized experimental conditions, Hg⁰ removal efficiencies reach 100, 94.9, 66.9, and 58.9% in heat/Fe²⁺/PMS/H₂O₂, heat/Mn²⁺/PMS/H₂O₂, heat/Fe²⁺/PMS, and heat/Mn²⁺/PMS systems, respectively. Hg⁰ removal processes in four systems belong to fast reaction and were controlled by mass transfer under optimized experimental conditions. © 2018 American Institute of Chemical Engineers AIChE J, 65: 161–174, 2019     

Visible light induced photocatalytic activity of Nb2O5/carbon cluster/Cr2O3 composite materials

Nano-sized Nb₂O₅/carbon cluster/Cr₂O₃ composite material was prepared by the calcination of NbCl₅/chromium acetylacetonate/epoxy resin complex under an argon atmosphere. The Pt-loaded Nb₂O₅/carbon cluster/Cr₂O₃ composite material shows the photocatalytic activity under visible light irradiation. The composite material successfully decomposed the water into H₂ and O₂ in the [H₂]/[O₂] ratio of 2. Electron spin resonance spectral examination suggests a two-step electron transfer in the process of Nb₂O₅ → carbon cluster → Cr₂O₃ → Pt.     

Influencing factors on electrochromic hysteresis performance of ruthenium purple produced by a WO3/Tris(2,2′-bipyridine)ruthenium(II)/polymer hybrid film

A [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine)/WO₃ hybrid (denoted as Ru-WO₃) film was prepared as a base layer on an indium tin oxide electrode by electrodeposition from a colloidal solution containing peroxotungstic acid, [Ru(bpy)₃]²⁺ and poly(sodium 4-styrenesulfonate). A ruthenium purple (RP, Fe^III₄[Ru^II(CN)₆]₃, denoted as Fe^III-Ru^II) layer was electrodeposited on a neat WO₃ film or a Ru-WO₃ film from an aqueous RP colloid solution to yield a WO₃/RP bilayer film or a Ru-WO₃/RP bilayer film, respectively. The spectrocyclic voltammetry measurement reveals that Fe^II-Ru^II is oxidized to Fe^III-Ru^II by a geared reaction of [Ru(bpy)₃]^2+/3+ and Fe^III-Ru^II is reduced by a geared reaction of H_xWO₃/WO₃ in the Ru-WO₃/RP film. These geared reactions produced electrochromic hysteresis of the RP layer. However, the absorbance change in the hysteresis was smaller than that for the Ru-WO₃/Prussian blue bilayer film reported previously, resulting from the lower electroactivities of any redox component for the Ru-WO₃/RP film. The lower electroactivities could be explained by the specific interface between the Ru-WO₃ and RP layers. It might contribute to either an increase of the interfacial resistance between the Ru-WO₃ and RP layers, or formation of the physically precise interface between the layers to make it difficult for counter ions to be transported in the interfacial liquid phase involved in the redox reactions in the film. The specific interface at the Ru-WO₃ and RP layers could be formed possibly by the electrostatic interaction between [Ru(bpy)₃]²⁺ and terminal [Ru(CN)₆]⁴⁻ moieties of RP. It could be suggested by the decreased redox potential of [Ru(bpy)₃]²⁺ in the Ru-WO₃ layer from 1.03 to 0.61 V by formation of the RP layer.     

Effects of NO2 ions on localised corrosion of steel in NaHCO3 + NaCl electrolytes

Pitting corrosion of carbon steel electrodes in 0.1 mol L⁻¹ NaHCO₃ + 0.02 mol L⁻¹ NaCl solutions was induced by anodic polarisation. The evolution of the breakdown potential E_b with NO₂⁻ concentration was investigated by linear voltammetry. E_b increased from −15 ± 5 mV/SCE for [NO₂⁻] = 0 up to 400 ± 50 mV/SCE for [NO₂⁻] = 0.1 mol L⁻¹. During anodic polarisation at potentials comprised between E_b([NO₂⁻] = 0) and E_b([NO₂⁻] ≠ 0), the behaviour of the whole electrode surface, followed by chronoamperometry, was compared to the behaviour of one single pit, followed via scanning vibrating electrode technique (SVET). Addition of a NaNO₂ solution after the beginning of the polarisation led to a rapid repassivation of pre-existing well-grown pits. In situ micro-Raman spectroscopy was then used to identify the corrosion products forming inside the pits. The first species to be detected in the presence of NO₂⁻ were mainly dissolved Fe(III) species, more likely [Fe^III(H₂O)₆]³⁺ complexes. Iron(II) carbonate FeCO₃, siderite, and carbonated green rust GR(CO₃²⁻) were also detected in the active pits, as in the absence of nitrite. But they were accompanied by maghemite γ-Fe₂O₃, a phase structurally similar to the passive film, that forms from the Fe(III) complexes. The Raman analyses then correlate with the SVET observations and confirm that the main effect of nitrite ions is to oxidize iron(II) into iron(III). The passive film would then form from the Fe(III) species still bound to the steel surface.     

Kinetics of phenol mineralization by Fenton-like oxidation

The kinetics of hydrogen peroxide decomposition and the mineralization rate of phenol in homogeneous aqueous solution (pH < 3) via Fenton-like reaction were studied. Results were correlated with the generation of hydroxyl radicals as well as with iron speciation. Batch experiments were carried out in de-ionized water in a completely mixed batch reactor under a wide range of experimental conditions (3500 ≤ [H₂O₂] ≤ 8250 mg/L; 100 mg/L ≤ [Fe] ≤ 2350 mg/L; 2.5 ≤ [H₂O₂]/[Fe] ≤ 83; 0 mg/L ≤ [TOC] ≤ 1000 mg/L). Results demonstrated that the rate of hydrogen peroxide decomposition, phenol mineralization and ferrous ions formation depended on both the initial concentration of the phenol and on the weight ratio between hydrogen peroxide and iron. A linear correlation was found between the mineralization rate of phenol and the decomposition rate of hydrogen peroxide indicated that 10 g of hydrogen peroxide was required to mineralize 1 g of phenol.     

Efficient photocatalytic activity of MnO2-loaded ZrO2/carbon cluster nanocomposite materials under visible light irradiation

Nano-sized ZrO₂/carbon cluster nanocomposite material was successfully prepared by the calcination of Zr(acac)₄/epoxy resin complex in air. The composite material obtained by calcining at 200 °C was treated with hydrogen hexachloroplatinate hexahydrate (H₂PtCl₆) to obtain Pt-loaded materials denoted as Ic₂₀₀Pt'sH's. The Pt-loaded material modified with MnO₂ particles efficiently decompose water into H₂ and O₂ with a [H₂]/[O₂] ratio of 2 under the irradiation of visible light (λ > 460 nm) through the electron transfer process of MnO₂ → carbon clusters → ZrO₂ → Pt.     

The sonochemical decolorisation of textile azo dye CI Reactive Orange 127

In the present study, Fenton and sono‐Fenton processes were applied to the oxidative decolorisation of synthetic textile wastewater including CI Reactive Orange 127 and polyvinyl alcohol. Process optimisation [pH, ferrous ion (Fe²⁺) and hydrogen peroxide (H₂O₂)], kinetic studies and their comparison were carried out for both of the processes. The sono‐Fenton process was performed by indirect sonication in an ultrasonic water bath, which was operated at a fixed 35‐kHz frequency and 80 W power. The optimum conditions were determined as [Fe²⁺] = 20 mg l^?1, [H₂O₂] = 15 mg l^?1 and pH = 3 for the Fenton process and [Fe²⁺] = 25 mg l^?1, [H₂O₂] = 5 mg l^?1 and pH = 3 for the sono‐Fenton process. The colour removals were 89.9% and 91.8% by the Fenton and sono‐Fenton processes, respectively. The highest decolorisation was achieved by the sono‐Fenton process because of the production of some oxidising agents as a result of sonication. Consequently, ultrasonic irradiation in the sono‐Fenton process slightly increased the colour removal to 91.8%, while decreasing the hydrogen peroxide dosage to one‐third of that of the Fenton process.