Oxidation Of Chlorophenols Research Articles

Oxidative degradation of phenols in sono-Fenton-like systems upon high-frequency ultrasound irradiation

The kinetics of oxidative degradation of phenol and chlorophenols upon acoustic cavitation in the megahertz range (1.7 MHz) is studied experimentally in model systems, and the involvement of in situ generated reactive oxygen species (ROSs) is demonstrated. The phenols subjected to high frequency ultrasound (HFUS) are ranked in terms of their rate of conversion: 2,4,6-trichlorophenol > 2,4-dichlorophenol ~ 2-chlorophenol > 4-chlorophenol ~ phenol. Oxidative degradation upon HFUS irradiation is most efficient at low concentrations of pollutants, due to the low steady-state concentrations of the in situ generated ROSs. A dramatic increase is observed in the efficiency of oxidation in several sonochemical oxidative systems (HFUS in combination with other chemical oxidative factors). The system with added Fe2+ (a sono-Fenton system) derives its efficiency from hydrogen peroxide generated in situ as a result of the recombination of OH radicals. The S2O82-/Fe2+/HFUS system has a synergetic effect on substrate oxidation that is attributed to a radical chain mechanism. In terms of the oxidation rates, degrees of conversion, and specific energy efficiencies of 4-chlorophenol oxidation based on the amount of oxidized substance per unit of expended energy the considered sonochemical oxidative systems form the series HFUS < S2O82-/HFUS < S2O82-/Fe2+/HFUS.

Graphene quantum dot-phthalocyanine polystyrene conjugate embedded in asymmetric polymer membranes for photocatalytic oxidation of 4-chlorophenol

The feasibility of using π–π stacking as a means of fixing unsubstituted Zn phthalocyanine (ZnPc) to a support prior to formation of photoactive polymer asymmetric membranes was explored. Stable ZnPc–graphene quantum dot-polystyrene conjugates (6.15 μmol/g ZnPc loading) were synthesized and embedded in polystyrene membranes which proved to be photoactive with a singlet oxygen quantum yield of 0.43 in ethanol and 0.37 in water. The membranes also proved to be active in the photocatalytic oxidation of 4-chlorophenol in water where the reaction followed second-order kinetics. At 3.24 × 10−4 mol L−1, the photo-oxidation of 4-chlorophenol was observed with a kobs of 35.9 L mol−1 min−1 and a half-life of 86 min.

Electrochemical Oxidation of 4-Chlorophenol Over a Carbon Paste Electrode Modified with ZnAl Layered Double Hydroxides

A study is presented on the electrochemical oxidation of 4-chlorophenol (4cp) in aqueous solution using a bare carbon paste electrode, CPE, and another one that was modified with ZnAl layered double hydroxides (CPE/ZnAl-LDH). The electro-oxidation was effected at pH values ranging from 3 up to 11. It was found through cyclic voltammetry that this process was irreversible, namely, there were no reduction peaks, and that depending on the nature of the electrode, the anodic current was limited either by adsorption (CPE) or diffusion (CPE/ZnAl-LDH). The energy required and the oxidation reaction rate depended on the pH and on the nature of the electrode, such that the greater rates were obtained when the CPE/ZnAl-LDH electrode and acid pHs were used.

Effect of vanadium on the catalytic activity of ceria towards wet peroxide oxidation of persistent and biorecalcitrant chlorinated organics

Chlorinated aromatic compounds are recalcitrant to biodegradation and conventional treatment methods Herein, we investigate the efficiency of catalysts in the oxidation of 4-chlorophenol (4-CP) and 2,4-dichlorophenoxyacetic acid over CexV1-xO2 (x: 0, 0.25, 0.5, 0.75, 1) nano oxides with hydrogen peroxide in water. The catalysts were characterised by temperature programmed reduction (H2-TPR) and desorption (NH3-TPD and CO2-TPD) techniques. Effect of reaction variables like catalyst dosage, H2O2 and reactant concentrations and temperature, were investigated. The results show that 500mg/L 4-CP is completely removed with 0.13mol/L of H2O2 over 500mg/L Ce0.75V0.25O2, within 135min with the total organic carbon (TOC) removal of 21.56%. Within 75min, 250mg/L 2,4-D is completely degraded by 0.08mol/L H2O2 over 500mg/L Ce0.5V0.5O2 with 30.15% TOC removal. The major degradation intermediates are phenol, benzoquinone and 2,5-hexane dione as identified by gas chromatography mass spectrometry (GC–MS). Based on these, a possible reaction mechanism is proposed. The stability and reusability of the mixed oxides during five consecutive cycles was experimented by X-ray diffraction (XRD) and surface area measurements. The catalytic efficiency is retained after five successive runs and the catalysts are texturally stable Scavenging experiments revealed the activation of reaction through the formation of hydroxyl radicals.

Electrocatalytic behaviour of surface confined pentanethio cobalt (II) binuclear phthalocyanines towards the oxidation of 4-chlorophenol

Cobalt binuclear phthalocyanine (CoBiPc) bearing pentanethio substituents at the peripheral positions were synthesized. The immobilization of the synthesized cobalt phthalocyanines on gold electrode was achieved using self-assembled monolayer method (SAM). X-ray photoelectron spectroscopy (XPS) and Kelvin Probe (KP) techniques were used to characterise the formation of monomeric and binuclear phthalocyanine SAMs on the gold surface. The phthalocyanine SAMs on gold electrodes were investigated for electrocatalytic oxidation of 4-chlorophenol. The electrocatalytic properties of tetra- and octa- pentanethio substituted cobalt binuclear phthalocyanine (CoBiPc) are compared with their tetra- and octa-pentanethio substituted phthalocyanine (CoPc). The SAMs modified gold electrode surfaces showed a peak current enhancement and stability and reduction in electrocatalytic potentials compared to the bare or unmodified electrodes towards the detection of the 4-chlorophenol. The SAMs of cobalt binuclear phthalocyanines exhibited more enhanced electrocatalytic properties in terms of stability, detection peak current and reduction of the electrocatalytic over potential.

Trace bromide ion impurity leads to formation of chlorobromoaromatic by-products in peroxymonosulfate-based oxidation of chlorophenols

Trace bromide (Br−) released from industrial effluents or brominated compounds is able to directly react with peroxymonosulfate (PMS) to generate a series of reactive oxidants which can oxidize and also halogenate organics. We report the identification and evolution of by-products during 2,4,6-trichlorophenol (TCP) degradation in the presence of PMS and trace Br−. The influencing factors, including Br− concentration and pH, were investigated. The depletion of TCP was accelerated with increasing trace Br− concentration (0–0.2 mM) and was affected by the initial pH (3.0–7.0). The chlorinated and brominated compounds were identified in simulated wastewater during treatment with PMS. Notably, the potential formation of chlorobromoaromatic by-products was demonstrated for the first time in the presence of PMS and trace Br−. The possible reaction pathways of TCP and its derivatives are discussed. These findings have important implications for the future applications of PMS-based oxidation processes.

Fabrication of a novel PbO2 electrode with a graphene nanosheet interlayer for electrochemical oxidation of 2-chlorophenol

A novel PbO2 electrode with a graphene nanosheet interlayer (marked as GNS-PbO2) was prepared combining electrophoretic deposition and electro-deposition technologies. The micro morphology, crystal structure and surface chemical states of GNS-PbO2 electrodes were characterized using scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Their electrochemical properties and stability were determined using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ·OH radicals test and accelerated life test, and compared with traditional PbO2 electrodes. Besides, their potential application in the electrochemical degradation of 2-chlorophenol (2-CP) was investigated. The GNS-PbO2 electrode possessed perfect octahedral β-PbO2 microcrystals, and its grain size was much smaller than that of traditional PbO2 electrode. It exhibited higher electrochemical activity than traditional PbO2 electrode due to its larger electrochemical active surface area and stronger ·OH radicals generation ability. The service lifetime of GNS-PbO2 electrode (107.9h) was 1.93 times longer than that of traditional PbO2 electrode (55.9h). The electrochemical degradation rate constant of 2-CP on GNS-PbO2 electrode (kapp=2.75×10−2min−1) is much higher than for PbO2 electrode (kapp=1.76×10−2min−1). 2-CP oxidation yielded intermediates including aromatic compounds (catechol, phenol and ortho-benzoquinone) and organic acids (oxalic acid, maleic acid and glutaconic acid), and a possible degradation pathway for 2-CP was proposed accordingly.

Titania-coated plastic optical fiber fabrics for remote photocatalytic degradation of aqueous pollutants

Plastic optical fiber fabrics are widely utilized as efficient support materials owing to their high flexibility. In this study, we have investigated a remote photocatalysis system using modified plastic optical fiber fabrics. We successfully deposited TiO2 onto a modified plastic optical fiber fabric using the dip-coating method. The drying temperature was fixed at 50°C in order to inhibit the decomposition of the fabric. The TiO2-coated woven plastic optical fiber fabric was applied to the photocatalytic degradation of methylene blue (MB) and the simultaneous oxidation of 4-chlorophenol (4-CP) and reduction of Cr(VI). The degradation of MB by direct photolysis, or through dark reactions of the adsorbed MB on the surface of the fabric, was not observed. MB degradation increased with increasing TiO2 loading, Pt deposition, increasing solution pH, and decreasing initial MB concentration. Repeated testing in the above-mentioned degradation and simultaneous redox reactions revealed that the TiO2-coated woven plastic optical fiber fabrics retain good activity after multiple cycles. On the basis of these results, we propose that plastic optical fiber fabrics together with photocatalysts are suitable for remote (in situ) advanced oxidation process useful for the remediation of contaminated soil or groundwater.

Sequential Process Combination of Photocatalytic Oxidation and Dark Reduction for the Removal of Organic Pollutants and Cr(VI) using Ag/TiO2.

We investigated a sequential photocatalysis-dark reaction, wherein organic pollutants were degraded on Ag/TiO2 under UV irradiation and the dark reduction of hexavalent chromium (Cr(VI)) was subsequently followed. The photocatalytic oxidation of 4-chlorophenol (4-CP), a test organic substrate, induced the generation of degradation intermediates and the storage of electrons in Ag/TiO2 which were then utilized for reducing Cr(VI) in the postirradiation period. The dark reduction efficiency of Cr(VI) was much higher with Ag/TiO2 (87%), compared with bare TiO2 (27%) and Pt/TiO2 (22%). The Cr(VI) removal by Ag/TiO2 (87%) was contributed by adsorption (31%), chemical reduction by intermediates of 4-CP degradation (26%), and reduction by electrons stored in Ag (30%). When formic acid, humic acid or ethanol was used as an alternative organic substrate, the electron storage effect was also observed. The postirradiation removal of Cr(VI) on Ag/TiO2 continued for hours, which is consistent with the observation that a residual potential persisted on the Ag/TiO2 electrode in the dark whereas little residual potential was observed on bare TiO2 and Pt/TiO2 electrodes. The stored electrons in Ag/TiO2 and their transfer to Cr(VI) were also indicated by the UV-visible absorption spectral change. Moreover, the electrons stored in the preirradiated Ag/TiO2 reacted with O2 with showing a sign of low-level OH radical generation in the dark period.

Recyclable Ag-coated Fe3O4@TiO2 for efficient photocatalytic oxidation of chlorophenol

In this study, a facile and efficient approach for fabricating Ag-coated Fe3O4@TiO2 particles with a good core–shell structure is demonstrated. The synthetic protocol involves coating successive layers of TiO2 nanoparticles onto a magnetic core using a sol-gel method at low temperature, followed by the deposition of silver nanoparticles on the surface of the Fe3O4@TiO2 particles through chemical reduction. The Ag-coated Fe3O4@TiO2 magnetic photocatalyst exhibited high photocatalytic activity in the degradation of Rhodamine B under visible light. Moreover, the Ag-coated Fe3O4@TiO2 photocatalyst showed enhanced photocatalytic properties when compared with a previous report concerning the oxidation of 2,4,6-trichlorophenol in aqueous solution. The renewable photocatalytic activity of the photocatalyst was also examined.

Catalytic oxidation of 4-chlorophenol on in-situ sulfur-doped activated carbon with sulfate radicals

Abstract In-situ S-doped activated carbon (ACS) was prepared and used as a heterogeneous catalyst to activate persulfate (PS) for 4-chlorophenol (4CP) oxidation. The effects of several operation parameters, including PS concentration, initial pH, ACS dosage, and reaction temperature, on 4CP degradation were investigated in detail via batch experiments. Results show that ACS exhibited excellent catalytic activity for PS activation and a complete 4CP degradation as well as 65.3% COD removal can be achieved in 170 min at 25 °C with ACS dosage of 0.1 g/L, PS/4CP molar ratio of 24/1 and initial pH of 4.4. The biodegradability was greatly improved after a 170 min reaction. Quenching tests reveal that SO 4 - was the dominant active species taking part in the degradation of 4CP. Based on the stability tests and the corresponding characterizations of ACS before and after use, it was speculated that the loss of the specific surface area and the change of the surface chemistry led to the significant deactivation of ACS. Meanwhile, a possible mechanism of PS activation on ACS was proposed.

Effect of Adsorption and Passivation Phenomena on the Electrochemical Oxidation of Phenol and 2-Chlorophenol at Carbon Black Diamond Composite Electrode

This work reports on the importance of adsorption and passivation phenomena during the electro-oxidation of phenolic mixture. A case study of the anodic oxidation of phenol and 2-chlorophenol was performed. A carbon black–diamond electrode with 20% carbon black (20CBD electrode) was used as the anode. The anodic oxidation behaviors of 100 mg/L phenol and 100 mg/L 2-chlorophenol on the 20CBD electrode were investigated using cyclic voltammetry in aqueous solutions of 0.25 M Na2SO4. The electrochemical impedance technique was used to investigate the effects of electrode passivation and the adsorption of phenol and 2-chlorophenol through the electrochemical degradation process. The results showed that oxidation of 2-chlorophenol was easier than that of phenol. Even in a 1:1 mixture of 2-chlorophenol and phenol, each at 100 mg/L, the removal rate of 2-chlorophenol was higher than that of phenol. After 6 h, up to 94% of the 2-chlorophenol had degraded, whereas only 20% of the phenol had degraded in the same ti...

Electrochemical behavior of palladium modified amino-functionalized macroporous copolymer

In this study, macroporous poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) was synthesized by suspension copolymerization, functionalized by ring-opening reaction of the pendant epoxy groups with diethylene triamine and used for immobilization of Pd(II) ions from chloride and nitrate solutions under batch experimental condition. The amino-functionalized sample and samples with immobilized Pd(II) ions were characterized by Fourier transform infrared spectroscopy (FTIR) analysis and scanning energy-dispersive X-ray spectroscopy (SEM-EDX). The electrochemical behavior of electrodes composed of synthesized samples was tested in 0.1M H2SO4 by means of cyclic voltammetry (CV). The shape of recorded CV showed dependence on the type of Pd-salt used for Pd immobilization. The reaction of oxidation of 4-chlorophenol (4-CP) from 0.1M H2SO4 at investigated samples was also studied. Electrooxidation of 4-CP resulted in passivation and formation of reversible hydroquinone/benzoquinone on both investigated electrodes, although hydroquinone/benzoquinone formation was more pronounced on Pd immobilized from nitrite solution.

Oxidation of Chlorophenols by MnO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Supported on Kaolinite

Chlorophenols (CPs) are of significant concern because of their wide use, toxicity and persistence in environments. In the present study, -MnO2 supported on kaolinite was used as an oxidant to oxidize three kinds of CPs, 4-chlorophenol (CP), 2, 4-dichlorophenol(DCP) and 2, 4, 6-trichlorophenol(TCP). XRD pattern showed that the synthetic MnO2 has a poor crystallinity, and SEM results revealed that MnO2 was evenly coated on kaolinite with a loading amount of 8.64mg/g. All three CPs were efficiently degraded by supported MnO2 with a removal order of 2, 4, 6-TCP>2, 4-DCP>4-CP. The degradation of CPs obviously accompanied with the release of Mn2+. Results also showed the increased oxidant’s dosage promotes the removal of CPs. The reaction of CPs with MnO2 is strictly pH-dependent, the removal of CPs decreased with pH increasing.

Dechlorination and oxidative degradation of 4-chlorophenol with nanostructured iron-silver alginate beads

In this work, bimetallic zerovalent iron-silver nanoparticles (NZVI-Ag) immobilized in calcium alginate beads were prepared and characterized. This material was tested as catalyst in the dechlorination and oxidation of 4-chlorophenol (CP-4). The bimetallic nanoparticles showed average size and BET surface area around 80nm and 22m2g−1, respectively, with morphology and crystallinity typical of nanometric metallic iron. 4-CP dechlorination was more efficient at pH 3 than at pH 5 and at the former was completed in 30min. Further addition of H2O2 allowed high TOC reduction, quite similar to the obtained with the bare metallic nanoparticles but with lower metal leaching.

Electrochemical mineralization of chlorophenol by ruthenium oxide coated titanium electrode

Electrochemical oxidation of 4-chlorophenol (CP) was investigated (in terms of chemical oxygen demand (COD) and CP removal efficiencies) by using a dimensionally stable anode (DSA) namely ruthenium oxide coated titanium (Ti/RuO2) electrode. Effect of process conditions such as current density (j), electrolyte concentration (m), initial pH (pHo), time (t) and initial CP concentration (Co) has been studied. Current efficiency (CE) and specific energy consumption (SEC) were also measured. Gas chromatograph-mass spectrometry (GC/MS) analysis was used to understand the CP mineralization mechanism which has been established on the basis of intermediates identified such as benzoquinone, hydroquinone and organic acids. Reaction kinetics was expressed by pseudo-first order kinetic model. Maximum COD removal efficiency of 96.7% and CP removal efficiency of 97.2%, respectively, was observed at j= 222.22A/m2, t= 180min, pHo= 5.2 and m= 400mg/l with SEC= 655kWh/kg COD. Operating cost based on the studies performed on laboratory scale EC reactor has been calculated and compared with those reported for other pollutants degradation.

Optimization of 4- chlorophenol Oxidation by Manganese Ferrite Nanocatalyst with Response Surface Methodology

Optimization of 4- chlorophenol Oxidation by Manganese Ferrite Nanocatalyst with Response Surface Methodology

Theoretical and experimental formation of low chlorinated dibenzo-p-dioxins and dibenzofurans in the Fenton oxidation of chlorophenol solutions

The formation of chlorinated and non-chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) has been experimentally investigated after the Fenton oxidation of 2-chlorophenol (2-CP, 15.56 mM) aqueous solutions by assessing the influence of iron concentration (0.09–2.88 mM), hydrogen peroxide dose (40.44–202.20 mM), temperature (20–70 °C) and chloride concentration (0–56.35 mM). The presence of chloride in the medium together with room temperature and substoichiometric Fenton conditions (40.44 mM H2O2) led to an increase in total PCDD/Fs concentration from less than 1 ng L−1 to 2 μg L−1. Results showed a dominance of the dichlorinated species (DCDD/Fs) in the homologue profile of total PCDD/Fs reaching values up to 1.5 μg L−1. Furthermore, the products distribution exhibited a gradual decrease in the homologue concentration as the chlorination degree increased from di-to octachloro-substituted positions. Considering the characteristics of the reaction medium, the experimental results, and the information gathered in bibliography with regard to the generation of active radicals from 2-chlorophenol, a mechanism describing the formation of low chlorinated PCDD/Fs in a Fenton oxidizing aqueous system has been proposed.

Oxidation of phenol and chlorophenols on platinized titanium anodes in an acidic medium

A comparative study of oxidation of phenol, 3-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol on Pt/Ti and Ce,Pt/Ti electrocatalysts is performed via cyclic voltammetry. It is shown that the surface morphology and roughness of the anode do not change after modification with cerium. The formal kinetic orders of electrooxidation of all compounds are found to be less than one. It is shown that the β temperature coefficients of the rate of oxidation of chlorophenols grow by 10 to 50% when the Ce,Pt/Ti anode is used at a substrate concentration of 1 mM. A tenfold increase in concentration reduces the effect of cerium additive, except for 3-chlorophenol: the latter exhibits a 250% increase in the β value, compared to the Pt/Ti anode.

The marriage of ferrocene and silicotungstate: An ingenious heterogeneous Fenton-like synergistic photocatalyst

The oxidation of 4-chlorophenol (4-CP) was firstly carried out by heterogeneous Fenton-like process in the presence of ferrocene-containing silicotungstate catalyst (denoted as FcSiW). The catalyst was successfully prepared by precipitation method in aqueous solution using ferrocene (Fc, or CpFeCp) and silicotungstic acid (SiW, or H4SiW12O40·xH2O) as raw materials and the intrinsic relationship between structure and catalytic activity was fully studied. Under the suitable conditions, the prepared FcSiW exhibited high catalytic activity, especially under irradiation conditions. Moreover, the catalyst showed good reusability without significant performance drop after successive experimental runs and high stability with very low iron leaching. The strong interaction resulting from the close contact between Fc and polyoxometalate (POM) species contributes to the charge-transition from Fc to POM, which is in favor of its photocatalysis. A possible catalytic mechanism revealing the synergistic effect between the Fenton-like reaction of ferricinium and photocatalysis of SiW12O404− anions in FcSiW/H2O2 system was proposed on the basis of experiment results and previous reports. This novel highly active heterogeneous catalyst has the potential for wide range of application in wastewater pollutants treatment.