Oxidation Of Pentachlorophenol Research Articles

Insights into oxidation of pentachlorophenol (PCP) by low-dose ferrate(VI) catalyzed with α-Fe2O3 nanoparticles

In this study, the catalytic performance of α-Fe2O3 nanoparticles (nα-Fe2O3) in the low-dose ferrate (Fe(VI)) system was systematically studied through the degradation of pentachlorophenol (PCP). Based on the established quadratic functions between nα-Fe2O3 amount and observed pseudo first-order rate constant (kobs), two linear correlation equations were offered to predict the optimum catalyst dosage and the maximum kobs at an applied Fe(VI) amount. Moreover, characterization and cycling experiments showed that nα-Fe2O3 has good stability and recyclability. According to the results of reactive species identification and quenching experiment and galvanic oxidation process, the catalytic mechanism was proposed that Fe(III) on the surface of nα-Fe2O3 may react with Fe(VI) to enhance the generation of highly reactive Fe(IV)/Fe(V) species, which rapidly extracted a single electron from PCP molecule for its further reaction. Besides, two possible PCP degradation pathways, i.e., single oxygen transfer mediated hydroxylation and single electron transfer initiated polymerization were proposed. The formation of coupling products that are prone to precipition and separation was largely improved. This study proved that nα-Fe2O3 can effectively catalyze PCP removal at low-dose Fe(VI), which provides some support for the application of Fe(VI) oxidation technology in water treatment in the context of low-carbon emissions.

A Highly Sensitive and Selective Electrochemical Sensor for Pentachlorophenol Based on Reduced Graphite Oxide-Silver Nanocomposites

Pentachlorophenol (PCP), commonly used as a wood preservative, pesticide, and fungicide, is the most toxic of all chlorophenols and can accumulate in living organisms. It is of great significance to construct a sensitive method for the detection of PCP in real samples. In this study, a simple, novel, and sensitive electrochemical sensor for pentachlorophenol (PCP) was constructed by modifying glassy carbon electrode (GCE) with silver-reduced graphene oxide (AgNPs-rGO) nanocomposites. Due to the increased surface area, the extraordinary electron-transfer properties, and a stronger enrichment effect of AgNPs-rGO for PCP, the sensor based on AgNPs-rGO-modified glassy carbon electrode exhibited excellent electrocatalytic activity for oxidation of PCP. Under the optimum conditions, the constructed PCP sensor shows a wide linear range of 0.008 to 10.0 μM. The detection limit is 0.001 μM, which is much lower than the recommended value of PCP in drinking water (0.0037 μM) set by the United States Environmental Protection Agency (US EPA). The sensor was successfully applied for the determination of PCP in vegetable with acceptable recoveries. The method was validated by high-performance liquid chromatography, which provided a new valuable platform for highly sensitive and rapid determination of PCP in real samples.

Application of persulfate with hydrodynamic cavitation and ferrous in the decomposition of pentachlorophenol.

Hydrodynamic cavitation (HC) and Fe(II) are advanced oxidation processes, in which pentachlorophenol (PCP) is treated by the redox method of activating persulfate (PS). The kinetics and mechanism of the HC and Fe(II) activation of PS were examined in aqueous solution using an electron spin resonance (ESR) spin trapping technique and radical trapping with pure compounds. The optimum ratio of Fe(II)/PS was 1:2, and the hydroxyl radical (HO) and sulfate radical (SO4-) generation rate were 5.56mMh-1 and 8.62μMh-1, respectively. The generation rate and Rct of HO and SO4- at pH 3 and 50°C in the Fe(II)/PS/HC system are 7584.6μMh-1, 0.013 and 24.02μMh-1, 3.95, respectively. The number of radicals was reduced as the pH increased, and it increased with increasing temperature. The PCP reaction rate constants was 4.39×10-2min-1 at pH 3 and 50°C. The activation energy was 10.68kJmol-1. In addition, the mechanism of PCP treatment in the Fe(II)/PS/HC system was a redox reaction, and the HO-/SO4- contribution was 81.1 and 18.9%, respectively. In this study, we first examined PCP oxidation through HO and SO4- quantification using only the Fe(II)/PS/HC process. Furthermore, the results provide the foundation for activation of PS by HC and Fe(II), but also provide a data basis for similar organic treatments other than PCP.

Ferrate(VI) oxidation of pentachlorophenol in water and soil

Although the use of ferrate (VI), an emerging green oxidant, has been widely investigated to remove organic pollutants in water, its ability to remediate contaminated soils has been scarcely evaluated. Here, we explore the use of ferrate (VI) to degrade a polychlorinated persistent compound, the pentachlorophenol (PCP), in aqueous solution and in an aged contaminated soil under batch, water-saturated and water-unsaturated flow conditions. The first results showed the prominent efficiency of ferrate (VI) over conventional oxidants (e.g. H2O2 and persulfate) in both matrices and at different oxidant doses. In aqueous solution, more than 80% of PCP was degraded by ferrate (VI) while complete removal was observed in soil under batch conditions. In column experiments, PCP removal by ferrate (VI) remained efficient but dependent on the flow rate and water saturation. Maximum PCP removal (95%) in columns was observed under water saturated conditions when ferrate (VI) (0.2 g g−1 of soil) was injected at a low flow rate (i.e. 0.025 mL min−1). This study has strong implications in the development of new sustainable processes based on ferrate (VI) for the remediation of different environmental compartments.

Biodegradation and biotransformation of pentachlorophenol by wood-decaying white rot fungus Phlebia acanthocystis TMIC34875

Pentachlorophenol (PCP) has been introduced into the environment mainly as a wood preservative and biocide. The degradation and transformation of PCP in liquid culture by wood-decaying fungus capable of degrading organochlorine pesticides was investigated in this study. The results of tolerance test showed that the tolerance level of Phlebia acanthocystis to PCP in potato dextrose agar medium was higher than that of other Phlebia species. At the end of 10 days of incubation, P. acanthocystis was able to remove 100% and 76% of PCP (25 μM) in low-nitrogen and potato dextrose broth media, respectively. The decrease of PCP in P. acanthocystis culture is accompanied by the formation of pentachloroanisole and p-tetrachlorohydroquinone via methylation and oxidation reactions. Moreover, the p-tetrachlorohydroquinone formed is rapidly converted to methylated products including tetrachloro-4-methoxyphenol and tetrachloro-1,4-dimethoxybenzene. The activities of lignin peroxidase and manganese peroxidase were found to increase in extracellular fluid from fungal culture treated with high-concentration PCP, with maximum values of 169.6 U/L and 73.4 U/L, respectively. The in vitro degradation of PCP and p-tetrachlorohydroquinone was confirmed using extracellular fluid of P. acanthocystis, suggested that the methylation of both compounds is related to extracellular enzymes. Degradation of PCP was efficiently inhibited by piperonyl butoxide or 1-aminobenzotriazole, demonstrating that cytochrome P450 monooxygenase is involved in fungal transformation of PCP, particularly in the oxidation of PCP to p-tetrachlorohydroquinone. Additionally, P. acanthocystis mineralized 9.3% of the PCP to 14CO2 in low-nitrogen culture during 42 days. Results obtained in the present study are in favor of the use of P. acanthocystis as a microbial tool of remediation of PCP-contaminated sites.

Mn(III)-ligand complexes as a catalyst in ligand-assisted oxidation of substituted phenols by permanganate in aqueous solution

Ligands can significantly increase the oxidation rates of phenolic compounds by MnO4−. This was often explained by the in situ formed Mn(III)- or Mn(X)-ligand complexes that can oxidize phenols faster than MnO4− can. This work discovered that Mn(III)-ligand complexes also acted as a catalyst for the oxidation of phenolic compounds by MnO4− (i.e., the catalytic role of Mn(III)-ligand). First, when phenol was mixed with MnO4− and pyrophosphate (PP, a representative ligand), Mn(III)-PP was found to form while phenol was quickly oxidized. However, the amount of phenol that was directly oxidized by Mn(III)-PP only accounted for ∼25% of phenol that was oxidized in the mixture, indicating that there were other pathways. Then, when pentachlorophenol (PCP) was used as another phenolic probe, the externally prepared Mn(III)-PP was observed to only slightly oxidize PCP, but its addition significantly accelerated PCP oxidation by MnO4−. The Mn(III)-PP concentration also remained unchanged during the above reaction, thus suggesting the catalyst role of Mn(III)-PP. This new pathway was further validated by successfully explaining all the experimental observations obtained so far, including the effect of pH, effects of different ligand amounts and types, product patterns, and the induction period. Finally, possible catalytic mechanisms of Mn(III)-ligand were discussed based on the experimental results.

Gallic acid mediated oxidation of pentachlorophenol by the Fenton reaction under mild oxidative conditions

AbstractBACKGROUNDThe present study demonstrates the decomposition of pentachlorophenol (PCP) by the Fenton reaction in the presence of gallic acid (GA). Unlike other studies, catalytic Fe2+ concentrations were used with respect to PCP in an effort to evaluate an environmentally benign Fenton system, studying the effect of phenolic‐type compounds widely found in the environment. The effect of operating variables was evaluated.RESULTSAt initial reaction times or at low H2O2 and Fe concentrations, GA enhanced PCP removal. At high H2O2 and Fe concentrations GA enhanced PCP removal only at initial reaction times. GA was the determinant factor controlling activity acting both as a chelating agent and reducer of Fe3+. Electron paramagnetic resonance (EPR) spectroscopy was applied to shed light on mechanistic aspects, verifying the interaction of GA with Fe ions. GA accelerated significantly the Fe3+/Fe2+ redox cycling. This enhanced the formation of hydroxyl radicals (HO·) as confirmed by in situ EPR spin trap experiments. A reaction mechanism was proposed including the redox cycle of GA quinoide forms.CONCLUSIONThe operational variables of a GA modified Fenton system are provided and mechanistic steps are discussed including PCP degradation, GA/Fe interaction, Fe3+/Fe2+ redox cycling and HO· formation. GA concentration controls the catalytic degradation of PCP. © 2017 Society of Chemical Industry

A novel electrochemical sensor for chlorophenols based on the enhancement effect of Al-doped mesoporous cellular foam

Al-doped mesoporous cellular foam (Al-MCF) was prepared and characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption isotherms and pore size distribution plots. An Al-MCF modified carbon paste electrode (Al-MCF/CPE) was developed, and both cyclic voltammetry and electrochemical impedance spectroscopy were employed to study the electrochemical properties of the Al-MCF/CPE. The electrochemical behaviors of pentachlorophenol (PCP) at different electrodes were investigated by cyclic voltammetry. Compared to bare CPE and mesoporous cellular foam (MCF) modified CPE (MCF/CPE), the Al-MCF/CPE showed a stronger enhancement effect on the electrochemical oxidation of PCP. Consequently, the determination of PCP was achieved via a convenient electrochemical method. Under optimal conditions, the oxidation peak current was linearly proportional to PCP concentration in the range of 0.10–5.0mgL−1, while the detection limit was 0.080mgL−1 (signal-to-noise ratio=3). The proposed method was found to be a convenient way for the determination of the total amount of chlorophenols (CPs).

Remediation of an aged PCP-contaminated soil by chemical oxidation under flow-through conditions

In this study the oxidation of pentachlorophenol (PCP) in an aged contaminated soil was performed under both water-unsaturated and water-saturated conditions using potassium permanganate (PM), potassium persulfate (PS) and hydrogen peroxide (HP). Overall, the results of PCP removal extent and oxidant decomposition indicated that the water content in column has no significant impact on the oxidation performance. The increase in flow rate from 0.025 to 2.5mLmin−1 decreased the oxidant decomposition as well as the PCP degradation extent, except for HP that is highly reactive. Kinetic limitations in column may explain the effect of residence time of oxidant on the degradation performance. Consistently, re-circulation of oxidant solutions in a closed loop system improved the oxidation efficiency and oxidant decomposition extents in case of PS and PM, but not for HP. Surprisingly, attempts to enhance the PCP availability in soil by using solubility agents or by heating did not improve the degradation efficiency in soil. The presence of methyl-β-cyclodextrin (M-β-CD) affects only the decomposition rate of HP, which is positively correlated with M-β-CD concentration. High persistence of HP could be advantageous where delivery of oxidants to zone-source of contamination can be limited by their high reactivity. Collectively, these results may have strong implications for the application of chemical oxidation under field conditions, particularly where oxidant injection mode in saturated or unsaturated zones is crucial in determining the remediation performance.

Axial ligand effect on the catalytic activity of biomimetic Fe-porphyrin catalyst: An experimental and DFT study

Electrostatic interactions occurring in the immediate environment of the metal center in native enzymes influence the charge distribution and electron donation ability, regulating activity. Herein, using an iron-porphyrin biomimetic complex, we have investigated the effect of the protonation state of the axial imidazole on the catalytic oxidation of pentachlorophenol. We show that the catalytic efficiency is drastically affected by the anionic state of the axial ligand. The chemical events occurring during the catalytic cycle were monitored by a detailed analytical study. EPR, UV–Vis and low temperature UV–Vis together with theoretical DFT and TD-DFT calculations provide evidence that deprotonation of the axial imidazole leads to increased electron donation ability to the central metal, enhancing the formation of ferryl species. Imidazole favored the formation of a pure porphyrin-radical model at the high-valent FeIVOPor+ state while imidazolate presented a significant axial ligand-radical character. The theoretical calculations suggest that the enhanced catalytic activity of the deprotonated conformation is attributed to the increased electron donation ability, favoring the formation of the ferryl species and suggesting that the “push” effect prevails over the “pull” effect.

Sensitive electrochemical sensor for the determination of pentachlorophenol in fish meat based on ZnSe quantum dots decorated multiwall carbon nanotubes nanocomposite

In this work, a very sensitive electrochemical sensor for the determination of pentachlorophenol (PCP) was constructed based on the electrocatalytic activity of the composite of ZnSe quantum dots (ZnSe QDs) decorated multiwall carbon nanotubes (MWCNTs) (ZnSe QDs-MWCNTs). The behaviors of PCP on the surface of ZnSe QDs-MWCNT modified electrode showed that the composite of ZnSe QDs-MWCNTs introduced a favorable access for the electron transfer and make an obvious electrocatalytic activity toward the oxidation of PCP. Differential pulse voltammetry (DPV) was used for the quantitative determination of PCP. Under the optimum conditions, the peak current of PCP was proportional to its concentration at the range of 8.0 × 10−8 to 4.0 × 10−6 mol L−1 with a detection limit 2.0 × 10−9 mol L−1 (S/N = 3). Compared with the reported papers, the proposed method was more sensitive and simple. The developed method was successfully applied for the determination of PCP in fish meat with satisfactory recoveries.

Efficient remediation of pentachlorophenol contaminated soil with tetrapolyphosphate washing and subsequent ZVI/Air treatment

In this study, we demonstrate that pentachlorophenol contaminated soil can be efficiently remediated with tetrapolyphosphate washing and subsequent zerovalent iron (ZVI)/Air treatment. 2mmolL−1 of tetrapolyphosphate could wash away 52.8% of pentachlorophenol (PCP) at pH 7.0 and 84.2% of pentachlorophenol at pH 11.0 from contaminated soil owing to the promotion effect of tetrapolyphosphate on the soil matrix dispersion and the subsequent solubilization of pentachlorophenol. More importantly, tetrapolyphosphate ions remained in the washing effluent could greatly enhance the molecular oxygen activation by ZVI to oxidize the desorbed PCP without any pH adjustment, and also avoid the competitive consumption of reactive oxygen species, as caused by the common organic surfactants in the washing effluent. Therefore, 85.1% of pentachlorophenol could be aerobically removed from the washing effluent by merely using 5gL−1 of ZVI. We also interestingly found that the dissolved iron ions released from the soil could enhance the oxidation of pentachlorophenol in the washing effluent, but the dissolved organic matter had the opposite effect. This study suggests the coupling tetrapolyphosphate washing and subsequent ZVI/Air treatment is an optional approach to remediate pentachlorophenol contaminated soil in view of its low cost and environmental benign.

Effect of humic acid on chemical oxidation of organic pollutants by iron(II) and H2O2: A dual mechanism

The capacity of Fenton reaction on the decomposition of pentachlorophenol (PCP) in the presence and absence of humic acid (HA) was evaluated. Numerous studies have shown that HA can act either as an enhancer or inhibitor of the Fenton reaction. Herein, by combining electron paramagnetic resonance (EPR) spectroscopic and catalytic data, it is shown that HA can act in a dual manner e.g. either as an enhancer or as an inhibitor for PCP oxidation depending on the initial Fe/HA ratio. A quantitative limit is established: (i) at low Fe/HA<1.17mmol/g the presence of HA resulted to a decrease of PCP decomposition while (ii) at high Fe/HA>1.17mmol/g a significant enhancement was observed. EPR spectroscopy revealed that, HA acted (i) as a chelator of Fe and (ii) as a redox agent. The data reveal the presence of two types of Fe-binding sites in HA: (a) strong Fe-binding sites, (b) weak Fe-binding sites susceptible to reduction.

The electrochemical oxidation of pentachlorophenol and its sensitive determination at chitosan modified carbon paste electrode

We report on a novel electrochemical method to detect trace pentachlorophenol (PCP) by using a chitosan (CS) modified carbon paste electrode (CS/CPE). Compared with that at a bare carbon paste electrode (CPE), the current response was greatly improved at the CS/CPE due to the enhancement effect of CS. Under optimal working conditions, the oxidation peak current of PCP was proportional to its concentration in the range of 1.0 × 10−7 to 5.0 × 10−6 and 5.0 × 10−6 to 1.0 × 10−4 mol/L, with an extremely low detection limit of 4.0 × 10−8 mol/L. Our method was successfully used to detect the PCP concentration in vegetable samples.

Indirect electrochemical oxidation of pentachlorophenol in the presence of different halides: behavior and mechanism

Indirect electrochemical oxidation (EO) of pentachlorophenol (PCP) wastewater was carried out in the presence of different halides through the electrogeneration of active halide (AH). The EO effect and electrochemical behaviors of PCP under different conditions are present in this paper. The cyclic voltammetry (CV) curves indicated higher electrogeneration efficiency of active halogen in NaBr solution. Chronoamperometric response proved the formation of passivating polymer on anode surface. The conversion rate of PCP was distinctly different for different halides following the order Br− ##xgt; Cl− ##xgt; F− ##xgt; I−. The proper oxidation potential of Br− to active bromine led to the optimal electrooxidation effect of Br−. With the rise of temperature the reaction rate decreased at first from 30 to 45°C and then increased from 45 to 60 °C. The complicated variation of PCP conversion on rising temperature was depicted by the electrochemical measurements and a mathematic model.

Involvement of Cytochrome P450 in Pentachlorophenol Transformation in a White Rot Fungus Phanerochaete chrysosporium

The occurrence of cytochrome P450 and P450-mediated pentachlorophenol oxidation in a white rot fungus Phanerochaete chrysosporium was demonstrated in this study. The carbon monoxide difference spectra indicated induction of P450 (103±13 pmol P450 per mg protein in the microsomal fraction) by pentachlorophenol. The pentachlorophenol oxidation by the microsomal P450 was NADPH-dependent at a rate of 19.0±1.2 pmol min−1 (mg protein)−1, which led to formation of tetrachlorohydroquinone and was significantly inhibited by piperonyl butoxide (a P450 inhibitor). Tetrachlorohydroquinone was also found in the cultures, while the extracellular ligninases which were reported to be involved in tetrachlorohydroquinone formation were undetectable. The formation of tetrachlorohydroquinone was not detectable in the cultures added with either piperonyl butoxide or cycloheximide (an inhibitor of de novo protein synthesis). These results revealed the pentachlorophenol oxidation by induced P450 in the fungus, and it should be the first time that P450-mediated pentachlorophenol oxidation was demonstrated in a microorganism. Furthermore, the addition of the P450 inhibitor to the cultures led to obvious increase of pentachlorophenol, suggesting that the relationship between P450 and pentachlorophenol methylation is worthy of further research.

Catalytic wet air oxidation of pentachlorophenol over Ru/ZrO2 and Ru/ZrSiO2 catalysts

ZrSiO2 and ZrO2 supports loaded with active component Ru were unprecedentedly evaluated in catalytic wet air oxidation reaction of pentachlorophenol (PCP). The study results showed that the specific surface area of ZrSiO2 which was prepared by high temperature aging method was much larger than that of ZrO2, and it performed a better catalytic activity in catalytic wet air oxidation after being loaded with Ru. When the initial concentration of PCP was 125mgL−1, PCP conversion reached 92% after 90min under the low temperature and pressure conditions of 180°C and 0.1MPa oxygen partial pressure. PCP conversion was increased by raising reaction temperature, increasing oxygen partial pressure, reducing the initial concentration of PCP and prolonging reaction time. The kinetics study of PCP in catalytic wet air oxidation showed that the catalytic wet air oxidation reaction of PCP obeyed first order kinetic model and its Arrhenius activation energy was 96.98kJmol−1. The main intermediates of PCP in CWAO were acetic acid, oxalic acid and chlorine ion.

Redox activity of CdTe quantum dots linked to nickel tetraaminophthalocyanine: Effects of adsorption versus electrodeposition on the catalytic oxidation of chlorophenols

Cadmium tellurite quantum dots (CdTe-QDs) are linked to nickel tetraamino phthalocyanine (CdTe-QDs-NiTAPc) through an amide bond. Differential pulse voltammetry shows that that NiTAPc stabilizes the QDs against oxidative disintegration into metallic products on oxidation. Electrocatalytic oxidation of 2, 4-dichlorophenol (DCP) and pentachlorophenol (PCP) on CdTe-QDs and CdTe-QDs-NiTAPc adsorbed or electrodeposited onto a gold electrode were studied. Adsorbed CdTe-QDs-NiTAPc shows the lowest potential for DCP and PCP oxidation and it is also more stable to fouling by PCP and its oxidation products compared to adsorbed CdTe-QDs without NiTAPc. Electrodeposited CdTe-QDs or CdTe-QDs-NiTAPc show the best activity in terms of enhanced currents towards the oxidation of the chlorophenols.

Determination of Pentachlorophenol at Carbon Nanotubes Modified Electrode Incorporated with &lt;I&gt;β&lt;/I&gt;-Cyclodextrin

A facile and reliable electrochemical technique at beta-cyclodextrin incorporated carbon nanotubes modified glassy carbon electrode (beta-CD/CNTs/GCE) was proposed for determination of pentachlorophenol (PCP). The electrochemical behavior of PCP at the beta-CD/CNTs/GCE was investigated by cyclic voltammetry and linear sweep voltammetry. The beta-CD/CNTs/GCE showed good analytical performance characteristics in electrocatalytic oxidation of PCP, compared with the simple carbon nanotube modified electrode (CNTs/GCE) and bare glassy carbon electrode (GCE). After accumulation for 5 min on beta-CD/CNTs/GCE, the peak current increased linearly with the concentration of PCP in the range from 8.0 x 10(-7) to 1.04 x 10(-5) mol/L. The detection limit was 4.0 x 10(-8) mol/L at 3 sigma level. The proposed electrode presented good repeatability for the determination of PCP in artificial wastewater, and the recovery was 97%-103%. This modified electrode combined the advantages of carbon nanotubes and supramolecular cyclodextrin, leading to new capabilities for electrochemical detection of PCP.

ANODIC DETERMINATION OF PENTACHLOROPHENOL FROM WATER USING CARBON NANOFIBER-BASED COMPOSITE ELECTRODE

The assessment of a carbon nanofiber-expanded graphite-epoxy composite (CNF-EG-Epoxy) electrode for the anodic determination of PCP (pentachlorophenol) is described. Cyclic voltammetry technique was used to characterize the electrochemical behaviour of PCP at CNF-EG-Epoxy electrode in 0.1 M Na2SO4 supporting electrolytes in order to establish the parameters for amperometric/voltammetric determination of PCP. The linear dependence of the current versus PCP concentration was reached in the concentration range between 0.75 to 15 μM PCP using cyclic voltammetry (CV), differential-pulsed voltammetry (DPV), chronoamperometry (CA), and multiple-pulsed amperometry (MPA). Under the conditions of CA application, the fouling effect of the electrode occurred, which was avoided by MPA application that assures in-situ electrochemical cleaning of the electrode. The best electroanalytical parameters of the sensitivity, the relative standard deviation, the lowest limit of detection and the limit of quantification were obtained by MPA application, revealing that CNF-EG-Epoxy electrode exhibited useful characteristics for electrochemical determination of PCP from aqueous solution. In addition, some mechanistic aspects regarding PCP oxidation on CNF-EG-Epoxy electrode were discussed by performing CV at different scan rates.