Comparative studies on the oxidative dechlorination of chlorophenols by a superoxide complex

Transition Metal Chemistry - The chlorophenols (CPs), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP), are potent environmental hazards. They can be...     

Hydroxyl radical reactions with 2-chlorophenol as a model for oxidation in supercritical water

To determine the detailed mechanism of 2-chlorophenol (2-CP) oxidation in supercritical water, both the experiments and theoretical calculations were conducted in this paper. A set of experiments was performed to oxidize 2-CP in supercritical water under temperatures of 380–420 °C, pressure of 25 MPa, residence times of 0–60 s, and H₂O₂ as oxidant. By determining the molar yields of products, the primary single-ring products were identified as chlorohydroquinone, 2,4-dichlorophenol (2,4-DCP), 2,6-DCP, and 4-CP. The trends for the molar yields of the four products were analyzed at various temperatures and residence times. And built upon the trends, the possible reaction pathways were conjectured. Subsequently, the reaction mechanism was further verified by theoretical calculations, in which density functional theory was adopted as the computational method. The calculated results have well illustrated the experimental results and ascertained the reaction paths we proposed.     

In situ encapsulation of laccase in nanofibers by electrospinning for development of enzyme biosensors for chlorophenol monitoring

A biosensor based on Trametes versicolor laccase (Lac) was developed for the determination of phenolic compounds. The biosensor was prepared by in situ electrospinning of a mixture of polyvinyl alcohol (PVA), Lac, PEO-PPO-PEO (F108) and gold nanoparticles (Au NPs), where F108 was used as an enzyme stabilizing additive and Au NPs was used to enhance the conductivity of the biosensor. Laser confocal scanning microscopy and electrochemical impedance spectroscopy proved that the enzyme was successfully encapsulated into the electrospun nanofibers. Under the optimal conditions, the lowest detection limit was found to be 0.04 μM (S/N = 3) for 2,4-DCP and the highest detection limit was found to be 12.10 μM for 4-CP. The sensitivity of the biosensor obtained in the linear range for chlorophenols followed the sequence 2,4-dichlorophenol (2,4-DCP) > 2,4,6-trichlorophenol (2,4,6-TCP) > 4-chlorophenol (4-CP). The sensing performance for chlorophenols was attributed to the suitable electrochemical interface of PVA/F108/Au NPs/Lac, resulting from biocompatibility, a high surface area-to-volume ratio (10.42 m(2) g(-1)) and superior mechanical properties of the electrospun nanofibers. The biosensor exhibited good repeatabilities of 7.6%, 2.8% and 9.0% (R.S.D.) and reproducibilities of 14.9%, 10.4% and 13.7% (R.S.D.) for 4-CP, 2,4-DCP and 2,4,6-TCP, respectively. Lac retained 65.8% of its initial activity after a 30-day storage period.     

A sensitive electrochemical chlorophenols sensor based on nanocomposite of ZnSe quantum dots and cetyltrimethylammonium bromide

In this work, a very sensitive and simple electrochemical sensor for chlorophenols (CPs) based on a nanocomposite of cetyltrimethylammonium bromide (CTAB) and ZnSe quantum dots (ZnSe–CTAB) through electrostatic self-assembly technology was built for the first time. The composite of ZnSe–CTAB introduced a favorable access for the electron transfer and gave superior electrocatalytic activity for the oxidation of CPs than ZnSe QDs and CTAB alone. Differential pulse voltammetry (DPV) was used for the quantitative determination of the CPs including 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP). Under the optimum conditions, the peak currents of the CPs were proportional to their concentrations in the range from 0.02 to 10.0 μM for 2-CP, 0.006 to 9.0 μM for 2,4-DCP, and 0.06 to 8.0 for PCP. The detection limits were 0.008 μM for 2-CP, 0.002 μM for 2,4-DCP, and 0.01 μM for PCP, respectively. The method was successfully applied for the determination of CPs in waste water with satisfactory recoveries. This ZnSe–CTAB electrode system provides operational access to design environment-friendly CPs sensors.     

Investigation of the interaction between chlorophenols and lysozyme in solution

The binding interactions of lysozyme with 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were investigated by UV-vis absorption, CD, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. The binding constants, quenching mechanism, and the number of binding sites were determined by the quenching of lysozyme fluorescence in presence of chlorophenols. H-bonds and hydrophobic interactions played major roles in stabilizing the chlorophenols-lysozyme complex. The distances r between chlorophenols and lysozyme were calculated to be 1.94nm, 2.75nm, 3.54nm, and 3.76nm for 2-CP, 2,4-DCP, 2,4,6-TCP, and PCP, respectively. The effects of chlorophenols on the conformation of lysozyme were analyzed using CD, synchronous fluorescence and three-dimensional fluorescence spectra.     

Enhanced photocatalytic activities of ZnO thin films: a comparative study of hybrid semiconductor nanomaterials

Nanostructure single ZnO, SnO₂, In₂O₃ and composite ZnO/SnO₂, ZnO/In₂O₃ and ZnO/SnO₂/In₂O₃ films were prepared using sol?Cgel method. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV?CVis spectroscopy. The photocatalytic activities of composite films were investigated using phenol (P), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 4-aminophenol (4-AP) as a model organic compounds under UV light irradiation. Hybrid semiconductor thin films showed a higher photocatalytic activity than single component ZnO, SnO₂ and In₂O₃ films. The substituted phenols degrade faster than phenol. The ease of degradation of phenols is different for each catalyst and the order of catalytic efficiency is also different for each phenol. The use of multiple components offered a higher control of their properties by varying the composition of the materials and related parameters such as morphology and interface. It was also found that the photocatalytic degradation of phenolic compounds on the composite films and single films followed pseudo-first order kinetics.     

Direct determination of chlorophenols in environmental water samples by hollow fiber supported ionic liquid membrane extraction coupled with high-performance liquid chromatography

The 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) ionic liquid was immobilized in the pores of a polypropylene hollow fiber for hollow fiber-protected liquid-phase microextraction. Analytes including 4-chlorophenol (4-CP), 3-chorophenol (3-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were extracted into this ionic liquid membrane, and back extracted into 10microL sodium hydroxide acceptor solution in the lumen of the hollow fiber. Then, the acceptor solution was withdrawn into the high-performance liquid chromatography (HPLC) microsyringe connected to the hollow fiber, and directly injected into the HPLC system for analysis. Some parameters that might affect the extraction efficiency were optimized, and low detection limits (0.5microgL(-1) for 4-CP, 3-CP, DCP and 1.0microgL(-1) for TCP) were obtained. Good repeatability was achieved because of the stability of the hollow fiber-supported ionic liquid membrane. The proposed procedure was applied for direct determination of the four chlorophenols in some real water samples including groundwater, river water, wastewater and tap water. All of the four chlorophenols in these water samples were under the limits of determination, and the recoveries were in the range of 70.0-95.7% at 5microgL(-1) spiked level.     

Degradation of chlorophenols in aqueous solution by γ-radiation

Degradation of chlorophenols (CPs) in aqueous solutions by γ-radiation was studied. The effect of absorbed dose on degradation, dechlorination and mineralization of CPs were investigated. The results indicated that the degradation of CPs, Cl⁻ release and mineralization increased with increase in absorbed dose. When the initial concentration was 100 mg L⁻¹ and the dosage was 6 kGy, the removal efficiencies of CPs were 44.54% for 2-CP, 91.46% for 3-CP, 82.72% for 4-CP and 93.25% for 2,4-DCP, respectively. The combination of irradiation and H₂O₂ leads to a synergistic effect, which remarkably increased the degradation efficiency of CPs and TOC removal. The kinetics of CPs during irradiation are also mentioned.     

Preconcentration and Determination of Chlorophenols in Wastewater with Dispersive Liquid–Liquid Microextraction Using Hydrophobic Deep Eutectic Solvents

Abstract

Hydrophobic deep eutectic solvents (DESs) were synthesized and developed for the preconcentration of three chlorophenols from wastewater by dispersive liquid–liquid microextraction (DLLME). The analyte concentrations were determined by high-performance liquid chromatography (HPLC). The hydrophobic DESs were prepared with the combination of hydrogen bond donors of decanoic acid or octanoic acid with different hydrogen bond acceptors of quaternary ammonium salts of tetrabutylammonium chloride, tetraoctylammonium chloride, methyltrioctylammonium chloride, and tetraheptylammonium chloride). Following the study of the stability and characterization by Fourier transform infrared spectroscopy, the hydrophobic DESs were developed as extractants and employed for the removal of 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) from wastewater. Using hydrophobic DESs as the microextraction solvents, several key parameters were optimized, including the type and volume of the hydrophobic DES, pH, and time of the extraction procedure. Under the optimized conditions, good recoveries from 90.8% to 93.0% were obtained for the three chlorophenols. The limits of detection were less than 0.05?µg/mL with relative standard deviations between 1.8% and 3.1%. The method was applied for the isolation and determination of synthetic chlorophenols in wastewater.     

Catalytic hydrodechlorination reaction of chlorophenols by Pd nanoparticles supported on graphene

Chlorophenols are widely used as industrial chemicals such as herbicides, insecticides, wood preservatives, and disinfectants. However, chlorophenols are very toxic materials and they have become the cause of current environmental issues. Hydrodechlorination (HDC) reaction is a more environmentally friendly removal method of chlorophenols than other methods. In this paper, Pd–modified graphene was prepared and applied to HDC reaction. Pd supported on graphene (refer to Pd/G) was prepared using the recently reported microwave irradiation method. The Pd(II)/GO was made by impregnation methods of palladium precursors in solution phase and was subsequently reduced to Pd/G by microwave irradiation. The morphological and chemical structure of the Pd/G was characterized by XRD, SEM, ICP-MS, EDS, and TEM. It was found that the graphene-based Pd catalyst showed the highest catalytic performance among Pd/Y, Pd/MCM-41, and Pd/G catalysts. This is attributed to the smaller particle size and higher dispersions of Pd nanoparticles on the graphene surface. The catalytic HDC of chlorophenols was investigated. For HDC reaction, 100 ppm solution of chlorophenols such as 4-chlorophenol, six isomers of dichlorophenol, and 2,3,5-trichlorophenol in isopropanol was treated with catalyst and base, such as Na₂CO₃ and K₂CO₃, under a hydrogen gas at ambient pressure. The progress of the chlorophenol decomposition was analyzed with GC. All chlorophenols were completely decomposed within 2 h in the 3 % Pd/G catalyst. The reaction pathway of chlorophenols was elucidated from the conversion of chlorophenols and selectivities of products. The reuse of the catalyst was also studied. The performance of the recycled catalyst in HDC reaction up to six successive runs was observed.     

Stir bar sorptive extraction with in situ derivatization and thermal desorption-gas chromatography-mass spectrometry for determination of chlorophenols in water and body fluid samples

A new method, stir bar sorptive extraction (SBSE) with in situ derivatization and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of chlorophenols, such as 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TrCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP), in tap water, river water and human urine samples, is described. The derivatization conditions with acetic acid anhydride and the SBSE conditions such as extraction time are investigated. Then, the stir bar is subjected to TD followed by GC-MS. The detection limits of the chlorophenols in tap water, river water and human urine samples are 1-2, 1-2, and 10-20 pg ml⁻¹ (ppt), respectively. The calibration curves for the chlorophenols are linear and have correlation coefficients higher than 0.99. The average recoveries of the chlorophenols in all the samples are higher than 95% (R.S.D. < 10%) with correction using added surrogate standards, 2,4-dichlorophenol-d₅, 2,4,6-trichlorophenol-¹³C₆, 2,3,4,6-tetrachlorophenol-¹³C₆ and pentachlorophenol-¹³C₆. This simple, accurate, sensitive and selective analytical method may be applicable to the determination of trace amounts of chlorophenols in liquid samples.     

KF promoted mesoporous γ-Al2O3 with strong basicity: Preparation,characterization and catalytic activitiy for transesterification to biodiesel

The present paper describes the preparation of KF/M-γ-Al₂O₃, efficient mesoporous solid bases. The procedure involves loading KF into a crystalline mesoporous γ-Al₂O₃ that was synthesized by the self-assembly of poly-4-vinylpyridine (P4VP) with Al³⁺ species. The synthesis is based on the strong acid-base interaction, hydrothermal treatment at 180°C and calcination at 550°C. Characterizations using XRD analysis and low temperature N₂ adsorption indicated that different amounts of KF could be introduced into crystalline mesoporous γ-Al₂O₃ to obtain catalysts with high BET surface areas, large pore volumes and uniform pore size distribution. Based on SEM images, KF/M-γ-Al₂O₃ catalysts have rough surface character and a large nanopore volume. CO₂-TPD curves registered for KF/M-γ-Al₂O₃ contain high temperature peaks, indicating strong basicity of the catalysts. Under the same reaction conditions KF/M-γ-Al₂O₃ catalysts exhibit much better activities for transesterification to biodiesel than KOH, NaOH, H₂SO₄, hydrotalcite and CaO. Enhanced activities appear to arise from strong basisity and large BET surface areas.     

The removal of chlorinated organic herbicide in water by gamma-irradiation

In this study, the radiation-induced degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in aqueous solution was studied under various conditions as a function of irradiation dose in the absence and presence of hydrogen peroxide. The obtained data confirmed that largest yield of radiolytic degradation is obtained in oxidation processes/ionizing radiation, where oxidation is carried out with hydroxyl radicals. For complete degradation of 50?ppm 2,4-D, a required dose was lower in the presence of hydrogen peroxide. The formed major toxic phenolic intermediates were 2,4-dichlorophenol (2,4-DCP) and 4-chlorophenol (4-CP). The chemical analysis of the 2,4-D and the intermediates resulted from the radiolytic degradation were performed using a gas chromatography associated to mass spectrometry (GC?CMS) with ion trap dedector (ITD) and ion chromatography (IC). The formation of chlorophenols in addition to chloride, formaldehyde and carboxylic acids was studied as a function of absorbed dose.     

Mixed hemimicelles solid-phase extraction of chlorophenols in environmental water samples with 1-hexadecyl-3-methylimidazolium bromide-coated Fe3O4 magnetic nanoparticles with high-performance liquid chromatographic analysis

In this paper, 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr)-coated Fe₃O₄ magnetic nanoparticles (NPs) as an adsorbent of mixed hemimicelles solid-phase extraction was investigated for the preconcentration of two chlorophenols (CPs) in environmental water samples prior to HPLC with UV detection at 285 nm. The high surface area and excellent adsorption capacity of the Fe₃O₄ NPs after modification with C₁₆mimBr were utilized adequately in the SPE process. By the rapid isolation of Fe₃O₄ NPs through placing a strong magnet on the bottom of beaker, the time-consuming preconcentration process of loading large volume sample in conventional SPE method with a column can be avoided. A comprehensive study of the adsorption conditions such as the zeta-potential of Fe₃O₄ NPs, added amounts of C₁₆mimBr, pH value, standing time and maximal extraction volume were also presented. Under optimized conditions, two analytes of 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were quantitatively determined. The method was then used to determine the two CPs in real environmental water samples. The accuracy of method was evaluated by recovery measurements on spiked samples. Good recovery results (74–90%) were achieved. It is important to note that satisfactory preconcentration factors and extraction recoveries for the two CPs were obtained with only a small amount of Fe₃O₄ NPs (40 mg) and C₁₆mimBr (24 mg).     

Surface plasmon resonance excited electron induction greatly extends H2 evolution and pollutant degradation activity of g-C3N4 under visible light irradiation

Energy crises and environmental pollution have sparked tremendous research work to handle their impacts. Herein, we fabricated Au/g-C₃N₄ nanocomposites to produce H₂ and degrade 2,4-dichlorophenol (2,4-DCP) under visible light and at different wavelengths. Interestingly, the optimized photocatalyst generated 114 μmol H₂ and degraded 25% 2,4-DCP in 1 hr as compared with 10 μmol H₂ generation and 8% 2,4-DCP degradation by pure g-C₃N₄. This improvement is credited to the extended light absorption and improved charge induction from gold to g-C₃N₄ even at 590 nm as confirmed from photoluminescence, surface photovoltage, and photoelectrochemical study of the samples. Moreover, the surface catalytic property of g-C₃N₄ was much improved after loading a proper amount of gold nanoparticles. We hope that this technique to photosensitize semiconductors with noble metal nanoparticles may provide a feasible way to construct surface plasmon resonance-assisted photocatalysts to cope with energy crises and environmental pollution simultaneously.     

The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu-Al hydrotalcite/clay composite

Liquid phase catalytic oxidation of chlorophenols (CPs) was carried out over Cu-Al hydrotalcite/clay composite at ambient temperature and pressure using hydrogen peroxide as oxidant. The results showed that the catalyst had high catalytic activity, with complete oxidation of 4-CP within 40 min at 40 °C. The content and position of chlorine on the aromatic ring had significantly different effects on the oxidation rate of CPs, with the rate sequence of phenol > monochlorophenol (MCP) > dichlorophenol (DCP) > trichlorophenol (TCP), 3-CP > 2-CP > 4-CP, and 3,5-DCP > 3,4-DCP > 2,5-DCP > 2,4-DCP > 2,6-DCP. This was ascribed to the interactions among σ-electron withdrawing conductive effect, π-electron donating conjugative effect, and steric hindrance effect of chlorine. It was evidenced that the catalytic peroxide oxidation of CPs in the first step was selective and rate-limiting, where chlorinated 1,4-benzoquinones formed.     

Efficient oxidative degradation of 2-chlorophenol and 4-chlorophenol over supported CuO-based catalysts

A series of metal oxide catalysts for catalytic oxidative degradation of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) were prepared, and the supported CuO catalysts were studied particularly. The supported CuO catalysts were characterized by XRD and NH3-TPD techniques, in which CuO/γ-Al2O3 exhibited high degradation activity. The addition of Na2O or K2O into CuO/γ-Al2O3 improved the oxidative degradation of CPs remarkably, in which Na2O was more efficient than K2O. Over CuO/γ-Al2O3-Na2O, CPs were completely converted and the liberation of the inorganic chloride from 2-CP or 4-CP reached 97% or 100% respectively at 30 ?C for 2 h. The supported CuO catalysts with good dispersion of CuO particles and less acid sites were favorable for the efficient oxidative degradation of CPs. In addition, the initial pH of the reaction solution was found to be an important factor which influenced the catalytic oxidative degradation of CPs and the initial pH of 11.2 and 9.8 was preferred for the oxidative degradation of 2-CP and 4-CP respectively over CuO/γ-Al2O3 catalyst.     

Evaluation of a magnetic polysulfone microcapsule containing organic modified montmorillonite as a novel solid-phase extraction sorbent with chlorophenols as model compounds

A porous polysulfone microcapsule containing organic modified montmorillonite and magnetic nanoparticles (OMMT-Fe₃O₄@PSF) has been successfully prepared by a phase-inversion method and evaluated as a magnetic solid-phase extraction (MSPE) sorbent for clean-up and enrichment of 4-chlorophenol (4-CP) and 2-chlorophenol (2-CP) in aqueous samples. Compared with a microcapsule containing the conventional extraction sorbent C18 (C18-Fe₃O₄@PSF), OMMT-Fe₃O₄@PSF had much lower cost, a faster adsorption rate, and superior uptake amounts for the investigated analytes. The proposed microcapsule has been developed for the extraction of 4-CP and 2-CP from environmental water samples and their analysis by high-performance liquid chromatography with UV detection (HPLC-UV). Various parameters, such as pH, extraction time, the mass of sorbent, and the desorption conditions, have been evaluated and the calibration curves of the chlorophenols were linear (R² ≥ 0.9985) in the range from 1.01 to 104.5 ng mL⁻¹. The limits of detection at a signal-to-noise (S/N) ratio of 3 were 0.22 and 0.17 ng mL⁻¹ and the limits of quantification calculated at S/N = 10 were 1.52 and 1.07 ng mL⁻¹ for 2-CP and 4-CP, respectively. The recoveries of 2-CP and 4-CP from natural water and the treated wastewater samples were in the range of 84.4-115% with relative standard deviations (RSDs) lower than 7.0%. The results have demonstrated the suitability of the MSPE approach for the analysis of trace chlorophenols in aqueous samples.     

The role of some metal ions in enhancement of photocatalytic activity of Fe2O3–V2O5 binary oxide

Fe₂O₃-V₂O₅ mixed oxides were synthesized with solid-state dispersion (SSD) and coprecipitation methods. In addition, transition metal oxides such as CuO, NiO, and CO₃O₄ were successfully loaded on the synthesized catalyst (Fe₂O₃-V₂O₅) using the SSD method. The composite catalysts were inspected for their photocatalytic activities in degrading 2,4-dichlorophenol under UV light enforcement. The produced samples were analyzed using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, photoluminescence, and the Brunauer–Emmett–Teller method. The addition of transition metal oxides improved the photocatalytic activity of Fe₂O₃-V₂O₅ (SSD). 1CuO wt% Fe₂O₃-V₂O₅ exhibited the highest percentage of 2,4-dichlorophenol degradation (100%) and the highest reaction rate (1.83 mg/L min) in 30 min. This finding is attributed to the distribution of CuO.     

Development of HPLC-MS/MS method for the simultaneous determination of environmental phenols in human urine

We present a sensitive method for simultaneous determination of bisphenol A (BPA), benzophenone-3 (BP-3), 4-tert-octylphenol (t-OP), ortho-phenylphenol (OPP), four parabens (methyl, ethyl, propyl, butyl parabens) and five chlorophenols (2,4-dichlorophenol (2,4-DCP), 2,5-dichlorophenol (2,5-DCP), 2,4,5-trichlorophenol (2,4,5-triclorophenol), 2,4,6-trichlorophenol (2,4,6-TCP), and triclosan (TCS)), in human urine by high-pressure liquid chromatography (HPLC) mass spectrometry (MS). Samples were processed using enzymatic deconjugation of glucuronides followed by solid phase extraction (SPE) on a C18 cartridge and the eluate was concentrated. Analytes were separated by reversed-phase HPLC and then detected by atmospheric pressure chemical ionisation (APCI) MS and quantified by isotope dilution method. We describe details for optimisation of each step of the procedure. The sample treatment steps are straightforward and not labour-intensive and, therefore, permit a high sample throughput with excellent prospects for automation. This method shows low inter-day variation, and detection limits for most of the compounds are below 1 ng/mL in 1 mL of urine. The method accuracy was also verified by the analysis of proficiency testing urine samples.