Oxidation Of Chlorophenols Research Articles

Nanoconfinement steers nonradical pathway transition in single atom fenton-like catalysis for improving oxidant utilization

The introduction of single-atom catalysts (SACs) into Fenton-like oxidation promises ultrafast water pollutant elimination, but the limited access to pollutants and oxidant by surface catalytic sites and the intensive oxidant consumption still severely restrict the decontamination performance. While nanoconfinement of SACs allows drastically enhanced decontamination reaction kinetics, the detailed regulatory mechanisms remain elusive. Here, we unveil that, apart from local enrichment of reactants, the catalytic pathway shift is also an important cause for the reactivity enhancement of nanoconfined SACs. The surface electronic structure of cobalt site is altered by confining it within the nanopores of mesostructured silica particles, which triggers a fundamental transition from singlet oxygen to electron transfer pathway for 4-chlorophenol oxidation. The changed pathway and accelerated interfacial mass transfer render the nanoconfined system up to 34.7-fold higher pollutant degradation rate and drastically raised peroxymonosulfate utilization efficiency (from 61.8% to 96.6%) relative to the unconfined control. It also demonstrates superior reactivity for the degradation of other electron-rich phenolic compounds, good environment robustness, and high stability for treating real lake water. Our findings deepen the knowledge of nanoconfined catalysis and may inspire innovations in low-carbon water purification technologies and other heterogeneous catalytic applications.

Unveiling the spatially confined oxidation processes in reactive electrochemical membranes

Electrocatalytic oxidation offers opportunities for sustainable environmental remediation, but it is often hampered by the slow mass transfer and short lives of electro-generated radicals. Here, we achieve a four times higher kinetic constant (18.9 min−1) for the oxidation of 4-chlorophenol on the reactive electrochemical membrane by reducing the pore size from 105 to 7 μm, with the predominate mechanism shifting from hydroxyl radical oxidation to direct electron transfer. More interestingly, such an enhancement effect is largely dependent on the molecular structure and its sensitivity to the direct electron transfer process. The spatial distributions of reactant and hydroxyl radicals are visualized via multiphysics simulation, revealing the compressed diffusion layer and restricted hydroxyl radical generation in the microchannels. This study demonstrates that both the reaction kinetics and the electron transfer pathway can be effectively regulated by the spatial confinement effect, which sheds light on the design of cost-effective electrochemical platforms for water purification and chemical synthesis.

Degradation and Extraction of Organochlorine Pollutants from Environmental Solids under Subcritical Water Conditions.

A subcritical water degradation and extraction method was developed to remediate environmental soils contaminated by highly recalcitrant organochlorine pollutants. Hydrogen peroxide was used to effectively decompose organochlorine pollutants under subcritical water conditions. As a method optimization study, the static wet oxidation of chlorophenols was first performed in subcritical water with and without added hydrogen peroxide. Complete oxidation was achieved using an added oxidant, and thus, the oxidation and extraction of chlorophenols from a sand matrix was then attempted. Complete oxidation and extraction with added oxidant were achieved within 30 min at 100 °C. We then investigated the subcritical water degradation and extraction of dieldrin, mirex, and p,p'-DDD. These organochlorine pesticides were not as easily oxidized as the chlorophenols, and the benefit of adding hydrogen peroxide was only clearly observed at 200 °C. Approximately a 20% increase in degradation was noted for each pesticide and insecticide at this temperature. Unfortunately, this difference was not observed with an increase in temperature to 250 °C, except in some cases, where the amount of degradation byproducts was reduced. Dieldrin and p,p'-DDD were essentially destroyed at 250 °C, while all the pesticides and the insecticides were completely removed from the sand at this temperature. The proposed method was then used to remediate a soil sample highly contaminated with DDT. The soil was obtained from the grounds of an old DDT mixing facility in Virginia and has been aging for several decades. Not only was 100% removal of DDT from this soil achieved using the proposed method at 250 °C, but also, the extracted DDT was completely destroyed during the process. The proposed remediation method, therefore, demonstrates a high potential as an efficient and environmentally sound technique for the detoxification of soils.

Selective Oxidation of Halophenols Catalyzed by an Artificial Miniaturized Peroxidase.

The development of artificial enzymes for application in sustainable technologies, such as the transformation of environmental pollutants or biomass, is one of the most challenging goals in metalloenzyme design. In this work, we describe the oxidation of mono-, di-, tri- and penta-halogenated phenols catalyzed by the artificial metalloenzyme Fe-MC6*a. It promoted the dehalogenation of 4-fluorophenol into the corresponding 1,4-benzoquinone, while under the same experimental conditions, 4-chloro, 4-bromo and 4-iodophenol were selectively converted into higher molecular weight compounds. Analysis of the 4-chlorophenol oxidation products clarified that oligomers based on C-O bonds were exclusively formed in this case. All results show that Fe-MC6*a holds intriguing enzymatic properties, as it catalyzes halophenol oxidation with substrate-dependent chemoselectivity.

Boron-doped diamond nanofilm on a Ti substrate possessing fast charge transfer: Strategy toward cost-effective electrochemical oxidation of refractory organic pollutants

This study suggests a breakthrough toward the high-cost issue of electrochemical degradation of refractory organic pollutants caused by adopting a boron-doped diamond (BDD) electrode. Specifically, effect of charge transfer capability of the BDD electrode on electrochemical oxidation of 4-chlorophenol (4-CP) and perfluorooctanoic acid (PFOA) is explored. Thin BDD nanofilm (thickness of ~400 nm) on a Ti substrate (BDD@Ti) was prepared to overcome the delamination of the BDD on the Ti via hot-filament chemical vapor deposition under optimum conditions. When compared with a commercial electrode (C-BDD, micron BDD film on a Nb substrate), inevitable metal-carbide layer formed at interface between BDD film and metal substrate is much thinner than that of C-BDD. The unique structural features of BDD@Ti facilitate a much faster charge transfer and degradation of both 4-CP and PFOA than C-BDD, which is attributed to shortening of electron pathway from surface to conductive substrate.

Free radical mechanism of toxic organic compound formations from o-chlorophenol.

Organic free radical intermediates are pivotal to our understanding of toxic chemicals formation from chlorophenols that widely exist in thermal processes. However, in most cases, multiple free radical intermediates exist and produce complex spectra that are hard to deconvolute. Identification of free radical intermediates is the current difficulty for detailed formation mechanisms of toxic products from chlorophenols. In this study, a universal bottom-up method was developed to identify the organic free radical intermediates. Candidate organic free radicals were firstly speculated according to the critical parameters obtained from experimental electron paramagnetic resonance (EPR) spectra and the calculated bond dissociation energies of precursors. Their theoretical spectra were then used retrospectively to justify the accordance with the experimental EPR spectra. Identification of the organic free radicals provides straightforward evidence for the formation pathways of pollutants from chlorophenol. Internal factors influencing formation of radical intermediates and the toxic products were also studied, including the ortho effect of the precursor, spin densities of the organic free radical intermediates, and steric hindrance effects of the molecular intermediates. In combination of the experimental results and theoretical calculations, detailed formation mechanisms of toxic pollutants intermediating by organic free radicals from thermal oxidation of chlorophenol were strongly evidenced.

TiO2-C nanocomposite synthesized via facile surfactant-assisted method as a part of less energy-consuming LED-based photocatalytic system for environmental applications

A novel facile method was used to incorporate carbon into the titania structure. An alternative synthesis method of carbon-doped TiO2 has been proposed by using a widely used and cheap surfactant. During the process, cetyltrimethylammonium bromide plays a dual role, as a morphology modifier and as a carbon source. The presented approach allows obtained TiO2-C nanostructures to be anatase nanocrystals with carbon being deposited either on the surface or between the TiO2 nanoparticles. The innovative nature of the research subject is related to the design of cheap LED solutions and facile synthesis of TiO2-C for use in novel energy-saving photocatalytic systems. Photocatalytic studies showed promising activity in the oxidation of 4-chlorophenol. Furthermore, it was indicated that LED-based photocatalytic systems allow a significant reduction in energy consumption compared to conventional photocatalytic sets. In addition, the high thermal efficiency of LED systems was confirmed with a thermal imaging camera. Hence, the presented novel LED photocatalytic systems can be an important part of a broad strategy for the protection of the environment.

Further Consideration of Effect of Fluoro-Carbon Chain Length on Catalytic Activity and Properties of Lead Dioxide-Based Surfactant Composites

Rate constant (k) for the lead(II) oxidation decreases from (4.06 ± 0.10) × 10−4 to (2.80 ± 0.10) × 10−4 ms−1 when 3 × 10−4 M of dopant C6F13SO3K is added to the deposition solution. The adsorption of C6F13SO3K on PbO2 is specific, which is confirmed by the shift of pH0 of the oxide to higher value. There are no visible differences when modifying lead dioxide with perfluorohexanesulfonate, the morphology of the composite is similar to the naked sample; as well as there are only slight deviations in the texture of the composites involved. It should be noted that using a long chain compound with perfluorinated hydrocarbon radical in order to achieve higher oxidation rates of organic compounds is not recommended since a perfluorinated hydrocarbon skeleton (longer than 4 carbon atoms) can block active centers taking part in water and 4-chlorophenol oxidation.

Electrochemical and Catalytic Properties of Carbon Dioxide-Activated Graphite Felt.

The commercial graphite felt GFA 10 was subjected to an activation process with the use of CO2 at 900 °C for 35 and 70 min. Pristine and heat-treated materials were characterized using various methods: low-temperature N2 adsorption, SEM, and EDS. Voltammetric measurements of GFA samples (before and after activation) as the working electrode were carried out. Voltammograms were recorded in aqueous solutions of 4-chlorophenol and sodium sulfate as supporting electrolyte. The catalytic activity of GFA samples in the process of 4-chlorophenol oxidation with the use of H2O2 was also investigated. The influence of graphite felt thermal activation in the CO2 atmosphere on its electrochemical and catalytic behavior was analyzed and discussed. Results of the investigation indicate that GFA activated in CO2 can be applied as an electrode material or catalytic material in the removal of organic compounds from industrial wastewater. However, the corrosion resistance of GFA, which is decreasing during the activation, needs to be refined.

(Invited) CdS/Pd Photocatalytic Bipolar Membrane for Selective Reduction and Oxidation Processes

A bipolar membrane with specific cation exchange and anion exchange properties between the two layers enables design of photocatalytically active membrane which also separate reaction compartments. The key advantage of such a membrane lies in the separation of oxidation and reduction processes while continue to engage in the photodriven reactions. The example of simultaneous oxidation of 4-chlorophenol and the reduction of 4-nitrophenol under visible light irradiation of the BPM-CdS/Pd shows its effectiveness in photocatalytic remediation of chemical contaminants. The CdS-Pd based bipolar membrane to carry out selective reduction and oxidation processes has also allowed us estimate the contribution of sacrificial donor oxidation in H2 production in water photoelectrolysis. The design and photocatalytic properties of this photocatalytic membrane will be discussed.

Kinetic modelling for concentration and toxicity changes during the oxidation of 4-chlorophenol by UV/H2O2

This work develops a kinetic model that allow to predict the water toxicity and the main degradation products concentration of aqueous solutions containing 4-chlorophenol oxidised by UV/H2O2. The kinetic model was developed grouping degradation products of similar toxicological nature: aromatics (hydroquinone, benzoquinone, 4-chlorocatechol and catechol), aliphatics (succinic, fumaric, maleic and malonic acids) and mineralised compounds (oxalic, acetic and formic acids). The degradation of each group versus time was described as a mathematical function of the rate constant of a second-order reaction involving the hydroxyl radical, the quantum yield of lump, the concentration of the hydroxyl radicals and the intensity of the emitted UV radiation. The photolytic and kinetic parameters characterising each lump were adjusted by experimental assays. The kinetic, mass balance and toxicity equations were solved using the Berkeley Madonna numerical calculation tool. Results showed that 4-chlorophenol would be completely removed during the first hour of the reaction, operating with oxidant molar ratios higher than R = 200 at pH 6.0 and UV = 24 W. Under these conditions, a decrease in the rate of total organic carbon (TOC) removal close to 50% from the initial value was observed. The solution colour, attributed to the presence of oxidation products as p-benzoquinone and hydroquinone, were oxidised to colourless species, that resulted in a decrease in the toxicity of the solutions (9.95 TU) and the aromaticity lost.

Efficient degradation of 4-chlorophenol over zirconium, nitrogen and sulphur doped cobalt nanoferrite catalysts

Cobalt ferrite and zirconium doped cobalt ferrite were prepared by coprecipitation method. Nirogen and sulphur ions were doped to it by wet impregnation and co precipitation techniques. The efficiency of the samples towards catalytic wet peroxide oxidation of 4-chlorophenol was checked. Doping increased the catalytic efficacy of cobalt ferrites towards the reaction; zirconium being the most efficient dopant. Complete conversion of 4-chlorophenol with appreciable reduction in chemical oxygen demand(COD) was noted at 50 °C with pollutant to hydrogen peroxide ratio of 1:15. Surface area and nature of the catalyst active surface played deciding role in the oxidation rreaction. The mechanism followed a heterogenous free radical catalysed path as evidenced from metal leaching and radical scavenging studies. The catalysts were magnetically recoverable and stable on repeated uses.

Advanced oxidation of 4-chlorophenol via combined pulsed light and sulfate radicals methods: Effect of co-existing anions

Pulsed light (PL) technology, which is based on photonic technology involves the application of broadband emission of light with short and high-power pulses is beginning to emerge for the treatment of wastes via advanced oxidation processes (AOP). The present work investigates the efficiency of PL as a light source for persulfate (PS) activation (PL/PS) and 4-chlorophenol)4-CP) degradation, an organic model pollutant. The influencing parameters on 4-CP degradation such as solution pH, reaction time, initial concentration of 4-CP, PS dose, pulse intensity and frequency, and distance from PL source are systematically investigated. With increasing pH from 3 to 9, the 4-CP degradation decreased from 49.79 ± 2.49 to 33.12 ± 1.66%. The 4-CP degradation followed the first order kinetics that was improved with increasing reaction time, PS dose, pulse intensity, frequency of pulse, and decreasing pH, initial 4-CP concentration and distance from the PL source. The presence of sulfate, chloride, and carbonate anions in the solution has the inhibitory effects on 4-CP degradation, while nitrate anion improved the performance of PL/PS system. In addition, presence of humic acid had an inhibitory effect on the PL/PS system, which led to a decrease of reaction rate constant and 4-CP degradation was performed in PL/PS system with OH, SO4−, O2- and 1O2 radicals. The contributions of OH and SO4− radicals were 46% and 51%, respectively for the 4-CP degradation and synergistic effect of PL/PS system showed a significant influence on 4-CP degradation while using a combination of PL and PS, suggesting that PL is an effective activator of PS.

Effect of Gliding Arc Plasma-Induced UV Light During the Photo-Fenton Oxidation of 4-Chlorophenol in Aqueous Solution

4-chlorophenol (4-CP) is recognized as a highly toxic organic which can cause damage effects on human life and the aquatic environment. Since conventional wastewater techniques were unable to remove non-biodegradable chlorophenols, advanced oxidation process was investigated to achieve this goal. Amongst them, non-thermal plasma was recently proposed as an alternative and promising technique. However, the energy efficiency of most non-thermal plasma technique is very low as well as the input energy is dissipated in many forms such as heat, UV radiation, electromagnetic waves, etc., that are not totally involved in the pollutant degradation. In this work, quantitative analyses of UV radiation and H2O2 in a moist air gliding arc plasma (glidarc) were performed using potassium ferrioxalate actinometry and peroxytitanyl complex method, respectively. The role of UV light emitted in gliding arc plasma was elucidated by performing parallel experiments: H2O2, glidarc alone, glidarc + H2O2, glidarc + H2O2 + Fe3+ (plasma-Photo-Fenton). The results show that the incorporation of Fenton reagents in 4-CP solution exposed to the plasma enhanced the yields of chemical active species, which were available for efficient removal and mineralization of 4-CP.

Enhanced reactivity of zero-valent aluminum/O2 by using Fe-bearing clays in 4-chlorophenol oxidation

Zero-valent aluminum (ZVAl) is a promising reductant because of its relatively low redox potential, which can efficiently activate molecular oxygen to generate reactive oxygen species. However, its long-term performance is limited by the intrinsic dense oxide layer and the passivation effect of the accumulative Al-(hydr)oxide on its surface during the reaction. In this study, four clay minerals with different compositions were mixed with ZVAl by ball milling to obtain four composites of ZVAl and clay (ZVAl-Clay), which were used to degrade a high concentration of 4-chlorophenol (4-CP) under ambient conditions. The oxidation efficiencies of different ZVAl-Clays were strongly relevant to Fe contained in the clay minerals. The Fe-free ZVAl-Clay presented poor oxidation performance, whereas the reaction efficiencies of those ZVAl composites with Fe-bearing clays exhibited varying degrees of improvement. In comparison with the original ZVAl, the highest oxidation rate increased by 23 times, the maximum increased OH production was approximately 8 times, and the corresponding mineralization efficiency improved by 38.7%. However, the levels of improved oxidation performance of various ZVAl-Clays were not positively correlated with their actual total Fe contents, and their degradation efficiencies might also be affected by other physical and/or chemical properties of different clays. The synergistic mechanism revealed by various characterizations was that electron transfer might occur from ZVAl to the structural Fe(III) of the clay through the basal plane or edge of clays triggered by ball milling. Thus, the partially produced Fe(II) on the clay surface promoted the Fenton-like reaction to decompose H2O2 into OH for efficient oxidation of 4-CP. In short, the ZVAl composites with Fe-bearing clays deserved further exploration as potential materials for efficient degradation of organic matters in wastewater samples.

Probing P25 TiO2 photocatalysis using photoinduced absorption spectroscopy (PIAS)

Photoinduced absorption spectroscopy, PIAS, is used for the first time to probe the kinetics exhibited by the most commonly employed powder photocatalyst, P25 TiO2, in mesoporous film form, in the photocatalysed oxidation of a commonly used test organic pollutant, 4-chlorophenol, 4CP. The results show that PIAS can provide previously unobtainable, invaluable, direct kinetic, and mechanistic, information concerning photogenerated holes in powdered photocatalysts.

Degradation Pathway and Kinetics of 4-chlorphenol by Sn/Sb-Mn-GAC Composite Particle Electrode

A composite particle electrode Sn/Sb-Mn-GAC was prepared by impregnation with granular activated carbon (GAC) as carrier. The surface morphology, phase composition and electrochemical properties of the particle electrode were characterized by scanning electron microscopy, X-ray diffraction and electrochemical workstation. The results show that the Sn/Sb-Mn-GAC particles have uniform grain size, good dispersity and high oxygen evolution potential. The Sn/Sb-Mn-GAC particle electrode was used to the electrochemical degradation of 4-chlorophenol. It was shown that 4-chlorophenol was almost completely removed after electrolyzing for 60 min. A large number of intermediates were produced during the degradation of 4-chlorophenol in the experimental system. The main intermediate products were benzoquinone, 4-chlorocatechol, hydroquinone, fumaric acid, oxalic acid, etc., eventually mineralized into water and carbon dioxide. The degradation pathway of 4-chlorophenol were preliminarily suggested through the analysis of intermediates in degradation process. The supported Sn/Sb-Mn-GAC particle electrode can be repeated used 4 times in three-dimensional electrochemical reactor and the kinetic model for the electrochemical oxidation of 4-chlorophenol was established. The experimental results show that the degradation process of 4-chlorophenol accords with the first-order kinetic model, the correlation coefficient is 0.98 or more. The kinetic rate constant k of Sn/Sb-Mn-GAC particle electrode is reduced when it is repeated used, but the treatment efficiency of 4-chlorophenol is still better. The results of research show that the three-dimensional electrochemical reactor using Sn/Sb-Mn-GAC particle electrode has promising application prospects in the treatment of phenolic wastewater.

Dissolved Silicate Enhances the Oxidation of Chlorophenols by Permanganate: Important Role of Silicate-Stabilized MnO2 Colloids.

Dissolved silicate is an important background constituent of natural waters, but there is little clarity regarding the effect of silicate on the oxidizing capability of permanganate (Mn(VII)) and on its efficiency for remediation applications. In the present study, we found that dissolved silicate, metasilicate or disilicate (DS), could significantly promote the oxidation of 2,4-dichlorophenol (2,4-DCP) by Mn(VII), and the extent of the promoting effect was even more evident than that of pyrophosphate (PP). The experiments showed that, unlike PP, DS was not capable of coordinating with Mn(III) ions, and the promoting effect of DS was not due to the oxidizing capability of complexed Mn(III). Instead, DS ions, as a weak base, could combine with the hydroxyl groups of MnO2 via hydrogen bonding to limit the growth of colloidal MnO2 particles. The DS-stabilized colloidal MnO2 particles, with hydrodynamic diameters less than 100 nm, could act as catalysts to enhance the oxidation of 2,4-DCP by Mn(VII). The best promoting effect of DS on the performance of Mn(VII) oxidant was achieved at the initial solution pH of 7, and the coexisting bicarbonate ions further improved the oxidation of 2,4-DCP in the Mn(VII)/DS system. Sand column experiments showed that the combined use of Mn(VII) and DS additive could mitigate the problem of permeability reduction of sand associated with the retention of MnO2 particles. This study not only deepens our understanding on the role of dissolved silicate in a Mn(VII) oxidation process but also provides an effective and green method to enhance the oxidizing capacity of Mn(VII)-based treatment systems.

Lead dioxide-SDS composites: Design and properties

Abstract The electrodeposition of PbO2 from a sodium dodecyl sulphate-containing medium has been investigated. The presence of sodium dodecyl sulfate in the deposition electrolyte leads to a slight inhibition of the deposition of lead dioxide. It has been found that the morphology and structure of composite materials differs significantly from lead dioxide. With an increase in the additive content in the composite, there is a transition from large-grained deposits to materials with submicron and nano-sized crystals. It is shown that anionic surfactants, sodium dodecyl sulfate in particular, are included in the growing lead dioxide. The changing in deposition conditions (temperature, pH and anodic current density) allows one to control the content of surfactant in the resulting oxide. It is possible to obtain a surfactant-oxide composite with the content of organic substance in the oxide up to 5.4 wt%. The electocatalytic activity of the materials involved was investigated in respect to oxygen evolution reaction and the oxidation of 4-chlorophenol. Oxygen overpotential on PbO2-SDS coatings decreases in comparison to non-modified sample because of a decrease in the degree of filling of oxygen-containing particles on the surface of the electrode, probably due to blocking by sulfate ions. The 4-chlorophenol oxidation rate is significantly increased on PbO2-SDS composites. Thus, already after 90 min of electrolysis on composites, contained 2 and 4.2 wt% SDS, all aromatic intermediates are destroyed, and only aliphatic acids are found in the solution.

Enhanced electrochemical decontamination and water permeation of titanium suboxide reactive electrochemical membrane based on sonoelectrochemistry

Reactive electrochemical membrane (REM) allows electrochemical oxidation (EO) water purification under flow-through operation, which improves mass transfer on the anode surface significantly. However, O2 evolution reaction (OER) may cause oxygen bubbles to be trapped in small-sized confined flow channels, and thus degrade long-term filterability and treatability of REM. In this study, ultrasound (ultrasonic vibrator, 28 kHz, 180 W) was applied to EO system (i. e. sonoelectrochemistry) containing titanium suboxide-REM (TiSO-REM) anode for enhanced oxidation of 4-chlorophenol (4-CP) target pollutant. Both experimental and modeling results demonstrated that ultrasound could mitigate the retention of O2 bubbles in the porous structures by destructing large-size bubbles, thus not only increasing permeate flux but also promoting local mass transfer. Meanwhile, oxidation rate of 4-CP for EO with ultrasound (EO-US, 0.0932 min−1) was 216% higher than that for EO without ultrasound (0.0258 min−1), due to enhanced mass transfer and OH production under the cavitation effect of ultrasound. Density functional theory (DFT) calculations confirmed the most efficient pathway of 4-CP removal to be direct electron transfer of 4-CP to form [4-CP]+, followed by subsequent oxidation mediated by OH produced from anodic water oxidation on TiSO-REM anode. Last, the stability of TiSO-REM could be improved considerably by application of ultrasound, due to alleviation of electrode deactivation and fouling, indicated by cyclic test, scan electron microscopy (SEM) observation and Fourier transform infrared spectroscopy (FT-IR) characterization. This study provides a proof-of-concept demonstration of ultrasound for enhanced EO of recalcitrant organic pollutants by REM anode, making decentralized wastewater treatment more efficient and more reliable.