Degradation Efficiency Of Pentachlorophenol Research Articles

Pentachlorophenol degradation in the heterogeneous catalytic o zonation process using Al2O3as a catalyst agent

In this study, the catalytic ozonation of pentachlorophenol (PCP) in the presence of aluminum oxide (Al2O3) and the formation of byproducts during ozonationhas been studied. Results showed that catalytic ozonation in the presence of Al2O3 can substantially enhance PCP degradation efficiency compared with the using only ozonation process. The influences of severalenvironmental parameters including pH of the solution, initial PCP concentration, dosage of Al2O3 and dissolved ozone concentration were also investigated. The highest degradation efficiency of PCP was achieved at conditions: pH 8, 1.87 g/LAl2O3, and 0.49 g/L dissolved ozone concentration. The catalytic activity of Al2O3 was linked to highly hydroxylated surface. The surface hydroxyl groups on Al2O3 were the active places during catalytic ozonation. According to the drastic changes in the color of solution during ozonationin this study and results of some previous researches, formation of the intermediate reaction products during ozonationwas verified.Free chloride ion released, which was favored at slightly alkaline solution, was also followed in catalytic ozonation process.

Pentachlorophenol degradation in the heterogeneous catalytic o zonation process using Al2O3as a catalyst agent

In this study, the catalytic ozonation of pentachlorophenol (PCP) in the presence of aluminum oxide (Al2O3) and the formation of byproducts during ozonation has been studied. Results showed that catalytic ozonation in the presence of Al2O3 can substantially enhance PCP degradation efficiency compared with the using only ozonation process. The influences of several environmental parameters including pH of the solution, initial PCP concentration, dosage of Al2O3 and dissolved ozone concentration were also investigated. The highest degradation efficiency of PCP was achieved at conditions: pH 8, 1.87 g/LAl2O3, and 0.49 g/L dissolved ozone concentration. The catalytic activity of Al2O3 was linked to highly hydroxylase surface. The surface hydroxyl groups on Al2O3 were the active places during catalytic ozonation. According to the drastic changes in the color of solution during ozonation this study and results of some previous researches, formation of the intermediate reaction products during ozonation was verified. Free chloride ion released, which was favored at slightly alkaline solution, was also followed in catalytic ozonation process.

Degradation of pentachlorophenol in peroxymonosulfate/heat system: Kinetics, mechanism, and theoretical calculations

In this work, we systematically investigated the transformation of pentachlorophenol (PCP) in the heat-activated peroxymonosulfate (PMS) system. The degradation efficiency of PCP increased with initial PMS concentration, temperature and pH. The calculated % reaction stoichiometric efficiency (RSE) reached up to 92.2%. SO42− was found to promote the degradation of PCP, because it significantly enhanced the generation of HO• and SO4•− as confirmed by EPR experiments. According to the radical quenching tests, SO4•− was the dominant reactive radical for PCP degradation. A total of 10 intermediates were identified, and hydroxylation, sulfate addition, dechlorination and oligomerization were speculated as main reaction pathways. Then, possible reactions between reactive radicals and substrate were calculated at the m062x/land2dz level to interpret the mechanisms of different reactions. It was found that ionic PCP had lower activation energy than molecular PCP, and hence showed higher reactivity towards SO4•− and HO• in the course of radical addition reaction. As for the coupling reaction, SO4•− more likely to react with ionic PCP to generate phenoxy radicals than HO•, due to the negative Gibbs free energy change. Meanwhile, the abstraction of an Cl atom by HO• was confirmed to be the first step for the formation of dechlorination products. In addition, toxicity evaluation by ECOSAR and TEST programs illustrated that the toxicity of reaction products was all lower than that of PCP. Findings of this work demonstrated the feasibility of this PMS/heat method for effective removal of PCP in contaminated waters.

High-performance electrocatalytic hydrodechlorination of pentachlorophenol by amorphous Ru-loaded polypyrrole/foam nickel electrode

Ru/polypyrrole/foam Ni composite electrodes were electrochemically deposited for application to electrocatalytic hydrodechlorination of pentachlorophenol (PCP) in aqueous solution. We characterized the Ru/polypyrrole/foam Ni composite electrode by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. The polypyrroles were uniformly distributed on the nickel foam and Ru particles in the size range of 5–8 nm formed an amorphous layer on the polypyrrole/foam Ni composite surface. Compared with the crystalline electrodes of the Ru/foam Ni electrode, the Ru/polypyrrole/foam Ni composite electrodes showed better electrocatalytic dechlorination efficiency and greater stability. At a Ru loading of 0.06 mg/cm2, cathode potential of −1.2 V, and H2SO4 concentration of 0.2 mol/L, the degradation efficiency of PCP reached 94.3% with a dechlorination efficiency of 88%. This performance was well maintained after 8 cycles of reuse.

H<sub>2</sub>O<sub>2</sub> regulates the production of reactive oxygen species in TiO<sub>2</sub> system and the degradation process of pentachlorophenol

The titanium dioxide photocatalytic oxidation technology of pentachlorophenol (PCP) has attracted widespread attention because of its high degradation efficiency and low toxicity. How to reasonably regulate the production of highly toxic intermediates during the degradation of PCP is currently the hotspot. The photocatalytic degradation of PCP is closely related to the production of reactive oxygen species (ROS). This article studied the effect of H2O2 addition on the production of ROS including •OH, O2•− and H2O2 in three different types of TiO2 photocatalytic systems and their effects on the degradation efficiency of PCP. The results showed that after H2O2 was added, the amount of three kinds of ROS produced by the P25 solution increased, and the degradation rate k of PCP increased. The anatase TiO2 solution produced less •OH, but more O2•− and H2O2 after H2O2 was added. The amount of three kinds of ROS produced by the rutile TiO2 solution increased, and the degradation rate of PCP increased by 50 times. The effects of three kinds of TiO2/H2O2 systems on the photocatalytic degradation of PCP and its intermediate acute toxicity were identified by high performance liquid chromatography and luminescence inhibition. The results showed that there were no highly toxic intermediate products such as tetrachloro-1,4-benzoquinone during the degradation process, and the acute toxicity during degradation was significantly reduced. These results indicated that the addition of H2O2 can regulate the ROS production and PCP degradation process in TiO2 photocatalytic system, and significantly reduced the acute toxicity during the degradation of PCP.

Photocatalytic Degradation of Pentachlorophenol Using ZnO Nanoparticles: Study of Intermediates and Toxicity

The photocatalytic degradation of pentachlorophenol (PCP) was carried out using ZnO nanoparticles (NPs) in the presence of sunlight. The effect of different ZnO NPs sizes was synthesized by sol–gel method as well as loading of ZnO NPs on degradation of PCP was investigated. The results showed that the sunny condition was the best to achieve higher efficiency due to the fact that higher energy of photon was available to accelerate rate of reaction. The highest degradation efficiency of PCP was achieved by smaller size of ZnO NPs as 20 nm with band gap and surface area as 3.198 eV and 26.23 m2/g, respectively. The optimum loading of ZnO NP to achieve higher efficiency of 99.6% was 1.0 g/l under 2 h of irradiation time. The photodegradation of PCP followed a pseudo-first order reaction and the observed rate constant was dependent on the ZnO NP loading. The pathway of PCP degradation was suggested according to the HPLC analysis where PCP was converted to nontoxic compounds such as acetic acid and oxalic acid. The toxicity of PCP before and after degradation was evaluated which indicated the removal of toxicity after degradation as sequence with degradation efficiency and confirmed within fragmentation of PCP degradation.

Photocatalytic degradation of pentachlorophenol by visible light Ν-F-TiO₂ in the presence of oxalate ions: optimization, modeling, and scavenging studies.

The efficiency of heterogeneous photocatalysis using N-F-TiO2 as photocatalyst to degrade a priority pollutant, pentachlorophenol (PCP), in the presence of oxalates (OA) was investigated in detail. Response surface methodology was used to optimize the effect of three variables (catalyst concentration, OA/PCP ratio, and pH) on the photocatalytic degradation of pentachlorophenol. A quadratic model was established as a functional relationship between three independent variables and the degradation efficiency of PCP. The results of model fitting and statistical analysis demonstrated that the pH played a key role in the degradation of PCP. Within the studied experimental ranges, the optimum conditions for maximum PCP degradation efficiency (97.5 %) were: catalyst concentration 600 mg L(-1), OA/PCP ratio 2, and pH 10. The contribution of HO(·), O2 (·-), and e(-) produced during the photocatalytic treatment was investigated with the addition of scavengers. The photocatalytic degradation was essentially proceeded through an oxidative mechanism at both acid and alkaline pH values by HO(.) and O2 (·-) radicals attack. It was found that O2 (·-) were the major reactive species involved in PCP degradation in pH 4 and HO(·) in pH 10.

Degradation and dechlorination of pentachlorophenol by microwave-activated persulfate.

The degradation performance of pentachlorophenol (PCP) by the microwave-activated persulfate (MW/PS) process was investigated in this study. The results indicated that degradation efficiency of PCP in the MW/PS process followed pseudo-first-order kinetics, and compared with conventional heating, microwave heating has a special effect of increasing the reaction rate and reducing the process time. A higher persulfate concentration and reaction temperature accelerated the PCP degradation rate. Meanwhile, increasing the pH value and ionic strength of the phosphate buffer slowed down the degradation rate. The addition of ethanol and tert-butyl alcohol as hydroxyl radical and sulfate radical scavengers proved that the sulfate radicals were the dominant active species in the MW/PS process. Gas chromatography-mass spectrometry (GC-MS) was employed to identify the intermediate products, and then a plausible degradation pathway involving dechlorination, hydrolysis, and mineralization was proposed. The acute toxicity of PCP, as tested with Photobacterium phosphoreum, Vibrio fischeri, and Vibrio qinghaiensis, was negated quickly during the MW/PS process, which was in agreement with the nearly complete mineralization of PCP. These results showed that the MW/PS process could achieve a high mineralization level in a short time, which provided an efficient way for PCP elimination from wastewater.

Kinetics studies on pentachlorophenol degradation in soil during pulsed discharge plasma process

Abstract Pentachlorophenol (PCP) degradation kinetics in soil during pulse discharge processes was studied experimentally and theoretically in terms of high-energy electrons, PCP initial concentration, oxygen concentration, and treatment time. Higher PCP degradation efficiency was obtained with more high-energy electrons; 83.9% of PCP was degraded at high-energy electrons 1.9 × 1012/pulse after 60 min's treatment, which decreased to 60.9% at high-energy electrons 6.8 × 1011/pulse. Lower PCP concentration, higher oxygen concentration and longer treatment time benefited PCP degradation. Numerical simulations were conducted to simulate PCP degradation processes. By qualitatively comparing the experimental and theoretical results, it was found that PCP degradation behaviors were exactly similar.

Application of Double-Dielectric Barrier Discharge Plasma for Removal of Pentachlorophenol from Wastewater Coupling with Activated Carbon Adsorption and Simultaneous Regeneration

Wastewater containing pentachlorophenol (PCP) was treated by granular activated carbon (GAC) adsorption and double-dielectric barrier discharge (D-DBD) plasma. A packed bed D-DBD reactor was applied for removal of PCP on GAC and GAC regeneration, where the discharge gap was filled with GAC. PCP degradation efficiency of 65% and GAC regeneration efficiency (RE) of 87% were achieved. Effects of discharge power, treatment time and O2 flow rate on PCP degradation and GAC regeneration were investigated. Increasing discharge power, treatment time and O2 flow rate were favorable for PCP degradation, and also contributed to GAC RE. C–Cl bonds in PCP were cleaved by D-DBD plasma. Effect of D-DBD plasma on physical and chemical properties of GAC during GAC regeneration process was characterized by N2 adsorption and Boehm titration. This study is expected to demonstrate the feasibility of applying D-DBD plasma for efficient organic wastewater treatment by coupling with GAC adsorption.

Degradation of pentachlorophenol in soil by pulsed corona discharge plasma

The remediation of pentachlorophenol (PCP) contaminated soil using pulsed corona discharge plasma was reported in this study. The effect of practical run parameters such as peak pulse voltage, pulse frequency, gas atmospheres (air, O 2, Ar and N 2), air flow rate and pollution time on PCP degradation was investigated, and the intermediate products were also studied. The results indicated that PCP degradation efficiency increased with an increase in peak pulse voltage or pulse frequency, due to the enhancement of energy input. There existed a maximal PCP degradation efficiency with the change of air flow rate. PCP degradation efficiencies under oxygen and air atmospheres were achieved 92% and 77% after 45 min of discharge treatment at 14.0 kV, respectively, which were only 19% and 8% under argon and nitrogen atmospheres, respectively. O 3 played an important role in PCP degradation. However, other processes also contributed to PCP degradation, such as N, N 2 +, N + and OH. The pollution time evidenced slight influence on PCP degradation. The main intermediate products produced during the treatment process were identified as tetrachlorocatechol, tetrachlorohydroquinone, acetic acid, formic acid and oxalic acid by HPLC/MS and ion chromatography. This study is expected to provide reference for the application of pulsed corona discharge in soil remediation.

Evaluation of the Potential of Pentachlorophenol Degradation in Soil by Pulsed Corona Discharge Plasma from Soil Characteristics

Chlorinated organics are frequently found as harmful soil contaminants and persisted for extended periods of time. A novel approach, named pulsed corona discharge plasma (PCDP), was employed for the degradation of pentachlorophenol (PCP) in soil. Experimental results showed that 87% of PCP could be smoothly removed in 60 min. Increasing pulse voltage, enhancing soil pH, lowering humic acid (HA) in soil and reducing granular size of the soil were found to be favorable for PCP degradation efficiency. Oxidation and physical processes simultaneously contributed to PCP removal in soil and ozone was the main factor in PCDP treatment. C-Cl bonds in PCP were cleaved during PCDP treatment by Fourier transform infrared spectroscopy (FTIR) analysis. The mineralization of PCP was confirmed by total organic carbon (TOC) and dechlorination analyses. The main intermediate products such as tetrachlorocatechol, tetrachlorohydroquinone, acetic acid, formic acid, and oxalic acid were identified by HPLC/MS and ion chromatography. A possible pathway of PCP degradation in soil in such a system was proposed.

Fabrication of needle-like ZnO nanorods arrays by a low-temperature seed-layer growth approach in solution

Uniform, large-scale, and well-aligned needle-like ZnO nanorods with good photoluminescence and photocatalysis properties on Zn substrates, have been successfully fabricated using a simple low-temperature seed-layer growth approach in solution (50 °C). The formation of ZnO seed-layer by the anodic oxidation technique (AOT) plays an important role in the subsequent growth of highly oriented ZnO nanorods arrays. Temperature also proved to be a significant factor in the growth of ZnO nanorods and had a great effect on their optical properties. X-ray diffraction (XRD) analysis, selected-area electron diffraction (SAED) pattern and high-resolution TEM (HRTEM) indicated that the needle-like ZnO nanorods were single crystal in nature and that they had grown up preferentially along the [0001] direction. The well-aligned ZnO nanorods arrays on Zn substrates exhibited strong UV emission at around 380 nm at room temperature. To investigate their potential as photocatalysts, degradation of pentachlorophenol (PCP) in aqueous solution was carried out using photocatalytic processes, with comparison to direct photolysis. After 1 h, the degradation efficiencies of PCP by direct photolysis and photocatalytic processes achieved 57% and 76% under given experimental conditions, respectively. This improved degradation efficiency of PCP illustrates that ZnO nanorods arrays on Zn substrates have good photocatalytic activity. This simple low-temperature seed-layer growth approach in solution resulted in the development of an effective and low-cost fabrication process for high-quality ZnO nanorods arrays with good optical and photocatalytic properties that can be applicable in many fields such as photocatalysis, photovoltaic cells, luminescent sensors, and photoconductive sensors.

Preparation of Zn-doped TiO2 nanotubes electrode and its application in pentachlorophenol photoelectrocatalytic degradation

Zn-doped titanium oxide (TiO2) nanotubes electrode was prepared on a titanium plate by direct anodic oxidation and immersing method in sequence. Field emission scanning electron microscopy (FESEM) showed that the Zn-doped TiO2 nanotubes were well aligned and organized into high density uniform arrays with diameter ranging from 50 to 90 nm. The length and the thickness were about 200 and 15 nm respectively. TiO2 anatase phase was identified by X-ray diffraction (XRD). X-ray photoelectronspectroscopy (XPS) indicated that Zn ions were mainly located on the surface of TiO2 nanotubes in form of ZnO clusters. Compared with TiO2 nanotubes electrode, about 20 nm red shift in the spectrum of UV-vis absorption was observed. The degradation of pentachlorophenol (PCP) in aqueous solution under the same condition (initial concentration of PCP: 20 mg/L; concentration of Na2SO4: 0.01 mol/L and pH: 7.03) was carried out using Zn-doped TiO2 nanotubes electrode and TiO2 nanotubes electrode. The degradation rates of PCP using Zn-doped TiO2 nanotubes electrode were found to be twice and 5.8 times as high as that using TiO2 nanotubes electrode by UV radiation (400 μw/cm2) and visible light radiation (4500 μw/cm2), respectively. 73.5% of PCP was removed using Zn-doped TiO2 nanotubes electrode against 48.5% removed using TiO2 nanotubes electrode in 120 min under UV radiation. While under visible light radiation, the degradation efficiency of PCP was 18.4% using Zn-doped TiO2 nanotubes electrode against 3.2% using TiO2 nanotubes electrode in 120 min. The optimum concentration of Zn doping was found to be 0.909%. The PCP degradation efficiencies of the 10 repeated experiments by Zn-doped TiO2 nanotubes electrode were rather stable with the deviation within 3.0%.

Degradation of pentachlorophenol by an electroenzymatic method using immobilized peroxidase enzyme

In this study, pentachlorophenol (PCP) was degraded by the electroenzymatic method, which combines the enzymatic catalysis and the electrogeneration of hydrogen peroxide (H2O2). The experiments were conducted in a two-compartment packed-bed reactor using horseradish peroxidase (HRP) immobilized electrode. The highest produc- tion of H2O2 and the current efficiency were observed at −0.4 V vs. Ag/AgCl and a flow rate of 1 mL/min. The highest initial degradation rate and degradation efficiency of PCP were achieved at pH 5 and 25 o C. Under the conditions, the electrolysis was compared with an electrochemical method. The presence of chloride ion indicates that PCP was de- chlorinated at the initial period of degradation. According to the proposed breakdown pathway and the intermediates, the electroenzymatic method showed an improved degradation ability compared to an electrochemical method.

Design and experimental study of immobilized soil bioreactor for in‐well biodegradation of pentach rophenol in groundwater

AbstractA novel system for in‐situ biological treatment of pentachlorophenol in groundwater is proposed in this work. It is based on the concept of soil immobilization, which has already been shown to be very efficient when applied to bioreactor engineering. For this paper, we used immobilized soil to develop a bioreactor system for an in‐situ (in‐well) biodegradation of pentachlorophenol (PCP). The process was carried out at 9dGC, a temperature typical for groundwater. The volumetric PCP degradation efficiency in the new system was very high – up to 400 mg/(L.h). The effect of some physicochemical parameters (temperature, substrate concentration) on the biodegradation kinetics was studied. The results obtained show that the application of soil immobilization to the in‐situ biodegradation of groundwater contaminated with PCP is very promising.