Destruction Kinetics of 2,4 Dichlorophenol Aqueous Solutions in an Atmospheric Pressure Dielectric Barrier Discharge in Oxygen

The processes of degradation of 2,4-dichlorophenol (2,4-DCP) aqueous solutions under the action of atmospheric pressure of DBD in oxygen were studied. The degradation of 2,4-DCP proceeds efficiently, the degree of decomposition reaching 100%. The degradation kinetics of 2,4-DCP obeys a formal first-order kinetic law on concentration of 2,4-DCP. The effective rate constants depend weakly on the experimental conditions and are equal to ~ 2 s^?1. Based on experimental data, the energy efficiency of 2,4-DCP decomposition was determined to be in the range of 0.039–0.173 molecules per 100 eV depending on the experimental conditions. The composition of the products was studied by gas chromatography, chromatography-mass spectrometry, UV/visible spectroscopy, fluorescent methods and some chemical methods. The main decomposition products present in the solution were found to be carboxylic acids, aldehydes and chloride ions, whereas carbon dioxide and molecular chlorine appear in the gas. The results obtained are compared with similar data from other advanced oxidation processes (AOP’s) methods.     

Destruction of 2,4 Dichlorophenol in an Atmospheric Pressure Dielectric Barrier Discharge in Oxygen

The processes of degradation of 2,4-dichlorophenol (2,4-DCP) under the action of atmospheric pressure of dielectric barrier discharge (DBD) in oxygen were studied. It was shown that the degradation of 2,4-DCP proceeds efficiently. Degree of decomposition reaches 90%. The degradation kinetics of 2,4-DCP obeys the formal first-order kinetic law on concentration of 2,4-DCP. The effective rate constants depend weakly on the experimental conditions and are equal to ~0.2 s^?1. Based on experimental data, the energy efficiency of decomposition of 2,4-DCP was determined. Depending on the conditions, the energy efficiency was in the range of (8–90) × 10^?3 molecules per 100 eV. The composition of the products was studied by gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), energy-dispersive X-ray spectroscopy (EDX), attenuated total reflection-fourier transform infrared (ATR-FTIR) spectroscopy, electron spin resonance (ESR) spectroscopy and UV/Visible spectroscopy. It was shown that about ~20% of 2,4-DCP is converted to CO₂, while the other part forms an organic film on the reactor wall. The substance formed is close to the carboxylic acids in chemical composition and exhibits electrical conductivity and paramagnetic properties. Almost all of the chlorine contained in the 2,4-DCP is released into the gas phase. The active species of the afterglow react with liquid hexane, forming the products of its oxidation. Some assumptions regarding the pathway of the process are discussed.     

2,4-二氯苯酚的电化学氧化降解反应研究

采用循环伏安法和原位红外光谱技术研究了2,4-二氯苯酚在Pt电极上的电化学氧化降解反应,结合Fukui函数值预测了2,4-二氯苯酚在电化学氧化过程中的反应位点. 结果表明,Pt电极对2,4-二氯苯酚有良好的电催化活性,2,4-二氯苯酚在电极表面反应主要有3个途径：直接通过电化学反应脱去氯离子,生成苯酚;在·OH的进攻下,C—Cl键断裂,4位Cl较2位Cl先脱去,生成苯二酚,并可进一步氧化生成苯醌以及不饱和羧酸;在·OH的进攻下发生苯环开环反应,生成含氯不饱和羧酸. 在1700 mV左右,2,4-二氯苯酚可经电化学氧化生成CO₂.     

Reductive dechlorination of 2,4-dichlorophenol using nanoscale Fe~0: influencing factors and possible mechanism

Nanoscale Fe0 was synthesized through a reductive method in this paper. The experiments were per-formed to investigate the reduction of 2,4-dichlorophenol (2,4-DCP) by nanoscale Fe0 under different conditions. The pathways for the reduction of 2,4-DCP by nanoscale Fe0 were discussed. Batch studies demonstrated that the mechanism includes adsorption, dechlorination and cleavage of the benzene ring. Dechlorination, which occurs after 2,4-DCP molecule is adsorbed on the interface of Fe particle, is an interfacial reaction. One or two chlorine atom can be removed from 2,4-DCP to form 2-chlorophenol, 4-chlorophenol or phenol. As the concentration of 2,4-DCP increased, the relative dechlorination ratio decreased. However, the reduced quantities of 2,4-DCP increased. Temperature can influence dechlo-rination rate and pathway. Dechlorination is prior to cleavage of the benzene ring at a higher tempera-ture, but at a lower temperature, adsorption may be the main pathway, and cleavage of the benzene ring may be prior to dechlorination.     

Reductive dechlorination of 2,4-dichlorophenol using nanoscale Fe<Superscript>0</Superscript>: influencing factors and possible mechanism

Nanoscale Fe⁰ was synthesized through a reductive method in this paper. The experiments were performed to investigate the reduction of 2,4-dichlorophenol (2,4-DCP) by nanoscale Fe⁰ under different conditions. The pathways for the reduction of 2,4-DCP by nanoscale Fe⁰ were discussed. Batch studies demonstrated that the mechanism includes adsorption, dechlorination and cleavage of the benzene ring. Dechlorination, which occurs after 2,4-DCP molecule is adsorbed on the interface of Fe particle, is an interfacial reaction. One or two chlorine atom can be removed from 2,4-DCP to form 2-chlorophenol, 4-chlorophenol or phenol. As the concentration of 2,4-DCP increased, the relative dechlorination ratio decreased. However, the reduced quantities of 2,4-DCP increased. Temperature can influence dechlorination rate and pathway. Dechlorination is prior to cleavage of the benzene ring at a higher temperature, but at a lower temperature, adsorption may be the main pathway, and cleavage of the benzene ring may be prior to dechlorination. Supported by the National Natural Science Foundation of China (Grant Nos. 50325824, 50678089) and the Excellent Young Teacher Program of MOE.     

Destruction of 2,4-Dichlorophenol in Water Solution Using a Combined Process of Sorption and Plasma Exposure to DBD

The results of studies of the decomposition of 2,4-dichlorophenol (2,4-DCP) in its aqueous solution under the action of atmospheric pressure DBD in an oxygen flow are presented. A new reactor design was used in which the discharge zone was filled with a sorbent (diatomite). It was found that the kinetics of decomposition obeys a first-order kinetic equation for the concentration of 2,4-DCP. The presence of an adsorbent significantly improves the parameters of the decomposition process. Decomposition rates, rate constants and energy efficiency are doubled. So, at a specific discharge power of 1.8 W/cm³ in the presence of a sorbent, the rate constant was ~1 s^?1, and without it, ~0.5 s^?1. The energy efficiency was 0.031 and 0.016 molecules per 100 eV, respectively. The parameters of the treated solution are improved in terms of its potential toxicity. The concentrations of the main decomposition products (aldehydes, carboxylic acids) in the presence of a sorbent are significantly less than without it. This is due to an increase in the rate of conversion of these products into carbon dioxide molecules. It was also shown that the decomposition of one 2,4-DCP molecule leads to the formation of two chloride ions in solution, and the ozone formed in the discharge does not significantly affect the destruction process.

     

Molecular structure, harmonic and anharmonic frequency calculations of 2,4-dichloropyrimidine and 4,6-dichloropyrimidine by HF and density functional methods

Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra of 2,4-DCP and 4,6-DCP was reported on the basis of the calculated potential energy distribution (PED). A comparison of theoretically calculated vibrational frequencies at B3LYP/6-311++G(d,p) with FT-IR and FT-Raman experimental data shows good agreement between them. Natural atomic charges of 2,4-DCP and 4,6-DCP were calculated and compared with pyrimidine molecule.     

Structure of chlorinated poly(vinyl chloride). XII. Configuration and reactivity of low-molecular-weight models of poly(vinyl chloride) in the course of chlorination

The chlorination of poly(vinyl chloride) (PVC) was investigated by means of low-molecular-weight models of PVC—a dimer and trimer of PVC, viz., 2,4-dichloropentane (2,4-DCP) and 2,4,6-trichloroheptane (2,4,67-TCH). Chlorinations of stereoisomeric mixtures of 2,4-DCP and 2,4,6-TCH have revealed that the d,1 form of 2,4-DCP (syndio-2,4-DCP) is more reactive in the chlorination than the meso form of 2,4-DCP (iso-2,4-DCP), while in the case of the chlorination of 2,4,6-TCH the reactivity of stereoisomers decreases in the order iso-> hetero->syndio-2,4,6-TCH; consequently, analogous structures of stereoisomers of 2,4-DCP and 2,4,6-TCH react in a reverse order and not in the same one. The qualitative order of reactivities of stereoisomers may be correlated formally with the magnitude of their dipole moments. The reactivity of stereoisomers of 2,4-DCP and 2,4,6-TCH decreases with increasing dipole moment.     

Molecularly imprinted solid-phase extraction and flow-injection chemiluminescence for trace analysis of 2,4-dichlorophenol in water samples

Highly sensitive flow-injection chemiluminescence (CL) combined with molecularly imprinted solid-phase extraction (MISPE) has been used for determination of 2,4-dichlorophenol (2,4-DCP) in water samples. The molecularly imprinted polymer (MIP) for 2,4-DCP was prepared by non-covalent molecular imprinting methods, using 4-vinylpyridine (4-VP) and ethylene glycol dimethacrylate (EGDMA) as the monomer and cross-linker, respectively. 2,4-DCP could be selectively adsorbed by the MIP and the adsorbed 2,4-DCP was determined by its enhancing effect on the weak chemiluminescence reaction between potassium permanganate and luminol. The enhanced CL intensity was linear in the range from 1 × 10⁻⁷ to 2 × 10⁻⁵g mL⁻¹. The LOD (S/N = 3) was 1.8 × 10⁻⁸g mL⁻¹, and the relative standard deviation (RSD) was 3.0% (n = 11) for 1.4 × 10⁻⁶g mL⁻¹. The proposed method had been successfully applied to the determination of 2,4-DCP in river water. Figure Effect of 4-VP content on the ultraviolet spectrum of 2,4-DCP in chloroform     

Removal of 2,4-dichlorophenol from aqueous solution by static-air-activated carbon fibers

Static-air-activated carbon fibers (ACFs) with lotus-root-like axially porous structure were used to adsorb 2,4-dichlorophenol (2,4-DCP) from aqueous solution. The adsorption isotherm was evaluated in the pH range 3.0-11.0. Results indicated that both Langmuir and Redlich-Peterson adsorption isotherms were appropriate for describing the adsorption characteristics of 2,4-DCP at various pH values and that lower pH values were favorable for adsorption. The adsorption of 2,4-DCP was controlled by the synergetic effects of pi-pi interaction and electrostatic attraction, and the former was dominant. Breakthrough curve results showed that the 2,4-DCP removal efficiency increased with an increase in the empty-bed contact time (EBCT). An EBCT of 0.660 min was sufficient for the adsorption of 2,4-DCP onto ACF, indicating a high adsorption rate. Desorption experiment results revealed that the ACF saturated with 2,4-DCP could be regenerated effectively by a 0.001 M NaOH solution.     

TiO2的低温制备及其对有毒有机污染物的降解

溶胶水热法制备了TiO₂粉末,用X射线衍射仪(XRD)、比表面积及孔径分析仪(BET)和透射电镜(TEM)对TiO₂进行了初步表征,结果显示:纳米TiO₂主要为锐钛矿相(含板钛矿相(121)),比表面积为106.2 m²/g.在紫外光(λ≤387 nm)照射条件下,以有机染料罗丹明B(Rhodamine B,RhB)和无色小分子2,4-二氯苯酚(2,4-dichlorophenol,2,4-DCP)的紫外光(λ≤387 nm)光催化降解试验为探针反应,低温(50℃)下制备的TiO₂粉末具有较高光催化活性,对RhB和2,4-DCP有较好的降解效果.通过分析紫外-可见光谱(UV-Vis)、红外光谱(FTIR)和总有机碳(TOC)测定,发现TiO₂/UV体系能使RhB和2,4-DCP发生有效的降解,反应5 h后RhB和7 h后2,4-DCP的矿化率分别达到81.2%和86.8%.同时,采用辣根过氧化物酶(POD)、N,N-二乙基对苯二胺(DPD)分光光度法和苯甲酸荧光光度法分别测定了在降解过程中H₂O₂和羟基自由基(.OH)的变化,表明TiO₂光催化机理涉及到.OH历程.     

Synthesis of cubic Ag@AgCl and Ag@AgBr plasmonic photocatalysts and comparison of their photocatalytic activity for degradation of methyl orange and 2,4-dichlorophenol

Uniform cubic Ag@AgCl and Ag@AgBr plasmonic photocatalysts with side length of 0.7 µm were synthesized by a facile green route, in which a controllable double-jet precipitation technique was employed to fabricate homogeneous cubic AgCl and AgBr grains while a photoreduction process was used to produce Ag nanoparticles (NPs) on the surface of AgCl and AgBr grains. The synthesized samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy (DRS). The photocatalytic activities of Ag@AgCl and Ag@AgBr were compared using degradation of methyl orange (MO) dye and 2,4-dichlorophenol (2,4-DCP) under visible-light irradiation. Ag@AgBr showed higher photocatalytic activity for MO degradation but weaker activity for 2,4-DCP decomposition. Possible degradation mechanisms are proposed to interpret these contrary paradoxical experimental results.     

担载CuO基催化剂上2,4-二氯酚的有效氧化降解

研究了2,4-二氯酚的催化氧化降解.结果表明,CuO/y-Al2O3催化剂表现出较高的活性,且碱土金属氧化物助剂的添加可进一步显著提高2,4-二氯酚氯离子的释放率,其中以SrO的促进作用最强,该催化剂循环使用3次,2,4-二氯酚转化率及氯离子的释放率均维持100％.X射线衍射和NH3程序升温脱附结果表明,催化剂上CuO...     

聚邻氨基苯硫酚/纳米金复合膜分子印迹传感器测定2, 4-二氯苯酚

在2,4-二氯苯酚(2,4-DCP)存在下, 在金电极表面自组装邻氨基苯硫酚(oATP)并电聚合oATP/金纳米粒子, 制得2,4-DCP印迹复合膜电化学传感器.采用循环伏安法和交流阻抗技术对传感器制备过程进行了表征, 以K₃Fe(CN)₆为探针, 间接对2,4-DCP进行定量分析.结果表明, 2,4-DCP在5.0×10^-8~1.2×10^-4 mol/L 浓度范围内与K₃Fe(CN)₆示差脉冲伏安曲线的峰电流呈线性关系(R²=0.9964), 检出限为1.5×10^-8 mol/L(S/N=3).该印迹传感器可在几种氯代酚干扰下选择性测定2,4-DCP.利用该传感器对环境水样进行加标回收检测, 回收率为95.2%~109.3%.     

Electrochemical sensor based on chlorohemin modified molecularly imprinted microgel for determination of 2,4-dichlorophenol

A newly designed molecularly imprinted polymer (MIP) was synthesized and successfully utilized as a recognition element of an amperometric sensor for 2,4-dichlorophenol (2,4-DCP) detection. The MIP with a well-defined structure could imitate the dehalogenative function of the natural enzyme chloroperoxidase for 2,4-DCP. Imprinted sensor was fabricated in situ on a glassy carbon electrode surface by drop-coating the 2,4-DCP imprinted microgel suspension and chitosan/Nafion mixture. Under optimized conditions, the sensor showed a linear response in the range of 5.0–100 μmol L⁻¹ with a detection limit of 1.6 μmol L⁻¹. Additionally, the imprinted sensor demonstrated higher affinity to target 2,4-DCP over competitive chlorophenolic compounds than non-imprinted sensor. It also exhibited good stability and acceptable repeatability. The proposed sensor could be used for the determination of 2,4-DCP in water samples with the recoveries of 96.2–111.8%, showing a promising potential in practical application.     

纳米级Pd/Fe双金属体系对水中2,4-二氯苯酚脱氯的催化作用

 利用化学沉淀法制备了纳米级Fe和纳米级Pd/Fe双金属催化剂,研究了它们对2,4-二氯苯酚(2,4-DCP)还原脱氯的催化性能. 结果表明,纳米级颗粒具有较高的比表面积和表面反应活性,其BET比表面积可达12.4 m2/g,当Pd/Fe用量为6 g/L时,2,4-DCP脱氯率达到90%以上. 脱氯效率与pH值、温度、钯含量和Pd/Fe投加量等因素有关. 2,4-DCP在脱氯过程中先生成2-氯苯酚和4-氯苯酚,最终生成苯酚,而少量的2,4-DCP可直接降解成苯酚.     

2,4-Dichlorophenol sorption on cyclodextrin polymers

The sorption of β-cyclodextrin polymer (β-CDP) and γ-cyclodextrin polymer (γ-CDP) toward 2,4-dichlorophenol (2,4-DCP) in aqueous solutions was investigated. The influence of sorption conditions including initial 2,4-DCP concentration, contact time and pH on sorption capability were discussed. Their sorption behaviors for 2,4-DCP were conducted and it was found the sorption kinetics followed the Ho and McKay equation and the film diffusion was the rate-determined step. The sorption isotherm can be correlated to Freundlich model and the sorption capacity on β-CDP was much larger than that on γ-CDP. The maximum sorption capacity of 2,4-DCP for β-CDP was measured to be 0.16 mmol/g with the initial concentration at 0.67 mmol/L at 288 K. The CDPs were easily recovered by ethanol as washing solvent and they could be used as a kind of recyclable sorbents.     

Graphitic solid core carbon nanorods grown on silica sands using electron cyclotron resonance chemical vapor deposition as a highly efficient and green sorbent for removal of phenol derivatives from water sources

In this study, graphitic solid core carbon nanorods (GSCNRs) were, for the first time, anchored to the surface of silica sands through the electron cyclotron resonance chemical vapor deposition method to provide coated silica sands as a new, low-cost, green, and efficient adsorbent for the removal of organic pollutants such as phenol and 2,4-dichlorophenol (2,4-DCP) from aqueous mediums. The characteristics of GSCNRs/SiO₂ were confirmed through Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy techniques. After the optimization of several parameters, the removal efficiency of phenol and 2,4-DCP using 1 g of adsorbent amount, the initial concentration of pollutants (10 mg/L phenol and 15 mg/L 2,4-DCP), a contact time of 10 min (phenol) and 20 min (2,4-DCP), and pH = 7 were 69 and 89%, respectively. The adsorption isotherm models of Langmuir and Freundlich, as well as pseudo-first-order and pseudo-second-order kinetic models, were examined under optimal conditions. Eventually, GSCNRs/SiO₂ was regenerated five times for the removal of phenol and 2,4-DCP. The removal efficiency of the tested contaminants from inlet raw water of a water treatment plant using the proposed adsorbent was investigated.     

Degradation of organic pollutants by visible light synergistic electro-Fenton oxidation process

Visible light irradiation combined with homogeneous iron and/or hydrogen peroxide to degrade organic dye rhodamine B (RhB) and small molecular compound 2,4-dichlorophenol (2,4-DCP) in a home-made bottle reactor was assessed. The concen-tration of oxidize species, Fe3+ and Fe2+ were determined during the degradation process. The results demonstrated that visible light irradiation combined with electro-Fenton improved the degradation efficiency. Moreover, both RhB and 2,4-DCP were mineralized during visible light synergistic electro-Fenton oxidation process. 95.0% TOC (total organic carbon) removal rate of RhB occurred after 90 min and 96.7% of COD (chemical oxygen demand) removal rate after 65 min of irradiation. 91.3% TOC removal rate of 2,4-DCP occurred after 16 h of irradiation and 99.9% COD removal rate occurred after 12 h of illumination. The degradation and oxidation process was dominated by the hydroxyl radical ( · OH) generated in the system. Both the impressed electricity and dye sensitization by visible light facilitated the conversion between Fe3+ and Fe 2+ , thus, improving Fenton reaction efficiency.     

Enhancement of photoelectric catalytic activity of TiO2 film via Polyaniline hybridization

A Polyaniline (PANI)/TiO₂ film coated on titanium foil was successfully prepared using the sol-gel method followed by a facile chemisorption. Compared with pristine TiO₂, the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation rates of 2,4-dichlorophenol (2,4-DCP) with the PANI/TiO₂ film were enhanced by 22.2% and 57.5%, respectively. 2,4-DCP can be mineralized more effectively in the presence of PANI/TiO₂ film. The best PEC degradation efficiency of 2,4-DCP with the PANI/TiO₂ film was acquired at an external potential of 1.5 V with a layer of 1 nm thick PANI. The PANI/TiO₂ film was characterized by Raman spectra, Fourier transform infrared spectra (FT-IR), Auger electron spectroscopy (AES), and electrochemical analysis. These results indicated that there was a chemical interaction on the interface of PANI and TiO₂. This interaction may be of significance to promote the migration efficiency of carriers and induce a synergetic effect to enhance the PC and PEC activities.