Degradation Rate Of 4-chlorophenol Research Articles

Synergistic Elimination of Chlorophenols Using a Single-Atom Nickel with Single-Walled Carbon Nanotubes: The Roles of Adsorption, Hydrodechlorination, and the Electro-Fenton Process.

Electrocatalytic degradation enables the efficient treatment of chlorinated pollutants (COPs); however, its application has been significantly hindered by the large amounts of unsafe intermediate products. In this study, we present a single-atom nickel with single-walled carbon nanotubes (SWCNTs) as an electrochemical reactor for the complete elimination of chlorophenols. Distinct products and reductive mechanisms were observed for Ni-N-C compared to Cu-N-C. Ni-N-C incorporation has a novel degradation pathway for efficient chlorophenol degradation involving hydrodechlorination and the electro-Fenton process. Most importantly, the weak adsorption between the chlorophenols and the SWCNTs promoted their dechlorination by the attached active atomic hydrogen (H*) formed on the Ni-N-C. Meanwhile, the SWCNTs improved the reduction of O2 to H2O2, which was subsequently decomposed by Ni-N-C to form hydroxyl radicals (·OH) for phenol oxidation. As a result, the degradation rate of 4-chlorophenol was increased by 5 and 10 times compared with those of the Ni-N-C and SWCNTs alone, respectively. The first-order reaction rate constant was 2.7 h-1, and the metal mass kinetics constant was 1956.5 min-1g-1. Aromatic COPs containing benzene rings could be degraded, but chloroacetic acids could not. This study demonstrates a new design for multifunctional electrochemical degradation that functions via dechlorination and the ·OH activation mechanism.

Potassium permanganate oxidation enhanced by infrared light and its application to natural water

Photocoupled permanganate (PM) is an effective way to enhance the oxidation efficiency of PM, however, the activation of PM by infrared has received little attention. This study aimed to investigate the ability of infrared light to activate PM. When coupled with infrared, the degradation rate of 4-chlorophenol (4-CP) is increased to 3.54 times of PM oxidation alone. The accelerated reaction was due to the formation of vibrationally excited PM by absorbing 3.1 kJ mol-1 infrared energy, which also leads to the primary reactive intermediates Mn(V/IV) in the reaction system. The infrared coupled PM system also showed 1.14–2.34 times promotion effect on other organic pollutants. Furthermore, solar composed of 45% infrared, coupled PM system showed excellent degradation performance, where the degradation of 4-CP in 10 L of tap water and river water was 68 and 23 times faster than in ultrapure water, respectively. The faster-increased degradation rate in natural waters is mainly due to the abundant inorganic ions, which can stabilize the manganese species, and then has a positive effect on 4-CP degradation. In summary, this work develops a energy-efficient photoactivated PM technology that utilizes infrared and provides new insights into the design of novel sunlight-powered oxidation processes for water treatment.

Peroxymonosulfate activation in ultrasound-driven molybdenum disulfide piezocatalysis: The effect of sulfur vacancy

Although peroxymonosulfate (PMS) can be efficiently activated by ultrasound-driven piezocatalyst, there are still uncertainties on the mechanisms. Herein, molybdenum disulfide piezocatalysts with different sulfur vacancy (VS) types were prepared by hydrothermal (MoS2–H) and solvothermal methods (MoS2–S). The configuration of Vs in MoS2 was characterized by X-ray photoemission spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR), and O2 diffuse reflectance infrared Fourier transform spectroscopy (O2-DRIFTS). Surface in-plane VS and edge VS dominated on MoS2–H and MoS2–S. MoS2–S exhibits higher PMS activation performance with 85.0% degradation rate of 4-chlorophenol within 2 h. Although in-plane VS feature a stronger PMS adsorption energy compared with edge VS (−1.64 vs. −0.94 eV), PMS activation is not favorable at the in-plane VS sites of MoS2 (MoS2–H). In piezo-polarized MoS2, the separated charge carriers accumulate at the edges, where edge VS (MoS2–S), as the active site, strengthens the coupling between electrons and PMS. As a result, the O–O bond length in PMS is increased from 1.467 to 1.470 Å, enabling the facile activation of PMS with the generation of more abundant ·OH and ·SO4− radicals. This work clearly explains the PMS activation mechanism from both experimental and theoretical aspects and provides directions to tailor the structure and atom vacancies of piezocatalysts.

Microwave synthesis of metal-doped ZnS photocatalysts and applications on degrading 4-chlorophenol using heterogeneous photocatalytic ozonation process

Photocatalysts can produce active species in the heterogeneous photocatalytic ozonation (HPO) process, which can efficiently degrade and mineralize organic pollutants. In this study, pristine ZnS and metal-doped (Cu, Ag, Bi, Ga, In) ZnS were synthesized by microwave method. The degradation rate of 4-chlorophenol (4-CP) in HPO process is ranked as Cu/ZnS > Bi/ZnS > Ag/ZnS > In/ZnS > Ga/ZnS > ZnS, which is attributed to the following reasons: (1) the schottky junction formed between ZnS and doped metal can effectively capture electrons as an electron trap, thus inhibiting the recombination of electron-hole pairs; (2) narrow bandgap of Cu/ZnS can enhance electron transport; (3) the valence bands of Ag/ZnS, Bi/ZnS, Ga/ZnS and In/ZnS were more positive than that of pristine ZnS to enhance the oxidization ability of holes. The experimental results showed that the optimal water-intake ozone dose optimal influent ozone dosage was 32 mg/l·min−1 under the optimal initial solution pH of 7. In addition, the possible mechanism of HPO process was proposed and clarified. We believe that metal-doped ZnS has a promising potential to be the photocatalyst for the degradation of organic pollutants.

Electrocatalytic degradation kinetic of 4-chlorophenol by the Pd/C gas-diffusion electrode system

A Pd/C gas-diffusion cathode which generated H2O2 through a two-electron reduction process of fed oxygen molecule was used to degrade 4-chlorophenol in an undivided electrolysis device. The kinetics of 4-chlorophenol degradation has been investigated by the electrochemical oxidation processes. By inspecting the relationship between the rate constants (k) and influencing factors, using first-order kinetics to describe the electrochemical oxidation process of 4-chlorophenol, a kinetic model of 4-chlorophenol degradation process was proposed to calculate the 4-chlorophenol effluent concentration: C = C0 exp( -3:76 × 10(-6) C(-0.5)0 J(2) M(-0.7) Q(0.17) Dt). It was found that the electrocatalytic degradation rate of 4-chlorophenol was affected by current density, electrode distance, air-feeding rate, electrolyte concentration and initial 4-chlorophenol concentration. The kinetics obtained from the experiments under corresponding electrochemical conditions could provide an accurate estimation of 4-chlorophenol effluent concentration and lead to better design of the electrochemical reactor.

4-Chlorophenol degradation with modified domestic microwave and hydrogen peroxide in aqueous solution

Aims: This study was conducted for degradation of 4-chlorophenol by microwave (MW) radiations alone and in combination with hydrogen peroxide from aqueous solution. Materials and Methods: A modified domestic microwave oven was used alone and in combination with hydrogen peroxide for removing 4-chlorophenol. Furthermore, the influences of pH value, irradiation time, the power of MW radiations, and the initial concentration of 4-chlorophenol were studied. Results: It was shown that 4-chlorophenol removal efficiency extremely depend on the concentration of hydrogen peroxide, pH value, MW irradiation power and initial 4-chlorophenol concentration. The optimum conditions obtained for the best degradation rate were pH = 10.5, H 2 O 2 concentration of about 0.1 mol/l, and MW irradiation power of about 600 W. Other result shows that the best degradation rate of 4-chlorophenol was obtained when initial 4-chlorophenol concentration was 50 mg/l. Also the amount of the specific energy consumption in this method was 17460 kwh/kg of the removed organic compound. Conclusion: This result shows that MW irradiation in the presence of hydrogen peroxide can greatly enhance the degradation of 4-chlorophenol. However, the high consumption of energy for this method must be taken into consideration.

Synthesis and characterization of La 2O 3/TiO 2− xF x and the visible light photocatalytic oxidation of 4-chlorophenol

In this work, we investigated the synergetic effect of La and F on the visible light photocatalytic activity of TiO 2 catalysts. La 2O 3/TiO 2− x F x photocatalysts were prepared by a simple sol-gel process using tetrabutyl titanate (TBT), La(NO 3) 3 and NH 4F as precursors. XPS results revealed that La 2O 3 accumulated on the surface of TiO 2, which enhanced the surface area of TiO 2 and inhibited the recombination of electron–hole pairs. It also showed that two kinds of fluorine species were formed and these increased the acid active sites and enhanced the oxidation potential of the photogenerated holes in the valance band. UV–vis diffuse reflection spectra of La 2O 3/TiO 2− x F x showed that intraband gap states were present and these are probably responsible for its absorption of visible light while the intrinsic absorption band was shifted slightly to a longer wavelength. At molar ratios of La and F to Ti of 1.5:100 and 5:100 and after calcination at 500 °C, the degradation rate of 4-chlorophenol (4-CP) over the sample was about 1.2–3.0 times higher than that of the other doped samples and undoped TiO 2. The total organic carbon (TOC) removal rates of 4-CP showed that 4-CP was mineralized efficiently in the presence of the sample under visible light illumination.

Characterization and Photocatalytic Properties of Transition Metal Doped TiO<sub>2</sub> and Nanocomposite TiO<sub>2</sub> Powders Synthesized by Mechanical Alloying

Transition metal doped TiO2 (Ni, Fe, Cu) and nanocomposite TiO2 powders with rutile phase were synthesized by mechanical alloying and heat treatment, and were characterized by XRD, TEM, UV-DRS, and PL (Photoluminescence). Photocatalytic activity was also investigated with the degradation rate of 4-chlorophenol and measured by total organic carbon analyzer. TEMEDP and XRD patterns showed that the transition metal doped powders (only alloyed powder) were in the form of rutile phase with the particle size of 20-30 nm. The average grain size of transition metal doped powders was in the range of less than 10 nm. However, after heat treatment, the alloyed powder formed composite of the titanate and rutile phase. The UV-DRS and PL investigation showed that Ni doped 8 wt% nanocomposite TiO2 had the higher wavelength range (600-660 nm) (2.0-1.9 eV) than that of the commercial P-25 powder(380-400 nm) by Degussa Co. indicating that the Ni 8 wt% doped nanocomposite TiO2 shifted the absorption into the visible light region and thus, enhanced the photocatalytic activity. Further, these results agreed well with TOC investigation. Formation of titanate in transition metal doped TiO2 due to heat treatment was found to control the grain growth of nano-sized TiO2 and to enhance its thermal stability at high temperature.

Identification of electrical degradation products of 4-chlorophenol in water.

The electrical decomposition of 4-chlorophenol in water was examined with iridium dioxide doped on atitanium electrode. A number of electrical degradation products of 4-chlorophenol, such as hydroquinone and chlorohydroquinone via the addition of hydroxyl radicals, and dichlorophenol through addition of chlorine radical, were observed as major products. Moreover, hydroxylated chlorobiphenylethers, hydroxylated dibenzo-p-dioxin/furans and hydroxylated chlorobiphenyls formed by a dimerization process during the electrolysis process of 4-chlorophenol were also observed. On the other hand, benzoquinone, muconic acid and aldehyde derivatives that were further oxidative products of hydroquinone formed by photocatalysis process, were not observed. The electrical decomposition products of 4-chlorophenol were trimethylsilylated and then identified by gas chromatography-mass spectrometry. The degradation rate of 4-chlorophenol in water by iridium oxide electrode was measured against the electrical process duration. After iridium electrical process for 120 min, about 50% of 4-chlorophenol was converted into a number of products through oxidation processes. On the basis of the identified products, the degradation pathways of 4-chlorophenol under electrolysis process were proposed.

Comparative photocatalytic degradation using natural and artificial UV-light of 4-chlorophenol as a representative compound in refinery wastewater

The comparison of the degradation of 4-chlorophenol, using sunlight and a UV-lamp, was carried out using two different catalysts, Degussa P25 and Hombikat UV 100. All experiments were performed after first optimizing the catalyst concentrations and pH. The optimal concentrations for Degussa P25 and Hombikat UV 100 occurred at 7 and 10 g/l, respectively. The optimal initial pH was found to be 5 for both catalysts. The degradation rate of 4-chlorophenol is 6.4 times and 1.6 times higher when using sunlight compared to the artificial UV-lamp for Degussa P25 and Hombikat UV 100, respectively. The degradation rate of 4-chlorophenol is six times higher, compared to Hombikat UV 100, at the optimal conditions, when using sunlight and Degussa P25 as the catalyst. The chloride produced during the reaction was measured and found to be highest for Degussa P25 with sunlight as the energy source.

Optimization of a photo-fenton prototype reactor

A prototype reactor for the Photo-Fenton method was applied for highly contaminated wastewaters up to a TOC of 1400 ppm and COD of 12000 mg/L. The influences of different light sources, iron concentrations and two glass sorts on the degradation rate of 4-Chlorophenol have been studied. The degradation rate increased with amount of Fe-catalyst. The use of quartz glass increased degradation rate by 50% with Hg-medium-pressure light sources.