Mechanism Of Phenol Degradation Research Articles

Pathway identification, enzyme activity and kinetic study for the biodegradation of phenol by Nocardia hydrocarbonoxydans NCIM 2386

Nocardia hydrocarbonoxydans NCIM 2386 (Nhy) can grow using phenol as a sole carbon source and has a strong ability to degrade phenol. The paper presents the main metabolism pathways and mechanism of phenol degradation by Nhy. Phenol was found to be degraded via meta cleavage of catechol by the action of enzyme catechol 2,3-dioxygenase. The enzyme was found to be both extracellular and cell bound. The cell bound and extracellular enzymes actively degraded phenol even in the absence of the organism. The rate of phenol degradation by extracellular enzymes as sole enzymatic process (in the absence of cells) was found to be almost similar to that with the whole cells, indicating the prominence of extracellular enzymes. Michaelis–Menten model was found to fit the degradation rate kinetics of total phenol for total phenol concentrations of less than 100 mg L−1 and also the degradation rate kinetics of catechol at catechol concentrations of less than 80 mg L−1 during the exponential growth phase of the organism. Michaelis– Menten model was found to fit the kinetics of catechol formation rate which is also equal to the actual rate of phenol degradation to catechol. Both phenol and catechol were found to be substrate inhibitory.

3D-hierarchically structured MnO2 for catalytic oxidation of phenol solutions by activation of peroxymonosulfate: Structure dependence and mechanism

Hierarchical materials have facilitated fascinating applications in heterogeneous catalysis due to that micro-sized bulk is easily separable and nano-sized sub-blocks can significantly enhance catalytic performance. In this study, corolla-like δ-MnO2 with sub-blocks of nanosheets, and urchin-shaped α-MnO2 with sub-blocks of nanorods were synthesized by a simple hydrothermal route. The hydrothermal temperature significantly influenced the crystal structure, morphology and textural structure of the obtained three-dimensional (3D) MnO2 catalysts. The catalytic activities of three samples prepared at 60, 100 and 110°C (denoted as Mn-60, -100 and -110, respectively) were thoroughly evaluated by activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol solutions. Based on first-order kinetics, the rate constants of Mn-60, -100 and -110 catalysts were determined to be 0.062, 0.132, and 0.075min−1, respectively. The activation energy of Mn-100 in catalytic oxidation of phenol solutions was estimated to be 25.3kJ/mol. The catalytic stability of Mn-100 was also tested and discussed by monitoring Mn leaching. Electron paramagnetic resonance (EPR), quenching tests, total organic carbon (TOC) analysis and identification of intermediates were applied to illustrate the activation processes of PMS and the mechanism of phenol degradation.

Chemically dealloyed MgCuGd metallic glass with enhanced catalytic activity in degradation of phenol

Nanoporous Cu with tunable pore size (20–50 nm) are synthesized through chemical dealloying of the Mg65Cu25Gd10 metallic glass in sulfuric acid solution. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated the formation of mixing structures consisting of amorphous matrix and fcc-Cu ligaments with nanoporous structure in the dealloyed samples. The nanoporous alloy obtained shows superior catalytic activity in degrading phenol-containing wastewater, e.g., the degradation rate increases by 2–4 times as compared to the un-dealloyed Mg-based metallic glass. It was also found that surface wettability plays an important role in degradation, which results in a better catalytic performance in the sample with coarser nanoporous structure although it has relatively less specific surface area as compared to the samples with finer pores. Finally, the mechanism for degradation of phenol is discussed.

Fe-clay-plate as a heterogeneous catalyst in photo-Fenton oxidation of phenol as probe molecule for water treatment

A novel heterogeneous photo-Fenton plate catalyst was prepared by immobilizing iron species on the surface of natural Tunisian clay. The activity of this structured catalyst was assayed in the degradation of phenol under UV irradiation at two different wavelengths (245nm, UVC, and 365nm, UVA, radiation). Phenol removal rate from the aqueous solution always increased in the presence of the Fe-plate catalyst, even under dark-Fenton conditions and for both 254 and 365nm UV radiation, confirming the efficiency of the prepared catalytic system in the Fenton process. HPLC analysis confirmed a phenol degradation mechanism towards an almost complete mineralization of the organic compound. An apparent activation energy of 48.7kJ/mol was calculated from the removal experiments performed at different reaction temperatures in the presence of the Fe-plate catalyst. Catalytic activity remains almost unaltered after five consecutive reaction cycles re-using the same Fe-plate. Catalyst stability was confirmed by means of TEM–EDX analysis, pointing to this novel plate catalyst as a promising option as a Fenton heterogeneous catalyst for the mineralization of organic compounds in wastewaters.

KI/H2O2 assisted synthesis and the changed properties of BiOCl photocatalysts

Abstract BiOCl photocatalysts with changed properties were synthesized successfully at room temperature through the design of synthetic route and the addition of KI or KI/H2O2. The properties of obtained BiOCl samples showed a certain difference in crystallinity, morphology, structure, specific surface area, composition, band gap energy and exterior color. These BiOCl photocatalysts exhibited excellent visible-light-induced photocatalytic activities towards the degradation of phenol in aqueous solution, and also exhibited good photocatalytic activity for the degradation of methylene orange (MO) and rhodamine B (RhB). The formation process of the BiOCl samples and the photocatalytic degradation mechanism of phenol were explored, and the relationship between the structure and performance was established. In addition, the photochemical stability of BiOCl samples was also investigated. The results showed that the as-prepared BiOCl exhibited excellent visible-light-induced photocatalytic activity, and the preparation method was simple and convenient for practical applications.

Effect of Lewis acid centres and H2O2-complexes on the photocatalytic degradation of phenol

A Ti–H2O2–phenol complex, not described until now, has been identified on the surface of Degussa P-25 and the new catalyst ECT-1023. This complex is considered to be responsible for the higher hydroquinone to catechol concentration ratio. It has been also shown that phenolates identified on the surface modify electrodonation that controls the generation of activating positions of the aromatic ring. The different strengths of the Lewis acid centres identified provide phenolates with different electrodonation ability. It has been observed that P-25 has Lewis acid centres with stronger acid character than those of ECT-1023. Thus, the mechanism of phenol degradation is affected by the formation of complexes with H2O2 and the distribution and strength of Lewis acid centres of the studied catalyst.

G-C3N4/TiO2 hybrid photocatalyst with wide absorption wavelength range and effective photogenerated charge separation

Not only for utilizing both visible and UV light but also for enhancing photogenerated charge separation capability, a hybrid photocatalyst composed of graphite-like carbon nitride (g-C3N4, mainly response to visible light) and TiO2 (response to UV light) was fabricated by a hydrolysis approach. The TEM images of g-C3N4/TiO2 samples displayed that TiO2 nanoparticles dispersed well on the surface of g-C3N4 sheet and the average size of TiO2 particles on g-C3N4 sheet was much smaller than that of TiO2 samples without g-C3N4 sheet, meaning the inhibiting TiO2 aggregation function of g-C3N4 sheet. The UV–Vis diffuse reflectance spectra displayed that the optical absorption range of g-C3N4/TiO2 hybrid was from 300 to 450nm, including both UV and visible light. The lower intensity of photoluminescence for g-C3N4/TiO2 than those for pristine g-C3N4 and TiO2, indicated that the recombination of photogenerated charge was inhibited effectively. Profiting from the above mentioned advantages, g-C3N4/TiO2 showed good photocatalysis capability. The pseudo-first-order kinetic constant of phenol degradation on g-C3N4/TiO2 was 2.41 and 3.12 times those on pristine g-C3N4 and TiO2, respectively. We also proposed the scheme for electron–hole separation and transport at the light-driven g-C3N4/TiO2 hybrid photocatalyst interface as well as the phenol degradation mechanism under full spectrum and visible light irradiation.

The degradation mechanism of phenol induced by ozone in wastes system

A distinct understanding for the degradation mechanism of phenol induced by ozone is very essential because the ozonation process, one of the advanced oxidation processes (AOPs), is attractive and popular in wastewater treatment. In the present work, the detailed reactions of ozone and phenol are investigated employing the density functional theory B3LYP method with the 6-311++G (d, p) basis set. The profiles of the potential energy surface are constructed and the possible reaction pathways are indicated. These detailed calculation results suggest two degradation reaction mechanisms. One is phenolic H atom abstraction mechanism, and the other is cyclo-addition and ring-opening mechanism. Considering the effect of solvent water, the calculated energy barriers and reaction enthalpies for the reaction of O3 and phenol in water phase are both lower than those in gas phase, though the degradation mechanisms are not changed. This reveals that these degradation reactions are more favorable in the water solvent. The main reaction products are C(6)H(5)OO· radical, a crucial precursor for forming PCDD/Fs and one ring-opening product, which are in good agreement with the experimental observations.

The effect of particle shape on the activity of nanocrystalline TiO2 photocatalysts in phenol decomposition. Part 3: The importance of surface quality

Bare TiO2 photocatalysts made up of polyhedral nanoparticles have been prepared by flame hydrolysis. In order to obtain deeper understanding of the interplay between the properties determining the photocatalytic performance, surface, aggregation and photocatalytic properties have been analyzed and compared. The aggregation of nanoparticles in aqueous solution of NaCl was determined by dynamic light scattering (DLS) technique. The average hydrodynamic diameters of the aggregates investigated under environmentally relevant conditions do not differ significantly in the pH range of 5–6. Zeta potential measurements were also done during DLS analysis, which revealed remarkably low pHIEP values for our flame made samples comparing to the commercial titanias. Furthermore an explicit correlation between the isoelectric points and the synthesis parameters was revealed. O 1s XP spectra for the high activity samples were also recorded and interpreted. Oxygen consumption experiments were used to test the photocatalytic activity in suspensions. The method was found to be not only rapid and inexpensive but also reasonably reproducible. Normalizing the oxygen consumption rate with the specific surface area of the sample and the concentration of the suspension, a good correlation could have been found with the traditionally determined photocatalytic activity. HPLC measurements were used to study the degradation mechanism of phenol via determining the concentration profile of various dihydroxy intermediates, i.e., hydroquinone (HQ) and pyrocatechol (PC). The quality of the photocatalyst strongly affects the maximum ratio of HQ:PC during the photocatalytic degradation process. For our catalysts higher pyrocatechol concentrations were measured than for Degussa P25. TOC measurements were used to follow the complete mineralization. Using our best photocatalysts (e.g., anatase:rutil ratio of 82:18 and mostly polyhedral particles, with 21m2/g BET surface area), phenol concentration decreased faster than for P25, however, the mineralization rate was somewhat lower. This can be attributed to the lower adsorption capacity of our polyhedral particles against PC and carboxylate containing intermediates formed during the more advanced stages of decomposition. These data elucidate, that hydrophilicity, O2-consumption properties and adsorption/complexation of the target compounds and their degradation products are equally important parameters in determining the photocatalytic performance of catalysts, which otherwise possess similar material properties.

Role of activated carbon features on the photocatalytic degradation of phenol

In this work we have investigated the role of porous carbon material used as a photocatalyst and a catalyst support in the carbon/titania composite in the photodegradation of phenol, and compared the results to those of bare titanium oxide. The immobilization of titania on an activated carbon provoked acceleration of the degradation rate under UV irradiation, which is likely to be attributed to the porosity of the carbon support. The identification of the degradation intermediates detected in the solution showed that the presence of the carbon support affects the nature of phenol degradation mechanism through the formation of different intermediates. Additionally, phenol photodecomposition rate over the carbon support outperformed that attained in the carbon/titania composite, suggesting an important self-photoactivity of the carbon support.

Effective Utilization of Visible Light (Including λ > 600 nm) in Phenol Degradation with p-Silicon Nanowire/TiO2 Core/Shell Heterojunction Array Cathode

For the sake of utilizing the light-harvesting ability of Si in pollution control, the p-silicon nanowire (SiNW)/TiO2 core/shell heterojunction arrays have been synthesized. Based on the surface photovoltage (SPV) measurement, these p-SiNW/TiO2 heterojunction arrays display considerable SPV response to the light with wavelength ranging from 300 to 700 nm. Under the protection of TiO2 shell, the SiNW core could harvest visible light stably in aqueous solution. The resistivity of the starting Si wafer has a distinct influence on the cathodic behaviors of p-SiNW/TiO2 arrays. The higher photocurrent is observed for the sample using the starting Si wafer with moderate resistivity, in contrast with those using high- or low-resistivity starting Si wafer. In the photoelectrocatalytic experiments of phenol degradation under visible light irradiation conditions, the kinetic constant using p-SiNW/TiO2 cathode (0.983 h(-1)) is 17.7 times larger than that (0.0523 h(-1)) of TiO2 film on p type Si wafer (p-Si/TiO2). This result demonstrates that p-SiNW/TiO2 cathode could utilize visible lightto decompose phenol with a considerable efficiency. The mechanism of phenol degradation is considered that the photogenerated electrons from p-SiNW/TiO2 cathode could be scavenged by dissolved oxygen first followed by generation of hydroxyl radicals species via a chain reaction, and finally phenol could be oxidized. By constructing this kind of heterojunctions, many other narrow-band gap semiconductors might be utilized as photocatalysts in pollution control, consequently, the optimal sunlight harvesting would be achieved.

Structure and photocatalytic activity studies of TiO 2-supported over Ce-modified Al-MCM-41

Ce-Al-MCM-41, TiO 2/Al-MCM-41 and TiO 2/Ce-Al-MCM-41 materials with varying contents of Ce (by impregnation) and TiO 2 loaded (by solid-state dispersion) on Al-MCM-41 support are prepared. The Ce modified and TiO 2 loaded composite systems are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS) techniques. The DRS and XPS of low Ce content (0.2–0.5 wt.%) modified Al-MCM-41 samples are showing more characteristic of Ce 3+ species wherein cerium in interaction with Al-MCM-41 and that of high Ce (0.8, 3.0 wt.%) content modified samples are showing the characteristic of both Ce 4+and Ce 3+species. A series of Ce-modified Al-MCM-41 and TiO 2 loaded composite catalysts are evaluated for photocatalytic degradation of phenol under UV irradiation. Low Ce content in Ce 3+ state on Al-MCM-41 is showing good photoactivity in comparison with high Ce content samples and pure ceria. The composite TiO 2/Ce-Al-MCM-41 is showing enhanced degradation activity due decreased rate of electron–hole recombination on TiO 2 surface by the redox properties of cerium. The photocatalyst TiO 2/Ce-Al-MCM-41 with an optimum of 10 wt.% TiO 2 and 0.3 wt.% Ce is showing maximum phenol degradation activity. The possible mechanism of phenol degradation on the composite photocatalyst is proposed.

Electrochemical Heterogeneous Catalytic Degradation of Wastewater Containing Phenol

An electrochemical-heterogeneous catalytic process was applied to remove phenol from wastewater. Three key factors-applied potential, supporting electrolyte concentration, and pH-were tested for their effects on the phenol removal. The optimal condition was determined as an applied potential of 25 V, Na(2)SO(4) concentration of 500 mg L(-1), and a pH of 2.5. Under the optimal condition, the phenol and chemical oxygen demand (COD) removals were 83.7% and 42.9%, respectively. The apparent kinetics of phenol removal could be expressed as a pseudo first-order reaction. In addition, a possible mechanism of phenol degradation was proposed based on the intermediate products.

A novel thermal degradation mechanism of phenol–formaldehyde type resins

The thermal degradation of phenol–formaldehyde resins (PFR) was studied using thermogravimetry analysis (TG) technique. The structural changes of thermal degradation of synthetical and commercial PFR were investigated by Fourier-transform infrared rays (FTIR) and solid-state 13C nuclear magnetic resonance ( 13C NMR) spectroscopy. The experimental results show that the degradation of PFR can be divided into three stages. Additional cross-links are formed and small exposed groups of the cured resin are removed in the first stage. In the second stage, methylene bridges decompose into methyl groups then both phenol and cresol homolog appear. The degradation of phenol group occurs in the third stage. According to these results, a novel degradation mechanism of phenol–formaldehyde type resins is proposed: the mainly degradation process of PFR is the decomposition reaction of methylene bridges in this mechanism instead of auto-oxidation of the methylene bridges in the prevenient mechanism.

Laser-enhanced photocatalytic degradation of organic pollutants from water using ZnO semiconductor catalyst

Wastewater contaminated with organic pollutants creates serious environmental problems. Laser induced photocatalysis has been investigated for removal of organic pollutant like phenol from water. The important mechanism for degradation of phenol by UV laser irradiation is redox reactions triggered by semiconductor catalyst in presence of water. In this study the potential of a ZnO semiconductor catalyst has been explored as an effective catalyst for the photodegradation of phenol using a Nd:YAG laser-emitting at 355 nm in UV-radiation in a batch reactor. The influences of different parameters such as catalyst concentration, UV-radiation intensity, and pH on the extent of photo degradation have been investigated. Overall degradation of phenol achieved was 70% after 60 minutes of laser irradiation of 100 ppm phenol solution in water. The reaction rate constant fit a first-order reaction model for phenol degradation and was estimated as 0.0088 min− 1. This study proved that laser induced photocatalytic removal of phenol is highly efficient as compared with the broadband spectral sources such as lamps being applied in majority of setups worldwide.

Microwave-assisted rapid fabrication of Co 3O 4 nanorods and application to the degradation of phenol

A novel microwave-assisted hydrothermal route for preparation of Co 3O 4 nanorods had been developed. The process contained two steps: first, nanorods of cobalt hydroxide carbonate were obtained from a mixed solution of 50 ml of 0.6 M Co(NO 3) 2·6H 2O and 2.4 g of urea under 500 W microwave irradiated for 3 min. Then, the cobalt hydroxide carbonate nanorods were calcined at 400 °C to fabricate pure cobaltic oxide (Co 3O 4) nanorods. Both nanorods were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), infrared (IR) and temperature-programmed reduction (TPR). The catalytic activity towards the degradation of phenol over Co 3O 4 nanorods was further studied under continuous bubbling of air through the liquid phase. The results showed that phenol was degraded into harmless products (CO 2 and malonic acid). The mechanism of phenol degradation was also discussed.

The characteristics and mechanisms of phenol biodegradation by Fusarium sp.

Fusarium sp. HJ01 can grow using phenol as only carbon resource and has strong ability of phenol degradation. The effect of pH, temperature and sucrose addition on biodegradative capacity of Fusarium sp. HJ01 was examined. The main metabolism pathways and mechanism of phenol degradation by HJ01 strain is described. This strain exhibited both cathecol 1,2-dioxygenase (C12) and cathecol 2,3-dioxygenase (C23) in free cell extracts obtained from cells grown exclusively on phenol or with sucrose added, suggesting that the intermediate cathecol can be oxidized in the catabolic pathway of ortho and meta fission. Mineral salts added in culture have an inhibition on both C12 and C23. These two enzymes can act and retain its catalytic ability over wide ranges of temperature and pH. C12 activity was optimal at pH 6.8 and 40 °C, with significant activity observed in the range from pH 3 to pH 8.8, and in the temperature range from 30 to 50 °C. In comparison with C12, the activity of C23 was slightly more sensitive to pH, C23 had a higher activity in alkalescence condition from pH 7.4 to pH 10.6 and was more stable at higher temperatures from 30 to 75 °C.

Plasmachemical oxidation processes in a hybrid gas–liquid electrical discharge reactor

Oxidation processes induced in water by pulsed electrical discharges generated simultaneously in the gas phase in close proximity to the water surface and directly in the liquid were investigated in a hybrid series gas–liquid electrical discharge reactor. The mechanism of phenol degradation was studied through its dependence on the gas phase and liquid phase compositions using pure argon and oxygen atmospheres above the liquid and different initial pH values in the aqueous solution. Phenol degradation was significantly enhanced in the hybrid-series reactor compared with the phenol removal by the single-liquid phase discharge reactor. Under an argon atmosphere the mechanism of phenol degradation was mainly caused by the electrophilic attack of OH· radicals produced by the liquid phase discharge directly in water and OH· radicals produced by the gas phase discharge at the gas–liquid interface. Under an oxygen atmosphere the formation of gaseous ozone dominated over the formation of OH· radicals, and the contribution of the gas phase discharge in this case was determined mainly by the dissolution of gaseous ozone into the water and its subsequent interaction with phenol. At high pH phenol was degraded, in addition to the direct attack by ozone, also through indirect reactions of OH· radicals formed via a peroxone process by the decomposition of dissolved ozone by hydrogen peroxide produced by the liquid phase discharge. Such a mechanism was proved by the detection of cis,cis-muconic acid and pH-dependent degradation of phenol, which resulted in significantly higher removal of phenol from alkaline solution observed under oxygen atmosphere than in argon.

A Comparative Study on Electrochemical Oxidation of Phenol in Two Types of Cells

Electrochemical oxidation of phenol was studied using Ti/IrO2/RuO2 anode and a carbon/polytetrafluoroethylene (C/PTFE) O2-fed cathode which generated hydrogen peroxide (H2O2) by the reduction of oxygen in the undivided cell and the divided cell with a cotton diaphragm. For degradation mechanism of phenol on the cathode and anode, two kinds of cells are similar. However, the basic condition of the cathodic compartment in the divided cell was prone to H2O2 changed to and HO 2 − and HO·. So, the mineralization of phenol in the divided cell was better than that in the undivided cell.

Synergetic effects of anodic–cathodic electrocatalysis for phenol degradation in the presence of iron(II)

A novel electrocatalysis method for phenol degradation was described using a beta-PbO2 anode modified with fluorine resin and a Ni-Cr-Ti alloy cathode. In case of air sparging at the cathodic zone, the techniques of anodic-cathodic electrocatalysis (ACEC) and ferrous ion catalyzed anodic-cathodic electrocatalysis (FACEC) in the presence of iron(II) were developed. Both of ACEC and FACEC were more effective than anodic electrocatalysis (AEC). The percentage of phenol eliminated by FACEC could increase by nearly 30% compared with that of AEC, and the current efficiency could reach to 70%. Important operating factors such as ferrous ion concentration, air-sparging rate and applied current were investigated and it was found that such beneficial effects could be achieved at a suitable current and ratio of the concentration of ferrous ion to the air sparged. The mechanism of phenol degradation is proposed to be the generation of hydroxyl radicals concerned with the two electrodes. Results also indicated that the process provided an efficient way to regenerate ferrous ion compared with the conventional Fenton's system.