Degradation Of Phenol In Water Research Articles

Efficient degradation of phenol in water by ball-milling modulated nitrogen-doped structured biochar

Presently, most kinds of biochar rely on the addition of transition metals to improve their electron transport capacity, thereby boosting the activation of oxidants. However, challenges such as the precipitation of transition metals and the chemical inertness of biochar are commonly encountered. Biochar with nitrogen-containing functional groups has emerged as a promising solution as oxidant activators. The nitrogen doping of biochar through ball milling is a straightforward, cost-effective, and efficient preparation method. To optimize the activation properties, a multi-step process involving roasting, ball milling, and tempering was employed to produce biochar. Sesame dregs was chosen as the precursor for this biochar. By optimizing the roasting temperature to 900 °C and using urea as the nitrogen source, biochar derived from sesame residue was successfully prepared. This biochar featured pyridine nitrogen as the primary functional group, exhibiting improved crystallinity and aromaticity. The activation of sodium persulfate (3.0 mM) with biochar eliminated phenol from wastewater with an initial concentration of 50 mg/L in just 15 minutes, achieving a remarkable mineralization rate of 96.77%. Even after undergoing six cycles of repeated use, the system consistently removed 97.73% of phenol within the same timeframe, maintaining a high mineralization rate of 86.77%. Notably, it was found that N-CN, N-6, and N-q were instrumental in stimulating reactive oxygen species (ROS), while ·OH, SO4·-, and 1O2 served as the primary ROS responsible for degrading phenol. The research also revealed a linear relationship between active oxygen sites and oxidized substances, offering insights into the mechanism of phenol degradation.

Biochar enhances microbial degradation of phenol in water: Response surface optimization

The utilization of biochar-immobilized microorganisms is an effective method for eliminating phenol from water. However, the main challenge to the practical implementation of this method is the high susceptibility of bacteria to environmental factors. In this study, biochar was used to reduce microbial susceptibility to high concentrations of phenol. Demineralized biochar obtained at high temperatures (600/800/1000 °C) was used to immobilize phenol-degrading bacteria (PDB) and enhance phenol removal. Biodegradation was inhibited by high concentrations of phenol (>1300 mg/L). In contrast, when microorganisms were combined with biochar, up to 82.4% phenol removal occurred, surpassing the efficacy of phenol degradation by a single microorganism (42%). Characterization techniques such as SEM, XRD, and XPS were used to analyze the properties and immobilization effect of biochar. The addition of biochar altered the dominant species of PDB to include Serratia, Ralstonia and Enterobacter. Response surface analysis indicated that both biochar pyrolysis temperature and experimental temperature significantly influenced the phenol removal rate. Thus, this paper provides methodological guidance for the application of biochar-immobilized microorganisms for phenol wastewater treatment.

Adsorption and catalytic degradation of phenol in water by a Mn, N co-doped biochar via a non-radical oxidation process

A modified biochar material (Mn/C-KOH) was synthesized from chitosan using KOH and MnCl2 as the activators via a one-pot pyrolysis process. The characterization suggested that the two activators promoted its textural properties, led to a surface area of 1223 m2/g and modified the surface chemical groups. Mn/C-KOH with a Mn-doping dosage of 0.27 wt% was an adsorbent and outstanding catalyst for removing phenol via peroxydisulfate (PDS) activation. A 55% adsorption rate of phenol was achieved within 10 min at a concentration of 30 mg/L. A 95% degradation rate and a 75% mineralization rate of phenol (30 mg/L) were obtained through the activation of PDS (200 mg/L). And, the catalytic degradation system could tolerate a wide pH range from 3 to 9. The intrinsic pyridinic N and CC/CC groups of the chitosan-derived biochar played dominant roles in the adsorption. The simultaneous activation of KOH and MnCl2 enhanced the proportion of CO groups of Mn/C-KOH, and CO groups served as the catalytic active sites for PDS activation. The electron transfer and 1O2-mediated non-radical processes that were induced by the formation of a dioxirane intermediate between Mn/C-KOH and PDS were responsible for the phenol degradation. This work offers a modification for the biomass-derived catalysts and is beneficial to the understanding of non-radical mechanism in AOPs.

Oxygen-enriched vacancy Co2MnO4 spinel catalyst activated peroxymonosulfate for degradation of phenol: Non-radical dominated reaction pathway

Spinel is a desirable catalyst for active peroxymonosulfate (PMS) to degrade organic pollutants in complex water matrix. In this study, spinel-type Co2MnO4 catalyst were successfully synthesized and employed as an efficient PMS activator for the degradation of phenol in water (up to 100 % within 45 min, degradation rate constant (k) is 0.076 min−1) at initial PH of 6.3. The excellent catalytic activity of Co2MnO4/PMS system was found to be attributed to its unique porous structure, oxygen vacancies and the synergistic effect of Co and Mn. Sulfate radicals (SO4−) and singlet oxygen (1O2) all contributed to phenol degradation, and 1O2, a non-radical pathway mainly provided by oxygen vacancies of Co2MnO4, is the dominant reactive species in the activation system. The Co2MnO4/PMS system had good resistance to the common inorganic anions (Cl−, HPO42−, HCO3− and NO3−) and exhibited great reusability due to the strong Co/Mn interaction. Finally, the phenol degradation mechanism in Co2MnO4/PMS system was also proposed based on the detected intermediates by GC–MS. Overall, the system composed of oxygen-enriched vacancy Co2MnO4 spinel catalyst and PMS has good degradation efficiency and is suitable for the remediation of organic pollutants in wastewater.

Motion-based phenol detection and degradation using 3D hierarchical AA-NiMn-CLDHs@HNTs-Ag nanomotors

A novel and facile strategy was applied for designing and fabricating a nanomotor-assisted dual-functional platform for sensitive detection and rapid degradation of phenol in water.

Investigating crystal plane effect of Co3O4 with various morphologies on catalytic activation of monopersulfate for degradation of phenol in water

As phenol represents as the most typical persistent organic pollutants in wastewater, SO4•−-involved chemical oxidation techniques using monopersulfate (MPS) have been regarded as a promising method to eliminate phenol. Since Co3O4 is the benchmark heterogeneous catalyst for activating MPS, it is highly critical to investigate shape-varied Co3O4 catalysts with well-defined crystal planes for activating MPS to degrade phenol. Thus, the aim of this study is to elucidate how different Co3O4 catalysts with various well-defined planes would influence catalytic activities for MPS activation. Specifically, three Co3O4 nanocrystals are fabricated: nanoplate (NP), nanobundle (NB), and nanocube (NC) with different dominant exposed facets of {1 1 2}, {1 1 0}, and {1 0 0}, respectively. As the facets of {1 1 2} and {1 1 0} consist of more abundant Co2+/Co3+, Co3O4-NP and Co3O4-NB exhibit noticeably higher catalytic activities then Co3O4-NC for activating MPS to degrade phenol. Nevertheless, since Co3O4-NP shows a much higher surface area than Co3O4-NB, Co3O4-NP could exhibit a relatively high catalytic activity in comparison to Co3O4-NB. In addition, Co3O4-NP also exhibits much faster degradation kinetics with a rate constant of 0.061 min−1 at 30 °C, and more resistance towards pH variation, with much stable reaction stoichiometric efficiencies (RSE) ranging from 0.034 to 0.039 at pH = 3 ~ 9, than the other two Co3O4 nanocrystals, making Co3O4-NP with the {1 1 2} facet a more outstanding Co3O4 for activating MPS to degrade phenol.

Determination of photocatalytic process parameters on phenol degradation using TiO2-MWCNT (cocoPAS) composite

Multi-walled carbon nanotubes (MWCNT) were prepared by treatment of cocoPas and titanium dioxide nanocomposites TiO2 – MWCNT (cocoPAS) prepared by stirring and mixing method was used as a photocatalyst for the degradation of phenol in water under light irradiation. The morphology and microstructure of the composites were characterized with SEM, FT-IR, BET, XRD and UV-visible spectrophotometer. The purpose of this study were synthesize TiO2-MWCNT (cocoPAS) composite and evaluate its performance for photodegradation phenol. It was found that the degree of photodegradation of phenol under UV light was highly dependent on the concentration of phenol and the degradation temperature. The presence of MWCNT worked as the adsorbent and electron acceptor to efficiently enhance the phenol photodegradation. The as-prepared nanotubes, with surfactant contents, showed high- photocatalytic activities with increase degradation. These results indicate that TiO2 – MWCNT (cocoPAS)composites using cocoPAS can be used to enhance degradation and can expand potential applications for the degradation of organic pollutants.

Oxidation of phenol by persulfate activated by zero-valent iron-biochar composites

Zero-valent iron [Fe(0)]-biochar composites, namely, Fe(0)-included biochar and biochar-coated Fe(0), were synthesized and their catalytic performance in the activation of persulfate for phenol degradation in water was evaluated. In the presence of the Fe(0)-biochar composites, Fe(0)-included biochar-persulfate and biochar-coated Fe(0)-persulfate systems showed higher phenol removal than a Fe(0)-persulfate system by 11.6% and 20.7%, respectively. The difference in phenol removal by persulfate between Fe(0)-included biochar and biochar-coated Fe(0) was because of the high surface area of and oxygen-containing surface functional groups on the biochar coating of the latter. Differences in the properties of these two composites may also be responsible for the different optimal persulfate concentrations and doses of the composites required in the Fe(0)-included biochar-persulfate and biochar-coated Fe(0)-persulfate systems. Under optimal conditions, phenol degradation in the aqueous phase exceeded 95% for both composites. Electron paramagnetic resonance analysis revealed that hydroxyl and sulfate radicals were formed in the Fe(0)-biochar composite-persulfate systems. The results of this study suggest that Fe(0)-biochar composites can enhance phenol degradation by persulfate in water.

Photocatalytic activity of visible-light-driven ternary Ag/Ag2S/ZnO nanocomposites for phenol degradation in water

Silver sulphide (Ag2S) and zinc oxide (ZnO) nanoparticles were synthesized through a sol-gel method. The Ag constituent of the ternary was achieved by photodesposition of the binary Ag2S/ZnO resulting in a color change from brownish grey to purple indicating its formation. The synthesised particles were characterised using Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDX) to confirm its elemental presence and morphology. The crystallinity of the nanoparticles was determined using the X-ray diffractometer (XRD), and Brunauer–Emmett–Teller (BET) analysis surface area was 4.95 m2g-1. The progressive degradation of phenol was analysed and results showed that under visible light, the ternary composite Ag/Ag2S/ZnO, exhibited the highest phenol degradation efficiency (95 %) compared to the constituent compounds, ZnO (37 %) and Ag2S/ZnO (83 %) after 6 h of visible light irradiation respectively. However, investigations have revealed that extrinsic factors such as pH of the solution, the initial concentration of phenol and photocatalyst dosage could significantly affect the overall system performance.

Constructing BiOBr/CoOx/g-C3N4 Z-scheme photocatalyst with CoOx as both redox mediator and cocatalyst for phenol degradation

Constructing Z-scheme heterostructure photocatalysts is an efficient method to improve the photocatalytic performance for degrading organic pollutants. Herein, the BiOBr/CoOx/g-C3N4 Z-scheme photocatalyst was constructed by integrating two-dimensional (2D) BiOBr and g-C3N4 components with introducing CoOx as both redox mediator and cocatalyst. The spectroscopic and photoelectrochemical analyses verified the higher efficiency of charge transfer and separation in the BiOBr/CoOx/g-C3N4 heterostructures. For photocatalytic degradation of phenol in water, the BiOBr/CoOx/g-C3N4 photocatalyst exhibited an apparent rate constant of 0.0579 min−1, which is 7.3, 4.3 and 3.0 times those from g-C3N4, BiOBr, and BiOBr/g-C3N4 samples, respectively. As identified by the control experiments and the in-situ electron spin resonance measurements, the photogenerated holes (h+), hydroxyl radical (·OH) and superoxide radical (·O2−) contributed together to the photocatalytic phenol degradation. The enhanced photocatalysis of BiOBr/CoOx/g-C3N4 heterostructures was attributed to its multiple virtues of broad photoabsorption region as well as favorable spatial separation and sufficient redox potentials of electrons and holes. The CoOx species could serve as a charge mediator to accelerate the interfacial charge transfer and a cocatalyst to promote the hole-driven oxidation reaction. This study develops a low-cost and high-efficiency photocatalyst for the removal of organic pollutants from aquatic environment as well as highlights an effective approach for the construction of all-solid-state Z-scheme photocatalyst.

Facile synthesis and characterisation of nanosized ZnO modified with Ag2S for visible-light-induced phenol degradation

This study investigates the synthesis, characterisation, and application of a visible-light activated binary nanocomposite catalyst for the degradation of phenol in water. Zinc oxide with a wide direct band gap (3.4 eV) is efficient under ultraviolet irradiation but shows less activity under visible light. Therefore, a sol-gel method was applied to modify it using silver sulphide whose band gap is much lower (1.1 eV) to shift the photosensitivity of the composite catalyst towards the visible light spectrum. The synthesised nanoparticles were characterised using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction which confirmed the purity of the synthesised material. At a catalyst loading of 1 gL-1, results showed that under visible light, the binary composite Ag2S/ZnO exhibited the highest phenol degradation efficiency of 50 % which was greater than ZnO that recorded a 16 % removal after 210 minutes of irradiation. These results support further development and application of visible-light-induced catalysts for photocatalytic degradation.

Iron(II) sulfate crystals assisted mechanochemical modification of microscale zero-valent aluminum (mZVAl) for oxidative degradation of phenol in water

Microscale zero-valent aluminum (mZVAl) is prone to surface passivation due to formation of the surface Al-(hydr)oxide layer, resulting in short reactive life. To overcome this critical drawback, we developed a mechanochemical ball milling approach to modify and activate commercially available mZVAl assisted by the fragile FeSO4·7H2O crystals. SEM-EDS and XPS analyses indicated that the particle surface of the mechanochemically modified mZVAl (Fe-mZVAlbm) was not only fractured with newly formed fresh reactive surfaces, but also attached with a rough layer of Fe-oxides that were uniformly distributed on mZVAl. While pristine mZVAl failed to degrade any phenol, Fe-mZVAlbm was able to rapidly degrade 88.8% within 90 min (initial phenol = 20 mg/L, pH = 2.50, dosage = 3 g/L) under normal oxic conditions, with a pseudo first-order rate constant of 0.040 min−1 and about 70.0% of phenol mineralized in 8 h. Moreover, Fe-mZVAlbm also showed prolonged reactive life, and no significant reactivity drop was evident after six cycles of consecutive runs for phenol degradation. The much enhanced reactivity and reactive longevity of Fe-mZVAlbm are attributed to the critical roles of the surface Fe-oxides, including 1) protecting the newly exposed reactive Al0 from being oxidized by side reactions, 2) serving as an electron mediator facilitating the electron transfer from the core Al0 reservoir to the exterior surface, and 3) acting as an Fe2+ source and a heterogeneous catalyst to enable the Fenton (-like) reactions. This study provides a novel and practical approach for preparing Fe-oxides modified mZVAl with enhanced and long-lasting reactivity.

Iron-containing palygorskite clay as Fenton reagent for the catalytic degradation of phenol in water.

Heterogeneous Fenton systems have great application prospects in the catalytic degradation of organic wastewater; however, they are still not widely used in operation due to the difficulty of preparing catalysts in low yields and the high manufacturing cost. Herein, we report that a pristine iron-containing palygorskite clay can be used as a Fenton catalyst reagent without any retreatment. The composition, morphology, and structure of palygorskite clay, as well as the distribution and content of Fe element in palygorskite, were characterized via several physicochemical techniques. The degradation reaction of phenol in water was carried out as a probe reaction for the palygorskite Fenton reagent. The effects of the palygorskite content, pH value, and hydrogen peroxide concentration on the degradation efficiency of phenol were studied. Under optimum operating conditions, the chemical oxygen demand (COD) degradation efficiency of phenol reaches 94% with a reaction temperature of 20 °C and a reaction time of 15 min.

Single-crystalline rutile TiO2 nanorod array on flexible Ti substrates for efficient photoelectrocatalytic degradation of phenol in water

Single-crystalline nanorods are intrinsic highways for charge transfer and hence ideal nanofeatures for efficient photoelectrochemical (PEC) degradations of pollutants in wastewater. Photocatalytic thin films on flexible substrates avoid the nuisance catalysts-recovering procedure and also allow for the flexible design in photocatalytic apparatus. We therefore directly deposited single-crystalline rutile TiO2 nanorod arrays on flexible and conductive Ti substrates through a hydrothermal technique and optimized the synthetic parameters to achieve an extremely high PEC activity towards phenol removal in water under UV light illumination. In the presence of tetrabutyltitanate (TBT) and HCl reactants under a hydrothermal environment, a balance in the erosion of the Ti substrate and the precipitation of TiO2 nanorods is found to be the key to tune the nanofeatures of the TiO2 thin films and in turn the PEC efficiency. The decreasing TBT concentration achieved a more sparsely distributed nanorod array, which significantly contributes to the PEC activity; yet too little TBT resulted in total dissolution of Ti plates. The PEC activity increased with increasing hydrothermal duration because of more loaded TiO2. The maximum reaction rate constant is 2.74 h−1, which is 39 times that of a commercial P25 TiO2 nanoparticulate film. The photocurrent stabilized at 0.9 mA/cm2 under the illumination of AM1.5G simulated solar light, suggesting a high separation efficiency of photogenerated holes and electrons along the single-crystalline rutile TiO2 nanorod arrays.

Comparative catalytic activity of pure, mixed and P-modified CoFe2O4 nanoparticles for water treatment at neutral pH

Nowadays, cobalt-based catalysts are becoming increasingly attractive for various reactions. In this work, the catalytic and photocatalytic activities of different cobalt ferrites were investigated for the degradation of phenol in water at neutral pH. Pure CoFe2O4 and mixed CoxNi1-xFe2O4 ferrites were synthesized using different precursors (chloride and nitrate). CoFe2O4 catalysts derived from chloride precursors showed a higher catalytic efficiency compared to those derived from nitrate precursors. Significant enhancement in the catalytic activities was observed when Ni was incorporated into CoFe2O4. Furthermore, the catalytic activities of phosphorus-modified cobalt ferrites (P-CoFe2O4) significantly improved the photocatalytic degradation of phenol.

Enhanced surface activation process of persulfate by modified bagasse biochar for degradation of phenol in water and soil: Active sites and electron transfer mechanism

Carbon-based catalysis for green and sustainable degradation of phenol in water and soil has attracted extensive concern. In this study, mesoporous biochar produced by bagasse calcination with KOH and CaCl2 modified activation (Ca/BS-800-KOH) was used to stimulate persulfate (PS) for the surface oxidation degradation of phenol, which exhibited excellent removal rate of 90% in 60 min (k = 0.0404 min−1) with a relatively low dosage (0.066 g/L). Compared with untreated materials (BS-800, 27% removal rate in 180 min), after KOH and CaCl2 treatment, the functional groups (COH), increased porosity, defective structure and the more efficient electron transfer of Ca/BS-800-KOH were probably responsible for its good adsorptive and catalytic performance, which also closely related to the inactivation of Ca/BS-800-KOH. In the (Ca/BS-800-KOH)/PS/phenol system, PS was successfully activated in the presence of catalyst, and radical and non-radical reaction pathways were firstly found, in which the non-radical pathway like 1O2 accelerated quickly the oxidative degradation of phenol. While in radical pathway involving SO4·− and ·OH, ·OH was the main oxidative species and also played an irreplaceable role in the degradation of phenol. The Ca/BS-800-KOH as a medium promotes the electron transfer between phenol (electron donor) and PS (electron acceptor), in which Ca accelerates the electron transfer rate on the surface of Ca/BS-800-KOH, thereby causing oxidative degradation of phenol. The superior removal efficiencies of common environmental pollutants (all more than 93%) and phenol in water (100%) and soil samples were found. This research proposed an insightful mechanism of the low cost and feasible carbon-material-based PS-AOPs in degrading organic pollutants.

Hybrid TiO2-Polyaniline Photocatalysts and their Application in Building Gypsum Plasters.

Hybrid materials of conjugated polymer and titanium(IV) oxide have attracted considerable attention concerning their potential benefits, including (i) efficient exploitation of visible light, (ii) a high adsorption capacity for organic contaminants, (iii) and effective charge carriers separation. The new class of the photocatalysts is promising for the removal of environmental pollutants in both aqueous and gaseous phases. For the first time, in this study, the polyaniline (PANI)–TiO2 hybrid composite was used for the degradation of phenol in water and toluene in the gas phase. Polyaniline–TiO2 was prepared by the in situ polymerization of aniline on the TiO2 surface. The obtained hybrid material was characterized by diffuse reflectance spectroscopy (DR/UV-Vis), X-ray diffraction (XRD), fast-Fourier transformation spectroscopy (FTIR), photoluminescence (PL) spectroscopy, microscopy analysis (SEM/TEM), and thermogravimetric analysis (TGA). An insight into the mechanism was shown based on the photodegradation analysis of charge carrier scavengers. Polyaniline is an efficient TiO2 photosensitizer for photodegradation in visible light (λ > 420 nm). The trapping experiments revealed that mainly h+ and ˙OH were the reactive oxygen species that were responsible for phenol degradation. Furthermore, the PANI–TiO2 hybrid nanocomposite was used in gypsum plaster to study the self-cleaning properties of the obtained building material. The effect of PANI–TiO2 content on the hydrophilic/hydrophobic properties and crystallographic structure of gypsum was studied. The obtained PANI–TiO2-modified gypsum plaster had improved photocatalytic activity in the reaction of toluene degradation under Vis light.

Degradation of phenol in water by Fe(II)-citrate activated persulfate oxidation

To enhance the degradation efficiency, complexing agent citric acid (CA) and trisodium citrate (TC) were introduced into the Fe(II)-persulfate (Fe2+/PS) oxidation system to degrade phenol. And the optimal operating conditions were determined. The results showed that Fe2+-citrate/PS system had higher degradation efficiency than the others. The optimal operating conditions to degrade phenol in water were: a PS concentration of 0.06 mol/L, a Fe2+ concentration of 0.02 mol/L and a TC concentration of 0.01 mol/L, while reaction temperature and the initial pH values had little influence on the phenol degradation.

Photocatalytic degradation of phenol in water under simulated sunlight by an ultrathin MgO coated Ag/TiO2 nanocomposite

Phenol is one of the most widespread, toxic and recalcitrant compounds in water sources. Due to its persistent nature, conventional wastewater treatment methods are not effective to remove or degrade phenol from water. In this work, novel photocatalysts were developed to effectively degrade phenol under simulated sunlight. The catalysts were composed of one-dimensional titanium dioxide (TiO2) nanorods decorated with silver (Ag) nanoparticles, coated by an ultrathin magnesium oxide (MgO) overlayer through atomic layer deposition (ALD). Material properties of prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–vis diffuse reflectance spectroscopy (UV–Vis DRS). The photocatalytic performance of phenol degradation under simulated sunlight was evaluated and correlated with the material properties. The Ag nanoparticles promoted light absorption and transfer of photo-induced electron-hole pairs from within TiO2 nanorods to the catalyst surface. The ultrathin MgO overlayer with a sub-nanometer thickness did not hinder charge transfer to the surface, but rather, it further increased the light absorption and inhibited surface charge recombination through a surface passivation effect, promoting phenol degradation. The photocatalytic reaction mechanism was investigated by examining hydroxyl and superoxide radical production in the photocatalytic system. The results from this work demonstrated a new strategy for fabricating efficient solar-driven photocatalysts for the degradation of persistent water contaminants.

Biogenic manganese oxide: An efficient peroxymonosulfate activation catalyst for tetracycline and phenol degradation in water

From the view of environment and easy availability, to develop the most efficient manganese oxide for peroxymonosulfate (PMS) activation is of great importance for the degradation of recalcitrant organic pollutants. In this study, biogenic manganese oxide (BioMnOx) exhibited an unprecedented efficiency than the most efficient 3D α-Mn2O3 prepared by chemical method. 100% of phenol degradation at 40 min and 99.4% of tetracycline removal at 60 min were achieved over BioMnOx with PMS, which was 3-fold faster than 3D α-Mn2O3. BioMnOx also has an excellent long-term stability and good performance toward the pollutants degradation at a wide pH range of 3.0–9.0. Most importantly, 1O2 was identified as the primary reactive species in BioMnOx/PMS system based on the trapping experiment and EPR analysis. The PMS activation over BioMnOx should follow a self-decomposition and energy quenching mechanism instead of electron transfer process as confirmed by the XPS analysis. Finally, the degradation pathways of tetracycline and phenol by 1O2 over BioMnOx were proposed according to HPLC and HPLC-MS results, which are greatly different from that by OH oxidation in the literature.