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Mass Spectrometric Imaging Reveals Photocatalytic Degradation Intermediates of Aromatic Organochlorines Resulting from Interfacial Photoelectron Transfer and Hydroxyl Radical Abstraction on Semiconductor Nanoparticles
摘要： Organochlorines are highly persistent and toxic contaminants that are widely distributed and accumulated in various aquatic or soil environments as well as food chains. Heterogeneous photocatalytic degradation of such pollutants by using semiconductor nanoparticles has been recognized as one of the effective purification ways. Understanding of degradation mechanisms and designing of highly efficient semiconductor nanoparticles require structural identification of various degradation intermediates that are difficult to achieve with current spectroscopic techniques. Herein a mass spectrometric approach was developed to tackle interfacial photoelectron transfer and hydroxyl radical abstraction on different semiconductor nanoparticles. Chlorobenzenes (including hexachlorobenzene and chlorothalonil) adsorbed on the surfaces of nanoparticles were found to instantly undergo dechlorination and ring dissociation through photoelectron capture dissociation and abstraction of a chlorine atom from aromatic C-Cl bond by hydroxyl radicals. Different intermediates have been unambiguously identified with experimental evidences provided by a Q-TOF mass spectrometer. It has been demonstrated that both electron density around atoms and steric effects of side chains contribute to the site selectivity for photoelectron capture and hydroxyl radical abstraction. But the energies needed for chemical bond cleavages and the stabilization of acquired charges play important roles in degradation efficiency. By using mass spectrometric imaging, photocatalytic differences of different semiconductor nanoparticles have been revealed.
关键词： Photoelectron Capture Dissociation,Interfacial Photoelectron Transfer,Chlorobenzenes,Mass Spectrometry,Hydroxyl Radical
更新于2025-09-23 15:23:52
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Degradation of tetracycline by medium pressure UV-activated peroxymonosulfate process: Influencing factors, degradation pathways, and toxicity evaluation
摘要： This study employed the medium pressure UV/peroxymonosulfate (MPUV/PMS), a new sulfate radical-based advanced oxidation process, to eliminate tetracycline (TTC) in water. At pH = 3.7, initial TTC concentration of 11.25 μM, PMS dosage of 0.2 mM and UV dose of 250 mJ cm-2, 82 % of TTC was degraded by MPUV/PMS. The second-order reaction rate constants of TTC with SO4?- and ?OH were found to be 1.4 × 1010 M-1 s-1 and 6.0 × 109 M-1 s-1, respectively. Radical quenching experiments indicated that ?OH played the major role in the degradation of TTC. Higher PMS dosage (0.1 mM~1.0 mM) and higher pH (3~11) could accelerate the TTC removal. Besides, the presence of Cl- (0.1 mM~5.0 mM) and CO32- (0.05 mM~0.5 mM) could also promote the reaction. Eight transformation products (TPs) were identified, and the potential degradation pathways mainly involved hydroxylation, demethylation and decarbonylation processes. The variation in the genotoxicity was investigated using the umu-test, and the results indicate that the genotoxicity of TTC after the MPUV/PMS treatment significantly increased during the initial stage. In addition, the ecotoxicity and mutagenicity of TTC and its TPs were predicted using quantitative structure-activity relationship (QSAR) analysis, and the results revealed that some TPs could have equivalent and even higher toxicity than TTC. MPUV/PMS showed better performance in TTC degradation in real waters than in Milli-Q water. MPUV/PMS is concluded to be an efficient method for removing TTC, but more attention should be paid to the changes of toxicity during this process.
关键词： Tetracycline,Toxicity,Hydroxyl radical,Sulfate radical,Transformation products
更新于2025-09-23 15:23:52
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The efficiency and mechanism in a novel electro-Fenton process assisted by anodic photocatalysis on advanced treatment of coal gasification wastewater
摘要： A novel dual-chamber photo-electrochemical oxidation system with Fe@Fe2O3/CF cathode was constructed by combining cathodic electro-Fenton and anodic photocatalysis for advanced treatment of biologically pretreated coal gasification wastewater (CGW). In the electro-Fenton cathode chamber, maximal chemical oxygen demand (COD) removal efficiency of 84.2% was arrived within 120 min at current density 10 mA/cm2, initial pH 3 and air flow rate 0.4 L/min for its initial concentration of 200 mg/L. Correspondingly, the effluent concentration of COD, BOD5, TOC and total phenols were 31.5, 3.9, 8.4 and 13.8 mg/L respectively, satisfying the stringent wastewater discharge standard. Moreover, the H2O2 concentration change and wastewater acute toxicity were analyzed. Furthermore, a reasonable degradation mechanism was proposed based on the contribution of hydroxyl radicals (%OH), and thus degradation pathway of phenol as typical pollutant was also speculated. The integrated system is confirmed to be high-effective and stable, and thus it is a potentially promising alternative for treatment toxic refractory industrial wastewater.
关键词： COD removal,Hydroxyl radical,Electro-Fenton,Fe@Fe2O3/CF,Coal gasification wastewater
更新于2025-09-23 15:23:52
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Heterogeneous degradation of organic contaminants in the photo-Fenton reaction employing pure cubic β-Fe2O3
摘要： Pure cubic β-Fe2O3 crystal, which can absorb visible light (< 650 nm) on account of the bandgap of 1.9 eV as a direct bandgap semiconductor, was employed as a low-cost and non-toxic catalyst for photo-Fenton reaction in this article. Diverse organic contaminants including rhodamine B (RhB), methyl orange (MO), alizarin red (AR) and phenol can be effectively degraded. In particular, the degradation of RhB were investigated detailedly. As such, hydroxyl radicals (%OH) were verified to act as considerable active species for the process by using terephthalic acid as an indicator. Degradation mechanism and intermediates of phenol in the photo-Fenton reaction was discovered by virtue of liquid chromatography-mass spectrometry (LCeMS). Notably, hydroxylation of phenol generated some intermediates, which are converted into H2O and CO2 eventually.
关键词： Photo-Fenton,H2O2,β-Fe2O3,Degradation,Hydroxyl radicals
更新于2025-09-23 15:22:29
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An Effective Approach to Improve the Photocatalytic Activity of Graphitic Carbon Nitride via Hydroxyl Surface Modification
摘要： In this work, we have developed a hydrothermal method to modify g-C3N4 with hydroxyl surface modification. Modified g-C3N4 has exhibited higher photocatalytic activity in the removal of phenolic compounds under visible light. The improvement may be due to the following merits: (1) Tuning of the hydrophobic surface of g-C3N4 to be hydrophilic; (2) improved adsorption energy, and (3) narrowed band gap for g-C3N4 after hydroxyl surface modification. This method is easy-to-operate, very effective in adding hydroxyl groups on the surface of C3N4, and may be extended to other systems to promote their photocatalytic activities in water treatment.
关键词： water treatment,photocatalysis,hydroxyl,surface modification,g-C3N4
更新于2025-09-23 15:22:29
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Degradation of haloacetonitriles with UV/peroxymonosulfate process: degradation pathway and the role of hydroxyl radicals
摘要： Haloacetonitriles (HANs), a specie of new emerging halogenated nitrogenous disinfection by-products (N-DBPs) including trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), monochloroacetonitrile (MCAN) and dibromoacetonitrile (DBAN), were more cytotoxic and genotoxic than the conventional DBPs. In this study, kinetics and mechanisms in the oxidization of HANs by UV/peroxymonosulfate (PMS) process were investigated. The degradation of chloroacetonitriles (CANs) in UV/PMS process was more remarkable than UV alone, PMS alone and UV/ H2O2 process. And the order of the rates of degradation of HANs was followed: TCAN > DCAN> MCAN, while DBAN was remarkably degraded by UV alone. The degradation of DCAN was accelerated by humic acid and Cl-, while suppressed by bicarbonate. Scavenging experiments showed that hydroxyl radical (?OH) was the predominant species in the reaction. According to the gas chromatography/mass spectrometer (GC/MS) analysis, the breakage of C-Cl bond was the dominant pathways in degradation of CANs.
关键词： Haloacetonitriles,UV/Peroxymonosulfate,Pathway,Hydroxyl radicals,Degradation
更新于2025-09-23 15:22:29
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Oxidative Degradation of Tannic Acid in Aqueous Solution by UV/S2O82? and UV/H2O2/Fe2+ Processes: A Comparative Study
摘要： Tannic acid (TA) is a major pollutant present in the wastewater generated from vegetable tanneries process and food processing. This work studied TA degradation by two advanced oxidation processes (APOs): UV irradiation at the wavelength of 254 nm in the presence of hydrogen peroxide (H2O2) and ferrous iron (photo-Fenton) and in the presence of potassium persulfate. The in?uence of certain experimental parameters such as K2S2O8, H2O2, Fe2+, and TA concentrations, initial pH and temperature was evaluated in order to obtain the highest ef?ciency in terms of aromatics (decay in UV absorbance at 276 nm) and TOC removals. Chemical oxidation of TA (0.1 mM) by UV/persulfate achieved 96.32% of aromatics removal and 54.41% of TOC removal under optimized conditions of pH = 9 and 53.10 mM of K2S2O8 after 60 min. The treatment of TA by photo-Fenton process successfully led to almost complete aromatics removal (99.32%) and high TOC removal (94.27%) from aqueous solutions containing 0.1 mM of TA at natural pH = 3 using 29.4 mM of H2O2 and 0.18 mM of Fe2+ at 25 ?C after 120 min. More ef?cient degradation of TA by photo-Fenton process than UV/persulfate was obtained, which con?rms that hydroxyl radicals are more powerful oxidants than sulfate radicals. The complete removal of organic pollution from natural waters can be accomplished by direct chemical oxidation via hydroxyl radicals generated from photocatalytic decomposition of H2O2.
关键词： hydroxyl radicals,degradation,photo-fenton,mineralization,UV/persulfate,sulfate radicals,Tannic acid
更新于2025-09-23 15:22:29
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Photocatalytic Degradation of Estriol Using Iron-Doped TiO2 under High and Low UV Irradiation
摘要： Iron-doped TiO2 nanoparticles (Fe-TiO2) were synthesized and photocatalitically investigated under high and low ?uence values of UV radiation. The Fe-TiO2 physical characterization was performed using X-ray Powder Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Diffuse Re?ectance Spectroscopy (DRS), and X-ray Photoelectron Spectroscopy (XPS). The XPS evidenced that the ferric ion (Fe3+) was in the TiO2 lattice and unintentionally added co-dopants were also present because of the precursors of the synthetic method. The Fe3+ concentration played a key role in the photocatalytic generation of hydroxyl radicals (?OH) and estriol (E3) degradation. Fe-TiO2 accomplished E3 degradation, and it was found that the catalyst with 0.3 at.% content of Fe (0.3 Fe-TiO2) enhanced the photocatalytic activity under low UV irradiation compared with TiO2 without intentionally added Fe (zero-iron TiO2) and Aeroxide? TiO2 P25. Furthermore, the enhanced photocatalytic activity of 0.3 Fe-TiO2 under low UV irradiation may have applications when radiation intensity must be controlled, as in medical applications, or when strong UV absorbing species are present in water.
关键词： hydroxyl radical,estriol,iron-doped TiO2,photocatalytic activity,low UV irradiation
更新于2025-09-23 15:22:29
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Determination of aminophylline based on fluorescence quenching of amino-functionalized graphene quantum dots induced by photoilluminated riboflavin-aminophylline system
摘要： A new method based on fluorescence spectroscopy for the sensitive determination of aminophylline (AP), an antiasthmatic drug, was developed in this work. Amino-functionalized graphene quantum dots (afGQDs) were synthesized based on a two-step method and they were characterized by transmission electron microscope, UV–vis absorption spectrum and infrared spectrum. The fluorescence of afGQDs was quenched by riboflavin (Rf) via both dynamic quenching and inner filter effect. Photoilluminated Rf-AP system in the presence of oxygen produced hydroxyl radicals (?OH). The latter accepted electrons from afGQDs owing to a photo-induced electron transfer process and led to the further fluorescence decline. The changing extent of the fluorescence intensity was found to be proportional to the concentration of AP in the range of 0.10–10 μg mL?1 and the limit of detection arrived at 40 ng mL?1. The proposed method was successfully employed for the determination of AP in a pharmaceutical sample and the recovery rate varied in the range of 99%–106%.
关键词： Riboflavin,Photoilluminated interaction,Amino-functionalized graphene quantum dots,Hydroxyl radicals,Aminophylline,Fluorescence quenching
更新于2025-09-23 15:21:01
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Peripherally functionalized based dendrimers as the template for synthesis of silver nanoparticles and investigation the affecting factors on their properties
摘要： Today, dendrimers (D) were introduced as a versatile template for the synthesis of nanoparticles (NPs). In this work, the stable silver nanoparticles (AgNPs) is successfully synthesized through the chemical reduction of AgNO3 using NaBH4 as a reducing agent. Synthesis of AgNPs was performed in the presence of different generations of citric acid-based dendrimers (G1, G2 and G3) and hydroxyl-terminated citric acid-based dendrimers (G1-OH, G2-OH and G3-OH). High-resolution transmission electron microscopy, electron diffraction and energy-dispersive X-ray analysis were used to characterize the synthesized AgNPs. UV–Vis results were used for the qualitative study of the synthesized AgNPs properties. With varying the molar ratio of dendrimer/Ag+, generations of dendrimers and the pH of the solution, the size and size distribution of AgNPs could be easily controlled at room temperature. The average diameter of the synthesized AgNPs in the presence of Gn-OH was in the range of 8–20 nm. Results show that G1-OH alkaline medium with 1:1 molar ratio of D/Ag is the optimum condition for the synthesis of AgNPs. All the obtained results from this study showed that controlling the medium conditions allows AgNPs with the desired size to be obtained.
关键词： Chemical reduction,Silver nanoparticles,Citric acid,Hydroxyl-terminated dendrimer,Dendrimer
更新于2025-09-23 15:21:01