Yongli Zhang

Non-photochemical production of singlet oxygen via activation of persulfate by carbon nanotubes

The reaction between persulfate (PS) and carbon nanotubes (CNTs) for the degradation of 2,4-dichlorophenol (2,4-DCP) was investigated. It was demonstrated that CNTs could efficiently activate PS for the degradation of 2,4-DCP. Results suggested that the neither hydroxyl radical (OH) nor sulfate radical (SO4-) was produced therein. For the first time, the generation of singlet oxygen (1O2) was proved by several methods including electron paramagnetic resonance spectrometry (EPR) and liquid chromatography mass spectrometry measurements. Moreover, the generation of the superoxide radical as a precursor of the singlet oxygen was also confirmed by using certain scavengers and EPR measurement, in which the presence of molecular oxygen was not required as a precursor of 1O2. The efficient generation of 1O2 using the PS/CNTs system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral conditions with the mineralization and toxicity evaluated. A kinetic model was developed to theoretically evaluate the adsorption and oxidation of 2,4-DCP on the CNTs. Accordingly, a catalytic mechanism was proposed involving the formation of a dioxirane intermediate between PS and CNTs, and the subsequent decomposition of this intermediate into 1O2.

Oxidation of 2,4-dichlorophenol by non-radical mechanism using persulfate activated by Fe/S modified carbon nanotubes.

The aim of this study was to develop a new approach for the activation of persulfate (PS) based on carbon nanotubes (CNTs). Fe/S modified carbon nanotubes (Fe/S-CNTs) were synthesized via impregnation-precipitation in the aqueous-phase synthesis method. The morphologies and chemical states of the catalysts were characterized and 2,4-dichlorophenol (2,4-DCP) was selected to investigate the degradation performance using Fe/S-CNTs with PS. The results reveal that the Fe/S-CNTs catalysts can significantly accelerate the removal of 2,4-DCP compared to single PS or PS/CNTs. The catalytic capacity is also enhanced by S modification and is affected by the solution pH. The iron loading content, PS concentration and catalyst dosage could play important roles in the degradation. A non-radical process of 2,4-DCP degradation is demonstrated for the first time in the results of the radical scavengers and chloride ionic, as well as persulfate decomposition. It is suggested that PS is first bonded with the sp(2)-hybridized system and activated by iron oxide particles and iron-sulfur complexes, then it reacts rapidly with the adsorbed 2,4-DCP.

Generation of hydrogen peroxide and hydroxyl radical resulting from oxygen-dependent oxidation of L-ascorbic acid via copper redox-catalyzed reactions

The generation of hydrogen peroxide (H2O2) and hydroxyl radical (HO˙) during the oxidation of L-ascorbic acid (L-AA) by oxygen with copper as a catalyst was investigated to set up the O2/Cu/L-AA process with benzoic acid (BA) as a probe reagent. The high concentration of H2O2 that is generated undergoes an intramolecular two-electron transfer and is further activated by the intermediate cuprous copper [Cu(I)] to yield HO˙ as a product, resulting in significant degradation of BA. Dehydroascorbic acid, 2,3-diketogulonic acid, and L-xylosone were the predominant detected products of the oxidation of L-AA. However, the generation of H2O2 and degradation of BA were regulated by variations in pH, which results from the contradiction between protonated L-AA that is difficult to chelate with Cu(II) via electron transfer and hydrogen ions (H+), which are indispensable for the generation of H2O2. Furthermore, the concentration of H2O2 and degradation of BA increased with an increase in the dosage of L-AA. Trace amounts of Cu(II) are effective for catalyzing the oxidation of L-AA, whereas the generation of H2O2 and degradation of BA increased with an increase in the dosage of Cu(II). Owing to the formation of Cu(I) chloride complexes or Cu(II) chloride complexes, the addition of chloride (Cl−) could inhibit the generation of H2O2 and degradation of BA.

Degradation of Bisphenol A Using Ozone/Persulfate Process: Kinetics and Mechanism

Advanced oxidation of bisphenol A (BPA) in aqueous system by O3/Na2S2O8 was investigated, the degradation of BPA was affected by ozone concentration, persulfate dosages, initial pH, and BPA concentration. Experimental results indicated that the degradation of BPA was proved to follow the pseudo-first order kinetics model and was enhanced with the increase of O3 concentration and the decrease of initial BPA concentration. pH played a significant role in the BPA removal especially under the alkaline condition. Free radical species in the O3/Na2S2O8 system were identified by using tertiary butyl alcohol (TBA) and ethanol (ETOH) as two probes, the results found that the major free radical was SO4− · at acidic condition (pH = 3), and the concentration of ·OH increased with the pH increased. Eight products were detected during the reaction according to liquid chromatograph-mass spectrometry analysis. Most of the intermediates contained quinonoid derivatives, carboxylic acid, and the relevant mechanism for BPA degradation by O3/Na2S2O8 system were proposed.

Degradation of 2,4-dichlorophenol by activating persulfate and peroxomonosulfate using micron or nanoscale zero-valent copper

The ability of persulfate (PS) and peroxymonosulfate (PMS) activated by micron or nanoscale zero-valent copper (ZVC or nZVC) to degrade 2,4-dichlorophenol (2,4-DCP) was quantified under various conditions. Mechanism investigation revealed that PS and PMS accelerated the corrosion of ZVC or nZVC to release Cu+ under acidic conditions. The in-situ generated Cu+ further decomposed PS or PMS to produce SO4- and OH, which then dramatically degraded 2,4-DCP. The kobs for 2,4-DCP removal followed pseudo-first-order kinetics, kobs of ZVC/PMS and nZVC/PMS systems were 10∼30 times greater than these in ZVC/PS and nZVC/PS systems. The nZVC/PMS system was most effective to remove 2,4-DCP which even did better than the nZVI/PMS system, with rate constant values ranging from 0.041 to 1.855min-1. At higher pH ZVC is ineffective, but nZVC can activate PS and PMS to significantly degrade 2,4-DCP at pH up to 7.3. The 2,4-DCP degradation pathway was found to involve dechloridation, dehydrogenation, hydroxylation, ring open and mineralization. 56.7% and 45.3% of TOC removals were respectively obtained in the ZVC/PMS and nZVC/PMS systems within 120min. This study helps to comprehend the application of zero-valent metals in reactive radicals-based oxidation processes and the reactivity of Cu+ as an activator of PS and PMS.

Persulfate-assisted photodegradation of diethylstilbestrol using monoclinic BiVO4 under visible-light irradiation

In this study, the photosynergistic performance of BiVO4 with persulfate (PS) is demonstrated under visible light irradiation for the first time. Diethylstilbestrol (DES) was selected as a reluctant compound, and factors including dosages of PS and catalyst, solution pHs, initial concertration of DES, and inorganic anions were evaluated. The morphology and chemical state of bismuth vanadate (BiVO4) was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy (DRS). It was found that the degradation of DES was promoted in either acid or alkaline solutions. The increase of PS and BiVO4 dosages was beneficial to the reactions, while incremental concentration of DES showed the inhibiting effect. By scavenging hVB+, Cl− was able to make the promotion, differentiated from the exsiting HCO− 3. Moreover, the photocatalytic mechanism for the BiVO4/PS/vis-light system was proposed by using several probe compounds (isopropanol, tert-butanol, and 1,4-benzoquinone), which consists of h+ VB/e− CB generation and recombination on the surface of BiVO4 as well as free radical oxidation in the solutions. The study provides a distinctive method to treat organic contaminants using visible light in the aqueous environment.

Analysis on the removal of ammonia nitrogen using peroxymonosulfate activated by nanoparticulate zero-valent iron

Nanoparticulate zero-valent iron (Fe0) was used to activate peroxymonosulfate (PMS) to remove low concentration of ammonia nitrogen in the aqueous system. The removal process was investigated under various conditions. It was indicated that the removal of

Feasible oxidation of 17β-estradiol using persulfate activated by Bi2WO6/Fe3O4 under visible light irradiation

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