Enhancement of iron-mediated activation of persulfate using catechin: From generation of reactive species to atenolol degradation in water

Elucidating the inhibitory effects of natural organic matter on the photodegradation of organic micropollutants: Atrazine as a probe compound

Natural organic matter (NOM) is a complex mixture of heterogeneous compounds with varying functional groups and molecular sizes. Understanding the impact of NOM on the generation of photochemically produced reactive intermediates (PPRIs) and their potential inhibitory effects on photolysis has remained challenging due to the variations in the reactivities and concentrations of these functional groups. To address this gap, tannic acid (TA), gallic acid (GA), catechin (CAT), and tryptophan (Trp), were chosen as potential substitutes for NOM. Their effects on the photochemical transformation process were evaluated and compared with the widely used Suwannee River NOM (SRNOM). Atrazine (ATZ) was selected as a probe organic micropollutant (OMP). In this investigation, a significantly higher concentration of HO• was observed compared to O21, and the triplet excited state ( NOM*3). The findings suggest that the substituted phenols, particularly those with carboxylate-substitutions, played a substantial role in HO• formation, while electron-rich moieties acted as antioxidants, consuming NOM*3. Hydroxyl, carboxylic, and amino acid were the active groups for O21 formation. However, the inhibitory effects induced by the NOM surrogates were significant and mainly attributed to the direct photolysis inhibition caused by the inner filter effect. The scope of this work was further extended to include SRNOM, where similar trends with less pronounced formation of PPRIs and inner filter effects were observed. Therefore, this study sheds some light on the role of the functional groups in NOM during photochemical transformations of OMPs, thereby deepening our understanding of their fate in aqueous systems.

A comparative study on Fe(III)/H2O2 and Fe(III)/S2O82- systems modified by catechin for the degradation of atenolol

The processes of Fe(III) activated persulfate (PS) and H₂O₂ modified by catechin (CAT) had been shown to be effective in degrading contaminants. In this study, the performance, mechanism, degradation pathways and products toxicity of PS (Fe(III)/PS/CAT) and H₂O₂ (Fe(III)/H₂O₂/CAT) systems were compared using atenolol (ATL) as a model contaminant. 91.0% of ATL degradation was reached after 60 min in H₂O₂ system which was much higher than that in PS system (52.4%) under the same experimental condition. CAT could react directly with H₂O₂ to produce small amounts of HO^• and the degradation efficiency of ATL was proportional to CAT concentration in H₂O₂ system. However, the optimal CAT concentration was 5 μM in PS system. The performance of H₂O₂ system was more susceptible to pH than that of PS system. Quenching experiments were conducted indicating that SO₄^•- and HO^• were produced in PS system while HO^• and O₂^•- accounted for ATL degradation in H₂O₂ system. Seven pathways with nine byproducts and eight pathways with twelve byproducts were put forward in PS and H₂O₂ systems respectively. Toxicity experiments showed that the inhibition rates of luminescent bacteria were both decreased about 25% after 60 min reaction in two systems. Although the software simulation result showed few intermediate products of both systems were More toxic than ATL, but the amounts of them were 1-2 orders of magnitude lower than ATL. Moreover, the mineralization rates were 16.4% and 19.0% in PS and H₂O₂ systems respectively.

Efficient removal of petroleum hydrocarbons from soil by percarbonate with catechin-promoted Fe(III)/Fe(II) redox cycling: Activation of ferrous and roles of ·OH and ·CO3. JOURNAL OF HAZARDOUS MATERIALS 2023;448:130875. [PMID: 36731317 DOI: 10.1016/j.jhazmat.2023.130875] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Advanced oxidation processes are widely used to remove petroleum hydrocarbons from soil, but usually consume large quantities of ferrous and acidify the soil. This study tested an advanced oxidation approach based on percarbonate in laboratory experiments. It removed 88% petroleum hydrocarbons in soil with a pH increase from 8.2 to 10.2. ·OH and ·CO₃^- were the main reactive species, and degraded 41% and 37% PHCs from soil respectively. The o-dihydroxybenzene structure in catechin was found to reduce ferric to ferrous, and prolong the generation of ·OH from 120 s to over 1800 s. The petroleum hydrocarbons were degraded to intermediates including alkanes and olefins through hydrogen-abstraction by ·OH and ·CO₃^-, and by dimerization and β-scission of alkyl radicals. These intermediates were then oxidized to CO₂ and H₂O by ·OH and ·CO₃^-. The main residual intermediates in the soil were low-molecular-weight n-alkanes and branched alkanes, and they were found to inhibit the growth of oats (Avena sativa L.) much less than the original petroleum hydrocarbons. These findings provide a fundamental basis for designing effective technologies which use percarbonate to remove organic pollutants.

Engineering single-atom Fe-Pyridine N4 sites to boost peroxymonosulfate activation for antibiotic degradation in a wide pH range

Single-atom Fe catalysts have shown great potential for Fenton-like technology in organic pollutant decomposition. However, the underlying reaction pathway and the identification of Fe active sites capable of activating peroxymonosulfate (PMS) across a wide pH range remain unknown. We presented a novel strategy for deciphering the production of singlet oxygen (¹O₂) by regulating the Fe active sites in this study. Fe single atoms loaded on nitrogen-doped porous carbon (Fe_SA-CN) catalysts were synthesized using a cage encapsulation method and compared to Fe-nanoparticle-loaded catalysts. It was discovered that Fe_SA-CN catalysts served as efficient PMS activators for pollutant decomposition over a wide pH range. Several analytical measurements and density functional theory calculations revealed that the pyridinic N-ligated Fe single atom (Fe-pyridine N₄) was involved in the production of ¹O₂ by the binding of two PMS ions, resulting in an excellent catalytic performance for PMS adsorption/activation. This work has the potential to not only improve the understanding of nonradical reaction pathway but to also provide a generalizable method for producing highly stable PMS activators with high activity for practical wastewater treatment.

Photochemical reaction of superoxide radicals with 1-naphthol

The photochemical reactions between 1-naphthol (1-NP) and the superoxide anion radical (O2•–) were investigated in detail by using 365 nm UV irradiation. The results showed that the conversion rate of 1-NP decreased with the increase of the initial concentration of 1-NP, whereas by increasing the pH and riboflavin concentration, the photochemical reaction was accelerated. The second-order reaction rate constant was estimated to be (3.64 ± 0.17) × 108 L mol−1 s−1. The major photolysis products identified by using gas chromatography – mass spectrometry (GC–MS) were 1,4-naphquinone and 2,3-epoxyresin-2,3-dihydro-1,4-naphquinone, and their reaction pathways were also discussed. An atmospheric model showed that both the bulk water reaction and the heterogeneous surface reaction deserve attention in atmospheric aqueous chemistry.

Enhanced activation of persulfate by Fe(III) and catechin without light: Reaction kinetics, parameters and mechanism

An environmental-friendly plant polyphenol, catechin (CAT), was applied in Fe(III) activated persulfate (PS) system for naproxen (NPX) degradation in this research. Reaction kinetics, parameters, NPX degradation products and reaction mechanism were investigated. Combining the results of quenching experiments as well as Electron Spin Resonance (ESR), it was observed that SO₄^•- was critical in NPX degradation, and the contribution of HO^• was minor in the Fe(III)/CAT/PS system. O₂^•- was generated during the reaction but did not contribute to NPX degradation. SO₄^•- and HO^• were produced from the PS activation by Fe(II), which was formed from the transient complexing and reduction process between Fe(III) and CAT. The effects of Fe(III), CAT, PS concentration and pH value on NPX degradation were evaluated. Moreover, the mineralization rate was 20.2%, and the toxicity of the treated solution were lower than the initial solution. Nine possible intermediates were determined when using LC-QTOF-MS to analyze, and three degradation pathways were put ward. The results proved that CAT could accelerate the redox cycle of Fe(III)/Fe(II), consequently to strengthen PS activation without light. It was a promising oxidation technology as it offered an energy-saving and hypo-toxic way for refractory organic pollutants treatment, and it was applicable at a comparatively wide pH range.

Iodometric spectrophotometric determination of peroxydisulfate in hydroxylamine-involved AOPs: 15 min or 15 s for oxidative coloration?

In this study, iodometric spectrophotometry, the most-used method for detecting peroxydisulfate (PDS), was modified by increasing the concentration of potassium iodide (KI) for realizing the immediate PDS determination and avoiding the interference of hydroxylamine. Kinetic studies showed that the reaction between PDS and I^- to generate the yellow-colored I₃^- followed the kinetic equation as [Formula: see text] . Detection time of the iodometric spectrophotometry was shortened from 15 min to 15 s when KI concentration was increased from 0.6 M to 4.8 M. Different with the previous iodometric spectrophotometry, the modified method using 4.8 M KI as the indicator was well tolerable to the interference of hydroxylamine at acidic pH conditions. The calibration curve of the modified method showed a well linear relationship (R² = 0.999) between the absorbance of I₃^- at 352 nm and PDS concentration in the range of 0-80 μM. The modified method was highly sensitive with the absorptivity of 2.5 × 10⁴ M^-1 cm^-1 and the limit of detection of 0.11 μM. Moreover, the modified method was successfully applied for monitoring the change of PDS concentration during the degradation of diclofenac with four different PDS-based AOPs, the calculated reaction stoichiometric efficiency (RSE(%)=DiclofenacdegradedPDSconsumed×100%) followed the order as heat/PDS system > hydroxylamine/Fe²⁺/PDS system > hydroxylamine/Cu²⁺/PDS system > Fe²⁺/PDS system.

Enhancement of Iron-Based Photo-Driven Processes by the Presence of Catechol Moieties

Photo-induced Advanced Oxidation Processes (AOPs) using H2O2 or S2O82− as radical precursors were assessed for the abatement of six different contaminants of emerging concern (CECs). In order to increase the efficiency of these AOPs at a wider pH range, the catechol organic functional compound was studied as a potential assistant in photo-driven iron-based processes. Different salinity regimes were also studied (in terms of Cl− concentration), namely low salt water (1 g·L−1) or a salt–water (30 g·L−1) matrix. Results obtained revealed that the presence of catechol could efficiently assist the photo-Fenton system and partly promote the photo-induced S2O82− system, which was highly dependent on salinity. Regarding the behavior of individual CECs, the photo-Fenton reaction was able to enhance the degradation of all six CECs, meanwhile the S2O82−-based process showed a moderate enhancement for acetaminophen, amoxicillin or clofibric acid. Finally, a response-surface methodology was employed to determine the effect of pH and catechol concentration on the different photo-driven processes. Catechol was removed during the degradation process. According to the results obtained, the presence of catechol in organic macromolecules can bring some advantages in water treatment for either freshwater (wastewater) or seawater (maritime or aquaculture industry).

Activation of persulfate and removal of ethyl-parathion from soil: Effect of microwave irradiation

Advanced persulfate oxidation technology is widely used in organic pollution control of super fund sites. In recent years, microwave radiation has been proven a promising method for persulfate activation. However, most of the prior works were focused on the treatment of polluted water, but there are few reports aiming at contaminated sites, especially the knowledge of using microwave activated persulfate technology to repair pesticide-contaminated sites. In this study, an effective activation/oxidation method for the remediation of pesticide-contaminated soil, i.e., microwave/persulfate, was developed to treat soil containing ethyl-parathion. The concentration of persulfate, reaction temperature, and time were optimised. The results showed that up to 77.32% of ethyl-parathion was removed with the addition of 0.1 mmol·persulfate·g^-1 soil under the microwave temperature of 60 °C. In comparison, 19.43% of ethyl-parathion was removed at the same reaction temperature under the condition of water bath activated persulfate. Electron paramagnetic resonance (EPR) spectroscopy combined with spin-trapping technology was used to detect reactive oxidation species, and OH and SO₄^- were observed in the microwave/persulfate system. Quenching experiments suggested that ethyl-parathion was degraded by the generated OH and SO₄^-. Paraoxon, phenylphosphoric acid, 4-nitrophenol, dimethyl ester phosphate, and some alkanes were the dominant oxidative products identified by gas chromatography-mass spectrometry (GC-MS) analysis. A possible pathway for ethyl-parathion degradation was proposed in this study. The results obtained serve as the guidance to the development of remediation technologies involving persulfate and microwave for soil contaminated by organic contaminants such as pesticides.