Degradation of the earthy and musty odorant 2,4,6-tricholoroanisole by persulfate activated with iron of different valences

Degradation of odorous 2,4,6-trichloroanisole in chlorinated water by UV-LED/chlorination: kinetics and influence factors

2,4,6-Trichloroanisole (2,4,6-TCA) has aroused a special concern for their odor problem and potential threats. In this study, the degradation of 2,4,6-TCA by UV/chlorination with different UV sources was compared, including low-pressure mercury lamp (LPUV, 254 nm) and ultraviolet light-emitting diode (UV-LED, 275 and 285 nm). The maximum removal of 2,4,6-TCA can be achieved by 275-nm UV-LED/chlorination in neutral and alkaline conditions which was 80.0%. The reaction, kinetics, and water matrix parameters on 2,4,6-TCA degradation were also evaluated. During UV-LED (275 nm)/chlorination, 2,4,6-TCA degradation was mainly caused by direct UV photolysis and indirect hydroxyl radical (HO·) oxidation, while reactive chlorine radicals (RCSs) had a negligible contribution. The second-order rate constant between HO· and 2,4,6-TCA was determined as 3.1 × 10⁹ M^-1 s^-1. Increasing initial chlorine dosage and decreasing 2,4,6-TCA concentration or pH value significantly promoted 2,4,6-TCA degradation during UV/chlorination process. The presence of natural organic matter (NOM) and bicarbonate (HCO₃^-) can inhibit 2,4,6-TCA degradation, while chloride ion (Cl^-) had a negligible effect. The kinetic model for 2,4,6-TCA degradation was established and validated, and the degradation pathways were proposed based on the identified intermediates. Furthermore, UV-LED (275 nm)/chlorination also exhibited a promising effect on 2,4,6-TCA removal in real water, which can be used to control 2,4,6-TCA pollution and odor problems.

Review of Advanced Oxidation Processes Based on Peracetic Acid for Organic Pollutants

In recent years, the removal of organic pollutants from water and wastewater has attracted more attention to different advanced oxidation processes (AOPs). There has been increasing interest in using peroxyacetic acid (PAA), an emerging oxidant with low or no toxic by-products, yet the promotion and application are limited by unclear activation mechanisms and complex preparation processes. This paper synthesized the related research results reported on the removal of organic pollutants by PAA-based AOPs. Based on the research of others, this paper not only introduced the preparation method and characteristics of PAA but also summarized the mechanism and reactivity of PAA activated by the free radical pathway and discussed the main influencing factors. Furthermore, the principle and application of the newly discovered methods of non-radical activation of PAA in recent years were also reviewed for the first time. Finally, the shortcomings and development of PAA-based AOPs were discussed and prospected. This review provides a reference for the development of activated PAA technology that can be practically applied to the treatment of organic pollutants in water.

Iron-based persulfate activation process for environmental decontamination in water and soil

Sulfate radical based advanced oxidation processes have been extensively studied for the degradation of environmental contaminants. Iron-based materials such as ferrous, ferric, ZVI, iron oxides, sulfides etc., and various natural iron minerals have been explored for activating persulfate to generate sulfate radicals. In this review, an overview of different iron activated persulfate systems and their application in the removal of organic pollutants and metals in water and soil are summarised. The chemistry behind the activation of persulfate by homogenous and heterogeneous iron-based materials with/without the assistance of electrochemical techniques are also discussed. Besides, the soil decontamination by iron persulfate system and a brief discussion on the ability of the persulfate system to reduce metals presence in wastewater are also summarised. Finally, future research prospects, believed to be useful for all researchers in this field, based on up to date research progress is also given.

Complexation of humic acid with Fe ions upon persulfate/ferrous oxidation: Further insight from spectral analysis

The complexation of humic acid (HA) with dissolved Fe ions is beneficial to 2,4-dinitrotoluene degradation by PS/Fe²⁺, while the mechanism on HA binding with Fe ions is still unclear and warrants further exploration. In this study, the binding characteristics of HA with Fe ions and structural variations of HA during the complexation with Fe ions were investigated. Synchronous fluorescence analysis showed that the complexation ability of HA with Fe species at acid (pH = 5.0) and neutral condition (pH = 7.0) is higher than that of alkaline condition (pH = 9.0 and 11.0). Different components in HA including humic-like fraction (C1), fulvic-like fraction (C2), protein-like fraction (C3), and microbial-derived humic-like fraction (C4) were identified by excitation emission matrix-parallel factor analysis (EEM-PARAFAC). The complexation ability of C1, C2, and C4 with Fe species is higher than that of C3, and C1 and C4 primarily contributed to the complexation of HA with Fe species. Moreover, the sequence of HA structural variation during the complexation with Fe species was elucidated by Fourier transform infrared spectroscopy coupled with two-dimensional correlation spectroscopy analysis (2D FTIR COS), and could be concluded as follows: ester→ quinoid rings→ aromatic groups→ aliphatic groups→ phenolic groups.

Significant acceleration of Fe2+/ peroxydisulfate oxidation towards sulfisoxazole by addition of MoS2

Activation of peroxydisulfate (PDS) by Fe²⁺ has been considered as an effective activation method to generate reactive oxygen species (ROS). However, the process is limited for the low production yield of ROS owing to the inefficient Fe³⁺/Fe²⁺ cycle. Herein, we demonstrated that Fe²⁺/PDS system in the presence of molybdenum sulfide (MoS₂) was significantly efficient for the degradation of sulfisoxazole (SIX). As a co-catalyst in the Fe²⁺/PDS system, MoS₂ could greatly enhance the Fe³⁺/Fe²⁺ cycle by the exposed Mo⁴⁺ active sites, which could also improve the PDS decomposition efficiency. As a result, the degradation efficiency of SIX in the MoS₂/Fe²⁺/PDS system could reach to as high as 97.1% within 40 min, which was in distinct comparison with the 45.5% achieved by Fe²⁺/PDS system without MoS₂. Besides, effects of various reaction conditions on SIX degradation were also evaluated during the experiments, including the dosages of MoS₂, Fe²⁺, PDS and initial solution pH and the coexisting inorganic anions. In addition, both of sulfate radicals and hydroxyl radicals were identified as the dominant active species for SIX degradation by the radical scavenging experiments and verified by electron paramagnetic resonance (EPR). This study provides a promising idea for the degradation of organic contaminants in water treatment based on Fe²⁺/PDS process.

Activated persulfate by iron-based materials used for refractory organics degradation: a review

Recently, the advanced oxidation processes (AOPs) based on sulfate radicals (SRs) for organics degradation have become the focus of water treatment research as the oxidation ability of SRs are higher than that of hydroxyl radicals (HRs). Since the AOP-SRs can effectively mineralize organics into carbon dioxide and water under the optimized operating conditions, they are used in the degradation of refractory organics such as dyes, pesticides, pharmaceuticals, and industrial additives. SRs can be produced by activating persulfate (PS) with ultraviolet, heat, ultrasound, microwave, transition metals, and carbon. The activation of PS in iron-based transition metals is widely studied because iron is an environmentally friendly and inexpensive material. This article reviews the mechanism and application of several iron-based materials, including ferrous iron (Fe²⁺), ferric iron (Fe³⁺), zero-valent iron (Fe⁰), nano-sized zero-valent iron (nFe⁰), materials-supported nFe⁰, and iron-containing compounds for PS activation to degrade refractory organics. In addition, the current challenges and perspectives of the practical application of PS activated by iron-based systems in wastewater treatment are analyzed and prospected.

Sunflower stalk-derived biochar enhanced thermal activation of persulfate for high efficient oxidation of p-nitrophenol

Sunflower stalk-derived biochars (BC) were prepared at various temperatures (i.e., 500, 650, and 1000 °C) and demonstrated as a highly efficient catalyst in persulfate (PS) activation for the oxidation of p-nitrophenol (PNP) at 60 °C. The apparent PNP oxidation rate constant in the BC500 (0.1543 L mol^-1 S^-1), BC650 (0.6062 L mol^-1 S^-1), or BC1000 (2.1379 L mol^-1 S^-1) containing PS system was about 2, 8 and 28 times higher than that in PS/PNP (0.0751 L mol^-1 S^-1) system, respectively. The effect of reaction temperature on PNP oxidation was also investigated. Furthermore, the radical quenching tests and electron paramagnetic resonance spectroscopy (EPR) were employed to investigate the sulfate and hydroxyl radicals for PNP oxidation. The Raman results suggested that the defective sites on biochars possess vital role for oxidation of PNP in PS system. The possible activation pathway of PS/BC was proposed that the defective sites on BC were involved for weakening the O-O bond in PS and subsequently cleaving O-O bond by heat to generate sulfate radical. The oxidation of PNP at low concentration (below 100 μg L^-1) was completely removed in urban wastewater by PS/BC system within 30 min. This work would provide new insights into PS activation by BC catalyst and afford a promising method for organic pollutant removal in high-temperature wastewater.

Highly Efficient Utilization of Nano-Fe(0) Embedded in Mesoporous Carbon for Activation of Peroxydisulfate

Nanoscale zerovalent iron (nZVI) particles have received much attention in environmental science and technology due to their unique electronic and chemical properties. However, the aggregation and oxidation of nZVI brings much difficulty in practical application of environmental remediation. In this study, we reported a composite nano-Fe(0)/mesoporous carbon by a chelation-assisted coassembly and carbothermal reduction strategy. Nano-Fe(0) particles with surface iron oxide (Fe₂O₃·FeO) were wrapped with graphitic layers which were uniformly dispersed in mesoporous carbon frameworks. The unique structure made the nano-Fe(0) particles stable in air for more than 20 days. It was used as a peroxydisulfate (PDS) activator for the oxidation treatment of 2,4,6-trichlorophenol (TCP). The TOF value of MCFe for TCP degradation is nearly 3 times higher than those of FeSO₄ and Fe₂O₃·FeO and nearly 2 times than that of commercial nZVI. The reactive oxygen species (ROS) including •SO₄^-, HO•, and •O₂^-, ¹O₂ are efficiently generated by PDS activation with MCFe. The PDS activation process by nano-Fe(0) particles was intrinsically induced by the ferrous ions (Fe(II)) continuously generated at the solid/aqueous interface. Namely, the nano-Fe(0) particles were highly efficiently utilized in sulfate radical-based advanced oxidation processes (SR-AOP). The porous structure also assists the absorption and transfer of TCP during the degradation process.

Preparation and application of magnetic nitrogen-doped rGO for persulfate activation

A heterogeneous catalyst (M-N-rGO) composed of stability enhanced magnetic iron oxide nanoparticles and nitrogen-doped reduced graphene oxide was synthesized and characterized by SEM, XRD, BET, and XPS. It showed excellent catalytic degradation properties in advanced oxidation technology. In the presence of 200 mg/L catalyst and 135 mg/L persulfate at pH 5, 95% of 10-20 mg/L methylene blue could be degraded in 90 min with the TOC removal efficiency of 50%. The rate constant based on pseudo-first-order kinetics ranged from 0.0227 to 0.0488/min in the temperature range of 15 to 32 °C, and the activation energy was 32.5 kJ/mol. Under the optimal operation conditions, 20 mg/L of 2,4-dichlorophneol (2,4-DCP) could be removed almost completely. EPR analysis showed that sulfate and hydroxyl radicals were responsible for degradation of pollutants, and radical quenching experiments indicated that nonradical pathway also played a role in pollutant removal. And a mechanism for M-N-rGO and persulfate system was elucidated. This catalyst was easy for preparation, low-cost, highly effective, convenient for separation, and could be used effectively for four times through 0.1 mol/L H₂SO₄ regeneration. It provided a choice for wastewater treatment in practice.