UV-LEDs assisted peroxymonosulfate/Fe2+ for oxidative removal of carmoisine: The effect of chloride ion

LED-irradiated photo-Fenton process on pollutant removal: outcomes, trends, and limitations

This manuscript critically reviews the state of the art on the application of photo-Fenton processes irradiated by light-emitting diode arrays (LED) with a focus on the removal of contaminants of emerging concern (CEC) from aqueous matrices. LEDs are clean, low-cost radiation sources with longer lifespan compared to mercury lamps. This study covers the influence of LED sources, wavelengths, and dose upon CEC removal, and the potential for disinfection, abatement of antibiotic-resistant bacteria (ARB), and genes (ARG). The bibliographic search was performed in Scopus database using keyword combinations and resulted in a portfolio containing 52 relevant articles published between 2010-2023. According to reviewed papers, LED photoreactor design has evolved in the past decade aiming to improve CEC degradation in aqueous matrices while reducing construction and operation costs, and energy consumption. Among several reactors (annular, fluidized bed, parallel plate, wireless, pathway systems, and microreactor) surveyed for their performance and scalability, LED chips and strips are particularly suitable for application due to their wide emission angle (≈120°) and small size (mm2), which allow for, respectively, efficient illumination coverage and flexible arrangement and design. LED microreactors are very efficient in the degradation of contaminants and scalable with reduced area requirements. Although most studies were performed in synthetic solutions and at laboratory scale, the externally LED irradiated cylindrical reactor was successful for application in full-scale municipal water treatment plants. Future studies should focus on evaluating CEC removal in wastewater using scalable devices for continuous operation of solar photo-Fenton at night.

The performance of a visible light-responsive material Fe3O4/Bi2WO6 cooperating with peroxymonosulfate to degrade bisphenol A

In this study, the visible light-responsive catalysts Fe3O4/Bi2WO6 were prepared and characterized by BET, SEM, EDS, XRD, XPS, and MPMS. The performances of five catalysts (0.05 Fe/Bi, 0.13 Fe/Bi, 0.17 Fe/Bi, 0.21 Fe/Bi, and 0.30 Fe/Bi) for photocatalytic degradation of bisphenol A under visible light (300-W Xe lamp) were compared. Among five catalysts, 0.17 Fe/Bi (the molar ratio of Fe3O4 to Bi2WO6 was 0.17) acquired the highest BPA photocatalytic removal of 90.2% at 120 min. With the synergistic effect between Vis/0.17 Fe/Bi and peroxymonosulfate (PMS), the BPA removal obtained was as high as 100% at 90 min ([BPA] = 100 mg/L, [0.17 Fe/Bi] = 1.25 g/L, [PMS] = 2.0 g/L, and T = 25 °C). After five times reused of 0.17 Fe/Bi, its removal of BPA dropped by 13.4% in presence of PMS, which demonstrated 0.17 Fe/Bi possessed relatively stable performance. High BPA degradation was attributed to the attacking effects of various oxide species (SO4•-, •OH, h+, O2•-) generated in the Fe3O4/Bi2WO6/PMS system under the cooperation of photocatalyst Fe3O4/Bi2WO6 and oxidizing agent PMS.

Sono-enhanced heterogeneous Fenton catalysis: magnetic halloysite nanotube synthesis and accelerated free radical generation

Although heterogeneous Fenton catalysis has captured increasing attention compared to its homogeneous counterpart, it still confronts some inherent drawbacks in use, such as the dilemma in solid-liquid separation and greater mass transfer resistance. Driven by the acoustic cavitation effect, herein, a sono-enhanced heterogeneous Fenton catalysis process was built to overcome the above two shortcomings, by rapidly synthesizing magnetic Fenton-like catalysts and accelerating electron transfer during the catalytic reaction. The results show that, compared to the traditional chemical coprecipitation method, Fe3O4 with smaller particle size and better crystallinity grew on the surface of halloysite nanotubes (HNTs) by using the sonochemical strategy, leading to displaying the higher catalytic activity toward the degradation of methylene blue (MB, improved by ~2.5 times). In parallel, more •OH and •O2- were produced after the ultrasound was further introduced to the routine Fenton-like catalysis system, thus highly accelerating the removal of MB (improved by ~50%). Besides, benefiting from the robust chemical integration of Fe3O4 and HNTs, Fe3O4@HNTs-S had a lower iron ion leaching in use, showing superior catalytic stability. The speed, simplicity, and generality, together with the enhanced mass transfer rate, make the use of ultrasound an enabling methodology to improve the heterogeneous Fenton catalysis.

A novel iron molybdate photocatalyst with heterojunction-like band gap structure for organic pollutant degradation by activation of persulfate under simulated sunlight irradiation

Advanced oxidation processes (AOPs) applied to wastewater treatment have become increasingly well developed and the ability of a single technology to remove difficult organic pollutants is limited. One of the main limiting factors is the insufficient variety and quantity of active species generated during the reaction process and catalyst failure. The coupling of the two methods is a practical and effective approach. In this study, different types of semiconductor persulfate (PS) activators, iron molybdate nanoparticles (I-FeMoO₄, II-FeMoO₄, and III-FeMoO₄), were synthesized by simple solvothermal and calcination methods and applied to photo-assisted activation of PS systems. In addition, the relationship between the intrinsic physicochemical and optoelectronic properties of FeMoO₄ and the catalytic degradation performance was revealed by a series of characterization tools, and the dominant catalysts were screened. At an unadjusted pH of 4.86, 0.6 g L^-1 of PS and 0.4 g L^-1 of I-FeMoO₄ could achieve efficient degradation of several difficult organic dye contaminants (rhodamine b (Rh B), methylene blue (MB), malachite green (MG), methyl orange (MO), and tartrazine (TTZ)) and other antibiotic contaminants (sulfamethoxazole (SMX), tetracycline (TC), norfloxacin (NOR), and carbamazepine (CBZ)) within 5-60 min. Possible degradation mechanisms in the I-FeMoO₄/PS/Light reaction system were suggested by radical trapping experiments and electron paramagnetic resonance (EPR) tests. Recovery tests demonstrated that I-FeMoO₄ has good recoverable stability and did not cause secondary pollution. Finally, our study provided a new perspective on the application of coupled wastewater treatment technologies in the practical treatment of organic wastewater.

Effect of metal doping (Me = Zn, Cu, Co, Mn) on the performance of bismuth ferrite as peroxymonosulfate activator for ciprofloxacin removal

In this study, a facile hydrothermal method was employed to prepare Me-doped Bi₂Fe₄O₉ (Me = Zn, Cu, Co, and Mn) as peroxymonosulfate (PMS) activator for ciprofloxacin (CIP) degradation. The characteristics of the Me-doped bismuth ferrites were investigated using various characterization instruments including SEM, TEM, FTIR and porosimeter indicating that the Me-doped Bi₂Fe₄O₉ with nanosheet-like square orthorhombic structure was successfully obtained. The catalytic activity of various Me-doped Bi₂Fe₄O₉ was compared and the results indicated that the Cu-doped Bi₂Fe₄O₉ at 0.08 wt.% (denoted as BFCuO-0.08) possessed the greatest catalytic activity (k_app = 0.085 min^-1) over other Me-doped Bi₂Fe₄O₉ under the same condition. The synergistic interaction between Cu, Fe and oxygen vacancies are the key factors which enhanced the performance of Me-doped Bi₂Fe₄O₉. The effects of catalyst loading, PMS dosage, and pH on CIP degradation were also investigated indicating that the performance increased with increasing catalyst loading, PMS dosage, and pH. Meanwhile, the dominant reactive oxygen species was identified using the chemical scavengers with SO₄^•-, ^•OH, and ¹O₂ playing a major role in CIP degradation. The performance of BFCuO-0.08 deteriorated in real water matrix (tap water, river water and secondary effluent) due to the presence of various water matrix species. Nevertheless, the BFCuO-0.08 catalyst possessed remarkable stability and can be reused for at least four successive cycles with >70% of CIP degradation efficiency indicating that it is a promising catalyst for antibiotics removal.

Fate of typical organic halogen compounds in the coexistence of endogenic chlorine atoms and exogenic X. CHEMOSPHERE 2022;309:136761. [PMID: 36220428 DOI: 10.1016/j.chemosphere.2022.136761]

The transformation of halogenated organics in advanced oxidation processes (AOPs) has been extensively investigated. However, we currently know little about the fate of halogenated pollutants in the presence of exogenic halides (Cl^- or Br^-). Herein, the degradability, mineralization rate, and accumulation capacity of adsorbable organic halogen (AOX) for chlorophenols (2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophenol (4-CP), and 2,4,6-trichlorophenol (TCP)) were compared in the Fe²⁺/persulfate (PS) process with the addition of exogenic halides. Results indicate that exogenic X^- can lead to a decrease in chlorophenols degradation and mineralization rate, undesirable accumulation of AOX, and generation of halogenated by-products which are more toxic than precursor chlorophenols. Results of kinetics modeling show that Cl₂^•- plays more important role than SO₄^•- with an addition of Cl^-, while SO₄^•-, Br₂^•-, and Br₂ are responsible for the effect of Br^-. As well, the effect of endogenic chlorine atoms on chlorophenols reveals that the degradability and AOX formation potential of 3-CP are highest while that of TCP are the lowest. This study demonstrates the significant influence of endogenic chlorine atoms and exogenic X^- on the fate of typical organic halogen compounds. Consequently, the X^- level and position/number of halogen atoms should be considered simultaneously when treating organohalogen compounds.

Synthesis of Bimetallic FeCu-MOF and Its Performance as Catalyst of Peroxymonosulfate for Degradation of Methylene Blue

Bimetallic MOFs have recently emerged as promising materials for wastewater treatment based on advanced oxidation processes. Herein, a new bimetallic MOF (FeCu-MOF) was fabricated by hydrothermal process. The structural, morphological, compositional and physicochemical properties of the as-synthesized bimetallic FeCu-MOF were characterized by XRD, FT-IR, SEM, TEM, BET, and XPS. TEM and XPS confirmed the homogeneous distribution of CuO₂ nanoparticles in the as-synthesized materials. The result of wastewater treatment indicated that 100% of MB was removed by 6.0 mM PMS activated with 0.6 g/L of FeCu-MOF in 30 min. The high catalytic performance of FeCu-MOF was probably due to the accelerated electron and mass transfer resulting from the existence of a homogeneous distribution of unsaturated metal sites and an abundant mesoporous structure. The obtained results from the competitive quenching tests demonstrated that sulfate radicals (SO₄^•-) were the major species responsible for MB oxidation. In addition, hydroxyl (·OH) and singlet oxygen (¹O₂) also had a nonnegligible role in the MB removal. Interestingly, the addition of acetate ion (CHCOO^-) promoted the removal of MB while other anions (including NO₂^-, H₂PO₄^-, SO₄^2-, HPO₄^2-, and HCO₃^-) inhibited the MB removal. Furthermore, a possible mechanism based on both heterogeneous and homogeneous activation of PMS was proposed, along with the MB degradation mechanism.

Nanomaterials photocatalytic activities for waste water treatment: a review

Water is necessary for the survival of life on Earth. A wide range of pollutants has contaminated water resources in the last few decades. The presence of contaminants incredibly different dyes in waste, potable, and surface water is hazardous to environmental and human health. Different types of dyes are the principal contaminants in water that need sudden attention because of their widespread domestic and industrial use. The toxic effects of these dyes and their ability to resist traditional water treatment procedures have inspired the researcher to develop an eco-friendly method that could effectively and efficiently degrade these toxic contaminants. Here, in this review, we explored the effective and economical methods of metal-based nanomaterials photocatalytic degradation for successfully removing dyes from wastewater. This study provides a tool for protecting the environment and human health. In addition, the insights into the transformation of solar energy for photocatalytic reduction of toxic metal ions and photocatalytic degradation of dyes contaminated wastewater will open a gate for water treatment research. The mechanism of photocatalytic degradation and the parameters that affect the photocatalytic activities of various photocatalysts have also been reported.

Degradation of Antibiotics via UV-Activated Peroxodisulfate or Peroxymonosulfate: A Review

The ultraviolet (UV)/H2O2, UV/O3, UV/peroxodisulfate (PDS) and UV/peroxymonosulfate (PMS) methods are called UV-based advanced oxidation processes. In the UV/H2O2 and UV/O3 processes, the free radicals generated are hydroxyl radicals (•OH), while in the UV/PDS and UV/PMS processes, sulfate radicals (SO4•−) predominate, accompanied by •OH. SO4•− are considered to be more advantageous than •OH in degrading organic substances, so the researches on activation of PDS and PMS have become a hot spot in recent years. Especially the utilization of UV-activated PDS and PMS in removing antibiotics in water has received much attention. Some influencing factors and mechanisms are constantly investigated and discussed in the UV/PDS and UV/PMS systems toward antibiotics degradation. However, a systematic review about UV/PDS and UV/PMS in eliminating antibiotics is lacking up to now. Therefore, this review is intended to present the properties of UV sources, antibiotics, and PDS (PMS), to discuss the application of UV/PDS (PMS) in degrading antibiotics from the aspects of effect, influencing factors and mechanism, and to analyze and propose future research directions.

Persulfate activation by ferrocene-based metal-organic framework microspheres for efficient oxidation of orange acid 7

Ferrocene-based metal-organic framework with different transition metals (M-Fc-MOFs, M = Fe, Mn, Co) was synthesized by a simple hydrothermal method and used as a heterogeneous catalyst for persulfate activation. The samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray electron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Meanwhile, the influences of factors such as catalyst dosage, persulfate concentration, and pH on the degradation of acid orange 7 (AO7) were studied in detail. The results showed that hollow cobalt-based ferrocenyl metal-organic framework microspheres (Co-Fc-MOFs) exhibited the best catalytic performance, which is closely related to the synergy of Fc/Fc⁺ and Co(II)/Co(III) cycles in persulfate activation. Free radical quenching studies indicated that both sulfate and hydroxyl appeared to contribute to the degradation of AO7.

Efficient degradation of Rhodamine B by magnetically recoverable Fe3O4-modified ternary CoFeCu-layered double hydroxides via activating peroxymonosulfate

Environment-friendly nano-catalysts capable of activating peroxymonosulfate (PMS) have received increasing attention recently. Nevertheless, traditional nano-catalysts are generally well dispersed and difficult to be separated from reaction system, so it is particularly important to develop nano-catalysts with both good catalytic activity and excellent recycling efficiency. In this work, magnetically recoverable Fe₃O₄-modified ternary CoFeCu-layered double hydroxides (Fe₃O₄/CoFeCu-LDHs) was prepared by a simple co-precipitation method and initially applied to activate PMS for the degradation of Rhodamine B (RhB). X-ray diffraction (XRD), fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller method (BET), and vibrating sample magnetometer (VSM) were applied to characterize morphology, structure, specific surface area and magnetism. In addition, the effects of several key parameters were evaluated. The Fe₃O₄/CoFeCu-LDHs exhibited high catalytic activity, and RhB degradation efficiency could reach 100% within 20 min by adding 0.2 g/L of catalyst and 1 mmol/L of PMS into 50 mg/L of RhB solution under a wide pH condition (3.0-7.0). Notably, the Fe₃O₄/CoFeCu-LDHs showed good super-paramagnetism and excellent stability, which could be effectively and quickly recovered under magnetic condition, and the degradation efficiency after ten cycles could still maintain 98.95%. Both radicals quenching tests and electron spin resonance (ESR) identified both HO• and SO₄^•- were involved and SO₄^•- played a dominant role on the RhB degradation. Finally, the chemical states of the sample's surface elements were measured by X-ray photoelectron spectroscopy (XPS), and the possible activation mechanism in Fe₃O₄/CoFeCu-LDHs/PMS system was proposed according to comprehensive analysis.

Accelerated organics degradation by peroxymonosulfate activated with biochar co-doped with nitrogen and sulfur

Engineered biochar is increasingly regarded as a cost-effective and eco-friendly peroxymonosulfate (PMS) activator. Herein, biochar doped with nitrogen and sulfur moieties was prepared by pyrolysis of wood shavings and doping precursor. The doping precursor consists of either urea, thiourea or 1:1 w/w mixture of urea and thiourea (denoted as NSB-U, NSB-T and NSB-UT, respectively). The physicochemical properties of the NSBs were extensively characterized, revealing that they are of noncrystalline carbon with porous structure. The NSBs were employed as PMS activator to degrade organic pollutants particularly methylene blue (MB). It was found that NSB-UT exhibited higher MB removal rate with k_app = 0.202 min^-1 due to its relatively high surface area and favorable intrinsic surface moieties (combination of graphitic N and thiophenic S). The effects of catalyst loading, PMS dosage and initial pH were evaluated. Positive enhancement of the MB removal rate can be obtained by carefully increasing the catalyst loading or PMS dosage. Meanwhile, the MB removal rate is greatly influenced by pH due to electrostatic interactions and pH dependent reactions. The NSB-UT can be reused for several cycles to some extent and its catalytic activity can be restored by thermal treatment. Based on the radical scavenger study and XPS analysis, the nonradical pathway facilitated by the graphitic N and thiophenic S active sites are revealed to be the dominant reaction pathway. Overall, the results of this study show that engineered biochar derived from locally available biowaste can be transformed into PMS activator for environmental applications.

Microwave photo-oxidation with diverse oxidants for Congo red degradation: effect of oxidants, degradation pathway and economic analysis

The present study investigated the efficacy of microwave photo-oxidation (MWPO) process with two oxidants i.e. persulphate (PS) and hydrogen peroxide (H₂O₂) for degradation of Congo red (CR). The result indicated a CR degradation efficiency of 98% and 96.8% with PS and H₂O₂, respectively, in 30 min of reaction with corresponding PS dosage of 50 mg/L and H₂O₂ dosage of 180 mg/L. The COD removal efficiency with the two oxidants were 97.7% and 94.9%, respectively. Higher dosages of oxidant and CR reduced the efficiency of the process in both the cases due to self-quenching. Effect of pH and initial CR concentration on CR removal efficiency also has been studied. Degradation of CR followed pseudo-first-order kinetics with a removal rate constant of 0.12/min and 0.09/min, respectively, with PS and H₂O₂. The main mechanism of CR degradation was cleavage of the benzene-benzene bond, cleavage of benzene-N bond and hydroxylation. Economic analysis of the MWPO process indicated an energy consumption of 18.3 kWh/g of CR removal and 18.4 kWh/g of COD removal. The process was effective in the rapid degradation and mineralization of high concentration of CR within 30 min.

Performance of UV/acetylacetone process for saline dye wastewater treatment: Kinetics and mechanism

Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has stimulated the quest for novel "halotolerant" chemical oxidation technology. Acetylacetone (AA) has proven to be a potent photo-activator in the degradation of dyes, but the applicability of UV/AA for saline wastewater treatment needs to be verified. In this study, degradation of crystal violet (CV) was investigated in the UV/AA system in the presence of various concentrations of exogenic Cl^- or Br^-. The results reveal that degradation, mineralization and even accumulation of adsorbable organic halides (AOX) were not significantly affected by the addition of Cl^- or Br^-. Rates of CV degradation were enhanced by elevating either AA dosage or solution acidity. An apparent kinetic rate equation was developed as r = -d[CV]/dt = k[CV]^a[AA]^b = (7.34 × 10^-4 mM^1-(a+b) min^-1) × [CV]^a=0.16 [AA]^b=0.97. In terms of results of radical quenching experiments, direct electron/energy transfer is considered as the major reaction mechanism, while either singlet oxygen or triplet state (³(AA)*) might be involved. Based on identification of degradation byproducts, a possible degradation pathway of CV in the UV/AA system is proposed.

One-step synthesis of Mn-doped MIL-53(Fe) for synergistically enhanced generation of sulfate radicals towards tetracycline degradation

Herein, Mn-doped MIL-53(Fe) were fabricated via one-pot solvothermal method and used for peroxymonosulfate (PMS) activation towards tetracycline (TC) degradation from aqueous solution. The characterizations of SEM, FTIR and XRD were utilized to reveal the morphology and structure of the materials. The results showed that Mn-MIL-53(Fe)-0.3 displayed the optimal catalytic performance, the removal efficiency of TC could reach 93.2%. Moreover, the catalytic activity of Mn-MIL-53(Fe) towards TC under different initial pH values, co-existing anions (Cl^-,CO₃^2- and SO₄^2-) and humic acid (HA) were investigated. The results of thermodynamic experiment suggested that the catalytic process was endothermic. In addition, integrated with capture experiments results and the characterization results of electron paramagnetic resonance (EPR), which revealed that SO₄^·- and HO^- were the reactive radicals involving in the reaction. More importantly, the possible activation mechanism was discussed in detail based on the X-ray photoelectron spectroscopy results. The active species were generated by the active sites of Fe(II) and Mn(II) on Mn-MIL-53(Fe) effectively activated PMS. Furthermore, the degradation intermediates and possible degradation pathway were investigated by LC-MS. Finally, the catalyst also showed good performance in actual wastewater and demonstrated good recyclability. The Mn-MIL-53(Fe)/PMS system exhibited a promising application prospect for antibiotic-containing waste water treatment.

Application of copper tailings combined with persulfate for better removing methyl orange from wastewater

In this paper, wasted copper tailings (CT) were used to activate persulfate (PS) to degrade azo dye methyl orange (MO). The results show that a large amount of FeS₂ contained in CT can slowly release Fe²⁺ in the aqueous solution to activate PS to generate reactive oxygen species to degrade MO. When the dosage of CT and PS was 2 g/L and 3 mM respectively, the MO degradation efficiency of 20 mg/L in the CT/PS system was 96.52% within 60 min. At the same time, it is found that CT has a certain adsorption capacity for MO, and the intra-particle diffusion model can well describe the adsorption process of MO by CT. The effects of related reaction parameters (CT dosage, PS dosage, initial MO concentration and solution pH) on MO degradation in CT/PS system were investigated. Compared with the direct addition of an equal amount of Fe²⁺ as in the CT/PS system, for homogeneous activated PS to degrade MO (Fe²⁺/PS), the results showed that the degradation efficiency of Fe²⁺/PS system for MO was lower than that of CT/PS system due to excessive Fe²⁺ consumption of SO₄ ^·-. By comparing the Fe²⁺ and Fe³⁺ concentrations in the two systems, it was found that the CT/PS system could maintain a low Fe²⁺ concentration during the reaction process, and the Fe²⁺ released by CT could be used by PS to degrade MO more efficiently. The free radical scavenging experiments showed that the reactive oxygen species in the CT/PS system was mainly SO₄ ^·-. This study not only proposed a new CT utilization approach, but also solved the problem of reduced degradation efficiency of organic pollutants caused by excessive Fe²⁺ in the Fenton-like reaction.

An efficient CuO-γFe2O3 composite activates persulfate for organic pollutants removal: Performance, advantages and mechanism

CuO-γFe₂O₃ was fabricated as a novel and effective persulfate (PS) catalyst to remove bio-refractory organic pollutants. Characterization results showed that CuO-γFe₂O₃ possessed a relatively large surface area among transition metal oxides which provided favorable adsorption and activation sites for PS to degrade pollutants. There was an obvious synergy between CuO and γFe₂O₃ in the composite, which played 84.7% role in Acid orange 7 (AO7) removal. Under the optimal conditions (CuO-γFe₂O₃ dosage = 0.6 g L^-1, PS dosage = 0.8 g L^-1, unadjusted solution pH), almost complete AO7 was rapidly eliminated in 5 min. Moreover, the wide workable pH range (2-13), good stability (0.82 mg L^-1 Cu leached, almost no Fe leached) and reusability (4 times) were the significant virtues of CuO-γFe₂O₃ for wastewater treatment. Besides, the reaction mechanism mainly based on the interaction among Cu(II/III) and Fe(II/III) species for sulfate radical (SO₄^-) generation was emphatically elucidated by the analyses of radicals, PS utilization, TOC removal and metal chemical states. Finally, CuO-γFe₂O₃+PS system displayed desirable removal of multiple organic pollutants with different molecular structures. In light of the prominent advantages of CuO-γFe₂O₃+PS, this work extended activated PS process in treating refractory organic wastewater.

Construction of Bi2O3/CuNiFe LDHs composite and its enhanced photocatalytic degradation of lomefloxacin with persulfate under simulated sunlight

Advanced oxidation methods based on photocatalysis and sulfate radicals have attached most interest towards contaminant degradation. However, there are a lack of coupling two methods in the field of pollutant degradation. In the present study, a new Bi₂O₃/CuNiFe LDHs composite was fabricated and it could efficiently activate persulfate (PS) for lomefloxacin (LOM) decomposition under simulated sunlight, in which 84.6% of LOM (10 mg·L^-1) was degraded over 40 min with 0.4 g·L^-1 of Bi₂O₃/CuNiFe LDHs composite and 0.74 mM of PS at natural pH. In addition, the Bi₂O₃/CuNiFe LDHs composite possessed good reusability and stability at least four runs. Moreover, active radical scavenging experiments indicated that hydroxyl radicals (HO·), sulfate radicals (SO₄·^-), superoxide radicals (O₂·^-) and hole (h⁺) were the main radicals under LOM degradation process. Subsequently, the possible degradation intermediates were determined and the decomposition pathways were put forward. At the same time, activated sludge inhibition experiments were performed to assess the variation of toxicity of LOM and its degradation intermediates during oxidation. Finally, possible reaction mechanism of Bi₂O₃/CuNiFe LDHs composite for PS activation under simulated sunlight was proposed.

Sustainable synthesis of modulated Fe-MOFs with enhanced catalyst performance for persulfate to degrade organic pollutants

In this study, four typical modulators (NH₄OH(A), CH₃COOH(B), CH₃COONa(C) and CH₃COONH₄(D)) were applied to modulate the microwave-assisted synthesis of Fe-MOFs. The effects of various modulators on the yield, electrochemistry activity and PS activation capacity of prepared catalysts were systematically investigated. The ideal modulator was revealed as the 7.5 mM CH₃COONH₄. Contributed by the defects caused by the dual effects of CH₃COONH₄, Fe-MOFs-D-7.5/PS system showed excellent orange G (OG) degradation with high reaction stoichiometric efficiency (RSE) and desirable recycling performance. The main radicals should be SO₄^·- and O₂^·- which were confirmed by EPR and chemical quenchers. Furthermore, the frontier molecular orbital (FMO) theory and dual descriptor (DD) method were employed in predicting radical attacking sites of OG. According to the results of theoretical computations and experimental detection, degradation pathways of OG in Fe-MOFs-D-7.5/PS system were proposed. Similar to the function of the battery, this study gives new insight into the possible mediatory roles of Fe-MOFs-D-7.5 in PS activation by transferring the electrons between PS and the unsaturated metal sites (CUS). The Fe-MOFs-D-7.5/PS system is a promising process for environmental remediation.

Heterogeneous activation of persulfate by ZnCoxFe2−xO4 loaded on rice hull carbon for degrading bisphenol A

Mechanism of the activation on PS by ZnCo_1.3Fe_0.7O₄-RHC for the degradation of BPA.

Octadecylamine degradation through catalytic activation of peroxymonosulfate by FeMn layered double hydroxide

A kind of heterogeneous catalyst, FeMn layered double hydroxide (Fe-Mn-LDH), was fabricated by coprecipitation process and used as PMS activator to degrade a novel organic pollutant octadecylamine (ODA). And the X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microcopy (TEM), Mapping and X-ray photoelectron spectra (XPS) measurements were utilized to characterize the fresh and used Fe-Mn-LDH. After a serious of degradation experiments, it was clearly to see that the activator possessed excellent activation property for PMS and was capable of removing 85% ODA (10 mg·L^-1) within 25 min obviously higher than pure PMS. Moreover, the effect of some elements (such as PMS consumption, catalyst consistence and initial pH value), different reaction system and catalyst repeatability on ODA degradation were also explored. And by identification of main radical experiment, SO₄^- and HO were both confirmed the primary radicals. What's more, extra anion and nature organic matter (NOM) addition experiment displayed that NOM, NO₃^- and CO₃^2- perform a negative effect on ODA degradation but Cl^- could promote it. In addition, repeated experiments and metal leaching after degradation showed good stability of Fe-Mn-LDH. Finally, based on the XPS and Gas Chromatography-Mass Spectrometer (GS-MS) technology, the possible degradation mechanism and pathway were proposed.

Heterogeneous activation of peroxymonosulfate using Mn-Fe layered double hydroxide: Performance and mechanism for organic pollutant degradation

On account of high oxidation ability of sulfate radical-based advanced oxidation processes (AOPs), the eco-friendly catalysts for peroxymonosulfate (PMS) activation have received considerable attentions. Previous studies mainly focused on Cobalt-based catalyst due to its high activation efficiency, such as Co₃O₄/MnO₂ and FeCo-layered double hydroxide (LDH), whereas Cobalt-based catalyst usually has serious risk to environment. To avoid this risk, MnFe-LDH was primarily synthesized in this research by simple co-precipitation and subsequently utilized as an effective catalyst for peroxymonosulfate (PMS) activation to degrade organic pollutants. The experimental results demonstrated that MnFe-LDH with a lower dosage (0.20 g/L) could efficiently activate PMS to achieve 97.56% removal of target organic pollutants Acid Orange 7 (AO7). The AO7 degradation process followed the pseudo-first-order kinetic well with an activation energy of 21.32 kJ/mol. The intrinsic influencing mechanism was also investigated. The quenching experiment and electron spin resonance (ESR) indicated that sulfate and hydroxyl radicals were produced by the effective activation of PMS by MnFe-LDH, resulting in a high rate of decolorization. The possible AO7 removal pathway in the constructed MnFe-LDH/PMS system was presented on the basis of UV-vis spectrum analysis and GC-MS, which suggested that the AO7 degradation was firstly initiated by breaking azo linkages, then generated phenyl and naphthalene intermediates and finally presented as ring-opening products. This effective MnFe-LDH/PMS system showed great application potential in the purification of wastewater contaminated by refractory organic pollutants.

Activation of peroxymonosulfate by BiOCl@Fe3O4 catalyst for the degradation of atenolol: Kinetics, parameters, products and mechanism

BiOCl@Fe₃O₄ photocatalyst was synthesized to activate peroxymonosulfate (PMS) for atenolol (ATL) degradation under simulated sunlight irradiation in present study. XRD, SEM, adsorbability and pore size distribution of BiOCl@Fe₃O₄ were analyzed. Magnetic BiOCl performed high activity in PMS activation and could be easily solid-liquid separation by applying an external magnetic field. Many parameters were inspected, including scavengers, PMS concentration, catalyst dosage, pH, anions (Cl^- and CO₃^-). h⁺, SO₄^-, HO, O₂^-, SO₅^- were involved in ATL degradation in BiOCl@Fe₃O₄/PMS/sunlight system. The second-order rate constant of the reaction between ATL and SO₄^- (k_ATL, _SO4-) was estimated via laser flash photolysis experiments. Moreover, ATL mineralization was followed by TOC analyzer. Twelve possible intermediate products were identified through LC-QTOF-MS analysis, and six ATL degradation pathways were concluded. This type of magnetic photocatalyst is characterized by ease of separation, high activation and good reusability. It may have application potential in refractory organic pollutants degradation.

N-doped hierarchically porous carbon for highly efficient metal-free catalytic activation of peroxymonosulfate in water: A non-radical mechanism

Metal-free carbo-catalyst has recently emerged as a promising candidate as a substituent for tradition-metal based heterogeneous catalyst for catalytic activation of peroxymonosulfate (PMS). However, most reported carbo-catalysts suffer from low catalytic efficiency and poor stability, thus a high-performance catalyst is urgently desired. In this study, a novel carbo-catalyst (NHPC-800), prepared by using tannic acid and dicyandiamide as renewable carbon/nitrogen feedstocks via a simple pyrolysis route, is reported as an activator of PMS with highly efficient catalytic ability and stability. The as-prepared NHPC-800 possesses as high as 22.4 atom% of nitrogen dopants and a hierarchically porous structure with abundant meso/macropores, accompanied by the abundant edges and wrinkles, which supply sufficient exposed catalytically active centers and fast electrons/mass transportations. Using rhodamine B as a model pollutant, the NHPC-800 shows a highly efficient catalytic ability which is superior to most reported carbo-catalysts and even some state-of-the-art metal catalysts. Based on competitive quenching experiments and electron paramagnetic resonance (EPR) results, a non-radical pathway involving the generation of ¹O₂ is responsible for the degradation of pollutants. Given that the NHPC-800 shows good recycling performance and strong resistance to adventitious interference such as anions and natural organic matters, we believe NHPC-800 can be a promising candidate for practical applications, and this study can provide inspirations for the further development of highly efficient carbo-catalysts.

Co3O4 nanocrystals/3D nitrogen-doped graphene aerogel: A synergistic hybrid for peroxymonosulfate activation toward the degradation of organic pollutants

3D porous Co₃O₄/nitrogen-doped graphene aerogel (NGA) hybrid for heterogeneous activation of peroxymonosulfate (PMS) was prepared by feasible hydrothermal and freeze-drying methods. The morphology, crystal structure and chemical composition of the catalyst were investigated by scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, Raman spectra and Fourier transform infrared spectroscopy. Co₃O₄/NGA at a high N doping level of 7.6% (in atomic percentage) exhibited excellent catalytic performance for acid orange 7 (AO7) degradation, with almost complete removal within 30 min. Moderate PMS content, higher temperature and lower solution pH conditions would facilitate the decomposition of AO7. The catalyst possesses excellent long-term stability and recycling performance with simple separation and post-treatment approaches. Kinetic model was developed to simulate the transformation of main active radical species and the AO7 oxidation profiles, considering effects of coexisting ions (Cl^- and HCO₃^-). Based on results of electron spin resonance, typical quenching tests and kinetic calculation, sulfate radicals play dominate role in AO7 degradation. Co₃O₄ nanocrystals and the new active sites created by nitrogen doping into graphene honeycomb network should synergistically contribute to the high degradation efficiency. This work has expanded the possibility of recyclable catalysts design for heterogeneous activation of PMS, with a dual catalytically active center and desirable stability.

Peroxymonosulfate/base process in saline wastewater treatment: The fight between alkalinity and chloride ions

Both Cl^- and base can affect PMS activation to produce reactive chlorine or oxygen species, but the overall effects of chloride on this emerging PMS/base technology in saline wastewater treatment are unknown. Here effectiveness of PMS/base, PMS/Cl^- and PMS/base/Cl^- is compared with a gradient concentration of chloride and alkalinity, by probing the degradation of methylene blue (MB). Both PMS/base and PMS/Cl^- systems can rapidly degrade MB due to the generation of singlet oxygen and reactive chlorine, respectively. Interestingly, dye degradation and adsorbable organic halides (AOX) formation are inhibited in the PMS/base/Cl^- system as high concentrations of Cl^- and base co-exist. Reaction of PMS with chloride diminishes the effective concentration of PMS by base activation, whereas in return high alkalinity decreases the oxidation capacity of reactive species. Therefore, this finding may have significant technical implications for evaluating the applicability of the emerging PMS/base technology and optimizing the conditions for AOX abatement in PMS-based processes.

Recent advances in application of UV light-emitting diodes for degrading organic pollutants in water through advanced oxidation processes: A review

Over the last decade, ultraviolet light-emitting diodes (UV LEDs) have attracted considerable attention as alternative mercury-free UV sources for water treatment purposes. This review is a comprehensive analysis of data reported in recent years (mostly, post 2014) on the application of UV LED-induced advanced oxidation processes (AOPs) to degrade organic pollutants, primarily dyes, phenols, pharmaceuticals, insecticides, estrogens and cyanotoxins, in aqueous media. Heterogeneous TiO₂-based photocatalysis in lab grade water using UVA LEDs is the most frequently applied method for treating organic contaminants. The effects of controlled periodic illumination, different TiO₂-based nanostructures and reactor types on degradation kinetics and mineralization are discussed. UVB and UVC LEDs have been used for photo-Fenton, photo-Fenton-like and UV/H₂O₂ treatment of pollutants, primarily, in model aqueous solutions. Notably, UV LED-activated persulfate/peroxymonosulfate processes were capable of providing degradation in DOC-containing waters. Wall-plug efficiency, energy-efficiency of UV LEDs and the energy requirements in terms of Electrical Energy per Order (E_EO) are discussed and compared. Despite the overall high degradation efficiency of the UV LED-based AOPs, practical implementation is still limited and at lab scale. More research on real water matrices at more environmentally relevant concentrations, as well as an estimation of energy requirements providing fluence-based kinetic data are required.

Combination of UVC-LEDs and ultrasound for peroxymonosulfate activation to degrade synthetic dye: influence of promotional and inhibitory agents and application for real wastewater

Several efforts have been carried out to present an efficient method for PMS activation. This work presented the use of UVC-LEDs (light emitting diodes) and US (ultrasound) to activate PMS for decolorization of Direct Orange 26 (DO26). The performance of UVC-LEDs/US/PMS process was effective in a broad range of pH (3.0-9.0). Complete decolorization was obtained in only 12 min in pH = 7.0 and 1.5 mM PMS. Bicarbonate and nitrite ions showed inhibitory effect on decolorization while sulfate, chloride, and nitrate had no significant effect on the performance of the process. Transition metals in homogenous (Fe²⁺ and Co²⁺) and heterogeneous forms (Fe₃O₄ and Co₃O₄) accelerated decolorization in UVC-LEDs/US/PMS system. The presence of turbidity declined the performance of UVC-LEDs/US/PMS through the prevention of PMS activation by UV and US. Compared to other oxidants (S₂O₈^2-, H₂O₂ and 2Na₂CO₃.3H₂O₂), PMS proved the higher function in decolorization of DO26 in UVC-LEDs/US/oxidant system. Scavenging experiments showed that ¹O₂, HO^•, and SO₄^•- contributed in the degradation of DO26. Moreover, the UVC-LEDs/US/PMS system could markedly increase the biodegradability of real textile wastewater. These results promised an effective process for degradation of organic pollutants from aquatic environment.