Sulfate Radical-based Advanced Oxidation Processes Research Articles

Mechanism of thermal activation of sulfite and its application in the heat–electro-S(IV) system for As(III) oxidation in water

In recent years, a new strategy of using sulfite (S(IV)) to replace persulfates (peroxydisulfate (PS) and peroxybisulfate (PMS)) for sulfate radical based advanced oxidation process (SR-AOP) has emerged as one of the potential alternatives in the field of AOPs. Although the thermal activation of PS and PMS has been investigated extensively, that of S(IV) has not yet been explored. In this work, As(III) oxidation in a heat–S(IV) system was investigated first to demonstrate the feasibility of thermal activation of S(IV). Results showed that S(IV) can be activated to oxidize As(III) by heating the reactant solution from room temperature to above 50℃. Almost complete oxidation of 5 μM As(III) in water at pH 7 with addition of 1 mM S(IV) was achieved at 70 °C within 30 min. As(III) oxidation in the heat–S(IV) system was strongly dependent on the dissolved oxygen in water. Radical-scavenging experiments and electron spin resonance analysis demonstrated that the main active species responsible for As(III) oxidation was SO4•−. On the basis of thermal activation, a new system of SR-AOPs, namely, heat–electro-S(IV) system, the coupling thermal and electrochemical activations was established with ruthenium-plated iridium electrodes at a voltage of 3 V. It achieved complete oxidation of 50 μM As(III) in water at pH 7 at 50 °C with the addition of 2 mM S(IV) after reaction for 30 min. This work provides a new activation method for SR-AOPs with S(IV) as the precursor of reactive species and helps in understanding the reaction of S(IV) autooxidation.

Effect of activated persulfate on the properties of contaminated soil and degradation behavior of PAHs

Sulfate radical-based advanced oxidation processes have been applied in the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil, during which sulfate can be activated in different ways. In this work, effects of four different ways (FeSO4, NaOH, H2O2, and Heat) activated sodium persulfate (PS) on PAHs removal and soil physicochemical properties (pH, organic matter, functional groups, surface morphology, and partial heavy metal elements) were compared, and the influencing factors and mechanism of soil PAHs removal by thermally activated PS were also studied. The results showed that at the dosage of 3% of persulfate, the removal efficiency of PAHs followed the sequences of Heat (91.4%) > FeSO4 (86.6%) > H2O2 (86.2%) > NaOH (72.9%). However, thermal activation decreased the soil pH and organic matter content more significantly than other treatments. The reaction tended to reach equilibrium at 6 h when the dosage of persulfate was 3% and the activation temperature was 60 °C, and the reaction obeyed pseudo-first-order kinetics. Through quenching experiments, it was found that the free radicals playing a dominant role in the oxidation process were sulfate radicals. Compared with pH, liquid to soil (L/S ratio) and the temperature had more significant impacts on the degradation efficiency of PAHs.

Synergistic degradation of sulfamethoxazole using peroxymonosulfate activated by Fe-Mn-Cu hollow spheres: Kinetics and mechanism studies

The synergistic effect of bimetallic or trimetallic oxide catalysts plays a vital role in sulfate radical-based advanced oxidation processes (SR-AOPs). Herein, a composite catalyst of iron-manganese-copper hollow spheres (FCMHS) was synthesized by hard template method and used for peroxymonosulfate (PMS) activation to degrade sulfamethoxazole (SMX). The catalytic activity of FCMHS was comprehensively evaluated under different conditions (including catalyst loading, PMS dosage, pH etc.). A removal efficiency of 99.1% and a mineralization efficiency of 39.7% for SMX were achieved under the optimal conditions. The kinetic studies demonstrated that the reaction rate for SMX removal by using FCMHS was about 3.5 times faster than that for using copper-manganese hollow spheres (CMHS). The enhanced catalytic performance mainly stemmed from the confined high instantaneous concentration of SMX in the local void space and the synergistic effects of Mn2+/Mn3+/Mn4+, Cu+/Cu2+/Cu3+ and Fe2+/Fe3+ redox cycles to generate radicals and non-radicals. More importantly, the introduction of iron oxide into CMHS substantially facilitated charge transfer at the interface between FCMHS and reaction solution, leading to a high rate and good product selectivity. Furthermore, SMX degradation pathways were proposed by LCMS-IT-TOF assisted with density functional theory (DFT) calculations, and the mechanism was proposed comprehensively. This study opens a reliable and promising avenue for the efficient treatment of antibiotics-polluted water based on trimetallic oxide catalysts.

Fabricating an oxygen-vacancy-rich urchin-like Co3O4 nanocatalyst to boost peroxymonosulfate activation to degrade high-concentration crystal violet

Due to the in-situ generation of reactive oxygen species (ROS), sulfate radical-based advanced oxidation processes (SR-AOPs) have emerged for the oxidative degradation of organic contaminants. Developing highly efficient heterogeneous catalysts is of great importance for SR-AOPs. In this work, an urchin-like Co3O4 nanocatalyst with oxygen vacancies (VO) was elaborately fabricated and employed for enhanced peroxymonosulfate (PMS) activation to degrade the high-concentration active dye crystal violet (CV). The obtained sample was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and N2 adsorption/desorption isotherms. Characterization results indicated that this unique VO-rich urchin-like Co3O4 nanocatalyst was endowed with a larger surface area and abundant reactive sites for PMS adsorption and activation. The experimental results of CV degradation showed that nearly complete removal of 100 mg L−1 CV could be realized within 30 min of reaction time under neutral conditions at room temperature, and the degradation process followed retarded-first-order kinetics. Electron paramagnetic resonance (EPR) spectra accompanied by quenching experiments of radicals demonstrated that the contribution of ROS to CV degradation followed this sequence: 1O2 > ▪OH > SO4▪- > O2▪-. The degradation pathways of CV were proposed by a combination of density functional theory (DFT) calculations along with frontier orbit theory while the toxicity of intermediate products was evaluated by quantitative structure-activity relationship (QSAR) prediction.

3D-printed heterogeneous Cu2O monoliths: Reusable supports for antibiotic treatment of wastewater

In this study, surfactant stabilized dispersions of the Cu2O microparticles in a commercially available photocurable resin were 3D printed into both porous and non-porous monoliths, and the heterogeneous Cu2O catalytic monolith with improved mass transfer characteristics was applied for antibiotic wastewater treatment. The physicochemical properties of catalytic monoliths were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermogravimetric. Ten intermediates were analyzed and identified by GC-MS, and the corresponding degradation pathways were proposed. Both numerical simulation and degradation experiments were used to explore the mass transfer mechanism and catalytic performance of the monoliths. The results showed that the 3D-printed monolith with a well-defined porous network exhibited a high ofloxacin degradation efficiency (100%) based on the sulfate radical-based advanced oxidation processes. In addition, the catalytic monolith showed sustained high activity over 7 reusable cycles demonstrating its feasibility in removal of antibiotics from wastewater.

Facile hydrothermal synthesis of co-glycerate as an efficient peroxymonosulfate activator for rhodamine B degradation

Sulfate radical based advanced oxidation processes (SR-AOPs) are regarded as a promising technology to degrade organic pollutants in water. Here, hydrothermally synthesized Co-glycerate (Co-G) microspheres are proposed as an efficient heterogeneous catalyst to activate peroxymonosulfate (PMS) for degradation of refractory organic pollutant rhodamine B (RhB) in aqueous solution. The presence of Co-G microspheres enhanced the degradation rate significantly with a short full degradation time (8 min) and a total organic carbon (TOC) removal exceeding 41% (10 min), thus implying the excellent catalytic performance of Co-G microspheres for PMS activation. Furthermore, the effects of PMS and catalyst concentration, initial pH value and co-existing ions on RhB degradation were investigated. Radical quenching and EPR tests identify that active species including SO4-·, HO·, O2-· and 1O2 are involved in the degradation process. Additionally, a possible reaction mechanism of PMS activation by Co-G microspheres for RhB degradation was suggested. This study can provide a new insight for design of cobalt-based heterogeneous catalysts as activators to activation PMS for pollutants degradation.

Assembly of UiO-66 onto Co-doped Fe3O4 nanoparticles to activate peroxymonosulfate for efficient degradation of fenitrothion and simultaneous in-situ adsorption of released phosphate

Although sulfate radical-based advanced oxidation processes (SR-AOPs) have shown great potential for the efficient degradation of various organic contaminants, there is few research on the removal of organophosphorus pesticides (OPPs) through SR-AOPs. In this work, Co-doped Fe3O4 magnetic particles encapsulated by zirconium-based metal-organic frameworks (Co-Fe3O4@UiO-66) were prepared and employed to activate peroxymonosulfate (PMS) for the elimination of fenitrothion (FNT) and the simultaneous in-situ adsorption of produced phosphate. The catalyst exhibited efficient catalytic performance, achieving above 90.0% removal of FNT (10 mg/L) in the presence of PMS (1 mM) within 60 min. Moreover, the produced phosphate during the degradation process was also completely adsorbed onto the catalyst. Both sulfate and hydroxyl radicals were responsible for the degradation of FNT. The degradation products of FNT in the system were identified and the possible pathways were proposed. This study represents a promising and adoptable strategy to develop other versatile composite nanomaterials in a green manner hence broadening its environmental application range, as it can not only remove OPPs by catalytic oxidation but also immobilize degraded phosphorus by adsorption.

Efficient degradation of atrazine through in-situ anchoring NiCo2O4 nanosheets on biochar to activate sulfite under neutral condition

Sulfite (S(IV)) is a promising substitute for sulfate radical-based advanced oxidation processes. Here, a composite of in-situ anchoring NiCo2O4 nanosheets on biochar (BC) was firstly employed as a heterogeneous activator for sulfite (NiCo2O4@BC-sulfite) to degrade atrazine (ATZ) in the neutral environment. The synergistic coupling of BC and NiCo2O4 endows the resulting composite excellent catalytic activity. 82% of the degradation ratio of ATZ (1 mg/L) could be achieved within 10 min at initial concentrations of 0.6 g/L NiCo2O4@BC, 3.0 mmol/L sulfite in neutral environment. When further supplementing sulfite into the system at 20 min (considering the depletion of sulfite), outstanding degradation efficiency (∼ 100%) were achieved in the next 10 min without any other energy input by the NiCo2O4@BC-sulfite system. The features of the prepared catalysts and the effects of some key parameters on ATZ degradation were systematically examined. A strong inner-sphere complexation (Co2+/Ni2+-SO32−) was explored between sulfite and the metal sites on the NiCo2O4@BC surface. The redox cycle of the surface metal efficiently mediated sulfite activation and triggered the series radical chain reactions. The generated radicals, in particular the surface-bound radicals were involved in ATZ degradation. High performance liquid chromatography-tandem mass spectrometry (LC-MS) technique was used to detect the degradation intermediates. Density functional theory (DFT) calculations were performed to illustrate the possible degradation pathways of ATZ. Finally, an underlying mechanism for ATZ removal was proposed. The present study offered a low-cost and sustainable catalyst for sulfite activation to remove ATZ in an environmentally friendly manner from wastewater.

Z-type ZnAl-LDO/Ag2S heterojunction activated peroxysulfate to degrade tetracycline hydrochloride under visible light efficiently

This study used electrostatic self-assembly and chemical deposition to construct a visible-light-driven Z-type ZnAl-LDO/Ag2S heterojunction composite material with active phase Zn/Al LDO. Then it is used as an efficient catalyst for photocatalysis (PC) coupled with sulfate radical based-advanced oxidation processes (SR-AOPs) to degrade tetracycline hydrochloride (TC-HCl) under visible light. The effects of ZnAl-LDO molar ratio, calcination temperature, Ag2S deposition amount, initial concentration of persulfate (PMS), initial solution pH, and catalyst dosage on the reaction were investigated. The results show that the combination of photocatalysis and SR-AOPs can significantly improve the degradation ability of pollutants. Under the action of 0.5 g/L ZnAl-LDO/Ag2S, pH = 7 and 6 mM PMS, within 35 min, 20 mg/L 100 mL of tetracycline hydrochloride can be completely degraded. The results of the scavenging experiment and ESR analysis show that SO4− and OH radicals are the leading free radicals that degrade tetracycline hydrochloride and verify the degradation mechanism. The ZnAl-LDO/Ag2S/PMS system has good structure and performance stability. This research has established the foundation for the design and optimization of the Photo-SR system and further promoted the broad application of the system in environmental treatment.

Insight into synergetic mechanism of CuyMn5-yOx/hG-activated peroxydisulfate enhances tetracycline antibiotics degradation and toxicity assessment

Tetracycline is a typical ecologically toxic antibiotic that easily causes environmental contamination. An attractive approach toward pollution control is the implementation of sulfate radical-based advanced oxidation processes (SO4·--AOPs), and in that regard, it is critical to generate and stabilize highly-oxidative species over an excellent catalytic system to degrade tetracycline antibiotics. In this work, we investigated a strategy for employing a synergetic role of CuOx to enlarge the MnsbnO covalency and tailor defect sites, which could enhance the intrinsic activity of CuyMn5-yOx/hG catalysts for boosted peroxydisulfate (PDS) activation and tetracycline degradation via radical and nonradical processes. Comprehensive characterization revealed that MnO bonds weakened, while the CuyMn5-yOx redox cycling provided the main active center for PDS activation by radical processes. Moreover, abundant defect sites of the carbon-based co-catalyst promoted the adsorption of PDS and tetracycline and, thus, their catalysis via nonradical processes. Structural characterization indicated that Cu2.5Mn2.5Ox/hG catalysts prepared using the solid-phase method significantly increased the ratio of defects sites and enlarged the MnsbnO covalency, enhancing PDS activation. Particularly, OH· and SO4·- radicals were critical reactive oxygen species, Mn(Cu) sbnO bond weakening, and defects are the key activation sites. Furthermore, degradation pathways, the toxicity of intermediate species, and the reaction mechanisms of the tetracycline degradation catalyzed by CuyMn5-yOx/hG were determined. Removing CONH2 functional groups and the C2-C3 structural sites ring-opening played a vital role in tetracycline degradation. The Cu2.5Mn2.5Ox/hG catalyst was demonstrated to be effective in tetracycline degradation with a low environmental impact, and our findings provide valuable novel insights for further development of efficient SO4·--AOPs catalysts.

Individual and combined degradation of N-heterocyclic compounds under sulfate radical-based advanced oxidation processes

Although the inhibitory effect of purines and phenols on the degradation of N-heterocyclic compounds under UV/peroxymonosulfate (PMS) has been reported, the understanding of contaminants' underlying mechanisms and kinetics is still very limited. In this study, five omnipresent nitrogenous bases (adenine, guanine, cytosine, thymine, and uracil) in the aquatic environment were used to study the inhibitory effect of N-heterocyclic compounds under UV/PMS by quantum chemical calculations. We found that HO• and SO4•− initiate base degradation with second-order rate constants of (0.11 – 15.6) × 109 M−1 s−1 and (7.25 – 13.5) × 109 M−1 s−1, respectively, and the primary products contain hydroxyl derivatives (HO-P), intermediate radicals (P(-H)•) and cationic radicals (P•+, only for purines). Because of the lower oxidation potentials of HO-P than their parent compounds (P), we first proposed a self-inhibition pathway in which HO-P can revert P(-H)• and P•+ back to P through H atom abstraction and single electron transfer reactions, respectively. A more significant self-inhibition was found in the degradation of uracil than that of adenine under UV/PMS because the former has a higher yield of hydroxylated derivatives. The main hydroxylated product (6-HO-U) of uracil repairs the uracil radical (U(-4H)•) at the reaction rate constants of 1.01 × 109 M−1 s−1. The combined degradation of bases showed that the reduction rate constants of purine cationic radicals have a linear relationship with the oxidation potentials of reductants. In the adenine-uracil mixture system, adenine inhibits uracil degradation by repairing U(-4H)• (2.33 × 105 M−1 s−1). This work revealed the mechanisms and kinetics of self-inhibition and joint-degradation of N-heterocyclic compounds, which is of great significance for understanding the collective removal of contaminants in the real water environment.

The application of sulfate radical-based advanced oxidation processes in hydrothermal treatment of activated sludge at different stages: A comparative study.

Integrating hydrothermal treatment (HT) and advanced oxidation processes (AOP) was proved to be a promising approach for improving sludge dewaterability. In this study, the EPS valorization under elevated temperature and sulfate radical-based AOP were investigated to clarify the valorization of organic matter in different EPS layers and its effects on the sludge dewaterability. Results indicated that the organic matters in the inner layer of EPS decreased sharply with the elevated temperature, and released into the soluble EPS. Sulfate radical-based AOP significantly accelerated the degradation of organics and microbial cells lysis, especially in the presence of ZVI. The protein with the higher hydrophobicity was detected under the AOP enhanced HT. A better synergistic effect on sludge dewaterability was obtained by integrated the AOP at the initial hydrothermal stage. 3D-EEM and parallel factor analysis indicated that the protein and microbial by-product like substances in tightly bound EPS significantly affected the dewaterability.

Hierarchical collagen fibers complexed with tannic acid and Fe3+ as a heterogeneous catalyst for enhancing sulfate radical-based advanced oxidation process.

Efficient sulfate radical-based advanced oxidation processes (SR-AOPs) are important for treating organic contaminants of industrial wastewater. To achieve this goal, tannic acid (TA)-modified skin collagen fibers (CFs) were prepared for the enhanced immobilization of Fe3+ based on multiple complexation interactions, resulting in a heterogeneous catalyst with more catalytic sites (defined as TA-Fe-CFs) for activating peroxymonosulfate (PMS). During the removal of an organic dye (rhodamine B, RhB) from water, the hierarchical TA-Fe-CFs exhibited excellent adsorption capacity at the early stage before the introduction of PMS, which can be ascribed to the π-π interaction between TA and aromatic RhB. Such improved mass transfer of target contaminants into the catalytic support was proved to be beneficial for improving the utilization efficiency of sulfate radicals in subsequent SR-AOPs. After introducing PMS, the reductive TA moieties of the heterogeneous catalyst were able to accelerate the redox cycle of Fe3+/Fe2+ in Fenton reactions, facilitating the activation of PMS to generate sulfate radicals for the degradation of organic RhB.

Combined solar activated sulfate radical-based advanced oxidation processes (SR-AOPs) and biofiltration for the remediation of dissolved organics in oil sands produced water

• Effective degradation of dissolved organics in produced water by solar activated SR-AOPs. • SO 4 •− , • OH and 1 O 2 reactive species were formed during solar activated SR-AOPs. • Better performance by solar activated peroxymonosulfate compared to persulfate. • Excellent mineralization of dissolved organic by post-treatment biofilm filtration. • Microbial profiling indicated presence of hydrocarbons and carboxylic acid degraders. This study reported for the first time the potential of sequential solar activated sulfate radical advanced oxidation processes (SR-AOPs) and fixed bed biofiltration for the enhanced remediation of dissolved organics in oil sands process water (OSPW). The effect of initial sulfate precursors namely persulfate (PS) and monopersulfate (PMS) was examined on the degradation of naphthenic acid (NA) surrogates and various classes of organics in real OSPW. Effluents from solar activated SR-AOPs treatment of OSPW at specific conditions were subjected to biofiltration for 45 days. Fast and complete degradation of 5-phenylvalveric acid (PVA) and up to 99% degradation of various organics in OSPW were achieved by the solar activated SR-AOPs. Radical scavenger and spin-trap electroparamagnetic spectrometry analysis showed that hydroxyl ( • OH) and sulfate (SO 4 •− ) radicals were the major reactive species generated and participated in the oxidation of organics in SR-AOPs treatment with either PS or PMS along with a small proportion of singlet oxygen. The biofiltration post-treatment showed significant mineralization of dissolved organics in treated OSPW, achieving over 60% and 40% reduction in DOC and COD, respectively, surpassing most of the reported studies for such combined approach. The bacterial metataxonomic analysis indicated significant enrichment of hydrocarbons and carboxylic acid degraders ( Sphingomonas and Sphingopyxis ) in the biofilters treating PMS pre-treated OSPW. However, for biofilters treating raw OSPW and PS, the bacterial community was dominated by hydrocarbon degraders and methanotrophs. The treated OSPW was found completely non-toxic for the OSPW treated with PMS-9 h and biofiltration. This demonstrates the potential of combined treatment for the effective remediation of the oil sand industry effluent.

Synergistically enhanced activation of persulfate for efficient oxidation of organic contaminants using a microscale zero-valent aluminum/Fe-bearing clay composite

Sulfate radical-based advanced oxidation processes have received increasing attention in contaminated water treatment. As an excellent electron donor, microscale zero-valent aluminum (mZVAl) is a promising persulfate (PS) activator. However, the natural oxide layer of mZVAl impedes electron transfer from the core metal. Herein, a composite comprising mZVAl and Fe-bearing clay (mZVAl-NaNAu-2) was obtained through the simple ball milling (BM), which synergistically activates PS for the efficient degradation of various organic contaminants, such as 4-chlorophenol, benzoic acid, nitrobenzene, phenol, and ofloxacin, in water. The sulfate radicals and hydroxyl radicals were the main reactive species but Fe(IV) was minor in this reaction. The BM can cause fracture of the mZVAl powder and promote exposure of the fresh Al0 surface. Various Fe species in mZVAl-NaNAu-2 at different reaction times were evaluated by extraction experiments, Mössbauer and XPS spectra. Approximately 47.0% of structural Fe(III) was reduced to Fe(II) after BM. The dissolved Fe(II) and structural trioctahedral Fe(II)-Fe(II)-Fe(II) entities were mainly responsible for the homogeneous and heterogeneous activation of PS, and corroded mZVAl acted as an “electron pool” to regenerate the aforementioned Fe(II) species continuously. The mZVAl-NaNAu-2/PS system also presented certain resistance to a natural organic matter and some anions, such as Cl- and NO3-. This study provided a new strategy for the efficient removal of organic contaminants from water and also solved the bottleneck of mZVAl in applications due to its dense oxide film.

Manganese oxides activated peroxymonosulfate for ciprofloxacin removal: Effect of oxygen vacancies and chemical states

Ciprofloxacin (CIP) as an anti-inflammatory drug is frequently detected in various water resources. Recently, Sulfate Radical-based advanced oxidation processes with manganese oxides have been recognized as a highly effective method for CIP degradation. Herein, ε-MnO2 was obtained through a convenient drying process. After different atmospheric treatments, MnO and Mn2O3 were fabricated for subsequent degradation experiments. The results show that MnO exhibits better catalytic activity than Mn2O3, with high removal efficiency of almost 84.3% for CIP. Quenching test and electron paramagnetic resonance spectra confirm that 1O2 is the dominant species during reaction, while ·OH and SO4·- play a supporting role. A related discussion about the role of valence states of Mn and oxygen vacancies is presented, which can provide a theoretical basis for further development of Mn/peroxymonosulfate system.

Treatment for landfill leachate through sequential multi-sand-layering filters coupled with sulfate radical-based advanced oxidation processes

Treatment for landfill leachate through sequential multi-sand-layering filters coupled with sulfate radical-based advanced oxidation processes

Evaluation of the Activation Procedure on Oxone Efficiency for Synthetic Olive Mill Wastewater Treatment

Wastewater from the olive oil industry is an environmental problem which is growing in the Mediterranean region. Presence of phenolic compounds and high organic matter load are characteristics of this effluent that make it difficult to treat. In this study, the applicability of sulfate radical based advanced oxidation processes (SRbAOPs), using peroxymonosulfate (PMS) as oxidant, was evaluated in the treatment of synthetic olive mill wastewater (OMW). Different procedures for PMS activation were studied such as activation by Fe(II), radiation (visible and UV-A) and ultrasounds. The operation conditions were optimized by testing pH values, Fe(II) and PMS loads. At optimal conditions ([PMS] = 1600 mg/L, [Fe2+] = 700 mg/L and pH = 5) 60 ± 2% COD removal was achieved. This process shows to be selective since complete degradation of 3,4,5-trimetoxybenzoic acid was obtained after 3 min of reaction. The addition of light, PMS/LED/Fe(II) and PMS/UV-A/Fe(II), did not increase the efficiency of organic matter removal, with 56 ± 2% and 58 ± 1% of COD removal, respectively, comparatively to PMS/Fe(II) (60 ± 2%). PMS activated by ultrasounds led to 52 ± 3% and 23 ± 2% removal of phenolic compounds and COD, respectively, after 60 min. Toxicity tests using Lepidium sativum showed that treatment with PMS/UV-A led to a treated sample with mild inhibition of plant growth.

Eliminating tetracycline antibiotics matrix via photoactivated sulfate radical-based advanced oxidation process over the immobilized MIL-88A: Batch and continuous experiments

• The immobilized MIL-88A(Fe) onto cotton fibers (MC) was prepared. • MC was used to achieve efficient and long-term elimination of tetracyclines matrix. • A fixed bed reactor is constructed from MC in a home-made annular setup. • MC displayed boosted long-term stability in both batch and fixed bed tests. This work demonstrates the successful immobilization of MIL-88A(Fe) MOF on cotton fibers to fabricate MIL-88A(Fe)/cotton fibers (MC) by an eco-friendly method. The prepared MC is used to activate peroxydisulfate for eliminating multiple tetracycline antibiotics, such as oxytetracycline (OTC), tetracycline (TTC), and chlortetracycline (CTC) in simulated wastewater under UV-light irradiation. The photoactivated sulfate radical-advanced oxidation processes (SR-AOPs) towards the removal of tetracycline antibiotics matrix (initial concentration of 10.0 mg/L) using MC were initially investigated using a batch method. The results reveal that 97.5% OTC, 95.2% TTC, and 100.0% CTC can be degraded in the MC/UV/PDS system in the presence of 2 g/L of MC and 1 mM of PDS. The degradation pathways of OTC, TTC, and CTC were clarified via liquid chromatography-mass spectrometry analysis and DFT calculations. The quantitative structure–activity relationship analysis shows that the tetracycline antibiotics are transformed into their corresponding intermediates with lower toxicity within 8.0 min. A self-designed fixed bed reactor, in which the MC was packed into the annular channel, was adopted to test the long-term operation possibility of the MC in the continuous photoactivated SR-AOP system. The findings demonstrate that the whole antibiotics matrix can be removed completely within 22 h. This work is the first to demonstrate the use of MOFs as catalysts for SR-AOP to achieve continuous purification of simulated wastewater. The findings highlight a new possibility for the use of MOFs in large-scale wastewater treatment over.

Prediction of Second-Order Rate Constants of Sulfate Radical with Aromatic Contaminants Using Quantitative Structure-Activity Relationship Model

Predicting the second-order rate constants between aromatic contaminants and a sulfate radical (kSO4•−) is vital for the screening of pollutants resistant to sulfate radical-based advanced oxidation processes. In this study, a quantitative structure-activity relationship (QSAR) model was developed to predict the values for aromatic contaminants. The relationship between logkSO4•− and three molecular descriptors (electron density, steric energy, and ratio between oxygen atoms and carbon atoms) was built through multiple linear regression. The goodness-of-fit, robustness, and predictive ability of the model were characterized statistically with indicators showing that the model was reliable and applicable. Electron density was found to be the most influential descriptor that contributed the most to logkSO4•−. All data points fell within the applicability domain, and no outliers existed in the training set. The comparison with other models indicates that the QSAR model performs well in elucidating the mechanism of the reaction between aromatic compounds and sulfate radicals.