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Biosensors and nanoscale analytical tools have shown huge growth in literature in the past 20 years, with a large number of reports on the topic of ‘ultrasensitive’, ‘cost-effective’, and ‘early detection’ tools with a potential of ‘mass-production’ cited on the web of science. Yet none of these tools are commercially available in the market or practically viable for mass production and use in pandemic diseases such as coronavirus disease 2019 (COVID-19). In this context, we review the technological challenges and opportunities of current bio/chemical sensors and analytical tools by critically analyzing the bottlenecks which have hindered the implementation of advanced sensing technologies in pandemic diseases. We also describe in brief COVID-19 by comparing it with other pandemic strains such as that of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) for the identification of features that enable biosensing. Moreover, we discuss visualization and characterization tools that can potentially be used not only for sensing applications but also to assist in speeding up the drug discovery and vaccine development process. Furthermore, we discuss the emerging monitoring mechanism, namely wastewater-based epidemiology, for early warning of the outbreak, focusing on sensors for rapid and on-site analysis of SARS-CoV2 in sewage. To conclude, we provide holistic insights into challenges associated with the quick translation of sensing technologies, policies, ethical issues, technology adoption, and an overall outlook of the role of the sensing technologies in pandemics.

Sulfamethazine (SMT) is extensively used as growth promoters and antibacterial drugs. In this study, premagnetized Fe0 was used to catalyze H2O2 decomposition (pre-Fe0/H2O2) in the presence of nitrilotriacetic acid (NTA) to remove SMT at neutral pH conditions. In all, 30.3% and 99.8% of SMT were removed by the pre-Fe0/H2O2 process (60 min) and the pre-Fe0-NTA/H2O2 process (30 min), respectively. The removal rate of SMT in the pre-Fe0-NTA/H2O2 process was 2.5 times larger than that in the Fe0-NTA/H2O2 process. Electron paramagnetic resonance signals indicated that more radicals were generated in the pre-Fe0-NTA/H2O2 system. SMT and NTA and their degradation by-products adsorbed on pre-Fe0 reduced the contact angle of the particle and prevented the formation of Fe3O4 on the particle surface, thus accelerating Fe0 corrosion. Tafel scan images confirmed the enhancement of Fe0 corrosion in the presence of NTA and magnetic field. The Fe0 corrosion rate (109) after 20 min of reaction was 6.61 cm/s in pre-Fe0-NTA/H2O2, much higher than that in Fe0/H2O2 (0.73 cm/s), pre-Fe0/H2O2 (1.47 cm/s) and Fe0-NTA/H2O2 (2.94 cm/s). Pre-Fe0-NTA/H2O2 could also keep the fast SMT removal with eight consecutive runs without the addition of pre-Fe0 and NTA and presented high efficiency for SMT removal in real municipal wastewater.

This study presents a novel pre-magnetized Fe0/ethylenediaminetetraacetic acid/air (pre-Fe0/EDTA/air) Fenton-like system to remove sulfamethazine (SMT). SMT removal only reached 10.6% in pre-Fe0/air system (0.2 g L−1, SMT 3 mg L−1, pH 5) while reached 88.5% in pre-Fe0/EDTA/air system within 1 h (0.2 g L−1, SMT 3 mg L−1, EDTA 2 mM, pH 5). EDTA could combine with FeII or FeIII to keep iron soluble in the solution and the fast activation of molecular oxygen by Fe-EDTA complex could induce the fast and more production of H2O2. It was found that much more H2O2 (5.1 mg L−1) and OH radical (26.4 μM) were produced in the pre-Fe0/EDTA/air system than in the pre-Fe0/air system (0.06 mg L−1, 0.6 μM) within 1 h. The degradation rate of SMT (1 0 3) in pre-Fe0/EDTA/air system (38.4 min−1) was also 2.3 times as large as that in the Fe0/EDTA/air system (17.0 min−1), owing to the fast corrosion rate of pre-Fe0. 81.5 mgL−1 total Fe ions could be generated in pre-Fe0/EDTA/air while 53.6 mg L−1 in Fe0/EDTA/air. Fe0 dosage (0.05–0.8 g L−1) and EDTA dosage (0–8 mM) were optimized and the optimal dosage for Fe0 and EDTA was 0.2 g L−1 and 2 mM, respectively. The degradation rate of SMT in pre-Fe0/EDTA/air system were 1.6–2.9 times at different initial pH (3–6) and 2.3–3.1 times in the presence of inorganic ions (SO42−, Cl− and HCO3−) and natural organic matter (NOM) compared with Fe0/EDTA/air system. Decrease of Fe0 contact angle in the presence of magnetization and EDTA enhanced the corrosion rate of Fe0. Accordingly, pre-Fe0/EDTA/air system would be a cost-effective and promising eco-friendly alternative for removal of SMT.

Emerging contaminants (ECs) have been frequently detected in the aquatic environment and have adverse effect on the environment. In our present study, four ECs (800 μgL−1 oxytetracycline (OTC) and tetracycline (TC); 400 μgL−1 sulfadiazine (SD) and sulfamethazine (SMT)) spiked into the secondary wastewater effluent (SWE) were treated by novel UV/pre-magnetized Fe0/PS process (UV/pre-Fe0/PS). TC, OTC and SMT could be completely removed within 30 min and 98.4% SD could be removed within 60 min, while less than 10%, 20% and 60% ECs could be removed by Fe0/PS, pre-Fe0/PS and UV process within 60 min. Synergetic factor values (6.1–12.3) in UV/pre-Fe0/PS were much larger than in UV/Fe0/PS (2.3–5.4) to remove various ECs, achieving 0.7–2.2 times enhancement in degradation rate constants and 45%–86% reduction in treatment costs. EPR spectra and scavenging tests by tert-butyl alcohol and methanol confirmed that not only faster and more SO4 − and OH radicals were produced but also their contributions to SMT removal were enhanced. Optimization of dosage of Fe0 (0–0.4 mM) and dosage of PS (0–0.4 mM) indicated that 0.2 mM Fe0 and 0.2 mM PS was the optimal dosage. Meanwhile, this process not only could enhance 0.7–15.8 times degradation rate constant but also could reduce about 14.3–97.9% costs to remove various ECs compared with US/Fe0/PS, ozonation, VUV/UV/Fe3+ and UV/H2O2 process. Moreover, it could enhance 1.4 times of degradation rate constant and reduce about 62% cost to remove SMT in another SWE, indicating the applicability in different wastewaters. Therefore, UV/pre-Fe0/PS process is promising and cost-effective to remove ECs in SWEs.

Nitrobenzene (NB) is toxic and resistant to biodegradation and widespread in surface water and groundwater. The persulfate (PS) system has been employed for the NB degradation and proved to be effective. Zero-valent iron (Fe0) has been used for the activation of PS (Fe0/PS) recently. However, the process exhibits a significant drawback of slow release of Fe2+ from Fe0, resulting in low efficiency of the approach as Fe2+ is the primary species for the PS activation. In this study, a weak magnetic field was utilized to pre-treat Fe0 for PS activation (pre-Fe0/PS) based on the magnetic memory of iron. The efficiency of the pre-Fe0/PS process was tested on the degradation of NB in simulated groundwater under anoxic conditions. The NB removal in the pre-Fe0/PS process was significantly enhanced compared with that in the Fe0/PS process. The effect of Fe0, PS, and NB concentration on the NB degradation was investigated. The influence of single inorganic ions, anion couples and humic acids as ubiquitous species in groundwater on the NB removal in the pre-Fe0/PS and Fe0/PS processes were studied and discussed. A column filled with pre-Fe0 was designed to test the NB removal in the pre-Fe0/PS process in a continuous-flow mode. The experimental results indicated that pre-Fe0/PS is a promising approach for the remediation of groundwater with high NB concentration.

Diclofenac sodium (DCF) is frequently detected as a non-steroidal pharmaceutical in the aquatic environment. In this study, the degradation of DCF in two heterogeneous systems, pre-magnetization Fe0/H2O2 (Pre-Fe0/H2O2) and Fe0/H2O2 system, was comparably studied. Our findings proved that Pre-Fe0 could significantly improve the degradation and dechlorination of DCF due to the change of Fe0 characteristics after pre-magnetization. Compared with Fe0/H2O2 process, Pre-Fe0/H2O2 process has 2.1-7.0 times higher rate constant for DCF degradation at different H2O2 dosages (0.25-2.0 mM), initial pH (3.0-6.0) and Fe0 dosages (0.25-1.5 mM). The characterizations by X-ray Photoelectron Spectroscopy and Electron Paramagnetic Resonance confirmed that the enhancement attributed to the increase of Fe0 corrosion and fast generation of OH. In addition, preliminary degradation mechanism was elucidated by major products identification using UPLC-MS, through which the degradation intermediates, such as 4-hydroxy-diclofenac or 5-hydroxydiclofenac, 2,6-dichloroaniline, phenylacetic acid, 1,3-dichlorobenzene and 2-aminophenylacetic acid were identified. Hydroxylation, decarboxylation, CN bond cleavage and ring-opening involving the attack of OH or other substances, were the main degradation mechanism. Therefore, Pre-Fe0/H2O2 process, which does not need extra energy and costly reagents, is an efficient and environmental-friendly process to degrade DCF.

Sulfamethazine (SMT) is widely used in human and veterinary medicine as growth promoters and antibacterial drugs and it can pose potential threats to human and ecosystem health. In this study, removal of SMT by ultrasound pre-magnetized Fe0/PS process was investigated for the first time. Degradation rate for removing SMT increased 3.3 folds and the synergy factor increased from 1.2 to 2.7 compared with US/Fe0/PS process. Affecting factors such as pH (3–10), Fe0 dosage (0–0.8 mM) and initial SMT concentration (0–10 mg L−1) were studied. Stronger signals of DMPO–OH and DMPO–SO4 adduct also illustrated more and faster SO4 − and OH radicals produced in the system. FeOOH was detected through the mossbauer spectrum which could both enhance the catalysis of H2O2 and activation of PS. The intermediates of the SMT degradation were investigated, and a degradation pathway was proposed. Higher correlation factor (△k and △S) in US/pre-magn-Fe0/PS system illustrated the good synergistic effect between US input power and magnetic field. Moreover, the process could efficiently remove SMT in municipal wastewater and keep pH neutral. So, US/pre-magn-Fe0/PS process is a energy saving and promising approach to remove antibiotics in real wastewater.

An efficient heterogeneous catalyst, pre-magnetized Fe 0 (pre-Fe 0 ) could significantly activate persulfate (PS) to remove Rhodamine B (RhB). The effect of pH, Fe 0 and PS dose on the RhB removal in the pre-Fe 0 /PS and Fe 0 /PS processes were investigated, and optimized by response surface methodology (RSM) to analyze the rate constants of the RhB removal in the pre-Fe 0 /PS process and Fe 0 /PS process ( f ). High RhB removal was obtained at low pH and high dose of Fe 0 and PS in both systems. Low Fe 0 and high PS dose and large pH would result in big value of f , and the simulated maximum f of 44.3 was achieved at 2 mM Fe 0 , 16 mM PS and pH 9. The synergetic factor of pre-Fe 0 /PS (45.6) was larger than that of Fe 0 /PS (21.4). The pre-Fe 0 /PS process presented 2.1–37.5 folds enhancement than the Fe 0 /PS process for the degradation of RhB. The RhB removal in the pre-Fe 0 /PS process was 1.5–11.2 folds enhancement than that of the Fe 0 /PS process in the presence of different anions and cations. Scanning Electron Microscope (SEM) results and the larger intensity of DMPO-SO 4 − adduct signal in the Electron Paramagnetic Resonance (EPR) confirmed the primary role of sulfate radicals generated from the reaction of PS with Fe 0 in the contaminant degradation. The pre-Fe 0 /PS process exhibited advantages over other processes to remove RhB in terms of contaminant removal, working pH range and chemical dose. Therefore, the pre-Fe 0 /PS process is a cost-effective approach for degrading RhB.

Nowadays, Fenton (Fe2+/H2O2) process is increasingly applied to wastewater treatment, however, the treatment efficiency would be inhibited largely when treated salty wastewater. To overcome this limitation, pre-magnetization (pre-magn-Fe0)/H2O2 process was investigated to treat salty wastewater, which could enhance the degradation rate of organic pollutants (1.2–171.2 folds enhancement) and reduce reagents dosage (save 75% H2O2) in salty system compared with Fe0/H2O2 process, using Orange G as the target pollutant and Na2SO4 as the model salty system. The characterizations by SEM, XRD and XPS and the intensity of DMPO–OH adduct signals in different processes confirmed this enhancement attributed to the increase of corrosion of Fe0 inducing fast catalysis of H2O2 and generation of hydroxyl radicals. Pre-magn-Fe0/H2O2 process could also have 5.9, 26.4 and 93.7 folds enhancement in NaCl, NaNO3 and Na2HPO4 salty system, respectively. Meanwhile, pre-magn-Fe0/H2O2 process could keep close performance in Na2SO4 and NaCl salty systems and have better performance in NaNO3 and Na2HPO4 salty systems than Fenton process. Pre-magn-Fe0/H2O2 process also had remarkable improvement (1.1–5.3 folds) on the removal of many refractory contaminants in salty system. Furthermore, it could also keep good performance in real reverse osmosis concentrated wastewater and petrochemical wastewater. Therefore, pre-magn-Fe0/H2O2 process is a more cost-effective process to treat salty wastewater, which could have not only improved performance than conventional system and Fe0/H2O2 process, but also good performance as Fenton process.

Coupling adsorption and advanced oxidation processes (AOPs), two widely used wastewater treatment technologies, has been an attractive idea pursued by many researchers. Although many studies have demonstrated that adsorption could facilitate AOPs such as persulfate (PS) activation, the inhibitory effect of adsorption on PS activation was ignored. In this work, both as adsorbents and catalysts, sucrose-derived carbon xerogels (CXs) were prepared to investigate the effect of adsorption on PS activation. The results showed that the specific surface areas (SSAs) and N contents of CXs varied with the HCl concentration. Among different CXs, CX-0.5 with the highest SSA and N content exhibited the highest adsorption capacity and catalytic activity for acid orange 7 (AO7) degradation by simultaneously adding CXs and PS, where the promoting effect of adsorption on catalysis was found. Quenching tests demonstrated that degradation of pollutants in the CX-0.5/PS system were mainly by nonradical pathway. However, the catalytic activities of CXs were inhibited after the pre-adsorption of AO7 on CXs. Comparing the molecular structures of several compounds, the sulfonic group on chemicals might play a crucial role in the inhibitory effect. We concluded that if CXs have the same adsorption sites for pollutants and PS, adsorption of pollutants would inhibit the catalytic PS activation. These findings provided a comprehensive understanding of the effect of adsorption on AOPs, which had a significant guidance for future researches and applications.

This study demonstrated a fast and efficient treatment of highly salty wastewater in a hydroxylamine (HA) enhanced Fe0/H2O2 system. The apparent rate constant (k) in Fe0-HA/H2O2 system could achieve 7.9 times higher than that in Fe0/H2O2 system using tartrazine as the target pollutant and Na2SO4 as the model salt. The value of k for removing tartrazine in the salty system by Fe0-HA/H2O2 process even 12.7 times higher than that in the conventional system which was attributed to the faster Fe0 corrosion rate in the salty system. Meanwhile, Fe0-HA/H2O2 process could obtain remarkable performance for highly salty wastewater treatment at wide salt concentration levels (0–0.2 M) and could also widen the application of pH to neutral pH. The characterizations by SEM and XPS, the intensity of DMPO–OH adduct signals and detection of Fe2+ and Fe3+ ions in different systems confirmed the good performance was owing to the faster Fe0 corrosion rate in the salty system and acceleration of Fe3+/Fe2+ recycle owing the addition of HA inducing fast catalysis of H2O2 and generation of hydroxyl radicals. Moreover, the value of k for removing tartrazine in various types of salty system by Fe0-HA/H2O2 process was 2.9–30.8 times larger than Fe0/H2O2 process demonstrating the good suitability of Fe0-HA/H2O2 process at various types of salty system. Therefore, this study will shed lights on the reactivity of the Fe0-HA/H2O2 system and provide an alternative pathway for removal of salty wastewater.

Highly efficient persulfate oxidation process activated with pre-magnetization Fe0 (pre-magnetization Fe0/PS) was employed to degrade Orange anthraquinone dye at different Fe0 dosages (1–8 mmol/L), initial pH levels (3–10) and PS dosages (2–8 mmol/L). Pre-magnetization Fe0/PS possessed 8.4–119.6 folds enhancement in degradation rate and could widen pH range and save 90% Fe0 and PS dosage when compared with conventional Fe0/PS process. And this effect was ascribed to the change of Fe0 characteristics after pre-magnetization. This significant improvement was also observed on the degradation of many refractory contaminants of tartrazine, phenol, 2,4-dichlorophenol (2,4-DCP), p-chlorophenol, chlorobenzene, nitrobenzene, p-nitrophenol and p-nitrchlorobenzene, which were 2.8–11.4 folds of those by Fe0/PS process. Pre-magnetization Fe0/PS is a more promising process since it does not require any change of the present water and wastewater treatment process, and does not need an extra energy source, costly materials, and complex equipment.

Advanced oxidation processes (AOPs) has great potential for wastewater treatment, but still limited in application due to their high cost for extensive reagent and energy demand, and restricted working conditions (e.g. narrow pH range). Here, AOPs based on pre-magnetization Fe0 (Pre-Fe0) were found to be highly efficient at wider pH conditions, partly solved the above problems. After pre-magnetization, Fe0 was supposed to be easier to be corroded, which remarkably improved processes (e.g., Pre-Fe0/H2O2, Pre-Fe0/K2S2O8) efficiency several to >100 folds and valid for many refractory contaminants (e.g. dyes, phenols, organic acids), compared with that conventional processes without pre-magnetization. Moreover, the process efficiency could be sustained by the recovery of magnetism of Pre-Fe0. Thus AOPs based on pre-Fe0 is more promising to take place of conventional Fe0 based AOPs since it is more efficient but does not require any change of the present water and wastewater treatment process, and does not need an extra energy source, costly materials, and complex equipment.

The abatement of chlorophenols is of great environmental importance. Though Fe0 can activate persulfate (PS) to improve performance, our findings proved that pre-magnetized Fe0 (Pre-Fe0) could significantly enhanced the degradation and dechlorination of 2,4-dichlorophenol (2,4-DCP), and this Pre-Fe0/PS process was more efficient than Fe(II)/PS. The Fe0 before and after magnetization was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), suggesting the acceleration of Fe2+ release after magnetization. The effects of some important operating parameters such as Fe0 dosage, PS dosage, pH, and initial 2,4-DCP concentration on the 2,4-DCP degradation and dechlorination by Pre-Fe0/PS were investigated and compared with that of Fe0/PS, observing a 1.9–5.2-fold enhancement in the degradation rate of 2,4-DCP. Although SO4− was the dominant active species responsible for 2,4-DCP degradation in two processes, pre-magnetization could promote more OH generation. Identified by GC–MS and IC, the degradation intermediates such as 4-chlorophenol (4-CP), 2-chlorophenol (2-CP), phenol, and some carboxylic acids were detected, and possible degradation pathway was proposed. This Pre-Fe0/PS process was also efficient for 4-chlorophenol and chlorobenzene degradation, obtaining a 5.2 and 3.2 folds enhancement, respectively. This work demonstrated that such a Pre-Fe0/PS would be very promising and environmental-friendly for organics degradation and dechlorination since pre-magnetization required no extra energy source while the introduction of Pre-Fe0 was rather simple and no need to change the present treatment system.

Molybdenum sulfide (MoS2) was for the first time used as a co-catalyst to enhance the performance of Fe0 based heterogeneous electro-Fenton (Fe0-EF) process for the degradation of sulfamethazine (SMT), which was belonging to the sulfonamide family and extensively used as growth promoters and antibacterial drugs. Compared with Fe0-EF process, MoS2/Fe0-EF process could enhance the rate constant of SMT degradation 2 times under the optimal conditions of current 50 mA, MoS2 dosage 0.02 g L-1, Fe0 dosage 0.224 g L-1, and initial pH 4, in which SMT could be completely degraded within 10 min while 42% TOC could be achieved after 60 min reaction. The role of MoS2 as co-catalyst in MoS2/Fe0-EF process and Fe2+/Fe3+ cycle was supported by iron elemental analysis, transmission election microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) characterizations. Owing to the characteristics of co-catalysis, MoS2 could greatly facilitate the Fe3+/Fe2+ recycle reaction by the exposed Mo4+ active sites, which significantly promoted the decomposition of H2O2 that generated in Fe0-EF system and improved the generation of hydroxyl radical. Besides, a possible degradation pathway of SMT was proposed and the stability of MoS2/Fe0-EF process for SMT removal and TOC mineralization was certified base on five consecutive runs. The real wastewater test and energy consumption and economic analysis confirmed its advantage and cost-effectiveness for application. In all, this study provides a new perspective for improving heterogeneous Fe0-EF process with MoS2 for highly efficient and rapid degradation of antibiotics.

A new modified Fenton-like process (pre-magnetization Fe 0 /H 2 O 2 ) was employed to enhance the degradation of organic pollutants and reduce reagents dosage, using azo dye of tartrazine as the model. Compared with Fe 0 /H 2 O 2 process, pre-magnetization Fe 0 /H 2 O 2 process could have 1.3–11.2 folds enhancement in the degradation rate of tartrazine at different Fe 0 dosages (0.5–4 mmol), initial pH levels (2–6.5) and H 2 O 2 dosages (0.25–2 mmol) owing to the change of Fe 0 characteristics after pre-magnetization. The contact angle of pre-magnetization Fe 0 decreased from 58.4° to 19.8° enhancing the hydrophilicity and BET increased from 0.15 m 2 /g to 1.94 m 2 /g, which improved the corrosion of Fe 0 and accelerated the generation of Fe 2+ . Similar to the case of tartrazine, pre-magnetization Fe 0 /H 2 O 2 process had remarkable improvement on many refractory contaminants. The degradation rate constant of methyl orange, orange, methylene blue, 2,4-dichlorophenol (2,4-DCP), acetylsalicylic acid, phenol and tetracycline by pre-magnetization Fe 0 /H 2 O 2 process was 5.2, 21.3, 9.2, 5.6, 12.3, 9.5 and 3 folds of that by Fe 0 /H 2 O 2 process, respectively. The “magnetic memory” of pre-magnetization Fe 0 could last 24 h which was suitable for off-site application, and the lost some or all “magnetic memory” could be recovered after second pre-magnetization. Pre-magnetization Fe 0 /H 2 O 2 is a more promising and highly efficient Fenton process since it does not require any change of the present water and wastewater treatment process, and does not need an extra energy source and complex equipment but can widen pH range and save more than 75% Fe 0 and H 2 O 2 dosages.

Ethylenediaminetetraacetic acid (EDTA) was used to enhance pre-magnetized Fe0/H2O2 process for sulfamethazine (SMT) removal at neutral pH. Only 19.4% SMT was removed in pre-Fe0/H2O2 within 60 min at neutral pH while 90.6% SMT was removed after addition of 0.1 mM EDTA. Meanwhile, k (103) value for SMT removal in pre-Fe0-EDTA/H2O2 was 1.3 folds larger than in Fe0-EDTA/H2O2. Single-factor experiments and response surface methodology (RSM) were used to optimize the system for SMT removal. Maximum k (103) value was 81.4 min−1 obtainning at conditions of Fe0 0.28 g L−1, EDTA 0.13 mM, and H2O2 36.2 μM. The presence of EDTA and magnetization could inhibit the generation of iron oxides, reduce the contact angle of Fe0, and improve the recovery of surface FeII which induced a faster catalytic decomposition of H2O2. The system could still achieve good performance for removing SMT after six consecutive reaction cycles. These results demonstrated that pre-Fe0-EDTA/H2O2 system has the potential application for wastewater treatment.

This study has investigated a novel jet-type reactor (vertical flow reactor) in order to improve the oxygen utilization for enhanced production of hydrogen peroxide (H2O2). In vertical flow electro-Fenton (EF) system, the effects of current density, water flow rate, Fe2+ concentration and initial pH were investigated for the removal of tetracycline hydrochloride. The efficient removal of tetracycline hydrochloride could reach 100% within 60 min under the current density of 24 mA cm−2, water flow rate of 10 L h−1 and pH of 3. The vertical flow reactor was relatively stable and reusable for the removal of pollutants. The removal rates of tetracycline hydrochloride and total organic carbon (TOC) were maintained at about 95% and 80%, respectively in a 5-time continuous runs. Moreover, the vertical flow reactor could efficiently remove a wide type of organic pollutants, and the TOC removals of acid magenta, rhodamine B, alizarin yellow R, orange Ⅳ and diclofenacdium were 75.96, 77.90, 61.27, 72.11 and 82.89%, respectively after 3 h of reaction time. Cathodic adsorption, anodization, and H2O2 oxidation played minor roles in the removal of tetracycline hydrochloride, while the OH radicals are the most pivotal oxidizing substance in the system. As compared with the traditional aeration, the vertical flow reactor has a high-speed jet flow state, which makes the liquid-gas mixture homogeneous, and renders it high oxygen absorption rate, cost effectiveness and high power efficiency for the degradation of pollutants.

In this work, the active carbon fibers (ACFs) was modified by zeolitic imidazolate framework-8 (ZIF-8) to prepare a novel modified electrode as cathode. The effect of different amount of ZIF-8 modified ACFs (0–0.30 g) on H2O2 production and electric energy consumption (EEC) were investigated and the optimal ZIF-8 amount was 0.15 g. Characterized by linear sweeping voltammetry (LSV), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), contact angle, and X-ray photoelectron spectroscopy (XPS) after modification were observed considerably changed. Some nanoparticles and oxygen-contained functional groups appeared on the ZIF-8/ACF cathode surface, which significantly enhanced the hydrophilic property and the electrochemical performance. It was observed that H2O2 production with 0.15 g-ZIF-8/ACF as cathode (1545.1 mg L−1) was much larger than with raw ACF as cathode (64.1 mg L−1). Meanwhile, H2O2 production could also achieve a balance in a high state of H2O2 production (around 1500 mg L−1) with low EEC ( OH radicals could be generated in the EF system with 0.15 g-ZIF-8/ACF. Therefore, EF system with ZIF-8/ACF cathode is a good alternative process for pollutant removal.

The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was conducted by anodic oxidation (AO) with a boron-doped diamond (BDD) anode, and was greatly enhanced by combination with electro-Fenton (EF) using carbon black modified graphite felt (CB-GF) as cathode. A high current density, low initial pH and high concentration of Na2SO4 favored for the 2,4-D degradation by AO. In EF, 2,4-D degradation rate increased 8 times after using CB-GF cathode, obtaining a higher mineralization current efficiency (53%) and a lower energy consumption (71.8 kWh kg−1 TOC) due to the higher generation of H2O2. It indicated that the mainly contributing radicals for 2,4-D degradation by AO was OH (57.5%), while the contribution improved to 92% by EF. Compared with AO, EF was more efficient and complete for 2,4-D degradation, confirmed by the detection of the main degradation intermediates and short-chain carboxylic acids. This work demonstrated that EF using BDD anode and high-performance CB-GF cathode was efficient for 2,4-D degradation, which would be a promising electrochemical advanced oxidation process for organic wastewater treatment.

International audience; The chlorinated phenoxy herbicide of 2,4-dichlorophenoxyacetic acid (2,4-D) was oxidized by thermally activated persulfate (TAP). This herbicide was studied for different persulfate dosages (0.97–7.29 g L−1), for varying initial pH levels (3–12) and temperatures (25–70 °C). Compared with Fe2+/PS, TAP could achieve a higher total organic carbon (TOC) removal under wider pH ranges of 3–12. Increasing the mole ratio of PS to 2,4-D favored for the decay of 2,4-D and the best performance was achieved at the ratio of 50. The 2,4-D degradation rate constant highly depended on the initial pH and temperature, in accordance with the Arrhenius model, with an apparent activation energy of 135.24 kJ mol−1. The study of scavenging radicals and the EPR confirmed the presence of both SO4− and OH. However, SO4− was the predominant oxidation radical for 2,4-D decay. The presence of both Cl− and CO32− inhibited the degradation of 2,4-D, whereas the effect of NO3− could be negligible. Verified by GC/MS, HPLC and ion chromatography, a possible degradation mechanism was proposed

2,4-dichlorophenoxyacetic acid (2,4-D) is one of the most applicable herbicides in the world, its residue in aquatic environment threatens the human health and ecosystems. In this study, for the first time, inexpensive Fe-C after pre-magnetization (Pre-Fe-C) was used as the heterogeneous catalyst to activate persulfate (PS) for 2,4-D degradation, proving that Pre-Fe-C could significantly improve the degradation and dechlorination. The results indicated the stability and reusability of Pre-Fe-C were much better than pre-magnetization Fe0 (Pre-Fe0), while the leaching iron ion was lower, indicating that using Pre-Fe-C not only reduced the post-treatment cost, but also enhanced the removal and dechlorination efficiency of 2,4-D. Several important parameters including initial pH, Fe-C dosage, PS concentration affecting 2,4-D degradation and dechlorination by Pre-Fe-C/PS were investigated and compared with that of Fe-C/PS, observing a 1.2-2.7 fold enhancement in the degradation rate of 2,4-D. The Fe-C and Pre-Fe-C were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and SEM-EDX-mapping, suggesting that the content of Fe and O changed more obviously after magnetization. The degradation intermediates, such as chloroquinol, 2-chlorophenol, were identified by a gas chromatography mass spectrometry (GC/MS) and an ion chromatography (IC), and a possible degradation pathway was proposed.

Efficient anode materials are essential to electrochemical advanced oxidation processes (EAOPs) for organic wastewater treatment. In this regard, blue TiO2 nanotube arrays (Blue-TNA) anode was prepared for the first time in formic acid electrolyte by electrochemical self-doping and applied for electrochemical degradation of contaminants. Characterized by XPS, Raman and Mott-Schottky curves, the formation of Ti3+ on Blue-TNA was confirmed. This anode was more efficient and had a higher hydroxyl radical production activity (1.7 × 10−14 M) than BDD (9.8 × 10-15 M), inducing a higher TOC and COD removal of 100 mg/L phenol with a lower energy consumption of 9.9 kW h/(kg COD) at current density 2.5 mA/cm2, pH 5 in 0.1 M Na2SO4, account for the lower accumulation of degradation intermediates. Both •OH and SO4•- were responsible for the degradation on Blue-TNA anode, while their contributions differed greatly with that of BDD, and could be affected and regulated by the operating parameters like current density, initial pH and Na2SO4 concentration. Blue-TNA anode represented a relative stable performance for 5 cycles degradation of 100 mg/L phenol for each cycle of 300 min, and such an oxidation capacity could be easily regenerated by electrochemical reduction in formic acid. Blue-TNA anode had an excellent performance on the TOC removal and MCE especially at low current density of 2.5 mA/cm2 when compared with other anodes. Therefore, Blue-TNA anode is hopeful a promising and cost-effective anode for electrochemical oxidation.

Hydrogen peroxide (H2O2) is a green oxidant that widely used in environmental remediation and chemical industries, hence the exploration of suitable modified cathode for the cost-effective electrochemical synthesis of H2O2 is of great importance. In this work, tert-butyl-anthraquinone (TBAQ) was attempted to modify four kinds of typical carbon materials (carbon aerogel, carbon nanotube (CNT), carbon black and graphene-doped carbon black) to fabricate gas diffusion electrode (GDE) to improve H2O2 production for potential use in electro-Fenton process. It was found that CNT-GDE containing 2% TBAQ had the highest H2O2 production (150.6 mg/L) with a high current efficiency (95%) and low energy consumption (2.43 kWh/(kg H2O2)) among four carbon materials because of the redox of TBAQ and more active sites (C–C sp3 carbon and oxygen-containing functional groups). The effects of TBAQ addition amount, current and initial pH on H2O2 performance were investigated. The presence of TBAQ could improve oxygen reduction activity, H2O2 selectivity and hydrophobicity to improve H2O2 production. Suitable current (50 mA) and initial pH benefited the enhancement in H2O2 production. The CNT-GDE containing 2% TBAQ showed better H2O2 production performance with good stability when comparing with literature, indicating promising for electro-Fenton application.