Efficient degradation of metronidazole with dual-cathode of acetylene black-PTFE/CoFe2O4-PTFE coupling persulfate

Unveiling electron transfer and radical transformation pathways in coupled electrocatalysis and persulfate oxidation reactions for complex pollutant removal

The degradation of multiple organic pollutants in wastewater via advanced oxidation processes might involve different radicals, of which the types and concentrations vary upon interacting with different pollutants. In this study, electrochemical activation of peroxymonosulfate (E/PMS) using advanced activated carbon cloth (ACC) as electrode was applied for simultaneous degradation of mixed pollutants, e.g., metronidazole (MNZ) and p-chloroaniline (PCA). 92.5 % of MNZ and 91.4 % of PCA can be degraded at the cathode and anode at a low current density and PMS concentration, respectively. The rate constants for the simultaneous removal of MNZ and PCA in the E/PMS/MNZ(PCA) system were 118 times and 6 times higher than those in the sole PMS system, and 2.5 times and 1.6 times higher than those in the E/Na2SO4/MNZ(PCA) system, respectively. Different electrochemical characteristics, EPR spectra and radical quenching tests verified that the degradation of MNZ and PCA in the optimal system proceeded primarily through non-radical-dominated oxidation, involving electron transfer and 1O2 effect. The system also exhibited low energy consumption (0.215 kWh/m-3·order-1), broad operational pH range, excellent removal efficiency for water matrix, and low by-products toxicity, indicating its strong potential for practical applications. The ACC, with its super stable, low cost, and electrochemical activity, make it as a promising materials applicable in the E/PMS system for degradation of multiple pollutants. The study further elucidated the mechanism of pollutant interaction with electrode materials in terms of radical and non-radical transformation, providing fundamental insight into the application of this system for treatment of complex wastewater.

A comparative review on the mitigation of metronidazole residues in aqueous media using various physico-chemical technologies

In the last few decades, pharmaceuticals have emerged as a new class of serious environmental pollutants. The presence of these emerging contaminants even in minimal amounts (micro- to nanograms) has side effects, and they can cause chronic toxicity to health and the environment. Furthermore, the presence of pharmaceutical contaminants in water resources leads to significant antibiotic resistance in bacteria. Hence, the removal of antibiotics from water resources is essential. Thus far, a wide range of methods, including adsorption, photodegradation, oxidation, photolysis, micro-/nanofiltration, and reverse osmosis, has been used to remove pharmaceutical contaminants from water systems. In this article, research related to the processes for the removal of metronidazole antibiotics from water and wastewater, including adsorption (carbon nanotubes (CNTs), magnetic nanocomposites, magnetic molecularly imprinted polymer (MMIP), and metal-organic frameworks), filtration, advanced oxidation processes (photocatalytic process, electrochemical advanced oxidation processes, sonolysis and sonocatalysis) and aqueous two-phase systems (ATPSs), was reviewed. Results reveal that advanced oxidation processes, especially photocatalytic and sonolysis processes, have high potential in removing MNZ (more than 90%).

Efficient degradation of bisphenol A and amino black 10B by magnetic composite Fe3O4@MOF-74 as catalyst

Metal-organic frameworks (MOFs) exhibit high chemical stability and porosity, and have been widely applied in various fields including selective adsorption and separation, sensors, and catalysis. When combined with Fe3O4, they effectively address issues such as aggregation of Fe3O4 particles and the difficulty in recovering MOFs as catalysts. Therefore, in this study, we used a simple solvothermal method as a catalyst to synthesize a high specific surface area magnetic composite Fe3O4@MOF-74, which was used to catalyze the degradation of bisphenol A (BPA) and amino black 10B in wastewater. We activated Na2S2O8 to generate radicals for oxidizing and degrading BPA and amino black 10B. Experimental results showed that at 35 °C, with Fe3O4@MOF-74 (Fe3O4: MOF-74=1:1) concentration of 0.2 g/L and Na2S2O8 concentration of 2 g/L, the catalytic effect is efficient and economical. Meanwhile, removal rates of BPA and amino black 10B exceeded 95.58 % over a broad pH range (pH 3-9). Furthermore, even after multiple cycles of use, Fe3O4@MOF-74 maintained catalytic degradation rates of BPA and amino black 10B above 93.24 % and 95.01 %, respectively. Additionally, in water samples, removal rates of BPA and amino black 10B exceeded 91.55 %. This study provides a new and efficient catalyst material for wastewater treatment, which is expected to play an important role in environmental remediation.

Mesoporous cobalt-manganese layered double hydroxides promote the activation of calcium sulfite for degradation and detoxification of metronidazole

Metronidazole (MNZ), a commonly used antibiotic, poses risks to water bodies and human health due to its potential carcinogenic, mutagenic, and genotoxic effects. In this study, mesoporous cobalt-manganese layered double hydroxides (CoxMny-LDH) with abundant oxygen vacancies (Ov) were successfully synthesized using the co-precipitation method and used to activate calcium sulfite (CaSO3) with slight soluble in water for MNZ degradation. The characterization results revealed that Co2Mn-LDH had higher specific areas and exhibited good crystallinity. Co2Mn-LDH/CaSO3 exhibited the best catalytic performance under optimal conditions, achieving a remarkable MNZ degradation efficiency of up to 98.1 % in only 8 min. Quenching experiments and electron paramagnetic resonance (EPR) tests showed that SO4•- and 1O2 played pivotal roles in the MNZ degradation process by activated CaSO3, while the redox cycles of Co2+/Co3+ and Mn3+/Mn4+ on the catalyst surface accelerated electron transfer, promoting radical generation. Three MNZ degradation routes were put forward based on the density functional theory (DFT) and liquid chromatography-mass spectrometer (LC-MS) analysis. Meanwhile, the toxicity analysis result demonstrated that the toxicity of intermediates post-catalytic reaction was decreased. Furthermore, the Co2Mn-LDH/CaSO3 system displayed excellent stability, reusability, and anti-interference capability, and achieved a comparably high removal efficiency across various organic pollutant water bodies. This study provides valuable insights into the development and optimization of effective heterogeneous catalysts for treating antibiotic-contaminated wastewater.

Rapid degradation and detoxification of metronidazole using calcium sulfite activated by CoCu two-dimensional layered bimetallic hydroxides: Performance, mechanism, and degradation pathway

In this study, cobalt copper-layered double hydroxides (CoCu-LDHs) were prepared by coprecipitation as catalysts to activate CaSO3 for metronidazole (MNZ) degradation. This is the first report on layered double hydroxides activating sulfite for the degradation of organic pollutants. Meanwhile, to address the issue of self-quenching reactions readily occurring in conventional sulfite advanced oxidation systems and resulting in low oxidant efficiency, CaSO3 with slightly soluble in water was used instead of commonly used Na2SO3, to improve the limitations of traditional systems. The results showed that in the CoCu-LDHs/CaSO3 system, the degradation rate of MNZ reached 98.7% within 5 min, representing a 23.0% increase compared to the CoCu-LDHs/Na2SO3 system. Owing to the excellent catalytic performance exhibited by CoCu-LDHs, characterizations including XRD, FTIR, SEM, TEM, BET and XPS were carried out to investigate this further. The results confirmed the successful synthesis of CoCu-LDH, and the activation mechanism study revealed that Co and Cu were considered to the main elements in activating CaSO3, demonstrating good synergistic effects. In addition, the oxygen vacancies on the catalyst surface also played a positive role in generating radicals and promoting electron transfer. Subsequently, the effects of Co/Cu ratio, catalyst dosage, oxidant concentration, pollutant concentration, pH and coexisting substances on MNZ degradation were investigated. Additionally, based on the LC-MS analysis of degradation products and toxicity tests, MNZ was transformed into different intermediates with low toxicity through four pathways, eventually mineralizing into inorganic small molecules. After six cycles, the MNZ degradation rate still reached 82.1%, exhibiting excellent stability and recyclability. In general, this study provides new ideas for activating sulfite, while providing theoretical support for subsequent research on sulfite advanced oxidation system.

Study on the photocatalytic degradation of metronidazole antibiotic in aqueous media with TiO2 under lab and pilot scale

Nowadays, the increased consumption of antibiotics, such as metronidazole (MTZ), leads to their introduction in wastewater as well as in the receiving surface waters due to their incomplete removal by conventional wastewater treatment plants. Heterogeneous photocatalysis is a versatile technology that can efficiently degrade such organic contaminants. In the present research, the photocatalytic degradation of MTZ with TiO₂ P25 was studied under lab and pilot (CPC reactor) conditions. The antibiotic was efficiently removed at high rates in both cases (100 % and 91 %) following pseudo-first order kinetics with rate constants equal to 0.0452 min^-1 (±RSD% = 0.68 % - 2.57 %) and 0.0462 L KJ^-1 (±RSD% = 8.94 % - 21.64 %) respectively. Also, by scavenging lab scale experiments, the contribution of the generated reactive species was investigated and hydroxy radicals (HO^•) were proposed as the predominant species. By applying high resolution mass spectrometry techniques, the transformation products (TPs) were identified and possible transformation pathways were proposed. The ecotoxicity of the TPs was assessed in silico using the ECOSAR software with the results revealing that most of them were less toxic than the parent compound. Similarly, the mutagenicity, developmental toxicity and bioconcentration factors of the TPs were predicted by utilizing the T.E.S.T. software and in their majority, were found to be less mutagenic and developmentally toxic than MTZ. The ecotoxicity monitoring with the Vibrio fischeri bioassay in both laboratory and pilot scale experiments indicated that through heterogeneous photocatalysis it is possible to reduce the toxicity of wastewater containing MTZ. Finally, the stability and reusability of the photocatalyst was investigated through three consecutive catalytic cycles with the results showing that the performance of TiO₂ decreased after each use. For the heterogeneous photocatalysis with TiO₂ to be a "real life" applicable technique, further studies focusing on catalyst regeneration and optimization of the catalytic conditions must be conducted.