Electrochemically enhanced iron oxide-modified carbon cathode toward improved heterogeneous electro-Fenton reaction for the degradation of norfloxacin

In this work, different iron-based cathode materials were prepared using two different approaches: a novel one-step approach, which involved the incorporation of iron oxide with Printex® L6 carbon/PTFE (PL6C/PTFE) on bare carbon felt (CF) and a two-step approach, where iron oxide is deposited onto CF previously modified with PL6C/PTFE. The results obtained from the physical characterization indicated that the presence of iron oxide homogeneously dispersed on the felt fibers with the CF 3-D network kept intact in the one-step approach; whereas the formation of iron oxide aggregates between the felt fibers for material obtained using the two-step approach. Among the iron oxide-based cathodes investigated, the iron-incorporated electrode exhibited the greatest efficiency in terms of the removal and mineralization of norfloxacin (NOR) under neutral pH (complete NOR removal in less than 30 min with around 50% mineralization after 90 min). The findings of this study show that the low cost and simple-to-prepare iron-modified carbon-based materials in HEF process led to the enhanced degradation of organic contaminants in aqueous solutions.

Low-coordinated Co-N3 sites induce peroxymonosulfate activation for norfloxacin degradation via high-valent cobalt-oxo species and electron transfer

The identification of reactive species in peroxymonosulfate (PMS) activation triggered by carbon-based single atom catalysts is the key to reveal the pollutant degradation mechanism. Herein, carbon-based single atom catalyst with low-coordinated Co-N₃ sites (Co_SA-N₃-C) was synthesized to active PMS for norfloxacin (NOR) degradation. The Co_SA-N₃-C/PMS system exhibited consistent high performance for oxidizing NOR over a wide pH range (3.0-11.0). The system also achieved complete NOR degradation in different water matrixes, high cycle stability and excellent degradation performance for other pollutants. Theoretical calculations confirmed that the catalytic activity was derived from the favorable electron density of low-coordinated Co-N₃ configuration, which was more conductive to PMS activation than other configurations. Electron paramagnetic resonance spectra, in-situ Raman analysis, solvent exchange (H₂O to D₂O), salt bridge and quenching experiments concluded that high-valent cobalt(IV)-oxo species (56.75%) and electron transfer (41.22%) contributed dominantly to NOR degradation. Moreover, ¹O₂ was generated in the activation process while not involved in pollutant degradation. This research demonstrates the specific contributions of nonradicals in PMS activation over Co-N₃ sites for pollutant degradation. It also offers updated perceptions for rational design of carbon-based single atom catalysts with appropriate coordination structure.

Binder-free NiO/MnO2 coated carbon based anodes for simultaneous norfloxacin removal, wastewater treatment and power generation in dual-chamber microbial fuel cell

Norfloxacin (NFX) is a commonly consumed synthetic antibiotic drug to cure many adverse infectious diseases of humans worldwide, but their presence in almost all aquatic environments has grown into severe global health concerns. In this study, the power performance of dual-chamber microbial fuel cells (MFCs) with two different types of base anodes (graphite felt and activated carbon cloth) were tested with a coating of NiO/MnO₂ for removal of NFX in wastewater. As transition metal oxides have excellent electrochemical stability and a higher specific capacitance, their application in MFC for antibiotic removal and wastewater treatment would be an interesting study. Four different NFX concentrations were studied in two different base material with a coating of NiO/MnO₂. Coating was done with 2 step hydro solvothermal method and modified anode surface was characterized by XRD and XPS analyses. Extracellular electron transfer between microorganisms and the modified anode improved significantly as a consequence of reduced internal resistance and a more biocompatible surface as measured by Electroscopy Impedance Spectroscopy (EIS) and polarization curves. NiO/MnO₂ coated graphite felt performed 1.2 fold better than the control plain graphite felt. Similar results were found for activated carbon cloth (ACC). Modified ACC performed 1.3 fold better than the control plain ACC.

Improving photocatalytic activity by construction of immobilized Z-scheme CdS/Au/TiO2 nanobelt photocatalyst for eliminating norfloxacin from water

To improve the photocatalytic activity of TiO₂ NBs under irradiation of solar light, an immobilized Z-scheme composite photocatalyst CdS/Au/TiO₂ NBs has been constructed. For the unique architectures, the TiO₂ NBs provide more absorption and reaction sites, the CdS nanoparticles enhance overall light harvesting, and Au acts as the electron transfer mediator, promoting the interfacial charge transfer and efficient separation of electrons and holes. The morphology, elements, crystal structure, optical and photoelectrochemical properties, and photocatalytic activity of CdS/Au/TiO₂ NBs were characterized. Results showed that CdS/Au/TiO₂ NBs possesses higher photocatalytic activity toward the degradation of antibiotic norfloxacin under irradiation of simulated sunlight, which is attributed to the synergetic interaction of increased light absorption and separation of photogenerated electrons and holes. Besides, the degradation of norfloxacin was promoted by HCO₃^-, but inhibited by NO₃^- and Cl^-. The radicals trapping experiments proved that superoxide radicals (O₂^-) was the dominating active species during the photocatalysis process. The photocatalytic degradation products of norfloxacin was analyzed, and nine intermediates were identified. Moreover, the photocatalytic degradation mechanism and photostability of CdS/Au/TiO₂ NBs were analyzed in detail. The matched energy levels and unique ternary Z-scheme design are the key for improved photocatalytic activity. The deactivation of CdS/Au/TiO₂ NBs after recycles mainly due to the release of CdS by photocorrosion and the loss of deposited Au.

Shuttle-like CeO2/g-C3N4 composite combined with persulfate for the enhanced photocatalytic degradation of norfloxacin under visible light

In this work, the shuttle-like CeO₂ modified g-C₃N₄ composite was synthesized and was combined with persulfate (PS) for the efficient photocatalytic degradation of norfloxacin (NOR) under visible light. Scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) emission spectra were used to characterize the structural and optical properties of the as-prepared catalysts. Active species trapping experiments demonstrated that additional sulfate radicals (·SO₄^-) formed upon the addition of PS which could cooperate with superoxide radicals (O₂^-), holes (h⁺) and hydroxyl radicals (OH) to decompose NOR. Singlet oxygen (¹O₂) was also formed during the reaction and acted as an important active species. The degradation products of NOR were also identified and analyzed by using LC-MS technology, and the possible degradation mechanism and pathways were proposed and discussed. This work indicated that the shuttle-like CeO₂ modified g-C₃N₄ coupled with PS displayed promising applications in the field of pharmaceutical wastewater purification.