(527e) Enhanced Stability and Activity of Series LaFexCu1-XO3 Perovskites for Ofloxacin Degradation from Wastewater: DFT Calculation, Mechanisms and Toxicity Evolution

In recent decades, the substantial production of wastewater by the pharmaceutical industry has prompted significant environmental apprehensions, primarily due to its detrimental impact on aquatic ecosystems and biodiversity [1]. A relevant example of pharmaceuticals detected in wastewater is ofloxacin (OFLX) (C₁₈H₂₀FN₃O₄), a member of the third generation of fluorinated quinolone antibiotics extensively prescribed for various bacterial infections. Several studies have been reported the levels of OFLX in various water settings, including sewage water (0.89 to 31.7 µg/L), hospital wastewater (35 µg/L), urban wastewater treatment plants (1.8 µg/L), and surface water (0.5 µg/L) [2,3]. Owing to potential toxicity, stable chemical structure, and low biodegradability, OFLX cannot be efficiently treat using conventional treatment methods. In the recent years, sulphate radical-based AOPs (SR-AOPs) have become more popular for degradation of emerging pollutants from aqueous media. Owing to stronger redox potential (2.5–3.1 V), higher selectivity of SO₄^{•−} radical compared to ^•OH radical, and longer life of (30–40 μs) SO₄^{•−} radical, SR-AOPs have demonstrated the excellent efficacy in degradation of emerging pollutants [4,5]. In order to further enhancing the efficacy of SR-AOPs, a series of perovskites were utilized and activated with peroxymonosulfate (PMS). In the present investigation, OFLX was degraded from aqueous media utilizing a series LaCu_xFe_1-xO₃ perovskites synthesized by citric sol-gel method and activated with PMS. The synthesized perovskite was characterized by various analytical techniques e.g., FESEM/EDX, TEM, BET, FTIR, XRD, XPS and EIS. Subsequently, the effects of crucial parameters such as PMS dosage (250-1000 g/L), catalyst dosage (250-1000 g/L), solution pH (2-12), and reaction temperature (25-55 ℃) were analyzed on OFLX degradation along with PMS consumption in the LaFe_xCu_1-xO₃/PMS system. To evaluate the bio-toxicity of OFLX and their intermediate products analysis by ECOSAR prediction model. Identification of major reactive oxygen species (ROS) generated in the LaFe_xCu_1-xO₃/PMS system for ofloxacin degradation along with the economic evaluation of the treatment process. DFT calculations (e.g., Fukui function, electrostatic potential (ESP) mapping, and HOMO-LUMO structure) were evaluated to identification of strong attacking sites on ofloxacin molecule.

Methodology

All the batch experiments for OFLX degradation were conducted in 250 mL three neck glass reactor containing the 100 mL of OFLX solution maintained at 25 ℃ temperature. The total reflux condenser was fitted on the top of the reactor for preventing the vapour loss. The aqueous solution of OFLX were prepared in Milli-pore water with desired concentrations (5-20 mg/L).The concentration of OFLX was analyzed by HPLC system (Waters India, Ltd.), equipped with C-18 column and UV detector at 295 nm wavelength. The eluent was a binary mixture of methanol and pure Milli-Q water (proportion 25:75 v/v); eluent flow rate was 0.8 mL/min and injection volume of 20 mL (manually injected) in isocratic mode.

Results and conclusions

In order to assess the catalytic activity of synthesized perovskites LaFe_xCu_1-xO₃ catalysts, some initial experimental trials were conducted for OFLX degradation in aqueous solution. The maximum removal of OFLX was observed 4.65%, 5.12%, 7.82%, and 6.74% with the corresponding catalysts 0.2LFC, 0.4LFC, 0.6LFC, and 0.8LFC, without using any oxidant (PMS) as shown in Fig. 1a. Interestingly, when solely employing 1 mM of the oxidizing agent, maximum removal of OFLX was noticed 5.89% under the pH 7.2 and reaction temperature 25°C. Furthermore, while both catalyst and oxidant doses were introduced simultaneously into aqueous media, all catalysts showed remarkable catalytic efficacy in removing ofloxacin, with removal rates of 26.84%, 28.68%, 34.85%, and 29.78%, under the reaction conditions (e.g., 0.5 g/L catalyst dose, 1 mM PMS dose, pH 7.3, and 25 ℃ reaction temperature). To better understand the quantitative contribution of reactive oxygen species (ROS) generated in the LaFe_xCu_1-xO₃/PMS system, a series radical quenching experiments were conducted with various quenchers i.e., tert-butyl alcohol (TBA), L-histidine (LH), and ethanol (EtOH). Combined with intermediates analyzed by GC-MS, DFT calculation and literature survey, the possible transformation pathways of OFLX degradation were proposed systematically. To assess the economic viability of the catalyst, five consecutive cycle experiments were conducted for ofloxacin degradation under the optimum operating condition.

Key conclusions

The present study demonstrates that catalyst 0.6LFC exhibited the excellent degradation performance toward OFLX in the LaFe_xCu_1-xO₃/PMS system. The quenching experiments reveals that SO₄^{•−} radicals was dominant ROS for OFLX degradation in the LaFe_xCu_1-xO₃/PMS system. Furthermore, six potential routs of OFLX degradation were proposed based on the DFT calculation study, intermediates identified by GC-MS analysis and existing literature.

References

1. Kumar, B. Prasad, S. Kumari, F. Bux, Mechanistic insight into SO₄^−/^•OH radical for enhancing stability and activity of LaMO₃ perovskite toward detoxification of bulk pharmaceutical wastewater: Stoichiometric efficiency and controlled leaching study, Sep. Purif. Technol. 319 (2023) 123967.
2. Su, J. Li, H. Yuan, B. Wang, Y. Wang, Y. Li, Y. Xing, Visible-light-driven photocatalytic degradation of ofloxacin by g-C3N4/NH2-MIL-88B(Fe) heterostructure: Mechanisms, DFT calculation, degradation pathway and toxicity evolution, Chem. Eng. J. 427 (2022).
3. Patidar, V.C. Srivastava, Mechanistic and kinetic insights of synergistic mineralization of ofloxacin using a sono-photo hybrid process, Chem. Eng. J. 403 (2021) 125736.
4. Liang, K. Gao, A. Zhou, Y. Fang, S. Su, L. Fu, M. Sun, X. Duan, Long-lasting performance of high-flux perovskite membrane for catalytic degradation of organic pollutants, Appl. Catal. B Environ. 327 (2023) 122440.
5. J. Qian, R. Ma, Z. Chen, G. Wang, Y. Zhang, Y. Du, Y. Chen, T. An, B. Ni, Hierarchical Co-Fe layered double hydroxides (LDH)/Ni foam composite as a recyclable peroxymonosulfate activator towards monomethyl hydrazine degradation: Enhanced electron transfer and ¹O₂ dominated non-radical pathway, Chem. Eng. J. (2023) 143554.