A novel synthesis of iron-oxy-halides (FOX)-based metallic microsponges (FOX-MS): an efficient photodegradation of antibiotics

The present study is related to the synthesis of metallic oxy halide nanosheets (FOX) assembled metallic micron-sponge (FOX-MS)-based photocatalytic materials using hydrothermal process to degrade tetracycline (TC) antibiotics. The synthesis of FOX-MS is accomplished by exchanging O⁻ with I⁻ that efficiently tunes the electronic structure (Fe₃O₄ or Fe₂O₃ to form FeOI) and band gap of FeOI. Interestingly, the band gap value decreases with increasing the reaction temperature from 120 to 180 °C attributed to the formation of stable FeOI due to maximum O⁻ exchange with I⁻. Scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy were used to characterize synthesized FOX-MS-based photocatalyst materials. Additionally, upon increasing the Fe metal amount (from 0.5 to 1 mM) during the synthesis the band gap decreases. However, further increment in the amount of Fe metal during synthesis increases the band gap value. The lower band gap value of ~ 1.82 eV with E_CB and E_VB value of 0.48 eV and 2.3 eV is in good agreement with the reported low band gap semiconductors for the degradation of various pollutants. The synthesized FOX-MS was efficiently degrading ~ 63% at 10 mgL⁻¹ of TC. Interestingly, Fenton activity of FOX-MS-based photocatalytic materials improved the TC degradation and achieved maximum degradation of ~ 94% at 10 mgL⁻¹ of TC antibiotics. The degradation of TC antibiotics was also performed under acidic and basic pH conditions to confirm the mechanistic pattern of degradation of TC using FeOI-based metallic microsponge. To the best of our knowledge, this is the first report of the synthesis of FeOI metallic microsponge using a hydrothermal process. Graphical abstract: (Figure presented.)