Order–Disorder Structure in Ni₃Sb₄CO₆F₆: Synthesis, Characterization, and Its Applications toward Photocatalytic Dye Degradation and Antibacterial Activities

Design of Ni3Sb4CO6F6, a metal carbon oxyfluoride [M–L–C–O–F] comprising a p-block cation, was carried out by incorporating a carbon atom inside the Sb4 tetrahedral void of Ni3Sb4O6F6. Single crystals of Ni3Sb4O6F6 and Ni3Sb4CO6F6 were grown by employing a hydrothermal synthesis technique. Single-crystal X-ray diffraction (SCXRD) studies show that the crystal structure of Ni3Sb4CO6F6 can be explained by both an ordered and a disordered structure model with cubic symmetry (SG: I4̅3m). Disorder generates the four split carbon sites due to symmetrically identical positions at (−x, −x, x) with the occupancy of one quarter of each carbon site of their total occupancy. On the other hand, disorder can be avoided by fixing the carbon site at (0, 0, 0), a special position with 100% occupancy at one site. Conversely, lowering of symmetry to tetragonal symmetry (SG: I4̅) provides comparatively low GOF and R values, which could also be a kind of structural modeling for Ni3Sb4CO6F6 considering the large data-to-parameter ratio. Insertion of carbon introduces an indirect band gap energy (Eg), i.e., 1.75 eV, in Ni3Sb4CO6F6 compared to the direct band gap energy of its parent compound, Ni3Sb4O6F6 (Eg = 3.25 eV), which was also confirmed from the theoretical study. Both Ni3Sb4O6F6 and Ni3Sb4CO6F6 were explored as efficient photocatalysts toward Methylene Blue dye degradation and excellent antibacterial agents against both Gram-positive and Gram-negative bacteria for the first time. The rate of dye degradation was greater for Ni3Sb4CO6F6, as evident from the kinetic study. The addition of 6% H2O2 further increases the rate of dye degradation in both cases. The photocatalysts were recycled up to seven consecutive cycles with 60 and 80% minimum degradation efficiencies for Ni3Sb4O6F6 and Ni3Sb4CO6F6, respectively. Radical scavenger test was also performed to investigate the responsible reactive oxygen species (ROS) in this photocatalytic dye degradation reaction. The antibacterial study was carried out with eight distinct bacterial strains, namely, Staphylococcus sp., Salmonella sp., Pseudomonas sp., Escherichia coli, Klebsiella sp., Bacillus sp., Enterobacter sp., and Proteus sp. The bacterial disinfection properties of each compound were monitored by examining the ability to suppress bacteria in liquid LB medium. The compounds were also characterized through energy-dispersive X-ray (EDS), Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and zeta potential study.