Hematite (α-Fe2O3) Nanoparticles Conjugated with Thiosemicarbazones: Hydrothermal-Assisted Synthesis, Characterization, Antibacterial, Antioxidant, and Photocatalytic Activities.

In the present study, pre-synthesized hematite (α-Fe2O3) nanoparticles (NPs) were functionalized with three thiosemicarbazone ligands (TSCs), namely salicylaldehyde thiosemicarbazone (STSC), vanillin thiosemicarbazone (VTSC), and 3-acetylpyridine thiosemicarbazone (3-APTSC), through a hydrothermal conjugation approach. The resulting α-Fe2O3/TSC nanoconjugates were characterized using UV-visible (UV-Vis), Fourier Transform Infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDX) analytical techniques. XRD analysis confirmed the crystalline nature of the nanoconjugates, with average crystallite sizes of 15.27 nm, 12.47 nm, and 11.15 nm for α-Fe2O3/STSC, α-Fe2O3/VTSC, and α-Fe2O3/3-APTSC, respectively. UV-vis analysis revealed absorption maxima at 297, 324, and 229 nm, with corresponding optical band-gap energies estimated at 2.66, 3.38, and 2.52 eV for the nanoconjugates. FT-IR and EDX analyses confirmed successful surface functionalization of α-Fe2O3 NPs with the respective TSCs. The nanoconjugates exhibited concentration-dependent antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Salmonella abony, with α-Fe2O3/3-APTSC showing the highest antibacterial efficacy. Antioxidant evaluation using the DPPH assay demonstrated 63.97%, 42.96%, and 74.47% radical-scavenging activities for α-Fe2O3/STSC, α-Fe2O3/VTSC, and α-Fe2O3/3-APTSC, respectively, whereas the same conjugates exhibited 65%, 63%, and 68% degradation of malachite green (MG) dye under visible-light irradiation in 90 min. Overall, α-Fe2O3/3-APTSC exhibited the most promising overall biological and photocatalytic performance. These findings demonstrate that thiosemicarbazone functionalization provides an effective strategy for enhancing the multifunctional properties of hematite NPs for potential environmental and biomedical applications.