Chiang Mai Journal of Science

     Bulk sulfur, a major byproduct produced from the petroleum desulfurization process worldwide, is underutilized partly due to its high hydrophobicity. A size reduction to nanoscale and an improved water dispersibility altogether is consequently crucial to upcycle this abundant resource and to capitalize on the antimicrobial and heavy metal capture properties of elemental sulfur. We report herein a new S/Fe₃O₄ nanocomposite (SUFEO) synthesized via the microwave-assisted rapid melting of bulk sulfur in the presence of superparamagnetic iron (III) oxide (Fe₃O₄) nanoparticles functionalized with non-toxic polyvinylpyrrolidone (PVP) surfactant. SUFEO nanoparticles were characterized via a combination of powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FTIR), Vibrating Sample Magnetometer (VSM), and zeta-potential measurements. Aqueous dispersion of spheroidal SUFEO with an average diameter of 68 ± 10 nm was stable with a zeta-potential of -46.7 mV being measured. SUFEO outperformed bulk sulfur control and removed 94% of Ag nanoparticles (Ag NPs) in 1 hour at a dosage of 30 mg. The removal process followed a pseudo-second-order model, in congruent with the well-known conversion of Ag and S to insoluble silver sulfide (Ag₂S). SUFEO exhibited positive dose-dependent inhibition against gram-positive S. aureus whereas the Fe₃O₄ control was found to be inactive. SUFEO has the potential to serve as a bifunctional agent for treating wastewater containing both heavy metals in their metallic forms and S. aureus.