Multifunctional CdSNPs@ZIF-8: Potential Antibacterial Agent against GFP-Expressing Escherichia coli and Staphylococcus aureus and Efficient Photocatalyst for Degradation of Methylene Blue.

Abstract

Multifunctional novel core–shell composites, CdSNPs@ZIF-8, have been synthesized by in situ encapsulation of different amounts of CdSNPs (150, 300, and 500 μL suspension of CdSNPs in methanol) in ZIF-8 at room temperature. These composites have been characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and diffuse reflectance spectroscopy techniques and Brunauer–Emmett–Teller surface analysis. XPS and HRTEM indicate the encapsulation of CdSNPs within ZIF-8 crystal without disturbing the crystal order of ZIF-8. The average size of embedded CdSNPs (determined by the particle size distribution from HRTEM) is found to be 16.34 nm. CdSNPs@ZIF-8 showed potential to be used as an antibacterial agent against the broad spectrum of bacterial strains such as Gram-positive Staphylococcus aureus and Gram-negative green fluorescent protein-expressing Escherichia coli in aqueous medium, as evident by various biophysical experiments, viz., 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, optical density and fluorescence spectroscopic studies, fluorescence and optical microscopic image analysis, disk diffusion assay, field emission scanning electron microscopy, and flow cytometry for reactive oxygen species induction assay. Further, the composite has been used as an efficient photocatalyst for the degradation of organic pollutants, such as methylene blue dye, in aqueous medium and found that the core–shell composite, CdSNPs@ZIF-8 (150 μL) (abbreviated as NC-1) (5 mg), exhibited higher photocatalytic activity (≈1.8 times) than CdSNPs for degradation of 90% of methylene blue (10 mL of 10 ppm) at pH ≥ 7 due to the synergetic effect. Therefore, in situ encapsulation of CdSNPs in ZIF-8 provides an easy executable measure for purification of wastewater effluents for the effective photocatalytic degradation of organic pollutants as well as to remove the bacterial contamination under sunlight.