Experimental and computational study of annealed nickel sulfide quantum dots for catalytic and antibacterial activity

This research investigates the hydrothermal synthesis and annealing duration effects on nickel sulfide (NiS2) quantum dots (QDs) for catalytic decolorization of methylene blue (MB) dye and antimicrobial efficacy. QD size increased with longer annealing, reducing catalytic activity. UV–vis, XRD, TEM, and FTIR analyses probed optical, structural, morphological, and vibrational features. XRD confirmed NiS2's anorthic structure, with crystallite size growing from 6.53 to 7.81 ​nm during extended annealing. UV–Vis exhibited a bathochromic shift, reflecting reduced band gap energy (Eg) in NiS2. TEM revealed NiS2 QD formation, with agglomerated QD average size increasing from 7.13 to 9.65 ​nm with prolonged annealing. Pure NiS2 showed significant MB decolorization (89.85%) in acidic conditions. Annealed NiS2 QDs demonstrated notable antibacterial activity, yielding a 6.15 ​mm inhibition zone against Escherichia coli (E. coli) compared to Ciprofloxacin. First-principles computations supported a robust interaction between MB and NiS2, evidenced by obtained adsorption energies. This study highlights the nuanced relationship between annealing duration, structural changes, and functional properties in NiS2 QDs, emphasizing their potential applications in catalysis and antibacterial interventions.