Green synthesis of silver nanoparticles using cauliflower waste and their multifaceted applications in photocatalytic degradation of methylene blue dye and Hg 2+ biosensing

Green synthesis of silver nanoparticles (AgNPs) using plant extracts has emerged as a viable environment-friendly method. The aim of the study was to biosynthesize AgNPs using cauliflower (Brassica oleracea var. botrytis) waste extract and further test their potential applications in photocatalytic degradation of methylene blue (MB) dye and Hg2+ biosensing. Optimum extract concentration, AgNO3 concentration, pH and temperature required for biosynthesis of stable AgNPs were determined by UV–visible spectroscopy. FT-IR, XRD, SEM, TEM, SAED, XPS and BET analysis were performed for characterizing AgNPs. MB dye degradation using AgNPs was determined by analyzing the intensity of dye absorption maxima at 664 nm. Specificity and sensitivity of biosynthesized AgNPs for Hg2+ ions were studied for assessing their biosensing abilities. Optimum conditions needed for biosynthesis of stable AgNPs were observed to be 3 ml extract, 0.5 mM AgNO3, pH 8.5 and microwave-assisted heating at 600 W for 5 min. FT-IR analysis showed that the extract contained necessary functional groups that facilitated biosynthesis of AgNPs. XRD, SEM, TEM, SAED, XPS results confirmed the formation of AgNPs. BET analysis showed that AgNPs had an average size of 35.08 nm and surface area of 19.22 m2/g. Maximum MB dye degradation percentage of 97.57% was obtained at 150 min without any significant silver leaching thereby, signifying notable photocatalytic property of AgNPs. Biosensing studies showed that AgNPs were specifically able to detect up to 0.1 mg/l Hg2+ ions. In summary, cauliflower waste served as a useful source of reducing agents for biosynthesizing AgNPs with promising environmental applications.