Biosynthesis of selenium nanoparticles with orange peel waste in microwave: characterization, and spectral properties

The objective of this study was to reuse agroindustrial waste from orange peels to obtain an orange peel aqueous extract (OPEa), used in the biosynthesis and characterization of selenium nanoparticles (SeNPs). The OPEa acted as a reducing and stabilizing agent in the synthesis of SeNPs, due to its polyphenolic compounds, such as flavonoids, alkaloids, terpenoids, and coumarins, identified by UHPLC-HRMS/MS. The synthesis of SeNPs was conducted in a microwave reactor, at 120 °C and 150 °C, for 30 min, using different volumetric proportions/concentrations between OPEa and sodium selenite (Na₂SeO₃) (5 and 10 mM), in ratios of 1:4, 2:3, 1:1, 3:2, and 4:1 (OPEa (mL) :Na 2 SeO 3(mL) ). The SeNPs were characterized by visual inspection, UV/Vis, DLS, pH, TEM, SEM, and EDX. The results showed that SeNPs were successfully biosynthesized under all conditions, exhibiting distinct characteristics depending on the synthesis conditions. The formation of SeNPs was confirmed by the chromatic transition from greenish tones to light yellow to intense red and by UV/Vis spectrometry, with absorption peaks in the range of 250–340 nm. The SeNPs exhibited a hydrodynamic diameter (HD) of 213.6–1296 nm, with mono- and polydispersity characteristics (PdI: 0.033–0.885) and Zeta potential (ZP) between − 24.2 to -54.9 mV. Among the conditions tested, SeNPs with the best characteristics presented more homogeneous UV/Vis bands, lower HD (273.2–282.8 nm), and PdI (0.089–0.231), high ZP (-34.4 to -36.5 mV), stable pH (6), clear, translucent, and pellet-free colloidal solution, spherical morphology, and selenium accounted for 20.17% of its elemental composition.