Model 1600

The reaction conditions of KS@GNPs were investigated by UV-visible spectrophotometer (UV-1800 240 V, Shimadzu Corporation, Koyoto, Japan) with 300 to 700 nm wavelength scanning range. The formation of KS@GNPs was confirmed by the Fourier transform infrared spectrophotometer (FTIR) (Perkin-Elmer Model 1600; Norwalk, CT, USA). Here, a pure KBr pellets (2 mg of GNPs were mixed with KBr) was used with the scanning range from 400 to 4000 cm⁻¹. The crystallinity of KS@GNPs was analyzed by X-ray diffractometer (X’pert PRO MPD, PANalytical BV, Almelo, The Netherlands) using an operating voltage 45 kV; a current of 40 mA, Cu radiation (1.54430 Å), and at a scanning rate 0.388/min within the region of 2 thetas between 5 and 90 °. The average particle size distribution and the surface charge were determined through a dynamic light scattering (DLS) equipment (Zeta plus 90, Brookhaven Instrument Co., Holtsville, NY, USA). The size, morphology, Energy Dispersive X-ray (EDX) spectrum, and selected electron diffraction (SAED) of KS@GNPs were evaluated by using HR-TEM (LEO-912AB OMEGA, LEO, Freising, Germany). A thin coat of the sample was prepared for TEM analysis by diffusing a drop of KS@GNPs solution on the cupper grid (operating voltage 200 eV).

FTIR spectroscopy was also used as a supplementary method to analyze the oxidative stability, evidencing the qualitative presence of primary and secondary oxidation products, according to Haider et al. (2017) [14 (link)]. The samples were prepared by the pellet method with anhydrous KBr powder (1:100 lyophilized samples to KBr ratio). The spectra were obtained by FTIR (Perkin-Elmer Model 1600 apparatus, Wellesley, MA, USA) in the 4000 to 650 cm⁻¹ region, using 16 scans at a resolution of 4 cm⁻¹. The background was measured with a pellet holder, with a pellet of pure KBr.

FTIR Perkin Elmer model 1600 equipment with according to Ph. Eur 2.2.24 general method for the determination of IR spectrum.