Infrared spectrophotometer

The surface structure and element changes of PG and PG-B were analyzed by a scanning electron microscope equipped with an energy-dispersive spectrometer (SEM-EDS, Prox, Phenom, The Netherlands). The Fourier transform infrared (FT-IR) spectra were recorded in the 4000–400 cm⁻¹ region by an infrared spectrophotometer (Thermo Nicolet, MA, Madison, WI, USA).

The morphology, particle size distribution and microstructure of STC-NPs obtained at 400°C were examined by TEM (Tecnai G220; FEI Company, USA) at 200 kV, and the lattice spacing and other internal structures were observed by HRTEM (JEN-1230; Japan Electron Optics Laboratory; Japan) and X-ray diffractometer (XRD). The optical information of STC-NPs was analysed using ultraviolet spectrophotometer (CECIL, Cambridge, UK) and fluorescence spectrophotometer (F-4500, Tokyo, Japan). An infrared spectrophotometer (Thermo, California, USA) was used to analyse the distribution of functional groups on the surface of STC-NPs from 4000–400 cm⁻¹. The elemental and surface compositions of NPs were observed by X-ray photoelectron spectroscopy (ESCALAB 250Xi, Thermo Fisher Scientific, USA).