Thermal analyzer

Fourier transform infrared spectroscopy (FTIR, Bruker, Karlsruhe, Germany) spectra were obtained on a Bruker VERTEX 70 using standard KBr-pellets in the range of 2200–400 cm⁻¹ with a resolution of 4 cm⁻¹. Thermogravimetric analysis (TGA) measurements were carried out in air at a heating rate of 10 °C min⁻¹ using a Thermal Analyzer (TA Instruments, New Castle, DE, USA). The average sizes and zeta potentials of FNDs were measured using a Delsa Nano C (BECKMAN COULTER Inc, Brea, CA, USA). Size distributions are represented by the particle number.

Information concerning the crystal structures of the synthesized samples was acquired by powder XRD (Bruker AXS D8 diffractometer) with Cu Kα radiation (λ = 1.5406 Å). Thermogravimetric analysis (TGA) was conducted under constant nitrogen flow on a TA thermal analyzer at a rate of 15 °C/min from 25 to 800 °C. The FTIR spectra were recorded using an Agilent FTIR spectrometer with KBr. The N₂ adsorption–desorption isotherms were collected using a Quanta Chrome Nova surface area and pore size analyzer at − 196 °C. The specific surface area of the samples was calculated by the BET method, and the total pore volume was determined from the volume of N₂ taken up by the samples at P/P⁰ = 0.95. Besides, the BJH method was used to calculate the pore size distribution of the samples using the desorption branch of the isotherm. The surface morphologies of the samples were scrutinized with E-SEM (Thermo Scientific Quattro S). The chemical compositions and mapping images of the samples were determined by EDX associated with the E-SEM instrument. The XPS spectra were recorded on a Thermo-Fisher Scientific spectrometer with monochromatic X-ray Al Kα radiation. The total organic carbon (TOC) was measured on Analytic Jena multi N/C 2100S TOC analyzer.

DSC was tested by using a thermal analyzer (TA Instruments, New Castle, DE, USA). SPI films (3–6 mg) were sealed in an aluminum pan and heated at a rate of 10 °C min⁻¹ from 30 to 200 °C under an N₂ atmosphere.