*3.3. Characterization of Samples*

The surface morphology and chemical composition of the prepared AAMs were analyzed by field emission scanning electron microscopy (FESEM; Carl Zeiss Microscopy GMbH, Jena, Germany) combined with energy-dispersive X-ray spectroscopy (EDS; analyzer at the Centre for Material Analysis, University of Oulu, Finland). The phase composition of AAMs was determined by powder X-ray diffraction (XRD) with a PANalytical X 0Pert Pro X-ray diffractometer (Malvern PANalytical, Almelo, The Netherlands). XRD analysis was performed by scanning two theta values between 10◦ and 70◦ with monochromatic Cu Kα1 (λ = 1.5406 Å) at 45 kV and 40 mA at a scan speed of 0.021 ◦/s. Crystalline phases were identified by HighScore Plus software using the Powder Diffraction File standards from the International Centre for Diffraction DATA ICDD (PDF-4+ 2020 RDB). Diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) was employed to investigate the degree of polymerization of the prepared samples. DRIFT spectra were recorded on a Bruker PMA 50 Vertex 80 V (Bruker, Billerica, MA, USA), equipped with a Harrick Praying Mantis diffuse reflection accessory and a high-temperature reaction chamber, by baseline measurement using KBr. Before analysis, the sample chamber was flushed with nitrogen (100 cm3/min), heated at a rate of 10 ◦C/min to the target temperature of 120 ◦C, and maintained at that temperature for 30 min. Measurements were conducted at 400–4000 cm−<sup>1</sup> with a resolution of 4 cm−<sup>1</sup> and 500 scans per minute. The specific surface areas and porosity were obtained from nitrogen adsorption–desorption isotherms at the liquid nitrogen temperature (–196 ◦C) by the Brunauer–Emmett–Teller (BET) method on a Micromeritics ASAP 2020 system (Micromeritics Instrument Corporation, Norcross, GA, USA). The pore size distribution was calculated by density functional theory (DFT) [66]. Furthermore, the main elements of the prepared samples (Al, Ca, Mg, Na, and Si) and the active metal Fe were analyzed by ICP-OES analysis (Thermo Electron iCAP 6500 Duo, Thermo Fisher Scientific, Waltham, MA, USA).
