Exploring the temperature-induced structural evolution and optical properties of an acid-based geopolymer incorporating CuO and Fe

The synthesis of a Cu/Fe-acid-based geopolymer (CFASP) involved the combination of Metakaolin, CuO, and Fe filings with diluted phosphoric acid. X-ray diffraction (XRD) analysis unveiled the presence of two crystalline phases within the geopolymer matrix at room temperature: the pyrophyllite-2M1 type structure and (Cu, Fe)3(PO4)2. Upon heating to 400 degrees C, the (Cu, Fe)3(PO4)2 phase was retained, while the pyrophyllite-2M1 phase transformed into pyrophyllite-A1. Further heating to 600 degrees C resulted in the disappearance of (Cu, Fe)3(PO4)2 peaks, leaving behind pyrophyllite-like structures, whereas at 1000 degrees C, iron and aluminum phosphate (Al, Fe)PO4 and metaphosphate (Fe, Al)(PO3)3 emerged alongside an amorphous phase. Raman spectroscopy delineated various entities and bonds, hinting at zeolite formation and the presence of Cu2O. The geopolymer network exhibited a uniform distribution of constituents with diverse structural configurations. Luminescence analysis uncovered fluorescence emission peaks and temperature-dependent bandgap energy, underscoring tailored optical properties essential for applications in construction and ceramics. The exceptional transparency and adjustable optical characteristics position CFASP favorably for innovative uses in architectural glazing and beyond.