Synthesis and characterization of limestone derived biphasic calcium silicate nanocomposites for coating and fuel cell applications

This paper reports for the first time, the synthesis and detailed characterization of biphasic nanocomposites consisting of an almost equimolar ratio (49.1:50.9) of tricalcium silicate and calcium silicate from limestone. The biphasic silicate nanocomposites were synthesized using a modified sol-gel method and subsequent calcination. The samples were characterized using UV-vis, FTIR, SEM, EDX, XRF, XRD, BET, TGA/DTA, and EIS. The analysis of the UV data showed a maximum absorption wavelength at 310 nm and a corresponding Tauc’s determined direct bandgap of 3.40 eV. FTIR analysis mainly identified Si-O vibrations, which confirms the presence of silicates as the major constituents of the nanocomposites. SEM revealed granular, porous morphologies. EDX and XRF data confirmed the presence of calcium, silicon and oxygen that constitute the nanocomposites with Al 2 O 3 and Fe 2 O 3 as dopants. XRF data indicated Ca (52.40%), Si (14.30%), O (32.23%) and a yield of 98.93%. The XRD data also showed the existence of tricalcium silicate phase (JCPDS 77–0376) with a sharp peak at 29.18 °, calcium silicate phase (at 2θ = 26.34, 39.18, 47.05 and 48.15 °), an average crystallite size of 2.89 nm (indicating better structure refinement), moderate micro strain, and a textural coefficient (2.06 ) that showed the tricalcium silicate plane as the preferred growth direction. Phase analysis through the calculation of composition indicated 49.1% Ca₃SiO₅ and 50.9% CaSiO 3 composition, which confirms a biphasic nanoparticle. Rietveld refinement quality parameters (Rp = 4.2%, R wp ) = 5.5%, R exp = 4.0%, χ² = 1.9) clearly showed an acceptable range that supports the characterizing parameters for the biphasic system. The nanoparticles also exhibited mesoporous properties, as indicated by the calculated porosity (46.5%), BET surface area (365.59 m2/g), and DFT-estimated pore diameter (2.65 nm). Thermal analysis of the nanocomposite indicated structural stability up to 400 °C before significant mass loss. Electrochemical impedance spectroscopy (EIS) revealed that the nanocomposite exhibits excellent corrosion resistance and a high capacity to enhance electrochemical activity, making it suitable for fuel cell-related applications. These findings suggest the multifunctional nature of the substance in protective coatings, fuel cells, and optoelectronic devices and offer a pathway to converting low-cost limestone into high-performance nanomaterials.