Variation of the properties of sol–gel synthesized bioactive glass 45S5 in organic and inorganic acid catalysts

Abstract

In this study, bioactive glass (BG) 45S5 powder with a quaternary composition of 45 wt% SiO₂, 24.5 wt% CaO, 24.5 wt% Na₂O, and 6 wt% P₂O₅ was synthesized via a sol–gel route using 1 M nitric acid (HNO₃), 1 M formic acid (HCOOH), and 1 M acetic acid (CH₃COOH) as catalytic media for facilitating hydrolysis and polycondensation reactions. The prepared sols turned into gels within 2–6 days; they were subsequently dried at 70 °C for 120 min and then heated at 900 °C for 5 h for BG formation to occur. The gels were then crushed manually using a mortar and pestle followed by pulverization to obtain the final powder structure. The resulting powders were then characterized by thermogravimetric analysis (TGA), surface area measurements (BET), Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy in coalescence with energy dispersive spectroscopy (SEM-EDS). The in vitro bioactivity of the prepared BG powder was studied by immersion in simulated body fluid (SBF) to check for the formation of a hydroxyapatite layer. SEM-EDS and Raman spectroscopy were performed both before and after the immersion of BG in SBF to validate the formation of the surface hydroxyapatite layer. The crystallinity, porosity and in vitro bioactivity of the BG samples were then compared to check the effects of variation of the catalyst on the properties of the synthesized BG through the sol–gel route. Particle sizes varied between 1 and 10 μm, with a non-uniform morphology. The EDS results suggest that BG prepared with AA as a catalyst exhibits the highest Ca/P ratio of 1.76 when immersed in the SBF, indicating the formation of the apatite layer. TGA studies revealed that mass loss occurs at a higher temperature for the BG prepared with AA and FA as a catalyst. The BET results suggest that the porosities of all the prepared BG samples fall within the mesoporous range of 2–50 nm, with samples prepared with the AA catalyst displaying the highest specific surface areas (SSA).