Effect of chromium (III) oxide concentration on optical and physical properties of glasses prepared from Eichhornia crassipes

Abstract

This research aims to investigate the influence of varying concentrations of chromium (III) oxide on the physical and optical properties of glass prepared from water hyacinth. Water hyacinth ash was utilized as a primary raw material to substitute conventional network modifiers such as CaO and K2O. Chemical composition analysis of the water hyacinth ash revealed significant amounts of K2O (55.31 wt%) and CaO (36.31 wt%) as key constituents. Experimental results indicated that as the Cr2O3 concentration increased from 0.00 to 0.05 mol%, the glass density exhibited an increasing trend from 2.5467 to 2.5515 g/cm3. This correlates with the rise in the average molecular weight of the system, while the molar volume decreased from 25.1163 to 25.0872 cm3/mol. Such changes signify a more compact structural arrangement within the glass network. The refractive index also increased with the dopant concentration, rising from 1.5382 to 1.5415, resulting from an increase in total molecular electronic polarizability. Optical absorption spectra displayed prominent absorption bands at wavelengths of 442 nm and 633 nm. These can be explained by Crystal Field Theory, specifically the electronic transitions within the d-orbitals of Cr3+ ions in an octahedral coordination, which caused the glass appearance to shift continuously from Light yellow and transparent to a deeper green. This is consistent with color measurement results in the CIE L*a*b* system, where the brightness (L*) decreased from 81.0465 to 55.4027 and the greenness (-a*) significantly increased from -1.6312 to -18.1764. These findings demonstrate that integrating water hyacinth with Cr2O3 doping can lead to the development of glass materials with unique optical properties and physical stability suitable for further applications in the materials science industry.