Fast and efficient green synthesis of CaWO4 NPs using eggshells as a biogenic calcium source: Structure, optical property, and morphology

Abstract

In summary, we report a fast, easy, and low-cost green synthesis approach to obtain calcium tungstate nanoparticles (CaWO4NPs_GS) using eggshells as a source of calcium by the sonochemistry method at room temperature. These nanomaterials were structurally characterized by X-ray diffraction (XRD) and Rietveld refinement analysis, where a pure phase with very close structural parameters with calcium tungstate nanoparticles was synthesized at the conventional route (CaWO4NPs_CS). All vibrational Raman active modes characteristic of symmetry point C4h6 were confirmed. An optical band gap value (Egap = 3.92(2) eV) for CaWO4NPs_GS lower than for CaWO4NPs_CS (Egap = 3.92(2) eV) was archived, and that is associated with the intermediate electronic levels due to the oxygen vacancy and micro-strain effect. Field Emission Scanning Electron Microscopy (FE-SEM) images show several nanoparticles with a particle size of 62.7 ± 1.3 nm for CaWO4NPs_CS and 48.7 ± 1.2 nm for CaWO4NPs_GS, where all elements characteristic of calcium tungstate (Ca, W, and O) were appointed by Energy Dispersive X-ray (EDX) analysis. While the photocatalytic performance of CaWO4NPs_GS was 2.5 times faster than CaWO4NPs_CS in the photodegradation of Rhodamine B (RhB) dye in an aqueous solution under UV light in 120 min. Therefore, confirming that chicken eggshell is a promissory raw material as a biogenic source of calcium ions for synthesizing calcium tungstate with promissory photocatalytic properties.