One-step green synthesis of WO3 nanoparticles using Spondia mombin aqueous extract: effect of solution pH and calcination temperature

Abstract

In this study, a novel green synthesis of tungsten trioxide (WO3) nanoparticles from ammonium paratungstate, (NH4)10W11O41·5H2O) and aqueous leaves extract of Spondias mombin was explored. The effect of solution pH (1, 4, 7,10,13) and calcination temperature (250°, 350°, 450°, 550°, 650 °C) on the morphological characteristics and surface area of the nanoparticles were examined. The prepared WO3 nanoparticles were characterized using High-Resolution Scanning Electron Microscopy (HRSEM), Energy-Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), Brunauer Emmett and Teller (BET), and X-ray Photoelectron Spectroscopy (XPS). The HRSEM analysis showed the formation of highly dispersed less agglomerated spherical-shaped structures at each studied pH and calcination temperature except at pH 13. The particle size of the WO3 nanoparticles increased with increase in pH in the order of 13.8 < 14.3 < 16.7 < 17.6 nm for pH 1, 4, 7, and 10, respectively. While there was no evidence of formation of WO3 nanoparticles of definite size at pH 13. XRD patterns confirmed the existence of only monoclinic phase of WO3 irrespective of the solution pH and calcination temperature with average crystallite sizes of about 27.14 nm, 14.39 nm, and 5.90 nm at pH 1, 3, and 5, respectively. The BET analysis established that as-synthesized samples had higher surface area (352.59 m2/g) at pH 1 and calcination temperature (550 °C) than a commercial available WO3 (19.42 m2/g). It was also found that the specific surface area of the samples decreased from 352.59 to 223.67 m2/g, as the solution pH increased from 1 to 10. While for calcination temperature over the range of 250–650 °C, the surface area increased from 156.34 to 352.59 m2/g. XPS demonstrated the presence of W atom in the oxidation state of + 6 and lattice oxygen as O2−. The facile green route to prepared WO3 nanoparticles was accomplished and calcination temperature and solution pH play crucial role on the shape, size, and surface area of the material.