Fabrication and characterization of multidimensional tungsten oxide networks

Abstract

Multidimensional WO 3 networks with hierarchical bimodal pores have been synchronously fabricated by concentrating a solution containing hydrogen peroxide, methanol, peroxo-polytungstic acid and poly ( n -vinylpyrrolidone) (PVP). The optical microscope, SEM, powder XRD, TG, HRTEM, and N2 adsorption (BET) techniques have been used to characterize the as-prepared and calcined WO 3 networks. The optical photographs of the as-prepared WO 3 and the SEM images of calcined WO 3 show that they possess multidimensional networks. WO 3 foams with multidimensional networks are stable no matter heat-treated or not, showing a self-supporting characteristic. The enlarged SEM image of the calcined WO 3 networks proves that the walls of the networks are assembled by WO 3 nanoparticles. The XRD spectra of the WO 3 exhibit that the as-prepared sample is amorphous and the calcined one is the orthorhombic structure. The N 2 adsorption analysis shows a type IV isotherm for calcined WO 3 networks. The hysteresis of N 2 desorption at p / p 0 > 0.6 clearly indicates the presence of mesopores and the sharp increase in the volume adsorbed near p / p 0 = 1 shows the existence of macropores. The mesopores in the walls of calcined WO 3 networks are observed in the HRTEM image. PVP used as a structure-directing agent is cheap and can stabilize the preparation solution.