Fabrication and characterization of multidimensional tungsten oxide networks

Multidimensional WO3 networks with hierarchical bimodal pores have been syn-chronously fabricated by concentrating a solution containing hydrogen peroxide, methanol, per-oxo-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 WO3 networks. The optical photographs of the as-prepared WO3 and the SEM images of calcined WO3 show that they possess multidimensional networks. WO3 foams with multidimensional networks are stable no matter heat-treated or not, showing a self-supporting characteristic. The enlarged SEM image of the calcined WO3 networks proves that the walls of the networks are assembled by WO3 nanoparticles. The XRD spectra of the WO3 exhibit that the as-prepared sample is amorphous and the calcined one is the orthorhombic structure. The N2 adsorption analysis shows a type IV isotherm for calcined WO3 networks. The hysteresis of N2 desorption at p/p0 > 0.6 clearly indicates the presence of mesopores and the sharp increase in the volume adsorbed near p/p0 = 1 shows the existence of macropores. The mesopores in the walls of calcined WO3 networks are observed in the HRTEM image. PVP used as a structure-directing agent is cheap and can stabilize the preparation solution.