Formation of porous niobium pentoxide via phase transformation

Niobium(V) alkoxides were directly prepared in a undivided electrolytic cell by using niobium metal as sacrificing anode, then niobium(V) alkoxides were directly hydrolyzed to gel-like deposits. The phase transformation of the gel-like product by heat treatments resulted in the formation of porous niobium pentoxide. IR, TG-DSC, XRD and SEM were used to characterize the structure of porous Nb₂O₅ and the gel-like products. Studies show that amorphous Nb₂O₅ secondary particles change into orthorhombic phase and form 2 μm spherical particles after calcination at 873 K. While monoclinic Nb₂O₅ is obtained after calcination at 1 173 K, the porous Nb₂O₅ with pore size of about 250 nm is finally formed following the phase transformation of spherical Nb ₂O₅ particles into rod like particles.