H. Kominami et al., Solvothermal synthesis of tantalum(V) oxide nanoparticles and their photocatalytic activities in aqueous suspension systems, PHYS CHEM P, 3(13), 2001, pp. 2697-2703
Tantalum(v) oxide (Ta2O5) powders were synthesized by a solvothermal reacti
on of tantalum pentabutoxide (TPB) in toluene at 473-573 K in the presence
of water. Ta2O5 powder with a large surface area (> 200 g(-1)) was obtained
at 473 and 523 K, and its X-ray diffraction patterns showed no clear peaks
of crystallites, while crystalline beta -phase Ta2O5 was obtained in the s
olvothermal process at 573 K. Post-calcination of the amorphous Ta2O5 at 97
3 K also induced crystallization into the beta -phase. These amorphous and
crystalline Ta2O5 particles were platinized and then used for photocatalyti
c production of hydrogen from 2-propanol in aqueous solution under deaerate
d conditions by irradiation at a wavelength > 300 nm. As-synthesized amorph
ous and crystalline beta -phase samples exhibited negligible rates of hydro
gen evolution, whereas crystalline beta -phase samples formed by post-calci
nation showed higher activity. Calcination of amorphous Ta2O5 prepared by h
ydrolysis of TPB under atmospheric pressure also increased the rate, which
is, however, ca. one third of that of Ta2O5 obtained via the solvothermal r
oute. Mineralization of acetic acid under aerated conditions was conducted
as a test reaction for photocatalytic decomposition of organic compounds. A
lso, in this reaction system, bare (not platinized) solvothermal Ta2O5 exhi
bited a higher rate of CO2 formation than other Ta2O5 samples. Photoirradia
tion at > 200 nm onto an aqueous 2-propanol suspension of platinized Ta2O5
under deaerated conditions yielded hydrogen and acetone in an early stage,
but CO2 was liberated by prolonged irradiation, suggesting that decompositi
on of acetone to CO2 proceeds even under deaerated conditions.