Transition metal oxide tubes synthesized by using ammonium tartrate crystal template

Transition metal oxide (TiO2, ZrO2, Nb2O5 and Ta2O5) tubes were synthesized by using organic crystal with needle-like form i.e. ammonium dl-tartrate as a template in sol-gel reaction. First, ammonium dl-tartrate crystals were precipitated and rapidly grown to needle-like form when concentrated ammonia was added to ethanol solution containing dl-tartaric acid. Next, the transition metal oxide was deposited only on the side faces of the template crystals when corresponding metal alkoxide was added into the ethanol solution containing the crystal templates and stirred. After deposition of the oxide layer on the side faces of the crystals, the central templates were removed by washing with water to form hollow tubes with rectangular outer shapes and inner channels. The size of the thus formed tubes were ca. 40-200 mum in length 1.3-5.9 mum in width, 1.0-4.9 mum in channel width and 0.2-0.7 mum in wall thickness. It was found from FT-IR and powder XRD that every kind of tube was present as amorphous oxide gel. The specific surface areas and pore size distribution of as-prepared tubes significantly varied depending on the kind of alkoxides. The uniformity of hydrolytic polycondensation of alkoxides and the amount of hydrated water in gel might affect the microporous structure of the tubes. The present template method using water-soluble ammonium dl-tartrate crystal could be effective for synthesizing micron-submicron sized transition metal oxide tubes according to a simple process.