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Crystalline nanotubes of γ-AlOOH and γ-Al2O3: hydrothermal synthesis, formation mechanism and catalytic performance

Crystalline nanotubes of γ-AlOOH and γ-Al2O3 have been synthesized. An anionic surfactant-assisted hydrothermal process yields γ-AlOOH nanotubes, and appropriate calcination treatment of the γ-AlOOH nanotubes yields γ-Al2O3 nanotubes. The nanotubes were characterized by XRD, SEM, TEM, TG-DSC, FTIR and nitrogen adsorption–desorption techniques. Both the γ-AlOOH and γ-Al2O3 nanotubes are crystalline, with a representative length of ∼500 nm and diameters of 20–40 nm. The γ-Al2O3 nanotubes exhibit a very high mesoporous specific surface area (SSA) of 201.0 m2 g−1 and a high mesopore volume of 0.68 cm3 g−1 with an average mesopore size of 27.7 nm, as well as a high microporous SSA of 186.0 m2 g−1 and a micropore volume of 0.08 cm3 g−1 with an average micropore size of 0.53 nm. The formation process was discussed and a possible mechanism was proposed, in which a lamellar phase was first formed by camphorsulfonic anions and Al(III) species, and then rolled up to form the crystalline nanotubes under the hydrothermal condition. The catalytic performance of the obtained γ- Al2O3 nanotubes was tested by using the dehydration of ethanol to ethylene as a probe reaction and it was shown that the obtained γ- Al2O3 nanotubes catalyst possesses a higher catalytic activity compared with the γ- Al2O3 nanoparticles.