238. Ionic liquid-assisted synthesis of mesoporous α-Ga2O3 hierarchical structures with enhanced …

Fig. 1 (a) XRD pattern and crystal structure (inset), (b) SEM image, (c) TEM image, (d) HRTEM image and SAED pattern (inset) of the as-prepared rhombohedral α-Ga2O3 hierarchical structures by calcining the α-GaOOH precursor at 450 °C for 3 h.

Fig. 2 (a) The UV-visible spectrum of the RhB dye after differentdegradation times in the presence of mesoporous α-Ga2O3 hierarchical structuresand under exposure to UV-light; (b) photocatalytic degradation curves of RhB by various photocatalysts under UV-light irradiation.

Di Li, et al, J. Mater. Chem. A 1, 12417 (2013)
https://doi.org/10.1039/c3ta12619f

(1) In a typical α-GaOOH synthesis procedure, 0.01 g of gallium nitrate hydrate (Ga(NO)3•xH2O) was dissolved in a mixed solution contained 20 mL of H2O, 5 mL of N,N-dimethylformamide (DMF) and 0.05 g of 1-butyl-3-methylimidazoliumhydroxide ([Bmim][OH]) to form a clear solution with magnetic stirring. The as-obtained solution was transferred to a 30 mL autoclave,
and sealed and heated at 180 °C for 24 h. Then, the autoclave was cooled to room temperature and the precipitate was collected after washing and drying at 60 °C in air. After calcining the as-prepared α-GaOOH hierarchical structure precursor at 450 °C for 3 h in air, mesoporous α-Ga2O3 hierarchical structures can be successfully obtained.
(2) All diffraction peaks can be indexed to orthorhombic α-GaOOH (JCPDS card, no. 06-0180) with lattice constants a=0.458 nm, b =0.98 nm and c= 0.297 nm, corresponding to the typical crystal structure (ICSD#409671).
(3) [Bmim][OH] is not only used as a soft template or a capping agent, but also can act as a precursor or modifier in the synthesis process and plays a key role in forming the α-GaOOH hierarchical structures. There could be a cooperative effect of [Bmim]+ ions and [OH]- ions in the formation of α-GaOOH hierarchical structures.
(4) The solid-state transformation of α-GaOOH to α-Ga2O3 by calcining is a topotactic process.
(5) The BET surface area is 35.94 m2g-1 and the pore size distribution calculated from the desorption branch of the nitrogen isotherm by the BJH method shows a range from 3 to 30 nm with 18.06 nm as the center.
(6) The greater adsorption ability of mesoporous α-Ga2O3 hierarchical structures is mostly ascribed to the larger BET surface area which is derived from the pore structures which can offer more active sites.