Controlled Synthesis of Monodispersed Sub‐50 nm Nanoporous In 2 O 3 Spheres and Their Photoelectrochemical Performance

Uniform nanoporous In 2 O 3 nanospheres with high surface areas were synthesized through a simple solvothermal route with ethylenediamine (en) as the solvent. The prepared In 2 O 3 nanospheres with diameters about 50 nm are composed of many nanoparticles with average sizes of ca. 5 nm. The unique nanospheres inherit both the large surface areas of the nanoparticles and the high crystallinity of bulky materials. The introduction of water or some other solvents into the reaction solution results in the formation of InOOH and In(OH) 3 particles indicating that en is indispensable for synthesis of In 2 O 3 with a nanoporous nanosphere structure. UV/Vis spectroscopy reveals that the band‐gap of synthesized In 2 O 3 nanospheres is about 2.95 eV, mostly close to that of the single‐crystalline bcc‐In 2 O 3 . The PL spectrum of the In 2 O 3 nanospheres shows two emission peaks located at 470 nm and 483 nm. The photocurrent of the prepared In 2 O 3 electrodes by electrophoretic deposition strongly depends on the calcination temperature. The highest photocurrent density up to 1.9 mA cm –2 at 0.65 V (vs. Ag/AgCl) in 0.1 M Na 2 SO 4 aqueous solution was recorded in the sample annealed at 550 °C. The high photocatalytic activity of the In 2 O 3 nanospheres can be attributed to the high surface area, and the large number of nanopores in the In 2 O 3 nanospheres.