Bio-inspired synthesis of TiO2 hollow nanospheres in agarose gels

[Display omitted] ► TiO2 hollow nanospheres are synthesized in agarose gels by a bio-inspired method. ► The nanospheres contain mesopores in the shell at about 3.8 and 5.5nm in size. ► The mesopores are formed after removing agarose fibers embedded in the TiO2 shell. ► TiO2 nanospheres display a comparative photocatalytic activity to Degussa P25. TiO2 hollow nanospheres have been synthesized in agarose gels by a bio-inspired method for the first time in this study. Their outer and inner diameter are about 99.7 and 56.8nm, respectively, and their shell has bimodal mesopores about 3.8 and 5.5nm in size. These mesopores may be formed through removing the agarose gel fibers embedded in the shell of TiO2 hollow nanospheres during their nucleation and growth. It is inferred that a spherical composite formed by protamine and agarose molecules takes a key role in the formation of TiO2 hollow nanospheres. After calcined at high temperature (400–600°C) for 2h, these TiO2 materials exhibit higher photocatalytic activity for the methyl orange decoloration than Degussa P25 under artificial solar light irradiation. This study may provide a novel and facile approach for the synthesis of metal oxide hollow nanospheres under mild conditions.