Ultrasound-assisted synthesis of macro-/mesoporous ZnO double-pyramids and their optical and photocatalytic properties

Highlights: ► Uniform ZnO double-pyramids with macro-/mesoporous structures have been prepared via ultrasound-assisted route. ► The porous ZnO exhibits narrowed band gap and intensive blue emission. ► High specific surface area leads to extraordinary photocatalytic activity. - Abstract: We report a facile, surfactant-free method for synthesizing double pyramid-like ZnO architectures via an ultrasound-assisted route. The morphology, microstructures, and porosity of the materials have been studied and the formation mechanism has been discussed. Uniform octahedral ZnC2O4 precursors were first formed during ultrasound irradiation, and then transformed to macro-/mesoporous ZnO with the preservation of original shape after calcination at 350 °C. The obtained hierarchical ZnO double-pyramids were composed of ZnO nanoparticles of ∼35 nm and pores with the main distribution between 20 and 100 nm. Raman and photoluminescence measurements reveal the presence of intrinsic defects in the porous ZnO, which accounts for the narrowed band gap (3.16 eV) and the sharp blue emission at 472 nm. Moreover, the ZnO product possesses large specific surface area and exhibits extraordinary photocatalytic activity to degrade organic pollutants.