A novel synthesis of hexagonal cylinder-like ZnO with an excellent performance by a surfactant-free microemulsion-hydrothermal method

[Display omitted] •A surfactant-free microemulsion (SFME) template method for the preparation of ZnO microcrystals was proposed.•The ZnO microcrystals transform from hexagonal cylinder-like (140℃) to hexagonal cylinder twinning (160℃) microcrystals.•The signal peak of the EPR spectra of the ZnO samples appears at g=1.956 due to oxygen vacancy.•The ZnO microcrystals synthesized at 140°C can significantly photocatalyze the degradation of 10 ppm MB solution.•This study provides a new way to prepare materials with high photocatalytic activity. A W/O surfactant-free microemulsion (SFME) template-hydrothermal method for the preparation of ZnO products was proposed. Using the SFME system containing hexane, propan-2-ol and water, hexagonal cylinder-like (twinning) ZnO microcrystals were synthesized. The XRD, SEM and TEM characterizations showed that the synthesized ZnO microcrystals have a hexagonal wurtzite structure. At hydrothermal temperatures of 120–140°C, hexagonal cylinder-like ZnO microcrystals were synthesized, whereas the hexagonal cylinder twinning ZnO microcrystals were obtained at 160°C. The growth mechanism of the ZnO microcrystals was also investigated. The EPR and XPS spectra of the synthesized ZnO products showed that there are oxygen vacancies on the ZnO surface. The photodegradation behavior of methylene blue (MB, 10ppm) with a UV-Hg lamp (250W) as the light source in ZnO aqueous suspension (0.3gL−1) was investigated. The ZnO product synthesized at 140℃ can significantly photocatalyze the degradation of lower concentration MB solutions. After 35min of irradiation, the photocatalytic decomposition rate reached 98.3%. It is hoped that this work could serve as an important stepping stone for establishing a novel hydrothermal method based on SFME system, therefore paving the way for other potential ideas on the application of SFME systems.