ZnO microrods to nanowalled microtubes: optimization using simple fluorescence microscopy and enhanced photocatalytic properties.

ZnO microtubes (MTs) of nanoscale wall thickness were prepared by synthesis of ZnO microrods (MRs) followed by etching the MRs to form MTs. ZnO MRs were synthesized by a simple solution growth method using zinc chloride and hexamine as precursors. Using KOH, ZnO MRs are etched into ZnO MTs. ZnO MTs were characterized by fluorescence microscopy (FM), X-ray diffraction, scanning electron microscopy, UV-Vis and photoluminescence spectroscopy. ZnO MTs have a diameter of ∼600 nm, wall thickness of 30-40 nm and length of ∼7 μm. The influence of the KOH concentration and etching time on ZnO MRs for the formation of the ZnO MTs were studied. The formation of nanowalled ZnO tubes from ZnO MRs is optimized by simple and inexpensive FM imaging. FM was utilized as a tool to observe the changes in optical properties on change in morphology from ZnO MRs to MTs. FM images reveal that at low KOH concentration (0.125 M) the tubes were not completely etched whereas at higher concentration (0.375 M) the tube walls were damaged. Etchant concentration (0.125 M) and etching time of 12 h were found to be the optimized parameters for the realization of ZnO MTs using FM analysis. ZnO MTs were tested as the catalyst for the photodegradation of the methylene blue dye. The result shows that the photodegradation efficiency of the tubes is twice as fast as compared to that of rods.