Morphological evolution of ZnO nanostructures and their aspect ratio-induced enhancement in photocatalytic properties

Abstract

This work presented controllable growth of ZnO nanostructures with different aspect ratios by the microwave irradiation method and investigated the photocatalytic degradation of methyl red (MR). X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) measurements showed that all ZnO nanostructures were of a hexagonal phase structure. It was revealed by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images that the morphology of ZnO can be effectively controlled as sheetlike, rod-like, brush-like, flower-like, prism-like, and pyramid-like only by changing the molar ratio (zinc acetate: KOH) and reaction time. With the increase of molar ratio and reaction time, modification in the E 2 (high) and E 1 (LO) Raman modes was observed. The energy band gap was found to be tuned by the aspect ratio of ZnO nanostructures. Photoluminescence spectroscopy revealed the low-intensity NBE emission and high and broad defect-related emission for high aspect ratio ( 14) nanorods. BET surface area porosity analysis confirmed the presence of a mesoporous network in all the nanostructures, showed high surface area and a uniform pore-size distribution for high aspect ratio nanorods. A terephthalic acid assay study confirmed the formation of hydroxyl radicals (OH) in MR dye solution treated with a ZnO nanostructures photocatalyst. The photodegradation of MR under UV light irradiation showed that ZnO nanorods with a high aspect ratio of $14 showed superior photodegradation ($98% degradation of MR within 60 min) than that of the lower aspect ratio nanostructures. The apparent reaction rate constant for high aspect ratio (14) nanorods was higher than that of the lower aspect ratio nanostructures. The enhancement in photocatalytic performance could be due to the high surface area and enhanced charge separation and transfer efficiency of photoinduced charge carriers in the high aspect ratio nanorods.

Fe–tannic acid complex dye as photo sensitizer for different morphological ZnO based DSSCs

“…The Zn 2+ and OH -ions concentrations are critical state as polymerizations process and then a white powder ZnO is dropped [19,21]. From to all discussion, microwave process may help to ZnO crystal developed.…”

Room-temperature fabrication of core-shell nano-ZnO/pollen grain biocomposite for adsorptive removal of organic dye from water

“…For n-ZnO/PG, the deconvolution procedure shows the presence of several chemistries of oxygen. The component OI at ~530 eV is typical for O 2ions in fully oxidized, stoichiometric environment of ZnO [27,28].…”

“…The one at ~531.1 eV (OII) is associated with O x− ions (x < 2) in the oxygen-deficient regions within the ZnO matrix and is related to oxygen vacancies [28]. As shown, the O1s spectrum of n-ZnO/PG contains a large component at ~532.2 eV (OIII), which is typically attributed to chemisorbed oxygen, dissociated oxygen, or OHgroups on the surface [28]. These three spectral components are also present in the fitted O1s spectrum of n-ZnO ( Fig.…”

Enhanced Photocatalytic Activity of ZnO Toward the Degradation of Methylene Blue Dye: Effects of Fe3+ and Sn4+ Doping

“…With the aid of ultraviolet (UV) light, the photogenerated electrons (e − ) and holes (h + ) in ZnO semiconductor can react with O 2 , OH − , and H 2 O to produce active species such as • O 2− and • OH. Organic pollutants in wastewater are eventually oxidized by these active species into small nontoxic organic compounds or inorganic substances such as H 2 O and CO 2 , thereby reducing pollution in the water environment.…”