ZnO Hierarchical Micro/Nanoarchitectures: Solvothermal Synthesis and Structurally Enhanced Photocatalytic Performance

Abstract

A novel ZnO hierarchical micro/nanoarchitecture is fabricated by a facile solvothermal approach in an aqueous solution of ethylenediamine (EDA). This complex architecture is of a core/shell structure, composed of dense nanosheet‐built networks that stand on a hexagonal‐pyramid‐like microcrystal (core part). The ZnO hexagonal micropyramid has external surfaces that consist of a basal plane (000${\bar 1}$) and lateral planes {0${\bar 1}$11}. The nanosheets are a uniform thickness of about 10 nm and have a single‐crystal structure with sheet‐planar surfaces as {2${\bar 1}\,{\bar 1}$0} planes. These nanosheets interlace and overlap each other with an angle of 60° or 120°, and assemble into a discernible net‐ or grid‐like morphology (about 100 nm in grid‐size) on the micropyramid, which shows a high specific surface area (185.6 m2 g−1). Such a ZnO micro/nanoarchitecture is new in the family of ZnO nanostructures. Its formation depends on the concentration of the EDA solution as well as on the type of zinc source. A two‐step sequential growth model is proposed based on observations from a time‐dependent morphology evolution process. Importantly, such structured ZnO has shown a strong structure‐induced enhancement of photocatalytic performance and has exhibited a much better photocatalytic property and durability for the photodegradation of methyl orange than that of other nanostructured ZnO, such as the powders of nanoparticles, nanosheets, and nanoneedles. This is mainly attributed to its higher surface‐to‐volume ratio and stability against aggregation. This work not only gives insight into understanding the hierarchical growth behaviour of complex ZnO micro/nanoarchitectures in a solution‐phase synthetic system, but also provides an efficient route to enhance the photocatalytic performance of ZnO, which could also be extended to other catalysts, such as the inherently excellent TiO2, if they are of the same hierarchical micro/nanoarchitecture with an open and porous nanostructured surface layer.

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…Under UV illumination, ZnO will generate electron and hole pairs able to generate hydrogen by water splitting [311], synthesize H 2 O 2 [312], and reduce graphene oxides to graphene [313]. In particular, the generated holes can be used to oxidize/decompose organic pollutants, such as rhodamine 6G [210], methyl orange [314], methylene blue [159], and formaldehyde [315]. Because of the presence of active defect sites-such as oxygen vacancies-on the surface, ZnO has also been used in industry as a catalyst for the synthesis of methanol from CO and H 2 [316], or as a supporting scaffold for other catalysts, such as Cu [317], Cu/Fe composites [318], CuO [319], Au [320], for oxidative steam reforming of methanol.…”

“…ZnO is unstable in acidic and basic media, so photocorrosion under UV illumination is considered to be one of the main reasons for the decrease in ZnO photocatalytic activity over time. Therefore ZnO is only suitable for photocatalytic applications in neutral environments [314].…”

Synthesis, characterization and activity of an immobilized photocatalyst: Natural porous diatomite supported titania nanoparticles

“…Semiconductor metal oxides, typically such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), tin oxide (SnO 2 ), nickel oxide (NiO) and cuprous oxide (Cu 2 O), have been used as photocatalysts [3][4][5][6][7]. Among them, TiO 2 is widely investigated because of its high photocatalytic activity, biological and chemical inertness, and non-toxic nature.…”

Microwave-assisted Synthesis of Hierarchical ZnO Nanostructures and Their Photocatalytic Properties

“…Specially, it has been demonstrated that the hierarchical architecture constructed by 2D nanosheets results in superior photocatalytic performance, as the porous structures among the nanosheets are favorable for efficient reactants transport and photo-energy harvesting 3,4 .…”