Thermal Annealing Induced Controllable Porosity and Photoactive Performance of 2D ZnO Sheets

Abstract

Porous ZnO sheets containing various degrees of a nanoscaled pore were successfully synthesized using a simple hydrothermal method and various postannealing procedures. The porosity features of the ZnO sheets can be easily tuned by changing both the annealing temperature and annealing atmosphere. The dense porous nature of ZnO sheets is beneficial to enhance light absorption. Moreover, the substantially increased oxygen vacancies in the ZnO sheets were observed especially after the hydrogen treatment as revealed in the X-ray photoelectron spectroscope and photoluminescence analyses. The high density of surface crystal defect enhanced the photoinduced electron-hole separation rate of the ZnO sheets, which is crucial for an improved photoactivity. The porous ZnO sheets formed at a hydrogen atmosphere exhibited superior photoactive performance than the porous ZnO sheets formed at the high-temperature ambient air annealing. The dense pores and massive crystal defects formed by a hydrogen atmosphere annealing in the ZnO crystals might account for the observed photoactive behaviors in this study.

Crystal Growth and Design of Disk/Filament ZnO-Decorated 1D TiO2 Composite Ceramics for Photoexcited Device Applications

“…Notably, the XRD results reveal (100) and (101) nonpolar planes dominated the crystallographic feature of the ZnO crystals decorated on the TiO 2 nanorod templates. A similar nonpolar crystallographic-plane-dominated ZnO crystal feature has been reported in chemical-route-derived 2D ZnO sheets [ 10 ]. It should be mentioned that the positively Zn 2+ -terminated (002) facets and negatively O 2− -terminated {002} polar surfaces of wurtzite ZnO are more reactive [ 15 ], and the fastest growth rate along the c -axis due to the higher surface energy of {002} planes is frequently observed in chemical-route-derived ZnO crystals [ 22 ].…”

“…Hydrothermal crystal growth is preferred for synthesizing free-standing TiO 2 nanorod arrays because this method enables large-area crystal growth, facile process parameter control, and the use of flexible substrate materials [ 7 , 8 , 9 ]. ZnO crystals, such as nanosheets or nanoplates, are promising components for photoexcited nanodevices [ 10 , 11 , 12 ]. Numerous synthesis methods, including chemical vapor deposition [ 13 ], evaporation [ 14 ], chemical bath deposition [ 15 ], and hydrothermal methods [ 10 ], have been proposed for fabricating sheet-, plate-, or disk-like ZnO crystal composites.…”

“…ZnO crystals, such as nanosheets or nanoplates, are promising components for photoexcited nanodevices [ 10 , 11 , 12 ]. Numerous synthesis methods, including chemical vapor deposition [ 13 ], evaporation [ 14 ], chemical bath deposition [ 15 ], and hydrothermal methods [ 10 ], have been proposed for fabricating sheet-, plate-, or disk-like ZnO crystal composites. In contrast to other methods, hydrothermal and chemical bath deposition methods can be used for fabricating homogeneous ZnO crystals with a large area distribution over substrates because these methods are simple, have low cost, require a low growth temperature, and provide a high yield.…”

Improved photoelectrode performance of chemical solution-derived Bi2O3 crystals via manipulation of crystal characterization

“…Small semicircular radii are typically attributed to photoelectrodes that exhibit small charge-transfer resistance; moreover, due to the small charge transfer resistance, there will be a higher separation efficiency of photogenerated electrons and holes in material systems. 2,16 From Fig. 12(b), the semi-circular radii of the Bi 2 O 3 photoelectrodes with a seed layer assisted crystal growth were smaller than those of the (Fig.…”

“…[11][12][13][14] Among various morphologies, nanosheet semiconductor oxides have drawn substantial research interest due to their unique geometry with outstanding electronic properties and high specic surface area, which could provide large amount of reaction sites and enable rapid charges generation and transport. 15,16 Till now, various synthetic methods have been explored to prepare sheet-or plate-like b-Bi 2 O 3 crystals with various surface features. 11,17 All the above sheet-or platelike Bi 2 O 3 products exhibited outstanding visible-light-driven light harvesting ability and photoactive performance.…”