Room temperature sintering of polar ZnO nanosheets: II-mechanism

Abstract

In a previous work by the authors (A. Fernández-Pérez el al., Room temperature sintering of polar ZnO nanosheets: I-evidence, 2017, DOI: 10.1039/C7CP02306E), polar ZnO nanosheets were stored at room temperature under different atmospheres and the evolution of their textural and crystal properties during storage was followed. It was found that the specific surface area of the nanosheets drastically decreased during storage, with a loss of up to 75%. The ZnO crystals increased in size mainly through the partial merging of their polar surfaces at the expense of narrow mesoporosity, in a process triggered by the action of moisture, oxygen and, in their absence, by light. In the present work, a set of spectroscopic techniques (FTIR, Raman and XPS) has been used in an attempt to unravel the mechanism behind this spontaneous sintering process. The mechanism starts with the molecular adsorption of water, which takes place on Zn atoms close to oxygen vacancies on the (100) surface, where HO dissociates to form two hydroxyl groups and to heal one oxygen vacancy. This process triggers the room temperature migration of Zn interstitials towards the outer surface of the polar region. What were previously interstitial Zn atoms now gradually occupy the mesopores, with interstitial oxygen being used to build up the O sublattice until total occupancy of the narrow mesoporosity is achieved.

Tunable, Hybrid 1D ZnO Nanostructures Obtained by Using Bio‐renewable Ferulic Acid as Support and its Applications

“…Though the surface area was lower (the maximum observed surface area being 58.3951 m 2 /g for ZnO@FA 0.5 ), more than 10 to 15 fold increase was noticed as compared to ZnO (3.175 m 2 /g) with the exception of ZnO@FA 1.0 in which case the increase was only three‐fold (9.2453 m 2 /g). The TiO 2 @FA formed the mesoporous powder with the comparatively higher surface area (142 m 2 /g) ,. Interestingly loading of FA caused the reduction in surface area in the case of TiO 2 @FA whereas the increase in surface area was noticed in ZnO@FA.…”

“…The adsorption isotherm in the case of TiO 2 @FA was classified as type‐IV while ZnO@FA are type‐III macroporous powders. ZnO itself has been reported to show storage induced changes in surface area …”

“…ZnO itself has been reported to show storage induced changes in surface area. [26] The thermogravimetric analysis (TGA) of FA revealed some interesting findings hitherto unreported. Both thermal and thermooxidative stability of FA (Table S2) looked similar probably highlighting FA being an effective antioxidant.…”

Synthesis of ZnO Nanoparticles Doped with Cobalt Using Bimetallic ZIFs as Sacrificial Agents

“…FTIR spectra of the samples are presented in Figure 7 . The spectra of samples 100Zn0Co and 100Zn0Co-T contained a peak at 505 cm −1 , which can be attributed to zinc oxide with oxygen vacancies [ 39 ]. The same peak could be observed on the spectrum of the 50Zn50Co sample, which contained a mixture of wurtzite and spinel structures according to XRD ( Table 2 ).…”

Efficient Photocatalytic Degradation of Malachite Green in Seawater by the Hybrid of Zinc-Oxide Nanorods Grown on Three-Dimensional (3D) Reduced Graphene Oxide(RGO)/Ni Foam

“…This ratio reduced to 1.02 in ZnO/RGO@NF, suggesting the removal of oxygen carrying functionalities and successful reduction of GO to RGO [42]. Meanwhile, the two bands at 437.5 and 582.8 cm −1 are the signature peaks of ZnO (corresponding to E 2 and E 1 modes of crystalline ZnO, respectively), showing the existence of ZnO in ZnO/RGO@NF [43]. Therefore, both XRD and Raman measurements confirm the successful synthesis of ZnO/RGO@NF composite.…”