Lattice defects of ZnO and hybrids with GO: Characterization, EPR and optoelectronic properties

Abstract

We have prepared and combined ZnO nanoparticles (ZnO-NPs) with different graphene oxide (GO) contents (10%, 20% and 30%) via microwave processing. The procedure provided well-dispersed ZnO-NPs between and onto the rGO layers (GZCs). The annealing temperature and graphene oxide contents affected the UV-Vis absorption, PL emission, defect-states of the ZnO, EPR signals, photo-electrochemical response and charge transfer properties. The HRTEM microscopy images of the GZCs showed interpenetrating structures and clearly visible vacancy defects. The results indicated that the defect sites (Zn interstitials, oxygen vacancy, ionized zinc vacancy and oxygen interstitials) significantly decreased after hybridization with GO. The photo-conversion efficiency of the GZC-10% (η = 13.1 x 10-3%), is 13 times higher than the ZnO-NPs (η = 1.02 x 10-3%) illustrating higher exciton production and separation efficiency of the GZCs under photo-excitation. The GZC-10% has lower (8-15 Ω) charge transfer resistance (Rct) compared to all the GZCs under same experimental conditions, therefore an important reason of better performance of the GZC 10%. The EPR spectra showed presence of radicals in all the samples with GZC 10% most intense signal among the different GZCs.

Photocatalytic Oxidation of Small Molecular Hydrocarbons over ZnO Nanostructures: The Difference between Methane and Ethylene and the Impact of Polar and Nonpolar Facets

“…The EPR spectra of ZnO nanosheets and nanorods collected at 100 K under various atmosphere and illumination conditions are shown in Figure . By comparing Figure a,b, it can be clearly found that two signals at g = 2.005 and 1.960 are observed under dark and air atmosphere owing to the presence of single-electron-trapped surface defects (V o + or O s – ) and the lattice electron capture sites (Zn + or V Zn – ), respectively, in both ZnO nanosheets and nanorods. ,− In case of nanosheets, the intensities of both the signals after irradiation were initially increased for a certain time. However, on introducing methane, the intensities of both the signals reduced slightly and continued to decrease gradually on extending the illumination time.…”

Photoluminescence and X-ray photoelectron spectroscopic study of milled-ZnO material prepared by high energy ball milling technique

“…In addition, the O1s peak at 531.7 and 531.9 eV normally associates to oxygen of surface adsorbed hydroxy group -OH and zinc hydroxide Zn(OH) 2 [24,[31][32][33][34][35][36]. However, there are no evidence of zinc hydroxide at Zn2p 3/2 which should appear at around 1022.5-1023.4 eV [27,37,38]. This behavior suggests that the surface state is stable with insignificant influence by milling process.…”

ZnO Based Resistive Random Access Memory Device: A Prospective Multifunctional Next-Generation Memory

“…Also, the formation of the bond by ZnO at the GO sheets is due to the presence of the following functional groups C-O, O-C=O, C=C, and C=O as shown in Fig. 21(c) and (d) show the disappearance of C=O peak (284.3 eV) and peak at (288.3 eV) that indicates the reduction of GO to rGO [226]. Therefore, the bonding between the ZnO and GO is a promising one.…”

“…The composite surface was found to possibly chemisorbed oxygen [222], thus generated quite several vacancy layer/pool that consequently enhances the crystalline of the film and device performance [214], [219], [222]- [224]. Moreover, Ahmed et al [226] demonstrates the optoelectronic characteristics of ZnO and GO contents using microwave techniques as depicted by Fig. 21.…”

“…However, developing it horizontally in the GO sheets may maximize the contact area between the films [235], reducing the operating voltage compared to using GO alone [226]. It is worth noting that GO film embedded with ZNs with a weight ratio of 15:1 (ZnO:GQD) tends to exhibit ultra-low operating power of approximately 75% lower than a device with pure ZnO nanocomposite.…”