In this study, ZnO/TiO 2 nanosheets were synthesized using a hydrothermal method followed by annealing. The resulting hierarchical ZnO–TiO 2 heterostructures exhibited improved gas-sensing performance compared with pure ZnO. We demonstrated that tuning the ratio of Zn to Ti components in the heterostructure allowed us to adjust the sensor stability , with the best- performing sample having a Zn:Ti ratio of 2:1. A notable reduction was observed in both the sensor response and recovery times, down to 22 and 17 s, respectively, by utilizing nanosheet- structured ZnO/TiO 2 heterojunctions. To gain insight into the interaction between the sensing materials and formaldehyde (HCHO) molecules, we performed first-principles calculations to examine the density of states , charge transfer, and energy of adsorption. Our approach to constructing heterogeneous structures contributes to overcoming the low desorption efficiency and slow response-recovery time of pure ZnO for gas-sensing applications.
Using nanomaterials to design and prepare photoanodes could enhance photoelectrochemical and photocathodic protection (PCP) performances. However, little is known about how the detailed nanostructure correlates with performance. Here, we report a morphologically tunable nano-ZnO semiconductor grown on a TiO 2 nanotube array (ZnO/TiO 2 ) for the PCP of nickel-coated magnesium alloy by manipulating the hydrothermal reaction temperature. While irregular ZnO nanosheet clusters were observed at relatively low and high temperatures, a smooth array of nanorods with a hexagonal cross-section structure was obtained at a moderate reaction temperature. Such nanostructure exhibited the optimum photoelectrochemical and PCP capacities, showing the highest photogenerated current density, which is 4.2 times higher than the single-component TiO 2 photoanode. The apparent enhancement in the performance of the ZnO/TiO 2 composite was related to the morphological regulation of the nano-ZnO and the formation of staggered gap heterojunction between ZnO and TiO 2 . This assessment is supported by the results from several characterizations, including a high-resolution transmission electron microscope , Mott-Schottky, and valence band X-ray photoelectron spectroscopy. These findings give a new insight into the relationship between the structure and photoelectrochemical performances of nano-ZnO, which has significant implications for designing and preparing high-efficiency photoanode in photocatalysis and corrosion protection .
Lijia Zhao,Shupeng Sun,Su Zhang,Zhi Liu,Baoyu Huang,Nan Wang,Jianwei Zhang,Xiaogan Li
The hollow ZnO @ TiO 2 heterostructured nanospheres were synthesized by hydrothermal method using carbon nanospheres as sacrificed templates. With UV activation, the response of ZnO @ TiO 2 based chemiresistive-type sensors to 10 ppm formaldehyde is 11.02 at room temperature which is 5.48 times larger than that of the pure hollow ZnO. The response and recovery time significantly reduced to 14 s and 16 s. Selectivity, stability and repeatability of the hollow ZnO @ TiO 2 based sensor under UV-activation have also been examined. The sensing mechanism of the sensor to formaldehyde have been investigated by AC impedance spectroscopy , in-situ DRIFTS , and DFT theoretical calculation.
Juan Wang,Guohong Wang,Xianhong Wei,Guo Liu,Jun Li
A ZnO/TiO 2 heterojunction photocatalyst based on ZnO nanoparticles embedded in the hierarchically structured TiO 2 framework containing parallel macroporous channels and thin mesoporous walls has been synthesized by a common calcination treatment using zinc chloride and tetrabutyl titanate as the raw materials. The materials properties of the ZnO/TiO 2 heterojunction photocatalysts have been carefully characterized with SEM/TEM, XRD, FTIR, XPS, BET analyses, UV–Vis absorption and photoluminescence spectroscopy. The photocatalytic performance for decomposition of Rhodamine B (RhB) under UV light irradiation has been systematically investigated in correlation with the materials structures. The apparent RhB degradation rate constant ( k ) has been determined to be 20.7 × 10 −3 min −1 for the optimal hybrid photocatalyst with 5 wt% of ZnO loading, significantly higher that of pure TiO 2 (12.2 × 10 −3 min −1 ) and pure ZnO nanoparticles (5.7 × 10 −3 min −1 ), respectively. Active species trapping experiments reveal that •OH and •O 2 − play the major roles in the photocatalytic reactions. The enhanced performance can be ascribed to the formation of a direct Z-scheme heterojunction structure between ZnO and TiO 2 in contrast to the usual type-II heterojunction.
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