In this paper, highly dispersed hierarchical coral spheres of CeO2/ZnO have been constructed through a facile template-free hydrothermal strategy, followed by an annealing treatment. The resulting coral spheres exhibit enhanced activity for acetone sensing compared with CeO2 or ZnO as well as excellent cyclability and long-term stability. At the optimum working temperature of 245 °C, by controlling the ratio of Ce/Zn, the highest response of the coral spheres towards 100 ppm acetone is up to 145, which is about 5.5 times that of ZnO coral spheres. The significantly improved gas sensing activity may be ascribed to the well-dispersed and assembled CeO2 nanoparticles on the surface of ZnO coral spheres and the heterojunctions between CeO2 and ZnO, which produced abundant oxygen vacancies in the CeO2/ZnO coral spheres.
Sun Linchao,Yao Zhengjun,Haidry Azhar Ali,Li Zhong,Fatima Qawareer,Xie Lijuan
The paper demonstrated cost-effective one-step hydrothermal process to synthesize TiO 2 microrods modified with Cr 2 O 3 nanoparticles. The crystal structure, microstructure and chemical composition of the obtained materials were characterized by XRD, SEM, TEM and EDS analysis. Subsequently, for gas sensor tests the sensors were fabricated onto a ceramic tube having a designed pair of Au electrodes with four Pt wires. The results indicate that the sensors based on the optimal content of Cr 2 O 3 nanoparticles modified TiO 2 microrods possess excellent gas-sensing performance to acetone. Specifically, the sensor based on optimal 3% Cr 2 O 3 modified TiO 2 microrods exhibited high response (15), fast response/recovery time (5/28 s), outstanding selectivity (against 100 ppm ethanol, methanol and formaldehyde) and good stability (1–40 days) towards 100 ppm acetone at 300 °C. Relying on the analysis, we infer that performance can be controlled by varying the Cr 2 O 3 contents. A plausible sensing mechanism is also discussed to explain the reasons for the enhanced acetone sensing with Cr 2 O 3 –TiO 2 heterostructures.
CeVO4 nanorods (NRs) were successfully synthesized via a one-step hydrothermal method using disodium edentate (EDTA) as a chelating agent. The CeVO4 NRs are assigned to the zircon-type tetragonal structure and exhibited pure single-crystals as determined by XRD analysis. FE-SEM images indicate that the as-prepared samples are present as square-section nanorods, and the length and sectional size of the CeVO4 NRs are found to be ∼1.5 μm and ∼100 nm, respectively. Moreover, the HRTEM images and SAED diffraction patterns confirm that the main exposed surfaces of the CeVO4 NRs were the (010) and (004) lattice planes with a high exposed percentage (ca. 96.77%) around the NRs and the growth direction was along the (200) lattice plane. The CeVO4 NRs presents a pure phase, with no other impurity phases identified from the FTIR and Raman spectra. XPS results indicate that the vanadium atoms on the surface exhibit a mixture of valence states, i.e., pentavalent state (V5+) and trivalent state (V3+), as dangling bonds around the oxygen vacancies were induced by EDTA desorption during hydrothermal process. An acetone gas sensor based on the CeVO4 NRs was fabricated, which exhibits a significant response (0.5 s) and recovery (80 s) with high selectivity at the optimum working temperature (108 °C). This is mainly due to the presence of the trivalent states (V3+), which serve as the active sites and provide a large number of oxygen vacancies (Vo) as identified by XPS and infrabar experiments at 300 ppm O2 (0.003 atm). Moreover, it has been demonstrated that the response to acetone for the gas sensor was crucially dependent on the adsorbed oxygen (Oads) on the (010) or (004) facets of the CeVO4 NRs, where the redox reaction with acetone occurred reversibly.
Pure NiO nanofibers and the In2O3–NiO one-dimensional heterogeneous nanofibers were prepared by electrospinning, and the gas sensing properties to acetone were also investigated. Material characterization proved that the heterogeneous nanofibers were composed of In2O3 and NiO, and the nanofibers exhibited an enhanced sensitivity to acetone. At the optimal working temperature, the response of In2O3–NiO nanofibers to 50 ppm acetone was more than 10 times higher than that of pure NiO nanofibers. The minimum detection limit of the heterogeneous nanofibers reached 10 ppb, while the pure NiO nanofibers only reached 100 ppb. Among acetone and the comparison gases (methanol, ethanol, triethylamine, ethyl acetate, and benzene), the heterogeneous nanofibers achieved the highest response to acetone. In addition, the heterogeneous nanofibers exhibited an improved response–recovery rate and good long-term stability. These results indicated that the In2O3–NiO one-dimensional heterogeneous nanofibers have great potential in low-concentration acetone detection. Combined with the material properties, the mechanism of the enhanced sensing properties was discussed in detail for the In2O3–NiO heterogeneous nanofibers.
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