To investigate the thermal decomposition of the precursors, Differential scanning calorimetry/thermogravimetric analyses (DSC/TGA) (SDT Q600, Ta instrument, Inc) were carried out under air in the temperature range from room temperature to 700 ��C. The surface areas were measured by using the neither Brunauer�CEmmett�CTeller (BET) method (Tristar 3000, Micromeritics Co. Ltd.).2.5. Gas Sensing CharacteristicsThe as-prepared precursors were prepared into a paste form and applied to an alumina substrate (size: 1.5 mm �� 1.5 mm, thickness: 0.25 mm) having two Au electrodes (electrode width: 1 mm, electrode spacing: 0.2 mm). The sensor element was heated to 500 ��C at 25 ��C/min and then treated at this temperature for 1 h for conversion into pure ZnO nanostructures and to decompose the organic content of the paste.
The sensor was placed in a quartz tube and the temperature of the furnace was stabilized at 400 ��C. A flow-through technique with a constant flow rate of 500 cm3/min was used and 4-way valve was employed to switch the gas atmospheres. The gas responses (S = Ra/Rg, Ra: resistance in dry air, Rg: resistance in gas) to 100 ppm C2H5OH, CO, H2, and C3H8 were measured at 400 ��C. The Inhibitors,Modulators,Libraries gas concentration was controlled by changing the mixing ratio of the parent gases (100 ppm C2H5OH, 100 ppm CO, 100 ppm H2, and 100 ppm C3H8, all in dry air balance) and dry synthetic air. The dc 2-probe resistance of the sensor was measured using an electrometer interfaced with a computer.3.?Results and DiscussionThe phase and composition of as-prepared precursors and ZnO nanostructures Inhibitors,Modulators,Libraries after heat treatment at 500 ��C for 1 h in air were examined by X-ray diffraction (XRD) (Figure 1).
The H-NS and NR precursors were identified as the mixture between hexagonal Inhibitors,Modulators,Libraries ZnO (JCPDS #79-0207) and orthorhombic Zn(OH)2 Inhibitors,Modulators,Libraries (JCPDS #76-1778)[Figure 1(a,c)]. The Zn(OH)2 phase content was higher in NR precursors. In contrast, the H-NR precursors were identified as crystalline ZnO phase without Zn(OH)2 [Figure 1(e)]. All the three precursors were converted into pure ZnO by heat treatment at 500 ��C for 1 h [Figure 1(b,d,f)].Figure 1.X-ray diffraction patterns of (a) H-NS precursors; (b) H-NS nanostructures; (c) Cilengitide NR precursors; (d) NR nanostructures; (e) H-NR precursors; and (f) H-NR nanostructures. H-NS, NR, and H-NR ZnO nanostructures were prepared by heat treatment of H-NS, NR, …As-prepared H-NS precursors were hierarchical structures assembled from nanosheets [Figure 2(a,b)]. The sizes of assembled hierarchical structures ranged from 3 to 5 ��m. Closer inspection revealed that the 2-dimensional nano-building blocks (nanosheets) are extremely thin (5�C10 nm) [Figure 2(c)]. directly The overall hierarchical morphology was maintained after heat treatment at 500 ��C for 1 h [Figure 2(d,e)].