Dependence of Al3+ on the growth mechanism of vertical standing ZnO nanowalls and their NO2 gas sensing properties

• Vertical standing ZnO nanowalls were prepared using Zn(CH3COO)2·2H2O and Al(NO3)3·9H2O as the seed solution source materials.
• The effect of Al3+ on the growth mechanism of the ZnO nanowalls was discussed.
• The ZnO nanowalls exhibited a better response toward 50 ppm NO2.

In the present work, vertically well-aligned of ZnO nanowalls were successfully obtained on ITO glass substrate via a facile two-step soft aqueous solution using Zn(CH3COO)2·2H2O and Al(NO3)3·9H2O as the source materials in seed solution. Results showed that Al3+ played a critical role in synthesizing ZnO nanowalls. The ZnAl2O4 buffer layer not only reduced the surface energy of ITO glass substrate but also supported easy nucleation for ZnO. The effect of growth aqueous solution on tailoring morphology was investigated. Moreover, gas sensors based on the vertical standing ZnO nanowall were fabricated to examine the responses to NO2 (1–50 ppm). The ZnO nanowalls exhibited a good response toward 50 ppm NO2 as high as 30 at the operating temperature of 220 °C. In addition, the ZnO nanowalls showed fast response (30 s) and recovery (48 s) time to NO2. These results showed that the vertical standing ZnO nanowalls were promising for NO2 sensor applications.