UV Light-Induced Reversible Wettability and Sensing Performance for Ca/Mg-Doped ZnO Nanostructures via Chemical Bath Deposition

Calcium-doped zinc oxide (CaZnO) and magnesium-doped zinc oxide (MgZnO) nanostructures were synthesized by a chemical bath deposition method. X-ray diffraction results revealed c-axis plane dominance for the ZnO and MgZnO samples, and a-axis plane dominance for the CaZnO samples. Scanning electron microscopy results showed well-aligned nanorods for the ZnO and MgZnO nanostructures. However, flower- and cotton-type surface was found for the Ca-doped samples. Energy-dispersive spectroscopy results confirmed the calcium and magnesium dopants. Band gap values of 3.20 eV and 3.34 eV were revealed for higher doping concentrations of calcium and magnesium, respectively. The super-hydrophobic state was observed for the 5% Mg-doped ZnO sample, with a water contact angle of 152°. However, a hydrophobic state was observed for the 5% Ca-doped ZnO sample, with a water contact angle of 90°. The super-hydrophilic state was detected for all samples by the induction of ultraviolet light. Better contact angle reduction rates with values of 0.022 and 0.023 were estimated for the calcium-doped nanostructure. The contact angle recovery time was also evaluated, and values of 35 h and 40 h were achieved for Ca- and Mg-doped samples, respectively. The ultraviolet sensing performance was evaluated for all the samples, and the best photo-response was obtained for the 5% Mg-doped ZnO sample.