Effect of temperature and pH on the wettability of electrodeposited n-type cuprous oxide films

Abstract

This research considers the temperature effect on wettability properties of electrodeposited n-type cuprous oxide (n-Cu2O) thin films, having focus on the role of bath pH and annealing temperature in their different values. In this research, n-type Cu2O films were produced using a three-electrode electrochemical cell containing an aqueous solution of sodium acetate and cupric acetate at 55°C, with the change in bath pH carried out by adding diluted acetic acid and NaOH. The films were deposited on titanium substrate at -200 mV vs Ag/AgCl for 40 minutes, and after that annealed in an air atmosphere at different temperatures increasing by 50°C increments starting from 100°C. The results of the photoresponse measurements confirmed the n-type nature of cuprous oxide. Crystal structure was determined by X-ray diffraction and the detailed surface morphology of the Cu2O thin films were examined using SEMs, which relate to the wettability characteristics of this material. The sessile drop method, utilizing ImageJ software based on Young's equation, showed that the contact angle measurements of wettability in the n-Cu2O substrates greatly depended on the pH of the electrodeposition bath and annealing temperature. The results revealed that the n-Cu2O films were hydrophilic when films were prepared at pH of 5.6, 6.23, 6.4, and 6.6. Interestingly, at pH 5.8, the contact angles exceeded 90° when the surfaces were annealed in an air atmosphere at temperatures of 100°C and 150°C and then allowed to return to room temperature, indicating the formation of hydrophobic surfaces. At pH 6.0, hydrophobicity was realized under annealing temperatures of 100°C, 150°C, and 200°C. XRD crystallographic analysis supported the formation of Cu2O with a cubic structure, while SEM details gave the surface morphology of the films. It serves as a very strong demonstration of the high degree of intercorrelation between wettability, pH, and annealing temperature in cost-effective routes toward hydrophobic n-Cu2O surfaces. By varying the pH and annealing temperature, it was possible to obtain both hydrophobic and non-hydrophobic surfaces. Knowing the wetting properties of n-type cuprous oxide facilitates many applications, such as the control of corrosion in coating technology and atmospheric water harvesting.