Advancements in Sol–Gel-Derived ZnO Thin Films: Electrochemical Characterization via Mott-Schottky, Photocurrent, Impedance Spectroscopy, and Photocatalytic Performance in Rhodamine B Degradation

This work investigates the impact of zinc acetate (ZnAc) precursor concentration on the electrochemical and photocatalytic performance of ZnO thin films synthesized via chemical solution deposition. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis revealed that increasing ZnAc concentration from 0.2 to 0.8 M significantly reduced charge transfer resistance and enhanced carrier density. The film prepared with 0.8 M ZnAc exhibited the lowest R ct (0.19 kΩ), highest double-layer capacitance (88.7 μF), and fastest interfacial charge transfer, indicating superior electrochemical behavior. Photocatalytic activity was evaluated using Rhodamine B (RhB) degradation under UV light. The ZnO-0.8 M film showed the most efficient degradation rate, with absorbance measurements confirming a continuous decrease in RhB concentration over time. The degradation mechanism was attributed to the generation of reactive oxygen species (·OH and ·O 2 − ) through UV-induced electron-hole pair excitation in ZnO, leading to oxidative decomposition of RhB into environmentally benign products. The structural properties and optimized charge transport of the ZnO-0.8 M film underlie its superior performance. These findings highlight the critical role of precursor concentration in tailoring ZnO thin film properties for advanced photoelectrochemical and photocatalytic applications.