A Simple and Sustainable Approach for the Conversion of Zinc Metal Waste into Zn–ZnO Structures: Structural, Optical, and Photocatalytic Properties

In this study, zinc shavings and turning waste generated during machining processes were compacted into disk-shaped samples, and the formation of ZnO on the surface was achieved through thermal treatment under an atmospheric environment. Photocatalytic tests were conducted on Zn–ZnO structures to assess their potential for application. The structural, morphological, and optical properties of the Zn-ZnO structure were systematically investigated using instrumental analysis equipment, including XRD, XPS, a UV–Vis spectrophotometer, and SEM. The results revealed that thermal oxidation at 400 °C led to the successful formation of a ZnO layer on the Zn metal surface while preserving the metallic Zn core. Optical measurements indicated a direct band gap of 3.29 eV and 3.28 eV for the heat-treated samples, consistent with ZnO semiconductor characteristics. Photocatalytic tests using methylene blue as a model organic pollutant showed degradation efficiencies of about 42–43% after heat treatment under visible-light irradiation. Overall, the findings indicate that zinc machining waste can be upcycled into functional Zn–ZnO photocatalytic materials through a simple and sustainable solid-state approach.