Cl-Doped ZnO Nanoparticles with Enhanced Photocatalytic Activity via Selective Surface Lixiviation: Implications for Acetaminophen Degradation

Selective surface lixiviation is commonly employed to quantify dopants segregated on the surface of nano oxides. In this study, we utilize this method as a strategy to enhance the photocatalytic activity of Cl-doped ZnO. Diffuse reflectance spectroscopy revealed that the dopant was not dissolved in a solid solution, and surface defects were confirmed through color measurements using the CIE Lab* system and electron paramagnetic resonance (EPR). X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) confirmed the presence of ZnCl₂ on the surface of doped ZnO samples. STEM EDS elemental mapping revealed an ∼6 nm-thick Cl-enriched surface layer at the edge of the ZnO nanoparticle. The selective lixiviation method effectively removed the Cl dopant from the surface of ZnO nanoparticles, as demonstrated by FTIR-DRIFT, while preserving the additive in the grain boundaries (GBs). This process mitigated chloride poisoning during photocatalysis by removing soluble Cl and enhancing electrical conductivity through GB segregation. These synergistic effects contributed to the improved photodegradation of the model contaminant acetaminophen, positioning lixiviated Cl-doped ZnO nanoparticles as highly effective for the target application of acetaminophen degradation.