Enhanced visible-light driven photocatalytic degradation of 2-chlorophenol using microwave-synthesized CoO/ZnO nanocomposites in aqueous media

Abstract

The photocatalytic mineralization of 2-chlorophenol (2-CP) in aqueous media was investigated using pure Zinc oxide (ZnO) and CoO-modified ZnO photocatalysts (CoO/ZnO). ZnO and CoO/ZnO composites were synthesized via two different routes: the sol–gel method and microwave irradiation, followed by calcination at 500 °C for 3 h in a muffle furnace. The synthesized materials were characterized by UV–vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM). Incorporation of cobalt oxide into the ZnO lattice reduced the band gap from 3.02 eV to 2.3 eV, significantly enhancing visible-light absorption. Under visible-light irradiation in the presence of 0.01 % H ₂ O ₂ , the CoO/ZnO photocatalyst achieved nearly complete degradation of 40 mg L ⁻¹ 2-CP within 120 min. At pH 4.0, degradation efficiencies for 40 mg L ⁻¹ 2-CP were 33.6 % for sol–gel-derived ZnO and 85.3 % for microwave-assisted CoO/ZnO. Furthermore, the CoO/ZnO photocatalyst exhibited excellent stability, retaining high photocatalytic activity over five consecutive reuse cycles. Kinetic analysis revealed a rate constant of 5.7 × 10 ⁻³  min ⁻¹ for CoO/ZnO, which is approximately two times higher than that of pure ZnO, indicating enhanced charge separation and improved generation of reactive oxygen species. These results demonstrate that microwave-synthesized CoO/ZnO nanocomposites are highly efficient and stable visible-light photocatalysts for the degradation of chlorinated phenolic pollutants in water.