DOI: https://doi.org/10.55373/mjchem.v27i2.64

Keywords: Chromium; methylene blue; photocatalytic degradation; photocatalyst; zinc oxide

Abstract

Zinc oxide (ZnO) semiconductor-based photocatalysts are widely utilized in water treatment due to their high photocatalytic performance. Herein, pure ZnO and chromium (Cr)-doped ZnO with varying weight % (wt. %) of Cr (1, 3 and 5 wt.%) were synthesized using a chemical mixing method. The morphology, composition, and crystallinity of the synthesized samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Photocatalytic activity was assessed by monitoring the degradation of methylene blue (MB) dye under UV light exposure. SEM images reveal that Cr-doped ZnO particles exhibit a rod-cubic morphology with uniform distribution and good dispersion. EDX confirms the presence of Zn, O, and Cr without any impurities, verifying sample purity. XRD analysis indicates that Cr doping influences crystallinity, with an average crystallite size ranging from 35.20 nm to 35.70 nm. A slight peak shift observed with lower Cr doping level suggests substitutional incorporation of Cr³⁺ ions at Zn²⁺ sites, causing minor lattice distortions. Photocatalytic degradation experiments demonstrate that Cr doping enhances ZnO’s performance. The 1 wt. % Cr-doped ZnO (CZ-1) photocatalyst demonstrates the highest activity, achieving 99.8% MB degradation with a rate constant, k of 0.0906 min^-1, surpassing both pure ZnO (CZ-0) and other Cr-doped variants (CZ-3 and CZ-5). The presence of Cr³⁺ ions enhance MB dye degradation by trapping electrons, reducing recombination, and generating reactive species under UV light. In conclusion, Cr-doped ZnO showed enhanced photocatalytic performance, making it a promising alternative for treating textile wastewater.