Bleaching of Congo red in the presence of ZnS nanoparticles, with dopant of Co²⁺ ion, as photocatalyst under UV and sunlight irradiations

Abstract

The bleaching of Congo red was studied in the presence of zinc sulphide nanoparticles doped with Co²⁺ ion. The nanoparticles of zinc sulphide, doped with cobalt, were synthesized by controlled coprecipitation in the presence of mercaptoethanol as a capping agent. The characterization of nanoparticles was studied using UV‐Vis spectra, XRD pattern and SEM and TEM images. The size of the nanoparticles was determined to be 10–40 nm. A maximum dye degradation of 94% was obtained under UV irradiation for 120 min. Also, a destruction of 98% was achieved under sunlight irradiation in 12 h at the optimum conditions. The photoreactivity and reproducibility of the proposed photocatalyst was compared with Degussa P25. The photodegradation of Congo red was investigated in real water containing carbonate, bicarbonate and sulphate ions. The pseudo‐first‐order rate constant, k, was 2.2 × 10⁻² min⁻¹ and 2.9 × 10⁻² h⁻¹ under UV and sunlight irradiations, respectively.

Keywords:

• zinc sulphide
• nanoparticles
• bleaching
• Congo red
• photodegradation