Enhanced photocatalytic activity of Cu and Ni-doped ZnO nanostructures: A comparative study of methyl orange dye degradation in aqueous solution

Heterogeneous photocatalysis has been considered one of the most effective and efficient tech-niques to remove organic contaminants from wastewater. The present work was designed to examine the photocatalytic performance of metal (Cu and Ni) doped ZnO nanocomposites in methyl orange (MO) dye degradation under UV light illumination. The wurtzite hexagonal structure was observed for both undoped/doped ZnO and a crystalline size ranging between 8.84 & PLUSMN; 0.71 to 12.91 & PLUSMN; 0.84 nm by X-ray diffraction (XRD) analysis. The scanning electron microscope (SEM) and energy dispersive X-ray (EDX) revealed the irregular spherical shape with particle diameter (34.43 & PLUSMN; 6.03 to 26.43 & PLUSMN; 4.14 nm) and ensured the purity of the individual elemental composition respectively. The chemical bonds (O-H group) and binding energy (1021.8 eV) were identified by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) re-sults respectively. The bandgap energy was decreased from 3.44 to 3.16 eV when Ni dopant was added to the ZnO lattice. The comparative photocatalytic activity was observed in undoped and doped nanocomposites and found to be 76.31%, 81.95%, 89.30%, and 83.39% for ZnO, Cu/ZnO, Ni/ZnO, and Cu/Ni/ZnO photocatalysts, respectively, for a particular dose (0.210 g) and dye concentration (10 mg L-1) after 180 min illumination of UV light. The photocatalytic perfor-mance was increased up to 94.40% with the increase of pH (12.0) whereas reduced (35.12%) with an increase in initial dye concentration (40 mg L-1) using Ni/ZnO nanocomposite. The Ni/ ZnO nanocomposite showed excellent reusability and was found 81% after four consecutive cy-cles. The best-fitted reaction kinetics was followed by pseudo-first-order and found reaction rate constant (0.0117 min-1) using Ni/ZnO nanocomposite. The enhanced photodegradation effi-ciency was observed due to decreases in bandgap energy and the crystalline size of the photo-catalyst. Therefore, Ni/ZnO nanocomposite could be used as an emerging photocatalyst to degrade bio-persistent organic dye compounds from textile wastewater.

Automated summary

This study examined the photocatalytic performance of metal (Cu and Ni) doped ZnO nanocomposites in the degradation of methyl orange dye. The results showed that Ni doping can decrease the bandgap energy of ZnO lattice, and the Ni/ZnO nanocomposite exhibited excellent reusability and a high reaction rate constant. Therefore, this nanocomposite could be used for the treatment of organic dyes in textile wastewater.