Fabrication of Cr–ZnO photocatalyst by starch-assisted sol–gel method for photodegradation of congo red under visible light

Abstract

In this work, a sol–gel method has been employed to fabricate Cr-doped ZnO nanoparticles (NPs) in the presence of starch at different annealing temperatures. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and Fourier transforms infrared spectroscopy (FTIR). All samples were defined as hexagonal wurtzite ZnO with particle sizes equal to 26, 22, and 31 nm for pure ZnO, Cr-doped ZnO at 500 °C and 700 °C, respectively. The Cr-doped ZnO photocatalyst at 500 °C shifted the band gap energy of ZnO from 3.16 to 3.09 eV. The nanomaterials' photocatalytic activity was tested through the photodegradation of congo red (CR) under visible light illumination. The results demonstrated that the Cr-doped ZnO annealed at 500 °C is an excellent photocatalyst with enhanced degradation competence towards CR dye by virtue of its reduced size and lower band gap energy. The kinetics of the photodegradation fitted the pseudo-first-order model while the mechanistic investigations revealed the great impact of h+ and ·OH on the degradation process. The starch-stabilized chromium-doped ZnO shows a high photocatalytic activity towards CR, indicating their possible environmental remediation application.