Monitoring Congo red discoloration using thermal properties in photocatalytic processes: A new approach

Abstract

Waste water contaminated with azo-derived dyes is the main cause of contamination of aquatic systems. The photocatalytic process is an alternative remediation technology to counter the negative effects of dyes in aqueous solutions. In this work, the photocatalytic potential of β-PbO nanoparticles to degrade Congo red was investigated. For the first time, monitoring photocatalysis by obtaining thermal diffusivity using thermal lens spectroscopy and thermal wave resonator cavity techniques is reported. The reaction was carried out under alkaline conditions with UVC light irradiation and in the presence of lead oxide nanoparticles. It was possible to recorded a decrease of the characteristic peak of Congo red around 497 nm in the UV-Vis spectra. Likewise, a decrease in thermal diffusivity from 15.53±0.026 × 10−4 cm2•s−1 to 13.96±0.045 × 10−4 cm2•s−1 was observed as the irradiation time increased. The azo-derived dye degradation reaction follows pseudo-first-order kinetics. The model used allowed calculating an apparent rate constant of 0.0188 min−1 and half-life of the Congo red of 36.8 min−1 in the presence of orthorhombic lead oxide. The experimental conditions allowed the degradation of the dye in a percentage up to 90%.