Visible-light-driven photocatalysis-assisted adsorption of azo dyes using Ag2O

In this study, a photocatalysis-assisted adsorption process was proposed to remove a typical azo dye , Congo red (CR), from wastewater, using Ag 2 O. The organic dyes were adsorbed using Ag 2 O, and photodegraded in situ under visible light irradiation, thus, eliminating the desorption step. The results indicated that the maximal adsorption capacity of Ag 2 O for CR reached 180.8 mg/g at the initial CR concentration of 300 mg/L and pH 7. The adsorption of CR could be described using the Langmuir equation, and obeyed the pseudo-second-order kinetic expression. The CR adsorbed by Ag 2 O was completely photodegraded in 35 min to regenerate the Ag 2 O adsorbent under visible light irradiation, and only a slight decrease in the performance of Ag 2 O was observed after four cycles. This photocatalysis-assisted adsorption process could be extended to other azo dyes including acid orange 7 and amido black 10B , but could not be applied to non-azo dyes such as rhodamine B and methylene blue . This adsorption behavior difference was ascribed to the similar molecular orbital structures of Ag 2 O and azo dyes.