Investigation into photocatalytic decolorisation of CI Reactive Black 5 using titanium dioxide nanopowder

Abstract

The photocatalytic decolorisation of CI Reactive Black 5 using titanium dioxide nanopowder as a catalyst was studied and the results obtained are discussed in terms of its decolorisation efficiency. All experiments were performed using a double‐walled quartz immersion well batch reactor in which the slurry form of the reactants was at its natural pH of 5.1. The performance of titanium dioxide nanopowder (size <25 nm; surface area 200–220 m2/g) was compared with that of reference titanium dioxide powder (size ca. 230 nm; surface area 11 m2/g); in both cases, the titanium dioxide samples were anatase. It was found that the photocatalytic decolorisation efficiencies obtained using titanium dioxide nanopowder were higher than those of the reference titanium dioxide powder, with the latter taking approximately 8 min longer to achieve almost complete decolorisation of 10 mg/l CI Reactive Black 5. The photocatalytic decolorisation rate of CI Reactive Black 5 using both titanium dioxide photocatalysts typically followed a first‐order reaction and the decolorisation kinetics were successfully fitted to a simplified Langmuir–Hinshelwood kinetic model. In addition, the effects of light type and intensity, catalyst loading and initial CI Reactive Black 5 concentration were investigated using titanium dioxide nanopowder as the photocatalyst in the decolorisation of the dye. This study shows that the recommended parameters for treating 10 mg/l CI Reactive Black 5 based on the experimental set‐up and operating conditions are an ultraviolet light power of 125 W (39.3 mW/cm2) and a 0.3‐g/l catalyst loading.