Photocatalytic degradation and kinetic modeling of azo dye using bimetallic photocatalysts: effect of synthesis and operational parameters

Industrial wastewaters are the major source polluting the surface and ground water resources. Pollutants released along with the untreated textile industry wastewaters are responsible for the great damage to the natural resources like water. Considering the hazardous effects of the azo dyes (textile coloring agents) and their byproducts, there is a need to develop cost-effective and efficient treatment method for the textile wastewaters as such dyes have been reported as toxic, mutagenic, and carcinogenic and can cause direct demolition of aquatic communities. One of the possible and effective treatment methods is the use of TiO2 photocatalysis due to its chemical stability, low cost, and non-toxic nature. The present study explored the photocatalytic potential of anatase-type of bimetallic Cu-Ni/TiO2 photocatalysts under visible light irradiation for possible photocatalytic degradation and mineralization of Methyl Orange (MO), as model azo dye. The focus was to correlate the synthesis (different calcination temperatures, phase composition of TiO2 either anatase or rutile, and metal ion loading in terms of concentration and composition (Cu:Ni)) and operational parameters (photocatalyst loading, pollutant concentration, and irradiation time) that were believed responsible for the enhanced photocatalytic performance. Blank experiments were carried out to check the effect of metal loading in comparison to bare TiO2 and effect of absence or presence of light and photocatalysts on MO photodegradation. Results obtained using bimetallic photocatalysts are promising as compared to bare TiO2 as 100% MO removal and similar to 90% %COD removal were obtained in 90 min of irradiation, obeying a pseudo-first-order kinetics with photocatalytic reaction via the Langmuir-Hinshelwood mechanism with a good linear fit. Photocatalysts synthesized using anatase TiO2 were reported with improved performance compared to rutile phase. It is evident that synthesis parameters influence photocatalyst performance directly. The higher rate constant (> 1) that proves the excellent adsorption capacity of the tested photocatalysts for tested pollutants on the surface may have a great prospective for photocatalytic water purification at neutral pH.