Photocatalytic Degradation of Acid Orange 7 Dye on TiO2 -Coated Layers Produced by Anatase Paste Calcination in A Batch-Mode Photoreactor: Role of Calcination Temperature

Abstract

Dyes are extensively used in the textile industry, and a considerable amount of water is consumed during the dyeing and finishing operations. These wastewaters are discharged in rivers or public sewage treatment plants and are highly coloured and contaminated. This creates a major environmental problem primarily due to substantial amounts of unfixed dyes released in wastewater. The dyes are characterized by low biodegradability, which makes them a source of pollution. The study sought to evaluate the effect of calcination temperature of TiO₂ anatase catalyst on the rate of Acid Orange 7 dye photocatalytic degradation, and determine the maximum absorption wavelength.  ) for dye Acid Orange 7 and quantify the absorbance of five dye Acid Orange 7 solutions while calibrating the UV-Vis spectrophotometer and determining dye molar extinction coefficient (ԑ). The photocatalytic degradation of Acid Orange 7 azo dye c = (1×10^-4 mol.L^-1) was used to investigate the efficiency of using TiO₂ anatase paste photocatalyst. Whereby, the TiO₂ anatase paste was immobilised on degreased microscopic glass (75mm×25mm), from an aqueous phase c = (10 g.L^-1) to cover a geometrical area of (8.75 cm²). The coated layers were calcined at temperature values of 300°C, 400°C, 600°C, 700°C, 800°C, and 900°C in a muffle furnace and used in a four-hole photocatalytic reactor under UV light irradiation. As a source of UV light, two Osram Eversun fluorescent tubes emitting light of wavelength between 320 nm and 400 nm ( maximum  λ= 355 nm) were used. A UV-Vis spectrophotometer CECIL 2021 was used to monitor changes in dye concentrations and determine the rate of photocatalytic degradation. The effect of calcination temperature on the efficiency of TiO₂ anatase paste catalyst for the removal of dyes was also studied. The results showed that Acid Orange 7 dye was effectively photodegraded using TiO₂ anatase paste under UV light irradiation. Calcination temperature influenced the resulting TiO₂ anatase paste photocatalytic activity, an increase in calcination temperature in the range 300°C-600°C resulted to a decrease of the dye i.e. 43.5%, in the rate of photocatalytic degradation. At higher calcination temperatures, i.e., 700-900°C, there is a significant increase, i.e., 51.4%, in the rate of photocatalytic degradation. The results show the optimum calcination temperature for TiO₂ anatase paste to be used for Acid Orange 7-dye degradation is 900°C and 30 minutes calcination time. The current study concludes effective removal of dye Acid Orange 7 from aqueous systems using TiO₂ anatase paste under UV light irradiation in a batch mode photocatalytic reactor.