Photocatalytic degradation of food colorant azo dyes using iron and fluorine co-doped TiO₂/SiO₂ nanocomposites: semi-pilot study cum density functional theory calculations

Remediation of hazardous azo dyes such as Allura Red, Sunset Yellow, and Tartrazine, from the wastewater of the food industries is of great importance. Here, we have used a custom-designed semi-pilot fixed-bed photoreactor to degrade these three important azo dyes via a photocatalytic approach using Fluorine and iron co-doped titanium dioxide/silica nanocomposite (F-Fe-TiO₂/SiO₂). The nanocomposite photocatalyst was synthesized by the sol–gel coupled dipping method and was characterized using several techniques. The as-developed photocatalyst showed a bandgap of 2.92 eV, allowing us to use it under both visible light and solar light irradiation. Additionally, density functional theory calculations were used to gain more insight into how the dopants (F and Fe) affect the bandgap of the photocatalyst. The photo-degradation process was optimized by investigating the effects of pH, the concentration of the dyes, and the flow rate of the wastewater solution. The results of this study suggest that the combination of the as-designed photocatalyst and photoreactor can significantly reduce the total organic carbon (TOC) content in the model wastewater including three azo dyes and therefore, have a great potential to be scaled up for industrial wastewater treatment via a green approach.