Effect of dye type on montmorillonite-supported Pr-doped TiO₂ composite photocatalsyt

Scarcity of water in today's world has led to scientific researches for finding smarter ways of discharging and re-using water located in the seas and lakes. That is how advanced oxidation technologies have emerged as one of the new discharging techniques to keep water sources clean. In our method we have synthesized praseodymium (Pr) doped TiO₂-Montmorillonite composite photocatalyst by using acid sol-gel method. Pr, in the group of rare earth metals, is known for its ability to form Lewis bases in order to break down aldehydes, amines, etc., by decreasing the crystal size and consequently increasing the surface area. We have used the mineral form of the bentonite clay (montmorillonite) to increase the surface area of our composite photocatalyst. Two types of azo dyes which are commercially known as Basic Yellow 28 (BY 28) and Basic Blue 41 (BB 41) were used in experimants. These dyes are composed of different chemical structures: BY 28 is known as azomethine dye (-CH=N-), whereas BB 41 has one azo bond (-N=N-). The initial model dye concentrations were 100 ppm. Amount of 1.0 g/l of photocatalyst was used throughout the experiments. In order to evaluate degradation efficiency results, the dissolved organic carbon analyzer was used. We have found the optimum dark adsorption time to be under 15 minutes. By stirring under 15 minutes in the dark we have achieved efficiency of 52.50% for BY 28 and 66.74% for BB 41. On the other hand, by stirring under UV-A light irradiation for two hours we have achieved the overall degradation efficiency of 86.30% for BY 28 and 92.39% for BB 41. Our results show that higher adsorption and overall efficiencies were observed in BB 41 than in BY 28. Moreover, according to Water Pollution Control Regulations, the chemical oxygen demand limitations for textile industry are between 200-400 mg/l. To evaluate the degradation characteristics of Pr-doped TiO₂-Montmorillonite composite, the change of chemical oxygen demand values with time for 100 mg/l of BY 28 and BB 41 were investigated. The obtained chemical oxygen demand values were 60.5 and 34.8 mg O₂/l after 2 hours of oxidation processes for BY 28 and BB 41. As it can be seen from the results, obtained values are below the limitations