Investigation of OH radicals formation on the surface of TiO2/N photocatalyst at the presence of terephthalic acid solution. Estimation of optimal conditions

• 415 mg TA/g TiO2/N was found to be the optimal for detection of OH radicals.
• Concentration of TA < 415 mg/g TiO2/N can conduct for non-linear formation of 2-HTA.
• Concentration of TA < 415 mg/g TiO2/N can conduct for high yield in 4-HBA.
• Concentration of TA > 415 mg/g TiO2/N can cause the inner filter effect.
• Fluorescence method is more convenient for 2-HTA analysis than HPLC.

The fluorescence technique for estimation of OH radicals formation on the surface of TiO2 photocatalyst has been reported. However in this method the linear dependence between formation of 2-hydroxyterephthalic acid (2-HTA) and irradiation time not always is obtained. In this paper the influence of TA concentration on the formation of 2-HTA at the presence of TiO2/N photocatalyst and UV irradiation is discussed. It was proved that for low concentration of TA, its transformation to 4-hydroxybenzoic acid (4-HBA) took place whereas at higher concentration of TA formation of both, 4-HBA and 2-HTA was noticed. However there is an optimal amount of TA at which the highest yield of 2-HTA could be obtained. For the excess amount of TA an inner filter effect was observed which resulted in the reducing the yield of 2-HTA formation. Two techniques, high performance liquid chromatography (HPLC) and fluorescence spectroscopy were applied for controlling formation of TA decomposition products.

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