Antipyrine removal by TiO₂ photocatalysis based on spinning disc reactor technology

The photo-degradation of the emerging contaminant antipyrine (AP) was studied and optimized in a novel photocatalytic spinning disc reactor (SDR). A heterogeneous process (UV/H₂O₂/TiO₂) was used. TiO₂ was immobilized on the surface of a glass disc using a sol-gel method. A factorial design of experiments followed by a Neural Networks fitting allowed the optimal conditions to be determined for treating 50 mg/L of AP. Under these conditions (pH = 4; [H₂O₂]₀ = 1500 mg/L; disc speed = 500 rpm; flowrate = 25 mL/s), AP was completely degraded in 120 min and regeneration of the disc allowed 10 cycles with no loss in efficiency. The value of the apparent volumetric rate constant was found to be 6.9·10^-4 s^-1 with no apparent mass transfer limitation. Based on the main intermediates identified, a mechanism is proposed for antipyrine photodegradation: Firstly, cleavage of the NN bond of penta-heterocycle leads to the formation of two aromatic acids and N-phenylpropanamide. An attack to the CN bond in the latter compound produces benzenamine. Finally, the phenyl ring of the aromatic intermediates are opened and molecular organic acids are formed.