Monitoring simultaneous photocatalytic-ozonation of mixture of pharmaceuticals in the presence of immobilized TiO₂ nanoparticles using MCR-ALS: Identification of intermediates and multi-response optimization approach

(Graph Presented) The present study has focused on the degradation of a mixture of three pharmaceuticals, i.e. methyldopa (MDP), nalidixic acid (NAD) and famotidine (FAM) which were quantified simultaneously during photocatalytic-ozonation process. The experiments were conducted in a semi-batch reactor where TiO₂ nanoparticles (crystallites mean size 8 nm) were immobilized on ceramic plates irradiated by UV-A light in the proximity of oxygen and/or ozone. The surface morphology and roughness of the bare and TiO₂-coated ceramic plates were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). An analytical methodology was successfully developed based on both recording ultraviolet-visible (UV-Vis) spectra during the degradation process and a data analysis using multivariate curve resolution with alternating least squares (MCR-ALS). This methodology enabled the researchers to obtain the concentration and spectral profiles of the chemical compounds which were involved in the process. A central composite design was used to study the effect of several factors on multiple responses namely MDP removal (Y₁), NAD removal (Y₂) and FAM removal (Y₃) in the simultaneous photocatalytic-ozonation of these pharmaceuticals. A multi-response optimization procedure based on global desirability of the factors was used to simultaneously maximize Y₁, Y₂ and Y₃. The results of the global desirability revealed that 8 mg/L MAD, 8 mg/L NAD, 8 mg/L FAM, 6 L/h ozone flow rate and a 30 min-reaction time were the best conditions under which the optimized values of various responses were Y₁ = 95.03%, Y₂ = 84.93% and Y₃ = 99.15%. Also, the intermediate products of pharmaceuticals generated in the photocatalytic-ozonation process were identified by gas chromatography coupled to mass spectrometry.