Abstract
The degradation of carbamazepine (CBZ) and ibuprofen (IBP) in aqueous matrices was investigated by TiO2 and ZnO photocatalysis initiated by UV-A and visible-light irradiation. Emphasis was given on the effect of operating parameters on the degradation effectiveness, such as catalyst type and loading (50 - 500 mg/L), initial drug concentration (10, 40, 80 mg/L) and wavelength of irradiation (200 - 600 nm). In an effort to understand the photocatalytic pathway for CBZ and IBP removal in terms of primary oxidants, the contribution of HO· was evaluated. With this scope, the radical-mediated process was suppressed by addition of an alcohol scavenger, isopropanol, (i-PrOH), described as the best free hydroxyl radical quencher. The photodegradation rate of the pharmaceuticals was monitored by high performance liquid chromatography (HPLC). According to the results, visible-light exposure, at λexc > 390 nm, takes place as a pure photocatalytic degradation reaction for both compounds. IBP was found to have overall high conversion rates, compared to CBZ. IBP oxidized fast under photocatalytic conditions, regardless the adverse effect of the increase of initial drug concentration, or low catalyst load, irradiation upon visible-light, by either titania or zinc oxide. Finally, addition of isopropanol showed a significant inhibition effect on the CBZ degradation, taken as an evidence of a solution-phase mechanism. In the case though of IBP degradation, the hole mechanism may be prevailing, suggested by the negligible effect upon addition of isopropanol indicating a direct electron transfer between holes (h+) and surface-bound IBP molecules. A plausible mechanism of IBP and CBZ photocatalysis was proposed and described.
Highlights
None can deny how significant is the continuous development and research on the area of synthesis and production of a variety of drugs of pharmaceutical importance for both mankind and animals
The type and catalyst load, together with the initial drug concentration effect were assessed as fundamental operational parameters in heterogeneous photocatalysis
Drug photocatalytic efficiency, indicated by the decrease of initial concentration, in each case was assessed by high performance liquid chromatography (HPLC) measurements at the indicated irradiation times
Summary
None can deny how significant is the continuous development and research on the area of synthesis and production of a variety of drugs of pharmaceutical importance for both mankind and animals. Within the last few years, both the occurrence and fate of pharmaceutical residues and their metabolites in environmental matrices, have attracted scientific interest These compounds are classified as emerging pollutants, while their main pathway into the environment is pharmaceutical industries, excretory products of medically treated humans and animals followed by their inefficient removal in wastewater treatment plants [1] [2]. They enter the environment after inappropriate disposal of unused or expired pharmaceuticals in the sewage system or in the garbage. Minor plants up to 25% [14]
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