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Heterogeneous photocatalysis of pharmaceutical metoclopramide using a NUV-LED/TiO2

Advanced oxidation processes (AOPs) have proven to be among the most effective techniques for the removal of micropollutants from water samples. Depending on the properties of the waste stream to be treated, AOPs can be employed either alone or coupled with other physicochemical and biological processes or as a tertiary treatment. One of the vital factors in photocatalytic processes is the source of light. Since widely used mercury lamps have several drawbacks, other sources of light are receiving more interest in last years. Light emitting diodes (LEDs) have several advantages over traditional UV lamps such as a better efficiency, lower power requirements and longer lifetimes. In addition, they are less harmful to the environment because they are free of toxicants (e.g. mercury). The aim of this study was to evaluate photocatalytic degradation of metoclopramide (MCP), a pharmaceutic widely used for stomach and esophageal problems. The experimental study included evaluation of MCP adsorption on the photocatalytic film (stirring „in the dark“), photolytic and photocatalytic degradation experiments. Near ultraviolet light emitting diode (NUV-LED) lamps with a peak wavelength of 405 nm and 365 nm (wavelengths that can be found in natural solar spectrum) were used as alternative light sources. TiO2 in a form of a film deposited on borosilicate glass ring placed on the bottom of the reactor was used. Process degradation efficiencies and evaluation of kinetic constants were based on HPLC-MS/MS analyses, which also enable identification and monitoring of MCP degradation products. Photodegradation of MCP followed pseudo-first- order kinetics, and the kinetic constant of photocatalysis at 365 nm was much higher (0.0247 min-1) than constant obtained at 405 nm (0.0046 min-1). Adsorption of MCP on photocatalytic film and its photolytic degradation were not observed. The chemical structures of two detected photodegradation products were suggested based on mass spectra.

pharmaceuticals, metoclopramide, advanced oxidation processes, photocatalysis, LED, titanium dioxide

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