The laboratory experiment by Herrera-Melián, et al., “Solar Photocatalytic Destruction of p-Nitrophenol” (1), utilizes colorimetric monitoring of the disappearance of p-nitrophenol in a TiO2-catalyzed photochemical reaction. This system is potentially attractive as a freshman chemistry or even high school chemistry experiment because it addresses an environmentally significant problem, gives results that can be observed visually as well as instrumentally, and affords experience using Beer’s law calibration and photometric analysis. However, the hazardous nature of p-nitrophenol, documented in that paper, necessitates the use of protective clothing and respirators by those handling that material.
We have adapted this experiment to use methyl red as the substrate for photolysis. Methyl red will be available in virtually any chemistry stockroom, is compatible with aqueous chemistry, and gives excellent results with this experiment. Our students carried out the photolysis in a UV photoreactor, which makes it possible to nearly destroy the methyl red within 30 minutes in the presence of TiO2, starting with a concentration of around 3 × 10–5 M methyl red. We filtered the samples for absorbance measurement using 4.5 µm HPLC filters and monitored the absorbance at 520 nm. A sample data set is shown in Figure 1.
Figure 1. Concentration of methyl red solution in UV photoreactor, with and without TiO2 catalyst.
Literature Cited
Herrera-Melián, J. A.; Doña-Rodriguez, J. M.; Tello Rendón, E.; A. Soler Vila; Brunet Quetglas, M.; Alvera Azcárate, A.; Pascual Pariente, L. J. Chem. Educ.2001,78, 775–777.
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