Blue Bottle Light Experiments for Demonstrating Basic Kinetics Features of Homogeneous and Heterogeneous Photoinduced Redox Reactions

The kinetics of photobleaching due to homogeneous and heterogeneous photo-induced electron transfer reactions are probed using modified versions of the Blue Bottle experiment in which light is used to drive the photobleaching of a redox dye (methylene blue, MB) by a sacrificial electron donor (SED) using either a homogeneously- or heterogeneously-dispersed photosensitizer; in this case, MB or TiO2, respectively; the latter photochemistry-based reactions are referred to as Blue Bottle Light (BBL) experiments. The SED was triethanolamine, TEOA, or glucose, GluH, for the homogeneous, or heterogeneous, BBL work, respectively, and in both systems a measure of the kinetics was taken as the reciprocal of the time needed to photobleach the system, ttb. For the homogenous, or clear, blue bottle light experiment, the observed variation of ttb as a function of incident light intensity, I and [TEOA] revealed a good fit with the steady state kinetic model derived from first principles for the photosystem. Similarly, for the heterogeneous, or cloudy, blue bottle light experiment the observed variation of ttb as a function of I, [GluH] and [TiO2] revealed a good fit with the often cited Langmuir-Hinshelwood type kinetics usually observed for such systems. The use of these clear and cloudy BBL systems in two laboratory classroom practicals is described briefly.