Photocatalytic degradation of dyes and model pollutants is the most widely published activity test in the field, which is exactly why sloppy versions are worthless: everyone can compare your numbers, so your numbers must mean something. Here is how to make them mean something.
Prepare the pollutant solution at a stated concentration, add catalyst at a stated loading, and stir in the dark to adsorption-desorption equilibrium, typically 30-60 minutes. The dark equilibration is not optional: without it, the first minutes of "degradation" are just adsorption. Sample at the end of the dark phase, that is your t=0.
Turn on the calibrated source, sample at fixed intervals, centrifuge or filter immediately to stop the heterogeneous reaction, and analyze the supernatant by UV-Vis or chromatography. Keep temperature and stirring constant throughout, degradation kinetics are temperature-sensitive.
Plot concentration versus time. If the plot is linear in time, quote a zero-order rate. Most photocatalytic degradations follow pseudo-first-order behavior at moderate substrate concentrations: fit ln(C/C0) versus time, quote the slope as k with units of per time. Report R², and never quote a rate constant from a fit over fewer than five points.
Report light source, intensity at the solution, catalyst loading, substrate identity and concentration, temperature and pH. Degradation rates without these seven numbers cannot be compared to anything, including your own next paper.
Perfectlight's photocatalytic reaction systems and calibrated light sources support standardized degradation testing; see solutions.
