Investigation of Para-Aminobenzoic Acid’s Photodegradation in Different pH Environments under UVB Light

Name: Jingyi Daniel Zhou
Majors: Chemistry, Mathematics
Advisors: Dr. Sarah Sobeck, Dr. Drew Pasteur
The vast use of UV-filters has been related to many recent environmental issues, including coral bleaching and inhibition of aquatic organisms’ light-dependent metabolic functions. Para-aminobenzoic acid (PABA) and its derivates are common sunscreen active ingredient that have been widely studied. Past studies have shown that polarity and pH of the solution environment are able to change the excited state processes, such as intramolecular charge transfer, that occurs following absorbance of UV light by PABA. Based on these studies, two hypotheses about the kinetics of the degradation of PABA in aqueous solutions are tested in this research: 1) the lower the pH, the slower the PABA degradation, and 2) the mechanism of PABA degradation has simpler kinetics in solutions with lower pH. This research applies mathematical modeling methods, using tools including Python and MATLAB, to test the hypotheses above and better understand the kinetics of PABA’s degradation in water. At the end of this research, a set of optimal mechanisms for PABA’s degradation at pH 2, 7, and 10 and corresponding rate constants were obtained. Even though there were some unavoidable uncertainty existing in the deconvolution model, by comparing the mechanisms mentioned above, both hypothesis 1) and 2) were still confirmed. For future work, weighting should be applied to the individual component signal in the model in order to increase quality of fitting. And finding a mathematical relationship between signal’s bandwidth in absorbance spectrum and other factors is also of interest to decrease uncertainty of deconvolution.