In an antibiotic degradation experiment using metals carbon composites to activate PMS, the results doesn't fit pseudo first or second order kinetics however the degradation efficiency is very high during the first 10 min.
You are facing a complex reaction with many elemental steps, each of which has its own rate coefficient. Depending on the current concentration, different components may e.g. be assumed quasi-stationary or quasi-equilibrated, so the changes in behaviour may change severely.