In order to identify some of the degraded products, if formed, which are not detected in supernatant are adsorbed on the clay composite, the plate layered with ZnO–clay nanocomposite was successively washed with water and the collective washings are subjected for LC–MS analysis. It is significant to note here that the LC–MS results indicated the formation identical products i.e. triphenoxy-phenol and adipic acid suggesting that these intermediates remained in the adsorbed state as well as they are not degraded further due to larger time of exposure to UV light. Significantly, the amount of adipic acid formed on the nanocomposite surface is almost 66% as compared to 34% of tripehnoxy-phenol suggesting that adsorbed triphenoxy-phenol is subsequently converted into adipic acid due to continuous exposure of UV light. However, lower concentration of adipic acid obtained for the supernatant as compared to triphenoxy-phenol. Moreover, this observation also suggests the highly efficient and selective process for phenol degradation under CSTR condition. The proposed mechanism of phenol degradation is schematically represented in Scheme 1b and can be summarized in the following sequence of photochemical reactions [39] (Eqs. (2–8)):