A plot of Ce/qe vs. Ce (Fig. 4) suggest that with increasing slope, there is increase in concentration and removal of phenol follows the first order reaction kinetics. The Langmuir parameters qm = 14.77 mg g−1 (monolayer capacity) and Ka = 0.677 L mg−1 (affinity towards binding sites) are determined from the slope and intercept of the plot (Fig. 4). It is observed that the adsorption capacity of ZnO–clay nanocomposite is significantly higher due bifunctional nature of catalyst wherein the ZnO can form complex with phenol while the acidic character of bentonite clay is responsible for binding and subsequent decomposition under UV irradiation. In addition, ZnO can easily release or store oxygen under different conditions to form large amount of oxygen vacancies on the surface, leading to affluent surface states. These two reasons probably account for the superior adsorption capacity of ZnO–clay nanocomposite.