Ozonation of p-nitrophenol at different pH values of water and the influence of radicals at acidic conditions

•Ozonation of p-nitrophenol was carried out at constant pH values of 2, 7 and 10.•Radical scavenger t-butanol was used for different t-butanol concentrations.•pH determines the relative production rates of the first intermediates.•Radicals play an important role in ozonation at low pH.•There exists t-butanol concentration for the slowest 4-nitrocathecol production.

Ozonation of p-nitrophenol solution was carried out without pH control and at constant pH values of 2, 7 and 10. The effect of radical scavenger t-butanol at pH 2 was studied for t-butanol concentrations of 0.0, 0.000225, 0.00225 and 0.0225 mol/dm3. The ozone decomposition rate was computed for each pH as a function of time on the basis of each experimental run. The consumed ozone dose was calculated at each pH and at each t-butanol concentration at pH 2. The results indicate that pH determines the relative production rates of the first intermediates, hydroquinone and 4-nitrocathecol, on the reaction path of p-nitrophenol decomposition and that radicals play an important role in ozonation at low pH. The results also indicate that there exists some optimum t-butanol concentration at which slowest 4-nitrocathecol production occurs, and further, there exists some optimum t-butanol concentration for highest consumed ozone dose per amount of decomposed p-nitrophenol at pH 2.