(a): H2O2 decomposition (left axis) and phenol transformation (right axis) catalyzed by goethite. Solid line: first order fit to the data. (b): stoichiometric efficiency in the presence of dissolved silica. Experiments were conducted at least triplicate and, instead of present the average value and standard deviation, all results were presented. [goethite] = 4 g/L, pH = 7, [PIPES] = 1 mM, [NaNO3] = 0.1 M. Except for the control experiment (inversed triangles), the H2O2 initial concentration in all experiments was [H2O2]0 = 20 mM.