where, A(ṽ)t is the integral absorption intensity of PS from 1780 -934 cm -1 (a.u.) at time t (min), and A(ṽ)e is the predicted integral absorption intensity of PS at equilibrium (a.u.). ka and kd are adsorption and desorption rate constants (min -1 ), respectively. PS adsorption and desorption isotherms at the diamond and goethite surfaces obtained over the range of experimental PS concentrations (14.1 -196.9 μM for diamond and 3.5 -196.9 μM for goethite) were fitted using the Langmuir model (Eq. 4)