In-situ ATR-FTIR (attenuated total reflectance-Fourier transform infrared) adsorption-desorption experiments and methodological details are reported in our pervious work . Briefly, adsorption and formation of PS-goethite associations were initiated by introducing PS solutions ([PS] = 3.5 -196.9 μM; I ≈10 mM KCl and pH = 5.0 were used to simulate a low ionic strength environment under mildly acidic conditions) over a hydrated goethite film formed at the surface of a diamond ATR crystal (GladiATR accessory, PIKE Technologies, MA; Figure ).