PS adsorption at the goethite and diamond surfaces followed the Elovich and pseudofirst-order (PFO) kinetic models, respectively (Figure , Table ). Since the steepness of the kinetic curves illustrate the initial rate of adsorption, we can qualitatively state that PS adsorbs more slowly but to a greater extent on goethite compared to diamond. This is most likely due to the greater surface area and heterogeneity of bonding energies at goethite's surface sites. We suggest that greater surface heterogeneity (e.g., energy barriers, active sites, surface roughness, electrostatic forces) on goethite may lead to multiple surface-associated reactions that result in logarithmic adsorption kinetics throughout the adsorption process. This is in contrast to PS adsorption on diamond where PFO driven adsorption kinetics is expected due to the homogenous and monolithic diamond surface. It has also been suggested that organic-organic interactions The Langmuir equilibrium isotherms of retained PS at the end of adsorption and desorption experiments indicate that, at the highest PS loading, ~73% of adsorbed PS remained on the goethite surface after desorption whereas ~25% remained adsorbed on the diamond surface after desorption (Figure and). Langmuir parameters also show goethite has a stronger affinity (KL) for PS molecules and a greater adsorption capacity (A∞) after desorption compared to the diamond (Table ). The greater affinity and capacity of goethite arises from its hydrophilic surface that is energetically favorable for adsorption of PS via its ionic and polar groups. PS interacts with the hydrophobic diamond surface via its nonpolar methyl groups which limit sorption strength and capacity. After desorption, when the loosely bonded and bulk PS are lost, the KL values are elevated. The PS adsorption-desorption envelopes (Figure ), however, depend strongly on the polarity of the surface and on PS loading, with more relative desorption from the diamond surface. Similar results were observed by Jeyachandran et al. , where protein (BSA) molecules adsorbed on GeOH via multiple hydrogen bonding, resulted in stronger interactions than with a polyester hydrophobic surface. Consequently, very little BSA was desorbed from the hydrophilic surface, whereas significant desorption (60%) occurred from the polyester surface.