Abstract
The adsorption kinetics, density and structural property of sodium oleate on Ca2+ activated quartz surface have been studied using the techniques of quartz crystal microbalance with dissipation (QCM-D) and atomic force microscope (AFM). The real-time measurements of frequency (Δf) and dissipation shifts (ΔD) with SiO2 coated sensor have revealed the changes in surface property of the quartz during the entire activation and adsorption process at different Ca2+ concentrations and pH's. An activation layer with an adsorption density of 89ng/cm2 was observed at pH=12.0. Since pseudo-first-order model fitted well with adsorption process of sodium oleate, the mass transfer (diffusion-controlled) was the rate determining step at pH12.0. Therefore, the reactions of RCOO−/(RCOO)22− and Ca(OH)+/Ca2+ is considered to be the dominant process in the solution at pH12.0 which generated (RCOO)2Ca precipitation and formed poorly-organized dissipative adsorption layer on activated quartz surface. Two distinct adsorption stages were identified from the different slopes K2>K3 and K3≤0.2 of ΔD−Δf plots which demonstrated the existence of conformational changes in the adsorption layer.
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