Interactions of cationic dendrimers with hematite mineral

Interactions of dendrimers on solid substrates are important in processes involving their coating, flocculation, sedimentation, etc. The adsorption of positively charged poly(amidoamine) dendrimers on hematite/water interface has been investigated in this work as a function of pH, ionic strength, and dendrimer generation by measuring the amount of dendrimers adsorbed and zeta potential changes upon adsorption. Two generations of dendrimers, G3 and G7, were selected, representing “earlier” and “later” generations. At pH 9, the adsorption density of G3 dendrimer on negatively charged hematite increased and reached a plateau with an increase in dendrimer concentration. At pH 4, there is no measurable adsorption of the dendrimer on positively charged hematite in 0.01 M NaCl solutions, and a “negative adsorption” in the distilled water, a condition of a much lower ionic strength showing that the interaction between the hematite surface and the dendrimers is governed mainly by the electrostatic forces. At pH 9, adsorption of G7 dendrimer on hematite is much higher than that of G3 dendrimer and it did not even reach a plateau in the tested dendrimer concentration range, a result consistent with the hypothesis that the adsorbed G7 dendrimers assume a compressed conformation while adsorbed G3 dendrimer molecules take more expanded conformation on the solid. With the increase in the adsorption of G3 dendrimer at pH 9, zeta potential of hematite changed from negative to positive and stayed constant when the adsorption reached a plateau. Clearly, deposition of dendrimers can be controlled by manipulating the interfaces and charge of the solid adsorbent such as hematite.