Dear Sir. Concerning your issue about the determination of the complexation of a polymer with iron oxide nanopartilces through potentiometric complexation. Iron oxide nanoparticles (NPs) exhibit great potential in water decontamination from arsenic. Embedding NPs inside porous hosts is a very promising approach to inhibit their undesirable but inherent aggregation as well as the subsequent capacity drop during application. In this study, we confined iron oxide NPs inside inert silicates (MPS) of varying pore sizes (3.0, 5.7 and 15.7 nm) and obtained three nanocomposite adsorbents. The effect of MPS pore size on As(V) adsorption by the resultant nanocomposite adsorbents was particularly focused. The maximum As(V) adsorption capacity of the nanocomposites was negatively correlated with their host pore size. Based on the in situ Gran plots of the nanocomposites, the narrower pore size of the host resulted in a higher surface hydroxyl density of the confined iron oxide NPs. More interestingly, the reactivity of the hydroxyl groups binding smaller NPs was significantly enhanced compared to the larger one, as indicated by the higher molar ratio of the adsorbed As to the hydroxyl groups. The effect of pH and competitive anions on As(V) adsorption was also studied to further examine the role of the host pore in tuning the properties of the resultant composites. The iron complexation of a fluorescent green pyoverdin siderophore produced by the environmental bacterium Pseudomonas putida was characterized by solution thermodynamic methods. Pyoverdin binds iron through three bidentate chelate groups, a catecholate, a hydroxamate, and an α-hydroxycarboxylic acid. The deprotonation constants of the free pyoverdin and Fe(III)−pyoverdin complex were determined through a series of potentiometric and spectrophotometric experiments. The ferric complex of pyoverdin forms at very low pH (pH < 2), but full iron coordination does not occur until neutral pH. The calculated pM value of 25.13 is slightly lower than that for pyoverdin PaA (pM = 27), which coordinates iron by a catecholate and two hydroxamate groups. The redox potential of Fe−pyoverdin was found to be very pH sensitive. At high pH (∼pH 9−11) where pyoverdin coordinates Fe in a hexadentate mode the redox potential is −0.480 V (NHE); however, at neutral pH where full Fe coordination is incomplete, the redox potential is more positive (E1/2 = −0.395 V). The positive shift in the redox potential and the partial dissociation of the Fe−pyoverdin complex with pH decrease provides a path toward in vivo iron release. I think the following below links may help you in your analysis:

http://pubs.rsc.org/en/content/articlelanding/2017/en/c6en00514d/unauth#!divAbstract

http://pubs.acs.org/doi/abs/10.1021/ic060196p

https://link.springer.com/article/10.1007/s11426-014-5285-6

https://nanoscalereslett.springeropen.com/articles/10.1186/1556-276X-9-198

Thanks

Dear Prof. Elgailani

Thank you so much for your comprehensive answer to my question. the papers are really helpful for my case. Would you please help me know if it is acceptable to predict the complexation behavior of the iron oxide nanoparticles by evaluating the complexation behavior of the iron (Fe3+ and Fe2+) salt solutions?

Best,

Dear Mr. Hodaei,

Your question is interesting in the way you try to understand the behaviour of your material in solution, which can be of potential value in applications such as adsorption. However, your writing mentions Fe2+ and Fe3+ as charge of iron, while the oxidation states II+ and III+ were mentioned, respectively. The apparently small difference has strong consequences to the overall speciation. No iron in such constellation is assumed free and ionic, but bond to oxygen. At the outer surface of FexOy nanoparticles, oxide or hydroxide groups will determine governing charge and interaction towards species. Avoid "complexation" as choice of interaction unitl you actually characterized that interaction mechanism . It is not likely FexOy have the potential to chelate certain compounds in solution.

Regarding the available analytical instrumentation, consider solid phase characterization, for instance using TEM-EDX, EELS, Mössbauer spectroscopy or XRD. The reference applies some of these techniques for the characterization of Fe3O4 nanopartikels in a porous host.

Best regards, Karel Folens

http://onlinelibrary.wiley.com/doi/10.1002/ejic.201600160/full