The Significant Influence of the pH Value on Citrate Coordination upon Modification of Superparamagnetic Iron Oxide Nanoparticles

Although citrates are commonly used to modify nanoparticles, attention is rarely paid how the modification parameters affect type of adsorption and, thus, possibly, properties modified particles. The relevance this and significant impact it can have demonstrated in study by examining effect pH upon superparamagnetic iron oxide nanoparticles (SPIONs) with citrate, using a citrate concentration that yields high molecular surface density but induces almost no coordination pressure. Relying first on number classical surfaces analyzing methods, clear pH-dependent differences be identified. Finally, consideration thermally induced redox behavior gives decisive clue unravel “citric acid mystery” put together the, until then, weak hints into an overall picture. This shows carboxyl groups linked oxidic dependently via hydrogen bonds hydroxide or coordinatively ions besides, also interact, certain extent, ammonia for adjustment. With these findings, finally possible explain observed when citrate-modified SPIONs coated silica (SiO2) redispersed after spray-drying.