Letter: The IEP of Carbonate-Free Neodymium(III) Oxide

Abstract

INTRODUCTIONSeveral metal oxides spontaneously react with atmospheric CO 2 to produce metal carbonates. The particles of these oxides, which have been exposed to atmospheric CO 2 are covered with carbonate layers. A relatively low mass fraction of carbonate may substantially change the surface properties of an oxide particle if it constitutes the external layer of that particle, which is the case for originally carbonate-free metal oxide exposed to atmospheric CO 2 . The presence of carbonate induces a shift in the points of zero charge and isoelectric points (PZC and IEP) of metal oxides to low pH. For example carbonatefree specimens of Y 2 O 3 had substantially higher PZC=IEP than the specimens containing carbonate. [1] Probably similar effects occur for oxides of scandium, lanthanum, and of trivalent lanthanides, which are chemical analogs of yttrium, but the effect of carbonate impurities on the PZC and IEP was mostly ignored in the studies devoted to surface charging of those materials.The availability of thermochemical data of lanthanide carbonates is limited, and the published results show substantial scatter, but the available data indicate that the oxides of lanthanides may spontaneously react with atmospheric CO 2 . For example DG f of Nd 2 (CO 3 ) 3 of À3219 kJmol À1 and of À3116 kJmol À1 is reported in the literature. [2,3] The latter article reports also DG f of NdOHCO 3 of À1476 kJmol À1 . Similar results have been published for other lanthanide carbonates. The above values suggest that DG of the reactions:

Metabolically Doping of 3D Diatomaceous Biosilica with Titanium

“…Furthermore, the lower IEP of TiO 2 nanoparticles can be attributed to the presence of carbonates on the surface of TiO 2 nanoparticles, as can be evidenced by the carbon signal in the EDX results ( Figure 4 ). Kosmulski et al [ 96 ] concluded that the presence of carbonate shifts the IEP of metal oxides to a lower pH. The obtained composites show the highest stability at pH 11 and 12, as for these pH values, each biomaterial has a zeta potential lower than −30 mV, which is the limiting potential for the stability of suspensions [ 97 ].…”