An EPR study of Cd2+ incorporation in vaterite

Abstract

13C-vaterite, the unstable calcium carbonate polymorph, doped with Cd2`was c-irradiated and the stable paramagnetic centres were studied using electron paramagnetic resonance (EPR) spectroscopy. The 13C isotope has nuclear spin (I \ 1/2) and as a consequence hyperÐne interaction with the unpaired electron occurs. This revealed all paramagnetic centres of carbonate origin, i.e. and free radicals. Two ~CO 3 ~~CO 2 paramagnetic centres induced by cadmium doped to vaterite, one characterized by and the other g a \ 1.9939 by were not split by the 13C-hyperÐne splitting. Therefore, these paramagnetic centres are most g b \ 1.9886, probably due to Cd ^O~. The locations of these paramagnetic centres in vaterite are determined and the role of cadmium in the formation of calcite crystals in the vaterite-precipitating system is discussed.

Photocatalytic Reduction of CO2 to CO in the Presence of H2 or CH4 as a Reductant over MgO

“…Therefore, the signals in Figure c were not derived from MgO but the CO 2 species adsorbed on MgO. It was reported that g = 1.998, 2002 and g = 2.007, 2.011, 2.022 are assigned to a CO 2 - radical and a CO 3 - radical, respectively. − Our results are also supported by this assignment. In our case, the signals of the CO 2 - radical and the CO 3 - radical remained after 1 h although the light illumination was stopped.…”

Multifunctional calcium carbonate microparticles: Synthesis and biological applications

“…16 Stabilization of the vaterite form of CaCO 3 can be acheived via presence of impurities of inorgainc or orgainc materials. 17,18 To stablize the vaterite phase, several research groups used organic impurites such as ovalbumin, 18 polypeptide, 19 double hydrophilic block copolymers, 20 and anionic starburst dendrimer. 21 Cai et al embedded gold nanoparticles (NPs) into the pores of CaCO 3 .…”

Non-aqueous formation of the calcium carbonate polymorph vaterite: astrophysical implications

“…Due to its industrial and commercial potential, there is a large body of literature that shows vaterite can be stabilized (often temporarily) in the presence of various different ions or organic and inorganic additives under widely differing experimental conditions, most of which are concerned with in vitro formation (e.g. Wray & Daniels 1957;Nassrallah-Aboukais et al 1998;Nothig-Laslo & Brecvić 1999;Han et al 2006;Nebel & Epple 2008;Wang et al 2009;Fernandez-Daz 2010;Gomez-Morales et al 2010), or as a post-formation coating (Vogel et al 2009). The origin of these stabilisation effects likely lies in the fact that vaterite, aragonite and calcite all have very similar values for their free energy (0.5-3 kJ/mol differences; Plummer & Busenberg 1982;Wolf et al 1996Wolf et al , 2000Baitalow et al 1998).…”

“…Wray & Daniels 1957;Nassrallah-Aboukais et al 1998;Nothig-Laslo & Brecvić 1999;Han et al 2006;Nebel & Epple 2008;Fernandez-Daz 2010;Gomez-Morales et al 2010), or as a post-formation coating (Vogel et al 2009). The origin of these stabilisation effects likely lies in the fact that vaterite, aragonite and calcite all have very similar values for their free energy (0.5-3 kJ/mol differences; Plummer & Busenberg 1982;Wolf et al 1996Wolf et al , 2000Baitalow et al 1998).…”