Static SIMS analysis of carbonate on basic alkali‐bearing surfaces

Abstract

Carbonate is a somewhat enigmatic anion in static secondary ion mass spectrometry (SIMS) because abundant ions containing intact CO 3 2− are not detected when analyzing alkaline-earth carbonate minerals common to the geochemical environment. In contrast, carbonate can be observed as an adduct ion when it is bound with alkali cations. In this study, carbonate was detected as the adduct Na 2 CO 3 ·Na + in the spectra of sodium carbonate, bicarbonate, hydroxide, oxalate, formate and nitrite and to a lesser extent nitrate. The appearance of the adduct Na 2 CO 3 ·Na + on hydroxide, oxalate, formate and nitrite surfaces was interpreted in terms of these basic surfaces fixing CO 2 from the ambient atmosphere. The low abundance of Na 2 CO 3 ·Na + in the static SIMS spectrum of sodium nitrate, compared with a significantly higher abundance in salts having stronger conjugate bases, suggested that the basicity of the conjugate anions correlated with aggressive CO 2 fixation; however, the appearance of Na 2 CO 3 ·Na + could not be explained simply in terms of solution basicity constants. The oxide molecular ion Na 2 O + and adducts NaOH·Na + and Na 2 O·Na + also constituted part of the carbonate spectral signature, and were observed in spectra from all the salts studied. In addition to the carbonate and oxide ions, a low-abundance oxalate ion series was observed that had the general formula Na 2−x H x C 2 O 4 ·Na + , where 0 < x < 2. Oxalate adsorption from the laboratory atmosphere was demonstrated but the oxalate ion series also was likely to be formed from reductive coupling occurring during the static SIMS bombardment event. The remarkable spectral similarity observed when comparing the sodium salts indicated that their surfaces shared common chemical speciation and that the chemistry of the surfaces was very different from the bulk of the particle.

The Role of Glyoxal as an Intermediate in the Electrochemical CO2 Reduction Reaction on Copper

“…Because the molecular weight of K 2 CO 3 matches the 138 g mol –1 molecular weight observed, we also considered the possibility of carbonate contamination affecting the data. Shaw et al observed carbonate-containing ions in their static SIMS experiments from sodium salts with no carbonate, such as NaOH, NaC 2 O 4 , etc . They attributed this to the absorption of CO 2 from the atmosphere .…”

“…Shaw et al observed carbonate-containing ions in their static SIMS experiments from sodium salts with no carbonate, such as NaOH, NaC 2 O 4 , etc. 72 They attributed this to the absorption of CO 2 from the atmosphere. 72 Furthermore, bicarbonate may also permeate through the Nafion membrane into the cathode compartment.…”

“…72 They attributed this to the absorption of CO 2 from the atmosphere. 72 Furthermore, bicarbonate may also permeate through the Nafion membrane into the cathode compartment. However, in the freeze-dried stock solutions (in KCl and PPB, Figures S18 and S19), even though KOH (which can strongly absorb CO 2 ) was present in the sample from the observed [KOH + K] + peaks, no carbonate-associated peaks were observed, indicating that atmospheric CO 2 adsorption can be neglected.…”