Fast diffusion-reaction in the composition and morphology of co-precipitated carbonates and nitrates of copper(II), magnesium(II) and zinc(II)
J.Michael Davidson †,* , Khellil Sefiane †,§ and Tiffany Wood ‡
†School of Engineering, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JL, U.K. § International Institute for Carbon Neutral Energy Research (I2CNER) Kyushu University, 744 Motooka, Nishi ku, Fukuoka 818 0395, Japan. ‡School of Physics and Astronomy, James Clerk Maxwell Building, University of Edinburgh, EH9 3JZ, U.K.
Email corresponding author at: [email protected]
Supplementary Information Index:
1. Table S1 Analytical data for the precipitation of copper in carbonate media. Table S2 Analytical data for the precipitation of zinc in carbonate media. Table S3 Analytical data for the precipitation of magnesium in carbonate media. 2. The infrared spectroscopy of colloidal carbonate precipitates p. S7 Figure S1 p. S10 Figure S2 p. S11 Figure S3 p. S12 Figure S4 p. S13 Figure S5 p. S14 3. Figure S6 XRD powder patterns of crystalline and amorphous materials p. S16 4. Videos: http://www.see.ed.ac.uk/~ksefiane/JMD movies/Magnesium.avi
http://www.see.ed.ac.uk/~ksefiane/JMD movies/Zinc.avi
1. Table S1 Analytical data for precipitation of copper in carbonate media
aSupernatant yielded crystalline chalconatronite on standing
Table S2 Analytical data for the precipitation of zinc in carbonate media
Table S2 - footnotes
Temperatures recorded in the table are celcius. aSample containing 5.25 mmol Zn on heating sequentially o o o o b →60 → 190 → 280 → 659 gave successively 0.355, 0./000, 2.18, and 0.798 mmol CO 2. 4.94 mmol ZnBC o o c on heating → 260 → 600 gave successively 1.17 and 0.780 mmol CO 2. 2.283g compressed unwashed gel, d 1.92(Na 2CO 3)·Zn 5(CO 3)1.85 (OH) 6.30 contained 2.126g water (83.7% w/w) 1.762g of compressed unwashed gel was treated with 20 mL of water, washed and filtered yielding 3.24 mmol ZnBC and from the filtrate and e f washings, 1.21 mmol Na 2CO 3. Na 2Zn 3(CO 3)4·3H 2o requires C=8.95, H=1.13%. 2.319g of comprerssed ZnBC o o gel was decomposed thermally →390 → 500 yielding 0.915 mmol and finally 0.980 mmol CO 2. Acid decomposition of the residue gave0.937 mmol CO 2 and by titration 2.46 mmol zinc. The analytical data g correspond to 1.84(Na 2CO 3)·Zn 5(CO 3)2.05 (OH) 7.08 . The water content was 84.8% w/w. An experiment using o 0.25M solutions: the thermal decomposition of 2.146g compressed ZnBC gel at 320 gave 1.81 mmol CO 2. With acid decomposition and sodium analysis (n=0.780, m=0.657) overall composition was h 1.64(Na 2CO 3)Zn 5(CO 3)2.26 (OH) 5.5 . The water content was 84.2% w/w. The pH of 0.5M Na 2CO 3 was raised to 12.2 with NaOH. The precipitate was a dense non gelatinous solid.
Table S3 Analytical data for the precipitation of magnesium in carbonate media
Table S3 - footnotes aBelow pH=10 crystalline nesquehonite is the main product identified by ir spectroscopy bunwashed samples with similar C, H, N analyses close to Na 2Mg 5(CO 3)5(OH) 2·nH 2O. n=6 requires: C, 9.85; H, 2.31%. nitrogen impurity ~5% molar. cthe sample changed morphology and colour (cream) during drying in vacuo . d79.4% w/w water. egel soaked for 16h and drained. gel had 71.2% w/w water. fnesquehonite g h c i crystallised from supernatant. 80.0% w/w water 0.25M MgCl 2; morphology, as in . 0.25M Na 2CO0 3, c j k 1.0M MgCl 2; morphology as in . 0.25M Na 2CO0 3, 1.0M MgCl 2; 76.9% w/w water. 1.0M MgCl 2; 75.5% w/w water.
4. Infrared spectroscopy of basic carbonate precipitates. The as formed basic carbonate colloidal precipitates studied in this investigation are difficult to characterise because there are not applicable physical methods. Infrared spectroscopy offers information that is limited by the apparent need to dry samples in vacuo before the spectrum can be collected due to the intense absorption by water which constitutes ~80% of the sample. We have found problems in both sample preparation and presentation of the dried colloids in the spectrometer and in the applicable instrumental methods and therefore assignments may be made only with caution. The instruments available have been two Perkin Elmer spectrometers: a scanning dispersive instrument and a Fourier transform type used in both ATR and open beam modes. The wavenumber range of interest was restricted to 1300 1650 cm 1, covering fundamentals of both carbonate and nitrate, to enable comparison of fluorolube mull transmission spectra with both FTIR ATR and KBr disc spectra (much favoured for work in this area) using dry powdered samples. The general result is that some features that appear in the mull spectra are absent in the ATR and KBr disc spectra. Figures S1a d make the ATR/mull comparison for ZnBC and the KBr disc/mull comparison for CuBC, showing absence of the 1350 cm 1 band that occurred in numerous mull spectra of such precipitates. Unfortunately a band at 1380 cm 1 from zinc basic nitrate 18 overlaps that of a fundamental of hydrozincite. Figure S5a (ATR) shows the sharp doublet spectrum of commercial amorphous hydrozincite precursor whereas in figure S5b (fluorolube mull) a 1350 cm 1 the band is almost resolved. Pure crystalline materials do not show this effect which may therefore be a property characteristic of mixed products from segregated reaction. Some ATR spectra of zinc basic carbonates, especially at pH<10, are sharp and closely similar to those of the crystalline mineral despite the compelling analytical evidence that they are not pure substances. It seems possible that our 2 phase materials have an external layer of basic carbonate which is scarcely penetrated by the evanescent wave. However less striking pressure effects on infrared spectra have also been noted. 34 A further feature of the weak penetration of the evanescent wave is that useful ATR spectra can be obtained from drained gels despite the ~80% water content (figure S1d) observed as a 1639cm 1 band. The FTIR ATR spectra of crystalline substances, such as chalconatronite and gerhardtite are sharp and duplicate published envelopes, and thus that from the initial precipitate from copper(II) at high pH is readily assigned (figure S2a).
Figure S2 (ATR from precipitated Zn(NO) 3)2), figure S3 (dispersive instrument, precipitated ZnCl 2) and figure S5 (ATR from precipitated Zn(NO) 3)2) show spectra from unwashed and washed gels at various
pH. General features are that washed precipitates are invariably less complicated mixtures than their unwashed counterparts. ATR spectra obtained from zinc basic carbonate are presented in figures S2b h, and show differences between washed and unwashed samples. Figures S2b 2e are spectra from two cycles of washing after which S2e is a sharp spectrum having frequencies of an amorphous hydrozincite precursor (1510, 1385 cm 1). Evidently in the spectrum from the initial precipitate (S2b) there are two additional, overlapping bands of similar intensity. After five washings, these two bands are partly removed (S2c). In figure S2d (unwashed) the 1352 cm 1 band is stronger than the overlapping “hydrozincite” one, but is removed by washing. The strong 1350 cm 1 band occurs in almost all spectra
(pH=11.6 – 9.2) using samples prepared from both Zn(NO 3)2 and ZnCl 2 and must therefore be assigned to a further basic carbonate gel, other than the hydrozincite precursor. Figure S2h shows that this compound leads to the major component of a spectrum derived from bulked single drop reactions. If this assignment is correct the presence of the 1350 cm 1 band confirms that unwashed precipitates are mixtures of basic carbonates. The fluorolube mull spectra from the dispersive spectrometer were invariably better resolved than the FTIR spectra. Figure S3 shows a doublet splitting of 10 cm 1 in the 1500 cm 1 peak from hydrozincite precursor typical of a large number of spectra from samples prepared at middle range pH~10.5 9.2 where the n values converge. Figure S3a,c correspond to the gel, B; 1 1 apparently neither Na 2CO 3 (1440 cm ) nor its hydrate (1450 cm ) are present as a pure phase; the frequency is lowered in a synthetic mixture (fgure S2g). The 1500 cm 1 doublet is absent and therefore the very strong 1460 cm 1 peak can be assigned to a carbonate complexed to Zn 2+ and Na + in some manner, whether molecular or short range. At low pH=7.88 the crystalline complex salt, 1 Na 2Zn 3(CO 3)4, (A), is formed, having a band centred at 1438 cm (figure S2f).
By comparison the fluorolube mull spectra in the zinc series are very complex (figure S3) Bands of the hydrozincite precursor are weak in the unwashed samples (S3a, S3c; pH=11.27, 10.15) and in the first washed sample (S3b). The 1350 cm 1 band is present from all unwashed and washed samples, but is weak. At pH=10.17 the unwashed and washed samples are apparently very similar and similar to the hydrozincite precursor, again consistent with the convergence of the chemical analyses. Initially and at high pH the spectra are quite different with a strong band at 1460 cm 1 (figures S3a, S3c) associated with the presence of sodium carbonate; the absence of strong absorption from hydrozincite precursor suggests that the latter is complexed by sodium carbonate in some way, as discussed in the main text. It
is here suggested that the differences between the ATR and mull spectra are connected with the segregated nature of the materials.
Figure S4 shows the fluorolube mull spectra of precipitated copper(II). For comparison purposes, in figures S4g and S4h spectra of authentic chalconatronite and gerhardtite are given.At the initial pH=11.3 the unwashed sample is mainly basic nitrate (S4a) and this is only slightly altered by washing (figure S4b). At pH=10.6 the spectrum of the unwashed precipitate (figure S4c) is very complex, as both both chalconatronite and georgeite (1470 cm 1) are present. Washing removes chalconatronite and the sample (S4d) is a mixture of georgeite and basic nitrate. At pH=10.2 the unwashed precipitate contains less nitrate relative to chalconatronite and georgeite. After washing the residue is mainly georgeite. All of the spectra presented in figures S4a – S4f show the 1350 cm 1 band that is evident in almost all Cu(II) and Zn(II) precipitates.
34 Friedrich, F.; Weidler, P. G. Contact pressure effects on vibrational bands of kaolinite during infrared spectroscopic measurements in a diamond attenuated total reflection cell. Appl. Spectrosc. 2010, 64 , 500 506.
Figure S1 Comparison of fluorolube mull spectra with those of compressed samples: CuBC precipitated at pH=10.62 (a) FTIR-ATR (b) FTIR-fluorolube mull; ZnBC precipitated at pH=10.53 (c) KBr disc, dispersive spectrum (d) fluorolube mull, dispersive spectrum. (e) CuBC precipitated at pH=11.18, FTIR-ATR of drained gel.
Figure S3 Comparison of unwashed and washed zinc(II) precipitates; fluorolube mull dispersive spectra. (a) pH=11.27, unwashed (b) pH=11.27, washed (c) pH=10.75, unwashed (d) pH=10.75, washed (e) pH=10.17, unwashed (f) pH=10.17, washed.
Figure S4 Copper basic carbonate precipitates. Infrared spectra from the dispersive spectrometer; fluorolube mulls. (a) pH= 11.3, unwashed (b) pH=11.3, washed. (c) pH=10.6 unwashed. (d) pH=10.6, washed. (e) pH=10.2, unwashed. (f) pH=10.2, washed. (g) crystalline chalconatronite (h) crystalline malachite.
Figure S5 FTIR spectra from zinc(II) nitrate normal mode precipitation by ATR and using fluorolube mulls. (a,b) zinc basic carbonate marketed by Durham Chemical Company (1989) as hydrozincite (amorphous). (c) collected single drop lamellae, unwashed. (d) collected single drop lamellae, washed. (e-h), pH=11.50: (e) drained gel, unwashed. (f) drained
gel, washed. (g) vacuum dried gel, unwashed. (h) vacuum dried gel, washed. (i-n) pH=11.35: (i) drained gel, unwashed. (j) drained gel, washed (k,l) vacuum dried gel, unwashed. (m,n) vacuum dried gel, washed.
3.
Figure S6 Representative X-ray powder diffraction spectra. (a) Sharp spectrum (with reference data) from synthetic malachite crystallised reversibly from a sodium free medium at pH = 5.35. (b) Vacuum dried zinc basic carbonate precipitated at: pH = 11.64-11.15 (upper); pH = 10.96-10.58 (middle) and pH = 10.58-10.32 (lower). The reference pattern, which does not correlate, is that of crystalline hydrozincite.The spectrum shows extensive amorphous background. The very broad background absorption is typical of the spectra of amorphous precipitates.