REPORT: APRIL 2008

DEUTERATED MINERALS

Abstract

The exchange of D2O with surface water on kaolinite and gamma alumina was observed using DRIFTS (spectral lines due to D2O or -O-D which are shifted compared with the equivalent line involving the 1H isotope). The experiments were carried out using the DRIFTS platform with a removal "environmental hood" attachment.

Introduction

This work was an extension of studies carried by Scott Wood on the exchange of surface water adsorbed onto minerals, for D2O from air saturated with this molecule.

DRIFTS analysis gives spectral lines due to D2O or -O-D which are shifted compared with the equivalent line involving the 1H isotope. The greater mass of the 2D isotope (double that of 1H), results in an increase in the reduced mass of any molecular vibrations. This in turn produces a shift, of a spectral line where a 1H atom is replaced by its 2D isotope, to lower wave number. This is known as the reduced mass effect (see Brian Smith; “Infrared Spectral Interpretation- A Systematic Approach p15-17)[1].

Minerals treated with D2O

The minerals treated

  1. Kaolinite from Edgar, Florida (supplied by Ward’s Natural Science) – surface area (as determined by BET) 27 m2/g.
  1. Γ-alumina supplied by Scientific Minerals Corporation (Bozeman Montana, USA) – surface area (as determined by BET) 51 m2/g.
  1. Halloysite. This sample was part of a supply at VIMS. It was a Clay mineral Standard (halloysite # 29) from Wagon Wheel Gap, Colorado Code 480150. It was obtained via Ward’s Natural Science. This material clumps together readily under ambient conditions – it needs grinding in a mortar & pestle and the surface area of the samples used is unknown.

Experiments done in 2007

Kaolinite purged with air saturated with D2O.

Method

The environmental chamber, a DRIFT unit accessory, was used to enclose mineral in the cup of the DRIFT unit. This unit allows gas to be purge through the chamber. Since the purge gas was to be saturated with D2O, the KBr windows of the chamber (which are soluble in water and thus would have become very cloudy) were replaced by ZnSe windows. The use of ZnSe allows a data collecting range of 4000 – 500 wavenumber. The observed signal when the aligning mirror was in place was strong but the signal with KBr in the sample cup was very weak (0.8 KM compared to >2 KM without the shood). Maximum peak values were of the order of 0.2 – 0.3 with kaolinite in the cup.

The micro-sampling cup which we have cannot be used with the environmental chamber – the base is too wide to fit into the cup holder.

GAS PURGING :

The dry air flow meter was adjusted to ‘30’. The flow was split such that ¼” diameter tubing went to the spectrometer chamber and 1/8” diameter tubing to the environmental chamber (EC). The air flow to the EC was passed through a bubbler which contained D2O and passed into the EC via the “sample port”. The “air in” port was covered with Teflon tape. The sample port inlet passes the gas to an outlet adjacent to the sample cup. The D2O saturated air exiting the EC was released into a flask containing “DRIERITE” to capture the D2O.

Results

Run1

Only the spectra collected at 0 and 50 minutes had 100 scans – the others has only 10 scans and thus are very noisy (a spectrum at 60 minutes also has 100 scans but this is not shown – it shows a slight increase in D2O over 50 min)

The purge gas was passed over the KW immediately after the commencement of dry air being bubbled into the D2O.

With the D2O purging, a decrease in peak height with time was observed for at peaks centered at

  • A peak centered at 1639 cm-1 (attributed to physical adsorbed water (Frost et al. (1999)[2] and Hoch and Bandara (2005)[3]).
  • The 3564- 2747 cm-1 region (shoulder on the lower wavenumber edge of the strong –OH adsorption region). Peaks in this region are attributed to water bands in the references above. The peak at 3450 is attributed by both papers as being the H-O-H in water (and by Hoch t al. (2005) as being due to the physically adsorbed water- and associated with the 1630 water bending peak observed in the material used).

New peaks (with peak height increasing as the purging time increases) were observed

  • 2515 cm-1 – strong broad peak increases with purging time (Figures 1 and 2). Figure 2 shows that some of the peak at 2515 cm-1 is due to physically adsorbed D2O replacing H2, since there is a corresponding decrease, with increasing purge time, in the region 3400 – 2800 cm-1 (shift of ~230 cm-1) but in addition to this, the total moisture load of the surface is increased by D2O.
  • 1430 cm-1 (can be attributed to a shift in the peak at 1637 cm-1 due to increased reduced mass whenD2O replaces H2O) shift of ~210 cm-1 (Figures 3 and 4).
  • In the –OH region for kalinite (3740 – 3600 cm-1) no correlation between peak height and the length of time of purging with D2O, was observed(Figure 5). The –OH groups are chemically bonded (chemi adsorbed)to the surface.

It should be noted thatin Figures 1 -4 it can be seen that over 15 minutes are required before any effect is observed. This may have been be due to the time required for the air above the D2O liquid to become saturated and thus transferred to the environmental hood.

Figure 1: Changes, with increasing purge time, in the 3000 – 2000 cm-1 region for kaolinite purged with dry air bubbled through D2O.

Figure 2: Changes, with increasing purge time, in the 3400 – 2200 cm-1 region for kaolinite purged with dry air bubbled through D2O.

Figure 3: Changes, with increasing purge time, in the 1750 – 1400 cm-1 region for kaolinite purged with dry air bubbled through D2O.

Figure 4 baseline corrected version of Figure 3 (some curves removed)

Figure 5: Changes, with increasing purge time, in the 3750 – 3600 cm-1 region for kaolinite purged with dry air bubbled through D2O ( black 0 min; green 30 min; red 50 min).

RUN 2

The environmental hood was purged with dry air for 20 min to remove any residual D2O.

Dry air was then passed through the bubbler – it should be noted that the atmosphere above the bubbler was already saturated with D2O.Spectra taken at 0, 10, 15, 20 and 25 minutes were all 10 scans and the spectra at 30 min and 60 min 100 scans.

The results of Run 2 were consistent with those of Run1. There was no increase in the height of the peak at 2500 cm-1 after 45 minutes of purging (red curve in Figure 6) (45 – 90 minutes showed no increase – MAYBE MOISTURE LOAD IS NOT INCREASING – THINK & RE-WRITE)

Experiments done in 2008

Treatment method

Phase 1

A 1 g sample of each mineral was mixed with D2O to form a slurry. After 24 h, on a rocker, excess liquid was decanted and the material was left to dry in the fume hood. It should be noted that the γ-alumina sample dried more quickly than the clay samples. The kaolinite sample took the longest to dry (it was 2 weeks before the sample was dry enough to re-grind).

Phase 2

Samples were retreated with a little more D2O and allowed to dry in a covered dish. In the case of kaolinite only a few of drops were added, so as to shorten the drying time. A small quantity of D2O was left in a pool in the dish to maintain a high humidity of D2O. When dry samples were placed in a small capped tube and stored in the dish.

RESULTS

Characterization of the halloysite sample[4]

Figure:1 (a; b; c) Red halloysite (as received); Black kaolinite (as received)

It should be noted that kaolinite is a product of halloysite dehydration. During DRIFTS the sample is purged with dry air and this will cause some dehydrayion of the material but this is assumed to be negligible because of the short residence time of the sample in the spectrometer (< 5 minutes).

In Figure 1(a) Halloysite is indicated by the strong peaks at 3696 and 3625 cm-1 (Al2OH stretching bands with each OH linked to two Al atoms) and weak bands at 3610 (intercalated water) and 3550 cm-1(surface OH groups bonded to interlayer water). There is evidence of peaks intermediate to those at 3696 and 3625 cm-1 but the relative intensities of these peaks are less than those observed for kaolinite (black curve in Figure 1) and so the material is consistent with a mix of halloysite and kaolinite.

The expected peak at ~920 cm-1 (as described by Joussein et al.1) is not observed.

In Figure (1b) peaks are observed at 1634cm-1 and 1653 cm-1for halloysite and for kaolinite (the relative strength of the 1634 cm-1peak being greater for kaolinite). These peaks are due to physic-sorbed water.

D2O treated minerals

Figure 2: Spectra shown on a common scale (note that these are not subtraction spectra)

RED : D2O treated (bold) and untreated γ-alumina

BLUE: D2O treated (bold) and untreated kaolinite

GREEN: D2O treated (bold) and untreated halloysite

Figure 2 shows that the kaolinite sample, which took ~ 2 weeks to dry before regrinding has no evidence of D2O. The γ-alumina and halloysite samples in, Figure 2, show the presence of both adsorbed H2O and D2O.

Earlier experiments in which air saturated with D2O was passed over kaolinite (in the environmental control hood of the spectrometer) showed ready exchange of the water peak at ~1638 cm-1(2002 results figures 1&2). Results ( Figure 3) showed that ~ 50 minutes was required for the exchange of the majority of the water. In this figure, also shown is the extent of D2O exchange on a kaolinite which was left for 3 days in covered dish with a quantity of D2O in an adjacent dish. This sample is also shown in Figure 4.

Figure 3: Kaolinite sample purged with air saturated with D2O. Green 75 min; Tan 50 min Pink 45 min; blue 25 min. black 0 min. The red curveis the washed- dried and then stored in an D2O atmosphere.

Kw

Fig 4 : RED as received KW; BLUE- KW exposed to D2O vapor over 3 days (covered dish) – transferred to small tube & sealed/

Γ-alumina

Fig 6: RED as received γ-alumina; BLUE- slurry with D2O formed, drained & dried. (Left in covered dish with D2O atmosphere then – transferred to small tube & sealed.

Halloysite

Fig 7 :RED as received γ-alumina; BLUE- slurry with D2O formed, drained & dried. (Left in covered dish with D2O atmosphere then – transferred to small tube & sealed.

It would appear that for the halloysite sample (Fig 7) the D2O added to the moisture content of the present sample, rather than replacing H2O.

ref[5] / KW / OH-OD exchange
3695 / 3696 / Inner surface hydroxyls / 2725
3670 / 3669 / “ / 2710
3650 / 3652 / “ / 2698
3620 / 3621 / Inner - hydroxyls / 2675

Note that the deuteration of the kaolinite in the reference was done using an expanded hydrazine-kaolinte complex at room temperature. The percentage of OH-OD exchange observed for the inn-surface hydroxyl vat=ried from 60 -67 % and that of the inner hydroxyls was only 22 %.

COMPARISON of results with those obtained by Scott WOODS (2003)

The experiments by Scott WOODS used the environmental hood. Purging was with N2 bubbled through D2O

  • The background spectrum was with KBr and an atmosphere of D2O purged N2.
  • The γ-alumina was heated to 125 C (and held at this temperature) to remove physi-sorbed water.

Figure X shows a comparison of the results obtained in 2003 with D2O purged N2 with those obtained by forming a slurry of γ-alumina in D2O (for 12 hours), decanting and then allowing the heavy water to evaporate.

Figure X:

2003 expts γ-alumina at 125 oC, purged with D2O: Red 15 min; aqua – 60 min .

2008 expts: Purple –initial material; Blue treated material.

Note in figure X that peaks due to adsorbed –OD groups appear at ~ 2500 cm-1 with an intensity ~ to peaks observed at 3500 cm-1

[1] Brian Smith (1998?) “Infrared Spectral Interpretation- A Systematic Approach”. CRC Press

[2] Frost, R.; Kristof, J.; Horvath, E.; Kloprogee, J.T. (1999) “Modification of the hydroxyl surfaces through the application of preassure and temperature, Part III”. Journal of Colloid and Interface Science214, 380-388.

[3] Hoch, M.; Bandara, A. (2005) “Determination of the adsorption process of tributyltin (TBT)and Monobutyltin (MBT) onto kaolinite surface using Fourier transform (FTIR) spectroscopy” . Colloids and Surfaces A: Physiochem. Eng. Aspects 253,117-124.

[4] Joussein, E., Petit, S., Churchman, J., Theng, B. Righi, D., and DElvaux, B. Halloysite clay minerals – a review. Clay minerals (2005) 40, 383-426.

[5] Ledoux, R. L. and White, J. L. (1964) “Infrared study of selective deuteration of kaolinite and halloysite at room temperature” Science 145-3627 p 47-49.