METHOD OF DETECTING AND/OR REMOVING SMALL COMPOUNDS FROM A GASEOUS OR LIQUID MEDIUM TECHNICAL FIELD This invention concerns a method for removing small compounds, such as elemental iodine and iodide compounds, for example methyliodide, as well as radon, from a gaseous or liquid medium. Furthermore, this invention concerns a method for detecting small compounds, such elemental iodine and iodide compounds, for example methyliodide, as well as radon in a gaseous or liquid medium.

BACKGROUND OF THE INVENTION Radionuclides, such as 122Rn and 121, and 13'1 represent hazardous pollutants. For humans, iodine (I2) is an essential element in the food chain being enriched in the thyroid gland.

This absorption is likewise given for its radionuclides 129, and 13lI, which emerge as a fact of the use of nuclear energy producing radioactive waste. Compared to 131I (t1/2 = 8.7 d) 129I has a considerably higher half-life (t1/2 = 1. 57*107 a) [J.

Handl, A. Pfau, F. W. Huth, Health Phys. 1990,58, 609]. At present, the anthropogenic 129 1 release into the biosphere does yet not cause a significant radiation exposure to humans.

However, if today's level of the 129I release will continue in future, danger may once arise.

Radon results from the radioactive decay of radium, a common element in rock and soil derived from the decay of uranium.

At ordinary temperatures radon is a colourless gas and has a short half life (the longest life isotope has a half life of less than 4 days). Inhalation of the element and its decay products which are collected on dust in the air may represent a serious hazard to humans. Recently, radon buildup in homes from the surrounding soil and rocks has become a safety issue and some areas around the world test homes for radon gas.

It is known that charcoal may, under certain conditions, be useful in removing iodine and iodide compounds, like organic iodide compounds. It is also known that the capacity and removal efficiency of charcoal for iodides is low if the relative humidity of the gaseous phase much exceeds 70 %, Also high temperatures effect the ability of charcoal to absorb iodide compounds as well as molecular iodine.

Iodine'waste products emerging in nuclear reactors are nowadays filtered of by inorganic materials. Silver-loaded zeolites [L. Puppe, J. Wilhelm, Eur. Pat. Appl., 5pp. ; A.

Kawaguchi, M. Fukushima, K. Miyahara, K. Matsumoto, Proc. DOE Nucl. Air Clean. Conf. 1983, 17th (Vol. 2), 1142; K. Arai, Jpn.

Kokai Tokkyo Koho, 3pp] are used, which are embedded in a ceramic matrix [V. A. Suvorova, V. N. Zyryanov, A. R.

Kotelnikov, Russ. , No further information given]. In these systems the iodine is bound as silveriodine and can deposited in this solid form. Thus the above system has the disadvantage that it cannot be reused.

Earlier investigations showed, that it is possible to include iodine into various organic compounds to form donor-acceptor type supramolecular solid state structures: Chain formation, intercalation, and filling of cavities [F. H. Herbstein, M.

Kapon, G. M. Reisner, Acta Crytallogr. Sect. B 1985,41, 348; M. Chachisvilis, I. Garcia-Ochoa, A. Douhal, A. H. Zewail, Chem. Phys. Lett. 1998, 293 (3, 4) 153; Th. Zenner, H. Zabel, J. Phys. Chem. 1993, 97, 8690] is known. With respect to a one dimensional confinement, sorption and transport properties of 12 in the zeolite MFI were investigated [M. Kocirik, J.

Kornatowski, V. Masarik, P. Novak, A. Zikanova, J. Maixner, Microporous Mesoporous Mater. 1998,23, 295].

Organic molecular materials with an open framework structure and properties like inorganic zeolite channel-type crystals are still rare objects among supramolecular solids. These materials show a sorption/desorption equilibrium of guest molecules. A particularly suited example is given by a spirocyclophane, tris (o-phenylenedioxy) cyclotriphosphazene (TPP) [H. R. Allcock, J. Am. Chem. Soc. 1964, 86, 2591]. A quasi-cylindrical channel topology was reported for TPP and solvent molecules such as benzene. After release of benzene, the channel structure is metastable, being observed up to a temperature of about 150 °C.

However, there has been no disclosure of effective detection or removal of small compounds such as radionuclides, such as 3lI or 122Rn.

SUMMARY OF THE INVENTION Applicants have now discovered, that TPP and its derivatives, such as halogenated TPP may be used for sorption and desorption of small compounds, such as elemental iodine and iodide compounds, for example methyliodide, as well as radon.

The key feature of the invention is the formation of an inclusion complex between TPP or a derivative thereof, such as halogenated, preferably fluorinated, chlorinated or brominated TPP, e. g. tris (o- tetrafluorophenylenedioxy) cyclotriphosphazene tris (o- tetrabromophenylenedioxy) cyclotriphosphazene, and tris (o- tetrachlorophenylenedioxy) cyclotriphosphazene, and said small compound. The formation of such an inclusion complex can then be used for the removal of said small compound from a gaseous or liquid medium or the detection of said small compound in a gaseous or liquid medium.

In a preferred embodiment TPP or a derivative thereof is solvated with tetrahydrofuran, toluene, acetone, acetonitrile, preferably with tetrahydrofuran (H. R. Allocock, L. A. Siegel J. Am. Chem. Soc. 1964, 86, 5140, H. R. Allcock, R. W. Allen, E. C. Bissell, L. A. Smeltz, M. Teeter, J. Am. Chem. Soc.

1976, 98, 5120)..

Thus, a first aspect of the present invention relates therefore to a method for removing small compounds, such as elemental iodine and iodide compounds, for example methyliodide, as well as radon, from a gaseous or liquid medium comprising the formation of the above described inclusion complex.

A second aspect of the present invention relates to a method for detecting small compounds, such as elemental iodine and iodide compounds, for example methyliodide, as well as radon, in a gaseous or liquid medium comprising the formation of the above described inclusion complex.

A further aspect of the invention provides a filter for removing small compounds, such as elemental iodine and iodide compounds, for example methyliodide, as well as radon, from a gaseous or liquid medium comprising the formation of the above described inclusion complex.

Yet a further aspect of the invention provides a sensor for detecting small compounds, such as elemental iodine and iodide compounds, for example methyliodide, as well as radon, in a gaseous or liquid medium comprising the formation of the above described inclusion complex. Such a sensor may preferably be an optical sensor for measuring refractive indices or an electrical sensor for measuring electrical conductivity or capacity.

SHORT DESCRIPTION OF THE FIGURES In the accompanying figures preferred embodiments of the invention are shown: Fig. 1: Crystals of TPP- (THF),,- (12) y featuring three states of the process of in-and out-diffusion of iodine and THF, respectively. a) initial state; b) early state where just capping faces were coloured; c.) final state, where iodine has stained crystals up to the centre.

Fig. 2: The effectiveness of filtering properties for removing I2 from the gas phase. a) TPP- (THF) 0. 45 with average particle size of 100-200 um in a tube (0 = 3 mm and a length of 5 cm). b) during a flow of saturated I2 (g)/N2 at 300 K after 7 h. c) under given conditions for approximately 18 h the maximum capacity of the absorber was exceeded.

DETAILED DESCRIPTION OF THE INVENTION In the organic zeolite TPP the channel wall is built up by non-ionic entities presenting n-electron density and steric moieties towards the accessible space. Depending on the acceptor properties of guest molecules, a considerable gain in stability can be expected.

Structurally, 12 molecules are all aligned parallel being surrounded by three phenyl rings, presenting n-electron clouds towards la. As reported for complexes for iodine with aromatic molecules [J. Joens, J. Org. Chem. 1989, 54, 1126], a SH°f of 8 -15 kJ/mol is supporting stable inclusion formation.

Inclusion formation of TPP, which shows good chemical and thermal (mp = 247 °C) stability, is known for a number of solvents, whereof the TPP-benzene compound showed zeolite properties (P. Sozzani, A. Comotti, R. Simonutti, T. Meersmann, J. W. Logan, Angew. Chem. 2000,112, 2807).

Applicants have now discovered, that TPP or a derivative thereof, such as halogenated, preferably fluorinated, chlorinated or brominated TPP, e. g. tris (o- tetrafluorophenylenedioxy) cyclotriphosphazene tris (o- tetrabromophenylenedioxy) cyclotriphosphazene, and tris (o- tetrachlorophenylenedioxy) cyclotriphosphazene, may be used for sorption and desorption of small compounds, such as elemental iodine and iodide compounds, for example methyliodide, as well as radon.

Preferably, TPP or a derivative thereof may be solvated, for example with tetrahydrofuran (THF), toluene, acetone, acetonitrile, and like solvents, preferably with THF.

More specifically, 12 inclusion formation with TPP and its derivatives was obtained by in-diffusion, co-crystallization and from solution growth. For example, Is inclusion formation by in-diffusion was observed, whereby colourless, transparent, needle-shaped (0.5-1 mm long) single crystals of TPP- (THF) 0. 6 and some crystals of iodine were encapsulated for inspection at 300 K (p (in)"0. 3 Torr) by a binocular. Just a few seconds after Is was brought into the system, staining started by capping faces, extending continuously into the volume (Fig. 1). After 1-2 days, most crystals were entirely stained (T. Hertzsch, F. Budde, E. Weber, J. Hulliger, Angew.

Chem. Int. Ed. 2002,41, 2281).

I2 inclusion formation with TPP was also obtained by co- crystallisation from the vapour and from solution growth using mesitylene. Co-crystallisation from the vapour was performed at temperatures of 180 °C to provide a sufficiently high vapour pressure of TPP. Co-crystallisation from mesitylene started at a temperature of 80-100° C and provided TPP- (12) y crystals with an 12 content in the range of x-0. 65 to 0.75 (maximum loading). No co-inclusion of mesitylene was observed. All obtained TPP-(I2) y crystals showed a remarkable thermal stability. According to TG and DSC measurements an efficient 12 (g) loss started above 150 °C and decomposition (melting) was found near T-250 OC. No significant weight loss at 25 °C under vacuum condition was noticed for 12 h of treatment.

All three reactions were producing hexagonal, dichroitic, purple to blackish single crystals. Depending on the conditions of preparation, the optical density of crystals was different. Obviously, the degree of loading could be varied.

For application as filter or sensor systems, the crystals obtained by crystallization from THF undergo only small structural charges for the accommodation of iodine.

Table 1 summarises the chemical composition of selected TPP- (THF) X-(I2) y and TPP- (12) y inclusion crystals. TPP- (THF) 0. 6 single crystals obtained by in-diffusion experiments retained most THF (x 0. 4) in the channels. However, it was also possible to increase the amount of 12 by a partial desorption of the template prior to in-diffusion: As a result TPP- (THF) 0. 35 crystals contained more iodine as compared to the TPP- (THF) 0. 6 material exposed to 12 at the same temperature.

Table 1: Composition of Decomposition Reaction conditions TPP-(thf)x' - (I2)y temperature [°C ] TPP- (THF) 0. 6 xl 0. 4 230-248 25 °C, 24 h Y = 0.16 TPP-(THF)0.35 x' = 0.25 238-249 25 °C, 24 h y = 0. 45 TPP, I2, 180 °C | Y = 0.40 | 244 - 244 249 evacuated TPP, I2, mesitylene y = 0. 65-0. 75 100 °C, slow 247-250 cooling Table 2 summarises the chemical composition of TPP- (THF)x-(Iz)y inclusion crystals obtained at various temperatures by in- diffusion: After in-diffusion experiments using TPP- (THF)x' (X' 0. 3-0.45) some THF remained in the channels. The ratio of m (I2)/m (TPP) (m = mass) showed clearly an increase of iodine if rising the temperature and the partial pressure of Is.

Table 2: 25 50 75 100 p (I2) =2. 1 p (T2) 11. 2 p (Tz) 47. 5 T L°C (Iz) P (12) = 0. 3 _ _ (Tpp) Torr Torr Torr Torr 1 h 0. 072 0. 088 0. 123 0. 179 24 h 0. 090 0. 120 0. 169 0. 238 Table 2 is clearly showing two important features: (i) loading is rather fast, (ii) at 25 °C 0.09 gr. I2 per gram TPP can be absorbed. This is many times higher then for charcoal. TPP- (THF) x-(I2) y crystals showed a high thermal stability: TG measurements revealed an efficient 12 ('g) loss just above 150 °C and followed by a decomposition at T 250°C.

Release of most Is at 25 °C and vacuum was not observed during 12 h.

The pronounced affinity of TPP- (THF), crystals for an uptake of Is makes this material interesting for a sensor application, such as an optical sensor for measuring refractive indices, or the recovery of radioactive 1-291released during the reprocessing of nuclear waste or radionuclides such as 122Rn.

The effectiveness of filtering properties for removing Is from the gas phase was tested by a set up shown in Fig. 2: 300 mg TPP- (THF) o. 45 with average particle size of 100-200 um was filled into a tube (0 = 3 mm) to make up a column of 5 cm length (Fig. a). A flow of 25 ml/min of saturated Is (g)/N2-gas at 300 K was passed through for 7 h (Fig. b). No Is could be found by passing the outlet through toluene. When running the filter tube at given conditions for approximately 18 h, absorption of iodine was no longer ensured, this because the maximum capacity of the absorber got exceeded (Fig. c).

Figure 2b shows a very sharp interface of TPP (THF) x/ TPP (THF) X (I2) y. This is a clear indication for a quantitative sorption process. Furthermore it was shown, that TPP- (THF), can pick up Is from H2O (1), indicating that the pressure of humidity during the sorption of I2 should represent no drawback on the efficiency of filtering.

Previous and present results support excellent inclusion properties of TPP even for simple atoms (Xe [P. Sozzani, A.

Comotti, R. Simonutti, T. Meersmann, J. W. Logan, Angew. Chem.

2000,112, 2807]) and diatomic species other than Is, (Br2, CH3-I). Particularly, CH3I and other iodide compounds can be included by diffusion from e. g. mesitylene solutions.

Further applications of TPP (THF) X-(I2) y crystals may result because of their electrical conductivity, in that TPP (THF) X crystals showed no measurable conductivity, whereas loading by Is (from the gas phase) increased the conductivity by several orders of magnitude. More specifically, electrical measurements on single crystals were performed by contacting them by liquid Ga. A special cell for mounting small crystals in between copper electrodes was constructed allowing to monitor crystals during measurements. An atmosphere of 1-2 bar SF6 (g) was used. Conductivity measurements (Keithley electrometer 6517A) were performed on 6 single crystals of TPP- (I2) y (y-0. 65-0.75, T = 25 °C) which were obtained from 2 different attempts of co-crystallisation from mesitylene. c values in the order of 10-6 to 10-8 Q-lm-3, were found for a potential U of 50 V. However, when exposing three of these crystals to a voltage of 50, an increase of the current I (up to a factor of 2) was observed with time. In cases were the voltage was set to 500-1000 V the conductivity could be enhanced by a factor of 30 to 300 depending on individual crystals. For crystals establishing stable currents after several hours, an anisotropy factor cl-lof about 30 was measured indicating a preferred conductivity along 12-chains in channels given by TPP. Thus, a sensor selective to Is may result from these properties.

The present invention is further illustrated in the following examples which are merely illustrative and not limiting the present invention in any way. Variations on these examples falling within the scope of the invention will be apparent to a person skilled in the art.

Examples Experimental 1H spectra were recorded on a Bruker-Spectroscopin AC 300 spectrometer. The UV/VIS spectra were measured on a Cary spectrometer.

Example 1: Preparation of TPP: Hexachlorocyclophosphazene (recrystallised in heptane), sublimed pyrocatechol and anhydrous sodium carbonate were mixed in dry THF. The resulting precipitate was filtered and dried. The product was purified by recrystallisation (toluene) and sublimation (p = 10-2 mbar, T = 210 °C).

Example 2: Preparation of tris (o- tetrafluorophenylenedioxy) cyclotriphosphazene : Hexachlorocyclophosphazene (recrystallised in heptane), tetrafluorocatechol (prepared according to well known procedures in the art; J. Burdon, V. A. Damodaran, J. C.

Tatlow, J. Chem. Soc. 1964, 763-765) and triethylamine were mixed in dry THF. The resulting precipitate was filtered, dried and purified.

The same procedure using tetrabromocatechol or tetrachlorocatechol as the starting material was used to obtain tris (o-tetrabromophenylenedioxy) cyclotriphosphazene and tris (o-tetrachlorophenylenedioxy) cyclotriphosphazene, respectively.

Example 3: Preparation of the TPP-(THF) x_clathrate : TPP was dissolved in THF at 65 °C. Single crystals up to several mm were obtained by slow cooling (1 °C/h). The ratio of TPP/ (THF), was determined by 1H-NMR (x &num 0. 60). Partially desolvated clathrate crystals were obtained when exposed to vacuum at room temperature for about 24 hours (x' 0.30). In the case of a complete desolvation most crystals transformed into the monoclinic form [H. R. Allcock, M. L. Levin, R. R.

Whittle, Inorg. Chem. , 1986,25, 41].

Example 4: Preparation of inclusion compounds with iodine TPP- (THF) x (I2) L 50 mg of TPP- (THF), crystals and 100 mg of iodine were sealed in ampoules (V 3 cm3) and placed into the homogeneous hot zone of a glass oven (Buchi GKR 50) for 1 hour or 1 day by various temperatures (25-100 °C).

Colour pictures were taken by a 3CCD colour video camera (DXC- 950P, Sony) with an electronic shutter for long time exposure.

No further image processing was applied.

Example 5: Preparation of inclusion compounds with methyliodide TPP-(THF) x, (MeI) y The same procedure as described under Example 4 was applied to obtain TPP- (THF) (MeI) y.

Example 6: Preparation of inclusion compounds with iodine TPP- (I2)y: (i) From the gasphase: Co-crystallisation was performed in ampoules (V &num 3 cm3) up to 180 °C with a small temperature gradient between iodine (1) and TPP (s).

(ii) From solution: Sublimated TPP and an excess of iodine were dissolved in mesitylene at 80-100 °C. Black single crystals, were obtained by slow cooling (1 °C h-1). The ratio of TPP/iodine was measured by UV/VIS using three independent series of crystals and standard solutions for iodine. The average content y of 12 varied in the range of 0.65 to 0.75 (maximum concentration) if different batches were analysed.

Example 7: Electrical conductivity measurements Electrical measurements on single crystals were performed by contacting them by liquid Ga. A special cell for mounting small crystals in between copper electrodes was constructed allowing to monitor crystals during measurements. An atmosphere of 1-2 bar SF6 (g) was used. Conductivity measurements (Keithley electrometer 6517A) were performed on 6 single crystals of TPP-(I2) y (y ~ 0. 65-0.75, T = 25 °C) which were obtained from 2 different attempts of co-crystallisation from mesitylene. a values in the order of 10-6 to 10-8 #-1m-1 were found for a potential U of 50 V. However, when exposing three of these crystals to a voltage of 50, an increase of the current I (up to a factor of 2) was observed with time. In cases were the voltage was set to 500-1000 V the conductivity could be enhanced by a factor of 30 to 300 depending on individual crystals. For crystals establishing stable currents after several hours, an anisotropy factor # / ## of about 30 was measured.