ACHIEVEMENTS

Achievements until 30 October 2002

     The contribution to performance of the project of scientifically research team of ISC, Kyiv, Ukraine (PPD - Dr. Yu. L.Zub, Co-Director - Prof. A.A.Chuiko).

1.1. Sub-Project: MODELING.

     Together with a team of Prof. Mark G. White (GIT) was executed the analysis of the literature for last 5-7 years , in which was described selective sorbtion of cesium (conclusions from this review having the important meaning for achievement of success of the project, are given further). As the most acceptable objects for functionalize of carriers (at use sol-gel of a method of their synthesis) have appeared calixarenes, among them the choice of modelling molecules was carried out. However even the elementary molecules of calixarenes, chosen for modeling, include significant number of atoms. Besides at attempt of the account of influence of a surface of carriers on specificity adsorbtion of cesium the atoms of clusters, simulating this surface will be added. Thus the quantity (amount) of atoms will increase and at the expense of atoms of spaser. Therefore, the presence in initial models (without the account of water of an environment at cesium atom) more than 50 atoms practically is excluded use of not empirical methods of account. Therefore as a method of modeling at the first stage the method of the molecular mechanics was chosen. This method was successfully applied at modeling calixarenes by group Prof. R.Ungaro (UP, Italy). Now there are programs realizing this method and adapted for РС. However it is necessary to tell, that in some cases there is a necessity for use and not empirical programs for account of charges of atoms on fragments of models. Therefore we acquired under the license such of the programs as GAMESS (Ames Lab, Iowa State University, USA), which realizes on РС both methods - both molecular mechanics, and quantum chemistry.

2.1. Sub-Project: INITIAL COMPOUNDS.

     The circuit of synthesis initial silica was originally chosen, containing calixarene functional groups (it is given below).

     Proceeding from this circuit, and also on the basis of the analysis of the literature the list necessary initial chemicals was prepared. These chemicals are ordered in Aldrich and Gelest. With the purpose of acceleration of performance of the project ISC has given - from the reserves - a part expensive initial silanes. Some of these silanes required clearing by rectification, as was executed.

3.1. Sub-Project: SYNTHESIS AND INVESTIGATION.

     Calixarenes are large enough on volume of a molecule. It is known, that the increase of the geometrical sizes of functional groups - at use of sol-gel methods of synthesis - conducts to essential reduction of a specific surface and inaccessibility of a significant part of functional groups. In this connection on the basis of experience of work of group of Dr. Yu.L. Zub in area sol-gel of technology and in view of the literary data was are chosen such circuits of synthesis, which should exclude negative influence of the size of functional group. Their feature is use in a course sol-gel of synthesis tricomponent systems (regarding silanes):

where R = Me, Et, i-Pr, etc.; R ' = calixarene, calixcrown; R ' = - (CH₂)₃NH₂, etc.

     Some reduction of the contents of necessary functional groups (R ') in this case is observed, however is kept density of matrixes. As the catalyst it is offered to use a fluor-ion, instead of derivative of tin. It will allow, changing his(its) concentration, to achieve different speeds of geling of initial systems and, thus, also to influence the structural - adsorbtion characteristics of final products - xerogels. Besides at use as catalysts derivative of tin (IV) the not porous matrixes are formed, as a rule. Besides connection of tin frequently incorporating in a matrix in a course sol-gel of synthesis. Thus, the choice of a new technique of synthesis sorbents, functionalized calixarenes by groups is carried out also.

     The contribution to performance of the project of scientifically research team of SSIT, St.-Petersburg, Russian Federation (Co-Director - Prof. A.A.Malygin).

4.1. Sub-Project: REACTOR.
Designing the procedure for preparation of FPS spheres.

     The first stage of project development in the field of designing the procedure for preparation of FPS spheres was the literature review and formulating of most perspective principles for industrial FSP spheres production.

     We proceed from a common scheme of formation of solid microspheres from liquid phase, presented at Figure below.

Common principal scheme of spheres formation

     It is clear that the most important stage is a sol and particles formation. The most usual way is to form sol from single phase solution as in the case of traditional technology of silica sol and gel preparation. The main grace of using single phase solutions is the simplicity of equipment. Disadvantages of such technique are the wide distribution of particles' size and essential dependence of that distribution on processing conditions (medium acidity, reagent concentrations and temperature) resulting also in bad control of surface functional composition.

     The another way of "liquid formation" is a two-phase technique: a sol of a substance is obtained in the column with two liquids which are not mixed one with another. Usually one uses an organic liquid in upper part of reaction space and water solution in the lower one. The organic phase solution is saturated by some monomer soluble in organic phase but insoluble or very slightly soluble in water. Water diffuse through the liquid interface to organic phase leading to hydrolysis of monomers near the interface and forming of small particles. These particles can drift to the water phase by the gravity forces in the case of their density is more then one of organic solvent. Such process is seemed to result in narrow distribution of particles size as well as more uniform composition of their surface due to slow speed of diffusion and therefore a low concentration of water in organic phase. One more advantage of such scheme is the possibility to obtain particles of a small size, and even regulate that size, by addition of organic compounds providing functionalization of microspheres surface what prevent their agglomeration and growth.

     The main problem of realization of such technique in the case of polysiloxane spheres preparation is that density of primary particles formed in the organic phase can be lower than one of water (i.e. 1000 kg/m3). Although the density of silica itself is significantly grater (about 2000 kg/m3), small polysiloxane particles arisen by polycondensation process would be not polymerized completely. This fact can lead to flotation of such particles near liquid interface accompanied by size dispersion and preventing of water diffuse flow to organic phase. The degree of polycondensation is controlled by both monomer concentration and temperature. Because of the first factor is also significant for size distribution, the temperature become a most perspective instrument to regulate polymerization degree. Namely it is possible to manage particle density by providing a zone with a higher temperature - a zone of particle densification.

     To establish the optimal densification parameters in addition to temperature the influence of water solution composition on the final formation and densification of spheres is also should be studied. For example, one of promoting additions can be an ammonia or other substance which can be easily removed by washing and at the same time providing slightly basic medium. Another tip is a catalysts using, such as organotin compounds well known in polyorganosiloxane chemistry.

     These factors make it necessary to study the influence of concentrational and temperature regimes on the process of polysiloxane spheres formation and their characteristics. Obviously this purpose requires mounting of some laboratory plant for regimes testing. A principal scheme of such laboratory installation is presented at Figure below.

The principal scheme of laboratory plant for testing regimes of polysiloxane microspheres formation

     The plant should consist of glass two-phase reactor 1 and equipment for spheres separation and liquid's flow providing. Reactor 1 is a glass column thermostatted by separate water-jackets 2 which allow providing a few different temperature zones. It includes two layers: the upper (A) for organic phases and a lower (B) for water one. Reactor also equipped by water inlet pipe 3, water container 4 and outlet pipe for spheres unload 5. Spheres would be unloaded to separator 6 with filtering plate 7. It is seemed to be environmentally and technically preferable to organize water solution recirculation by contour 5 - 6 - 4 - 3 using recircular pump 8.

     The preparation process should be the following. Zone B is filled by water solution from container 4 to level upper than pipe 3. Zone A is filled by organic solvent which then would saturated by siloxane reagent from feeder 8, for example, by dropping liquid reagent with constant rate. Polysiloxane spheres will be formed in organic layer due to slow hydrolysis process and then drift down to water solution zone. The conditions in the upper part of zone B must provide the densification of particles and it determination is one of goals of project. Assuming particles become dense enough to go down to the bottom of reactor 1 they would be transported to separator 6 through pipe 5. Here water solution is separated and directed back to container 4 by pump 9. Valves 10 and 11 allow regulating flow rate and balance between separation speed and container 4 volume. Then particles can be unloading from separator 6 either manually or by pouring due to a slant of a plate.

     The contribution to performance of the project of scientifically research team of GIT, Atlanta, USA (NPD - Prof. Mark G. White).

2.1. Sub-Project: MODELING.

     Literature survey. A preliminary survey of the literature was completed in the early summer of 2002 and distributed to members of the teams. Subsequently, the Georgia Tech team visited two facilities in the USA (Savannah River National Laboratories, Aiken South Carolina; and Oak Ridge National Laboratories, Oak Ridge Tennessee) that could have an interest in the technology being developed by the members of this project team. As are result of these discussions, we were led to a body of literature developed by a French team of investigators who had developed silica adsorbents containing agents selective to Cs cations ( Duhart, A., et al., Selective removal of cesium from model nuclear waste solutions using a solid membrane composed on an unsymmetrical calix[4]arene-bis-crown-6 bonded to an immobilized polysiloxane backbone. J. Mem. Sci., 2001: p. 145-155.) . These investigators synthesized a family of calixcrowns having two crown ether moieties attached to the calix ring. Subsequently, these were incorporated into a silica matrix to form the adsorbent; however, these efforts were not completely successful for several reasons. First, the hydrophilicity of the silica matrix adversely affects the selectivity of the solid to sequester soft cations such as Cs in favor of hard cations such as Na that form hydration complexes with water because the calix agents used as the selective binding agent by Duhart et al. required a hydrophobic environment to enhance the selectivity of Cs over Na. This result may lead us to consider means to avoid this problem by incorporating other organic molecules into the silica matrix that will regulate its hydrophilicity. Secondly, the specific surface area of the polysiloxane solid devised by Duhart, et al was low (~15 m²/g). This problem has already been solved by the Zub group and thus will not present a real problem.

     Subsequent conversations with the team at Oak Ridge National laboratories lead by Dr. Bruce Moyer related to the success of modeling the properties of the calix-agents for selective removal of Cs from waste waters. The successful model must include not only the calix-agent and the target cation but also must include the solvent water. These calix agents are successful in selectively sequestering Cs cations over Na cations because of the difference in the "hardness" of the cation in forming hydrates. Modeling efforts that do not include water as the solvent always show that Na cations are sequestered in preference to Cs cations; however, those few modeling studies that include water as the solvent do correctly predict the Cs selectivity. Moreover, it appears that the host silica (vide supra) plays an important secondary role insofar as if the host is too hydrophilic then the selectivity for Cs is compromised. Thus, the successful model must include the solvent and the host. Such a large ensemble can only be modeled by approximate methods and rule out all ab-initio methods for the present.

3.1. Sub-Project: SYNTHESIS AND INVESTIGATION.

     At performance of the project is planned widely to use various modern physical methods for research received sorbents, including solid-state NMR on various nucleuses (¹³С, ²⁹Si, etc). But as calixarenes are complex difficult enough objects, was decided(solved) on the first stage to study with the help NMR spectroscopy more simple xerogels (sorbents), containing only simple spacers. It will allow to lead (carry out) original "calibration" of this method.

     Characterization of polysiloxanes by NMR. The Kiev group sent to the Georgia Tech group several polysiloxanes containing simple organic spacers so that we could "calibrate" our NMR analysis before the superadsorbents were sent to us. We began by examining the 13C-MAS-NMR spectra of polysiloxanes containing the following organic molecules: 1) alkyl carboxyles, 2) alkyl amines, 3) alkyl thiols, 4) alkyl tin compounds and fluor-ion as catalysts. The results are shown in one figure (Fig. 1) with the summary of the 13C resonances in Table 1.

     The sample, FPS-1, contains the following ligands: Si(CH₂)₃SH (with n-Bu₂Sn(CH₃COO)₂). Accordingly we expect to see alkyl carbons bonded to carbons, bonded to Si, bonded to Sn and bonded to S; plus carbonyl carbonyls as in an anhydride. The data, Figure 1, shows two very large peaks at 10.88 and 27.23 ppm plus three small peaks at 17.74, 39.99, and 60.38 ppm. The two larger peaks are expected to characterize C-C and C-S species.

     The sample, FPS-2, was developed from the following ligands: Si(CH₂)₃SH and Si(CH₂)₃NH₂ . The ratio of ligands SH/NH₂ = 1/1 in this sample. Thus, we expect to see at least three different types of carbons: C-Si, C-C, C-N and C-S. Indeed, we see three principle resonances at 9.97, 21.15 and 41.94 ppm. However, the peak at 21.15 shows a downfield shoulder at ~30 ppm.

     Sample ZPC-19 shows the same ligand as FPS-1 but some of these ligands are attached to a catalyst with F-. Thus, we expect to see the same principle resonances as that shown in Fig. 1 and this has been observed (10.82 and 27.10 ppm) with two more small peaks at 17.7, 51.43 and 59.69 ppm.

     Sample FPSH-2-4 (Fig. 4) shows the following ligands: Si(CH₂)₂COOH. This ligand shows three different types of carbons, C-Si, C-COOH and O-C=O. The observed resonances are 6.98, 13.28, 26.98, 61.59, and 176.44 ppm.

     Assignment of resonances. General texts on organic chemistry and NMR will be used to begin the process of assignment of peaks to structures. The goal for this initial work is to make qualitative assignments of peak resonances to structures in the solid. We begin with a table of assignments taken from the text Solomons and Fryhle. (Solomons, G. and C. Fryhle, Organic Chemistry, 7TH Edition, John Wiley and Sons, Inc.)

     From this simple table we expect that Si-C should show the smallest shifts downfield from TMS. Thus, the resonances at 6-10 ppm are tentatively assigned to Si-C. All of the samples in Figures 1-4 will have Si-C carbons. The carbons in carboxylic acids should show the highest shift downfield from the standard. We see that sample FPSH-2-4 does have a peak at 176 ppm that is consistent with the resonance expected for a carboxylic acid group.

      Consider now the NMR spectrum of n-pentylamine having the structure shown below: Below each carbon is the resonance from the C-NMR spectrum. Notice the 1o carbon shows a resonance at 14.3 ppm whereas the C attached to the amine shows a resonance of 42.5 ppm. We may apply these data to the assignment of peaks in FPS-2. The peak at 41.0 ppm is probably best assigned to the amine ligand in this solid. The 2° C's have shifts between 23 - 34 ppm depending upon its proximity to the amine.

      Now consider the NMR spectrum of pentanoic acid having the structure shown below: Again the resonance is shown below each carbon. It is remarkable that the resonances for the C's in this carboxylic acid are very similar to those in the pentylamine for the 1° and 2° C's not part of the amine/acid group. Thus, we expect that the primary and secondary carbons in the amine ligands FPS-2 to show very similar resonances to the primary and secondary carbons in the carboxylic acid ligands in FPSH-2-4 which is what we observe. The carboxylic acid ligand in FPSH-2-4 shows a resonance of 176 ppm which is close the resonance observed in pentanoic acid at 179.7 ppm.

      From these preliminary considerations we may the following tentative assignments of the NMR data.

      Thus, NMR spectra already concerning simple systems are complex (difficult) and specify feature of a structure of a superficial layer synthesized xerogels. These results are very useful and will allow to make correct reference and in NMR spectra of more difficult systems.

      The contribution to performance of the project of scientifically research team of UP, Parma, Italy (Co-Director - Prof. G. Predieri).

2.1. Sub-Project: MODELING.

      Prof. G.Predieri has established communication (connection) with Prof. R.Ungaro, which research group also works in UP and during last 10 years are engaged in synthesis of calixarenes and research by their selective sorbtion of cesium. The arrangement on the further cooperation of two groups in this area was achieved. Prof. R.Ungaro has picked up necessary prints of the works and has sent them to Kyiv to Dr. Yu.L. Zub. The significant help in selection for the Kiev group of the necessary literature has rendered and Prof. G.Predieri and Dr. D.Cauzzi from UP.

3.1. Sub-Project: SYNTHESIS AND INVESTIGATION.

      Prof. G.Predieri has agreed to accept from a beginning of 2003 of the young researcher from group of Dr. Yu.L. Zub (PhD Student Inna Mel'nyk) for work in his laboratory. Thus the necessary support (some chemicals, advices) from group Prof. R.Ungaro will be rendered.

      The contribution to performance of the project of Co-director Prof. R.V.Parish (UMIST, Manchester, U.K.) consist in selection and transfer of the necessary literature for the Kyiv group, and also in a summer residence of the recommendations at a choice of techniques sol-gel sinthesis.