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Solubility phase equilibrium in ternary system fullerenol C60(OH)24 and praseodymium salt: PrCl3-C60(OH)24-H2O at 25 °C
G. A. Glushnev1, Ayat Kanbar1, V. A. Keskinov1, N. A. Charykov1'2, K. N. Semenov1'4'6, Z. K. Shaimardanov3, B. K. Shaimardanova3, N. A. Kulenova3, D. G. Letenko5
1 St. Petersburg State Technological Institute (Technical University), Moskovsky prospect, 26,
St. Petersburg, 190013, Russia 2 St. Petersburg Electrotechnical University "LETI", ul. Professora Popova 5, 197376 St. Petersburg, Russia 3D. Serikbayev East Kazakhstan state technical university, A. K. Protozanov Street, 69, Ust-Kamenogorsk,
070004, The Republic of Kazakhstan 4 St. Petersburg State University, 7/9 Universitetskaya emb., St. Petersburg, 199034, Russia 5St.Petersburg State University of Architecture and Civil Engineering (SPSUACE), 2nd Krasnoarmeiskaya St. 4,
190005 St. Petersburg, Russia 6Pavlov First St. Petersburg StateMedical University L'va Tolstogo str. 6-8 St. Petersburg, 197022, Russia
keskinov@mail.ru
PACS 61.48.+C DOI 10.17586/2220-8054-2020-11-4-462-467
Solubility diagram was investigated by the method of saturation in ampules at 25 ± 0.02 °C for 4 hours. The solubility diagram of the PrCl3-C6o(OH)24-H2O ternary system at 25 °C occurs as simple eutonics, consisting of two branches, corresponding to the crystallization of crystal-hydrates: PrCl3 • 7H2O and C60(OH)24 • 18H2O. The diagram contains one non-variant point each - eutonics, which corresponds to saturation with pair of crystal-hydrates simultaneously. The diagram also contains very short branch of PrCl3 • 7H2O crystallization, and long branch of C60(OH)24 • 18H2O, where the effect of fullerenol salt-out is distinctly observed.
Keywords: fullerene C60, arginine, octo-adduct, lutetium chloride, solubility diagram, ternary system, simple eutonic. Received: 6 April 2020 Revised: 29 May 2020
1. Introduction
This article continues the cycle of publications, concerning the synthesis, identification and physico-chemical, physical, bio-chemical, biological properties investigation of the amino-acid-light fullerene adducts [1-19]. This article is devoted to the investigation of the solubility diagram for systems containing water soluble fullerene nano-clusters, inorganic salt, including rare earth metals and actinoids, and water, as the solvent [20-24]. In prior research, it was shown, that water soluble fullerene nano-clusters (with amino-acid adducts, poly-hydroxylated forms -fullerenols, complex ethers with carboxylic acids) have a very strong salting-out effect at addition of inorganic salts or their crystal-hydrates, and the salting-out effect is most strongly pronounced for salts of 4-f and 5-f elements, somewhat weaker for the salts of d-elements, and even weaker for the salts of p- and s-elements. So, such 4-f element salts (as PrCl3) may be effectively used for precipitation (by the salting-out effect) of fullerene nano-clusters (as C6o(OH)24) and it is possible that separation from the matrix solution and purification occurs virtually without losses of nanoclusters. Currently, separation from the matrix solution and purification of fullerene nanoclusters is carried out, as a rule, by multistage (often triple) methanol (or methyl-acetate, or ethanol)-water recrystallization, which leads to the following:
- considerable losses of nanoclusters, because solubility of last ones in methanole with water impurities solutions is more or less considerable;
- nanoclusters for the same reasons contain a significant amount of impurities;
- recrystallization process itself is laborious.
2. Reagents
In the present investigation we used rare earth chloride PrCl3, synthesized from the "chemical pure" oxide Pr6O11 by treatment of "pure for the analysis" HCl with following vacuum drying. Fullerenol C60-C60 (OH)24 was synthesized by from the bromine derivative C60Br24 by the treatment of these product by boiling water-dioxane mixture with the dissolved NaOH. Then sodium fullerenes forms C60(OH)24—(ONa)^ were neutralized and washed in the
Soxlet-extractor bymethanol+HCl liquid phase. So, PrCl3 and C6o(OH)24 with purity « 99.3 and 97.7 mass. %, correspondingly, were synthesized.
3. Experimental method
Solubility diagrams were investigated by the method of saturation in ampules at 25 ± 0.02 °C for 4 hours in the conditions of shaker-thermostate with shaking frequency of « 2 Hz. For the prevention of Pr3+ precipitation in the form Pr(OH)3, some drops of HCl was added to the heterogeneous systems, to approximate fixation of pH « 3.0 -3.5 a.un.
The concentration of PrCl3 were determined by complexometric titration with trilon-B (disodium salt of ethylenediamine-tetraacetic acid - EDTA), titration conditions were the following: acetic buffer, indicator - 2 - 3 drops of 1-% Xylenol orange solution, color transition from violet to lemon-yellow [25].
Concentration of C60(OH)24 was determined with the help of absorption electronic spectroscopy according to optical density at wavelength A = 330 nm - D330 (Ultraviolet-Visible Electronic Specto-photometer Shimadzu, wavelength 200 < A < 900 nm). Typical spectrum for C60(OH)24 water solution is represented in Fig. 1(a).
(a)
(b)
Fig. 1. Electronic spectrum of C6o(OH)24 water solution (concentration of C60(OH)24 C = 0.625 g/dm3) (a) and validity of Bouguer-Lambert-Beer Law in C60(OH)24 aqueous solutions at wavelength A = 330 nm, optical path of l = 1 cm (b)
In Fig. 1(b), the validity of Bouguer-Lambert-Beer Law in C60(OH)24 water solutions in the nearest UV spectral diapazone is represented. One can see the almost complete linearity of the dependence of optical density at wavelength A = 330 nm on the solution concentration. One can see, that, althought spectrum has no any expressed absorption
peaks, we can calculate C60(OH)24 concentration in g/dm3, from optical density at wavelength A = 330 nm, according to Bouguer-Lambert-Beer law by the formule:
Cc60(0H)24 (g/dm3) = 0.609 • D330 d = 1 cm). (1)
Density of the solutions were determined with the help of quartz picnometers with operating volume V « 5 cm3. Errors in the determination of PrCl3 concentration was S « 2.5 relative %, C60(OH)24 S « 5 relative % , density £ « 0.1 relative %.
4. Experimental data discussion
Solubility diagram in the ternary system PrCl3-C60(OH)24-H2O at 25 °C is represented in the Fig. 2 and Table 1. In Fig. 3, the dependence of the densities of saturated solutions in ternary system PrCl3-C60(OH)24-H2O at 25 °C is depicted.
800
0 5 10 15 20 25 30 35 40
Concentration of filierend =Cc ( M 24 { g/dnf)
Fig. 2. Solubility in ternary system PrCl3-C60(OH)24-H2O at 25 °C
TABLE 1. Solubility in the PrCl3-C60(OH)24-H2O ternary system at 25 °C
Num Density P (g/cm3) Optical density D (a.u.) Concentration Ceo(OH)24 (g/dm3) Concentration PrCl3 (g/dm3) Solid Phase
1 1.030 68.8 38.5 0.000 Ceo(OH)24 • 18H2O
2 1.034 34.5 19.3 17.3 Ceo(OH)24 • 18H2O
3 1.041 20.9 11.7 33.9 C60(OH)24 • 18H2O
4 1.070 6.20 3.47 59.2 C60(OH)24 • 18H2O
5 1.085 3.13 1.75 77.2 C60(OH)24 • 18H2O
6 1.329 0.950 0.532 320 C60(OH)24 • 18H2O
7 1.603 0.025 0.014 747 C60(OH)24 • I8H2O+ PrCl3 • 7H2O
8 1.603 — 0.000 747 PrCl3 • 7H2O
The solubility diagram of in the PrCl3-C60(OH)24-H2O ternary system at 25 °C occurs due to simple eu-tonics [26-28], consisting of two branches, corresponds to crystallization of crystal-hydrates: PrCl3 • 7H2O and C60(OH)24 • 18H2O. Diagrams contains one non-variant point - eutonics, which corresponds to saturation the pair of crystal-hydrates simultaneously. The diagram contains a very short branch for PrCl3 • 7H2O and a long branch for C60(OH)24 • 18H2O crystallization, where the effect of fullerenol salt-out is observed distinctly.
E
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 300
Concentration PrClj^C^ ( g/dm3)
Fig. 3. Density of saturated solutions in the PrCl3-C60(OH)24-H2O ternary system at 25 °C
5. Interpretation of obtained solubility data according to empirical Sechenov equation and modified Debye equation
We also made an attempt to describe obtained solubility data according to the empirical Sechenov equation (eq. (2)) and modified Debye equation (eq. (3)):
ln(CC60(OH)24/CC6C>(OH)24) = -^^PrC^ (2)
where: C°60(OH)24 - solubility of non-electrolyte C60(OH)24 in H2O, CC6C(OH)24 - solubility of C60(OH)24 in ternary system, CPrCl3 - electrolyte PrCl3 concentration, Ks - Sechenov empirical constant:
CC60(OH)24/CC60(OH)24 = KD CPrCl3 + ACP/Cl3 where: KD and A - fitting parameters of Debye model.
The results of approximation by Sechenov equation is represented in Fig. 4.
(3)
Fig. 4. Approximation of solubility diagram in ternary system PrCl3-C60(OH)24-H2O at 25 °C by Sechenov equation in the 0 < CPrCl3 < 77.2 g/dm3 concentration range
From Fig. 4, one can see, that eq. (2) very precisely describes the crystallization curve of C60(OH)24 • 18H2O. In more concentrated solutions (77.2 < CPrCl3 < 747 g/dm3) the descrepancy between calculated and experimental data increases many times, to our opinion, for the following reasons:
- PrCl3 even remotely ceases to be a strong electrolyte (ion pairs and ion associates formation);
- C60(OH)24 in all saturated solutions it detects huge positive deviations from ideality by implementing a multistage sequential hierarchical association [29].
Exactly the same occurs when applying the Debye equation (3) - see Fig. 5, but the concentration range maybe considerably expanded: 0 < CPrCl3 < 320 g/dm3 (calculation was provided with the help of software package Origin, subprogram Nonlinear curve fit).
Fig. 5. Approximation of solubility diagram in ternary system PrCl3-C6o(OH)24-H2O at 25 °C by Debye equation in concentration range 0 < CPrCl3 < 320 g/dm3
6. Conclusions
The solubility diagram of the PrCl3-C60(OH)24-H2O ternary system at 25 °C occurs as simple eutonics, consisting of two branches, corresponding to crystallization of crystal-hydrates: PrCl3 • 7H2O and C60(OH)24 • 18H2O. The diagram contains one non-variant point each - eutonics, which correspond to saturation with pair of crystal-hydrates simultaneously. The diagram also contains very short branch of PrCl3 • 7H2O crystallization, and long branch of C60(OH)24 • 18H2O, where the effect of fullerenol salt-out is distinctly observed. The diagram in the range of low rare earth salt concentrations may be more or less precisely described by Sechenov or Debye equations.
Acknowledgements
This work was supported by Russian Foundation for Basic Research (RFBR) (Projects Nos. 18-08-00143 A, 19-015-00469 A, and 19-016-00003 A).
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