ISSN 00360236, Russian Journal of Inorganic Chemistry, 2015, Vol. 60, No. 9, pp. 1027–1033. © Pleiades Publishing, Ltd., 2015. Original Russian Text © A.D. Yapryntsev, L.S. Skogareva, A.E. Gol’dt, A.E. Baranchikov, V.K. Ivanov, 2015, published in Zhurnal Neorganicheskoi Khimii, 2015, Vol. 60, No. 9, pp. 1131–1138.
SYNTHESIS AND PROPERTIES OF INORGANIC COMPOUNDS
Synthesis of a Peroxo Derivative of Layered Yttrium Hydroxide A. D. Yapryntseva, L. S. Skogarevab, A. E. Gol’dta, b, A. E. Baranchikovb, and V. K. Ivanovb, c a
b
Moscow State University, Moscow, 119991 Russia Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii pr. 31, 119991 Russia c National Research Tomsk University, pr. Lenina 36, Tomsk, 634050 Russia email:
[email protected] Received March 16, 2015
Abstract—A stable yttrium peroxo compound containing 6.7% active (peroxide) oxygen is prepared by react ing layered yttrium hydroxonitrate Y4(OH)10(NO3)2 ⋅ xH2O with 12% or 87% aq. H2O2 at 0°C. The active oxygen in this compound is in the form of HO2− and O22− groups as probed by IR and Raman spectroscopy. The thermolysis of the yttrium peroxo compound yields nanosized (6 nm) yttrium oxide. DOI: 10.1134/S0036023615090211
Layered double hydroxides (LDHs) [1, 2] and recently discovered layered rareearth hydroxides (LRHs) [3, 4] are of interest primarily due to their unique chemical properties, for they are the only known representatives of inorganic anionexchange compounds. Their chemical modification, for exam ple, by incorporating interlayer anions of organic or inorganic acids, offers great opportunities for design of multifunctional materials. The chemical composition of LRHs can be formu lated as [Ln4(OH)10(H2O)4]2+[A]2–, where Ln = a lan thanide or yttrium and A = Cl– or NO3− [3, 4]. Layered rareearth hydroxides are in part structural analogues of LDHs. Chains of eight and ninecoordinate lan thanide cations linked by OH bridges alternate in [Ln 4(OH)10(H 2O)4 ]2n+ layers in their structure [5]. Lay ered rareearth hydroxides are also much similar to LDHs in chemical properties. Layered double hydroxides are known to form sta ble peroxo derivatives as a result of heterophase ion exchange between an LDH and hydrogen peroxide in concentrated aqueous solution or vapor [6]. No data about similar compounds of LRHs were found in the literature; data about yttrium peroxide compounds are also scarce. The preparation of hydrated yttrium per oxide Y4O9 ⋅ xH2O [7] and yttrium hydroperoxocar bonate was mentioned [8]. In our opinion that peroxo derivatives of LRHs are of special interest for the abil ity of their peroxo groups to easily decompose at high temperatures to yield ultrafine yttrium oxide powders. Therefore, the goal of this study was to prepare a peroxo derivative of layered yttrium hydroxide (LYH) and to characterize it by physicochemical methods.
EXPERIMENTAL The starting chemicals used were yttrium(III) nitrate hexahydrate (99.8%, CAS 13494989), sodium nitrate (99%), and hexamethylenetetramine (HMT) (99%, CAS 100970). Concentrated (87%) aqueous hydrogen peroxide was prepared by distilla tion of commercially available ~50% aq. H2O2; 12% aq. H2O2 was prepared by dilution of perhydrol (35% H2O2). Syntheses involving hydrogen peroxide were carried out in predeactivated glassware, which was consecutively treated with 10% KOH, 2 N HNO3, and 30% H2O2. Synthesis 1. Layered yttrium hydroxide was pre pared by the following protocol. To 10 mL of 5.5 M aqueous solution of Y(NO3)3 ⋅ 6H2O, 10 mL of 0.7 M aqueous solution of HMT and 10 mL of aqueous NaNO3 were added. The resulting reaction mixture was placed into a 100mL Teflon autoclave (filled by ~30%) and subjected to microwaveassisted hydro thermal treatment in a Berghof Speedwave MWS four setup at 180°C for 30 min. The heating rate was 30 K/min. Once the treatment was over, the autoclave was air cooled; the precipitate was separated by decantation, several times washed with distilled water, and then dried at ~75% relative humidity and 60°С. Synthesis 2. LYH samples (~0.5 g) prepared as described above were exposed to 12% or 87% aq. H2O2 (precooled to 0°C), for 2 h under permanent stirring. The initial aqueous hydrogen peroxide had pH 5 (12%) and pH 1 (87%). Then, powders were separated by filtering at 0°C and washed consecutively with cool ethanol and diethyl ether. The samples prepared in this manner were stored over anhydrone in a desiccator at a temperature not higher than 10°С.
1027
1028
YAPRYNTSEV et al.
002
I, arb. units 10000 9000 8000 7000 6000
620 040
3000
004
004
4000
220
5000
2000
а 1000 b
0 5
10
15
20
25
30 35 2θ, deg
40
45
50
55
60
Fig. 1. Xray powder diffraction patterns for layered yttrium hydroxonitrate (a) before and (b) after treatment with 12% aq. H2O2. The asterisk marks a minor carbonate phase.
Some of the samples prepared as described above were heat treated; these samples were placed into an open vertical tubular furnace preheated to 580°C and exposed to this temperature for 10 min. After the exposure, the samples were withdrawn from the fur nace to air. Chemical analysis. The active (peroxide) oxygen was determined permanganatometrically [7, 9]. IR spectra of powders were recorded on Perkin Elmer Spectrum One in the range 520–4000 cm–1. Raman spectra were recorded on a Renishaw inVia Reflex spectrometer (laser wavelength: 514 nm). The hydrogen peroxide bands in IR and Raman spectra were assigned according to [10, 11]; the bands from water, carbonate, nitrate, and hydroxide groups were assigned according to [10, 12, 13]. Xray powder diffraction patterns were recorded on a Bruker D8 Advance diffractometer (CuKα radiation) at a goniometer rotation speed of 2°2θ/min. Microstructure of the samples was studied in lay ered compound samples using scanning electron microscopy at an accelerating voltage of 1 kV (Carl Zeiss NVision 40 microscope). RESULTS AND DISCUSSION The layered yttrium hydroxide was prepared by the method we have suggested previously which involve microwaveassisted hydrothermal treatment in the presence of HMT [14]. Earlier we used this and similar protocols to prepare layered gadolinium [15] and europium [16] hydroxonitrates and to prepare some
simple oxides, specifically ZnO [17], TiO2 [18], and CeO2 [19]. The hydrolysis of aqueous HMT solutions under heating yields formaldehyde and ammonium hydrox ide by the following scheme [20]:
(CH 2 )6N 4 + 6H 2O → 6H 2CO + 4NH3, (1.1) NH3 + H 2O → NH 4OH. The HMT hydrolysis rate increase considerably under hydrothermal conditions, so the time taken to form inorganic reaction products can be considerably shortened. Figure 1 shows Xray powder diffraction patterns for an LYH sample and for the product of its reaction with 12% aqueous hydrogen peroxide. The diffraction pattern of the precursor LYH was indexed in accor dance with the literature data for the compound Y4(OH)10(NO3)2 ⋅ xH2O [21–23]. One can see from Fig. 1, spectrum (b) that hydrogen peroxide treatment results in considerable amorphization, likely due to a partial dissolution of the precursor caused by hydrogen peroxide (an acid medium) and to the disordering of metal–hydroxide layers. From Fig. 1, spectrum (b) it also follows that the reflection from line 002 in the reaction product of LYH and hydrogen peroxide slightly shifts toward smaller angles. This effect cannot be interpreted as arising from the interlayer peroxide – groups of the LYH, for the peroxide anion and NO 3 anion have quite close ionic radii (1.7 and 1.8 Å, respectively) [24, 25]. The treatment of LYH samples with aqueous hydrogen peroxide, regardless of its initial concentra
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SYNTHESIS OF A PEROXO DERIVATIVE
1029
100 95 а
90 85 Absorption, %
80
b
75 70
c
65 60 55 50 45 4000
3500
3000
2500
2000 ~ ν, cm–1
1500
1000
500
Fig. 2. IR spectra of (а) layered yttrium hydroxonitrate and (b, c) products of its treatment with aqueous hydrogen peroxide at various concentrations: (b) 12% H2O2 and (c) 87% H2O2.
tion, yields a rather stable compound containing 6.7 wt % active (peroxide) oxygen, as determined per manganatometrically. Noteworthy, this value is ~2.5 times smaller than the percentage calculated for the hypothetical yttrium peroxide Y2(O2)3. The kinetic analysis of decomposition of thus prepared peroxo compound showed that its decomposition rate during storage inside a closed vessel at 8 ± 1°C was about 0.05% active oxygen per day. The IR spectra of an untreated LYH sample and the products of its reaction with aq. H2O2 of various concen trations are shown in Fig. 2 and described in Table 1. The IR absorption spectra of peroxo compounds are almost identical and independent of the initial hydrogen peroxide concentration. The band at 1395 cm–1 corresponds to the bending vibrations of hydroperoxo groups δ(OOH). Although the stretching vibrations of peroxide bond ν(O–O) are IRinactive, they yet appear as a lowintensity band at ~846 cm–1. The bands corresponding to the vibrations of nitrate groups lie in their ordinary spectral ranges. The absorption bands characteristic of carbonate groups are observed in the spectra due to a minor impurity of yttrium carbonate compounds contained in the pre cursor compound [14]. Carbonate compounds are a frequent impurity in LRHs [23, 26], in particular in those prepared in the presence of HMT, for HMT at high temperatures and in the presence of oxygen in the reaction system can decompose to evolve carbon diox ide [19]: RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
CH 2O + 1 O2 → HCOOH, 2 HCOOH + 1 O2 → CO2 + H 2O. 2
(1.2)
The appearance of absorption bands of carbonate ions in the products of reaction of LYH and hydrogen peroxide and their apparent absence in the precursor compound are likely due to the lower solubility of yttrium carbonate derivatives in acidic H2O2 solutions compared to the major LYH phase. As a result, the carbonate percentage in reaction products increases in the progress of reaction. The stretching vibrations bands ν(OH) in yttrium peroxo derivatives have more diffuse profiles than in precursor LYH samples, indirectly proving that the suggested disordering of metal–hydroxide layers does occur upon the reaction of LYH with hydrogen perox ide. From the shift of Y–O stretching vibrations toward the longer wavelengths, it can be inferred that this disordering occurs both relative to neighboring layers and inside a layer. The measured Raman spectra are shown in Fig. 3 (Table 2). The spectra of reaction products of LYH with 12% or 87% aq. hydrogen peroxide feature lines from the stretching vibrations of a nitrate group typical of the precursor LYH (at 1048–1054 cm–1) and lines at 1084 and 1088 cm–1, which we assigned to the vibrations of carbonate groups [12]. Vol. 60
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YAPRYNTSEV et al.
Table 1. Assignment of IR bands in layered yttrium hydroxonitrate and products of its treatment with aqueous hydrogen peroxide of various concentrations Band peak, cm–1 Assignment LYH
LYH + 12% H2O2
LYH + 87% H2O2
3648, 3557 3600 ~3400
3600 3381
3600 3375
ν(OH) ν(OH) ν(H2O)
~3226
3228
3223
ν(H2O)
1634 ~1516
1638 1508
1637 1511
δ(HOH)
1411
2–
–
ν ( CO 3 ), ν ( NO 3 ) 2–
ν ( CO 3 ) 1396
1395
ν(OOH), ν ( CO 3 )
1342
1344
1333
ν ( NO 3 )
1091
1084
1087
ν ( CO 3 )
1051
1045
1041
ν ( NO 3 ), δ(OH)
846
846
ν(O–O), δ ( CO 3 )
825
818
δ ( NO 3 )
774
δ ( CO 3 )
822 784
2–
–
2– –
2–
–
2–
740
741
747
δ ( NO 3 ), δ ( CO 3 )
686, 703
686
686
δ ( CO 3 )
543
638
651
ν(Y–O) [12]
–
2–
2–
Table 2. Assignment of Raman bands in layered yttrium hydroxonitrate and products of its treatment with aqueous hydro gen peroxide of various concentrations (12 and 87%) Band peak, cm–1 LYH
1054
716
Assignment
LYH + 12% H2O2
LYH + 87% H2O2
1084
1088
ν ( CO 3 )
1050
1048
828 811
840 829
ν ( NO 3 ), δ(OH) ν(O–O) [6, 10, 27] ν(O–O) [6, 10, 27]
744
750
ν4 ( CO 3 ), δ(Y–O–O) [10, 27]
714
713
δ ( NO 3 )
The shift of the stretching vibrations of peroxide bond in the Raman spectra of LYH peroxo derivatives relative to the ν(O–O) line of pure hydrogen peroxide is 69 and 51 cm–1, respectively (811 and 829 cm–1, respectively, against 880 cm–1 for liquid or crystalline H2O2). The lowintensity line in the region of ~750 cm–1
2– –
2–
–
is likely to correspond to the bending mode δ(Y–O–O) 2–
or stretching mode ν4 ( CO 3 ) . The ν(O–O) lines in Raman spectra lie in the lowfrequency region where the line of peroxide ion O22− typically appears (830– 840 cm–1). A line at 830 cm–1 appears, for example, in
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SYNTHESIS OF A PEROXO DERIVATIVE I, arb. units 30000
1031
1048
25000
1050 829
20000
1054 811
1088
15000 1084
10000
c b
5000 716 а
0 700
800
900
1000
~ ν, cm–1
1100
1200
Fig. 3. Raman spectra of (a) layered yttrium hydroxonitrate and (b, c) products of its treatment with aqueous hydrogen peroxide at various concentrations: (b) 12% H2O2 and (c) 87% H2O2.
the Raman spectrum of calcium peroxide CaO2 ⋅ 8H2O (the Goldschmidt ionic radii of Ca2+ and Y3+ are both 1.06 Å) [28]. The formation of LYH peroxo derivatives is likely to involve a partial replacement of hydroxide groups in LYH layers by hydroperoxo groups to form a hydrop eroxo derivative OOH Y H2O
H O
OOH
Y O HHO 2
H O
OOH
Y O HHO 2
H O
OH
Y O HHO 2
or the replacement of water molecules coordinated to yttrium ions by hydrogen peroxide molecules to yield a peroxo solvate. Meanwhile, the spectra do not fea ture the line corresponding to the vibrations of solvat ing H2O2 (at ~860 cm–1), so that the presence of per oxo solvates in the reaction product can be ruled out. In light of the foregoing, the most likely scenario is that the product of reaction between LYH and hydro gen peroxide contains two types of peroxo groups, namely: hydroperoxo groups (HO 2− ) in the coordina tion sphere of Y3+ or in interlayer spaces of LYH and peroxo groups (O22−), which can play the role of bridg ing ligands. The linear heating of LYH peroxo derivatives at 10 K/min resulted first in the decomposition of perox ides and elimination of physically bound water (~100°C), and then in the thermolysis of nitratecon RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
taining yttrium compounds to yttrium oxide (
