Synthesis and Crystal Structure of a New Vanadyl Phosphate [H 0.6 (VO) 3 (PO 4 ) 3 (H 2 O) 3 ]·4H 2 O and Its Conversion to Porous Products
ABSTRACT Yellow layered VOPO4·2H2O was found to spontaneously, but slowly, convert to a green phase [H0.6(VO)3(PO4)3(H2O) 3]·4H2O upon standing in air. This phase could be prepared hydrothermally from V2O5 + H3PO4 with a small amount of reducing agent added. Single-crystal X-ray analysis gave a = 7.371(3) Å, b = 26.373(11) Å, c = 8.827(4) Å, β = 106.777-(7)°, space group P21/c, and Z = 4. The two vanadyl phosphates are related because the c axis of the green phase is √2·a where a is the a-unit cell dimension of the yellow tetragonal VOPO4·2H2O and the b axis is √2·3a. The green phase was found to intercalate approximately 2 mol of alkylamines/vanadium. A modified gel technique based upon mixtures of amine-intercalated vanadyl phosphate and nickel acetate were utilized to obtain microporous products with nickel polymers. Surface areas as high as 400 m2/g were obtained with pore diameters of 10 to as large as 23 Å. The pore size depended upon the nature of the alcohol solvent, the size of the amine used to enlarge the interlayer space, and the temperature of calcination.
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ABSTRACT: Highly porous vanadium phosphorus oxides (V–P oxides) of high specific surface area were synthesized by thermal treatment of layered vanadyl n-butylphosphate in N2. The surface area of V–P oxides was greatly increased by thermal treatment within a temperature range of 500–550 K, and reached 225 m2g−1 after treatment at 568 K. The N2 adsorption–desorption isotherm of V–P oxide is a Type IV isotherm, indicating that this material is mesoporous. Micropore and mesopore size distributions were determined from Saito–Foley analysis using an Ar adsorption isotherm and Dollimore–Heal analysis using an N2 desorption isotherm, respectively. The pores show a bimodal distribution in the micropore and mesopore region, and the micropores show a broad distribution with small volume (0.004 cm3g−1). The mesopores, which have a size of 4.4 nm and a volume of 0.272 cm3g−1, were probably formed from fractures of microcrystallites along layers of vanadyl n-butylphosphate.Microporous and Mesoporous Materials 07/2002; 54(3):277-283. DOI:10.1016/S1387-1811(02)00388-8 · 3.45 Impact Factor
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ABSTRACT: A new vanadium(III) phosphate, (NH4)[V(PO4)F], has been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure has been solved from X-ray single crystal data. The compound crystallizes in the Pnna orthorhombic space group, with the unit-cell parameters a=12.982(2), b=10.608(1), c=6.4789(6)Å and Z=8. The final R factors were R1=0.077 [all data] and wR2=0.068. The crystal structure consists of a three-dimensional framework formed by VO4F2 octahedra and tetrahedral (PO4)3− phosphate anions. The vanadium(III) cations from the VO4F2 octahedra are linked through the fluorine atoms giving rise to zig-zag chains. The ammonium cations are located in the cavities of the structure compensating the anionic charge of the [V(PO4)F]− inorganic skeleton. The IR spectrum shows the characteristic bands of the phosphate anion. The diffuse reflectance spectroscopy allowed us to calculate the Dq and Racah parameters. The values are Dq=1540, B=505 and C=2460 cm−1. Magnetic measurements indicate the existence of weak ferromagnetic interactions.Journal of Solid State Chemistry 06/2003; 173(1-173):101-108. DOI:10.1016/S0022-4596(03)00098-7 · 2.13 Impact Factor
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ABSTRACT: A detailed electrochemical study of Li intercalation/deintercalation in VOPO4 compounds with various inserted molecules (H2O, HCOOH and CH3COOH) is presented. For VOPO42H2O, water oxidation is responsible for capacity fading. In order to improve the cyclability, the electrochemical behavior of other intercalated VOPO4 compounds, such as VOPO4H2O, VOPO4HCOOH and VOPO40.78CH3COOH, has been studied. For all these materials, the intercalation (deintercalation) takes place in several steps. The electrochemical study of the monohydrate indicates that the vanadium-coordinated water molecule is more stable than the second water molecule towards cycling. The highest initial specific capacity values (approximately 100mAh/g) are obtained for the compounds with the largest interlayer space. Upon cycling, the pillaring molecules are destroyed by a high-potential oxidation process, yielding a collapse of the 2D structure and thus a loss of crystallinity. As a result, the observed specific capacity is the same for all the materials after a long cycling. This capacity is higher than the anhydrous one.Journal of Solid State Electrochemistry 03/2004; 8(5):322-329. DOI:10.1007/s10008-003-0456-y · 2.45 Impact Factor