Synthesis and atmospheric instability of well crystallized rod-shaped V2O4 2H2O powders prepared in an aqueous solution

Abstract

Synthesis of well crystallized rod-shaped V 2 O 4 ・2H 2 O powders of 100 nm in width in an aqueous solution containing NH 4 VO 3 and N 2 H 4 ・H 2 O under atmospheric pressure had been investigated. The optimal conditions for atmospherically hot-water treatment at 95°C were found to be as follows: pH 2.5-3.5 and an appropriate amount of N 2 H 4 ・H 2 O. How the solution conditions affect the crystal structures and morphologies of the products is discussed. At pH＜2.5, no precipitates formed. At pH 4.0-4.5, V 10 O 24 ・12H 2 O would generally be obtained if N 2 H 4 ・H 2 O was excessive. It was independent of reduction of NH 4 VO 3 solution to tetravalent solids on the dosage of reducing agent N 2 H 4 ・H 2 O. The morphologies of the V 2 O 4 ・2H 2 O had no obvious relationship with the pH and the dosage of N 2 H 4 ・H 2 O. It seems that before treated at 95°C the products were sheet-shaped, and then cleaved along specific crystalline directions after treated, forming rod bunches. The stability of V 2 O 4 ・2H 2 O in acid solution and in air was also investigated. The results showed that V 2 O 4 ・2H 2 O was unstable in air and could undergo oxidization to be a quasiamorphous rod-shaped V 10 O 24 ・12H 2 O, especially at high pH, with excessive N 2 H 4 ・H 2 O, drying at 150°C in flowing air, and/or being exposed to air for several days.

Synthesis and formation mechanism of VO2(A) nanoplates with intrinsic peroxidase-like activity

“…40 This phase was found to be stable when temperature was increased to 160 C. Their solution synthesis and thermal stability have been previously fully analyzed by our group. 39 Bunches of microrods (1-8 mm in length and 0.5-1 mm in diameter) consisting of tiny nanoparticle nuclei have been observed at 140 and 160 C, as shown in the insets of and VO 2 (A) (Fig. 3c).…”

Solution Processing of Nanoceramic VO2 Thin Films for Application to Smart Windows

“…[4][5] In the past several years, we have worked to develop a solution-based process for VO 2 -based thin films with a special emphasis on their preparation, thermochromic property study and application to smart windows. 43,44,[60][61][62][63][64][65][66][67][68][69][70][71][72] Polymer-assisted deposition (PAD) process was realized for the preparation of VO 2 and VO 2 -based multilayered films. The method enables us to facially control over the film thickness, morphology and optical constants.…”

Nanoparticles of Low-Valence Vanadium Oxyhydroxides: Reaction Mechanisms and Polymorphism Control by Low-Temperature Aqueous Chemistry

“…) 44. Gain's hydrate is obtained as 40 nm large, 300 nm-1 m long and only a few nanometers thick twisted ribbons, with a length distribution that corresponds to the length polydispersity of final Häggite nanowires.…”