A comparative study on reactions of n-alkylamines with tungstic acids with various W-O octahedral layers: Novel evidence for the “dissolution-reorganization” mechanism

The aim of this paper was to provide a convincing experimental research to demonstrate a dissolution-reorganization mechanism for the formation of tungstate-based inorganic-organic hybrid nanobelts by comparatively investigating the reaction behaviors of H2WO4 and H2W2O7·xH2O with n-alkylamines (CmH2m+1NH2, m = 4-10). The formation of tungstate-based hybrid nanobelts derived from the reactions between n-alkylamines and H2WO4 with single-octahedral W-O layers was investigated with a detailed comparison with those between n-alkylamines and H2W2O7·xH2O with double-octahedral W-O layers. H2WO4 and H2W2O7·xH2O reacted with n-alkylamines, respectively, in reverse-microemulsion-like media. The obtained products were characterized by XRD, FT-IR, TG-DTA and SEM. The results indicated that the products derived from H2WO4 and those from H2W2O7·xH2O were similar in compositions, microstructures and morphologies. The structural analysis indicated the products were tungstate-based inorganic-organic hybrid one-dimensional belts with highly ordered lamellar structures by alternately stacking organic n-alkylammonium bilayers and inorganic single-octahedral W-O layers. The n-alkyl chains in the above hybrid nanobelts from H2WO4 and H2W2O7·xH2O took on a bilayer arrangement with tilt angles of 65° and 74°, respectively. The similarities in the microstructures of the products from H2W2O7·xH2O and H2WO4 demonstrated that the double-octahedral W-O layers of H2W2O7·xH2O were decomposed during the reactions. The changes of inorganic W-O layers and the morphologic changes of the tungstic-acid precursors before and after the reactions corroborated the dissolution-reorganization mechanism.