Influence of pH and ionic strength on vanadium(V) oxides formation.: From V2O5•nH2O gels to crystalline NaV3O8•1.5H2O

Na+ and TMA(+) intercalated M(0.3)V(2)O(5)(.)1.5H(2)O ( M = Na+ and TMA(+)) precipitates have been synthesized by adding chloride salts MCl or bases MOH to a metavanadate solution which was acidified using a proton exchange resin. As evidenced by X-ray diffraction, these vanadium oxides exhibit the layered structure of the V(2)O(5)(.)1.8H(2)O xerogels in which Na+ and TMA+ cations are intercalated between the layers. These precipitates result from the assembly of ribbon-like particles but in contrast to the V(2)O(5)(.)1.8H(2)O xerogels, the particles are no longer stacked on flat surfaces and their assembly is disorganized as evidenced by SEM and TEM. Depending on the final pH of the acidified metavanadate solution, the Na(0.3)V(2)O(5)(.)1.5H(2)O phase can be thermodynamically stable or can evolve with time. At a pH. 3, the Na(0.3)V(2)O(5)(.)1.5H(2)O phase disappears after a few days and is transformed to the crystalline NaV(3)O(8)(.)1.5H(2)O phase. The vanadium oxide phases were all characterized by X-ray diffraction, SEM, TEM, TGA, IR and V-51 MAS NMR.