Hydrothermal synthesis, structural, and spectroscopic studies of vanadium substituted ETS-4

Titano-vanadium silicate with the structure of ETS-4 has been hydrothermally synthesized to produce V-ETS-4. Direct comparison between ETS-4 and V-ETS-4 showed successful isomorphous substitution of titanium by vanadium. The existence of vanadium is confirmed by energy dispersive X-ray spectrometry (EDS). ⁵¹V and ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy revealed that the vanadium is present as V⁴⁺ and prefers the octahedral site in the ETS-4 structure. Diffuse reflectance ultraviolet–visible (DR UV–Vis) and Raman spectroscopy analyses showed the existence of five- and six-coordinated V⁴⁺, which partly substitute TiO₅ square-pyramids and interrupts the chains of TiO₆ octahedra in the ETS-4 structure. This isomorphous substitution also impacts the thermal stability of V-ETS-4 and it was observed by differential scanning calorimetry (DSC).