Large scale synthesis of pure VSH-1 and its characterization

A method to produce pure VSH-1 in large quantities (∼20 g) was developed. The reagents were silica sol, V2O5, H2SO4, KOH, and ethanol. The crystals adopted distorted octahedral shapes. The total surface area of the pristine VSH-1 with the general formula of K2(VO)(Si4O10)·H2O was 76 m2/g, indicating that a significant portion of the pores are occupied by K+ ions. Analyses of the diffuse-reflectance UV–Vis spectra of Mn+-VSH-1 (Mn+ = K+, Na+, Ca2+, Pb2+, and Zn2+) revealed that the bands that appear in the 200–400 nm region arise due to the D–A–A triad charge-transfer (CT) interaction among the V4+, O2−, and Mn+, and the 447, 590, and 879 nm bands arise due to the d–d transition of V4+. The measured atomic magnetic moment (μ) was 1.73 BM, indicating that all the V atoms exist in V4+. The ESR spectrum of VSH-1 showed a strong signal due to V4+ with the g value of 1.959 with ΔHpp value of 131 G. The Raman spectra of Mn+-VSH-1 revealed the existence of strong VO stretching at 955 cm−1, and other peaks at 373 (weak), 453 (weak), 534 (weak), 620 (medium), 800 (weak), and 1072 (weak) cm−1. The VO stretching band shifted to a higher energy region upon increasing the Sanderson’s electronegativity of Mn+. The thermogravimetric (TGA) analysis showed that VSH-1 is thermally stable up to 550 °C and above which the oxidation of V4+ occurs and the structure collapse.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Facile synthesis of vanadosilicate (VSH-1). ► Ion-exchanged properties. ► XRD, SEM, HR-TEM, DR UV–Vis, Raman, absorption, SQUID and ESR characterization. ► D–A–A (donor–acceptor–acceptor) triad charge-transfer (CT) interaction.