Preparation of polyoxometalate compound (NH4)6(β-P2W18O62)/SiO2 by sol-gel method and its characterization

Abstract

Preparation of polyoxometalate compound of (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O supported with silica derived from the hydrolysis of tetraethyl orthosilicate by sol-gel method has been conducted. The compound was synthesized and characterized using FT-IR spectrophotometer, crystallinity using XRD analysis and the determination of acidity via quantitatively and qualitatively. Qualitative analysis was performed using ammonia and pyridine adsorption and quantitative analysis using potentiometric titration. FT-IR spectrum of (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O appeared in wavenumber 786.96 cm^-1 (W-O_C-W), 918.12 cm^-1 (W-O_e-W), 964.41 cm^-1 (W=O), 1087.85 cm^-1 (P-O), 3572.17 cm^-1 (O-H),  1404.18 cm^-1 (N-H) reinforced with wavenumber 1612.49 cm^-1 with show vibration  NH dari NH⁺, and to  (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O/SiO₂ appears in wavenumbers 794.67 cm^-1 (W-O_c-W), 918.12 cm^-1 (W-O_e-W), 1049.28 cm^-1 (W=O), 1087.85  cm^-1 (P-O), 3564.15 cm^-1 (O-H), 470.63 cm^-1 (Si-O). Diffraction pattern of (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O and (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O/SiO₂ compound show high crystanillity. The acidic properties showed (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O/SiO₂ more acidic than (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O. Analysis of the effect of temperature on the stability of the compounds polyoxometalate (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O/SiO₂ show that the temperature of 600ºC the shift in  wavenumbers of the compounds caused by vibration  W=O, W-O_C-W,  W-O_e-W has been lost. This shows that at a temperatures of 600ºC on heating can cause changes in the structure of polyoxometalate (NH₄)₆(β-P₂W₁₈O₆₂)nH₂O/SiO_2.

Keywords : (NH₄)₆(β-P₂W₁₈O₆₂).nH₂O, Polyoxometalate, SiO₂