High Surface Area Mesoporous GaPO4–SiO2 Sol–Gel Glasses: Structural Investigation by Advanced Solid-State NMR

Abstract

Mesoporous silica–gallium phosphate glasses along the composition line, xGaPO4–(1 – x)SiO2 (x = 0.5, 0.33, 0.20, 0.14, and 0.11, respectively) were prepared via the sol–gel route. This glass-forming range is significantly wider than that accessible by previously reported routes. The glasses exhibit a mesoporous structure with surface areas around 400 m2/g, after calcination at 650 °C. The structural evolution from liquid to gel to glass was analyzed by liquid and advanced solid-state nuclear magnetic resonance techniques. The NMR results indicate that the glasses consist of GaPO4 and SiO2 nanodomains. With increasing GaPO4 content, the sizes of the GaPO4 domains become larger. Evidence for the connection of both domains at their interfaces by P–O–Si and Ga–O–Si linkages is presented by advanced 71Ga, 31P, and 29Si high-resolution dipolar solid-state NMR methods.