Microwave-Assisted Citrate-Mediated Hydrothermal Synthesis of Mono- and Multi-Metal Silicates Supported on Stöber Silica and Mesoporous Silica Substrates

Metal silicates have far reaching applications that include catalysis, pollutant remediation, and energy storage. Conventional syntheses are timely (6–48 h) and often incorporate multiple metals inhomogeneously into the silicate framework, thus limiting predictable tailorability. Here, we report a microwave-assisted citrate-mediated hydrothermal synthesis of mono- and multimetal silicate coatings on Stöber silica spheres and mesoporous silica (SBA-15). Using microwave irradiation facilitates rapid and uniform heating and reduces reaction times to 20 min. These heating characteristics, combined with citrate modulated metal ion release, prevent unwanted oxidation and provide homogeneous deposition of metal silicates onto the silica templates. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy provide confirmation of the formation of metal silicates, showing characteristic binding motifs and binding energy shifts. Transmission electron microscopy coupled with energy dispersive X-ray spectroscopy demonstrates the preservation of the silica template morphology and the formation of a uniform metal silicate shell. Nitrogen adsorption studies verified the retention of the mesoporous silica structure and high surface area (>240 m2/g), confirming the versatility of this synthesis on fragile silica templates. This work demonstrates a versatile approach toward synthesizing metal silicates with controlled composition and morphology that offer opportunities for tailoring catalytic materials.