Magnetite–Silica–Gold Nanocomposite: One-Pot Single-Step Synthesis and Its Application for Solvent-Free Oxidation of Benzyl Alcohol

A simple and innovative method for a single-step–one-pot room temperature synthesis of magnetite–silica–gold nanocomposite has been demonstrated. This simple process involves a combination of different reactions occurring simultaneously. Specifically, coprecipitation of iron salts, reduction of gold chloride, and formation of silica, all at one instance, result in a unique nanocomposite of iron oxide, silica, and gold. The well-known method of coprecipitation of iron salts to form iron oxide nanoparticles has been modified suitably to include sodium silicate (silica source) instead of an alkali (for coprecipitation). Gold chloride premixed in sodium silicate, prior to reaction, gives the third and important functionality: gold nanoparticles, which can act as a catalyst. The nanocomposite so formed is stable due to the silica network, is magnetically separable, has high surface area, and is catalytically active. The composite has been characterized by a host of different techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive analysis using X-rays, X-ray photoelectron spectroscopy, transmission electron microscopy, zeta potential measurements, dynamic light scattering, BET surface area measurements, and magnetic measurements. The catalytic feature of this composite was verified by a model reaction involving oxidation of benzyl alcohol to benzaldehyde by molecular oxygen. The nanocomposite was found to show high conversion efficiency with excellent selectivity and recyclability. High surface area of the nanocomposite and efficient surface passivation by silica framework coupled with facile access to catalytic gold nanoparticles make the current nanocomposite highly efficient. The existing material and the process are innovative and can be extended to incorporate other active materials of interest. More importantly, the synthesis approach is “greener” (one-pot, single-step, aqueous, room temperature, avoiding toxic chemicals and harsh reducing agents, scalable, and industrially economic process). The composite was further found to be catalytically active, magnetically separable, and reusable for the solvent-free oxidation of benzyl alcohol at atmospheric pressure and without the use of harsh oxidizing agents, thereby making our approach extremely promising for industrial applications.