Functionalized diatom biosilica decorated with nanoparticles: synthesis, characterization, catalytic oxidation, and dye scavenging applications

Diatoms are unicellular photosynthetic algae that occur in all water territories on earth. Their cell walls comprise amorphous siliceous material, biosilica, called a frustule. Attributable to their highly porous structure, diatom biosilica is a promising renewable material for various applications such as catalysis, drug delivery systems, adsorbents, and bio-photonics. In the current work, to enhance the properties of diatoms (Aulocoseira sp.), they were surface-functionalized with thiol groups and decorated with silver or gold nanoparticles. Comprising diatoms biosilica (DE) as catalyst support with Nobel metal nanoparticles as active species, the two series of catalysts, DE-SH-AuNP and DE-SH-AgNP, were synthesized. The material was characterized by various spectroscopic techniques such as SEM-EDAX, BET surface area, FT-IR, XRD, TEM, 29Si-NMR, and TGA-DTA analysis. With a homogeneous nanoparticle distribution, diatom biosilica exhibited very high nanoparticle-loading (AgNP and AuNP) capacities. The synthesized catalysts DE-SH-AuNP and DE-SH-AgNP were investigated for oxidation of D-glucose to D-gluconic acid, an essential chemical intermediate in the pharmaceutical and food industry. Additionally, the catalysts were also investigated for environmental applications like dye degradation studies for methylene blue (MB) and crystal violet (CV) using UV–visible spectroscopy. The catalysts exhibited excellent activity for the oxidation of D-glucose with 78% conversion over DE-XSH-Ag and 87% conversion over DE-XSH-Au respectively. The preliminary results of dye degradation studies reveal the potential of materials in environmental applications.