Green Synthesis of SiO2 Nanoparticles from Egyptian White Sand Using Submerged and Solid-State Culture of Fungi

This work aims to successfully produce silica nanoparticles (SNPs) from Egyptian white sand using the fungal bioleaching process as a cost-effective and eco-friendly approach. The impact of fungus cultivation techniques (submerged culture SMC and solid-state culture SSC) on the characteristics of the produced SNPs has been investigated. In addition, the most promising fungal isolates for each culture method were selected and identified by morphological and molecular methods. The biosynthesized SNPs were fully characterized by DLS, FTIR, XRD, SEM, EDX, and HRTEM studies. DLS results showed that Aspergillus niger solid-state culture had developed SNPs with a mean particle size distribution of about 3.6 nm, whereas Penicillium crustosum submerged culture developed SNPs with 50.7 nm. SEM images revealed that the prepared SNPs under SMC and SSC have sphere-shaped particles with smooth surfaces and semi-homogeneous characteristics. Moreover, the HRTEM imaging confirmed the spherical shape with an average size of 3.5 and 28.8 nm for the nanosilica synthesized during solid-state and submerged culture, respectively. Based on the results, we recommended using SSC to produce silica nanoparticles from white sand with a small nano-size, high purity, and better economical production. The scientific advances focused on some particular fungi's capacity to manufacture SNPs with high purity, small size, and techniques that were both economical and environmentally beneficial. Graphical Abstract