Biosynthesis of SiO₂ nanoparticles from bamboo leaves for tanning wastewater treatment and mechanical properties of HMPC-SiO₂ nanocomposite

The application of biological methods for synthesizing nanomaterials is advancing the field of nanotechnology. This study aims to explore the feasibility of using bamboo leaf-derived silicon dioxide nanoparticles (SiO₂-NPs) for the treatment of tanning wastewater, specifically investigating the mechanical properties of hydroxypropyl methylcellulose (HPMC)-SiO₂ nanocomposite films. Biosynthesized SiO₂-NPs were characterized through multiple spectral and electron microscopic techniques, revealing a sphere-like structure with a size distribution around 30 nm. Tanning wastewater treatment was conducted under two conditions: darkness and sunlight exposure. SiO₂-NPs at concentrations of 0.25, 0.5, 0.75, and 1.0 mg/L were evaluated over various contact durations (30, 60, 90, 120, 150, 180, and 210 min) under both conditions. The maximum discoloration rate of 82.61% was achieved at a dosage of 1.0 mg/L after 210 min under sunlight exposure. Following treatment with SiO₂-NPs under optimal conditions, the levels of heavy metals were reduced by 71.61%, 77.48%, 92.83%, and 72.13% for Cd, Pb, Cr (VI), and Ni. The high removal efficiency of heavy metals using 1 mg/mL of SiO₂-NPs can be attributed to the availability of numerous adsorption sites. Additionally, the adsorption isotherm reveals the R² (0.9632) values; the Freundlich model is clearly the most appropriate for Cr (VI) adsorption on SiO₂-NPs. This suggests that Cr (VI) ions adsorb onto SiO₂-NPs via multilayer formation. Furthermore, the impact of biosynthesized SiO₂-NPs embedded in the HPMC polymer matrix on the materials mechanical properties was examined. The fabricated nanocomposite films demonstrated enhanced mechanical properties, with an increase in elongation at break from 29.63 to 37.54%, indicating improved ductility. Additionally, the tensile strength of the nanocomposite film increased from 45.21 MPa in pure HPMC to 86.47 MPa in HPMC-SiO₂ nanocomposites, resulting in a 47.71% improvement. Overall, the plant-synthesized SiO₂-NPs exhibit promising catalytic properties and are considered a potential eco-friendly nanocatalyst for the wastewater treatment process.