Nano-Silica Synthesis from Rice Husk Waste and Its Use as a Paper Sheet Anti-Aging Coating with Density Functional Theory (DFT) Insights
Mona A. El-Sabour, Mohamed El-Sakhawy*, Hebat-Allah S. Tohamy
Cellulose and Paper Department, National Research Centre, 33 El Bohouth Str., Dokki, Giza, Egypt
* Corresponding Author: Mohamed El-Sakhawy. Email: 
Journal of Renewable Materials https://doi.org/10.32604/jrm.2026.02026-0030
Received 25 February 2026; Accepted 22 July 2026; Published online 12 August 2026
Abstract
Paper ages naturally by heat, oxidation, and hydrolysis, which cause a progressive loss of mechanical strength. This study achieved a high yield of 93% amorphous SiO
2 from rice husk waste through controlled calcination at 450°C (3 h) and 800°C (2 h), alkaline extraction with 2.5 N NaOH, acid precipitation with 1 N HCl and freeze-drying. The resulting nano-silica particles were incorporated into a 3% w/v hydroxyethyl cellulose (HEC) binder to prepare a 2% w/v impregnation solution, which was applied to paper sheets by soaking for 0–20 min. Structural analyses (FTIR, XRD, SEM) confirmed the successful preparation of hydroxylated amorphous silica and uniform deposition on paper fibers. Optimal mechanical performance was achieved at soaking times of 10–15 min, where a maximum weight percent gain (WPG) of 35.27% was recorded. Post-aging tensile strength and elongation improved by up to 25% and 94%, respectively, compared to uncoated paper. The limiting oxygen index (LOI) values increased from 18.0 to 22.3 vol.%, indicating improved flame retardancy. Density Functional Theory (DFT) calculations revealed that the nano-silica coated paper exhibited a wider HOMO–LUMO energy gap (1.342 to 1.803 eV) and higher chemical hardness (0.671 to 0.902 eV), confirming enhanced chemical stability and reduced susceptibility to oxidative degradation. This study combine bio-derived nano-silica from rice husk waste with DFT quantum chemical analysis to elucidate the molecular-level anti-aging mechanism of a paper coating system. The study demonstrates a sustainable route for converting agricultural waste into functional nanomaterials for paper preservation and performance enhancement.
Keywords
Flame retardancy; paper aging; nano-silica; rice husk valorization; DFT calculations; sustainable coatings
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