Extraction and characterization of nanosilica from bamboo pellets

Abstract

Bamboo is an abundant, fast-growing, and renewable resource rich in silica, offering the dual benefits of clean energy production and the recovery of valuable materials. This study focuses on the extraction and characterization of nanosilica from bamboo pellets, aiming to promote sustainable utilization of bamboo biomass while adding economic value through the production of a high-demand material. Nanosilica has a wide range of applications, including catalysis, drug delivery, gene therapy, additives in plastics and food, pigments, pesticides, thin-film substrates, and thermal insulation. The findings highlight the potential of bamboo for multipurpose use, supporting both environmental sustainability and industrial innovation. In this study, the leaves, culm sheath, and culm of Bambusa vulgaris Schrad. and Bambusa bambos (L.) Voss. were employed for pellet production and subsequent nanosilica extraction. These species were selected for their wide availability and abundant supply, ensuring a sustainable and readily accessible source of raw material. Bamboo pellets were produced using an optimized 20% corn starch binder, and their physical and fuel characteristics were examined to determine their effectiveness as a solid biofuel and their potential for subsequent silica extraction. The culm showed the highest calorific value, emphasizing its strong suitability as a biofuel feedstock owing to its greater carbon-rich lignocellulosic content. For nanosilica extraction, the pellets were pretreated with a Deep Eutectic Solvent (DES) composed of choline chloride and oxalic acid. DES was chosen for its ability to efficiently break down the lignocellulosic structure of bamboo, improving silica release while being environmentally friendly, non-toxic, and more sustainable than conventional chemical methods. A 15% Deep Eutectic Solvent (DES) was identified as the most effective pretreatment. Following DES treatment, the biomass was calcinated at an optimized temperature of 600 °C for 12 hours to produce silica, which was subsequently converted into nanosilica via the sol-gel method. In this process, the silica was dissolved in 5 M NaOH to form sodium silicate, which was then neutralized with 3 M HCl to yield a nanosilica gel. The gel was centrifuged, thoroughly washed with double-distilled water, and dried in an electric oven at 50 °C for 3 hours to obtain nanosilica powder. Across both species, the leaf biomass yielded the highest silica content, reflecting its greater phytolith concentration, whereas the culm showed the lowest recovery. In both species, the leaves produced the highest silica yields in DES-treated samples (0.62 g and 0.51 g) and in untreated controls (1.24 g and 0.72 g), followed by the culm sheath. The culm exhibited the lowest yields, with DES-treated samples yielding 0.05 g and 0.03 g, and untreated controls 0.10 g and 0.07 g for Bambusa vulgaris and Bambusa bambos, respectively. Despite the higher residue mass in the control samples, the DES-treated samples produced silica of superior purity due to more effective removal of organic and mineral impurities. The extracted silica and synthesized nanosilica were comprehensively characterized using SEM, TEM, FTIR, XRD, and TGA, confirming the formation of amorphous and thermally stable nanosilica with complete removal of organic matter. SEM revealed irregular, loosely aggregated granules, while TEM showed cloud-like nanoscale agglomerates, characteristic of biogenic and sol–gel-derived silica. FTIR spectra displayed a prominent band at ~1040 cm⁻¹, corresponding to Si–O–Si asymmetric stretching and confirming siloxane network formation, with additional bands between 450-795 cm⁻¹ assigned to Si–O–Si and Si–OH bonds. XRD analysis showed a crystallinity index of 40.8% for raw bamboo (Leaves), decreasing to 24.31% for nanosilica, reflecting its predominantly amorphous nature. TGA revealed the typical three-stage degradation of lignocellulosic biomass, with major mass loss from hemicellulose, cellulose, and lignin decomposition in raw materials, and confirmed the thermal stability of the nanosilica powder. The study establishes bamboo pellets as a viable feedstock for the sustainable extraction of high-purity nanosilica. The process integrates eco-friendly pretreatment, efficient thermal conversion, and reliable characterization methods. The findings highlight the potential for developing scalable nanosilica production technologies and open avenues for using bamboo-derived nanosilica in applications such as adsorption, composites, coatings, and material science innovations.