Cellulose–POSS–Silica/Gold Core–Shell Hybrid Nanocomposites: One‑Step Sol‑Gel Synthesis and Multifunctional Properties

Abstract

We present a streamlined, one‑step sol‑gel route to fabricate cellulose–polyhedral oligomeric silsesquioxanes (POSS) hybrids incorporating silica cores coated with a uniform gold shell. The process simultaneously hydrolyses tetraethyl orthosilicate (TEOS) and reduces chloroaurate (HAuCl₄) in the presence of formic acid, while γ‑aminopropyl triethoxysilane (γ‑APTES) grafts amine‑functionalized POSS onto cellulose. Two variants were studied: (1) a conventional sol‑gel sequence and (2) a PVA/THPC‑mediated approach. Characterization by FT‑IR, Raman, XRD, UV‑VIS, photoluminescence, SEM/EDS, TEM, TGA/DSC, and BET confirmed successful core–shell formation, uniform dispersion, high optical transparency, and enhanced thermal stability.

Background

Nanotechnology’s intersection with polymer science has driven the development of hybrid materials for flexible electronics, sensors, and biocompatible devices. Silica–gold core–shell nanoparticles offer tunable optical, thermal, and catalytic properties, yet traditional multistep syntheses are laborious. By integrating cellulose, a renewable, biodegradable polymer, with POSS, we create a robust matrix that stabilizes the nanoparticles and enables scalable production. The sol‑gel process provides a low‑temperature, solution‑phase route that preserves the cellulose’s functional groups while grafting inorganic networks.

Methods

Materials

Cellulose (DP = 4500) was purified with LiCl/DMAc, and reagents (TEOS, HAuCl₄, γ‑APTES, THPC, PVA) were sourced from standard suppliers. All reactions were conducted under nitrogen to prevent oxidation.

Synthesis

Method 1 (Sol‑Gel): 0.5 g cellulose and 0.35 g POSS‑amine were dissolved in 50 mL DMAc, stirred at 95 °C for 3 h, then 2 mL γ‑APTES and 2 g TEOS were added. HAuCl₄ (0.002–0.004 M) and 10 g water/formic acid were introduced, and the mixture was refluxed for 12 h. The product was washed with ethanol and dried at 95 °C.

Method 2 (PVA/THPC): Identical initial steps were followed, with 0.2 g PVA and 5 mL THPC added after 2 h. The mixture was refluxed for 12 h, purified, and dried similarly.

Characterization

FT‑IR (KBr, 8 cm⁻¹), Raman (He‑Ne, 580–600 nm), XRD (Cu Kα), UV‑VIS (λ = 200–800 nm), PL (He‑Cd, 325 nm), SEM/EDS (Hitachi S‑4200), TEM (JEOL 100CX), TGA/DSC (TA 2050, 10 °C/min), and BET (BELSORP) were employed to probe chemical structure, morphology, crystallinity, optical behavior, and surface area.

Results and Discussion

Structural Confirmation

FT‑IR spectra displayed characteristic Si–O–Si, Si–O–Au, and amide peaks, confirming successful grafting and core–shell formation. XRD patterns revealed fcc gold peaks at 2θ = 22.56°, 25.14°, 27.90°, and 30.08°, alongside cellulose-POSS signals, indicating crystalline gold shells around silica cores.

Optical Properties

UV‑VIS transmittance showed high transparency across the visible range for both methods, with a surface plasmon resonance band near 520 nm. PL spectra exhibited red‑shifted emission peaks (441–497 nm) and a bandgap of 2.3–2.8 eV, attributed to quantum‑size effects of the gold shell.

Morphology

SEM images revealed monodisperse, uniform nanoparticles with reduced agglomeration in the PVA/THPC method. TEM confirmed core diameters of ~50 nm with silica shell thicknesses tunable from 20 to 100 nm, depending on TEOS concentration.

Thermal Stability

TGA curves displayed three degradation stages: 85–100 °C (adsorbed water), 100–450 °C (cellulose decomposition), and 450–1000 °C (inorganic residue). Char yields reached 44.5% (Method 1) and 34.5% (Method 2), demonstrating enhanced thermal resilience.

Surface Area

BET analysis yielded surface areas of 16.6 m²/g (Method 1) and 34.2 m²/g (Method 2), with corresponding micropore volumes indicating improved porosity due to PVA/THPC treatment.

Conclusions

Both sol‑gel approaches successfully produce cellulose–POSS–silica/gold hybrids with homogeneous core–shell architecture, optical transparency, and superior thermal stability. The PVA/THPC method affords finer control over shell thickness and surface area, offering a versatile platform for next‑generation flexible electronics and bio‑sensing applications.