Synthesis of Silica Aerogel from Rice Husk Modified Trimethylchlorosilane (TMCS) as an Adsorbent for Methylene Blue

Abstract

This study investigated the synthesis and silylation of biomass-derived silica aerogels from rice husk ash for methylene blue (MB) adsorption under ambient-pressure drying (APD). Surface modification was conducted using trimethylchlorosilane (TMCS) in an ethanol/n-hexane co-solvent system to prevent capillary-induced pore collapse. The optimal silylation ratio (1:2:1 of silica:TMCS:n-hexane) yielded a superhydrophobic aerogel with a water contact angle of 152°, specific surface area of 795 m²/g, pore volume of 5.75 cm³/g, and 97.8% porosity. Fourier transform infrared (FTIR) spectroscopy confirmed successful surface modification, as evidenced by the appearance of Si–O–CH₃ (962 cm⁻¹) and –Si(CH₃)₃ (2950 cm⁻¹) peaks, while X-ray diffraction (XRD) verified the preserved amorphous silica framework with a broad peak at 2θ = 22°. The optimized aerogel achieved maximum MB removal efficiency of 97.9% within 70 min (C₀ 20 ppm) and an equilibrium capacity of 14.03 mg/g at 60 ppm. Non-linear modeling revealed that the adsorption was best described by pseudo-second-order kinetics (R²=0.9935) and the Langmuir isotherm (R²=0.9845), confirming a homogeneous, monolayer chemisorption mechanism.