A Simple Method to Synthesize Novel Mesoporous Carbon–silica Composites from the By-product of Ethanol Production

Abstract

Carbon-silica composites with mesoporous structures were synthesized from low-cost materials by conventional heating. The carbon source used was vinasse, a by-product of ethanol production from molasses, while Na₂SiO₃ and K₂SiO₃ were utilized as low cost and abundantly available silica sources as alternatives to tetraethyl orthosilicate (TEOS). The simple preparation method was adopted as follows: vinasse was dehydrated with 50% H₂SO₄ (1:2 in weight ratio) to produce carbon, after which the silica source was added with weight ratio of vinasse:silica source 0.8:1, 0.2:1 and 0.5:1 for Na₂SiO₃, K₂SiO₃ and TEOS, respectively. The mixture was stirred and heated at 80 °C for 6 h, washed with water, and dried at 120 °C for 3 h to obtain the carbon-silica composites. Composites were characterized by N₂ adsorption-desorption, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), moisture content, ash content, slurry pH, point of zero charge (pHPZC) and bulk density. The composites exhibited BET (Brunauer–Emmett–Teller) surface areas of 443, 354 and 570 m²/g and average pore diameters of 5.20, 5.52 and 7.63 nm when using Na₂SiO₃, K₂SiO₃ and TEOS, respectively, as silica sources. The carbon-silica composites were highly mesoporous, accounting for around 71-80% of the total volume. FTIR analysis showed the presence of Si–O–Si bond for all composites. According to TGA results, the adsorbents were thermally stable up to 700 °C. The slurry pH and pHPZC of each composite was very similar with acidic character (slurry pH 2.63–6.80 and pHPZC 2.95–7.00). The bulk density of composites was 560–660 kg/m³, higher than some commercial activated carbons. These results indicated that the mesoporous carbon-silica composites prepared from vinasse and low-cost silica sources were promising functional materials for use as potential adsorbents.