Synthesis of SiO2-Al2O3 composite aerogel from fly ash: a low-cost and facile approach

A low-cost and simple method was proposed to synthesize SiO2-Al2O3 composite aerogel from fly ash by alkali fusion-acid leaching-ambient pressure drying process just in 3 days for the first time. The effect of the leaching solution's pH value upon micro-structure and properties of the as-prepared SiO2-Al2O3 composite aerogel was intensively studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N-2 adsorption-desorption, and Fourier transform infrared spectrometry. The as-formed SiO2-Al2O3 aerogel possessed high specific surface area (abbreviated as SSA) of 800 m(2)/g when the pH value was controlled at 2.7-3.1 (almost up to 900 m(2)/g at pH = 2.7). Meanwhile, the aerogel exhibited good thermal stability. After calcination at 900 degrees C for 2 h, the aerogel still remained an amorphous structure with a SSA of 77.88 m(2)/g. In addition, the related formation mechanism was also discussed.