Impact of supercritical drying and heat treatment on physical properties of titania/silica aerogel monolithic and its applications

TiO 2–SiO 2 monolithic aerogels were homogeneously prepared using sol–gel method. Critical point of drying time of TiO 2–SiO 2 gels with ethanol was studied at 30–120 min. Subsequently, the gels were dried with supercritical ethanol, resulting in amorphous aerogels that crystallized following heat treatment at 550 °C for 1–5 h. TiO 2–SiO 2 gel should be supercritical dried for 30 min from economic point of view and heat treated for 5 h. SEM images of representative TiO 2–SiO 2 aerogel morphologies were monolithic aerogel. ▪ TiO 2–SiO 2 monolithic aerogels were homogeneously prepared using sol–gel method. Critical point of drying of TiO 2–SiO 2 gels with ethanol was studied for 30, 60, 90 and 120 min. Subsequently, the gels were dried with supercritical ethanol, resulting in amorphous aerogels that crystallized following heat treatment at 550 °C from 1 to 5 h. The TiO 2–SiO 2 aerogels were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface area measurements. The molar ratio of SiO 2:TiO 2 was 6 and the synthetic strategy revealed that TiO 2–SiO 2 aerogel, had a surface area ∼868 m 2/g, particle size ∼40 nm, density ∼0.17 g/cm 3 and 80% porosity. The finding indicated that from economic point of view, TiO 2–SiO 2 gel should be supercritical dried for 30 min and heat-treated for 5 h. The TiO 2–SiO 2 aerogel monoliths photocatalyst synthesized using sol–gel method provided insight into the characteristics that make a photocatalyst material well-suited for photodegradation of phenol and cyanide in an industrial waste stream containing Cl −, S 2− and NH 4 +. Interestingly, after multiple reuse cycles (i.e. ≥7), photodegradation systems with regenerated photocatalyst showed a slightly decreasing of photoactivity ∼2–4%. The overall kinetics of photodegradation of either phenol or cyanide using TiO 2–SiO 2 aerogel photocatalyst was found to be of first order.