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

Abstract

Abstract TiO2–SiO2 monolithic aerogels were homogeneously prepared using sol–gel method. Critical point of drying of TiO2–SiO2 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 TiO2–SiO2 aerogels were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface area measurements. The molar ratio of SiO2:TiO2 was 6 and the synthetic strategy revealed that TiO2–SiO2 aerogel, had a surface area ∼868 m2/g, particle size ∼40 nm, density ∼0.17 g/cm3 and 80% porosity. The finding indicated that from economic point of view, TiO2–SiO2 gel should be supercritical dried for 30 min and heat-treated for 5 h. The TiO2–SiO2 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−, S2− and NH4+. 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 TiO2–SiO2 aerogel photocatalyst was found to be of first order.