SiO2 aerogel monolith allows ultralow amounts of TiO2 for the fast and efficient removal of gaseous pollutants

Coupled adsorption and photocatalytic oxidation brings high expectations regarding the fast and efficient removal of gaseous pollutants in air. However, to fabricate an adsorbent–photocatalyst composite, coating of a photocatalyst on adsorbent support inevitably results in loss of adsorption and light blocking on interior surfaces. In this work, we attempt to develop an adsorbent–photocatalyst monolith composite, which not only perfectly retains original high adsorption capacity, but also allows complete penetration of UV light through the whole monolith. We employ a SiO2 aerogel monolith with a diameter of 2.5 cm and thickness of 0.7 cm as adsorbent and support. After atomic layer deposition (ALD) followed by calcination, 0.32–1.25 wt% TiO2 is dispersed on the skeleton of the SiO2 aerogel. In spite of such a low level of loading, the monolith composites exhibit fast and efficient removal of gaseous acetaldehyde and NO. Therein, the best performance is achieved at a loading of 0.6 wt% TiO2. By dark adsorption, the acetaldehyde pollutant with initial concentration of 200 ppm can be adsorbed by 54% within 10 min. Moreover, the light transmittance at 387 nm can be retained as high as 6% after penetrating through the whole monolith, confirming that all loaded TiO2 nanoparticles can participate in the photocatalytic oxidation of acetaldehyde. Under UV irradiation with intensity close to natural sunlight, the preadsorbed acetaldehyde can be completely mineralized into CO2 by photocatalytic oxidation in another 60 min, benefiting from the ultradispersion of TiO2 nanoparticles inside the SiO2 aerogel. The study provides a novel three-dimensional model of an adsorbent–photocatalyst composite for the fast and efficient removal of gaseous pollutants.