Ultrasound-assisted synthesis of high surface area amorphous TiO2 for adsorption and its crystallization to photocatalytically active materials

High photocatalytic activity in TiO₂ demands both good crystallinity for low-loss charge transport, and a large accessible surface for efficient mass transfer. Conventional synthetic procedures involve a calcination step that typically improves the overall crystallinity, but at the expense of available surface area. Alternative crystallization methods that preserve texture are thus desirable. In this work, high-power ultrasound was applied in two stages to create TiO₂ with both high surface area and controlled crystallinity. First, probe sonication during sol-gel synthesis suppressed early network collapse, producing highly dispersed amorphous TiO₂ with interparticle porosity and surface areas ranging up to 500 m² g^-1. It is demonstrated this amorphous material is an excellent adsorbent using VOC uptake (acetaldehyde, toluene) experiments. Second, crystallization was induced by ultrasonication in a reduced reaction volume to raise delivered power density. XRD and SAED showed progressive formation of anatase, while N₂ sorption indicated good texture retention compared to thermal calcination. Sonication amplitude and time variation revealed a processing window wherein sufficiently crystalline photoactive materials can be obtained, while surface area remained high as well. The obtained materials were tested toward gas phase acetaldehyde degradation. The ultrasonicated material outperformed the thermally calcined analogue as well as commercial P25, highlighting the synergy between phase composition and accessible surface. These results showed ultrasound as a practical route to tailor the crystallinity-porosity balance in TiO₂ when morphology retention is critical, while also providing power density calibration for transferring conditions across reactor geometries.