Role of Morphology in Phase-Engineered TiO₂ Nanostructures: Comparative Assessment of Anatase and Brookite for Emerging Aqueous Pollutant Degradation and NOx Abatement

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Abstract
This study investigates the synthesis of shape-controlled titanium dioxide (TiO₂) nanoparticles via a hydrothermal method, examining the influence of pH variation (8, 10, 12, and 14) and subsequent thermal treatments (200°C and 230°C) on phase transitions and morphological transformations. The resulting TiO₂ nanostructures—including nanorods, nanotubes, nanoflowers, elongated bipyramids, and irregular flower-like assemblies—undergo phase transitions from anatase to brookite. Their photocatalytic performance is assessed for aqueous pollutant degradation and NOx abatement. TiO₂ synthesized at lower pH (8-10), exhibiting anatase-phase nanotubular and elongated bipyramidal morphologies, achieves near-complete photodegradation of phenol, methomyl, and diclofenac in both Milli-Q and stormwater matrices. Conversely, brookite-rich TiO₂ phases, formed at higher pH (12-14), show limited liquid-phase activity but excel in NOx abatement, making them promising candidates for air purification applications. These findings highlight the pivotal role of phase composition and morphology in optimizing photocatalytic performance, offering a strategic approach for the scalable development of efficient TiO₂-based photocatalysts for environmental remediation.

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