The sonophotocatalytic degradation of pharmaceuticals in water by MnOₓ-TiO₂ systems with tuned band-gaps

Advanced oxidation processes (AOPs) are technologies to degrade organic pollutants to carbon dioxide and water with an eco-friendly approach to form reactive hydroxyl radicals. Photocatalysis is an AOP whereby TiO₂ is the most adopted photocatalyst. However, TiO₂ features a wide (3.2 eV) and fast electron-hole recombination. When Mn is embedded in TiO₂, it shifts the absorption wavelength towards the visible region of light, making it active for natural light applications. We present a systematic study of how the textural and optical properties of Mn-doped TiO₂ vary with ultrasound applied during synthesis. We varied ultrasound power, pulse length, and power density (by changing the amount of solvent). Ultrasound produced mesoporous MnOₓ-TiO₂ powders with a higher surface area (101-158 m(2) g(-1)), pore volume (0-13-0.29 cc g(-1)), and smaller particle size (4-10 mu m) than those obtained with a conventional sol-gel method (48-129 m(2) g(-1), 0.14-0.21 cc g(-1), 181 mu m, respectively). Surprisingly, the catalysts obtained with ultrasound had a content of brookite that was at least 28%, while the traditional sol-gel samples only had 7%. The samples synthesized with ultrasound had a wider distribution of the band-gaps, in the 1.6-1.91 eV range, while traditional ones ranged from 1.72 eV to 1.8 eV. We tested activity in the sonophotocatalytic degradation of two model pollutants (amoxicillin and acetaminophen). The catalysts synthesized with ultrasound were up to 50% more active than the traditional samples.

Mots clés

ultrasound; photocatalysis; sol-gel; tio2; mn oxides; band-gap; ultrasound assisted synthesis; tio2 nano-particles; photocatalytic activity; mesoporous tio2; sonochemical synthesis; removal; acetaminophen; adsorption; acid; nanoparticles