Photocatalytic ZnO Foams for Micropollutant Degradation

Photocatalytic foams can concomitantly overcome the disadvantages of slurry and immobilized photocatalysts in water treatment. However, foams have, so far, been restricted to nanoparticles grafting onto inert foam substrates, with the consequent risk of nanoparticle release into the environment. In this work, self-supporting, highly porous photocatalytic zinc oxide (ZnO) foams are produced using a combination of liquid templating and sintering for the first time. Systematic changes in sintering times and temperature affect the foams’ morphology and structure, in turn controlling their photocatalytic activity and stability. Sintering at 900 °C and decreasing sintering times from 20 to 6 h lead to a doubling in surface-area-to-volume ratio and a 30% increase in pore diameter, resulting in a near doubling of the overall quantum yield and degradation kinetics. However, photocorrosion and Zn leaching increase markedly for the shortest sintering time. Optimal sintering conditions at 900 °C for 12 h yield foams capable of effectively degrading the model micropollutant carbamazepine under UV irradiation with high stability, showing no performance decrease over five irradiation cycles corresponding to 20 h of use. This study paves the way to producing self-supporting, highly stable photocatalytic foams for the removal of organic micropollutants in water treatment.