Photocatalytic degradation of phenol in water under simulated sunlight by an ultrathin MgO coated Ag/TiO2 nanocomposite.

Phenol is one of the most widespread, toxic and recalcitrant compounds in water sources. Due to its persistent nature, conventional wastewater treatment methods are not effective to remove or degrade phenol from water. In this work, novel photocatalysts were developed to effectively degrade phenol under simulated sunlight. The catalysts were composed of one-dimensional titanium dioxide (TiO2) nanorods decorated with silver (Ag) nanoparticles, coated by an ultrathin magnesium oxide (MgO) overlayer through atomic layer deposition (ALD). Material properties of prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis diffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic performance of phenol degradation under simulated sunlight was evaluated and correlated with the material properties. The Ag nanoparticles promoted light absorption and transfer of photo-induced electron-hole pairs from within TiO2 nanorods to the catalyst surface. The ultrathin MgO overlayer with a sub-nanometer thickness did not hinder charge transfer to the surface, but rather, it further increased the light absorption and inhibited surface charge recombination through a surface passivation effect, promoting phenol degradation. The photocatalytic reaction mechanism was investigated by examining hydroxyl and superoxide radical production in the photocatalytic system. The results from this work demonstrated a new strategy for fabricating efficient solar-driven photocatalysts for the degradation of persistent water contaminants.