Visible Light Photocatalytic MoO3-Based Nanomaterials Synthesis, the Effect of Polymer Coatings on Their Photocatalytic Activity and Dissolution, and Their Applications in Water Treatment

Water reuse is becoming increasingly important as water sources are being depleted or becoming progressively contaminated. Photocatalytic metal oxide semiconductors such as MoO3 have shown much promise in water decontamination as they can generate reactive oxygen species (ROS) that degrade pollutants. MoO3 is an environmentally friendly, low-cost, visible light photocatalyst that has gained much popularity in research due to its effectiveness. Furthermore, MoO3 morphology and surface chemistry are easily controlled during synthesis. In this work, MoO3-based photocatalysts were studied to determine their efficacy in water treatment and to discover methods to improve their properties. MoO3 photocatalytic activity was shown to improve as the number of oxygen vacancies was increased. Even though MoO3 photocatalysts demonstrated high contaminant removal, their stability in water is poor. High dissolution was observed in a wide pH range and particle aggregation was elevated in the presence of inorganic and organic compounds, resulting in diminished photocatalytic activity. However, material dissolution was significantly reduced in the presence of inorganic and organic matter, indicating that coatings may be beneficial in improving the utility of the photocatalyst for water treatment. Hence, conductive polymers such as polypyrrole (PPy) and polyaniline (PANI) were studied as coatings for magnetic MoO3 to determine their effect on material dissolution and photocatalytic activity. In addition, to provide insight on the effects of the base nanomaterial on the polymerization of PPy and PANI, the polymerization kinetics of PPy and PANI on two different base MoO3 nanomaterials were investigated. It was determined that a higher amount of oxygen vacancies in the MoO3 base nanomaterials resulted in smaller polymer chains and faster polymerization on top of the nanomaterials. In addition, both coatings significantly reduced material dissolution while improving photocatalytic activity. A magnetic core was also added to the base material to facilitate photocatalyst removal from water. The PANI-coated magnetic MoO3 was further studied, demonstrating high tetracycline degradation by ROS produced via the oxidation of water by photogenerated holes on the surface of PANI after electron excitation using visible light. This work demonstrates that use of conductive polymer coatings is an excellent method in improving photocatalytic properties of nanomaterials.