Immobilization of Photocatalytic ZnO Nanocaps on Planar and Curved Surfaces for the Photodegradation of Organic Contaminants in Water

Nanoparticles are widely used as photocatalysts to effectively remove organic contaminants in water. However, additional separation steps are needed to recycle the dispersed photocatalysts from the treated water. This study demonstrates a simple strategy to fabricate surface-bound catalytic nanoparticles for water treatment. In our approach, catalytic zinc oxide (ZnO) nanocaps were immobilized on planar and curved substrates by in-situ fabrication from surface nanodroplets using a newly established solvent exchange process (SEP). The size distribution, surface coverage, and porosity of the nanocaps can be controlled by changing the solution composition during the SEP on both planar and curved surfaces. The photocatalytic performance of ZnO nanocaps under solar light was evaluated by comparing the degradation of three model compounds (methyl orange (MO) and two antibiotics norfloxacin (NFX) and sulfamethoxazole (SMX)). Nonporous ZnO nanocaps immobilized on a curved glass surface showed good performance for contaminants degradation, achieving over 90% removal of MO, NFX and SMX in 20 h under solar irradiation of 1 sun intensity, compared to the negligible degradation percentages (except for NFX) without nanocaps. Our results suggest that nonporous ZnO nanocaps immobilized on the inner surface of a transparent container are a promising and sustainable approach for solar-driven water treatment.