Tae Joo Park

Silver Quantum Cluster (Ag9)-Grafted Graphitic Carbon Nitride Nanosheets for Photocatalytic Hydrogen Generation and Dye Degradation

We report the visible-light photocatalytic properties of a composite system consisting of silver quantum clusters [Ag9 (H2 MSA)7 ] (H2 MSA=mercaptosuccinic acid) embedded on graphitic carbon nitride nanosheets (AgQCs-GCN). The composites were prepared through a simple chemical route; their structural, chemical, morphological, and optical properties were characterized by using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, transmission electron microscopy, UV/Vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy. Embedment of [Ag9 (H2 MSA)7 ] on graphitic carbon nitride nanosheets (GCN) resulted in extended visible-light absorption through multiple single-electron transitions in Ag quantum clusters and an effective electronic structure for hydroxyl radical generation, which enabled increased activity in the photocatalytic degradation of methylene blue and methyl orange dye molecules compared with pristine GCN and silver nanoparticle-grafted GCN (AgNPs-GCN). Similarly, the amount of hydrogen generated by using AgQCs-GCN was 1.7 times higher than pristine GCN. However, the rate of hydrogen generated using AgQCs-GCN was slightly less than that of AgNPs-GCN because of surface hydroxyl radical formation. The plausible photocatalytic processes are discussed in detail.

Superior Photostability and Photocatalytic Activity of ZnO Nanoparticles Coated with Ultrathin TiO2 Layers through Atomic‐Layer Deposition

Atomic-layer deposition (ALD) is a thin-film growth technology that allows for conformal growth of thin films with atomic-level control over their thickness. Although ALD is successful in the semiconductor manufacturing industry, its feasibility for nanoparticle coating has been less explored. Herein, the ALD coating of TiO2 layers on ZnO nanoparticles by employing a specialized rotary reactor is demonstrated. The photocatalytic activity and photostability of ZnO nanoparticles coated with TiO2 layers by ALD and chemical methods were examined by the photodegradation of Rhodamine B dye under UV irradiation. Even though the photocatalytic activity of the presynthesized ZnO nanoparticles is higher than that of commercial P25 TiO2 nanoparticles, their activity tends to decline due to severe photocorrosion. The chemically synthesized TiO2 coating layer on ZnO resulted in severely declined photoactivity despite the improved photostability. However, ultrathin and conformal ALD TiO2 coatings (≈ 0.75-1.5 nm) on ZnO improved its photostability without degradation of photocatalytic activity. Surprisingly, the photostability is comparable to that of pure TiO2, and the photocatalytic activity to that of pure ZnO.

Deformation assisted fabrication of uniform spindle, tube and rod shaped nanoscale 3D TiO2 architectures and their photocatalytic activity

Fabrication of three-dimensional (3D) TiO2 nanoscale architectures with spindle, tube and rod shapes, by a novel deformation assisted approach is demonstrated. Plausible growth mechanisms are predicted based on morphological investigations. Improved photocatalytic reduction of Cr(VI) is observed using the fabricated nanostructures under visible light irradiation.