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

• Published in: Chemistry : a European journal Vol. 21; no. 52; pp. 19136 - 19141
• Main Authors: Sridharan, Kishore, Jang, Eunyong, Park, Young Min, Park, Tae Joo
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 21-12-2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Atomic layer epitaxy; atomic-layer-deposition; Catalytic activity; Chemistry; Coatings; core-shell structures; Electronics industry; Film growth; Irradiation; Manufacturing industry; Nanoparticles; Photocatalysis; photochemistry; Photodegradation; Rhodamine; rotary ALD; Semiconductors; Thin films; Titanium dioxide; Ultraviolet radiation; Zinc oxide; core-shell structures; atomic-layer-deposition; nanoparticles; rotary ALD; photochemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201502876

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.
Rotary coating: Presynthesized ZnO nanoparticles were coated with TiO2 by atomic‐layer deposition in a modified rotary reactor. Hierarchically structured ZnO nanoparticles exhibited higher photocatalytic activity than benchmark P25 TiO2 nanoparticles, but were photocorroded during cyclic usage. Ultrathin ALD TiO2 layers effectively inhibited photocorrosion and enabled ZnO nanoparticles to retain their photocatalytic activity.