Facile Preparation of ZnO/CNTs Nanocomposites via ALD for Photocatalysis Applications

Abstract

Vertically aligned carbon nanotubes (VA-CNTs) of 2.3 μm in height were produced by thermal chemical vapor deposition (TCVD) on Si/SiO 2 substrates. These carbon arrays were coated with zinc oxide (ZnO) via atomic layer deposition (ALD) technique. Conformal, uniform and very thin films (max. 26 nm) around the CNTs were obtained after 200 ALD cycles. The photocatalytic performance of these nanocomposite materials was tested in the degradation of rhodamine B, a harmful dye present in food and textile wastewaters. The optimal degradation performance is already obtained after 100 ALD cycles on [a] I. the precursors' materials separated during their reaction. [8] The cycle is repeated until a desired film thickness is obtained, usually of a few dozens of nanometers. Thus, this technique ensures precise film thickness control and excellent material coverage, even on 3D structures. Due to their unique combination of properties, the functionalization of the CNTs by ALD with a metal oxide semiconductor aiming photocatalytic applications is a quite challenging and actual research topic. For instance, Feng et al. [9] used nanocomposite CNT membranes containing TiO 2 and ZnO deposited by ALD to improve the photocatalytic Inês E. Oliveira is a PhD student of Science and Materials Engineering at the University of Aveiro in Portugal. Her research revolves mostly around the areas of carbon nanomaterials and photocatalysis. Currently, her doctoral research investigates the degradation of some organic pollutants from water using sunlight and carbon nanomaterials. She takes an approach that consists on the production of vertically aligned carbon nanotubes (CNTs) and coating with metal oxides semiconductors via atomic layer deposition (ALD). . His work focuses on catalysis and catalysed reactions, with thermal and photo activation, for environmental applications, energy and fine chemical synthesis. Published over 180 articles (h index of 42, over 4 800 citations), acted as supervisor of 12 PhD students and 6 Post-Doctoral fellows, in addition to many MSc students.

Impact of atomic layer deposited TiO2 on the photocatalytic efficiency of TiO2/w-VA-CNT nanocomposite materials

“…Additionally, these findings can be understood considering that the photocatalytic process is a photon assisted chemical reaction taking place at the material's surface, making it strongly affected by the exposed surface area, and the improved photocatalytic efficiency can be attributed to the synergistic effect between the metal oxides and carbon nanotubes, rather than its individual components. 20 In this context, the 200 ALD cycles were kept fixed while the deposition temperature was varied from 100 °C to 300 °C to evaluate the impact of the amorphous and crystalline nature of the TiO 2 films on the photocatalytic activity towards RhB degradation. Fig.…”

Water treatment based on atomically engineered materials: Atomic layer deposition and beyond

“…For instance, Oliveira et al fabricated ZnO ALD coatings on vertically aligned carbon nanotubes (CNTs). 115 Photogenerated electrons effectively migrated from the conduction band of ZnO to the CNTs, diminishing the recombination of charge carriers to some extent. Thus, the optimized 100-cycle ZnO ALD-coated CNT composites resulted in 77% RhB degradation after 7 h under UV irradiation, ca.…”

Si/SiO2/Al2O3 Supported Growth of CNT Forest for the Production of La/ZnO/CNT Photocatalyst for Hydrogen Production

“…The electrons become trapped in CNT structure and therefore do not spontaneously return to the valance band. Oliveira et al [7] revealed the better photocatalytic performance of ZnO/CNTs photocatalyst than the pristine ZnO probably due to a shift in the absorption light range. The photocatalytic activity can be further improved by combining rare-earth elements with ZnO/CNTs system.…”