Photocatalytic degradation of methylene blue at nanostructured ZnO thin films

Kulis-Kapuscinska A, Kwoka M, Borysiewicz MA, Wojciechowski T, Licciardello N, Sgarzi M, Cuniberti G (2023)

Publication Type: Journal article

Publication year: 2023

Journal

Nanotechnology Institute of Physics: Hybrid Open Access

Book Volume: 34

Article Number: 155702

Journal Issue: 15

DOI: 10.1088/1361-6528/aca910

Abstract

The photocatalytic degradation of the wastewater dye pollutant methylene blue (MB) at ZnO nanostructured porous thin films, deposited by direct current reactive magnetron sputtering on Si substrates, was studied. It was observed that over 4 photocatalytic cycles (0.3 mg · l−1 MB solution, 540 minUV irradiation), the rate constant k of MB degradation decreased by ∼50%, varying in the range (1.54 ÷ 0.78) · 10-9 (mol·l−1·min−1). For a deeper analysis of the photodegradation mechanism, detailed information on the nanostructured ZnO surface morphology and local surface and subsurface chemistry (nonstoichiometry) were obtained by using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) as complementary analytical methods. The SEM studies revealed that at the surface of the nanostructured ZnO thin films a coral reef structure containing polycrystalline coral dendrites is present, and that, after the photocatalytic experiments, the sizes of individual crystallites increased, varying in the range 43 ÷ 76 nm for the longer axis, and in the range 28 ÷ 58 nm for the shorter axis. In turn, the XPS studies showed a slight non-stoichiometry, mainly defined by the relative [O]/[Zn] concentration of ca. 1.4, whereas [C]/[Zn] was ca. 1.2, both before and after the photocatalytic experiments. This phenomenon was directly related to the presence of superficial ZnO lattice oxygen atoms that can participate in the oxidation of the adsorbed MB molecules, as well as to the presence of surface hydroxyl groups acting as hole-acceptors to produce OH· radicals, which can be responsible for the generation of superoxide ions. In addition, after experiments, the XPS measurements revealed the presence of carboxyl and carbonyl functional groups, ascribable to the oxidation by-products formed during the photodegradation of MB.

Involved external institutions

Silesian University of Technology Gliwice PL Poland (PL) Institute Of Microelectronics And Photonics (IMIF) PL Poland (PL) Polska Akademia Nauk (PAN) / Polish Academy of Sciences PL Poland (PL) Technische Universität Dresden DE Germany (DE) Università Ca’ Foscari IT Italy (IT)

How to cite

APA:

Kulis-Kapuscinska, A., Kwoka, M., Borysiewicz, M.A., Wojciechowski, T., Licciardello, N., Sgarzi, M., & Cuniberti, G. (2023). Photocatalytic degradation of methylene blue at nanostructured ZnO thin films. Nanotechnology, 34(15). https://dx.doi.org/10.1088/1361-6528/aca910

MLA:

Kulis-Kapuscinska, Anna, et al. "Photocatalytic degradation of methylene blue at nanostructured ZnO thin films." Nanotechnology 34.15 (2023).

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