ZnO (Ag-N) Nanorods Films Optimized for Photocatalytic Water Purification

Luis Sanchez,Miguel Sosa,Bryan Yauri,Clemente Luyo,Carlos Castillo,Juan M Rodriguez,Roberto Candal,Silvia Ponce,Willy Cruz

doi:10.3390/coatings9110767

Abstract

ZnO nanorods (NRs) films, nitrogen-doped (ZnO:N), and ZnO doped with nitrogen and decorated with silver nanostructures (ZnO:N-Ag) NRs films were vertically supported on undoped and N doped ZnO seed layers by a wet chemical method. The obtained films were characterized structurally by X-ray diffraction. Morphological and elemental analysis was performed by scanning electron microscopy, including an energy dispersive X-ray spectroscopy facility and their optical properties by Ultraviolet-Visible Spectroscopy. Analysis performed in the NRs films showed that the nitrogen content in the seed layer strongly affected their structure and morphology. The mean diameter of ZnO NRs ranged from 70 to 190 nm. As the nitrogen content in the seed layer increased, the mean diameter of ZnO:N NRs increased from 132 to 250 nm and the diameter dispersion decreased. This diameter increase occurs simultaneously with the incorporation of nitrogen into the ZnO crystal lattice and the increase in the volume of the unit cell, calculated using the X-ray diffraction patterns and confirmed by a slight shift in the XRD angle. The diffractograms indicated that the NRs have a hexagonal wurtzite structure, with preferential growth direction along the c axis. The SEM images confirmed the presence of metallic silver in the form of nanoparticles dispersed on the NRs films. Finally, the degradation of methyl orange (MO) in an aqueous solution was studied by UV-vis irradiation of NRs films contained in the bulk of aqueous MO solutions. We found a significant enhancement of the photocatalytic degradation efficiency, with ZnO:N-Ag NRs film being more efficient than ZnO:N NRs film, and the latter better than the ZnO NRs film.

Highlights

The use of nanostructured semiconductors for photocatalysis has attracted significant attention due to their potential applications for water and air decontamination [1,2,3]
The diameter, density, and the thickness of the NR films displayed a clear trend with the amount of N at the solution used to prepare the seed layers
The micrographs show that zinc oxide (ZnO) NRs grown onto an undoped seed layer were thinner, more dispersed, and worse oriented than ZnO:N NRs grown onto N-doped ZnO seed layers

Summary

Introduction

The use of nanostructured semiconductors for photocatalysis has attracted significant attention due to their potential applications for water and air decontamination [1,2,3]. Using nonmetals as a carbon, nitrogen, and sulfur results in a modification of the conduction band to more negative potentials, narrowing the optical bandgap, i.e. enlarging the absorption to lower energies of the solar spectra [18,19,20,21]. Photocatalytic efficiency of ZnO NRs can be further increased by the formation of heterostructured photocatalysts by associating ZnO and noble metal particles. This effect is due to the well-known electron collector capacity of metal nanoparticles, that improve charge carriers separation decreasing, the recombination [24,25]. It has recently been reported that ZnO doped with silver nanoparticles improves the electron transfer process and photochemical stability, making them a better photocatalyst [26,27,28]

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