Optical Properties of ZnO Nanoparticles on the Porous Structure of Mordenites and ZSM-5

Abstract

ZnO nanoparticles ranging from 2 to 10 nm were grown on ZSM-5 and mordenite zeolite hosts with different SiO2/Al2O3 molar ratios (MR). Formation of ZnO nanoparticles in the samples was confirmed by TEM. XRD and nitrogen adsorption measurements revealed that the zeolite structure is not destroyed. Surface Zn concentration was calculated from XPS data. ZnO nanoparticles in the zeolite matrix were studied by UV-Vis, diffuse reflectance and cathodoluminescence (CL) spectroscopies. CL revealed three different emissions from ZnO nanoparticles, approximately 3.1, 2.8 and 2.5 eV. The ZnO band-edge emission was associated with blue defects-related and oxygen vacancies emissions. The generation of the point defects at the interface explains the presence of this blue band.

Inception and Trapping of ZnO Nanoparticles within Desilicated Mordenite and ZSM‐5 Zeolites

“…1021.2-1022.5 eV. [27]. Bulk ZnO XPS spectra (Figure 3, curve 1) display an intense peak at 1022.5 eV in agreement with Ref.…”

“…Afterward, the exchanged zeolites were treated with 0.01 N aqueous NaOH over 7 h while maintaining a pH of 9.0. This pH level was kept constant throughout the reaction by means of a dropwise addition of diluted NaOH aqueous solution; any variation from this value was quickly addressed in order to retain the lowest Zn(OH) 2 pH solubility value [27]. Subsequently, the samples were filtered and repeatedly washed with an excess of de-ionized water.…”

“…columns S1 and S2) that is observed after the calcination process generally increases due to the thermal diffusion of Zn atoms from the bulk. Moreover, individual ZnO nanoparticles can also make their way to the external surface of the zeolite crystals [27,28]. ZnO surface particles can be clearly identified by TEM as rods (Figures 2b -2d) and their size is estimated to lie between 2 and 10 nm (see Figures 2a and 2c).…”

“…The secondary volume filling [26] of the A channels in ZSM-5 is equivalent to the accumulation of an adsorbed layer of about one or two molecular N 2 diameters. In our previous studies [27], ZnO nanoparticles could be confined within zeolite matrices; the optical properties of the resultant nanocomposites could be correlated with the particle size and point defects that exist at the ZnO/zeolite interface. Another study [20] has shown that the narrow, straight channels of the H-ZSM-5 zeolite allow only a small amount of ZnO clusters to be introduced into them; furthermore, microparticles (instead of nanoparticles) of ZnO are located on the external surface rather than in the internal pores of H-ZSM-5.…”

Mordenite-Supported Ag+-Cu2+-Zn2+ Trimetallic System: A Variety of Nanospecies Obtained via Thermal Reduction in Hydrogen Followed by Cooling in an Air or Hydrogen Atmosphere

“…Undoubtedly, the preparation of the nano-dispersed particles of semiconductor zinc oxide is of considerable interest for the creation of photocatalysts [46,47] or compounds with oligodynamic properties [48,49]. There is an extensive range of methods for such syntheses; for example, the preprecipitation of zinc hydroxide via treatment in alkaline solutions with a controlled pH, followed by calcination to prepare ZnO [50,51]. Zinc ions can be reduced to a metallic state by reduction treatment at temperatures above 550 °C [52].…”