Synthesis of nitrogen-doped ZnO by sol-gel method: characterization and its application on visible photocatalytic degradation of 2,4-D and picloram herbicides.

In this work, nitrogen-doped ZnO material was synthesized by the sol-gel method using zinc acetate as the precursor and urea as the nitrogen source (15, 20, 25 and 30% wt.). For comparative purposes, bare ZnO was also prepared. The influence of N doping on structural, morphological, optical and photocatalytic properties was investigated. The synthesized catalysts were characterized by XRD, SEM-EDS, diffuse reflectance UV-Vis spectroscopy, BET and XPS analysis. The photocatalytic activity of N-doped ZnO catalysts was evaluated during the degradation of a mixture of herbicides (2,4-D and picloram) under visible radiation ≥400 nm. The photo-absorption wavelength range of the N-doped ZnO samples was shifted to longer wavelength compared to those of the unmodified ZnO. Among different amounts of dopant agent, the 30% N-doped ZnO material showed higher visible-light activity compared with pure ZnO. Several degradation by-products were identified by using HPLC and ESI-MS/MS. The enhancement of visible photocatalytic activity of the N-doped ZnO semiconductor could be mainly due to their capability in reducing the electron-hole pair recombination.

Optical properties of ZnO nanoparticles on the porous structure of mordenites and ZSM-5.

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.

Observation of sulfur on the surface of giant aurothiol nanoclusters.

We report the study of aurothiol nanoclusters using high-resolution electron microscopy, energy loss spectroscopy, X-ray photoelectron spectroscopy, Auger spectroscopy, and microscopy. It is concluded that the sulfur atoms are located on the surface of the gold nanoparticles in both (100) and (111) microfacets. The X-ray photoelectron spectroscopy data show that there is a Au-Au bond as well as a Au-S bond. Auger depth profile measurements made by sputtering of the nanoparticles corroborates that the sulfur is located on the surface of the nanoparticle. Quantitative Auger analysis indicates a ratio Au/S between approximately 1.79 and 1.98.