Effect of Post-Synthesis Treatments on the Properties of ZnS Nanoparticles: An Experimental and Computational Study

Elena Balantseva,Anna Maria Ferrari,Gloria Berlier,Bruno Camino

doi:10.2516/ogst/2015010

Abstract

This work deals with the characterization of ZnS NanoParticles (NP), prepared by precipitation employing thioacetamide as sulfur source at different reaction time length. The attention is focused on the modification induced on structural, surface and electronic properties of ZnS NP by post-synthesis treatments. These were aimed at removing from the samples surface adsorbed reactants, by washing or thermal treatments, both in air or vacuum. The effect of these parameters is followed by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform InfraRed (FTIR), gas-volumetric and ThermoGravimetric Analysis (TGA). Moreover, the effect of nanostructuration on the semiconducting material band gap is evaluated by Diffuse Reflectance UV-Vis (DR UV-Vis) spectroscopy. Density Functional Theory (DFT) calculations have been employed to clarify the role of the adsorbed reactants on the surface stability and to assess the relationship between particle size and band gap value.

Highlights

Since the first discovery by Honda and Fujishima, photocatalyst hydrogen production has attracted strong consideration [1]
The significant reduction of this peak only for treatment at very high T (Fig. 4d) indicates an irreversible character of the adsorption, in agreement with the strong computed adsorption energy for 111-D. This finding suggests the presence in the ZnS NP of small extension of the (111) polar surface stabilized by the adsorption of foreign species from the synthesis solution. It is worth mentioning a recent report that combining Fourier Transform InfraRed (FTIR) observations and Density Functional Theory (DFT) calculations, has investigated the adsorption properties of CO molecules, used as a probe for acidic Lewis surface sites; this study has demonstrated that CO experienced only one type of sites belonging to the (110) surface [29]
ZnS NP photocatalysts were prepared by precipitation with TAA and acetate as sulfur and zinc sources, respectively, by modifying reaction time length

Summary

Introduction

Since the first discovery by Honda and Fujishima, photocatalyst hydrogen production has attracted strong consideration [1]. As an alternative ZnS can produce H2 effectively without noble metal co-catalyst, due to its high conduction band position, but the wide band gap (3.7 eV) implies that only ultraviolet radiation can be employed to produce electron/hole couples [10]. This is the reason why band gap engineering has been proposed to modify the electronic properties of ZnS and improve its visible light harvesting efficacy [11,12,13]

Methods

Results

Conclusion