Selective adsorption–deposition of gold nanoparticles onto monodispersed hydrothermal carbon spherules: a reduction–deposition coupled mechanism

Abstract

Hydrothermal carbon spherules (HCSs) can be loaded with a variety of metal nanoparticles for various applications. In this work, three types of HCSs were prepared from saccharides (mono-, di- and poly-saccharides) by a modified hydrothermal method using glucose, sucrose and starch as sources. Au nanoparticles can be deposited onto the HCSs through a regular adsorption process. For comparison, the HCSs made from mono-saccharide glucose (HCSs-M) have a higher adsorption capacity for Au(III) from aqueous acidic chloride media. The adsorption behaviors for AuCl₄⁻ by HCSs-M were systematically investigated. HCSs-M shows a high selectivity for Au(III) towards Pd(II), Pt(VI), Rh(III) and some relevant base metals such as Fe(III), Co(II), Cu(II) and Ni(II). An extra reductant glycine can not only significantly improve the adsorption capacities and selectivity, but also accelerate the adsorption rate. The Langmuir isotherm model and the 2nd-order kinetics model can properly describe the adsorption behaviors of AuCl₄⁻. The adsorption mechanism of Au(III) by HCSs has been confirmed by XPS, XRD, TG, FTIR, SEM and TEM techniques, which demonstrate that AuCl₄⁻ deposited onto the HCSs has been reduced to Au⁰. On the basis of this phenomenon, a reduction–deposition coupled mechanism has been proposed. The current research illustrates the prospect for HCSs to be used as effective adsorbents for the selective adsorption separation of Au(III) from chloride media. It also demonstrates the possibility to integrate the selective recovery of gold from complex industrial waste streams and the fabrication of functional carbon materials through loading with gold nanoparticles.