Obtaining electrostatically bound CdS-SiO2 aggregates from electrophoretic concentrates of CdS nanoparticles

Abstract

Nonaqueous electrophoresis reveals that the electrokinetic potential of CdS nanoparticles increases slightly (85-120 mV) along with the concentration (0-5 × 10 -3 M) of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in n-decane, while negatively charged SiO 2 particles acquire positive charge (switching from -75 up to +135 mV). The energies of interparticle interactions in CdS-CdS and CdS-SiO 2 systems are calculated from these parameters and the literature values of the Hamaker constants according to the Deryaguin-Landau-Verwey-Overbeek (DLVO) theory. It is concluded that the presence of a minimum (2.5 k B T) on the potential dependences of the CdS-SiO 2 system indicates the formation of CdS-SiO 2 aggregates electrostatically bound by heterocoagulation at low concentrations of AOT. The luminescent properties of the obtained ultrafine CdS-SiO 2 powders depend on the CdS content. INTRODUCTIONNanoparticles of metal chalcogenides (quantum dots) are of interest in many areas of nanochemistry [1]. When transplanting quantum dots into different (flat, spherical, porous) surfaces of metals [2], oxides [3] and carbon nanotubes [4], structures with new properties, are formed that can be used in a variety of high-tech applications. These include photovoltaic converters of solar energy [5], light-emitting elements [6], improved luminescence in sensor devices [7], and many others.The most widespread chemical methods for applying coatings of quantum dots are growing nanoparticles directly on a surface via chemical deposition (Chemical Bath Deposition, or CBD) and chemical coating via the layered adsorption of ions (Successive Ionic layer Adsorption and Reaction, or Silar) [8]. In the latter, the powder or substrate are placed in a solution of one of the reactants and then washed and placed in a solution with a second reagent. A serious drawback of this technique is the formation of a huge number of nanoparticle agglomerates that can degrade the useful properties of the obtained structural compositions. In photovoltaics for example, the recombination of electron-hole pairs occurs in agglomerates of the nanoparticles of CdS (CdSe) wide-bandgap semiconductors. This reduces the photocurrent in photo-