Copper-silica nanocomposites tailored by the sol-gel route

Nanocomposite silica glassy layers (host) containing copper-based species (guest) were developed and tailored by the sol-gel route. The systems were obtained by starting from ethanolic solutions of tetraethoxysilane (Si(OC2H5)4, TEOS) and copper(II) acetate (Cu(CH3COO)2‚4H2O) in a single-step process and subsequently annealed ex situ under different atmospheres (air, nitrogen, or 4% H2 in N2 mixture). In particular, the attention was focused on the possibility of tailoring the system composition and microstructure through a proper choice of the treatment temperatures (100-900 °C), duration (1-5 h), and environment. The composite evolution under annealing was investigated by glancing incidence X-ray diffraction, optical absorption spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Pure copper-silica-based nanosystems, with guest composition ranging from CuO to Cu and controllable particle size and distribution, were obtained. The stepwise formation of CuO, Cu2O, and Cu nanoclusters in the silica network as a function of the adopted conditions is critically discussed, highlighting the crucial points involved in the design and development of composites endowed with peculiar chemicophysical properties.