Synthesis and comparative photocatalytic activity of CuO layers on SiO$_{2}$ substrates

Using the thermodynamic and kinetic approaches, it was found that Cu(NH$_{3}$)$^{2+}_{4 aq}$ complex predominating at 23$^{\circ}$C spontaneously decomposes at elevated temperatures, forming CuO precipitate in a bulk solution and a layer (CuO||SiO$_{2}$) on the surface of silica glass. The rates of these heterogeneous processes are fairly well described by the 1st-order reaction of decay of the Cu(NH$_{3}$)$^{2+}_{4 aq}$ complex. The formation of the CuO precipitate and layer is a two-step kinetic process. The rate of precipitate formation dominates above 65$^{\circ}$C while the rate of the layer formation prevails below this value. The CuO$\parallel$SiO$_{2}$ material synthesized below 65 possesses an optical bandgap of (1.25 0.05) eV, which is smaller compared to the crystals of commercial CuO. The CuO||SiO$_{2}$ material displays a photocatalytic activity in the reaction of UV-decomposition of benzoquinone-hydroquinone. It was discovered that the photocatalytic activity depends on the thickness of the photocatalyst layer.