It is well known that materials based on zinc oxide are one of the most effective among oxide photocatalysts and bactericidal solids [1-5]. ZnO-based heterostructural composites containing various semiconductor and metal nanoparticles, are especially effective [5-10].
Cu-containing ZnO-Al2O3 nanocomposites demonstrate high photocatalytic and bactericidal properties and are considered also as effective catalyst for reforming CO2 to different organic compounds and potential materials for sensors [11-14]. It was established in [12] that ZnO nanomaterials doped with copper exhibit good antibacterial activity, which increases with increasing level of copper doping.
Different methods have been applied for the preparation of Cu-containing ZnO nanomaterials: glucothermal method [7], co-precipitation [11,15], polymer-salt [16], etc. Polymer-salt method based on the application of initial solutions containing metals salts and soluble organic polymers is widely used for the preparation of different materials [9,10,16-20].
The generation of reactive oxygen species (singlet oxygen [17,21-23], superoxide radicals [24,25], hydroxyl radical [21,24]) plays the key role in photocatalytic processes and materials bactericidal activity [21-24]. Characteristics of exciting radiation, electronic structure, and morphology of materials affect the efficiency of their photogeneration [21–24, 26, 27].
The highly dispersive materials, consisting of small nanoparticles with high surface area, show higher photocatalytic properties and antibacterial activity compared with macroscopic ones [27]. The decrease of the size of photoactive particles and the optimization of materials morphology are used for the enhancement of their photocatalytic and bactericidal efficiency [22,23,28-31]. It is known [22, 23, 32] that the sizes of crystals in two-component oxide composites are smaller than in one-component analogs obtained by the same method under similar technological conditions. This phenomenon has been used to reduce the size of crystals and improve the characteristics of photoactive materials [22, 23].
In [17,22,23] this approach was used for the fabrication of highly dispersive photoactive materials ZnO-Al2O3 [17], ZnO-SnO2 [22] and ZnO-MgO-Ag [23]. The temperature-time schemes of technological processes used in [17,22,23] provide the simultaneous formation of different crystals (ZnO+γAl2O3 [17], ZnO+SnO2 [22] and ZnO+MgO [23]) without their chemical interaction.
In this work, we used a higher temperature for the formation of ZnO-based composites to obtain photoactive materials consisting of a mixture of close-packed small hexagonal ZnO crystals and cubic ZnAl2O4 crystals. The simultaneous formation of different crystals prohibits their growth and the aggregation and provides the formation of the material structure consisting of small particles with high specific surface area.
Photocatalytic and bactericidal properties of ZnO are well-known [28-30,33,34]. Also, the application of ZnAl2O4 nanoparticles as photocatalytic material was studied in [4-7,35-40]. The literature data about ZnAl2O4 band gap value vary from ~ 3,9 eV to more than 6.0 eV [9, 41-43]. Cu additions can improve photocatalytic characteristics of ZnAl2O4 [11].
Solid-phase synthesis of ZnAl2O4 is high-temperature (1300°C) technological process [44,45]. The application of liquid-phase methods such as sol-gel [40,46,47] and hydrothermal process [48] allows decreasing the synthesis temperature.
The aim of this work was the low-temperature synthesis of Cu-doped ZnO-ZnAl2O4 nanocomposites and the study of their structure, luminescent and bactericidal properties, and the ability to singlet oxygen photogeneration.