## 1 Introduction  
All over the world today there is a shortage of clean water due to rapid population growth, environmental degradation, uncontrolled disposals from industrial enterprises, and the widespread introduction of chemical technologies in agriculture. Despite the widespread construction of modern treatment facilities, it is not possible to achieve complete wastewater treatment. This is due to the presence of difficult-to-oxidize organic pollutants, the most common of which are phenol-containing substances and antibiotics. Traditional treatment methods include mainly biological treatment and a number of physicochemical methods such as adsorption, ion exchange, and reverse osmosis. The disadvantages of these methods include the non-destructive nature of cleaning, high energy and operating costs, low efficiency, and the generation of large amounts of waste. In recent years, environmentally friendly and energy-efficient advanced oxidation technologies have been actively developed, among which photocatalysis (PC) occupies an important place [1,2]. An important advantage of PC is the possibility of oxidation at relatively low concentrations of pollutants [3], which is important for the mineralization of toxic organic pollutants with low maximum permissible concentrations. The efficiency of PC is determined by the efficiency of formation and separation of photo-charges. For a long time, the main photocatalyst produced on an industrial scale was titanium dioxide (TiO\({}_{2}\)) from Degussa (P-25) [4]. The disadvantage of TiO\({}_{2}\) is its significant band gap (Eg = 3.2 eV) and its maximum photocatalytic activity when irradiated with ultraviolet (UV) light. Ultraviolet radiation makes up only 5-7% of solar radiation. At the same time, visible radiation makes up about 45% and the search for photocatalysts active in the visible region is very relevant. A huge number of works are devoted to heterostructural and composite photocatalysts exhibiting activity in the visible region [5; 6; 7; 8; 9; 10]. Despite individual studies demonstrating the effectiveness of hybrid photocatalysts, the traditionally utilized TiO\({}_{2}\) still remains the most popular. This is due to the lack of economically accessible technology for mass production of hybrid photocatalysts. As an alternative to TiO\({}_{2}\), ZnO [11; 12], which is not inferior in efficiency and availability, has recently been actively studied. Despite the similarity of the band gap of ZnO (3.37 eV) with TiO\({}_{2}\) (3.2 eV), a distinctive feature of the band structure of ZnO is the presence of isolated energy levels in the band gap associated with point defects, mainly oxygen vacancies [13]. With a significant increase in the concentration of vacancies, photosensitivity can expand into the visible region of the spectrum. Dislocations are an additional source of levels in forbidden zones. The band structure is distorted around the dislocation core and a level is introduced closer to the center of the band gap. In n-type crystals, which include ZnO, dislocations can capture electrons and prevent their recombination. The highest concentration of defects is observed in crystals synthesized under conditions that are far from ideal: high saturation, unstable temperature gradient, and chaotic influx of atoms. Such conditions can be created using plasma synthesis of metal-oxide structures [14]. Plasma synthesis using gas-discharge plasma is not only energy-efficient but also has high productivity. Of greatest interest is the microwave (MW) discharge at atmospheric pressure, which has a much higher charge density and, consequently, greater reactivity compared to other discharges at the same power. In some types of atmospheric pressure discharges (corona, spark, and arc), plasma is \"contaminated\" by the material of internal discharge electrodes. This can be avoided for microwave discharges excited in chambers in the absence of direct contact with the metal electrodes, which is of fundamental importance in the generation of high-purity plasma.