## 1 Introduction  
Nowadays, accessible clean water and energy resources are among the highest priorities for sustainable economic growth and societal wellbeing. Water scarcity is a growing worldwide problem, so it is imperative that wastewater is treated and re-used in industrial processes, irrigation, and feeding to livestock, thus saving potable water for drinking. Research activities focus on the synthesis of new materials for use in energy-efficient processes for water treatment by using doped metal oxides with a reduced bandgap, which allows photocatalysis in the visible region of the electromagnetic spectrum [1; 2]. Different types of pollutants such as pharmaceuticals, dyes, pesticides, etc., are widespread and may interact with the environment through different pathways. In the present work, as relevant environmental pollutants, methylene blue (MB) dye and rhodamine B (RhB) dye were selected as complex compounds for decomposition from an aqueous medium because of their often-frequent occurrence in the environment. MB and RhB are widely utilized for industrial production purposes such as dyeing and printing on textile, leathers, papers, and also on plastics [3; 4; 5]. Organic pollutants are entering the water cycle through wastewater release into the environment. Very toxic and cancerogenic residual dyes and their metabolites already have a strong impact on ecosystems. Moreover, these organic pollutants can be very harmful to living organisms, especially if they enter the food chain [6; 7; 8; 9; 10]. Thus, the removal of them from water is a huge challenge and an emergency assignment. Conventional wastewater treatment plants (WWTP) are not adequately designed for the removal of dyes, their metabolites, or transformation products. Hence, the removal of dyes and their degradation products from industrial wastewater before discharging into the environment requires necessary treatment [11; 12]. To degrade the mentioned harmful compounds present in the environment, researchers are globally looking for an effective approach such as Advanced oxidation processes (AOPs). Nowadays, the AOPs have received considerable attention as alternative wastewater treatment processes, which may be implemented in conventional wastewater treatment processes to ameliorate their removal efficiency. The photocatalytic oxidation process, especially heterogeneous photocatalysis, is one of the AOPs that is increasingly being explored due to its relatively efficient degradation and environmentally benign impact [6; 13; 14; 15; 16]. This technology can be a clean, green, and sustainable alternative to conventional wastewater treatment technologies [17; 18]. Currently, there are different materials that can be used as heterogeneous photocatalysts, but titanium dioxide (TiO\({}_{2}\)) arises like the one with widespread use. This semiconductor material presents extraordinary properties for degradation of organic matter dissolved in water; its low environmental impact, cheapness, high chemical and thermal stability, and pollution-free process to remove low concentration pollutants, as well as biocompatibility, are relevant features for its application [2; 19; 20; 21]. TiO\({}_{2}\) photocatalysts are usually very active under ultraviolet (UV) irradiation when the wavelength is lower than 387 nm. The major pitfalls in the practical application of heterogeneous TiO\({}_{2}\) based semiconductor photocatalysis are the wide bandgap energy and quick recombination of the photogenerated electron-hole pairs [22; 23]. Therefore, the application of TiO\({}_{2}\) as a photocatalyst shows low efficiencies in the decomposition of effluent organic compounds under solar light. In global solar spectra that reach the Earth's surface, UV part amounts around 3-5%, while almost 45% is visible light [9; 11]. New photocatalysts are being designed in the form of nanocomposite materials to overcome their current limitations assigned to the fact of being mostly active only under UV radiation [22; 23; 24; 25].