## 4 Discussion  
The conducted studies focused on evaluating the photocatalytic activity of Ti(IV)-oxo complexes stabilized with \(\alpha\)-hydroxycarboxylic ligands, which were incorporated into a PMMA matrix. The compounds studied included [Ti\({}_{3}\)O\({}^{3}\)Pr\({}_{20}\)(man)\({}_{4}\)] (**1**), [Ti\({}_{4}\)O(O\({}^{3}\)Pr)\({}_{10}\)(O\({}_{3}\)C\({}_{14}\)H\({}_{8}\))\({}_{2}\)] (**2**), and [Ti\({}_{6}\)O\({}_{4}\)(O\({}^{3}\)Pr)\({}_{2}\)(O\({}_{3}\)C\({}_{14}\)H\({}_{8}\))\({}_{4}\)(O\({}_{2}\)CEt)\({}_{6}\)] (**3**), which had been structurally and spectroscopically characterized in our earlier research [31,32]. Additionally, composites containing K[Ru(Hedta)Cl].2H\({}_{2}\)O (**4**) and [Ru(pic)\({}_{3}\)].H\({}_{2}\)O (**5**) were investigated. Figure 9: Recycling MB decolorization tests of composite materials PMMA + Comp. 20 wt.% (Comp. = (**1**), (**2**), (**3**), (**4**), and (**5**)) irradiated with visible light. These Ru(III) complexes were synthesized via reactions of aququencholorouthenate(III) hydrate or ruthenium(III) chloride with EDTA or picolinic acid [38,64]. One of the aims of this research was to determine the possibility for the fabrication of surface-active composite coatings of the PMMA + Comp. type (Comp. = TOCs or Ru(III) complexes). The formation of such systems was crucial to protecting the structure of the studied compounds from hydrolysis or dissolution processes and minimizing nanograin aggregation. It is noteworthy that previous studies on the photocatalytic activity of TOCs primarily involved powdered forms. Thus, a significant stage of the research was confirming the structure of complexes **(1)**-**(5)** after their incorporation into the PMMA matrix. A comparison of the Raman spectra for complexes **(1)**-**(5)** and the PMMA + **(1)**-**(5)** composites revealed that embedding these complexes into the PMMA matrix did not induce significant structural changes. For multinuclear oxo-Ti(IV) complexes **(1)**-**(3)**, the stability of their structure within the composite was further confirmed through XAS studies. In the initial stage of the study, we aimed to determine how the introduction of Ti(IV) or Ru(III) complexes into a polymer matrix influences the adsorption of organic dyes. Most of the insights into the sorption properties of Ti(IV) and Ru(III) compounds come from studies on metal-organic frameworks (MOFs) [65, 66, 67, 68, 69, 70], which are valued for their high porosity, structural diversity, and highly active dye adsorption sites [71, 72, 73]. The amount of dye adsorbed depends on the dye's structure and is influenced by the electron density of the adsorbents [74]. For example, MB and CV molecules are smaller than RhB, allowing more of them to interact with TOCs or Ru(III) complexes. In our previous work, we demonstrated that introducing an additional ligand into the structure of compound **(3)** increases the electron density due to chelate rings and free carboxyl groups [31]. In contrast, compound **(2)** contains significantly fewer electron-dense areas. We hypothesize that electron-dense regions attract dye molecules, as the positively charged nitrogen in the dye structure is generally inclined to interact with electron-rich surface groups [75]. Molecular electrostatic maps of mandelic acid suggest that the hydroxyl group is most susceptible to nucleophilic attack [76,77]. However, in compound **(1)**, this hydroxyl group is coordinated, potentially reducing the electron density. For Ru(III) complexes containing EDTA and picolinate ligands, the highest electron density is expected in the C=O groups [78,79]. This effect aligns with studies on EDTA-containing copper complexes, where the C=O groups exhibit high electronegativity, while the rest of the molecule remains neutral [78]. The reduced adsorption efficiency of Ru(III) complexes, especially compared to titanium compounds, such as **(3)**, may be attributed to their smaller size, which limits the electron-dense surface area available for interactions with dye molecules.