## 2 Materials and Methods
### Characterization Techniques  
The structural characterisation of the obtained nanoparticles was undertaken through X-ray diffraction (XRD). The equipment used was an INEL Equinox 3000 diffractometer, which works in reflection mode, and it is equipped with a curved multidetector. The wavelength used was the one characteristic of Co, K\(\alpha\) radiation (\(\lambda\) = 1.7903 A). The mean crystallite size was calculated with the Scherrer method [45]. The lattice parameter was calculated using Celref version 3 refinement software [46]. TEM images were obtained by scanning transmission electron microscopy (STEM) using a Hitachi HD2700 Electron Microscope (Hitachi, Tokyo, Japan). Absorption spectra were recorded using a JASCOV570 UV-VIS-NIR Spectrophotometer equipped with an absolute reflectivity measurement JASCO ARN-475 accessory. Luminescent characteristics of samples were evaluated based on emission spectra registered with a Wavell JASCO FP-6500 spectrofluorimeter, equipped with a PMT R928 photomultiplier (glass filter UG1--Reichmann Feinoptik, GER). Electron paramagnetic resonance (EPR) spectroscopy measurements of powder samples were carried out using a Bruker E-500 ELEXSYS spectrometer (Karlsruhe, Germany) at room temperature under identical conditions: The measurements were conducted at Xband (9.52 GHz) microwave power 2 mW, with a modulation frequency of 100 kHz. To determine the reactive oxygen species (ROS) generation, the EPR spectrometer coupled with the spin trapping probe technique was used. As the spin trapping reagent, DMPO was used. The nanoparticles (10 mg) were dispersed in DMSO (1 mL) and homogenized in an ultrasound bath (30 min) before use. DMPO of 0.2 mol/L concentration was added to the solution. The obtained solution was subjected to visible irradiation for 25 min and immediately before measurement transferred into the quartz flat cell, optimized for liquid measurements. The photodegradation of Rhodamine B (RhB) was carried out in a Laboratory-Visible-Reactor system using a 400 W halogen lamp (Osram) [47]. The catalyst (5 mg) was suspended in an aqueous solution of RhB (1.0 \(\times\) 10\({}^{-5}\) mol\(\cdot\)L\({}^{-1}\), 10 mL) and then the mixture was stirred in the dark to achieve the adsorption equilibrium on the catalyst surface. Each degradation experiment was continuously conducted for 6 h. The mixture (3.5 mL) was withdrawn for analysis every 60 min. After separating the catalyst from the suspensions by centrifugation, the solution was analysed by the UV-Vis spectrophotometer by recording the maximum absorbance of RhB at 554 nm.  
RhB removal rate is calculated using the following equation:  
\[\text{Removal rate}=\frac{A_{0}-A_{t}}{A_{0}}\times 100\]  
where A\({}_{0}\) and A\({}_{t}\) represent the RhB absorbance initially and at time t, respectively.  
The HPLC analyses were performed on a Jasco HPLC chromatograph (Jasco International Co., Ltd., Tokyo, Japan) that was equipped with an intelligent pump, PU-980, a ternary gradient unit, LG-980-02, an intelligent column thermostat, CO-2060 Plus, an intelligent detector, UV-975, an intelligent fluorescence detector, FP-2020 Plus, and an injection valve that was equipped with a 20 \(\upmu\)L sample loop (Rheodyne, Thermo Fischer Scientific, Waltham, MA, USA). The system was controlled, and the experimental data processed with the ChromPass software (version v1.7, Jasco International Co., Ltd., Tokyo, Japan). Separation was performed on a Gemini chromatographic column (5\(\upmu\)C18, 110 A, 250 \(\times\) 4.6 mm, Phenomenex, Torrance, CA, USA) at 21 \({}^{\circ}\)C. Isocratic elution was performed with 45% of acetonitrile with 55% of 0.1% H\({}_{3}\)PO\({}_{4}\) buffer. The flow rate was 1 mL/min and the injection volume was set to 20 \(\upmu\)L. UV detection was performed by fluorescence at the excitation and emission wavelengths set at 535 nm and 580 nm. All the experiments were performed in triplicate. The determination of rhodamine B was performed according to the adapted method described by [PERSON] et al. [48].