## 2 Materials and Methods  
Ammonium hydroxide and cerium sulfate tetrahydrate were both of analytical grade purity (p.a.) and purchased from PENTA chemicals. 2,4,6-trichlorophenol of 98% purity was purchased from Sigma-Aldrich. Ceria nanoparticles used for all experiments were prepared via a fast and simple precipitation method, where an aqueous solution of cerium (IV) sulfate and an ammonium water solution reacted [28]. Firstly, a saturated solution of cerium (IV) sulfate was prepared, which equaled the ratio of 6.5 g of cerium (IV) sulfate tetrahydrate to 10 g of distilled water. For the precipitation, a 25% aqueous ammonium solution was used, which was added dropwise until it reached a slightly alkaline environment. The formed suspension was washed multiple times with distilled water for the removal of ammonium sulfate byproduct. After having the nanoparticles washed, the centrifugation process was applied to remove the vast majority of the water and to hasten the drying process. After having the nanoparticles centrifuged, the nanoparticles were dried in a vacuum dryer at 35 \({}^{\circ}\)C at 0.2 atm. Alumina crucibles were used for the thermal treatment experiment. Each crucible was filled with approximately 200 mg of ceria nanoparticles. The heating of the samples was performed in a furnace with a static air atmosphere and a heating rate of 10 \({}^{\circ}\)C/min. Target temperatures were as follows: 300 \({}^{\circ}\)C, 600 \({}^{\circ}\)C, 900 \({}^{\circ}\)C and 1100 \({}^{\circ}\)C. When the final temperature was reached, each sample was taken out of the furnace and cooled rapidly to room temperature. Samples were termed according to their final temperatures as TT-300, TT-600, TT-900, and TT-1100. The nontreated sample (i.e., the reference sample) of the initial nanoparticles was termed TT-25. Imnobilization of ceria nanoparticles by the thermal treatment was demonstrated by attaching the same dose of non-treated ceria nanoparticles in the 5% ethanol dispersion to the roughened silica glass and alumina underlays respectively, with subsequent air drying. In order to create an immobilized layer, the samples were heated in a furnace with a static air atmosphere at a heating rate of 10 \({}^{\circ}\)C/min to the final temperature 1100 \({}^{\circ}\)C.  
The samples were then characterized by XRD, which was performed at room temperature using the Bruker 2D Phaser powder diffractometer with Bragg-Brentano parafocusing geometry, equipped with a Co lamp generating \(\lambda=0.1789\) nm, and the setup used U = 40 kV, I = 40 mA. The data were scanned over the angular range of 10-80\({}^{\circ}\) (28) with a step size of 0.019\({}^{\circ}\) (28). Panalytical X'Pert HighScore Plus software was used for XRD data analysis and for the calculations of nanoparticle sizes using the Debye-Scherrer calculator. The diffraction patterns were processed without background subtraction. High-resolution transmission electron microscopy (HR-TEM) was performed using an EFTEM Jeol 2200 FS microscope (Jeol, Japan). A 200 kV acceleration voltage was used for measurement. Sample preparation was attained by drop-casting the suspension (1 mg mL\({}^{-1}\) in water) on a TEM grid (Cu, 200 mesh, Formvar/carbon) and drying it at 50 \({}^{\circ}\)C for 12 h. Structural characteristics were obtained from selected area electron diffraction (SAED). The Brunauer-Emmett-Teller (BET) analysis of specific surfaces was performed using the NOVAtouch LX2 (Quantachrome Instruments) sorption analyzer. All samples were outgassed for 10 h at 100 \({}^{\circ}\)C under a high vacuum. A nitrogen-cooled (77 K) detector was used for evaluation of the results using BET analysis and Kelvin equations. The Quantachrome software was used for the evaluation of measured data and for the determination of the surface area. The morphology was investigated using SEM with an FEG electron source (a Tescan Lyra dual-beam microscope). To conduct the measurements, all samples were placed on carbon conductive tape. Each measurement was carried out using a 10 kV electron beam.