*2.2. Thermogravimmetric Analysis of the WO3 Xerogles*

Thermogravimetric (TG) measurements of WO3 sols, prepared with different solvents, were performed using Mettler Toledo TGA/DSC1 instrument (Mettler Toledo, Schwerzenbach, Switzerland). Samples were heated from room temperature to 500 ◦C with the hating rate of 5 K min-1 under the dynamic air flow (100 mL min-1). 75 μL of the prepared sol was pipetted into 150 μL platinum crucible and dried under air for 24 h. After drying, masses of the samples used for analyses were around 15 mg. The blank curve was subtracted.

Dynamic TG curves of all three samples are shown in Figure 2. The course of thermal decomposition is similar for xerogels B and C, where ethanol and 2-propanol were used as a solvent while the mass-loss curve has a different course in the case of xerogel A, where the solvent was a mixture of 2-propoxy ethanol and 2-propanol. We ascribe the first step, which takes place from room temperature to approximately 200 ◦C, to solvent evaporation. In this step mass-loss rate is higher in the case of xerogel B and C. Up to 185 ◦C, xerogel B losses 6.0% of the initial mass, while xerogel C 8.10% and xerogel A 4.5%, respectively. The second and the third step, where condensation reactions continue, are partially overlapped. For xerogel B mass loss is additional 3.0% in a temperature range from 270 ◦C to 350 ◦C and from 350 ◦C to 430 ◦C another 0.5%. Similar behavior is observed for xerogel C except that the second step begins at higher temperature, i.e., 325 ◦C. Successive reactions are much more overlapped in the case of xerogel A. Second step occurs in a temperature range from 185 ◦C to approximately 270 ◦C with a mass loss of 3.8% and turns then to the third step with a slower mass loss. Mass for the sample A is not constant even at 500 ◦C.

**Figure 2.** TG measurement of the WO3 xerogels prepared with different solvents: xerogel A with 2-propoxy ethanol and 2-propanol; xerogel B with ethanol and xerogel C with 2-propanol.
