1.1 Tga/dsc-ftir characterization of oxide nanaoparticles  (Page 3/4)

Synthesis and characterization of wo _3-x Nanorods

The synthesis of WO _3-x nanorods is based on the method published by Lee et al. A slurry mixture of Me ₃ NO∙2H ₂ O, oleylamine and W(CO) ₆ was heated up to 250 °C at a rate of 3 °C/min ( [link] ). The mixture was aged at this temperature for 3 hours before cooling down to room temperature.

Multiple color variations were observed between 100 - 250 °C with the final product having a dark blue color. Tungsten oxide nanorods (W ₁₈ O ₄₉ identified by XRD) with a diameter of 7±2 nm and 50±2 nm long were acquired after centrifugation of the product solution. A TEM image of the W ₁₈ O ₄₉ nanorods is shown in [link] .

Thermogravimetric analysis (tga)/differential scanning calorimetry (dsc)

Thermogravimetric analysis (TGA) is a technique widely used for determining the organic and inorganic content of various materials. Its basic rule of function is the high precision measurement of weight gain/loss with increasing temperature under inert or reactive atmospheres. Each weight change corresponds to physical (crystallization, phase transformation) or chemical (oxidation, reduction, reaction) processes that take place by increasing the temperature. The sample is placed into platinum or alumina pan and along with an empty or standard pan are placed onto two high precision balances inside a high temperature oven. A method for pretreating the samples is selected and the procedure is initiated. Differential scanning calorimetry (DSC) is a technique usually accompanying TGA and is used for calculating enthalpy energy changes or heat capacity changes associated with phase transitions and/or ligand-binding energy cleavage.

In [link] the TGA/DSC plot acquired for the ligand decomposition of WO _3-x nanorods is presented. The sample was heated at constant rate under N ₂ atmosphere up to 195 °C for removing moisture and then up to 700 °C for removing the oleylamine ligands. It is important to use an inert gas for performing such a study to avoid any premature oxidation and/or capping agent combustion. 26.5% of the weight loss is due to oleylamine evaporations which means about 0.004 moles per gram of sample. After isothermal heating at 700 °C for 25 min the flow was switched to air for oxidizing the ligand-free WO _3-x to WO ₃ . From the DSC curve we noticed the following changes of the weight corrected heat flow:

1. From 0 – 10 min assigned to water evaporation.
2. From 65 – 75 min assigned to OA evaporation.
3. From 155 – 164 min assigned to WO _3-x oxidation.
4. From 168 – 175 min is also due to further oxidation of W ⁵⁺ atoms.

The heat flow increase during the WO _3-x to WO ₃ oxidation is proportional to the crystal phase defects (or W atoms of oxidation state +5) and can be used for performing qualitative studies between different WO _x nanoparticles.

The detailed information about the procedure used to acquire the TGA/DSC plot shown in [link] is as follows.

1. Select gas (N ₂ with flow rate 50 mL/min.)
2. Ramp 20 °C/min to 200 °C.
3. Isothermal for 20 min.
4. Ramp 5 °C/min to 700 °C.
5. Isothermal for 25 min.
6. Select gas (air).
7. Isothermal for 20 min.
8. Ramp 10 °C/min to 850 °C.
9. Cool down