3.4 Thermal Analysis (TGA)
The thermal analysis of TG, DTA, and DTG is taken from a magnetic metal-organic framework sample NiFe2O4@SiO2@HKUST-1 with 30% (weight) and is shown in Fig. (7). Thermal analyses (TG, DTA, DTG) are used to determine the thermal stability of the metal-organic framework. As can be seen, two weight reductions are seen in the thermal analysis of the graph (TG) and this is due to the synthesis process. The first weight loss reported at 150-200 °C was related to the removal of guest molecules (solvent: water and ethanol) inside the pores of the metal-organic framework and gases adsorbed on the surface and partially related to the decomposition of organic groups such as (Carboxyl groups, etc.) on the surface of the magnetic nanocomposite, which is attributed in the diagram (DTA) along with an exothermic peak in this range. The second weight loss in the range of 300-400 °C is usually due to the restructuring of the metal-organic framework, mostly related to the metal oxides present in the metal-organic framework. It is reported that severe weight loss at 350 °C signifies the collapse and complete decomposition of the HKUST-1 metalorganic framework, and here the severe weight loss at 355 °C occurs when the structure of the metal-organic framework NiFe2O4@SiO2@HKUST-1 begins breaks down. It can be concluded that the metal-organic framework NiFe2O4@SiO2@HKUST-1 has thermal stability at temperatures above about 350 °C.
Fig (7): thermal analysis of TG, DTA, and DTG for magnetic metal-organic framework sample NiFe2O4@SiO2@HKUST-1 with 30% (weight)
The peak in the DTA curve is reported the presence of sharp peaks in region 300 and 400 °C indicates crystal deformation and the presence of a broad peak in zone 200-70 °C due to chemical reactions as well as the presence of a broad peak from 400 to 750 °C thermal decomposition. The endothermic peaks can also be observed between 1100 and 750 °C due to the compacting of the metal-organic composite because mass loss occurs up to about 400 °C [54-56].