Thermal decomposition of copper (II) acetylacetonate in supercritical carbon dioxide: In situ observation via UV-vis spectroscopy

•Thermal decomposition of Cu(II) acetylacetonate in scCO2 was investigated.•In situ UV-vis spectroscopy was employed to avoid the effect of substrate.•Kinetics of the decomposition reaction at 423-453 K and 15-25 MPa were studied.•Activation energy of decomposition decreased with increasing pressure.•Activation energy was lower than those observed in air and in vacuum.

The thermal decomposition of copper (II) acetylacetonate (Cu(II)(acac)2) in supercritical carbon dioxide (scCO2) was investigated via in situ UV-vis spectroscopy. Release of acetylacetone ligands from the central metal atom was observed as the initial step in the decomposition. The kinetics of the decomposition at 423-453 K and 15-25 MPa in scCO2 were studied. The decomposition reaction generally followed the first-order kinetics. The reaction rate was slightly increased with an increase in the pressure, due to changes in the scCO2 density. The activation energy of the decomposition was calculated as 60.3 kJmol−1 at 15 MPa, 56.3 kJmol−1 at 20 MPa and 52.4 kJmol−1 at 25 MPa, which are lower values than those observed in air and in vacuum. The pressure dependence of the activation energy of the decomposition reaction was clarified quantitatively for the first time, and revealed the energy conservation benefit of using scCO2 as a process solvent for a variety of metal/metal oxide deposition process of nanomaterials.

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