Reaction of hydrous inorganic metal salts in CO2 expanded ethanol: Fabrication of nanostructured materials via supercritical technology

The fabrication of nanostructured materials from hydrous inorganic metal salt processed in supercritical CO2 (scCO2) expanded liquids has advantages to obtain good results. However, the behavior of the inorganic salts and the detailed reaction mechanism are still unknown up to now. In this work, the actual behavior of hydrous inorganic metal salts in CO2 expanded ethanol at the temperature of 50–200 °C, including the phase behavior, deposition mechanism, reaction rate and the effect of templates on the deposition were systematically investigated by using XRD, FTIR, CHN-analysis, TGA, ICP-AES. A series of experimental parameters such as CO2 flow rate, expand procedure, reaction temperature and time have been discussed, as well as the roles of CO2 and H2O (often originated from salts and/or solvent but always neglected) were studied in this contribution. Significantly, a coordination–decomposition (C–D) was proved to be the converting mechanism for the precipitation of the hydrous inorganic metal salts, rather than the fuzzy decomposition.

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► The actual behavior of hydrous inorganic metal salts in supercritical CO2 expanded ethanol was studied at the first time.
► The deposition mechanism of inorganic metal salts, reaction rate and the effect of templates on the deposition were systematically investigated.
► A series of experimental parameters and procedures have been discussed and optimized carefully, which will benefit the readers to repeat the experiment.
► The roles of CO2 and H2O (often originated from salts and/or solvent but always neglected) were discussed in detail.
► Coordination–decomposition (C–D) was proved to be the converting mechanism for the precipitation of the hydrous inorganic metal salts, rather than the fuzzy decomposition.