关键词: 超临界CO₂脱附, 介孔材料, 快速泄压, 结晶动力学, 纳米颗粒

Abstract:

Based on the classical nucleation theory and the related models of crystallization kinetics in the supercritical field, the main factors and laws affecting the nucleation rate are analyzed. Inorganic salt precursor was dissolved in supercritical carbon dioxide with the assistance of co-solvents, and it was deposited in the silicon-based SBA-15. When depressurized rate was increased gradually for the initial stage of depressurization (0.05—18 MPa/min, 20—14 MPa), the average particle size of supported nanoparticles gradually decreased to 1.5 nm from TEM observation, which is close to the typical crystal nucleus size of 1 nm. However, an increasing trend of metal loading had emerged. The critical nucleation radius of the crystal was taken as 0.5 nm, and nucleation rate in the nozzle of the rapid expansion of supercritical solution (RESS) process was calculated by Türk model and Debenedetti model, compared with the initial nucleation rate of population balance model (PBM) of supercritical anti-solvent (SAS), which was considered as the boundary condition of PBM. The nucleation rates calculated based on these three models were close to the estimated nucleation rate by Cu loading of the as-deposited sample under the rapid depressurization method. In the depressurization stage subsequent to the supercritical deposition stage, the desorption of CO₂ under supercritical conditions may be an inductive factor to nucleation of the metal precursor adsorbed on the surface of the supports, and the nucleation rate of the nanoparticles and the metal loading supported on SBA-15 could be controlled by the amount of instantaneous desorption of CO₂. The experimental and theoretical foundation were formed to investigate the performance of SAS process in micro-scale material.

Key words: supercritical CO₂ deposition, mesoporous material, rapid depressurization, crystallization kinetics, nanoparticles