**Acknowledgements**

*Advanced Supercritical Fluids Technologies*

of a versatile method for coating silica particles used as model substrates, with either a hydrophilic (polyethylene glycol PEG) or hydrophobic polymer (hydroxyl-terminated polybutadiene, HTPB) using a supercritical antisolvent process (**Figure 10**). The principle of the precipitation from compressed antisolvent PCA techniques

In order to effectively exploit the advantages of "green" processing in scCO2, Roy et al. describe the successful grafting of a model drug (salicylic acid, SA) on TiO2 nanoparticles [35]. The chosen active compound could react with the nanoparticle surfaces through the carboxylic and hydroxyl groups. The functionalization of the TiO2 surface was performed in mild conditions, at 40**°**C and 16 MPa for a short period of time, up to 2 hours. The thermogravimetric analysis shows a calculated amount of drug SA deposited on TiO2 nanopowder of approximately 8 wt%, and the SEM images of coated samples do not reveal rod-like crystals specific for solid salicylic acid, which confirm the absence of residual drug other than the coating

In the last decades, methods to perform functionalization of nanoparticles using scCO2 were reported, as viable alternative to classical synthesis and showing

The recent works in supercritical fluids demonstrate the multiplicity of advantages in synthesis of nanomaterials, either organic or inorganic. Complex synthesis of hybrid materials consisting in nanoparticles deposited on other structures (carbon nanotubes) or core-shell nanoparticles was also developed in scCO2.

remarkable advantage of reduced impact on the environment.

is allowing the contact of the polymeric solution with the scCO2 as antisolvent, when a succession of different phenomena governed by hydrodynamic, precipitation kinetics, thermodynamic, and mass-transfer effects result eventually in the precipitation of an organic shell on the nanoparticles dispersed previously in the polymeric solution. According to the polymer used (PEG or PBHT) and the reaction conditions, various sizes of the deposited polymeric shell have been obtained, from 3 to 28 nm, by simply modification of polymer concentration in the initial

*The variation of polymeric shell thicknesses on nanoparticles as a function of the initial mass fraction of* 

*polymer in the initial solution (reprinted with permission from ref 34).*

**174**

solution (**Figure 10**).

**Figure 10.**

deposited on nanoparticles.

**6. Conclusion**

This work was supported by grants of the Romanian National Authority for Scientific Research and Innovation, CCCDI - UEFISCDI, project number PN-III-P1- 1.2-PCCDI-2017-0743/P5, and PN-III-P1-1.2-PCCDI-2017-0428/P2 within PNCDI III.
