Plasma deposition of long-lasting hydrophilic coatings on alumina micro-particles

The research of versatile, simple and inexpensive approaches for chemically decorating micro-nanomaterials is a challenge in the field of functional surfaces in general, and in particular in plasma processing. Decorating ceramic particles with oxygen containing (O-containing) functionalities can render such materials very suitable as catalyst supports and adsorbents, or for manufacturing membranes and sensors. This paper describes a material processing consisting of a plasma-deposition step with CO2/C2H4 mixtures followed, or not, by a plasma-grafting step in CO2/H2 blends. In this way, alumina mesoporous microparticles have been functionalized with coatings decorated with carboxylic groups (COOH surface density up to 3.3 ± 0.6 × 10−9 mol/cm2) stable up to 1 month both in air and in water. A home-made rotating radiofrequency (RF, 13.56 MHz) driven plasma reactor has been used, whose gentle agitation allows homogeneous coating of the particles. The low environmental impact, the safety of the reagents used, together with the effective coating of the particles, render the proposed approach highly competitive with respect to conventional functionalization processes based on wet chemistry.