Physical and chemical properties of a silica-based sorbent with a grafted complex of copper acetoacetic ester

Abstract

Nanoporous mineral oxides can radically change their physical and chemical properties as a result of chemical modification of the surface. This is one of the reasons for the development of methods for the directed synthesis of materials based on nanoporous mineral oxides and their widespread use under the conditions of gas chromatography. The purpose of this work was to obtain a gas chromatographic sorbent with a grafted layer of copper acetoacetic ether by the method of sequential assembly on the surface of Silochrom S-120 which included the stage of its chlorination.

Thermal analysis data indicated the stability of the studied complex of copper ethylacetoacetate up to 210°C. It was found by the method of adsorption porosimetry that the chemical modification of SiO₂ results in a reduction in the specific surface area and porosity. The results of elemental analysis were used to calculate the amount of the grafted layer, the surface density of the grafted groups, and the thickness of the layer of copper ethylacetoacetate on the silica surface.

The adsorption processes of organic compounds (n-alkanes, halogen substituted alkanes, 1-nitropropane, heptene-1, aromatic hydrocarbons, ketones, and alcohols) capable of various types of intermolecular interactions with Silochrom S-120 and a sorbent based on it were studied by gas chromatography. SiO₂ modification by copper ethylacetoacetate led to a pronounced increase in the Henry constants of adsorption of alcohols, ketones, and aromatic hydrocarbons due to occurrence of donor-acceptor, orientational, and π-interactions “adsorbate-adsorbent”. The calculated thermodynamic characteristics (q̅_dif,1, and ) indicated an increase in the adsorption potential of the new sorbent, which resulted in an increase in the heat and entropy of the adsorption of the tested compounds. The experimental data were used to determine that the chemical modification of SiO₂ by copper acetoacetic ether leads to an increase in the contribution of specific interactions to the heat of adsorption. What is more, the largest values of Δq̅_dif,1(spec) are characteristic of organic compounds prone to the formation of hydrogen bonds and donor-acceptor complex formation. The analysis of the compensating thermodynamic dependences showed that entropy is the key thermodynamic parameter during the adsorption of organic compounds on the studied sorbents. The resulting sorbent was tested for the separation of mixtures of organic compounds of various classes, including saturated and unsaturated hydrocarbons, alcohols, aldehydes, and ketones.