Specific and non-specific interactions of procaine with activated carbon surfaces

The adsorption of procaine on eight activated carbon surfaces from simulated intestinal fluid (SIF) was evaluated using a rotating bottle method and isoperibol calorimetry. The adsorption data were fit using the modified Langmuir-like equation to calculate the non-specific and specific adsorption capacities. The surface atomic compositions were determined by X-ray photoelectron spectroscopy (XPS). A linear relationship was found between the relative non-specific adsorption capacity and the unoxidized hydrocarbon content of the activated carbon surfaces, which indicated that the non-specific adsorption site for procaine is the bare carbon surface. The apparent area occupied per procaine molecule, calculated from the specific capacity, was linearly correlated to the sum of the relative percentages of the CO and OCO functional states on the surfaces. This suggested that the primary adsorption sites for procaine on the activated carbon surfaces were the oxygen-containing functional states of CO and OCO, where procaine was adsorbed via hydrogen bonding. The differential heats of displacement for procaine on the four activated carbon surfaces are approximately equal to each other, which indicated that the interactions between procaine and the functional states on all surfaces are energetically equivalent.

The linear relationship between the relative non-specific adsorption capacity and the hydrocarbon content indicated that the non-specific adsorption site for procaine is the bare carbon surface. A positive correlation between the apparent area occupied per procaine molecule and the sum of the relative percentages of the CO and OC=O functional states suggested that the primary adsorption sites for procaine on the activated carbon surfaces were the oxygen-containing functional states of CO and OC=O.Figure optionsDownload high-quality image (73 K)Download as PowerPoint slideHighlights
► Procaine adsorbed on activated carbon via hydrophobic and hydrogen bonding.
► The non-specific adsorption site for procaine is the bare carbon surface.
► The primary adsorption sites for procaine are the CO and OCO functionalities.
► The differential heats of displacement are constant for all activated carbons.