Influence of the counter-anion of imidazolium ILs on the interface adsorption was studied.

Generally, the activity of halide counter anions in the adsorption appeared in the order of I⁻ > Br⁻ > Cl⁻.

The alkyl chain length with the same counter anion has predominant influence on variations.

The experimental data were precisely reproduced by the Szyszkowski adsorption equation.

The adsorption parameters for each IL were obtained and their variations were demonstrated.