Charge-Transfer-No-Bond Adsorption

The theory of charge-transfer complex is applied to adsorption on metals and semiconductors. The heat of adsorption at zero coverage is given in terms of the ionization energy of the adsorbate, the electronic work function of the adsorbent, an image energy, and an interaction energy. For metals a linear relationship between heat (at zero coverage) and extent of adsorption is deduced from two of the simpler forms of theoretical isotherms. The functional dependence of the extent of adsorption on the ionization energy of the adsorbate is thus obtained. The treatment for semiconductors is modified to take into account the space charge generated in the semiconductor on adsorption. This treatment is shown to be consistent with reported experimental data for adsorption on iron powder of long chain nitriles, esters, alcohols, amines, and thiols.