Surface modification of carbon black by oxidation and its influence on the activity of immobilized catalase and iron-phthalocyanines

A non-porous carbon black is oxidized using different reagents (H2O2 3 M, HNO3 0.3 M at 95 degrees C, O-2 at 400 and 600 degrees C) and used as support for the enzyme catalase as well as for iron-phthalocyanines, enzyme mimics, Characterization of the oxidized carbons is done by X-ray photoelectron spectroscopy, gas-adsorption and electrophoretic mobility measurements, The treatments do not change the texture of the carbon black. Hydrogen peroxide and nitric acid increase the surface oxygen concentration, and make the charge of the carbon surface more negative, whereas oxidation with molecular oxygen has the opposite effect, The surfaces with a higher oxygen content and negative charge preserve a higher activity of adsorbed catalase, presumably because less deformation of the enzyme occurs as a result of higher repulsive electrostatic interactions and lower hydrophobic interactions. The same order is found for the dismutase-like activity of the iron-phthalocyanines supported on the carbon; the selective oxidation of hydrocarbons, i.e. the oxygenase activity follows the reverse order. Thus, sorption effects determine the selectivity of iron-phthalocyanine. Zeolite Y, which has a higher electrical charge and surface oxygen concentration compared to the oxidized carbons, is responsible for a higher ratio of dismutase-like activity with respect to oxygenase-like activity.