Changes in surface heterogeneity of multi-walled carbon nanotubes due to adsorption of poly(acrylic acid) by derivative isotherm summation method

The heterogeneity of surface energy of multi-walled carbon nanotubes (MWNTs) before and after the adsorption of poly(acrylic acid) (PAA) is investigated on the basis of low-pressure adsorption isotherms of nitrogen at 77 K using derivative isotherm summation (DIS) method. Two types of dominant energetic surfaces are recognized in the pure MWNTs. While raising the adsorption amount of PAA, significant decrease in both the specific surface area and the heterogeneity of surface energy is found. It is indicated in detail that the contribution of high-energy surface reduces remarkably due to screening effect of adsorbed PAA, and PAA molecules could block some interparticle pores resulting in the decrease in total surface area of MWNTs. DIS analysis of the low-pressure data of the nitrogen adsorption isotherms was shown to be a feasible and effective tool to characterize the surface heterogeneity of nanoparticles.