Highly sensitive and reproducible quantification of oxygenated surface groups on carbon nanomaterials

Abstract

The quantification of surface groups is a key characterization for different carbon materials as their behavior in colloidal dispersion, their interaction with proteins, drugs or polymers as well as their aggregation behavior strongly depend on the type and number of surface groups. Some of the most challenging groups are those containing oxygen as the typical characterization methods do not allow for a highly sensitive and reproducible quantification of carboxylic, lactonic and alcoholic groups. The only known wet-chemical method that is able to yield quantitative results is the Boehm titration. However, this method is also known to be extremely demanding regarding procedure compliance, requires large amounts of sample, and leads to rather large standard deviations. Here we report on a significantly improved titration method for the quantification of oxygen containing surface groups. All methodical aspects like sample preparation, reaction time, filtration medium, volumetric and gravimetric methods have been optimized, leading to the detection of carboxylic, lactonic and alcoholic groups with a standard deviation of ±1 μmol/g while using only small amounts of sample material. The method has been successfully applied on a broad variety of hydrophilic and hydrophobic carbon materials including nanodiamond, partially graphitized nanodiamond, multiwall carbon nanotubes and acetylene black.