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Abstract

The acidic and basic properties of vapour grown carbon nanofibers (VGCNFs) have been tuned by treatment of the oxidized CNFs with NH3. The effect of treatment temperature on the types of nitrogen functionalities introduced was evaluated by synchrotron based X-ray photoelectron spectroscopy (XPS), while the impact of the preparation methods on the surface acid-base properties was investigated by potentiometric titration, microcalorimetry and zeta potential measurements. The samples functionalised via amination are characterised by the coexistence of acidic and basic O and N sites. The population of O and N species is temperature dependent. In particular, at 873K, nitrogen is stabilised in substitutional position of the graphitic structure, as heterocyclic-like moieties. The surface presents heterogeneously distributed and energetically different basic sites. A small amount of strong basic sites give rise to a differential heat of CO2 adsorption of 150 kJ/mol. Functionalization treatment carried out at 473K, introduces nitrogen moieties with basic character, however with about 90 kJ/mol, the maximum heat of adsorption was significantly lower. In the latter sample energetically different basic sites coexist with part of the acidic oxygen groups introduced during the oxidative step. At this condition a bi-functional acidic and basic surface is obtained with high hydrophilic character. The functionalization procedure presented in this work allows high versatility and flexibility in tailoring the surface chemistry of nanocarbon material to specific needs. This work shows the potentiality of N-containing nanocarbon material as CO2 traps.