Consequences of nitrogen surface groups on the performance of carbon nanotubes for the abatement of water emerging pollutants by adsorption and electrocatalytic methods

Abstract

Multiwall Carbon nanotubes (MWCNTs) are a new class of mesoporous materials where the internal cylindrical volume can be accessible by one or the two ends. Also in some cases the mesopores can be closed by fullerene caps acting as covers, giving place to the bamboo-like structures. In addition these nanomaterials can be developed with modified surface functionalities either during the preparation procedures or by subsequent chemical treatments [1]. Among the many possible applications of MWCNTs can be cited those related with their adsorption and catalytic properties. In particular taking advantage of their electrical conductivity properties can be used as electrocatalysts to remove by oxidation organic pollutants from waste waters. In this type of application is very important to obtain information about the adsorption-interaction of the pollutant molecules over the MWCNTs surface. In this communication we present a correlation of the surface characteristics of two MWCNTs with their capacity to adsorb emerging pollutant. In the present study we have comparatively studied two MWCNTs. The first is a commercial available material (from Nanocyl company), which present a N2 adsorption isotherm typical of mesoporous materials with a surface area of 350 m2/g. The second MWCNTs sample is lab prepared, which were obtained by growing the nanotubes over a Fe/SiO2 catalyst in a bed fluidized reactor [1], using acetonitrile as carbon source (N-CNTS sample). In this case the predominant structures are bamboo like ones (SBET=500m2/g), and then a big part of the mesopores are not accessible to emerging molecules. Also significant these N-CNTs exhibit at their surface a high value of nitrogen adatoms, closed to 5.5% as detected by XPS. The experiments of adsorption were performed¿. It should be noticed that comparison from the point of view of ¿emerging pollutant¿ adsorption of the Nanocyl MWCNTs with carbon nanofibers (CNFs from Pyrographs), either graphitized or not, reveals that the former sample is a good candidate for this application, which is not the case for the CNFs. Less differences can be observed when comparatively studied Nanocyl and N-CNTs samples, but based on the surface characterization we can conclude that both the accessibility to the mesopores and the presence of nitrogen surface groups affect the adsorption of the ¿emerging pollutant¿.