Heterogeneity of multiwalled carbon nanotubes based on adsorption of simple aromatic compounds from aqueous solutions

Abstract

The surface heterogeneity of multiwalled carbon nanotubes (MWCNTs) is studied on the basis of adsorption isotherms from dilute aqueous phenol and dopamine solutions at various pH values. The generalized Langmuir-Freundlich (GLF) isotherm equation was applied to investigate the cooperative effect of the surface heterogeneity and the lateral interactions between the adsorbates. The theoretical isosteric heats of adsorption were obtained assuming that the heat of adsorption profile reveals both the energetic heterogeneity of the adsorption system and the strength of the interactions between the neighboring molecules. The adsorption energy distribution (AED) functions were calculated by using algorithm based on a regularization method. The great advantage of this method is that the regularization makes no assumption about the shape of the obtained energy distribution functions. Analysis of the isosteric heats of adsorption for MWCNTs showed that the influence of the surface heterogeneity is much stronger than the role of the lateral interactions. The most typical adsorption heat is 20-22 kJ/mol for both phenol and dopamine. After purification of nanotubes, heat value for phenol dropped to 16-17 kJ/mol. The range of the energy distribution is only slightly influenced by the surface chemistry of the nanotubes in the aqueous conditions.

The influence of geometric heterogeneity of closed carbon nanotube bundles on benzene adsorption from the gaseous phase-Monte Carlo simulations

“…Membranes composed of carbon nanotubes (so-called carbon nanotube forests) have been recently synthesized and found to function well as environmental sensors or superior adsorbents for removing many kinds of organic pollutants such as dioxin and volatile aromatic organic compounds from air streams and aqueous solutions, and of course C 6 H 6 (Agnihotri et al 2005;Bittner et al 2003;Castillejos et al 2012;Eswaramoorthy et al 1999;Jing et al 2004;Long and Yang 2001;Peng et al2003;Penza et al2004;Podkościelny et al 2014;Star et al2003;Sumanasekera et al 2002;Wiśniewski et al 2015a). The problem of adsorption of organic compounds inside carbon nanotube (CNT) type materials has been also discussed on the basis of theoretical studies (Bhide and Yashonath 2000;Irving et al 2004;Menon et al 2000;Pańczyk et al 2014;Podkościelny et al 2014;Takaba et al 1995;.…”

Adsorption of phenol from aqueous solutions on original and oxidized multiwalled carbon nanotubes

“…The adsorption mechanism of phenol is complex. The driving forces are ''p-p'' electrondonor-acceptor interactions between aromatic molecules and the polarizable graphene sheets of MWCNTs (Chen et al, 2008;Pan and Xing, 2008;Podkos´cielny et al, 2014;Shen et al, 2009;Sheng et al, 2010). Both electron-donator and electron-acceptor groups on benzene ring can increase the adsorption on MWCNTs.…”

“…The next stage of our studies is analyzing heat effects accompanying adsorption of phenol on MWCNTs (Nieszporek et al, 2009;Podkos´cielny and Nieszporek, 2011;Podkos´cielny et al, 2014). Unfortunately, the experimental heats of adsorption were inaccessible for the analyzed adsorption systems, so we could calculate the theoretical ones only.…”

“…The proper analysis regarding the heat effects accompanying the adsorption phenomenon provides additional information on the analyzed adsorption systems (Nieszporek et al, 2009;Podkos´cielny and Nieszporek, 2011;Podkos´cielny et al, 2014). The elementary equation which enables to obtain expressions for isosteric heats of adsorption q st has the following form:…”

“…Multiwalled carbon nanotubes (MWCNTs) can be used for effective removal of aromatic organic compounds like phenol, nitrophenols, chlorophenols, etc., from contaminated water (Arasteh et al, 2010;Li et al, 2013;Liao et al, 2008;Pan and Zhang, 2014;Podkos´cielny et al, 2014;Shen et al, 2009;To´th et al, 2012;Wis´niewski et al, 2012;Wu et al, 2012;Yang and Xing, 2010;Yang et al, 2016).…”