Toggle Main Menu Toggle Search

Open Access padlockePrints

Role of surface functional groups in the adsorption kinetics of water vapor on microporous activated carbons

Lookup NU author(s): Dr Ashleigh Fletcher, Yaprak Uygur, Emeritus Professor Mark Thomas

Downloads

Full text for this publication is not currently held within this repository. Alternative links are provided below where available.


Abstract

Activated carbons have both hydrophilic surface oxygen functional groups, which act as primary adsorption centers for water vapor, and hydrophobic graphene layers on which nonpolar species are primarily adsorbed. The aim of this research was to investigate the effects of oxygen surface functional groups, in activated carbons, on the adsorption characteristics of water vapor. Activated carbon G was oxidized using nitric acid and then heat treated in the range 387-894 K to produce a suite of adsorbents with varying oxygen contents in the range 0.4-21.5 wt % daf, but very similar porous structure characteristics, thereby minimizing effects due to changes in porous structure. The type and concentration of surface oxygen groups present in each sample were assessed using TPD, FTIR, Boehm titration, and analytical methods. Water vapor adsorption at low relative pressure was dramatically enhanced by the presence of functional groups, in particular, carboxylic groups. Kinetic profiles for each pressure increment were modeled using a set of nested kinetic models, which allow the adsorption kinetics to be analyzed in relation to the adsorption mechanism. Relationships between water adsorption kinetics at low surface coverage and the type and concentration of oxygen surface functional groups were observed. A two component double exponential kinetic model was used when carboxylic groups were present in significant amounts with a slow kinetic component associated with adsorption on these groups. In the case of carbons where carboxylic groups were only present in, at most, relatively small amounts, a stretched exponential kinetic model was used and the rate constants in the low-pressure region decreased linearly with increasing Henry's Law constant and oxygen content. The results indicate the importance of adsorbate-adsorbent interactions in water adsorption kinetics and are consistent with a site-to-site hopping mechanism between functional groups. © 2007 American Chemical Society.


Publication metadata

Author(s): Fletcher AJ, Uygur Y, Thomas M

Publication type: Article

Publication status: Published

Journal: Journal of Physical Chemistry C

Year: 2007

Volume: 111

Issue: 23

Pages: 8349-8359

ISSN (print): 1932-7447

ISSN (electronic): 1932-7455

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/jp070815v

DOI: 10.1021/jp070815v


Altmetrics

Altmetrics provided by Altmetric


Actions

Find at Newcastle University icon    Link to this publication


Share