AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP22
Imaging the Structure of Natural Organic Matter Adsorbed onto Carbonaceous Surfaces with Atomic Force Microscopy

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: J. Gorham, Johns Hopkins University
Authors: J. Gorham, Johns Hopkins University
H. Fairbrother, Johns Hopkins University
Correspondent: Click to Email
Developing a microscopic understanding of the adsorbate layers formed by Natural Organic Matter (NOM) on carbonaceous surfaces is useful in developing more realistic models under environmental conditions. This information could also have important technological ramifications for water treatment strategies where NOM reduces the adsorptive capacity of activated carbons. In this study, the adsorption of NOM (obtained from the Great Dismal Swamp, VA) on Highly Ordered Pyrolytic Graphite (HOPG) has been studied at the liquid-solid interface using Atomic Force Microscopy (AFM). In these studies HOPG was used to model the extended graphene sheets that characterize the exposed surface of activated carbons. Under low pH conditions (pH 4.0), NOM particles were observed to cover the entire HOPG surface with a layer thickness of ~2 nm. Evidence of ordered adsorbate structures involving NOM were observed at low pH. As the pH of the NOM solution increased, the surface concentration of NOM decreased systematically; at pH 10, <10% of the HOPG was covered by adsorbed NOM. Particle size was also influenced by pH with the average size of adsorbed structures being greater at higher pH. The structure of adsorbed NOM was significantly modified by drying with "ring like" structures and larger NOM aggregates observed. Results will also be presented on the effect of ionic strength on the structure of the adsorbate layer.