Naslov
Atomic Force Microscopy of Soil and Stream Fulvic Acids

Autori
Namjesnik-Dejanović, Ksenija ; Maurice, Patricija A.

Izvornik
Colloids and surfaces. A, Physicochemical and engineering aspects (0927-7757) 120 (1997), 1-3;

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Atomic force microscopy; Fulvic acid conformations

Sažetak
Atomic force microscopy (AFM) was used to image fulvic acid (FA) deposited from aqueous solution on to the basal-plane surfaces of freshly cleaved muscovite, and allowed to air dry. Two fulvic acid samples were used: a soil fulvic acid (SFA) prepared by NaOH extraction from a muck soil underlying a freshwater fen in the New Jersey Pinelands and the IHSS standard Suwannee River fulvic acid (SRFA). The use of tapping-mode AFM (TMAFM), a relatively new technique which reduces the lateral frictional forces generally associated with contact-mode AFM, allowed excellent images of delicate FA structures to be obtained with minimal sample disturbance. Four main structures were observed on SFA. At low concentrations, spong-like structures consisting of rings (ť15 nm in diameter) appeared, along with small spheres (10–50 nm). At higher concentrations, aggregates of spheres formed branches and chain-like assemblies. At very high surface coverage, perforated sheets were observed. On some samples, all of these structures were apparent, perhaps owing to concentrations gradients on drying. SRFA smaples were only imagined at higher concentrations. Spheres, aggregated branches, and perforated sheets were apparent. The results agree with previous work by Stevenson and Schnitzer [Soil Sci., 133(1992) 179], who applied TEM to soil Fas freeze-dried on muscovite. However, the TEM images did not detect the smaller spheres and sponge-like structures observed by AFM at low concentrations. The relevance of imaging dried samples remains questionable; hence, it is hoped in the future to use new in situ TMAFM to image Fas sorbed to surfaces in solutions. Although TMAFM provided excellent images, a variety of artifacts and potential problems were encountered, as discussed.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA