Scanning force microscopy of two‐dimensional structure formation in thin humic acid films

Mertig, Michael; Klemm, Denis; Zänker, Harald; Pompe, W.

doi:10.1002/sia.1173

Cited by 8 publications

(6 citation statements)

References 25 publications

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“…9 The concentration of HAs in water is not directly accessible to common analytical methods due to their heterogeneous chemical structure. 10,11 Instead, total organic carbon (TOC) and absorbance of ultraviolet light at 254 nm (UV 254 ) are used as group parameters to represent the concentration of HSs in water. 12,13 Spectrophotometry utilizes the capacity of HSs to absorb ultraviolet light at 254 nm, which increases with their content of aromatic rings, the ratio between aromatic and aliphatic carbon, the total carbon content in the water, and the molecular weights of the HSs.…”

Section: Introductionmentioning

confidence: 99%

Quantification of humic acids in surface water: effects of divalent cations, pH, and filtration

Rodrigues

Brito

Janknecht³

et al. 2009

J. Environ. Monit.

150

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Humic acids (HAs) content of raw water is an important analytical parameter in water treatment facilities because HAs in the presence of chlorine may lead to the formation of dangerous by-products (e.g., trihalomethanes). The concentration of HAs in water is not directly accessible by common analytical methods due to their heterogeneous chemical structure. The aim of this study was to compare two methods to assess humic acids (HAs) in surface water namely absorbance of ultraviolet light at 254 nm (UV(254)) and total organic carbon (TOC), as well as to evaluate the effects of calcium and magnesium concentrations, pH and sample filtration on the methods' results. An aqueous solution of a commercial HA with 10 mg L(-1) was used in the present work. Quantification of the HA was carried out by both UV(254) and TOC (combustion-infrared method) measurements. UV(254) results were converted to TOC using a calibration curve. The effects of calcium (0-136.3 mg L(-1)) and magnesium (0-34.5 mg L(-1)) concentrations, pH (4.0, 7.0 and 9.0) and sample filtration on UV(254) and TOC measurements of the HA suspension were evaluated. More accurate TOC values of HA suspensions were obtained by the combustion-infrared method than by the UV(254) absorbance method. The higher differences of TOC values between unfiltered and filtered samples were detected in the presence of calcium at pH 9.0 using the spectrophotometric method.

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Section: Introductionmentioning

confidence: 99%

Quantification of humic acids in surface water: effects of divalent cations, pH, and filtration

Rodrigues

Brito

Janknecht³

et al. 2009

J. Environ. Monit.

150

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“…Other in situ methods, such as FTIR microscopy (Gregoriou and Rodman, 2002; Aparicio et al, 2002), that use intact samples embedded in poly‐resins and thin sections allow a spatially resolved analysis of surfaces (Mertig et al, 2002) and a spatial allocation of functional characteristics of organic components to micromorphological structures (Zieba‐Palus, 1997; Aparicio et al, 2002; He et al, 2002). However, the FTIR signals of the resins may overlap with those of the OM in the sample (Arocena et al, 1995).…”

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confidence: 99%

DRIFT Mapping of Organic Matter Composition at Intact Soil Aggregate Surfaces

Leue

Ellerbrock

Gerke

2010

Vadose Zone Journal

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In structured soils, interaction of percolating water and reactive solutes with the soil matrix is often restricted to the outer surfaces of the preferential flow paths. Such surfaces of soil aggregates and biopores are mostly covered by organic matter (OM) that finally controls wettability, sorption, and transfer properties of the flow pathways. However, the local OM properties along such surfaces are largely unknown to date because the coatings are relatively thin and vulnerable. The objective of this study was to determine and compare the local two‐dimensional distribution of soil OM composition at intact aggregate surfaces that serve as preferential flow paths. The Fourier transformed infrared spectroscopy in diffuse reflectance mode (diffuse reflectance infrared Fourier transform, DRIFT) was applied to determine transects and grids of OM functional group data (i.e., CH/CO ratios) on undisturbed and intact surfaces of soil aggregate samples using a DRIFT mapping procedure in 1‐mm steps. The aggregate sample surfaces could be distinguished by DRIFT mapping in areas from earthworm burrows, root channels, and aggregate coatings. The water drop infiltration time of these structural surfaces appeared to correspond with CH/CO ratios for uncoated crack surfaces but less so for earthworm burrows. The results show that coatings at preferential flow‐path surfaces differed locally in terms of OM composition, distribution, and possibly also in wettability, indicating yet unknown implications for preferential movement of water and reactive solutes.

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“…Given the nature of these materials, the use of thin films decreases the fluorescence contribution that can interfere with signal collection in Raman spectroscopy. The published work on humic substances as thin films has been primarily morphological, employing atomic force microscopy (AFM). , It is demonstrated here that FA associate to form nano- and microsized micelles with fractal geometries, dependent upon the pH value of the FA solution cast onto glass slides or gold island films. Spectroscopic characterization is achieved using micro-Raman and infrared absorption microspectroscopy, and the enhanced results obtained in surface-enhanced vibrational spectroscopy experiments allow for the extraction of information on both the structure and organization of thin solid films. , Previously published work on the surface-enhanced Raman scattering (SERS) of humic substances has been carried out on colloids, − electrodes, − and silver island films. − The surface-enhanced infrared absorption (SEIRA) , and surface-enhanced infrared reflection absorption (SEIRRA) of FA, reported here for the first time, give rise to better resolved IR spectra for characterization of surface functional groups under conditions different from normal infrared absorption measurements.…”

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confidence: 99%

Surface-Enhanced Vibrational Microspectroscopy of Fulvic Acid Micelles

2004

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Micro-Raman spectroscopy, infrared absorption microspectroscopy, and AFM images of nano- or microsized micelles formed by fulvic acid (FA) solutions, prepared at different pHs, and cast on glass slides or gold island films, are reported. FA films cast on gold islands are characterized by surface-enhanced infrared absorption (SEIRA), surface-enhanced infrared reflection absorption, and surface-enhanced Raman scattering (SERS). Based on spectral evidence, it is expected that the chemisorption of FA on gold island films takes place through thiol groups, which become more active as pH increases. The SEIRA spectra of these films show increased peak intensity, as well as improved band resolution. Microspectroscopy SERS studies show that, at pH 5, FA form small aggregates on gold surfaces. At pH 8, FA tends to expand due to electrostatic repulsion, giving rise to a fractal surface composed of different domains. SERS studies of these domains reveal that the most polar molecules are located on the external faces. At pH 11, fractal conformations are even more pronounced and give rise to radial patterned structures. At this pH, the position of fulvic acid molecules in the fractal micelles is the same as observed at pH 8. In this way, SERS can be viewed as a powerful tool for the analysis of the composition, apparent contribution of the surface functional groups of FA films, and the FA building blocks (i.e., catechol, gallic, salicylic, or ftalic acids) in the structures of these materials.

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Scanning force microscopy of two‐dimensional structure formation in thin humic acid films

Cited by 8 publications

References 25 publications

Quantification of humic acids in surface water: effects of divalent cations, pH, and filtration

Quantification of humic acids in surface water: effects of divalent cations, pH, and filtration

DRIFT Mapping of Organic Matter Composition at Intact Soil Aggregate Surfaces

Surface-Enhanced Vibrational Microspectroscopy of Fulvic Acid Micelles

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