Size and Charge Evaluation of Standard Humic and Fulvic Acids as Crucial Factors to Determine Their Environmental Behavior and Impact

Abstract

In this work, the size and charge of humic and fulvic standards purchased from the International Humic Substances Society are presented and discussed. The secondary structure of humic substances in water environment as well as the size and shape of the dissolved humic species and their changes are ill-defined, very dynamic and can be strongly affected by environmental conditions as the concentration, pH, and ionic strength. They have a strong propensity to aggregate which control their interactions with other components, mobility, and functioning in the environment. Particle size distributions were determined by means of dynamic light scattering, zeta potential by Doppler electrophoresis. The intensity, volume, and number particle size distribution were obtained. Two or three different size fractions were detected in the studied systems. Large macroparticles (>1 μm) were observed in the majority of them, mainly in the case of more concentrated solutions. Medium fractions of fulvic submicroparticles had higher average diameters (500–1,200 nm) than those in humic acids (300–600 nm). Small nanoparticles (<100 nm) were detected mainly in alkaline solutions. Fulvic acids with more functional groups (active sites) can form more easily bigger particles mainly in medium concentration region. Alkaline conditions supported the expansion of humic and fulvic coils and liberation of small particles from them. The colloidal stability, indicated by more negative zeta potentials, was higher for humic acids. In the case of fulvic acids, the colloidal stability increased with increasing pH as a result of the dissociation of their functional groups. The increase of particle size corresponded usually with higher stability.

Radiolabeling Technique of Silver Nanoparticles (AgNPs) with Iodine-131 Radionuclide

“…The radionuclide purity is more than 99.9 % (by gamma-ray spectrometer) without other radionuclide impurities. This result complies with the radiopharmaceutical requirement for radionuclidic purity, i.e., ≥ 99.9 % [22].…”

The combined influence of hydrophobicity, charge and molecular weight on natural organic matter removal by ion exchange and coagulation

“…While such compounds are attracted to the exchange sites of the resin, the size of these molecules can be limiting. The hydrodynamic radii of these molecules have been determined to be >1.1 nm, with aggregated molecules having diameters in the micro meter range (Kawahigashi et al, 2011;Klučáková, 2018). Size exclusion phenomena can therefore occur as the microporous gel-type resins, with pore sizes typically < 2-4 nm can restrict compounds such as HA and FA to the exterior regions of the resin (Bhandari et al, 2016;Harland, 1994).…”

Characterization of coal-based fulvic acid and the construction of a fulvic acid molecular model

“…The results of titration experiments with acidic functional groups showed that the carboxyl group content in FA was approximately three times the phenolic hydroxyl group content. Combined with the spectral data for oxygen-containing functional groups in the range of 1000-1800 cm À1 and the relative content of oxygen, the molecular 3,21,[23][24][25][26][27][29][30][31] with the ndings of past research on HA and FA, the numbers and positions of functional groups were continuously adjusted to approximate the experimental test parameters. The resulting two-dimensional planar molecular structure model of FA is shown in Fig.…”