Spontaneous aggregation of humic acid observed with AFM at different pH

Colombo, Claudio; Palumbo, Giuseppe; Angelico, Ruggero; Cho, Hyen Goo; Francioso, Ornella; Ertani, Andrea; Nardi, Serenella

doi:10.1016/j.chemosphere.2015.08.010

Cited by 66 publications

(40 citation statements)

References 42 publications

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“…7). It corresponded to the thickness of 1.5e3 layers of the adsorbed LHA, which nearly doubled that reported by Colombo et al (2015) due to the higher concentration of LHA in the present study. It should be noted that both the MMT surface and humic substances often had negative charges, therefore, it was difficult for a direct adsorption and/or intercalation of humic substances to minerals due to electrostatic repulsion.…”

Section: Co-aggregation Of Asphaltene With Humic Substances In the Omsupporting

confidence: 38%

“…5B). This conformation could be interpreted by the lignin-carbohydrate complex mechanism currently proposed by Colombo et al (2015) that (i) 14 units of 1e4 phenylpropanoid were connected by the b-O-4 linkages to form oligomer chains which were stabilized by covalent and hydrogen bonds, and (ii) 45e50 linear helical chains looped spirally to form a ring-like central cavity which was driven by the dipole-dipole and van der Walls interactions. As identified in the MD simulation (Fig.…”

Section: Co-aggregation Of Asphaltene With Humic Substances In the Ommentioning

confidence: 96%

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Insights into asphaltene aggregation in the Na-montmorillonite interlayer

Zhu

Chen

2016

Chemosphere

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Section: Co-aggregation Of Asphaltene With Humic Substances In the Omsupporting

confidence: 38%

Section: Co-aggregation Of Asphaltene With Humic Substances In the Ommentioning

confidence: 96%

Insights into asphaltene aggregation in the Na-montmorillonite interlayer

Zhu

Chen

2016

Chemosphere

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“…Humic acids (HAs) were extracted from Leonardite using the method recommended by the International Humic Substances Society (IHSS). A commercial liquid mixture of humic substances (Leonardite, CIFO, Italy) was treated with a 0.1 M Na 4 P 2 O 7 solution, titrated at pH 11.0 with 0.5 M NaOH and under N 2 atmosphere at 25°C for 24 h (Schnitzer, 1978;Colombo et al, 2015a). The fraction containing HAs was purified and concentrated via acidification (pH 2.0) of the extract with 12 M HCl and subsequent centrifugation of the suspension at 8000 g for 20 min.…”

Section: Humic Acid Extractionmentioning

confidence: 99%

Iron oxide‐humic acid coprecipitates as iron source for cucumber plants

Iorio

Colombo

Angelico

et al. 2019

J. Plant Nutr. Soil Sci.

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In soil, iron (Fe) solubility depends on complex interactions between Fe minerals and organic matter, but very little is known about plant availability of Fe present in Fe oxides associated with humic substances. For this purpose, this study investigates the effect of Fe mineral crystallinity in the presence of humic acids (HA) on Fe availability to plants. Four Fe–HA mineral coprecipitates were prepared, either in the presence or absence of oxygen, i.e., two goethite (G)‐HA samples containing large amounts of Fe as nanocrystalline goethite and ferrihydrite mixed phases, and two magnetite (M)‐HA samples containing crystalline magnetite. Bioavailability studies were conducted in hydroponic systems on cucumber plants (Cucumis sativus L.) grown under Fe deficient conditions and supplied with the Fe–HA coprecipitates containing goethite or magnetite. Results showed that plants grown in the presence of Fe–HA coprecipitates exhibited a complete recovery from Fe deficiency, albeit less efficiently than plants resupplied with Fe‐chelate fertilizer used as control (Fe‐diethylene triamine penta acetic acid, Fe‐DTPA). However, the supply with either G‐ or M–HA coprecipitates produced different effects on plants: G–HA‐treated plants showed a higher Fe content in leaves, while M–HA‐treated plants displayed a higher leaf biomass and SPAD (Soil–Plant Analysis Development) index recovery, as compared to Fe‐DTPA. The distribution of macronutrients in the leaves, as imaged by micro X‐ray fluorescence (µXRF) spectroscopy, was different in G–HA and M–HA‐treated plants. In particular, plants supplied with the poorly crystalline G–HA coprecipitate with a lower Fe/HA ratio showed features more similar to those of fully recovered plants (supplied with Fe‐DTPA). These results highlight the importance of mineral crystallinity of Fe–HA coprecipitates on Fe bioavailability and Fe uptake in hydroponic experiments. In addition, the present data demonstrate that cucumber plants can efficiently mobilize Fe, even from goethite and ferrihydrite mixed phases and magnetite, which are usually considered unavailable for plant nutrition.

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“…Structures of HS have primarily been investigated by fractionation into HA and FA in response to changes in pH ( Corrado et al, 2008; Šmejkalová and Piccolo , 2008; Colombo et al, 2015). At alkaline pH values (Fig.…”

Section: Structure Of Hsmentioning

confidence: 99%

“…When HS is acidified with weakly acidic solutions, apparent molecular sizes significantly decrease or disaggregate as weak noncovalent interactions, such as van der Waals, π‐π, and CH‐π, are disrupted ( Šmejkalová and Piccolo , 2008). HS collapse at the low pH values (< 3) because of protonation of carboxylate groups that favor an increase in the number of intra‐ and intermolecular hydrogen bonds inside the humic macromolecules ( Colombo et al, 2015; Fig.1). The formation of new H‐bonding and disruption of hydrophobic interactions may favor the bioavailability of HS small aggregates released into soil solution as a consequence of root exudation of weak organic acids ( Piccolo et al, 2003).…”

Section: Structure Of Hsmentioning

confidence: 99%