Aspects of protonation and deprotonation of humic scid durface on molecular conformation

Abstract

As densidades superficiais de carga de ácidos húmicos foram determinadas por titulação potenciométrica e condutimétrica simultâneas. Também foi observada a influência do pH na conformação molecular através de espectroscopia de UV-Vis e microscopia eletrônica de varredura (MEV). A densidade de carga superficial para todas as amostras de ácido húmico é aproximadamente zero na faixa de pH 3,5-6,0. A influência do pH na condensação molecular foi observada pela determinação do índice b na equação de Doty e Steiner. Os altos valores de b foram obtidos na região ácida, indicando uma conformação condensada, devido à fraca interação atrativa. Além disso, na região alcalina, a densidade de carga na superfície da molécula é mais negativa, o que favorece o aumento da repulsão e dispersão das partículas, levando à formação de estruturas micelares como consequência da característica anfifílica dos ácidos húmicos.The surface charge densities for humic acids (HAs) were determined by simultaneous potentiometric and conductimetric titrations. It was also observed the pH influence on molecular conformation by UV-Vis spectroscopy measurements and scanning electron microscopy (SEM) images. The surface charge densities are approximately zero at the pH range 3.5 to 6.0 for all samples. The pH influence on molecular condensation level was observed by the determination of the b index from Doty and Steiner equation. High values of b were obtained at acid region indicating a condensed conformation due to weak attractive interactions whereas around the neutral region the repulsive intramolecular forces take place leading to an extended conformation of humic molecules. Moreover, at very alkaline region, the charge density on molecule surface is more negative, increasing repulsion and dispersion of the particles and also takes place formation of micelle-like structure because of the amphyphylic feature of HA samples.

Mobility and Retention of Rare Earth Elements in Porous Media

“…At pH > 6, HA molecules are deprotonated, yielding a negative charge density on the molecule. The continuous deprotonation of HA with increasing pH decreases HA adsorption on the sand as the solution pH increases. , …”

“…The continuous deprotonation of HA with increasing pH decreases HA adsorption on the sand as the solution pH increases. 54 , 55 …”

Influence of pH, depth and humic acid on metal and metalloids recovery from municipal solid waste landfills

“…As depth is increased, the humification process increases. HA is weakly acidic with carboxylic-and phenolic-OH groups (Prado et al, 2011).…”

Aluminiumhydroxychlorid‐Flockungsmittel aus dem Kupferrecycling aus Abfällen der Leiterplattenproduktion

“…In diesem pH‐Bereich liegt typischerweise der isoelektrische Punkt der enthaltenen organischen Substanzen. , Die Protonierung bewirkt eine Kompensation negativer Ladungen, und das Zetapotenzial der kolloidalen Feststoffe wird schrittweise erhöht (Abb. ).…”

“…In diesem pH-Bereich liegt typischerweise der isoelektrische Punkt der enthaltenen organischen Substanzen. [19,21]…”