Effects of pH, Ca- and SO4-concentration on surface charge and colloidal stability of goethite and hematite – consequences for the adsorption of anionic organic substances

Clay Minerals ◽  
2010 ◽  
Vol 45 (1) ◽  
pp. 1-13 ◽  
Author(s):  
J. Walsch ◽  
S. Dultz
Keyword(s):  
Surface Charge ◽  
Colloidal Stability ◽  
Streaming Potential ◽  
Cationic Polyelectrolyte ◽  
Solution Chemistry ◽  
Point Of Zero Charge ◽  
Stability Field ◽  
Fe Oxides ◽  
Multivalent Ions ◽  
Polyelectrolyte Titration

AbstractSoil solution chemistry, especially pH and the presence of multivalent ions, affects the surface charge (SC) of Fe oxides and accordingly colloidal stability and sorption properties. The SC of synthetic goethite and hematite was quantified in the presence of different electrolytes (NaCl, CaCl2, Na2SO4and CaSO4) by combining the streaming potential with polyelectrolyte titration. The point of zero charge (PZC) for goethite was observed at pH 8.2 and the stability field around the PZC, where colloids are flocculated, is more extended (±1 pH unit) than that of hematite with a PZC at pH 7.1 (±0.5 pH unit). The SC decreases with increasing SO4concentration, indicating adsorption of SO4on the oxide, whereas the presence of Ca increases the SC. At pH 4, the addition of 0.1 mmol l–1Na2SO4induced a decrease in SC from 1.5 to 0.380 μmolcm–2for goethite and from 0.85 to 0.42 μmolcm–2for hematite. In a suspension with 0.1 mmol l–1Na2SO4, the number of colloids is already reduced, and both oxides flocculate rapidly and completely at >0.5 mmol l–1Na2SO4. While the addition of SO4did not affect charge titrations with the cationic polyelectrolyte, the anionic polyelectrolyte formed complexes with Ca, resulting in an overestimation of positive SC. The electrolyte CaSO4is most efficient at keeping goethite and hematite in the pH range 4–10 in the flocculated state. Besides pH, the presence of multivalent ions should also be considered when predicting colloid mediated transport and adsorption properties of anionic substances by Fe oxides in soil systems.

scholarly journals Advancement of Measurement Techniques for Tunable Resistive Pulse Sensing

2021 ◽  
Author(s):  
◽  
Eva Weatherall
Keyword(s):  
Surface Charge ◽  
Pore Size ◽  
Applied Voltage ◽  
Particle Surface ◽  
Streaming Potential ◽  
Pore Surface ◽  
Size Distributions ◽  
Ζ Potential ◽  
Resistive Pulse ◽  
Tunable Resistive Pulse Sensing

<p>Tunable resistive pulse sensing (TRPS) is a particle-by-particle analysis technique combining the Coulter principle with size-tunable pores. TRPS can be used to characterize biological and synthetic particles 50 nm - 20 µm in diameter. Information is obtained from the resistive pulse signal, a transient change in ionic current observed when a particle passes through the pore. TRPS has been shown to provide excellent resolution and accuracy for measuring particle size and concentration as well as providing information about particle charge. TRPS is therefore applicable to many industrial and fundamental research areas involving aptamers, drug delivery particles, extracellular vesicles and other biological particle types. Advancement of this technology requires a better understanding of the technique, particularly in the area of particle surface charge measurement and this Thesis helps to provide that understanding.  In this work, firstly particle ζ-potential measurement using TRPS was investigated. A number of different measurement methods are presented and the uncertainties associated with each method are outlined. The ζ-potential for a variety of particles with different surface charges were measured in a range of electrolytes.  Particle ζ-potential measurements were then improved upon with the addition of streaming potential measurements to measure the pore surface charge. The ζ-potential of the pore surface, which makes a significant contribution to particle ζ-potential calculations, was measured using a set up which works alongside the qNano. Streaming potential measurements were also used to investigate changes in the pore surface charge following application of number of different chemical coatings. The volume of data collected and detail of analysis in this work (including uncertainties) is unprecedented in TRPS ζ potential measurements.  Biphasic pulses arising from the charge on the particles were investigated. The pulse is conventionally resistive, but biphasic pulses which include both resistive and conductive components are significant for less than 50 mM salt concentrations when measuring 200 nm particles. The experimental variables investigated include the concentration of the electrolyte, particle charge, pore size, applied voltage, and the direction of particlemotion. Conductive pulse size was seen to decrease with increasing electrolyte concentration and pore size and increase with applied voltage. A linear relationship was found between conductive pulse magnitude and particle surface group density. The influence of direction of motion on conductive pulses was consistent with concentration polarization of an ion selective pore. Biphasic pulses were also seen to affect conventional TRPS particle size measurements.  Finally, size distribution broadening due to varying particle trajectories was investigated. Pulse size distributions for monodisperse particles became broader when the pore size was increased and featured two distinct peaks. Relatively large pulses are produced by particles with trajectories passing near to the edge of the pore. Other experiments determined that pulse size distributions are independent of applied voltage but broaden with increasing pressure applied across the membrane.</p>

scholarly journals Effect of Ionic Compounds of Different Valences on the Stability of Titanium Oxide Colloids

2018 ◽  
Vol 2 (3) ◽  
pp. 32 ◽  
Author(s):  
Szabolcs Muráth ◽  
Szilárd Sáringer ◽  
Zoltán Somosi ◽  
István Szilágyi
Keyword(s):  
Titanium Oxide ◽  
Colloidal Stability ◽  
Heterogeneous Systems ◽  
Multivalent Ions ◽  
Aggregation Behaviour ◽  
Ionic Compounds ◽  
Oxide Particles ◽  
Synthetic Routes ◽  
The Stability

Titanium oxide particles of various morphologies have been prepared for applications of scientific or industrial interest in recent decades. Besides development of novel synthetic routes and solid-state characterization of the obtained particles, colloidal stability of titanium oxide dispersions was the focus of numerous research groups due to the high importance of this topic in applications in heterogeneous systems. The influence of dissolved ionic compounds, including monovalent salts, multivalent ions and polyelectrolytes, on the charging and aggregation behaviour of titanium oxide materials of spherical and elongated structures will be discussed in the present review.

Surface Charge and Adsorption Characteristics for Fluoride of Hexadecyltrimethylammonium Modified Vermiculite

2013 ◽  
Vol 781-784 ◽  
pp. 2265-2268 ◽  
Author(s):  
Shi Yong Wei ◽  
Xu Hong Deng
Keyword(s):  
Aqueous Solutions ◽  
Surface Charge ◽  
Adsorption Capacity ◽  
Langmuir Model ◽  
Point Of Zero Charge ◽  
Hexadecyltrimethylammonium Bromide ◽  
Fluoride Ions ◽  
Langmuir Adsorption ◽  
Adsorption Characteristics ◽  
Adsorption Data

HDTMA-modified vermiculite (HDTMA-Ver) was formed in a suspension by the interactions between vermiculite and hexadecyltrimethylammonium bromide (HDTMA). For vermiculite and HDTMA-Ver, the pH of the point of zero charge (pHpzc) is 3.16 and 5.09, the surface charge at pH 4.5 is-0.167 and 0.083 mmol/g, and the Langmuir adsorption capacity (qmax) is 4.98 and 8.67 mg/g, respectively. The adsorption data for fluoride by vermiculite and HDTMA-Ver could be fitted by Langmuir model. The as-prepared HDTMA-Ver exhibited excellent ability to remove fluoride ions from aqueous solutions.

Colloidal dynamics of soil clay under the effect of fine-sized biochars: Implication for biochar amendment towards preventing clay loss and soil erosion

2020 ◽  
Author(s):  
Nga T. Mai ◽  
Nga T. T. Pham ◽  
Anh T. Q. Nguyen ◽  
Anh T. N. Nguyen ◽  
Anh M. Nguyen ◽  
...  
Keyword(s):  
Soil Erosion ◽  
Surface Charge ◽  
Clay Fraction ◽  
Test Tube ◽  
Soil Clays ◽  
Soil Clay ◽  
Ph Range ◽  
Polyelectrolyte Titration ◽  
Repulsive Forces ◽  
Biochar Amendment

&lt;p&gt;In soils clay loss by leaching and surface runoff is one of the initial steps increasing the risk of erosion. Here we set out to determine the effect of fine-sized biochar amendment on colloidal dynamics of soil clay, with the aim of answering whether biochar addition enhances or curbs soil erosion. Fine-sized biochar samples were prepared from fern Dicranopteris linearis&amp;#8217;s biomass under non-biochar-oriented pyrolysis (open heating) and biochar-oriented pyrolysis (N&lt;sub&gt;2&lt;/sub&gt;-supported heating) over a temperature range from 400 to 900&amp;#176;C. The clay fraction (&lt; 2 &amp;#181;m) separated from a clay-rich soil in a hilly area of the Red River basin containing relatively high amounts of kaolinite was tested for its dispersion properties under the presence of the prepared biochars. Surface charge of biochar-soil clay mixtures was determined by polyelectrolyte titration using a particle charge detector, while corresponding colloidal properties of the mixtures were examined by the test tube method. Both, the soil clay fraction and biochar samples showed strongly negative surface charge and their surface charge was variable depending on pH. In a pH range from 3 to 10 and at an electrolyte background of 0.01 M NaCl, surface charge of the clay fraction decreased from -1.68 to -44.75 mmol&lt;sub&gt;c&lt;/sub&gt; Kg&lt;sup&gt;-1&lt;/sup&gt;, while the biochars surface charge varied from -0.6 to -48.8 mmol&lt;sub&gt;c&lt;/sub&gt; Kg&lt;sup&gt;-1&lt;/sup&gt;. Soil clays were more strongly dispersed in the presence of biochars by increasing electrostatic repulsive forces. The biochar preparation method had a crucial role for surface charge properties of biochars and in consequence colloidal dynamics of biochar-clay mixtures. The N&lt;sub&gt;2&lt;/sub&gt;-supported pyrolysis at lower temperatures does not increase charge density but creates a more porous structure, thereby increasing the total negative net charges. As a result, the N&lt;sub&gt;2&lt;/sub&gt;-supported biochars favor clay dispersion more effectively, while the open-pyrolysis biochars showed lesser effects. Our results indicate that fine-sized biochar amendments generally enhance the risk of clay loss, however, such techniques for creating low-charged biochars can help to decrease clay dispersibility when applying biochar for soil.&lt;/p&gt;

The colloidal stability of variable-charge mineral suspensions

Clay Minerals ◽  
1987 ◽  
Vol 22 (1) ◽  
pp. 93-107 ◽  
Author(s):  
F. Bartoli ◽  
R. Philippy
Keyword(s):  
Light Scattering ◽  
Rayleigh Scattering ◽  
Colloidal Stability ◽  
Aggregate Size ◽  
Point Of Zero Charge ◽  
Diffraction Scattering ◽  
Variable Charge ◽  
Alumina Gel ◽  
Mineral Suspensions ◽  
Scattering Index

AbstractA method of analysing the colloidal stability of variable-charge mineral suspensions as a function of pH is described, which combines light scattering with soluble element and surface charge measurements. The absorbance of the suspensions closely follows the A = k−m equation, where m = −dlgA/dlgλ is an aggregate light-scattering index which is inversely related to the limiting sedimentation speed v = dA600nm/dt. Usually, suspensions of variable-charge minerals scatter less near their point of zero charge where the aggregation process is a maximum, in contrast to environments where they are charged and well-dispersed. Although the morphology of goethite is that of elongated needles, kaolinite plates, and imogolite tubes, the coalesced sphere approach of the Mie theory allows rapid correlation of the absorbance at 600 nm with aggregate-size distribution, indirectly measured by the light- scattering aggregate-size index m confirmed by electron microscopy experiments. Kaolinite and goethite suspensions obey the diffraction scattering law with a variation in size of 2–20 µm from the dispersed to the aggregated particles. Imogolite and alumina gel suspensions possibly obey the anomalous diffraction scattering law and are present as 0·05–1 µm aggregates of their 50–100 Å structural units. Silica gel and the more dispersed imogolite suspensions possibly obey the anomalous Rayleigh scattering law with a variation of aggregate size from 700–3000 Å.

Using variable charge characteristics to understand the exchangeable cation status of oxic soils

Soil Research ◽  
1984 ◽  
Vol 22 (1) ◽  
pp. 71 ◽  
Author(s):  
GP Gillman
Keyword(s):  
Surface Charge ◽  
Soil Ph ◽  
Negative Charge ◽  
Positive Charge ◽  
Exchangeable Cations ◽  
Point Of Zero Charge ◽  
Exchangeable Cation ◽  
Charge Measurement ◽  
Variable Charge ◽  
Variable Surface

The model of Uehara and Gillman was used to estimate the amounts of permanent surface charge, and variable surface charge at soil pH, in two soils from the high rainfall region of coastal Queensland. For each soil series, samples from virgin rain-forest were compared with soil collected from nearby sugarcane fields. One soil contained relatively large amounts of permanent negative charge (up to 3 m.e. per 100g), and hence was moderately supplied with exchangeable cations, while the other soil was dominated by variable charge components and at soil pH contained sufficient positive charge to reduce exchangeable cations to near zero values, despite the presence of about 1 m.e. per 100 g of permanent negative charge. In the latter the position of soil pH with respect to the point of zero charge is of utmost importance for the development of cation exchange capacity. The effect of adsorbed sulfate on positive charge measurement, and valency of the ion used for negative charge measurement, are briefly discussed.

scholarly journals Advancement of Measurement Techniques for Tunable Resistive Pulse Sensing

2021 ◽  
Author(s):  
◽  
Eva Weatherall
Keyword(s):  
Surface Charge ◽  
Pore Size ◽  
Applied Voltage ◽  
Particle Surface ◽  
Streaming Potential ◽  
Pore Surface ◽  
Size Distributions ◽  
Ζ Potential ◽  
Resistive Pulse ◽  
Tunable Resistive Pulse Sensing

<p>Tunable resistive pulse sensing (TRPS) is a particle-by-particle analysis technique combining the Coulter principle with size-tunable pores. TRPS can be used to characterize biological and synthetic particles 50 nm - 20 µm in diameter. Information is obtained from the resistive pulse signal, a transient change in ionic current observed when a particle passes through the pore. TRPS has been shown to provide excellent resolution and accuracy for measuring particle size and concentration as well as providing information about particle charge. TRPS is therefore applicable to many industrial and fundamental research areas involving aptamers, drug delivery particles, extracellular vesicles and other biological particle types. Advancement of this technology requires a better understanding of the technique, particularly in the area of particle surface charge measurement and this Thesis helps to provide that understanding.  In this work, firstly particle ζ-potential measurement using TRPS was investigated. A number of different measurement methods are presented and the uncertainties associated with each method are outlined. The ζ-potential for a variety of particles with different surface charges were measured in a range of electrolytes.  Particle ζ-potential measurements were then improved upon with the addition of streaming potential measurements to measure the pore surface charge. The ζ-potential of the pore surface, which makes a significant contribution to particle ζ-potential calculations, was measured using a set up which works alongside the qNano. Streaming potential measurements were also used to investigate changes in the pore surface charge following application of number of different chemical coatings. The volume of data collected and detail of analysis in this work (including uncertainties) is unprecedented in TRPS ζ potential measurements.  Biphasic pulses arising from the charge on the particles were investigated. The pulse is conventionally resistive, but biphasic pulses which include both resistive and conductive components are significant for less than 50 mM salt concentrations when measuring 200 nm particles. The experimental variables investigated include the concentration of the electrolyte, particle charge, pore size, applied voltage, and the direction of particlemotion. Conductive pulse size was seen to decrease with increasing electrolyte concentration and pore size and increase with applied voltage. A linear relationship was found between conductive pulse magnitude and particle surface group density. The influence of direction of motion on conductive pulses was consistent with concentration polarization of an ion selective pore. Biphasic pulses were also seen to affect conventional TRPS particle size measurements.  Finally, size distribution broadening due to varying particle trajectories was investigated. Pulse size distributions for monodisperse particles became broader when the pore size was increased and featured two distinct peaks. Relatively large pulses are produced by particles with trajectories passing near to the edge of the pore. Other experiments determined that pulse size distributions are independent of applied voltage but broaden with increasing pressure applied across the membrane.</p>

scholarly journals Bacterial surface charge in “layers”: revealed by wash buffers of different ionic strength

2018 ◽  
Author(s):  
Wenfa Ng ◽  
Yen-Peng Ting
Keyword(s):  
Ionic Strength ◽  
Zeta Potential ◽  
Surface Charge ◽  
Cell Envelope ◽  
Cell Mass ◽  
Culture Broth ◽  
Point Of Zero Charge ◽  
Bacterial Surface ◽  
Incomplete Removal ◽  
Wash Buffer

Bacterial surface charge derives its meaning from the cell’s environment such as the solution in contact with the cell. Determining the surface charge of bacteria in its native environment requires measuring the proxy variable, zeta potential, using cells obtained from field studies. However, lack of adequate cell mass and concerns over measurement of a mixed species consortia rather than a specific species meant that bacterial surface charge measurement require biomass obtained from pure culture. Often grown in rich medium where myriad proteins and ions nonspecifically adsorbed onto the cell envelope or peptidoglycan layer, standard procedures for preparing the cell mass incorporated repeated steps of washing and centrifugation with various wash buffers, the efficacies of which are poorly understood. This report describes the results of a systematic study on how wash buffers of different composition and ionic strength affect the efficiency of removing nonspecifically adsorbed biomolecules and ions from Escherichia coli DH5α (ATCC 53868) cultured aerobically (shake flask, 37 oC and 230 rpm) in LB Lennox medium with 2 g/L glucose and a formulated medium. Using zeta potential-pH profiles over pH 1 to 12 as readout, the results showed that efficiency of removing nonspecifically adsorbed ions and metabolites positively correlated with wash buffer ionic strength. More importantly, 0.15M ionic strength (i.e., 9 g/L NaCl) seemed to be the minimum below which there was incomplete removal of nonspecifically adsorbed biomolecules. On the other hand, high ionic strength of 0.6M (e.g., 0.1M sodium citrate) significantly changed the point of zero charge (pHzpc), a reference marker for removal of ions intrinsic to the cell envelope. Collectively, results obtained inform wash buffer choice with regards to preserving cell envelope integrity, and avoidance of adsorption of buffer ions such as citrate. But, is there a true cell surface charge? Yes, but how do we define it in number of “layers” of adsorbed biomolecules? Philosophically, cells in culture broth are coated with layers of metabolites, proteins and ions. Hence, desire to reveal the true surface charge is essentially a decoating process, where wash buffers of increasing ionic strength remove each layer via charge screening. However, where is the endpoint? This research offers a different perspective and answer. Imagine a single bacterium suspended in LB medium, where there is constant adsorption and desorption of biomolecules as the cell grows: what is its relevant surface charge? It is the one where the loosely associated ions and metabolites are removed while retaining the nonspecifically adsorbed ions and biomolecules. Thus, deionized water wash provides a good estimate of the bacterial surface charge as grown in specific medium.

A chip device to determine surface charge properties of confluent cell monolayers by measuring streaming potential

Lab on a Chip ◽  
2020 ◽  
Vol 20 (20) ◽  
pp. 3792-3805 ◽  
Author(s):  
András Kincses ◽  
Ana R. Santa-Maria ◽  
Fruzsina R. Walter ◽  
László Dér ◽  
Nóra Horányi ◽  
...  
Keyword(s):  
Cell Surface ◽  
Surface Charge ◽  
Streaming Potential ◽  
Cell Monolayers ◽  
Biological Barriers ◽  
Cell Surface Charge ◽  
Cell Layers ◽  
Confluent Cell

Chip device to monitor streaming potential of confluent cell layers reflecting cell surface charge important for the function of biological barriers.

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