Effect of ionic strength on the adsorption of cationic polyelectrolytes onto alumina studied using electroacoustic measurements

Development of gold plasmonic nanoparticles for detection of polydiallyldimethylammonium chloride at Umgeni water treatment plants: An optimised study and case application

Background

Polydiallyldimethylammonium chloride (poly-(DADMAC) is used in many drinking water treatment plants in most parts of the world as a flocculant to remove suspended solids from raw water. However, it is very important that residual poly-(DADMAC) is monitored because it disintegrates into a carcinogenic compound known as N-nitrosodimethylamine (NDMA) during the treatment of drinking water.

Methods

In this work, the gold nanoparticle method is optimised for the detection of poly-(DADMAC), where the gold nanoparticles were stabilised with trisodium citrate and then used in quantifying poly-(DADMAC) by Ultraviolet-Visible-Near Infrared spectrophotometry. The optimised method was able to measure poly-(DADMAC) at low concentrations of 1.000 μg L^-1 in drinking water with limits of detection and limits of quantification of 0.3302 and 1.101 μg L^-1, respectively.

Significant results

The method was applied to two different water treatment plants and the concentration of poly-(DADMAC) found during stages of the water treatment process ranged from 1.013 to 33.63 μg L^-1. The average poly-(DADMAC) concentrate concentration that is dosed for coagulation in Umgeni Water plant A was 7.889 μg L^-1 while in plant B was 19.28 μg L^-1. Residual poly-(DADMAC) concentration in drinking water was within the accepted limit of 50.00 μg L^-1, regulated by the World Health Organisation (WHO).

Adsorption behavior of methyl orange onto an aluminum-based metal organic framework, MIL-68(Al)

MIL-68(Al), a powdered aluminum-based metal organic framework (MOF), was synthesized and used to explore its adsorption behavior toward methyl orange (MO). The adsorption isotherm, thermodynamics, kinetics, and some key operating factors as well as changes in the material's structure were investigated. The adsorption isotherm conformed to the Langmuir isotherm model and the maximum equilibrium adsorption capacity was 341.30 mg g^-1. Thermodynamic data demonstrated that the adsorption process was spontaneous, endothermic and showed positive entropy. For kinetics, the process of MO adsorption onto MIL-68(Al) was more suitably described by a pseudo-second-order model. Electrostatic and hydrogen-bonding interactions contributed to dye adsorption, with electrostatic interactions considered to be the principal binding force between adsorbent and adsorbate. Furthermore, MIL-68(Al) maintained a stable structure after adsorption. From these results, MIL-68(Al) was suggested here to be a stable MOF adsorbent for removing MO from aqueous solution.

Isoelectric points and points of zero charge of metal (hydr)oxides: 50years after Parks' review

The pH-dependent surface charging of metal (hydr)oxides is reviewed on the occasion of the 50th anniversary of the publication by G.A. Parks: "Isoelectric points of solid oxides, solid hydroxides, and aqueous hydroxo complex systems" in Chemical Reviews. The point of zero charge (PZC) and isoelectric point (IEP) became standard parameters to characterize metal oxides in aqueous dispersions, and they define adsorption (surface excess) of ions, stability against coagulation, rheological properties of dispersions, etc. They are commonly used in many branches of science including mineral processing, soil science, materials science, geochemistry, environmental engineering, and corrosion science. Parks established standard procedures and experimental conditions which are required to obtain reliable and reproducible values of PZC and IEP. The field is very active, and the number of related papers exceeds 300 a year, and the standards established by Parks remain still valid. Relevant experimental techniques improved over the years, especially the measurements of electrophoretic mobility became easier and more reliable, are the numerical values of PZC and IEP compiled by Parks were confirmed by contemporary publications with a few exceptions. The present paper is an up-to-date compilation of the values of PZC and IEP of metal oxides. Unlike in former reviews by the same author, which were more comprehensive, only limited number of selected results are presented and discussed here. On top of the results obtained by means of classical methods (titration and electrokinetic methods), new methods and correlations found over the recent 50years are presented.

Biosensor utilizing a liquid crystal/water interface functionalized with poly(4-cyanobiphenyl-4'-oxyundecylacrylate-b-((2-dimethyl amino) ethyl methacrylate))

The interface between the nematic liquid crystal, 4-cyano-4'-pentylbiphenyl (5CB) and water within a transmission electron microscopy (TEM) grid cell coated with the pH-dependent weak cationic amphiphilic block copolymer poly((4-cyanobiphenyl-4'-oxyundecylacrylate)-b-((2-dimethyl amino) ethyl methacrylate)) (LCP-b-PDMAEMA) (which was successfully synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization) was subsequently evaluated for protein and deoxyribonucleic acid (DNA) detection. The LCP-b-PDMAEMA monolayer was fabricated using a Langmuir Blodgett trough, transferred to the 5CB-filled TEM grid, and placed on the octadecyltrichlorosilane-coated glass (TEMPDMAEMA) in such a way that the LCP chains were immersed in the 5CB while the PDMAEMA chains were pointed away from the 5CB surface and immersed in water. Several model proteins such as bovine serum albumin (BSA), hemoglobin (Hb), and chymotrypsinogen (ChTg) were tested at pH values ranging from 2 to 12 to determine the role of the charge state of the protein on protein detection by a weak polyelectrolyte such as PDMAEMA. PDMAEMA contains cationic and neutral states below and above the pKa value, respectively, and is thus able to absorb proteins below its pKa threshold through electrostatic interactions. BSA exhibited a homeotropic to planar (H-P) change in orientation within the TEMPDMAEMA grid cell at concentrations greater than 0.02wt% within the pH range between the isoelectric point (pI) of BSA and the pKa of PDMAEMA, where the charge states of BSA and PDMAEMA were negative and positive, respectively. However, this change in orientation did not occur with other proteins that exhibited a pI higher than the pKa of PDMAEMA due to the electrostatic repulsions resulting from their same cationic charges. This result indicates that the electrostatic interactions between proteins and PDMAEMA are a major contributing factor for protein detection by the H-P transformation within the TEMPDMAEMA grid cell. DNA, a pH-independent strong anionic polyelectrolyte, was also tested with the TEMPDMAEMA grid cell, and it exhibited an H-P transformation at the charged state of PDMAEMA below its pKa threshold at concentrations higher than 0.01wt%. Thus, we demonstrated that the TEMPDMAEMA grid cell effectively facilitated the detection of negatively charged biomaterials (i.e.; protein and DNA) through the H-P transformation using the polarized optical microscope. This simple and inexpensive experimental set-up for non-specific biomaterial detection lays the basic groundwork for developing effective biosensors using polyelectrolytes.

Coagulation of wood extractives in chemical pulp bleaching filtrate by cationic polyelectrolytes

The purpose of this research was to investigate the effectiveness of short-chain cationic polyelectrolytes of different molecular weights and charge densities in reducing turbidity and selectively removing toxic wood extractives from chemical birch pulp filtrate. The effects of chemical type, dosage and temperature were of interest. An effective performance was achieved with a copolymer of acrylamide and methacrylate of medium molecular weight and medium charge density at 72 degrees C and pH 5-6. The dosage range optimum for reducing the turbidity was 102-142 mg/L. Up to 92% of the wood extractives was selectively removed.

Microscopical characterization of nanocapsules templated on ionic crystals and biological cells toward biomedical applications

Nanocapsules, fuzzy assemblies of polyelectrolyte, represent a comparatively new class of colloids with controlled nanostructure and tunable properties. Due to the fact that the core as well as the dissolution influences the wall texture and the properties of the hollow capsules, the use of carbonate crystals as template is most convenient. Yeast cells constitute as a core candidate as well. They are a good system for testing the protective ability of shells and the permeability of the walls with respect to the needs of biological systems, namely, feeding and stability against attacks. The main features of the nanocapsules have been studied by two-photon, confocal, and atomic force microscopy. Nanocapsules are of biomedical interest because they can be used, for example, for the controlled release and targeting of drugs as well as for the protection of enzymes, proteins, and foreign cells.

Super-stoichiometric charge neutralization in particle-polyelectrolyte systems

The adsorption of poly(vinylamine) (PVA) on poly(styrene sulfate) latex particles is studied, and its consequences on the charging behavior and suspension stability are investigated. The adsorption process is assessed by batch depletion experiments and time-resolved electrophoretic mobility measurements. The adsorption of PVA appears to be basically irreversible. The rate of adsorption decreases with decreasing polymer dose. At low polymer dose, the polymer coverage corresponds to the amount of the polyelectrolyte added, while at high polymer dose, the polymer coverage saturates the surface. Stability ratios are determined by dynamic light scattering, and strongly depend on the polymer dose and salt level. The aggregation is rapid near the isoelectric point (IEP), and it slows down when moving away from it. The charge neutralization is highly nonstoichiometric with charging ratios (CR) larger than unity, meaning that several charges on an adsorbed polyelectrolyte chain are necessary to neutralize a single charge on the particle surface. By comparing the IEP for particles and polyelectrolytes of different charge densities, we find a strong dependence of the CR on the mismatch between the average distances between individual charges on the surface and on the polyelectrolyte. A simple model is proposed to explain this trend.

Review of the measurement of zeta potentials in concentrated aqueous suspensions using electroacoustics

This paper reviews the technique of electroacoustics as it has been applied to aqueous suspensions of inorganic particles. It starts by charting the development of the technique from its earliest beginnings in the 1930s to the present day. The technique has become well established in the last decade with the advent of the Acoustosizer and the Acoustosizer II. Illustrations of how the technique can be used are given based on the author's own experience, especially the measurement of iso electric points, the adsorption of polyelectrolytes, the effect of ionic strength, the effect of powder surface area and the dissolution of material from powders. Some new data on (a) the adsorption of different molecular weights of polyacrylic acid onto alumina and (b) titanium dioxide suspensions are also presented.