Formation Of Hemimicelles Research Articles

A novel switchable collector for selective flotation of fine copper oxide from silica

A novel pseudo-Gemini collector (PGC) featuring pH-responsive collecting power and enhanced selectivity is developed for flotation recovery of fine copper oxides from silica. The switchable PGC is formed through ionic pairing between protonated triethylenetetramine (TETA) and deprotonated oleic acid (OA) and is referred to as T-OA. The formation of T-OA was characterized by determining its critical micelle concentration of 0.6 mM at pH 10, which is much lower than that of 2.5 mM for its counterpart of OA, demonstrating a stronger surface activity of the novel T-OA collector for hemimicelle formation. Micro-flotation results showed a CuO recovery of over 90% at T-OA concentrations as low as 0.01 mM and pH 10, at which the collector exists in pseudo-Gemini form. Adjusting the flotation pH to 5 switched T-OA to monomeric form of OA with a lower surface activity but a higher selectivity which was further improved by removal of activating ions from silica by TETA. Introducing T-OA of higher collecting power in the rougher stage and then switching to a lower collecting power form of higher selectivity in the subsequent cleaner stage enhanced the flotation separation of fine CuO from silica. Zeta potential measurements indicated adsorption of T-OA on copper oxide at pH 5 and 10 with the hydrophobicity of copper oxide being stronger at alkaline conditions than that at acidic conditions as determined by contact angle measurement. The switchability of T-OA activity on CuO surfaces was illustrated by contact angle and in situ particle size distribution measurements. The reversible adsorption of T-OA on copper oxide at pH 10 was shown by QCM-D results. The results in the current study using switchable T-OA provide a clear direction for design of switchable collectors to achieve the control of the collecting performance and selectivity during the flotation processes, enhanced overall flotation performance.

Removal of perfluorooctanoic acid via polyethyleneimine modified graphene oxide: Effects of water matrices and understanding mechanisms

This research aimed to evaluate the adsorption behaviors and mechanisms of perfluorooctanoic acid (PFOA) onto polyethyleneimine modified graphene oxide (GO-PEI) from aqueous solutions. The adsorption capacity was significantly improved by doping polyethyleneimine (PEI) onto graphene oxide (GO). The Brunauer-Emmett-Teller (BET) isotherm model was considered as the best isotherm model in describing the PFOA adsorption onto GO-PEI3 (wPEI/wGO = 3). GO-PEI3 exhibited high adsorption capacity (qe = 368.2 mg/g, calculated from BET isotherm model) and excellent stability. The maximum monolayer amount of PFOA adsorption onto GO-PEI3 (qm = 231.2 mg/g) was successfully evaluated. The calculated saturated concentration (Cs = 169.9 mg/L) of PFOA on GO-PEI3 closely agrees with its critical micelle concentration (CMC = 157.0 mg/L), suggesting the formation of multilayer hemi-micelles or micelles PFOA structures on the surface of GO-PEI3. PFOA adsorption onto GO-PEI3 was inhibited by several factors including: the presence of humic acid (HA) by competing with the adsorption sites, background salts through the double-layer compression effect, and the competition from soluble ions for the amine or amide functional groups on GO-PEI3. Finally, both the FT-IR and XPS results confirmed that the adsorption of PFOA onto GO-PEI3 was through electrostatic attraction and hydrophobic interaction (physical adsorption), but not chemical adsorption. This work provides fundamental knowledge both in understanding the adsorption behavior through the BET isotherm model and in developing a stable adsorbent for PFOA adsorption. In addition, the findings highlight the potential of PFOA remediation from wastewater systems using GO-PEI in engineering applications.

Graywater treatment of emerging pollutant linear alkylbenzene sulfonate by adsorption with leather shave waste activated carbon.

The purpose of this research is to evaluate the use of leather shave waste activated carbon (ACLW) as an alternative for the treatment of wastewater containing linear alkylbenzene sulfonate (LAS). Batch adsorption tests were carried out (pH effect, isotherms, kinetics). The activated carbon was tested for its life cycle by desorption with solvent and it was further evaluated as real wastewater treatment for bath graywater. Under the optimum pH of 2.5, kinetic studies showed a better correlation with the pseudo-second order model, with an activation energy of 27.5kJmol-1. Equilibrium isotherms correlated better with the double layer model, indicating hemi-micelle formation and performing a high-affinity isotherm. Adsorption was shown to be endothermic (∆H0 = + 73.89kJmol-1), entropy driven (∆S0 = + 0.46kJmol-1K-1), and occurring spontaneously. The use of ethanol solution was effective for the regeneration of the adsorbent. Adsorption was applied in real wastewater, removing contaminants from bath graywater, especially anionic surfactants with up to 95% removal efficiency.

The interaction of frothers with hydrophobic and hydrophilic sites of coal particles in NaCl solution

Frothers are added in coal and mineral flotation to assist the formation of small air bubbles and stable froth. However, we have found that frothers can also adsorb on hydrophobic and hydrophilic sites of coal particles in flotation. In the current study, the interaction of two widely used frothers with coal particles in NaCl solution was investigated. While focused beam reflectance monitor was applied to measure the aggregation of coal particles, surface tension was measured to understand the aggregation of frother molecules. It was found that the adsorption of frothers on coal particles in NaCl solution was influenced by the NaCl-modified properties of frother molecules and coal particles. The presence of NaCl enhanced the intermolecular interaction between frothers and water and also facilitated the aggregation of coal particles. On hydrophobic sites, the hydrophobic interaction (CH/ π) between frothers and coal particles could be easily replaced by the stronger π/π interaction between coal particles, while on hydrophilic sites, the hydrophilic interaction between frothers and coal particles could be enhanced through ion-dipole attraction. Whether the hydrophobic interaction or the hydrophilic interaction played a dominant role in frother adsorption depended on the ratio of hydrophobic to hydrophilic sites and the formation of hemimicelles of frother molecules.

Influence of Surfactant Additives on Photochemical Synthesized Silver Nanoparticles using UV Pulsed Laser Irradiations in Aqueous Silver Nitrate Solution

The effect of different additives on the AgNPs formation process was explored in this study. AgNPs were synthesized in an aqueous solution of silver nitrate-containing surfactants by photoreduction of silver ions. The concentration dependency of AgNPs formation suggested that stability was induced by the equilibrium of AgNPs adsorbed by surfactants with higher carbon chain molecules such as SDS and AOT. These results open up a new window both for structural control and the development process. It also indicated that different additives had an impact on the morphology of NPs. The hydrocarbon chain influenced the growth process and demonstrated that <10 carbon chain surfactants such as SMS, SOS, did not constitute the CGC and had a minor effect on the mechanism of growth. However, the NPs formation begun at a lower limit indicated as CGC. It was observed only with hydrocarbon chains of > 10 carbon atoms such as AOT, SDS. Fluorescence results confirmed that after laser irradiation, hemi-micelle formation after the development of AgNPs.

Hemimicelle formation of semi-fluorocarbon chains at air–water interface: coarse-grained molecular dynamics study with an extension of the SPICA force field

The hemimicelle formation of long-chain semi-fluorocarbon diblocks at the air – water interface is studied using coarse-grained molecular dynamics simulations with a SPICA force field. From a series of simulations with varying the number of chains, the critical saturated size of a single micelle was predicted; its structural metrics such as the hexagonal chain packing order, density distribution, shape, mean diameter, and the orientation of the fluorinated (F-blocks) and hydrogenated segments (H-blocks) at the interface were found to be consistent with the previous experimental and atomistic simulation results. The diblock assemblies larger than the saturated size spontaneously split into multiple micelles separated by a metastable parallel phase (P-phase). This P-phase could be the reason for the non-coalescence and elastic behaviour of the hemimicelle assemblies. From the simulation with a low molecular arrangement area, the mechanism of the micelle formation of saturated sizes is illustrated. The results reveal that the mutual-phobicity and interfacial tension difference of F- and H-blocks with the water are sufficient to drive the self-assembly and can provide a significant thermodynamic stability to the micelles, where the increasing packing strain between the layer curvature and the planarizing water surface tension can determine the size of the saturated hemimicelles.

Metal cation complexes as dispersing agents for non-aqueous powder suspensions

Formulation of high solid load slurries is an important aspect in achieving dense, high quality ceramic green body shaping by additive manufacturing techniques. To this end, the understanding and control of interparticle interactions in non-aqueous organic slurry systems is imperative. With nanosized powders gaining increasing interest, particle stabilization by long-chain polymeric dispersants is undesirable due to the high exclusion volume associated and the subsequent decrease in the maximum solid load of the suspension. In this study, we focus on the stabilization mechanisms provided by metal cation complexes in methyl ethyl ketone and isopropanol-based spinel slurries. Special focus is given to chromium (III) 2-ethylhexanoate. Hemi-micelle formation at the powder surface in methyl ethyl ketone is suggested as a highly efficient stabilization mechanism. Complexes of metal dopant cations may open new pathways towards future advances in ceramic slurry formulation, especially in the field of additive manufacturing. Furthermore, the importance of solvation forces is discussed on the basis of the protic or aprotic character of the solvent used.

Langmuir Films of Perfluorinated Fatty Alcohols: Evidence of Spontaneous Formation of Solid Aggregates at Zero Surface Pressure and Very Low Surface Density.

In this work, Langmuir films of two highly fluorinated fatty alcohols, CF3(CF2)12CH2OH (F14OH) and CF3(CF2)16CH2OH (F18OH), were studied. Atomic Force Microscopy (AFM) images of the films transferred at zero surface pressure and low surface density onto the surface of silicon wafers by the Langmuir-Blodgett technique revealed, for the first time, the existence of solid-like domains with well-defined mostly hexagonal (starry) shapes in the case of F18OH, and with an entangled structure of threads in the case of F14OH. A (20:80) molar mixture of the two alcohols displayed a surprising combination of the two patterns: hexagonal domains surrounded by zigzagging threads, clearly demonstrating that the two alcohols segregate during the 2D crystallization process. Grazing Incidence X-ray Diffraction (GIXD) measurements confirmed that the molecules of both alcohols organize in 2D hexagonal lattices. Atomistic Molecular Dynamics (MD) simulations provide a visualization of the structure of the domains and allow a molecular-level interpretation of the experimental observations. The simulation results clearly showed that perfluorinated alcohols have an intrinsic tendency to aggregate, even at very low surface density. The formed domains are highly organized compared to those of hydrogenated alcohols with similar chain length. Very probably, this tendency is a consequence of the characteristic stiffness of the perfluorinated chains. The diffraction spectrum calculated from the simulation trajectories compares favorably with the experimental spectra, fully validating the simulations and the proposed interpretation. The present results highlight for the first time an inherent tendency of perfluorinated chains to aggregate, even at very low surface density, forming highly organized 2D structures. We believe these findings are important to fully understand related phenomena, such as the formation of hemi-micelles of semifluorinated alkanes at the surface of water and the 2D segregation in mixed Langmuir films of hydrogenated and fluorinated fatty acids.

Adsorption of Perfluorooctane sulfonate (PFOS) onto metal oxides modified biochar

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant (POP), which poses potential toxicity to biotic and abiotic ecosystem. Adsorption of PFOS from soil and water has emerged as promising remediation practice due to low cost, high removal performance, low environmental impact, and recalcitrant to induce secondary contamination. In this study, red mud modified sawdust (RMSDN600) and unmodified sawdust (SDN600) were prepared for sorption of PFOS from aqueous solution. The presence of magnetites (Fe 3 O 4 ), ferrihydrites, and desilicated minerals are identified in the RMSDN600 using XRD (X-ray diffraction) and XANES (X-ray absorption near-edge structure). Sorption isotherm for RMSD600 and SDN600 showed close-fitting with Langmuir and Freundlich model demonstrated monolayer and multilayer sorption of PFOS over the active sites of the adsorbents. The potential formation of micelles and hemi-micelles can occur in interparticle porous biochars as the concentration of PFOS exceeds critical hemi-micelle concentration (4.57–45.7 mg/L). The kinetic study followed Pseudo-second-order model for both adsorbents, demonstrated both physisorption and chemisorption of PFOS. The results revealed the adsorption of PFOS was governed by both hydrophobic and electrostatic interaction, with hydrophobic interaction as the dominant sorption mechanism. The higher adsorption capacity for RMSDN600 (194.6 mg/g) was recorded than that for SDN600 (178.6 mg/g) at pH 3.1 due to the abundance of protonated metal-based functional groups, and more ordered graphitic carbon structure resulting from catalytic degradation and transformation of cellulose and hemicellulose. Aromatic structure can potentially enhance PFOS sorption by non-ionic interaction. In contrast, metal-based and other oxygen-containing functional groups of adsorbents enhance adsorption capacity through electrostatic interaction and ion exchange reactions. Lower solution pH and smaller particle size of the adsorbents could also enhance sorption of PFOS from aqueous phase. • Carbon content, surface area, and porosity of biochar reduced after modification with metal oxides. • Iron minerals in red mud transformed to magnetites, and ferrihydrites in RMSDN600. • Highly pyrolyzed (600 °C) hydrophobic biosorbents favor PFOS adsorption. • Metal oxide modified biochar has more ordered aromatic structure than the raw biochar. • The adsorption capacity was 178.1 and 194.6 mg/g for SDN600 and RMSDN600.

In English

This review analyses the authors’ recent and related works on electrokinetic properties and colloidal stability of aqueous suspension of multiwalled carbon nanotubes (CNTs) in the presence of surfactants and nanoparticles. Selected adsorptive properties of carbon nanotubes are also considered. The applicability of classical theories of electrophoresis for description of electrophoretic mobility of carbon nanotubes is discussed. Examples on the ζ-potential of CNTs in aqueous suspensions as a function of pH and concentration of electrolytes (KCl, CaCl 2 and AlCl 3 ) are given. Additions of cetyltrimethylammonium bromide (CTAB) cationic surfactant below the critical micelle formation concentration (CMC) values give a reduction and then an overcharging the CNT surface because of accumulation of the surfactant ions in the Stern layer. At concentrations above CMC the substantial drop in ζ is observed. It is due to the shift of the shear plane toward solution as a result of formation of hemi-micelles on the surface. An increase in the mass ratio of artificial mineral Laponite (Lap) in suspension (X) from 0 to 0.4 results in a monotonic decrease of the ζ-potential of CNT + Lap hybrids with reaching its plateau value ≈ –32 mV at X ≥ 0.4 that corresponds to the ζ of “pure” Lap platelets. This evidences the high surface coverage of nanotubes surface with Lap at X ≥ 0.4. The major methods to improve the dispersibility of carbon nanotubes, their colloidal stability and adsorptive properties are briefly discussed, namely: stabilization in mixtures of water and organic solvents; functionalization by chemical treatment; stabilization by additives of surfactants or polymers and hybridization by addition of supplementary stabilizing nanoparticles. CNTs can be significantly debundled in “good” solvents, such as 1-cyclohexyl-2-pyrrolidone, N,N-dimethylformamide, or N-methyl-2-pyrrolidone. It is demonstrated that the dispersibility of CNTs is a complex function of the type of surfactant, its concentration and the surfactant/CNTs ratio. The optimum concentration of CTAB to achieve homogeneous aqueous dispersion of carbon nanotubes was identified to be near the CMC. Additions of CTAB significantly modify the size distribution of CNTs and a sharp transition from small primary aggregates to large secondary aggregates at concentrations above CMC is observed. At optimal concentration of Lap the nanotube particles get well stabilized, and a stepwise increase of sedimentation stability is observed. We have shown also that CNT + Lap hybrids can be effectively used for removal of methylene blue dye from aqueous systems. The kinetics and mechanisms of adsorption are elucidated.

Enhanced adsorption of perfluorooctanoic acid (PFOA) from water by granular activated carbon supported magnetite nanoparticles

A new composite material (Fe3O4@GAC, Fe3O4 nanoparticles loaded on a commercial granular activated carbon (GAC)) was prepared through a facile hydrothermal process at controlled Fe2+:Fe3+ molar ratios in air. Fe3O4@GAC was thoroughly characterized and tested for adsorption of perfluorooctanoic acid (PFOA) in water. Fe3O4@GAC(2:1), prepared at an Fe2+:Fe3+ molar ratio of 2:1, showed the best PFOA removal and offered 28.8% higher adsorption capacity than the parent GAC at final pH 4.0. The enhanced adsorption of PFOA was attributed to concurrent hydrophobic, electrostatic and complexation interactions between PFOA, GAC and Fe3O4. GAC in the composite played an important role for PFOA adsorption. The presence of Ca2+ ions (10 mM) at final pH 5.0–10.0 more than doubled the PFOA equilibrium uptake of PFOA by Fe3O4@GAC(2:1) due to the calcium bridging effect between PFOA and the Si-OH or Fe-OH groups in Fe3O4@GAC(2:1), and because of the Ca2+-modification induced formation of PFOA hemi-micelles on the surface or in the relatively large pores (2.27 nm) of Fe3O4@GAC(2:1). Fe3O4@GAC(2:1) was amenable to efficient regeneration using a mixture of NaOH solution and methanol. Fe3O4@GAC holds the potential to be used as a simple and low-cost adsorbent for enhanced adsorption of PFOA, especially in waters of high hardness and alkalinity.

Electrodeposition-Assisted Rapid Preparation of Pt Nanocluster/3D Graphene Hybrid Nanozymes with Outstanding Multiple Oxidase-Like Activity for Distinguishing Colorimetric Determination of Dihydroxybenzene Isomers.

Here, we demonstrate a facile bottom-up strategy to fabricate Pt nanoclusters (Pt NCs) grafted onto three-dimensional graphene foam (3D GF) assisted by cetyltrimethyl ammonium bromide (CTAB) using the electrodeposition method. The homogeneous grafting of Pt NC onto 3D GF is due to the formation of hemimicelles above some CTAB concentration. With the unique nanocluster structure and the high content of Pt0, the Pt NC/3D GF nanohybrid exhibits extremely high activity and shows higher reusability and stability. Apart from the intrinsic oxidase-like activity with 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate, the Pt NC/3D GF nanohybrid can act simultaneously as an effective polyphenol oxidase (PPO) mimic, such as tyrosinase, catechol oxidase, and laccase. More importantly, utilizing intrinsic catechol oxidase-like activity and the oxidase-like activity with TMB as the substrate of the nanohybrid, distinguishing colorimetric determination of dihydroxybenzene isomers (catechol and hydroquinone) is performed. Distinguishing colorimetric analysis of dihydroxybenzene isomers was first developed using nanozymes. The present work provides a simple bottom-up approach for the reasonable fabrication of various nanostructured nanozymes with excellent performance using the electrodeposition method assisted with surfactants.

Evaluating perfluorooctanesulfonate oxidation in permanganate systems.

Permanganate (PM) has shown to be able to oxidize a range of organic contaminants including perfluorooctane sulfonate (PFOS). However, mechanisms of PFOS removal by PM have been questioned. To provide clarity to what may be happening to PFOS in PM systems, here we evaluated the ability of PM on PFOS destruction by conducting studies similar to previous studies that reported PFOS destruction which included PM solutions and PM combined with persulfate (PS). We also evaluated if addition of various soluble catalysts could enhance PM's potential to breakdown PFOS. We observed no PFOS destruction by PM. We also show that the F- and SO42- generation reported in a published study as evidence that PM was breaking bonds in PFOS were found below or not significantly higher than reported limits of quantitation and that SO42- impurities in technical PM approach the reported SO42- levels. For PM-PS systems, heterogeneous PFOS distribution was observed when subsampling reaction vessels at different depths and "salting-out" of PFOS was evident. In addition, subsequent sonication and filtering of the samples led to the apparent disappearance of most of the PFOS, which was an artifact arising from the behavior of PFOS aggregates or potential hemi-micelle formation. Given these findings, addition of salts may have application for collecting or concentrating PFOS and other PFAAs in a remediation or water treatment strategy.

Physical functionalization of multi-walled carbon nanotubes for enhanced dispersibility in aqueous medium

Noncovalent functionalization of multi-walled carbon nanotubes (MWCNTs) by anionic surfactants (sodium dodecylbenzene sulfonate; SDBS and sodium cholate; SC) results in stable aqueous dispersions. SDBS showed better dispersing efficiency at lower concentration than that of SC due to the stabilizing π-π stacking induced by the presence of benzene ring in the tail of SBDS. The hemimicelle formation on the surface of nanotubes is likely to be the dominant dispersion mechanism that imparts higher colloidal stability for the MWCNTs in aqueous medium.

Interfacial Chemistry of Conical Fullerene Amphiphiles in Water.

Amphiphiles are used for a variety of applications in our daily life and in industrial processes. They typically possess hydrophobic and hydrophilic moieties within the molecule, thereby performing a myriad of functions through the formation of two- and three-dimensional assemblies in water, such as Gibbs monolayers and micelles. However, these functions are often inseparable because they emerge from the same structural feature of the molecule, and are difficult to control because the structural diversity is limited to either long-chain hydrocarbons bearing a polar end group(s) or polymers bearing polar groups exposed to the exterior surface. In this Account, we describe the chemistry of a new class of amphiphiles, conical fullerene amphiphiles (CFAs), utilizing a superhydrophobic [60]fullerene group as a nonpolar apex with added structural features to make it soluble in water. By selective functionalization of only one side of the fullerene molecule, the CFA molecules spontaneously assemble in water through strong hydrophobic interactions among the fullerene apexes and exhibit unusual supramolecular and interfacial behavior. They form unilamellar micelles and vesicles at a critical aggregation concentration as low as micromolar, not showing any air-water and oil-water interfacial activity. The strong preference for self-assembly in water over monolayer formation at an air-water interface makes CFAs unique among conventional nonpolymeric surfactants. The CFA assemblies are often so mechanically robust that they can be transferred to the surface of a solid substrate and analyzed by high-resolution microscopy. Because of this rigid conical structure of a few nanometers in size, CFA molecules aggregate readily in water to form a hierarchical assembly with biomolecules and nanomaterials while maintaining the structural integrity of the CFA aggregate to form multicomponent agglomerates of controllable structural features. For instance, tissue-selective in vivo transport of DNA and siRNA has been achieved. Hybridization of a CFA vesicle with a transition metal catalyst enables the construction of a structurally defined nanospace and an interface for precise control of the nanoscale morphology of polymers. Solubilization of hydrophobic nanocarbons and nanoparticles is also achieved through hemimicelle formation on solid surfaces. The examples reported here illustrate the potential of the conical fullerene motif for the design of amphiphiles as well as supramolecular structures at molecular and tens of nanometers scale.

Modified magnetic chitosan nanoparticles based on mixed hemimicelle of sodium dodecyl sulfate for enhanced removal and trace determination of three organophosphorus pesticides from natural waters

Mixed hemimicelle SDS-coated magnetic chitosan nanoparticles (MHMS-MCNPs) were utilized as an efficacious adsorbent for both removal and preconcentration of pesticides named diazinon, phosalone and chlorpyrifos. In this method, the formation of mixed hemimicelles made up of SDS on the surface of MCNPs leads to solubilization and the retention of target analytes by strong hydrophobic and electrostatic interactions, which has been realized for the first time in magnetic chitosan nanoparticles support. Different parameters affecting the adsorption of pesticides were optimized as rFemoval efficiency by response surface methodology and one variable at a time. Under the optimum condition, adsorption equilibrium data were fitted well to the Langmuir isotherm. Extraction recoveries for 5 ng mL−1 of diazinon, phosalone and chlorpyrifos were 99%, 98% and 96%, respectively; with relative standard deviations values were lower than 4.6% for five replications of extraction. Limit of detection obtained for mentioned pesticides were <0.09 ng mL−1. Eventually, MHMS-MCNPs were successfully applied for both removal and trace determination of pesticides in surface and ground environmental and waste water samples collected from various places in northern Iran.

Conical Ionic Amphiphiles Endowed with Micellization Ability but Lacking Air-Water and Oil-Water Interfacial Activity.

Micellization in water and reduction of the surface tension at water interfaces with air and oil are two archetypical properties of surfactants, caused by self-aggregation and Gibbs monolayer formation at the interfaces, respectively. We present here a new type of amphiphiles that possess a conical shape consisting of a hydrophobic apex and five ionic termini at the base of the cone. The conical shape and the high charge density cooperatively impede monolayer formation at the interfaces, hence preventing foaming and emulsification. On the other hand, the conical shape strongly assists micelle formation in water and hemimicelle formation on a solid surface to promote dissolution of nanoparticles such as magnetic nanoparticles and nanocarbons in water. The well-defined shape and charge locations distinguish the new amphiphiles from known polymer amphiphiles that show similar surface activity.

Evaluation of a mixed anionic-nonionic surfactant modified eggshell membrane as an advantageous adsorbent for the solid-phase extraction of Sudan I-IV as model analytes.

The coadsorption of mixed anionic-nonionic surfactants, sodium dodecylbenzenesulfonate with Triton X-100, on the surface of eggshell membrane was investigated based on adsorption isotherms to improve the solid-phase extraction performance of eggshell membrane toward organic contaminants. Results showed that even though excess Triton X-100 might inhibit the adsorption of sodium dodecylbenzenesulfonate, a low dosage of Triton X-100 can significantly improve sodium dodecylbenzenesulfonate modification and enhance the extraction efficiency of eggshell membrane from 73.7 to 100.4% because of the formation of mixed hemimicelles. The highest recovery was achieved at 2:8 (Triton X-100/sodium dodecylbenzenesulfonate mass ratios), and multiple mechanisms involving π-π interactions, hydrophobic effect, and π-π electron donor-acceptor interactions contributed to the strong extraction affinity. When mixed, the Triton X-100 and sodium dodecylbenzenesulfonate modified eggshell membrane packed cartridge coupled with high-performance liquid chromatography was applied for the simultaneous determination of trace Sudan I-IV, and low detection limits (0.16-0.26ng/L) were achieved with satisfactory linearity (R2 >0.999) in 10-10000μg/L. For real samples, Sudan II and III in one chilli sauce sample were found at 4.3 and 1.7μg/kg. Sudan I-IV recoveries at three spiked levels were 87.4-102.9% with precisions <6.8%. Comparison with commonly used solid-phase extraction adsorbents and methods further reflected the superiorities of the proposed adsorbent in sensitivity, retention ability, and applicability.

Characterization of frothers and their behavior using partial molar Excess Gibbs energy

Frothers, which are widely used as key reagents in the flotation of ores, are generally alcohols of varying structures. There is abundant experimental data which illustrates that frothers cause changes in froth behavior, bubble size/coalescence and surface tension and that these changes are closely associated with changes in the molecular structure of the frothers. Partial molar Excess Gibbs energy is a thermodynamic property which quantifies the difference between the partial molar value of the Gibbs energy of a species in a real mixture and that for the same species in an ideal mixture and this difference in mixture properties is due to differences in the molecular structures of the constituent species. It is thus reasonable to hypothesize that partial molar Excess Gibbs energy may be a useful parameter to quantify the changes which occur when using frothers of different molecular structures. In this paper it is shown that there is a generally strong relationship between measured characteristics such as froth volume/height, surface tension, hemi-micelle formation and the partial molar Excess Gibbs energy of alcohol frothers and these correlations provide robust evidence that many of the characteristics of frothers are strongly related to their molecular structure which in turn is related to the total surface area, molecular volume, and molar volume of the molecule, the molecular weight of the constituent functional groups and the interaction energies between the species present.

Entropic nature of the adsorption of sodium dodecylbenzenesulfonate on nanoparticles of aluminum and iron oxides in aqueous medium

The adsorption of anionic surfactant sodium dodecylbenzenesulfonate (SDBS) from aqueous solution on the hydrophilic surfaces of aluminum oxide and iron oxide nanoparticles is studied via UV spectrophotometry, electrophoretic light scattering, and isothermal microcalorimetry. It is shown that the isotherms of the adsorption of SDBS on the surfaces of both oxides in the area of concentrations up to 0.6 mmol/L is linear. It is found that the positive zeta potential of the surfaces of the particles falls to zero and shifts toward the range of negative values due to adsorption. The adsorption of SDBS is characterized by positive enthalpy values over the investigated range of concentrations, while the loss of energy during adsorption indicates it is of an entropic nature. It is concluded that the probable cause of the increase in entropy is the dehydration of SDBS molecules during on surface adsorption. The obtained results are discussed in terms of the formation of hemimicelles of surfactant on the hydrophilic surfaces of metal oxide nanoparticles in an aqueous medium.