Search

Fluorographene (FG) ultra-thin films are directly grown on flexible and non-flexible insulating silicate substrates and are characterized in terms of their structural and electronic properties. FG ...

We have examined mixtures of toluene, a Newtonian liquid, with several non-Newtonian liquids (i.e. surfactants) across the full composition range, from pure toluene to pure surfactant, for the purpose of exploring their rheological properties. Surfactants of similar viscosities but significantly different molecular weights were chosen, in order to verify the role of the molecular chain length. We discovered that the classical mixing rule, based on excess activation energy, succeeds for mixtures with shorter molecular chain, but fails for mixtures with longer ones. We suggest here a hypothesis which explains this difference as the result of expanding-collapsing of flexible long-chain molecules in shear flow. In order to support this hypothesis, we applied longitudinal rheology measurements which reproduce such oscillatory effects under the controlled conditions of an ultrasound longitudinal wave. This method confirms that there are qualitative differences in the rheology of these liquids mixtures with short and long molecular chains.

Monolayers of different mutants of bacteriorhodopsin (bR) with purple membranes are deposited on gold (Au) substrates. Optical measurements and density functional theory-based electronic structure ...

We report a novel Raman technique that allows fast and reliable ex vivo assessment of the irritability of personal care cleansing products to the skin in terms of the molecular-level effects such as retention of water by corneocytes, change in the packing order and content of intercellular lipids, and the structure of keratin. We test this technique for the single surfactants (dodecyl glucoside, sodium dodecyl sulfate, sodium cocoyl glycinate, lauramidopropyl betaine) that are typically used in personal care, as well as on three types of commercial soap bars (“superfat”, “syndet”, and “combar”). We find that soaking of the skin for prolonged time in pure water can cause unfolding of keratin, which is commonly considered as a signature of “harshness” when dealing with the surfactant formulations. Moreover, molecular-level signatures of irritability of the test surfactants and soaps at brief (10 min) exposure times do not follow the trend expected from their critical micelle concentrations (CMC) and collagen swelling. In particular, dodecyl glucoside has positive impact on the barrier properties of the stratum corneum (SC) and apparent detergency properties (solubilizes lipids without affecting their packing order). We also find that two qualitatively different soap bars (“superfat” and “syndet”) are similarly mild under the conditions studied, while the “combar” soap has detergency properties. These results demonstrate that to improve methodology of predicting irritability of a surfactant-based formulation, we need to study more systematically the molecular-level responses of the SC to exposure.

Interactions between polymer and surfactant provide the system a variety of properties that can be readily used by industries to achieve desired features for their products and formulations. Inclusion of a third component to the binary system is expected to present synergistic or antagonistic effects, and also lead to preferred advantages, such as reduced quantities of the components to present a comparable performance and improved environmental-benignity. In this study a sugar-based surfactant n-Dodecyl β-D-Maltoside (DM) is introduced into an oppositely charged hydrophobically modified polyelectrolyte-surfactant system comprised by a guar grafted with hydroxypropyl trimethyl ammonium chloride (Guar-HTAC) and Sodium Dodecylsulfate (SDS). By following the pattern curves of surface tension, polarity and turbidity profiles, it was found that DM plays a crucial role in the interaction process: DM leads to the formation of a soluble but surface active complex which has not been observed in the Guar-HTAC/SDS and SDS/DM systems; since DM cooperates with SDS to form micelles at much lower SDS concentrations, under certain conditions it is SDS/DM micelles instead of single SDS or DM molecules that interact with Guar-HTAC. Such behaviors are believed to be resulted from the structures of the complexes formed by the three components. Molecular structures of these formed complexes need to be investigated following this study.

To separate siderite from carbonate-bearing iron ore efficiently, specific adsorption configurations and effective species were investigated to compare the adsorption differences of sodium oleate (NaOL) on siderite and hematite surfaces. The species were analysed in neutral conditions, under which the direct flotation of siderite from hematite and quartz was carried out. Changes in the zeta potential, Fourier-transform infrared spectroscopy spectra and X-ray photoelectron spectroscopy spectra caused by the adsorption of oleate species were compared to confirm the adsorbed species on siderite and hematite. Molecular dynamics simulations were carried out to further verify the specific adsorption configurations. Chemisorption of oleate species was detected on both siderite and hematite. The differences in the relative concentration changes of the elements indicate that NaOL worked on siderite and hematite via adsorption of various groups or species. The main functional species were RCOO− for siderite and RCOOH RCOO− for hematite. A strong chemical bond formed as RCOO− directly acted upon the Fe of siderite. The carbon chains bent and interweaved to form the hydrophobic layer on siderite. The two chains of RCOOH RCOO− laid upon hematite via weak chemical bonds and hydrogen bonds. Van der Waals and hydrophobic forces were the main interforces of the two chains.

Pregelatinized starch (PS) was used for the selective flocculation and flotation of fine siderite in a carbonate-containing iron ore. With PS, the flotation of fine siderite was improved. The repulsive forces between fine siderite particles and the attractive forces between siderite and hematite or quartz were decreased after treatment with PS, indicating that the aggregation of siderite was enhanced and the aggregations of mixed minerals were weakened. An analysis of the changes in X-ray photoelectron spectra showed that coordination bonds were formed when PS was adsorbed on siderite and hematite. However, PS could not adsorb on quartz. Moreover, the molecular simulation showed that the main mechanism for PS adsorption on siderite was confirmed as a "tail model" with end -OH coordinated with Fe2+. The bridge connection of PS enhanced the flocculation of fine siderite. The flotation of fine siderite was also enhanced. For hematite treated with PS, the combination of coordination bond and hydrogen bond resulted in the "loop model" and "train model" as the main adsorption mechanisms of PS. The molecules covered the hematite surface and prevented the adsorption of the collector. The flotation of hematite was depressed. As a result, the selective flocculation and flotation of fine siderite were realized.

Colloids which adsorb to and straddle a fluid interface form monolayers that are paradigms of particle dynamics on a two dimensional fluid landscape. The dynamics is typically inertialess (Stokes flows) and dominated by interfacial tension so the interface is undeformed by the flow, and pairwise drag coefficients can be calculated. Here the hydrodynamic interaction between identical spherical colloids on a planar gas/liquid interface is calculated as a function of separation distance and immersion depth. Drag coefficients (normalized by the coefficient for an isolated particle on the surface) are computed numerically for the four canonical interactions. The first two are motions along the line of centres, either with the particles mutually approaching each other or moving in the same direction (in tandem). The second two are motions perpendicular to the line of centres, either oppositely directed (shear) or in the same direction (tandem). For mutual approach and shear, the normalized coefficients increase with a decrease in separation due to lubrication forces, and become infinite on contact when the particle is more than half immersed. However, they remain bounded at contact when the particles are less than half immersed because they do not contact underneath the liquid. For in-tandem motion, the normalized coefficients decrease with a decrease in separation; they collapse, for all immersion depths, to the dependence of the drag coefficient on separation for two particles moving in tandem in an infinite medium. The coefficients are used to compute separation against time for colloids driven together by capillary attraction.

Poly(acrylic acid) and alkyl modified poly(acrylic acid) nanoparticles were formed by the reverse microemulsion technique. Scanning electron microspectroscopy, zeta potential measurements and fluorescence spectroscopy were used for their characterization. It was observed that they are in the range 80–100 nm and their surface charge is pH dependent. The particles were assessed for their ability to extract drugs such as amitriptyline and bupivacaine from bulk fluid for their potential application as scavengers for overdosed drugs. In normal saline (0.9% NaCl) unmodified poly(acrylic acid) nanoparticles (per gram) extracted 81 mg amitriptyline and 62 mg bupivacaine in 5 minutes, whereas for the alkyl modified poly(acrylic acid) nanoparticles, extractions were 68 mg and 51 mg amitriptyline and bupivacaine respectively per gram of nanoparticles used.

Flotation separation and recovery of value minerals from ores containing fibrous silicate minerals are known to be quite challenging. Earlier studies have established that the metallurgical challenges (poor selectivity and recovery, high energy consumption, etc.) arise from the impact of the fibrous minerals (with high aspect ratio) on pulp rheology, which was found be rather complex. The complex rheological behavior of ore suspensions containing particles with high aspect ratio and its influence on flotation outcome are investigated in this study. Flotation tests and rheological measurements were carried out with both ores (containing fibrous minerals) and a model system comprising nylon fibers (chemically inert) added to a copper ore that had no fibrous mineral. These studies allowed the determination of contributions of physical properties of the fiber to pulp rheological behavior. Optical microscopy images of the fiber pulp indicated that the fibers entangled to form two levels of microstructures: two-dimensional (2D) aggregates under semi-dilute ( 30% solids. The yield stress (σ) values determined for the fiber pulp were logarithmically related to the volume fraction of the 2D/3D structures. The relationships developed here for different ARs showed that the yield stress of a flotation pulp changes with respect to shape, size, and the concentrations of the microstructures. Implications to the effects of such entangle networks on selectivity of flotation separation are discussed.

The aim of the study was to develop methods to investigate xanthate decomposition in an ore pulp under simulated flotation conditions. A method was developed to collect, analyze, and quantify the decomposition products generated during the simulated flotation. After adequate validation, this setup was applied to study xanthate decomposition under: a) conditions similar to those typically used for sulfide ore flotation, and b) longer time scale, greater temperature, greater xanthate concentration, and reduced pH (all of which are expected to promote decomposition and enhance CS2 generation). By examining the effects of time, ore loading and xanthate concentration, it was found that minerals have a major impact on decreasing xanthate decomposition due to multiple interactions occurring among xanthate and the minerals, leading to a variety of compounds with varying decomposition kinetics. The decomposition of these compounds altogether is believed to be slower compared to that of free xanthate ions in homogeneous solutions, so the overall decomposition is less in the presence of minerals. Understanding the decomposition behavior of those species is crucial for elucidation of the overall xanthate decomposition behavior in complex ore pulp systems.

This study examines the translation and rotation of a spherical colloid straddling the (upper) air/liquid interface of a thin, planar, liquid film bounded from below by either a solid or a gas/liquid interface. The goal is to obtain numerical solutions for the hydrodynamic flow in order to understand the influence of the film thickness and the lower interface boundary condition. When the colloid translates on a film above a solid, the viscous resistance increases significantly as the film thickness decreases due to the fluid-solid interaction, while on a free lamella, the drag decreases due to the proximity to the free (gas/liquid) surface. When the colloid rotates, the contact line of the interface moves relative to the colloid surface. If no-slip is assumed, the stress becomes infinite and prevents the rotation. Here finite slip is used to resolve the singularity, and for small values of the slip coefficient, the rotational viscous resistance is dominated by the contact line stress and is surprisingly less dependent on the film thickness and the lower interface boundary condition. For a colloid rotating on a semi-infinite liquid layer, the rotational resistance is largest when the colloid just breaches the interface from the liquid side.

The surfactin biosurfactants exhibit a unique form of molecular architecture, a heptapeptide lactone ring (LR) associated with a β-hydroxy fatty-acid tail. Their surface-active properties largely d...

Heterogeneous electroreduction of CO2 has received considerable attention in the past decade. However, none of the earlier reviews has been dedicated to nitrogen-containing polymers (N-polymers) as an emerging platform for conversion of CO2 to industrially useful chemicals. The term 'platform' is used here to underscore that the role of N-polymers is not only to serve as direct catalysts (through loaded metals) but also as co-catalysts/promoters and stabilizing agents. This review covers the current state, advantages, challenges, and prospects of the application of N-polymer-metal composites, also referred as polymer functionalized, coated, or modified electrodes, as well as functional hybrid materials, for the electrocatalytic conversion of CO2. It briefly surveys the efficiencies of the N-polymer-metal electrodes already used for this application, methods of their fabrication, and proposed mechanisms of their catalytic activities.

Recently, halide perovskites have upstaged decades of solar cell development by reaching power conversion efficiencies that surpass the performance of polycrystalline silicon. The efficiency improvement in the perovskite cells is related to repeated recycling between photons and electron–hole pairs, reduced recombination losses, and increased carrier lifetimes. Here, we demonstrate a novel approach toward augmenting the perovskite solar cell efficiency by invoking the Förster Resonance Energy Transfer (FRET) mechanism. FRET occurs in the near-field region as the bacteriorhodopsin (bR) protein, and perovskite has similar optical gaps. Titanium dioxide functionalized with the bR protein is shown to accelerate the electron injection from excitons produced in the perovskite layer. FRET predicts the strength of long-range excitonic transport between the perovskite and bR layers. Solar cells incorporating TiO2/bR layers are found to exhibit much higher photovoltaic performance as compared to baseline cells without bR. These results open the opportunity to develop a new class of bioperovskite solar cells with improved performance and stability. Post-print / Final draft

This study introduces an "anti-adhesive force" at the interface of solid hydrate and liquid solution phases. The force was induced by the presence of hydrophobic silica nanoparticles or one of the common anti-agglomerants (AAs), sorbitan monolaurate (Span 20), at the interface. The anti-adhesive force, which is defined as the maximum pushing force that does not induce the formation of a capillary bridge between the cyclopentane (CP) hydrate particle and the aqueous solution, was measured using a microbalance. Both hydrophobic silica nanoparticles and Span 20 can inhibit adhesion between the CP hydrate probe and the aqueous phase because silica nanoparticles have an aggregative property at the interface, and Span 20 enables the hydrate surface to be wetted with oil. Adding water-soluble sodium dodecyl sulfate (SDS) to the nanoparticle system cannot affect the aggregative property or the distribution of silica nanoparticles at the interface and, thus, cannot change the anti-adhesive effect. However, the combined system of Span 20 and SDS dramatically reduces the interfacial tension: emulsion drops were formed at the interface without any energy input and were adsorbed on the CP hydrate surface, which can cause the growth of hydrate particles. Silica nanoparticles have a good anti-adhesive performance with a relatively smaller dosage and are less influenced by the presence of molecular surfactants; consequently, these nanoparticles may have a good potential for hydrate inhibition as AAs.

Evaluation of the impacts of reagents on SHE (safety, health, and the environment) is crucial for industries, regulatory agencies, and governments; however, it is a nontrivial task and there has not been universal acceptance of metrics or tools for this purpose. We have been developing an evaluation tool called Greenness Index to provide a holistic assessment of reagents used in various industries. Analysis by means of this tool is based on information found in reagent SDSs (Safety Data Sheets) plus metrics for various consequences when the reagent is used in a particular application. SDSs contain information on the various properties of a reagent and how it impacts SHE from cradle to grave; however, these summaries rarely consider the multifarious possibilities of how the reagent may transform during use in an application. Including such features in a more complete evaluation of the SHE impact of a reagent is the ultimate goal of our efforts to develop Greenness Index. Efforts reported here are in the preliminary step of representing the panoply of SHE information found in SDSs in a manner that allows a more holistic, multi-parametric comparison of reagents. Five clusters (Health Impact, General Properties, Odor, Fire Safety, and Stability) of attributes that are combined to form a total evaluation were created based on widely accepted sustainability guidelines such as the Green Chemistry 12 Principles and Green Engineering 12 Principles. Sorting and binning algorithms were developed to quantify each attribute and cluster of attributes, resulting in quantitative scores for each. Scores are displayed graphically to help visualize the relative Greenness of the reagent. Displays are in the form of a hierarchy of spider-diagrams. This Greenness Index method has been applied in a variety of instances to specific reagents used in various industries such as mineral processing and personal care. Greenness Index analysis of PAX (Potassium Amyl Xanthate), commonly used as a flotation reagent in mineral processing, is described here as an example. Results from such an analysis can be incorporated into a decision making process that facilitates the selection of greener reagents and provides valuable insights to improve and develop sustainable practices.

Xanthate is one of the commonly used collectors in froth flotation beneficiation of sulfide ores. It decomposes and generates toxic compounds such as carbon disulfide (CS2) which is a concern in the mining industry. A vast body of literature exists for studies on xanthate/mineral interactions, but xanthate decomposition under various conditions (e.g., in solutions or flotation pulps) is not fully understood. We have undertaken detailed studies to fill this knowledge gap, and this paper shows our study of the xanthate decomposition in aqueous solutions in the absence of minerals. This condition has not been appropriately examined by past researchers, while decomposition under this condition is used as control to other complicated ones (e.g., in flotation pulps). A GC–MS based method was developed to directly measure the decomposition products in the gas phase. Decomposition kinetics was then established based on the generation of CS2. Decomposition followed the first order kinetics, and the rate constant for Sodium iso-Butyl Xanthate (SIBX) at neutral pH level was determined to be 9.3 × 10−4 h−1 at 25 °C, 1.7 × 10−2 h−1 at 50 °C and 1.3 × 10−1 h−1 at 70 °C. The effect of pH on decomposition behavior was examined in the pH range of 1.5–12.5. We determined experimentally a maximum in the extent of decomposition as a function of pH, which was predicted theoretically in literature. A mechanism involving multiple reactions that occurred in parallel or sequentially along with the decomposition was proposed to explain the observed change of xanthate decomposition over the entire pH range. These results offer valuable insights and can serve as the basis to mitigate the detrimental effects of xanthate decomposition in plant operations, for example, by modifying plant parameters to reduce xanthate decomposition without sacrificing its performance.

Speciation at the calcite-water interface and surface charge of calcite are essential for calcite usage in interfacial-dependent applications. The transfer of dissolved Ca2+ ions between the electrical double layer (EDL) and the interface is a key step in the speciation process. The ice-like layer water-molecules at the interface represents a barrier that restricts this transmittance unless the dissolved Ca2+ ions in the EDL attain a threshold (minimum) entropy state – a saturation level – where the electric field acting on the dissolved Ca2+ ions could be stronger enough for their movement through the ice-like layer. This threshold state was estimated to be at aEDL Ca2+ level ~5 × 10−4 M/m2 (dissolved Ca2+ ions content in EDL’/‘interfacial area’). The transmitted Ca2+ ions chemisorb at the interfacial carbonate sites (> CO 3 2 - ) and lead to speciation of calcium carbonate ion complexes (>CO3-Ca - ( H 2 O ) x + , x: degree of hydration) and polymorphs. Therefore, the surface charging behavior of calcite, subsequent to interfacial adsorption of the dissolved Ca2+ ions, relies on the degree of hydration and the polymorphic characteristics of these complexes.

We resolve the long-standing controversy about the first step of the CO(2) electroreduction to fuels in aqueous electrolytes by providing direct spectroscopic evidence that the first intermediate of the CO(2) conversion to formate on copper is a carboxylate anion *CO(2)(−) coordinated to the surface through one of its C–O bonds. We identify this intermediate and gain insight into its formation, its chemical and electronic properties, as well as its dependence on the electrode potential by taking advantage of a cutting-edge methodology that includes operando surface-enhanced Raman scattering (SERS) empowered by isotope exchange and electrochemical Stark effects, reaction kinetics (Tafel) analysis, and density functional theory (DFT) simulations. The SERS spectra are measured on an operating Cu surface. These results advance the mechanistic understanding of CO(2) electroreduction and its selectivity to carbon monoxide and formate.

Significance The understanding of a catalytic reaction starts with understanding its first elementary step. Surprisingly, despite the large number of studies, it is unclear whether one common or two different first intermediates control the selectivity of CO 2 electroreduction to formate and CO. We settle this controversy for Cu, which is best known for its unique capacity to synthesize C 1+ products but is just emerging as a superior earth-abundant catalyst for CO and formate. We provide solid experimental and theoretical support of the one common first-intermediate (Hori’s) model, the first intermediate being carboxylate. This outcome is an essential milestone toward accurate specification of the reaction descriptors in the growing effort to accelerate the discovery of a viable CO 2 electroreduction catalyst.

The micro-polarity anisotropy behaviour across the aqueous phase of a SDS (sodium dodecyl sulphonate)–hexane reverse micelle (RM) relies on the SDS packing in the oil–water interfacial self-assembled surfactant structure of the RM.

Supported micron-sized molybdenum disulfide (MoS2) has been extensively studied for catalytic synthesis of Higher Alcohols Synthesis (HAS) from synthesis gas (syngas). However, the process is associated with low space–time–yield (STY) and poor selectivity under high temperature (300–325 °C) and high pressure (10–20 MPa) operation, making it unattractive for commercial application. Nano-sized MoS2 catalyst particles improve selectivity to alcohols but the yields are low possibly due to catalyst aggregation and mass transfer limitations. This study describes the use of oil-in-polyethylene glycol (PEG) microemulsion-based encapsulation of hydrophobic catalyst nanoparticles (MoS2) to prevent aggregation, increase surface area and increase mass transfer across the two phases. In this study, nano-sized MoS2 was first synthesized by sonolysis of hexacarbonyl molybdenum and yellow sulfur in hexadecane in

The world continues to rely heavily on petroleum as a primary energy source. However, a great fraction of the oil-in-place remains inaccessible to traditional recovery means. This review presents an update on the use of biotechnology to improve residual crude oil production from oil wells as a tertiary oil recovery method known as “microbial enhanced oil recovery” (MEOR). Our focus has been to critically discuss and analyze the recent research trends in this field, with special attention devoted to separately assessing both laboratory and field cases to better demonstrate the progress being made across different MEOR techniques. MEOR strategies reviewed here include the uses of selective plugging, biopolymers, wettability alterations, bioacids, biosolvents, and biosurfactants. Additionally, the emerging contributions of genetically-engineered microorganisms for MEOR purposes (GEMEOR) and enzyme-enhanced oil recovery (EEOR) are also analyzed. While further research must still be done to optimize MEOR methods for the oil industry, biotechnology-based methods hold much promise for oil recovery operations as well as for oil spill remediation.

One of main challenges in developing clinically relevant engineered cartilage is overcoming limited nutrient diffusion due to progressive elaboration of extracellular matrix at the periphery of the construct. Macro-channels have been used to decrease the nutrient path-length; however, the channels become occluded with matrix within weeks in culture, reducing nutrient diffusion. Alternatively, microparticles can be imbedded throughout the scaffold to provide localized nutrient delivery. In this study, we evaluated biocompatibility of polysebacic anhydride (PSA) polymers and the effectiveness of PSA-based microparticles for short-term delivery of nutrients in engineered cartilage. PSA-based microparticles were biocompatible with juvenile bovine chondrocytes for concentrations up to 2mg/mL; however, cytotoxicity was observed at 20mg/mL. Cytotoxicity at high concentrations is likely due to intracellular accumulation of PSA degradation products and resulting lipotoxicity. Cytotoxicity of PSA was partially reversed in the presence of bovine serum albumin. In conclusion, the findings from this study demonstrate concentration-dependent biocompatibility of PSA-based microparticles and potential application as a nutrient delivery vehicle that can be imbedded in scaffolds for tissue engineering.

Two surfactants, namely, dodecanoylglycinate and dodecanoylsarcosinate, differing only in a methyl group vs. a hydrogen atom on the amide nitrogen, have been studied with respect to solution behavior and adsorption at the air–water, oil-water and calcium carbonate-water interfaces. It was found that the ability of the glycinate surfactant of forming intermolecular hydrogen bonds via the amide group leads to tighter molecular packing, which greatly influenced the behavior at interfaces. Based on this molecular observation, potential applications were considered and emulsification, foaming and wetting tests were carried out. It could be concluded from this work that a minor change in the structure of a surfactant molecule can be very significant for technological systems and processes.

Aiming at developing a safe and efficient alternative to traditional drinking water disinfection, this work successfully synthesized a novel antibacterial material with high surface area, ultra large pore size and tunable loading of immobilized lysozyme. The immobilized enzymes exhibit high antibacterial efficacy without forming carcinogenic disinfection byproducts. Critical immobilization parameters were optimized to keep the activity of the immobilized enzyme at a high level. The immobilization of lysozymes on 3DOm COOH could be confirmed by the characterizations of transmission electron microscopy, X-ray diffraction and Zeta-Potential. In addition, the structural stability of lysozymes on 3DOm COOH were studied by Fourier transform infrared spectroscopy. The antibacterial performance of 3DOm COOH-Lyz were specifically investigated based on the disinfection efficacy of Staphylococcus aureus in water. The results revealed that the immobilization capacity and relative activity of immobilized lysozyme were 814mg/g carrier and 80%, respectively, under the optimal immobilization conditions. And the antibacterial material with the initial mass ratio of lysozyme and 3DOm COOH as 3:1 exhibited maximum bacteria removal efficiency (98.1%) at pH 5. Moreover, the reusability test indicated that 3DOm COOH-Lyz has certain operational stability, and remains 82% bacterial removal efficiency even in the fifth cycle, which provides a promising application for safe and efficient drinking water disinfection in small-scale and emergency water treatment.

The effects of fatty acids on oppositely charged polyelectrolyte–surfactant interactions are experimentally investigated. It was observed that dodecanoic (lauric) acid (LA) disrupts the well-established reported interaction between the anionic surfactant sodium dodecylethersulfate (SDES) and the cationic polymer guar modified with grafted hydroxypropyl trimethyl ammonium chloride (Jaguar C13 BF). Surface tension measurements showed that, at the known surfactant Critical Aggregation Concentration (CAC), SDES binds to the partly surface active polymer, which is transformed into a soluble complex. The complex reaches insolubility when the polymer is entirely neutralized by SDES, and is re-solubilized in excess of surfactant micelles. The interaction pattern is relatively similar when the polymer interacts with a mixed SDES-LA system at LA molar fraction below its solubility limit in SDES. Interestingly, when the LA molar fraction exceeds the solubility limit in SDES and solid fatty acid aggregates form, preferential binding of the polymer to the LA in solid form was observed. Similar behavior was seen in emulsion systems containing the same oppositely charged polymer–surfactant pair, where polymer-induced flocculation is expected due to bridging of oil droplets upon dilution. In this case, the preferential adsorption of the polymer to the fatty acid in solid form prevents the polymer from acting as flocculant.

Achieving a stable and robust dispersion of ultrafine particles in concentrated electrolytes is challenging due to the shielding of electrostatic repulsion. Stable dispersion of ultrafine particles in concentrated electrolytes is critical for several applications, including electro-codeposition of ceramic particles in protective metal coatings. We achieved the steric stabilization of SiC micro- and nano-particles in highly concentrated electroplating Watts solutions using their controlled coating with linear and branched polyethyleneimines (PEI) as dispersants. Branched polyethyleneimine of 60,000 MW effectively disperses both microparticles and nanoparticles at a concentration of 1000 ppm. However, lower polymer dosages and smaller polymers fail to disperse, presumably due to insufficient coverage and bridging flocculation. Dispersion stability correlates well with the adsorption density of PEI on microparticles. We discuss the results in the framework of DLVO theory and suggest possible dispersion mechanisms. However, though the dispersion is enhanced with extended adsorption time, the residual PEI in solution adversely affects electroplating. We overcome this drawback by precoating the particles with the polymer and resuspending them in Watts solution. With this novel approach, we obtained robust dispersions. These results offer new possibilities to control dispersion at high electrolyte concentration, as well as bring new insights into the dispersion phenomenon.

Particulates of 1 to 100 nanometers size are being increasingly used for a variety of clinical and commercial purposes due to their large surface-to-volume ratio and unique physico-chemical, mechanical and electronic properties. While utilizing them for their beneficial functions, it has become vital to heed recent alerts on their toxic biological effects in order that benign systems might be developed. In this paper we review emerging mechanisms of nanotoxicity and possible means for remediation. Challenges in monitoring, characterizing and remediation of nanoparticles are also presented.

We have developed a novel metal-free highly robust recyclable electrosorbent for removal Pb(II) from water. It is based on a cost-efficient and biocompatible conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) which is synthesized through a facile green chemistry route. This electrosorbent demonstrates superior adsorption-desorption properties and recyclability as compared to conventional lead adsorbents and the same sorbent but without electrostimulation. Specifically, its Pb(II) uptake (>800 mg/g without saturation in the presence of excessive NaCl, Ca and Fe) is three-fold higher, while adsorption and desorption kinetics at 400 ppb Pb(II) are faster than without electrostimulation. Importantly, the electrosorbent has 100% reversibility and excellent stability for at least 30 adsorption-desorption cycles and after one-month storage in water. Using XPS and Raman spectroscopy, we link the outstanding properties of the electrosorbent to its unique cation-exchange properties which are enhanced by applied potential. Our results demonstrate a novel strategy for facile manufacturing of cost-effective robust recyclable electrosorbents from conjugated conducting polymers, as well as advantages of electrochemical stimulation for achieving highly repeatable electrosorption and reclamation of valuable metals from their dilute solutions in complex aqueous matrices.

With an increasing concern on environment and health, the issue of decomposition of various mining reagents which generates harmful impacts need to be timely handled. DTC (Dithiocarbamate), which play a similar role as xanthate in flotation as collector, was under investigation in this study using the systematic method developed for xanthate (Part I) to understand the effects of metal ions on the decomposition. It was found that DTC and xanthate have similarities with respect to decomposition: Cu2+ suppresses while Fe3+ promotes its decomposition; with an increase in the alkyl chain length, decomposition becomes weaker. With the same alkyl chain length, DTC decomposes less than xanthate. These observations can be explained by the molecular structures of the reagent anion and the derivatives such as dimer and metal complex (similar to xanthate, DTC forms cuprous or ferric DTC and di-DTC when interacting with Cu2+ or Fe3+). The longer the alkyl chain, the stronger the -CS2 moiety attaches to the R2N- in DTC or the RO- in xanthate, so the lower the decomposition of xanthate or DTC is. The -CS2 moiety attaches to the R2N- in DTC stronger than that to the RO- in xanthate, making xanthate decompose more than DTC. A proposed order of easiness for the -CS2 moiety to break up from xanthate or DTC is: cuprous complex

An earlier study (Part I) indicated that Cu2+ ion suppresses while Fe3+ ion promotes xanthate decomposition into CS2. The main factor responsible for the disparate effects was proposed to be the differences in interactions between xanthate and metal ions in solution. UV–vis and FTIR spectrometers were used to examine the products of such interactions in the liquid and precipitate phases, respectively. For both metal ions, it was found that metal xanthate (i.e. cupric xanthate Cu2X2 and ferric xanthate FeX3) and dixanthogen (X2) are formed. Although for different metal ions metal xanthate and dixanthogen are formed by different mechanisms, generation of CS2 in the gas phase can be correlated to the formation and decomposition of the metal xanthate and dixanthogen. It was found that metal xanthate and dixanthogen both are responsible for the effects of metal ions on SIBX decomposition: with the increase of Cu/SIBX ratio, decrease of CS2 is accompanied by the decrease of Cu2X2 and X2; with the increase of Fe/SIBX ratio, increases of CS2 are accompanied by the increase of FeX3 and X2. Which compound, metal xanthate or dixanthogen, play a more important role in affecting the decomposition could not be determined yet. Further studies is also required to elucidate the mechanisms how Cu2X2, FeX3 and X2 are quantitatively determining the overall decomposition kinetics.

The mining industry faces increasing regulatory pressure from hazardous reagents used in mineral processing operations. Xanthates, a common class of collectors used in flotation, have come under scrutiny in recent years for their potential to present significant HSE (Health, Safety and Environmental) hazards resulting from their propensity to generate toxic compounds (such as CS2) during transportation, storage, use and disposal. Interactions between xanthate and metal ions are ubiquitous in flotation systems, and the products formed are known to influence mineral separation efficiency and selectivity. The effect of such interactions (and the products formed) on the overall decomposition of xanthate is not well known. A method was developed to enable a systematic and integrated analysis of compositional changes in gas, liquid and precipitate phases of a closed system comprising xanthate solution and metal ions (Cu2+ or Fe3+). A study of compositional changes in the gas phase indicated that Cu2+ suppresses decomposition of xanthate into CS2, and the magnitude of the effect increases with an increase in temperature. Fe3+ ions, on the other hand, promote decomposition; however, the effect of increasing temperature on decomposition is confounded by the oxidative effect of Fe3+ ions. How Cu2+ and Fe3+ ions affect decomposition in terms of the decomposition products is the focus of Part I and the mechanistic aspects of the effect of Cu2+ and Fe3+ ions are discussed in Part II.

The fracking industry faces various challenges although technologies have been advanced in the hydraulic fracturing and horizontal drilling. Treatment for the water used after the fracking process is one of the key issues preventing hydraulic fracturing from being widely implemented. Especially the chemicals that are used for various purposes during fracking remain in the water that flows back to the surface. Reports have been seen that the problematic chemicals used in the fracking process cause HSE (Health, Safety and Environment) issues. Before any chemical used in the fracking is eliminated or replaced with alternatives, its greenness should be evaluated. A tool called Greenness Index was used in this study to evaluate several typical chemicals used in the current fracking process. SDS (Safety Data Sheet) information was used by Greenness Index to assess the chemicals. It was found that with similar amount of SDS information available, citric acid is relatively greener than ammonium persulfate. SDS information of guar gum is less than that of citric acid and ammonium persulfate, but the evaluation for guar gum still indicates that it is a green chemical based on the limited data from its SDS. When more information with respect to how they behave during the fracking process is available, Greenness Index can provide more comprehensive evaluations.

Two biosurfactants, surfactin and fatty acyl-glutamate, were produced from genetically-modified strains of Bacillus subtilis on 2% glucose and mineral salts media in shake-flasks and bioreactors. Biosurfactant synthesis ceased when the main carbohydrate source was completely depleted. Surfactin titers were ∼30-fold higher than fatty acyl-glutamate in the same medium. When bacteria were grown in large aerated bioreactors, biosurfactants mostly partitioned to the foam fraction, which was recovered. Dispersion effectiveness of surfactin and fatty acyl-glutamate was evaluated by measuring the critical micelle concentration (CMC) and dispersant-to-oil ratio (DOR). The CMC values for surfactin and fatty acyl-glutamate in double deionized distilled water were 0.015 and 0.10 g/L, respectively. However, CMC values were higher, 0.02 and 0.4 g/L for surfactin and fatty acyl-glutamate, respectively, in 12 parts per trillion (ppt) Instant Ocean ® sea salt, which has been partly attributed to saline-induced conformational changes in the solvated ionic species of the biosurfactants. The DORs for surfactin and fatty acyl-glutamate were 1:96 and 1:12, respectively, in water. In Instant Ocean ® solutions containing 12 ppt sea salt, these decreased to 1:30 and 1:4, respectively, suggesting reduction in oil dispersing efficiency of both surfactants in saline. Surfactant toxicities were assessed using the Gulf killifish, Fundulus grandis , which is common in estuarine habitats of the Gulf of Mexico. Surfactin was 10-fold more toxic than fatty acyl-glutamate. A commercial surfactant, sodium laurel sulfate, had intermediate toxicity. Raising the salinity from 5 to 25 ppt increased the toxicity of all three surfactants; however, the increase was the lowest for fatty acyl-glutamate.

Activities of the enzymes, protease subtilisin and horse radish peroxidase (HRP) have been increased 50 and 40%, respectively, in the presence of the nonionic surfactant, alkyl polyglucoside, compared with the activities in buffer alone. This enzyme hyperactivity reaches a peak at 3.0 mm of surfactant. Investigation into the structure of surfactant aggregates indicates "giant" micelle superstructures at this range of surfactant concentration of 1.7 μm in diameter--dramatically decreasing to 60 and 70 nm at higher surfactant concentrations, while surface tension measurements indicate two critical micelle concentration inflection points at 0.2 and 5.0 mm, which suggests transitions in micelle structure with respect to concentration. Furthermore, electron spin resonance (ESR) indicates that the micelles in first critical micelle concentration regime are loosely packed relative to the second aggregate phase. We hypothesize that this loose packing results in diminished hydration shell repulsion between the micelles, leading to the large, micrometer-sized aggregates. We further hypothesize that it is the interaction with these loosely packed micelles that affects the flexibility of the HRP and protease enzyme structure. Time-resolved fluorescence anisotropy of subtilisin in Brij-30 indicates increasing flexibility of catalytic active site with surfactant concentration. This is correlated with an increase in enzymatic activity.

This work addresses the adsorption of two Gemini surfactants at the cyclopentane (CP) hydrate-water interface. The Gemini surfactants investigated here are Dowfax C6L and Dowfax 2A1 that have two anionic head groups and one hydrophobic tail group. The adsorption of these surfactants was quantified using adsorption isotherms and the adsorption isotherms were determined using liquid-liquid titrations. Even if the Gemini surfactant adsorption isotherms show multi-layer adsorption, they possess the first Langmuir layer with the second adsorption layer only evident in the 2A1 adsorption isotherm. Zeta potentials of CP hydrate particles in the surfactant solution of various concentrations of Dowfax C6L and Dowfax 2A1 were measured to further explain their adsorption behavior at the CP hydrate-water interface. Zeta potentials of alumina particles as a model particle system in different concentrations of sodium dodecyl sulfate (SDS), Dowfax C6L and Dowfax 2A1 were also measured to confirm the configuration of all the surfactants at the interface. The determination of the isotherms and zeta-potentials provides an understanding framework for the adsorption behavior of the two Gemini surfactants at the hydrate-water interface.

The effect of a cationic dispersant, polyethyleneimine (PEI) on the co-deposition of 45–55 nm and 1.0 μm SiC particles with Ni on a rotating disk electrode is investigated. Addition of 500 ppm of PEI into a Watts bath increases the SiC fraction in the nano-composites without affecting the electrodeposition kinetics, however films have undesired properties, as evidenced by cracks. A pre-coating procedure, in which nano-particles are treated with 500 ppm PEI prior to introduction into the plating bath is described. The pre-coating method increases the SiC incorporation to values as high as 23 vol%, one of the highest reported values for nano-particles in electrodeposited films, without decreasing the current efficiency. In addition, the pre-coating method facilitates bath-composition optimization when, for example, leveling agents are employed; otherwise the leveling agent and PEI competitively adsorb onto the SiC particles. The efficacy of employing the pre-coating procedure in manufacturing, where plating baths need a long life, may be satisfactory. Strategies where dispersants are first attached to ceramic particles prior to integration into a plating bath containing other additives may lead to high volume fractions of particles thus harder deposits. The detailed procedures to achieve high-volume fractions required modification when transitioning from micron- to nano-sized particles.

The activated sludge (AS) flocculability markedly improved after the addition of Al 3+ and Fe 3+ compared to Ca 2+ at a concentration of 2 mEq/L. Though the energy barrier decreased about 30% when Ca 2+ was added, the AS flocculability did not improve substantially. This indicates that extended DLVO theory can explain AS flocculation with Al 3+ and Fe 3+ as additives but is not appropriate for Ca 2+ . In addition, no matter which cation was added, the AS flocculability was highly correlated to the loosely bound extracellular polymeric substances (LB-EPS) content. The majority of added Ca 2+ remained in the bulk solution (about 92%), whereas almost all of the Al 3+ and Fe 3+ added was found in the pellet (about 98%). The cation’ ability to bind to the AS is closely related to the energy barrier and LB-EPS contents, therefore it is the core reason behind the AS flocculation changes observed upon the addition of multivalent cations.