Organic Surfactants Research Articles

Free-Radical Dispersion Polymerization of Ethylene with Laponite to Polyethylene–Clay Nanocomposite Particles

Composite clay/polymer nanoparticle dispersions have been studied for many different polymers but remained elusive for polyolefins even though polyolefins are an important class of polymers and are also industrially applied in the form of aqueous dispersions. Despite the hydrophobic and apolar nature of polyethylene, aqueous nanocomposite dispersions are formed via heterogeneous free-radical polymerization in the presence of the synthetic smectite clay Laponite-RD at relatively mild conditions (250 atm, 85 °C). The clay nanoplatelets effectively contribute to colloidal stability of the polyolefin particles formed and strongly enhance particle formation during the aqueous polymerization. Evolution of the polymer–clay interaction at an early stage of particle formation is instrumental, and initiator-derived polar end groups are decisively involved. The clay enhances polymerization yields and promotes the formation of smaller particles. Stable dispersions with polymer contents of up to 24% were obtained without the need of additional organic surfactants.

Adsorption behaviors of aflatoxin B1 and zearalenone by organo-rectorite modified with quaternary ammonium salts

Organo-rectorites (ORts) modified with different quaternary ammonium salts were prepared to remove polar mycotoxin aflatoxin B1 (AFB1) and weak polar, hydrophobic mycotoxin zearalenone (ZER). The structural and surface properties of the prepared ORts were studied. The intercalation of organic cationic surfactants expanded the interlayer of rectorite and increased the hydrophobicity. In vitro adsorption experiments were carried out to simulate the in vivo conditions of gastrointestinal tract of animals by a batch mode. The prepared ORts showed super enhanced adsorption capacities towards AFB1 and ZER compared with raw rectorite, indicating the effectiveness of the prepared ORts as mycotoxins adsorbents. The ORts modified with longer chain surfactant molecules possessed a higher adsorption capacity towards mycotoxins. In addition, with increasing the modifier dosage, the adsorption capacity increased first and then decreased. The best adsorption capacity was achieved when the dosage of the modifier increased to 2.0CEC. The adsorption of both AFB1 and ZER onto ORts could be well described by Langmuir model. In the binary-contaminant system, the existence of AFB1 would bring negative effect to the adsorption of ZER. On the other hand, the adsorption of ZER was in favor of the adsorption of AFB1 molecules. The solution pH had negligible influence on the adsorption process of ORts both in single system and binary system, indicating no desorption occurred when the adsorbents pass through from stomach to intestine as animal feed. This study demonstrates that the received ORts could be a promising adsorbent for detoxication of different mycotoxins in real application.

Synthesis and catalytic performance of hierarchically structured MOR zeolites by a dual-functional templating approach

Novel hierarchical MOR zeolites have been successfully synthesized via a one-step dual-functional templating strategy utilizing gemini organic surfactant (C18-2-8) through hydrothermal process. After a period of ∼96 h for crystallization, the hierarchy MOR zeolite with a larger BET (412.0 m2/g), abundant intracrystalline mesopores (average mesopore size distribution of 4.55 nm), and more accessible acid sites can be synthesized. The XRD study revealed a long range structural ordering of mesoporous and a good crystallinity of microporous structure. The results indicated that the surfactant acted as a dual-functional template for generating both micropores and mesopores simultaneously. Compared with conventional MOR zeolite, hierarchically structured MOR zeolite not only has higher activity and stability, but also can avoid side-reaction taking place in ethanol dehydration reactions. This hierarchical micro/mesostructured mordenite zeolite may be a candidate for practical industrial applications especially in those reactions where bulky molecules are involved.

Investigation of organic media and surfactant sensitization in non-aqueous phase hydride generation-atomic fluorescence spectrometric determination of antimony

This work was the expansion and in-depth study based on the previously established non-aqueous phase HG system. Aiming at the determination of antimony by the developed non-aqueous phase HG, the effect of different organic media and the sensitization effect of surfactant on the non-aqueous phase HG reaction were investigated. As an important condition, organic media has an important influence on this method. This study found that the surfactant Triton X-114 had very good sensitization effect for non-aqueous HG reaction. The sensitization effect of surfactant in different organic media was different. Among the investigated media, the comprehensive performance of octanol was the best under the sensitization effect of surfactant. Compared with the analytical performance of not adding surfactant, the sensitization factor of the surfactant was 1.55. The sensitization effect of surfactant Triton X-114 on the HG reaction in the octanol media was very significant, which greatly improved the analytical performance of the non-aqueous HG method. Under the optimal conditions, the limit of detection (LOD) was 0.04 μg/L. Compared to conventional HG-AFS, the efficiency of non-aqueous phase HG and the analytical performance of the developed method was considerably improved.

Solvent-Assisted Surface Engineering for High-Performance All-Inorganic Perovskite Nanocrystal Light-Emitting Diodes.

All-inorganic cesium halide perovskite nanocrystals have attracted much interest in optoelectronic applications for the sake of the readily adjustable band gaps, high photoluminescence quantum yield, pure color emission, and affordable cost. However, because of the ineluctable utilization of organic surfactants during the synthesis, the structural and optical properties of CsPbBr3 nanocrystals degrade upon transforming from colloidal solutions to solid thin films, which plagues the device operation. Here, we develop a novel solvent-assisted surface engineering strategy, producing high-quality CsPbBr3 thin films for device applications. A good solvent is first introduced as an assembly trigger to conduct assembly in a one-dimensional direction, which is then interrupted by adding a nonsolvent. The nonsolvent drives the adjacent nanoparticles connecting in a two-dimensional direction. Assembled CsPbBr3 nanocrystal thin films are densely packed and very smooth with a surface roughness of ∼4.8 nm, which is highly desirable for carrier transport in a light-emitting diode (LED) device. Meanwhile, the film stability is apparently improved. Benefiting from this facile and reliable strategy, we have achieved remarkably improved performance of CsPbBr3 nanocrystal-based LEDs. Our results not only enrich the methods of nanocrystal surface engineering but also shed light on developing high-performance LEDs.

Comparative study on treatment of kitchen wastewater using a mixed microalgal culture and an aerobic bacterial culture: kinetic evaluation and FAME analysis.

Microalgae-based treatment systems have been successfully used for the polishing of domestic wastewater. Research is underway in studying the suitability of using these systems as main treatment units. This study focuses on comparing the performances of a mixed microalgal culture and an aerobic bacterial culture, based on the kinetic evaluation, in removing organic carbon from a kitchen wastewater. The two systems were operated at six different solid retention times (SRTs)-2, 4, 6, 8, 10, and 12days in continuous mode. The influent and effluent samples were analyzed for chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), phosphates, and surfactants. Steady-state kinetics (k, Ks, Y, and kd) for organic carbon removal were obtained by fitting experimental data in linearized Michaelis-Menten and Monod equations. The mixed microalgal system showed similar or better performance in COD and TN removal (88 and 85%, respectively) when compared with the COD and TN removal by the aerobic bacterial system (89 and 48%). A maximum lipid yield of 40% (w/w of dry biomass) was observed in the microalgal system. Saturated fatty acids accounted for 50% of the total observed FAME species. The study indicates that the mixed microalgal culture is capable of treating kitchen wastewater and has the potential to replace aerobic bacteria in biological treatment systems in certain cases.

Reconfiguring droplet interface bilayer networks through sacrificial membranes.

The droplet interface bilayer platform allows for the fabrication of stimuli-responsive microfluidic materials, using phospholipids as an organic surfactant in water-in-oil mixtures. In this approach, lipid-coated droplets are adhered together in arranged networks, forming lipid bilayer membranes with embedded transporters and establishing selective exchange pathways between neighboring aqueous subcompartments. The resulting material is a biologically inspired droplet-based material that exhibits emergent properties wherein different droplets accomplish different functions, similar to multicellular organisms. These networks have been successfully applied towards biomolecular sensing and energy harvesting applications. However, unlike their source of inspiration, these droplet structures are often static. This limitation not only renders the networks unable to adapt or modify their structure and function after formation but also limits their long term use as passive ionic exchange between neighboring droplet pairs may initiate immediately after the membranes are established. This work addresses this shortcoming by rupturing selected sacrificial membranes within the collections of droplets to rearrange the remaining droplets into new configurations, redirecting the droplet-droplet exchange pathways. This is accomplished through electrical shocks applied between selected droplets. Experimental outcomes are compared to predictions provided by a coupled mechanical-electrical model for the droplet networks, and then advanced configurations are proposed using this model.

Effect of surface modification using a sulfate-based surfactant on the electrochemical performance of Ni-rich cathode materials

Ni-rich layered oxides (Ni-rich NCM) have received much attention owing to their high specific capacity, but poor cycling performance attributed to their inferior surface properties is still considered to be a bottleneck preventing the expansion of the wider adoption of these materials in lithium-ion batteries (LIBs). In this work, we propose one-step efficient surface modification process which utilizes an organic surfactant (SDS) with a sulfate functional group in order to improve the surface stability of Ni-rich NCM materials. The surface modification provides a sulfate-embedded cathode-electrolyte interphase (CEI) layer on the Ni-rich NCM surface, which includes a SOx functional group. All of cells employing SDS-treated NCM cathode exhibit higher specific capacity retention after 100 cycles. Among these, the cell cycled with the 0.5% SDS-treated Ni-rich NCM cathode exhibited specific capacity retention of 91.9%, which is a remarkable increase compared with the cell cycled with bare NCM811 (69.6%). Additional analyses of the cycled electrodes indicated that the better cycling performance of the SDS-treated NCM811 cathode is attributable to the stabilization of the NCM811 surface; less electrolyte decomposition was observed in a cycled SDS-treated NCM811 cathode when analyzed by SEM, EIS, and XPS.

Two-dimensional (2D) amorphous antimony (III) trisulfide nanosheets: Synthesis, photoelectronic property and their transformation to crystalline 1D micro/nanorods

Two-dimensional (2D) crystal materials have attracted intensive research interest because of their multifunctionality. However, the 2D nanosheets (NSs) of amorphous semiconductors are far less explored. We demonstrate here the colloidal synthesis of 2D amorphous antimony (III) trisulfide (Sb2S3) NSs in the mixture solution of different long-chain primary amines. These organic amines act as soft template to define the 2D growth through the coordination of metal cations with amine group. The resultant NSs exhibit distinct 2D characteristic with the thickness of 2–4 nm and the length × width dimensions ranging from several hundreds of nanometer to one to several micrometers. Their photoelectronic property has been evaluated in the indium tin oxide (ITO)/Sb2S3/ITO model device, showing fast temporal photoresponse and photoswitch ability. Through a solid-state thermal-annealing process, the amorphous NSs can be converted to 1D crystalline micro/nanorods, which is due to the high structural anisotropy of crystal phase (stibnite). TG-DSC thermal analysis reveals that the amorphous-crystalline phase transformation is companied by the desorption and/or decomposition of organic surfactant molecules and the S loss.

One-step solid state synthesis of PtCo nanocubes/graphene nanocomposites as advanced oxygen reduction reaction electrocatalysts

Here, we report the synthesis of PtCo nanocubes with core–shell structure on graphene surface by a novel solid state method. Since no organic agent and surfactant was used during the synthesis process, the PtCo nanocubes surface is definite clean. The mean grain size of PtCo nanocubes is just about 5 nm, and PtCo nanocubes possess core-shell structure with PtCo core and a thin Pt-rich shell (about 3–5 atomic layers) on the surface. Compared with commercial Pt/C catalyst, the PtCo nanocubes exhibit an 8.4 times mass activity enhancement toward oxygen reduction reaction (ORR). Besides, the PtCo nanocubes show extreme high electrochemical durability.

119Sn Mössbauer spectroscopy of the time-resolved evolution of SnCl3− ligand structure on the surface of growing platinum nanoparticles

The importance of stabilizing ligands cannot be understated for the colloidal synthesis of nanoparticles as well as their dispersion and assembly into macro-structures such as electrodes. We have recently demonstrated a novel all-inorganic ligand approach to Pt nanoparticle synthesis where surface-adsorbed Sn serves as both reducing agent and stabilizing ligand, producing remarkably monodispersed nanoparticles. By eliminating the need to remove organic surfactants prior to nanoparticle incorporation into electrodes, we were able to use electrostatic assembly to achieve well-defined nanoparticle dispersions in contrast to the aggregated structures common in the field. The approach has allowed us to elucidate the nature of structure sensitivity for electrocatalytic oxygen reduction reaction in acidic and alkaline media. In this paper, we provide a detailed investigation of the evolution of surface-adsorbed Sn-Pt ligand interaction during Pt nanoparticle growth. We show that surface adsorbed SnCl3− exists as pyramidally coordinated to the Pt nanoparticle through Sn-Pt bond formation, resulting in a distorted tetrahedrally coordinated Sn-moiety. Furthermore, we show the shift in the bond charge distribution as the Pt is reduced from its initial Pt2+ state to its metallic state. Direct evidence for the distorted tetrahedral coordination of Pt-SnCl3− and the shift in Sn-Pt bond charge during nanoparticle growth emerges from the 119Sn Mossbauer quadrupole splitting (QS) and Isomer-shift (IS) respectively. Evolution of the structure and chemistry of inorganic complexes during nanoparticle growth has never before been demonstrated and our work is the first to identify the strength of the Sn-Pt interaction in these systems. Such an understanding of nanoparticle surface chemistry will permit extension of this technique to other metals and macro-structures.

Design, fabrication and characterization of multi-layer graphene reinforced nanostructured functionally graded cemented carbides

Effect of predesigned multi-layer graphene (MLG) gradient on the microstructure as well as mechanical properties of MLG/WC-Co hardmetal has been investigated. Varied organic solvents and surfactants were used to identify the best combination of dispersing medium and dispersant for the dispersion of MLG. Six kinds of designed functionally graded MLG/WC-Co alloys were prepared employing two-step sintering (TSS) method. Results demonstrated that MLG can enhance the densification process and inhibit the grain growth. Meanwhile, MLG with a predesigned gradient opposite the predesigned cobalt gradient can maximally enhance the stability of predesigned cobalt gradient during liquid phase sintering, the generation of residual surface compressive stress and the mechanical properties of MLG/WC-Co composite. The enhancing mechanisms of cobalt gradient stability were systematically discussed by combining theoretical consideration with experimentation.

Zirconium diselenite microstructures, formation and mechanism

In this work, a series of microstructures of zirconium diselenite (Zr(SeO3)2) has been prepared via a simple precipitation method at room temperature without adding any organic surfactants. Phase purity of the sample has been checked by X-ray Diffraction. From the SEM, FESEM, and TEM images spheroid nanoparticles to the starfish-like structure of zirconium diselenite are detected. The morphological evolution processes were investigated carefully following time-dependent experiments and a growth mechanism has been proposed. Two different crystal growth processes, the oriented attachment process accompanying the Ostwald ripening process were held responsible for the formation of a structure resembling starfish having four arms.

A halotolerant bifunctional β-xylosidase/α-l-arabinofuranosidase from Colletotrichum graminicola: Purification and biochemical characterization

A β-xylosidase from Colletotrichum graminicola (Bxcg) was purified. The enzyme showed high halotolerance, retaining about 63% of the control activity in the presence of 2.5molL−1 NaCl. The presence of NaCl has not affected the optimum reaction temperature (65°C), but the optimum pH was slightly altered (from 4.5 to 5.0) at high salt concentrations. Bxcg was fully stable at 50°C for 24h and over a wide pH range even in the presence of NaCl. In the absence of salt Bxcg hydrolyzed p-nitrophenyl-β-d-xylopyranoside with maximum velocity of 348.8±11.5Umg−1 and high catalytic efficiency (1432.7±47.3Lmmol−1s−1). Bxcg revealed to be a bifunctional enzyme with both β-xylosidase and α-l-arabinofuranosidase activities, and hydrolyzed xylooligosaccharides containing up to six pentose residues. The enzyme showed high synergistic effect (3.1-fold) with an endo-xylanase for the hydrolysis of beechwood xylan, either in the absence or presence of 0.5molL−1 NaCl, and was tolerant to different organic solvents and surfactants. This is the first report of a halotolerant bifunctional β-xylosidase/α-l-arabinofuranosidase from C. graminicola, and the enzyme showed attractive properties for application in lignocellulose hydrolysis, particularly under high salinity and/or in the presence of residues of pretreatment steps.

Antimicrobial activity of organoclays based on quaternary alkylammonium and alkylphosphonium surfactants and montmorillonite

Abstract Organoclays are mostly materials composed of clay minerals modified with organic surfactants, predominantly of an alkylammonium type. Such hybrid materials often exhibit properties which are superior to those of their components. The main objective of this study was to characterize the antimicrobial activity and physico-chemical properties of tetrabutylammonium (TBA), dodecyltrimethylammonium (DDA), and tetrabutylphosphonium (TBP) cations, and the effectiveness of the organoclays composed of montmorillonite SWy-2 (Mt) and those cations. Their activity was tested on the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. Prior to the determination of their antimicrobial activity, organoclays were characterized using X-ray diffraction and infrared spectroscopy. The results confirmed the irreversible adsorption of organic cations onto the surface of Mt and the stability of the complexes in the medium used for biological experiments. The cytotoxicity of the organic cations on a HeLa cell line determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reduction assay proved to be dependent mainly on the type of surfactant. While DDA with long alkyl chains fully inhibited surviving HeLa cells at concentrations of 1 and 0.5 mmol L−1, lower concentrations (0.1 and 0.05 mmol L−1) were not toxic. On the other hand, TBA and TBP also exhibited a very low toxicity at the higher concentrations. DDA alone exhibited the highest antimicrobial properties. It inhibited surviving S. aureus and E. coli at a concentration of 1 mmol L−1, estimated by the determination of colony forming units (CFU). Both TBA and TPB were only effective at a concentration of 10 mmol L−1. All organoclays were prepared with a ratio of organic cation/Mt of 10−3 mol g−1 at a concentration ≤ 1 mmol L−1. The antimicrobial effect of Mt alone was negligible and did not interfere with the effect of the organic cations. At this concentration, the most effective organoclay was based on DDA, which reduced the survival of both S. aureus and E. coli by over 93%. The organoclays based on TBA and TBP exhibited much lower antimicrobial effectiveness. The effectiveness of organic cations bound to the surface of Mt particles at a concentration of 0.1 mmol L−1 was similar with S. aureus and lower with E. coli compared to that of the respective surfactant solutions. The results of this work provided new knowledge on the biological activities of the selected quaternary ammonium and phosphonium cations, which are often used in organoclays. The antimicrobial activity of the organoclays should be considered when they are applied as carriers of bioactive substances or in other applications dealing with biological systems.

Slip of Alkanes Confined between Surfactant Monolayers Adsorbed on Solid Surfaces.

The slip and friction behavior of n-hexadecane, confined between organic friction modifier surfactant films adsorbed on hematite surfaces, has been studied using nonequilibrium molecular dynamics simulations. The influence of the surfactant type and coverage, as well as the applied shear rate and pressure, has been investigated. A measurable slip length is only observed for surfactant films with a high surface coverage, which provide smooth interfaces between well-defined surfactant and hexadecane layers. Slip commences above a critical shear rate, beyond which the slip length first increases with increasing shear rate and then asymptotes toward a constant value. The maximum slip length increases significantly with increasing pressure. Systems and conditions which show a larger slip length typically give a lower friction coefficient. Generally, the friction coefficient increases linearly with logarithmic shear rate; however, it shows a much stronger shear rate dependency at low pressure than at high pressure. Relating slip and friction, slip only occurs above a critical shear stress, after which the slip length first increases linearly with increasing shear stress and then asymptotes. This behavior is well-described using previously proposed slip models. This study provides a more detailed understanding of the slip of alkanes on surfactant monolayers. It also suggests that high coverage surfactant films can significantly reduce friction by promoting slip, even when the surfaces are well-separated by a lubricant.

Geopolymer assembly by emulsion templating: Emulsion stability and hardening mechanisms

This work investigates emulsion templating to synthesize hexadecane oil/geopolymer composites. In a system with hexadecane as the internal (dispersed) phase and an alkali activated continuous phase without added surfactant, adding aluminosilicate clay particles does not increase resistance against creaming or coalescence, while adding a surfactant (L35 or CTAB) stabilizes the solid-liquid interface. Infrared studies and rheological studies of the associated geopolymerization determined that the presence of the organic phase or surfactant has no significant effect on the geopolymerization kinetics, as determined by the change in time of the Si-O-T IR stretching frequency and the rheological moduli involved during the process. The stabilization of the organic template is reminiscent of Pickering emulsion even though we employ a much greater amount of inorganic material for geopolymer formation. Although the addition of surfactant has a significant effect on the behavior of the paste, the percolation of the network remains unmodified, highlighting the fact that the phenomenon is not dependent on viscosity. Finally, rheological measurements were used to obtain the mass fractal dimension of the as-made gel network, which is able to differentiate the interfacial effect between surfactant molecules with a slightly denser interphase when a cationic surfactant is used.

Ultrafine agarose-coated superparamagnetic iron oxide nanoparticles (AC-SPIONs): a promising sorbent for drug delivery applications

A method for one-step synthesis of ultrafine agarose-coated superparamagnetic iron oxide nanoparticles (AC-SPIONs) was developed. The method is facile and fast and requires no organic solvent or surfactant. The average particle size of the prepared AC-SPIONs was only 20–40 nm with a narrow size distribution and with large saturation magnetization at room temperature. The obtained ultrafine nanogel particles were characterized by scanning electron microscopy, energy-dispersive X-ray analysis, Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer techniques. The AC-SPIONs were epoxy-activated by epichlorohydrin and aminated by ammonium hydroxide. The amination of the particles was investigated by the Kaiser test. The adsorption of two model compounds (gallic acid and ellagic acid) on the functionalized nanoparticles and their releases from them were investigated spectrophotometrically in three different pH values under biological conditions. The functionalized AC-SPIONs displayed good adsorption and in vitro drug release in a phosphate-buffered saline (pH 7.4). The ultrafine AC-SPIONs can be potentially used in magnetic solid-phase extraction, drug delivery, protein purification and enzyme immobilization methods.

Free-standing red phosphorous/silver sponge monolith as an efficient and easily recyclable macroscale photocatalyst for organic pollutant degradation under visible light irradiation

Traditional nano-sized photocatalysts in powdery form suffer from difficulties in recyclability, and have to be immobilized before practical applications. In this study, red phosphorous/silver (red P/Ag) sponge monolith was discovered to be a new free-standing macroscale photocatalyst, which was fabricated by a one-pot hydrothermal method without using any organic surfactants or templates for the first time. The elemental red P not only functioned as a reducing agent in the formation of Ag sponge monolith during the synthesis processes, but also as the active photocatalyst in-situ immobilized onto the Ag sponge. The as-prepared red P/Ag sponge monolith showed enhanced photocatalytic activity than that of traditional pure powdery red P by a factor of 3.1 times for organic pollutants (i.e. Rhodamine 6G, phenol) degradation under visible light irradiation. The enhancement was mainly attributed to the function of Ag sponge served as good electron sink to trap photo-generated electrons. More importantly, such free-standing macroscale photocatalyst can be easily recycled without activity deterioration. As a proof of concept, this work provides new insights into not only for the development of red P-based elemental photocatalysts, but also for the one-pot fabrication of novel free-standing macroscale materials with excellent photocatalytic activity for practical environmental applications.

Application of organic- and nanoparticle-modified foams in foamed concrete: Reinforcement and stabilization mechanisms

In this study, an ultra-stable foam used for foamed concrete was fabricated by modifying the gas–liquid interface by coupling the effects of an organic surfactant and nanoparticles. A serial of techniques was employed to study the products and microstructure development of foam and foamed concrete, respectively. The results show that nano-silica and hydroxypropyl methylcellulose can slow the coalescence and disproportionation of the bubbles by adsorbing at the air bubble surface and increasing the viscosity of cell wall paste, thus preventing gas transfer and hindering physical drainage between the gaseous and liquid phases. Also, a more homogeneous and finer pore structure is generated with the inclusion of the organic surfactant and nanoparticles. The pozzolanic reaction between the nano-silica and Ca(OH)2 results in an increased C-S-H content and the densification of the cell wall structure. In addition, the stability of foamed concrete with modification and relevant stabilization mechanisms were also investigated.