Scale-Dependent Rheology of Synovial Fluid Lubricating Macromolecules.

Synovial fluid (SF) is the complex biofluid that facilitates the exceptional lubrication of articular cartilage in joints. Its primary lubricating macromolecules, the linear polysaccharide hyaluronic acid (HA) and the mucin-like glycoprotein proteoglycan 4 (PRG4 or lubricin), interact synergistically to reduce boundary friction. However, the precise manner in which these molecules influence the rheological properties of SF remains unclear. This study aimed to elucidate this by employing confocal microscopy and multiscale rheometry to examine the microstructure and rheology of solutions containing recombinant human PRG4 (rhPRG4) and HA. Contrary to previous assumptions of an extensive HA-rhPRG4 network, it is discovered that rhPRG4 primarily forms stiff, gel-like aggregates. The properties of these aggregates, including their size and stiffness, are found to be influenced by the viscoelastic characteristics of the surrounding HA matrix. Consequently, the rheology of this system is not governed by a single length scale, but instead responds as a disordered, hierarchical network with solid-like rhPRG4 aggregates distributed throughout the continuous HA phase. These findings provide new insights into the biomechanical function of PRG4 in cartilage lubrication and may have implications in the development of HA-based therapies for joint diseases like osteoarthritis.

On the Stability of Pickering and Classical Nanoemulsions: Theory and Experiments.

Emulsification is a crucial technique for mixing immiscible liquids into droplets in various industries, such as food, cosmetics, biomedicine, agrochemistry, and petrochemistry. Quantitative analysis of the stability is pivotal before the utilization of these emulsions. Differences in X-ray attenuation for emulsion components and surface relaxation of the droplets may contribute to X-ray CT imaging and low-field NMR spectroscopy as viable techniques to quantify emulsion stability. In this study, Pickering (stabilized solely by nanoparticles) and Classical (stabilized solely by low molecular weight polymers) nanoemulsions were prepared with a high-energy method. NMR and X-ray CT were employed to constantly monitor the two types of nanoemulsions until phase separation. The creaming rates calculated from NMR match well with the results obtained from X-ray CT. Furthermore, we show that Stokes' law coupled with the classical Lifshitz-Slyozov-Wagner theory underestimates the creaming rate of the nanoemulsions compared to the experimental results from NMR and X-ray CT imaging. A new theory is proposed by fully incorporating the effects of Pickering nanoparticles, hydrocarbon types, volume fraction, size distribution, and flocculation on the droplet coarsening. The theoretical results agree well with the experimentally measured creaming rates. It reveals that the attachment of nanoparticles onto a droplet surface decreases the mass transfer for hydrocarbon molecules to move from the bulk aqueous phase into other droplets, thus slowing the Ostwald ripening. Therefore, Pickering nanoemulsions show a better stability behavior compared to Classical nanoemulsions. The impacts of hydrocarbon and emulsification energy on the stability of nanoemulsions are reported. These findings demonstrate that the stability of the nanoemulsions can be manipulated and optimized for a specific application, setting the stage for subsequent investigations of these nanodroplets.

The Critical Role of Environmental Synergies in the Creation of Bionanohybrid Microbes.

A wide range of bacteria can synthesize surface-associated nanoparticles (SANs) through exogenous metal ions reacting with sulfide produced via cysteine metabolism, resulting in the emergence of a biological-nanoparticle hybrid (bionanohybrid). The attached nanoparticles may couple to extracellular electron transfer, facilitating de novo photoelectrochemical processes. While SAN-cell coupling in hybrid organisms is opening a range of biotechnological possibilities, observation of bionanohybrids in nature is not commonly reported and their lab-based behavior remains difficult to control. We describe the critical role environmental synergy (microbial growth stage, cell densities, cysteine, and exogenous metal concentrations) plays in controlling the form and occurrence of Escherichia coli and Moorella thermoacetica bionanohybrids. SAN development depends on an appropriate cell density to metal ratio, with too few cells resulting in nanoparticle suppression through cytotoxicity or inhibition of cysteine conversion, and with too many cells diluting the number and size of particles produced. This cell number is governed by the concentration of cysteine present, which acts to protect the cells from metal ion toxicity. Exposing cells to metal and cysteine during the lag phase leads to SAN development, whereas cells in the exponential growth phase predominantly produce dispersed nanoparticles. Applying these principles more broadly, E. coli is shown to biosynthesize composite Bi/Cu sulfide SANs, and Clostridioides difficile can be coaxed into a bionanohybrid lifestyle by fine-tuning the cysteine dosage. Bionanohybrids maintain a remarkable ability for binary fission and sustained growth, opening doors to the production of SANs tailored to specific technological functions. IMPORTANCE Some bacteria can produce nanoscale-sized particles, which remain attached to the surface of the organism. The surface association of these nanoparticles creates a new mode of interaction between the microbe's environment and its internal cellular function, giving rise to a new hybrid lifeform, a biological nanoparticle hybrid (bionanohybrid). These hybrid organisms gain new or enhanced biological functions, and thus their creation opens a wide range of biotechnological possibilities. Despite this potential, the fundamental controls on bionanohybrid formation and occurrence remain poorly constrained. In this study, Escherichia coli K-12, Moorella thermoacetica, and Clostridioides difficile were used to test the combined influences of the growth phase, cell density, cysteine dose, and metal concentration in determining single and composite metal sulfide surface-associated nanoparticle production. The significance of this study is that it defined the critical synergies controlling nanoparticle formation on bacterial cell surfaces, unlocking the potential for bionanohybrid applications in a range of organisms.

Inhibition of Sulfate Reduction and Cell Division by Desulfovibrio desulfuricans Coated in Palladium Metal.

The growth of sulfate-reducing bacteria (SRB) and associated hydrogen sulfide production can be problematic in a range of industries such that inhibition strategies are needed. A range of SRB can reduce metal ions, a strategy that has been utilized for bioremediation, metal recovery, and synthesis of precious metal catalysts. In some instances, the metal remains bound to the cell surface, and the impact of this coating on bacterial cell division and metabolism has not previously been reported. In this study, Desulfovibrio desulfuricans cells (1g dry weight) enabled the reduction of up to 1500 mmol (157.5 g) palladium (Pd) ions, resulting in cells being coated in approximately 1 µm of metal. Thickly coated cells were no longer able to metabolize or divide, ultimately leading to the death of the population. Increasing Pd coating led to prolonged inhibition of sulfate reduction, which ceased completely after cells had been coated with 1200 mmol Pd g-1 dry cells. Less Pd nanoparticle coating permitted cells to carry out sulfate reduction and divide, allowing the population to recover over time as surface-associated Pd diminished. Overcoming inhibition in this way was more rapid using lactate as the electron donor, compared to formate. When using formate as an electron donor, preferential Pd(II) reduction took place in the presence of 100 mM sulfate. The inhibition of important metabolic pathways using a biologically enabled casing in metal highlights a new mechanism for the development of microbial control strategies. IMPORTANCE Microbial reduction of sulfate to hydrogen sulfide is highly undesirable in several industrial settings. Some sulfate-reducing bacteria are also able to transform metal ions in their environment into metal phases that remain attached to their outer cell surface. This study demonstrates the remarkable extent to which Desulfovibrio desulfuricans can be coated with locally generated metal nanoparticles, with individual cells carrying more than 100 times their mass of palladium metal. Moreover, it reveals the effect of metal coating on metabolism and replication for a wide range of metal loadings, with bacteria unable to reduce sulfate to sulfide beyond a specific threshold. These findings present a foundation for a novel means of modulating the activity of sulfate-reducing bacteria.

Dispersibility of Poly(vinyl acetate) Modified Silica Nanoparticles in Carbon Dioxide with Several Cosolvents.

The dispersibility and stabilization of silica nanoparticles with surface-capped poly(vinyl acetate) (PVAc) chains are examined in carbon dioxide with four different cosolvents. Three surface coverages of silica-PVAc were formed by using different weight ratios of the silica and PVAc. The dispersibilities of three silica-PVAc nanoparticles in CO2 with the four cosolvents were tested in a rotatable high-pressure variable-volume view cell. The effects of surface coverage, cosolvent type, pressure, and particle concentration on dispersion were investigated. Results show that, in the experimental pressure range (5.5 to 20 MPa), the pressure has no significant effect on the dispersion of nanoparticles, and the cosolvent is the key factor in dispersing silica-PVAc particles in CO2. 1-Butanol is an adequate cosolvent to disperse silica-PVAc in CO2 with any coverage of PVAc on the surface of the particles when the concentration of particles is smaller than 0.31 wt %. Ethanol can only improve the dispersibility of particles with a high surface coverage of PVAc when the concentration of particles is smaller than 0.14 wt %. 1-Hexanol and ethyl acetate cannot disperse the particles in CO2 with any coverage of PVAc. Molecular dynamics simulations were carried out to study the nanoparticle-CO2-cosolvent dispersions. Results suggest that 1-butanol has a good solubility in the CO2 condensed phase and can effectively absorb onto the nanoparticle surface, which help to prevent the formation of nanoparticle aggregation. The precipitation of nanoparticles in the nanoparticle/1-hexanol/CO2 and nanoparticle/ethyl acetate/CO2 systems is attributed to the relatively low solubility of CO2 in 1-hexanol and ethyl acetate. The precipitation of nanoparticles in the nanoparticle/ethanol/CO2 system is the result of less hindrance of ethanol molecules to the aggregation of nanoparticles.

The Significance of Graphene Oxide-Polyacrylamide Interactions on the Stability and Microstructure of Oil-in-Water Emulsions.

The emulsification of oil in water by nanoparticles can be facilitated by the addition of costabilizers, such as polymers and surfactants. The enhanced properties of the resulting emulsions are usually attributed to nanoparticle/costabilizer synergy; however, the mechanism of this synergistic effect and its impacts on emulsion stability and microstructure remain unclear. Here, we study the synergistic interaction of graphene oxide (GO) and a high molecular weight anionic polyacrylamide (PAM) in stabilization of paraffin oil/water emulsion systems. We show that the addition of PAM reduces the amount of GO required to stabilize an emulsion significantly. In order to probe the synergistic effect of GO and PAM, we analytically analyze the oil-free GO and GO-PAM dispersions and directly image their morphology via Cryo-TEM and atomic force microscopy (AFM). X-ray diffraction results confirm the adsorption of PAM molecules onto GO sheets resulting in the formation of ultimate GO-PAM complexes. The adsorption phenomenon is a consequence of hydrogen bonding and acid-base interactions, conceivably leading to a resilient electron-donor-acceptor complex. The microstructure of emulsions is captured with two-color fluorescent microscopy and Cryo-TEM. The acquired images display the localization of GO-PAM complexes at the interface while large amount of GO-PAM flocs coexist at the interface and in between oil droplets. Localization of such complexes and flocs at the interface is found to be responsible for their slow creaming rates compared to their GO counterparts. Mechanical properties of both dispersions and emulsions are studied by shear rheology. Rheological measurements confirm that GO-PAM complexes have a higher desorption energy from the interface resulting in higher critical shear strain of GO-PAM emulsions. The results, with insights into both structure and rheology, form a foundational understanding for integration of other polymers and nanoparticles in emulsion systems, which enables efficient design of these systems for an application of interest.

Insight on Methane Foam Stability and Texture via Adsorption of Surfactants on Oppositely Charged Nanoparticles.

We report the phase behavior of a dispersion of alumina-coated silica nanoparticles in the presence of an anionic surfactant (sodium fatty alcohol polyoxyethylene ether sulfate), and then describe the influence of surfactant/nanoparticle concentration ratio on the stability of methane foam as a potential fluid for enhanced oil recovery application. The surface tension of the methane/aqueous phase interface, surface charge, and size of the particle aggregates and amount of surfactant adsorption were characterized as a function of surfactant/nanoparticle ratio. Five adsorption stages, which are described in terms of the extent and type of the surfactant coverage on the nanoparticle surface, explain the behavior of the solution at different surfactant/nanoparticle ratios. The static foam generation experiments were conducted to monitor the variation of the foam stability and texture over the defined adsorption stages. The surface tension trends illustrate that the affinity of nanoparticles for the gas-liquid interface is strongly affected by the adsorption extent of AES molecules on the particle surface. At high surfactant/nanoparticle ratio, the adsorbed surfactant bilayer causes a high hydrophilicity of the particles that significantly pushed the particles away from the gas-liquid interface. At the most hydrophobic state of the particles which occurred at the ratio of 0.2, the foam structure collapsed quickly. The most stable foam with fine texture was found at surfactant/nanoparticle ratio less than 0.008 at which the particles are partially covered with surfactants and have smaller aggregate size. The findings provide a better understanding of the interaction between oppositely charged nanoparticle/surfactant pairs and how that interaction affects foam stability. It is demonstrated that substitution of absolute concentration by surfactant/nanoparticle ratio can truly govern the foam stability and texture. The results can be beneficial to predict the foam behavior in its numerous applications and whether interactions will be synergistic, antagonistic, or neutral.

Analysis of network formation and long-term stability in silica nanoparticle stabilized emulsions.

Emulsions are widely used in industrial applications, including in food sciences, cosmetics, and enhanced oil recovery. For these industries, an in depth understanding of the stability and rheological properties of emulsions under both static and dynamic conditions is vital to their successful application. Presented here is a thorough assessment of a model nanoparticle (NP) stabilized dodecane-in-water emulsion as a route to improved understanding of the relationship between NP properties, microstructure and droplet-droplet interactions on the stability and rheological properties of emulsions. Emulsions are obtained here with low NP loadings without the need for added electrolyte through the use of an optimized silica NP (SNP) surface modification procedure. The prepared emulsions were characterized via optical microscopy, cryo-scanning electron microscopy (cryo-SEM), zeta potential analysis and laser scanning confocal microscopy (LSCM), enabling quantification of the emulsion droplet size, SNP interfacial coverage/morphology and surface charge. The correlation of these properties with the rheology of the emulsions is investigated through small amplitude oscillatory shear experiments which provide significant insight into the origins of the emulsions' rheological behavior and their stability. In addition, long-term stability, droplet-droplet network formation and microstructural evolution are found to be readily detectable shortly after preparation through measured progression of the emulsion's rheological properties.

Stabilization of Oil-in-Water Emulsions with Noninterfacially Adsorbed Particles.

Classical (surfactant stabilized) and Pickering (particle stabilized) type emulsions have been widely studied to elucidate the mechanisms by which emulsion stabilization is achieved. In Pickering emulsions, a key defining factor is that the stabilizing particles reside at the liquid-liquid interface providing a mechanical barrier to droplet coalescence. This interfacial adsorption is achieved through the use of nanoparticles that are partially wet by both liquid phases, often through covalent surface modification of or surfactant adsorption to the nanoparticle surfaces. Herein, we demonstrate particle-induced stabilization of an oil-in-water emulsion with fully water wet nanoparticles (no interfacial adsorption) via synergistic interaction with low concentrations of surfactants. Laser scanning confocal microscopy analysis allows for unique and vital insights into the properties of these emulsions via both three-dimensional imaging and real-time monitoring of particle dynamics at the oil-water interface. Investigation of these "non-Pickering" particle stabilized emulsions suggests that the nonadsorbed particles impart stability to the emulsion primarily via entropic forces imparted by the accumulation of silica nanoparticles in the coherent phase between dispersed oil droplets.

Synergistic formation and stabilization of oil-in-water emulsions by a weakly interacting mixture of zwitterionic surfactant and silica nanoparticles.

Oil-in-water emulsions were formed and stabilized at low amphiphile concentrations by combining hydrophilic nanoparticles (NPs) (i.e., bare colloidal silica) with a weakly interacting zwitterionic surfactant, caprylamidopropyl betaine, to generate a high hydrophilic-lipophilic balance. The weak interaction of the NPs with surfactant was quantified with contact angle measurements. Emulsions were characterized by static light scattering to determine the droplet size distributions, optical photography to quantify phase separation due to creaming, and both optical and electron microscopy to determine emulsion microstructure. The NPs and surfactant acted synergistically to produce finer emulsions with a greater stability to coalescence relative to the behavior with either NPs or surfactant alone. As a consequence of the weak adsorption of the highly hydrophilic surfactant on the anionic NPs along with the high critical micelle concentration, an unusually large surfactant concentration was available to adsorb at the oil-water interface and lower the interfacial tension. The synergy for emulsion formation and stabilization for the two amphiphiles was even greater in the case of a high-salinity synthetic seawater aqueous phase. Here, higher NP adsorption at the oil-water interface was caused by electrostatic screening of interactions between (1) NPs and the anionic oil-water interface and (2) between the NPs. This greater adsorption as well as partial flocculation of the NPs provided a more efficient barrier to droplet coalescence.

pH-dependent transport of metal cations in porous media.

We study the effect of pH-dependent adsorption and hydrodynamic dispersion on cation transport through a reactive porous medium with a hydrophilic surface. We investigate how competitive adsorption between a proton and a metal (which in some situations of practical interest may also be a radionuclide) can facilitate the migration of a certain fraction of the latter. We performed laboratory experiments using a chromatographic column filled with silica beads coated with iron oxide and flooded initially with an acidic solution (pH ≈ 3) and then with an alkaline solution (pH > 7) containing either sodium, potassium, lithium, calcium, magnesium, or barium. The composition of each injected solution was chosen to represent one of two possible theoretical predictions, either a retarded shock and a fast pulse, that is, traveling at the interstitial fluid velocity, or only a retarded shock. Highly resolved breakthrough curves measured with inline ion chromatography allowed us to observe in all cases agreement with theoretical predictions, including numerous observations of a fast pulse. The fast pulse is the result of the interaction between pH-dependent adsorption and hydrodynamic dispersion and has previously been observed in systems with strontium. Here, we show the fast pulse arises also in the case of other cations allowing a generalization of the physical mechanism underlying this phenomenon and consideration of it as a new fast transport behavior. A one-dimensional reactive transport model for an incompressible fluid was developed combining surface complexation with mass conservation equations for a solute and the acidity (difference between the total proton and hydroxide concentration). In all cases, the model agrees with the measurements capturing the underlying physics of the overall transport behavior. Our results suggest that the interplay between pH-dependent adsorption and hydrodynamic dispersion can give rise to the rapid migration of metals through reactive porous media with potential effects on, for example, the performance of subsurface engineering infrastructures for pollutant containment, the mobilization of metal contaminants by brine acidified upon contact with CO2 during geologic carbon storage, and the chromatographic separation processes in industrial applications.

A novel synthesis method of magnetic Janus particles for wastewater applications.

HYPOTHESIS: Magnetic particles are widely used in many adsorption and removal processes. Among the many types of magnetic colloids, magnetic Janus particles offer significant possibilities for the effective removal of several components from aqueous solutions. Nevertheless, the synthesis of structures integrating different types of materials requires scalable fabrication processes to overcome the limitations of the available methodologies. Herein, we hypothesized a fabrication process for dual-surface functionalized magnetic Janus particles. EXPERIMENTS: The primary silica particles with surface-attached amine groups are further asymmetrically modified by iron oxide nanoparticles, exploiting Pickering emulsion and electroless deposition techniques. The dual surface functionality of the particles is designed for its versatility and demonstrated in two wastewater-related applications. FINDINGS: We show that our design can simultaneously remove chromium (VI) and phenol from aqueous solution. The fabricated magnetic-responsive Janus particles are also an effective adsorbent for genomic Deoxyribonucleic acid (DNA) and show superior performance to commercial magnetic beads. Thus, this study provides a novel platform for designing magnetic Janus particles with multifunctional surfaces for wastewater treatment applications.

Stabilization of iron oxide nanoparticles in high sodium and calcium brine at high temperatures with adsorbed sulfonated copolymers.

A series of sulfonated random and block copolymers were adsorbed on the surface of ~100 nm iron oxide (IO) nanoparticles (NPs) to provide colloidal stability in extremely concentrated brine composed of 8% wt NaCl + 2% wt CaCl2 (API brine; 1.4 M NaCl + 0.2 M CaCl2) at 90 °C. A combinatorial materials chemistry approach, which employed Ca(2+)-mediated adsorption of anionic acrylic acid-containing sulfonated polymers to preformed citrate-stabilized IO nanoclusters, enabled the investigation of a large number of polymer coatings. Initially a series of poly(2-methyl-2-acrylamidopropanesulfonate-co-acrylic acid) (poly(AMPS-co-AA)) (1:8 to 1:1 mol:mol), poly(styrenesulfonate-block-acrylic acid) (2.4:1 mol:mol), and poly(styrenesulfonate-alt-maleic acid) (3:1 mol:mol) copolymers were screened for solubility in API brine at 90 °C. The ratio of AMPS to AA groups was varied to balance the requirement of colloid dispersibility at high salinity (provided by AMPS) against the need for anchoring of the polymers to the iron oxide surface (via the AA). Steric stabilization of IO NPs coated with poly(AMPS-co-AA) (1:1 mol:mol) provided colloidal stability in API brine at room temperature and 90 °C for up to 1 month. The particles were characterized before and after coating at ambient and elevated temperatures by a variety of techniques including colloidal stability experiments, dynamic light scattering, zeta potential, and thermogravimetric analysis.

Experimental evidence for self-limiting reactive flow through a fractured cement core: implications for time-dependent wellbore leakage.

We present a set of reactive transport experiments in cement fractures. The experiments simulate coupling between flow and reaction when acidic, CO(2)-rich fluids flow along a leaky wellbore. An analog dilute acid with a pH between 2.0 and 3.15 was injected at constant rate between 0.3 and 9.4 cm/s into a fractured cement core. Pressure differential across the core and effluent pH were measured to track flow path evolution, which was analyzed with electron microscopy after injection. In many experiments reaction was restricted within relatively narrow, tortuous channels along the fracture surface. The observations are consistent with coupling between flow and dissolution/precipitation. Injected acid reacts along the fracture surface to leach calcium from cement phases. Ahead of the reaction front, high pH pore fluid mixes with calcium-rich water and induces mineral precipitation. Increases in the pressure differential for most experiments indicate that precipitation can be sufficient to restrict flow. Experimental data from this study combined with published field evidence for mineral precipitation along cemented annuli suggests that leakage of CO(2)-rich fluids along a wellbore may seal the leakage pathway if the initial aperture is small and residence time allows mobilization and precipitation of minerals along the fracture.

Control of interfacial instabilities through variable injection rate in a radial Hele-Shaw cell: A nonlinear approach for late-time analysis.

In this paper, the nonlinear behavior of immiscible viscous fingering in a circular Hele-Shaw cell under the action of different time-dependent injection flow rate schemes is assessed numerically. Unlike previous studies which addressed the infinite viscosity ratio (inviscid-viscous flow), the problem is tackled by paying special attention to flows with finite viscosity ratio (viscous flow) in which the viscosity of the displacing and the displaced fluids can have any arbitrary value. Systematic numerical simulations based on a complex-variable formulation of Cauchy-Green barycentric coordinates are performed at different mobility ratios and capillary numbers with a focus on the late-time fully nonlinear regime. Additionally, numerical optimization is used to obtain the optimal flow rate schedule through a second-order weakly nonlinear stability analysis in contrast to previous studies in which the optimal flow rate was obtained entirely based on linear stability analysis. It is demonstrated that, irrespective of the values of the mobility ratio and/or the capillary number, for patterns whose constant injection counterpart exhibits linear flow regime, the curvature-driven relaxation time is comparable with the operational time of the time-dependent injection flow rate controlling schemes, and most of the controlling schemes work very well and suppress the fingering phenomenon remarkably with the maximum recovery improvement of 15%. As the nonlinearity of the system increases, the schemes may still perform well, but their effectiveness is more pronounced in patterns with less nonlinearity in their constant injection counterpart than those with higher nonlinearity. As the nonlinearity increases, the curvature-driven relaxation time becomes longer than the operational time of the schemes, leading to a reduction in their effectiveness. Additionally, it is shown that employment of the second-order weakly nonlinear stability analysis to formulate the objective function does not result in any remarkable variation in the obtained optimal flow rate schedule.

Multifunctional fully biobased aerogels for water remediation: Applications for dye and heavy metal adsorption and oil/water separation.

Water ecosystem contamination from industrial pollutants is an emerging threat to both humans and native species, making it a point of global concern. In this work, fully biobased aerogels (FBAs) were developed by using low-cost cellulose filament (CF), chitosan (CS), citric acid (CA), and a simple and scalable approach, for water remediation applications. The FBAs displayed superior mechanical properties (up to ∼65 kPa m3 kg-1 specific Young's modulus and ∼111 kJ/m3 energy absorption) due to CA acting as a covalent crosslinker in addition to the natural hydrogen bonding and electrostatic interactions between CF and CS. The addition of CS and CA increased the variety of functional groups (carboxylic acid, hydroxyl and amines) on the materials' surface, resulting in super-high dye and heavy metal adsorption capacities (619 mg/g and 206 mg/g for methylene blue and copper, respectively). Further modification of FBAs with a simple approach using methyltrimethoxysilane endowed aerogel oleophilic and hydrophobic properties. The developed FBAs showed a fast performance in water and oil/organic solvents separation with more than 96% efficiency. Besides, the FBA sorbents could be regenerated and reused for multiple cycles without any significant impact on their performance. Moreover, thanks to the presence of amine groups by addition of CS, FBAs also displayed antibacterial properties by preventing the growth of Escherichia coli on their surface. This work demonstrates the preparation of FBAs from abundant, sustainable, and inexpensive natural resources for applications in wastewater purification.

Formation of biologically influenced palladium microstructures by Desulfovibrio desulfuricans and Desulfovibrio ferrophilus IS5.

A range of Desulfovibrio spp. can reduce metal ions to form metallic nanoparticles that remain attached to their surfaces. The bioreduction of palladium (Pd) has been given considerable attention due to its extensive use in areas of catalysis and electronics and other technological domains. In this study we report, for the first time, evidence for Pd(II) reduction by the highly corrosive Desulfovibrio ferrophilus IS5 strain to form surface attached Pd nanoparticles, as well as rapid formation of Pd(0) coated microbial nanowires. These filaments reached up to 8 µm in length and led to the formation of a tightly bound group of interconnected cells with enhanced ability to attach to a low carbon steel surface. Moreover, when supplied with high concentrations of Pd (≥ 100 mmol Pd(II) g-1 dry cells), both Desulfovibrio desulfuricans and D. ferrophilus IS5 formed bacteria/Pd hybrid porous microstructures comprising millions of cells. These three-dimensional structures reached up to 3 mm in diameter with a dose of 1200 mmol Pd(II) g-1 dry cells. Under suitable hydrodynamic conditions during reduction, two-dimensional nanosheets of Pd metal were formed that were up to several cm in length. Lower dosing of Pd(II) for promoting rapid synthesis of metal coated nanowires and enhanced attachment of cells onto metal surfaces could improve the efficiency of various biotechnological applications such as microbial fuel cells. Formation of biologically stimulated Pd microstructures could lead to a novel way to produce metal scaffolds or nanosheets for a wide variety of applications.

Stabilization of superparamagnetic iron oxide nanoclusters in concentrated brine with cross-linked polymer shells.

Iron oxide nanoparticles, in the form of sub-100-nm clusters, were synthesized in the presence of poly(acrylic acid) (PAA) or poly(styrene sulfonate-alt-maleic acid) (PSS-alt-MA) to provide electrosteric stabilization. The superparamagnetic nanoclusters were characterized using a superconducting quantum interference device (SQUID), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and zeta potential measurements. To anchor the polymer shell on the nanoparticle surface, the polymer was cross-linked for a range of cross-linking densities. For nanoclusters with only 12% (w/w) PSS-alt-MA, electrosteric stabilization was sufficient even in 8 wt % NaCl. For PAA, the cross-linked polymer shell was essentially permanent and did not desorb even upon dilution of the nanoparticles for iron oxide concentrations down to 0.014 wt %. Without cross-linking, over half of the polymer desorbed from the particle surfaces. This general approach of the adsorption of polymer stabilizers onto nanoparticles followed by cross-linking may be utilized for a wide variety of cross-linkable polymers without the need to form covalent bonds between the nanoparticles and polymer stabilizer. Thus, this cross-linking approach is an efficient and inexpensive method of stabilizing nanoparticles for large-scale applications, including the electromagnetic imaging of subsurface reservoirs, even at high salinity.

Elucidating the effect of enzymatic polymerized polysaccharide particle morphology on emulsion properties.

Exploiting the shape of Pickering stabilizers offers the ability to unlock the full potential of nanoparticle-stabilized emulsions for applications in enhanced oil recovery, pharmaceuticals, cosmetics, and coatings. In this work, we utilize engineered polysaccharide particles derived from the enzymatic polymerization of glucose from sucrose with controlled shape for the stabilization of dodecane-in-water emulsions. Altering the particle shape (spherical aggregates, fibrids, or platelets), while maintaining a neutral surface charge allows for a systematic examination of the role of particle shape in the stabilization of emulsions. We find that platelet-shaped particles reduce the interfacial tension and result in the smallest droplet size, while emulsions stabilized by aggregates and fibrids are governed by a network of particles in the continuous phase. Exploiting the synergy between these particles allowed for the tuning of their microstructure and rheological signature which allows us to map and tailor these emulsions for a wider variety of applications.