Oxidant-Induced High-Efficient Mussel-Inspired Modification on PVDF Membrane with Superhydrophilicity and Underwater Superoleophobicity Characteristics for Oil/Water Separation

In this work, a facile one-step approach was developed to modify hydrophobic polyvinylidene fluoride (PVDF) microfiltration membrane with superhydrophilicity and underwater superoleophobicity properties via a high-efficient deposition of polydopamine (PDA) coating oxidized by sodium periodate in a slightly acidic environment (pH = 5.0). In contrast to the traditional PDA coating on hydrophobic membranes autoxidized by O₂ in a weak basic buffer solution, the superhydrophilicity and ultrahigh pure water permeability (about 11 934 L m^–2 h^–1 under 0.038 MPa) of the PDA-decorated PVDF membrane are derived from optimized chemical oxidation without postmodifications or additional reactants. The as-prepared membrane exhibits excellent oil/water separation ability evaluated by water fluxes and oil rejection ratios of various oil/water mixtures and oil-in-water emulsions. Moreover, the outstanding antifouling performance and reusability of the PDA-modified PVDF membrane provide a long-term durability for many potential applications. The modified membrane also exhibits excellent chemical stability in harsh pH environments and mechanical stability for practical applications

Highly Stable and Efficient Catalyst with In Situ Exsolved Fe–Ni Alloy Nanospheres Socketed on an Oxygen Deficient Perovskite for Direct CO₂ Electrolysis

The massive emission of carbon dioxide (CO₂), the major portion of greenhouse gases, has negatively affected our ecosystem. Developing new technologies to effectively reduce CO₂ emission or convert CO₂ to useful products has never been more imperative. In response to this challenge, we herein developed novel in situ exsolved Fe–Ni alloy nanospheres uniformly socketed on an oxygen-deficient perovskite [La­(Sr)­Fe­(Ni)] as a highly stable and efficient catalyst for the effective conversion of CO₂ to carbon monoxide (CO) in a high-temperature solid oxide electrolysis cell (HT-SOEC). The symmetry between the reduction and reoxidation cycles of this catalyst indicates its good redox reversibility. The cathodic reaction kinetics for CO₂ electrolysis is significantly improved with a polarization resistance as low as 0.272 Ω cm². In addition, a remarkably enhanced current density of 1.78 A cm^–2, along with a high Faraday efficiency (∼98.8%), was achieved at 1.6 V and 850 °C. Moreover, the potentiostatic stability test of up to 100 h showed that the cell was stable without any noticeable coking in a CO₂/CO (70:30) flow at an applied potential of 0.6 V (vs OCV) and 850 °C. The increased oxygen vacancies together with the in situ exsolved nanospheres on the perovskite backbone ensures sufficiently active sites and consequently improves the electrochemical performance for the efficient CO₂ conversion. Therefore, this newly developed perovskite can be a promising cathode material for HT-SOEC. More generally, this study points to a new direction to develop highly efficient catalysts in the form of the perovskite oxides with perfectly in situ exsolved metal/bimetal nanospheres

Dewatering Bitumen Emulsions Using Interfacially Active Organic Composite Absorbent Particles

One of the major challenges in petroleum production is the formation of undesirable emulsions, which often leads to an increased cost for downstream operations. This problem is exacerbated for bitumen, which contains a greater fraction of interfacially active materials known to stabilize small emulsified water droplets that are extremely difficult to separate. To accelerate separation of emulsified water droplets from bitumen, chemical demulsifiers are extensively used to modify interfacial properties, promote droplet flocculation, and facilitate coalescence of the emulsified droplets. However, the use of chemical demulsifiers is rather system-specific as a result of the overdosing phenomenon. As an alternative to chemical demulsification, composite absorbent particles, prepared by dehydrating well-designed water-in-oil emulsion droplets, were proposed to promote dewatering of water-in-diluted bitumen emulsions. The composite particles were composed of nanosize magnetic particles dispersed in an absorbent matrix coated with an interfacially active material. The composite structure combines the absorptive capacity of sodium carboxymethyl cellulose for water with the interfacial activity of ethylcellulose while retaining the magnetic responsiveness of dispersed Fe₃O₄ nanoparticles. Using composite absorbent particles, nearly complete dewatering of water-in-diluted bitumen emulsions was achieved by increasing the dosage of absorbent particles. The dewatering rate was improved using smaller particles of greater specific surface area or increasing mixing intensity to promote contact between absorbent particles and emulsified water droplets. Although the surface of composite absorbent particles was initially suitable for dispersing in non-aqueous media, the subsequent change in wettability upon absorption of water (hydration) caused hydrated absorbent particles to aggregate, providing an opportunity for regeneration/reuse of hydrated particles by first separation particles from diluted bitumen through gravity separation or a filtration process

Understanding Copper Activation and Xanthate Adsorption on Sphalerite by Time-of-Flight Secondary Ion Mass Spectrometry, X‑ray Photoelectron Spectroscopy, and in Situ Scanning Electrochemical Microscopy

In situ scanning electrochemical microscopy (SECM) was applied for the first time to study the copper activation and subsequent xanthate adsorption on sphalerite. The corresponding surface compositions were analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The probe approach curve (PAC) using SECM shows that unactivated and activated sphalerite surfaces have negative current feedback and partially positive current feedback, respectively, suggesting that Cu_<i>x</i>S is formed on the sphalerite after copper activation. The copper activation of sphalerite strongly depends on the surface heterogeneity (e.g., presence of polishing defects, chemical composition), impacting the subsequent xanthate adsorption process. The SECM, ToF-SIMS, and XPS analyses show that during the copper activation the polishing defects, which have high excess surface energy, tend to consume more copper ions, resulting in Cu-rich regions by forming CuS-like species, while Fe oxide/hydroxide forms at Fe-rich regions. The XPS spectra further confirm that the CuS-like species involve Cu­(I) and S­(−I). The SECM imaging shows that after xanthate adsorption the current response at the Cu-rich regions decreases because of the formation of cuprous xanthate (CuX) and dixanthogen (X₂) while increases at the Fe-rich regions mainly due to the chemisorption of xanthate on Fe oxide/hydroxide. Our results shed light on the fundamental understanding of the electrochemical processes on sphalerite surface associated with its copper activation and subsequent xanthate adsorption in flotation

Structural Evolutions of ZnS Nanoparticles in Hydrated and Bare States

Suitable optoelectronic properties and the nontoxic nature of ZnS quantum dots capacitate exciting applications for these nanomaterials especially in the field of biomedical imaging. However, the structural stability of ZnS nanoparticles has been shown to be challenging since they potentially are prone to autonomous structural evolutions in ambient conditions. Thus, it is essential to build an understanding about the structural evolution of ZnS nanoparticles, especially in aqueous environment, before implementing them for in vivo applications. In this study we compared the structure of ZnS nanoparticles relaxed in a vacuum and in water using a classical molecular dynamics method. Structural analyses showed that the previously observed three-phase structure of bare nanoparticles is not formed in the hydrated state. The bulk of hydrated nanoparticles has more crystalline structure; however, the dynamic heterogeneity in their surface relaxation makes them more polar compared to bare nanoparticles. This heterogeneity is more severe in hydrated wurtzite nanoparticles, causing them to show larger dipole moments. Analyzing the structure of water in the first hydration shell of the surface atoms shows that water is mainly adsorbed to the nanoparticles’ surface through Zn–O interaction, which causes the structure of water in the first hydration shell to be discontinuous

A Molecular Dynamics Study of the Effect of Asphaltenes on Toluene/Water Interfacial Tension: Surfactant or Solute?

A series of molecular dynamics simulations were performed to investigate the effects of model asphaltenes on the toluene/water interfacial tension (IFT) under high temperature and pressure conditions. In the absence of model asphaltenes, the toluene/water IFT monotonically decreases with increasing temperature, whereas, with the presence of model asphaltenes, especially at high concentrations, such monotonic dependence no longer holds. Furthermore, in contrast with the decreasing trend of IFT with increasing model asphaltene concentration at low temperature (300 K), increasing concentration at high temperature (473 K) leads to increasing IFT. This relation can even be nonmonotonic at moderate temperatures (373 and 423 K). Through detailed analysis on the distribution of model asphaltenes with respect to the interface, such complex behaviors are found to result from the delicate balance between miscibility of toluene/water phases, solubility of model asphaltenes, and hydrogen bonds formed between water and model asphaltenes. By increasing the temperature, the solubility of model asphaltenes in toluene is enhanced, leading to their transition from being a surfactant to being a solute. The effect of pressure was found to be very limited under all model asphaltene concentrations. Our results here present, for the first time, a complete picture of the coupled effect of (high) temperature and asphaltene concentration on IFT, and the methodology employed can be extended to many other two-phase or multiphase systems in the presence of interface-active chemicals

Probing the Adsorption of Polycyclic Aromatic Compounds onto Water Droplets Using Molecular Dynamics Simulations

A series of molecular dynamics (MD) simulations were performed to probe the adsorption behaviors of polycyclic aromatic compounds (PACs) from <i>n</i>-heptane and toluene onto water droplets. In <i>n</i>-heptane, the simulations revealed distinct adsorbed structures of PAC molecules on the water droplets with different sizes. In the system with a small water droplet (radius 1.86 nm), the adsorbed PAC aggregate renders a straight one-dimensional (1D) structure; contrarily, in the presence of a large water droplet (radius 3.10 nm), a bent 1D structure of nonzero curvature is formed. Such size effect is a result from the delicate balance between the deformation energy required for adsorption and the available attractions between the PAC and water molecules. While the adsorbed structures are sensitive to the size of the water droplet at relatively low PAC concentration in <i>n</i>-heptane, the size effect in toluene is only prominent when the concentration of PAC molecules is sufficiently high

Probing the Hydrophobic Interaction between Air Bubbles and Partially Hydrophobic Surfaces Using Atomic Force Microscopy

The hydrophobic interaction plays an essential role in various natural phenomena and industrial processes. Previous studies on the hydrophobic interaction focused mainly on the interaction between hydrophobic solid surfaces for which the effective range of hydrophobic attraction was reported to vary from ∼10 nm to >1 μm. Here, we report studies of the interaction between an air bubble in water used as a probe attached to the cantilever of an atomic force microscope and partially hydrophobized mica surfaces. No bubble attachment was observed for bare hydrophilic mica, but attachment behaviors and attraction with an exponential decay length of 0.8–1.0 nm were observed between the air bubble and partially hydrophobized mica as characterized by a water contact angle on the mica surface that varied from 45° to 85°. Our results demonstrate the important roles of the additional attraction at partially hydrophobized surfaces and hydrodynamic conditions in bubble attachment to substrate surfaces and provide new insights into the basic understanding of this interaction mechanism in various applications such as mineral flotation

Underwater Adhesion of a Stimuli-Responsive Polymer on Highly Oriented Pyrolytic Graphite: A Single-Molecule Force Study

Exploration aiming to understand how a single polymer chain interacts with interested solid–water interface and its dependence on the environmental stimulus is critical, as it is important for a variety of scientific research and practical applications, such as underwater adhesives or smart systems for controlled attachment/detachment. Here, by single molecule force spectroscopy (SMFS), results on underwater adhesion of a single stimuli-responsive polymer chain on a model hydrophobic surface are reported. Salt concentration was used as an effective stimulus for the transition of the stimuli-responsive polymer from hydrophilic (solvophilic) hydrated state to hydrophobic (solvophobic) state in SMFS experiment. The probed equilibrium single-molecule adhesion force that changed from 45 to 76 pN with increasing salt concentration were free of other interactions that are responsible for cohesions, indicating that solvent quality is critical in determining the strength of single-molecule interfacial adhesion. Moreover, the derived simple quantitative thermodynamic model by combining single-molecule detachment mechanics with hydration free energy illustrated that higher single-molecule adhesion force was resulted from higher solvation/hydration free energy. The experimental study and theoretical analysis presented in this work quantitatively revealed the role of hydrophobic and more general solvophobic interactions in single-molecule level and shed light on the molecular structure optimization for desired applications, such as underwater adhesives or smart interfaces

Biodiesel-Assisted Ambient Aqueous Bitumen Extraction (BA³BE) from Athabasca Oil Sands

The water-based extraction process has been almost exclusively used in the current industry for Athabasca oil sands extraction to produce bitumen and heavy oil. However, the current method is facing various challenges, primarily including high energy intensity, poor processability with poor-quality ores, large consumption of fresh water, and concerns on considerable volume of tailings. Although the technology of using nonaqueous solvent as extraction medium has numerous advantages, problems such as solvent loss to tailings and high capital/operating costs are difficult to address. A biodiesel-assisted ambient aqueous bitumen extraction (BA³BE) process has been herein proposed as an alternative to water-based and solvent-based extraction processes. The results showed a significant improvement in both froth quality and bitumen recovery (increased from ∼10% to ∼80% with biodiesel addition) for processing poor-quality ores at ambient temperature (25 °C), which is much lower than the temperatures used in the current industrial practice (40–55 °C). The aqueous tailings generated in the BA³BE process were found to feature faster settling and enhanced densification, which is favorable for recovering processing water and improving land reclamation. Furthermore, the innovative BA³BE extraction process requires similar facilities and procedures as the current industrial processes, which can be considered as an advantage for commercialization