Comprehensive Electrokinetic-Assisted Separation of Oil Emulsion with Ultrahigh Flux

Demulsification with simultaneous water purification by coupling filtration and enhanced oil droplet coalescence at anode interface in an electrochemical reactor

With the increasing demand of recycling disposal of industrial wastewater, oil-in-water (O/W) emulsion has been paid much attention in recent years owing to its high oil content. However, due to the presence of surfactant and salt, the emulsion was usually stable with complex physicochemical interfacial properties leading to increased processing difficulty. Herein, a novel flow-through electrode-based demulsification reactor (FEDR) was well designed for the treatment of saline O/W emulsion. In contrast to 53.7% for electrical demulsification only and 80.3% for filtration only, the COD removal efficiency increased to 92.8% under FEDR system. Moreover, the pore size of electrode and the applied voltage were two key factors that governed the FEDR demulsification performance. By observing the morphology of oil droplets deposited layer after different operation conditions and the behavior of oil droplets at the electrode surface under different voltage conditions, the mechanism was proposed that the oil droplets first accumulated on the surface of flow-through electrode by sieving effect, subsequently the gathered oil droplets could further coalesce with the promoting effect of the anode, leading to a high-performing demulsification. This study offers an attractive option of using flow-through electrode to accomplish the oil recovery with simultaneous water purification.

Sources, colloidal characteristics, and separation technologies for highly hazardous waste nanoemulsions

Nanoemulsions play a crucial role in various industries. However, their application often results in hazardous waste, posing significant risks to human health and the environment. Effective management and separation of waste nanoemulsions requires special attention and effort. This review provides a comprehensive understanding of waste nanoemulsions, covering their sources, characteristics, and suitable treatment technologies, intending to mitigate their environmental impact. This study examines the evolution of nanoemulsions from beneficial products to hazardous wastes, provides an overview of the production processes, fate, and hazards of waste nanoemulsions, and highlights the critical characteristics that affect their stability. The latest advancements in separating waste nanoemulsions for recovering oil and reusable water resources are also presented, providing a comprehensive comparison and evaluation of the current treatment techniques. This review addresses the significant challenges in nanoemulsion treatment, provides insights into future research directions, and offers valuable implications for the development of more effective strategies to mitigate the hazards associated with waste nanoemulsions.

Waste for Waste: Interface-Intensified Durable Superhydrophilic-Superoleophobic Collagen Fiber Membrane for Efficient Separation of Cationic Surfactant-Stabilized Oil-in-Water Emulsions

Cationic surfactant-stabilized oil-in-water emulsions pose a significant challenge in separation due to the presence of surfactants. Herein, we develop a collagen-fiber-based CFM-PMDA-TiO2 membrane with unique infiltration properties capable of efficiently separating cationic surfactant-stabilized oil-in-water emulsions by exploiting the charge-demulsification effect. The membrane exhibits superhydrophilic and submerged superoleophobic properties, making it highly suitable for separating a wide range of commercially available cationic surfactant-stabilized oil-in-water microemulsions and nanoemulsions, which demonstrates an exceptional separation efficiency as high as 99.86% and an impressive flux of up to 1436.40 L m-2 h-1. Furthermore, even after a strong subjecting of the membrane to sandpaper abrasion and a full 15 time use, the separation efficacy of oil-in-water emulsions is retained, highlighting the durability, reusability, and economic viability. We propose that these features are enabled by the electrostatic interactions triggered from pyromellitic dianhydride (PMDA) and superhydrophilic-superoleophobic membrane intensified by the TiO2 on the unique collagen fiber membrane. Outcomes emphasize the versatility and potential of our membrane in addressing emulsified oily wastewater hurdles.

Superhydrophilic and Underwater Superoleophobic Copper Mesh Coated with Bamboo Cellulose Hydrogel for Efficient Oil/Water Separation

Super-wetting interface materials have shown great potential for applications in oil-water separation. Hydrogel-based materials, in particular, have been extensively studied for separating water from oily wastewater due to their unique hydrophilicity and excellent anti-oil effect. In this study, a superhydrophilic and underwater superoleophobic bamboo cellulose hydrogel-coated mesh was fabricated using a feasible and eco-friendly dip-coating method. The process involved dissolving bamboo cellulose in a green alkaline/urea aqueous solvent system, followed by regeneration in ethanol solvent, without the addition of surface modifiers. The resulting membrane exhibited excellent special wettability, with superhydrophilicity and underwater superoleophobicity, enabling oil-water separation through a gravity-driven "water-removing" mode. The super-wetting composite membrane demonstrated a high separation efficiency of higher than 98% and a permeate flux of up to 9168 L·m-2·h-1 for numerous oil/water mixtures. It also maintained a separation efficiency of >95% even after 10 cycles of separation, indicating its long-term stability. This study presents a green, simple, cost-effective, and environmentally friendly approach for fabricating superhydrophilic surfaces to achieve oil-water separation. It also highlights the potential of bamboo-based materials in the field of oil-water separation.

Sequential Demulsification through the Hydrophobic-Hydrophilic-Hydrophobic Filtration Layer toward High-Performing Oil Recovery

Demulsification using membranes is a promising method to coalesce highly stable emulsified oil droplets for oil recovery. Nevertheless, a structure of the current filtration medium that is not efficient for oil droplet coalescence impedes rapid permeability, thereby inevitably restricting their practical applications. Herein, we report a hydrophobic-hydrophilic-hydrophobic (3H) demulsification medium that exhibits a benchmark permeability of ∼2.1 × 104 L m-2 h-1 with a demulsification efficiency of >98.0%. Remarkably, this 3H demulsification medium maintains over 90% demulsification efficiency in the oil-in-water (O/W) emulsions with a wide range of surfactant concentrations, which shows excellent applicability. Based on the combined results of quasi situ microscope images and molecular dynamics simulations, we show that the polydimethylsiloxane-modified hydrophobic layer facilitates the capture and coalescence of oil droplets, the hydrophilic inner layer assists in squeezing the coalescence of enlarged droplets, and the third hydrophobic layer accelerates the discharge of demulsified oil to sustain permeability. The sequential demulsification mechanism between this 3H filtration layer provides a general guide for designing a demulsifying membrane with high demulsification efficiency and high flux toward oil recovery.

Robust Janus Superwetting Textile with Large Pore Sizes for Oil-in-Water Emulsion Separation

Developing advanced oil-water separation technology is significant for environmental conservation. According to the synergetic effects of the size-sieving mechanism, superwetting materials with small pore sizes have been designed to realize high-efficiency separation for oil-water emulsions. However, the separation flux limited by the pore size and the weakness of the superwetting material impede its practical application severely. Herein, we construct a robust Janus superwetting textile with large pore sizes for oil-in-water emulsion separation. The pristine textile is coated by the as-prepared CuO nanoparticles as the bottom layer with superhydrophilicity and then grafted by 1-octadecanethiol as the top layer with superhydrophobicity to construct the Janus textile. When used as a filter, the superhydrophobic layer acts as the nucleation site to coalesce the small oil droplets facilely. Then, the coalesced oil fills the pores of the superhydrophobic layer and selectively permeates it but is blocked by the superhydrophilic layer with large pore sizes. Utilizing the unique separation mechanism, the Janus textile realizes efficient and rapid separation. Even after multicycle separation, hot liquid immersion for 24 h, tribological test for 60 min, and sandpaper abrasion for 500 cycles, the Janus textile still retains the superwettability and excellent separation performance, manifesting outstanding stability to resist severe damage. This separation strategy provides a novel guideline for high-efficiency and high-flux emulsion separation and practical application.

Antimicrobial cellulose paper tuned with chitosan fibers for high-flux oil/water separation

Separating films with both high efficiency and large flux are desperately needed to meet the rising demand for the treatment of oily wastewater, while traditional oil/water separation papers with high separation efficiency usually suffered from low flux due to the unsuitable size of filtration pores. Herein, we report a bio-based porous, superhydrophobic, and antimicrobial hybrid cellulose paper with tunable porous structures for high flux oil/water separation. The size of pores in the hybrid paper can be tuned by both physical supports provided by the chitosan fibers and the chemical shielding supplied by the hydrophobic modification. The hybrid paper with increased porosity (20.73 μm; 35.15 %) and excellent antibacterial properties can efficiently separate a wide range of oil/water mixtures, solely by gravity, with outstanding flux (maximum of 23,692.69 L m^-2 h^-1), tiny oil interception, and high efficiency of over 99 %. This work provides new sights in the development of durable and low-cost functional papers for rapid and efficient oil/water separation.

Novel Strategy of Polymers in Combination with Silica Particles for Reversible Control of Oil-Water Interface

Hybrid smart emulsification systems are highly applicable in manipulating oil-in-water (O/W) droplets. Herein, novel switchable block polymers containing both zwitterionic and tertiary amine pendent groups were designed and synthesized to combine with charged silica particles to stabilize the O/W emulsion responsive to pH. This study was carried out in O/W emulsions stabilized with the polymer and silica particles under different pH conditions. The emulsion system was also simulated using molecular dynamics simulation to reveal the mechanism at molecular levels, thus gaining insight into the relationships between the emulsifying properties and the molecular interaction of the mixed system. Upon acidification of the continuous aqueous phase, protonated polymers with excellent hydrophilicity were induced by charged silica particles to cause rapid emulsion coalescence. In alkaline media, the mixed system conversely stabilized the O/W emulsions, cutting polymer consumption by over three-quarters. The emulsification and demulsification can be switched alternately by tuning the pH conditions. The applications exhibited excellent efficiency in separating heavy oil/water emulsions and proved the high conversion rate in emulsion polymerization. Overall, with this novel strategy to relieve tedious modifications on particle surfaces and massive consumption of polymers, the designed responsive emulsification systems can impart intelligent and controllable chemical reactivity to emulsions on demand in a more affordable and sustainable way.

Piezoelectricity induced by pulsed hydraulic pressure enables in situ membrane demulsification and oil/water separation

Recovering oil from oily wastewater is not only for economic gains but also for mitigating environmental pollution. However, demulsification of oil droplets stabilized with surfactants is challenging because of their low surface energy. Although the widely used oil/water separation membrane technologies based on size screening have attracted considerable attention in the past few decades, they are incapable of demulsification of stabilized oil emulsions and the membrane concentrates often require post-processing. Herein, the piezoelectric ceramic membrane (PCM), which can respond to the inherent transmembrane pressure in the pressure-driven membrane processes, was employed to transform hydraulic pressure pulses into electroactive responses to in situ demulsification. The pulsed transmembrane pressure on the PCM results in the generation of considerable rapid voltage oscillations over 3.2 V and a locally high electric field intensity of 7.2 × 10⁷ V/m, which is capable of electrocoalescence with no additional stimuli or high voltage devices. Negative dielectrophoresis (DEP) force occurred in this membrane process and repelled the large size of oil after demulsification away from the PCM surface, ensuring continuous membrane demulsification and oil/water separation. Overall, PCM provides a further opportunity to develop an environmentally friendly and energy-saving electroresponsive membrane technology for practical applications in wastewater treatment.

Upcycling Waste Pine nut Shell Membrane for Highly Efficient Separation of Crude Oil-in-Water Emulsion

Discharge of oily sewage and frequent oil spills have caused serious harm to human production, life, and ecological environment. Due to the presence of a large number of surfactants in water, these oil-water mixtures are easy to form oil-in-water emulsion, which is difficult to separate by traditional methods. At the same time, the water-soluble pollutants such as dyes and heavy metal ions in oily wastewater also cause great harm to the human body and the environment. A pine nut shell is a kind of common domestic waste material. Herein, an underwater superoleophobic pine nut shell membrane (PNSM) was prepared by the simple pumping filtration method, which realized the separation of oil-in-water emulsion and adsorption of dyes and heavy metal ions. In addition, the filter membrane can be used for separating corrosive emulsions of strong acid, strong alkali, and 3.5% NaCl solutions (simulated seawater). Besides, the PNSM showed excellent toughness and flexibility. Due to the abovementioned performance, this cost-efficient and environmentally friendly membrane can be a promising candidate for multifunctional oily water remediation.