Facile Fabrication of Cyclodextrin-Modified Magnetic Particles for Effective Demulsification from Various Types of Emulsions

Demulsification of Pickering emulsions: advances in understanding mechanisms to applications

Pickering emulsions are ultra-stable dispersions of two immiscible fluids stabilized by solid or microgel particles rather than molecular surfactants. Although their ultra-stability is a signature performance indicator, often such high stability hinders their demulsification, i.e., prevents the droplet coalescence that is needed for phase separation on demand, or release of the active ingredients encapsulated within droplets and/or to recover the particles themselves, which may be catalysts, for example. This review aims to provide theoretical and experimental insights on demulsification of Pickering emulsions, in particular identifying the mechanisms of particle dislodgment from the interface in biological and non-biological applications. Even though the adhesion of particles to the interface can appear irreversible, it is possible to detach particles via (1) alteration of particle wettability, and/or (2) particle dissolution, affecting the particle radius by introducing a range of physical conditions: pH, temperature, heat, shear, or magnetic fields; or via treatment with chemical/biochemical additives, including surfactants, enzymes, salts, or bacteria. Many of these changes ultimately influence the interfacial rheology of the particle-laden interface, which is sometimes underestimated. There is increasing momentum to create responsive Pickering particles such that they offer switchable wettability (demulsification and re-emulsification) when these conditions are changed. Demulsification via wettability alteration seems like the modus operandi whilst particle dissolution remains only partially explored, largely dominated by food digestion-related studies where Pickering particles are digested using gastrointestinal enzymes. Overall, this review aims to stimulate new thinking about the control of demulsification of Pickering emulsions for release of active ingredients associated with these ultra-stable emulsions.

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.

Effective separation of water-in-oil emulsions using an under-medium superlyophilic membrane with hierarchical pores

Separating water-in-oil emulsions is important in terms of environmental protection and resource recovery. To address the challenges posed by the water-oil interface, superwetting materials have been designed to accomplish separation through filtration and adsorption. Superhydrophobic membranes prevent the permeation of water droplets owing to extreme repellence and their size-sieving abilities. However, their use in remediating water-contaminated oil is limited by high oil viscosities. Meanwhile, in-air superhydrophilic sorbents are rarely employed for the separation of water-in-oil emulsions due to the thermodynamic and kinetic limitations of water adsorption in oil. Herein, the integration of an under-medium superlyophilic membrane with the hierarchical porous structure of wood is presented for filtration-driven selective adsorption of water from surfactant-stabilized (10 g/L) water-in-oil emulsions. Compared to filtration through a natural wood membrane or direct adsorption using an under-oil superhydrophilic wood membrane, the under-medium superlyophilic wood membrane demonstrated high separation efficiencies of > 99.95% even when applied to the regeneration of high-viscosity lubricating (6.3 mPa s) and edible (50.5 mPa s) oils, exhibiting viscosity-dependent fluxes and excellent stability. Moreover, the cost of purifying 200 mL of lubricating oil using the modified wood membrane was much lower than the oil's market price and required a low energy consumption of ca. 1.72 kWh. ENVIRONMENTAL IMPLICATION: The ever-growing use of petroleum and industrial/domestic oil products has led to excessive (estimated at a million tons per year) output of waste oils. Because direct discharge of waste oils into the environment causes serious pollution problems, separating water-in-oil emulsions is important in terms of environmental protection and resource recovery. Here filtration-driven water adsorption has been demonstrated to be a feasible method for the remediation of water-contaminated waste oils, even those that are highly viscous.

Review on demulsification techniques for oil/water emulsion: Comparison of recyclable and irretrievable approaches

Since the establishment of the first global refinery in 1856, crude oil has remained one of the most lucrative natural resources worldwide. However, during the extraction process from reservoirs, crude oil gets contaminated with sediments, water, and other impurities. The presence of pressure, shear forces, and surface-active compounds in crude oil leads to the formation of unwanted oil/water emulsions. These emulsions can take the form of water-in-oil (W/O) emulsions, where water droplets disperse continuously in crude oil, or oil-in-water (O/W) emulsions, where crude oil droplets are suspended in water. To prevent the spread of water and inorganic salts, these emulsions need to be treated and eliminated. In existing literature, different demulsification procedures have shown varying outcomes in effectively treating oil/water emulsions. The observed discrepancies have been attributed to various factors such as temperature, salinity, pH, droplet size, and emulsifier concentrations. It is crucial to identify the most effective demulsification approach for oil/water separation while adhering to environmental regulations and minimizing costs for the petroleum sector. Therefore, this study aims to explore and review recent advancements in two popular demulsification techniques: chemical demulsification and magnetic nanoparticles-based (MNP) demulsification. The advantages and disadvantages of each technique are assessed, with the magnetic approach emerging as the most promising due to its desirable efficiency and compliance with environmental and economic concerns. The findings of this report are expected to have a significant impact on the overall process of separating oil and water, benefiting the oil and gas industry, as well as other relevant sectors in achieving the circular economy.

Preparation of Hydrophobic Octadecylphosphonic Acid-Coated Magnetite Nanoparticles for the Demulsification of n-Hexane-in-Water Nanoemulsions

To design more environmentally friendly, economical, and efficient demulsifiers for oily wastewater treatment, hydrophobic octadecylphosphonic acid (ODPA)-modified Fe3O4 nanoparticles (referred to as Fe3O4@ODPA) were prepared by condensation of hydroxyl groups between ODPA and Fe3O4 nanoparticles using the co-precipitation method. The prepared magnetite nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric/differential thermogravimetric (TG/DTG) analysis. The water contact angles (θW) of Fe3O4@ODPA nanoparticles were more than 120°, indicating hydrophobic nature, and the diameter of the obtained spherical-shaped magnetite nanoparticles was 12-15 nm. The ODPA coating amount (AO) (coating weight per gram Fe3O4) and specific surface area (SO) of Fe3O4@ODPA were 0.124-0.144 g·g-1 and 78.65-91.01 m2·g-1, respectively. To evaluate the demulsification ability, stability, and reusability, the magnetite nanoparticles were used to demulsify an n-hexane-in-water nanoemulsion. The effects of the magnetite nanoparticle dosage (CS), pH value of nanoemulsion, and NaCl or CaCl2 electrolytes on the demulsification efficiency (RO) were investigated. The RO of Fe3O4@ODPA samples was found to be higher than that of bare Fe3O4 samples (S0, ST, and SN) under all CS values. With the increase in CS, the RO of Fe3O4@ODPA samples initially increased and then approached equilibrium value at Cs = 80.0 g·L-1. A maximum RO of ~93% was achieved at CS = 100.0 g·L-1 for the Fe3O4@ODPA sample S2. The pH and two electrolytes had a minor effect on RO. The Fe3O4@ODPA nanoparticles maintained high RO even after being reused for demulsification 11 times. This indicates that the hydrophobic Fe3O4@ODPA samples can be used as an effective magnetite demulsifer for oil-in-water nanoemulsions.

Recent advances in the design and use of Pickering emulsions for wastewater treatment applications

Pickering emulsions have recently emerged as versatile systems capable of targeting many applications of wastewater treatment. The unique properties, which include high emulsion stability, easy preparation, low toxicity, and stimuli-responsiveness, pave the way for advances in common pollutant control processes. This review aims to provide a comprehensive overview on different aspects in the Pickering emulsion design focusing on the key structural relations and their implications in specific applications. The first section is dedicated to the critical parameters governing the Pickering emulsion type, droplet size and stability. Furthermore, a section describing methods for demulsification and particle recovery is included, in which various stimuli have been explored. Finally, the most potent applications of Pickering emulsions such as photocatalytic degradation, adsorption, extraction, and separation of common wastewater pollutants are presented and discussed with a great deal of attention towards the efficacy, current limitations, and future potential. Recognizing the rise of innovative Pickering emulsion solutions is expected to induce profound effects facilitating the technology transfer to industrial processes.

Demulsification Performance and Mechanism of Tertiary Amine Polymer-Grafted Magnetic Nanoparticles in Surfactant-Free Oil-in-Water Emulsion

Numerous cationic magnetic nanoparticles (MNPs) have previously been developed for demulsifying oil-in-water (O/W) emulsion, and results showed that the cationic MNPs could effectively flocculate and remove the negatively charged oil droplets via charge attraction; however, to the best of our knowledge, there are no research reports regarding the synergetic influence of both the positive charge density and interfacial activity of MNPs on the demulsification performance. In this study, three tertiary amine polymer-grafted MNPs, namely, poly(2-dimethylaminoethyl acrylate)-grafted MNPs (M-PDMAEA), poly(2-dimethylamino)ethyl methacrylate)-grafted MNPs (M-PDMAEMA), and poly(2-diethylaminoethyl methacrylate)-grafted MNPs (M-PDEAEMA), were synthesized and evaluated for their demulsification performance. Results demonstrated that a high positive charge density and superior interfacial activity of MNPs could cause partial oil droplet re-dispersion when excessive MNPs were introduced, leading to a lower magnetic separation efficiency and narrower demulsification window. Herein, a demulsification window is defined as a range of nanoparticle dosages in which the MNPs can effectively demulsify the O/W emulsion under certain conditions. For highly positively charged MNPs, their good interfacial activity could aggravate the formation of a narrower demulsification window. When tertiary amine polymer-grafted MNPs carried a lower positive charge density or weak interfacial activity, that is, M-PDMAEA at pH 4.0, M-PDMAEMA at pH 5.0-9.0, and M-PDEAEMA at pH 9.0-10.0, wide demulsification windows were observed. Additionally, a recycling experiment suggested that MNPs could maintain high demulsification efficiency up to at least five cycles, indicating their satisfactory recyclability. The three tertiary amine polymer-grafted MNPs can be potentially used for efficient demulsification from surfactant-free O/W emulsion in various pH ranges.

Nano-modification of carboxylated polyether for enhanced room temperature demulsification of oil-water emulsions: Synthesis, performance and mechanisms

Oil-water emulsions separation is frequently required considering the production and environmental issues. Herein, a nano-modification strategy has been proposed for carboxylated poly(propylene oxide)-poly(ethylene oxide) block polyether (mANP) using epoxy-functionalized magnetic nanoparticles (Fe₃O₄@SiO₂-GPTMS), achieving the construction of a highly efficient demulsifier (M-mANP). Bottle tests showed that M-mANP could separate over 98.5% of water from the asphaltene-stabilized water-in-oil (W/O) emulsion at mANP concentration of 150 ppm within 2 min at room temperature. The demulsification efficiency for crude oil-in-water emulsion was nearly 100%. According to interfacial tension and wettability tests, the nano-modification endows M-mANP with good amphiphilicity and high interfacial activity, which enables M-mANP to rapidly adsorb at the oil-water interface. Molecular dynamics simulation shows that abundant oxygen-containing groups (hydroxyl, ether bond, ester and carboxyl groups, Fe-O and Si-O bond) in M-mANP could strengthen the interaction with water, facilitating the replacement of asphaltene molecules at interfacial film. Observation of demulsification process by microscope reveals that the nano-size promotes M-mANP to bridge small dispersed droplets, enhancing the flocculation and coalescence of droplets. The nano-modified carboxylated polyether with outstanding demulsification ability shows a promising application for the treatment of different oil-water emulsions.

Destructing surfactant network in nanoemulsions by positively charged magnetic nanorods to enhance oil-water separation

The separation of ultrafine oil droplets from wasted nanoemulsions stabilized with high concentration of surfactants is precondition for oil reuse and the safe discharge of effluent. However, the double barriers of the interfacial film and network structures formed by surfactants in nanoemulsions significantly impede the oil-water separation. To destroy these surfactant protective layers, we proposed a newly-developed polyethyleneimine micelle template approach to achieve simultaneous surface charge manipulation and morphology transformation of magnetic nanospheres to magnetic nanorods. The results revealed that positively charged magnetic nanospheres exhibited limited separation performance of nanoemulsions, with a maximum chemical oxygen demand (COD) removal of 50%, whereas magnetic nanorods achieved more than 95% COD removal in less than 30 s. The magnetic nanorods were also applicable to wasted nanoemulsions from different sources and exhibited excellent resistance to wide pH changes. Owing to their unique one-dimensional structure, the interfacial dispersion of magnetic nanorods was significantly promoted, leading to the efficient capture of surfactants and widespread destruction of both the interfacial film and network structure, which facilitated droplet merging into the oil phase. The easy-to-prepare and easy-to-tune strategy in this study paves a feasible avenue to simultaneously tailor surface charge and morphology of magnetic nanoparticles, and reveals the huge potential of morphology manipulation for producing high-performance nanomaterials to be applied in complex interfacial interaction process. We believe that the newly-developed magnetic-nanorods significantly contribute to hazardous oily waste remediation and advances technology evolution toward problematic oil-pollution control.

Green Preparation of a Carboxymethyl Cellulose-Coated Membrane for Highly Efficient Separation of Crude Oil-In-Water Emulsions

Developing high-performance membranes is an extremely significant strategy to combat increasing severe oil pollution. However, most of the previously reported superwettable membranes have been inevitably involved with the use of toxic solvents and complicated preparation processes. In addition, most of them lacked the capacity of separating crude oil-in-water emulsions. Herein, a facile and green strategy is employed to fabricate a polytetrafluoroethylene (PTFE) membrane with a mixed suspension of PDA@ZIF-8 and carboxymethyl cellulose (CMC) using water as a solvent via the vacuum filtration method. Combining hydrophilic property with micro-nano-roughness, the CMC-PDA@ZIF-8-coated PTFE membrane (CPZP membrane) exhibits excellent underwater superoleophobicity. More importantly, the separation efficiency of various surfactant-stabilized oil-in-water emulsions including crude oil/water emulsion is higher than 99.2% with a flux up to 1306.5 L m^-2 h^-1, and the separation performance remains nearly the same after 10 cycles. Moreover, outstanding underwater superoleophobic and self-cleaning properties are maintained after long-distance sandpaper abrasion and multiple bending tests. Meanwhile, its exceptional separation performance is still maintained in harsh environments (3.5 wt % NaCl, 1 M HCl, 60 °C hot water) even after immersing it for 24 h. Therefore, this green-prepared and high-performance membrane has tremendous application prospects in treating oily wastewater.

Demulsification of Heavy Oil-in-Water Emulsion by a Novel Janus Graphene Oxide Nanosheet: Experiments and Molecular Dynamic Simulations

Various nanoparticles have been applied as chemical demulsifiers to separate the crude-oil-in-water emulsion in the petroleum industry, including graphene oxide (GO). In this study, the Janus amphiphilic graphene oxide (JGO) was prepared by asymmetrical chemical modification on one side of the GO surface with n-octylamine. The JGO structure was verified by Fourier-transform infrared spectra (FTIR), transmission electron microscopy (TEM), and contact angle measurements. Compared with GO, JGO showed a superior ability to break the heavy oil-in-water emulsion with a demulsification efficiency reaching up to 98.25% at the optimal concentration (40 mg/L). The effects of pH and temperature on the JGO’s demulsification efficiency were also investigated. Based on the results of interfacial dilatational rheology measurement and molecular dynamic simulation, it was speculated that the intensive interaction between JGO and asphaltenes should be responsible for the excellent demulsification performance of JGO. This work not only provided a potential high-performance demulsifier for the separation of crude-oil-in-water emulsion, but also proposed novel insights to the mechanism of GO-based demulsifiers.

Recyclable amine-functionalized carbon nanotubes for the separation of oily wastewater

In this work, a CNTs-NH₂ demulsifier was prepared by grafting ethylenediamine on the surface of carbon nanotubes to break oily wastewater. The physicochemical and interfacial properties of CNTs-NH₂ were characterized and analyzed. It showed that CNTs-NH₂ had an eminent amphipathicity and high interfacial activity, which allows it to sharply migrates to the interface and effectively interacts with interfacial film by the combined action of π-π interaction and electrostatic attraction. The demulsification tests exhibited that CNTs-NH₂ could effectively remove emulsified oil from the oily wastewater. It could be used at acidic and neutral conditions, and high salinity. Moreover, it could be recycled and still maintained its interfacial activity, thusly vastly enhancing the application scope. The light transmittance was up to 88.1% and the corresponding oil removal rate was 99.2% with 100 mg/L of CNTs-NH₂ for 30 min. The oil removal rate of CNTs-NH₂ remained above 97.8% after 6 cycles. This work provides a deep understanding on the design of demulsifier and its demulsification mechanism.

Amidoxime modified Fe3O4@TiO2 particles for antibacterial and efficient uranium extraction from seawater

Uranium extraction and recovery play a critical role in guaranteeing the sustainable nuclear energy supply and protecting the environmental safety. The ideal uranium sorbents possess high adsorption capacity, excellent selectivity and reusability, as well as outstanding antimicrobial property, which are greatly desired for the real application of uranium extraction from seawater. To address this challenge, a novel magnetic core-shell adsorbent was designed and fabricated by a facile method. The obtained amidoximed Fe₃O₄@TiO₂ particles (Fe₃O₄@TiO₂-AO) achieved equilibrium in 2 h and the maximum adsorption capacity calculated from Langmuir model is 217.0 mg/g. The adsorption kinetics followed the pseudo-second-order model. Meanwhile, the Fe₃O₄@TiO₂-AO exhibited great selectivity when competitive metal ions and anions coexisted. In addition, the magnetic Fe₃O₄@TiO₂-AO could be conveniently separated and collected by an external magnetic field, the regeneration efficiency maintained at 78.5% even after ten adsorption-desorption cycles. In natural seawater, the uranium uptake reached 87.5 μg/g in 33 days. Furthermore, the TiO₂ contained adsorbent showed effective photo induced bactericidal properties against both E. coli and S. aureus. The Fe₃O₄@TiO₂-AO with great U(VI) adsorption performance is highly promising in uranium extraction and reclamation.

Effective remediation of petrochemical originated pollutants using engineered materials with multifunctional entities

The highly robust, effective, and sustainable remediation of hydrocarbon-contaminated wastewater matrices, which is mainly generated from petroleum and related petrochemical industries, is of supreme interest. Owing to the notable presence of suspended solids, oil, and grease, organic matter, highly toxic elements, high salts, and recalcitrant chemicals, crude oil emulsions, and hydrocarbon-contaminated wastewater are considered a potential threat to the environments, animals, plants, and humans. To effectively tackle this challenging issue, magnetic hybrid materials assembled at nano- and micro-scale with unique structural, chemical, and functional entities are considered robust candidates for demulsification purposes. The current research era on magnetic materials has superwettability, leading to an effective system of superwettability, which is vibrant and promising. The wettability of magnetic and magnetic hybrid materials explaining the theme of superhydrophobicity and superhydrophilicity under the liquid. Herein, we reviewed the applications of magnetic nanoparticles (MNPs) as effective demulsifiers. The demulsifier wettability, dose, pH, salinity, and surface morphology of compelling, magnetic nanoparticles are the main hidden factors in effective demulsifiers. There is a comprehensive discussion on the reuse and recyclability of MNPs after oil, water separation. Furthermore, the main challenges, coupled with the magnetic nanoparticles in the effective separation of emulsions, are intensified in detail. This review will compare the current literature and the utilization of MNPs for the demulsification of oil and water emulsions. This is envisioned that the MNPs would be critical in the petroleum and petrochemical industry to effectively eliminate water from a crude oil emulsion.

Adsorption property and mechanism of polyacrylate-divinylbenzene microspheres for removal of trace organic micropollutants from water

In this study, polyacrylate-divinylbenzene (PADVB) microspheres were facilely prepared via the precipitation polymerization method, and the microspheres were used as an efficient adsorbent for the removal of trace level organic micropollutants (OMPs) from environmental waters. Preparation conditions of PADVB microspheres were optimized, and the characterizations of the microspheres were performed using a scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), and N₂ adsorption/desorption isotherms. The microspheres had broad-spectrum adsorption ability for various organic micropollutants containing hydroxy, amidogen, aromatic or heteroaromatic ring in their chemical structure, such as atrazine, 2,4 dichlorophenol, 2,4 dibromophenol, 2,6 dichlorophenol, sulfamethoxazole, estradiol, and bisphenol A. Besides, the effects of initial concentration, initial pH value, adsorption time, and the type of adsorbates on the adsorption performance were investigated systematically. PADVB microspheres could be used for removing trace OMPs from environmental water. Monolayer and homogeneous sorption process occurred on the surface of PADVB microspheres through chemisorption mechanisms. The X-ray photoelectron spectroscopy (XPS) and FT-IR spectrum of PADVB microspheres before and after adsorption proved that the OMPs adsorption onto PADVB microspheres was mainly due to the formation of the hydrogen bond and π-π electron-donor-acceptor (EDA) interactions. Besides, PADVB microspheres can be recovered for reuse via (low-pressure) microfiltration and could be regenerated sufficiently by using 80% (v/v) ethanol.

Mitigation of environmentally hazardous pollutants by magnetically responsive composite materials

At present, environmental contamination has become an emerging issue among researchers. These facts are due to the adverse impacts of an alarming number of recalcitrant contaminants that can affect both humans and animals. There is an urgent need to develop eco-friendly approaches to mitigate the effects of toxic pollutants from the environment. Magnetically responsive composite-based sorbents are very interesting and popular materials for pollutant abatement owing to the high specific surface area, superior adsorption capacity, and magnetic properties, which make their easy separation from sample solution/media. In this review article, we discuss various synthesis approaches, key physicochemical properties, and applications of magnetic composites for pollutant removal. Current gaps for coping with contamination are identified, and a comprehensive outlook in pollutant treatment using magnetic composites is outlined. This study unveils new horizons to researches for better understanding the properties of magnetically-composite-based sorbents and their application in environmental remediation.

Cyclodextrin-based dispersive liquid-liquid microextraction for the determination of fungicides in water, juice, and vinegar samples via HPLC

Cyclodextrin-based dispersive liquid-liquid microextraction (CD-DLLME) was developed for the determination of triazole and strobilurin fungicides in water, juice, and vinegar samples using high-performance liquid chromatography-diode-array detection (HPLC-DAD). Undecanol, which is a green solvent, was selected as the extraction solvent. A cyclodextrin aqueous solution was chosen as the dispersion solvent and demulsifier to avoid the use of a toxic dispersion solvent and eliminate the centrifugation step. Dispersion and phase separation were completed within 1 and 60 s, respectively. The linear range of this method was 1 to 100 µg L^-1. The limits of detection were 0.3 μg L^-1 along with the preconcentration factor of 133 and enrichment factor of 124. The recovery was 83.2% to 103.2%. This pretreatment method was fast, simple, and environmentally friendly and was successfully applied to the analysis of triazole and strobilurin fungicide residues in water, juice, and vinegar samples.

Coupling magnetic particles with flocculants to enhance demulsification and separation of waste cutting emulsion for engineering applications

Magnetic particles were coupled with a flocculant to enhance the demulsification and separation of waste cutting emulsions. The optimal magnetic particle size and critical magnetic field conditions were investigated to achieve large-scale engineering application of magnetic demulsification separation for waste cutting emulsion treatment. The micro-scale magnetic particles were found to show comparable effects to nano-scale magnetic particles on enhancing the demulsification and separation of cutting emulsions, which are beneficial for broadening the selectivity of low-cost magnetic particles. The critical magnetic separation region was determined to be an area 40 mm from the magnetic field source. Compared to the flocculant demulsification, the magnetic demulsification separation exhibited a significant advantage in accelerating flocs-water separation by decreasing the separation time of flocs from 180-240 min to less than 15 min, compressing the flocs by reducing the floc volume ratio from 60%-90% to lower than 20%, and showing excellent adaptability to the variable properties of waste cutting emulsions. Coupled with the design of the magnetic disk separator, continuous demulsification separation of the waste cutting emulsion was achieved at 1.0 t/hr for at least 10 hr to obtain clear effluent with 81% chemical oxygen demand removal and 89% turbidity reduction. This study demonstrates the feasibility of applying magnetic demulsification separation to large-scale continuous treatment of waste emulsion. Moreover, it addresses the flocs-water separation problems that occur in practical flocculant demulsification engineering applications.

Strong influence of surfactants on virgin hydrophobic microplastics adsorbing ionic organic pollutants

Microplastic (MP) pollution has become an area of increasing concern because MPs accumulate various types of pollutants. Many previous studies have explored the interactions between MPs and hydrophobic pollutants. However, little research has been conducted on hydrophilic pollutants, which are of much higher concentration and ubiquitous in environment. Surfactants cause hydrophobic MPs to become hydrophilic, which may significantly enhance their capacities to adsorb hydrophilic pollutants. This study explored the influence of co-existing surfactants on the adsorption of ionic organic pollutants by MPs, and found that the presence of an ionic surfactant could significantly enhance the capacity of polyvinyl chloride (PVC, 0.2 mm) MPs to adsorb pollutants with opposite charges. The Langmuir methylene blue adsorption capacity of PVC could be increased from 172 to 4417 ppm in the presence of a sodium dodecyl benzene sulfonate surfactant. Nonionic surfactants impeded the adsorption of both cationic and anionic pollutants due to the steric resistance of the hydrophilic polyethelene glycol chains. The electrostatic interaction mechanism dominated the interfacial behaviors of ionic pollutants on surfactant-adsorbed MP interfaces. The effects of the surfactants were further verified using four different model pollutants and six surfactants. The adsorption capacities of real environmental MPs, including PVC, polyethylene (PE), polypropylene (PP), and polystyrene (PS), increased by three to twenty-six times. The adsorption properties of MPs may be determined by the presence of co-existing surfactants, rather than their polymer species or additives.

Surfactant stealth effect of microplastics in traditional coagulation process observed via 3-D fluorescence imaging

Microplastics (MPs) have aroused rising social concerns. Although amounts of surfactants exist in wastewater and are expected to alter the surface properties of MPs significantly as they are designed to be adsorbed by hydrophobic particles. However, rare works have been done on the influence of surfactants on the coagulation removal process of MPs which was thought to be an effective way to remove MPs together with other natural particles, such as clay. We used 3-D fluorescence imaging to track the coagulation removal process of polystyrene MPs. Our results indicate that nonionic surfactant, tween 20 in ppm scale, could inhibit the coagulation removal of polystyrene MPs significantly. Residue MPs in the effluent is proportional with the surfactant concentration and increases up to tens of times, which will lead to a dramatic increase in their potential environmental risks. Apparent size effect exists in the coagulation in which smaller MPs can escape from the coagulation removal more easily. Mechanism study suggests that the steric resistance of the hydrophilic flexible polyethylene glycol (PEG) layer formed by tween 20 adsorbed on MP surface inhibits clay deposition and thus hinders subsequent agglomeration and precipitation. A surfactant stealth effect, which is used in the design of nanomedicine to avoid the human immune recognition and clearance of nano-drugs from blood circulation, also exists in the coagulation removal process of MPs. Our finding not only proves the strong influence of surfactants on MPs but also will stimulate related studies on other latent surfactant effects of MPs.

Acceleration of floc-water separation and floc reduction with magnetic nanoparticles during demulsification of complex waste cutting emulsions

Waste cutting emulsions are difficult to treat efficiently owing to their complex composition and stable emulsified structure. As an important treatment method for emulsions, chemical demulsification is faced with challenges such as low flocs-water separation rates and high sludge production. Hence, in this study, Fe₃O₄ magnetic nanoparticles (MNPs) were used to enhance chemical demulsification performance for treating waste cutting emulsions under a magnetic field. The addition of MNPs significantly decreased the time required to attain sludge-water separation and sludge compression equilibrium, from 210 to 20 min. In addition, the volume percentage of sludge produced at the equilibrium state was reduced from 45% to 10%. This excellent flocculation-separation performance was stable over a pH range of 3-11. The magnetization of the flocculants and oil droplets to form a flocculant-MNP-oil droplet composite, and the magnetic transfer of the composite were two key processes that enhanced the separation of cutting emulsions. Specifically, the interactions among MNPs, flocculants, and oil droplets were important in the magnetization process, which was controlled by the structures and properties of the three components. Under the magnetic field, the magnetized flocculant-MNP-oil droplet composites were considerably accelerated and separated from water, and the sludge was simultaneously compressed. Thus, this study expands the applicability of magnetic separation techniques in the treatment of complex waste cutting emulsions.

Application of biosurfactant surfactin as a pH-switchable biodemulsifier for efficient oil recovery from waste crude oil

Efficient oil separation is the most desirable, but still challenging solution for the waste crude oil problem. This study developed biosurfactant surfactin as a novel pH-switchable biodemulsifier for efficient oil separation. As found, surfactin demulsification achieved a quite well oil separation ratio of over 95% on model emulsions after 20 min at 50 °C. The validity of this demulsification process should be mainly based on the readily lost stabilization ability of surfactin in emulsions triggered by acid addition. Then, surfactin (0.2 g/L) treatment with the aid of ethanol (2%) to improve its distribution could recover over 95% of oil from waste crude oil. After treated by surfactin, the separated oil phase contains tiny water (less than 0.5%) and thus can be reused for resource recycling to reach a compromised balance between satisfying the strict environmental regulations and decreasing the high treatment costs. Hence, in consideration of high demulsification efficiency, environmental-friendly properties and cost-efficiency, surfactin has a great potential for industrial applications for oil recovery from waste crude oil which is a severe problem presents in most of the petroleum-related factories.

Study on demulsification and deoiling for O/W emulsion by microbubble pretreated resin

The microbubble pretreated resin was used for demulsification and deoiling of the simulated O/W emulsion. The demulsification and deoiling performance and the influencing factors were investigated systematically. Experimental results indicate that the microbubble pretreated resin reaches a 97% oil removal within 80 min; on the contrary, oil removals are 90% and 85% for NaOH solution soaked and un-pretreated resins respectively. After five repeated runs, the oil removal of microbubble pretreated resin can be maintained at over 70%. The demulsification mechanism was revealed by comparing zeta potential, surface tension, contact angle of the emulsion in treatment, and the characterization results of the resin before and after use. Three possible pathways of demulsification were concluded and the ranking contributions can be shown below. Pathway 1: Competitive trapping of surfactant. The cationic groups of the resin combine with the anionic groups of the surfactant and drag them away from the oil particle surface. Pathway 2: Distribution equilibrium of surfactant. Free surfactants in the emulsion are captured by resin and reduce the concentration of uncombined surfactant. This results in surfactants on the oil particle partly detaching from the oil surface to maintain the adsorption-desorption equilibrium of the surfactant. Pathway 3: Adsorption coalescence.

Removal of Emulsified Oil from Aqueous Environment by Using Polyvinylpyrrolidone-Coated Magnetic Nanoparticles

In recent years, a large amount of emulsified oily wastewaters were produced from petroleum and food industries, resulting in severe environmental problems. In this study, a series of polyvinylpyrrolidone (PVP)-coated Fe3O4 magnetic nanoparticles (MNPs) were prepared via one-step solvothermal method by introducing various amounts or types of PVP. The synthesized MNPs were characterized by multiple techniques, and their demulsification performances were evaluated in petrochemical and vegetable oil wastewaters, respectively. Results showed that the introduction of PVP in solvothermal process could significantly enhance the demulsification efficiency of MNPs, although excessive addition of PVP could not further increase its efficiency. Moreover, the effects of pH, surfactant concentration of wastewater, and the recycle number of MNPs on the demulsification performance were investigated in detail. It was found that the demulsification efficiency decreased with the increase of pH and surfactant concentration, and the synthetic MNPs were still effective after being reused for 5 cycles under acidic and neutral conditions. It is expected that the development of the PVP-coated MNPs can provide a simple and powerful route for the oily wastewater treatment.

Modification of Supramolecular Membranes with 3D Hydrophilic Slide-Rings for the Improvement of Antifouling Properties and Effective Separation

A three-dimensional (3D) strategy for the fabrication of ethylene vinyl alcohol (EVAL) membranes with a dynamic surface was developed based on sliding supramolecular polymer brushes (SSPBs). The SSPBs with a 3D hydrophilic structure were introduced into the alkyne-EVAL membrane matrix via an azide-alkyne click coupling reaction. The self-mobile hydrophilic slide-rings in the SSPB provided a proactive exclusion system. This resulted in reduced direct contact of the membrane surface with multiple pollutants such as bovine serum albumin (BSA) and oil droplets. The EVAL-SSPB membrane demonstrated increased surface hydrophilicity, underwater oleophobicity, and antifouling properties. More importantly, the abundant hydrophilic rings in the membrane matrix result in supramolecular assembly and efficient hydrophilic sliding channels. This resulted in a dramatic increase in the water flux [2000 L/(m² h)] while retaining a 96% rejection of BSA and oil/water emulsions. The results of the study indicate that three effects of the cyclodextrins rings, i.e., the hydrophilic effect, the exclusion effect, and the sliding effect, enabled the improved membrane performance. The demonstrated 3D fabrication strategy is versatile, facile, and scalable, which allows for its application to various other membranes. The fabricated materials possess excellent permeability and separation efficiencies, which make them attractive candidates for use as separation membranes with novel functions.

Maleic Anhydride Cross-Linked β-Cyclodextrin-Conjugated Magnetic Nanoadsorbent: An Ecofriendly Approach for Simultaneous Adsorption of Hydrophilic and Hydrophobic Dyes

A magnetic nanoadsorbent with a cross-linked β-Cyclodextrin maleic anhydride polymer capable of simultaneous removal of hydrophilic and hydrophobic dyes was developed with high efficacy and desorption/recycling efficiency. The effect of various parameters (concentration, adsorbent dosage, contact time, pH, and temperature) was evaluated to assess the optimum adsorption conditions. The superparamagnetic nanoadsorbent (SPNA) could be easily separated by magnetic decantation and showed maximum removal of malachite green with 97.2% adsorption efficiency. Studies on simultaneous adsorption of dyes from a mixture were performed and the adsorption capacity was calculated. Interestingly, the phenomenon of competitive adsorption was observed. The adsorption process can be fitted well into the Langmuir isotherm model and follows pseudo-second-order kinetics. SPNA could be effectively regenerated and recycled at least five times without any significant loss in removal efficiency. SPNA could be an ideal adsorbent for water remediation because of excellent dye removal efficiency in addition to chemical stability, ease of synthesis, and better reusability.

One-step synthesis of versatile magnetic nanoparticles for efficiently removing emulsified oil droplets and cationic and anionic heavy metal ions from the aqueous environment

Versatile polyethyleneimine (PEI)-coated Fe₃O₄ magnetic nanoparticles (MNPs) have been synthesized by a one-step solvothermal method. The morphologies, structures, and properties of MNPs prepared for different reaction times have been characterized through various techniques. The synthesized MNPs were then used to separate emulsified oil and cationic and anionic heavy metal ions from the aqueous environment; moreover, the effects of the temperature, pH, and ionic strength of aqueous media, the solvothermal reaction time, and the number of reuse cycles on the removal efficiency have been investigated in detail. The results showed that pseudo-second-order kinetics and the Langmuir isotherm well described the adsorption processes of Cu(II) and Cr(VI). The Langmuir model yielded maximum adsorption capacities of 66.6 mg g^-1 for Cu(II) and 54.5 mg g^-1 for Cr(VI) at pH 5.0 and 25 °C. The synthetic MNPs could also efficiently separate diesel oil or olive oil droplets stabilized by sodium dodecyl sulfate from aqueous media. Moreover, these MNPs could be recycled five times without showing significant loss in separation efficiency. Notably, the synthesized PEI-coated MNPs could simultaneously separate emulsified oil and cationic and anionic heavy metal ions from multicomponent wastewater. Such versatile PEI-coated MNPs displayed good affinity towards emulsified oil and cationic and anionic heavy metal ions, showing great potential for practical applications in the treatment of complicated industrial wastewater matrices. Graphical abstract Simultaneous separation of emulsified oil and cationic and anionic heavy metal ions from aqueous media by using polyethyleneimine-coated Fe₃O₄ magnetic nanoparticles.