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Fluorinated-Polyether-Grafted Graphene-Oxide Magnetic Composite Material for Oil–Water Separation

Key Laboratory of Enhanced Oil Recovery, Ministry of Education, Northeast Petroleum University, Daqing 163318, China
Heilongjiang Provincial Key Laboratory of Oilfield Applied Chemistry and Technology, Daqing Normal University, Daqing 163712, China
Department of Chemical Engineering and Safety, Binzhou University, Binzhou 256603, China
Author to whom correspondence should be addressed.
AppliedChem 2023, 3(3), 400-413;
Submission received: 18 June 2023 / Revised: 22 July 2023 / Accepted: 26 July 2023 / Published: 17 August 2023


In this study, a new type of highly efficient and recyclable magnetic-fluorine-containing polyether composite demulsifier (Fe3O4@G-F) was synthesized by the solvothermal method to solve the demulsification problem of oil–water emulsion. Fe3O4@G-F was successfully prepared by grafting fluorinated polyether onto Fe3O4 and graphene-oxide composites. Fe3O4@G-F was characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Taking the self-made crude-oil emulsion as the experimental object, the demulsification mechanism of the demulsifier and the influence of external factors, such as the temperature and pH value, on the demulsification performance of the demulsifier are discussed. The results show that the demulsification efficiency of the Fe3O4@G-F emulsion can reach 91.38% within 30 min at a demulsifier dosage of 750 mg/L, pH of 6, and a demulsification temperature of 60 °C. In neutral and acidic environments, the demulsification rate of the demulsifier is more than 90%. In addition, Fe3O4@G-F has been proven to have good magnetic effects. Under the action of an external magnetic field, Fe3O4@G-F can be recycled and reused in a two-phase system four times, and the demulsification efficiency is higher than 70%. This magnetic nanoparticle demulsifier has broad application prospects for various industrial and environmental processes in an energy-saving manner.

1. Introduction

As oil fields approach their later stages of exploitation, ensuring the continuous and stable production of crude oil is paramount. The implementation of tertiary oil recovery technologies, such as polymer flooding, has significantly enhanced the stability of crude-oil-produced fluid [1,2,3]. The improper treatment of oil–water emulsions may lead to elevated production costs, dimished quality of petroleum products, and severe ecological consequences that are difficult to predict [4,5]. Achieving efficient demulsification is an urgent problem for each oilfield due to the uncertainty and complexity of the composition of crude oil emulsions. The use of demulsifiers, which are amphiphilic and structurally adjustable chemical reagents, has become the most widely used demulsification method because of their convenient and efficient characteristics [6,7,8]. The distinctive nanoscale dimensions of nanoparticles and the magnetic characteristics of materials have garnered significant research attention, focusing on their application in demulsification. Researchers aim to diversify demulsifiers and enhance their performance by incorporating these unique features [9,10,11,12].
The properties of a compound change after it is combined with the fluorine element. The interaction between the fluorine atom and the carbon chain skeleton ensures that the compound has good friction resistance, weather resistance, thermodynamic stability, high surface activity, etc., so the fluorine-containing material has a unique role in coating, sterilization, cleaning, and medicine [13,14,15]. A fluorinated polyether demulsifier is used to introduce the fluorine element with high surface activity into the original polyether demulsifier. It was found that [16,17,18] a fluorinated polyether demulsifier can quickly reduce the oil–water interfacial tension and accelerate the aggregation of water droplets. Compared with traditional demulsifiers, it has better demulsification effects. Zhang et al. [19] prepared a series of novel fluorosilicone copolymers through atom-transfer radical polymerization (ATRP). The demulsification performance of the coal tar/water emulsion at low temperatures was evaluated using a bottle test. Studies have shown that the copolymer has little effect on the interfacial tension of the emulsion, but that it significantly reduces the elasticity of the interfacial film. The removal rate of low-temperature coal tar (LCT) in the emulsion is more than 90%, and the copolymer has a good demulsification performance. Wei et al. [20] synthesized an FB-series fluorinated polyether demulsifier via block polymerization. The results showed that at a demulsification temperature of 60 °C and an ffb4 fluorinated polyether demulsifier dosage of 100 mg/L, the overall dehydration rate (%) of 50 mL of crude oil emulsion in the Liaohe Oilfield reached 90.33% within 2 h, which was better than the demulsifier currently used in Liaohe crude oil. Therefore, the use of fluorine-containing surfactants and demulsifier-composite demulsification has become a research focus.
Fluorinated polyether demulsifiers have good demulsification performance, but they are expensive and toxic to the environment. The aim of this study was to synthesize an environmentally friendly magnetic fluorinated polyether demulsifier by introducing magnetic nanoparticles. Magnetic nano-demulsifiers can be separated from the emulsion under the action of an external magnetic field without causing secondary pollution and can be reused after washing [21,22]. In addition, the π–π bond formed on the surface of the demulsifier and the oil droplet accelerates oil droplet polymerization via the magnetic effect. Among various magnetic nanomaterials, Fe3O4 has become a research focus in recent years due to its low toxicity, easy availability in raw materials, relatively simple synthesis process, and excellent performance [23,24,25,26]. Azizi et al. [12] synthesized Fe3O4 magnetic nanoparticles (MNPs) through an electrochemical method and mixed them with commercially available demulsifiers to improve the demulsification of high asphaltene content (13 wt%). The experimental results showed that Fe3O4 magnetic nanoparticles can be circulated at least three times, the demulsification efficiency (%) can be increased by 10%, and the settling time is shortened by 6 h. The efficient demulsification ability and performance of Fe3O4 magnetic nanoparticles in W/O demulsification processes were revealed. Feng et al. [27] used shellfish-excited polydopamine as a binder to immobilize commercial polyether demulsifiers (AE1910, SP169, and AR321) on the surfaces of Fe3O4 nanoparticles to synthesize a simple new magnetic recoverable demulsifier. The demulsification efficiencies of the three nanoparticles in the crude oil emulsion were 98.00%, 91.63%, and 94.33%, respectively. Furthermore, Fe3O4@PDA@AE1910 can be used for eight cycles of water/n-decane emulsion, and the residual demulsification rate of crude oil emulsions can reach 77.81% after three cycles. After three cycles of Fe3O4@PDA@AE1910, the residual demulsification rate of crude oil emulsions can reach 77.81%. Evidently, these experimental demulsification results are gratifying. We speculate that this is due to the good synergistic demulsification effect of Fe3O4 with the three types of commercial polyether demulsifiers. The presence of polydopamine coating provides more sites for the grafting of polyether demulsifiers so that the polyether molecules are better attached to Fe3O4. Therefore, it is necessary to introduce a material that can provide more grafting sites. GO has a large specific surface area, excellent stability, and a large number of oxygen-containing active groups such as carboxyl, hydroxyl, and epoxy groups on the surface. It is easy to modify the surface using biologically active factors and is one of the most popular materials [28,29]. In the field of oil–water emulsion treatment, graphene oxide sheet is highly regarded as an amphiphilic surfactant due to its hydrophobic carbon skeleton and hydrophilic carboxyl and hydroxyl groups. By combining these properties, graphene oxide sheets can exhibit excellent oil–water separation performance. This is achieved via a synergistic demulsification effect when they are combined with other demulsification materials. Therefore, the utilization of graphene oxide sheets in conjunction with other demulsification materials has the potential to significantly enhance the efficiency of emulsion treatment processes [30,31,32,33].
This paper focuses on optimizing the performance of a new fluorine-containing block polyether demulsifier synthesized by the team [34] by incorporating graphene oxide and iron oxide. In order to achieve this, a magnetic demulsifier with properties, such as being environmentally friendly, having a high demulsification rate, and recyclability, was synthesized by grafting fluorinated polyether onto graphene oxide and combining it with ferric oxide. The structure and physicochemical properties of the demulsifier were characterized. Furthermore, the effects of factors such as demulsifier dosage, emulsion pH value, and temperature on demulsification were investigated using a bottle test. The optimal demulsification conditions were determined and the demulsification mechanism of Fe3O4@G-F was explored. Due to the reusability of the demulsifier, it can be used for crude oil demulsification multiple times while maintaining the performance of the demulsifier.

2. Experimental Section

2.1. Materials

Fluorinated polyether was prepared according to the report [35]. Fe(acac)3 was purchased from Shanghai Aladdin Industrial Co., Ltd., Shanghai, China. Oleic acid, oleylamine, and graphene were purchased from Shanghai McLean Biochemical Technology Co., Ltd. (Shanghai, China). Benzyl Ether was purchased from Merck Chemical (Shanghai, China). All chemicals used in the production process were of analytical grade. The dehydrated crude oil was supplied by a heavy oil block in Liaohe Oilfield.

2.2. One-Pot Preparation of Magnetic Demulsifiers

The preparation process of the fluorinated polyether and Fe3O4@F can be found in the attachment. Fe3O4@G-F was prepared using a one-pot method (Figure 1). Firstly, 0.001 mol iron acetylacetonate, 0.003 mol oleic acid, 0.003 mol oleylamine, 5 g fluorinated polyether, 30 mL dibenzyl ether solvent, and 0.05 g/0.10 g/0.15 g/0.20 g GO were added to the beaker. Subsequently, the material in the beaker was stirred evenly and ultrasonically dispersed for 30 min. The reagents in the beaker were poured into the reactor, and the air in the reactor was removed using nitrogen. The reactor was then placed in a muffle furnace at 230 °C for 5 h. After the heat-preservation experiment, the reactor was taken out and placed in the air for natural cooling. After the reaction, the product in the kettle was taken out, the magnetic demulsifier product was separated by a magnet, and a 1:1 volume mixture of ethanol and n-hexane was added to the product to clean the magnetic demulsifier product 3–5 times. Finally, the product was dried at 60 °C for 12 h to obtain a magnetic demulsifier. The samples with GO content of 0.05 g, 0.1 g, 0.15 g, and 0.2 g were recorded as Fe3O4@G1-F, Fe3O4@G2-F, Fe3O4@G-F, and Fe3O4@G4-F, respectively.

2.3. Preparation of Crude Oil Emulsion

The oil–water emulsion with a mass fraction of 50% was prepared. NaCl was dissolved in deionized water (0.5 mol/L, NaCl) to prepare the brine, and then 100 mL of crude oil and 100 mL of brine were heated to 60 °C, respectively. The brine was added to the preheated distilled water three times and stirred at 11,000 rpm for 30 min to obtain a stable oil–water emulsion.

2.4. Demulsification Performance Test

According to SY-T 5281-2000, the demulsification performance of Fe3O4@G-F was evaluated using a bottle test. First, the pre-prepared crude oil emulsion was packaged separately, and each test tube was filled with 20 mL of the emulsion and then placed in a water bath at 60 °C for 5 min to prevent the solidification of droplets in the emulsion. Then, according to the experimental requirements, the pre-configured demulsifier was added without adding the control group. The test tube was shaken back and forth 100 times within 1 min to completely mix the demulsifier with the crude oil emulsion. Finally, the test tube was placed in a 60 °C water bath for static sedimentation, and the demulsification effect was observed after 5 min, 10 min, 15 min, 20 min, 25 min, and 30 min, respectively. The demulsification performance is expressed by the following equation:
R = C 0 C C 0 × 100 %
where R (%) is the oil removal ratio, C 0 (mgL−1) represents the initial oil content of the emulsions, and C (mgL−1) is the oil content during the process of demulsification.

2.5. Demulsification Recovery Test

The recyclability of the Fe3O4@G-F magnetic demulsifier was evaluated by repeated use times. After the demulsification experiment, the obtained reagent was placed in an external magnetic field to recover the Fe3O4@G-F magnetic demulsifier. The recovered product underwent a series of washing steps, which included washing with n-hexane, followed by an ultrasonic cleaner for 15 min. After the demulsifier was fully dispersed, it was recovered by an external magnetic field and washed 3-4 times until the solution was colorless and transparent. Finally, the product was dried in a vacuum oven at 60 °C for 6 h, and the next experiment was repeated.

3. Results and Discussion

3.1. Characterization of Modified Fluoropolyether

3.1.1. Infrared Spectra of Different Materials

Figure 2 shows the infrared spectra of graphene oxide, Fe3O4, and their composites. The infrared spectrum was collected using the KBr tabletting method. The scanning number was set to 32, the range of spectral acquisition was 400~4000 cm−1, and the optical frequency was 1 cm−1. It can be seen from the spectrum comparison that the Fe3O4@GO composite was similar to GO. There was a stretching vibration absorption peak of -OH at 3375 cm−1, a stretching vibration peak of C=O at 1725 cm−1, and a bending vibration peak of C=C at 1631 cm−1. There were stretching vibration absorption peaks of C-OH and bending vibration peaks of C-O-C were observed at 381 cm−1 and 1052 cm−1, respectively. However, the C-O-C stretching vibration absorption peak of GO at 1052 cm−1 disappeared in Fe3O4@GO, and the characteristic peak intensity of the other functional groups was significantly weakened. The characteristic stretching vibration peak of Fe-O-Fe was observed at 556 cm−1 in the Fe3O4 spectrum. The characteristic stretching vibration peak of Fe-O-Fe can be clearly seen in the Fe3O4/GO spectrum at 523 cm−1, which has a red shift, indicating that Fe3O4 may be compounded with GO by a coordination reaction [35,36]. In the FTIR spectrum of Fe3O4@G-F, the tensile vibration peaks of CH and CH2 appeared at 2912 cm−1 and 2840 cm−1, respectively, and the tensile vibration absorption peak of the C-F bond appeared at 1186 cm−1. The spectral results showed that the surface of Fe3O4@G was grafted with fluorinated polyether, and Fe3O4@G-F was successfully prepared.

3.1.2. XPS of Modified Fluorinated Polyether

The valence state and chemical composition of Fe3O4@G-F were further studied using XPS. Figure 3 shows the full XPS full spectrum of Fe3O4@G-F and the Fe 2p, O 1s, and C 1s peak diagrams. In the full spectrum of Fe3O4@G-F, the signals of Fe, F, O, and C elements appeared at about 711.0 eV, 683.8 eV, 532.6 eV, and 285.1 eV, respectively. It can be seen from the Fe2p spectrum in Figure 3b that the two dominant peaks at 710.4 and 726.3 eV belong to Fe 2p3/2 and Fe 2p1/2 spin-orbit peaks, respectively. At the same time, the peaks at 712.4 eV and 726.0 eV are consistent with the Fe3+ ions of the Fe-O bond. The other two peaks at 710.2 eV and 723.6 eV were assigned to Fe2+ ions [37]. In the C1s peak spectrum (Figure 3c), C1s can be divided into three strong peaks and one weak peak, which are C-C/C-H, C-OH, epoxy group, and O=C=O, respectively. The two peaks in Figure 3d correspond to C=O and C-O, respectively. This result is in excellent correspondence with the elemental composition of the sample obtained from the infrared spectrum. Spectroscopic and crystallographic evidence further confirmed the successful combination of the fluorinated polyether, Fe3O4, and GO.

3.1.3. TEM and SEM of Composite Materials

The SEM and TEM images of the composites are shown in Figure 4. Figure 4a demonstrates that the morphology of the Fe3O4@F particles is irregular and the agglomeration between particles is significant. It was further observed by TEM that the Fe3O4 nanoparticles were tightly wrapped by outer granular fluorinated polyether molecules. Consequently, it can be inferred that the encapsulation of fluorinated polyether molecules led to different aggregation sizes and adhesion of the Fe3O4@F particles. Comparing Fe3O4@G-F with different GO (Figure 4e–f), it can be seen that Fe3O4@G-F is a stacked nanosheet with a smooth surface and obvious wrinkles at the edge of the sheet. Fe3O4@G2-F consists of stacked nanoflakes, and the crystal is slightly rough without obvious edge folds. The surfaces of the Fe3O4@G1-F and the Fe3O4@G4-F are not smooth and are attached to Fe3O4@F particles, without obvious edge wrinkles. There are obvious differences in the morphology of Fe3O4@G-F with different GO content. This is due to the lack of polymerization sites with fluorinated polyether and Fe3O4 when the amount of GO added is small, resulting in the three materials not being fully compounded. The excessive addition of GO causes graphene to stack, leading to a lack of polymerization sites. Further observation of Fe3O4@G-F (Figure 4b) by TEM shows that fluorinated polyether molecules are uniformly dispersed in GO, and most of the orthorhombic Fe3O4 is attached to the lamellar folds and corners of graphene oxide. This is because the surface area of the GO wrinkle is large, which is beneficial for the attachment of the magnetic Fe3O4 nanoparticles. Therefore, we can conclude that the optimal addition amount of GO in Fe3O4@G-F is 0.15 g.

3.1.4. TGA of Modified Fluoropolyether

The thermal properties of various magnetic composites were studied using TGA analysis. From Figure 5, it can be seen that at 50 °C–100 °C, each composite material has a weight loss rate of 2%, which is due to the water in the air adsorbed by the nanoscale ferroferric oxide. The weight loss behavior of Fe3O4@F at 328 °C–406 °C is related to the pyrolysis of the polymer chain of the fluorinated polyether. The relatively slight weight loss at 400 °C to 500 °C is due to the partial self-condensation of iron hydroxide. Compared to Fe3O4@F, the thermal stability of the modified fluorinated polyether decreased. The modified fluorinated polyether has two obvious weight loss stages. The first stage of weight loss occurs at 170 °C–250 °C. This is mainly due to the cracking of oxygen-containing functional groups in graphene oxide to produce gas, and the large amount of heat released during the cracking process further aggravates the cracking reaction. The second stage occurs between 328 °C and 406 °C. The weight loss in this stage is not only related to the pyrolysis of the polymer chain of the fluoropolyether ether but also includes the oxidation and evaporation of carbon in GO. According to the thermogravimetric curves of magnetic fluoropolyethers with different GO contents, thermal weight loss is the most obvious when the GO content is 0.15 g. Insufficient amounts of added GO do not significantly decrease thermal weight loss. Excessive amounts of added GO cause graphene sheets to stack due to strong van der Waals attraction, increasing stability. The discussion that the optimal addition amount of GO in the modified fluoropolyether is 0.15 g was further verified. The subsequent performance tests of the demulsifiers were all based on Fe3O4@G-F.

3.1.5. VSM of Modified Fluorinated

The magnetic properties of Fe3O4 and its composites were tested using a VSM magnetization loop test. It can be seen from Figure 6 that Fe3O4, Fe3O4@G, Fe3O4-F, and Fe3O4@G-F all exhibit superparamagnetic behavior, and their magnetic saturation values are 65.9, 41.05, 45.8, and 35.6 emu/g, respectively. The magnetic saturation values of the composites decreased due to the magnetic field-shielding effect of the fluorinated polyether and GO. Among all types of Fe3O4 composites, Fe3O4-F has the highest magnetic saturation value since the smaller fluorinated polyether molecules have little effect on the magnetic response of Fe3O4. Despite a decrease in magnetic saturation, the Fe3O4@G-F composite demulsifier retains its superparamagnetic properties at room temperature. This allows for the effortless separation of the demulsifier from the emulsion using an external magnetic field.

3.2. The Demulsification Performance of Modified Fluorinated Polyether

3.2.1. Effect of Demulsifier Dosage on Demulsification Performance

Figure 7 shows the effect of different doses of the Fe3O4@G-F magnetic demulsifier (150, 300, 450, 600, 750, and 900 mg/L) on the demulsification performance of the crude oil emulsion at an experimental temperature of 60 °C. It can be seen from Figure 7a that the demulsification performance is the best when the dosage of Fe3O4@G-F magnetic demulsifier is 750 mg/L, and the demulsification rate can reach 90.54%. After the addition of the Fe3O4@G-F magnetic demulsifier, the demulsification efficiency was more than 50% within 5 min. After demulsification, the separated water has high transparency, and there is a small amount of crude oil sticking to the wall, with an obvious phase separation boundary. This indicates that the Fe3O4@G-F magnetic demulsifier is a very effective demulsifier for oily wastewater. When the amount of demulsifier is 0–750 mg/L, the demulsification rate increases with an increase in the demulsifier dose. When the amount of demulsifier is more than 750 mg/L, the demulsification rate decreases with an increase in the amount of demulsifier. This is due to the amphiphilicity of Fe3O4@G-F. At a certain mass fraction, the demulsifier molecules become saturated and reach their maximum adsorption capacity at the oil–water interface. The excessive demulsifier molecules continue to migrate to the oil–water interface, resulting in emulsification. Thickening the oil–water interface film enhances emulsion stability but reduces demulsification efficiency. Therefore, the optimum dosage of Fe3O4@G-F magnetic demulsifier is 750 mg/L.

3.2.2. Effects of Time and Temperature on Demulsification Performance

Four groups of control experiments at different temperatures (35 °C, 45 °C, 60 °C, and 75 °C) were set up to observe the demulsification effect of Fe3O4@G-F within 30 min when the addition amount was 750 mg/L. The demulsification effect of the Fe3O4@G-F magnetic demulsifier at different times and different temperatures is shown in Figure 8. It can be observed from the figure that the demulsification efficiency increases with an increase in the demulsification time and demulsification temperature. When the demulsification temperature is 75 °C and the action time is 30 min, the demulsification efficiency reaches the highest value of 91.02%. When the demulsification temperature is 60 °C and the action time is 25 min, the demulsification efficiency is 90.03%. When the action time reaches 25 min, the solution becomes clear and the oil droplets hang less. With an increase in the action time, the change in solution clarity is not obvious. The horizontal comparison curve shows that although extending the action time to 30 min improves the demulsification efficiency of the demulsifier, the increase is not significant. Evidently, increasing the temperature and prolonging the action time increases the production cost. Therefore, from the perspective of engineering applications, the action time of the Fe3O4@G-F magnetic demulsifier is set to 25 min, and the temperature is set to 60 °C.

3.2.3. Effect of pH on Demulsification Performance

Figure 9 shows the effect of different pH values on the demulsification performance of Fe3O4@G-F at an experimental temperature of 60 °C and an additional amount of Fe3O4@G-F at 750 mg/L. When pH = 6, Fe3O4@G-F has the best demulsification performance of up to 91.38%. The demulsification rate was 89.43% at pH = 5, and the demulsification rate exceeded 85% under neutral conditions, indicating that the demulsifier had better performance in neutral and acidic environments. This is because the Fe3O4@G-F surface carries a positive charge under acidic and neutral conditions. The negative charge on the oil droplets attracts Fe3O4@G-F, promoting the adsorption of demulsifier molecules. This aids in the coalescence and separation of the oil and water. However, the demulsification rate was low at pH 8 and 9, and the demulsification rate did not exceed 85%. This is because, under alkaline conditions, the negative charge on the surface of Fe3O4@G-F and the oil droplets undergo electrostatic repulsion, which reduces the adsorption capacity of the demulsifier and leads to a decrease in the demulsification rate.

3.2.4. Recovery Performance Test

The experimental temperature of the recycling test was 60 °C, the amount of demulsifier was 750 mg/L, and the action time was 25 min. The results are shown in Figure 10. Although the demulsification efficiency of the Fe3O4@G-F decreased with an increase in the number of cycles, it showed excellent demulsification performance in the first four cycles, and the demulsification rate exceeded 70%. The demulsification efficiency of the demulsifier sharply decreased after six cycles, reaching only 16.91% and 9.8% in the 7th and 8th cycles, respectively. This may be due to the fact that the asphalt and resin in the crude oil are adsorbed on the surface of the demulsifier molecule during the demulsification process. The n-hexane solvent cannot dissolve all the components of the crude oil, and the decrease in the magnetic response of Fe3O4@G-F leads to a decrease in the recovery rate. In summary, the Fe3O4@G-F magnetic demulsifier not only has excellent demulsification performance but can also can be recycled from oil–water two-phase system due to its unique magnetic response performance. It solves a series of environmental problems caused by the difficulty in separating traditional chemical demulsifiers after the reaction.

3.3. The Demulsification Mechanism of Fe3O4@G-F

Here, we propose a demulsification mechanism of the Fe3O4@G-F magnetic demulsifier, as shown in Figure 11. First, the Fe3O4@G-F magnetic demulsifier has ultra-high surface activity due to the presence of C-F bonds. After Fe3O4@G-F was added to the crude oil emulsion, it could quickly reach the oil–water interfacial film, replacing the natural emulsifiers such as asphaltenes and resins on the oil–water interfacial film to form a new easily broken interfacial film. The surface of the demulsifier contains a dendritic fluorine-containing polyether, which acts as a bridge for promoting the coalescence of oil droplets via a pulling effect. When oil droplets accumulate to a certain extent, they float to the upper part of the test tube under the action of gravity to achieve the separation of the oil phase and water phase. Second, GO can produce strong π-π interactions with asphaltenes, resins, and other organic compounds by virtue of its conjugated aromatic ring structure, so the demulsifier can be adsorbed to the oil droplets in the emulsion. Then, the hydrophobic Fe3O4 carries positive charges under acidic and neutral conditions. The adsorption capacity of Fe3O4@G-F was enhanced by the electrostatic interactions between Fe3O4 and negatively charged oil droplets. In addition, the nanoscale GO and Fe3O4 particles have the characteristics of a large specific surface area and many adsorption sites, and the two can have a better synergistic effect. Finally, Fe3O4@G-F has magnetic responsiveness. Under the action of an external magnetic field, it can be recovered from the two-phase system and recycled after cleaning.

4. Conclusions

An efficient and recyclable magnetic fluorinated polyether demulsifier (Fe3O4@G-F) was prepared using a solvothermal method. The demulsification performance of the magnetic composite materials in different external environments was compared using the bottle test method, and the optimal demulsification conditions were optimized. The higher demulsification rate of Fe3O4@G-F was due to the synergistic demulsification effect of GO and Fe3O4. On the other hand, due to the existence of the C-F bond in Fe3O4@G-F, the demulsifier has an ultra-high surface activity. Fe3O4@G-F can quickly reach the oil–water interface film and replace natural emulsifiers, such as asphaltenes and resins on the oil–water interface film to form a new fragile interface film. The dendritic fluorine-containing polyether on the surface of the demulsifier can act as a bridge to promote the coalescence of oil droplets via the pulling effect. The demulsification performance of Fe3O4@G-F was greatly affected by the pH, which is suitable for neutral and acidic environments. The results showed that the demulsification efficiency of the Fe3O4@G-F emulsion can reach 91.38% within 30 min at a demulsifier dosage of 750 mg/L, pH of 6, and demulsification temperature of 60 °C. In addition, Fe3O4@G-F was recovered and recycled from the two-phase system four times under the action of an external magnetic field. Fe3O4@G-F provides a new approach for the preparation of fluorinated high-efficiency demulsifiers and the treatment of environmental problems caused by crude oil pollution.

Author Contributions

C.L.: conceptualization, methodology, writing—reviewing and editing. L.W.: software and supervision. X.J.: validation and formal analysis. Y.G.: investigation and preparation. H.G.: investigation and preparation. X.G.: investigation and software. All authors have read and agreed to the published version of the manuscript.


This work was supported by the Natural Science Foundation of Heilongjiang (grant nos. LH2022E025) and the Innovation Ability Promotion Project of Sci-Tech SMEs in Shandong Province (grant nos. 2022TSGC1376).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The authors confirm that the data supporting the findings of this study are available within the article.

Conflicts of Interest

The authors declare no conflict of interest.


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Figure 1. Preparation of the Fe3O4@G-F.
Figure 1. Preparation of the Fe3O4@G-F.
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Figure 2. Infrared spectra of different materials.
Figure 2. Infrared spectra of different materials.
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Figure 3. XPS of modified fluoropolyether. (a) XPS full spectrum, (b) Fe 2p peak, (c) O 1s peak, and (d) C 1s peak.
Figure 3. XPS of modified fluoropolyether. (a) XPS full spectrum, (b) Fe 2p peak, (c) O 1s peak, and (d) C 1s peak.
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Figure 4. TEM and SEM of composite materials. SEM and TEM of Fe3O4@F (a) and Fe3O4@G-F (b); SEM of Fe3O4@G1-F (c), Fe3O4@G2-F (d), Fe3O4@G-F (e), and Fe3O4@G4-F (f) with different GO content.
Figure 4. TEM and SEM of composite materials. SEM and TEM of Fe3O4@F (a) and Fe3O4@G-F (b); SEM of Fe3O4@G1-F (c), Fe3O4@G2-F (d), Fe3O4@G-F (e), and Fe3O4@G4-F (f) with different GO content.
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Figure 5. TGA of modified fluoropolyether.
Figure 5. TGA of modified fluoropolyether.
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Figure 6. VSM of modified fluoropolyether.
Figure 6. VSM of modified fluoropolyether.
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Figure 7. (a) Demulsification efficiency with different dosages of demulsifier; (b) demulsification effect of different dosages of the Fe3O4@G-F demulsifier at 60 °C for 30 min.
Figure 7. (a) Demulsification efficiency with different dosages of demulsifier; (b) demulsification effect of different dosages of the Fe3O4@G-F demulsifier at 60 °C for 30 min.
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Figure 8. Demulsification efficiency curves at different temperatures and different times.
Figure 8. Demulsification efficiency curves at different temperatures and different times.
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Figure 9. (a) Demulsification efficiency at different pH values, (b) demulsification effect of the Fe3O4@G-F magnetic demulsifier with time at 60 °C, the Fe3O4@C-F dosage of 750 mg/L, and pH = 6.
Figure 9. (a) Demulsification efficiency at different pH values, (b) demulsification effect of the Fe3O4@G-F magnetic demulsifier with time at 60 °C, the Fe3O4@C-F dosage of 750 mg/L, and pH = 6.
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Figure 10. Fe3O4@G-F recovery performance test.
Figure 10. Fe3O4@G-F recovery performance test.
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Figure 11. The demulsification mechanism of Fe3O4@G-F.
Figure 11. The demulsification mechanism of Fe3O4@G-F.
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MDPI and ACS Style

Liu, C.; Wei, L.; Jia, X.; Gu, Y.; Guo, H.; Geng, X. Fluorinated-Polyether-Grafted Graphene-Oxide Magnetic Composite Material for Oil–Water Separation. AppliedChem 2023, 3, 400-413.

AMA Style

Liu C, Wei L, Jia X, Gu Y, Guo H, Geng X. Fluorinated-Polyether-Grafted Graphene-Oxide Magnetic Composite Material for Oil–Water Separation. AppliedChem. 2023; 3(3):400-413.

Chicago/Turabian Style

Liu, Chao, Lixin Wei, Xinlei Jia, Yuxin Gu, Haiying Guo, and Xiaoheng Geng. 2023. "Fluorinated-Polyether-Grafted Graphene-Oxide Magnetic Composite Material for Oil–Water Separation" AppliedChem 3, no. 3: 400-413.

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