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Pei X, Song W. CO 2-Triggered Hierarchical-Pore UiO-66-Based Pickering Emulsions for Efficient and Recyclable Suzuki-Miyaura Cross-Coupling in Biphasic Systems. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:15046-15054. [PMID: 37812683 DOI: 10.1021/acs.langmuir.3c02011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/11/2023]
Abstract
Hierarchical-pore metal-organic frameworks (H-MOFs) are considered to be emerging stabilizers for Pickering emulsion formation because of their hierarchically arranged pores, tailorable structures, and ultrahigh surface areas. However, stimulus-triggered Pickering emulsions built by H-MOFs have been seldom presented to date despite their great significance in diverse applications. Herein, by grafting Pd(OAc)2 on the hierarchical-pore zirconium MOF UiO-66, namely, H-UiO-66, with the aid of 1-alkyl-3-methylimidazolium 2-cyanopyrrolide salts ([CnMIM][2-CN-Pyr], n = 4, 6, and 8), a series of Pd(OAc)2-[CnMIM][2-CN-Pyr]@H-UiO-66 have been developed and utilized as emulsifiers for constructing CO2-switching Pickering emulsions. It was found that Pd(OAc)2-[CnMIM][2-CN-Pyr]@H-UiO-66 was able to stabilize the n-hexane-water mixture to form a Pickering emulsion even at an amount of 0.5 wt %. Upon alternate addition of CO2 and N2 at normal pressure, Pickering emulsions could be smartly converted between demulsification and re-emulsification. Through combining varieties of spectroscopic techniques, the mechanism of the switchable phase transformation lay in the acid-base reaction of ionic liquids with CO2 on H-UiO-66 and the creation of more hydrophilic salts, which reduced the wettability of the emulsifier and destabilized the emulsion. As an example of application, the stimulus-triggered Pickering emulsion was employed as a palladium-catalyzed Suzuki-Miyaura cross-coupling microreactor to achieve the combination of chemical reactions, isolation of products, and recovery of catalysts.
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Affiliation(s)
- Xiaoyan Pei
- College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang, Henan 464000, P. R. China
| | - Wangyue Song
- College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang, Henan 464000, P. R. China
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2
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He R, Sun S, Cui J, Chi M, Wang Z, Hu S. pH/magnetic dual responsive Pickering emulsion stabilized by Fe 3O 4@SiO 2@chitosan nanoparticles. Phys Chem Chem Phys 2023; 25:25780-25788. [PMID: 37724345 DOI: 10.1039/d3cp03400c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/20/2023]
Abstract
In recent years, Pickering emulsifiers have been widely used in various production fields due to their excellent structural stability, biocompatibility and environmental friendliness. For some applications, it is required that the emulsifier can quickly respond to environmental stimuli and control the transition between stable and unstable emulsions. In this paper, we report a novel composite Pickering emulsifier with Fe3O4 as the core and magnetic response recognition body, silica as the intermediate protective layer, and chitosan (CS) of different molecular weights to endow solid particles with surface activity and pH-responsive properties. This emulsifier can stabilize the emulsion in the emulsion system with deionized water as the aqueous phase and liquid paraffin as the oil phase and can control the demulsification of the formed emulsion under the dual pH/magnetic stimulation. The experimental results show that Fe3O4@SiO2@CS has good paramagnetism and pH responsiveness. The particle size of the composite emulsifier nanoparticles is between 90 nm and 120 nm, and the best stabilizing effect of the emulsion is achieved when the dosage is 0.5 wt%. In the pH range of 3-11, the emulsifier can rapidly demulsify a stable paraffin oil-water emulsion system under the action of a magnetic field of strength 0.4 T. The pH response of the emulsifier is as follows: when pH ≤ 2, the system can form a stable emulsion, which is composed of fully protonated chitosan as a free chain segment and Fe3O4@SiO2. Emulsion stabilization was achieved with monolithic Fe3O4@SiO2@CS as an emulsifier at pH > 2, and demulsification was achieved at pH ≈ pKb (CS) at 298 K. The research in this paper can provide a feasible idea and synthesis method for the preparation of organic-inorganic composite structure emulsifier.
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Affiliation(s)
- Runna He
- School of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China.
| | - Shuangqing Sun
- School of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China.
- Institute of Advanced Materials, China University of Petroleum (East China), Qingdao 266580, China
| | - Jianpeng Cui
- School of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China.
| | - Mingshuo Chi
- School of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China.
| | - Zhikun Wang
- School of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China.
- Institute of Advanced Materials, China University of Petroleum (East China), Qingdao 266580, China
| | - Songqing Hu
- School of Materials Science and Engineering, China University of Petroleum (East China), Qingdao 266580, China.
- Institute of Advanced Materials, China University of Petroleum (East China), Qingdao 266580, China
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Pei X, Liu J, Song W, Xu D, Wang Z, Xie Y. CO 2-Switchable Hierarchically Porous Zirconium-Based MOF-Stabilized Pickering Emulsions for Recyclable Efficient Interfacial Catalysis. MATERIALS (BASEL, SWITZERLAND) 2023; 16:1675. [PMID: 36837307 PMCID: PMC9960431 DOI: 10.3390/ma16041675] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/24/2022] [Revised: 01/08/2023] [Accepted: 02/07/2023] [Indexed: 06/18/2023]
Abstract
Stimuli-responsive Pickering emulsions are recently being progressively utilized as advanced catalyzed systems for green and sustainable chemical conversion. Hierarchically porous metal-organic frameworks (H-MOFs) are regarded as promising candidates for the fabrication of Pickering emulsions because of the features of tunable porosity, high specific surface area and structure diversity. However, CO2-switchable Pickering emulsions formed by hierarchically porous zirconium-based MOFs have never been seen. In this work, a novel kind of the amine-functionalized hierarchically porous UiO-66-(OH)2 (H-UiO-66-(OH)2) has been developed using a post-synthetic modification of H-UiO-66-(OH)2 by (3-aminopropyl)trimethoxysilane (APTMS), 3-(2-aminoethylamino)propyltrimethoxysilane (AEAPTMS) and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEAEAPTMS), and employed as emulsifiers for the construction of Pickering emulsions. It was found that the functionalized H-UiO-66-(OH)2 could stabilize a mixture of toluene and water to give an emulsion even at 0.25 wt % content. Interestingly, the formed Pickering emulsions could be reversibly transformed between demulsification and re-emulsification with alternate addition or removal of CO2. Spectral investigation indicated that the mechanism of the switching is attributed to the reaction of CO2 with amino silane on the MOF and the generation of hydrophilic salts, leading to a reduction in MOF wettability. Based on this strategy, a highly efficient and controlled Knoevenagel condensation reaction has been gained by using the emulsion as a mini-reactor and the emulsifier as a catalyst, and the coupling of catalysis reaction, product isolation and MOF recyclability has become accessible for a sustainable chemical process.
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4
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Yu H, Chang X, Li Q, Sun X, Li A, Zhang Z, Zhao W. One-step self-assembly for fabricating dual responsive fluorescent aggregates. Colloids Surf A Physicochem Eng Asp 2022. [DOI: 10.1016/j.colsurfa.2021.127979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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5
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Zhang Z, Li Q, Sun N, Liu Y, Ge S, Che H, Li A. The preparation of stimulus-responsive Pickering emulsion and its application in preparing microspheres. J DISPER SCI TECHNOL 2022. [DOI: 10.1080/01932691.2021.2025070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Zhaoyu Zhang
- School of Materials Science and Engineering, Shandong University of Technology, Zibo, Shandong, P.R. China
| | - Qiuhong Li
- School of Materials Science and Engineering, Shandong University of Technology, Zibo, Shandong, P.R. China
| | - Ning Sun
- School of Materials Science and Engineering, Shandong University of Technology, Zibo, Shandong, P.R. China
| | - Yunxiao Liu
- Dezhou Linglong Tire Co., Ltd, Dezhou, Shandong, P.R. China
| | - Shujin Ge
- School of Materials Science and Engineering, Shandong University of Technology, Zibo, Shandong, P.R. China
| | - Hongyan Che
- School of Materials Science and Engineering, Shandong University of Technology, Zibo, Shandong, P.R. China
| | - Aixiang Li
- School of Materials Science and Engineering, Shandong University of Technology, Zibo, Shandong, P.R. China
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6
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Ge S, Zhang S, Chang X, Li A, Wang W, Li Q, Wang Z. Redox and pH-responsive emulsions based on TiO2 nanoparticles and ferrocene derivates. NEW J CHEM 2022. [DOI: 10.1039/d2nj03500f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We synthesized a novel surfactant ferrocene azine (FcA) and developed a redox and pH-responsive emulsion stabilized by TiO2 nanoparticles and oxidized ferrocene azine (Fc+A) with fluorescence through simple mixing instead...
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8
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Xie D, Jiang Y, Zhang Y, Song B. Salt-Resistant Switchable Pickering Emulsions Stabilized by Mesoporous Nanosilica Hydrophobized In Situ by pH-Insensitive Surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:5846-5853. [PMID: 33945685 DOI: 10.1021/acs.langmuir.1c00231] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Novel oil-in-water (O/W) Pickering emulsions (PEs) were prepared using mesoporous nanosilica in combination with a pH-insensitive cationic surfactant as a stabilizer and show an interesting sensitivity to acids and bases. Adding a suitable amount of NaOH (nNaOH/ncationic surfactant ≥ 1) led to prompt demulsification within 10 s. Upon further adding HCl solutions (nHCl/nNaOH = 1), stable PEs re-formed after homogenization. These emulsions remained stable for over 30 days after 60 cycles, switching from stable to unstable and back to stable states, and showed a high salt tolerance. A mechanism for the switching of the Pickering emulsion (PE) to unstable and back to stable states was derived and involved anionic and neutral forms of hydroxyl groups at the mesopores of the mesoporous silica nanoparticles (MSNPs). This work reveals a switchable PE system involving a pH-insensitive surfactant, in which the species of oils and cationic surfactants can be arbitrarily selected, a feature that greatly expands the applicability of PEs.
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Affiliation(s)
- Danhua Xie
- Fujian Provincial Key Laboratory of Featured Materials in Biochemical Industry, College of Chemistry and Materials, Ningde Normal University, Ningde, Fujian 352100, China
| | - Yulong Jiang
- Fujian Provincial Key Laboratory of Featured Materials in Biochemical Industry, College of Chemistry and Materials, Ningde Normal University, Ningde, Fujian 352100, China
| | - Yunjin Zhang
- Fujian Provincial Key Laboratory of Featured Materials in Biochemical Industry, College of Chemistry and Materials, Ningde Normal University, Ningde, Fujian 352100, China
- College of Chemistry, Fuzhou University, Fuzhou, Fujian 350002, China
| | - Binglei Song
- Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical & Materials Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China
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Sun N, Li Q, Luo D, Sui P, Jiang Q, Liu J, Li A, Si W, Ma Y. Dual-Responsive Pickering Emulsion Stabilized by Fe3O4 Nanoparticles Hydrophobized in Situ with an Electrochemical Active Molecule. Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2020.125588] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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10
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Zhang H, Wu J, Jiang J, Cui Z, Xia W. Redox-Responsive Oil-In-Dispersion Emulsions Stabilized by Similarly Charged Ferrocene Surfactants and Alumina Nanoparticles. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:14589-14596. [PMID: 33226816 DOI: 10.1021/acs.langmuir.0c02350] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A redox-responsive oil-in-dispersion emulsion was developed by using a cationic ferrocene surfactant (FcCOC10N) and Al2O3 nanoparticles, in which the required concentrations of FcCOC10N and Al2O3 nanoparticles are as low as 0.001 mM (≈0.005 cmc) and 0.006 wt %, respectively. Rapid demulsification can be successfully achieved through a redox trigger, resulting from the transition of FcCOC10N from a normal cationic surfactant form into a strongly hydrophilic Bola type form (Fc+COC10N). Moreover, Fc+COC10N together with the particles almost resides in the aqueous phase and can be recovered after the reduction reaction. Not only the amount of surfactant and nanoparticles are significantly reduced but also the emulsifier (surfactant and alumina) can be recycled and reused from the aqueous phase, which is a sustainable and economical strategy for various applications.
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Affiliation(s)
- Haojie Zhang
- The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, P.R. China
| | - Jia Wu
- China Tobacco Jiangsu Industrial Co. LTD, No. 29 Xinglong Street, Nanjing, Jiangsu 210000, China
| | - Jianzhong Jiang
- The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, P.R. China
| | - Zhenggang Cui
- The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, P.R. China
| | - Wenshui Xia
- State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, P.R. China
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11
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Li X, Zhu P, Lv X, Yan G, Lu H. Redox and Doubly pH-Switchable Pickering Emulsion. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:14288-14295. [PMID: 33201711 DOI: 10.1021/acs.langmuir.0c02505] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In this work, a novel Pickering emulsion is stabilized by silica nanoparticles functioned with a redox and pH-responsive surfactant FA-DMDA-Ox that is prepared simply by direct neutralization of ferrocenecarboxylic acid (FA) and N,N-dimethyldodecylamine (DMDA) and exhibits redox and doubly pH-switchable behavior. Here, the Pickering emulsion can be stabilized easily by combining hydrophilic silica nanoparticles with less than 0.1 wt % FA-DMDA-Ox. After adding Na2SO3 and H2O2 alternately, the demulsification and emulsification of this Pickering emulsion are controlled reversibly. Moreover, the emulsion is switched "off" upon the addition of HCl and switched "on" upon the addition of NaOH and is also switched off upon the addition of NaOH and switched on upon the addition of HCl, which demonstrate the doubly pH-switchable behavior. Based on the analysis of ζ-potential, contact angle, and adsorbed amount of silica nanoparticles, the pH and redox-switchable mechanism of the Pickering emulsion are analyzed. Here, the redox-switchable behavior is induced by the reversible adsorption and desorption of FA-DMDA-Ox on the surface of silica nanoparticles. The pH-switchable behavior is driven by the controllable dispersion systems of silica nanoparticles and FA-DMDA-Ox because of the doubly pH switchability of FA-DMDA-Ox. More importantly, upon adding fresh oil after removing the original oil, the Pickering emulsion is recycled three times. Hence, the multiswitchable Pickering emulsion can be expected to be treated as a multifunctional material in practical applications, such as oil or wax removal in the petroleum industry.
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Affiliation(s)
- Xiaojiang Li
- College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China
| | - Peiyao Zhu
- College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China
| | - Xin Lv
- State Key Laboratory of Natural Gas Hydrates, Beijing 100028, P. R. China
| | - Guijiang Yan
- College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China
| | - Hongsheng Lu
- State Key Laboratory of Natural Gas Hydrates, Beijing 100028, P. R. China
- College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China
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12
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Luo R, Dong J, Luo Y. pH-Responsive Pickering emulsion stabilized by polymer-coated silica nanoaggregates and applied to recyclable interfacial catalysis. RSC Adv 2020; 10:42423-42431. [PMID: 35516758 PMCID: PMC9057990 DOI: 10.1039/d0ra07957j] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Accepted: 11/16/2020] [Indexed: 11/21/2022] Open
Abstract
We first synthesized a diblock copolymer poly[tert-butyl methacrylate]-b-poly[3-(trimethoxysilyl)propyl methacrylate] (PtBMA-b-PTMSPMA) through reversible addition–fragmentation chain transfer (RAFT) living radical polymerization and grafted it onto fumed silica by converting the PTMSPMA segment to silanol and the PtBMA segment to polymethylacrylic acid (PMAA) in the presence of trifluoroacetic acid in order to obtain PMAA brush-coated silica nanoaggregates P-Si. TEM, DLS, FTIR, and TGA results confirmed the successful modification of the starting materials. The nanoaggregates flocculated and stabilized a toluene-in-water Pickering emulsion at low pH, while the nanoaggregates were well dispersed in water and broke the emulsion under both neutral and basic conditions. Alternatively, the addition of acid/base induced emulsification/demulsification cycles that were sustained for several cycles. Moreover, when the P-Si was mixed with Rh-loaded silica, Rh-Si, the mixture had the same pH-responsive Pickering emulsion behavior as the single P-Si. This Pickering emulsion system can be used in the biphasic interfacial catalytic hydrogenation of olefins and had excellent yields under a hydrogen atmosphere. The yield of Pickering emulsion catalysis rapidly reached more than 99% in 3 h, while that of the demulsified mixture failed to reach 20% in 4 h, which verified the promotion of catalysis by the Pickering emulsion. Base-induced demulsification can be used to separate the products and recycle the catalyst. This pH-responsive Pickering emulsion catalytic system was capable of several cycles of reuse, and there was no significant decrease in catalytic efficiency even after eight cycles. We synthesized a diblock copolymer and grafted it onto fumed silica in the presence of trifluoroacetic acid to obtain a pH-responsive Pickering emulsion system stabilized by polymer-coated nanoaggregates, P-Si.![]()
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Affiliation(s)
- Ruidong Luo
- Engineering Research Center of Organosilicon Compounds & Materials, Ministry of Education, College of Chemistry and Molecular Sciences, Wuhan University Wuhan 430072 PR China
| | - Jinfeng Dong
- Engineering Research Center of Organosilicon Compounds & Materials, Ministry of Education, College of Chemistry and Molecular Sciences, Wuhan University Wuhan 430072 PR China
| | - Yunbai Luo
- Engineering Research Center of Organosilicon Compounds & Materials, Ministry of Education, College of Chemistry and Molecular Sciences, Wuhan University Wuhan 430072 PR China
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Zhang N, Wang F, Cai C, Sun Q, Zhang K, Li A, Weng J, Li Q. Noncovalent
modification of
self‐assembled
functionalized
COF
by
PNIPAM
and its properties of Pickering emulsion. J CHIN CHEM SOC-TAIP 2020. [DOI: 10.1002/jccs.202000089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Na Zhang
- School of Materials Science and Engineering Shandong University of Technology Zibo China
| | - Fei Wang
- School of Materials Science and Engineering Shandong University of Technology Zibo China
| | - Chang‐chen Cai
- School of Materials Science and Engineering Shandong University of Technology Zibo China
| | - Qian Sun
- School of Materials Science and Engineering Shandong University of Technology Zibo China
| | - Kai Zhang
- School of Materials Science and Engineering Shandong University of Technology Zibo China
| | - Ai‐xiang Li
- School of Materials Science and Engineering Shandong University of Technology Zibo China
| | - Jun‐ying Weng
- School of Materials Science and Engineering Shandong University of Technology Zibo China
| | - Qiu‐hong Li
- School of Materials Science and Engineering Shandong University of Technology Zibo China
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14
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Sun N, Li Q, Jiang Q, Li A, Si W, Wang W. Dual responsive pickering emulsions based on ferric oxide nanoparticles and ferrocene derivates. J DISPER SCI TECHNOL 2020. [DOI: 10.1080/01932691.2019.1637753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Ning Sun
- School of Material Science and Engineering, Shandong University of Technology, Zibo, Shandong, P. R. China
| | - Qiuhong Li
- School of Material Science and Engineering, Shandong University of Technology, Zibo, Shandong, P. R. China
| | - Qiuyan Jiang
- School of Material Science and Engineering, Shandong University of Technology, Zibo, Shandong, P. R. China
| | - Aixiang Li
- School of Material Science and Engineering, Shandong University of Technology, Zibo, Shandong, P. R. China
| | - Weimeng Si
- School of Material Science and Engineering, Shandong University of Technology, Zibo, Shandong, P. R. China
| | - Weiwei Wang
- School of Material Science and Engineering, Shandong University of Technology, Zibo, Shandong, P. R. China
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Real-Time Analysis of the Stability of Oil-In-Water Pickering Emulsion by Electrochemical Impedance Spectroscopy. Molecules 2020; 25:molecules25122904. [PMID: 32599776 PMCID: PMC7355891 DOI: 10.3390/molecules25122904] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 06/19/2020] [Accepted: 06/22/2020] [Indexed: 11/16/2022] Open
Abstract
In this paper, electrical impedance spectroscopy (EIS) was applied to investigate the stability of oil-in-water (O/W) Pickering emulsions prepared with negatively charged silica nanoparticles in combination with a trace amount of redox switchable fluorescent molecules, ferrocene azine (FcA). Electrical impedance values of emulsions obtained at different emulsification speeds were estimated according to the frequency response data with frequencies ranging from 1 MHz to 1 Hz. The equivalent circuit model of toluene-in-water emulsion was established by the resistor (RO/W) and capacitor (CO/W) in parallel connection. Nyquist diagrams for the emulsions prepared by toluene and water were characterized by the formation of one semi-circle. The droplet size distribution is one of the important factors that affect the stability of the emulsion, except for the volume fraction of water and oil, the size of stabilizing particles, etc. The average particle size of the emulsion droplets decreased as the emulsification speed increased, indicating the higher stability of the emulsion. It was found that the fitted impedance value RO/W of the emulsion decreased with decreasing particle size prepared at different emulsification speeds and storage time by performing real-time EIS detection techniques. The results suggested that EIS could be used to characterize the stability of a toluene-in-water emulsion stabilized by FcA modified silica nanoparticles. Moreover, based on the good electrochemical activity of the FcA molecule, the stability of the Pickering emulsion can be modulated by adding oxidant and reductant and detected by EIS in real-time.
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