Redox-Responsive Pickering Emulsions Based on Silica Nanoparticles and Electrochemical Active Fluorescent Molecules

Abstract

In this paper, we report a novel redox-responsive water-in-oil Pickering emulsion stabilized by negatively charged silica nanoparticles in combination with a trace amount of redox switchable fluorescent molecule ferrocene azine (FcA), in which ferrocene serves as a redox-sensitive group and anthryl unit serves as a fluorescence emission center. By alternately adding oxidants and reducing agents at a moderate condition, the amphiphilicity of silica nanoparticles changes because of the adsorption of Fc+A and the desorption of FcA on the silica surface. On the one hand, the stability of emulsions can be transformed between stable and unstable at ambient temperature via redox trigger and the regulation process can be cycled at least three times. On the other hand, the fluorescent intensity of the FcA molecule can be regulated by redox stimuli; thus, the change in fluorescent behavior of the emulsion droplets is observed upon redox cycles, which makes it useful in the fluorescent label of stimuli-responsive Pickering emulsions. This work provides a deep understanding of the regulation mechanism of Pickering emulsions upon redox stimuli and opens the new way for in situ fluorescent label of stimulus-responsive Pickering emulsions without introducing additional fluorescent molecules.

Real-Time Analysis of the Stability of Oil-In-Water Pickering Emulsion by Electrochemical Impedance Spectroscopy

“…All reagents were used as received without further purification. Oxidized FcA (Fc + A) modified SiO 2 solid particles were prepared according to the procedures reported in the literature [ 18 ]. The morphology of SiO 2 particles can be characterized by SEM, as shown in Figure 11 .…”

“…Oil-in-water (O/W) Pickering emulsion was prepared by combining the electrochemically active fluorescent molecule, ferrocene azine (FcA) with negatively charged silica nanoparticles as the solid particle emulsifier, which was explored in previous work [ 18 ]. Herein, previous work was extended by measuring the frequency response data of the O/W Pickering emulsion combining with the electrochemical impedance spectroscopy.…”

Template-free fabrication of magnetic mesoporous poly(ionic liquid)s: efficient interfacial catalysts for hydrogenation reaction and transesterification of soybean oil

“…The type of stimuli response includes single or multiple stimuli such as pH, temperature, light, external force field, CO 2 , ionic strength, etc. 16–21 This system makes the biphasic reaction greener and more environmentally friendly, so it is commonly used in various reactions such as hydrogenation, 22,23 epoxidation, 24,25 and hydroformylation. 26–28…”

pH-Responsive Pickering emulsion stabilized by polymer-coated silica nanoaggregates and applied to recyclable interfacial catalysis

“…Stimuli-responsive Pickering emulsions have been well developed in recent decades, 6 and many stimuli, including CO 2 / N 2 , 7-11 pH, [12][13][14][15][16][17][18][19] temperature, [20][21][22][23][24][25] redox reduction, 26 light, [27][28][29] and double stimuli, [30][31][32][33][34][35][36] have been used to induce the demulsication or phase inversion of Pickering emulsions. Manipulating the pH by alternately adding acid or base to the system is simple and easy to implement.…”