Buckling Effect of Sole Zeolitic Imidazolate Framework-8 Nanoparticles Adsorbed at the Water/Oil Interface

Abstract

The buckling phenomenon of sole zeolitic imidazolate framework-8 (ZIF-8) particles adsorbed at the water/oil interface was systematically studied. The droplet of ZIF-8 water dispersion was pended in oil for a certain time period and manually extracted to decrease the volume. With the reduction of interfacial area, the ZIF-8 particles were jammed together to form a wrinkling solid film at the water/oil interface, which could withstand the extraction of the droplet and be regenerated. The size and concentration of the particles affected the assembly kinetics. The rapidest assembly was observed for the medium-sized ZIF-8 particles (m-ZIF-8) among the three sizes tested (1.81 μm, 258 nm, and 51 nm). The droplet of 0.91 wt % m-ZIF-8 reached a nearly full surface coverage in 13 min, faster than those with the lower concentration of 0.46 or 0.28 wt %. The pH of the solution, ranging between 6 and 10.7, affected both the assembly kinetics and film stability. Cryo-scanning electron microscopy images of frozen m-ZIF-8-stabilized Picking emulsions showed a monolayer of ZIF-8 wetted by both oil and water phases. The observed buckling effect could be attributed to the stable adsorption of ZIF-8 at the water/oil interface and the interparticle interactions, related to the unique surface chemistry and polyhedral shape of the ZIF-8 crystals. This work provided some understanding on the interfacial property of ZIF-8 and the mechanism of sole ZIF-8-stabilized Pickering emulsions.

Hierarchically Porous Monolith with High MOF Accessibility and Strengthened Mechanical Properties using Water‐in‐Oil High Internal Phase Emulsion Template

“…ZIF‐8 particles with micron size were prepared according to the reported literature with some minor modifications. [ 29,30 ] Scanning electron microscopy (SEM) revealed that the obtained particles were rhombic dodecahedral in shape with an average size of 1.8 µm (Figure S1, Supporting Information). Powder X‐ray diffraction (XRD) further confirmed the crystal structure of ZIF‐8, showing the same diffraction peaks as the simulated pattern (Figure S1, Supporting Information).…”

“…ZIF‐8 was synthesized according to the literature with some minor modifications. [ 29,30 ] Typically, 8.11 g 1‐methylimidazole and 8.11 g 2‐methylimidazole were dissolved in 500 mL methanol. 7.34 g Zn(NO 3 ) 2 ⋅6H 2 O was dissolved in 500 mL methanol.…”

“…ZIF‐8 was chosen because it has suitable wettability for assembly at the oil/water interface and it is easy to prepare. [ 29 ] Moreover, different from other MOFs used in the preparation of HIPEs, ZIF‐8 particles with micrometer size were adopted. This size was comparable to the wall thickness of the poly‐HIPEs, making it possible for MOF particles to penetrate the cellular wall, and thus avoiding the problem of MOF embedment.…”

Lipase-Immobilized Cellulosic Capsules with Water Absorbency for Enhanced Pickering Interfacial Biocatalysis

“…To overcome the limitation, the oil–water interfacial area could be increased by forming oil-in-water (O/W) or water-in-oil (W/O) emulsions using surfactants/particles. − The particle-stabilized emulsions, so-called Pickering emulsions, , have been shown to be excellent platforms for interfacial reactions, a process named Pickering interfacial catalysis (PIC). ,− Because of the protection by the particle layer, dissolved enzymes in the aqueous phase are less exposed to the organic phase, reducing the possibility of their deactivation by the organic phase . However, the catalysis efficiency of free enzymes in Pickering emulsion systems is still restricted by diffusional limitations, resulting from the diffusing time the enzymes spend on locating close to the oil–water interface …”

Probing the Interactions between Pickering Emulsion Droplets Stabilized with pH-Responsive Nanoparticles

“…Emulsions play an important role in a wide range of chemical and industrial fields, such as oil industry, − food engineering, , pharmaceuticals, and cosmetics . Emulsions are usually formed by mixing two or more immiscible liquids (e.g., oil and water) with interfacially active materials, such as surfactants, asphaltenes, , and nano/microparticles. − The emulsions stabilized with particles are commonly called Pickering emulsions, which have been studied for more than a century following Pickering’s pioneering work in 1907 . It is generally accepted that the particles with partial wettability in both aqueous and organic phases can adsorb to the oil/water interface.…”