pH-Responsive Gas–Water–Solid Interface for Multiphase Catalysis

Abstract

Despite their wide utility in laboratory synthesis and industrial fabrication, gas-water-solid multiphase catalysis reactions often suffer from low reaction efficiency because of the low solubility of gases in water. Using a surface-modification protocol, interface-active silica nanoparticles were synthesized. Such nanoparticles can assemble at the gas-water interface, stabilizing micrometer-sized gas bubbles in water, and disassemble by tuning of the aqueous phase pH. The ability to stabilize gas microbubbles can be finely tuned through variation of the surface-modification protocol. As proof of this concept, Pd and Au were deposited on these silica nanoparticles, leading to interface-active catalysts for aqueous hydrogenation and oxidation, respectively. With such catalysts, conventional gas-water-solid multiphase reactions can be transformed to H2 or O2 microbubble reaction systems. The resultant microbubble reaction systems exhibit significant catalysis efficiency enhancement effects compared with conventional multiphase reactions. The significant improvement is attributed to the pronounced increase in reaction interface area that allows for the direct contact of gas, water, and solid phases. At the end of reaction, the microbubbles can be removed from the reaction systems through changing the pH, allowing product separation and catalyst recycling. Interestingly, the alcohol oxidation activation energy for the microbubble systems is much lower than that for the conventional multiphase reaction, also indicating that the developed microbubble system may be a valuable platform to design innovative multiphase catalysis reactions.

Naked-eye point-of-care testing platform based on a pH-responsive superwetting surface: toward the non-invasive detection of glucose

“…The measurements revealed that the zeta potential values at pH 5 and pH 7 were positive, which meant that negative ions could approach the positive ions on the surface of the pH-SiNPs because of the protonation of the amino groups on the pH-SiNPs 39 . However, the zeta potential value decreased to nearly −28 mV at pH 9, indicating that few negative ions attached to the surface of the pH-SiNPs 39 .…”

“…The highest peak at a binding energy of 532.0 eV corresponding to the O1 s peak illustrated the presence of abundant Si-O-Si group formed by the reaction of the organosilanes with the silica nanoparticles. A peak at approximately 103.6 eV, which is the Si2 p peak of SiO 2 , showed that there was little bare space on the silica nanoparticles 14,39 . These facts demonstrated that organosilanes were successfully grafted on the surface of the silica nanoparticles.…”

“…1a, AEPTMS and OTMS were important ingredients for achieving the pH response. AEPTMS has hydrophilic properties in acidic solutions due to the protonation of the pH-sensitive amino groups, and OTMS possesses superhydrophobic properties 14,39 . In the presence of a solution with a pH of 1, the surface was completely wetted within 1 s, and the CA was approximately 0°owing to the protonation of AEPTMS (Figure S3A and Movie S1).…”

“…In addition, even when the working pressure decreased to 0.5 atm, the superwetting surface still exhibited satisfactory performance (CA = 151.2°± 1.8°), which means it can be used over 5000 m above sea level. Unlike the pressure-based method 39 , the CA-based method is suitable for application in all countries.…”

Tuning Amphiphilicity of Particles for Controllable Pickering Emulsion

“…The control of Pickering emulsions plays a pivotal part in many significant processes, for example, oil extraction and recovery [29,30], emulsion polymerization [31,32,33,34], and heterogeneous catalysis [35,36,37]. In this regard, many endeavors have been made in developing controllable Pickering emulsions.…”