Foam Silica Films Synthesized by Calcium Chloride-Assisted Emulsification

Abstract

The development of porous films presenting accessible high specific surface area is important to design new adsorbents, sensors or catalyst supports. Here, we describe a simple method to prepare a foam silica coating by using an evaporation induced emulsification method assisted by calcium chloride. An alcoholic silica sol containing calcium chloride and a poly(ethylene oxide) containing polymer is deposited on a substrate by dip-coating. The alcohol evaporation induces a phase separation between a silica-rich phase and a calciumrich one. The droplets size increases via a coalescence process until the sol gelation, which determines the final pore size comprised between 100 nm and 3 µm. Thermal analysis and droplet evaporation monitoring both confirm that the solvent departure is delayed by the presence of calcium chloride into the sol. Influence of the polymer nature on the porosity is discussed. Using a block copolymer such as the Pluronic F-127, which strongly stabilizes the emulsion, allows to reach a low pore size (400 nm) while on the opposite, we propose to use a short poly(ethylene glycol) (PEG) such as the PEG-400, which weakly stabilizes it, leading 2 to larger pores (2-3 microns). Moreover, we show that adding a zirconium salt (ZrOCl 2 .8H 2 O) into the silica sol speeds up the condensation step of the silica network and leads to the decreasing in the pore size.

Sustainable Coordination Polymer-Based Catalyst and Its Application in the Nitroaromatic Hydrogenation under Mild Conditions

“…Recently, various methods were developed by chemists for immobilizing active centers to improve the efficiency of the catalysts . Stabilization of the catalysts on solid supports is one of the simplest methods to modify the efficiency and recycling of catalysts. , The most commonly used solids are zeolites, carbon materials, mesoporous SiO 2 , magnetic materials, and so on. − Coordination polymers (CPs) are solid-state constructions involving reiterated coordination units extending in one, two, or three dimensions . These organic–inorganic solids with infinite and uniform building blocks are constructed from polydentate organic ligands as linkers and metallic ions or metal-containing clusters as nodes. − Nowadays, CPs have received much attention due to their unique structural properties such as various metal sites, highly ordered porosity, high surface area, functional organic linkers, and good biocompatibility. − Due to these outstanding physicochemical properties, CPs can be utilized for a wide variety of applications in catalysis, photocatalysis, sensors, gas storage, biomedicine, water remediation, separation, and electrocatalysis. , …”

Characterization of silica-PEG-CaCl2 composite sorbents in an open thermochemical heat storage reactor

“…In the 1990s, they developed a procedure for synthesizing porous silica for separation applications on the basis of silica-PEG composites produced by a sol-gel method. We were also inspired by a previous work [24] dealing with the development of porous coatings, in which we described phase separation phenomena in a system based on silica / PEG and assisted by calcium chloride. A two-fold strategy is proposed in this paper to stabilize the salt (calcium chloride) in a solid matrix.…”