Preparation And Applications Of Liquid Core Microcapsules

Microcapsules show many potential applications in a wide range of research fields including catalysis,drug delivery and medical imaging.Their particle sizes,wall thicknesses and pore diameters could be finely engineered.Among various kinds of microcapsules,the Pickering emulsion templated microcapsules exhibited superior advantages in confining immiscible liquids by tuning the surface wettability of the solid nanoparticles.And through interfacial chemical reactions,solid bounded microcapsules with liquid as core can be formed easily.The liquid droplets confined in the solid microcapsules are as free as the bulk liquid.Moreover,due to the unique permeability of the shell,the microcapsles can be utilized as efficient microreactors,in which the reactions take place with unsurpassed efficiency and specificity like the living cell.More importantly,such microcapsules with liquid as core and solid material as shell integrate the features of liquid and solid together,providing a new opportunity for heterogeneous catalysis.Especially,encapsulating viscous or corrosive liquids to form solid microcapsules is meaningful for industrial production,since the fabricated microcapsule catalysts possess the advantages of high activity,easy separation and recyc ling.In this study,we have successfully synthesized microcapsules with corrosive sulfuric acid or viscous ionic liquid as core taking Pickering emulsion as template followed by a chemical cross-linking process.Also,continuous flow reactions were further performed to verify the practicability of our method.In the Pickering gas-liquid system,solid nanoparticles could be adsorbed on the liquid-air interfaces forming “dry liquid” without addition of the oil phase,which is applicable for dispersion and package of concentrated sulfuric acid.Super hydrophobic SiO2 nanoparticles?SN-F?with corrosion resistance were prepared by modification of SiO2 nanoparticles?SN?with 1H,1H,2H,2Hperfluorooctanetrimethoxysilane.Then,“dry concentrated sulfuric acid” which is sulfuric acid in air inverse bubble was prepared by mixing SN-F and 90 % concentrated sulfuric acid at high stirring speed.The influence of the contents of SN-F for the formation of "dry concentrated sulfuric acid" was investigated.And uniform spherical "dry concentrated sulfuric acid" with a diameter of 100²00 ?m could be got as the amount of SN-F is 5 wt%.Interestingly,the prepared“dry concentrated sulfuric acid” possess high surface area,excellent mechanical strength,of which the morphology could be maintained even after 18 months.Also,in order to further improve the mechanical strength of the “dry concentrated sulfuric acid”,a gas phase crosslinking method was preliminarily explored.The microcapsules with ionic liquid as core were fabricated by a chemical cross-linking method using ionic liquid based Pickering emulsion as template.The morphology and structure w ere fully characterized by SEM,EDS and N2 physical sorption,and their permeability,mechanical strength and polar solvent resistance were also investigated.Fluorescent molecular probes were utilized to explore the permeability of the microcapsules with different shell thicknesses.It was found that the microcapsules allow uptake and release of fluorescent molecules through the silica shell.And the permeability increased with the thickness of the shell decreasing.The mechanical strength tests verified the availability of the microcapsules for industrial fixed bed,which could be still stable under 1 MPa of hydraulic pressure and 55 mL/L of velocity even after 72 hours.These unique properties of the obtained microcapsules including large surface area,tunable size and permeability,excellent mechanical strength ensured their applicability in fixed bed.The catalytic performance of the microcapsules with ionic liquid as core in continuous flow reaction was studied using D,L^-1-benzyl alcohol kinetic resolution as a model reaction.CALB enzyme was in situ dissolved in the ionic liquid core.The influences of particle size,shell thickness on the reaction were investigated and the kinetic parameters in continuous-flow reaction system were measured,such as,Michaelis constant Km,the maximum reaction rate Vmax.and reaction constant kcat.And Km is 0.1 mol·L^-1,Vmax is 3.2×10-3 mol·min^-1 and kcat.is 6.7×102 min^-1,demonstrating that the microcapsules possess high catalytic ability in continuous flow reaction system.Applying the microcapsules to the reaction of D L^-1-,benzyl alcohol with vinyl acetate whose substrate concentration is 0.35 mol/L and flow rate was 2 m L/h,the conversion is above 49.9 %,the enantiomeric excess of ee% is 99%.Notably,the reaction efficiency is still maintained after 1500 h.For extending the substrate,the reactions were carried out for 200 hours,and the enantiomeric excess ee% was still kept at about 99%,further indicating that the microcapsules are applicable and stable in continuous flow system.