Article for preparation and application of Airgel Microspheres

Airgel Microspheres new material having unique structures, both constructed of nanoscale materials, there are micron size, aerogels also has specific heat, sound, light, electrical properties, and complex three-dimensional network topology, a wide range of potential applications in the fields of biomedicine, environmental remediation, functional carrier, such as energy storage and conversion. Currently, Airgel Microspheres become a hot topic of new materials, research systems are mainly silica airgel microspheres, microspheres cellulose aerogels, resorcinol – formaldehyde / carbon airgel microspheres graphene airgel microspheres and the like.

First, an overview of airgel microspheres

Airgel Microspheres, also called airgel microspheres, with different common bulk airgel, is a special structure of the new materials, both construction of nanoscale materials, have micron sizes (typically between 1 ~ 1000μm), and also has the same macro-block airgel porous three-dimensional network structure.

FIG. 1 graphene airgel microspheres

The range of potential applications researchers as Airgel Microspheres airgel, the airgel is possible to expand, such as super adsorbents, pharmaceutical / catalyst carrier, a functional composite particles, osmotic film. This is because compared to the airgel Airgel Microspheres block having a series of more excellent properties, for example: as a catalyst carrier, has a larger specific surface area provides more active reaction center; as a filler, having good fluidity is easy to uniform dispersion, and the like properties are unlikely to cause stress concentration. Therefore, the use of airgel can improve the efficiency and broaden the application of airgel to a large extent.

Second, the method of airgel microspheres

Since the characteristic (high porosity, network structure, etc.) itself airgel, airgel general situ microspheres, the main process starts with an emulsion method, a spray method, or a ball drop Preparation of organic / aqueous hydrogel microspheres, the microspheres and then the solvent is replaced by air drying by supercritical CO2, freeze-drying and other drying mode, thereby obtaining an open cell structure having a complicated airgel Microspheres.

1, an emulsion method

is a precursor emulsion sol dispersed in the oil phase is formed W / O emulsion or inverse suspension, then by increasing the temperature, addition of a catalyst like manner the precursor sol a sol – gel conversion, hydrogel microbeads formed, then after a certain procedures are dried airgel microspheres.

FIG. 2 Emulsion Preparation Method Airgel Microspheres process scheme

Researchers first emulsion by mixing ethyl silicate, ethanol, acetic acid, stirred for 30min at 50 ℃, using TiO2 was added, stirring was continued then aqueous ammonia was added to adjust the pH 8-9 was added an oil phase, wherein the oil phase is a mixture of 1 volume ratio to form a water / oil emulsion, stirring was continued for 5-10min, gradually forming a titanium – aerosilicon microspheres, followed by multiple washing with methanol, filtered off with suction, airgel microspheres separated from the emulsion, after suction filtration aged wet gel, and finally the wet gel under conditions of normal pressure and dried 40 ℃ , prepared TiO2 / SiO2 airgel microspheres.

FIG. 3 TiO2 / SiO2 Airgel Microspheres FIG SEM

emulsion is the most commonly used method airgel microspheres. Its advantages are: high yield, suitable for large scale preparation of airgel microspheres, while the emulsion prepared by size-controlled conditions regulated kind and amount of a surfactant, stirring speed, high sphericity Airgel Microspheres powder particles. The disadvantages are: the manufacturing process more complicated and difficult to completely wash away the surfactants.

2, a spray method

refers to spraying the precursor solution is atomized into a coagulation bath after coagulation, directly airgel microspheres and then after a certain drying process. Using electrostatic spray techniques and in situ radial freezing, liquid nitrogen – ethyl acetate as a coagulation bath, the graphene oxide in the coagulation bath solution was frozen into spherical droplets dispersed, the graphene oxide is formed microspheres ice, and then freeze- dried, to obtain graphene oxide airgel microspheres. Such low-density microspheres, rich channels and due to the radial growth of ice crystals formed like a unique emission center channel structure, potential use in the field of adsorbents, catalyst carriers and the like.

FIG electrostatic spray 4 – Preparation of freeze-situ radial graphene Oxidation process schematic Airgel Microspheres

Researchers by electrospray ionization and freeze drying or the like, prepared having good adsorption properties graphene airgel microspheres. Process using an aqueous dispersion of graphene as a precursor, by the electrical equipment is atomized into fine droplets sprayed with liquid nitrogen cooled receiving hexane, graphene is frozen microdroplets will soon become ice microspheres graphene , which is then setAt -50 ° C, under a pressure below 20Pa lyophilized 24h, to obtain graphene airgel microspheres. Preparation flowchart

FIG 5 SYSTEM electrospray graphene airgel microspheres

Currently, in addition to spraying electrostatic spraying, and high-pressure spraying, ultrasonic spraying, these atomizing method, to select a suitable coagulating bath, can be easily prepared airgel microspheres particles. However, high pressure spray and ultrasonic atomizers can not be prepared monodisperse microspheres, and the microspheres obtained low degree regular morphology. The electrostatic spraying technology through appropriate parameter adjustments, to a large extent can solve this problem, so more and more attention of researchers.

3, the ball drop method

is the use of globules of globules Airgel Microspheres prepared legal process is simple, just into the sol was added dropwise into the coagulation bath can. Using sodium silicate solution as a precursor, which was added dropwise to aqueous ammonia, sodium silicate when contacting a droplet of aqueous ammonia, and begin hydrolysis polycondensation reaction to form a hydrogel microspheres after washing and drying, is obtained having nanopore silica airgel microspheres. The sodium alginate solution dropwise into CaCl2 solution, crosslinked sodium alginate, a hydrogel microspheres formed, then after solvent exchange and drying to obtain a supercritical carbon dioxide airgel alginate microspheres.

4, another method

of Nano Nano Technology Institute, Chinese Academy of bionic solenoid-operated using inkjet printing – marbles liquid – composition of supercritical fluid extraction strategies, and the successful preparation of monodisperse, size can be control graphene airgel microspheres.

FIG. 6 inkjet printing – marbles liquid – Preparation of supercritical fluid technology in conjunction graphene airgel microspheres

The first process is a method using an aqueous dispersion of graphene oxide as a precursor, inkjet printing technology monodisperse droplet precursor; then using a liquid marbles manipulation technology and shape of the droplet is maintained, i.e. graphene oxide droplet printing fine powder silica airgel ; graphene oxide after liquid \”marbles\” prolonged standing in an enclosed environment, to obtain graphene hydrogel microbeads; finally supercritical drying was monodisperse graphene airgel microspheres. The graphene airgel microsphere size dispersion coefficient between 4.9-6.4%, and having a good rolling resistance, a high specific surface area, high porosity, Good conductivity and excellent hydrophobicity.

Third, the application of airgel microspheres

Currently, airgel silica microspheres can be classified into an inorganic oxide represented microsphere airgel, a carbon airgel and organic polymeric microspheres airgel microspheres thereof (e.g. starch, whey / chitosan airgel microspheres and the like) three, which have a wide range of applications in the adsorptive separation, biomedical, energy storage, organic catalysis.

1, silica airgel microspheres application

in photocatalysis, TiO2 / SiO2 composite airgel microspheres having a large specific surface area and a unique internal mesoporous structure, when the degradation of methylene blue as the photocatalyst, airgel microspheres exhibit catalytic activity far higher than the commercial titanium oxide photocatalyst, but also better than the bulk titania / silica airgel composite, which exhibits potential applications in photocatalysis. After

FIG. 7 SiO2 Airgel Microspheres SEM images

In the biomedical field, SiO2 airgel microspheres are subjected to a surface hydrophobic treatment as a drug carrier, the successful implementation of Pueblo Dove release under the control of pH regulation. This approach provides another mechanism of drug release at stimulation (such as heat, pH, enzymes, etc.), could greatly expand the range of applications in the field of pharmaceutical controlled release airgel.

2, carbon-based airgel microspheres Application

carbon yl airgel microspheres due to its unique surface properties, electrical conductivity and high specific surface area, having a value of energy storage in the adsorptive separation and the like. In the field of adsorption, having a graphene oxide airgel microspheres diverging central microchannels structure to common organic solvents and oils exhibit excellent adsorption performance up to 60g · g-1 ~ 214g · g-1 and higher recycling performance, reflecting its enormous potential for application in water treatment.

FIG. 8 has a central divergent graphene oxide airgel microspheres SEM microporous channel structure

In the field of energy storage, a carbon-based mesoporous Airgel Microspheres ball, when an electrode of a supercapacitor performance is very good, with a high specific capacitance (187.08F · g-1) and excellent cycle stability (greater than 5000 times the coulombic efficiency can be maintained at over 99%) and lower resistance .

3, an organic polymer airgel microspheres Applications

an organic polymer airgel microspheres polysaccharides mainly comprising polyethylene Airgel Microspheres and cellulose acetate airgel microspheres, because of their excellent biocompatibility and rich surface functional groups, in adsorptive separation, bio medicine, organic catalysis has important application value.