Aerogel with hierarchical pore structure formed using pulsed laser technology, and preparation method and use thereof

Abstract

Disclosed are an aerogel with a hierarchical pore structure formed using a pulsed laser technology, and a preparation method and use thereof. In the preparation method, a nano silicon-containing inorganic material as a freezing element, a biomass polymer as a cross-linking agent, and deionized water as a solvent are mixed and a resulting mixture is left to stand and gelatinized to obtain a hydrogel; the hydrogel is frozen to form ice crystals therein, and the ice crystals are removed by freeze-drying to obtain a micron-nano porous aerogel; the micron-nano porous aerogel is subjected to customized millimeter-scale punching using a pulsed laser to obtain an aerogel with a millimeter-micron-nano hierarchical pore structure.

Claims

1. An aerogel with a hierarchical pore structure formed using a pulsed laser technology, the aerogel being a silicon-containing inorganic-organic composite aerogel with a millimeter-micron-nano hierarchical pore structure, and being formed by subjecting a micron-nano silicon-containing inorganic-organic composite aerogel to customized millimeter-scale punching using a pulsed laser, wherein the micron-nano silicon-containing inorganic-organic composite aerogel is prepared by a process comprising: mixing a nano silicon-containing inorganic material, a biomass polymer, and deionized water as a solvent to obtain a mixture, leaving the mixture to stand, and gelatinizing to obtain a nano silicon-containing inorganic-organic composite hydrogel, the biomass polymer comprising polyvinyl alcohol, agar, and glutaraldehyde; and freezing the nano silicon-containing inorganic-organic composite hydrogel to form ice crystals therein, and removing the ice crystals therein by freeze-drying to obtain the micron-nano silicon-containing inorganic-organic composite aerogel; and wherein a size, a shape, and a number of millimeter-scale pores in the aerogel with the hierarchical pore structure are controlled by the pulsed laser, thereby obtaining the silicon-containing inorganic-organic composite aerogel with the millimeter-micron-nano hierarchical pore structure.

2. The aerogel with the hierarchical pore structure formed using the pulsed laser technology as claimed in claim 1, wherein the nano silicon-containing inorganic material comprises at least one of MoSi.sub.2, SiO.sub.2, and Si.sub.3N.sub.4.

3. A method for preparing the aerogel with the hierarchical pore structure formed using the pulsed laser technology as claimed in claim 1, comprising the steps of: step 1), preparing the nano silicon-containing inorganic-organic composite hydrogel, comprising: providing polyvinyl alcohol and agar, adding deionized water thereto, and dissolving the polyvinyl alcohol and the agar by heating to obtain a homogeneous solution; adding a glutaraldehyde solution into the homogeneous solution, and subjecting a resulting mixture to cross-linking to obtain a cross-linked solution; adding a nano silicon-containing inorganic powder into the cross-linked solution to obtain a nano silicon-containing inorganic-organic composite colloidal sol; and leaving the nano silicon-containing inorganic-organic composite colloidal sol to stand, and gelatinizing to obtain the nano silicon-containing inorganic-organic composite hydrogel; step 2), preparing the micron-nano silicon-containing inorganic-organic composite aerogel, comprising: freezing the nano silicon-containing inorganic-organic composite hydrogel obtained in step 1) to form the ice crystals therein, and vacuum freeze-drying to remove the ice crystals and obtain the micron-nano silicon-containing inorganic-organic composite aerogel; and step 3), producing the silicon-containing inorganic-organic composite aerogel with a millimeter-micron-nano hierarchical pore structure, comprising: subjecting the micron-nano silicon-containing inorganic-organic composite aerogel to punching processing using the pulsed laser technology to form the millimeter-scale pore structure, wherein the punching processing is performed by: setting the pulsed laser with a frequency of 20 Hz, a pulse-width of 5,000 ps, a scanning speed of 50 mm/s to 150 mm/s, a laser power of 3% to 8%, and a laser spot of 1 mm; selecting a millimeter-scale pore shape; and punching the micron-nano silicon-containing inorganic-organic composite aerogel from top to bottom using a laser light source to form the millimeter-scale pores, wherein the size, the shape, and the number of the millimeter-scale pores in the aerogel with the hierarchical pore structure are controlled by the pulsed laser, thereby forming the silicon-containing inorganic-organic composite aerogel with the millimeter-micron-nano hierarchical pore structure.

4. The method as claimed in claim 3, wherein in step 1) the nano silicon-containing inorganic-organic composite colloidal sol comprises 1 wt % to 4 wt % of the polyvinyl alcohol, 1 wt % to 2 wt % of the agar, and 0.02 wt % to 1 wt % of the nano silicon-containing inorganic powder.

5. The method as claimed in claim 3, wherein in step 2) the nano silicon-containing inorganic-organic composite hydrogel is frozen at a temperature of ?30? C. to ?80? C.

6. The method as claimed in claim 3, wherein the millimeter-scale pore shape comprises at least one of a square, a circle, and a polygon.

7. The method as claimed in claim 3, wherein the nano silicon-containing inorganic powder comprises at least one of MoSi.sub.2, SiO.sub.2, and Si.sub.3N.sub.4.

8. A solar-driven method for desalinating seawater, comprising the steps of: combining the aerogel with the hierarchical pore structure formed using the pulsed laser technology as claimed in claim 1, a polystyrene foam as a thermal insulation layer, and a fiber absorbent paper, and assembling into an evaporator, wherein the aerogel is to absorb solar energy, and the fiber absorbent paper is to transport seawater; and evaporating the seawater by using the evaporator to obtain fresh water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) To describe the technical solutions of the present disclosure more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments.

(2) Apparently, the accompanying drawings in the following descriptions show merely some embodiments of the present disclosure, and those of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

(3) FIG. 1 shows a schematic flowchart for preparing a MoSi.sub.2 aerogel with a millimeter-micron-nano hierarchical pore structure in an embodiment of the present disclosure.

(4) FIG. 2 shows macroscopic photos of the MoSi.sub.2 aerogel with a millimeter-micron-nano hierarchical pore structure before and after punching using a pulsed laser in Examples 1 to 3 of the present disclosure.

(5) FIGS. 3A to 3D show scanning electron microscope (SEM) images of the MoSi.sub.2 aerogel with a hierarchical pore structure in Example 1 of the present disclosure, in which, FIG. 3A represents a micron-nano pore structure on the surface of MoSi.sub.2 aerogel; FIG. 3B represents a microstructure within millimeter-scale channels after punching of MoSi.sub.2 aerogel; FIG. 3C represents an internal pore structure of the original MoSi.sub.2 aerogel; and FIG. 3D represents an enlarged view of the microstructure within the millimeter-scale channels of MoSi.sub.2 aerogel.

(6) FIG. 4 shows densities of the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore structure synthesized in Examples 1 to 3 of the present disclosure.

(7) FIG. 5 shows swelling properties of the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore structure synthesized in Examples 1 to 3 of the present disclosure.

(8) FIG. 6A and FIG. 6B show physical pictures of the aerogel before and after adding nano MoSi.sub.2 material according to an embodiment of the present disclosure during a flame-retardant performance test, respectively.

(9) FIG. 7A and FIG. 7B show mass losses and evaporation rates of the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore structure synthesized in Examples 1 to 3 of the present disclosure under one sun illumination intensity within 60 min, respectively.

(10) FIG. 8 shows physical pictures of the self-dissolution of salts over time in the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore structure synthesized in Examples 1 to 3 of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) The preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings, so that the advantages and features of the present disclosure can be more easily understood by those skilled in the art, and thus the protection scope of the present disclosure can be defined more clearly.

(12) It should be noted that the original MoSi.sub.2 aerogel in the present disclosure refers to a micron-nano MoSi.sub.2 aerogel without pulsed laser punching.

Example 1

(13) In Example 1, a MoSi.sub.2 aerogel with a macroscopic pore of 5*5 circular pore matrix was prepared. As shown in FIG. 1, the MoSi.sub.2 aerogel with a millimeter-micron-nano hierarchical pore structure was prepared according to the following procedures: Step 1, preparation of a MoSi.sub.2 hydrogel: 2 wt % agar and 1 wt % polyvinyl alcohol powder were placed in a beaker, and dissolved in 100 mL of deionized water by heating to 90? C. and magnetically stirring for 1 h, obtaining a homogeneous solution. 100 ?L of a glutaraldehyde solution with a concentration 50 wt % was added to the homogeneous solution and the resulting mixture was stirred for 10 min. A MoSi.sub.2 powder with a mass fraction of 0.02 wt % was slowly added thereto and the resulting mixture was magnetically stirred until a uniform black solution was obtained.

(14) The black solution was poured into a prefabricated mold with a dimension of 100 mm*100 mm*10 mm, left to stand for 5 min and gelled, thereby forming the MoSi.sub.2 hydrogel with a certain toughness. Step 2, preparation of a MoSi.sub.2 aerogel with a micro-nano pore structure: The MoSi.sub.2 hydrogel obtained in step 1 was frozen in a refrigerator at ?80? C. for 24 h, forming ice crystals. The frozen hydrogel was taken out and placed in a freeze dryer at ?80? C. and vacuum dried for 48 h, obtaining the MoSi.sub.2 aerogel with a micro-nano pore structure. Step 3, synthesis of a MoSi.sub.2 aerogel with a millimeter-micron-nano hierarchical pore structure: The aerogel obtained in step 2 was cut, obtaining a square aerogel with a dimension of 30 mm*30 mm. The micron-nano-scale MoSi.sub.2 aerogel was subjected to punching processing customized with a millimeter-scale pore pattern using a pulsed laser. The punching processing customized with a millimeter-scale pore pattern was performed as follows: the pulsed laser was set with a frequency of 20, a pulse-width of 5,000, a scanning speed of 100 mm/s, and a laser power of 8%; the pore shape was set to be a circle with a diameter of 1 mm, and the pore spacing was set, thereby designing and programming a 5*5 circular pore matrix; the pulsed laser was started, and the MoSi.sub.2 aerogel was punched from top to bottom using a laser light source, forming millimeter-scale pores. After punching for 30 s, the punching processing was completed, obtaining a MoSi.sub.2 aerogel with a P5?5 pattern shown in FIG. 2, millimeter-scale pores including vertically-oriented through pores, and three-dimensionally-connected micron-nano hierarchical pores shown in FIGS. 3A to 3D.
Use in Photothermal Seawater Desalination

(15) After testing, the MoSi.sub.2 aerogel with P5?5 hierarchical pores in Example 1 had a water evaporation rate of 1.39 kg.Math.m.sup.?2.Math.h.sup.?1.

Example 2

(16) In Example 2, a MoSi.sub.2 aerogel with millimeter-scale pores of a 6*6 circular pore matrix was prepared. It was prepared according to procedures as described in Example 1, except that: in step 3 of this example, a 6*6 circular pore matrix rather than a 5*5 circular pore matrix of Example 1 was designed and programmed, with other parameters of the pulsed laser and operating steps unchanged, to verify the number adjustability of the millimeter-scale pores in the aerogel according to the present disclosure with a proviso that the macroscopic shape did not collapse. An aerogel was obtained with a hierarchical pore structure of P6?6 mm pore shown in FIG. 2.

(17) After testing, the MoSi.sub.2 aerogel with P6?6 hierarchical pores in Example 2 had a water evaporation rate of 1.26 kg.Math.m.sup.?2.Math.h.sup.?1.

Example 3

(18) In Example 3, a MoSi.sub.2 aerogel with macroscopic pores of a 7*7 square pore matrix was prepared. It was prepared according to the procedures as described in Example 1, except that: in step 3 of this example, a 7*7 square pore matrix rather than a 5*5 circular pore matrix of Example 1 was designed and programmed, with other parameters of the pulsed laser and operating steps unchanged, to verify that the millimeter-scale pore pattern of the aerogel according to the present disclosure could be accurately customized. An aerogel was obtained with a hierarchical pore structure of millimeter-scale pores in P7?7 mm pore size shown in FIG. 2.

(19) After testing, the MoSi.sub.2 aerogel with P7?7 hierarchical pores in Example 3 had a water evaporation rate of 1.13 kg.Math.m.sup.?2.Math.h.sup.?1.

(20) FIG. 2 shows macroscopic photos of the MoSi.sub.2 aerogel with a millimeter-micron-nano hierarchical pore structure before and after punching using a pulsed laser in Examples 1 to 3 of the present disclosure. As can be seen from FIG. 2, the MoSi.sub.2 aerogel prepared in the present disclosure shows desirable macro formability, no cracks or obvious shrinkage deformation on the surface, and has good cutting and processing properties. After punching using a pulsed laser, no destructive phenomenon occurs in the aerogel, such as ablation and structural collapse. The aerogel still maintains stable macrostructural characteristics, even when the number of millimeter-scale pores increases and the pore shape changes, which achieves advantages of customized processing of a millimeter-scale pore pattern, adjustable number of pores, and controllable pore size distribution. After the MoSi.sub.2 aerogel with hierarchical pore structure was soaked in water, the surface turned black due to the removal of gelatinization; however, the pore shape did not collapse, and the macroscopic shape of the aerogel was not damaged, proving that the aerogel with hierarchical pores maintain excellent strength and toughness.

(21) FIGS. 3A to 3D show SEM images of the MoSi.sub.2 aerogel with a hierarchical pore structure in Example 1 of the present disclosure. As shown in FIG. 3A, there is an elliptical micronscale pore structure on the surface of MoSi.sub.2 aerogel not punched using laser, with a large number of nanoscale pores evenly distributed on the network framework. As shown in FIG. 3B, after punching processing using pulsed laser, a framework of the through-pore is carbonized at high temperature, the surface turns black, and the cross-linking bonds are broken, forming a layered stacked microstructure. FIG. 3D shows a partially enlarged view of FIG. 3B, and shows that there are wrinkles on the surface of the fractured pore framework, as well as a gap structure assembled layer by layer. FIG. 3C shows the internal pore structure of MoSi.sub.2 aerogel not punched using laser. As can be seen from FIG. 3C, the aerogel framework grew larger and has unidirectional pores.

(22) FIG. 4 shows densities of the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore in Examples 1 to 3 of the present disclosure, which are 0.039, 0.036, 0.034, and 0.033 g/cm.sup.3 respectively. As can be seen from FIG. 4, as the number of millimeter-scale pores in the aerogel increases, the density gradually decreases, with a small difference, indicating that punching using laser causes little impact on the mass of the aerogel.

(23) FIG. 5 shows swelling rates of the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore in Examples 1 to 3 of the present disclosure, which are 17.3%, 18.8%, 19.3% and 21.4% respectively. As can be seen from FIG. 5, as the number of millimeter-scale pores in the aerogel increases, the swelling rate gradually increases, proving that the water absorption capacity of the aerogel increases and the water saturation becomes higher. Compared with the original MoSi.sub.2 aerogel with a larger degree of cross-linking, the millimeter-scale pores provide more penetration paths for aqueous solutions. Moreover, the broken cross-linking bonds reduce the penetration resistance of the aqueous solution, allowing the aerogel with hierarchical pore structure that includes more millimeter-scale pores to absorb more water during the same time period.

(24) FIG. 6A and FIG. 6B show physical pictures of the aerogel before and after adding nano MoSi.sub.2 material according to an embodiment of the present disclosure during a flame-retardant performance test, respectively. As can be seen from FIG. 6A and FIG. 6B, before adding MoSi.sub.2 nanomaterials, the polyvinyl alcohol/agar aerogel is burned continuously within 14 s, while the burning of the polyvinyl alcohol/agar/MoSi.sub.2 aerogel stops automatically at 14 s, proving that the addition of the nano MoSi.sub.2 material enhances the flame-retardance of the aerogel. This may be because MoSi.sub.2 exhibits high temperature stability and could act as a thermal insulator, forming a desirable physical barrier during the combustion, and thereby effectively preventing adjacent parts from continuing to burn.

(25) FIG. 7A and FIG. 7B show mass losses and evaporation rates of the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore structure synthesized in Examples 1 to 3 of the present disclosure under one sun illumination intensity within 60 min, respectively. As can be seen from FIG. 7A and FIG. 7B, for the original MoSi.sub.2 aerogel, a rapid mass loss is maintained within the first 30 min of evaporation; however, from 30 min to 60 min, the mass loss slows down significantly. This was because the large cross-linking degree of the original MoSi.sub.2 aerogel causes a low water supply, with a water supply rate lower than the evaporation rate. When the number of millimeter-scale straight through-pores was P5?5, the evaporation rate increases significantly due to the increased water supply rate. When the number of millimeter-scale straight through-pores further increases, the evaporation rate decreases because the increased number of millimeter-scale pores, results in a decreased light absorption area. It can be concluded that, by controlling the appropriate number of millimeter-scale pores, and minimizing area loss with a proviso of increasing water supply rate and ensuring water supply capacity, the solar evaporation performance of the MoSi.sub.2 aerogels with a hierarchical pore structure is effectively improved.

(26) FIG. 8 shows physical pictures of the self-dissolution of salts over time in the original MoSi.sub.2 aerogel and the MoSi.sub.2 aerogels with a hierarchical pore structure synthesized in Examples 1 to 3 of the present disclosure. As can be seen from FIG. 8, when salt is deposited on the surface of different aerogels, as time goes by, the salt dissolution efficiency ranks from high to low as follows: P7?7>P6?6>P5?5>original MoSi.sub.2 aerogel. Compared with the original aerogel of micro-nano structure, the increase in the number of millimeter-scale pores improves the internal mass transfer efficiency of MoSi.sub.2 aerogel and endows it with a self-cleaning function. This further proves the necessity of designing and constructing an aerogel with a millimeter-micron-nano hierarchical pore structure.

(27) The above are only specific examples of the present disclosure, but the scope of the present disclosure is not limited to these examples. Any change or replacement that could be conceived without creative labor should fall within the scope of the present disclosure. Therefore, the scope of the present disclosure should be subject to the scope defined by the claims.