CN111218025A

CN111218025A - Tree-like photo-thermal hydrogel and preparation method and application thereof

Info

Publication number: CN111218025A
Application number: CN202010018651.9A
Authority: CN
Inventors: 武培怡; 于振川
Original assignee: Donghua University
Current assignee: Donghua University; National Dong Hwa University
Priority date: 2020-01-08
Filing date: 2020-01-08
Publication date: 2020-06-02

Abstract

The invention relates to a tree-like photo-thermal hydrogel and a preparation method and application thereof. Compared with the published similar research work, the invention has outstanding light absorption rate and evaporation rate; the preparation method is simple, has excellent performance and good application prospect, and can be widely applied to the fields of seawater desalination, sewage treatment and the like.

Description

Tree-like photo-thermal hydrogel and preparation method and application thereof

Technical Field

The invention belongs to the technical field of water treatment, and particularly relates to a tree-like photo-thermal hydrogel and a preparation method and application thereof.

Background

Water has become an increasingly scarce resource worldwide as one of the most important resources in people's daily life and industrial production. It is estimated that by 2025, 18 million people will live in water resource-scarce areas (Nature News,2015,517, 6.). The recovery of clean water from waste water or seawater is considered an effective way to address water shortages. Water treatment techniques such as Reverse Osmosis (RO), thermal distillation, etc. have been used to produce clean water for the past several decades. However, these techniques are still not feasible in most underdeveloped countries due to their high energy consumption and the need for complex infrastructure and large centralised facilities. Solar photothermal evaporation, a sustainable method for treating sewage by using solar energy to generate steam, is considered as a low-cost, high-benefit and environment-friendly way for producing clean water. Through research in recent years, it is recognized that there are several main principles for designing an efficient solar photo-thermal evaporation system: (1) the absorption of sunlight is improved; (2) optimizing heat management and reducing heat loss; (3) providing a good water transmission channel; (4) promoting the release of steam. In recent years, various Materials of different structures, such as 2D structure film Materials (Journal of Materials Chemistry A,2018,6, 963-. However, the dense structure of the membrane material of the 2D structure and the disordered pore size distribution and network structure of the aerogel material of the 3D structure will limit the transport of water and the release of steam, resulting in a lower amount of steam generation.

In nature, trees play a vital role in the global water circulation. When they are subjected to photosynthesis, water is continuously transported from the root to the top of the trunk due to transpiration of the vertically arranged microchannels and blades. Based on the above, high performance solar photo-thermal evaporation material composed entirely of natural wood was developed (Joule,2017,1,588-&Environmental Science,2019,12, 1558-. The micro-channels vertically arranged in the wood can be fastThe water transport of (a) provides an open channel and also allows for the undisturbed release of water vapour. In order to prepare high-performance solar photo-thermal evaporation materials, the hydrophilicity of wood is improved by adopting a method of alkali treatment and in-situ lignin removal, but the evaporation rate is still lower than 1.3kg/m²h¹(Journal of Materials Chemistry A,2019,7,13036-13042；ACS applied materials&interfaces,2019,11,26032 and 26037) to be further improved.

Disclosure of Invention

The technical problem to be solved by the invention is to provide the tree-like photothermal hydrogel and the preparation method and the application thereof, and compared with the published similar research work, the tree-like photothermal hydrogel has outstanding light absorption rate and evaporation rate.

The invention provides a tree-like photothermal hydrogel which is a structure formed by directionally freezing MXene nanosheets and a polyvinyl alcohol solution and provided with vertically arranged channels inside.

The invention also provides a preparation method of the tree-imitating photo-thermal hydrogel, which comprises the following steps:

adding polyvinyl alcohol (PVA) into water, heating to 70-90 ℃ and dissolving to obtain PVA solution; adding MXene nanosheets into the PVA solution, and uniformly stirring and dispersing; pouring the dispersed solution into a mold, then placing the mold on a copper column partially immersed in a liquid nitrogen bath, and obtaining aerogel after the solution is completely frozen; freeze-drying and washing the aerogel, and fully swelling the aerogel in deionized water to obtain the tree-like photo-thermal hydrogel which is marked as TIH; wherein the mass ratio of the MXene nanosheets to the PVA is 0.01-0.1: 5-12.5.

The molecular weight of the PVA is 31000, 61000, 135000 or 145000.

The mass-volume ratio of the PVA to the water is 5-12.5g:100 mL.

The preparation method of the MXene nanosheet comprises the following steps:

dissolving 2-5g of lithium fluoride in 40-200ml of solvent to obtain a lithium fluoride solution; adding 2-5g Ti into the solution under ice bath₃AlC₂Stirring for 5-30 min; heating the solution to 30-40 ℃, and stirring for 24-48 hours; reaction junctionAfter that, centrifuging at the rotating speed of 3000-; re-dispersing the centrifuged residue into deionized water, and performing ultrasonic treatment for 0.5-2 hours; centrifuging the solution after the ultrasonic treatment at the rotating speed of 3000-5000rpm for 0.5-2 hours; and (4) taking the upper layer solution, and freeze-drying to obtain the MXene nanosheet.

The solvent is water or hydrochloric acid.

The invention also provides application of the tree-imitating photo-thermal hydrogel, which is applied to photo-thermal water evaporation.

The method comprises the following specific steps: the wood-imitation photothermal hydrogel was placed on polystyrene foam covered with filter paper. Another strip of filter paper was passed through the polystyrene foam with one end attached to the filter paper on the polystyrene foam and the other end extending beyond the filter paper. The polystyrene foam is floated on a container (with the hydrogel side upward) containing seawater (or dye solution) to form a photothermal evaporation system. The photothermal evaporation system was placed under a standard solar simulator and the weight change was measured using a balance.

Advantageous effects

The tree-like photo-thermal hydrogel obtained by the invention has 97% of absorption rate to light with the wavelength of 250-2500 nm. Under standard sunlight, the water evaporation rate can reach 2.71kg/m²h¹. The photothermal evaporation system consisting of the imitated tree photothermal hydrogel material can reduce the salt content in seawater by 3 orders of magnitude, and can remove 99.9 percent of dye in dye-containing wastewater. Therefore, the tree-like photothermal hydrogel obtained by the invention has outstanding light absorption rate and evaporation rate compared with the published similar research work. The invention has simple preparation method and excellent performance, the energy source is green and renewable solar energy, other energy is not required to be consumed, and the invention has good application prospect and can be widely applied to the fields of seawater desalination and sewage treatment.

Drawings

Fig. 1 is a schematic diagram of the preparation of a two-dimensional sheet material MXene.

FIG. 2a is a scanning probe microscope image of MXene; fig. 2b is a transmission electron microscope image of MXene.

FIG. 3 is a schematic diagram of the preparation of a simulated tree photothermal hydrogel TIH.

FIG. 4 is a field emission scanning electron microscope image of TIH.

FIG. 5 is a graph of the absorption of PVA and TIH for different wavelengths of light.

FIG. 6 shows the temperature of pure water and TIH as a function of time in standard sunlight.

FIG. 7 shows the evaporation rates of different TIH samples in standard sunlight.

FIG. 8a shows the concentration of 4 ions in seawater before and after evaporation; FIG. 8b is the change in dye concentration in solution before and after evaporation.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

(1) 2g of lithium fluoride are dissolved in 40ml of solvent. To the solution was slowly added 2g of Ti under ice-bath₃AlC₂And stirred for 5 minutes. The solution was heated to 35 ℃ and stirred for 24 hours. After the reaction is finished, centrifuging at 3500rpm and washing with solvent, and repeating for multiple times until the pH value of the upper layer solution is 6-7. The centrifuged residue was redispersed in deionized water and sonicated for 1 hour. The sonicated solution was centrifuged at 3500rpm for 1 hour. And (4) taking the upper layer solution, and freeze-drying to obtain the MXene nanosheet.

(2) 5g of PVA were dissolved by heating to 80 ℃ in 100ml of water. Adding 50mg of MXene nanosheets obtained in step (1) to 10ml of PVA solution, and stirring to uniformly disperse the MXene nanosheets. The dispersed solution was poured into a teflon mold, which was then placed on a copper cylinder partially immersed in a liquid nitrogen bath. After the solution was completely frozen, the sample was freeze-dried. The freeze-dried aerogel was washed several times with deionized water and fully swollen in deionized water to give a photothermal hydrogel (noted as TIH 1).

Fig. 1 is a preparation method of MXene nanosheets. Mainly comprises acid etching of Ti₃AlC₂And (5) carrying out ultrasonic treatment and centrifugation on the aluminum layer to obtain the MXene nanosheet. The MXene nanosheets are successfully prepared through characterization by a scanning probe microscope and a transmission electron microscope, and the thickness of the layer of the MXene nanosheets is about 1.6nm (figure 2). Mixing MXene with PVA solution, freezing directionally to control the growth of ice crystal, and freeze drying to obtain the final product (figure 3). The photothermal hydrogel prepared was demonstrated to have good orientation by characterization by field emission scanning electron microscopy (fig. 4). The width of the vertically oriented channels in the photothermal hydrogel is between 5 and 8 μm. The ultraviolet visible near-infrared absorption spectrum analysis shows that the TIH1 has better absorption for the light with the wavelength of 250-2500nm, and the absorption rate is more than 97 percent (figure 5). Under standard solar radiation, the temperature of TIH1 increased with time (fig. 6). After 1 hour of irradiation, the temperature of the TIH1 can reach 34.4 ℃, which is obviously higher than that of pure water, and the TIH1 has good photo-thermal conversion effect. The evaporation effect of the photothermal evaporation system consisting of TIH1 under the irradiation of standard sunlight is shown in figure 7, and the evaporation rate can reach 2.03kg/m²h¹. The effect of the photothermal evaporation system composed of hydrogel on the purification of seawater and dye-containing wastewater is shown in fig. 8. After treatment, the content of 4 ions (sodium ions, calcium ions, potassium ions and magnesium ions) in the seawater is reduced by 3 orders of magnitude. In the wastewater containing the dye, ultraviolet absorption peaks of brilliant blue and rhodamine B disappear. The photo-thermal evaporation system formed by the hydrogel can realize seawater desalination and wastewater purification.

Example 2

(2) 7.5g of PVA were dissolved in 100ml of water by heating to 80 ℃. Adding 50mg of MXene nanosheets obtained in step (1) to 10ml of PVA solution, and stirring to uniformly disperse the MXene nanosheets. The dispersed solution was poured into a teflon mold, which was then placed on a copper cylinder partially immersed in a liquid nitrogen bath. After the solution was completely frozen, the sample was freeze-dried. The freeze-dried aerogel was washed several times with deionized water and fully swollen in deionized water to give a photothermal hydrogel (noted as TIH 2).

The ultraviolet visible near-infrared absorption spectrum analysis shows that the TIH2 has better absorption for the light with the wavelength of 250-2500nm, and the absorption rate is more than 97 percent (figure 5). Under standard solar radiation, the temperature of TIH2 increased with time (fig. 6). After 1 hour of irradiation, the temperature of TIH2 can reach 35.7 ℃, which is obviously higher than that of pure water, and the TIH2 has good photo-thermal conversion effect. The evaporation effect of the photothermal evaporation system consisting of TIH2 under the irradiation of standard sunlight is shown in figure 7, and the evaporation rate can reach 2.30kg/m²h¹。

Example 3

(2) 10g of PVA was dissolved by heating to 80 ℃ in 100ml of water. Adding 50mg of MXene nanosheets obtained in step (1) to 10ml of PVA solution, and stirring to uniformly disperse the MXene nanosheets. The dispersed solution was poured into a teflon mold, which was then placed on a copper cylinder partially immersed in a liquid nitrogen bath. After the solution was completely frozen, the sample was freeze-dried. The freeze-dried aerogel was washed several times with deionized water and fully swollen in deionized water to give a photothermal hydrogel (noted as TIH 3).

The ultraviolet visible near-infrared absorption spectrum analysis shows that the TIH3 has better absorption for the light with the wavelength of 250-2500nm, and the absorption rate is more than 97 percent (figure 5). Under standard solar radiation, the temperature of TIH3 increased with time (fig. 6). After 1 hour of irradiation, the temperature of TIH3 can reach 35.9 ℃, which is obviously higher than that of pure water, and the TIH3 has good photo-thermal conversion effect. The evaporation effect of the photothermal evaporation system consisting of TIH3 under the irradiation of standard sunlight is shown in figure 7, and the evaporation rate can reach 2.71kg/m²h¹。

Example 4

(1) 2g of lithium fluoride are dissolved in 40ml of solvent. To this solution was slowly added 2g of Ti under ice-bath₃AlC₂And stirred for 5 minutes. The solution was heated to 35 ℃ and stirred for 24 hours. After the reaction is finished, centrifuging at 3500rpm and washing with solvent, and repeating for multiple times until the pH value of the upper layer solution is 6-7. The centrifuged residue was redispersed in deionized water and sonicated for 1 hour. The sonicated solution was centrifuged at 3500rpm for 1 hour. And (4) taking the upper layer solution, and freeze-drying to obtain the MXene nanosheet.

(2) 12.5g of PVA were dissolved in 100ml of water by heating to 80 ℃. Adding 50mg of MXene nanosheets obtained in step (1) to 10ml of PVA solution, and stirring to uniformly disperse the MXene nanosheets. The dispersed solution was poured into a teflon mold, which was then placed on a copper cylinder partially immersed in a liquid nitrogen bath. After the solution was completely frozen, the sample was freeze-dried. The freeze-dried aerogel was washed several times with deionized water and fully swollen in deionized water to give a photothermal hydrogel (noted as TIH 4).

The ultraviolet visible near-infrared absorption spectrum analysis shows that the TIH4 has better absorption for the light with the wavelength of 250-2500nm, and the absorption rate is more than 97 percent (figure 5). Under standard solar radiation, the temperature of TIH4 increased with time (fig. 6). After 1 hour of irradiation, the temperature of TIH4 can reach 36.5 ℃, which is obviously higher than that of pure water, and the TIH4 has good photo-thermal conversion effect. The evaporation effect of the photothermal evaporation system consisting of TIH4 under the irradiation of standard sunlight is shown in figure 7, and the evaporation rate can reach 2.62kg/m²h¹。

Claims

1. A kind of imitative trees light and heat aquogel, characterized by: the tree-imitating photo-thermal hydrogel is a structure with vertically arranged channels inside formed by directionally freezing MXene nanosheets and polyvinyl alcohol solution.

2. A preparation method of the tree-imitated photo-thermal hydrogel comprises the following steps:

adding polyvinyl alcohol (PVA) into water, heating to 70-90 ℃ and dissolving to obtain PVA solution; adding MXene nanosheets into the PVA solution, and uniformly stirring and dispersing; pouring the dispersed solution into a mold, then placing the mold on a copper column partially immersed in a liquid nitrogen bath, and obtaining aerogel after the solution is completely frozen; freeze-drying and washing the aerogel, and fully swelling the aerogel in deionized water to obtain the tree-like photo-thermal hydrogel; wherein the mass ratio of the MXene nanosheets to the PVA is 0.01-0.1: 5-12.5.

3. The method of claim 2, wherein: the molecular weight of the PVA is 31000, 61000, 135000 or 145000.

4. The method of claim 2, wherein: the mass-volume ratio of the PVA to the water is 5-12.5g:100 mL.

5. The method of claim 2, wherein: the preparation method of the MXene nanosheet comprises the following steps:

dissolving 2-5g of lithium fluoride in 40-200ml of solvent to obtain a lithium fluoride solution; adding 2-5g of Ti into the solution under ice bath₃AlC₂Stirring for 5-30 min; heating the solution to 30-40 ℃, and stirring for 24-48 hours; after the reaction is finished, centrifuging at the rotating speed of 3000-; re-dispersing the centrifuged residue into deionized water, and performing ultrasonic treatment for 0.5-2 hours; centrifuging the solution after the ultrasonic treatment at the rotating speed of 3000-5000rpm for 0.5-2 hours; taking the upper layer solution out of the reactor,and (5) carrying out freeze drying to obtain the MXene nanosheet.

6. The method of claim 5, wherein: the solvent is water or hydrochloric acid.

7. The use of the tree-like photothermal hydrogel of claim 1, wherein: is applied to photo-thermal water evaporation.