CN109879344B

CN109879344B - Photo-thermal evaporation surface and preparation and application thereof

Info

Publication number: CN109879344B
Application number: CN201910166979.2A
Authority: CN
Inventors: 徐进良; 闫鑫
Original assignee: North China Electric Power University
Current assignee: North China Electric Power University
Priority date: 2019-03-06
Filing date: 2019-03-06
Publication date: 2020-06-19
Anticipated expiration: 2039-03-06
Also published as: CN109879344A

Abstract

The invention discloses a photo-thermal evaporation surface and preparation and application thereof, belonging to the technical field of solar photo-thermal utilization. The photothermal evaporation surface is a substrate surface attached with an array type porous microstructure which is periodically arranged, and the porous microstructure is a coffee annular structure formed by accumulating nanoparticles; specifically, a micro-droplet generator is utilized to periodically arrange nano-fluid droplets on the surface of a substrate in an array manner, and the droplets are heated to be evaporated to dryness, so that an array type periodically arranged coffee annular porous microstructure is formed on the surface of the substrate. The photo-thermal evaporation surface provided by the invention has high photo-thermal conversion efficiency, can be repeatedly used, has very small dosage of nano fluid required for preparing the high-efficiency photo-thermal evaporation surface and low cost, and is beneficial to industrial application.

Description

Photo-thermal evaporation surface and preparation and application thereof

Technical Field

The invention belongs to the technical field of solar photo-thermal utilization, and particularly relates to a photo-thermal evaporation surface and preparation and application thereof.

Background

The evaporation process is visible everywhere in daily life, and is widely applied to the fields of ship power, power generation, seawater desalination, chemical production and the like. The existing technologies for absorbing solar energy to generate steam mainly comprise integral absorption of nano fluid, surface absorption of high-efficiency solar photo-thermal conversion film, spectrum selective absorption film and the like. However, in these absorption methods, the bulk absorption of the nanofluid has the disadvantages of high consumption of nanoparticles and high cost, and is not suitable for large-scale industrial application; the efficient solar photo-thermal conversion film takes a porous material as a framework, photo-thermal conversion nano particles are attached to the surface of the porous material, and the problems of unstable performance and more dependence on the matching between the porous material and the nano particles exist; the spectral selective absorption film is the most widely used material, but can only be coated on the outer surface of the material, and liquid is heated by means of heat conduction of the material, so that heat loss is large and efficiency is low.

Disclosure of Invention

The invention aims to provide a photothermal evaporation surface and preparation and application thereof, and the specific technical scheme is as follows:

the photothermal evaporation surface is characterized in that an array type porous microstructure periodically arranged is attached to the surface of a substrate, and the porous microstructure is a coffee annular structure formed by accumulating nanoparticles.

The substrate material is glass, a silicon wafer, organic glass or metal; among them, the glass is preferably quartz glass.

The nano particles are one or a composite material consisting of a plurality of metal, metal oxide and non-metal inorganic particles.

The substrate material has a hydrophobic surface and the nanoparticles have a hydrophilic surface.

The preparation method of the photo-thermal evaporation surface comprises the steps of utilizing a micro-droplet generator to array nano-fluid droplets on the surface of a substrate periodically, heating the nano-fluid droplets to evaporate the droplets to dryness, and forming an array type periodically-arranged annular coffee porous microstructure on the surface of the substrate.

The surface of the substrate needs to be polished to ensure that the roughness of the surface of the substrate is submicron; the surface of the substrate is cleaned before use: and ultrasonically cleaning the substrate by using acetone, alcohol and deionized water in sequence, blow-drying the substrate by using nitrogen, and repeating the cleaning process for 3-4 times to ensure that no organic dirt is attached to the surface of the substrate.

Preferably, the acetone is analytically pure and the alcohol is preferably absolute ethanol.

The nano fluid is a colloidal solution containing nano particles; specifically, a micro-droplet generator is used for generating nano-fluid droplets with a certain volume, and the nano-fluid droplets are periodically attached to the surface of a substrate in an array mode according to a certain rule.

Further, the nanofluids are prepared using a "one-step" or "two-step" process: the 'one-step method' is that a chemical synthesis method is adopted to prepare colloidal solution containing nano particles at one time; the "two-step process" refers to dispersing the nanoparticles in a suitable solvent and stabilizing the colloidal solution by ultrasonic dispersion and addition of an active agent.

Further, the volume of the nano-fluid drop generated by the micro-drop generator is determined by the concentration of the nano-fluid, the diameter of a contact circle and the size of a contact angle.

Furthermore, the array type periodic arrangement is a radial arrangement, a concentric circle arrangement, a checkerboard arrangement or a regular hexagon arrangement; the distance between adjacent nano fluid droplets is larger than or equal to the diameter of a contact surface between the nano fluid droplets and the surface of the substrate, so that the droplets are prevented from polymerizing.

Specifically, the droplet is evaporated by heating the surface of the substrate attached with the array-type periodically arranged droplets by illumination or heating the substrate. Radial flow is generated inside the liquid drops in the evaporation process, and the nanoparticles are accumulated at the contact line under the action of the radial flow to form a coffee annular porous microstructure; after the droplets are evaporated to dryness, the porous microstructure of the coffee ring will remain on the substrate surface and just absorb all the incident solar energy.

Further, the porous microstructure absorbs solar energy by one or more of intrinsic absorption, plasmon resonance effect, or multiple scattering absorption.

Further, light heating means: the substrate surface on which the liquid droplets are placed is placed in the irradiation range of a light source such as sunlight, a solar simulator or an infrared radiation lamp, and the liquid droplets are evaporated to dryness by absorbing radiation energy.

Further, substrate heating means: the surface of the substrate on which the droplets are placed is placed on a hot plate and the droplets are evaporated to dryness using heat conducted by the substrate.

The photo-thermal evaporation surface is applied to solar photo-thermal utilization, a clear water film is attached to the photo-thermal evaporation surface and automatically breaks to form a liquid drop array, under the irradiation of sunlight, nano particles accumulated on the surface of a substrate absorb solar energy to heat liquid drops, and liquid in the liquid drops is converted into vapor, so that the solar photo-thermal generation of steam is realized.

The photothermal evaporation surface is applied to seawater desalination, a seawater film is attached to the photothermal evaporation surface, the seawater film automatically breaks to form a seawater droplet array, and liquid in the seawater droplets is converted into vapor by heating, so that the seawater desalination is realized.

The photothermal evaporation surface is applied to sewage treatment, a layer of sewage film is attached to the photothermal evaporation surface, the sewage film automatically breaks to form a sewage droplet array, and liquid in the sewage droplets is converted into vapor by heating, so that sewage treatment is realized.

The photothermal evaporation surface is heated by solar light, electric heating or radiation heating and the like in the application process of seawater desalination and sewage treatment.

The heating mode is solar light irradiation, and the seawater desalination and sewage treatment are realized by using solar light heat.

The arrangement mode of the liquid drop array formed by the automatic breaking of the clear water film, the seawater film and the sewage film is the same as that of the porous microstructure on the surface of the substrate.

During the evaporation period of the heat absorbed by the liquid drops, clean water, seawater or sewage is continuously supplemented on the surface of the substrate, and the solar photo-thermal steam generation, seawater desalination or sewage treatment is continuously realized.

The preparation and the working principle of the photo-thermal evaporation surface of the invention are as follows: the micro-droplet generator is used for placing a plurality of nano-fluid droplets with a certain volume on the surface of a clean substrate according to a certain rule, in the process of heating the substrate or heating by solar radiation, the radial flow in the droplets can carry nano-particles to move to a droplet contact line, after the droplets are dried by distillation, the nano-particles can be stacked at the contact line to form a 'coffee ring' pattern, the pattern is a porous microstructure formed by stacking the nano-particles, the particles are in close contact with each other and are coupled with incident solar energy, and the photo-thermal conversion efficiency is enhanced. A layer of clear water film is attached to the surface of a substrate, and because the region with accumulated particles shows hydrophilicity and the region without accumulated particles shows hydrophobicity, the clear water film can automatically break to form a small droplet array under the action of different wettability, and the form of the droplet array is the same as that of a nano fluid droplet array during surface preparation. Then, the substrate is placed under the irradiation of sunlight, the nano particles accumulated on the surface of the substrate interact with solar energy, the solar energy is converted into heat energy to heat the liquid drops, and the liquid drops absorb the heat to evaporate. During the evaporation period, clear water, seawater or sewage is continuously supplemented on the surface of the substrate, the clear water, the seawater or the sewage is converted into clean steam, and the aims of solar photo-thermal steam generation, seawater desalination or sewage treatment are continuously and efficiently achieved.

The invention has the beneficial effects that:

(1) the invention skillfully combines the coffee ring effect and the characteristic that the nano particles efficiently absorb solar energy, the nano particles in the liquid drop are tightly self-assembled on the surface of the substrate, the distance between the particles is reduced, and the efficient photo-thermal evaporation surface is obtained.

(2) Compared with the traditional solar heating evaporation surface, the photo-thermal evaporation surface provided by the invention can ensure that large-scale array liquid drops are formed, the liquid drops formed on the surface can effectively increase the area of a gas-liquid interface, and the photo-thermal steam generation efficiency is improved; on the other hand, the nanoparticles attached to the surface of the substrate can efficiently absorb solar energy, and liquid drops are heated to be converted into water vapor, so that efficient and continuous photo-thermal steam generation is realized, the photo-thermal conversion efficiency is high, and the method has wide application prospects in the fields of seawater desalination, sewage treatment, solar energy utilization and the like.

(3) The photo-thermal evaporation surface provided by the invention has the advantages of reliable and stable structure, strong adaptability and reusability, and the dosage of the nano fluid required for preparing the high-efficiency photo-thermal evaporation surface is very small, so that the highest steam gas production efficiency can be obtained by using the least amount of nano particles; saving material, low cost and being beneficial to industrial application.

Drawings

FIG. 1 is a flow chart of the photothermal evaporation surface preparation of the present invention;

FIG. 2 is a schematic view of the photothermal evaporation surface structure of the present invention;

FIG. 3 is a schematic diagram of the principle of the photothermal evaporation surface of the present invention applied to solar photothermal utilization;

description of reference numerals: 1-a substrate; 2-cleaning fluid; 3-a micro-droplet generator; 4-nanofluids; 5-a nanofluid droplet; 6-solar simulator; 7-nanoparticles; 8-radial flow inside the droplet; 9- "coffee ring" like porous microstructure; 10-photothermal evaporation surface; 3 11 3- 3 " 3 coffee 3 ring 3" 3 shaped 3 porous 3 microstructure 3 A 3- 3 A 3 section 3; 3 12-clear water.

FIG. 4 is a graph showing the change in the evaporation volume of a single drop of clear water on the photo-thermal evaporation surface of the present invention versus the evaporation volume of the single drop of clear water on a common surface under solar illumination.

Detailed Description

The invention provides a photothermal evaporation surface and preparation and application thereof, and the invention is further described by combining the drawings and an embodiment.

The photo-thermal evaporation surface preparation flow chart shown in the attached figure 1 mainly comprises three steps: (1) cleaning the surface of the substrate; (2) the nano-fluid droplets are arranged on the surface of the substrate in a periodic array manner; (3) the droplets are evaporated to dryness by heating.

The specific operation of the substrate surface cleaning treatment in step (1) is shown in FIGS. 1-a and 1-b. In fig. 1-a, a substrate 1 is immersed in a cleaning liquid 2, and a cleaning treatment is performed on the surface of the substrate 1 in an ultrasonic cleaning machine; the cleaning solution 2 is acetone, absolute ethyl alcohol and deionized water respectively; organic dirt on the surface of the substrate 1 can be removed by utilizing good solubility of organic solvents such as acetone and absolute ethyl alcohol to organic matters and combining ultrasonic oscillation; then, the acetone and the absolute ethyl alcohol remaining on the surface of the substrate 1 are removed by using deionized water. Finally, the surface of the substrate 1 is blown dry with high purity nitrogen gas as shown in FIG. 1-b.

The specific operation of periodically arranging nano-fluid droplets and attaching the nano-fluid droplets to the surface of the substrate in the step (2) is shown in fig. 1-c. The nano fluid 4 is filled in the micro-droplet generator 3, and nano particles dispersed in the nano fluid are one or a composite material consisting of a plurality of metal, metal oxide or non-metal inorganic particles. A volumetric amount of nano-fluidic droplets 5 are generated by a micro-droplet generator 3 and placed on the surface of the substrate 1 in a periodic array arrangement to form an array of nano-fluidic droplets, as shown in fig. 1-c.

The periodic array arrangement of the nano fluid droplets 5 can be in a periodic form such as radial arrangement, concentric circle arrangement, checkerboard arrangement, regular hexagon arrangement and the like, and the distance between adjacent nano fluid droplets 5 is not less than the diameter of the contact surface between the nano fluid droplets 5 and the surface of the substrate 1, so that the droplets are prevented from being polymerized.

The heating in the step (3) to evaporate the liquid drops to dryness is shown in figures 1-d and 1-e; placing the substrate attached with the nano-fluid droplets 5 arranged in a periodic array manner obtained in the step (2) under a solar simulator 6 for irradiation, as shown in 1-d; the nanoparticles 7 in the nanofluid droplets 5 absorb solar energy, converting photothermal to thermal energy to heat the surrounding liquid, and the liquid in the droplets is evaporated to steam, during which evaporation the radial flow 8 inside the droplets carries the nanoparticles 7 towards the contact line, where they are finally deposited, as shown in fig. 1-e.

FIG. 2 is a schematic view of the photothermal evaporation surface structure obtained by the preparation process shown in FIG. 1. After the nano fluid droplets 5 are evaporated to dryness, a coffee ring-shaped porous microstructure 9 formed by accumulating nano particles is left on the surface of the substrate 1, and a patterned efficient photothermal evaporation surface 10 with nano particle adhesion is formed; wherein the distribution of the porous microstructure 9 in the shape of a "coffee ring" on the surface of the substrate is shown in detail in figure 2-a. The top view of the substrate surface nanoparticle microstructure is shown in fig. 2-c, and the porous microstructures 9 in the shape of "coffee ring" are arranged on the substrate surface in a periodic array.

3 3 3 fig. 3 3 3 2 3 3 3- 3 3 3 b 3 3 3 is 3 3 3 a 3 3 3 sectional 3 3 3 view 3 3 3 a 3 3 3- 3 3 3 a 3 3 3 of 3 3 3 the 3 3 3 " 3 3 3 coffee 3 3 3 ring 3 3 3" 3 3 3 shaped 3 3 3 structure 3 3 3 9 3 3 3 formed 3 3 3 by 3 3 3 the 3 3 3 nanoparticles 3 3 3 stacked 3 3 3 in 3 3 3 fig. 3 3 3 2 3 3 3- 3 3 3 a 3 3 3, 3 3 3 specifically 3 3 3, 3 3 3 see 3 3 3 the 3 3 3 section 3 3 3 a 3 3 3- 3 3 3 a 3 3 3 of 3 3 3 the 3 3 3 " 3 3 3 coffee 3 3 3 ring 3 3 3" 3 3 3 shaped 3 3 3 porous 3 3 3 microstructure 3 3 3 11 3 3 3, 3 3 3 and 3 3 3 it 3 3 3 can 3 3 3 be 3 3 3 seen 3 3 3 that 3 3 3 the 3 3 3 nanoparticles 3 3 3 in 3 3 3 the 3 3 3 " 3 3 3 coffee 3 3 3 ring 3 3 3" 3 3 3 shaped 3 3 3 porous 3 3 3 microstructure 3 3 3 9 3 3 3 are 3 3 3 in 3 3 3 close 3 3 3 contact 3 3 3. 3 3 3

Fig. 2-d is a scanning electron microscope image of the "coffee ring" shaped porous microstructure 9, and it can be seen from the microstructure of the "coffee ring" shaped porous microstructure 9 shown in fig. 2-d that the "coffee ring" shaped porous microstructure 9 is formed by stacking nanoparticles.

FIG. 3 is a schematic diagram of the principle of the photothermal evaporation surface of the present invention applied to solar photothermal utilization. Wherein: the photothermal evaporation surface obtained by the manufacturing process shown in fig. 1 is immersed in clean water 12, or covered with a water film, as shown in fig. 3-a. Under the action of surface energy, the clear water forms droplets at the positions where the nanoparticles are deposited by itself, as shown in fig. 3-b. Placing the high-efficiency photothermal evaporation surface with the attached liquid drop under the irradiation of sunlight, and generating heat to heat the liquid drop due to the interaction between the nanoparticles and the incident light because the nanoparticles exist at the contact line, as shown in fig. 3-c; the liquid drops are evaporated and converted into water vapor, and after evaporation is finished, a water film can be continuously covered on the liquid drops to form liquid drop array evaporation, so that solar photo-thermal steam generation is continuously realized.

FIG. 4 is a change curve of the solar irradiation evaporation volume of a single clear water droplet on a photothermal evaporation surface with only one porous microstructure and a common surface. The photothermal evaporation surface substrate material is quartz glass, the concentration of gold nanofluid used for forming the porous microstructure is 10 mu g/mL, the volume of liquid drops generated by the micro-liquid drop generator is 2 mu L, the contact angle of the liquid drops on the substrate surface is 81 degrees, and the diameter of a contact surface is 2.1 millimeters; the photothermal evaporation surface has only one porous microstructure. The common surface substrate material is quartz glass without any surface modification treatment. The heating mode is solar illumination.

Example 1

A highly efficient photothermal evaporation surface was prepared according to the following method:

the substrate surface was made of quartz glass, 200 mm long, 200 mm wide and 2 mm thick. And polishing the surface of the quartz glass, wherein the surface roughness is in a submicron level. And sequentially cleaning the glass substrate by using acetone, absolute ethyl alcohol and deionized water in an ultrasonic cleaning machine to remove organic dirt on the surface, and drying the glass substrate by using nitrogen for later use.

The nanofluid is gold nanofluid with the concentration of 10 mu g/mL, and the diameter of gold nanoparticles is 18 nanometers. The nano-fluid is loaded into the micro-droplet generator and fixed on the coordinate table, and the coordinate table is moved by the controller, thereby generating droplets at the designated positions. The volume of the liquid drop generated by the micro-liquid drop generator is 2 muL, the contact angle of the liquid drop on the surface of the substrate is 81 degrees, and the diameter of the contact surface is 2.1 millimeters. The droplets were placed in a square grid array with a spacing of 4 mm.

Placing the substrate with the attached liquid drops under a solar simulator, wherein the irradiation intensity of the solar simulator is 1kW/m². After the liquid drops on the surface of the substrate are evaporated to dryness, yellow coffee annular patterns can be observed on the surface, and the coffee annular patterns are porous microstructures formed by accumulating the nanoparticles; thus obtaining the high-efficiency photo-thermal evaporation surface.

The prepared efficient photothermal evaporation surface is immersed in clear water, then the clear water is taken out, liquid drops are formed in a nanoparticle deposition area by the clear water, the nanoparticles absorb solar photothermal conversion under the irradiation of solar energy, the clear water liquid drops are heated for evaporation, and efficient solar energy generation of steam is achieved.

Claims

1. The photothermal evaporation surface is characterized in that an array type periodically arranged porous microstructure is attached to the surface of a substrate, and the porous microstructure is a coffee annular structure formed by accumulating nanoparticles;

2. The photothermal evaporation surface of claim 1 wherein said substrate material is glass, silicon wafer, plexiglass or metal; the nano particles are one or a composite material consisting of a plurality of metal, metal oxide and non-metal inorganic particles.

3. A method for preparing the photothermal evaporation surface according to claim 1 or 2, wherein the microfluidic droplets are periodically arranged on the surface of the substrate in an array form by using a micro droplet generator, and the droplets are evaporated by heating, so that the coffee annular porous microstructure periodically arranged in an array form is formed on the surface of the substrate.

4. The method of claim 3, wherein the nanofluid is a colloidal solution containing nanoparticles.

5. The production method according to claim 3, wherein the substrate surface roughness is in a submicron order; the surface of the substrate is cleaned before use: the method comprises the steps of sequentially ultrasonically cleaning the glass substrate by using acetone, alcohol and deionized water, and blow-drying the glass substrate by using nitrogen.

6. The method of claim 3, wherein the arrayed periodic arrangement is a radial arrangement, a concentric circle arrangement, a checkerboard arrangement, or a regular hexagonal arrangement; the distance between the adjacent nano fluid droplets is larger than or equal to the diameter of the contact surface between the nano fluid droplets and the surface of the substrate.

7. The application of the photothermal evaporation surface of claim 1 or 2 in solar photothermal utilization, wherein a clear water film is attached to the photothermal evaporation surface, the clear water film automatically breaks to form a droplet array, under the irradiation of sunlight, nanoparticles accumulated on the substrate surface absorb solar energy to heat droplets, and the liquid in the droplets is converted into water vapor, so that solar photothermal steam generation is realized.

8. The use of the photothermal evaporation surface of claim 1 or 2 for desalination of sea water, wherein a sea water film is attached to the photothermal evaporation surface, the sea water film automatically breaks to form an array of sea water droplets, and heating is performed to convert liquid in the sea water droplets into steam, thereby desalinating sea water.

9. Use of the photothermal evaporation surface according to claim 1 or 2 for wastewater treatment, wherein a wastewater membrane is attached to the photothermal evaporation surface, the wastewater membrane automatically breaks to form an array of wastewater droplets, and heating is performed to convert liquid in the wastewater droplets into steam, thereby performing wastewater treatment.