阅读说明：本技术 一种光催化-光热膜蒸馏用复合膜的制备方法 (Preparation method of composite membrane for photocatalysis-photothermal membrane distillation ) 是由 康卫民 刘梦瑶 王春艳 鞠敬鸽 黄宇婷 胡伟 史佳丽 于 2021-08-27 设计创作，主要内容包括：本发明提供了一种光催化-光热膜蒸馏用复合膜的制备方法,所述制备方法包括以下步骤：(1)复合光热光催化剂的制备；(2)疏水纳米纤维膜的制备；(3)喷涂法制备光催化-光热层。制备氧化石墨烯/银/氧化铈复合光热光催化剂,将其通过喷涂法固定在纳米纤维膜表面,膜作为催化剂载体,集成了膜的选择透过性、光热转化性能和催化剂的催化活性,使复合膜兼具分离、光热和反应三重功能,同时解决了粉体催化剂难回收的问题。复合膜在光催化-光热膜蒸馏测试中表现出良好的稳定性、较高的可见光催化活性和高效优异的分离效果。本发明所述的制备光催化-光热膜蒸馏用复合膜的方法,所需装置简单、可重复性高,在水处理领域具有广阔的应有前景。(The invention provides a preparation method of a composite membrane for photocatalysis-photothermal membrane distillation, which comprises the following steps: (1) preparing a composite photo-thermal photocatalyst; (2) preparing a hydrophobic nanofiber membrane; (3) the spray coating method is used for preparing the photocatalysis-photothermal layer. The graphene oxide/silver/cerium oxide composite photo-thermal photocatalyst is prepared and fixed on the surface of a nanofiber membrane by a spraying method, and the membrane is used as a catalyst carrier, so that the selective permeability, photo-thermal conversion performance and catalytic activity of the catalyst of the membrane are integrated, the composite membrane has the triple functions of separation, photo-thermal and reaction, and the problem that the powder catalyst is difficult to recover is solved. The composite membrane shows good stability, higher visible light catalytic activity and high-efficiency excellent separation effect in a photocatalysis-photothermal membrane distillation test. The method for preparing the composite membrane for photocatalysis-photothermal membrane distillation, disclosed by the invention, has the advantages of simple required device, high repeatability and wide application prospect in the field of water treatment.)

1. A preparation method of a composite membrane for photocatalysis-photothermal membrane distillation is characterized by comprising the following steps:

(1) preparing a composite photo-thermal photocatalyst: dissolving cerous nitrate and urea in distilled water according to a certain proportion, pouring into a reaction kettle, carrying out hydrothermal reaction at a certain temperature, washing the product with ethanol, and drying in vacuum to obtain cerium oxide (CeO)₂) And (3) nanoparticles. Weighing a certain amount of Graphene Oxide (GO) and dispersing the graphene oxide into distilled water, adding a certain amount of silver nitrate, stirring the mixture at room temperature for 1-2 h, adding sodium citrate powder, placing the mixture in a water bath at 80-100 ℃ for reaction for 3-6 h, cooling to room temperature, centrifuging the product, washing with distilled water, and freeze-drying to obtain the GO @ Ag nano composite material; mixing the CeO2 nano particles and the GO @ Ag nano composite material according to a certain proportion to prepare the composite photo-thermal photocatalyst.

(2) Preparing a hydrophobic nanofiber membrane: adding a certain amount of polyvinylidene fluoride (PVDF) powder into an N, N-dimethylformamide solvent, heating to 50-60 ℃, continuously stirring and dissolving for 2-6 hours to obtain a PVDF spinning solution, and performing electrostatic spinning on the spinning solution by using an electrostatic spinning technology to obtain the PVDF hydrophobic nanofiber membrane.

(3) Preparing a photocatalytic-photothermal layer by a spraying method: dispersing the composite photo-thermal photocatalyst obtained in the step (1) in a polyvinyl alcohol (PVA) solution, carrying out ultrasonic treatment for 3-6 h, pouring the mixed solution into a spray gun, spraying the mixed solution on the hydrophobic nanofiber membrane prepared in the step (1), drying the membrane by using an air blower, coating the membrane again, adjusting the thickness of the coating according to the spraying frequency, and finally heating the membrane at 150-180 ℃ for 1-2 h to crosslink the PVA to prepare the composite membrane for photo-catalytic-photo-thermal membrane distillation.

2. The preparation method according to claim 1, wherein in the step (1), the molar ratio of the cerium nitrate to the urea is 1: 18-22, the hydrothermal reaction temperature is 140-180 ℃, and the reaction time is 2-18h, the content of graphene oxide is 0.2-0.8 mg/ml, the content of silver nitrate is 2.3-2.8 mg/ml, the content of sodium citrate is 2-5 mg/ml, and CeO₂The mixing mass ratio of the nano particles to the GO @ Ag nano composite material is (1-3) to 1.

3. The preparation method according to claim 1, wherein the mass fraction of the polyvinylidene fluoride PVDF in the step (2) is 10-22%, the electrostatic spinning parameter voltage is 15-25 kV, the receiving distance is 15-20 cm, and the spinning speed is 0.5-1.0 mL/h.

4. The preparation method of claim 1, wherein in the step (3), the mass fraction of the PVA solution is 0.75-2%, the content of the composite photothermal photocatalyst is 10-30 mg/ml, the spraying distance is 10-20 cm, the air pressure is maintained at 0.2-0.6 MPa, the spraying time is 2-4 s, and the spraying frequency is 1-4 times.

Technical Field

The invention belongs to the technical field of application of a photocatalysis-photothermal membrane distillation system, and particularly relates to a preparation method of a composite membrane for photocatalysis-photothermal membrane distillation.

Background

The rapid development of the dye manufacturing and textile industries has led to the discharge of large amounts of organic dyes into the water, seriously jeopardizing the aquatic environment and human health. The printing and dyeing wastewater has the characteristics of large chromaticity, high temperature, high chemical oxygen demand, poor biodegradability and the like, and the removal of the dye is a challenge to wastewater treatment facilities. The photocatalysis method is a new method for efficiently treating printing and dyeing wastewater in recent years, utilizes a light source to degrade pollutants, has mild reaction conditions, no secondary pollutants, no toxicity, low energy consumption and low operation cost in the photocatalysis process. But the intermediate products generated by the photocatalytic degradation and some ions cannot be removed at all, and some harmfulness still exists. The development of photocatalysts has limited the development of photocatalytic technology, and most of the common photocatalysts are semiconductors, including oxides, sulfides, phosphides, and metal-free photocatalysts. Wherein cerium oxide (CeO)₂) As a rare earth oxide which is relatively cheap and has extremely wide application, the rare earth oxide is an important photocatalytic material due to the advantages of excellent oxygen storage and release capacity, no toxicity, no secondary pollution and the like. But CeO₂The problems of wide band gap, low utilization rate of visible light, wave band which can only absorb ultraviolet light, easy recombination of photo-generated electron hole pairs and the like exist. In order to improve the photocatalytic efficiency of the material, noble metals and ions are generally adoptedThe method of doping the sub-elements or compounding the sub-elements with other semiconductor materials is used for expanding the light absorption range of the materials and effectively inhibiting the recombination of photo-generated electrons and holes. The capacity loss and difficult recycling of the catalyst caused by difficult recovery of the photocatalytic nanoparticles are also problems which need to be solved urgently.

Another technique in water treatment is membrane separation. The membrane separation technology has the advantages of simplicity, modular design, easy maintenance and good rejection rate in the water treatment process. The membrane distillation technology takes a high-porosity hydrophobic membrane as a separation medium, takes the temperature difference between two sides of the membrane as a driving force, and enables clean water to enter a cold side from a hot polluted side through three steps of evaporation, transfer and condensation, so that the membrane separation technology for purifying waste water and producing clean water is realized. In the photo-thermal membrane distillation process reported in recent years, the surface temperature of the membrane is increased by the surface photo-thermal conversion layer under the assistance of light so as to provide a heat source mass transfer driving force and further reduce the energy consumption of the membrane distillation process. Photothermal membrane distillation is a complete physical process and does not involve degradation of contaminants.

By combining photothermal membrane distillation and photocatalysis, the synergistic effect of the two can be shown. The photocatalyst can effectively degrade pollutants deposited on the surface of the membrane and effectively relieve membrane pollution, the membrane can fix the photocatalyst, so that the photocatalyst can be fully contacted with the pollutants, the effect of degrading the pollutants is achieved, the high-efficiency separation of clean water and the pollutants is realized, and the research field of the water treatment technology is effectively widened by the technology.

Aiming at the problems, the invention combines the photocatalysis-photothermal membrane distillation technology to develop the composite membrane for photocatalysis-photothermal membrane distillation, prepares the composite photothermal photocatalyst by preparing the graphene oxide/silver/cerium oxide, enlarges the CeO by the plasma resonance effect on the surface of the noble metal and the full spectrum absorption characteristic of the graphene oxide₂The light absorption range of the catalyst and the effective inhibition of the recombination of photo-generated electrons and holes to ensure that CeO₂The photocatalytic activity is improved. The composite photo-thermal photocatalyst is fixed on the surface of the nanofiber membrane by a simple spraying method, and a separation membrane is utilizedAs a carrier for catalyst immobilization, the membrane integrates the selective permeability, the photothermal conversion performance and the catalytic activity of a catalyst, so that the membrane has the functions of photothermal, reaction and separation, and simultaneously, the temperature difference generated on two sides of the membrane is used as a driving force by utilizing solar energy, so that a product can be separated from a reaction system. The membrane can realize continuous operation, the dispersibility, the stability and the reusability of the catalyst are improved, the photocatalyst can effectively degrade pollutants deposited on the surface of the membrane, the membrane pollution is effectively relieved, the reinforcement of a reaction-separation coupling process is realized, and the membrane has very wide application prospect in the field of water treatment.

Disclosure of Invention

The invention provides a preparation method of a composite membrane for photocatalysis-photothermal membrane distillation, which is characterized in that a graphene oxide/silver/cerium oxide composite photothermal photocatalyst is prepared and fixed on the surface of a nanofiber membrane by a simple spraying method, and the composite membrane for photocatalysis-photothermal membrane distillation is developed and used for water treatment.

A preparation method of a composite membrane for photocatalysis-photothermal membrane distillation comprises the following steps:

(1) preparing a composite photo-thermal photocatalyst: dissolving cerous nitrate and urea in distilled water according to a certain proportion, pouring into a reaction kettle, carrying out hydrothermal reaction at a certain temperature, washing the product with ethanol, and drying in vacuum to obtain cerium oxide (CeO)₂) And (3) nanoparticles. Weighing a certain amount of Graphene Oxide (GO) and dispersing the graphene oxide into distilled water, adding a certain amount of silver nitrate, stirring the mixture at room temperature for 1-2 h, adding sodium citrate powder, placing the mixture in a water bath at 80-100 ℃ for reaction for 3-6 h, cooling to room temperature, centrifuging the product, washing with distilled water, and freeze-drying to obtain the GO @ Ag nano composite material; adding CeO₂The nano particles and the GO @ Ag nano composite material are mixed according to a certain proportion to prepare the composite photo-thermal photocatalyst.

(2) Preparing a hydrophobic nanofiber membrane: adding a certain amount of polyvinylidene fluoride (PVDF) powder into an N, N-dimethylformamide solvent, heating to 50-60 ℃, continuously stirring and dissolving for 2-6 hours to obtain a PVDF spinning solution, and performing electrostatic spinning on the spinning solution by using an electrostatic spinning technology to obtain the PVDF hydrophobic nanofiber membrane.

(3) Preparing a photocatalytic-photothermal layer by a spraying method: dispersing the composite photo-thermal photocatalyst obtained in the step (1) in a polyvinyl alcohol (PVA) solution, carrying out ultrasonic treatment for 3-6 h, pouring the mixed solution into a spray gun, spraying the mixed solution on the hydrophobic nanofiber membrane prepared in the step (1), drying the membrane by using an air blower, coating the membrane again, adjusting the thickness of the coating according to the spraying frequency, and finally heating the membrane at 150-180 ℃ for 1-2 h to crosslink the PVA to prepare the composite membrane for photo-catalytic-photo-thermal membrane distillation.

Preferably, the molar ratio of the cerium nitrate to the urea in the step (1) is 1: 18-22.

Preferably, the hydrothermal reaction temperature in the step (1) is 140-180 ℃, and the reaction time is 2-18 h.

Preferably, in the step (1), the content of the graphene oxide is 0.2-0.8 mg/ml, the content of silver nitrate is 2.3-2.8 mg/ml, and the content of sodium citrate is 2-5 mg/ml.

Preferably, the CeO in the step (1)₂The mixing mass ratio of the nano particles to the GO @ Ag nano composite material is (1-3) to 1.

Preferably, the mass fraction of the polyvinylidene fluoride PVDF in the step (2) is 10-22%.

Preferably, the electrostatic spinning parameter voltage in the step (2) is 15-25 kV, the receiving distance is 15-20 cm, and the spinning speed is 0.5-1.0 mL/h.

Preferably, the PVA solution in the step (3) has a mass fraction of 0.75-2% and the content of the composite photo-thermal photocatalyst is 10-30 mg/ml.

Preferably, in the step (3), in the spraying process, the spraying distance is 10-20 cm, the air pressure is kept at 0.2-0.6 Mpa, the spraying time is 2-4 s, and the spraying frequency is 1-4 times.

Compared with the prior art, the invention has the following advantages and outstanding effects: (1) the photocatalysis-photothermal membrane distillation is combined, the selective permeability, photothermal conversion performance and catalytic activity of a catalyst of the membrane are integrated, the membrane has the functions of photothermal, reaction and separation, and meanwhile, the temperature difference generated on the two sides of the membrane is used as a driving force by utilizing solar energy, so that a product can be obtained from a reaction bodyThe system is separated, and the energy consumption problem of water treatment is further solved. (2) The photocatalyst is fixed on the surface of the membrane by adopting a spraying method, and can effectively degrade pollutants deposited on the surface of the membrane, effectively relieve membrane pollution, ensure that the photocatalyst can be fully contacted with the pollutants, achieve the effect of degrading the pollutants, realize the efficient separation of clean water and the pollutants, and the process has inherent simplicity and is easy to operate. (3) The composite photo-thermal photocatalyst is simple and feasible to prepare, safe and efficient, and enlarges CeO₂The catalyst has light absorption range, and can inhibit the recombination of photo-generated electrons and holes effectively to raise the photocatalytic activity. The composite membrane has good photocatalytic performance and photothermal conversion performance, good hydrophobicity and stability, can be repeatedly utilized, and solves the problem that the powder catalyst is difficult to recover. The method for preparing the composite membrane for photocatalysis-photothermal membrane distillation, disclosed by the invention, has the advantages of simple required device, high repeatability and wide application prospect in the aspect of water treatment.

Drawings

FIG. 1 is a flow chart of the preparation of the composite membrane for photocatalytic-photothermal membrane distillation according to the present invention.

FIG. 2 shows CeO prepared by the method of example 1₂Electron microscopy of nanoparticles.

FIG. 3 is an electron micrograph of GO @ Ag nanocomposite prepared using example 1 of the present invention.

FIG. 4 is an electron micrograph of a PVDF nanofiber membrane prepared by using example 1 of the present invention.

Detailed Description

The present invention will be further described with reference to the following specific examples.

Example 1

(1) Preparing a composite photo-thermal photocatalyst: dissolving cerous nitrate and urea in distilled water at a molar ratio of 1: 18, pouring into a reaction kettle, performing hydrothermal reaction at 160 deg.C for 10 hr, washing the product with ethanol, and vacuum drying to obtain cerium oxide (CeO)₂) And (3) nanoparticles. Weighing 0.5g of Graphene Oxide (GO) and dispersing into 1L of distilled water, adding 2.5g of silver nitrate, stirring the mixture at room temperature for 1h, adding 3g of sodium citrate powder, and placing the mixture in a water bath at 90 ℃ for reactionCooling to room temperature for 4h, centrifuging the product, washing with distilled water, and freeze-drying to obtain the GO @ Ag nanocomposite; adding CeO₂Mixing the nano particles and the GO @ Ag nano composite material according to the proportion of 1: 1 to prepare the composite photo-thermal photocatalyst. FIG. 2 shows CeO prepared by the method of example 1₂An electron microscope image of the nanoparticles, and fig. 3 is an electron microscope image of the GO @ Ag nanocomposite prepared by using example 1 of the present invention.

(2) Preparing a hydrophobic nanofiber membrane: weighing 1g of polyvinylidene fluoride (PVDF) powder, slowly adding the PVDF powder into 9g of N, N-dimethylformamide solvent, heating to 50 ℃, continuously stirring and dissolving for 3 hours until the solution is clear and transparent to obtain 10% PVDF spinning solution, and performing electrostatic spinning on the spinning solution by using an electrostatic spinning technology to obtain the PVDF hydrophobic nanofiber membrane. FIG. 4 is an electron micrograph of a PVDF nanofiber membrane prepared by using example 1 of the present invention.

(3) Preparing a photocatalytic-photothermal layer by a spraying method: weighing 2g of the composite photothermal photocatalyst obtained in the step (1) and dispersing in 100ml of 1% PVA solution, carrying out ultrasonic treatment until the solution is uniformly dispersed, pouring the mixed solution into a spray gun, spraying the mixed solution on the hydrophobic nanofiber membrane prepared in the step (1), drying the membrane by using an air blower, coating the membrane again, keeping the spraying distance at 15cm, keeping the air pressure at 0.4MPa, spraying the membrane for 3s, spraying the membrane for 3 times, and finally heating the membrane at 180 ℃ for 2 hours to crosslink the PVA to prepare the composite membrane for photocatalytic-photothermal membrane distillation.

(4) Photocatalytic-photothermal membrane distillation test: the photo-thermal membrane distillation performance of the prepared membrane is tested by a direct contact type membrane distillation system consisting of a solar simulator, a glass mold, an electronic balance, a conductivity meter, a peristaltic pump and a constant temperature water tank. The temperatures of the permeate and feed were maintained at 20 ℃ throughout with a constant temperature water tank. The feed liquid and the penetrating fluid are circulated by a peristaltic pump, the constant flow is 0.25L/min, and the feed liquid is a mixed liquid consisting of 3.5 wt% of NaCl and 10mg/L of rhodamine B in percentage by mass. Setting the illumination intensity to be 1kW/m²Test area 2X 2cm². . The conductivity change of the permeate as well as the permeate flux change were recorded by the membrane distillation software as measured by a conductivity meter and balance. Measuring initial feeding liquid and photocatalytic degradation by ultraviolet-visible spectrophotometerAnd (5) solving the absorbance of the feed liquid, and measuring the temperature change of the surface of the membrane by using an infrared thermal imager. The permeate flux J is calculated by the weight change of the permeate and is calculated from the following equation:

J＝ΔM/(ΔT×S)

in the formula: j is the flux (kg/m)²h) Δ M permeate weight gain (kg), Δ T run time (h), S Membrane effective area (cm)²)

The salt cut-off rate R is calculated from the conductivity of the permeate and is calculated from the following formula:

R＝[(C_f-C_p)/C_f]×100％

in the formula: r Retention, C_fConcentration of feed solution (g/L), C_pConcentration of permeate (g/L). The solution concentration can be calculated from the conductivity based on a linear relationship between conductivity and concentration.

The degradation rate D is calculated by absorbance and is calculated by the following formula:

D＝(1-A₀/A)×100％

in the formula: a. the₀In order to degrade the absorbance of the feed liquid before degradation, A is the absorbance of the feed liquid after photocatalytic degradation for a certain time.

The prepared composite membrane for the photocatalysis-photothermal membrane distillation has the advantages that the surface temperature of the membrane can reach 59.4 ℃ after 100s illumination under the condition of simulating one sun illumination, and the permeation flux can reach 0.96kg/m after the photocatalysis-photothermal membrane distillation test for 8 hours²h, the retention rate is stabilized to be more than 99.9 percent, the degradation rate of the brine containing rhodamine B dye can reach 95.1 percent, and after the brine containing rhodamine B dye is repeatedly used for 5 times, the good structure and the good photocatalytic performance are still maintained.

Example 2

(1) Preparing a composite photo-thermal photocatalyst: dissolving cerous nitrate and urea in distilled water at a molar ratio of 1: 18, pouring into a reaction kettle, performing hydrothermal reaction at 160 deg.C for 10 hr, washing the product with ethanol, and vacuum drying to obtain cerium oxide (CeO)₂) And (3) nanoparticles. Weighing 0.5g of Graphene Oxide (GO) and dispersing into 1L of distilled water, adding 2.5g of silver nitrate, stirring the mixture at room temperature for 1h, adding 3g of sodium citrate powder, placing in a water bath at 90 ℃ for reaction for 4h,cooling to room temperature, centrifuging the product, washing with distilled water, and freeze-drying to obtain the GO @ Ag nanocomposite; adding CeO₂Mixing the nano particles and the GO @ Ag nano composite material according to the ratio of 2: 1 to prepare the composite photo-thermal photocatalyst.

(2) The same as in example 1.

(3) The same as in example 1.

(4) The same as in example 1.

The prepared composite membrane for the photocatalysis-photothermal membrane distillation has the advantages that under the condition of simulating one solar illumination, the surface temperature of the membrane can reach 58.3 ℃ after the membrane is illuminated for 100s, the permeation flux can reach 0.88kg/m < 2 > 2h after the photocatalysis-photothermal membrane distillation test is carried out for 8h, the retention rate is stable to be more than 99.9%, the degradation rate of the rhodamine B dye-containing brine can reach 97.3%, and the composite membrane still keeps good structure and photocatalysis performance after being repeatedly used for 5 times.

Example 3

(1) Preparing a composite photo-thermal photocatalyst: dissolving cerous nitrate and urea in distilled water at a molar ratio of 1: 18, pouring into a reaction kettle, performing hydrothermal reaction at 160 deg.C for 10 hr, washing the product with ethanol, and vacuum drying to obtain cerium oxide (CeO)₂) And (3) nanoparticles. Weighing 0.5g of Graphene Oxide (GO) and dispersing into 1L of distilled water, adding 2.5g of silver nitrate, stirring the mixture at room temperature for 1h, adding 3g of sodium citrate powder, placing in a water bath at 90 ℃ for reaction for 4h, cooling to room temperature, centrifuging the product, washing with distilled water, and freeze-drying to obtain the GO @ Ag nano composite material; adding CeO₂Mixing the nano particles and the GO @ Ag nano composite material according to the ratio of 3: 1 to prepare the composite photo-thermal photocatalyst.

(2) The same as in example 1.

(3) The same as in example 1.

(4) The same as in example 1.

The prepared composite membrane for the photocatalysis-photothermal membrane distillation has the advantages that under the condition of simulating one solar illumination, the surface temperature of the membrane can reach 55.8 ℃ after the membrane is illuminated for 100s, the permeation flux can reach 0.63kg/m < 2 > 2h after the photocatalysis-photothermal membrane distillation test is carried out for 8h, the retention rate is stable to be more than 99.9%, the degradation rate of the rhodamine B dye-containing brine can reach 98%, and the composite membrane still keeps good structure and photocatalysis performance after being repeatedly used for 5 times.