Photocatalytic porous skeleton for microalgae carbon sequestration as well as preparation method and application of photocatalytic porous skeleton

Abstract

The invention belongs to the technical field of CO2 capture and utilization, and particularly relates to a photocatalytic porous skeleton for microalgae carbon sequestration and a preparation method and application thereof. The photocatalytic porous skeleton comprises a porous skeleton, and a carbon black layer, a carbon nanotube layer and a photocatalyst layer which are sequentially arranged on the porous skeleton, the porous framework is made of polyurethane sponge; the photocatalyst is g-C3N4 / TiO2 (titanium dioxide). The photocatalytic porous skeleton prepared by the invention can obviously enhance the carbon sequestration effect of photosynthesis of microalgae, can double the CO2 removal rate of a column type microalgae photobioreactor with the capacity of 100L, and can convert captured CO2 into organic matters.

Description

Technical Field

[0001] The present invention belongs to CO 2 The field of capture and utilization technology specifically relates to a photocatalytic porous skeleton for microalgae carbon fixation and a preparation method and application thereof. Background Art

[0002] The exploitation and utilization of fossil energy leads to the increase of CO 2 The concentration continues to rise, and the resulting greenhouse effect will bring about global warming, environmental problems such as greenhouse gas emissions, and greenhouse gas emissions. In the long run, using microalgae photosynthesis to convert CO 2 Converted into organic substances such as glucose, protein, carbohydrates and lipids, while releasing O 2 , is an economically feasible and environmentally sustainable carbon sequestration technology.

[0003] At present, microalgae carbon fixation technology has been used to fix high concentrations of CO with a concentration of 10-20% v / v in flue gas from power plants and cement plants. 2 Compared with the centralized emission of high concentration CO 2 , low concentrations of CO below 1% v / v in confined spaces or direct air 2 The capture scenarios are more abundant and dispersed, and the available CO 2 Therefore, the development of low concentration CO 2 Microalgae capture technology can effectively complement centralized carbon fixation and has broad application prospects.

[0004] However, when microalgae capture low concentrations of CO 2 When the mass transfer gradient is small, it is difficult for the microalgae to effectively absorb enough carbon source from the environment for photosynthesis, resulting in a significant decrease in the growth and carbon fixation efficiency of the microalgae. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a photocatalytic porous skeleton for microalgae carbon fixation and a preparation method and application thereof. 3 N 4 / TiO 2 Carbon black and carbon nanotubes are used as photocatalyst carriers to ensure the generation and transmission of photogenerated electrons, inhibit the recombination of photogenerated electrons and holes, and enhance the photocatalytic reduction of CO in complex microalgae suspensions. 2 performance; using polyurethane sponge as a porous skeleton for loading photocatalysts, and attaching photocatalysts to the surface of the porous skeleton to form a photocatalytic porous skeleton, which is used in the process of microalgae carbon fixation; it can effectively prevent microalgae cells from forming clusters with nanoparticles as the core, thereby avoiding long-term close contact between the photocatalyst and some microalgae cells, resulting in damage and destruction of the cell structure, affecting the normal growth and carbon fixation efficiency of the microalgae.

[0006] The first object of the present invention is to provide a photocatalytic porous skeleton for microalgae carbon fixation, wherein the photocatalytic porous skeleton comprises a porous skeleton, a carbon black layer, a carbon nanotube layer and a photocatalyst layer are sequentially arranged on the porous skeleton.

[0007] It should be noted that the present invention is to capture CO by photocatalytic reduction based on microalgae photosynthesis with the help of photocatalysts. 2 Therefore, the photocatalyst selected in the present invention needs to ensure that it still has the photocatalytic reduction of CO in the microalgae suspension. 2 The performance of the photocatalyst is good, and the presence of the photocatalyst does not affect the normal growth of microalgae cells in the microalgae suspension. 3 N 4 / TiO 2 It has the advantages of stable physical and chemical properties, low toxicity, low cost and easy synthesis. 3 N 4 / TiO 2 It can be excited by visible light, and under the irradiation of visible light, water and carbon dioxide are synthesized into organic substances such as formic acid and acetic acid, and oxygen is released, which has the basis for coordinated operation with microalgae photosynthesis; preferably, the photocatalyst is gC 3 N 4 / TiO 2 .

[0008] Since the prior art has been 3 N 4 / TiO 2 The research is limited to the photocatalytic reduction of CO under laboratory conditions. 2 , and the catalytic environment used was Na 2 SO 4 , NaOH and Na 2 CO 3 In addition, the present invention explores gC 3 N 4 / TiO 2 Low concentrations of CO in complex microalgae suspensions 2 The photocatalytic properties of the algae were studied to obtain a photocatalytic porous skeleton that synergizes with microalgae cells for the treatment of low-concentration CO in confined spaces or direct air. 2 Preferably, the gC 3 N 4 Content is TiO 2 4% to 6%.

[0009] It should also be noted that if the photocatalyst is directly mixed with the microalgae suspension, the microalgae cells in the microalgae suspension will form clusters in the microalgae suspension with the nanoparticles of the photocatalyst as the core, inhibiting the light collection of the microalgae cells; in addition, the nanoparticles of the photocatalyst will be in close contact with some microalgae cells for a long time, and the hydroxyl radicals and reactive oxygen free radicals produced by them will destroy the structure of the microalgae cells in the microalgae suspension, thereby affecting the photosynthesis of the microalgae cells. The present invention attaches the photocatalyst to the surface of the porous skeleton, which can effectively prevent the microalgae cells from forming clusters with the nanoparticles of the photocatalyst as the core, thereby avoiding damage and destruction of the cell structure caused by the long-term close contact between the photocatalyst and some microalgae cells. Polyurethane sponge is cheap and easy to obtain, has stable physical and chemical properties and is lightweight, and is a widely used porous material; preferably, the porous skeleton is a polyurethane sponge.

[0010] In addition, in order to improve the photocatalytic reduction of CO 2 The present invention uses carbon black and carbon nanotubes as gC 3 N 4 / TiO 2 carrier to ensure the generation and transmission of photogenerated electrons, inhibit the recombination of photogenerated electrons and holes, and improve gC 3 N 4 / TiO 2 Low concentrations of CO in complex microalgae suspensions 2 Photocatalytic reduction of CO 2 performance, thus achieving low concentration CO in confined space or direct air 2 Distributed biological efficient removal.

[0011] The second object of the present invention is to provide a method for preparing the above-mentioned photocatalytic porous framework, comprising the following steps:

[0012] Step 1: Preparation of gC 3 N 4 / TiO 2 : In gC 3 N 4 and TiO 2 As raw material, gC 3 N 4 and TiO 2 Ultrasonic dispersion to obtain gC 3 N 4 / TiO 2 .

[0013] It should be noted that gC 3 N 4 / TiO 2 The specific preparation process of the photocatalyst is as follows: 2Under the atmosphere, melamine is heated at 500℃~600℃ for 1h~2h to obtain gC 3 N 4 ; gC 3 N 4 Add to the solvent and ultrasonicate for 30min to 60min to completely disperse it to obtain gC 3 N 4 Solution; TiO 2 Powder dispersed in gC 3 N 4 The solution was stirred for 24 h to obtain gC 3 N 4 / TiO 2 Solution; gC 3 N 4 / TiO 2 The solution was centrifuged at a speed of 8000 r / min to 10000 r / min and vacuum dried at 100 °C for 24 h to obtain gC 3 N 4 / TiO 2 Photocatalyst.

[0014] Preferably, the solvent is one of methanol and ethanol.

[0015] Step 2, preparing three slurries: using carbon black as a carrier, using Nafion solution and sodium dodecylbenzene sulfonate as adhesives, mixing carbon black, Nafion solution, sodium dodecylbenzene sulfonate and a solvent to obtain a carbon black slurry.

[0016] The carbon nanotubes are used as carriers, Nafion solution and sodium dodecylbenzene sulfonate are used as adhesives, and the carbon nanotubes, Nafion solution, sodium dodecylbenzene sulfonate and solvent are mixed to obtain carbon nanotube slurry.

[0017] G C 3 N 4 / TiO 2 , Nafion solution and solvent are mixed to obtain photocatalyst slurry.

[0018] It should be noted that the carbon black slurry of the present invention uses carbon black as a carrier, Nafion solution and sodium dodecylbenzene sulfonate as adhesives. Since carbon black is conductive and has large particle size, it can form a rough conductive coating after being attached to the surface of the polyurethane sponge. As a carbon black slurry, it can assist and strengthen the adhesion of carbon nanotube slurry and photocatalyst slurry, and improve the overall stability and durability of the coating; at the same time, Nafion solution can not only improve the adhesion of carbon black slurry, but also has conductivity, and is a suitable adhesive. In the carbon nanotube slurry, carbon nanotubes are used as carriers. The conductivity of carbon nanotubes is better than that of carbon black, and the fine texture can promote gC 3 N4 / TiO 2 Photocatalysts separate photogenerated electrons and holes. In addition, photocatalysts need to be in direct contact with light, so the photocatalyst slurry is mainly composed of photocatalysts, which are attached to the outermost layer of the polyurethane substrate; at the same time, the photocatalyst slurry has good dispersibility and does not need to be modified by adding surfactants.

[0019] Preferably, the usage ratio of carbon black, Nafion solution and sodium dodecylbenzene sulfonate in the carbon black slurry is 1 g: 1.8 mL to 2.2 mL: 0.1 g.

[0020] The usage ratio of the carbon nanotubes, the Nafion solution and the sodium dodecylbenzene sulfonate in the carbon nanotube slurry is 0.5 g: 1.8 mL to 2.2 mL: 0.1 g.

[0021] The photocatalyst slurry contains gC 3 N 4 / TiO 2 The usage ratio of Nafion solution is 0.1g:0.9mL~1.1mL.

[0022] Step 3, preparing a photocatalytic porous skeleton: immersing the pretreated polyurethane sponge in a carbon black slurry for the first slurry coating, so that the carbon black in the carbon black slurry adheres to the polyurethane sponge to form a carbon black layer, thereby obtaining a first porous skeleton.

[0023] The first porous skeleton is immersed in carbon nanotube slurry for a second slurry coating, so that the carbon nanotubes in the carbon nanotube slurry are attached to the first porous skeleton to form a carbon nanotube layer, thereby obtaining a second porous skeleton.

[0024] The second porous framework is immersed in the photocatalyst slurry for the third slurry coating, so that the gC in the photocatalyst slurry 3 N 4 / TiO 2 A photocatalyst layer is formed by attaching to the second porous skeleton to obtain a photocatalytic porous skeleton.

[0025] Preferably, the duration of each slurry hanging is 10 minutes to 20 minutes.

[0026] It should be noted that the present invention needs to be coated with slurry three times. Since the carbon black in the carbon black slurry is conductive and has large particle size, it can form a rough conductive coating after adhering to the surface of the polyurethane sponge; therefore, the pretreated polyurethane sponge is immersed in the carbon black slurry for the first coating, and the first porous skeleton formed can assist and strengthen the adhesion of the carbon nanotube slurry and the photocatalyst slurry, and improve the overall stability and durability of the coating. In addition, the carbon nanotube slurry uses carbon nanotubes with better conductivity than carbon black as carriers, and the first porous skeleton is immersed in the carbon nanotube slurry for coating, and the carbon nanotubes in the second porous skeleton promote gC3 N 4 / TiO 2 Photocatalyst photogenerated electrons and holes are separated. In addition, the photocatalyst needs to be directly exposed to light, and the second porous skeleton is immersed in the photocatalyst slurry for the third slurrying, and the photocatalyst slurry is mainly composed of photocatalyst, so that the photocatalyst in the photocatalyst slurry is attached to the outermost layer of the polyurethane sponge substrate, thereby preparing a photocatalytic porous skeleton.

[0027] In addition, before the polyurethane sponge is coated with slurry, it needs to be pretreated to improve the adhesion of the slurry to the porous skeleton. The pretreatment process of the present invention includes: placing the polyurethane sponge in a concentration of 0.1 mol·L -1 The polyurethane sponge fiber is heated in a sodium hydroxide solution at 80°C to 100°C for 0.5h to 1h. The sodium hydroxide solution can etch the polyurethane sponge fiber to make it serrated, which helps the adhesion of the slurry to the polyurethane sponge fiber.

[0028] The third object of the present invention is to provide the use of the above-mentioned photocatalytic porous framework in microalgae carbon fixation.

[0029] Preferably, the method of using the photocatalytic porous skeleton to fix carbon using microalgae in a microalgae suspension is:

[0030] The photocatalytic porous framework was placed in a microalgae suspension and directly applied to a column photobioreactor. 2 The column photobioreactor was fed from the bottom to promote mixing, and the inlet and outlet CO 2 Volume flow rate to obtain CO 2 removal rate.

[0031] Preferably, the initial concentration of the microalgae suspension is 0.5 g·L -1 , the volume of the microalgae suspension is 100 L, the CO 2 The intake concentration is 0.8% v / v and the intake rate is 5 L min -1 .

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The photocatalytic porous skeleton of the present invention comprises a porous skeleton and a carbon black layer, a carbon nanotube layer and a photocatalyst layer sequentially arranged on the porous skeleton. The present invention uses carbon black and carbon nanotubes as carriers of the photocatalyst; the carbon black is conductive and has large particle size, and the rough carbon black layer formed after being attached to the surface of the polyurethane sponge serves as the first porous skeleton; it can assist and strengthen the adhesion of the second porous skeleton and the third porous skeleton, and improve the overall stability and durability of the photocatalytic porous skeleton. The carbon nanotube layer has better conductivity than carbon black and has a fine texture, and is formed after being attached to the surface of the first porous skeleton, and serves as the second porous skeleton; it can promote the separation of photogenerated electrons and holes in the photocatalyst, and improve the photocatalytic performance of the photocatalyst. The present invention uses gC 3 N 4 / TiO 2 As a photocatalyst, gC 3 N 4 / TiO 2 The photocatalyst layer formed after being attached to the surface of the second porous skeleton is the outermost layer and directly contacts the light for photocatalysis. In addition, the photocatalytic porous skeleton formed by attaching the carbon black layer, the carbon nanotube layer and the photocatalyst layer to the surface of the porous skeleton in sequence is used in the process of microalgae carbon fixation; it can effectively prevent the microalgae cells from forming clusters with nanoparticles as the core, thereby avoiding the long-term close contact between the nanoparticles and some microalgae cells, resulting in damage and destruction of the cell structure. At the same time, the photocatalytic porous skeleton optimizes the flow field distribution through the porous structure to inhibit the aggregation of microalgae. It solves the problem that the direct placement of photocatalysts will cause the aggregation of microalgae cells, thereby affecting the growth of microalgae and the low carbon fixation efficiency.

[0034] The photocatalytic porous skeleton prepared by the present invention can convert low concentration CO into 2 In addition, the photocatalytic porous skeleton prepared by the present invention can significantly enhance the carbon fixation effect of microalgae photosynthesis, and can convert the CO2 of a columnar microalgae photobioreactor with a capacity of 100L into 2 The removal rate is doubled and the captured CO 2 The photocatalytic porous framework has low cost and good stability, and can achieve low-concentration CO in confined space or direct air. 2 Distributed biological efficient removal of CO 2 The capture and utilization fields show great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the appearance picture of the finished photocatalytic porous framework prepared in Example 1 of the present invention.

[0036] Figure 2The microscopic morphology of the photocatalytic porous skeleton prepared in Example 1 of the present invention; wherein, (a) and (b) are the photocatalytic porous skeletons before slurry coating, and (c) and (d) are the photocatalytic porous skeletons after slurry coating.

[0037] Figure 3 The validation curve of the photocatalytic porous skeleton prepared in Example 1 of the present invention in the microalgae suspension; wherein (a) is under air intake conditions, and (b) is 0.8% v / v CO 2 Intake conditions.

[0038] Figure 4 The photocatalytic porous framework prepared in Example 1 of the present invention is used in the photobioreactor for CO 2 Removal rate; where (a) is the CO removal rate without adding photocatalytic porous framework 2 Removal rate, (b) CO added to the photocatalytic porous framework 2 Removal rate. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings.

[0040] In the description of the present invention, unless otherwise specified, all reagents used are commercially available and all methods used are conventional techniques in the art.

[0041] Example 1

[0042] This embodiment provides a method for preparing a photocatalytic porous skeleton for carbon fixation in microalgae.

[0043] Step 1: Preparation of gC 3 N 4 / TiO 2 :

[0044] 1.1) In N 2 In the atmosphere, 5 g of melamine was heated at 550 ° C for 2 h to obtain gC 3 N 4 .

[0045] 1.2) Weigh 0.1g of gC 3 N 4 Add 50 mL of methanol and disperse completely by ultrasonication for 30 min to obtain gC 3 N 4 Solution.

[0046] 1.3) 1.9 g of TiO 2 Add the above gC 3 N 4The solution was stirred for 24 h to obtain gC 3 N 4 / TiO 2 Solution.

[0047] 1.4) gC 3 N 4 / TiO 2 The solution was centrifuged at 8000 r / min and dried under vacuum at 100°C until the methanol was completely evaporated to obtain gC 3 N 4 / TiO 2 .

[0048] Step 2: Prepare three slurries:

[0049] 2.1) Add 1 g of carbon black, 2 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate into 20 mL of anhydrous ethanol and disperse by ultrasonic for 10 min to obtain a carbon black slurry.

[0050] 2.2) 0.5 g of carbon nanotubes, 2 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate were added to 20 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a carbon nanotube slurry.

[0051] 2.3) 0.5g of gC 3 N 4 / TiO 2 The photocatalyst and 5 mL of a 5% Nafion solution were added to 10 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a photocatalyst slurry.

[0052] Step 3: Preparation of photocatalytic porous framework:

[0053] 4.1) Select a polyurethane sponge with a pore density of 60 PPI. The sponge is a cylinder with a bottom diameter of 5 cm and a height of 3 cm. Place the polyurethane sponge in a 0.1 mol·L -1 The mixture was placed in a NaOH solution, heated to 80°C and maintained for 30 min. After being taken out, it was repeatedly rinsed with deionized water and dried at room temperature to obtain a pretreated polyurethane sponge.

[0054] 4.2) Immerse the pretreated polyurethane sponge in the carbon black slurry for the first time for 10 minutes, take out and drain the excess slurry and place it in a vacuum drying oven at 100° C. for 5 hours to obtain a first porous skeleton.

[0055] 4.3) The first porous framework was immersed in the carbon nanotube slurry, and the slurry was hung for 10 minutes for the second time, and dried at 100° C. for 5 hours to obtain a second porous framework.

[0056] 4.4) Immersing the second porous skeleton into the photocatalyst slurry, hanging the slurry for a third time for 10 minutes, and drying at room temperature for 24 hours to obtain a third porous skeleton, namely a photocatalytic porous skeleton.

[0057] Example 2

[0058] This embodiment provides a method for preparing a photocatalytic porous skeleton for carbon fixation in microalgae.

[0059] The difference between this embodiment and embodiment 1 is:

[0060] This embodiment uses a polyurethane sponge with a pore density of 30 PPI.

[0061] Example 3

[0062] This embodiment provides a method for preparing a photocatalytic porous skeleton for carbon fixation in microalgae.

[0063] The difference between this embodiment and embodiment 1 is:

[0064] This embodiment uses a polyurethane sponge with a pore density of 20 PPI.

[0065] Example 4

[0066] This embodiment provides a method for preparing a photocatalytic porous skeleton for carbon fixation in microalgae.

[0067] The difference between this embodiment and embodiment 1 is:

[0068] This embodiment uses a polyurethane sponge with a pore density of 10 PPI.

[0069] Example 5

[0070] This embodiment provides a method for preparing a photocatalytic porous skeleton for carbon fixation in microalgae.

[0071] Step 1: Preparation of gC 3 N 4 / TiO 2 :

[0072] 1.1) In N 2 In the atmosphere, 5 g of melamine was heated at 500 ° C for 2 h to obtain gC 3 N 4 .

[0073] 1.2) Weigh 0.1g of gC 3 N 4 Add 50 mL of methanol and disperse completely by ultrasonication for 30 min to obtain gC 3 N 4 Solution.

[0074] 1.3) 2.5 g of TiO 2 Add the above gC 3 N 4 The solution was stirred for 24 h to obtain gC 3 N 4 / TiO 2 Solution.

[0075] 1.4) gC 3 N 4 / TiO 2 The solution was centrifuged at 8000 r / min and dried under vacuum at 100°C until the methanol was completely evaporated to obtain gC 3 N 4 / TiO 2 .

[0076] Step 2: Prepare three slurries:

[0077] 2.1) Add 1 g of carbon black, 1.8 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate into 20 mL of anhydrous ethanol and disperse by ultrasonic for 10 min to obtain a carbon black slurry.

[0078] 2.2) 0.5 g of carbon nanotubes, 1.8 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate were added to 20 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a carbon nanotube slurry.

[0079] 2.3) 0.5g of gC 3 N 4 / TiO 2 The photocatalyst and 4.5 mL of a 5% Nafion solution were added to 10 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a photocatalyst slurry.

[0080] Step 3: Preparation of photocatalytic porous framework:

[0081] 4.1) Select a polyurethane sponge with a pore density of 60 PPI. The sponge is a cylinder with a bottom diameter of 5 cm and a height of 3 cm. Place the polyurethane sponge in a 0.1 mol·L -1 The mixture was placed in a NaOH solution, heated to 80°C and maintained for 30 min. After being taken out, it was repeatedly rinsed with deionized water and dried at room temperature to obtain a pretreated polyurethane sponge.

[0082] 4.2) Immerse the pretreated polyurethane sponge in the carbon black slurry for the first time for 15 minutes, take out and drain the excess slurry and place it in a vacuum drying oven at 100° C. for 5 hours to obtain the first porous skeleton.

[0083] 4.3) Immerse the first porous framework into the carbon nanotube slurry, dip-coat for the second time for 15 min, and dry at 100 °C for 5 h to obtain the second porous framework.

[0084] 4.4) Immerse the second porous framework into the photocatalyst slurry, dip-coat for the third time for 15 min, and dry at room temperature for 24 h to obtain the photocatalytic porous framework.

[0085] Example 6

[0086] This example provides a method for preparing a photocatalytic porous framework for microalgae carbon fixation.

[0087] Step 1: Prepare g-C 3 N 4 / TiO 2 :

[0088] 1.1) Under N 2 atmosphere, heat 5 g of melamine at a heating temperature of 600 °C for 2 h to obtain g-C 3 N 4 .

[0089] 1.2) Weigh 0.1 g of g-C 3 N 4 and add it to 50 mL of methanol, and ultrasonically disperse for 30 min for complete dispersion to obtain a g-C 3 N 4 solution.

[0090] 1.3) Add 1.6 g of TiO 2 to the above-mentioned g-C 3 N 4 solution, and stir for 24 h to obtain a g-C 3 N 4 / TiO 2 solution.

[0091] 1.4) Centrifuge the g-C 3 N 4 / TiO 2 solution in a centrifuge at a rotational speed of 8000 r / min, and vacuum dry at 100 °C until the methanol completely volatilizes to obtain g-C 3 N 4 / TiO 2 .

[0092] Step 2: Prepare three slurries:

[0093] 2.1) Add 1 g of carbon black, 2.2 mL of a 5% Nafion solution, and 0.1 g of sodium dodecylbenzenesulfonate to 20 mL of absolute ethanol, and ultrasonically disperse for 10 min to obtain a carbon black slurry.

[0094] 2.2) 0.5 g of carbon nanotubes, 2.2 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate were added to 20 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a carbon nanotube slurry.

[0095] 2.3) 0.5g of gC 3 N 4 / TiO 2 The photocatalyst and 5.5 mL of a 5% Nafion solution were added to 10 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a photocatalyst slurry.

[0096] Step 3: Preparation of photocatalytic porous framework:

[0097] 4.1) Select a polyurethane sponge with a pore density of 60 PPI. The sponge is a cylinder with a bottom diameter of 5 cm and a height of 3 cm. Place the polyurethane sponge in a 0.1 mol·L -1 The mixture was placed in a NaOH solution, heated to 80°C and maintained for 30 min. After being taken out, it was repeatedly rinsed with deionized water and dried at room temperature to obtain a pretreated polyurethane sponge.

[0098] 4.2) Immerse the pretreated polyurethane sponge in the carbon black slurry for the first time for 20 minutes, take out and drain the excess slurry and place it in a vacuum drying oven at 100° C. for 5 hours to obtain a first porous skeleton.

[0099] 4.3) The first porous framework was immersed in the carbon nanotube slurry, and the slurry was hung for a second time for 20 minutes, and dried at 100° C. for 5 hours to obtain a second porous framework.

[0100] 4.4) Immersing the second porous skeleton into the photocatalyst slurry, hanging the slurry for a third time for 20 minutes, and drying at room temperature for 24 hours to obtain a photocatalytic porous skeleton.

[0101] Comparative Example 1

[0102] This comparative example provides a method for preparing a photocatalytic porous skeleton for microalgae carbon fixation.

[0103] Step 1: Preparation of gC 3 N 4 / TiO 2 :

[0104] 1.1) In N 2 In the atmosphere, 5 g of melamine was heated at 550 ° C for 2 h to obtain gC 3 N 4 .

[0105] 1.2) Weigh 0.1g of gC 3 N4 Add 50 mL of methanol and disperse completely by ultrasonication for 30 min to obtain gC 3 N 4 Solution.

[0106] 1.3) 1.9 g of TiO 2 Add the above gC 3 N 4 The solution was stirred for 24 h to obtain gC 3 N 4 / TiO 2 Solution.

[0107] 1.4) gC 3 N 4 / TiO 2 The solution was centrifuged at 8000 r / min and dried under vacuum at 100°C until the methanol was completely evaporated to obtain gC 3 N 4 / TiO 2 .

[0108] Step 2: Prepare two slurries:

[0109] 2.1) Add 1 g of carbon black, 2 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate into 20 mL of anhydrous ethanol and disperse by ultrasonic for 10 min to obtain a carbon black slurry.

[0110] 2.2) 0.5 g of carbon nanotubes, 2 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate were added to 20 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a carbon nanotube slurry.

[0111] Step 3: Preparation of photocatalytic porous framework:

[0112] 4.1) Select a polyurethane sponge with a pore density of 60 PPI. The sponge is a cylinder with a bottom diameter of 5 cm and a height of 3 cm. Place the polyurethane sponge in a 0.1 mol·L -1 The mixture was placed in a NaOH solution, heated to 80°C and maintained for 30 min. After being taken out, it was repeatedly rinsed with deionized water and dried at room temperature to obtain a pretreated polyurethane sponge.

[0113] 4.2) Immerse the pretreated polyurethane sponge in the carbon black slurry for the first time for 10 minutes, take out and drain the excess slurry and place it in a vacuum drying oven at 100° C. for 5 hours to obtain a first porous skeleton.

[0114] 4.3) The first porous framework was immersed in the carbon nanotube slurry, and the slurry was hung for 10 minutes for the second time, and dried at 100° C. for 5 hours to obtain a second porous framework.

[0115] The difference between this comparative example and Example 1 is:

[0116] In this comparative example, no photocatalyst slurry was prepared, and the porous skeleton was not immersed in the photocatalyst slurry.

[0117] Comparative Example 2

[0118] This comparative example provides a method for preparing a photocatalytic porous skeleton for microalgae carbon fixation.

[0119] Step 1: Preparation of gC 3 N 4 / TiO 2 :

[0120] 1.1) In N 2 In the atmosphere, 5 g of melamine was heated at 550 ° C for 2 h to obtain gC 3 N 4 .

[0121] 1.2) Weigh 0.1g of gC 3 N 4 Add 50 mL of methanol and disperse completely by ultrasonication for 30 min to obtain gC 3 N 4 Solution.

[0122] 1.3) 1.9 g of TiO 2 Add the above gC 3 N 4 The solution was stirred for 24 h to obtain gC 3 N 4 / TiO 2 Solution.

[0123] 1.4) gC 3 N 4 / TiO 2 The solution was centrifuged at 8000 r / min and dried under vacuum at 100°C until the methanol was completely evaporated to obtain gC 3 N 4 / TiO 2 .

[0124] Step 2: Prepare two slurries:

[0125] 2.1) Add 1 g of carbon black, 2 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate into 20 mL of anhydrous ethanol and disperse by ultrasonic for 10 min to obtain a carbon black slurry.

[0126] 2.2) 0.5g of gC3 N 4 / TiO 2 The photocatalyst and 5 mL of a 5% Nafion solution were added to 10 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a photocatalyst slurry.

[0127] Step 3: Preparation of photocatalytic porous framework:

[0128] 4.1) Select a polyurethane sponge with a pore density of 60 PPI. The sponge is a cylinder with a bottom diameter of 5 cm and a height of 3 cm. Place the polyurethane sponge in a 0.1 mol·L -1 The mixture was placed in a NaOH solution, heated to 80°C and maintained for 30 min. After being taken out, it was repeatedly rinsed with deionized water and dried at room temperature to obtain a pretreated polyurethane sponge.

[0129] 4.2) Immerse the pretreated polyurethane sponge in the carbon black slurry for the first time for 10 minutes, take out and drain the excess slurry and place it in a vacuum drying oven at 100° C. for 5 hours to obtain a first porous skeleton.

[0130] 4.3) The first porous skeleton was immersed in the photocatalyst slurry, and the slurry was hung for a second time for 10 minutes, and dried at 100° C. for 5 hours to obtain a second porous skeleton.

[0131] The difference between this comparative example and Example 1 is:

[0132] In this comparative example, no carbon nanotube slurry was prepared, and the porous skeleton was not immersed in the carbon nanotube slurry.

[0133] Comparative Example 3

[0134] This comparative example provides a method for preparing a photocatalytic porous skeleton for microalgae carbon fixation.

[0135] Step 1: Preparation of gC 3 N 4 / TiO 2 :

[0136] 1.1) In N 2 In the atmosphere, 5 g of melamine was heated at 550 ° C for 2 h to obtain gC 3 N 4 .

[0137] 1.2) Weigh 0.1g of gC 3 N 4 Add 50 mL of methanol and disperse completely by ultrasonication for 30 min to obtain gC 3 N 4 Solution.

[0138] 1.3) 1.9 g of TiO2 Add the above gC 3 N 4 The solution was stirred for 24 h to obtain gC 3 N 4 / TiO 2 Solution.

[0139] 1.4) gC 3 N 4 / TiO 2 The solution was centrifuged at 8000 r / min and dried under vacuum at 100°C until the methanol was completely evaporated to obtain gC 3 N 4 / TiO 2 .

[0140] Step 2: Prepare two slurries:

[0141] 2.1) 0.5 g of carbon nanotubes, 2 mL of 5% Nafion solution and 0.1 g of sodium dodecylbenzene sulfonate were added to 20 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a carbon nanotube slurry.

[0142] 2.2) 0.5g of gC 3 N 4 / TiO 2 The photocatalyst and 5 mL of a 5% Nafion solution were added to 10 mL of anhydrous ethanol and ultrasonically dispersed for 10 min to obtain a photocatalyst slurry.

[0143] Step 3: Preparation of photocatalytic porous framework:

[0144] 4.1) Select a polyurethane sponge with a pore density of 60 PPI. The sponge is a cylinder with a bottom diameter of 5 cm and a height of 3 cm. Place the polyurethane sponge in a 0.1 mol·L -1 The mixture was placed in a NaOH solution, heated to 80°C and maintained for 30 min. After being taken out, it was repeatedly rinsed with deionized water and dried at room temperature to obtain a pretreated polyurethane sponge.

[0145] 4.2) Immerse the pretreated polyurethane sponge in the carbon nanotube slurry for the first time for 10 minutes, take out and drain the excess slurry and place it in a vacuum drying oven at 100° C. for 5 hours to obtain a first porous skeleton.

[0146] 4.3) The first porous skeleton was immersed in the photocatalyst slurry, and the slurry was hung for a second time for 10 minutes, and dried at 100° C. for 5 hours to obtain a second porous skeleton.

[0147] The difference between this comparative example and Example 1 is:

[0148] In this comparative example, no carbon black slurry was prepared, and the porous skeleton was not immersed in the carbon black slurry.

[0149] Figure 1 This is the appearance of the finished photocatalytic porous framework prepared in Example 1. Figure 1 It can be seen that the photocatalytic slurry is evenly coated on the surface of the polyurethane sponge fiber.

[0150] Experimental testing

[0151] 1. Surface morphology test

[0152] Figure 2 The appearance morphology of the photocatalytic porous framework prepared in Example 1 before and after slurry coating; (a) and (b) are before slurry coating, and (c) and (d) are after slurry coating. Figure 2 (a) and Figure 2 As can be seen from (b) in the figure, after pretreatment with NaOH solution, the edges of the polyurethane sponge fibers are jagged, but the surface is flat and smooth. As can be seen from Figures (c) and (d), after three slurrying, the photocatalytic slurry is evenly coated on the surface of the polyurethane sponge fibers without changing the macroporous structure of the sponge. The porosity of the photocatalytic porous skeleton after slurrying can reach 97%. In addition, the porous structure can optimize the flow field of the microalgae suspension and avoid the aggregation of microalgae cells. The slurrying process did not have any effect on the ductility of the sponge. At the same time, the carbon black and carbon nanotubes in the photocatalytic slurry greatly enhanced the conductivity of the photocatalytic porous skeleton, and its axial conductivity was 2mS cm -1 , the photogenerated electrons are transmitted smoothly, which can ensure the photocatalytic reduction of CO 2 The occurrence of the process.

[0153] 2. Effectiveness test

[0154] In order to investigate the carbon fixation performance of the photocatalytic porous framework under different solution conditions, the present invention sets up 4 groups of experiments, namely: 150mL 50mM phosphate buffer solution, the photocatalytic porous framework of Example 1 placed in 150mL 50mM phosphate buffer solution, 150mL algae solution, and the photocatalytic porous framework of Example 1 placed in 150mL algae solution. The concentration of algae solution is 0.5g·L -1 , the light source is LED light, the light intensity is 8000lx. The air flow rate is 50cc·min -1 The inlet conditions are air and CO 2 The concentrations were 0.04% v / v and 0.8% v / v CO 2. The reaction device is a 200mL volumetric flask, and the mouth of the flask is sealed with a rubber stopper. The air inlet pipe is directly inserted into the porous interior. The chemical oxygen demand of the solution is obtained by testing with a multi-parameter water quality analyzer. The English name of chemical oxygen demand is Chemical Oxygen Demand, abbreviated as COD in English. The COD of the solution in 4 groups of tests is tested every 2 hours, and the measurement is continuous for 12 hours. During the test, the sample to be tested is centrifuged, and the supernatant is taken to test the COD. The experiment was repeated 3 times, and the data are presented as mean ± standard deviation.

[0155] Figure 3 The effectiveness of the photocatalytic porous skeleton prepared in Example 1 in a microalgae suspension was verified; wherein (a) was under air intake conditions, and (b) was 0.8% v / v CO 2 Intake air condition. Figure 3 As can be seen from (a) in the figure, under air intake conditions, that is, CO 2 When the concentration was 0.04% v / v, after adding the photocatalytic skeleton into the phosphate buffer solution, the chemical oxygen demand in the phosphate buffer solution increased from 4.67±0.24 mg·L -1 Increased to 8.18±0.41mg·L -1 After adding the photocatalytic skeleton into the microalgae suspension, the chemical oxygen demand in the microalgae suspension increased from 4.72±0.26mg·L -1 Increased to 17.54±1.37mg·L -1 .from Figure 4 As can be seen from (b), at 0.8% v / vCO 2 Under the condition of air inlet, the chemical oxygen demand yield of the photocatalytic porous framework in phosphate buffer solution and microalgae suspension reached 1.61 mg L -1 ·h -1 and 1.86 mg·L -1 ·h -1 This indicates that the photocatalytic porous skeleton prepared by the present invention can effectively capture low-concentration CO in both phosphate buffer solution and microalgae suspension. 2 and convert it into organic matter.

[0156] 3.CO 2 Removal rate test

[0157] The photocatalytic porous frameworks prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were directly applied to a columnar photobioreactor. The full name of the columnar photobioreactor is Photobioreactor, or PBR for short. The bottom diameter of the columnar PBR is 40 cm and the height is 80 cm. The material is resin glass. When the PBR is running, the algae liquid volume is 60 L and the intake air is CO 2 and air mixture, CO 2The volume flow rate percentage is in the range of 0.65-0.85% v / v, and the air intake rate is 5L·min -1 .CO 2 Inlet and outlet CO 2 The volume flow rate was measured by a gas flow meter. The reactor was sealed with a rubber ring and screws, and had good airtightness. The light source was an internal and external LED light strip. During the experiment, the light intensity at the reactor wall was about 8000 lx. The light-dark cycle was 12h:12h. The algae species was Chlorella vulgaris, with an initial concentration of 0.5 g·L -1 The temperature is controlled at 25±2℃. The carbon fixation rate of PBR can be determined by CO 2 Removal rate is expressed as CO 2 Removal rate refers to the inlet and outlet CO 2 The ratio of the volume ratio difference to the inlet volume ratio reflects the carbon fixation capacity of PBR.

[0158] Figure 4 The photocatalytic porous framework prepared in Example 1 was used for CO 2 Removal rate; where (a) is the CO removal rate without adding photocatalytic porous framework 2 Removal rate, (b) CO added to the photocatalytic porous framework 2 Removal rate. Figure 4 As can be seen from (a) in the figure, when no photocatalytic porous framework is added, CO 2 The removal rate is 12%. After adding 6 pieces of photocatalytic porous frameworks, Figure 4 As shown in (b), CO 2 The removal rate of CO can be increased to 22%. 2 The removal rates were 21% and 20% respectively.

[0159] Compared with Example 1, the CO of the photocatalytic porous framework prepared in Examples 2 to 4 is 2 The removal rates were 15%, 15%, and 13%, respectively. Since the pore sizes of the polyurethane sponges used in Examples 2 to 4 were 30 PPI, 20 PPI, and 10 PPI, respectively, as the pore size decreased, the CO removal rate of the photocatalytic porous skeleton increased. 2 The removal rate is weakened. The preferred pore size of the polyurethane sponge of the present invention is 60 PPI. This shows that the photocatalytic porous skeleton prepared by the present invention has a good effect on low concentration CO 2 The microalgae suspension has a certain carbon fixation capacity, which proves the feasibility of the present invention.

[0160] CO of the photocatalytic porous framework prepared in Comparative Examples 1 to 3 2The removal rates were 12%, 13% and 13% respectively; since the porous skeleton prepared in Comparative Example 1 was not immersed in the photocatalytic slurry, the porous skeleton in Comparative Example 1 was only attached with a carbon black layer and a carbon nanotube layer, and only the carbon fixation effect of the microalgae was achieved. 2 The removal rate was only 12%; the porous framework prepared in Comparative Example 2 was not immersed in the carbon nanotube slurry, and only the carbon black in the carbon black slurry was used as the carrier of the photocatalyst, gC 3 N 4 / TiO 2 The photocatalytic carbon fixation effect of 2 The removal rate was 13%; the porous framework prepared in Comparative Example 3 was not immersed in the carbon black slurry, and only the carbon black in the carbon nanotube slurry was used as a carrier of the photocatalyst, gC 3 N 4 / TiO 2 The photocatalytic carbon fixation effect of 2 The removal rate is 13%, and the adhesion of the porous skeleton is poor. This shows that the present invention prepares carbon black slurry, carbon nanotube slurry and photocatalyst slurry, and sequentially coats the slurry to form a carbon black layer, a carbon nanotube layer and a photocatalyst layer on the porous skeleton in sequence; effectively inhibits the aggregation of microalgae, and at the same time, can significantly enhance the carbon fixation effect of microalgae photosynthesis.

[0161] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, once those skilled in the art know the basic creative concept, they can make other changes and modifications to these embodiments, and these changes and modifications all fall within the scope of the present invention.

[0162] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. If these modifications and variations of the present invention fall within the scope of the equivalent technology of the present invention, the present invention is also intended to include these modifications and variations.

Claims

1. A photocatalytic porous framework for microalgae carbon fixation, characterized in that: The photocatalytic porous skeleton comprises a porous skeleton and a carbon black layer, a carbon nanotube layer and a photocatalyst layer sequentially arranged on the porous skeleton; The porous skeleton is a polyurethane sponge; The photocatalyst is g-C3N4 / TiO2.

2. The photocatalytic porous framework according to claim 1, characterized in that: The pore density of the polyurethane sponge is 10PPI-60PPI.

3. The photocatalytic porous framework according to claim 1, characterized in that: The g-C3N4 content is 4% to 6% of TiO2.

4. A method for preparing a photocatalytic porous framework according to any one of claims 1 to 3, characterized in that: The following steps are involved: Preparation of g-C3N4 / TiO2: g-C3N4 and TiO2 are used as raw materials, and g-C3N4 and TiO2 are ultrasonically dispersed by co-precipitation method to obtain g-C3N4 / TiO2; Three kinds of slurries were prepared: using carbon black as a carrier, using Nafion solution and sodium dodecylbenzene sulfonate as adhesives, and mixing carbon black, Nafion solution, sodium dodecylbenzene sulfonate and solvent to obtain carbon black slurry; Using carbon nanotubes as carriers, using Nafion solution and sodium dodecylbenzene sulfonate as adhesives, mixing the carbon nanotubes, the Nafion solution, the sodium dodecylbenzene sulfonate and a solvent to obtain a carbon nanotube slurry; mixing g-C3N4 / TiO2, Nafion solution and solvent to obtain photocatalyst slurry; Preparation of a photocatalytic porous skeleton: immersing the pretreated polyurethane sponge in a carbon black slurry for a first slurrying, so that the carbon black slurry adheres to the polyurethane sponge to form a carbon black layer, thereby obtaining a first porous skeleton; Immersing the first porous framework in carbon nanotube slurry for a second slurrying, so that the carbon nanotube slurry adheres to the first porous framework to form a carbon nanotube layer, thereby obtaining a second porous framework; The second porous skeleton is immersed in the photocatalyst slurry for a third slurry coating, so that the g-C3N4 / TiO2 in the photocatalyst slurry adheres to the second porous skeleton to form a photocatalyst layer, thereby obtaining a photocatalytic porous skeleton.

5. The method for preparing a photocatalytic porous framework according to claim 4, characterized in that: The usage ratio of carbon black, Nafion solution and sodium dodecylbenzene sulfonate in the carbon black slurry is 1g:1.8mL-2.2mL:0.1g.

6. The method for preparing a photocatalytic porous framework according to claim 4, characterized in that: The usage ratio of the carbon nanotubes, the Nafion solution and the sodium dodecylbenzene sulfonate in the carbon nanotube slurry is 0.5 g: 1.8 mL to 2.2 mL: 0.1 g.

7. The method for preparing a photocatalytic porous framework according to claim 4, characterized in that: The dosage ratio of g-C3N4 / TiO2 and Nafion solution in the photocatalyst slurry is 0.1g:0.9mL~1.1mL.

8. The method for preparing a photocatalytic porous framework according to claim 4, characterized in that: The time for each slurry hanging is 10 minutes to 20 minutes.

9. Use of the photocatalytic porous framework according to claim 1 in carbon fixation in microalgae.

10. The use according to claim 9, characterized in that: The method for fixing carbon in microalgae in a microalgae suspension by the photocatalytic porous skeleton is as follows: The photocatalytic porous skeleton was placed in a microalgae suspension and directly applied to a column photobioreactor. CO2 was introduced from the bottom of the column photobioreactor to promote mixing, and the CO2 removal rate was obtained by detecting the inlet and outlet CO2 volume flow rates.

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