A red mud-based magnetic photothermal catalyst, a preparation method and application thereof

Abstract

The application relates to a red mud-based magnetic photo-thermal catalyst and a preparation method and application thereof. The preparation method comprises the following steps: mixing red mud powder and a foaming agent solution, placing the mixture in a sealed container, heating and reacting to obtain a porous precursor; ball-milling the porous precursor and a photoactive component to obtain a photoactive component-loaded precursor; and calcining the photoactive component-loaded precursor to obtain the red mud-based magnetic photo-thermal catalyst; the photoactive component comprises any one or a combination of at least two of cerium dioxide nanoparticles, titanium dioxide nanoparticles, bismuth oxide nanoparticles, g-C3N4 or tungsten trioxide nanoparticles; and the foaming agent in the foaming agent solution comprises ammonium bicarbonate and / or urea. The application combines the resource utilization of red mud with the formic acid hydrogen storage technology, realizes the reduction, harmless and high-value utilization of red mud, provides a low-cost and green new way for the industrialization of hydrogen energy, and has important significance.

Description

Technical Field

[0001] This invention relates to the field of high-value utilization technology of solid waste resources, specifically to the resource utilization of red mud, and particularly to a red mud-based magnetic photothermal catalyst, its preparation method, and its application. Background Technology

[0002] Red mud, a large amount of highly alkaline solid waste generated during the aluminum industry, is rich in Fe2O3 (content 20wt%~40wt%), Si, Mg and other usable elements. However, its highly alkaline nature with a pH value as high as 10~13 not only makes it unsuitable for direct use as building materials or soil conditioners, but also causes environmental problems such as soil alkalization and groundwater pollution due to its large-scale stockpiling. It is an environmental problem that the aluminum industry urgently needs to solve.

[0003] CN118598554A discloses a method and system for the resource utilization of large-scale industrial solid waste red mud. The method involves mixing red mud and sulfuric acid residue evenly in a mixer, using the sulfuric acid residue and red mud to perform a neutralization reaction to lower the pH value; then using a peroxide reaction to generate peroxide, which is vaporized in a microwave rotary furnace at a temperature above 657°C. The peroxide is absorbed by a recovery device to generate alkali, which is then used as an industrial raw material; finally, the rotary furnace is heated by electromagnetic induction to produce microcrystalline glass, which is then used as a raw material for cement preparation.

[0004] CN117800678A discloses a red mud-based water-resistant roadbed material and its preparation method using sulfuric acid-modified red mud. The method involves adding concentrated sulfuric acid solution to a solid waste red mud sample, stirring thoroughly, and allowing it to stand naturally to obtain a modified solid waste red mud sample. A solid waste plasticizing water-resistant agent and water are then added to the modified solid waste red mud sample, dispersed evenly, followed by the addition of cement, stirring thoroughly, pressing into shape, and curing to obtain the water-resistant roadbed material. This modification treatment of red mud enables the prepared roadbed material to possess water resistance, preventing the leaching of water-soluble alkalis and metal ions from the red mud, achieving environmental friendliness, and solving the pollution problem of red mud.

[0005] CN117772762A discloses a multiphase flow reactive distillation method for dealkali removal and carbon fixation of large-volume industrial solid waste red mud. The red mud slurry is pumped to the top of a reactive distillation tower, where it comes into countercurrent contact with flue gas through multi-stage through-flow trays and packing. Acidic gases in the flue gas react with alkalis in the slurry in a highly efficient reactive distillation process. The flue gas, after dust removal, carbon removal, and desulfurization, flows out from the top of the reactive distillation tower, while the dealkali-removed and carbon-fixed red mud slurry flows out from the bottom of the tower and is dehydrated of concentrated brine. The dehydrated red mud slurry is then diluted again with some wash brine and pumped to the top of a water washing desalination tower for countercurrent water washing and desalination. The dehydrated red mud slurry flowing out from the bottom of the water washing desalination tower is dehydrated and discharged for resource utilization. The wash brine flowing out from the top of the water washing desalination tower is partially used to dilute the dehydrated red mud slurry, and the remainder is mixed with concentrated brine and sent back to the alumina extraction section.

[0006] Most existing red mud resource utilization technologies require acid washing to neutralize its alkalinity or complex processing steps, which not only increases processing costs but also wastes the potential utilization value of its inherent alkalinity, failing to achieve a positive transformation of red mud characteristics. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a red mud-based magnetic photothermal catalyst, its preparation method, and its application. This invention combines the resource utilization of red mud with formic acid hydrogen storage technology, achieving reduced-volume, harmless, and high-value utilization of red mud while providing a low-cost, green new approach for the industrialization of hydrogen energy, which is of great significance.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a red mud-based magnetic photothermal catalyst, the method comprising: Red mud powder and foaming agent solution are mixed and placed in a sealed container for heating and reaction to obtain a porous precursor. The porous precursor is then ball-milled and mixed with a photoactive component to obtain a photoactive component-supported precursor. The photoactive component-supported precursor is calcined to obtain the red mud-based magnetic photothermal catalyst. The photoactive component includes any one or a combination of at least two of cerium dioxide nanoparticles, titanium dioxide nanoparticles, bismuth oxide nanoparticles, g-C3N4, or tungsten trioxide nanoparticles. The foaming agent in the foaming agent solution includes ammonium bicarbonate and / or urea.

[0009] This invention uses red mud powder as the sole matrix material and ammonium bicarbonate and / or urea as foaming agents. The two are heated and reacted in a sealed container. The CO2 and NH3 bubbles generated by the decomposition of the foaming agent expand and connect within the red mud powder matrix, forming a porous precursor with interconnected channels. This provides pathways for mass transfer of formic acid molecules and contact with basic sites. Simultaneously, the NH3 generated by decomposition creates a stable, weakly alkaline atmosphere in the sealed system, preventing the loss of basic sites in the red mud and ensuring that the red mud-based magnetic photothermal catalyst can provide stable basic active centers for formic acid dehydrogenation without the need for external alkaline additives. Furthermore, the porous precursor… The surface of the red mud powder is uniformly loaded with photoactive components cerium dioxide nanoparticles and / or titanium dioxide nanoparticles. Through calcination, Fe2O3 in the red mud powder is transformed in situ into the Fe3O4 magnetic phase, giving the red mud-based magnetic photothermal catalyst strong magnetism, enabling it to achieve complete solid-liquid separation under an external magnetic field. At the same time, the loaded active components form a tight heterojunction with Fe3O4, stabilizing the catalyst band gap at 2.1 eV~2.4 eV and giving it visible light response characteristics. Thus, it can drive the formic acid dehydrogenation reaction at room temperature and pressure based on the localized surface plasmon resonance (LSPR) photothermal effect, achieving photothermal synergy.

[0010] Preferably, the concentration of the foaming agent solution is 3wt%~5wt%.

[0011] Preferably, the mass of the foaming agent in the foaming agent solution is 2wt% to 6wt% of the mass of the red mud powder.

[0012] Preferably, the temperature of the heating reaction is 80℃~100℃.

[0013] Preferably, the heating reaction time is 1h to 3h.

[0014] Preferably, the mass of the photoactive component is 0.5wt% to 2wt% of the mass of the porous precursor.

[0015] Preferably, the D50 particle size of the photoactive component is 5nm~15nm.

[0016] Preferably, the rotational speed of the ball mill is 300 rpm to 500 rpm.

[0017] Preferably, the ball milling time is 20 min to 60 min.

[0018] Preferably, the calcination is carried out under an inert atmosphere.

[0019] Preferably, the heating rate of the calcination is 2℃ / min to 5℃ / min.

[0020] Preferably, the calcination temperature is 500℃~700℃.

[0021] Preferably, the calcination time is 2h to 4h.

[0022] Preferably, the red mud powder is obtained by drying and crushing Bayer process red mud from the aluminum industry, and then passing it through a 200-400 mesh sieve.

[0023] In a second aspect, the present invention provides a red mud-based magnetic photothermal catalyst, which is prepared by the preparation method described in the first aspect; the band gap of the red mud-based magnetic photothermal catalyst is 2.1 eV to 2.4 eV.

[0024] Thirdly, the present invention provides an application of the red mud-based magnetic photothermal catalyst as described in the second aspect, wherein the red mud-based magnetic photothermal catalyst is used in photothermal synergistic catalysis of formic acid to produce hydrogen.

[0025] Preferably, the method for applying the red mud-based magnetic photothermal catalyst to photothermal synergistic catalysis of formic acid to produce hydrogen includes: The red mud-based magnetic photothermal catalyst and formic acid solution are placed in a sealed container, and nitrogen and / or inert gas are continuously introduced to expel oxygen from the sealed container. A visible light source is turned on to carry out the formic acid hydrogen production reaction. After the formic acid hydrogen production reaction is completed, a magnetic field is applied to separate the solid and liquid. The separated red mud-based magnetic photothermal catalyst is recycled for the next batch of formic acid hydrogen production reaction.

[0026] Preferably, the volume ratio of formic acid to water in the formic acid solution is 1:(0~1).

[0027] Preferably, the solid-liquid ratio of the red mud-based magnetic photothermal catalyst to the formic acid solution is 0.1 g / mL to 0.3 g / mL.

[0028] Preferably, the wavelength of the visible light source is 380nm~780nm.

[0029] Preferably, the power density of the visible light source is 50 mW / cm². 2 ~200mW / cm 2 .

[0030] Preferably, the temperature for the hydrogen production reaction of formic acid is 25°C to 50°C.

[0031] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the intrinsic alkaline sites of red mud as catalytic active centers to achieve highly selective dehydrogenation of formic acid without the addition of external alkaline aids. Simultaneously, by constructing a magnetic-photocoupled photothermal synergistic catalytic system, it eliminates the dependence on high-temperature and high-pressure reaction conditions, achieving stable dehydrogenation of formic acid to hydrogen production under visible light irradiation at ambient temperature and pressure (25℃~50℃, atmospheric pressure), significantly reducing hydrogen production energy consumption and meeting the core requirements of safe hydrogen supply scenarios. Furthermore, by utilizing the intrinsic iron-rich properties of red mud, the red mud-based magnetic photothermal catalyst is magnetic, easy to separate, and can be recycled and reused. Attached Figure Description

[0032] Figure 1 This is a diagram showing the phase composition of the red mud used in the embodiments of the present invention.

[0033] Figure 2 This is a diagram showing the effect of separating the red mud-based magnetic photothermal catalyst from the reaction products under an external magnetic field in Application Example 1. Detailed Implementation

[0034] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the preparation examples and / or application examples are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0035] The scope of this invention can be defined by lower and upper limits. The selected lower and upper limits define the boundaries of a specific range. The range defined in this way can be defined by the inclusion or exclusion of endpoints. Any endpoint can be independently selected for inclusion or exclusion, and all lower and upper limits can be arbitrarily combined to form new ranges. That is, any lower limit can be combined with any upper limit to form an effective range. For example, if the ranges of 60~120 and 80~110 are listed for specific parameters, it should be understood that the ranges of 60~110 and 80~120 also fall within the scope of this invention. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are also listed, then all ranges of 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5 fall within the scope of this invention. In this invention, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any integer among 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0036] In this invention, "a combination of at least two" refers to a quantity greater than or equal to 2 unless otherwise specified. For example, "any one or a combination of at least two" means that any one of the listed items can be selected, or a combination of at least two of the listed items formed in a manner that does not conflict and enables the implementation of this invention. In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" means a set consisting of A, B, and combinations of A and B, where "containing A and / or B" can be understood, depending on the context of the statement, as containing A, containing B, or simultaneously containing both A and B. In this invention, "optional" means that the corresponding feature, component, step or solution is not necessary, that is, it is selected from either "with" or "without". If there are multiple "optional" limitations in a technical solution, unless otherwise specified and there is no technical conflict or mutual constraint, each "optional" limitation is independent and does not affect the others.

[0037] In this invention, technical features or solutions described using open-ended terms such as "comprising" or "including" do not exclude additional non-conflicting elements beyond the listed elements unless otherwise specified. They are considered to disclose both closed features or solutions consisting solely of the listed elements and open-ended features or solutions that may include additional non-conflicting elements beyond the listed elements. For example, if A includes a1, a2, and a3, unless otherwise specified, this means that A can consist only of a1, a2, and a3, or it can include other non-conflicting elements based on a1, a2, and a3. This corresponds to the disclosure of technical solutions such as "A consists of a1, a2, and a3," "A is selected from a1, a2, and a3," and "A not only includes a1, a2, and a3, but may also include other non-conflicting elements." All embodiments and optional embodiments of this invention, unless otherwise specified and without technical conflict, can be combined to form new technical solutions, and such combinations fall within the scope of this invention. The phrase "preparation example and / or application example" mentioned in this invention means that a specific feature, structure, or characteristic described in conjunction with a preparation example and / or application example may be included in at least one preparation example and / or application example or embodiment of the invention. The appearance of this phrase in various locations in the specification does not necessarily refer to the same preparation example and / or application example, nor is it an independent or alternative preparation example and / or application example mutually exclusive with other preparation examples and / or application examples. Those skilled in the art can explicitly and implicitly understand that the preparation examples and / or application examples described in this invention can be combined with other preparation examples and / or application examples that do not conflict with the technology. The ordinal numbers "first," "second," "third," and "fourth" used in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect" in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0038] In this invention, the order in which the steps are written in the methods described in the preparation examples and / or application examples does not imply a strict execution order. The actual execution order of each step should be determined based on its function and possible internal logic. Unless otherwise specified, all steps of this invention can be executed in the order they are written or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0039] In the field of formic acid dehydrogenation technology, whether it is a homogeneous catalytic system or a heterogeneous catalytic system, in order to improve the dehydrogenation activity, it is necessary to add 0.5 to 2 equivalents of organic / inorganic base additives such as triethylamine, sodium formate, and NaOH. The addition of alkali not only significantly increases the cost of raw materials, but also aggravates the corrosion of reaction equipment, increases the difficulty of product separation and purification, and the alkaline waste liquid generated is prone to secondary pollution, which completely violates the core positioning of green and clean hydrogen energy.

[0040] This invention combines the resource utilization of red mud with formic acid hydrogen storage technology. By utilizing the intrinsic alkaline sites of red mud as catalytic active centers, it achieves highly selective dehydrogenation of formic acid without the addition of external alkaline aids. While utilizing red mud in a reduced, harmless, and high-value manner, it provides a low-cost and green new approach for the industrialization of hydrogen energy, which is of great significance.

[0041] In one specific embodiment, the present invention provides a method for preparing a red mud-based magnetic photothermal catalyst, the method comprising: Red mud powder and foaming agent solution are mixed and placed in a sealed container for heating and reaction to obtain a porous precursor. The porous precursor is then ball-milled and mixed with a photoactive component to obtain a photoactive component-supported precursor. The photoactive component-supported precursor is calcined to obtain the red mud-based magnetic photothermal catalyst. The photoactive component includes any one or a combination of at least two of cerium dioxide nanoparticles, titanium dioxide nanoparticles, bismuth oxide nanoparticles, g-C3N4, or tungsten trioxide nanoparticles. The foaming agent in the foaming agent solution includes ammonium bicarbonate and / or urea.

[0042] This invention uses red mud powder as the sole matrix material and ammonium bicarbonate and / or urea as foaming agents. The two are heated and reacted in a sealed container. The CO2 and NH3 bubbles generated by the decomposition of the foaming agent expand and connect within the red mud powder matrix, forming a porous precursor with interconnected channels. This provides pathways for mass transfer of formic acid molecules and contact with basic sites. Simultaneously, the NH3 generated by decomposition creates a stable, weakly alkaline atmosphere in the sealed system, preventing the loss of basic sites in the red mud and ensuring that the red mud-based magnetic photothermal catalyst can provide stable basic active centers for formic acid dehydrogenation without the need for external alkaline additives. Furthermore, the porous precursor… The surface of the red mud powder is uniformly loaded with photoactive components cerium dioxide nanoparticles and / or titanium dioxide nanoparticles. Through calcination, Fe2O3 in the red mud powder is transformed in situ into the Fe3O4 magnetic phase, giving the red mud-based magnetic photothermal catalyst strong magnetism, enabling it to achieve complete solid-liquid separation under an external magnetic field. At the same time, the loaded active components form a tight heterojunction with Fe3O4, stabilizing the catalyst band gap at 2.1 eV~2.4 eV and giving it visible light response characteristics. Thus, it can drive the formic acid dehydrogenation reaction at room temperature and pressure based on the localized surface plasmon resonance (LSPR) photothermal effect, achieving photothermal synergy.

[0043] In this invention, the sealed container may be, for example, a reaction vessel, and the mixing method of red mud powder and sodium bicarbonate aqueous solution includes stirring and / or ultrasonic dispersion.

[0044] By adjusting the concentration of the foaming agent solution, the temperature and time of the heating reaction, the pore size of the interconnected channels in the porous precursor can be controlled within the range of 20nm to 150nm, providing a channel for mass transfer of formic acid molecules and contact with basic sites.

[0045] In some embodiments, the concentration of the foaming agent solution is 3wt% to 5wt%, for example, it can be 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%.

[0046] In some embodiments, the mass of the foaming agent in the foaming agent solution is 2wt% to 6wt% of the mass of the red mud powder, for example, it can be 2wt%, 3wt%, 4wt%, 5wt% or 6wt%.

[0047] In some embodiments, the temperature of the heating reaction is 80°C to 100°C, for example, it can be 80°C, 85°C, 90°C, 95°C or 100°C.

[0048] In some embodiments, the heating reaction time is 1h to 3h, for example, it can be 1h, 1.5h, 2h, 2.5h or 3h.

[0049] In this invention, the photoresponse characteristics of the red mud-based magnetic photothermal catalyst are controlled by adjusting the amount of photoactive component added. This ensures that the photoactive component forms a sufficient heterojunction with Fe3O4 while avoiding the photoactive component covering the alkaline active sites on the catalyst surface, thus affecting the catalytic effect.

[0050] In some embodiments, the mass of the photoactive component is 0.5wt% to 2wt% of the porous precursor mass, for example, it can be 0.5wt%, 0.75wt%, 1wt%, 1.25wt%, 1.5wt%, 1.75wt% or 2wt%.

[0051] In some embodiments, the D50 particle size of the photoactive component is 5nm to 15nm, for example, it can be 5nm, 7nm, 9nm, 10nm, 12nm, 13nm, 14nm or 15nm.

[0052] In some embodiments, the ball mill rotates at a speed of 300 rpm to 500 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm.

[0053] In some embodiments, the ball milling time is 20 min to 60 min, for example, it can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0054] In some embodiments, the calcination is carried out under an inert atmosphere. In this invention, the inert atmosphere includes nitrogen and / or an inert gas. The inert gas in this invention includes argon and / or helium.

[0055] This invention involves calcination under an inert atmosphere. By maintaining an inert atmosphere and a weakly alkaline environment throughout the entire process, the intrinsic alkaline sites of the red mud are not destroyed or lost, providing a core guarantee for alkali-free catalysis.

[0056] By controlling the calcination temperature and time, Fe2O3 can be fully transformed into the Fe3O4 magnetic phase in situ, while avoiding the collapse of the pores in the porous precursor, which would reduce the specific surface area and decrease the exposure of alkaline sites.

[0057] In some embodiments, the heating rate of the calcination is 2℃ / min to 5℃ / min, for example, it can be 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min.

[0058] In some embodiments, the calcination temperature is 500°C to 700°C, for example, it can be 500°C, 550°C, 600°C, 650°C or 700°C.

[0059] In some embodiments, the calcination time is 2h to 4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h.

[0060] In some embodiments, the red mud powder is obtained by sequentially drying and crushing Bayer process red mud from the aluminum industry, and then passing it through a 200-400 mesh sieve, for example, 200 mesh, 250 mesh, 300 mesh, 350 mesh, or 400 mesh. In this invention, the temperature and time for drying the red mud are not particularly limited, with the aim of achieving complete removal of free water.

[0061] In another specific embodiment, the present invention provides a red mud-based magnetic photothermal catalyst, which is prepared by the preparation method described in the aforementioned specific embodiment; the band gap of the red mud-based magnetic photothermal catalyst is 2.1 eV to 2.4 eV, for example, it can be 2.1 eV, 2.2 eV, 2.3 eV or 2.4 eV.

[0062] In yet another embodiment, the present invention provides an application of the red mud-based magnetic photothermal catalyst as described in another embodiment above, wherein the red mud-based magnetic photothermal catalyst is used for photothermal synergistic catalysis of formic acid to produce hydrogen.

[0063] In some embodiments, the method of applying the red mud-based magnetic photothermal catalyst to photothermal synergistic catalysis of formic acid to hydrogen production includes: The red mud-based magnetic photothermal catalyst and formic acid solution are placed in a sealed container, and nitrogen and / or inert gas are continuously introduced to expel oxygen from the sealed container. A visible light source is turned on to carry out the formic acid hydrogen production reaction. After the formic acid hydrogen production reaction is completed, a magnetic field is applied to separate the solid and liquid. The separated red mud-based magnetic photothermal catalyst is recycled for the next batch of formic acid hydrogen production reaction.

[0064] When the red mud-based magnetic photothermal catalyst prepared by the method provided in this invention is applied to the catalytic hydrogen production reaction of formic acid, it achieves efficient dehydrogenation of formic acid through photothermal synergy without the need for any additional alkaline additives or harsh conditions such as high temperature and high pressure, and the hydrogen purity is above 99.9%, exhibiting excellent dehydrogenation selectivity.

[0065] Furthermore, since Fe2O3 in the red mud powder is fully transformed into the Fe3O4 magnetic phase in situ, after the reaction, only a magnetic field needs to be applied. Under the action of the magnetic field, the red mud-based magnetic photothermal catalyst and the reaction products are rapidly separated. The separated red mud-based magnetic photothermal catalyst does not require any regeneration treatment. It can be directly added to a new formic acid aqueous solution to carry out the next round of cyclic reaction. During the cycle, the basic site, magnetic and photoresponse performance of the catalyst remain stable, which significantly shortens the batch preparation cycle and realizes the long-life recycling of the red mud-based magnetic photothermal catalyst.

[0066] In some embodiments, the volume ratio of formic acid to water in the formic acid solution is 1:(0~1), for example, it can be 1:0, 1:0.2, 1:0.4, 1:0.6, 1:0.8 or 1:1.

[0067] In this invention, when the formic acid content in the formic acid solution is high, in order to avoid the formic acid volatilizing and spreading and polluting the products, those skilled in the art can add a reflux device as needed.

[0068] In some embodiments, the solid-liquid ratio of the red mud-based magnetic photothermal catalyst to the formic acid solution is 0.1 g / mL to 0.3 g / mL, for example, it can be 0.1 g / mL, 0.15 g / mL, 0.2 g / mL, 0.25 g / mL or 0.3 g / mL.

[0069] In some embodiments, the wavelength of the visible light source is 380nm to 780nm, for example, it can be 380nm, 480nm, 580nm, 680nm or 780nm.

[0070] In some embodiments, the power density of the visible light source is 50 mW / cm². 2 ~200mW / cm 2 For example, it could be 50mW / cm 2 70mW / cm 2 90mW / cm 2 100mW / cm 2 120mW / cm 2 140mW / cm 2 160mW / cm 2 180mW / cm 2 Or 200mW / cm 2 .

[0071] In some embodiments, the temperature of the formic acid hydrogen production reaction is 25°C to 50°C, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C or 50°C.

[0072] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0073] To clearly illustrate the technical solution of this invention, the red mud powder in the specific embodiment is obtained by drying red mud from Binzhou Weiqiao Aluminum Industry's Bayer process at 105°C, ball milling, and then passing it through a 300-mesh sieve. The phase composition and content of the red mud powder are as follows: Figure 1 As shown in Table 1, the main phases are as follows.

[0074] Table 1 Red mud powder was dispersed in carbon dioxide-free deionized water at a solid-liquid ratio of 0.1 g / mL and stirred for 30 min. The pH value of the supernatant was tested and found to be 11.8.

[0075] The above description is only for clearly illustrating the technical solution of the present invention and is not intended to further limit the present invention.

[0076] Preparation Example 1 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst, the preparation method comprising: (1) The red mud powder and the ammonium bicarbonate aqueous solution with a concentration of 4wt% were stirred and mixed according to the mass of ammonium bicarbonate being 4wt% of the red mud powder. The mixture was placed in a reaction vessel and heated at 90°C for 2 hours to obtain a porous precursor.

[0077] (2) The porous precursor and the cerium dioxide nanoparticles with a D50 particle size of 10 nm were ball-milled together with the porous precursor at a mass of 1 wt% of the porous precursor. The ball milling speed was set to 500 rpm and the mixture was ball-milled for 30 min to obtain the cerium dioxide-loaded precursor.

[0078] (3) The cerium dioxide supported precursor was placed in a tube furnace under a nitrogen atmosphere and heated to 600°C at a heating rate of 5°C / min and calcined for 3 hours to obtain the red mud-based magnetic photothermal catalyst.

[0079] Preparation Example 2 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst, the preparation method comprising: (1) The red mud powder and the 5wt% ammonium bicarbonate aqueous solution were stirred and mixed according to the mass of ammonium bicarbonate being 5wt% of the mass of red mud powder. The mixture was placed in a reaction vessel and heated at 80°C for 3 hours to obtain a porous precursor.

[0080] (2) The porous precursor and titanium dioxide nanoparticles with a D50 particle size of 5 nm were ball-milled together with the porous precursor at a mass of 1.5 wt% of the porous precursor. The ball milling speed was set to 1000 rpm and the mixture was ball-milled for 20 min to obtain the titanium dioxide supported precursor.

[0081] (3) The titanium dioxide supported precursor was placed in an argon atmosphere and heated to 700°C at a heating rate of 5°C / min, and calcined for 2 hours to obtain the red mud-based magnetic photothermal catalyst.

[0082] Preparation Example 3 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst, the preparation method comprising: (1) The red mud powder and the urea aqueous solution with a concentration of 3wt% were mixed and stirred according to the mass of urea being 3wt% of the mass of red mud powder. The mixture was placed in a reaction vessel and heated at 100°C for 1 hour to obtain a porous precursor.

[0083] (2) The porous precursor and cerium dioxide nanoparticles with a D50 particle size of 15 nm were ball-milled together with the porous precursor at a mass of 0.5 wt% of the porous precursor. The ball milling speed was set to 300 rpm and the mixture was ball-milled for 60 min to obtain the cerium dioxide-loaded precursor.

[0084] (3) The cerium dioxide supported precursor was placed in a nitrogen atmosphere and heated to 500°C at a heating rate of 2°C / min, and calcined for 4 hours to obtain the red mud-based magnetic photothermal catalyst.

[0085] Preparation Example 4 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst. Except for the heating reaction temperature of 75°C in step (1), the preparation method is the same as that in preparation example 1.

[0086] Preparation Example 5 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst. Except for the heating reaction temperature of 105°C in step (1), the preparation method is the same as that in preparation example 1.

[0087] Preparation Example 6 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst. Except for step (2), in which the mass of cerium dioxide nanoparticles is 0.3 wt% of the mass of the porous precursor, the preparation method is the same as that in preparation example 1.

[0088] Preparation Example 7 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst. Except for step (2), in which the mass of cerium dioxide nanoparticles is 2.2 wt% of the mass of the porous precursor, the preparation method is the same as that in preparation example 1.

[0089] Preparation Example 8 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst. Except for the calcination temperature of 450°C in step (3), the preparation method is the same as that in preparation example 1.

[0090] Preparation Example 9 This preparation example provides a method for preparing a red mud-based magnetic photothermal catalyst. Except for the calcination temperature of 750°C in step (3), the preparation method is the same as that in preparation example 1.

[0091] Comparative Preparation Example 1 This comparative preparation example provides a method for preparing a red mud-based magnetic photocatalyst. The preparation method is the same as that in Preparation Example 1, except that the red mud powder is first neutralized and washed with an excess of 15wt% dilute hydrochloric acid, then washed three times with deionized water, the pH of the filtrate is tested to be 7, and then the red mud powder that was not acid-washed in step (1) of Preparation Example 1 is replaced with red mud powder with neutral pH after acid washing, and then mixed with ammonium bicarbonate aqueous solution and heated for reaction.

[0092] Comparative Preparation Example 2 This comparative preparation example provides a method for preparing a red mud-based magnetic photocatalyst. The preparation method is the same as that in Preparation Example 1, except that step (1) is omitted and step (2) involves directly mixing red mud powder with cerium dioxide nanoparticles.

[0093] Application Example 1 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Example 1 to photothermal synergistic catalysis of formic acid to hydrogen production, including: (1) Prepare a formic acid solution with a volume ratio of formic acid to water of 1:0.25. Place the red mud-based magnetic photothermal catalyst prepared in Example 1 and the formic acid solution in a closed reactor with a quartz window. The solid-liquid ratio of the red mud-based magnetic photothermal catalyst to the formic acid solution is 0.25 g / mL. Nitrogen gas is continuously introduced to remove oxygen from the closed container.

[0094] (2) Under atmospheric pressure and 25°C conditions, turn on a visible light source with a wavelength of 450nm and set the power density to 100mW / cm². 2 The formic acid hydrogen production reaction is carried out; after the formic acid hydrogen production reaction is completed, a permanent magnet is set outside the reactor to apply a magnetic field, and the catalyst completely settles within 10 seconds, with a separation effect as shown. Figure 2 As shown, after solid-liquid separation, the separated red mud-based magnetic photothermal catalyst is recycled for the next batch of formic acid hydrogen production reaction.

[0095] Application Example 2 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Example 2 to photothermal synergistic catalysis of formic acid to hydrogen production, including: (1) The red mud-based magnetic photothermal catalyst prepared in Preparation Example 2 and anhydrous formic acid were placed in a closed reactor with a quartz window. The solid-liquid ratio of the red mud-based magnetic photothermal catalyst to the formic acid solution was 0.3 g / mL. Argon gas was continuously introduced to remove oxygen from the closed container.

[0096] (2) Under atmospheric pressure and 35°C conditions, turn on a visible light source with a wavelength of 580nm and set the power density to 50mW / cm². 2 The formic acid hydrogen production reaction is carried out; after the formic acid hydrogen production reaction is completed, a permanent magnet is set outside the reactor to apply a magnetic field. Within 10 seconds, the catalyst completely settles and the solid and liquid are separated. The separated red mud-based magnetic photothermal catalyst is recycled for the next batch of formic acid hydrogen production reaction.

[0097] Application Example 3 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Example 3 to photothermal synergistic catalysis of formic acid to hydrogen production, including: (1) Prepare a formic acid solution with a volume ratio of formic acid to water of 1:1. Place the red mud-based magnetic photothermal catalyst prepared in Example 3 and the formic acid solution in a closed reactor with a quartz window. The solid-liquid ratio of the red mud-based magnetic photothermal catalyst to the formic acid solution is 0.1 g / mL. Nitrogen gas is continuously introduced to remove oxygen from the closed container.

[0098] (2) Under atmospheric pressure and 350℃ conditions, turn on a visible light source with a wavelength of 680nm and set the power density to 50mW / cm². 2 The formic acid hydrogen production reaction is carried out; after the formic acid hydrogen production reaction is completed, a permanent magnet is set outside the reactor to apply a magnetic field. Within 10 seconds, the catalyst completely settles and the solid and liquid are separated. The separated red mud-based magnetic photothermal catalyst is recycled for the next batch of formic acid hydrogen production reaction.

[0099] Application Example 4 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Preparation Example 4 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 4 by the same mass, the rest is the same as in Application Example 1.

[0100] Application Example 5 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Preparation Example 5 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 5 by the same mass, the rest is the same as in Application Example 1.

[0101] Application Example 6 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Preparation Example 6 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 6 by the same mass, the rest is the same as in Application Example 1.

[0102] Application Example 7 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Preparation Example 7 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 7 by the same mass, the rest is the same as in Application Example 1.

[0103] Application Example 8 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Preparation Example 8 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 8 by the same mass, the rest is the same as in Application Example 1.

[0104] Application Example 9 This application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Preparation Example 9 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 9 by the same mass, the rest is the same as in Application Example 1.

[0105] Comparative Application Example 1 This comparative application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Comparative Preparation Example 1 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Comparative Preparation Example 1 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 by the same mass, all other aspects are the same as in Application Example 1.

[0106] Comparative Application Example 2 This comparative application example provides a method for applying the red mud-based magnetic photothermal catalyst prepared in Comparative Preparation Example 2 to photothermal synergistic catalysis of formic acid to produce hydrogen. Except for replacing the red mud-based magnetic photothermal catalyst prepared in Comparative Preparation Example 2 with the red mud-based magnetic photothermal catalyst prepared in Preparation Example 1 by the same mass, all other aspects are the same as in Application Example 1.

[0107] Comparative Application Example 3 This comparative application example provides a method for using a red mud-based magnetic photothermal catalyst to catalyze the production of hydrogen from formic acid. Except for step (2) where the visible light source is not turned on, the rest is the same as in application example 1.

[0108] Performance testing: With a solid-liquid ratio of 0.1 g / mL, the red mud-based magnetic photocatalysts prepared in all the above preparation examples and the comparative preparation examples were placed in carbon dioxide-free deionized water for extraction and stirring for 30 min. The pH of the supernatant was tested, and the test results are shown in Table 2.

[0109] The average pore size and specific surface area of ​​the red mud-based magnetic photocatalysts prepared in all the above preparation examples and the comparative preparation examples were tested by nitrogen adsorption-desorption BET test method. The test results are shown in Table 2.

[0110] Gas chromatography was used to test the concentration ratio of H2 and CO in the dehydrogenation products of all the above application examples and the comparative application examples, and the hydrogen production rate was also tested. The test results are shown in Table 2.

[0111] Table 2 Based on the test results in Table 2, this invention constructs a magnetic-photothermal synergistic catalytic system, utilizing the intrinsic alkaline sites of red mud as catalytic active centers to achieve highly selective dehydrogenation of formic acid without the addition of external alkaline aids. Simultaneously, by utilizing photothermal synergy, it eliminates the dependence on high-temperature and high-pressure reaction conditions, achieving stable dehydrogenation of formic acid to hydrogen production under visible light irradiation at ambient temperature and pressure (25℃~50℃, atmospheric pressure), significantly reducing hydrogen production energy consumption and meeting the core requirements of safe hydrogen supply scenarios. Furthermore, by utilizing the intrinsic iron-rich characteristics of red mud, the red mud-based magnetic photothermal catalyst is magnetic, easy to separate, and can be recycled and reused.

[0112] Based on the test results of Preparation Examples 1, 4, and 5, and Application Examples 1, 4, and 5, if the concentration of the ammonium bicarbonate aqueous solution is too low, the number of CO2 and NH3 bubbles generated during the heating reaction will be too small, insufficient to construct enough channels in the red mud powder matrix. This will lead to a decrease in the average pore size and specific surface area of ​​the prepared red mud-based magnetic photothermal catalyst, which is not conducive to the mass transfer of formic acid and a decrease in the contact efficiency between formic acid and basic active sites, resulting in a decrease in the performance of catalyzing formic acid dehydrogenation. If the concentration of the sodium bicarbonate aqueous solution is too high, CO2 and NH3 bubbles will be generated violently during the heating reaction. The strong impact force will destroy some of the thin-walled channels in the red mud powder matrix, shielding the basic active sites. This also shows a decrease in the average pore size and specific surface area of ​​the prepared red mud-based magnetic photothermal catalyst, a decrease in the contact efficiency between formic acid and basic active sites, and a decrease in the performance of catalyzing formic acid dehydrogenation.

[0113] Based on the test results of Preparation Examples 1, 6, and 7, and Application Examples 1, 6, and 7, if the amount of cerium dioxide nanoparticles added is too small, the number of heterojunctions formed between the cerium dioxide nanoparticles and Fe3O4 will be too small, resulting in insufficient photoresponse and decreased photothermal synergy, thus reducing the performance of catalyzing formic acid dehydrogenation. If the amount of cerium dioxide nanoparticles added is too large, the cerium dioxide nanoparticles will excessively coat the surface of the porous precursor or enter the pores, covering the basic active sites, which will also lead to decreased photothermal synergy and reduced performance of catalyzing formic acid dehydrogenation.

[0114] Based on the test results of Preparation Example 1, Preparation Example 8, and Preparation Example 9, and Application Example 1, Application Example 8, and Application Example 9, if the calcination temperature in step (3) is too low, Fe2O3 in the red mud cannot be fully transformed into the Fe3O4 magnetic phase in situ, resulting in too few heterojunctions formed between cerium dioxide nanoparticles and Fe3O4, insufficient light response, and insufficient magnetism, which is not conducive to solid-liquid separation after the reaction. If the calcination temperature in step (3) is too high, some pores will collapse, resulting in a significant decrease in specific surface area, masking of alkaline active sites, and a decrease in the catalytic performance of formic acid dehydrogenation.

[0115] Based on the test results of Preparation Example 1 and Comparative Preparation Example 1, as well as Application Example 1 and Comparative Application Example 1, if the red mud powder is acid-washed, its intrinsic alkalinity disappears. In the process of catalyzing the dehydrogenation of formic acid, there are no alkaline active sites for catalytic reaction, resulting in a significant decrease in the ability of the red mud-based magnetic photocatalyst to catalyze the dehydrogenation of formic acid.

[0116] Based on the test results of Preparation Example 1 and Comparative Preparation Example 2, as well as Application Example 1 and Comparative Application Example 2, if the red mud powder is not foamed, sufficient pore structure cannot be constructed, which is not conducive to the mass transfer of formic acid and the contact between formic acid and basic active sites, and also leads to a significant decrease in the ability of red mud-based magnetic photocatalyst to catalyze the dehydrogenation of formic acid.

[0117] Based on the test results of Application Example 1 and Comparative Application Example 3, if a visible light source is not turned on during the catalytic formic acid dehydrogenation reaction, the photothermal synergistic effect cannot be exerted, and the ability to catalyze formic acid dehydrogenation is significantly reduced.

[0118] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a red mud-based magnetic photothermal catalyst, characterized in that, The preparation method includes: Red mud powder and foaming agent solution are mixed and placed in a sealed container for heating and reaction to obtain a porous precursor; the porous precursor is ball-milled and mixed with a photoactive component to obtain a photoactive component-supported precursor; the photoactive component-supported precursor is calcined to obtain the red mud-based magnetic photothermal catalyst. The photoactive component includes any one or a combination of at least two of the following: cerium dioxide nanoparticles, titanium dioxide nanoparticles, bismuth oxide nanoparticles, g-C3N4 or tungsten trioxide nanoparticles. The foaming agent in the foaming agent solution includes ammonium bicarbonate and / or urea.

2. The preparation method according to claim 1, characterized in that, The concentration of the foaming agent solution is 3wt%~5wt%; And / or, the mass of the foaming agent in the foaming agent solution is 2wt% to 6wt% of the mass of the red mud powder.

3. The preparation method according to claim 1, characterized in that, The temperature of the heating reaction is 80℃~100℃; And / or, the heating reaction time is 1h to 3h.

4. The preparation method according to claim 1, characterized in that, The mass of the photoactive component is 0.5wt%~2wt% of the porous precursor. And / or, the D50 particle size of the photoactive component is 5nm~15nm; And / or, the rotational speed of the ball mill is 300 rpm to 500 rpm; And / or, the ball milling time is 20 min to 60 min.

5. The preparation method according to claim 1, characterized in that, The calcination is carried out under an inert atmosphere; And / or, the heating rate of the calcination is 2℃ / min to 5℃ / min; And / or, the calcination temperature is 500℃~700℃; And / or, the calcination time is 2h~4h.

6. The preparation method according to claim 1, characterized in that, The red mud powder is obtained by drying and crushing Bayer process red mud from the aluminum industry, and then passing it through a 200-400 mesh sieve.

7. A red mud-based magnetic photothermal catalyst, characterized in that, The red mud-based magnetic photothermal catalyst is prepared by the preparation method according to any one of claims 1 to 6; The band gap of the red mud-based magnetic photothermal catalyst is 2.1 eV to 2.4 eV.

8. An application of the red mud-based magnetic photothermal catalyst as described in claim 7, characterized in that, The red mud-based magnetic photothermal catalyst is used for photothermal synergistic catalysis of formic acid to produce hydrogen.

9. The application as described in claim 8, characterized in that, The method for applying the red mud-based magnetic photothermal catalyst to photothermal synergistic catalysis of formic acid hydrogen production includes: The red mud-based magnetic photothermal catalyst and formic acid solution are placed in a sealed container, and nitrogen and / or inert gas are continuously introduced to expel oxygen from the sealed container. A visible light source is turned on to carry out the formic acid hydrogen production reaction. After the formic acid hydrogen production reaction is completed, a magnetic field is applied to separate the solid and liquid. The separated red mud-based magnetic photothermal catalyst is recycled for the next batch of formic acid hydrogen production reaction.

10. The application as described in claim 9, characterized in that, The volume ratio of formic acid to water in the formic acid solution is 1:(0~1); And / or, the solid-liquid ratio of the red mud-based magnetic photothermal catalyst to the formic acid solution is 0.1 g / mL to 0.3 g / mL; And / or, the wavelength of the visible light source is 380nm~780nm; And / or, the power density of the visible light source is 50 mW / cm². 2 ~200mW / cm 2 ; And / or, the temperature of the formic acid hydrogen production reaction is 25°C to 50°C.

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