CN113000006B - Magnesium hydroxide adsorption material, preparation method and application - Google Patents

Abstract

The inventor provides a magnesium hydroxide adsorption material and a preparation method thereof. The magnesium hydroxide adsorption material is magnesium hydroxide in a hexagonal crystal phase, and its form is a coral-like porous structure constructed by elementary nanosheets; the preparation method comprises the following steps : Mix magnesium oxide, citrate, and deionized water, stir evenly, seal in a high-pressure reactor, and react hydrothermally to obtain the first suspension; Separation and drying: The first suspension is subjected to solid-liquid separation, and after separation The resulting precipitate was dried to obtain a magnesium hydroxide adsorbent material. The magnesium hydroxide adsorption material is synthesized in one step by hydrothermal reaction of citrate, magnesium oxide, and deionized water. It has high specific surface area, high pore volume, and stable surface structure, and can be applied to adsorb cadmium ions and/or lead ions. The invention not only has low investment and is easy to operate, but also produces no waste and is environmentally friendly, so that the application range is wide.

Description

A kind of magnesium hydroxide adsorption material, preparation method and application

technical field

The invention relates to the technical field of inorganic functional materials, in particular to a magnesium hydroxide adsorption material, a preparation method and an application.

Background technique

With the development of industry in recent decades, heavy metal pollution in water has become a worldwide environmental problem. Untreated industrial wastewater containing heavy metal ions such as Pb(II), Cd(II), As(V), and Ni(II) is discharged into the environment indiscriminately, causing serious environmental problems. These heavy metal ions are extremely stable, highly toxic, non-biodegradable and carcinogenic, and extremely harmful to human life and ecosystems. Therefore, the removal of heavy metal ions from industrial emissions is necessary and urgent and required by law.

In the field of environmental remediation, magnesium hydroxide (MH) is known as a green and safe water treatment agent, which can be used for neutralization of acid-containing wastewater, decolorization of dye wastewater, adsorption and removal of heavy metal wastewater, etc. Generally speaking, the adsorption effect of MH materials is determined by the larger specific surface area, pore volume and surface defects. Although some magnesium oxide products have extremely high specific surface area and pore volume, which can meet the above requirements, the actual adsorption capacity drops sharply due to pore blockage caused by hydration in the actual water environment. Essentially, the adsorption behavior of magnesium oxide is mainly based on its surface hydration product MH. Therefore, developing active MH adsorbents with stable structures is currently an effective strategy for heavy metal ion removal.

The current synthesis of MH materials mainly focuses on the wet precipitation method of Mg ²⁺ solution, sol-gel method, magnesium oxide hydration method, microemulsion method, etc. However, most methods inevitably produce harmful by-products and are often costly and difficult to mass-produce. Even so, active MH adsorbents with high specific surface area and high pore volume and good adsorption performance are still difficult to obtain. Although some nano-MH products have high specific surface area and sufficient surface defects, the decrease in adsorption capacity due to agglomeration is still difficult to solve and difficult for practical application. Chinese patent applications with application number: 201510944007.3 and application number: 200610041984.3 also disclose MH materials with different structures and their preparation processes.

Contents of the invention

In order to solve the current problem that the adsorption capacity of MH adsorption materials decreases after agglomeration, the inventors provide a magnesium hydroxide adsorption material with high specific surface area, high pore volume and stable structure and a preparation method thereof.

The inventor provides a magnesium hydroxide adsorption material, the magnesium hydroxide adsorption material is magnesium hydroxide in a hexagonal crystal phase, and its form is a coral-like porous structure constructed by elementary nanosheets.

The coral-like porous structure is self-assembled from nanosheets obtained after magnesium hydroxide recrystallization. The overall size of the coral-like structures is several micrometers. (generally within 10μm)

In the prior art, nanoparticles have a large specific surface area and high surface energy, so they tend to agglomerate together to reduce the surface energy. If there is no design intervention, in order to reduce the surface energy most efficiently, the nanoparticles will choose the largest exposed surface for contact stacking, thereby forming a relatively compact agglomeration structure, minimizing the specific surface area and reducing the surface energy. At the same time, due to its tight agglomerated structure, the pore volume must also be low.

In the present invention, the magnesium hydroxide adsorption material is a coral-like porous structure, which is also a stable structure formed by self-assembly stacking after the recrystallization of the magnesium hydroxide product under the action of citrate; its structure is compared with the magnesium hydroxide adsorption of the prior art. The specific surface area of the material is large, the pore volume is large, and the adsorption capacity is strong.

Further, the thickness of the elementary nanosheets of the magnesium hydroxide adsorption material is 20-40nm.

Further, the specific surface area of the magnesium hydroxide adsorption material is 45-170m ² /g, and the pore volume is 0.4-0.8cm ³ /g.

The inventor also provides a kind of preparation method of magnesium hydroxide adsorption material, comprises the following steps:

Hydrothermal reaction: mix magnesium oxide, citrate, and deionized water, stir evenly, seal in a high-pressure reactor for hydrothermal reaction, and obtain the first suspension;

Separation and drying: The first suspension is subjected to solid-liquid separation, and the precipitate obtained after separation is dried to obtain a magnesium hydroxide adsorption material.

The inventor found in the research that: citrate can control the shape and size of magnesium hydroxide during the reaction process, and according to the concentration of citrate, it can control the self-assembly behavior of nano-magnesium hydroxide and recrystallize in magnesium hydroxide. The process promotes the formation of pores, and the nano-magnesium hydroxide with different porous structures and shapes can be regulated by the concentration of citrate.

Citrate can be derived from citric acid and soluble citrate.

In addition, after the solid-liquid separation of the reacted product, the citrate molecule will not remain in the final product magnesium hydroxide adsorption material, so the filtrate can be reused and recycled, and the whole process has no by-product emissions, which is simple and economical.

Further, the mass of the citrate is 5%-50% of the mass of the magnesium oxide.

Further, in the hydrothermal reaction step, the hydrothermal reaction is carried out at 160-200° C. for more than 4 hours. The hydrothermal temperature has an effect on the morphology and size of magnesium hydroxide.

Further, the mass ratio of the deionized water to the magnesium oxide is 45:1.

Further, in the separation and drying step, the precipitate is dried at 80° C. for 12 hours to obtain the magnesium hydroxide adsorption material.

The inventor further provides the use of the magnesium hydroxide adsorption material for adsorbing cadmium ions and/or lead ions.

The inventor also provides the use of the magnesium hydroxide adsorption material as an adsorption carrier for preparing a catalyst.

Different from the existing technology, the above technical scheme synthesizes MH adsorption material in one step through hydrothermal reaction of citrate, magnesium oxide and deionized water. It has high specific surface area, high pore volume and stable surface structure, and can be applied to adsorb cadmium ions and/or Or the use of lead ions. When citrate (5wt%-50wt%), its specific surface area is in the range of 45-170m ² /g, pore volume is in the range of 0.4-0.8cm ³ /g, has high specific surface area and pore volume, and can be controlled by lemon The amount of acid radical added and the hydrothermal temperature are used to adjust the specific surface area and pore volume. The synthesized MH adsorption material has an adsorption efficiency of nearly 100% for Pb ²⁺ and over 93% for Cd ²⁺ ; in the presence of Na ⁺ , Ca ²⁺ , K ⁺ , Mg ²⁺ , Co ²⁺ , In the presence of ²⁺ and other coexisting cations, the adsorption efficiency can still maintain more than 90%. The invention not only has low investment and is easy to operate, but also produces no waste and is environmentally friendly, so that the application range is wide.

Description of drawings

Fig. 1 is the SEM picture of MH product when no citrate group is added in embodiment 2.

Fig. 2 is the SEM image of the product at different citrate dosages; wherein the citrate dosage a 5wt%; b 10wt%; c 15wt%; d 20wt%; e 25wt%; f 30wt%.

Fig. 3 is the corresponding XRD of the product at different citrate dosages as shown in Fig. 2, wherein the citrate content a 5wt%; b10wt%; c 15wt%; d 20wt%; e 25wt%; f 30wt%.

Figure 4 is a diagram of the removal efficiency of Pb ²⁺ or Cd ²⁺ for a certain adsorption time (25°C, 1000mg/L).

Figure 5 is a graph showing the influence of coexisting cations on the adsorption efficiency.

Detailed ways

In order to explain in detail the technical content, structural features, achieved goals and effects of the technical solution, the following will be described in detail in conjunction with specific embodiments and accompanying drawings.

In this embodiment, Xwt% citrate means that the mass of citrate added in the preparation process is Xwt% magnesium oxide.

The preparation of embodiment 1 magnesium hydroxide (MH) adsorption material,

Weigh the following raw materials by weight: 1g of magnesium oxide, 0.2g of citrate, 45ml of deionized water, put the above substances in a hydrothermal kettle and mix them evenly. Place in a blast drying oven, heat up to 160°C for hydrothermal reaction for 4h. Take out the reaction kettle and cool it to room temperature, then filter to obtain a white filter cake, wash and dry at 80°C for 12 hours, and finally obtain a coral-like porous MH adsorption material (specific surface area 159.3381m ² /g, pore volume 0.746610cm ³ /g)

1. Removal of lead ions in wastewater.

Take by weighing 0.1 g of the MH adsorption material prepared in Example 1 at room temperature and place it in a beaker containing 500-6000 mg/L of lead waste water, perform adsorption at a rotating speed of 20 rpm, and get the supernatant after reaching the adsorption equilibrium to centrifuge. Dilute, measure the remaining lead ion concentration after its adsorption with ICP, after calculating the ability to adsorb lead is 4535mg/g.

2. Removal of cadmium ions in wastewater.

Weigh 0.1 g of the MH adsorption material prepared in Example 1 at room temperature and place it in a beaker containing 500-6000 mg/L of cadmium wastewater, and perform adsorption at a speed of 20 rpm. After reaching adsorption equilibrium, take the supernatant and centrifuge. Dilute, and use ICP to measure the remaining cadmium ion concentration after adsorption, and the calculated adsorption capacity of cadmium is 3530mg/g.

Embodiment 2 (comparative example)

Compared with Example 1, the rest of the conditions were unchanged, but no citrate was added. What thus obtained is only hexagonal flake particles with uneven size, as shown in Fig. 1 (the specific surface area of the MH adsorption material is 15.8125 m ² /g, and the pore volume is 0.103080 cm 3 /g).

1. Removal of lead ions in wastewater.

Take by weighing 0.1 g of the MH adsorption material of Example 2 at room temperature and place it in a beaker containing 1000 mg/L of lead waste water, adsorb at 20 rpm at a rotating speed, get the supernatant after reaching the adsorption equilibrium and centrifuge, dilute, and use ICP The concentration of lead ions after its adsorption was measured, and the ability to adsorb lead was calculated to be 917mg/g.

2. Removal of cadmium ions in wastewater.

Take by weighing 0.1 g of the MH adsorbent material of Example 2 at room temperature and place it in a beaker containing 1000 mg/L of cadmium waste water, adsorb at a rotating speed of 20 rpm, get the supernatant after reaching adsorption equilibrium, centrifuge, dilute, and use ICP The cadmium ion concentration after its adsorption was measured, and the ability to adsorb cadmium was calculated to be 176mg/g.

Embodiment 3: (5wt% citrate)

Compared with Example 1, the process parameters are: magnesium oxide 1g citrate 0.05g deionized water 45ml hydrothermal temperature 180°C

Finally obtain coral-like porous magnesium hydroxide (specific surface area 47.5166m ² /g, pore volume 0.412276cm ³ /g)

Embodiment 4: (5wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.05g deionized water 45ml hydrothermal temperature 200°C to finally obtain a coral-like porous MH product (specific surface area 48.3228m ² /g, pore volume 0.42786cm ³ /g)

Embodiment 5: (5wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.05g deionized water 45ml hydrothermal temperature 160°C to finally obtain a coral-like porous MH product (specific surface area 45.5198m ² /g, pore volume 0.396676cm ³ /g)

Embodiment 6: (10wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.1g deionized water 45ml hydrothermal temperature 180°C to finally obtain coral-like porous MH adsorption material (specific surface area 74.0877m ² /g, pore volume 0.581121cm ³ /g)

Embodiment 7: (10wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.1g deionized water 45ml hydrothermal temperature 200°C to finally obtain coral-like porous MH product (specific surface area 76.3500m ² /g, pore volume 0.603726cm ³ /g)

Embodiment 8: (10wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.1g deionized water 45ml hydrothermal temperature 160°C to finally obtain coral-like porous MH product (specific surface area 73.0800m ² /g, pore volume 0.577126cm ³ /g)

Embodiment 9: (15wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.15g deionized water 45ml hydrothermal temperature 200°C to finally obtain coral-like porous MH adsorption material (specific surface area 136.8818m ² /g, pore volume 0.724537cm ³ /g)

Embodiment 10: (15wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.15g deionized water 45ml hydrothermal temperature 180°C to finally obtain coral-like porous MH product (specific surface area 125.1238m ² /g, pore volume 0.704482cm ³ /g)

Embodiment 11: (15wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.15g deionized water 45ml hydrothermal temperature 160°C to finally obtain coral-like porous MH adsorption material (specific surface area 112.2178m ² /g, pore volume 0.651182cm ³ /g)

Embodiment 12: (20wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.2g deionized water 45ml hydrothermal temperature 200°C to finally obtain coral-like porous MH product (specific surface area 169m ² /g, pore volume 0.793223cm ³ /g)

Embodiment 13: (20wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.2g deionized water 45ml hydrothermal temperature 180°C to finally obtain coral-like porous MH adsorption material (specific surface area 163.8446m ² /g, pore volume 0.764223cm ³ /g)

Embodiment 14: (25wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.25g deionized water 45ml hydrothermal temperature 160°C to finally obtain coral-like porous MH adsorption material (specific surface area 142.3248m ² /g, pore volume 0.734267cm ³ /g)

Embodiment 15: (25wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.25g deionized water 45ml hydrothermal temperature 180°C to finally obtain coral-like porous MH product (specific surface area 145.1231m ² /g, pore volume 0.743325cm ³ /g)

Embodiment 16: (25wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.25g deionized water 45ml hydrothermal temperature 200°C to finally obtain coral-like porous MH adsorption material (specific surface area 146.2256m ² /g, pore volume 0.748952cm ³ /g)

Embodiment 17: (30wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.3g deionized water 45ml hydrothermal temperature 160°C to finally obtain coral-like porous MH product (specific surface area 134.8248m ² /g, pore volume 0.693644cm ³ /g)

Embodiment 18: (30wt% citrate)

The process parameters are: Magnesium Oxide 1g Citrate 0.3g Deionized Water 45ml Hydrothermal temperature 180°C to finally obtain coral-like porous MH product (specific surface area 137.1256m ² /g, pore volume 0.705236cm ³ /g)

Embodiment 19: (30wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.3g deionized water 45ml hydrothermal temperature 200°C to finally obtain coral-like porous MH adsorption material (specific surface area 139.5568m ² /g, pore volume 0.717532cm ³ /g)

Embodiment 20: (40wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.4g deionized water 45ml hydrothermal temperature 160°C to finally obtain coral-like porous MH adsorption material (specific surface area 121.1314m ² /g, pore volume 0.607056cm ³ /g)

Embodiment 21: (50wt% citrate)

The process parameters are: magnesium oxide 1g citrate 0.5g deionized water 45ml hydrothermal temperature 160°C to finally obtain coral-like porous MH adsorption material (specific surface area 109.7073m ² /g, pore volume 0.539270cm ³ /g)

It can be seen from the data of the above examples that when the input amount of citrate is 20 wt%, the specific surface area and pore volume of the obtained MH adsorption material product are the largest. The higher the hydrothermal temperature, the larger the specific surface area and pore volume of the obtained MH adsorption material product. When the amount of citrate (5wt%-50wt%) is different, the specific surface area is 45-170m ² /g, and the pore volume is controllable in the range of 0.4-0.8cm ³ /g.

Taking the hydrothermal temperature of 160°C as an example, the corresponding specific surface area and pore structure parameters are shown in Table 1. The final product of the MH adsorption material is shown in Figure 2, in which the thickness of the coral flakes is 20-40nm, and the overall plane measurement size is in the order of microns ( 1-10um). Its corresponding XRD is shown in Figure 3, and it can be seen from Figure 3 that the product belongs to the hexagonal crystal phase magnesium hydroxide (JCPDS 44-1482), and there is no miscellaneous peak of citrate, indicating that the product is pure magnesium hydroxide.

Table 1. Ratio table and pore parameter statistics table of MH adsorption materials

The MH (20wt%) prepared in Example 1 has excellent adsorption and removal capacity for Pb ²⁺ and Cd ²⁺ , as shown in Figure 4, within 60 minutes, the Pb ²⁺ adsorption efficiency can reach nearly 100%. Make the Cd ²⁺ adsorption efficiency reach more than 93%. At the same time, it ^{has a} strong anti-interference ability. As shown ^{in Figure 5} , ^the adsorption efficiency of can still maintain more than 90%,

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is a relationship between these entities or operations. There is no such actual relationship or order between them. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or terminal equipment comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements identified, or also include elements inherent in such a process, method, article, or end-equipment. Without further limitations, an element defined by the words "comprising..." or "comprising..." does not exclude the presence of additional elements in the process, method, article or terminal device comprising said element. In addition, in this article, "greater than", "less than", "exceeding" and so on are understood as not including the original number; "above", "below", "within" and so on are understood as including the original number.

It should be noted that although the foregoing embodiments have been described herein, the scope of protection of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, the changes and modifications made to the embodiments described herein, or the equivalent structure or equivalent process conversion made by using the description of the present invention and the contents of the accompanying drawings, directly or indirectly apply the above technical solutions In other related technical fields, all are included in the patent protection scope of the present invention.

Claims (5)

1. The preparation method of the magnesium hydroxide adsorbing material is characterized by comprising the following steps of:

hydrothermal reaction: mixing magnesium oxide, citrate and deionized water, uniformly stirring, sealing in a high-pressure reaction kettle, and carrying out hydrothermal reaction to obtain a first suspension;

separation and drying: carrying out solid-liquid separation on the first suspension, and drying a precipitate obtained after separation to obtain a magnesium hydroxide adsorbing material;

the mass of the citrate is 5% -50% of that of the magnesium oxide;

the hydrothermal reaction step is that hydrothermal reaction is carried out for more than 4 hours at the temperature of 160-200 ℃;

the mass ratio of the deionized water to the magnesium oxide is 45;

in the separation and drying step, the precipitate is dried for 12 hours at the temperature of 80 ℃ to obtain a magnesium hydroxide adsorbing material;

the magnesium hydroxide adsorption material is hexagonal phase magnesium hydroxide, and the form of the magnesium hydroxide adsorption material is a coralline porous structure constructed by element nanosheets; the thickness of the element nano-sheet of the magnesium hydroxide adsorption material is 20-40nm; the magnesium hydroxide adsorbing material has a specific surface area of 45-170 m/g and a pore volume of 0.4-0.8cm thin section/g;

the magnesium hydroxide adsorbing material has specific adsorption capacity on cadmium ions and/or lead ions and Na resistance ⁺ 、Ca ^{2 +} 、K ⁺ 、Mg ²⁺ 、Co ²⁺ 、Ni ²⁺ Cation interference capacity; in the presence of Na ⁺ 、Ca ²⁺ 、K ⁺ 、Mg ²⁺ 、Co ²⁺ 、Ni ²⁺ In the environment of cation, cadmium ion and lead ion are specifically adsorbed.

2. The preparation method of claim 1, wherein the citrate is 10% -50% of the magnesium oxide by mass.

3. A magnesium hydroxide adsorbent material produced by the method for producing a magnesium hydroxide adsorbent material according to claim 1 or 2.

4. Use of the magnesium hydroxide adsorption material of claim 3 for adsorbing cadmium and/or lead ions.

5. Use of the magnesium hydroxide adsorbent material according to claim 3 as an adsorption carrier for the preparation of catalysts.

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