CN111943238A - A kind of preparation method of porous fluffy magnesia - Google Patents

Abstract

The invention discloses a preparation method of porous pompon magnesium oxide, which belongs to the field of inorganic materials, and particularly relates to MgCl₂·6H₂O and K₂CO₃The precursor is sintered to obtain the porous pompon-shaped magnesium oxide after the raw materials are reacted by a hydrothermal method. According to the invention, magnesium chloride hexahydrate and anhydrous potassium carbonate are used as raw materials, a basic magnesium carbonate precursor is synthesized by a hydrothermal method, and the precursor is sintered at a high temperature to prepare the hierarchical porous pompon-like magnesium oxide with good crystallinity and large specific surface area.

Description

A kind of preparation method of porous fluffy magnesia

technical field

The present invention is in the field of inorganic materials, in particular to a preparation method of porous puff-shaped magnesium oxide.

Background technique

As an important inorganic material, magnesium oxide is an ionic compound with a face-centered cubic crystal structure. Nowadays, the gradual upgrading of industrialization and the continuous development of high-tech functional materials have broadened the application field of magnesium oxide inorganic materials. The properties of materials mainly depend on their shape, size and structure, which greatly promotes the scientific research on the synthesis of inorganic materials with special morphological structures. For example, due to its special skeleton structure, large specific surface area and catalytic activity, porous magnesium oxide is often widely used in the field of environmental protection and catalysis in industry to adsorb toxic gases, CO ₂ and heavy metal ions in wastewater and As a catalyst for the conversion of polyols, this greatly facilitates the research and preparation of porous magnesia. In the prior art, the existing magnesia powders are porous rod-shaped magnesia powder, mesoporous magnesia particles, porous magnesia fibers, and porous flaky magnesia, and the above-mentioned porous magnesia samples have a small pore size and a single pore size. The application of magnesium oxide is limited.

SUMMARY OF THE INVENTION

In order to realize the above-mentioned problems, the present invention provides a preparation method of porous puff-shaped magnesium oxide. The present invention adopts a hydrothermal method to prepare magnesium chloride hexahydrate and anhydrous potassium carbonate as reactants to prepare a compound with good crystallinity, large specific surface area and Mesoporous and macroporous graded porous puff-like magnesia.

In order to achieve the above object, the present invention adopts the following technical solutions:

A preparation method of porous fluffy magnesia, which uses MgCl ₂ ·6H ₂ O and K ₂ CO ₃ as raw materials, reacts by a hydrothermal method, and sinters the obtained precursor to obtain porous fluffy magnesia.

Further, including the following steps, (1) weigh MgCl ₂ 6H ₂ O into deionized water, stir until dissolved, and obtain MgCl ₂ solution; (2) weigh K ₂ CO ₃ in deionized water, stir until dissolved, Obtain the K ₂ CO ₃ solution; (3) slowly drop the MgCl ₂ solution into the K ₂ CO ₃ solution to obtain a white mixture; (4) carry out the hydrothermal reaction of the white mixture under constant temperature conditions, take out after the end and naturally cool to room temperature , the reactant was sequentially washed with deionized water and absolute ethanol, centrifuged, and then dried to a constant weight to obtain a precursor; (5) the obtained precursor was sintered and kept warm to obtain porous fluffy spherical magnesia.

Further, in step (5), the sintering temperature is 500-800°C.

Further, the equivalent ratio of MgCl ₂ ·6H ₂ O to K ₂ CO ₃ is 1:1.

Further, the concentration of the MgCl ₂ solution is 0.4 mol/L, and the concentration of the K ₂ CO ₃ solution is 0.67 mol/L.

Further, the hydrothermal reaction in step (4) is specifically as follows: transferring the white mixture to an autoclave lined with polytetrafluoroethylene for reaction; the filling rate of the autoclave is 75-85%; The reaction kettle is placed in a box-type resistance furnace for hydrothermal treatment at 180-200°C and constant temperature for 2-3 hours.

Further, the hydrothermal reaction in step (4) is specifically as follows: transferring the white mixture to an autoclave lined with polytetrafluoroethylene for reaction, and the filling rate of the autoclave is 80%. Put it into a box-type resistance furnace for hydrothermal treatment at 180°C and a constant temperature for 2 hours.

Further, in step (5), the holding time is 3-4h.

Further, in step (5), the sintering temperature is 800°C.

Compared with the prior art, the beneficial effects of the present invention are:

(1) the present invention takes magnesium chloride hexahydrate and anhydrous potassium carbonate as raw materials, adopts hydrothermal synthesis to obtain basic magnesium carbonate precursor, and sinters the precursor at high temperature to prepare a component with good crystallinity and large specific surface area The grade of porous puff-like magnesia has a comparative area of 17-21 m ² ·g ^-1 and a porosity of 75-86%. The porous puff-like magnesia obtained by the preparation method of the invention has high purity, and the magnesia has the same morphology under different sintering temperatures, and the preparation process is stable, and all of the magnesia has a porous puff-like shape.

(2) The porous puff-like magnesia of the present invention has two pore structures, mesopores (2-50 nm) and macropores (>50 nm), the proportion of mesopores is 1-8%, and the proportion of macropores is 99-92%. Mesopores and macropores play important roles in different fields. Mesoporous materials have regular pore size and can increase the specific surface area of the material. The existence of macropores can improve the transport rate of substances and facilitate the transport and transfer of macromolecular substances. Porous materials have the properties of high porosity, large specific surface area, and low bulk density. The unique hierarchical porous structure expands the application performance of porous magnesium oxide, especially in adsorption applications.

(3) The sintering degree of the present invention is 500-800 ° C. During the sintering process, the grain size, specific surface area and porosity of the porous puff-like magnesia increase with the increase of temperature, wherein the sintering temperature is At 800°C, magnesium oxide samples with high crystallinity and large specific surface area can be obtained. At this time, the grain size is about 51.26 μm, the porosity is 85.1577%, and the specific surface area is 20.62 m ² /g.

Description of drawings

Fig. 1 is the XRD curve of precursor basic magnesium carbonate;

Fig. 2 is the SEM image of the precursor basic magnesium carbonate;

Fig. 3 is the TG curve of precursor;

Fig. 4 is the XRD curve of porous fluffy spherical magnesia obtained in Example 1-3;

Fig. 5 is the magnesium oxide SEM image obtained by embodiment 1-3;

Fig. 6 is the nitrogen adsorption and desorption curve of the porous puff-shaped magnesia obtained in Example 1-3;

Fig. 7 is a pore size distribution diagram of the porous puff-like magnesia obtained in Examples 1-3.

Detailed ways

The present invention will be further described below with reference to the embodiments, and the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

(1) Weigh 12.198g MgCl ₂ ·6H ₂ O and put it into a 250mL beaker, weigh 150mL of deionized water with a measuring cylinder and pour it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a MgCl solution _;

(2) weigh 8.292g K ₂ CO ₃ into a 100mL beaker, measure 90 mL of deionized water and put it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a K ₂ CO ₃ solution;

( ₃ ) MgCl solution is slowly added dropwise in anhydrous potassium carbonate solution to obtain white mixture;

(4) The above-mentioned white mixture is transferred to the autoclave lined with polytetrafluoroethylene to react, and the filling rate of the reaction kettle is 80%. Hydrothermal treatment was carried out under the condition of 1 hour, and after the end, it was taken out and naturally cooled to room temperature. The reactants were washed with deionized water and absolute ethanol respectively and centrifuged, and then dried to constant weight in a blast drying oven at 100 ° C. , get the precursor;

(4) The obtained precursor is sintered at a high temperature at a temperature of 500° C., and kept for 3 hours to obtain porous puff-shaped magnesia.

Example 2

(1) Weigh 12.198g MgCl ₂ ·6H ₂ O and put it into a 250mL beaker, weigh 150mL of deionized water with a measuring cylinder and pour it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a MgCl solution _;

(2) Weigh 8.292g K ₂ CO ₃ into a 100mL beaker, measure 90 mL of deionized water and put it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a K ₂ CO ₃ solution;

( ₃ ) MgCl solution is slowly added dropwise in anhydrous potassium carbonate solution to obtain white mixture;

(4) The above-mentioned white mixture is transferred to the autoclave lined with polytetrafluoroethylene to react, and the filling rate of the reaction kettle is 80%. Hydrothermal treatment was carried out under the condition of 1 hour, and after the end, it was taken out and naturally cooled to room temperature. The reactants were washed with deionized water and absolute ethanol respectively and centrifuged, and then dried to constant weight in a blast drying oven at 100 ° C. , get the precursor;

(4) The obtained precursor is sintered at a high temperature at a temperature of 650° C., and kept for 3 hours to obtain porous puff-shaped magnesia.

Example 3

(1) Weigh 12.198g MgCl ₂ ·6H ₂ O and put it into a 250mL beaker, weigh 150mL of deionized water with a measuring cylinder and pour it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a MgCl solution _;

(2) Weigh 8.292g K ₂ CO ₃ into a 100mL beaker, measure 90 mL of deionized water and put it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a K ₂ CO ₃ solution;

( ₃ ) MgCl solution is slowly added dropwise in anhydrous potassium carbonate solution to obtain white mixture;

(4) The above-mentioned white mixture is transferred to the autoclave lined with polytetrafluoroethylene to react, and the filling rate of the reaction kettle is 80%. Hydrothermal treatment was carried out under the condition of 1 hour, and after the end, it was taken out and naturally cooled to room temperature. The reactants were washed with deionized water and absolute ethanol respectively and centrifuged, and then dried to constant weight in a blast drying oven at 100 ° C. , get the precursor;

(4) The obtained precursor is sintered at a high temperature at a temperature of 800° C. and kept for 3 hours to obtain porous puff-shaped magnesia.

Example 4

(1) Weigh 12.198g MgCl ₂ ·6H ₂ O and put it into a beaker, get 150mL of deionized water and pour it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a MgCl solution _;

(2) Weigh 8.292g K ₂ CO ₃ into a beaker, take 90 mL of deionized water and put it into the beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a K ₂ CO ₃ solution;

( ₃ ) MgCl solution is slowly added dropwise in anhydrous potassium carbonate solution to obtain white mixture;

(4) Transfer the above-mentioned white mixture to an autoclave lined with polytetrafluoroethylene for reaction, and the filling rate of the reaction kettle is 75%. Hydrothermal treatment was carried out under the condition of 1 hour, and after the end, it was taken out and naturally cooled to room temperature. The reactants were washed with deionized water and absolute ethanol respectively and centrifuged, and then dried to constant weight in a blast drying oven at 100 ° C. , get the precursor;

(4) The obtained precursor is sintered at a high temperature at a temperature of 800° C., and kept for 4 hours to obtain porous puff-shaped magnesia.

Example 5

(1) Weigh 36.594g MgCl ₂ 6H ₂ O and put it into a container, pour 450 mL of deionized water into a beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a MgCl solution _;

(2) weigh 24.876g K ₂ CO ₃ into a container, take 270 mL of deionized water and put it into a beaker, stir it with a magnetic heating stirrer to fully dissolve it, and obtain a K ₂ CO ₃ solution;

( ₃ ) MgCl solution is slowly added dropwise in anhydrous potassium carbonate solution to obtain white mixture;

(4) The above-mentioned white mixture is transferred to the autoclave whose inner lining is polytetrafluoroethylene to react, and the filling rate of the reaction kettle is 85%. Hydrothermal treatment was carried out under the condition of 1 hour, and after the end, it was taken out and naturally cooled to room temperature. The reactants were washed with deionized water and absolute ethanol respectively and centrifuged, and then dried to constant weight in a blast drying oven at 100 ° C. , get the precursor;

(4) The obtained precursor is sintered at a high temperature at a temperature of 800° C., and kept for 4 hours to obtain porous puff-shaped magnesia. 1. Characterize the precursor:

1. Characterization of precursor phases

Figure 1 is the XRD pattern of the precursor, as shown in Figure 1, it can be seen from the observation that the diffraction peak is sharp and the basic line is smooth, indicating that the precursor has good crystallinity, and the characteristic diffraction peak of the precursor is consistent with the standard diffraction card 25-0513 , when the main crystal plane diffraction peaks 2θ in the spectrum are 9.6°, 13.8°, 15.3°, and 30.8°, which correspond to the (100), (110), (011), (310) planes of the crystal grains, respectively. It can be seen that the precursor is Basic magnesium carbonate, its molecular formula is: 4MgCO ₃ ·Mg(OH) ₂ ·4H ₂ O.

2. Characterization of precursor morphology

Figure 2 is the SEM image of the precursor. As shown in Figure 2, it can be seen from the figure that the morphology of the prepared precursor is a sheet-like structure of different sizes, and the arrangement is chaotic and irregular, and the dispersion is not good. There is a certain aggregation and overlap between the slices.

3. Thermogravimetric analysis of precursors

Figure 3 shows the TG curve of the basic magnesium carbonate precursor heated from room temperature to 800 °C at a heating rate of 5 °C/min. It can be seen from Figure 3 that the thermal decomposition process of the precursor is mainly completed in two stages. At 135-335 ℃, with the increase of temperature, the precursor basic magnesium carbonate is decomposed by heat and loses 4 crystal waters, the actual weight loss is 14.36%, the theoretical weight loss is 15.45%, the difference between the two is not big, at this time, the reaction The equation is:

4MgCO ₃ ·Mg(OH) ₂ ·4H ₂ O→4MgCO ₃ ·Mg(OH) ₂ +4H ₂ O↑

In the second stage, at 335-585 °C, the weight loss rate is relatively large, and the basic magnesium carbonate continues to be decomposed by heat, loses structural water, releases _CO2 gas and generates magnesium oxide. The theoretical weight loss is 41.63%, and the actual weight loss is 42.72%. The actual weight loss is not much different from the theoretical weight loss. The total weight loss of basic magnesium carbonate is 57.08%, which is the same as the theoretical weight loss of 57.08% when decomposed into magnesium oxide. The reaction equation is:

4MgCO ₃ ·Mg(OH) ₂ →5MgO+4CO ₂ ↑+H ₂ O↑

2. Characterize the porous puff-shaped magnesia obtained in Example 1-3:

1. Phase characterization

The porous puff-shaped magnesium oxide obtained in Examples 1-3 was characterized by a DMAX1400 X-ray diffractometer, and the XRD curve of the sample is shown in FIG. 4 . It can be seen from Fig. 4 that with the increase of the sintering temperature, the position of the diffraction peak of the XRD curve of the porous puff-like magnesia hardly changes, but the peak intensity keeps increasing and the peak shape becomes sharper, indicating that the obtained porous puff-like magnesia crystals are more crystalline. Perfect, the five characteristic diffraction peaks in Figure 4 are completely consistent with the standard spectrum of magnesium oxide (JCPDS87-0651). The diffraction peaks of magnesium oxide at 2θ are 37.0°, 43.0°, 62.4°, 74.8°, 78.7°, corresponding to crystal The (111), (200), (220), (311), (222) planes of the grains show that the sample is magnesium oxide with a cubic crystal structure.

In Example 1, when the sintering temperature is 500 °C, the peak shape of the XRD curve of the magnesium oxide sample is broadened and the peak value is small, which indicates that at this sintering temperature, the crystallinity of the magnesium oxide sample is low and there are lattice defects, and the XRD pattern of the sample is in the When 2θ is 37.0°, there is almost no peak, indicating that the decomposition of the precursor is incomplete, which is consistent with the results of thermogravimetric analysis. The obtained magnesium oxide sample is in a transition state between crystalline and amorphous.

In Example 2, the sintering temperature was 650°C. Compared with the XRD pattern of the porous puff-like magnesia obtained in Example 1, the peak shape was sharper, the broadening of the XRD characteristic peaks was reduced, and the peak value was significantly increased. Magnesium is in a crystalline state, and the crystallinity is further improved.

In Example 3, the sintering temperature was 800°C, the obtained porous fluffy spherical magnesia had a sharp peak shape, a reduced peak width, and a further increase in the peak intensity. At this time, the sample had good crystallinity and high purity, and the grain size was further improved. grow up.

2. Morphological characterization

The porous puff-shaped magnesium oxide obtained in Examples 1-3 was scanned and observed under an electron microscope to obtain a SEM image, as shown in FIG. 5 . It can be seen from Figure 5 that the other experimental conditions of Examples 1-3 remain unchanged, and only using different sintering temperatures, the morphology of the porous puff-shaped magnesium oxide has undergone great changes. The magnesium oxide is transformed into a porous puff-like structure, because the sheet-like structure has a high surface energy. With the increase of temperature, the product tends to decrease in surface energy and entropy, and finally form a spherical structure, and At the same sintering temperature, the samples have good dispersibility and uniform size. After different sintering temperatures, the prepared magnesia samples are all porous fluffy spherical magnesia, indicating that the sintering temperature affects the morphology of the samples in the range of 500-800 °C At the same time, as the temperature increases, the grain size gradually increases, and this trend is consistent with the results of the XRD analysis above. When the sintering temperature is 500 °C, 650 °C and 800 °C, the corresponding The sample particle sizes are approximately 26.60 μm, 28.76 μm and 51.26 μm.

3. Characterization of Pore Structure

Figure 6 is the nitrogen adsorption and desorption curves of the porous puff-shaped magnesia obtained in Example 1-3. It can be seen from Figure 6 that the nitrogen adsorption and desorption of the sample magnesia prepared at temperatures of 500°C, 650°C and 800°C The curves belong to the same type and are classified according to the International Union of Theoretical (Chemistry) and Applied Chemistry (IUPAC): all three isotherms belong to the IV type. When the relative pressure is low, the two isotherms of desorption and adsorption almost coincide, and when the relative pressure is relatively low, the two isotherms of desorption and adsorption almost coincide. When the pressure is high (P/P0>0.8), the desorption isotherm and the adsorption isotherm begin to separate, forming a mesoporous hysteresis loop, which belongs to the H ₃ type, indicating that the obtained porous fluffy spherical magnesia is Narrow voids formed by the accumulation of flake-like particles, which are consistent with the SEM observations.

The pore size distribution diagram of the porous puff-shaped magnesium oxide obtained in Examples 1-3 was measured by mercury intrusion method, as shown in Figure 7. It can be seen from the figure that the prepared porous puff-shaped magnesium oxide sample has a large pore size distribution range. There are two kinds of pore structures, mesopores (2～50nm) and macropores (>50nm), among which macropores are the main ones. The pore size distribution curve presents a bimodal shape, and the boundary pore size of the bimodal is about 550-3900 nm. As the sintering temperature increases, the peak value of the pore size distribution curve shifts to the right, and the pore size distribution area moves to the large pore area.

Table 1 shows the pore structure parameters of the porous puff-shaped magnesium oxide obtained in Examples 1-3. With the increase of sintering temperature, the specific surface area, porosity and intermediate pore size of porous puff-like magnesia gradually increased, the proportion of mesopores gradually decreased, and the macropores gradually increased. The surface area and porosity are the largest, and the specific surface area is 20.62 m ² /g and the porosity is 85.1577%. Table 1 Sample MgO pore structure parameters

Specific surface area/m²·g^-1 Porosity,% Intermediate pore size/nm 2～50nm/% >50nm/% Example 1 17.48 75.6328 48.50 7.6281 92.3719 Example 2 20.19 84.0197 78.20 3.1961 96.8040 Example 3 20.62 85.1577 107.20 1.4074 98.5926

At different sintering temperatures, the grain size of porous puff-like magnesia increases gradually with the increase of temperature. Among them, the grain size is the largest at 800 °C, which is 51.26 μm. At the same time, when the sintering temperature is 800 °C, the prepared Porous puff-shaped magnesium oxide has good crystallinity, and has the largest specific surface area and porosity, which are 20.62 m ² /g and 85.1577%, respectively.

Claims (10)

1. a preparation method of porous fluffy spherical magnesia, is characterized in that, with MgCl ₂ 6H ₂ O and K ₂ CO ₃ as raw materials, after adopting hydrothermal reaction for 2-3 hours, gained precursor is sintered to obtain porous Pompous magnesia. 2. the preparation method of a kind of porous pompomed magnesia according to claim 1, is characterized in that, (1) Weigh MgCl ₂ ·6H ₂ O into deionized water, stir until dissolved, and obtain MgCl ₂ solution; (2) Weigh K ₂ CO ₃ deionized water, stir until dissolved, and obtain K ₂ CO ₃ solution; (3) The MgCl ₂ solution was slowly added dropwise to the K ₂ CO ₃ solution to obtain a white mixture; (4) The white mixture is subjected to a hydrothermal reaction at a constant temperature, taken out after the end and naturally cooled to room temperature, the reactant is washed with deionized water and anhydrous ethanol in turn and centrifuged, and then dried to a constant weight to obtain a precursor ; (5) The obtained precursor is sintered and kept warm to obtain porous puff-shaped magnesia. 3 . The method for preparing porous puff-shaped magnesia according to claim 2 , wherein, in step (5), the sintering temperature is 500-800° C. 4 . 4 . The method for preparing a porous puff-shaped magnesia according to claim 1 , wherein the equivalence ratio of the MgCl ₂ ·6H ₂ O to K ₂ CO ₃ is 1:1. 5 . 5. the preparation method of a kind of porous fluffy magnesia according to claim ₂ , is characterized in that, the concentration of described MgCl solution is 0.4mol/L, and the concentration of described _K2CO solution is _0.67mol / L. 6 . The method for preparing a porous puff-shaped magnesia according to claim 2 , wherein the hydrothermal reaction in step (4) is specifically, transferring the white mixture to the inner lining of polytetrafluoroethylene. 7 . The reaction is carried out in the high pressure autoclave, the filling rate of the reactor is 75-85%, the sealed reactor is put into the box-type resistance furnace at 180-200 ℃, and the hydrothermal reaction treatment is carried out under the condition of constant temperature for 2-3 hours. 7 . The preparation method of porous puff-shaped magnesia according to claim 2 , wherein the hydrothermal reaction in step (4) is specifically: transferring the white mixture to the inner lining of polytetrafluoroethylene. 8 . The reaction was carried out in an autoclave, the filling rate of the reactor was 80%, and the sealed reactor was placed in a box-type resistance furnace at 180 °C and a constant temperature for 2 hours for hydrothermal treatment. 8 . The method for preparing porous puff-shaped magnesia according to claim 2 , wherein, in step (5), the holding time is 3-4h. 9 . 9 . The method for preparing porous puff-shaped magnesia according to claim 3 , wherein in step (5), the sintering temperature is 800° C. 10 . 10. A porous fluffy magnesia, characterized in that the porous fluffy magnesia has a comparative area of 17-21 m ² ·g ^-1 , a porosity of 75-86%, and contains mesopores and macropores Two pore structures, the proportion of mesopores is 1-8%, and the proportion of macropores is 99-92%.

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