A layered adsorbent containing hydroxyl vacancies and preparation method thereof

Abstract

The present invention discloses a layered adsorbent containing hydroxyl vacancies and a preparation method thereof. The method comprises dispersing a ternary hydrotalcite precursor in water, etching with an acid solution, centrifuging and washing until neutral, and drying to obtain the layered adsorbent containing hydroxyl vacancies. The present invention introduces tetravalent metal ions into the hydrotalcite layer to generate hydroxyl vacancies, and then uses acid etching to further increase the number of hydroxyl vacancies and adsorption active sites. Theoretical calculations show that increasing the hydroxyl vacancies in the hydrotalcite layer can significantly increase the adsorption energy between the π electrons and the layered adsorbent, thereby having a high adsorption capacity for VOCs and aromatic hydrocarbon molecules in wastewater, with an adsorption capacity of up to 70 mg / g. The adsorbent prepared by the present invention is low-cost, simple in method, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of layered inorganic functional materials, and particularly relates to a layered adsorbent containing hydroxyl vacancies and a preparation method thereof. Background Art

[0002] Aromatic hydrocarbons have a wide range of applications in petrochemicals, materials manufacturing, and pharmaceutical manufacturing. Aromatic hydrocarbons can be categorized as either natural or anthropogenic. The former primarily originates from biosynthesis in nature and is present in a relatively low proportion; the latter primarily originates from the incomplete combustion of organic matter such as coal and petroleum. They are widely distributed and can be found in the air, water, and soil. Aromatic hydrocarbons are carcinogenic, teratogenic, and mutagenic, posing significant potential hazards to the ecological environment, organisms, and human health. Existing aromatic hydrocarbon treatment technologies primarily include combustion, absorption, condensation, adsorption, combustion, biological, and combined methods for treating volatile organic compounds (VOCs). Adsorption is the most widely used method, offering numerous advantages, including simple design and operation, low investment and maintenance costs, and the absence of undesirable byproducts. It allows for the economical and environmentally friendly treatment of aromatic hydrocarbons. The development of simple, rapid, and environmentally friendly adsorbents has become a research hotspot.

[0003] Layered double hydroxides (LDHs), also known as hydrotalcite, are a typical host-guest layered structure compound. The metal ions in the host layer form a hexacoordinated octahedral configuration with hydroxyl groups. The octahedral units share edges to form a two-dimensional layer of positively charged hydrotalcite. The layers are stacked along the third dimension to form an ordered layered structure under the support of interlayer anions. The general expression of hydrotalcite is [M II 1-x M III x (OH)2][A n- ]x / n·zH2O. Among them, M II For divalent metal ions (such as Mg 2+ , Ca 2+ 、Zn 2+ etc.), M III For trivalent metal ions (such as Cr 3+ 、Al 3+ 、Fe 3 + 、V 3+ 、Ga 3+ etc.), A n- For anions (such as CO3 2- 、Cl - 、NO3 - 、SO4 2- ), which can balance the charge and keep the hydrotalcite as a whole electrically neutral. x=MIII / M II +M III For pure hydrotalcite, the x value is between 0.2 and 0.33. Hydrotalcite has an adjustable chemical composition and unique structure and properties. Specifically, the elemental composition of the main layer, the charge distribution of the main layer, the type and number of interlayer anions, and the interlayer spacing can be controlled. Hydrotalcites with greatly different chemical properties can be obtained, which enables them to be designed for specific uses. Hydrotalcite has good thermal stability and renewability, a loose and porous morphology and a large specific surface area, which are conducive to the exposure of adsorption active sites. As an adsorption material, it is widely used in the adsorption treatment of heavy metals and anionic dyes, but research on the adsorption of aromatic hydrocarbons is still limited. Summary of the Invention

[0004] The purpose of the present invention is to provide a layered adsorbent containing hydroxyl vacancies and a preparation method thereof.

[0005] The preparation method of the layered adsorbent containing hydroxyl vacancies is as follows: dispersing a ternary hydrotalcite precursor in water, etching with acid, centrifuging and washing to neutrality after etching, and drying to obtain the layered adsorbent containing hydroxyl vacancies.

[0006] The lamellar metal ions of the ternary hydrotalcite precursor consist of divalent metal ions, trivalent metal ions and tetravalent metal ions.

[0007] The divalent metal ion is selected from Mg 2+ 、Zn 2+ , Ca 2+ 、Cu 2+ 、Ni 2+ 、Co 2+ 、Fe 2+ 、Mn 2+ or Cd 2+ One or more of the .

[0008] The trivalent metal ion is selected from Al 3+ 、Ni 3+ 、Co 3+ 、Fe 3+ 、Mn 3+ Cr 3+ 、V 3+ or Ti 3+ One or more of the .

[0009] The tetravalent metal ion is selected from Zr 4+ 、Sn 4+ 、Mn 4+ 、Ti 4+ One or more of the .

[0010] The molar ratio of the divalent metal ions to the trivalent metal ions is 2-4, and the molar ratio of the trivalent metal ions to the tetravalent metal ions is 1-10.

[0011] The concentration of the acid solution is 0.1-1 mol / L.

[0012] The acid solution is selected from one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, phosphorous acid, formic acid and acetic acid.

[0013] The method for using the layered adsorbent containing hydroxyl vacancies is as follows: adding the layered adsorbent containing hydroxyl vacancies to waste liquid containing aromatic hydrocarbons for oscillation adsorption, or filtering and adsorbing the waste gas containing aromatic hydrocarbons through the layered adsorbent containing hydroxyl vacancies to remove aromatic hydrocarbons.

[0014] The aromatic hydrocarbons are one or more of benzene, toluene, xylene, ethylbenzene, styrene, phenylacetylene, cumene, biphenyl, naphthalene, anthracene and phenanthrene.

[0015] This invention introduces tetravalent metal ions into the hydrotalcite lamellae to create hydroxyl vacancies, which are then further increased through acid etching to increase the number of hydroxyl vacancies and adsorption active sites. Theoretical calculations show that increasing the number of hydroxyl vacancies in the hydrotalcite lamellae significantly increases the adsorption energy between π electrons and hydroxyl vacancies, resulting in a high adsorption capacity for VOCs and aromatic hydrocarbons in wastewater, reaching up to 70 mg / g. The adsorbent prepared by this invention is low-cost, simple, and has promising application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 XRD pattern of MgAlZr-LDH.

[0017] Figure 2 SEM image of MgAlZr-LDH.

[0018] Figure 3 SEM image of MgAlZr-LDH-VOH.

[0019] Figure 4 XPS O1s pattern of MgAl-LDH.

[0020] Figure 5 XPS O1s pattern of MgAlZr-LDH.

[0021] Figure 6 XPS O1s pattern of MgAlZr-LDH-VOH. DETAILED DESCRIPTION

[0022] Example 1

[0023] 1) Prepare a mixed metal salt solution: weigh 28.13g of aluminum nitrate, 43.62g of magnesium nitrate, and 17.34g of zirconium oxynitrate and completely dissolve them in deionized water to 150mL; prepare an alkaline solution: weigh 18g of sodium hydroxide and 15.9g of sodium carbonate and completely dissolve them in deionized water to 150mL. Clean the rotating liquid film reactor, set the speed to 3000rpm, and simultaneously introduce the mixed metal salt solution and alkaline solution into the rotating liquid film reactor for rapid nucleation. Transfer the obtained white slurry to a 500mL four-necked flask and reflux at 100℃ for crystallization for 6h. Centrifuge the slurry with deionized water until neutral and dry it to obtain Mg2AlZr-LDH. XPS analysis reveals that oxygen exists in hydrotalcite primarily in two chemical forms. The O 1s spectrum is characterized by two peaks: the 531.8 eV peak (O1) is associated with surface hydroxyl groups (M-OH) on the hydrotalcite, and the 532.9 eV peak (O2) is consistent with amorphous carbon oxygen and surface-adsorbed water molecules. The resulting hydroxyl oxygen accounts for 60.8% of surface oxygen, lower than the 77.9% observed in Mg2Al-LDH synthesized using the same method, indicating the presence of hydroxyl vacancies in the hydrotalcite laminae.

[0024] 2.0 g of Mg2AlZr-LDH sample was dissolved in 200 mL of deionized water and ultrasonically dispersed into a uniform hydrotalcite slurry. 10 mL of a prepared dilute nitric acid solution (pH 1) was added and magnetically stirred for 30 minutes. The hydrotalcite slurry was then centrifuged, washed to neutrality, and dried at 60°C to obtain nitric acid-etched Mg2AlZr-LDH, designated sample Mg2AlZr-LDH-VOH. XPS analysis revealed that the proportion of hydroxyl oxygen in the surface oxygen element was 48.7%.

[0025] The calculation model was established using Materials Studio software: First, the structural models of Mg2Al-LDH and Mg2AlZr-LDH were constructed. The spatial point group is then constructed by removing the hydroxyl groups on the (001) crystal plane of the constructed Mg2AlZr-LDH structure model to establish a Mg2AlZr-LDH-VOH model containing hydroxyl vacancies. The (003) crystal plane is the main layer of hydrotalcite and is the preferentially exposed crystal plane in hydrotalcite. The (001) crystal plane of the hydrotalcite model is cut to establish a structure containing two metal layers and two layers of interlayer anions CO3 2- And the structural model of H2O molecule, and add The vacuum layer is used to ignore the interaction caused by the periodicity in the z direction. Benzene in aromatic hydrocarbons is selected as the adsorbate, and the adsorption energy of benzene molecules on different hydrotalcite (001) crystal plane metal sites is calculated respectively. All spin-polarized density functional theory (DFT) calculations are completed by the Vienna ab initio simulation package (VASP). The projected augmented plane wave (PAW) pseudopotential method is used to simplify the inner electrons. The Perdew-Burke-Ernzerhof (PBE) functional in the generalized gradient approximation (GGA) is used to describe the electron exchange-correlation interaction. The cutoff energy is set to 400 eV in the structure optimization process, and the convergence thresholds of energy and force are 10 -5 and A 3 × 3 × 1 k-point grid was used to sample the Brillouin zone. The DFT-D3 (BJ) method proposed by Grimme was used for dispersion correction to take into account the interaction between the adsorbed molecules and the material. The adsorption energy of benzene molecules (E ads ) is calculated by the following formula:

[0026] E ads =E total -E substrate -E molecule

[0027] Among them E total is the total energy of the adsorption structure, E substrate and E molecule are the energies of the (001) crystal plane of clean hydrotalcite and isolated molecular benzene, respectively. By definition, a negative E ads It means that it can adsorb benzene molecules.

[0028]

[0029] The study found that the insertion of tetravalent metal ions creates hydroxyl vacancies, where benzene molecules tend to adsorb, making the overall structure more stable. The adsorption energy of benzene molecules at hydroxyl vacancies is -1.64 eV, significantly higher than the absolute value of the adsorption energy of benzene molecules at metal sites.

[0030] Application Example 1

[0031] Hydrotalcite benzene adsorption experiment: Two 100mL Erlenmeyer flasks were used. 80mg of the Mg2AlZr-LDH-VOH hydrotalcite adsorbent prepared in Example 1 was added to one flask. The other flask was left unadsorbed as a blank control. 50mL of a 200ppm benzene aqueous solution was added to both flasks simultaneously. The flasks were then placed in a thermostat at 20°C for 5 hours of mixing and adsorption. The suspension was then filtered, and the absorbance of the filtrate was measured using a UV spectrophotometer to determine the corresponding benzene concentration. The amount of benzene adsorbed was calculated as follows:

[0032]

[0033] Where q e is the adsorption capacity of benzene (mg / g), C0 is the concentration of benzene in the blank sample without adsorbent (mg / L); C e is the concentration of benzene in the sample to which the adsorbent is added (mg / L); V is the volume of the benzene aqueous solution (mL); and M is the mass of the sample to which the adsorbent is added (mg).

[0034] The calculated adsorption capacity of the adsorbent for benzene is 69.89 mg / g.

[0035] Example 2

[0036] 1) Prepare a mixed metal salt solution: weigh 18.76g of aluminum nitrate, 44.62g of zinc nitrate and 5.78g of zirconium oxynitrate and completely dissolve them in deionized water to 200mL; prepare an alkaline solution: weigh 14.4g of sodium hydroxide and 15.9g of sodium carbonate and completely dissolve them in deionized water to 200mL. Clean the rotating liquid film reactor, set the speed to 3000rpm, and let the mixed metal salt solution and alkaline solution enter the rotating liquid film reactor at the same time for rapid nucleation. Transfer the obtained white slurry to a 500mL four-necked flask and reflux at 80℃ for crystallization for 8h. Centrifuge the slurry with deionized water until it is neutral, and dry it to obtain Zn3Al1Zr 0.5 The XPS test showed that the proportion of hydroxyl oxygen in the surface oxygen element was 52.33%, which was lower than the 72.61% of Zn3Al-LDH synthesized by the same method, indicating that hydroxyl vacancies were generated in the hydrotalcite layer.

[0037] 2) Add 3.0g Zn3Al1Zr into 300mL of deionized water 0.5 -LDH sample was dissolved and ultrasonically dispersed into a uniform hydrotalcite slurry. 20 mL of 1 M dilute hydrochloric acid solution was added and then magnetically stirred for 20 min. After that, the hydrotalcite slurry was centrifuged, washed to neutrality, and dried at 60 ° C to obtain Zn3Al1Zr after nitric acid etching. 0.5 -LDH, recorded as sample Zn3Al1Zr 0.5 -LDH-VOH. XPS analysis shows that the proportion of hydroxyl oxygen in the surface oxygen element is 44.8%.

[0038] Example 3

[0039] 1) Prepare a mixed metal salt solution: weigh 20.27g of ferric chloride, 30.5g of magnesium chloride and 3.91g of tin tetrachloride and completely dissolve them in deionized water to 150mL; prepare an alkaline solution: weigh 18g of sodium hydroxide and 15.9g of sodium carbonate and completely dissolve them in deionized water to 150mL. Clean the rotating liquid film reactor, set the speed to 3000rpm, and let the mixed metal salt solution and alkaline solution enter the rotating liquid film reactor at the same time for rapid nucleation. Transfer the obtained white slurry to a 500mL four-necked flask and reflux at 90℃ for crystallization for 10h. Centrifuge the slurry with deionized water until it is neutral, and dry it to obtain Mg2Fe1Sn 0.2 The XPS test showed that the proportion of hydroxyl oxygen in the surface oxygen element was 65.17%, which was lower than the 74.8% of Mg2Fe-LDH synthesized by the same method, indicating that hydroxyl vacancies were generated in the hydrotalcite layer.

[0040] 4.0 g of Mg2Fe1Sn0.2-LDH sample was dissolved in 400 mL of deionized water and ultrasonically dispersed into a uniform hydrotalcite slurry. 50 mL of a prepared 0.5 M dilute formic acid solution was added, followed by magnetic stirring for 1 hour. The hydrotalcite slurry was centrifuged, washed to neutrality, and dried at 60°C to obtain nitric acid-etched Mg2Fe1Sn0.2-LDH, designated as sample Mg2Fe1Sn0.2-LDH-VOH. XPS analysis revealed that the proportion of hydroxyl oxygen in the surface oxygen element was 40.3%.

Claims

1. A method for using a layered adsorbent containing hydroxyl vacancies, characterized in that: The specific operation of the method of use is: adding the layered adsorbent containing hydroxyl vacancies to the waste liquid containing aromatic hydrocarbons for oscillation adsorption, or filtering the waste gas containing aromatic hydrocarbons through the layered adsorbent containing hydroxyl vacancies to remove the aromatic hydrocarbons by adsorption; The preparation method of the layered adsorbent containing hydroxyl vacancies is as follows: dispersing a ternary hydrotalcite precursor in water, etching with acid, centrifuging and washing to neutrality after etching, and drying to obtain the layered adsorbent containing hydroxyl vacancies; The lamellar metal ions of the ternary hydrotalcite precursor consist of divalent metal ions, trivalent metal ions and tetravalent metal ions.

2. The method of use according to claim 1, characterized in that: The divalent metal ion is selected from Mg 2+ 、Zn 2+ , Ca 2 + 、Cu 2+ 、Ni 2+ 、Co 2+ 、Fe 2+ 、Mn 2+ or Cd 2+ One or more of the .

3. The method of use according to claim 1, wherein: The trivalent metal ion is selected from Al 3+ 、Ni 3+ 、Co 3 + 、Fe 3+ 、Mn 3+ Cr 3+ 、V 3+ or Ti 3+ One or more of the .

4. The method of use according to claim 1, wherein: The tetravalent metal ion is selected from Zr 4+ 、Sn 4+ 、Mn 4 + 、Ti 4+ One or more of the .

5. The method of use according to claim 1, characterized in that: The molar ratio of the divalent metal ions to the trivalent metal ions is 2-4, and the molar ratio of the trivalent metal ions to the tetravalent metal ions is 1-10.

6. The method of use according to claim 1, characterized in that: The concentration of the acid solution is 0.1-1 mol / L.

7. The method of use according to claim 1, characterized in that: The acid solution is selected from one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, phosphorous acid, formic acid and acetic acid.

8. The method of use according to claim 1, characterized in that: The aromatic hydrocarbons are one or more of benzene, toluene, xylene, ethylbenzene, styrene, phenylacetylene, cumene, biphenyl, naphthalene, anthracene and phenanthrene.

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