Amino modified titanium-based MOF composite material and preparation method thereof

Abstract

The invention discloses an amino-modified titanium-based MOF composite material and a preparation method thereof, and belongs to the technical field of sewage treatment.The preparation method comprises the steps that graphene aerogel powder serves as a carrier, titanium-based MOF containing a Ti-O-Mn heterostructure is loaded on the surface, then dopamine polymerization is conducted to obtain amino-modified titanium-based MOF powder, the amino-modified titanium-based MOF powder serves as a cross-linking site, and the amino-modified titanium-based MOF composite material is obtained. The surface of the amino-modified titanium-based MOF powder is coated with polyimide with a three-dimensional network structure, and the polyimide has a good removal rate on heavy metals in the aspect of sewage degradation and has excellent stability and recoverability; by constructing a three-dimensional network structure, the specific surface area of the polyimide film is increased, the synergistic effect of the polyimide film and titanium-based MOF is improved, polyimide is an organic high-molecular polymer and has high chemical inertness and a stable aromatic heterocyclic structure unit, amino is fixed through high crosslinking density, and the stability of the amino is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and specifically relates to an amino-modified titanium-based MOF composite material and a preparation method thereof. Background Art

[0002] Despite significant progress and remarkable achievements in resource and environmental protection, water pollution remains a pressing issue in my country. Many lakes and reservoirs are experiencing severe eutrophication due to excessive nitrogen and phosphorus concentrations, and toxic substances are negatively impacting aquatic life. Heavy metal and organic pollution have become major water quality issues.

[0003] Adsorption is a simple, easy-to-use, and inexpensive method for wastewater treatment. Recent research in this area has focused on identifying relatively low-cost adsorbents, such as montmorillonite, kaolin, scalyptus, and mineral silicates. However, for any adsorbent, adsorption performance remains the most critical technical indicator.

[0004] Metal-organic framework (MOF) is an ordered porous crystalline material with the characteristics of high surface area and large pore volume. It has been widely used in the field of adsorption. Since its invention, titanium-based MOFs have been widely studied and applied to water treatment. However, titanium-based MOFs still have certain defects. For example, nano-form MOFs are difficult to separate in water treatment and easily cause secondary pollution. Due to the size effect of nano-MOFs, they are easy to agglomerate. These defects hinder the exposure of MOFs active sites, resulting in insufficient hydrothermal stability and low photocatalytic efficiency.

[0005] Therefore, for the treatment of pollutant wastewater, it is particularly important to find a titanium-based MOFs adsorbent with excellent adsorption performance and strong adsorption specificity. Summary of the Invention

[0006] The purpose of the present invention is to provide an amino-modified titanium-based MOF composite material and a preparation method thereof. Graphene aerogel powder is used as a carrier, a titanium-based MOF containing a Ti-O-Mn heterostructure is loaded on the surface, and dopamine polymerization is performed to obtain amino-modified titanium-based MOF powder. Using this as a cross-linking site, a three-dimensional network structure of polyimide is constructed and coated on the surface of the amino-modified titanium-based MOF powder. In terms of wastewater degradation, the composite material has a good removal rate for heavy metals and has excellent stability and recyclability.

[0007] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing an amino-modified titanium-based MOF composite material comprises the following steps: Step 1: Using graphene oxide and fumed silica as raw materials, graphene aerogel powder is prepared by utilizing hydrogen bond cross-linking and grinding.

[0008] Step 2: The carboxyl groups on the surface of the graphene aerogel powder are combined with the hydroxyl groups on the surface of 2,5-dihydroxyterephthalic acid through an esterification reaction. Titanium tetrachloride is used as the titanium source to hydrothermally synthesize titanium-based MOF on the surface of the graphene aerogel powder. Manganese chloride is then used as the manganese source to grow manganese oxide on the surface of the titanium-based MOF to form a heterogeneous structure, thereby obtaining manganese oxide-modified titanium-based MOF adsorption powder.

[0009] Step 3: The titanium-based MOF adsorption powder is modified by coating manganese oxide with polydopamine to obtain amino-modified titanium-based MOF powder.

[0010] Step 4: Using 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy)benzene, and 3,5-diaminobenzoic acid as raw materials, acetic anhydride and pyridine as imidization reagents, and melamine as a cross-linking agent, combined with the auxiliary cross-linking effect of amino-modified titanium-based MOF powder, an amino-modified titanium-based MOF composite material was prepared.

[0011] Furthermore, the specific preparation steps of graphene aerogel powder are as follows: Graphene oxide and deionized water were added to a reactor, stirred at 20-25°C and 500-600 r / min for 20-30 minutes, and then fumed silica was added. The mixture was stirred for 30-40 minutes and transferred to a freeze dryer. The mixture was freeze-dried at a vacuum degree of -0.085 MPa for 24-26 hours. The product was then transferred to a muffle furnace, heated to 300-340°C under a nitrogen atmosphere and kept warm for 10-12 hours. The product was then ground and pulverized to obtain graphene aerogel powder.

[0012] Furthermore, the usage ratio of graphene oxide, deionized water and fumed silica is 300-400 g: 2-3 L: 50-60 g.

[0013] Furthermore, the specific preparation steps of manganese oxide modified titanium-based MOF adsorption powder are as follows: The modified graphene aerogel powder, titanium tetrachloride and N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, stirred at 120-130°C and 500-600 r / min for 14-15 hours, and then manganese chloride was added. The stirring was continued for 10-12 hours, and the mixture was naturally cooled to room temperature. The mixture was centrifuged at 10000-12000 r / min for 5-6 minutes and filtered. The filter cake was washed with N,N-dimethylformamide and methanol for 2-3 times respectively, and vacuum dried at 60-80°C for 1-2 hours to obtain manganese oxide-modified titanium-based MOF adsorption powder.

[0014] Furthermore, the usage ratio of the modified graphene aerogel powder, titanium tetrachloride, N,N-dimethylformamide and manganese chloride is 120-130 g: 80-90 g: 2-3 L: 40-50 g.

[0015] Furthermore, the specific preparation steps of the modified graphene aerogel powder are as follows: 140-160 g of graphene aerogel powder, 150-170 g of 2,5-dihydroxyterephthalic acid and 2-3 L of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, stirred at 20-25 ° C and 500-600 r / min for 20-30 min, then heated to 80-90 ° C, added 4-5 mL of triethylamine, continued stirring for 1-2 h, filtered, and the filter cake was washed with deionized water and anhydrous ethanol 2-3 times respectively, and vacuum dried at 60-80 ° C for 1-2 h to obtain modified graphene aerogel powder.

[0016] Furthermore, the usage ratio of graphene aerogel powder, 2,5-dihydroxyterephthalic acid, N,N-dimethylformamide and triethylamine is 140-160 g: 150-170 g: 2-3 L: 4-5 mL.

[0017] Furthermore, the specific preparation steps of amino-modified titanium-based MOF powder are as follows: A Tris-HCl solution with a concentration of 0.38 mmol / L and a NaOH solution with a concentration of 0.1 mol / L were added to the reactor, stirred at 20-25 ° C and 500-600 r / min for 20-30 minutes, and the pH value was adjusted to 8.5-9. Then, the manganese oxide-modified titanium-based MOF adsorption powder was dispersed in deionized water and added to the reactor, and then DA was added. The ultrasonic fraction was 60-70 minutes, and the stirring reaction was continued for 24-26 hours. After filtering, the filter cake was washed with deionized water and anhydrous ethanol for 2-3 times respectively, and vacuum dried at 60-80 ° C for 1-2 hours to obtain amino-modified titanium-based MOF powder.

[0018] Furthermore, the usage ratio of Tris-HCl solution, NaOH solution, manganese oxide modified titanium-based MOF adsorption powder, deionized water and DA is 120-150 mL: 12-14 mL: 120-140 g: 400-500 mL: 50-60 g.

[0019] Furthermore, the specific preparation steps of the amino-modified titanium-based MOF composite material are as follows: 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy)benzene, 3,5-diaminobenzoic acid and N-methyl-2-pyrrolidone are added to a reactor, and stirred at 0-4°C and 500-600r / min for 20-30min under nitrogen protection. Then, melamine and amino-modified titanium-based MOF powder are added, and stirring is continued for 1-2h. Then, the mixture is heated to 20-25°C and stirred for 4-5h. Then, acetic anhydride and pyridine are added to the reactor, and stirring is continued for 36-38h. The mixture is filtered, and the filter cake is washed with deionized water and anhydrous ethanol 2-3 times, respectively, and vacuum dried at 60-80°C for 1-2h to obtain an amino-modified titanium-based MOF composite material.

[0020] Furthermore, the usage ratio of 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy)benzene, 3,5-diaminobenzoic acid, N-methyl-2-pyrrolidone, melamine, amino-modified titanium-based MOF powder, acetic anhydride and pyridine is 150-160 g: 120-130 g: 50-60 g: 500-600 mL: 4-5 g: 40-50 g: 20-30 g: 15-20 g.

[0021] Beneficial effects of the present invention: 1. The amino-modified titanium-based MOF composite material prepared by the present invention has a good removal rate for heavy metals in terms of wastewater degradation. After five acid washing, adsorption and desorption cycles, the adsorption rate of heavy metals only decreased by 10%, indicating that the amino-modified titanium-based MOF composite material has excellent stability and recyclability.

[0022] 2. The amino-modified titanium-based MOF composite material of the present invention is prepared by using graphene aerogel powder as a carrier, loading a titanium-based MOF containing a Ti-O-Mn heterostructure on the surface, and performing dopamine polymerization to obtain amino-modified titanium-based MOF powder. Using this as a cross-linking site, a three-dimensional network structure of polyimide is constructed and coated on the surface of the amino-modified titanium-based MOF powder to obtain an amino-modified titanium-based MOF composite material. Polyimide can effectively enhance visible light absorption, prolong the life of photogenerated charges, and improve catalytic activity. However, it also has problems such as a narrow light absorption range, severe photogenerated charge recombination, few active sites, poor stability, and a small surface area. By constructing a three-dimensional network structure, the specific surface area of ​​the polyimide film is increased, and the synergistic effect with the titanium-based MOF is increased. In addition, polyimide is an organic high molecular polymer with strong chemical inertness and stable aromatic heterocyclic structural units, which makes it have the advantages of corrosion resistance, non-toxicity, and excellent mechanical properties.

[0023] 3. After being coated with dopamine polymerization, the arrangement of the amino groups does not exist in the same plane due to steric hindrance, resulting in some amino groups participating in cross-linking. The retained amino groups can serve as Lewis basic sites to promote the hydrolysis or nucleophilic substitution reaction of pollutants. After protonation, the amino groups strengthen the electrostatic attraction to anionic pollutants. However, after acid washing and regeneration, the amino groups are easily lost due to the competitive coordination of hydrogen ions. The formation of a three-dimensional network structure fixes the amino groups through high cross-linking density, thereby improving the stability of the amino groups.

[0024] 4. The manganese oxide-modified titanium-based MOF adsorption powder of the present invention is prepared by simultaneously adding manganese salt during the solvent thermal synthesis of titanium-based MOF. Manganese ions can partially replace the coordination sites of titanium ions to form Ti-O-Mn bonds, thereby forming a Ti-O-Mn heterostructure to obtain manganese oxide-modified titanium-based MOF adsorption powder. The doping of manganese oxide can reduce the carrier recombination rate, improve the utilization rate of photogenerated electrons, and promote the photocatalytic efficiency of titanium-based MOF. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only 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 ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] Example 1: A method for preparing an amino-modified titanium-based MOF composite material, comprising the following steps: S1: Add 300g of graphene oxide and 2L of deionized water into a reactor, stir at 20℃ and 500r / min for 20min, then add 50g of fumed silica, continue stirring for 30min, transfer to a freeze dryer, and freeze-dry for 24h at a vacuum degree of -0.085MPa. Then transfer the product to a muffle furnace, heat to 300℃ under a nitrogen atmosphere and keep warm for 10h, grind and crush to obtain graphene aerogel powder.

[0027] The silanol (Si-OH) of fumed silica forms hydrogen bonds with oxygen-containing groups on the surface of graphene oxide to form a physical cross-linked network, and graphene aerogel powder is obtained after calcination.

[0028] S2: 140 g of graphene aerogel powder, 150 g of 2,5-dihydroxyterephthalic acid and 2 L of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, stirred at 20°C and 500 r / min for 20 min, then heated to 80°C, 4 mL of triethylamine was added, and stirring was continued for 1 h. The filter cake was washed twice with deionized water and anhydrous ethanol, respectively, and vacuum dried at 60°C for 1 h to obtain modified graphene aerogel powder.

[0029] S3: Add 120g of modified graphene aerogel powder, 80g of titanium tetrachloride and 2L of N,N-dimethylformamide into a polytetrafluoroethylene-lined reactor, stir at 120°C and 500r / min for 14h, then add 40g of manganese chloride, continue stirring for 10h, cool naturally to room temperature, centrifuge at 10000r / min for 5min, filter, wash the filter cake with N,N-dimethylformamide and methanol twice respectively, and dry in vacuum at 60°C for 1h to obtain manganese oxide modified titanium-based MOF adsorption powder.

[0030] The carboxyl groups on the surface of the graphene aerogel powder and the hydroxyl groups of 2,5-dihydroxyterephthalic acid undergo an esterification reaction under heating and the action of catalyst triethylamine, and the reaction monomer 2,5-dihydroxyterephthalic acid is grafted onto the surface of the graphene aerogel powder, which is then hydrothermally synthesized with titanium metal ions. Manganese salts are added during the solvent thermal synthesis of the titanium-based MOF. Manganese ions can partially replace the coordination sites of titanium ions to form Ti-O-Mn bonds, thereby forming a Ti-O-Mn heterostructure to obtain manganese oxide-modified titanium-based MOF adsorption powder. S4: 120 mL of 0.38 mmol / L Tris-HCl solution and 12 mL of 0.1 mol / L NaOH solution were added to the reactor, stirred at 20°C and 500 r / min for 20 min, and the pH value was adjusted to 8.5. Then, 120 g of manganese oxide-modified titanium-based MOF adsorption powder was dispersed in 400 mL of deionized water and added to the reactor. Then, 50 g of DA was added, and the ultrasonic fraction was 60 min. The stirring reaction was continued for 24 h, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol respectively, and dried in vacuum at 60°C for 1 h to obtain amino-modified titanium-based MOF powder.

[0031] Amino-modified titanium-based MOF powder was obtained by self-polymerization of dopamine on manganese oxide-modified titanium-based MOF powder.

[0032] S5: 150 g of 4,4'-oxydiphthalic anhydride, 120 g of 1,3-bis(4'-aminophenoxy)benzene, 50 g of 3,5-diaminobenzoic acid and 500 mL of N-methyl-2-pyrrolidone were added to a reactor. Under nitrogen protection, the mixture was stirred at 0°C and 500 r / min for 20 min. Then, 4-5 g of melamine and 40 g of amino-modified titanium-based MOF powder were added. The mixture was stirred for 1 h, then heated to 20°C and stirred for 4 h. Then, 20 g of acetic anhydride and 15 g of pyridine were added to the reactor. The mixture was stirred for 36 h and filtered. The filter cake was washed twice with deionized water and anhydrous ethanol respectively to remove unreacted monomers and dried in vacuo at 60°C for 1 h to obtain an amino-modified titanium-based MOF composite material.

[0033] Using 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy)benzene, and 3,5-diaminobenzoic acid as raw materials, the amino groups carried on the surface of amino-modified titanium-based MOF powder were used as cross-linking sites to construct a three-dimensional network structure, thereby obtaining an amino-modified titanium-based MOF composite material.

[0034] Example 2: A method for preparing an amino-modified titanium-based MOF composite material, comprising the following steps: S1: Add 350g of graphene oxide and 2.5L of deionized water into a reactor, stir at 22.5℃ and 550r / min for 25min, then add 55g of fumed silica, continue stirring for 35min, transfer to a freeze dryer, and freeze-dry for 25h at a vacuum degree of -0.085MPa. Then transfer the product to a muffle furnace, heat to 320℃ under a nitrogen atmosphere and keep warm for 11h, grind and crush to obtain graphene aerogel powder.

[0035] S2: 150 g of graphene aerogel powder, 160 g of 2,5-dihydroxyterephthalic acid and 2.5 L of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, stirred at 22.5 ° C and 550 r / min for 25 min, then heated to 85 ° C, 4.5 mL of triethylamine was added, and stirring was continued for 1.5 h. The filter cake was washed twice with deionized water and anhydrous ethanol respectively, and vacuum dried at 70 ° C for 1.5 h to obtain modified graphene aerogel powder.

[0036] S3: Add 125g of modified graphene aerogel powder, 85g of titanium tetrachloride and 2.5L of N,N-dimethylformamide into a polytetrafluoroethylene-lined reactor, stir at 125°C and 550r / min for 14.5h, then add 45g of manganese chloride and continue stirring for 11h. Cool naturally to room temperature, centrifuge at 11000r / min for 5.5min, filter, wash the filter cake with N,N-dimethylformamide and methanol twice respectively, and dry in vacuum at 70°C for 1.5h to obtain manganese oxide-modified titanium-based MOF adsorption powder.

[0037] S4: 130 mL of 0.38 mmol / L Tris-HCl solution and 13 mL of 0.1 mol / L NaOH solution were added to the reactor, stirred at 22.5 ° C and 550 r / min for 25 minutes, and the pH value was adjusted to 8.75. Then, 130 g of manganese oxide-modified titanium-based MOF adsorption powder was dispersed in 450 mL of deionized water and added to the reactor. Then, 55 g of DA was added, and the ultrasonic fraction was 65 minutes. The stirring reaction was continued for 25 hours, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol respectively, and vacuum dried at 70 ° C for 1.5 hours to obtain amino-modified titanium-based MOF powder.

[0038] S5: 155 g of 4,4'-oxydiphthalic anhydride, 125 g of 1,3-bis(4'-aminophenoxy)benzene, 55 g of 3,5-diaminobenzoic acid and 550 mL of N-methyl-2-pyrrolidone were added to a reactor. Under nitrogen protection, the mixture was stirred at 2°C and 550 r / min for 25 min. Then, 4-5 g of melamine and 45 g of amino-modified titanium-based MOF powder were added. The mixture was stirred for 1.5 h, then heated to 22.5°C and stirred for 4.5 h. Then, 25 g of acetic anhydride and 17.5 g of pyridine were added to the reactor. The mixture was stirred for 37 h and filtered. The filter cake was washed twice with deionized water and anhydrous ethanol respectively to remove unreacted monomers and dried in vacuo at 70°C for 1.5 h to obtain an amino-modified titanium-based MOF composite material.

[0039] Example 3: A method for preparing an amino-modified titanium-based MOF composite material, comprising the following steps: S1: Add 400g of graphene oxide and 3L of deionized water into a reactor, stir at 25°C and 600r / min for 30min, then add 60g of fumed silica, continue stirring for 40min, transfer to a freeze dryer, and freeze-dry for 26h at a vacuum degree of -0.085MPa. Then transfer the product to a muffle furnace, heat to 340°C under a nitrogen atmosphere, keep warm for 12h, grind and crush to obtain graphene aerogel powder.

[0040] S2: 160 g of graphene aerogel powder, 170 g of 2,5-dihydroxyterephthalic acid and 3 L of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, stirred at 25 ° C and 600 r / min for 30 min, then heated to 90 ° C, added 5 mL of triethylamine, and continued to stir for 2 h. The filter cake was washed with deionized water and anhydrous ethanol three times respectively, and vacuum dried at 80 ° C for 2 h to obtain modified graphene aerogel powder.

[0041] S3: 130 g of modified graphene aerogel powder, 90 g of titanium tetrachloride and 3 L of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, stirred at 130 ° C and 600 r / min for 15 h, then 50 g of manganese chloride was added, and stirring was continued for 12 h. Naturally cooled to room temperature, centrifuged at 12000 r / min for 6 min, filtered, and the filter cake was washed with N,N-dimethylformamide and methanol three times respectively, and vacuum dried at 80 ° C for 2 h to obtain manganese oxide modified titanium-based MOF adsorption powder.

[0042] S4: 150 mL of 0.38 mmol / L Tris-HCl solution and 14 mL of 0.1 mol / L NaOH solution were added to the reactor, stirred at 25 ° C and 600 r / min for 30 minutes, and the pH value was adjusted to 9. Then 140 g of manganese oxide-modified titanium-based MOF adsorption powder was dispersed in 500 mL of deionized water and added to the reactor. Then 60 g of DA was added and ultrasonicated for 70 minutes. The reaction was continued by stirring for 26 hours, filtered, and the filter cake was washed with deionized water and anhydrous ethanol three times respectively, and vacuum dried at 80 ° C for 2 hours to obtain amino-modified titanium-based MOF powder.

[0043] S5: 160 g of 4,4'-oxydiphthalic anhydride, 130 g of 1,3-bis(4'-aminophenoxy)benzene, 60 g of 3,5-diaminobenzoic acid and 600 mL of N-methyl-2-pyrrolidone were added to a reactor. Under nitrogen protection, the mixture was stirred at 4°C and 600 r / min for 30 min. Then, 4-5 g of melamine and 50 g of amino-modified titanium-based MOF powder were added. The mixture was stirred for 2 h, then heated to 25°C and stirred for 5 h. Then, 30 g of acetic anhydride and 20 g of pyridine were added to the reactor. The mixture was stirred for 38 h and filtered. The filter cake was washed with deionized water and anhydrous ethanol three times respectively to remove unreacted monomers and dried in vacuo at 80°C for 2 h to obtain an amino-modified titanium-based MOF composite material.

[0044] Comparative Example 1: Based on Example 3, triethylamine in step S2 was omitted to prevent the esterification reaction, and the remaining steps remained unchanged to prepare an amino-modified titanium-based MOF composite material.

[0045] Comparative Example 2: Based on Example 3, the manganese chloride in step S2 was omitted, and the other steps remained unchanged to prepare an amino-modified titanium-based MOF composite material.

[0046] Comparative Example 3: Based on Example 3, the amino-modified titanium-based MOF powder prepared in step S3 was directly used as an amino-modified titanium-based MOF composite material without being processed in step S4.

[0047] The performance of the amino-modified titanium-based MOF composite materials obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was tested to determine the Pb 2+ 、Cu 2+ Cr 6+ The removal rate (%) is shown in Table 1 and Table 2: Table 1 Heavy metal removal rate test table project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[Pb 2 ]]> 99.88 99.92 99.95 82.12 79.32 70.21 <![CDATA[Cu 2+ ]]> 99.89 99.93 99.97 82.15 79.36 70.29 <![CDATA[Cr 6+ ]]> 99.86 99.91 99.96 82.10 79.26 70.12 Table 2 Heavy metal removal rate test table after 5 acid washing adsorption and desorption cycles project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[Pb 2 ]]> 89.81 89.86 89.98 72.15 69.36 52.12 <![CDATA[Cu 2+ ]]> 89.90 90.56 91.32 72.12 69.39 53.29 <![CDATA[Cr 6+ ]]> 89.82 89.93 90.21 72.23 69.26 52.31 As can be seen from Table 1, the amino-modified titanium-based MOF composite materials prepared in Examples 1 to 3 have significantly better removal rates for heavy metals than the comparative examples, indicating that the amino-modified titanium-based MOF composite materials prepared in the present invention have excellent chelating effects on heavy metals. Moreover, after 5 acid washing, adsorption and desorption cycles, the adsorption rate of the amino-modified titanium-based MOF composite materials for heavy metals only decreases by 10%, indicating that the amino-modified titanium-based MOF composite materials have excellent stability and recyclability.

[0048] In Comparative Example 1, triethylamine is discarded, so that it cannot undergo esterification reaction. The carboxyl groups on the surface of the graphene aerogel powder and the hydroxyl groups of 2,5-dihydroxyterephthalic acid undergo esterification reaction under heating and catalysis of triethylamine. The esterification reaction grafts the reaction monomer 2,5-dihydroxyterephthalic acid on the surface of the graphene aerogel powder, promotes the subsequent coordination of 2,5-dihydroxyterephthalic acid with metal titanium ions, and hydrothermally synthesizes titanium-based MOF materials. The catalysis of triethylamine is lost, resulting in the subsequent generation of titanium-based MOF easily agglomerating on the surface of the graphene aerogel.

[0049] In Comparative Example 2, manganese chloride was discarded, and manganese salt was added simultaneously in the solvent thermal synthesis of titanium-based MOF. Manganese ions can partially replace the coordination sites of titanium ions to form Ti-O-Mn bonds, thereby forming a Ti-O-Mn heterostructure. The doping of manganese chloride can reduce the carrier recombination rate, improve the utilization rate of photogenerated electrons, and promote the photocatalytic efficiency of titanium-based MOF. Therefore, the loss of manganese chloride has reduced the chelation effect on heavy metals.

[0050] In Comparative Example 3, amino-modified titanium-based MOF powder is directly used as amino-modified titanium-based MOF composite material, with 4,4'-oxydiphthalic anhydride, 1,3-di(4'-aminophenoxy)benzene, and 3,5-diaminobenzoic acid as raw materials. The amino groups carried on the surface of amino-modified titanium-based MOF powder are used as cross-linking sites to construct a three-dimensional network structure of polyimide film covered on amino-modified titanium-based MOF powder. Polyimide can effectively enhance visible light absorption, extend the life of photogenerated charge, and improve catalytic activity, but it also has a narrow light absorption range. , serious photogenerated charge recombination, few active sites, poor stability and small surface area, etc. By constructing a three-dimensional network structure, the specific surface area of ​​the polyimide membrane is increased, and the synergistic effect with the titanium-based MOF is increased. Therefore, after loss, the chelation effect of heavy metals is significantly reduced. Polyimide is an organic polymer with strong chemical inertness and stable aromatic heterocyclic structural units, which makes it corrosion-resistant, non-toxic and has excellent mechanical properties. The heavy metal removal rate after 5 acid washing adsorption and desorption cycles after loss is significantly lower than that of the control group.

[0051] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations can be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing an amino-modified titanium-based MOF composite material, characterized in that: The steps include: Step 1: Using graphene oxide and fumed silica as raw materials, graphene aerogel powder is prepared by utilizing hydrogen bond cross-linking and grinding. Step 2: The carboxyl groups on the surface of the graphene aerogel powder are combined with the hydroxyl groups on the surface of 2,5-dihydroxyterephthalic acid through an esterification reaction. Titanium tetrachloride is used as a titanium source to hydrothermally synthesize a titanium-based MOF on the surface of the graphene aerogel powder. Manganese chloride is then used as a manganese source to grow manganese oxide on the surface of the titanium-based MOF to form a heterogeneous structure, thereby obtaining manganese oxide-modified titanium-based MOF adsorption powder; Step 3: Coating the manganese oxide-modified titanium-based MOF adsorption powder with polydopamine to obtain amino-modified titanium-based MOF powder; Step 4: Using 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy)benzene, and 3,5-diaminobenzoic acid as raw materials, acetic anhydride and pyridine as imidization reagents, and melamine as a cross-linking agent, combined with the auxiliary cross-linking effect of amino-modified titanium-based MOF powder, an amino-modified titanium-based MOF composite material was prepared.

2. The method for preparing an amino-modified titanium-based MOF composite material according to claim 1, characterized in that: The specific preparation steps of the graphene aerogel powder are as follows: Graphene oxide and deionized water were added to a reactor, stirred at 20-25°C and 500-600 r / min for 20-30 min, and then fumed silica was added. The mixture was stirred for 30-40 min, and then transferred to a freeze dryer. The mixture was freeze-dried at a vacuum degree of -0.085 MPa for 24-26 h. The product was then transferred to a muffle furnace, heated to 300-340°C under a nitrogen atmosphere, and kept warm for 10-12 h. The product was then ground and pulverized to obtain graphene aerogel powder.

3. The method for preparing an amino-modified titanium-based MOF composite material according to claim 2, characterized in that: The usage ratio of the graphene oxide, deionized water and fumed silica is 300-400 g: 2-3 L: 50-60 g.

4. The method for preparing an amino-modified titanium-based MOF composite material according to claim 1, characterized in that: The specific preparation steps of the manganese oxide modified titanium-based MOF adsorption powder are as follows: The modified graphene aerogel powder, titanium tetrachloride and N,N-dimethylformamide were added to a polytetrafluoroethylene-lined reactor, stirred at 120-130°C and 500-600 r / min for 14-15 hours, and then manganese chloride was added, and stirring was continued for 10-12 hours. The mixture was naturally cooled and centrifuged at 10000-12000 r / min for 5-6 minutes. The mixture was filtered, washed and vacuum dried to obtain manganese oxide-modified titanium-based MOF adsorption powder; The usage ratio of the modified graphene aerogel powder, titanium tetrachloride, N,N-dimethylformamide and manganese chloride is 120-130 g: 80-90 g: 2-3 L: 40-50 g.

5. The method for preparing an amino-modified titanium-based MOF composite material according to claim 1, characterized in that: The specific preparation steps of modified graphene aerogel powder are as follows: Adding graphene aerogel powder, 2,5-dihydroxyterephthalic acid and N,N-dimethylformamide into a polytetrafluoroethylene-lined reactor, stirring at 20-25°C and 500-600 r / min for 20-30 minutes, then heating to 80-90°C, adding triethylamine, continuing stirring for 1-2 hours, filtering, washing, and vacuum drying to obtain modified graphene aerogel powder; The usage ratio of the graphene aerogel powder, 2,5-dihydroxyterephthalic acid, N,N-dimethylformamide and triethylamine is 140-160 g: 150-170 g: 2-3 L: 4-5 mL.

6. The method for preparing an amino-modified titanium-based MOF composite material according to claim 1, characterized in that: The specific preparation steps of the amino-modified titanium-based MOF powder are as follows: A Tris-HCl solution with a concentration of 0.38 mmol / L and a NaOH solution with a concentration of 0.1 mol / L were added to the reactor, stirred at 20-25°C and 500-600 r / min for 20-30 min, and the pH value was adjusted to 8.5-9. Then, the manganese oxide-modified titanium-based MOF adsorption powder was dispersed in deionized water and added to the reactor, and then DA was added, ultrasonicated for 60-70 min, and the reaction was continued by stirring for 24-26 h. The mixture was filtered, washed, and vacuum dried to obtain amino-modified titanium-based MOF powder.

7. The method for preparing an amino-modified titanium-based MOF composite material according to claim 6, characterized in that: The usage ratio of the Tris-HCl solution, the NaOH solution, the manganese oxide-modified titanium-based MOF adsorption powder, the deionized water and the DA is 120-150 mL: 12-14 mL: 120-140 g: 400-500 mL: 50-60 g.

8. The method for preparing an amino-modified titanium-based MOF composite material according to claim 1, characterized in that: The specific preparation steps of the amino-modified titanium-based MOF composite material are as follows: 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy)benzene, 3,5-diaminobenzoic acid and N-methyl-2-pyrrolidone were added to a reactor, and stirred at 0-4°C and 500-600 r / min for 20-30 minutes under nitrogen protection. Then, melamine and amino-modified titanium-based MOF powder were added, and stirring was continued for 1-2 hours. Then, the mixture was heated to 20-25°C and stirred for 4-5 hours. Then, acetic anhydride and pyridine were added to the reactor, and stirring was continued for 36-38 hours. The mixture was filtered, washed, and vacuum dried to obtain an amino-modified titanium-based MOF composite material.

9. The method for preparing an amino-modified titanium-based MOF composite material according to claim 8, characterized in that: The usage ratio of the 4,4'-oxydiphthalic anhydride, 1,3-bis(4'-aminophenoxy)benzene, 3,5-diaminobenzoic acid, N-methyl-2-pyrrolidone, melamine, amino-modified titanium-based MOF powder, acetic anhydride and pyridine is 150-160 g: 120-130 g: 50-60 g: 500-600 mL: 4-5 g: 40-50 g: 20-30 g: 15-20 g.

10. An amino-modified titanium-based MOF composite material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.