A method for removing heavy metal ions

Abstract

The application discloses a method for removing heavy metal ions, which comprises the following steps: mixing a modified fabric with a solution containing heavy metal ions for a period of time, and then taking out the modified fabric, so that the heavy metal ions are removed; or passing the solution containing heavy metal ions through the modified fabric, so that the heavy metal ions are removed. Comparative tests on the adsorption of the modified fabric to Cr(VI) in water show that CF-FA-UiO-66-NH2 has the best adsorption effect, and the adsorption capacity of CF-FA-UiO-66-NH2 is 3.297 mg / g at 25 DEG C. Research shows that the adsorption of CF-FA-UiO-66-NH2 to Cr(VI) in the aqueous solution is best at pH 2, and the competitive positive metal ions have no obvious influence on the adsorption of Cr(VI), and the adsorption kinetics model of CF-FA-UiO-66-NH2 is consistent with a quasi-second kinetics model. Moreover, the modified fabric has certain filter separation function to Cr(VI).

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection, and relates to a method for removing heavy metal ions, in particular a method for removing chromium ions by means of adsorption filtration and the like. BACKGROUND

[0002] In recent years, heavy metal pollution of water bodies has attracted widespread attention due to its harmful effects on human health and aquatic organisms. Among them, chromium pollution is a problem that needs to be solved urgently in many parts of the world. This metal pollutant usually has two oxidation states: trivalent Cr(III) and hexavalent Cr(VI), and the toxicity depends on the oxidation state. The highly toxic Cr(VI) form is easily soluble in water and exists in the form of chromate or dichromate depending on the pH value. In water bodies, Cr(VI) is more mobile than Cr(III) ions in solution and is one of the most polluting substances that can cause various diseases such as skin cancer, respiratory obstruction, irritation, lung cancer, immune effects, mutagenic effects, and genotoxic effects [see: A review: Engineered nanomaterials for photoreduction of Cr (VI) to Cr (III)]. Therefore, it is of great significance to find an economical and effective method to reduce the concentration of Cr(VI) related compounds in water bodies. Currently, common methods include ion exchange, microbial degradation, chemical reduction, precipitation, and adsorption. Among them, the adsorption method has been widely used in the removal of Cr(VI) due to its simplicity and practicality.

[0003] At present, some common adsorbents have been used to adsorb Cr(VI) ions, such as carbon-based adsorbents (carbon nanotubes, graphene, activated carbon), polysaccharide-based nanomaterials (cellulose nanomaterials, chitosan composites, biological flocculants), but the existing materials generally have poor adsorption capacity, slow adsorption rate, and low recovery rate. In recent years, metal-organic framework materials have overcome the above shortcomings and have emerged in wastewater treatment due to their excellent structural characteristics. However, traditional metal-organic framework materials are in powder form, which limits their application in industrial water treatment due to their easy aggregation and difficulty in separation. Therefore, how to simplify the preparation and application of metal-organic framework materials has become the focus of attention. SUMMARY

[0004] The application discloses the influence of controllable morphology and different surface roughness of a UiO-66-NH2 fabric on Cr(VI) adsorption, and preliminarily explores the modified fabric adsorption kinetics, selective adsorption and Cr(VI) filtration interception effect. Comparative tests on the use of the modified fabric for Cr(VI) adsorption in water show that the CF-FA-UiO-66-NH2 has the best adsorption effect, and the adsorption capacity is 3.297 mg / g at 25 DEG C. Research shows that the CF-FA-UiO-66-NH2 has the best Cr(VI) adsorption in water solution at pH 2, and the competitive positive metal ions have no obvious influence on the Cr(VI) adsorption, and the adsorption kinetics model accords with the pseudo-second-order kinetics model. Moreover, the modified fabric has certain Cr(VI) filtration separation function, the double-layer modified fabric is used for solution filtration treatment, the residual concentration can reach 11.308 ppm after one filtration, and the Cr(VI) concentration in the filtrate gradually decreases with the increase of the filtration times, and the residual concentration of Cr(VI) in the filtrate is 9.1388 ppm after six filtrations, so the CF-FA-UiO-66-NH2 is a relatively ideal Cr(VI) filtration removal material.

[0005] The application adopts the following technical scheme:

[0006] A method for removing heavy metal ions, comprising the following steps: mixing the modified fabric with a solution containing heavy metals for a period of time, and then taking out to remove the heavy metal ions; or passing the solution containing heavy metals through the modified fabric to remove the heavy metal ions.

[0007] In the application, the heavy metal ions include trivalent Cr(III) and hexavalent Cr(VI), and preferably, the heavy metal ions are hexavalent Cr(VI).

[0008] In the application, when the modified fabric is mixed with the solution containing heavy metals, the pH of the solution containing heavy metals is 1-10, and preferably, the pH of the solution containing heavy metals is 2-9, such as 2-5; and the mixing time is 1-20 hours, and preferably, the mixing time is 5-15 hours.

[0009] In the application, the preparation method of the modified fabric comprises the following steps: taking the fabric as a raw material, obtaining a modified fabric through a diazo radical polymerization method, and then growing a metal organic framework on the surface of the fabric in situ to obtain the modified fabric.

[0010] In the application, the modified fabric is obtained by diazo radical polymerization method using fabric as raw material, including the following steps: hydrochloric acid, sodium nitrite, amino benzoic acid are subjected to diazotization reaction, then the fabric is immersed, a reducing agent is added, and the modified fabric is obtained by reaction at 20-40℃ for 15-30 hours, which is called CF-PH-COOH. Preferably, the amino benzoic acid is m-amino benzoic acid, and the reducing agent is vitamin C (VC); preferably, the diazotization reaction temperature is 0℃ or below, and the time is 0.5-2 hours. Preferably, the fabric is cotton fabric.

[0011] As an example, the application adds hydrochloric acid and sodium nitrite into a reaction container, then the temperature is reduced to 0℃ or below, magnetic stirring is carried out, then amino benzoic acid is added, and diazotization reaction is carried out, generating aromatic diazonium salt; the cotton fabric is immersed in the above solution, a reducing agent is added, the temperature is raised to about 30℃, and reaction is carried out under insulation, obtaining the modified fabric.

[0012] In the application, the metal organic framework is grown in situ on the surface of the fabric, including the following steps: the modified fabric is immersed in a metal ion precursor solution, then amino terephthalic acid is added, and reflux reaction is carried out, obtaining the modified fabric, wherein the metal ion precursor solution includes Zr compound and alkyl acid, preferably, the Zr compound is ZrCl4, the alkyl acid includes formic acid and acetic acid, and the amino terephthalic acid is 2-amino terephthalic acid (BDC-NH2). Preferably, the mass ratio of the Zr compound to the amino terephthalic acid is 1: (0.6-1.2), preferably 1: (0.8-1.1). The amount ratio of the Zr compound to the alkyl acid is (30-65) mg: 1 mL. The application constructs the UiO-66 and UiO-66-NH2 coating layer with different particle sizes, uniform particle size distribution and uniform distribution on the fabric. The UiO-66 and UiO-66-NH2 crystals are grown in situ on the surface of the fabric, and the prepared fabric is coded as CF-UiO-66 and CF-UiO-66-NH2.

[0013] The modified cotton fabric obtained by diazo radical polymerization is used to prepare the UiO-66-NH2 fabric in one step under normal pressure and mild reaction conditions, and formic acid or acetic acid is used to regulate the in-situ growth of the UiO-66-NH2 morphology on the fabric surface. As an example, the preparation method of the modified fabric obtained by in-situ growth of metal organic framework on the fabric surface is as follows: first, ZrCl4 is dissolved in a round-bottom flask containing DMF and acetic acid (or formic acid), deionized water is added to promote dissolution, and ultrasonic treatment is performed until the metal ion precursor solution is clear; CF-PH-COOH is taken and magnetically stirred in the metal ion precursor solution at room temperature, then BDC-NH2 is dissolved in DMF and added to the flask for mixing, and reflux reaction is carried out for different times, such as 4-24 h. After the reaction is completed, the fabric is washed with DMF and anhydrous ethanol to wash away the unreacted raw materials and unattached crystals, vacuum dried, and the modified fabric, called CF-UiO-66-NH2, is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Carboxylated cotton fabric after diazo radical polymerization at different multiples: ×1000 (a); ×10000 (b); ×30000 (c).

[0015] Figure 2 Growth of raw cotton fabric and carboxylated fabric: Raw-CF-HAc1-UiO-66-4h (a); CF-HAc1-UiO-66-4h (b); Raw-CF-HAc1-UiO-66-NH2-4h (c); CF-HAc1-UiO-66-NH2-4h (d).

[0016] Figure 3 Growth of UiO-66 on carboxylated fabric under different types and concentrations of regulators: CF-HAc1-UiO-66-24h (a); CF-HAc2-UiO-66-24h (b); CF-FA-UiO-66-24h (c); TEM image of HAc1-UiO-66-24h (d).

[0017] Figure 4 Growth of UiO-66-NH2 on modified fabric under corresponding types and concentrations of regulators: CF-HAc1-UiO-66-NH2-24h (a); CF-HAc2-UiO-66-NH2-24h (b); CF-FA-UiO-66-NH2-24h (c); TEM image of FA-UiO-66-NH2-24h (d).

[0018] Figure 5(a) CF-HAc1-UiO-66-12h; (b) CF-HAc1-UiO-66-24h; (c) CF-HAc2-UiO-66-12h; (d) CF-HAc2-UiO-66-24h; (e) CF-FA-UiO-66-12h; (f) CF-FA-UiO-66-24h.

[0019] Figure 6 (a) CF-HAc1-UiO-66-NH2-12h; (b) CF-HAc1-UiO-66-NH2-24h; (c) CF-HAc2-UiO-66-NH2-12h; (d) CF-HAc2-UiO-66-NH2-24h; (e) CF-FA-UiO-66-NH2-12h; (f) CF-FA-UiO-66-NH2-24h.

[0020] Figure 7 (a) CF-Ph-COOH; (b) CF-HAc2-UiO-66-NH2-24h; (c) CF-FA-UiO-66-NH2-24h.

[0021] Figure 8 (a) FT-IR; (b) XRD; (c) TGA; (d) XPS survey; (e) C fine spectrum of CF-Ph-COOH; (f) N fine spectrum of CF-FA-UiO-66-NH2 before adsorbing Cr(VI); (g) N fine spectrum of CF-FA-UiO-66-NH2 after adsorbing Cr(VI).

[0022] Figure 9 (a) CF-Ph-COOH; (b) CF-HAc2-UiO-66-NH2-24h; (c) CF-FA-UiO-66-NH2-24h.

[0023] Figure 10 (a) CF-Ph-COOH; (b) CF-HAc2-UiO-66-NH2-24h; (c) CF-FA-UiO-66-NH2-24h.

[0024] Figure 11 (a) CF-Ph-COOH; (b) CF-HAc2-UiO-66-NH2-24h; (c) CF-FA-UiO-66-NH2-24h.

[0025] Figure 12Residual concentration of Cr(VI) in filtrate after 1-6 times filtration of double-layer CF-FA-UiO-66-NH2 and 6 times filtration of single-layer sample for Cr(VI) solution. DETAILED DESCRIPTION

[0026] The present application diazotizes m-carboxyaniline to obtain aromatic diazonium salt, and performs diazonium radical polymerization on the surface of cotton fabric to obtain carboxylated cotton fabric (CF-Ph-COOH). The carboxyl group on the surface of the modified fabric can be fully complexed with zirconium ions (Zr). The organic ligand 2-amino terephthalic acid is controlled by acetic acid or formic acid to generate metal organic framework with zirconium ions, and the modified fabric CF-HAc1-UiO-66-NH2 and CF-HAc2-UiO-66-NH2, CF-FA-UiO-66-NH2 with controllable morphology are prepared. Comparative test of the modified fabric for adsorption of Cr(VI) in water shows that CF-FA-UiO-66-NH2 has the best adsorption effect, and the adsorption capacity at 25℃ is 3.297mg / g. Studies show that the adsorption of CF-FA-UiO-66-NH2 for Cr(VI) in aqueous solution is best at pH 2, and the competitive positive metal ions have no obvious effect on the adsorption of Cr(VI), and the adsorption kinetics model conforms to the pseudo-second-order kinetics model. Moreover, the modified fabric has certain filter separation function for Cr(VI).

[0027] The technical progress of the present application is illustrated by specific experiments below, and the raw materials are all conventional products. The specific preparation operation and performance test are conventional technologies. Among them, the specification of cotton fabric is 114g / m 2 , from Nantong Shengbao Lu Spun Textile Co., Ltd.; and the standard solution of chromium and other metals is from the National Non-ferrous Metal and Electronic Material Analysis and Test Center.

[0028] Fourier infrared spectrum analysis. Place a 4cm×4cm single-layer sample on a diamond ATR crystal table, compact the collection head, set the scanning range to 600-4000cm -1 , and scan 16 times with a resolution of 4cm -1 .

[0029] Field emission scanning electron microscope (SEM) observation. The size of the fabric sample is appropriately pasted on the electron microscope sample table with conductive glue, the ion sputtering coating instrument is turned on, the sample table is placed at multiple angles for 4-5 times of gold plating, and the gold plating time is 70s each time.

[0030] X-ray energy spectrum analysis (EDS). The X-ray energy spectrum analyzer equipped with high-resolution field emission scanning electron microscope (Regulus8230) can be used to characterize the element distribution of each sample. The sample preparation method also needs to use conductive glue to fix the sample to be tested on the sample table, and if the sample is plated, the energy spectrum shows the sample and plated elements.

[0031] Transmission electron microscope (TEM) observation. Transmission electron microscope (TEM) can also be used to observe the microstructure of the nanomaterials. The sample preparation method is as follows: a small amount of dried metal organic framework material powder is dispersed in anhydrous ethanol, ultrasonic dispersion for 30 min, a small amount of dispersion liquid is sucked onto a microgrid copper mesh (150 mesh), and dried in an oven.

[0032] X-ray photoelectron spectrometer test (XPS). X-ray photoelectron spectrometer test can test and analyze the chemical composition of carboxylated fabric and modified fabric. A 5mm x 5mm fabric to be tested is adhered to the XPS sample table, a monochromatic AlKa source is used as the X-ray source, the energy is 1486.6eV, and the working pressure in the cabin is about 4.0x10 -9 Pa, and the binding energy at 284.8ev is corrected by C-C chemical state.

[0033] Full-automatic air permeability tester. The full-automatic air permeability tester can test and compare the air permeability of the modified fabric. According to the standard GB / T 5453-1997 "Textiles-Determination of air permeability of fabrics", the test parameters are determined as follows: test pressure: test area: 20 cm2, test pressure: 100 Pa, diameter: 3Φ. Each sample is measured five times and the average value is taken.

[0034] Thermogravimetric (TGA) analysis. The thermal stability and components of the fabric before and after modification are studied by thermogravimetric analysis test. 3-5mg of the sample with length, width and height less than 1mm is taken and placed in a special crucible for weighing to obtain the change of mass with temperature. The corresponding parameters for testing are as follows: temperature range is 30-800℃, heating rate is 20℃ / min, and atmosphere is N2.

[0035] Breaking strength test of fabric. The tensile strength of the fabric before and after modification is tested, and the tensile speed is unified to 100 mm / min according to the standard, the fabric width is 5 cm, the self length is 30 cm, and the clamping length is 25 cm.

[0036] Stiffness test of fabric. According to GB / T18318.1-2009 "Determination of bending properties of textiles", the bending stiffness of the treated and untreated cotton fabric is tested. The test conditions are as follows: the angle between the light source and the horizontal plane is 41.5°, the environmental temperature is 25℃, and the humidity is 65%. Each fabric sample with a length of 20cm is laid on the water platform, and the speed is 4 pushing the pressure plate. The sample moves forward synchronously, and the bending stiffness of the unit width is calculated by the following formula 2-1:

[0037] G=m×C 3 x10 -3 (Formula 2-1)

[0038] In the above formula, G represents the bending stiffness of the sample per unit width (mN-m); m represents the mass per unit area of the sample (g / m2); and C represents the average bending length of the sample (m). 2

[0039] Super-depth microscope test. The surface morphology and roughness of the modified fabric are characterized by using a KEYENCE VHX-70 super-depth microscope, and 3D imaging scanning is performed.

[0040] X-ray diffractometer (XRD) test. The diffraction pattern of the cotton fabric and the modified fabric is analyzed by using an X-ray diffractometer (XRD), and the test conditions are as follows: the fabric with a size of 2 cm x 2 cm is pasted on a glass sheet and placed on the corresponding sample plate to ensure the flatness of the working surface, the scanning angle range is 5-70°, the test rate is 7.3° / min, and the test target is a copper target.

[0041] Colorimeter. The apparent color depth K / S value of the fabric can be measured by using an Ultrascan PRO, D65 is used as the light source, the observation angle is set to 10°, the sample is folded twice, and the average value of four measurement data is taken.

[0042] Inductively coupled plasma emission spectrometer (ICP-OES) test. The residual concentration of metal ions in the aqueous solution is tested by using an inductively coupled plasma emission spectrometer. The specific test instrument condition settings are as follows: RF power = 1150 w, pump speed = 50 rmp, auxiliary gas flow rate is 0.5 L / min, atomizer gas flow rate is 0.5 L / min, and driving gas flow rate is general. After calibrating with the corresponding standard solution, the test can be performed.

[0043] Example 1 Preparation of carboxylated fabric (CF-PH-COOH)

[0044] 960 mL of 1M hydrochloric acid was added to the reaction vessel, 1.822 g of sodium nitrite was added at 15°C, and then the cold bath temperature was lowered to below 0°C, and magnetic stirring was performed for 10 min; 3.288 g of m-aminobenzoic acid was added, and the diazotization reaction was performed for 1 h to generate aromatic diazonium salt. The cotton fabric with a size of 8 x 16 cm 2 was immersed in the above solution, 424.0 mg of reducing agent VC was added, the temperature was raised to 30°C, and the reaction was performed for 24 h.

[0045] After the reaction was completed, the fabric was washed several times by ultrasonic cleaning in water, and then it was placed in an oven at 50°C for drying to obtain the carboxylated fabric CF-PH-COOH. In order to introduce active groups that can realize in-situ growth of metal organic frameworks on the fiber surface, the fabric surface was modified by diazonium radical polymerization to obtain CF-PH-COOH, and the surface morphology thereof is as shown in Figure 1 ​SEM observation can be seen that, compared with the smooth surface of the original cotton fabric, a layer of dense and tiny nanosphere structure is generated on the surface of the fabric after activation treatment.

[0046] Example Two Fabric Preparation of UiO-66 and UiO-66-NH2

[0047] By adjusting the ratio of organic ligand to metal salt, changing the type and amount of formic acid or acetic acid, different particle size and uniform distribution of UiO-66 and UiO-66-NH2 coating layer are constructed on the fabric. The crystal of UiO-66 and UiO-66-NH2 grows in situ on the surface of the fabric, and the fabric codes prepared are CF-UiO-66 and CF-UiO-66-NH2.

[0048] During preparation, first 251.6mg ZrCl4 is dissolved in a round-bottom flask containing 15mL DMF and 4mL acetic acid, 50µl deionized water is added to promote dissolution, and ultrasonic treatment is performed until the metal ion precursor solution is clear. Take 4cm×4cm CF-PH-COOH and soak it in DMF, and after regular washing, it is magnetically stirred in the metal ion precursor solution at room temperature for 10min. Then, 271.6mg of terephthalic acid (BDC) or 2-amino terephthalic acid (BDC-NH2) is dissolved in 15mL DMF and added to the flask for mixing, and the temperature is raised to 120°C for reflux reaction for different times, which are set to 4, 12, and 24h respectively. After the reaction is completed, the fabric is washed with DMF and anhydrous ethanol to remove unreacted raw materials and unattached crystals, and then dried under vacuum at 50°C to obtain the modified fabric CF-UiO-66 or CF-UiO-66-NH2.

[0049] As a control, the original cotton fabric is used instead of CF-PH-COOH; further, in order to change the growth of UiO-66 and UiO-66-NH2 on the fabric, the amount of ZrCl4 is changed to 262.5mg, the amount of BDC / BDC-NH2 is changed to 1.119mmmol, the amount of acetic acid is changed to 8.5mL, the amount of DMF in the metal ion precursor solution is changed to 10mL, and the reaction time is set to 12h and 24h to prepare different coated fabrics. In addition, the acetic acid is replaced with 6.5mL formic acid to investigate the effect on the growth of defective UiO-66 and UiO-66-NH2.

[0050] The raw cotton fabric and activated fabric surface were compared for growing crystals. The reaction was carried out for 4 h at an acetic acid concentration of 2.33 M, and the resulting fabrics were named Raw-CF-HAc1-UiO-66-4h, CF-HAc1-UiO-66-4h, Raw-CF-HAc1-UiO-66-NH2-4h, and CF-HAc1-UiO-66-NH2-4h, respectively. The observation of the growth of UiO-66 and UiO-66-NH2 on the fabric surface before and after activation showed that Figure 2 ), the crystal layer structure of UiO-66 and UiO-66-NH2 formed on the surface of the raw cotton fabric was incomplete, and most of the crystals were broken nuclei. The reason was that the combination of UiO-66 and UiO-66-NH2 with the raw cotton fabric was poor. In contrast, the activated fabric surface was covered with dense and uniform UiO-66 and UiO-66-NH2, indicating that the abundant carboxyl groups on the activated fabric surface could act as binding sites for zirconium metal clusters or zirconium ions, thereby forming nucleation sites for the crystal growth of UiO-66 and UiO-66-NH2, and then initiating the in-situ growth of metal organic frameworks. The mass transfer resistance of metal clusters and organic ligands was small during the growth due to the porous structure of the fabric and the presence of a large number of gaps between the fibers, so the fabric surface could form a complete crystal structure.

[0051] The reaction time was fixed at 24 h, and the modified fabrics were prepared under different carboxylic acid dosages. When the acetic acid concentration was 2.33 M, the fabrics were CF-HAc1-UiO-66-24h and CF-HAc1-UiO-66-NH2-24h, and when the acetic acid concentration was 4.96 M, the fabrics were CF-HAc2-UiO-66-24h and CF-HAc2-UiO-66-NH2-24h. The modified fabrics prepared with formic acid were CF-FA-UiO-66-24h and CF-FA-UiO-66-NH2-24h. The changes in the growth morphology on the fabric surface were observed by SEM Figure 3 ). Figure 3 It can be seen that under the adjustment of acetic acid and formic acid with a concentration of 4.96 M, the crystals on the fabric surface all showed regular octahedral shapes with clear boundaries, and the former formed larger crystal grains. However, under a lower concentration of 2.33 M, the formed crystals showed a transition state from spherical to octahedral, and could not grow into larger grains. This indicates that both formic acid and acetic acid can compete with terephthalic acid, reducing the nucleation rate during growth and promoting the regular growth of UiO-66 crystals. Figure 3 The TEM images of UiO-66 crystals under the adjustment of 4.96 M acetic acid are listed in Table d, and the particle size of the prepared metal organic framework was about 600 nm.

[0052] The influence of formic acid and acetic acid on the growth of UiO-66-NH2 on the modified fabric when 2-amino terephthalic acid was used as the ligand is shown inFigure 4 The growth results were similar to UiO-66, but the large particle size crystal particles on the surface of CF-HAc2-UiO-66-24h could not be obtained. The crystal size of CF-FA-UiO-66-NH2-24h was about 375 nm particles (TEM Figure 4 , the particles showed a smooth octahedral morphology.

[0053] In the growth of UiO-66 and UiO-66-NH2 on the carboxylated fabric surface, the reaction time was shortened to 12 h, and the morphology of the reaction for 24 h could be observed. It can be seen from Figure 5 that when the reaction time is 12 h, the growth of UiO-66 on the fabric is not complete, and some particles are still small crystals. Under the adjustment of 4.96 M acetic acid, the crystals still have obvious growth after 12 h. When the functional group -NH2 ligand is grown in situ on the fiber surface, the situation changes. According to Figure 6 the growth of UiO-66-NH2 listed in Table 1, under the same preparation conditions, the reaction of 12 h on the fabric surface, UiO-66-NH2 has been fully grown on the fabric surface. Subsequently, unless otherwise specified, the time of in-situ growth of UiO-66 and UiO-66-NH2 on the fabric in the examples of the present application is determined as 24 h.

[0054] Figure 7 EDS spectra of CF-Ph-COOH, CF-HAc2-UiO-66-24h and CF-FA-UiO-66-NH2-24h. It can be seen that the carboxyl grafted cotton fabric by aromatic free radical polymerization is only composed of C, H and O, and CF-HAc2-UiO-66-24h and CF-FA-UiO-66-NH2-24h have more Zr and N element of -NH2 containing ligand.

[0055] In order to further understand the chemical composition and structure of the fabric before and after modification, the modified fabric was analyzed by infrared spectrum, XRD spectrum, TGA and XPS.

[0056] It can be seen from Figure 8 a that CF-Ph-COOH has a C=O stretching vibration peak at 1716.6 cm -1 , and a benzene ring-CH=CH- bending vibration peak at 1431.1 cm -1 . In addition, Zr-O and Zr-O2 characteristic absorption peaks exist on CF-HAc-UiO-66 and CF-FA-UiO-66-NH2, which are located at 667.3 cm -1 and 769.6 cm -1 , respectively. At 1577.7 cm -1C=O stretching vibration caused by terephthalic acid participation. The N-H stretching vibration region at 3338.6 cm -1 and the C-N structure shear stretching at 1269.1 cm -1 both further demonstrate the successful loading of UiO-66-NH2 on the fabric.

[0057] The XRD patterns provide the diffraction patterns of the fabric and the modified fabric, which clearly show the chemical composition of the samples, Figure 8 Table b details the relevant characteristic diffraction peaks of each fabric. Compared with the original cotton and the carboxylated fabric, the experimental data exhibit obvious diffraction peaks at 7.4° and 8.5°, which correspond to the two most representative diffraction signals of the UiO-66 series crystals. The XRD data obtained on the modified fabric are perfectly consistent with the reference crystal UiO-66 and UiO-66-NH2 recorded data, which is sufficient to show that the presence of formic acid (FA) and acetic acid (HAc) does not affect the in-situ growth of UiO-66 and UiO-66-NH2 on the fabric.

[0058] TGA can be used to evaluate the thermal performance of the original cotton and the modified fabric. Referring to Figure 8 Table c, the decomposition process of the fabric with the surface-introduced carboxyl aromatic polymer chain is basically the same as that of the original cotton, and the carbon residue rate is 13.6%, which is slightly higher than that of the original cotton. In the range of 30-150℃, the mass loss of CF-HAc-UiO-66 is about 8.1%, while the mass loss of CF-FA-UiO-66-NH2 in the range of 30℃-80℃ is 2.9%, which can be attributed to the loss of water and solvent in the structure of the metal-organic framework material. The fabric and the modified fabric both start to decompose sharply at about 320℃, during which the crystalline region of the cotton fabric is destroyed and starts to crack into levoglucosan small molecule products and gas. The degradation process of the fabric ends at about 470℃, while the decomposition of the organic ligand in the skeleton is completed at about 580℃. Finally, the residual rates of CF-HAc-UiO-66 and CF-FA-UiO-66-NH2 are 25.83% and 21.90%, respectively.

[0059] Figure 8 Table d lists the XPS full spectrum of the fabric after grafting the aromatic carboxyl polymer chain and CF-FA-UiO-66-NH2 before and after adsorbing Cr(VI). The carboxylated fabric contains N element, which is because the diazonium salt reacts with the residual aromatic amine to form azo compounds. On CF-FA-UiO-66-NH2, C, O, Zr, and N elements are present, and Cr element is additionally present after adsorbing Cr(VI).

[0060] Figure 8 Tables e-g show the peak fitting of the C or N fine spectrum, which further illustrates the surface structure of the sample and its changes. In the high-resolution C1s spectrum (Figure 10 ) in 289.02, 286.53, 284.80 eV, which corresponded to C=0, C-N and C-C, respectively. Meanwhile, the XPS-N spectra of CF-FA-UiO-66-NH2 before and after adsorption were compared. The N1s HR-XPS before adsorption showed N=N, -NH2 and =C-N peaks at 401.38, 400.26 and 399.2 eV, respectively, which proved the existence of FA-UiO-66-NH2 on the fabric again. After the sample adsorbed Cr(VI), the N1s HR-XPS still showed the above peaks, but the intensity of the -NH2 attribution peak was lower, and a -NH 3+ , which was mainly because the amine functional groups on the surface of UiO-66-NH2 were protonated under acidic conditions.

[0061] Example Three Analysis of the Physical Properties of the Fabric before and after Modification

[0062] The physical properties of the original cotton fabric, CF-Ph-COOH, CF-HAc2-UiO-6 and CF-FA-UiO-66-NH2 were analyzed to compare the differences between the modified fabric and the original cotton fabric, so as to ensure that the prepared composite material has excellent adsorption performance while still having the advantages of the original fabric. The results are shown in Table 1 below. From Table 1, the air permeability of CF, CF-Ph-COOH, CF-HAc2-UiO-6 and CF-FA-UiO-66-NH2 is 287.78 mm / s, 302.80 mm / s, 250.26 mm / s, 250.44 mm / s, respectively. It can be seen that the air permeability of the carboxylated fabric treated in acidic medium is slightly improved compared with the original cotton, but the porosity of the modified fabric is smaller, so the air permeability decreases slightly. The bending stiffness data show that the fabric has a certain flexibility before and after modification, and the value of the modified composite fabric is similar to that of the original cotton.

[0063] Table 1 Comparison of the physical properties of the fabric before and after modification

[0064]

[0065] Table 2 gives the color characteristic index of each sample fabric. It can be seen that CF and CF-Ph-COOH are yellow-white and light yellow, respectively, and CF-HAc-UiO-66 and CF-FA-UiO-66-NH2 are orange-yellow and white, respectively, which is consistent with the color of the corresponding crystal powder. This can indicate that the UiO-66 series crystals are uniformly distributed on the surface of the fabric, and the growth on the interface of the grafted carboxyl polymer chain does not change its appearance.

[0066] Table 2 Color characteristic index of the fabric before and after modification

[0067]

[0068] Example Four Adsorption of Cr(VI) in water

[0069] 1. Adsorption of Cr(VI) in solution by fabrics with different surface morphology

[0070] Potassium dichromate was used as a pollution source template to prepare a 42 mg / L Cr(VI) solution. 20 mL of each solution was taken and adjusted to pH 2 with 5% dilute hydrochloric acid. 0.1 g of modified composite fabric material (CF-HAc1-UiO-66, CF-HAc2-UiO-66, CF-FA-UiO-66, CF-HAc1-UiO-66-NH2, CF-HAc2-UiO-66-NH2 or CF-FA-UiO-66-NH2) was added to the solution. The mixture was shaken at 45 rpm in a water bath constant temperature shaker at 30°C for 12 h.

[0071] The residual concentration of Cr(VI) after adsorption by the UiO-66 and UiO-66-NH2 composite fabrics was measured to compare the adsorption efficiency of the fabrics, and the results were compared with those of the original cotton fabric and the carboxyl fabric. When the original cotton fabric and the carboxyl fabric were directly used to adsorb Cr(VI), it was found that although the surfaces of the two fabrics were rich in -OH and -COOH, the adsorption effect was poor because they were not loaded with UiO-66 or its derivatives. By testing the Cr(VI) concentration in the residual solution after adsorption, it was found that the adsorption efficiency of the original cotton fabric and the carboxyl fabric was 0.3% and 1.1%, respectively. At the same time, it was found that the adsorption efficiency of the UiO-66-NH2 series composite fabric was significantly higher than that of the UiO-66 series fabric, and the adsorption effect of CF-FA-UiO-66-NH2 was the best (see Figure 9 ). CF-FA-UiO-66-NH2 was subsequently used to investigate the adsorption-related properties.

[0072] 2. Adsorption at different pH values

[0073] A 25 mL Cr(VI) solution with a concentration of 30 ppm was prepared, and 0.1 g of CF-FA-UiO-66-NH2 was added to the solution. The mixture was slowly shaken at 45 rpm in a water bath constant temperature shaker at 25°C for 12 h. The pH range was set to 2-9. Experiments were conducted on CF-FA-UiO-66-NH2 in the pH range of 2-9, and it was found that the adsorption of Cr(VI) decreased significantly when the pH was greater than 3 (see Figure 10 ).

[0074] 3. Adsorption time

[0075] A 25 mL Cr(VI) solution with pH = 2 and concentration of 30 ppm was prepared, and 0.1 g of CF-FA-UiO-66-NH2 was added. At each interval, a small amount of solution was taken for testing the concentration change of the treatment solution over time. The data of the formic acid-regulated UiO-66-NH2 composite fabric adsorption were fitted using a quasi-second kinetic model (see Figure 11 ), with a high fitting degree and R 2 = 0.99947, indicating that the interaction force between CF-FA-UiO-66-NH2 and chromium ions in water is mainly van der Waals force and electrostatic force. During 240-540 min, the adsorption capacity increased from 3.266 mg / g to 3.297 mg / g.

[0076] Example Five Filtration and separation operation of Cr(VI)

[0077] Two 15 mL Cr(VI) solutions with a concentration of 20 ppm were prepared, and CF-FA-UiO-66-NH2 fabric samples with a diameter of 1.5 cm were placed on the sand core of the filter funnel in a single layer or double-layered form. The initial Cr(VI) solution was poured into the microfiltration cup, and after the solution passed through the fabric, a small amount of solution was taken for testing the residual Cr(VI) concentration. During the cycle filtration, the filtrate obtained from the previous filtration was poured into the filter cup again for the next filtration and separation. The whole process was repeated for 6 cycles, and the Cr(VI) concentration in the solution after each filtration cycle was measured.

[0078] Due to the fast adsorption rate of CF-FA-UiO-66-NH2 for Cr(VI), the modified fabric was used as a filter material to treat a Cr(VI) aqueous solution with a certain concentration. Referring to Figure 12 , the residual concentration of Cr(VI) after 1-6 times of filtration and treatment of the metal ion solution by single-layer and double-layer modified fabric was compared. After 6 cycles of filtration, the residual Cr(VI) concentration in the filtrate was 16.236 ppm. When double-layer modified fabric was used for solution filtration and treatment, the residual concentration after 1 cycle of filtration could reach 11.308 ppm, and the Cr(VI) concentration in the filtrate gradually decreased with the increase of the number of filtrations. After 6 cycles of filtration, the residual Cr(VI) concentration in the filtrate was 9.1388 ppm, indicating that CF-FA-UiO-66-NH2 is an ideal Cr(VI) filter removal material.

[0079] The present application uses sodium nitrite and dilute hydrochloric acid to prepare an aqueous nitrous acid solution, and at low temperature, m-amino benzoic acid is added to generate an aromatic diazonium salt, and free radical polymerization is carried out on the surface of the cotton fabric to generate an aromatic carboxyl polymer, and a carboxylated fabric for in-situ growth of crystals is prepared. The surface structure is characterized by means of FT-IR, EDS, XPS and the like. In the presence of acetic acid or formic acid adjuster, zirconium tetrachloride, terephthalic acid or 2-amino terephthalic acid is used as a ligand, and UiO-66 and UiO-66-NH2 are in-situ grown on the surface of the carboxylated fabric. By adjusting the ratio of organic ligand and metal ion, the content of carboxylic acid adjuster and the reaction time, the growth of the two kinds of crystals in different morphologies on the fabric surface is regulated, and different modified fabric materials are prepared. The adsorption performance of the modified fabric for Cr(VI) is tested, and it is found that the adsorption performance of the UiO-66-NH2 fabric is better than that of the UiO-66 fabric, and the modified fabric with the strongest adsorption capacity is CF-FA-UiO-66-NH2 (5.47M formic acid). The CF-FA-UiO-66-NH2 is used to test the adsorption and filtration separation performance for Cr(VI) in the solution. The adsorption effect of the CF-FA-UiO-66-NH2 is the best at pH=2, and the adsorption kinetics curve conforms to the pseudo-second-order kinetics model. It is measured that the double-layer modified fabric has a good filtration retention effect for Cr(VI) in the solution.

Claims

1. A method for removing heavy metal ions, characterized by, The modified fabric is mixed with a solution containing heavy metals for a period of time and then removed to remove the heavy metal ions; or the solution containing heavy metals is passed through the modified fabric to remove the heavy metal ions. The heavy metal ions are hexavalent Cr(VI); the preparation method of the modified fabric comprises the following steps: taking a fabric as a raw material, obtaining a modified fabric by a diazo radical polymerization method, and then growing a metal organic framework on the surface of the fabric in situ to obtain the modified fabric; the step of taking the fabric as the raw material and obtaining the modified fabric by the diazo radical polymerization method comprises the following steps: diazotizing hydrochloric acid, sodium nitrite and amino benzoic acid, then immersing the fabric, adding a reducing agent, and reacting at 20-40 DEG C for 15-30 hours to obtain the modified fabric; the step of growing the metal organic framework on the surface of the fabric in situ comprises the following steps: immersing the modified fabric in a metal ion precursor solution, then adding amino terephthalic acid, and refluxing to obtain the modified fabric, wherein the metal ion precursor solution comprises a Zr compound and an alkyl acid. When the modified fabric is mixed with the solution containing heavy metals, the pH of the solution containing heavy metals is 1-3; and the mixing time is 1-20 hours.

2. The method of claim 1, wherein the heavy metal ions are selected from the group consisting of lead, cadmium, mercury, arsenic, chromium, and selenium. The Zr compound is ZrCl4, the alkyl acid comprises formic acid and acetic acid, and the amino terephthalic acid is 2-amino terephthalic acid.

3. The method of claim 1, wherein the heavy metal ions are removed by the method, The mass ratio of the Zr compound to the amino terephthalic acid is 1:(0.6-1.2); and the dosage ratio of the Zr compound to the alkyl acid is (30-65) mg:1 mL.

4. The method of removing heavy metal ions according to claim 1, wherein, The preparation method of the modified fabric comprises the following steps: taking a fabric as a raw material, obtaining a modified fabric by a diazo radical polymerization method, and then growing a metal organic framework on the surface of the fabric in situ to obtain the modified fabric; the step of taking the fabric as the raw material and obtaining the modified fabric by the diazo radical polymerization method comprises the following steps: diazotizing hydrochloric acid, sodium nitrite and amino benzoic acid, then immersing the fabric, adding a reducing agent, and reacting at 20-40 DEG C for 15-30 hours to obtain the modified fabric; the step of growing the metal organic framework on the surface of the fabric in situ comprises the following steps: immersing the modified fabric in a metal ion precursor solution, then adding amino terephthalic acid, and refluxing to obtain the modified fabric, wherein the metal ion precursor solution comprises a Zr compound and an alkyl acid; and the heavy metal ions are hexavalent Cr(VI).

5. A modified fabric for removing heavy metal ions, characterized by, ​

Images