Novel composite adsorption material, preparation method thereof and application of novel composite adsorption material in detection of lead content in plants

Abstract

The invention discloses a novel composite adsorption material, a preparation method thereof and application of the novel composite adsorption material in detection of lead content in plants. According to the preparation method disclosed by the invention, aMIL-68 (In)-NH2 is synthesized by adopting DES for the first time, and aMIL-68 (In)-NH2 and TiO2 are combined for the first time to prepare a novel composite adsorption material aMIL-68 (In)-NH2-TiO2. According to the invention, the novel composite adsorption material is also used as a DMSPE adsorbent, high-selectivity adsorption is carried out on Pb < 2 + > by regulating and controlling the pH value, and then the adsorption material is combined with ICP-OES, so that a method for rapidly, simply, conveniently, efficiently and selectively measuring Pb < 2 + > in plant Angelica sinensis is established, a new method is provided for monitoring trace Pb < 2 + > in an actual sample, and the method is simple, rapid, efficient and low in cost. The sensitivity of analyzing and measuring lead by an instrument can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of analytical chemistry, and particularly relates to a novel composite adsorbent, a preparation method thereof, and an application thereof in detecting the lead content in plants. Background Art

[0002] Angelica sinensis (Oliv.) Diels is a plant of the Umbelliferae family. It tastes sweet with a spicy flavor and is warm in nature, and has the effects of enriching blood and promoting blood circulation. It is commonly used in rheumatism, arthritis, and carbuncle abscess ulcers. However, with the rapid development of industry and agriculture, frequent sewage discharge, mining activities, and overuse of industrial and agricultural chemicals have led to increasingly serious heavy metal ion pollution. Heavy metal ions are non-degradable and will exist in the ecosystem and food chain indefinitely, exposing humans to high levels of pollution. Among them, lead (Pb 2+ ) is a powerful developmental neurotoxin. Even very low exposure levels can reduce the IQ of children, cause acute or chronic damage to the immune system, digestive system, and nervous system, and even lead to cancer. Therefore, accurately determining Pb 2+ in Angelica sinensis has important significance.

[0003] There are still some challenges in directly determining trace elements in actual samples by ICP-OES. The complex matrix in actual samples will produce matrix effects, and the concentration of target elements may be lower than the LOD value of ICP-OES. To overcome these problems, appropriate sample pretreatment techniques are usually required before detection to selectively separate and enrich target elements, remove the matrix, and make the target elements suitable for subsequent ICP-OES analysis. Dispersive micro-solid phase extraction (DMSPE) is to disperse a small amount of adsorbent in a liquid sample, and the adsorbent directly acts on the target analyte. However, selecting a suitable adsorbent is a necessary step in developing a reliable DMSPE procedure. Traditional adsorbents include metal oxides, activated carbon, and organic polymers, etc., which have disadvantages such as slow binding kinetics, poor selectivity, limited adsorption rate, and insufficient adaptability to the removal of various pollutants. Therefore, it is urgent to develop an ideal adsorption material with high porosity, high selectivity, and more abundant adsorption sites. Summary of the Invention

[0004] The purpose of the present invention is to provide a novel composite adsorbent, a preparation method thereof, and an application thereof in detecting the lead content in plants. The present invention uses aMIL-68(In)-NH2-TiO2 as a DMSPE adsorbent and conducts highly selective adsorption on Pb 2+ by regulating the pH value, and then combines it with ICP-OES to establish a rapid, simple, efficient, and selective method for determining Pb 2+ in Angelica sinensis, providing a method for trace Pb 2+The monitoring provides a new method.

[0005] To achieve the above invention purpose, the present invention is implemented by the following technical solutions:

[0006] The present invention provides a preparation method of a novel composite adsorbent material, which comprises the following steps:

[0007] (1) Mix choline chloride and urea evenly at high temperature to obtain DES;

[0008] (2) Dissolve indium nitrate hydrate and 2-aminoterephthalic acid in the mixed solution of DES and water in the step (1), stir evenly at high temperature, and after cooling and centrifuging, the precipitate is washed and dried to obtain aMIL-68(In)-NH2;

[0009] (3) Disperse the aMIL-68(In)-NH2 in the step (2) evenly in anhydrous ethanol and ammonia water, then drop tetrabutyl titanate into the dispersion liquid, after the reaction, centrifuge to collect the precipitate, wash and dry it to obtain the novel composite adsorbent material aMIL-68(In)-NH2-TiO2.

[0010] Further, in the step (1), the molar ratio of choline chloride to urea is 1:2-4; the high temperature is 80 °C.

[0011] Preferably, in the step (1), the molar ratio of choline chloride to urea is 1:2.

[0012] Further, in the step (2), the volume ratio of DES to water is 1-5:1-2; the mass ratio of the dosages of indium nitrate hydrate and 2-aminoterephthalic acid is 1-3:1, the concentration of indium nitrate hydrate in the mixed solution is 100 mg / mL to 200 mg / mL, and the temperature of the high-temperature stirring is 100 °C.

[0013] Preferably, in the step (2), the volume ratio of DES to water is 1:1.

[0014] Further, in the step (3), the dosage of tetrabutyl titanate is 0.01–0.35 mL.

[0015] Preferably, in the step (3), the dosage of tetrabutyl titanate is 0.15 mL.

[0016] The present invention also provides the novel composite adsorbent material prepared by the above preparation method, whose specific surface area is not less than 110 m 2 / g, and the pore diameter is not less than 9 nm.

[0017] The present invention also provides the application of the novel composite adsorbent material in detecting the lead content in plants.

[0018] The present invention also provides a method for detecting lead content in plants by combining a pH-regulated DMSPE separation technique with ICP-OES, which comprises the following steps:

[0019] (1) After digesting and removing acid from the plant, a test solution is obtained;

[0020] (2) Adding the novel composite adsorbent to the test solution, adjusting the pH to 2 - 8, then shaking for adsorption, and completing and recovering the adsorption by the adsorbent;

[0021] (3) Adding an eluent to the recovered adsorbent for elution, then separating the adsorbent, and detecting the lead content of the obtained eluate.

[0022] Preferably, in step (2), the pH is adjusted to 3.

[0023] Further, in step (2), the dosage of the novel composite adsorbent is 15 - 40 mg; the dosage of the test solution is 50 mL; the adsorption time is 1 - 7 min, and the adsorption temperature is 5 - 45 °C.

[0024] Preferably, in step (2), the dosage of the novel composite adsorbent is 30 mg; the adsorption time is 3 min, and the adsorption temperature is 25 °C.

[0025] Further, in step (3), the eluent is an HNO3 solution with a concentration of 0.1 - 2.5 mol / L, and the addition amount is 1.5 mL; the elution temperature is 10 - 60 °C, and the elution time is 2 - 26 min.

[0026] Preferably, in step (3), the eluent is an HNO3 solution with a concentration of 1 mol / L; the elution temperature is 50 °C, and the elution time is 14 min.

[0027] Further, the plant is Angelica acutiloba.

[0028] Further, the detection limit and quantification limit of lead in Angelica acutiloba detected by the combined method are 0.10 μg / L and 0.32 μg / L respectively.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] 1. The present invention first synthesizes aMIL-68(In)-NH2 using DES, and for the first time combines aMIL-68(In)-NH2 with TiO2 to prepare a novel composite material aMIL-68(In)-NH2-TiO2, and uses it as an adsorbent for DMSPE for trace Pb2+ For the selective separation and enrichment, the trace Pb can be regulated by adjusting the pH 2+ for highly selective extraction.

[0031] 2. The aMIL-68(In)-NH2-TiO2 of the present invention has good adsorption capacity and adsorption selectivity for lead. The established coupling method improves the sensitivity of the instrument, and its successful application in the medicinal plant Angelica sinensis samples is conducive to promoting the quality control of actual samples. Description of the Drawings

[0032] Figure 1 FT-IR diagrams of aMIL-68(In)-NH2 (a), aTiO2 (b), and aMIL-68(In)-NH2-TiO2 (c).

[0033] Figure 2 N2 adsorption / desorption isotherm curves.

[0034] Figure 3 Zata potential diagrams.

[0035] Figure 4 TEM diagrams of aMIL-68(In)-NH2 (A–B), aTiO2 (C–D), aMIL-68(In)-NH2-TiO2 (E–F), and aMIL-68(In)-NH2-TiO2 (G–H).

[0036] Figure 5 Optimization of the DES ratio.

[0037] Figure 6 Optimization of the DES-water mixture ratio.

[0038] Figure 7 Optimization of tetrabutyl titanate.

[0039] Figure 8 Optimization of pH.

[0040] Figure 9 Optimization of the adsorption time.

[0041] Figure 10 Optimization of the adsorbent dosage.

[0042] Figure 11 Optimization of the adsorption temperature.

[0043] Figure 12 Optimization of the eluent concentration.

[0044] Figure 13 Optimization of the elution temperature.

[0045] Figure 14For the optimization of the elution time.

[0046] Figure 15 For the comparison of the extraction performance of the adsorbent before and after modification. Specific implementation mode

[0047] The technical solution of the present invention will be further described in detail in conjunction with the following specific examples.

[0048] In the following examples, unless otherwise specified, the experimental methods used are all conventional methods, and the materials, reagents, etc. used can be purchased from biological or chemical reagent companies.

[0049] Example 1: Preparation of aMIL-68(In)-NH2-TiO2

[0050] I. Material preparation

[0051] 1. Preparation of DES

[0052] Choline chloride and urea were stirred at 80 °C in a molar ratio of 1:2 until transparent to obtain DES.

[0053] 2. Preparation of aMIL-68(In)-NH2

[0054] Indium nitrate hydrate (1050 mg) and 2-aminoterephthalic acid (460 mg) were dissolved in a DES-water mixture (20 mL, volume ratio of DES to water is 1:1) and placed in a round-bottom flask. After magnetic stirring at 100 °C for 5 h, the round-bottom flask was taken out of the oil bath. After the temperature dropped to 25 °C, the suspension was collected and centrifuged. The precipitate was ultrasonically washed with methanol three times to remove the DES residues on the surface. Finally, the obtained aMIL-68(In)-NH2 was vacuum dried at 60 °C.

[0055] 3. Synthesis of aMIL-68(In)-NH2-TiO2

[0056] The prepared aMIL-68(In)-NH2 (80 mg) was uniformly dispersed in anhydrous ethanol (10 mL) by ultrasonic wave, and then ammonia water (0.2 mL) was added. After stirring at room temperature for 5 min to make the mixture uniformly dispersed. Then, under stirring, 0.15 mL of tetrabutyl titanate was added dropwise to the dispersion. After reacting for 10 min, the product aMIL-68(In)-NH2-TiO2 nanoparticles were collected by centrifugation, washed several times with ethanol, and vacuum dried at 60 °C.

[0057] The preparation method of aTiO2 is the same as the above method except that aMIL-68(In)-NH2 is not added.

[0058] II. Material characterization

[0059] 1. The Fourier transform infrared spectra (FT-IR) of the prepared aMIL-68(In)-NH2, aTiO2, and aMIL-68(In)-NH2-TiO2 were measured by the KBr method. The results are as Figure 1 shown. The peaks of aMIL-68(In)-NH2 and aMIL-68(In)-NH2-TiO2 at 770 cm –1 , 768 cm –1 can be attributed to the out-of-plane bending vibration of C-H; 1260 cm –1 is for the stretching vibration of C-O; 1377 cm –1 and 1619 cm –1 are the characteristic peaks of C-N and C=N bonds. The strong absorption peaks of aTiO2 and aMIL-68(In)-NH2-TiO2 at 532 cm –1 , 509 cm –1 can be attributed to the vibration peaks of Ti-O bonds. The absorption peaks at 3430 cm –1 , 3420 cm –1 , and 3424 cm –1 in the FT-IR spectra of aMIL-68(In)-NH2, aTiO2, and aMIL-68(In)-NH2-TiO2 can be attributed to the vibration peaks of -OH bonds. In the FT-IR spectrum of aMIL-68(In)-NH2-TiO2, the peaks appearing in the spectra of aMIL-68(In)-NH2 and aTiO2 can be observed, which can preliminarily prove the successful preparation of aMIL-68(In)-NH2-TiO2 from the surface groups of the material.

[0060] 2. The N2 adsorption and desorption isotherms of aMIL-68(In)-NH2, aTiO2, and aMIL-68(In)-NH2-TiO2 are as Figure 2 shown. They exhibit type-IV isotherms and H3-type hysteresis loops, indicating that these samples are mesoporous materials related to slit-shaped pores. The specific surface area of aMIL-68(In)-NH2 is 70.62 m 2 / g, and the pore diameter is 16.09 nm. The specific surface area of aTiO2 is 335.36 m 2 / g, and the pore diameter is 4.30 nm. The specific surface area of MIL-68(In)-NH2-TiO2 is 113.69 m 2 / g, and the pore diameter is 9.37 nm. The specific surface area of aMIL-68(In)-NH2-TiO2 after adsorbing Pb 2+ is 141.61 m 2 / g, with a pore size of 7.95 nm. Compared with aTiO2, aTiO2 has a larger specific surface area, while aMIL-68(In)-NH2 has a larger pore size. After the two are combined, the specific surface area and pore size of aMIL-68(In)-NH2-TiO2 are both at a suitable value. aMIL-68(In)-NH2-TiO2 adsorbs Pb 2+ The specific surface area becomes larger, but the pore size becomes smaller because Pb 2+ is adsorbed on the surface of aMIL-68(In)-NH2-TiO2, increasing its specific surface area. Some of the ions enter the pores of the material, thus occupying part of the pores and making them smaller.

[0061] 3. The Zeta potential of the prepared material aMIL-68(In)-NH2-TiO2 is as Figure 3 shown. In a solution with a pH of 2, the particles of aMIL-68(In)-NH2, aTiO2, and aMIL-68(In)-NH2-TiO2 are all positively charged. This may be because there are more hydrogen ions under extremely acidic conditions, and the material is protonated and does not adsorb any ions. In a solution with a pH of 3, the particles of aMIL-68(In)-NH2, aTiO2, and aMIL-68(In)-NH2-TiO2 are all positively charged, but the charge value decreases slightly compared to when the pH is 2. At this time, aTiO2 can adsorb Pb 2+ , Cu 2+ , Cr 3+ , Cd 2+ , Al 3+ ; The MOF selectively adsorbs Pb 2+ . This is because the unprotonated material can just adsorb Pb 2+ . In solutions with a pH of 4 and a pH of 5, except for aMIL-68(In)-NH2, the particles of aTiO2 and aMIL-68(In)-NH2-TiO2 are all negatively charged, and the positively charged metal ions are easily adsorbed.

[0062] 4. Transmission electron microscopy (TEM) is an important tool for observing and studying the morphology of materials. Figure 4 A - B shows the structure of aMIL-68(In)-NH2 particles, with a rough surface and many irregular pores. Figure 4 C - D shows the structure of TiO2 particles, with a surface that is slightly smoother than that of aMIL-68(In)-NH2 particles. In Figure 4 The structure of aMIL-68(In)-NH2-TiO2 particles shown in E - F just combines the morphologies of the two. Figure 4 G - H shows aMIL-68(In)-NH2-TiO2 adsorbing Pb2+ The subsequent morphology is rougher than that without Pb adsorption 2+ because Pb occupies the adsorption sites on the material surface 2+ .

[0063] Example 2: Conditions Affecting Dispersive Micro-Solid Phase Extraction (DMSPE)

[0064] I. Process of Coupling DMSPE with ICP-OES

[0065] The extraction process was carried out in a 50 mL centrifuge tube. 30 mg of aMIL-68(In)-NH2-TiO2 prepared in Example 1 was added to a 50 mL standard solution containing Pb 2+ . The pH was adjusted to 3 with 1 mol / L NaOH and HNO3 and made up to 50 mL to make the Pb 2+ concentration 0.1 μg / mL. The centrifuge tube was placed in an oscillation incubator, shaken and then centrifuged to separate the adsorbent. The supernatant was removed and measured by ICP-OES. The blank sample was ultrapure water without Pb 2+ standard solution, and other conditions were the same as those of the experimental group. During this process, the ratio of DES, the ratio of DES-water mixture and the dosage of TNBT were investigated. Then the extraction conditions were optimized, including: adsorption time, adsorption temperature, adsorbent dosage, adsorption pH. Equation (1) was used to calculate the adsorption rate

[0066] During the elution process, 1.5 mL of 1.0 mol / L HNO3 solution was added to the recovered adsorbent and shaken at 250 rpm for a certain time at a certain temperature. The adsorbent was centrifuged and the eluate was analyzed by ICP-OES. The blank sample was the desorption solution of the blank group in the previous step under the same conditions as the experimental group. During this process, the eluent concentration, elution temperature and elution time were optimized. Equation (2) was used to calculate the elution rate

[0067] (1)

[0068] (2)

[0069] In the formula, η (%) represents the adsorption rate; C0 (μg / mL) and C (μg / mL) are the metal ion concentrations in the sample before and after adsorption; E (%) represents the desorption rate; C E (μg / mL) is the metal ion concentration in the eluate; V E (mL) is the volume of the eluate; V (mL) is the initial volume of the sample solution

[0070] II. Optimization of DMSPE Conditions

[0071] To achieve the best extraction performance of DMSPE, the adsorbent was first optimized, including the ratio of DES, the ratio of DES-water mixture, and the dosage of tetrabutyl titanate. Then, the extraction conditions were optimized, including adsorption time, adsorption temperature, adsorbent dosage, adsorption pH, eluent concentration, elution temperature, and elution time. Except for the variables, other conditions were the same as those in Example 1 and the above experiments.

[0072] 1. Optimization of the DES ratio

[0073] Among the DESs prepared with different molar ratios (1:1, 1:2, 1:3, 1:4), the hydrogen bond forces between HBA and HBD are different, and their physical properties are different, which will affect the synthesis of aMIL-68(In)-NH2, and thus lead to differences in the adsorption performance of aMIL-68(In)-NH2-TiO2. As Figure 5 shown, when the DES ratio is 1:2, the adsorption performance is the best, and the DES is the most stable under this ratio. Therefore, in the subsequent experiments, the DES ratio of 1:2 was selected to synthesize aMIL-68(In)-NH2.

[0074] 2. Optimization of the DES-water mixture ratio

[0075] Using the DES-water mixture (volume ratios of 5:1, 4:1, 3:1, 2:1, 1:1, 1:2) as the reaction solvent for synthesizing aMIL-68(In)-NH2, adding an appropriate amount of water to the prepared DES can reduce the viscosity of the DES and make the properties of the prepared materials better. As Figure 6 shown, when the DES-water mixture is 1:1, the adsorption performance for Pb 2+ is the best. Therefore, in the subsequent experiments, the DES-water ratio of 1:1 was selected to synthesize aMIL-68(In)-NH2.

[0076] 3. Optimization of the dosage of tetrabutyl titanate

[0077] Tetrabutyl titanate is the main raw material for synthesizing TiO2. The composite amount of TiO2 in the final adsorption material aMIL-68(In)-NH2-TiO2 will affect its adsorption performance. Too little or too much dosage may lead to low adsorption rate problems. In this experiment, the dosages of tetrabutyl titanate were 0.1 mL, 0.15 mL, 0.25 mL, and 0.35 mL respectively. As Figure 7 shown, when the TNBT dosage is 0.15 mL, the adsorption performance for Pb 2+ is the best. Therefore, in the subsequent experiments, the TNBT dosage of 0.15 mL was selected.

[0078] 4. Optimization of the influence of pH

[0079] The pH value of the solution affects the ionization of metal ions, the concentration of hydrogen ions on the surface of the material, the adsorption equilibrium and the adsorption kinetics. It plays an important role in determining the surface characteristics of the adsorbent and the degree of ionization of the adsorbate, which ultimately affects the adsorption of trace Pb by aMIL-68(In)-NH2-TiO2. 2+ Adsorption. Figure 8 As shown in the figure, for aMIL-68(In)-NH2-TiO2, the pH value of the solution when adsorbing metal ions largely determines its selectivity. At pH 2, the material has a very low selectivity for Pb 2+ The adsorption rate of H is less than 20%, and there is almost no adsorption of other ions. + The more, the more H + While competing with heavy metal ions for binding sites, the material surface is positively charged, which can reduce the adsorption of cationic heavy metals through electrostatic repulsion. At this time, the removal efficiency of pollutants is the lowest. As the pH gradually increases, the removal rate gradually increases. The reason is that the electrostatic repulsion gradually decreases, the surface of the material gradually becomes negatively charged, and the electrostatic attraction increases. When the pH is greater than or equal to 4, the material can adsorb a variety of metal ions and can be used as a broad-spectrum adsorbent, which is expected to achieve the adsorption of a variety of heavy metals in actual samples. However, when the pH is 3, the material has no effect on Pb 2+ The adsorption rate is 96%, and it does not adsorb other metal ions, achieving the goal of Pb 2+ Therefore, pH = 3 was selected as the optimal experimental condition in subsequent experiments.

[0080] 5. Optimization of adsorption time

[0081] aMIL-68(In)-NH2-TiO2 and Pb 2+ Sufficient mixing time is required to reach extraction equilibrium. The effect of extraction time was studied by varying the shaking time from 1–7 min (1 min interval). Figure 9 As shown in the figure, the adsorption rate is the best when the adsorption time is 3 min.

[0082] 6. Optimization of adsorbent dosage

[0083] aMIL-68(In)-NH2-TiO2 and Pb 2+ Sufficient amount of adsorbent is required to achieve good extraction performance. The effect of extraction time was studied by varying the amount of adsorbent aMIL-68(In)-NH2-TiO2 from 15–40 mg (10 mg interval). Figure 10 As shown in the figure, the adsorption rate is the best when 30 mg is adsorbed, so 30 mg is selected as the optimal adsorbent dosage in subsequent experiments.

[0084] 7. Optimization of adsorption temperature

[0085] Adjust the pH of the solution to 3, add 30 mg of the adsorbent, and oscillate for 3 min to reach equilibrium. Then, study the effect of temperature on the adsorption of Pb 2+ at 5–45 °C. The results are as Figure 11 shown. Whether at low or high temperatures, the adsorption efficiency tends to level off, indicating that the extraction of Pb 2+ by the adsorbent is hardly affected by temperature. To simplify the extraction process, room temperature (25 °C) was selected for subsequent experiments.

[0086] 8. Optimization of the eluent concentration

[0087] Under the elution conditions of 60 °C and 14 min, study the effect of eluent concentration in the range of 0.1–2.5 mol / L on the adsorption of Pb 2+ . The results are as Figure 12 shown. As the eluent concentration gradually increases, the elution rate also increases. When it is higher than 1 mol / L, the elution rate basically levels off. Therefore, an eluent concentration of 1 mol / L was selected for subsequent experiments.

[0088] 9. Optimization of the elution temperature

[0089] Under the elution conditions of 1 mol / L nitric acid and oscillation for 14 min, study the effect of elution temperature in the range of 10–60 °C on the adsorption of Pb 2+ . The results are as Figure 13 shown. As the elution temperature increases, the elution rate also increases accordingly. However, when the elution temperature is higher than 50 °C, the elution rate decreases. Therefore, an elution temperature of 50 °C was selected for subsequent experiments.

[0090] 10. Optimization of the elution time

[0091] Metal ions can be eluted from the adsorbent in an acidic environment because H + in the solution competes with metal ions for the binding sites on the surface of the adsorbent. In this experiment, 1 mol / L HNO3 was selected to elute Pb 2+ from aMIL-68(In)-NH2-TiO2. Under acidic conditions (1.50 mL of 1 mol / L HNO3) at 50 °C, the effect of elution time on the desorption efficiency of aMIL-68(In)-NH2-TiO2 was studied. As Figure 14 shown, as the elution time prolongs, the desorption efficiency gradually increases and reaches the best at 14 min. Subsequently, the desorption efficiency gradually decreases, which may be due to the fact that after a long oscillation time, some desorbed Pb 2+ is re-adsorbed by aMIL-68(In)-NH2-TiO2.

[0092] III. Comparison of the extraction performance of the adsorbent before and after modification

[0093] Pb in actual samples 2+ Pb often coexists with other metal ions in actual samples. Therefore, adsorption selectivity is also a key factor in evaluating the performance of materials. The adsorption performances of aMIL-68(In)-NH2, aTiO2 and aMIL-68(In)-NH2-TiO2 were compared under the conditions of pH 3, adsorbent dosage of 30 mg and adsorption time of 4 min. The results are as Figure 15 shown. aMIL-68(In)-NH2 does not adsorb any ions under acidic conditions, and aTiO2 adsorbs Al 3+ , Cd 2+ , Pb 2+ , Cu 2+ , Cr 3+ . aMIL-68(In)-NH2-TiO2 can selectively adsorb Pb 2+ highly, which may be due to the hard-soft acid-base (HSAB) principle. Pb 2+ has a better affinity with oxygen / nitrogen-containing groups, thus showing excellent selectivity for Pb 2+ .

[0094] Example 3: Determination of Pb in Angelica sinensis (Oliv.) Diels 2+ Determination

[0095] 1. Sample collection and preparation

[0096] The authentic medicinal material Angelica sinensis (Oliv.) Diels in Yunnan was collected from Binchuan County, Dali Prefecture, Yunnan Province; Muding County, Chuxiong Prefecture, Yunnan Province; Machang Village, Heqing County, Dali Prefecture, Yunnan Province. The collected medicinal materials were washed, dried, pulverized and sieved through a 120-mesh sieve. 0.5000 g of sample powder was accurately weighed and put into a digestion tank. Then 8.0 mL of HNO3, 2.0 mL of H2O2 (30%) and 2.0 mL of ultrapure water were added to the digestion tank, and digestion was carried out according to the microwave digestion program in Table 1. After the digestion program ended, it was placed on an acid-evaporating instrument at 130 °C to evaporate the acid for about 3.5 h. Subsequently, when the solution was clear, it was cooled to room temperature and transferred to a 10 mL volumetric flask, and made up to the mark with ultrapure water for subsequent determination.

[0097] Table 1 Microwave digestion program

[0098]

[0099] 2. Preparation of aMIL-68(In)-NH2-TiO2

[0100] (1) Preparation of DES

[0101] Choline chloride and urea were stirred at 80 °C until transparent according to a molar ratio of 1:2.

[0102] (2) Preparation of aMIL-68(In)-NH2

[0103] Indium(III) nitrate hydrate (1050 mg) and 2-aminoterephthalic acid (460 mg) were dissolved in a DES-water mixture (20 mL, volume ratio of DES to water is 1:1) and placed in a round-bottom flask. After magnetic stirring at 100 °C for 5 h, the round-bottom flask was removed from the oil bath. After the temperature dropped to 25 °C, the suspension was collected and centrifuged. The precipitate was ultrasonically washed three times with methanol to remove the DES residues on the surface. Finally, the obtained aMIL-68(In)-NH2 was dried in vacuo at 60 °C.

[0104] (3) Synthesis of aMIL-68(In)-NH2-TiO2

[0105] The prepared aMIL-68(In)-NH2 (80 mg) was uniformly dispersed in anhydrous ethanol (10 mL) by ultrasonic treatment, and then ammonia water (0.2 mL) was added. The mixture was stirred at room temperature for 5 min to make it uniformly dispersed. Then, under stirring, 0.15 mL of tetrabutyl titanate was added dropwise to the dispersion. After reacting for 10 min, the product aMIL-68(In)-NH2-TiO2 nanoparticles were collected by centrifugation, washed three times with ethanol, and dried in vacuo at 60 °C.

[0106] 3. Process of the combination of aMIL-68(In)-NH2-TiO2 and ICP-OES

[0107] The extraction process was carried out in a 50 mL centrifuge tube. 30 mg of aMIL-68(In)-NH2-TiO2 was added to 50 mL of the Angelica acutiloba Kitagawa sample solution; the pH was adjusted to 3 with 1 mol / L NaOH and HNO3 and made up to 50 mL. The centrifuge tube was placed in an oscillation incubator and oscillated at 25 °C for 3 min, then the adsorbent was separated by a magnet, and the supernatant was removed. 1.5 mL of 1.0 mol / L HNO3 solution was added to the recovered adsorbent, and it was oscillated and eluted at 50 °C for 14 min. The adsorbent was separated by a magnet, and the eluate was determined for the content of Pb by inductively coupled plasma optical emission spectrometry. 2+ content.

[0108] The results are shown in Table 2. The determination results of the actual samples are in good agreement with those of ICP-MS. The results of the actual samples are highly consistent with the ICP-MS results. The Pb 2+ contents in Angelica acutiloba Kitagawa did not exceed the limit values. The recoveries of the standard addition tests were in the range of 92.0–105%, all within the acceptable limits.

[0109] Table 2 Pb in Angelica acutiloba Kitagawa 2+Analysis results (±standard deviation of three replicates)

[0110]

[0111] Note: a S1: Binchuan County, Dali Bai Autonomous Prefecture, Yunnan Province; b S2: Mouding County, Chuxiong Prefecture, Yunnan Province; c S3: Machang Village, Heqing County, Dali Prefecture, Yunnan Province.

[0112] 4. Interference experiment

[0113] There are usually many substances interfering with Pb extraction in actual samples. Therefore, the anti-interference experiment is an important step in the extraction of target ions. The effects of potential interfering ions were studied, as shown in Table 3. The anti-interference ability of this method was studied using an analytical solution containing 0.1 µg / mL Pb 2+ In the recovery range of 91.5–108%, it can be regarded as interference-free. 2+ Table 3 Tolerance limits of coexisting ions for the determination of Pb

[0114] (0.1 μg / mL) (n = 3) 2+

[0115]

[0116] 5. Analytical performance

[0117] On the basis of optimizing the DMSPE conditions, the analytical performance of this method was evaluated, and the results are shown in Table 4 for Pb 2+ The enrichment factor (EF) was 30.6, the limit of detection (LOD) was 0.10 μg / L, and the limit of quantification (LOQ) was 0.32 μg / L. The intra-day and inter-day precision of this method was evaluated on the same day and for three consecutive days, respectively. The intra-day precision was 0.22%, and the inter-day precision was 0.66%. The low RSD values verified the good precision of this method.

[0118] Table 4 Analytical performance

[0119] Note: a LOD, limit of detection, is based on the 3.3σ criterion of 11 blank measurements; b LOQ, limit of quantification, is based on the 10σ criterion of 11 blank measurements; c EF, enrichment multiple, is calculated according to the ratio of the slopes of the standard curves of DMSPE and direct determination of lead by ICP-OES.

[0120] ​The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, for those of ordinary skill in the art, it is still possible to modify the technical solutions described in the foregoing embodiments, or to equivalently replace some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions required to be protected by the present invention.

Claims

1. A preparation method of a novel composite adsorbent material, characterized in that, It includes the following steps: (1) Mix choline chloride and urea evenly at high temperature to obtain DES; (2) Dissolve indium nitrate hydrate and 2-aminoterephthalic acid in the mixed solution of DES and water in step (1), stir evenly at high temperature, and after cooling and centrifuging, wash and dry the precipitate to obtain aMIL-68(In)-NH2; (3) Disperse aMIL-68(In)-NH2 in step (2) evenly in absolute ethanol and ammonia water, then drop tetrabutyl titanate into the dispersion liquid, after reaction, centrifuge to collect the precipitate, wash and dry to obtain the novel composite adsorbent aMIL-68(In)-NH2-TiO2.

2. The preparation method according to claim 1, characterized in that, In step (1), the molar ratio of choline chloride to urea is 1:2 - 4.

3. The preparation method according to claim 1, wherein In step (2), the volume ratio of DES to water is 1 - 5:1 - 2; the mass ratio of the dosages of indium nitrate hydrate and 2-aminoterephthalic acid is 1 - 3:1, and the concentration of indium nitrate hydrate in the mixed solution is 100 mg / mL - 200 mg / mL.

4. The preparation method according to claim 1, characterized in that, In step (3), the dosage of tetrabutyl titanate is 0.01 - 0.35 mL.

5. The novel composite adsorbent material prepared by the preparation method according to any one of claims 1-4, characterized in that, The specific surface area of the novel composite adsorbent material is not less than 110 m 2 / g, and the pore diameter is not less than 9 nm.

6. Application of the novel composite adsorbent according to claim 5 in detecting the lead content in plants.

7. A method for detecting lead content in plants by coupling a DMSPE separation technique based on pH regulation with ICP-OES, characterized in that, It includes the following steps: (1) After digesting and removing acid from the plant, obtain the test solution; (2) Add the novel composite adsorbent according to claim 5 to the test solution, adjust the pH to 2 - 8, then shake and adsorb, and complete and recover the adsorption by the adsorbent; (3) Add an eluent to the recovered adsorbent for elution, then separate the adsorbent, and detect the lead content of the obtained eluate.

8. The method for detecting the lead content in plants according to claim 7, characterized in that, In step (2), the dosage of the novel composite adsorbent is 15–40 mg; the dosage of the test solution is 50 mL; the adsorption time is 1 - 7 min, and the adsorption temperature is 5 - 45 °C.

9. The method for detecting the lead content in plants according to claim 7, wherein, In step (3), the eluent is an HNO3 solution with a concentration of 0.1–2.5 mol / L, and the added amount is 1.5 mL; the elution temperature is 10–60 °C, and the elution time is 2–26 min.

10. The method for detecting the lead content in plants according to claim 7, wherein The plant is Angelica acutiloba.

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