A hydrogel material and a method for preparing the same

Abstract

The application discloses a preparation method of a hydrogel material, comprising the following steps: preparing a HKUST-1 / g-C3N4 composite material; and reacting the HKUST-1 / g-C3N4 composite material with sodium alginate to obtain the hydrogel material. The application also provides the hydrogel material prepared by the method. The application combines HKUST-1 with g-C3N4 nanosheets (HKUST-1 / g-C3N4), and then constructs a composite hydrogel material (HCS) by combining the HKUST-1 / g-C3N4 material with sodium alginate, so as to be used as a high-efficiency adsorbent for capturing U(VI) from an aqueous solution. The adsorption behavior of U(VI) on the HCS is studied through a static experiment, and the mechanism is analyzed through characterization. The results show that the HCS has good physical and chemical stability in an aqueous solution, is easy to be separated from a liquid, and has high adsorption performance on uranium under visible light.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detection equipment, in particular to a hydrogel material and a preparation method thereof. BACKGROUND

[0002] Uranium is the main resource of nuclear energy, which can be released into the environment through various activities, such as nuclear fuel manufacturing, ore mining and processing, and nuclear weapon production. There is a large amount of residual uranium pollution in groundwater, and hexavalent uranium (U(VI)) is a key component in radioactive wastewater, which has high mobility, strong chemical toxicity and radiation toxicity, and will continue to pose a threat to water resources and even human life for a long time in the future.

[0003] Many methods are widely used to remove U(VI), such as adsorption, cation exchange, chemical precipitation and photoreduction fixation. Among these methods, the adsorption method is promising due to its cost-effectiveness and easy operation. Activated carbon, resins and zeolite clay minerals are commonly used to remove uranium, however, these materials have low practical application value due to limited adsorption capacity. Although new emerging materials such as amorphous porous organic polymers, metal organic frameworks (MOFs) have been developed, there are problems in modification and analysis during the application of porous organic polymers, and there are problems of solid-liquid separation and secondary pollution in metal organic frameworks (MOFs). Moreover, there are inherent limitations in using physical and chemical adsorption properties to adsorb uranyl ions, which hinders the substantial improvement of the adsorption capacity of the material. That is, the adsorption capacity of uranyl ions is limited to the number of active sites, and one active adsorption site can usually capture one or several uranyl ions through chemical bonding. Due to the positive points of the adsorbed uranyl ions, more uranyl ions are repelled from approaching the nearby adsorption sites under the coulomb effect, resulting in a significant reduction in the number of active adsorption sites.

[0004] Therefore, how to improve the adsorption capacity of the adsorption material for uranyl ions is a technical problem to be solved by those skilled in the art. SUMMARY

[0005] To solve the above technical problems, the first object of the present application is to provide a preparation method of a hydrogel material; the second object of the present application is to provide a hydrogel material prepared by the above preparation method; the present application combines HKUST-1 with g-C3N4 nanosheets (HKUST-1 / g-C3N4), and then constructs a composite hydrogel material (HCS) by combining the HKUST-1 / g-C3N4 material with sodium alginate as a high-efficiency adsorbent for capturing U(VI) from aqueous solution. The adsorption behavior of U(VI) on HCS is studied through static experiments, and the mechanism is analyzed through characterization. The results show that HCS has good physical and chemical stability in aqueous solution, is easy to separate solid-liquid, and has high adsorption performance for uranium under visible light.

[0006] The technical scheme provided by the application is as follows:

[0007] A preparation method of a hydrogel material, comprising the following steps:

[0008] Preparation of HKUST-1 / g-C3N4 composite material;

[0009] The HKUST-1 / g-C3N4 composite material is reacted with sodium alginate to obtain the hydrogel material.

[0010] Preferably, the step of preparing the HKUST-1 / g-C3N4 composite material is:

[0011] Copper nitrate trihydrate and 1,3,5-benzene tricarboxylic acid are respectively prepared into solutions, mixed after ultrasonic treatment, g-C3N4 is added, ultrasonic treatment is continued, then reaction is carried out under heating conditions, and natural cooling is carried out.

[0012] Preferably, the step of preparing the HKUST-1 / g-C3N4 composite material is specifically:

[0013] Copper nitrate trihydrate is dissolved in water, ultrasonic treatment is carried out for 10-15 min, and a first solution is obtained;

[0014] N,N-dimethylformamide is dissolved in anhydrous ethanol, then 1,3,5-benzene tricarboxylic acid is added, ultrasonic treatment is carried out for 20-25 min, and a second solution is obtained;

[0015] The first solution and the second solution are mixed, g-C3N4 is added, ultrasonic treatment is carried out for 1-1.5 h, then reaction is carried out at 120±0.5 DEG C for 16 h, and natural cooling is carried out.

[0016] Preferably, the step of preparing the HKUST-1 / g-C3N4 composite material is specifically:

[0017] Preferably, the mass ratio of copper nitrate trihydrate to 1,3,5-benzene tricarboxylic acid and g-C3N4 is 63:110:(10-90).

[0018] Preferably, the step of reacting the HKUST-1 / g-C3N4 composite material with sodium alginate is:

[0019] Sodium alginate and the HKUST-1 / g-C3N4 composite material are added into water, stirring and mixing are carried out, then a CaCl2 solution is slowly added, standing is carried out overnight, freeze-drying is carried out, and the hydrogel material is obtained.

[0020] Preferably, the mass ratio of the HKUST-1 / g-C3N4 composite material, sodium alginate and CaCl2 is 1:1:(3-4).

[0021] Preferably, the sodium alginate and the HKUST-1 / g-C3N4 composite material are added to water, stirred magnetically at room temperature for 1-1.5 h, the stirring rate is 480-500 rpm; then CaCl2 solution is slowly added, and after standing overnight, washed with water for 3-5 times, and freeze-dried for 12-14 h to obtain the hydrogel material.

[0022] Preferably, the g-C3N4 is prepared by the following method: urea is heated at a rate of 2 ℃ / min to 550 ℃, and kept for 4-6 h, and after natural cooling to room temperature, the g-C3N4 is collected and ground into powder.

[0023] A hydrogel material prepared by any of the above preparation methods.

[0024] As a new photocatalytic material with a graphite-like phase structure, graphite carbon nitride (g-C3N4) is a polymer layered material, which has the characteristics of non-toxic, cheap raw materials, visible light response, easy preparation and significant physical and chemical stability.

[0025] The CAS number of HKUST-1 is 222404-02-6, and the molecular formula is: 18 H 12 Cu3O 15 The present application utilizes copper nitrate trihydrate, 1,3,5-benzenetricarboxylic acid and g-C3N4 to directly prepare g-C3N4-wrapped HKUST-1.

[0026] The combination of HKUST-1 and g-C3N4 forms a two-dimensional / three-dimensional hybrid structure, and the flexible layered structure of g-C3N4 is similar to graphene, which can be anchored and wrapped on HKUST-1, thereby forming a close contact interface between g-C3N4 and HKUST-1; the framework topology structure of g-C3N4 is based on two basic components, i.e. s-triazine (C3N3) and tri-s-triazine (C6N7) rings, and U(VI) can be reduced by g-C3N4 and deposited in the form of a metamict nanoparticle. Through the photocatalytic process, since the influence of electrostatic repulsion is overcome, the adsorption capacity is no longer limited by the number of adsorption sites, and the adsorption capacity in the solution can be greatly improved.

[0027] The present application combines HKUST-1 with g-C3N4 nanosheets (HKUST-1 / g-C3N4), and then constructs a composite hydrogel material (HCS) by combining the HKUST-1 / g-C3N4 material with sodium alginate as a high-efficiency adsorbent for capturing U(VI) from aqueous solution. The adsorption behavior of U(VI) on HCS is studied by static experiment, and the mechanism is analyzed by characterization. The results show that HCS has good physical and chemical stability in aqueous solution, is easy to separate solid-liquid, and has high adsorption performance for uranium under visible light. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0029] Figure 1 The infrared spectrum of HKUST-1, g-C3N4 and HC1S;

[0030] Figure 2 The SEM image of HK1CN-1 / sodium alginate (HC1S);

[0031] Figure 3 The SEM-EDS image of HK1CN-1 / sodium alginate (HC1S) after adsorbing uranium;

[0032] Figure 4 (a), (b), (c) and (d) are TEM images of g-C3N4, HKUST-1, HK1CN and HC1S, respectively;

[0033] Figure 5 (a) and (b) are TEM images of HC1S-U

[0034] Figure 6 The schematic diagram of the effect of different composite ratios of materials on U(VI) adsorption;

[0035] Figure 7 The schematic diagram of the effect of different sacrificial agents on U(VI) adsorption;

[0036] Figure 8 The schematic diagram of the effect of pH value on U(VI) adsorption by HK1CN-1 / sodium alginate (HC1S);

[0037] Figure 9 The zeta potential diagram of HK1CN-1 / sodium alginate (HC1S);

[0038] Figure 10 The schematic diagram of the effect of initial concentration of uranium on U(VI) adsorption;

[0039] Figure 11 The schematic diagram of the effect of HK1CN-1 / sodium alginate (HC1S) dosage on adsorption;

[0040] Figure 12 The schematic diagram of the effect of time and light on U(VI) adsorption. DETAILED DESCRIPTION

[0041] In order for those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0042] The present application uses IR Prestige 21 instrument to test Fourier transform infrared spectrum. The Japanese Hitachi Regulus 8100 instrument is used to test scanning electron microscope (SEM) and X-ray energy spectrum (EDS). The British Malvern ZS90 is used to test the zeta potential.

[0043] Example 1

[0044] Take a 100 mL capacity alumina crucible with a lid and accurately weigh 84.0 g of urea into it, place the crucible in a muffle furnace and slowly heat it to 550℃ at a heating rate of 2℃ / min, and keep the temperature for 4 h, and after natural cooling to room temperature, collect the light yellow product to obtain the required g-C3N4, which can be ground into powder with an agate mortar before use.

[0045] Accurately weigh 0.63 g of copper nitrate trihydrate (Cu(NO3)2·3H2O) into 10 mL of distilled water and ultrasonic for 10 min; accurately measure 20 ml of N,N-dimethylformamide (DMF, C3H7NO) and 20 ml of anhydrous ethanol (C2H6O) into the same beaker and mix, and then add 1.1 g of 1,3,5-benzenetricarboxylic acid (H3BTC, C9H6O6) into the mixed solution and ultrasonic for 20 min.

[0046] Accurately weigh 100 mg of g-C3N4 into the mixed solution of copper nitrate and 1,3,5-benzenetricarboxylic acid, and ultrasonic for 1 h, then transfer the mixed solution into a 100 mL polytetrafluoroethylene stainless steel autoclave. After being placed in a 120℃ air drying oven for 16 h, the blue crystals are taken out and naturally cooled to room temperature, and the sample is washed with DMF and anhydrous ethanol solution alternately, for 3 cycles, and dried in a 70℃ oven overnight to obtain the HKUST-1 / g-C3N4 composite material (HK1CN).

[0047] The HKUST-1 / g-C3N4 composite material prepared by 100 mg of g-C3N4, 0.63 g of copper nitrate trihydrate and 1.1 g of 1,3,5-benzenetricarboxylic acid is named as HK1CN-1.

[0048] Following the above preparation method, 300 mg and 900 mg of g-C3N4 were accurately weighed and reacted with 0.63 g of copper nitrate trihydrate and 1.1 g of 1,3,5-benzenetricarboxylic acid to prepare HKUST-1 / g-C3N4 composite materials, which were named HK1CN-3 and HK1CN-9, respectively.

[0049] Accurately weigh 800 mg of sodium alginate and 800 mg of HK1CN (HK1CN-1, HK1CN-3, or HK1CN-9 are all 800 mg) into a 100 mL beaker, add 30 mL of ultrapure water and mix well. Then, stir the mixture at 480 rpm with a magnetic stirrer for 1 hour at room temperature. Slowly add the mixture dropwise to 120.00 mL of 0.20 mol / L CaCl2 solution using a 10.0 mL syringe, let stand overnight, and wash repeatedly with ultrapure water several times. Finally, freeze-dry the sample in a freeze dryer for 12 hours to obtain HCS composite hydrogel beads, which are the desired hydrogel material.

[0050] Depending on whether the HKUST-1 / g-C3N4 composite material used is HK1CN-1, HK1CN-3, or HK1CN-9, the resulting HCS composite hydrogel beads are named HC1S, HC3S, and HC9S, respectively.

[0051] Comparative Example 1

[0052] The preparation method of HKUST-1 / sodium alginate (HS) is as follows:

[0053] HKUST-1 was prepared using a solvothermal method:

[0054] Accurately weigh 0.63 g of copper nitrate trihydrate (Cu(NO3)2·3H2O) and dissolve it in 10 mL of distilled water, then sonicate for 10 min. Accurately measure 20 mL of N,N-dimethylformamide (DMF, C3H7NO) and 20 mL of anhydrous ethanol (C2H6O) and mix them in the same small beaker. Add 1.1 g of 1,3,5-benzenetricarboxylic acid (H3BTC, C9H6O6) to the mixed solution and sonicate for 20 min.

[0055] The two solutions were mixed and sonicated for 30 min, then transferred to a 100 mL polytetrafluoroethylene-lined autoclave. The autoclave was placed in a 120 °C oven and reacted for 16 h. The resulting blue crystals, after naturally cooling to room temperature, were removed and washed with DMF and anhydrous ethanol solutions alternately three times. The samples were then dried overnight in a 70 °C oven to obtain HKUST-1.

[0056] Accurately weigh 800 mg of sodium alginate and 800 mg of HKUST-1 into a 100 mL beaker, then add 30 mL of ultrapure water and mix well, then use a magnetic stirrer to stir the mixture at a speed of 480 rpm at room temperature for 1 h. Slowly drop the mixed mixture into 120.00 mL of 0.20 mol / L CaCl2 solution with a 10.0 mL syringe, stand overnight, and then wash repeatedly with ultrapure water several times. The sample was dried in a freeze dryer for 12 h, and the HS composite hydrogel beads were obtained, which were the desired hydrogel material.

[0057] Comparative Example 2

[0058] The preparation method of g-C3N4 / sodium alginate (CS) is as follows:

[0059] Take a 100 mL capacity alumina crucible with a lid and accurately weigh 84.0 g of urea into it. Place the crucible in a muffle furnace and slowly heat it to 550℃ at a heating rate of 2℃ / min, and keep the temperature for 4 h. After natural cooling to room temperature, collect the light yellow product to obtain the desired g-C3N4. Grind the g-C3N4 into powder with a agate mortar.

[0060] Accurately weigh 800 mg of sodium alginate and 800 mg of g-C3N4 into a 100 mL beaker, then add 30 mL of ultrapure water and mix well, then use a magnetic stirrer to stir the mixture at a speed of 480 rpm at room temperature for 1 h. Slowly drop the mixed mixture into 120.00 mL of 0.20 mol / L CaCl2 solution with a 10.0 mL syringe, stand overnight, and then wash repeatedly with ultrapure water several times. The sample was dried in a freeze dryer for 12 h, and the CS composite hydrogel beads were obtained, which were the desired hydrogel material.

[0061] Characterization of the above substances and U(VI) adsorption experiments

[0062] I. Instruments used for material characterization

[0063] The Fourier transform infrared spectrum of the sample was recorded using an IR Prestige 21 instrument. The scanning electron microscope (SEM) and X-ray energy spectrum (EDS) of the sample before and after adsorbing uranyl ions were determined using a Japanese Hitachi Regulus 8100 instrument. The zeta potential of the sample was characterized using a Malvern ZS90 instrument.

[0064] II. Adsorption experiments

[0065] (1) Preparation of uranium standard solution

[0066] Accurately weigh a certain amount of uranyl nitrate (UO2(NO3)2·6H2O) standard substance into a beaker, dissolve it, stir well with a glass rod, transfer it to a 2L volumetric flask, dilute to the mark with deionized water, and mix well. This is the required 1g / L uranium standard stock solution. Other concentrations of uranium solutions required in subsequent experiments can be obtained by serially diluting the prepared 1g / L uranium standard stock solution.

[0067] (2) Uranium Concentration Testing Method

[0068] The concentration of uranium in solution was determined using the arsene III spectrophotometric method (National Standard of the People's Republic of China, EJ 267.4-1984). The specific preparation steps for the relevant reagents are as follows:

[0069] Chloroacetic acid-sodium acetate buffer solution (pH 2.5): Dissolve CH3COONa in water, then gradually add C2H3O2Cl until the pH is adjusted to 2.5 to obtain the desired buffer solution.

[0070] Azoarsine III solution (0.5 g / L): Accurately weigh 1 g of azoarsine III into a beaker, dissolve it in a small amount of distilled water, transfer it to a 2 L volumetric flask, dilute to volume with distilled water, and shake well to obtain the desired azoarsine III solution.

[0071] Plotting the uranium standard curve

[0072] Prepare uranium standard solutions of 0 mg / L, 2.5 mg / L, 5 mg / L, 7.5 mg / L, and 10 mg / L respectively, and take 1 mL of each solution into a 25 mL volumetric flask. Add 5 mL of pH 2.5 chloroacetic acid-sodium acetate buffer solution and 1 mL of 0.5 g / L azoarsine III solution in sequence. Make up to volume with distilled water and shake well. After standing for 20 minutes, measure the absorbance A at a wavelength of 652 nm. Plot a standard curve with uranium solution concentration (C) as the abscissa and the absorbance (A) corresponding to the concentration as the ordinate. Calculate the uranium content in the solution using the relevant formula based on the measured A value.

[0073] 1) Sample concentration determination

[0074] After the adsorption process is complete, add an appropriate amount of uranium solution to a 25 mL volumetric flask and proceed with the above steps. The adsorption efficiency R and adsorption capacity Q of uranium by HCS are calculated. e It can be obtained from formula (1) and formula (2) respectively:

[0075]

[0076]

[0077] In the formula, R (%) is the adsorption rate; C0 (mg / L) is the uranium concentration in the solution before the adsorption reaction; Ce (mg / L) is the uranium concentration in the solution after the adsorption reaction; V (L) is the volume of the uranium solution; m (g) is the adsorbent dosage; Q e (mg / g) is the adsorption capacity, i.e., the uranium content adsorbed on the adsorbent.

[0078] (3) Batch test

[0079] The basic characteristics of a typical test in the static adsorption condition are as follows: first, take an appropriate amount of prepared uranium solution of the required concentration, and adjust it to the required pH with a small amount of 0.01 mol / L sodium hydroxide (NaOH) solution and 0.01 mol / L hydrogen chloride (HCl) solution; then add a certain amount of adsorbent to the treated uranium solution; adopt the batch test method, and shake the required time on a constant temperature shaker with a constant speed; finally, determine the residual uranium concentration in the solution after adsorption, and calculate the uranium adsorption rate and adsorption capacity of the adsorbent under the corresponding conditions. Each experimental group consists of one blank sample (without adding adsorbent material) and three parallel test samples to minimize experimental errors.

[0080] Through the above typical experiments, single-factor experiments are further conducted on the influence of material ratio, sacrificial agent, initial pH value of uranium solution, initial uranium concentration of solution, dosage, and adsorption time on the adsorption effect, to explore the best conditions and performance of the composite material for adsorbing uranium. The specific content is as follows:

[0081] 1) In 40 mL of uranium solution with pH = 5 and initial concentration of 5 mg / L, 4 mg of HKUST-1 / sodium alginate (HS), HK1CN-1 / sodium alginate (HC1S), HK1CN-3 / sodium alginate (HC3S), HK1CN-9 / sodium alginate (HC9S), and g-C3N 4 / sodium alginate (CS) material, under the conditions of constant temperature reaction for 15 h at 30°C with a shaking speed of 180 rpm and light illumination, the influence of the composite material before and after the modification and different modification ratios on the adsorption of U(VI) is explored to seek the best composite material;

[0082] 2) In 30 mL of uranium solution with pH = 4 and initial concentration of 5 mg / L, 4 mg of HK1CN-1 / sodium alginate (HC1S) material is added, and then 1 mL of methanol, 1 mL of ethanol, and 1 mL of ethylene glycol are added, respectively, under the conditions of constant temperature reaction for 40 h at 25°C with a shaking speed of 180 rpm and light illumination, to explore the influence of the presence or absence of sacrificial agent and different sacrificial agents on the adsorption of U(VI);

[0083] 3) Add 4 mg of HK1CN-1 / sodium alginate (HC1S) material to 40 mL of uranium solutions with different pH (3-9) and an initial concentration of 16 mg / L. The solution was reacted at a constant temperature of 25 °C and 180 rpm under light conditions for 40 h to investigate the effect of different pH on U(VI) adsorption.

[0084] 4) 4 mg of HK1CN-1 / sodium alginate (HC1S) material was added to 40 mL of uranium solutions with different initial concentrations (0.5 mg / L, 1 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, 50 mg / L, 100 mg / L, 150 mg / L) at pH=5. The solutions were reacted at a constant temperature of 25℃ and 180 rpm under light conditions for 46 h to investigate the effect of the initial concentration of uranium solution on U(VI) adsorption.

[0085] 5) Different masses of HK1CN-1 / sodium alginate (HC1S) (0.5mg, 1mg, 2mg, 3mg, 4mg, 5mg, 6mg, 10mg) were added to 40mL of uranium solution with pH=4 and initial concentration of 10mg / L. The solution was reacted for different times (15h) under constant temperature and light conditions in a shaker at 25℃ and 180rpm to investigate the optimal solid-liquid ratio for U(VI) adsorption.

[0086] 6) 6 mg of HK1CN-1 / sodium alginate (HC1S) was added to 60 mL of uranium solution with pH = 4 and an initial concentration of 10 mg / L. The solution was reacted at a constant temperature for different times (1 h, 4 h, 8 h, 12 h, 18 h, 24 h, 36 h, 40 h, 44 h, 48 h, 50 h) under light conditions on a shaker at 30 °C and a rotation speed of 180 rpm. A similar control experiment was also conducted under no-light conditions to investigate the effects of light exposure and the duration of the adsorption reaction on the adsorption of U(VI).

[0087] The experimental results are summarized as follows:

[0088] Figure 1 Infrared spectra of HKUST-1, g-C3N4, and HC1S.

[0089] from Figure 1 It can be seen from this that for g-C3N4 at 1640cm -1 1573cm -1 and 1462cm -1 The characteristic spectral band centered on heptaazine-derived stretching vibrations is observed at lower frequencies, around 1320 cm⁻¹. -1 and 1240cm -1 The characteristic peaks of the strong bimodal stretching vibration of the aromatic C3N4 heterocycle belong to the tertiary amine (3C-N) and secondary amine (2C-N), respectively. Furthermore, a peak at 803 cm⁻¹ was also observed. -1characteristic peaks of typical triazine ring; at 1635 cm -1 and 1583 cm -1 (-COO-asymmetric stretching vibration peak), 1447 cm -1 (benzene ring characteristic band C=C) and 1375 cm -1 (-COO-symmetric stretching vibration peak), 760 cm -1 and 727 cm -1 (=C-H stretching), 478 cm -1 (Cu-O stretching vibration) characteristic vibration bands from HKUST-1 appeared; 3200 cm -1 mainly due to the vibration of-NH2, -NH- and -OH groups. It can be seen that HKUST-1, g-C3N4 and HC1S are successfully prepared.

[0090] Figure 2 SEM images of HK1CN-1 / sodium alginate (HC1S). Figure 3 SEM-EDS images of HK1CN-1 / sodium alginate (HC1S) after adsorbing uranium.

[0091] It can be seen from Figure 2 (a) and (b) that the adsorbent is irregular spherical, the surface is loose and porous and is covered with many substances, and the larger surface area provides favorable contact conditions for contacting uranium; Figure 3 (a) and (b) provide direct evidence that HC1S can adsorb uranium.

[0092] Figure 4 (a), (b), (c) and (d) are TEM images of g-C3N4, HKUST-1, HK1CN and HC1S, respectively. Figure 5 (a) and (b) are TEM images of HC1S-U.

[0093] It can be seen from Figure 4 (a), Figure 4 (b) that HKUST-1, g-C3N4, Figure 4 (c) and Figure 4 (d) prove that HKUST-1 is successfully embedded in g-C3N4, and the synthesized material is uneven, which is beneficial to uranium adsorption. Figure 5 (a) and Figure 5 (b) are TEM images of HC1S after uranium adsorption, and the distribution area of U element can be clearly seen corresponding to black rod-like and needle-like, which shows that HC1S material adsorbs uranium on the surface and reduces it to precipitate.

[0094] Figure 6The effect of different composite ratio materials on U(VI) adsorption was shown (pH = 5, Co = 5 mg / L, m = 4.00 mg, V = 40 mL, t = 15 h, T = 303.15 K).

[0095] The adsorption performance of the composite materials before and after modification and at different modification ratios was explored under light conditions to find the best composite material. Figure 6 It can be seen that the adsorption performance of the composite material HKUST-1 / sodium alginate (HS) is better than that of g-C3N4 / sodium alginate (CS), and the uranium adsorption performance of HK1CN-1 / sodium alginate (HC1S), HK1CN-3 / sodium alginate (HC3S), and HK1CN-9 / sodium alginate (HC9S) decreases in turn, and the uranium adsorption performance of HK1CN-1 / sodium alginate (HC1S) is higher than that of HKUST-1 / sodium alginate (HS) and g-C3N4 / sodium alginate (CS). It can be seen that appropriate g-C3N4 can improve the uranium adsorption performance, and when the proportion of g-C3N4 is too high, the adsorption effect will decrease, so the best uranium adsorption material HK1CN-1 / sodium alginate (HC1S) is selected for subsequent experiments.

[0096] Figure 7 The effect of different sacrificial agents on U(VI) adsorption was shown (pH = 4, Co = 5 mg / L, m = 4.00 mg, V = 30 mL, t = 40 h, T = 298.15 K).

[0097] Generally, a sacrificial agent is added during the photocatalytic reduction process. Under visible light irradiation, the sacrificial agent transfers electrons to the photocatalytic material, reducing the number of holes generated by light induction, reducing the recombination rate of photo-generated electrons, and thus improving the reduction efficiency of uranium. In this paper, methanol, ethanol, and ethylene glycol were added as sacrificial agents for comparative tests to explore the effect of sacrificial agents on uranium adsorption. Figure 7 It can be seen that the uranium removal effect is better without adding a sacrificial agent. HK1CN-1 / sodium alginate (HC1S) as a photocatalytic reduction uranium adsorption material avoids pollution of water bodies by sacrificial agents, and has good application prospects.

[0098] Figure 8 The effect of pH on the adsorption of U(VI) by HK1CN-1 / sodium alginate (HC1S) was shown. Figure 9 The zeta potential of HK1CN-1 / sodium alginate (HC1S) was shown (Co = 16 mg / L, m = 4.00 mg, V = 40 mL, t = 40 h, T = 298.15 K)

[0099] The uranium adsorption performance of HK1CN-1 / sodium alginate (HC1S) at different pH (3-8) was explored to select the best adsorption pH. Figures 8-9It can be seen that the uranium adsorption performance of HC1S increases first and then decreases with the increase of pH, and the uranium adsorption performance of the material is best at pH = 5, reaching 133.75 mg / L, and the uranium adsorption performance decreases with the continuous increase of pH. The reason is that when pH < 5, there are a large number of protons in the solution, which not only competes with U(VI) for adsorption sites, but also protonates the material surface, so that the HC1S obtains fewer electrons per unit time, thereby affecting its photocatalytic efficiency, so the uranium adsorption performance is relatively low at pH < 5. At pH = 5, it can be seen from the potential diagram of the material that the material surface is negatively charged, and the negatively charged material can consume part of the H + in the solution + , reducing the consumption of e - , which is conducive to the transfer of e - to HC1S, improving the photocatalytic efficiency of HC1S, and improving the removal rate of uranium. When pH > 5, U(VI) mainly exists in the form of (UO2)3(OH)7 - and UO2(OH)3 - , and the electrostatic repulsion between these two forms of U(VI) and the negatively charged catalyst surface affects the capture of the material on uranium, resulting in a lower removal rate of the material on uranium at high pH. In summary, the removal effect of HK1CN-1 / HC1S is best at pH = 5.

[0100] Figure 10 Effect of initial uranium concentration on U(VI) adsorption (pH = 5, m = 4.00 mg, V = 40 mL, t = 46 h, T = 298.15 K)

[0101] The uranium adsorption performance of HK1CN-1 / HC1S under different concentrations was investigated, and Figure 10 it can be seen that the adsorption sites of HK1CN-1 / HC1S are more utilized with the increase of the initial concentration of uranium solution, so the uranium adsorption capacity is higher and higher, and the adsorption capacity can reach 574.78 mg / g at 150 mg / L.

[0102] Figure 11 Effect of HK1CN-1 / HC1S dosage on adsorption.

[0103] The effect of different dosages of HK1CN-1 / HC1S adsorbent on the removal rate of uranium was investigated to find the most suitable solid-liquid ratio. From Figure 11It can be seen that with the increase of solid-liquid ratio, the adsorption capacity and adsorption rate of HK1CN-1 / sodium alginate (HC1S) for uranium gradually increase, and the maximum adsorption rate is reached when the solid-liquid ratio is 0.10 g / L. This trend is consistent with the expectation, because the increase of adsorbent dosage provides more adsorption active sites for the adsorption of hexavalent uranium. However, with the increase of solid-liquid ratio, when the solid-liquid ratio is greater than 0.10 g / L, the residual adsorption binding sites are too many because the uranium ions in the solution are basically adsorbed, and the adsorption rate increases, and the corresponding adsorption capacity decreases. It can be considered that the optimal solid-liquid ratio is 0.10 g / L, at this time, high adsorption efficiency can be maintained while saving materials. Therefore, the adsorbent dosage and the volume ratio of uranium solution in the subsequent test are set to 0.10 g / L.

[0104] Figure 12 The influence of display time and light on the adsorption of U(VI) (pH = 5, Co = 10 mg / L, m = 6.00 mg, V = 60 mL, T = 298.15 K)

[0105] Figure 12 The relationship between the adsorption of hexavalent uranium by HK1CN-1 / sodium alginate (HC1S) and the adsorption time is described. The adsorption efficiency rapidly rises at the initial stage of adsorption, and then slowly rises, and reaches equilibrium at 48 h of adsorption saturation. At the same time, a similar control test is carried out under no light conditions, and it can be seen that the HK1CN-1 / sodium alginate (HC1S) has better light effect, so the material has good adsorption performance for uranium and has the effect of photocatalytic reduction.

[0106] In summary, the influence of pH, ratio, light, initial uranium concentration and other conditions on the uranium adsorption and reduction performance of the system is systematically explored, and the research shows that the HK1CN-1 / sodium alginate (HC1S) has good removal performance for uranium in aqueous solution, and under the condition of visible LED light, the maximum adsorption capacity can reach 574.78 mg g-1, and no additional sacrificial agent is needed in the whole process.

[0107] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those of ordinary skill in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a hydrogel material, characterized in that, Includes the following steps: Preparation of HKUST-1 / g-C3N4 composite material; A hydrogel material was prepared by reacting HKUST-1 / g-C3N4 composite material with sodium alginate. The prepared hydrogel material is used to adsorb U(VI).

2. The preparation method according to claim 1, characterized in that, The steps for preparing the HKUST-1 / g-C3N4 composite material are as follows: Copper nitrate trihydrate and 1,3,5-benzenetricarboxylic acid were prepared into solutions, sonicated, and then mixed. g-C3N4 was added, and sonication was continued. The mixture was then reacted under heating conditions and allowed to cool naturally to obtain the final product.

3. The preparation method according to claim 2, characterized in that, The specific steps for preparing the HKUST-1 / g-C3N4 composite material are as follows: Dissolve copper nitrate trihydrate in water and sonicate for 10-15 minutes to obtain the first solution; Dissolve N,N-dimethylformamide in anhydrous ethanol, then add 1,3,5-benzenetricarboxylic acid, and sonicate for 20-25 minutes to obtain a second solution; Mix the first and second solutions, add g-C3N4, sonicate for 1-1.5 h, then react at 120±0.5℃ for 16 h, and allow to cool naturally to obtain the final product.

4. The preparation method according to claim 3, characterized in that, It also includes the step of washing the prepared HKUST-1 / g-C3N4 composite material alternately with N,N-dimethylformamide and anhydrous ethanol 2-3 times, and then drying it at 70±0.5℃.

5. The preparation method according to any one of claims 2-4, characterized in that, The mass ratio of copper nitrate trihydrate to 1,3,5-benzenetricarboxylic acid and g-C3N4 is 63:110:(10-90).

6. The preparation method according to claim 1, characterized in that, The steps for reacting the HKUST-1 / g-C3N4 composite material with sodium alginate are as follows: Sodium alginate and HKUST-1 / g-C3N4 composite material were added to water and stirred until well mixed. Then, CaCl2 solution was slowly added, and the mixture was allowed to stand overnight and freeze-dried to obtain the hydrogel material.

7. The preparation method according to claim 6, characterized in that, The mass ratio of HKUST-1 / g-C3N4 composite material, sodium alginate, and CaCl2 is 1:1:(3-4).

8. The preparation method according to claim 6, characterized in that, Sodium alginate and HKUST-1 / g-C3N4 composite material were added to water and mixed by magnetic stirring at room temperature for 1-1.5 hours at a stirring speed of 480-500 rpm. Then, CaCl2 solution was slowly added, and the mixture was allowed to stand overnight. After washing with water 3-5 times, the mixture was freeze-dried for 12-14 hours to obtain the hydrogel material.

9. The preparation method according to claim 1, characterized in that, g-C3N4 was prepared by the following method: urea was heated to 550℃ at a rate of 2℃ / min, and the reaction was maintained at this temperature for 4-6 hours. After naturally cooling to room temperature, g-C3N4 was collected and ground into powder.

10. A hydrogel material, characterized in that, It is prepared by any one of claims 1-9.

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