Method for removing Cr(VI) and RhB from wastewater using pollutant-modified NH2-MIL-125(Ti)

Abstract

This invention discloses a method for removing Cr(VI) and RhB from wastewater using pollutant-modified NH2-MIL-125(Ti), belonging to the field of wastewater treatment. This invention uses either Cr(VI) or RhB alone to modify NH2-MIL-125(Ti), obtaining modified adsorbents RhB-NM and Cr(VI)-NM. RhB-NM is then used to remove Cr(VI) from the wastewater, and Cr(VI)-NM is used to remove RhB. The adsorbents RhB-NM and Cr(VI)-NM used in this invention exhibit high photocatalytic efficiency. After 120 min of photocatalytic reaction, the reduction efficiency of RhB-NM for Cr(VI) is 99.1%, and the degradation efficiency of Cr(VI)-NM for RhB is 100%. Compared with the removal of Cr(VI) and RhB by NH2-MIL-125, the removal efficiency is significantly improved.

Description

Technical Field

[0001] This invention relates to a method for removing Cr(VI) and RhB from wastewater using pollutant-modified NH2-MIL-125(Ti), and belongs to the field of wastewater treatment. Background Technology

[0002] Metal-organic frameworks (MOFs) not only possess large specific surface areas, ultra-high porosity, and good stability, but also exhibit photocatalytic activity in the photoelectrons and holes generated by some MOFs under visible light irradiation, making them widely applicable in environmental remediation, energy production, and biomedical imaging.

[0003] Pollutants in water bodies often exist in non-single forms, frequently exhibiting co-occurrence and complex interactions. The mutual influence of multiple pollutants not only exacerbates water pollution but also increases the difficulty of pollutant detection, quantification, and removal. As a Ti-based MOF in the MIL class, NH2-MIL-125(Ti) possesses specific functional groups (such as -COOH, -OH, and -NH2), making it more readily adsorbent of heavy metals and organic pollutants in water. Furthermore, NH2-MIL-125(Ti) is also a good photocatalyst, capable of photocatalytic reactions under visible light. However, its short photogenerated carrier lifetime and low light absorption or charge utilization limit its photocatalytic efficiency.

[0004] Currently, researchers have explored numerous methods to improve its photocatalytic activity. For example, some researchers utilized the Schiff base reaction between the aldehyde and -NH2 groups in NH2-MIL-125(Ti) to prepare aromatic heterocyclic-grafted NH2-MIL-125(Ti) via a post-grafting method, thereby enhancing its performance in selectively oxidizing alcohols under visible light. Others combined different proportions of graphitic carbon nitride (g-C3N4) and NH2-MIL-125(Ti) to prepare the hybrid material g-C3N4 / NH2-MIL-125. Experimental results showed that g-C3N4 / NH2-MIL-125 could completely degrade the target pollutant diclofenac within 2 hours, with a degradation rate of 0.0282 min. -1 The concentration of NH2-MIL-125 is almost three times that of the original NH2-MIL-125 and more than four times that of g-C3N4. Researchers have successfully prepared MIL(125)-NH2 / TiO2 by coating NH2-MIL-125(Ti) onto orderly titanium dioxide nanorods via a hydrothermal reaction. Experiments have confirmed that MIL(125)-NH2 / TiO2 exhibits high light absorption and charge separation efficiency, promoting water splitting. However, these methods suffer from drawbacks such as complex modification processes and the need for additional chemical reagents. Summary of the Invention

[0005] [Technical Issues]

[0006] Currently, methods for preparing improved photocatalytic performance of NH2-MIL-125(Ti) mainly include noble metal deposition, ion doping, semiconductor composite, morphology control, and dye sensitization. Noble metal materials are scarce and expensive; ion doping requires selection of ions based on the material's physicochemical properties and lattice parameters; furthermore, single-ion modification methods have limited enhancement of photocatalytic activity. In recent years, researchers have often employed co-doping with two or more ions or combined ion doping with other modification methods to obtain nanomaterials with optimal photocatalytic activity.

[0007] [Technical Solution]

[0008] To address the aforementioned problems, this invention modifies NH2-MIL-125(Ti) with either Cr(VI) (hexavalent chromium) or RhB (rhodamine B) to obtain modified adsorbents RhB-NM and Cr(VI)-NM. RhB-NM is then used to remove Cr(VI) from the wastewater, and Cr(VI)-NM is used to remove RhB from the wastewater. The method of this invention is simple, has low preparation cost, and exhibits good cycle stability.

[0009] The first objective of this invention is to provide a method for removing Cr(VI) and RhB from wastewater using pollutant-modified NH2-MIL-125(Ti), comprising the following steps:

[0010] (1) Preparation of pollutant-modified NH2-MIL-125(Ti):

[0011] First, prepare Cr(VI) solution and RhB solution. Then, add NH2-MIL-125(Ti) to Cr(VI) solution and RhB solution respectively. Under complete darkness, shake the mixture thoroughly to react. After the reaction is complete, centrifuge to collect the precipitate, wash it, and dry it to obtain the modified adsorbents RhB-NM and Cr(VI)-NM.

[0012] (2) Removal of Cr(VI) and RhB from wastewater:

[0013] The modified adsorbent RhB-NM was added to wastewater containing Cr(VI) and stirred in complete darkness to reach adsorption-desorption equilibrium. Then, the light source was turned on, the room temperature was maintained, and the photocatalytic reaction was carried out. The light source was then turned off, and the reaction ended.

[0014] The modified adsorbent Cr(VI)-NM was added to the wastewater containing RhB and stirred in complete darkness to reach adsorption-desorption equilibrium. Then, the light source was turned on, the room temperature was maintained, and the photocatalytic reaction was carried out. The light source was then turned off, and the reaction ended.

[0015] In one embodiment of the present invention, the concentrations of the Cr(VI) solution and the RhB solution in step (1) are 10-100 mg·L⁻¹. -1 More preferably 40 mg·L -1 .

[0016] In one embodiment of the present invention, the ratio of NH2-MIL-125(Ti) and Cr(VI) solution in step (1) is 0.1-1.0 mg:1 mL; more preferably 1 mg:1 mL.

[0017] In one embodiment of the present invention, the ratio of NH2-MIL-125(Ti) and RhB solution in step (1) is 0.1-1.0 mg:1 mL; more preferably 1 mg:1 mL.

[0018] In one embodiment of the present invention, the conditions for the oscillating reaction in step (1) are 288-328 K and 100-300 r·min. -1 The reaction is carried out at 5-7 h; more preferably at 308 K and 200 r·min. -1 The reaction was carried out for 6 hours.

[0019] In one embodiment of the present invention, the washing in step (1) is washing with deionized water; the drying is drying at 55-65°C for 5-7 hours.

[0020] In one embodiment of the present invention, the modified adsorbent RhB-NM prepared in step (1) is a red powder; Cr(VI)-NM is a yellowish-brown powder.

[0021] In one embodiment of the present invention, the NH2-MIL-125(Ti) mentioned in step (1) is synthesized by a surfactant-assisted hydrothermal method; specifically, it includes the following steps:

[0022] Weigh 0.3697 g of 2-aminoterephthalic acid and 0.1 g of polyvinylpyrrolidone (PVP) into a 35 mL pressure-resistant reaction tube, and add 10 mL of N,N-dimethylformamide (DMF) and 10 mL of methanol (MeOH) to the reaction tube to obtain a mixed solution;

[0023] The mixed solution was stirred at room temperature for half an hour, and then 300 μL of tetraisopropyl titanate was quickly added. The mixture was heated at 150 °C for 12 hours. After cooling to room temperature, the yellow powder was collected by centrifugation. The yellow powder was washed three times with DMF and methanol to remove unreacted organic ligands. The powder was dried at 60 °C for 24 hours to obtain a bright yellow powder NH2-MIL-125(Ti).

[0024] In one embodiment of the present invention, the wastewater containing Cr(VI) and RhB in step (2) needs to be adjusted to pH 2-10 using 0.1M HCl solution and NaOH solution.

[0025] In one embodiment of the present invention, in step (2), the ratio of the modified adsorbent RhB-NM to the Cr(VI)-containing wastewater is 10-100 mg:100 mL, more preferably 40 mg:100 mL; the concentration of Cr(VI) in the Cr(VI)-containing wastewater is 10-100 mg·L⁻¹. -1 .

[0026] In one embodiment of the present invention, in step (2), the ratio of the modified adsorbent Cr(VI)-NM to the wastewater containing RhB is 10-100 mg:100 mL, more preferably 40 mg:100 mL; the concentration of RhB in the wastewater containing RhB is 10-100 mg·L⁻¹. -1 .

[0027] In one embodiment of the present invention, the light source in step (2) is visible light, specifically a 300W xenon lamp as the visible light source (the cutoff filter is 420nm).

[0028] In one embodiment of the present invention, step (2) requires stirring for 50-70 minutes to reach adsorption-desorption equilibrium.

[0029] In one embodiment of the present invention, the photocatalytic reaction time in step (2) is 20-140 min, more preferably 120 min.

[0030] The second objective of this invention is the application of the method described herein in the field of wastewater treatment.

[0031] In one embodiment of the present invention, the wastewater contains Cr(VI) and RhB.

[0032] [Beneficial Effects]

[0033] (1) The present invention is simple to operate and has the characteristics of good adsorption performance, high stability and no addition of secondary pollutants. It has good application prospects in the treatment of water polluted by heavy metals and organic pollutants.

[0034] (2) The adsorbents RhB-NM and Cr(VI)-NM used in this invention have good stability and repeatability; excellent regeneration ability; and the adsorption capacity of Cr(VI) and RhB remains at a high level after 4 adsorption cycles.

[0035] (3) The adsorbents RhB-NM and Cr(VI)-NM used in this invention have high photocatalytic efficiency. After 120 min of photocatalytic reaction, the reduction efficiency of RhB-NM for Cr(VI) is 99.1%, and the degradation efficiency of Cr(VI)-NM for RhB is 100%. Compared with the removal of Cr(VI) and RhB by NH2-MIL-125, the removal efficiency is significantly improved. Attached Figure Description

[0036] Figure 1 The images are scanning electron microscope images of RhB-NM and Cr(VI)-NM, where (a) is RhB-NM and (b) is Cr(VI)-NM.

[0037] Figure 2 The PL spectra (a), band gap (b), and instantaneous photocurrent response (c) of NH2-MIL-125(Ti), RhB-NM, and Cr(VI)-NM are shown.

[0038] Figure 3 The effects of different materials on catalytic performance and its rate (a) and removal rate constant (b).

[0039] Figure 4 The effect of different pH values ​​on the reduction of Cr(VI) by RhB-NM (a) and its removal rate constant (b), and the effect of different pH values ​​on the reduction of RhB by Cr(VI)-NM and its removal rate constant (d).

[0040] Figure 5 The effects of different dosages on the reduction of Cr(VI) by RhB-NM (a) and its removal rate constant (b), and the effects of different dosages on the reduction of RhB by Cr(VI)-NM (c) and its removal rate constant (d).

[0041] Figure 6 Photocatalytic removal rate of Cr(VI) by RhB-NM at different cycle numbers (a) and photocatalytic removal rate of RhB by Cr(VI)-NM at different cycle numbers (b). Detailed Implementation

[0042] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0043] Test method:

[0044] 1. Specific surface area and pore size distribution analysis (BET)

[0045] The sample to be tested was taken and a suitable amount of sample was subjected to full analysis using a Micromeritics ASAP2460 gas adsorption analyzer from Micromeritics, USA, to obtain the specific surface area and pore size distribution of the sample.

[0046] 2. Field emission scanning electron microscopy (SEM) test

[0047] The sample to be tested was adhered to the conductive adhesive on the sample stage, and any unadhered sample was blown away with a bulb syringe. The surface was then gold-plated, and the morphology was scanned using a Sigma 300 field emission scanning electron microscope from Zeiss GmbH, Germany.

[0048] 3. Photoluminescence test (PL)

[0049] An appropriate amount of the sample to be tested was compressed into a pellet, and the photoluminescence spectrum in the range of 300-600 nm was measured using an Edinburgh FLS1000 steady-state / transient fluorescence spectrometer with an excitation wavelength of 320 nm.

[0050] 4. Ultraviolet-Vis Diffuse Reflectance Test (UV-Vis DRS)

[0051] The powder to be tested was placed in a powder bath and pressed into a tablet for later use. Using BaSO4 as a reference, the test was performed on a Shimadzu UV-3600i Plus UV-Vis-NIR spectrophotometer with a scanning wavelength range of 200-800nm.

[0052] 5. Electrochemical testing

[0053] Electrochemical tests and analyses were performed using a 0.5 M Na₂SO₄ solution (pH = 7.0) as the electrolyte on a CHI760E electrochemical workstation from Shanghai Chenhua Instrument Co., Ltd. In the three-electrode system, the working electrode was prepared on fluorine-doped SnO₂ transparent conductive glass (FTO glass), with a Pt electrode as the counter electrode and an Ag / AgCl electrode as the reference electrode. A 300 W xenon lamp was used as the white light source, and the transient photocurrent response (it test) was measured.

[0054] The NH2-MIL-125(Ti) used in the examples was synthesized via a surfactant-assisted hydrothermal method; specifically, the following steps were included:

[0055] Weigh 0.3697 g of 2-aminoterephthalic acid and 0.1 g of polyvinylpyrrolidone (PVP) into a 35 mL pressure-resistant reaction tube, and add 10 mL of N,N-dimethylformamide (DMF) and 10 mL of methanol (MeOH) to the reaction tube to obtain a mixed solution;

[0056] The mixed solution was stirred at room temperature for half an hour, and then 300 μL of tetraisopropyl titanate was quickly added. The mixture was heated at 150 °C for 12 hours. After cooling to room temperature, the yellow powder was collected by centrifugation. The yellow powder was washed three times with DMF and methanol to remove unreacted organic ligands. The powder was dried at 60 °C for 24 hours to obtain a bright yellow powder NH2-MIL-125(Ti).

[0057] Example 1

[0058] The preparation method of pollutant-modified NH2-MIL-125(Ti) includes the following steps:

[0059] First, prepare solutions with a concentration of 40 mg·L⁻¹. -1 Cr(VI) solution and RhB solution were prepared, and then 100 mg of NH2-MIL-125(Ti) was added to 250 mL flasks containing 100 mL of Cr(VI) solution or RhB solution, respectively. The mixtures were then incubated at 308 K for 200 rpm in complete darkness. -1 The mixture was shaken thoroughly for 6 hours. After the reaction was complete, the precipitate was collected by centrifugation, washed three times with deionized water, and dried at 60°C for 6 hours to obtain the modified adsorbents, namely red powder RhB-NM and yellowish-brown powder Cr(VI)-NM.

[0060] The performance of the modified adsorbents, red powder RhB-NM and yellowish-brown powder Cr(VI)-NM, was tested, and the test results are shown in Table 1 below:

[0061] Table 1 shows the test results for specific surface area, average pore size, and pore volume. From Table 1, it can be seen that the S0 of RhB-NM and Cr(VI)-NM... BET They are 760.651m respectively 2 g -1 703.408m 2 g -1 Compared with NH2-MIL-125(Ti), the specific surface areas of RhB-NM and Cr(VI)-NM are smaller, indicating that Cr(VI) and RhB are successfully adsorbed onto N. H2 -MIL-125(Ti) pores, causing partial blockage of the channels.

[0062] Table 1

[0063] Material <![CDATA[Specific surface area / (m 2 g -1 )]]> Average pore size / nm <![CDATA[Pore volume / (cm 3 g -1 )]]> <![CDATA[NH2-MIL-125(Ti)]]> 871.582 3.123 0.115288 <![CDATA[RhB-NH2-MIL-125(Ti)]]> 760.651 3.696 0.242813 <![CDATA[Cr(VI)-NH2-MIL-125(Ti)]]> 703.408 3.780 0.168364

[0064] Figure 1 Scanning electron microscope (SEM) images of RhB-NM and Cr(VI)-NM are shown, where (a) is RhB-NM and (b) is Cr(VI)-NM. Figure 1It can be seen that RhB-NM and Cr(VI)-NM still have a quadrilateral plate structure with a diameter of 2μm and a thickness of 300nm, which is consistent with NH2-MIL-125(Ti), indicating that the morphology did not change significantly after modification.

[0065] Figure 2 The PL spectra (a), band gap (b), and transient photocurrent response (c) of NH2-MIL-125(Ti), RhB-NM, and Cr(VI)-NM are shown. Figure 2 It can be seen that NH2-MIL-125(Ti) exhibits a strong fluorescence peak, while the luminescence intensity of RhB-NM and Cr(VI)-NM is significantly reduced. This indicates that RhB-NM and Cr(VI)-NM have higher separation efficiency of photogenerated electron-hole pairs and extended photogenerated carrier lifetime. Therefore, RhB on RhB-NM traps photogenerated holes, and Cr(VI) on Cr(VI)-NM traps photoexcited electrons, which plays a positive role in suppressing the recombination of photogenerated electron-hole pairs. This allows photoexcited carriers to rapidly transfer to the particle surface, thereby avoiding the recombination of photogenerated carriers.

[0066] Example 2: RhB-NM+Cr(VI)

[0067] The removal of Cr(VI) from wastewater using the modified adsorbent red powder RhB-NM includes the following steps:

[0068] Add 40 mg of modified adsorbent RhB-NM to 100 mL of a solution with pH 4 and a Cr(VI) concentration of 40 mg / L. -1 In the wastewater, the mixture was stirred for 60 minutes in complete darkness to reach adsorption-desorption equilibrium. Then, a 300W xenon lamp (with a cutoff filter of 420nm) was used as the visible light source, and the photocatalytic reaction was carried out at room temperature for 120 minutes. The light source was then turned off, and the reaction ended. The concentration of Cr(VI) in the filtrate was determined using an atomic absorption spectrophotometer and a UV-Vis spectrophotometer.

[0069] Example 3: Cr(VI)-NM+RhB

[0070] The removal of RhB from wastewater using yellowish-brown powder Cr(VI)-NM includes the following steps:

[0071] Add 40 mg of the modified adsorbent Cr(VI)-NM to 100 mL of RhB with a concentration of 40 mg / L. -1In the wastewater, the mixture was stirred for 60 minutes in complete darkness to reach adsorption-desorption equilibrium. Then, a 300W xenon lamp (with a cutoff filter of 420nm) was used as the visible light source, and the photocatalytic reaction was carried out at room temperature for 120 minutes. The light source was then turned off, and the reaction ended. The concentration of RhB in the filtrate was determined using an atomic absorption spectrophotometer and a UV-Vis spectrophotometer.

[0072] Comparative Example 1NH2-MIL-125(Ti)+Cr(VI)

[0073] NH2-MIL-125(Ti) was used to replace RhB-NM in Example 2, and everything else remained the same as in Example 2.

[0074] Comparative Example: 2NH2-MIL-125(Ti)+RhB

[0075] NH2-MIL-125(Ti) was used to replace Cr(VI)-NM in Example 3, and everything else remained the same as in Example 3.

[0076] Test results are as follows Figure 3 :

[0077] from Figure 3 It can be seen that under visible light irradiation, the removal efficiency of RhB-NM for Cr(VI) and Cr(VI)-NM for RhB is significantly higher than that of NH2-MIL-125(Ti) for Cr(VI) and RhB. Within 120 min, the removal rate of Cr(VI) by RhB-NM is 99.1%, and the removal rate of RhB by Cr(VI)-NM is 100%. Moreover, the removal rate constants of RhB-NM for Cr(VI) and Cr(VI)-NM for RhB are 3.2 times and 4.6 times that of NH2-MIL-125(Ti) for Cr(VI) and RhB, respectively. Loading Cr(VI) and RhB onto the surface of NH2-MIL-125(Ti) can greatly shorten the time required for the photocatalytic reaction.

[0078] Example 4

[0079] The Cr(VI) concentration in Example 2 was adjusted to 40 mg / L. -1 The pH of the wastewater was 2, 4, 6, 8, and 10; other parameters remained the same as in Example 2.

[0080] Example 5

[0081] The RhB concentration in Example 3 was adjusted to 40 mg / L. -1 The pH of the wastewater was 2, 4, 6, 8, and 10; other parameters remained the same as in Example 3.

[0082] The results are as follows Figure 4:

[0083] from Figure 4 It can be seen that the reduction efficiency and rate constant of Cr(VI) are significantly higher in acidic environments than under neutral and alkaline conditions. The highest reduction rate (99.1%) and rate constant of Cr(VI) are observed at pH 4. Compared with the reduction of Cr(VI) by NH2-MIL-125(Ti), the reduction efficiency of RhB-NM for Cr(VI) is significantly improved, and the rate constant is also significantly increased to 0.04109 min⁻¹. -1 ;

[0084] Between pH 2 and 8, the removal rate of RhB in the solution was less affected by the solution pH, and almost all RhB was completely degraded after 60 min. However, the degradation rate constants showed significant differences. At pH 6, after 120 min of light irradiation, Cr(VI)-NM exhibited the largest degradation rate constant for RhB, at 0.07891 min. -1 .

[0085] Example 6

[0086] The dosage of the modified adsorbent RhB-NM in Example 2 was adjusted to 10, 70, and 100 mg, with a concentration of 0.1 g / L. -1 0.7g L -1 1g L -1 Everything else remains the same as in Example 2.

[0087] Example 7

[0088] The dosage of the modified adsorbent Cr(VI)-NM in Example 3 was adjusted to 10, 70, and 100 mg, with a concentration of 0.1 g / L. -1 0.7g L -1 1g L -1 Everything else is the same as in Example 3.

[0089] The results are as follows Figure 5 :

[0090] from Figure 5 It can be seen that the removal efficiency of Cr(VI) and RhB is closely related to the catalyst dosage. When the catalyst dosage increases from 0.1 g / L... -1 Increased to 1.0 g / L -1 At that time, the removal rates of Cr(VI) and RhB increased to 99.1% and 100%, respectively. This was achieved as the catalyst dosage increased from 0.1 g / L. -1 Further increase to 0.4g L -1 At that time, it could be observed that the removal amounts of Cr(VI) and RhB both increased rapidly. The dosage of the material was further increased to 1.0 g / L.-1 Subsequently, the removal rate of Cr(VI) in the system increased slowly. The material dosage increased from 0.4 g / L. -1 Increase to 1g / L -1 At that time, the increase in catalytic removal efficiency of RhB-NM for Cr(VI) and Cr(VI)-NM for RhB was not significant. This is because excessive catalyst in the reaction system may agglomerate, and the number of active reaction sites did not increase significantly. At the same time, excessive catalyst will cause light scattering and affect the transmittance of the solution, thus failing to significantly improve the removal rate of Cr(VI) and RhB.

[0091] Example 8

[0092] The adsorbent was used in four cycles according to the method in Example 2.

[0093] Example 9

[0094] The adsorbent was used in four cycles according to the method in Example 3.

[0095] The results are as follows Figure 6 :

[0096] from Figure 6 It can be seen that after four cycles of experiments, the photocatalytic removal rate of Cr(VI) by RhB-NM decreased from 99.1% to 81.3%, and the photodegradation efficiency of RhB by Cr(VI)-NM decreased from 100% to 94.0%, but still maintained good photocatalytic activity. In summary, RhB-NM and Cr(VI)-NM have good stability and reusability.

[0097] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for removing hexavalent chromium and rhodamine B from wastewater using pollutant-modified NH2-MIL-125(Ti), characterized in that, Includes the following steps: (1) Preparation of pollutant-modified NH2-MIL-125(Ti): First, prepare a hexavalent chromium (Cr(VI)) solution and a rhodamine B (RhB) solution. Then, add NH2-MIL-125 (Ti) to the Cr(VI) solution and the RhB solution respectively. Under complete darkness, shake the mixture thoroughly to allow the reaction to proceed. After the reaction is complete, centrifuge to collect the precipitate, wash it, and dry it to obtain the modified adsorbents RhB-NM and Cr(VI)-NM. (2) Removal of Cr(VI) and RhB from wastewater: The modified adsorbent RhB-NM was added to wastewater containing Cr(VI) and stirred in complete darkness to reach adsorption-desorption equilibrium. Then, the light source was turned on, the room temperature was maintained, and the photocatalytic reaction was carried out. The light source was then turned off, and the reaction ended. The modified adsorbent Cr(VI)-NM was added to the wastewater containing RhB and stirred in complete darkness to reach adsorption-desorption equilibrium. Then, the light source was turned on, the room temperature was maintained, and the photocatalytic reaction was carried out. The light source was then turned off, and the reaction ended.

2. The method according to claim 1, characterized in that, The concentrations of the Cr(VI) solution and RhB solution mentioned in step (1) are 10-100 mg·L. -1 .

3. The method according to claim 1, characterized in that, The ratio of NH2-MIL-125(Ti) and hexavalent chromium Cr(VI) solution in step (1) is 0.1-1.0 mg: 1 mL; the ratio of NH2-MIL-125(Ti) and rhodamine B RhB solution in step (1) is 0.1-1.0 mg: 1 mL.

4. The method according to claim 1, characterized in that, In step (2), the wastewater containing Cr(VI) and RhB needs to be adjusted to pH 2-10 using 0.1M HCl solution and NaOH solution.

5. The method according to claim 1, characterized in that, In step (2), the ratio of modified adsorbent RhB-NM to Cr(VI)-containing wastewater is 10-100 mg: 100 mL; the concentration of Cr(VI) in the Cr(VI)-containing wastewater is 10-100 mg·L⁻¹. -1 .

6. The method according to claim 1, characterized in that, In step (2), the ratio of modified adsorbent Cr(VI)-NM to wastewater containing RhB is 10-100 mg: 100 mL; the concentration of RhB in the wastewater is 10-100 mg·L⁻¹. -1 .

7. The method according to claim 1, characterized in that, The conditions for the oscillating reaction described in step (1) are 288-328 K and 100-300 r·min. -1 The reaction was carried out for 5-7 hours.

8. The method according to claim 1, characterized in that, In step (2), stirring is required for 50-70 min to reach adsorption-desorption equilibrium; the photocatalytic reaction time in step (2) is 20-140 min.

9. The method according to claim 1, characterized in that, In step (2), the light source is visible light.

10. The application of the method according to any one of claims 1-9 in the field of wastewater treatment.

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