Modified ceramic tubular membrane, its preparation method and application

Abstract

The application belongs to the technical field of ozone catalytic oxidation and water treatment, and particularly relates to a modified ceramic tubular membrane and a preparation method and application thereof. Ni-Fe LDH / SnO2 is prepared by loading nickel-iron layered double hydroxide (Ni-Fe LDH) on SnO2 nanoparticles, and is coated on the surface of a ceramic tubular membrane as a catalytic layer to obtain a Ni-Fe LDH / SnO2 ozone catalytic ceramic tubular membrane. The heterojunction formed by the combination of Ni-Fe LDH and SnO2 can effectively improve charge transfer, interface oxidation and reduction and other reactions, and further promote the catalytic performance. In addition, the high-activity components are uniformly loaded on the surface of the ceramic membrane and in the membrane holes, and the layered structure is distinct, which effectively improves the roughness and hydrophilicity of the membrane surface, and is beneficial to the prevention and treatment of membrane pollution. The modified ceramic membrane is applied to the treatment of mixed dye contaminated water, and can realize efficient removal of organic pollutants, and has good anti-membrane pollution ability and strong stability.

Description

Technical Field

[0001] The invention relates to a modified ceramic tubular membrane and a preparation method thereof, and applies the modified ceramic tubular membrane to catalytic ozone oxidation-membrane filtration coupling treatment of polluted water, belonging to the technical field of ozone catalytic oxidation and water treatment. Background Art

[0002] Membrane filtration technology is an advanced method for deep water treatment. It achieves molecular-level filtration through the selective separation properties of membrane materials under the influence of driving forces such as pressure and concentration. Among various membrane materials, ceramic membranes (CM), which belong to the inorganic membrane category, have been increasingly researched and applied in recent years due to their high mechanical strength, thermal stability, and chemical stability, enabling them to maintain stable operation for extended periods under extremely polluted conditions. However, the limited separation function and membrane fouling caused by the accumulation of pollutants during the water treatment process have limited the further application of CM.

[0003] Combining ozone oxidation with CM filtration can create a synergistic effect, effectively alleviating the aforementioned issues. During this combined process, the CM material catalyzes ozone oxidation to generate active species such as hydroxyl radicals through pathways such as metal redox and surface hydroxyl conversion. This not only further enhances pollutant treatment efficiency through collaborative filtration but also significantly reduces membrane fouling rates. Therefore, the CM's catalytic ozone activity is a key factor influencing the effectiveness of the combined CM filtration-ozonation catalytic oxidation treatment and controlling the degree of membrane fouling. Previous studies have proposed methods such as coating, doping, and sintering to load highly active components onto the CM, allowing for functional modification aimed at improving membrane catalytic performance.

[0004] The invention with publication number CN117797658A provides a ceramic membrane with a catalytic ozone oxidation functional layer, and the catalytic coating is prepared by preparing a manganese oxide slurry coating liquid. The invention with publication number CN117225202A provides a method for preparing a catalytic ozonation Mn-alkaline earth metal / ceramic membrane, which improves the activity of catalytic ozonation treatment of organic wastewater. However, in the current research on metal-modified CM, there are still some shortcomings that need to be overcome and improved: First, from the perspective of the ozone catalytic oxidation mechanism, the constructed high-activity components still have room for further optimization and regulation in promoting electron transfer for redox reactions; second, some modification methods cannot take into account the excellent performance of both catalytic and filtration functions, resulting in the synergistic effect being difficult to fully exert. Therefore, it is necessary to study more efficient CM materials. Summary of the Invention

[0005] To address the problems of the prior art, the present invention provides a modified ceramic tubular membrane, its preparation method, and its application. In the present invention, nickel-iron layered double hydroxide (Ni-Fe LDH) is loaded onto SnO2 nanoparticles to produce Ni-FeLDH / SnO2, which is then coated onto the surface of a ceramic tubular membrane (CM) as a reinforced catalytic layer. By using the Ni-Fe LDH / SnO2 composite material as the highly active component for ozone catalysis and coating it, the ceramic tubular membrane is modified, significantly improving the membrane's surface properties, membrane retention rate, and catalytic performance.

[0006] The technical solutions of the present invention are as follows:

[0007] One of the purposes of the present invention is to provide a modified ceramic tubular membrane having a composite catalytic layer deposited on its surface; the composite catalytic layer is composed of SnO2 nanoparticles loaded with nickel-iron layered double hydroxide.

[0008] Furthermore, the mass ratio of nickel-iron layered double hydroxide to SnO2 in the composite catalyst layer is (1-3):1.

[0009] A second object of the present invention is to provide a method for preparing the modified ceramic tubular membrane, which comprises the following steps:

[0010] S1. Preparation of SnO2 nanoparticles: Slowly dropwise adding a NaOH solution to an aqueous solution containing a tin source to adjust the solution pH to 9, and continuously stirring the solution at room temperature until a yellow / white gel forms; the gel is washed with a mixed solution of distilled water and ethanol, dried and dehydrated, and calcined at 550°C to obtain SnO2 nanoparticles;

[0011] S2. Loading nickel-iron layered double hydroxide: SnO2 nanoparticles were added to a metal salt solution containing Ni(NO3)2·6H2O and Fe(NO3)3·9H2O, and an alkaline solution containing NaOH and Na2CO3 was added dropwise thereto and stirred for at least 2 hours; the solution was then transferred to a Teflon-lined autoclave and reacted at 120°C for 6 hours. The sample was centrifuged, washed, and dried to obtain a SnO2-loaded nickel-iron layered double hydroxide complex;

[0012] S3, composite catalytic layer deposition: SnO2 loaded nickel-iron layered double hydroxide composite is dispersed in water to obtain composite suspension; the composite suspension is prepared by Figure 1 The device shown is sprayed on the surface of a ceramic tubular membrane under the drive of nitrogen at least 0.3 MPa to deposit a composite catalytic layer. The catalytic layer is deposited 1 to 3 times according to the same method to adjust the coating thickness; the obtained ceramic tubular membrane is then vacuum dried and cured at 50°C for at least 24 hours to obtain the modified ceramic tubular membrane.

[0013] Further, the tin source in step S1 is crystalline tin tetrachloride (SnCl4), and the dosage of the tin source is 0.02 g / mL.

[0014] Further, the distilled water and the ethanol mixed washing solution in step S1 are in a ratio of 1:1, and the calcination time of the gel at 550 DEG C is preferably 2 h.

[0015] Further, the metal ion concentration of the metal salt solution in step S2 is 0.54 mol / L, the molar ratio of Ni(NO3)2.6H2O to Fe(NO3)3.9H2O is 3:1, the composition of the alkaline solution is 1.2 mol / L NaOH and 0.32 mol / L Na2CO3, and the volume ratio of the alkaline solution to the metal salt solution is 1:1.

[0016] Further, the mass ratio of the nickel-iron layered double hydroxide Ni-Fe LDH to SnO2 in the composite in step S2 is (1-3):1.

[0017] Further, the CM used in step S3 is a commercial membrane composed of an alpha-Al2O3 support layer and a ZrO2 filter layer, and the total filtration area of the CM is 0.00133 m 2 (the internal dimensions are 25.4 mm (diameter) x 100 mm (height)), and the average pore size is 100 nm.

[0018] Further, the dosage of the SnO2 loaded nickel-iron layered double hydroxide composite in the composite suspension in step S3 is 0.2 g / L.

[0019] The third object of the present application is to apply the modified ceramic tubular membrane to catalytic ozone oxidation-membrane filtration coupled treatment of mixed dye contaminated water.

[0020] The present application also provides a treatment process for mixed dye contaminated water, which comprises the following steps: mixing ozone water with mixed dye contaminated water, and the volume ratio of ozone water to mixed dye contaminated water is 1:1; and then passing the mixed contaminated water through the modified ceramic tubular membrane reactor at a flow rate of 20 mL / min to perform catalytic ozone oxidation degradation of the mixed dyes.

[0021] Further, the pollutants of the mixed dye contaminated water can be one or more of rhodamine B, acid blue 92 and malachite green 92.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The application proposes to prepare a modified ceramic tubular membrane by depositing a composite catalytic layer on the surface of the ceramic tubular membrane, the composite catalytic layer being Ni-Fe LDH / SnO2, the composite catalytic layer having a low surface roughness, an adjustable catalytic layer thickness and excellent anti-pollution ability, the microstructure (particle size, pore size and porosity) and performance (hydrophilicity and stability) of the membrane surface being improved by the attachment of nanoparticles on the surface of the ceramic membrane; at the same time, the ceramic membrane modified by the Ni-Fe LDH / SnO2 composite catalytic layer has the functions of photosensitivity and sterilization, which can further improve the treatment effect of the catalytic ozone oxidation filtration combined process and reduce the degree of membrane pollution.

[0024] 2. The application also provides a catalytic ozone oxidation membrane filtration process using a Ni-Fe LDH / SnO2 enhanced catalytic layer modified ceramic tubular membrane, the ceramic membrane being used as a carrier, after the Ni-Fe LDH / SnO2 heterojunction composite structure is loaded on the surface of the ceramic membrane filtration layer, the synergistic effect of the two pairs of redox couples (Ni 2+ / Ni 3+ and Fe 2+ / Fe 3+ ) and the presence of SnO2 enhance the electron transfer ability, at the same time, the surface of SnO2 has a large number of hydroxyl groups, which further accelerates the decomposition of ozone and forms active oxygen substances, degrading macromolecular substances deposited on the membrane surface into small molecular substances, or even directly degrading them into CO2 and H2O.

[0025] 3. According to the catalytic ozone oxidation membrane filtration process and characterization test, the enhanced catalytic layer modified ceramic tubular membrane has an increase of about 20% to 30% in the removal rate of mixed pollutants compared with the unmodified ceramic membrane, the flow rate of the pollutants and ozone water being 20 mL / min, the ozone concentration being 4 mg / L, the mixed pollutant concentration being 50 mg / L, and the reaction time being 1 h, and the membrane flux changes gently in long-term operation, which proves that the catalytic membrane has excellent ozone catalytic ability and anti-membrane pollution ability. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The device is used for depositing a Ni-Fe LDH / SnO2 composite catalytic layer for preparing a modified ceramic membrane.

[0027] Figure 2SEM images and property performance comparison of different materials, wherein Fig. (a) is the SEM image of Sn02, Fig. (b, c) are the SEM images of Ni-Fe LDH / Sn02 composite catalytic layer with mass ratio of 2:1, Fig. (d) is the XRD pattern of Ni-Fe LDH / Sn02 composite catalytic layer with different mass ratios, Fig. (e) is the RhB degradation rate constant of Ni-Fe LDH / Sn02 composite catalytic layer with different mass ratios, Sn02 and Ni-Fe LDH, and Fig. (f) is the COD removal rate of Ni-Fe LDH / Sn02 composite catalytic layer with different mass ratios, Sn02 and Ni-Fe LDH.

[0028] Figure 3 SEM images of surface and cross-section of original ceramic membrane and modified ceramic membrane, wherein Fig. (a, e) is CM, Fig. (b, f) is NFS-1 / CM, Fig. (c, g) is NFS-2 / CM, and Fig. (d, h) is NFS-3 / CM.

[0029] Figure 4 AFM images of original ceramic membrane and modified membrane, wherein Fig. (a) is CM, Fig. (b) is NFS-1 / CM, Fig. (c) is NFS-2 / CM, and Fig. (d) is NFS-3 / CM.

[0030] Figure 5 Contact angle measurement of original ceramic membrane and modified membrane, wherein Fig. (a) is CM, Fig. (b) is NFS-1 / CM, Fig. (c) is NFS-2 / CM, and Fig. (d) is NFS-3 / CM.

[0031] Figure 6 Removal effect (a) and COD removal rate (b) of mixed dyes of original ceramic membrane and modified membrane.

[0032] Figure 7 Effect of HA on removal efficiency of mixed dyes (a) and normalized membrane flux (b) of NFS-2 / CM.

[0033] Figure 8 Stability of modified membrane: (a) membrane flux, (b) membrane flux recovery with different cleaning agents.

[0034] Figure 9 High-resolution XPS spectra and electrochemical impedance spectra of NFS-2 / CM before and after catalytic ozonation, wherein (a) is Fe 2p XPS spectrum, (b) is Ni 2p XPS spectrum, (c) is O1s XPS spectrum, (d) is Sn 3d XPS spectrum, and (e) is electrochemical impedance spectrum. DETAILED DESCRIPTION

[0035] The application will be further described below in connection with the drawings and preferred embodiments, the embodiments are given only to illustrate the application, and are not intended to limit the scope of the application.

[0036] The materials, reagents and the like used in the following examples can be obtained commercially unless otherwise specified, and the methods used in the following examples are conventional unless otherwise specified.

[0037] Example 1

[0038] The present embodiment provides a modified ceramic tubular membrane, which has a composite catalytic layer deposited on the surface of the ceramic tubular membrane; the composite catalytic layer is composed of SnO2 nanoparticles loaded with nickel-iron layered double hydroxide; the mass ratio of nickel-iron layered double hydroxide Ni-Fe LDH to SnO2 in the composite catalytic layer is 3:1; and the composite catalytic layer has a coating number of 1.

[0039] The preparation method of the modified ceramic tubular membrane comprises the following steps:

[0040] S1, preparing SnO2 nanoparticles: 1 g of SnCl4 is dissolved in 50 mL of distilled water, magnetically stirred at room temperature for 30 min, 6M NaOH solution is slowly added to adjust the pH to 9, and stirring is continued at room temperature for 12 h until a yellow / white gel is obtained; the obtained gel is centrifuged at 5000 rpm for 5 minutes, then washed with a 50:50 v / v mixed solution of distilled water: ethanol three times to remove undissolved particulate impurities. The purified gel is dried at 80°C for 24 h, then ground and calcined at 550°C for 2 h with a heating rate of 4°C / min to obtain SnO2 nanoparticles;

[0041] S2, loading nickel-iron layered double hydroxide: 0.4 g of SnO2 nanoparticles is added to 25 mL of a metal salt solution containing 10.125 mmol of Ni(NO3)2·6H2O and 3.375 mmol of Fe(NO3)3·9H2O, and then 25 mL of an alkaline solution containing 0.03 mol of NaOH and 0.008 mol of Na2CO3 is added dropwise and stirred for 2 h; then the solution is transferred to a Teflon-lined autoclave and reacted at 120°C for 6 h, and the reaction product is centrifuged, washed and dried to obtain a Ni-Fe LDH / SnO2 composite;

[0042] S3, depositing a composite catalytic layer: 0.2 g of Ni-Fe LDH / SnO2 composite is added to 1 L of deionized water and ultrasonicated for 30 min to disperse it. The composite suspension is passed through a Whatman filter paper under vacuum to remove the unreacted particles, and then the filtrate is collected and used as the catalyst slurry. The ceramic tubular membrane is immersed in the catalyst slurry and the membrane is rotated at a speed of 0.5 rpm for 1 h to deposit the composite catalytic layer on the surface of the ceramic tubular membrane. Figure 1The device shown is sprayed on the surface of the ceramic tubular membrane under the driving of 0.3 MPa nitrogen to deposit to form a Ni-Fe LDH / SnO2 composite catalytic layer, the coating is 1 time, and then the obtained modified membrane is vacuum dried and solidified at 50 DEG C for 24 h to obtain a modified ceramic tubular membrane.

[0043] Example 2

[0044] The embodiment provides a modified ceramic tubular membrane, which is different from the modified ceramic tubular membrane in example 1 in that:

[0045] The mass ratio of the nickel-iron layered double hydroxide Ni-Fe LDH to SnO2 in the composite catalytic layer is 2:1.

[0046] The preparation method of the modified ceramic tubular membrane is different from the preparation method in example 1 in that:

[0047] The adding amount of the SnO2 nanoparticles in step S2 is 0.6 g.

[0048] The coating times of the composite catalytic layer are the same as those in example 1, and the preparation steps of the SnO2 nanoparticles and the deposition steps of the composite catalytic layer are the same as those in example 1, which will not be described herein again.

[0049] Example 3

[0050] The embodiment provides a modified ceramic tubular membrane, which is different from the modified ceramic tubular membrane in example 1 in that:

[0051] The mass ratio of the nickel-iron layered double hydroxide Ni-Fe LDH to SnO2 in the composite catalytic layer is 1:1.

[0052] The preparation method of the modified ceramic tubular membrane is different from the preparation method in example 1 in that:

[0053] The adding amount of the SnO2 nanoparticles in step S2 is 1.2 g.

[0054] The coating times of the composite catalytic layer are the same as those in example 1, and the preparation steps of the SnO2 nanoparticles and the deposition steps of the composite catalytic layer are the same as those in example 1, which will not be described herein again.

[0055] Example 4

[0056] The embodiment provides a preparation method of a modified ceramic tubular membrane, which is different from the preparation method in example 1 in that:

[0057] The coating times of the composite catalytic layer are 2 times.

[0058] The preparation method of the modified ceramic tubular membrane is different from the preparation method in example 1 in that:

[0059] The coating times of the composite catalytic layer in step S3 is 2 times.

[0060] The mass ratio of the nickel-iron layered double hydroxide Ni-Fe LDH to SnO2 in the composite catalytic layer is the same as that in Example 1, and the preparation steps of the SnO2 nanoparticles and the steps of loading the nickel-iron layered double hydroxide are the same as those in Example 1, which will not be repeated here.

[0061] Example 5

[0062] The preparation method of the modified ceramic tubular membrane provided in this embodiment is different from that in Example 1 in that:

[0063] The coating times of the composite catalytic layer is 3 times.

[0064] The preparation method of the modified ceramic tubular membrane is different from that in Example 1 in that:

[0065] The coating times of the composite catalytic layer in step S3 is 3 times.

[0066] The mass ratio of the nickel-iron layered double hydroxide Ni-Fe LDH to SnO2 in the composite catalytic layer is the same as that in Example 1, and the preparation steps of the SnO2 nanoparticles and the steps of loading the nickel-iron layered double hydroxide are the same as those in Example 1, which will not be repeated here.

[0067] Performance test

[0068] (1) Physicochemical properties of the Ni-Fe LDH / SnO2 catalytic layer of the modified ceramic tubular membrane

[0069] The Ni-Fe LDH / SnO2 composite catalytic layers of the modified ceramic tubular membranes with different mass ratios of Ni-Fe LDH to SnO2 described in Examples 1-3 were subjected to SEM, XRD and ozone oxidation performance tests to study the physicochemical properties of the Ni-Fe LDH / SnO2 composite catalytic layer.

[0070] The SEM images of SnO2 and Ni-Fe LDH / SnO2 are shown in Figure 2 a-c, the morphology of SnO2 is square particles with smooth surface and large nanosize, and the surface of SnO2 is covered with a layer of Ni-Fe LDH, which is well distributed on the surface. Figure 2 d is the XRD pattern of the Ni-Fe LDH / SnO2 composite material with different mass ratios of Ni-Fe LDH to SnO2, and the Ni-Fe LDH / SnO2 composite material with different mass ratios shows clear Ni-Fe LDH and SnO2 diffraction peaks, indicating that the composite catalytic layer is composed of Ni-Fe LDH and SnO2.

[0071] The catalytic ozone oxidation and degradation of dye pollutants performance of Ni-Fe LDH / SnO2 composite catalytic layer with different mass ratios were evaluated. Rhodamine B (RhB) was used as water pollutants, and the experiment was carried out according to the following steps: Ni-Fe LDH / SnO2 composite was added to a conical reactor containing 400 mL of RhB solution, and stirring was continued for 30 min to achieve adsorption / desorption equilibrium, then gaseous ozone was introduced into the reactor from the ozone generator. Reaction conditions: Ni-Fe LDH / SnO2 composite dosage = 0.5 g / L, RhB concentration = 50 mg / L, ozone flow = 50 mg / h, pH = 8.

[0072] The results of performance evaluation are shown in Figure 2 e and f, compared with the same amount of SnO2 and Ni-Fe LDH, the catalytic ozone reaction rate and COD removal rate of Ni-Fe LDH / SnO2 composite catalytic layer with different Ni-Fe LDH:SnO2 mass ratios were significantly improved, and showed high catalytic ozone activity; with the increase of Ni-Fe LDH:SnO2 mass ratio from 1 to 3, the RhB degradation of Ni-Fe LDH / SnO2 composite catalytic layer gradually increased, the reaction rate increased to 0.059 min -1 , and the final COD removal rate was close to 90%.

[0073] In summary, the Ni-Fe LDH / SnO2 composite catalytic layer with different Ni-Fe LDH:SnO2 mass ratios has similar physicochemical properties, and shows high catalytic ozone activity and high COD removal rate; with the increase of Ni-Fe LDH:SnO2 mass ratio, the catalytic ozone activity of the catalytic layer is also improved.

[0074] (2) Physicochemical properties of modified ceramic membranes

[0075] SEM and AFM were used to characterize the modified ceramic membranes with different membrane layer thicknesses of Example 1, Example 4, and Example 5. According to the number of coating layers, the samples were named NFS-1 / CM, NFS-2 / CM, and NFS-3 / CM.

[0076] Figure 3 a-d are SEM images of the surface of the original ceramic membrane (CM) and the modified ceramic membranes NFS-1 / CM, NFS-2 / CM, and NFS-3 / CM with different catalytic layer thicknesses. Compared with the modified membranes, the pore structure of CM is clearly visible. With the increase of coating times, Ni-Fe LDH / SnO2 continuously covers the membrane pores, and the membrane surface becomes more and more dense. Figure 3e-h are the cross-section SEM images of CM and modified membranes. The layered structure of modified membranes is clear, from bottom to top, respectively, the support layer Al2O3, the filter layer ZrO2 and the catalytic layer Ni-Fe LDH / SnO2. The coating times of Ni-Fe LDH / SnO2 coating layer present a certain linear relationship with its thickness, and the thickness of coating 1 time, 2 times and 3 times is 18, 26 and 35 μm respectively.

[0077] The surface roughness of CM and modified membranes was analyzed by AFM, as shown in Figure 4 The roughness parameters of each sample were calculated according to the scanning area of 5.0 μm x 5.0 μm. It can be clearly seen that the modified membrane is smoother than the CM, and the roughness decreases from 256 nm to 76.7 nm with the increase of the coating times of Ni-Fe LDH / SnO2. This is because the Ni-Fe LDH / SnO2 particles fill the holes in the filter layer and reduce the hills on the surface of the membrane, which is consistent with the previous SEM observation results. The surface hydrophilicity of CM and modified membranes was analyzed by contact angle measuring instrument, as shown in Figure 5 With the increase of the coating times of Ni-Fe LDH / SnO2, the surface hydrophilicity of the modified membrane gradually increases, and the contact angle gradually decreases from 79.74 ± 1.52° to 13.17 ± 0.32°.

[0078] In general, the modified ceramic tubular membrane of the present application all shows high hydrophilicity, compared with the original CM, the modified ceramic tubular membrane is smoother than the original CM, which helps to reduce the accumulation of pollutants on the membrane surface and alleviate the membrane pollution to some extent, and is more conducive to the water treatment application of the membrane material; at the same time, with the increase of the thickness of the membrane layer, the surface hydrophilicity of the modified membrane gradually increases, and the catalytic layer with sufficient thickness can provide more active sites to activate ozone.

[0079] (3) The efficiency of modified membrane catalytic ozone oxidation-filtration treatment of dye pollutants

[0080] In order to elaborate the performance of the modified ceramic tubular membrane of the present application in catalytic ozone oxidation and filtration of dye pollutants, taking the mixed dye pollution water containing rhodamine B (RhB), acid blue (MG), malachite green 92 (AB92) and other pollutants as an example, NFS-1 / CM, NFS-2 / CM and NFS-3 / CM were applied to catalytic ozone oxidation-membrane filtration coupling treatment of mixed dye pollution water, and the experiment was carried out according to the following steps:

[0081] S1, modified ceramic tubular membrane ozone catalytic reaction: using ozone generator to 300 mL / min flow to 1.5L water tank to dissolve and gas water pre-mixed to make ozone water, and using ozone detector to monitor the dissolved ozone concentration; mixed dye contaminated water is prepared in the original water tank; the ozone water and mixed dye contaminated water are sent into the membrane reactor at a volume ratio of 1:1 and a flow rate of 20 mL / min to carry out catalytic ozone oxidation degradation;

[0082] Among them, the pollutants in the mixed dye contaminated water include: rhodamine B (RhB), acid blue (MG), malachite green 92 (AB92);

[0083] S2, water quality detection: the water flow is filtered from the inside to the outside of the composite membrane, and the sample is extracted from the sampling port for subsequent analysis at a certain reaction time. The sample is filtered through a pore size of 0.45 μm microfiber filter before analysis. During water feeding, the pump speed is changed to control the hydraulic time, the pressure of the membrane reactor inlet and outlet is automatically monitored to calculate the TMP, and the clean water outlet flow is recorded to calculate the membrane flux change at the corresponding time. The residual concentration (Ct) of RhB, MG and AB92 is measured by measuring the absorbance change at 554 nm, 572 nm and 618 nm respectively by ultraviolet spectrophotometer, and the degradation efficiency of mixed dye pollutants is evaluated comprehensively. COD removal is determined by national standard dichromate method.

[0084] The concentrations of RhB, MG and AB92 in the mixed dye contaminated water of different samples in the experiment are the same; the concentration of ozone water used in the experiment of different samples is 4 mg / L.

[0085] The experimental results are as follows:

[0086] Figure 6 a and b are the removal efficiency of mixed dyes and COD removal rate of different modified ceramic tubular membranes, the reaction conditions are: mixed dye contaminated water and ozone water volume ratio 1:1, flow rate 20 mL / min, ozone 4 mg / L, mixed dye RhB 5 mg / L, MG 5 mg / L, AB92 5 mg / L. CM only removes about 60% of the mixed dyes in 60 min, while NFS-1 / CM, NFS-2 / CM and NFS-3 / CM respectively reach about 80%, 85% and 90% removal rate, which is significantly improved. There is also a significant difference between different membrane materials in terms of COD removal, which shows that due to the existence of catalytic layer, it promotes the catalytic ozone oxidation process and provides stronger oxidation ability, so that the dye pollutants can be effectively degraded and mineralized.

[0087] Humic acid (HA) as one of the typical natural organic matter (NOM) components, like inorganic ions, significantly affects the treatment effect in the actual wastewater treatment process.Figure 7 a The effect of different HA dosages on the removal of mixed dyes by NFS-2 / CM, with a reaction condition of 1:1 of mixed dyes contaminated water to ozone water, 20 mL / min of flow rate, 4 mg / L of ozone, 5 mg / L of RhB, 5 mg / L of MG, and 5 mg / L of AB92. The results show that the removal of mixed pollutants decreases from 80% to 65% as the HA concentration increases from 15 ppm to 60 ppm. At the same time, due to the macromolecular structure of HA, it not only affects the removal of target pollutants, but also significantly affects the membrane flux. As shown in Figure 7 b, when the HA concentration is 15 ppm, the normalized membrane flux of NFS-2 / CM decreases from 80% to 60%, which is higher than 45% of CM, indicating that the enhanced active species generation by ozone catalytic oxidation can effectively convert macromolecular organic matters such as HA into smaller molecular products, and alleviate the membrane pollution behavior. However, when the HA concentration is high, HA not only inhibits ozone catalytic oxidation, but also continuously accumulates on the membrane surface, thereby exacerbating the membrane pollution.

[0088] The change trend of membrane flux and the removal performance of pollutants of modified ceramic tubular membrane under long-time operation are shown in Figure 8 a, the reaction conditions are as follows: the flow rate of feed is 20 mL / min, the volume ratio of feed to O3(aq) water is 1:1, RhB = 5 mg / L, AB92 = 5 mg / L, MG = 5 mg / L, HA = 15 mg / L, and O3(aq) = 4 mg / L. Due to the presence of the catalytic layer, the modified membrane shows excellent performance in terms of membrane pollution resistance. It can still maintain a normalized membrane flux of 60% after 300 min of operation. Two cleaning methods were studied after the cycle experiment. One is to use deionized water instead of pollutants to run the modified membrane under the same experimental conditions for 30 minutes. The other is to use ozone aqueous solution under the same conditions. As shown in Figure 8 b, after cleaning with deionized water, NFS-2 / CM and CM recover to 80% and 60% of the initial membrane flux, respectively, while after cleaning with ozone aqueous solution, the membrane flux recovers to 88% and 65%, respectively. This may be that during the ozone water cleaning process, the HA coated on the surface is decomposed by ozone, and the high molecular weight HA molecules are decomposed into smaller fragments, which can pass through the membrane pores, at the same time, the hydrophobic part of HA is converted into hydrophilic reaction products.

[0089] In order to further explore the catalytic ozone oxidation mechanism of the modified ceramic tubular membrane, XPS analysis was performed on the chemical composition and valence state change of NFS-2 / CM modified ceramic tubular membrane before and after catalytic ozone oxidation. As shown in Figure 9 a, in the peak fitting of Fe 2p 3 / 2 , Fe mainly exists in the form of multi-valence state, and the proportion of Fe 3+ increases from 57% to 67% after the reaction, indicating that Fe2+ Part of the oxygen was oxidized to Fe 3+ . Figure 9 b is the Ni 2p spectrum, the change of Ni 2+ proportion before and after the reaction shows that Ni ion is the main active site in the process of ozone catalytic oxidation and exists in the form of multi-valence state on the surface of the catalyst to participate in the reaction. In addition, the SnO2 surface has rich hydroxyl groups and can accelerate the decomposition of ozone and form active oxygen substances. In the O 1s spectrum, Figure 9 c), the binding energy of 531.4 eV represents the hydroxyl functional group (M-OH), and the surface hydroxyl content increases from 50% to 68% after the reaction, which shows that the hydroxyl group on the metal surface interacts with ozone. Figure 9 d is the Sn 3d spectrum, and the binding energies are 486.5 eV and 494.9 eV, respectively, which do not change significantly before and after the reaction, indicating the stability of SnO2. Finally, from Figure 9 e, it can be seen that compared with pure SnO2 and NiFe-LDH, Ni-Fe LDH / SnO2 shows a relatively small arc radius, indicating that the resistance to charge transfer is reduced, which is conducive to electron transfer. Therefore, in the reaction system, the synergistic effect of the two pairs of redox couples enhances the electron transfer ability, accelerating the occurrence of redox reaction; the resistance of Ni-Fe LDH doped with SnO2 becomes smaller, indicating that the resistance to electron transfer is smaller, and at the same time, the SnO2 surface has rich hydroxyl groups, which can further accelerate the decomposition of ozone and form active oxygen substances.

Claims

1. A modified ceramic tubular membrane for treating mixed dye-contaminated water by catalytic ozone oxidation-membrane filtration coupling, characterized in that: A composite catalytic layer is deposited on the surface of the modified ceramic tubular membrane; the composite catalytic layer is composed of SnO2 nanoparticles loaded with nickel-iron layered double hydroxide; The preparation of the modified ceramic tubular membrane comprises the following specific steps: S1. Preparation of SnO2 nanoparticles: Slowly dropwise adding a NaOH solution to an aqueous solution containing crystalline tin tetrachloride to adjust the solution pH to 9, and continuously stirring the solution at room temperature until a yellow or white gel appears; the gel is washed, dried and dehydrated, and calcined at 550°C to obtain SnO2 nanoparticles; S2. Loading nickel-iron layered double hydroxide: Add SnO2 nanoparticles to a metal salt solution containing Ni(NO3)2·6H2O and Fe(NO3)3·9H2O, add an alkaline solution containing NaOH and Na2CO3 dropwise and continue stirring for at least 2 h; The solution was then transferred to an autoclave and reacted at 120 °C for 6 h. The sample was centrifuged, washed, and dried to obtain SnO2-loaded nickel-iron layered double hydroxide composite. S3, composite catalytic layer deposition: dispersing the SnO2-loaded nickel-iron layered double hydroxide composite in water to obtain a composite suspension; The composite suspension is sprayed onto the surface of a ceramic tubular membrane under a nitrogen pressure of at least 0.3 MPa to form a composite catalytic layer. The catalytic layer is deposited 1 to 3 times according to the same method to adjust the coating thickness. The obtained ceramic tubular membrane is then vacuum dried and cured at 50°C for at least 24 hours to obtain the modified ceramic tubular membrane.

2. The modified ceramic tubular membrane for treating mixed dye-contaminated water by catalytic ozone oxidation-membrane filtration coupling according to claim 1, characterized in that: The mass ratio of nickel-iron layered double hydroxide to SnO2 in the composite catalytic layer is (1-3):

1.

3. The modified ceramic tubular membrane for treating mixed dye-contaminated water by catalytic ozone oxidation-membrane filtration coupling according to claim 1, characterized in that: The concentration of tin in the aqueous solution containing crystalline tin tetrachloride in step S1 is 0.02 g / mL.

4. The modified ceramic tubular membrane for treating mixed dye-contaminated water by catalytic ozone oxidation-membrane filtration coupling according to claim 1, characterized in that: The metal ion concentration of the metal salt solution in step S2 is 0.54 mol / L, and the molar ratio of Ni(NO3)2·6H2O to Fe(NO3)3·9H2O is 3:

1.

5. The modified ceramic tubular membrane for treating mixed dye-contaminated water by catalytic ozone oxidation-membrane filtration coupling according to claim 1, characterized in that: The alkaline solution is composed of 1.2 mol / L NaOH and 0.32 mol / L Na2CO3, and the volume ratio of the added alkaline solution to the metal salt solution is 1:

1.

6. The modified ceramic tubular membrane for treating mixed dye-contaminated water by catalytic ozone oxidation-membrane filtration coupling according to claim 1, characterized in that: The addition amount of SnO2 loaded nickel-iron layered double hydroxide composite in the composite suspension in step S3 is 0.2 g / L.

7. A process for treating water contaminated by mixed dyes, characterized in that: The steps include: Ozone water and mixed dye-contaminated water are mixed to obtain mixed contaminated water, wherein the volume ratio of ozone water to mixed dye-contaminated water is 1:1; and then the mixed contaminated water is passed through a reactor loaded with a modified ceramic tubular membrane for catalytic ozone oxidation-membrane filtration coupled treatment of mixed dye-contaminated water as described in any one of claims 1 to 6 at a flow rate of 20 mL / min to perform catalytic ozone oxidation degradation of the mixed dye-contaminated water.

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