Cerium oxide nanoparticle coating of ceramic membranes for filtration

Abstract

The present invention is related to the coating of ceramic membrane (8) surfaces with cerium oxide nanoparticles and the use of these membranes for filtration. It also comprises the development of membranes that provide high removal efficiency and flux in water / wastewater treatment (filtration) and enable the high recovery of materials that cannot be sufficiently retained during filtration.

Description

[0001] CERIUM OXIDE NANOPARTICLE COATING OF CERAMIC MEMBRANES FOR FILTRATION

[0002] Field of the Invention

[0003] The present invention relates to coating the surface of ceramic membranes with cerium oxide nanoparticles and using these membranes for filtration.

[0004] State of the Art

[0005] The use of membrane technology for purification and separation processes used today is remarkable. The pore size and membrane type of the membranes (e.g. organic, inorganic, ceramic) selected for these processes are important. Membrane filtration is a separation technology used to separate molecules / compounds when a driving force, such as pressure, is applied to the membrane. The effectiveness of membrane filtration depends on factors such as the size of the molecules to be separated, membrane pore size, solvent density and applied pressure. Inorganic membranes, known for their chemical and thermal stability, are used in various applications such as drinking water production, textile wastewater treatment, electronics industry wastewater treatment, fruit juice concentrate production, and wastewater treatment. The advantages of inorganic membranes compared to polymeric membranes are long-term stability, applicability and reusability under various conditions, and resistance to aggressive cleaning methods and harsh conditions. Inorganic membranes are preferred in challenging processes such as wastewaters containing radioactive materials, concentrated organic wastes, and oil and grease, where polymeric membranes cannot be used.

[0006] Cerium oxide nanoparticles have gained attention due to their beneficial applications in biological systems, electronics, optoelectronics and water purification. Cerium oxide nanoparticles play an important role in blocking reactive oxygen or nitrogen species due to their different charge states. The ratio of Ce3+to Ce4+on the surface is influenced by the microenvironment. Therefore, the chosen synthesis method has a significant effect on the activity of cerium oxide nanoparticles.

[0007] Various film coating methods can be used to coat the surface of ceramic membranes. It has been shown in the literature that ceramic surfaces can be coated with perovskite (manganite, cobaltite, ferrite and gallate) and lanthanum nickelate films using the spray pyrolysis method. In addition, the deposition of cerium oxide nanoparticles on different substrates using different methods has been reported in the literature. Among the coating methods, ultrasonic spray pyrolysis (USP) method is an effective method for producing the stoichiometric thin films. This method provides material savings of up to 80% compared to other methods, enabling the production of films with desired thickness that adhere well to the substrate surface. In the USP coating method, various parameters such as solution flow rate, forming gas and gas pressure, nozzle diameter, distance of the nozzle from the substrate and substrate temperature, can be controlled. This is very important in terms of the quality and performance of the resulting films. In addition, the controllability of coating parameters enables the fabrication of surfaces with the desired properties (rough or smooth). The tunability of the substrate temperature during USP coating affects the nature of the chemical reaction of the film formation, which has an impact on the deposition of the precursor material and therefore on the homogeneity of the films. Annealing of the substrate after coating affects the crystallinity, grain size and grain distribution of thin films.

[0008] The document numbered CN103643275A, seen in the state of the art, describes a method for preparing titanium oxide ceramic coating on the lead alloy surface. The method is characterized by adopting a pre-prepared method of chemical conversion coating followed by placing a lead alloy in an electrolyte containing alcohol and tetrabutyl titanate as a base, performing pulsed direct or alternating voltage output, and preparing titanium oxide ceramic coating on the lead. The alloy surface was formed under the influence of a liquid phase plasma. The titanium oxide ceramic coating prepared by the method has better bonding strength and better corrosion resistance with lead alloy (substrate), improves the corrosion resistance of lead alloy in humid environment, reduces the precipitation of lead ions of lead alloy in the environment.

[0009] The document numbered CN104474918A, seen in the prior art, describes a method for preparing a ceramic ultrafiltration membrane for washing in aluminum oxide production. The method comprises the steps of: adding an adhesive, plasticizer and water into the spherical aluminum oxide as the raw material, mixing thoroughly; performing pug grinding, preparing a support body blank using the extrusion molding; drying the raw material, and sintering to prepare a ceramic support body; taking spherical aluminum oxide as raw material, forming a membrane on the ceramic support body by using suspension dip coating method and drying it to form a transition layer; using aluminum salt as raw material, coating sol membrane liquid on the surface of the transition layer by in-situ bonding method; drying the wet membrane in air, baking, roasting and naturally cooling to obtain filtration membrane for washing in aluminum oxide production.

[0010] The document numbered CN104841292A, seen in the state of the art, describes an ozone-catalytic functional ceramic membrane, its preparation method, and a circulating coating device. The integration of membrane filtration and ozone-catalytic functions cannot be achieved, membrane fouling cannot be effectively eliminated, and similar issues arise. Using a tubular ceramic membrane as the carrier, a single-component or multi-component metal oxides are loaded by impregnation method. Then a manganese oxide dip coating solution is prepared, and a catalytic coating layer is formed on the membrane surface. Stratification is achieved by the layer-by-layer dip coating method. The invention aims to establish a stereoscopic multistage catalyst system, simultaneously improve the catalytic efficiency of the separation layer and the support layer of the ceramic membrane and achieve the permeation of an ozone-catalytic effect into the entire ceramic membrane to fully realize the overall catalytic effect.

[0011] The document numbered CN106145421A, seen in the known art, describes a method for separating fresh water using a disc type trapezoidal magneto cerium oxide yarn generator. The method for freshwater separation using a disc-type trapezoidal magneto cerium oxide yarn generator comprises a seawater pretreatment tank, a pretreated seawater suction pipe, a start-up suction pipe, a high- pressure start-up pump, a pipeline T-junction, and a reverse osmosis membrane.

[0012] The document numbered CN107473532A, seen in the state of the art, describes a method and a device for treating waste emulsion water. The main process comprises oil isolation on wobble plates, flocculation treatment, sedimentation from wobble plates, coarse filtration, ceramic membrane filtration, biochemical treatment (anaerobic treatment, first stage aerobiotic treatment, oxygen deficiency treatment, second stage aerobiotic treatment). This is followed by the production of treated water. The treatment method for waste emulsion water can effectively remove oil pollutants and particulate matter in the wastewater. When a ceramic membrane is adopted for filtration, the fine oil droplets in the emulsions can be removed, even though this process leads to membrane fouling. It is prevented by a filter aid to increase the filtration flow; by adopting ceramic membrane anti-blocking structure, the problem of particulate matter in the filter aid blocking the ceramic membrane tube is solved.

[0013] The document numbered CN113318608A, seen in the prior art, describes a dynamic catalytic water treatment ceramic membrane and its application. It is mainly related to a dynamic catalytic water treatment ceramic membrane, which consists of a ceramic membrane and a dynamic catalytic functional layer formed on the surface of the ceramic membrane. The dynamic catalytic functional layer here is a metal alkoxide thin film layer on the surfaces of titanium dioxide particles. The method has the characteristics that the filtration function of the ceramic membrane layer is not compromised, the filtering resistance and permeation flux of the ceramic membrane are not affected, at the same time, the utilization efficiency of ozone is improved, ozone is catalyzed and activated. Hydroxyl radicals degrade organic impurity and the formation of membrane foulants is effectively removed. The document numbered CN115364670A, seen in the state of the art , describes a method for preparation of a modified spherical alumina ceramic microfiltration membrane for oil-water separation. This method consists of preparation of a spherical aluminum oxide microfiltration membrane by selecting a spherical aluminum oxide microfiltration membrane as the raw material and precipitating nano zirconium oxide evenly. An organic material hexadecyl trimethoxy silicon layer is grafted by a homogeneous hydrothermal method to obtain a spherical aluminum oxide ceramic membrane layer and a modified spherical aluminum oxide ceramic microfiltration membrane for oilwater separation.

[0014] In the preferred methods in the known state of the art, the disadvantages such as the lack of membranes that provide high removal efficiency and flux in water / wastewater treatment (filtration); the existence of deficiencies in the recovery of materials that cannot be sufficiently retained during filtration, the use of commercial or membranes with low removal efficiency and flux in water / wastewater treatment (filtration), recovery, and the lack of high recovery rates of materials that cannot be sufficiently retained during filtration have necessitated the need for research and development in this area.

[0015] Object of the Invention

[0016] The object of the present invention is to synthesize cerium oxide nanoparticles in a laboratory and to coat ceramic membranes with these cerium oxide nanoparticles by USP (ultrasonic spray pyrolysis) method.

[0017] The object of the present invention is to use the ceramic membranes for water / wastewater treatment and valuable material recovery after coating them with cerium oxide nanoparticles.

[0018] The object of the present invention is to demonstrate that ceramic membranes are successfully coated with cerium oxide nanoparticles using Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM).

[0019] The object of the present invention is to coat ceramic membranes with cerium oxide nanoparticles using the USP (ultrasonic spray pyrolysis) method and use them for filtration and recovery.

[0020] The object of the present invention is to characterize ceramic membranes coated with cerium oxide nanoparticles by FTIR, XRD and SEM.

[0021] Brief Description of the Invention The present invention relates to the synthesis of cerium oxide nanoparticles in a laboratory environment, the coating of ceramic membranes with cerium oxide nanoparticles by USP method and the use of these membranes for water / wastewater treatment and valuable material recovery. Cerium oxide nanoparticles-coated ceramic membranes prepared by the USP method were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Characterization results show that ceramic membranes were successfully coated with cerium oxide nanoparticles. Distilled water was filtrated with membranes coated with cerium oxide nanoparticles under optimum conditions. Quercetin was chosen as a model compound to represent both the recovery and treatment performance of the synthesized membranes. Quercetin filtration with both bare membranes and membranes coated with cerium oxide nanoparticles and quercetin recovery using ethanol were tested. Compared to bare membranes, membranes coated with cerium oxide nanoparticles showed higher distilled water flux, quercetin removal efficiency and quercetin recovery from the membrane surface. Coating of ceramic membranes with cerium oxide nanoparticles using the USP method, and their use for filtration and recovery was carried out for the first time in this study.

[0022] Description of the Figures

[0023] Figure - 1 XRD Pattern of Cerium Oxide Nanoparticles Coated Ceramic Membrane

[0024] Figure - 2 SEM Images of Cerium Oxide Nanoparticles Coated Ceramic Membrane by Using the Ultrasonic Spray Pyrolysis (USP) Method

[0025] Figure - 3 FTIR Spectra of Cerium Oxide Nanoparticles Coated Ceramic Membrane

[0026] Figure - 4 Schematic Representation of USP System and Components

[0027] Part Reference Numbers:

[0028] 1. Syringe Driver

[0029] 2. Spraying mechanism

[0030] 2.1. Nozzle

[0031] 3. Computer

[0032] 4. Glass Chamber

[0033] 5. Air compressor 5.1. Pressure Controller

[0034] 6. Frequency Generator

[0035] 7. Magnetic Stirrer

[0036] 8. Membrane

[0037] Detailed Description of the Invention

[0038] In the first stage of the invention, cerium oxide nanoparticles were synthesised. A 100 mL of 0.01 M cerium nitrate solution was prepared. A 0.04M 100 mL NaOH solution was prepared. 2 mL of 10% polyvinylpyrrolidone (PVP, Mw = 360000) solution prepared with distilled water was added to the NaOH solution and mixed. Cerium nitrate solution was added dropwise to the homogeneous solution and stirred for 1 hour. The resulting precipitate was washed with ethanol and water and dried overnight at 80°C. Finally, the dried precipitate was calcined at 525°C for 2 hours.

[0039] The method for obtaining cerium oxide nanoparticles comprises the steps: dissolving cerium nitrate in distilled water, dissolving NaOH in distilled water, dissolving polyvinylpyrrolidone in distilled water, adding the prepared polyvinylpyrrolidone solution to the NaOH solution, mixing the same until a homogeneous solution is obtained, adding cerium nitrate solution to the homogeneous NaOH solution and mixing the same, precipitating the cerium oxide nanoparticles in the mixture, washing the obtained precipitate with ethanol and water, drying the washed precipitate, and calcining the dried precipitate. It is 0.01 M 100 mL cerium nitrate solution. It is 0.04 M 100 mL NaOH solution. It comprises the preparation of 10% (PVP, Mw = 360000) polyvinylpyrrolidone solution. It comprises adding 2 mL of polyvinylpyrrolidone solution to the NaOH solution and mixed. It comprises the step of adding cerium oxide solution dropwise to NaOH solution and mixing for 1 hour. The process comprises the step of drying the washed precipitate at 80°C for 24 hours. The process comprises the step of calcining the dried precipitate at 525°C for 2 hours.

[0040] A solution of 6.25 mM cerium oxide nanoparticles in isopropyl alcohol was prepared for coating ceramic membranes (8) using the USP (ultrasonic spray pyrolysis) method. Ceramic membranes (8) were coated with cerium oxide nanoparticles using a USP device.

[0041] The USP device used for coating is in a closed glass chamber (4) that provides atmospheric control. The shaping atmospheric gas, which directs the droplet cloud formed by spraying onto the membranes (8), is supplied by an air compressor (5) capable of generating 6 Bar pressure. The gas passes through a pressure controller (5.1) before being applied to the nozzle tip (2.1) of the spraying mechanism (2) at 1 psi pressure. The nozzle (2.1), which creates the spray droplets, is fixed to a computer (3) controlled holder that can move in 3 axes (x, y and z). At the tip of this spray nozzle (2.1), there is a piezoelectric atomiser, which is powered by an external ultrasonic frequency generator (6) (120 kHz), can reduce the size of the sprayed droplets to microns scale. The solution to be sprayed is delivered to the tip of the nozzle (2.1) with a digitally controlled syringe driver (1) at a controlled flow rate of 1 mL / min.

[0042] While the solution is sprayed vertically onto the membrane (8) surfaces to be coated, the distance between the nozzle (2.1) and the membrane (8) is set to z = 10 cm. The scanning was repeated 150 times to ensure the desired coating, using the tip of the nozzle (2.1), which was controlled by a computer (3) and scan an area of (x=15)x(y=15) cm2. Heating is required for removing the solvents in the solution droplets that reach to the surface of the membrane (8) to be coated and the pyrolysis process to occur. For this purpose, the membranes (8) to be coated were placed on the heater of a magnetic stirrer (7), which is equipped with a thermocouple. The temperature was fixed at 350 °C, and the membranes were maintained at this temperature for 15 minutes to reach thermal equilibrium, before starting the spraying process. The temperature was kept constant throughout the entire coating process. After the coating process was completed, the heater of the magnetic stirrer (7) was turned off and the coated membranes (8) were kept in the USP glass chamber (4) to cool to room temperature. A schematic representation of the USP system and its components is given in Figure-4.

[0043] The USP method for coating membranes used for filtration with cerium oxide nanoparticles, comprising the following steps; dissolving cerium oxide nanoparticles in isopropyl alcohol, heating the membrane (8) on the heater of the magnetic stirrer (7) to 350 °C, coating the membrane (8) with cerium oxide nanoparticles by spraying method, allowing the coated membrane (8) to cool. It is a solution prepared by dissolving 6.25 mM cerium oxide nanoparticles in isopropyl alcohol. It is a 9 cm diameter ceramic membrane with a pore size of 1 kDa. The heated membrane (8) is left to reach thermal equilibrium for 15 minutes before the spraying process begins. It comprises placing the membrane (8) on the heater of the magnetic stirrer (7) with a real time temperature control by a thermocouple, maintaining a temperature of 350 °C. So that the solvents in the solution droplets reaching the surface of the membrane (8) to be coated are removed and the pyrolysis process occurs. In the spraying method, there is a spraying mechanism (2) containing a nozzle (2.1) that generates spray droplets. It comprises a piezoelectric vibrating component, powered by an external ultrasonic frequency generator (6), that can reduce the size of the droplets spraying from the tip of the spray nozzle (2.1) to micron scale. The process comprises the cooling of the coated membrane (8) at room temperature. XRD patterns of ceramic membranes (8) coated with cerium oxide nanoparticles are given in Figure- 1. XRD measurements were taken with Bruker's D8 Advance Twin-Twin instrument, and the analyses were performed using Bruker's EVA software and ICDD database. The XRD patterns indicate the presence of TiO2and yttrium zirconium oxide in the ceramic membrane (8). According to the ICDD database, the XRD patterns for CeO2, TiO2and yttrium zirconium oxide correspond to PDF 03-065- 2975, PDF 00-021-1276 and PDF 00-048-0224, respectively. Crystal sizes can be calculated from the full width at half maximum (FWHM) values of the main peak. The crystal size was calculated as 223.4 A using EVA software following the Debye-Scherrer equation.

[0044] The SEM images of cerium oxide nanoparticles coated ceramic membranes (8) are given in Figure-2. It can be seen that the surface of the membrane (8) is completely covered with cerium oxide nanoparticles. The average cerium oxide nanoparticles size was calculated as ~33 nm. These results indicate that in the USP coating system, the nozzle (2.1) disperses the cerium oxide nanoparticles on the membrane (8) surface with minimal agglomeration.

[0045] The FTIR spectra of the cerium oxide nanoparticles coated ceramic membranes (8) are shown in Figure-3. The peak observed at wave number -476 cm'1is attributed to the Ce-0 vibration of the CeO2crystal. This new peak observed in the ceramic membrane (8) coated with cerium oxide nanoparticles shows that the ceramic membranes (8) have been successfully coated with cerium oxide nanoparticles.

[0046] Cerium oxide nanoparticles coated ceramic membranes (8) were subjected to distilled water filtration for 3 hours at room temperature under 1 bar pressure. A cross-flow (tangential flow) membrane test unit was used for filtration tests. The active membrane area in the membrane (8) cell used during filtration was 52.81 cm2. After distilled water filtration, a 50 mg / L quercetin filtration was carried out for 1 hour under 1 bar pressure at room temperature. Then, to recover the quercetin retained on the membranes (8) surface, a backwashing with ethanol was performed for 1 hour. Quercetin concentration was determined using HPLC. The data obtained from the filtration tests are presented in Table 1. All tests were repeated at least three times and average values, and standard deviations are reported. Compared to the bare membranes, the cerium oxide nanoparticles coated ceramic membranes (8) showed higher distilled water flux, quercetin removal efficiency and quercetin recovery from the membranes (8) surface . The cerium oxide nanoparticles coated ceramic membranes (8) showed approximately 55% higher quercetin recovery compared to the bare membrane. Table 1. Filtration test results.

[0047] Coating of ceramic membranes (8) with cerium oxide nanoparticles using the USP method has been done for the first time in the context of the present invention. The filtration process with ceramic membranes (8) coated with cerium oxide nanoparticles by the USP method have also been carried out for the first time within the scope of this invention. Recovery tests with ceramic membranes (8) coated with cerium oxide nanoparticles have been conducted for the first time in the context of this invention as well.

[0048] The coating process of the ceramic membranes (8) subject to this invention is not limited to ceramic membranes (8) only. In different preferred embodiments of the invention, membranes with different pore sizes and diameters have been coated with cerium oxide nanoparticles.

[0049] In another preferred embodiment of the invention, ceramic membranes produced by TAMI with a pore size of 1 kDa and a diameter of 9 cm were used.

[0050] In a different preferred embodiment of the invention, 9 cm diameter membranes with 150 kDa pore size were used.

[0051] In a different preferred embodiment of the invention, 9 cm diameter membranes with 15 kDa pore size were used.

[0052] In a different preferred embodiment of the invention, 4.7 cm diameter membranes with 1 kDa pore size were used.

[0053] In different preferred applications of the invention, cerium oxide nanoparticles are coated on membranes of all pore sizes and all diameters.

Claims

CLAIMS1. A method for obtaining cerium oxide nanoparticles characterized by comprising the steps of; a. dissolving cerium nitrate in distilled water, b. dissolving NaOH in distilled water, c. dissolving polyvinylpyrrolidone in distilled water, d. adding the prepared polyvinylpyrrolidone solution to the NaOH solution, e. mixing the solution until it becomes homogeneous, f. adding cerium nitrate solution to the homogeneous NaOH solution and mixing the resulting solution, g. precipitation of cerium oxide nanoparticles in the mixture, h. washing the resulting precipitate with ethanol and water, i. drying the same, j. calcining the dried precipitate.

2. The method for obtaining cerium oxide nanoparticles according to claim 1, characterized in that; 0,01 M 100 mL cerium nitrate solution in the step "a".

3. The method for obtaining cerium oxide nanoparticles according to claim 1, characterized in that; 0,04 M 100 mL NaOH solution in step "b".

4. The method for obtaining cerium oxide nanoparticles according to claim 1, characterized by comprising; the step of preparing a 10% polyvinylpyrrolidone solution in the step "c".

5. The method for obtaining cerium oxide nanoparticles according to claim 1, wherein 2 mL of polyvinylpyrrolidone solution is added to NaOH solution and mixed in step "d".

6. The method for obtaining cerium oxide nanoparticles according to any one of the preceding claims, characterized by comprising; the step of adding cerium oxide solution by dropwise to NaOH solution and mixing for 1 hour in step "f".

7. The method for obtaining cerium oxide nanoparticles according to any one of the preceding claims, characterized by comprising; the step of drying the washed precipitate at 80°C for 24 hours in step "i".

8. The method for obtaining cerium oxide nanoparticles according to any one of the preceding claims, characterized by comprising; the step of calcining the dried precipitate at 525°C for 2 hours in step "j".

9. An ultrasonic spray pyrolysis method for coating membranes used for filtration with cerium oxide nanoparticles, comprising the process steps of; a. dissolving cerium oxide nanoparticles in isopropyl alcohol, b. heating the membrane (8) on the heater of the magnetic stirrer (7) up to 350°C, c. coating the membrane (8) with cerium oxide nanoparticles using the spraying method, d. allowing the coated membrane (8) to cool.

10. The ultrasonic spray pyrolysis method according to claim 9, wherein the solution prepared by dissolving 6.25 mM cerium oxide nanoparticles in isopropyl alcohol in step "a".

11. The ultrasonic spray pyrolysis method according to claim 9, characterized by comprising; the membrane in step "b" is a 9 cm diameter ceramic membrane with a pore size of 1 kDa.

12. The ultrasonic spray pyrolysis method according to claim 9 or claim 11, characterized by comprising; the step of allowing the membrane (8) heated in step "b" to reach thermal equilibrium.

13. The ultrasonic spray pyrolysis method according to claim 9, characterized by comprising; the step of keeping the membrane heated in step "c" for 15 minutes to reach thermal equilibrium.

14. The ultrasonic spray pyrolysis method according to claim 9 or claim 13, characterized by comprising; the step of placing the membrane (8) on the heater of the magnetic stirrer (7) with a real time temperature control by a thermocouple, to 350°C in order to remove the solvents in the solution droplets reaching the surface of the membrane (8) to be coated and to initiate the pyrolysis process.

15. The ultrasonic spray pyrolysis method according to claim 9, characterized by comprising; the step of forming spray droplets by a spray mechanism (2) that has a nozzle (2.1) in the spraying method in step "c".

16. The ultrasonic spray pyrolysis method according to claim 9 or claim 15, characterized by comprising ; the step reducing the size of the droplets sprayed from the tip of the spray nozzle (2.1) to the micron scale by a piezoelectric vibrating component fed by an external ultrasonic frequency generator (6) in the step "c.

17. The ultrasonic spray pyrolysis method according to claim 9, characterized by comprising; the step of cooling the coated membrane (8) at room temperature, in step d.

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