KR20220046386A - Filter based on photocatalyst - Google Patents

Abstract

The present invention provides a method for manufacturing a photocatalyst filter, including the steps of: electrospinning a solution containing nanofibers on a support to manufacture a non-woven fabric to which nanofibers are attached; and immersing the nanofiber-attached support in a photocatalyst suspension to self-assemble the photocatalyst on the nanofibers.

Description

FILTER BASED ON PHOTOCATALYST

The present invention relates to a photocatalyst-based filter, and more particularly, to a low-cost and high-efficiency photocatalytic filter using self-assembly of nanofibers and photocatalytic nanoparticles synthesized by an electrospinning process.

In order to solve the global problem related to energy and water shortage, a rapid and energy-efficient water purification method is required. Photocatalytic decomposition using solar energy and semiconductor photocatalytic materials is of great interest to remove organic pollutants from wastewater because solar energy is considered an inexpensive green energy source and is readily available in most climates. It is recognized as one of the promising technologies for environmental improvement due to its safe and energy-saving properties. Much research is currently focused on the development of highly efficient, economical, and versatile photocatalysts, modules and systems for environmental applications.

To date, various photocatalytic nanoparticles with high photocatalytic efficiency have been developed along with advantages such as high quantum yield, stability against photocorrosion, insolubility in water, low toxicity and low cost. However, the photocatalytic nanoparticles are easily agglomerated to minimize the surface energy during photocatalytic decomposition, which tends to decrease the overall photocatalytic efficiency. In addition, it is difficult to separate, recover, and recycle nanoparticles dispersed in a solution after photocatalytic decomposition of harmful organic pollutants. That is, the photocatalyst itself can become a pollutant, and considering the process for solving this problem, air and water purification using photocatalyst nanoparticles is not economical compared to the existing method.

To overcome these shortcomings of nano-sized particulate photocatalysts, it is essential to immobilize small nanoparticles on specific support materials. Immobilized photocatalytic nanoparticles are much more suitable for industrial large-scale systems, as they do not require a filtration device for liquid-solid separation at the end of the process, reducing initial and operating costs, making them more economically suitable for large-scale industries. However, the immobilized photocatalyst has a disadvantage in that the decomposition efficiency is lowered mainly due to the reduction of the reaction surface. Therefore, it is important to develop support materials and structures with high porosity, large specific surface area, as well as suitable mechanical properties, thermal resistance, low density, chemical stability, low cost, abundance and high external mass transfer in immobilized photocatalytic technology. .

Polymer materials are superior to metal-, ceramic- and carbon-based supports such as glass, alumina, quartz and stainless steel, activated carbon, carbon nanotubes, graphene and graphite due to their flexibility, formability, toughness, cost-effectiveness and light weight. It has attracted attention as a potential and suitable catalyst support. Polyvinylidene fluoride (PVDF), polyaniline, polyamine, polysulfone, polyurethane, polyester, polyacrylonitrile and polytetrafluoroethylene have been studied as support materials for photocatalytic degradation. From a geometrical point of view, ultra-long polymer nanofibers prepared by simple and cost-effective electrospinning techniques, compared to porous masses, thick films and microscale fibers, due to their 3D open structure, high porosity and large aspect ratio It has been recognized as the most suitable support. These properties allow the photocatalyst to be immobilized on the support at high density without agglomeration.

Various photocatalytic decomposition studies based on electrospun polymer nanofibers containing semiconductor nanoparticles prepared by mixing nanoparticles in a polymer solution for electrospinning have been reported, but this method is based on the fraction of nanoparticles located on the surface of the nanofiber support. The advantages of electrospun nanofibers cannot be fully exploited due to their limitations. Recently, another approach based on a solvothermal process for completely immobilizing photocatalytic nanoparticles on the surface of an electrospun polymer nanofiber support has been studied. This method has the advantage that very small nanoparticles can be placed on the surface of the fiber, but there is a limit in the fraction of the introduced nanoparticles, and there are limitations in that the nanofibers are fixed again on other supports due to the great flexibility.

Korean Patent Registration No. 10-1641123

The present invention is to provide a new type of photocatalytic filter using an industrially feasible method to overcome the above-mentioned limitations of the existing photocatalytic filter based on an electrospun polymer nanofiber support.

The filter of the present invention consists of three layers comprising a photocatalyst, polymer nanofibers such as electrospun electrospun polyvinylidene fluoride (PVDF), and a non-woven polyethylene terephthalate (PET) fabric. In order to efficiently and economically manufacture a filter, poly(styrene-alt-maleic anhydride; PSMA) having a carboxyl group was first added to a PVDF solution as a self-assembly reagent. PSMA/PVDF nanofibers were synthesized by introducing and electrospinning this solution on a non-woven PET fabric.Then, by fixing it on the fabric by high-temperature compression, a photocatalytic support capable of solving the problem due to the flexibility of the nanofibers was formed. did

The present invention comprises the steps of: electrospinning a polymer solution on a support to prepare a nonwoven fabric to which nanofibers are attached; and self-assembling the photocatalyst on the nanofibers by immersing the support to which the nanofibers are attached in a photocatalyst suspension.

The photocatalyst is TiO ₂ , ZnO, Bi ₂ O ₃ , BaTiO ₃ , Fe ₂ O ₃ , V ₂ O ₅ , SnO ₂ , WO ₃ , Ga ₂ O ₃ , CuS, ZnS, CdS, CdSe, gC ₃ N ₄ , etc. It may be any one selected from the group comprising

The support may be a non-woven fabric.

The nanofiber is polyvinylidene fluoride (PVDF), polyisosulfone (PES), polysulfone (PS), polyacrylonitrile (PAN), cellulose acetate (CA) and poly (styrene-co-maleimide), Poly(styrene-acrylonitrile), poly(styrene-co-methylmethacrylate), poly(styrene-alt-maleic anhydride) (PSMA), and the like may include any one or more selected from the group consisting of.

The weight ratio of PVDF to PSMA may be 9:1 to 5:5.

In the present invention, the specific surface area of the support can be increased by using the electrospinning process, the photocatalyst can be fixed to the support by self-assembly, and the filter can be efficiently manufactured in a short time.

The photocatalyst-based filter of the present invention can be used as a filter for air purification and water treatment.

1 is a schematic view showing a photocatalyst filter made of a nano-sized photocatalyst and a support prepared by electrospun nanofibers and nonwoven fabric.
2 is a schematic diagram showing the electrospinning process used in the present invention.
3A, B, and C show SEM images of electrospun fibers, and D, E, and F of FIG. 3 are diagrams showing a membrane self-assembled with a 2% titanium dioxide solution.
4 is a view showing ATR-FTIR spectra of PVDF, PVDF/PSMA, PVDF/PSMA-titanium dioxide self-assembled membranes.
5 is a view showing the TGA of SM-1-titanium dioxide, SM-3-titanium dioxide and SM-5-titanium dioxide.
6 shows absorption spectra of MB solutions when photocatalytic properties were evaluated using membranes with or without titanium dioxide at different times.
7 is a diagram illustrating the photocatalytic decomposition of MBs with or without titanium dioxide.
8 is a diagram showing the color change of MB adsorbed on the SMT-5 membrane when exposed to light in the air.
9 is an XPS spectrum result of SM-5 and self-assembled SM-5-titanium dioxide.
10 is an XPS spectrum result of titanium dioxide and self-assembled SM-5-titanium dioxide.

The present invention will be specifically described with reference to the following examples. However, the present invention should not be construed as being limited to the following examples.

Commercially available titanium dioxide (P25, Evonik Industries, Germany) and nonwoven fabric (PET 39, Namyang Nonwovens Co., Ltd., Korea) were used as photocatalysts and supports, respectively. polyvinylidene fluoride (PVDF, Mw=570,000), poly(styrene-alt-maleic anhydride) (PSMA, 13wt% in H ₂ O), N,N-dimethylacetamide (DMAc, anhydride, 99.8%) and acetone (>99.5%) was purchased from Sigma Aldrich and all reagents were analytical grade and used as such without further purification.

PVDF and PVDF/PSMA nanofibers were synthesized using electrospinning. A viscous solution for electrospinning was prepared by dissolving PVDF and PSMA in a mixture of DMAc and acetone in a ratio of 3:7 under stirring at a speed of 300 rpm at 50° C. for 2 hours. After confirming that all chemicals were dissolved, the solution was degassed by ultrasonication for 1 hour. The concentration of the total polymer combined with PVDF and PSMA was 16 wt %, and the weight ratio of PVDF to PSMA was 10:0, 9:1. Various changes were made to 7:3 and 5:5. The prepared solution was loaded into a plastic syringe with a needle attached with an inner diameter of 250 μm, and placed in front of a rotating metal collector to have a fixed distance of 12 cm between the nozzle and the collector. The feed rate of the precursor solution was adjusted at a rate of 2 ml/h by a syringe pump (KDS200, KD Scientifid Inc.), and the solution was negatively charged to 15 kV by a power supply (HV60, NanoNC Co., Ltd). A metal barrel on a column coated with a nonwoven acted as a collector and rotated at 300 rpm during electrospinning. Environmental conditions were kept constant at 45° C. and a relative humidity of 20%.

The spun nanofibers on the nonwoven were dried at 80° C. overnight in a drying box. Hereinafter, the prepared samples were named SM-0, SM-1, SM-3 and SM-5, respectively, according to the ratios of PSMA to PVDF (0:10, 1:9, 3:7 and 5:5), respectively. do. Finally, the titanium dioxide nanoparticles were self-assembled onto the nanofibers by immersing the electrospun PVDF and PVDF/PSMA samples in a 2 wt% aqueous titanium dioxide suspension for 1 week. The sample was then washed several times with deionized water to remove weakly bound nanoparticles and dried at room temperature. Hereinafter, SM-0, SM-1, SM-3 and SM-5 in which titanium dioxide nanoparticles are self-assembled are referred to as SMT-0, SMT-1 or SM-1-titanium dioxide, SMT-3 or SM, respectively. -3-Titanium dioxide, and SMT-5 or SM-T-Titanium dioxide. Here, the self-assembly of titanium dioxide is formed by the functional group formed by PSMA. In the case of SMT-0, PSMA was not present, so that the titanium dioxide was not substantially self-assembled.

Before and after adding the titanium dioxide nanoparticles, the microstructural properties of the nanofibers were observed by field emission scanning electron microscopy (FE-SEM, Hitachi, Japan). Thermogravimetric analysis (TGA) was performed to determine the amount of self-assembled titanium dioxide nanoparticles. The thermogravimetric analysis was performed using a TGA/DTA 6300 thermogravimetric analyzer at a heating rate of 10° C./min in air. The prepared membranes were characterized by an attenuated total reflection Fourier transform infrared spectrometer with a universal ATR sampling instrument (ATR-FTIR, PerkinElmer Spectrum One, USA). Spectra were collected at 2 cm ^-1 spectral resolution in the 4000-250 cm ^-1 range using 4 scans. Several samples were analyzed using X-ray photoelectron spectroscopy (XPS, K-ALPHA ⁺ , Thermo Fisher Scientific, USA), and the C1 peak of graphitic carbon (BE=284.6 eV) was used as a reference for charge transfer observation. The binding energy was corrected.

The photocatalytic activity of the SMT-5 sample was observed by measuring the photolysis rate of methylene blue (MB). It was confirmed from the decolorization of MB during photocatalytic degradation, based on the Beer-Lambert law, which shows a linear relationship between the absorbance and concentration of the absorbing species. Experiments were performed using a 1×10 ^-5 M MB aqueous solution and a solar simulator equipped with a 300 W xenon lamp and an Air Mass 1.5 Global Filter that simulates solar radiation reaching the Earth's surface at a zenith angle of 48.2°. Prior to irradiation, the suspension was placed in the dark with stirring for 30 min to establish adsorption-desorption equilibrium. During the experiment, the suspension was magnetically stirred in a water bath at 25°C. A series of specific volumes of samples were withdrawn at selected times for analysis and centrifuged for measurement. The residual concentration of MB was measured by UV/vis spectrometer (UV-vis DRS, UV-2600, SHIMADZU, Japan).

result

The shape of titanium dioxide before and after self-assembly was observed using FE-SEM. 3A, B and C show SEM images of electrospun fibers. The spun sample shows a well-formed fibrous structure with a smooth surface. The nanofibers are randomly oriented in the form of a nonwoven fabric. Fiber diameter decreases with increasing PSMA concentration in the blend solution. The smaller the diameter of the fiber, the more likely PSMA is exposed to the surface of the fiber. 3D, E and F show membranes self-assembled with 2% titanium dioxide solution at each PSMA content. Unlike before self-assembly, the fiber surface was roughened. Indeed, as the PSMA content increased, the surface roughness of the fibers increased. This means that as the amount of PSMA increases, there is a large amount of titanium dioxide on the fiber surface.

In order to understand the self-assembly mechanism of titanium dioxide on the PSMA/PVDF blend membrane, the pure PVDF membrane, the blend membrane and the self-assembled membrane by electrospinning were observed by ATR-FTIR, and the results are shown in FIG. 4 .

-CF ₂ and -CH ₂ stretching bands of PVDF appear at 1178 cm ^-1 and 1400 cm ^-1 , respectively. On the other hand, in the PVDF/PSMA blend membrane, additional peaks are observed at 1780 cm ⁻¹ and 1705 cm ⁻¹ . The band at 1780 cm ⁻¹ is due to the symmetric anhydride C=0 stretching mode of the maleic anhydride group, and the peak near 1700 cm ⁻¹ is due to the C=0 stretching mode of the carboxylic acid group.

The most significant change due to titanium dioxide bonding is the bonding of polymer peaks less than 800 cm ⁻¹ . It is shifted by a single broad absorption peaked at a lower frequency. Due to the various Ti-O vibrational modes, the region may contain overlapping peaks. As a result, when these PVDF/PSMA blend membranes were immersed in a titanium dioxide nanoparticle solution for a specific time, it was confirmed that the titanium dioxide nanoparticles self-assembled with carboxyl groups on the membrane surface.

To observe some changes due to immobilization conditions, such as PSMA concentration, thermal stability was analyzed. Titanium dioxide showed no apparent weight loss from room temperature to 700°C. However, the self-assembled membrane with titanium dioxide showed a weight loss pattern, as shown in FIG. 5 . In addition, it can be seen that the amount of self-assembled TiO ₂ is increased through a weight change that is decreased as the added PSMA concentration is increased. The compositions of SM-1, SM-3, and SM-5 of FIG. 5 are shown in Table 1 below. In Table 1, the unit of each component is wt%, and is a weight ratio with respect to a total of 100% by weight of DMAc and acetone.

In the case of the nonwoven fabric, it is composed of PE and PP, and has endothermic peaks at 130°C and 165°C, respectively. And, the melting point of PVDF is about 170°C. However, when the nonwoven fabric and PVDF are composite membranes, the thermal stability is stable up to 370°C. Due to loss of PVDF/nonwoven polymer chains, weight loss occurs between 370°C and 430°C. Consequently, depending on the PSMA content, the amount of self-assembled titanium dioxide is 7.5% for SM-1, 16% for SM-3, and 33% for SM-5.

Methylene blue, a widely used organic dye, was selected as a contaminant to investigate the photocatalytic activity of self-assembled titanium dioxide membranes. Photocatalytic activity is measured by the degradation of MBs under visible light irradiation. 6 shows absorption spectra of MB solutions when photocatalytic properties were evaluated using membranes with or without titanium dioxide at different times. In FIG. 6, Blank represents the change in the concentration of MB solution with time when light is irradiated to MB solution in a state where a photocatalytic filter is not used, and NWF is the concentration of MB solution when a nonwoven fabric containing no titanium dioxide is used. indicate change. Since SMT-0 does not self-assemble titanium dioxide, only nonwoven fabric and polymer nanofibers exist. The UV-vis absorption spectrum according to the time of the MB solution shows that the maximum absorbance at 664 nm is greatly reduced after 60 minutes of irradiation.

The normalized optical density change of MB at 664 nm is used to evaluate the photocatalytic activity. The C/C ₀ change over the reaction time is used to estimate the rate of degradation, where C ₀ is the original concentration of the dye and C is the concentration of the filtrate taken during the reaction. The photocatalytic degradation of MBs of membranes with and without titanium dioxide is shown in FIG. 7 .

In general, the degradation of dyes can follow a quasi-first-order kinetic reaction using the simplified Langmuir-Hinshelwood model.

lnC ₀ /C=kt

where t is the visible light irradiation time, and k is the apparent first-order rate constant determined from a linear analysis of the data shown in FIG. 7 . The constant k value of 0.05 g of P25 was 0.6960, and the k value of the prepared sample SM-5-titanium dioxide membrane was 0.0343. As a result, 0.0025 g of titanium dioxide nanoparticles were fixed on the membrane surface of about 2.5 cm * 3 cm. 8 is a diagram showing the color change of MB adsorbed on the SMT-5 membrane when exposed to light in the air. It shows that the MB adsorbed on the photocatalytic filter is decomposed according to the exposure time to light.

As shown in FIGS. 9 and 10 , X-ray photoelectron spectroscopy (XPS) was performed to more clearly measure the interaction between the components. By measuring wide-scan XPS spectra over a large energy range at low resolution, elements present in the grafted titanium dioxide nanoparticles were identified. In SM-5, the peaks at 284.64 and 532.26 eV correspond to C _1s and O _1s , respectively. However, after self-assembly of titanium dioxide nanoparticles, the peaks of Ti 2p were observed at 454.9 and 460.3 eV for SM-5-titanium dioxide, indicating that organic PSMA chains were grafted from inorganic titanium dioxide.

To investigate the chemical state and electronic structure of Ti ⁴⁺ of the original titanium dioxide (P25) and SM-5-titanium dioxide, the Ti 2p region of the narrow scan XPS spectrum was measured. 10 shows a high-resolution XPS spectrum of the Ti 2p region of each sample. Ti 2p was measured to be 457.88 to 463.49 Ev for the original titanium dioxide (P25). The Ti 2p ₃ peak shifted from 457.88 eV of the original titanium dioxide to 458.48 eV in SM-5-titanium dioxide, and the content in Ti 2p ₁ as well as binding energy showed a similar trend. This is presumed to be because titanium dioxide is partially reduced by the formation of Ti ³⁺ on the surface of SM-5-titanium dioxide.

The present invention can provide a photocatalyst fixed membrane through self-assembly between -COOH groups of electrospun fibers and photocatalytic nanoparticles. The grafting conditions of the photocatalyst are determined by the content of PSMA. The photocatalyst chemically reacts on the surface of the PSMA/PVDF electrospun fiber, and as the content of PSMA increases, the amount increases. The photocatalytic activity properties of the immobilized photocatalytic membrane were confirmed by the dependence of the amount of photocatalyst on the decomposition of methylene blue.

Claims (5)

Electrospinning a solution containing nanofibers on a support to prepare a nonwoven fabric to which nanofibers are attached; and
Self-assembly of the photocatalyst on the nanofibers by immersing the support to which the nanofibers are attached in a photocatalyst suspension; The method of claim 1,
The photocatalyst is TiO ₂ , ZnO, Bi ₂ O ₃ , BaTiO ₃ , Fe ₂ O ₃ , V ₂ O ₅ , SnO ₂ , WO ₃ , Ga ₂ O ₃ , CuS, ZnS, CdS, CdSe, gC ₃ N ₄ A method of manufacturing any one type of photocatalytic filter selected from the group comprising: 3. The method of claim 2,
The method for manufacturing a photocatalytic filter wherein the support is a non-woven fabric. 4. The method of claim 3,
The nanofibers are polyvinylidene fluoride (PVDF), polyisosulfone (PES), polysulfone (PS), polyacrylonitrile (PAN), celerose acetate (CA) and poly(styrene-co-maleimide) , poly(styrene-acrylonitrile), poly(styrene-co-methylmethacrylate), poly(styrene-alt-maleic anhydride) (PSMA) of a photocatalytic filter comprising at least one selected from the group consisting of manufacturing method. 5. The method of claim 4,
The method of manufacturing a photocatalytic filter wherein the weight ratio of PVDF to PSMA is 9:1 to 5:5.

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