KR102586404B1 - Filter based on photocatalyst - Google Patents

Abstract

The present invention includes the steps of electrospinning a solution containing nanofibers on a support to produce a nonwoven fabric with nanofibers attached; and self-assembling the photocatalyst onto the nanofibers by immersing the support to which the nanofibers are attached in a photocatalyst suspension.

Description

Photocatalyst based filter{FILTER BASED ON PHOTOCATALYST}

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

To solve global problems related to energy and water shortages, rapid and energy-efficient water purification methods are required. Photocatalytic degradation using solar energy and semiconductor photocatalytic materials has received much attention for the removal of 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, with advantages such as high quantum yield, stability against photocorrosion, insolubility in water, low toxicity, and low cost. However, photocatalytic nanoparticles are prone to agglomeration to minimize surface energy during photocatalytic decomposition, resulting in reduced overall photocatalytic efficiency. Additionally, it is difficult to separate, recover, and recycle nanoparticles dispersed in solution after photocatalytic decomposition of harmful organic pollutants. In other words, the photocatalyst itself can become a pollutant, and considering the process to solve this problem, air and water purification using photocatalyst nanoparticles is not economical compared to existing methods.

To overcome these drawbacks of nanosized 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 because they do not require filtration devices 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, immobilized photocatalysts have the disadvantage of reduced decomposition efficiency mainly due to reduction of the reaction surface. Therefore, in immobilized photocatalyst technology, it is important to develop support materials and structures with high porosity, large specific surface area, as well as appropriate mechanical properties, thermal resistance, low density, chemical stability, low cost, abundance and high external mass transfer. .

Polymer materials are known for their flexibility, formability, toughness, cost-effectiveness and lightweight compared to metal-, ceramic- and carbon-based supports such as glass, alumina, quartz and stainless steel, activated carbon, carbon nanotubes, graphene and graphite. It 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 due to their 3D open structure, high porosity and large aspect ratio compared to porous materials, thick films and microsized fibers. It has been recognized as the most suitable support. These properties allow the photocatalyst to be fixed to the support at high density without agglomeration.

Various photocatalytic degradation studies based on electrospun polymer nanofibers containing semiconductor nanoparticles prepared by mixing the nanoparticles in a polymer solution for electrospinning have been reported, but these methods do not allow for the fraction of nanoparticles located on the surface of the nanofiber support. Because of the limitations, the advantages of electrospun nanofibers cannot be fully exploited. Recently, a different approach based on solvothermal processes has been studied to fully immobilize photocatalytic nanoparticles on the surface of electrospun polymer nanofiber supports. This method has the advantage of being able to place very small nanoparticles on the surface of the fiber, but there is a limit to the fraction of nanoparticles introduced, and due to the great flexibility of the nanofiber, there is a limitation that it can be re-fixed to another support.

Korean Patent No. 10-1641123

The present invention provides a new type of photocatalytic filter using an industrially viable method to overcome the above-described limitations of existing photocatalytic filters based on electrospun polymer nanofiber supports.

The filter of the present invention is composed of three layers including a photocatalyst, polymer nanofibers such as electrospun polyvinylidene fluoride (PVDF), and non-woven polyethylene terephthalate (PET) fabric. To manufacture the filter efficiently and economically, poly(styrene-alt-maleic anhydride (PSMA)) having a carboxyl group was first added to the PVDF solution as a self-assembly reactant. PSMA/PVDF nanofibers were synthesized by electrospinning this solution onto a non-woven PET fabric and then fixing it on the fabric by high-temperature compression to form a photocatalyst support that can solve the problems caused by the flexibility of nanofibers. did.

The present invention includes the steps of electrospinning a polymer solution on a support to produce a nonwoven fabric with attached nanofibers; and self-assembling the photocatalyst onto 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 containing.

The support may be a non-woven fabric.

The nanofibers include polyvinylidene fluoride (PVDF), polyisersulfone (PES), polysulfone (PS), polyacrylonitrile (PAN), cellulose acetate (CA) and poly(styrene-co-maleimide), It may include any one or more selected from the group including poly(styrene-acrylonitrile), poly(styrene-co-methyl methacrylate), poly(styrene-alt-maleic anhydride) (PSMA), etc.

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

The present invention can increase the specific surface area of the support using an electrospinning process and fix the photocatalyst to the support through self-assembly, making it possible to efficiently manufacture a filter in a short time.

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

Figure 1 is a schematic diagram showing a photocatalytic filter made of a support made of electrospun nanofibers and nonwoven fabric and a nano-sized photocatalyst.
Figure 2 is a schematic diagram showing the electrospinning process used in the present invention.
Figures 3A, B, and C show SEM images of electrospun fibers, and Figures 3D, E, and F show membranes self-assembled with a 2% titanium dioxide solution.
Figure 4 shows ATR-FTIR spectra of PVDF, PVDF/PSMA, and PVDF/PSMA-titanium dioxide self-assembled membranes.
Figure 5 is a diagram showing the TGA of SM-1-titanium dioxide, SM-3-titanium dioxide, and SM-5-titanium dioxide.
Figure 6 shows the absorption spectra of MB solutions when their photocatalytic properties were evaluated utilizing membranes with and without titanium dioxide at different times.
Figure 7 is a diagram showing the photocatalytic decomposition of MB in membranes with and without titanium dioxide.
Figure 8 is a diagram showing the color change of MB adsorbed on the SMT-5 membrane when exposed to light in the air.
Figure 9 shows the XPS spectrum results of SM-5 and self-assembled SM-5-titanium dioxide.
Figure 10 shows the XPS spectrum results 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 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 the photocatalyst and support, respectively. Polyvinylidene fluoride (PVDF, Mw=570,000), poly(styrene-alt-maleic anhydride) (PSMA, 13 wt% in H ₂ O), N,N-dimethylacetamide (DMAc, anhydrous, 99.8%), and acetone. (>99.5%) was purchased from Sigma Aldrich, and all reagents were of analytical grade and used as is without further purification.

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

The spun nanofibers on the nonwoven fabric were dried at 80°C in a drying box overnight. Hereinafter, the prepared samples are named SM-0, SM-1, SM-3, and SM-5, respectively, according to the ratio of PSMA to PVDF (0:10, 1:9, 3:7, and 5:5). do. Finally, titanium dioxide nanoparticles were self-assembled onto nanofibers by immersing the electrospun PVDF and PVDF/PSMA samples in 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 with self-assembled titanium dioxide nanoparticles 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 and titanium dioxide was not substantially self-assembled.

Before and after adding titanium dioxide nanoparticles, the microstructural characteristics 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 attenuated total reflection Fourier transform infrared spectrometry with a universal ATR sampling instrument (ATR-FTIR, PerkinElmer Spectrum One, USA). Spectra were collected at a spectral resolution ^{of 2 cm -1 in} the range of 4000 to 250 cm -1 using four scans. Several samples ^were analyzed using Binding energy was corrected.

The photocatalytic activity of the SMT-5 sample was observed by measuring the photodecomposition rate of methylene blue (MB). This was confirmed from the decolorization of MB during photocatalytic decomposition, based on the Beer-Lambert law, which indicates a linear relationship between absorbance and concentration of absorbing species. The experiments were performed using a solar simulator equipped with a 1 × 10 ^-5 M MB aqueous solution, 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°. Before 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 morphology of titanium dioxide before and after self-assembly was observed using FE-SEM. Figures 3A, B, and C show SEM images of electrospun fibers. The spun sample shows a well-formed fibrous structure with a smooth surface. Nanofibers are randomly oriented in a nonwoven form. The fiber diameter decreases with increasing PSMA concentration in the blend solution. The smaller the diameter of the fiber, the easier it is for PSMA to be exposed to the surface of the fiber. Figure 3D, E, and F show membranes self-assembled with 2% titanium dioxide solution at each PSMA content. Unlike before self-assembly, the fiber surface became rough. In fact, as the PSMA content increased, the surface roughness of the fibers increased. This means that as the amount of PSMA increases, more titanium dioxide exists on the fiber surface.

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 Figure 4.

The -CF ₂ and -CH ₂ stretching bands of PVDF appear at 1178 cm ^-1 and 1400 cm ^-1 , respectively. Meanwhile, 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 binding is the binding of the polymer peak below 800 cm ^-1 . It is shifted by a single broad absorption peaking at a lower frequency. Due to the various Ti-O vibration modes, the region may contain overlapping peaks. As a result, it was confirmed that when these PVDF/PSMA blend membranes were immersed in a titanium dioxide nanoparticle solution for a certain period of time, 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 did not show a clear weight loss from room temperature to 700°C. However, the self-assembled membrane with titanium dioxide showed a weight loss pattern, as shown in Figure 5. In addition, it can be seen that the amount of self-assembled TiO ₂ increases through a weight change that decreases as the added PSMA concentration increases. The compositions of SM-1, SM-3, and SM-5 in Figure 5 are shown in Table 1 below. In Table 1, the unit of each component is wt%, which is the weight ratio with respect to the total of 100% by weight of DMAc and acetone.

In the case of nonwoven fabric, it is composed of PE and PP and has endothermic peaks at 130℃ and 165℃, 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. Weight loss occurs between 370°C and 430°C due to loss of PVDF/nonwoven polymer chains. As a result, 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 decomposition of MB under visible light irradiation. Figure 6 shows the absorption spectra of MB solutions when their photocatalytic properties were evaluated utilizing membranes with and without titanium dioxide at different times. In Figure 6, Blank represents the change in concentration of the MB solution over time when light is irradiated to the MB solution without a photocatalytic filter, and NWF represents the concentration of the MB solution when a non-woven fabric containing no titanium dioxide is used. represents change. In SMT-0, titanium dioxide does not self-assemble, so only non-woven fabric and polymer nanofibers exist. The time-dependent UV-vis absorption spectrum of the MB solution shows that the maximum absorption at 664 nm decreases significantly after 60 minutes of irradiation.

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

In general, the degradation of dyes can follow pseudo-first-order kinetics 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 linear analysis of the data shown in Figure 7. The constant k value of 0.05 g of P25 is 0.6960, and the k value of the prepared sample SM-5-titanium dioxide membrane is 0.0343. As a result, 0.0025 g of titanium dioxide nanoparticles are fixed on the surface of a membrane measuring approximately 2.5 cm * 3 cm. Figure 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 MB adsorbed on the photocatalyst filter decomposes depending on the time exposed to light.

As shown in Figures 9 and 10, X-ray photoelectron spectroscopy (XPS) was performed to more clearly measure the interactions between components. Wide-scan XPS spectra spanning a low-resolution to large energy range were measured to identify the elements present in the grafted titanium dioxide nanoparticles. 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⁺ in pristine titanium dioxide (P25) and SM-5-titanium dioxide, the Ti 2p region of the narrow scan XPS spectrum was measured. Figure 10 shows high-resolution XPS spectra 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 moved from 457.88 eV of the original titanium dioxide to 458.48 eV in SM-5-titanium dioxide, and not only the binding energy but also the content of Ti 2p ₁ 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 anchoring membrane through self-assembly between -COOH groups of electrospun fibers and photocatalyst nanoparticles. The grafting conditions of the photocatalyst are determined by the content of PSMA. The photocatalyst reacts chemically on the surface of the PSMA/PVDF electrospun fiber, and as the PSMA content increases, the amount increases. The photocatalytic activity properties of the immobilized photocatalytic membrane were confirmed by the dependence of the decomposition of methylene blue on the amount of photocatalyst.

Claims (5)

Producing a nonwoven fabric with nanofibers attached by electrospinning a solution containing nanofibers on a support; and
A step of self-assembling the photocatalyst onto the nanofibers by immersing the support to which the nanofibers are attached in a photocatalyst suspension,
The nanofibers include polyvinylidene fluoride (PVDF) and poly(styrene-alt-maleic anhydride) (PSMA), the weight ratio of PVDF to PSMA is 5:5, and the photocatalyst is TiO _2. Manufacturing method. delete According to claim 1,
A method of manufacturing a photocatalytic filter wherein the support is a non-woven fabric. delete delete