Method for producing palladium-gold-silver trimetallic hybrid nanostructure and hybrid nanostructure produced thereby

Abstract

The present invention relates to a method for producing a palladium-gold-silver trimetallic hybrid nanostructure, which comprises a step of growing nanocrystals containing gold (Au) and silver (Ag) on a seed made of palladium (Pd) nanocrystals through a seed-mediated growth method, and to a hybrid nanostructure produced thereby. According to the present invention, it is possible to synthesize a palladium-gold-silver (Pd-AuAg) trimetallic hybrid nanostructure by growing nanocrystals containing gold (Au) and silver (Ag) having plasmonic properties on a specific location, not the entire surface, of a seed made of palladium (Pd) nanocrystals having high catalytic activity. In particular, by controlling the concentrations of gold (Au) precursors and silver (Ag) precursors during the seed-mediated growth process, it is possible to successfully synthesize Pd-AuAg trimetallic nanohybrid materials with various heterogeneous structures, such as octapod-like, bumpy, and Janus structures.

Description

Method for manufacturing palladium-gold-silver trimetallic hybrid nanostructure and hybrid nanostructure manufactured thereby

[0001] The present invention relates to a method for manufacturing a hybrid nanostructure in which two or more types of metals are combined, and to a hybrid nanostructure manufactured thereby, and more specifically, to a method for manufacturing a palladium-gold-silver (Pd-AuAg) trimetallic hybrid nanostructure capable of controlling the heterogeneous nanostructure of the manufactured hybrid nanostructure, and to a hybrid nanostructure manufactured thereby.

[0002] Precious metal nanoparticles have been effectively utilized as catalyst materials in various reactions, such as hydrogenation, chemical reaction improvement, and organic material synthesis, in the fields of chemistry, medicine, and the environment due to their high activity, selectivity, and chemical stability.

[0003] In particular, noble metal hybrid nanostructures composed of two or more types of metals rather than a single component are attracting attention as promising materials for highly active catalysts because they exhibit synergetic effects that surpass the physical / chemical properties of each component.

[0004] Meanwhile, among chemical synthesis methods that can mass-produce noble metal nanoparticles with uniform size and shape at relatively low cost, seed-mediated growth is a powerful and effective method for producing hybrid nanostructures with controllable heterogeneous nanostructures.

[0005] However, the development of a synthetic method that can grow other metal components at specific and controlled locations rather than on the entire surface of a nano-substrate composed of one of two or more metals still faces many challenges.

[0006] The technical problem to be solved by the present invention is to provide a method for synthesizing a palladium-gold-silver (Pd-AuAg) trimetallic hybrid nanostructure by using a palladium (Pd) nanocrystal having high catalytic activity as a seed and growing nanocrystals composed of gold (Au) and silver (Ag) having plasmonic properties at a specific location on the surface of the palladium (Pd) seed, and a Pd-AuAg trimetallic hybrid nanostructure manufactured thereby.

[0007] In order to achieve the above technical task, the present invention proposes a method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure, which comprises the step of growing nanocrystals containing gold (Au) and silver (Ag) on ​​a seed made of palladium (Pd) nanocrystals through a seed-mediated growth method, but growing the nanocrystals containing gold (Au) and silver (Ag) at a specific location rather than the entire surface of the seed.

[0008] At this time, the seed made of the palladium (Pd) nanocrystals may have a shape such as a nanocube, nanoplate, nanorod, etc., but is not necessarily limited to these.

[0009] Preferably, the method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure according to the present invention is characterized by reacting a solution containing palladium (Pd) nanocubes and a reducing agent with a solution containing a gold (Au) precursor and a silver (Ag) precursor to grow island-structured nanocrystals containing gold (Au) and silver (Ag) on ​​palladium (Pd) nanocubes.

[0010] At this time, by controlling the concentration of the solution containing the gold (Au) precursor and the silver (Ag) precursor, the position at which the island-structured nanocrystals grow can be controlled, thereby manufacturing a hybrid nanostructure having different heterogeneous nanostructures.

[0011] For example, by growing island-structured nanocrystals containing gold (Au) and silver (Ag) at each edge of the palladium (Pd) nanocube, a palladium-gold-silver trimetallic hybrid nanostructure with an octapod-like structure can be synthesized.

[0012] In addition, a palladium-gold-silver trimetallic hybrid nanostructure with a bumpy structure can be synthesized by growing island-structured nanocrystals on each edge and each face of the palladium (Pd) nanocube.

[0013] A Janus-structured palladium-gold-silver trimetallic hybrid nanostructure can be synthesized by overgrowing island-structured nanocrystals on a specific surface of the above palladium (Pd) nanocube.

[0014] Meanwhile, the gold (Au) precursor may be chloroauric acid (HAuCl4), the silver (Ag) precursor may be silver nitrate (AgNO3), and the reducing agent may be polyvinylpyrrolidone (PVP), but is not necessarily limited to these, and other known gold (Au) precursors, silver (Ag) precursors, and reducing agents may be used as long as they are suitable for the purpose to be achieved through the present invention.

[0015] And, in another aspect of the present invention, the present invention proposes a palladium-gold-silver trimetallic hybrid nanostructure manufactured according to the above method.

[0016] Furthermore, in another aspect of the present invention, the present invention proposes a heterogeneous catalyst that can be applied to a continuous flow chemical reaction, such as a reduction reaction of Cr(VI) ions to Cr(III) ions in an aqueous solution, as a catalyst composed of a hydrogel impregnated with the palladium-gold-silver trimetallic hybrid nanostructure.

[0017] According to the present invention, a palladium-gold-silver (Pd-AuAg) trimetallic hybrid nanostructure can be synthesized by growing nanocrystals composed of gold (Au) and silver (Ag) having plasmonic properties at specific locations on the surface of a seed composed of palladium (Pd) nanocrystals having high catalytic activity, and in particular, by controlling the concentrations of gold (Au) precursors and silver (Ag) precursors during the seed-mediated growth process, a Pd-AuAg trimetallic nanohybrid material having various heterogeneous structures such as an octapod-like, bumpy, and Janus structure can be successfully synthesized.

[0018] In addition, the Pd-AuAg trimetallic hybrid nanocomposite manufactured according to the present invention exhibits high catalytic activity as a catalyst in a reaction of chemical reduction of toxic Cr(VI) ions into relatively less toxic Cr(III) ions in an aqueous solution, and in particular, the Pd-AuAg trimetallic nanohybrid having a bumpy structure in which nanocrystals composed of Au-Ag alloys grow on various parts of the surface of palladium nanocrystal seeds, exhibits the best catalytic activity due to its high surface roughness.

[0019] In addition, the catalyst manufactured by impregnating the Pd-AuAg tripolar hybrid nanocomposite manufactured according to the present invention into a biopolymer-based hydrogel exhibits high activity and stability even in continuous flow catalysis, and shows long-term durability and reliability with no significant decrease in catalytic activity even when stored at room temperature for a long time in a dried state and then restored by swelling.

[0020] (a) TEM image and (b)-(c) HR-TEM images of Fig. 1 show the Pd nanocube used as a seed in the present example, and (d) TEM image, (e)-(f) HR-TEM images and (g) elemental mapping image show the Pd-AuAg hybrid nanostructure with an octapod-like structure manufactured in the present example.

[0021] The (a) TEM image, (b)-(c) HR-TEM images and (d) elemental mapping images of FIG. 2 show the Pd-AuAg hybrid nanostructure with a bumpy surface structure manufactured in the present example according to the present invention.

[0022] (a) TEM image, (b)-(c) HR-TEM images, and (d) elemental mapping image of FIG. 3 show the Janus-structured Pd-AuAg hybrid nanostructure manufactured in the present example.

[0023] Figure 4 schematically shows the structural change according to experimental conditions of a Pd-AuAg hybrid nanostructure that can be synthesized by the method according to the present invention.

[0024] Figure 5(a) is a UV-Vis absorption spectrum recorded at 5-minute intervals for the catalytic reduction reaction of Cr(VI) to Cr(III) in the presence of Pd-AuAg hybrid nanostructures with a bumpy structure, and Figure 5(b) is a (C0-C) spectrum for the catalytic reduction reaction of Cr(VI) to Cr(III) in the presence of Pd nanocubes and Pd-AuAg hybrid nanostructures with different heterostructures, respectively. t ) / C0(C t is the concentration of Cr(VI) at time t and C0 is the initial concentration of Cr(VI)) as a function of reaction time (t).

[0025] FIG. 6(a) is a schematic diagram of a synthesis process of a nanocomposite hydrogel material impregnated with a bumpy-structured Pd-AuAg hybrid nanostructure synthesized by the present invention, and FIG. 6(b) is a schematic diagram showing the use of a continuous flow reactor for a reaction of chemical reduction of Cr(VI) to Cr(III) in an aqueous solution using the synthesized nanocomposite hydrogel material.

[0026] Figures 7(a) to 7(d) show the results of measuring the catalytic activity according to the alginate (Alg) content, catalyst (Pd-AuAg hybrid nanocomposite) content, graphene oxide (GO) content, and flow rate contained in the nanocomposite hydrogel for the reduction reaction of Cr(VI) to Cr(III).

[0027] Figure 8(a) shows the results of measuring the change in catalytic activity according to the number of times the nanocomposite hydrogel material was repeatedly used in a continuous flow reactor for a chemical reduction reaction from Cr(VI) to Cr(III) in an aqueous solution, and Figure 8(b) shows the results of measuring the change in catalytic activity of the nanocomposite hydrogel material according to the reaction time.

[0028] Figure 9 shows the results of measuring the catalytic activity for the reduction reaction of Cr(VI) to Cr(III) of a nanocomposite hydrogel that was dried at room temperature, aged for a certain period of time (2 weeks or 4 weeks), and then restored by swelling with water, and a nanocomposite hydrogel (fresh sample) that was not subjected to the drying and aging process.

[0029] In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0030] Embodiments according to the concept of the present invention may be subject to various modifications and take various forms. Therefore, specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit embodiments according to the concept of the present invention to specific disclosed forms, and it should be understood that all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention are included.

[0031] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprises" or "has" indicate the presence of a described feature, number, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0032] Hereinafter, the present invention will be described in more detail by way of an example.

[0033] The embodiments described herein may be modified in various ways, and the scope of this specification is not to be construed as limited to the embodiments described below. The embodiments described herein are provided to more fully explain this specification to those of ordinary skill in the art.

[0034] <Example>

[0035] 1. Synthesis of palladium (Pd) nanocubes

[0036] Deionized water (DI water) (8 mL) was added to a 20 mL glass vial containing 100 mg of polyvinylpyrrolidone (PVP; Mw ∼ 55 kDa), 900 mg of potassium bromide (KBr), and 60 mg of ascorbic acid (AA), and the vial was heated at 85 °C with stirring for 10 min. The palladium (Pd) precursor was prepared by dissolving 57 mg of sodium tetrachloride (Na2PdCl4) in 3 mL of deionized water, and the palladium precursor aqueous solution was then injected into the first vial using a glass pipette, and the mixture was reacted at 85 °C for 3 h. Palladium nanocubes were collected by centrifugation at 13,000 rpm for 30 min and washed three times with deionized water.

[0037] 2. Synthesis of trimetallic Pd-AuAg hybrid nanostructures

[0038] Pd-AuAg nanostructures were obtained by reacting Pd nanocube seeds with different contents of gold (Au) precursor and silver (Ag) precursor mixed solutions. First, PVP (Mw ∼ 55 kDa, 300 mg) was dissolved in 5 mL of deionized water. The Pd nanocube seed solution (0.197 mg in 10 μL) was added to the PVP aqueous solution, and the resulting mixture was heated in an oil bath at 100 °C for 10 min. A mixed solution (0.1 mL) of aqueous chloroauric acid (HAuCl4) and aqueous silver nitrate (AgNO3) solutions having the same molar ratio and a final concentration of 20 mM was added using a syringe pump at 10 mL h -1The resulting Pd nanocube seed solution was injected at a flow rate of 13,000 rpm and reacted at 100°C for 2 h. The product was centrifuged at 13,000 rpm for 8 min and washed three times with deionized water to obtain trimetallic octapod-like Pd-AuAg hybrid nanostructures. Pd-AuAg hybrid nanostructures with different heterostructures, i.e., bumpy Pd-AuAg hybrid nanostructures and Janus Pd-AuAg hybrid nanostructures, were synthesized by changing the amounts of Au and Ag precursor mixture solutions to 0.15 mL and 0.4 mL, respectively.

[0039] 3. Synthesis of Alg / GO hydrogel embedded with Pd-AuAg hybrid nanostructures

[0040] Ten mg of graphene oxide (GO) was dissolved in 2.5 mL of deionized water under ultrasonic treatment. The synthesized Pd-AuAg hybrid nanostructures (0.8 mg in 500 mL) were added to the GO aqueous solution, followed by the addition of an aqueous solution of sodium alginate (Na-Alg) (75 mg in 3 mL), and the resulting mixture was freeze-dried for 24 h. The freeze-dried sample was immersed in calcium chloride (CaCl2) (5 wt%, 6 mL) for 12 h to cross-link Alg, and then washed three times with deionized water.

[0041] 4. Catalytic reduction of hexavalent chromium

[0042] To investigate the most optimal nanostructure for the catalytic reduction of Cr(VI), a batch reaction was performed in a cuvette. 2 mL of aqueous potassium dichromate (K2Cr2O7) solution was added to a vial containing 80 mg of Pd-AuAg nanocatalyst particles and 100 mL of formic acid (25 M). The reduction of Cr(VI) to Cr(III) in the presence of nanocatalysts and formic acid was monitored by evaluating the absorbance peak of Cr(VI) at 350 nm every 5 min using a UV-Vis spectrophotometer. The catalytic reduction was controlled by the fundamental parameter C t / C0(C t where C0 is the initial concentration of Cr(VI) and C0 is the concentration of Cr(VI) at a specific time t. To investigate the catalytic performance and stability of the Alg / GO / Pd-AuAg nanocomposite hydrogel in a continuous flow reaction, the nanocomposite hydrogel was placed inside a 6 mL disposable syringe (HSW Normject), and then 4 mL of potassium dichromate (K2Cr2O7) aqueous solution (0.3 mM) and 200 mL of formic acid (25 M) were added to the syringe containing the nanocomposite hydrogel, and the syringe was connected to a syringe pump. The flow rate of the syringe pump was 5 mL h -1 was set to . The concentration of the reduced Cr(VI) solution was measured after the solution dripped from the syringe and the syringe was emptied. After the catalytic reduction process, the nanocomposite hydrogel was washed three times with deionized water and dried in an oven for 1 h before being used in another cycle.

[0043] <Experimental Example>

[0044] The synthesis of Pd nanocubes was performed in an aqueous solution using polyvinylpyrrolidone (PVP) as a stabilizer and potassium bromide (KBr) as a capping agent. The Pd metal precursor was reduced with ascorbic acid (AA), a safe and easy-to-handle reducing agent, and the reaction solution was heated at 85°C for 3 h. The resulting Pd nanocubes were uniform in size and shape and were obtained in high yield (Fig. 1(a)). The size of the synthesized Pd nanocubes was measured to be approximately 24±2 nm. In the synthesis of Pd nanocubes, KBr was used as a Br - Br plays an important role in the synthesis of Pd nanocubes because ions are selectively chemically adsorbed on the {100} facet of Pd nanocrystals, thereby changing the surface free energy of the other facets. - Oxidative etching by ions also occurred selectively along the {100} planes of Pd, leading to anisotropic growth of Pd nanoparticles. HR-TEM analysis results showed that the Pd nanocubes exhibited a distinct single-crystal structure (Fig. 1(b) and Fig. 1(c)). The interplanar distance along the {100} planes of Pd, which has a face-centered cubic (FCC) structure, was found to be approximately 0.2 nm. The Pd nanocubes shown in Fig. 1(a) were used as seeds and Au was grown in an aqueous solution with PVP. 3+ and Ag + Seeds of Au and Ag were grown on Pd nanocubes by chemical reduction of ions. At this time, Au for PVP 3+ and Ag +The molar ratio of ions was maintained at 22.5 and the synthesis was performed at 100°C. The TEM image (Fig. 1(d)) of the synthesized hybrid nanostructure shows a morphology that is clearly different from the conventional core-shell structure. Specifically, rather than a uniform shell being formed over the entire surface of the Pd nanocube, a nanoisland is formed at the edge of a single Pd nanocube, forming an octapod-shaped structure. HR-TEM and STEM analyses were performed to characterize the crystallographic structure of the nanoisland and determine the chemical composition of the hybrid nanostructure. According to the HR-TEM images (Fig. 1(e) and 1(f)), a single-crystal arrangement with an interplanar distance (d-spacing) of 0.23 nm is observed in the nanoisland. This arrangement is attributed to the {111} planes of Au and Ag in a face-centered cubic (FCC) structure. Elemental mapping data within individual Pd-AuAg hybrid nanoplates show that Au is predominantly detected in the nanoislands, while Ag is distributed on the nanoislands and the Pd basal face (Fig. 1(g)). These results demonstrate that Au and Ag grow from Pd nanocube seeds in different modes.

[0045] During seed-mediated growth, two growth modes can occur: island growth and layer-by-layer growth, depending on the lattice match between the substrate and overgrowth materials and the synthesis conditions. When the reduction reaction proceeds rapidly, there is insufficient time for the deposited atoms to migrate across the entire seed surface to form a single, large grain. Instead, they form islands on the seed surface. Conversely, when the deposition rate is low, layer-by-layer growth dominates over island growth.

[0046] Au by PVP in the presence of Pd nanocube seeds 3+ and Ag +In a system where ions are simultaneously reduced, the deposition rate of Au atoms is expected to be faster than that of Ag atoms due to the difference in reduction potential. Ag + The standard reduction potential of / Ag is 0.8 V versus the standard hydrogen electrode (SHE) of AuCl4 - / Au (1.0 V vs. SHE). Therefore, due to the reaction (1) below, the reduced Ag atoms are rapidly oxidized and Au 3+ The ions can be further reduced without the action of a reducing agent (PVP).

[0047]

[0048] As a result, the deposition rate of Au atoms is significantly higher and follows an island growth mode. The surface energy is high and the colloidal stabilizer (PVP) and capping agent (Br - The edge sites of Pd nanocubes loosely capped by Ag ions serve as the primary sites for Au island formation. In contrast, the deposition rate of Ag atoms is relatively low, and a layer-by-layer growth mode is preferred. Despite using the same molar ratio of Ag and Au precursors in the seed-mediated growth process, the Pd / Au / Ag atomic ratio of the Pd-AuAg hybrid nanostructures was found to be approximately 50:40:10, confirming a higher deposition rate of Au compared to Ag.

[0049] Through the present invention, Ag + The presence of ions was found to have a strong influence on the structure of the resulting hybrid nanostructures. According to the TEM image (not shown) of the hybrid nanostructures synthesized through the same seed-mediated growth reaction as in the above example, with only the addition of the Au precursor (HAuCl4) without the Ag precursor (AgNO3), Ag + When the reaction was performed in the absence of ions, Au islands of various sizes irregularly formed on the Pd cube seeds could be clearly observed. During the synthesis of Au nanocrystals, Ag +Inclusion of ions is known to control the development of Au nanocrystals by altering the growth reaction rate through underpotential deposition (UPD) as described above. In addition, Ag + It has been reported that Ag ions suppress the anisotropic growth of Au crystals during the growth of Au nanocrystals. Therefore, Ag + In the presence of ions, a large number of small nanoislands can grow on the surface and edges of Pd nanocubes.

[0050] In particular, the morphology of the Pd-AuAg hybrid nanostructures synthesized using Pd nanocubes as seeds can be changed by varying the concentrations of the Au and Ag precursors during the seed growth process. Increasing the concentrations of the Au and Ag precursors by a factor of 1.5 increases the size of the islands at the edges of the Pd nanocubes and forms islands on the surface of the Pd nanocubes, resulting in bumpy Pd-AuAg hybrid nanostructures with enhanced nanoscale roughness (Fig. 2(a)). HR-TEM analysis results show that the interplanar distance (d-spacing) of 0.23 nm corresponding to the {111} planes of FCC Au and Ag is observed in the nanoisland region (Figs. 2(b) and 2(c)), indicating that the crystallinity of the nanoislands is different from that of the Pd nanocube seeds. The STEM-EDS elemental mapping analysis results are almost identical to those in Fig. 1, with Au observed primarily in the islands and Ag distributed on the islands and the Pd basal plane (Fig. 2(d)). Furthermore, the hybrid nanostructure was found to have an atomic ratio of approximately 45:46:9 for Pd, Au, and Ag, respectively.

[0051] A fourfold increase in the concentration of Au and Ag precursors resulted in the Pd-AuAg hybrid nanostructures shown in Fig. 3(a). Based on the HR-TEM and elemental mapping analyses in Figs. 3(b) to 3(d), respectively, the overgrowth behavior of Au and Ag in the Pd nanocubes remained unchanged. That is, Au was primarily found in islands, and Ag was distributed on the islands and the Pd basal plane. However, Au overgrowth proceeded only at a single site in each Pd nanocube, resulting in mushroom-shaped Janus nanostructures. This multi-site to single-site transition growth has been previously observed for Au overgrowth on Pd nanorods or Pd nanocubes, and Ostwald ripening induced by the size difference of the Au nanoislands has been proposed as a mechanism explaining this phenomenon. The atomic ratios of Pd, Au, and Ag in the Janus hybrid nanostructures were determined to be 33:58:9, respectively.

[0052] Since the localized surface plasmon resonance (LSPR) characteristics of noble metal nanocrystals are sensitive to morphology and composition, extinction spectra of Pd-AuAg hybrid nanostructures were obtained. After overgrowth of Au and Ag on Pd nanocubes, a strong absorption peak was observed at 510–535 nm, whereas the spectrum of Pd nanocubes did not exhibit strong surface plasmon resonance (SPR) absorption in the visible and near-infrared (NIR) region. Since the peak value is similar to that reported for AuAg hybrid nanoparticles with high Au composition in the same size range, the peak is related to the LSPR peak of the deposited AuAg nanoislands. Reflecting the size sensitivity of the LSPR peak of the AuAg nanoislands, the peak slightly red-shifted as the hybrid nanostructures evolved from an octapod-like structure to a Janus-like structure.

[0053] According to the XRD patterns of the Pd nanocubes and Pd-AuAg trimetallic hybrid nanostructures, strong peaks were observed at 40.2°, 46.7°, and 68.2°, which were assigned to the {111}, {200}, and {220} planes of FCC Pd, respectively (JCPDS no. 05-0681). After the overgrowth of Au and Ag, in addition to the peaks of Pd, new strong peaks appeared at 38.3°, 44.6°, and 64.5°, which may be attributed to the reflections of the {111}, {200}, and {220} planes of typical FCC Au and Ag (JCPDS 04-0784 and JCPDS 04-0783). Since Au and Ag have the same FCC crystal structure and similar lattice constants, the peaks overlap extensively in the XRD patterns of the Pd-AuAg trimetallic hybrid nanostructures. As the hybrid nanostructures evolved from an octapod-like structure to a Janus-like structure, the intensities of the peaks associated with FCC Au and Ag slightly increased, reflecting the increased incorporation ratio of Au and Ag. The morphological evolution by seed growth of AuAg on Pd nanocube seeds is schematically illustrated in Figure 4.

[0054] Pd nanocrystals were demonstrated to function as highly efficient catalysts for the reduction of Cr(VI) to Cr(III) in the presence of formic acid (HCOOH). According to the proposed mechanism, the reduction of Cr(VI) to Cr(III) in the presence of Pd nanocrystals and formic acid (HCOOH) occurs via the dehydrogenation of HCOOH to produce H2 and CO2 as follows.

[0055]

[0056] It is believed that H2 molecules generated by dehydrogenation of HCOOH are adsorbed on the surface of Pd nanocatalysts and promote the reduction of Cr(VI) to Cr(III) through the H2 transfer pathway.

[0057]

[0058] The absorption spectrum of Cr(VI) in aqueous solution shows a distinct peak at 350 nm (Fig. 5(a)). When the reduction reaction was carried out in the presence of a catalyst, the peak intensity gradually decreased with increasing reaction time. When the conversion of Cr(VI) to Cr(III) was completed, the peak at 350 nm almost completely disappeared. The catalytic conversion was determined by the basic parameter C t / C0(C t is the concentration of Cr(VI) at a specific time t and C0 is the initial concentration of Cr(VI).

[0059] To evaluate the activity of Pd-AuAg hybrid nanostructures as catalysts for the reduction of Cr(VI), a series of experiments were performed in the same manner using different types of Pd-AuAg hybrid nanostructures as catalysts in batch reactions. As shown in Fig. 5(b), the bumpy Pd-AuAg hybrid nanostructures exhibited the highest catalytic activity, completely reducing Cr(VI) in 15 min. The Janus- and octapod-like Pd-AuAg hybrid nanostructures took 20 and 25 min, respectively, to completely reduce Cr(VI). When pure Pd nanocubes were used, only 64% of Cr(VI) was reduced within 25 min. These results clearly demonstrate that the Pd-AuAg hybrid nanostructures synthesized in the examples of the present invention exhibit high catalytic activity due to the synergistic interaction between metals in the Pd / Au / Ag trimetallic alloy structure. AuAg nanoislands grown on Pd nanocubes can increase the surface area of ​​the nanocubes, promote the dehydrogenation of formic acid, and enhance electron transfer. Among the hybrid nanostructures, the one with a rough structure exhibited the highest catalytic activity, which may be due to its enhanced catalytic performance compared to other hybrid nanostructures with relatively smooth surfaces due to its complex secondary geometry and high nanoscale roughness.

[0060] For quantitative comparison of catalytic activity, ln(C t / C0) vs. t plotted showed a linear relationship. These results indicate that the catalytic reduction of Cr(VI) follows the pseudo-first-order kinetic equation ln(C t / C0) = K app t (where K appis the apparent rate constant. K of the bumpy Pd-AuAg hybrid nanostructure app Silver 0.167 min -1 was determined to be Pd nanocubes (0.039 min -1 ), octapod-type Pd-AuAg hybrid nanostructure (0.069 min -1 ) and Janus Pd-AuAg hybrid nanostructures (0.109 min -1 ) is higher than that of the rugged Pd-AuAg hybrid nanostructures prepared in this example. The catalytic activity of the rugged Pd-AuAg hybrid nanostructures prepared in this example was compared with that of previously reported noble metal-based heterogeneous catalysts. For easy comparison, K app The activity parameter k was introduced by dividing the total weight of the catalyst used in the reaction. The k value of the bumpy Pd-AuAg hybrid nanostructure was 0.202 mg -1 min -1 was calculated as , which is in line with the previously reported values ​​of heterogeneous catalysts (0.00017 ~ 0.185 mg -1 min -1 ) was found to be higher.

[0061] Due to the high surface energy of metal nanocrystals, they tend to aggregate easily, and their small size makes them difficult to separate and reuse. To address these issues, it was necessary to immobilize the metal nanocrystals on a solid support to utilize them as catalysts and maintain and optimize their sustainability. Hydrogels are polymer networks that can retain a large amount of water and, when swollen, possess a high specific surface area and interconnected pores. These characteristics make hydrogels suitable as catalyst support materials, as reactive molecules in water can easily diffuse through the hydrogel surface and interact with the catalyst within the hydrogel. In this example, an Alg / GO hydrogel embedded with the synthesized bumpy Pd-AuAg hybrid nanostructures was prepared and used as a heterogeneous catalyst in a flow reaction. Specifically, Na-Alg, GO, and Pd-AuAg hybrid nanostructures were uniformly mixed in deionized water, moisture in the mixture was removed by freeze-drying, the freeze-dried sample was immersed in calcium chloride (CaCl2) to cross-link the Alg chains, and then washed with deionized water to prepare an Alg / GO hydrogel containing bumpy Pd-AuAg hybrid nanostructures (Fig. 6(a)).

[0062] The FT-IR spectrum of the nanocomposite hydrogel was compared with the spectra of pure Ca-Alg hydrogel and pure GO. The FT-IR spectrum of the Ca-Alg hydrogel had a peak at 3296 cm -1 , which is attributed to the stretching vibration of the OH bond. Another notable spectral feature is the peak at 1590 and 1415 cm -1 There is a peak at 1024 cm, which represents the asymmetric and symmetric stretching vibrations of -COO-, respectively. -1 The peak observed in is due to the stretching vibration of the CO bond present in the hydrogel. The FT-IR spectrum of GO has a peak at 3292 cm-1 OH elastic vibration at 1713 cm -1 C=O vibration at 1589 cm -1 C=C elastic vibration, 1038 cm -1 It showed several peaks including alkoxy CO vibrations. The FT-IR spectrum of the nanocomposite hydrogel showed a combination of absorption bands of both Ca-Alg hydrogel and GO, confirming the presence of both components in the nanocomposite hydrogel.

[0063] The catalytic reduction of Cr(VI) was performed as follows. An aqueous solution containing potassium dichromate (K2Cr2O7) and formic acid, which was injected into a syringe containing a nanocomposite hydrogel, flowed through the syringe and penetrated into the nanocomposite hydrogel through the action of a syringe pump. The reduction of Cr(VI) was promoted by the catalytic reaction of the Pd-AuAg hybrid nanostructures incorporated into the hydrogel. The aqueous solution containing Cr(III) converted from Cr(VI) flowed out of the tube. A schematic diagram of the continuous flow reactor system for the reduction of Cr(VI) to Cr(III) is shown in Fig. 6(b).

[0064] To optimize the catalytic activity of a heterogeneous catalyst based on nanocomposite hydrogels in a continuous flow catalysis for the reduction of Cr(VI), we first investigated the effect of Alg content. In nanocomposite hydrogels, the crosslinking density of the hydrogel is related to the amount of Alg. An increase in crosslinking density leads to a decrease in porosity, which hinders the diffusion and transport of water molecules within and across the hydrogel network, ultimately resulting in a decrease in catalytic activity. However, a low crosslinking density weakens the hydrogel and causes it to collapse during the catalytic reaction. To balance the catalytic activity and maintain the mechanical strength of the one-dimensional nanocomposite hydrogel, the Alg content was set to 75 mg (Fig. 7(a)). In addition, the effect of the content of the rugged Pd-AuAg hybrid nanostructures used in the synthesis of the nanocomposite hydrogel was investigated. As shown in Fig. 7(b), the conversion of Cr(VI) to Cr(III) in the flow reaction gradually increased as the content of Pd-AuAg hybrid nanostructures in the nanocomposite hydrogel increased. When the content of Pd-AuAg hybrid nanostructures exceeded 0.8 mg, the catalytic conversion of Cr(VI) was almost completed, indicating that the optimal result was obtained when the content of Pd-AuAg hybrid nanostructures in the nanocomposite hydrogel was 0.8 mg. Fig. 7(c) shows that the conversion of Cr(VI) in the flow reaction also increased as the content of GO in the nanocomposite hydrogel increased. However, when the amount of GO was more than 10 mg, the improvement in catalytic performance was not significant. As can be seen in Fig. 7(d), the flow rate of the reaction solution in the reactor was 15 mL h -1 2.5 mL h in -1 As the flow rate is lowered, the residence time of the reactants in the reactor gradually increases. The diffusion of the reactants into the hydrogel is enhanced, and the accessibility of the catalyst is maximized, thereby improving the catalytic activity. Considering the catalytic performance and reaction efficiency including the reaction time, the flow rate is set to 5 mL h -1 was set to .

[0065] Under optimized reaction conditions, the nanocomposite hydrogel exhibited excellent catalytic activity, reaching a Cr(VI) conversion of close to 98% in a flow reaction. Even in a cyclic experiment using 4 mL of aqueous reaction solution repeatedly, the catalytic activity only slightly decreased over four cycles (Fig. 8(a)). The conversion by the nanocomposite hydrogel can be assumed to be a combination of Cr(VI) uptake into the hydrogel matrix and catalytic reduction to Cr(III). To confirm the contribution of Cr(VI) uptake by the nanocomposite hydrogel, the Cr(VI) removal process was performed using a hydrogel without the Pd-AuAg hybrid nanostructures. In the absence of the Pd-AuAg hybrid nanostructures, the Cr(VI) removal efficiency was found to be less than 25% and gradually decreased as the number of experimental cycles increased (Fig. 8(a)). These experimental results demonstrate that the nanocomposite hydrogel-based heterogeneous catalyst can efficiently absorb Cr(VI) ions from an aqueous solution into the hydrogel and convert almost all of the Cr(VI) ions into Cr(III) ions through the catalytic action of the Pd-AuAg hybrid nanostructures present within the hydrogel. It should be noted that the catalytic reaction system proposed in this example is sensitive to changes in the pH of the reaction solution because formic acid was used as a reducing agent. According to the inventors' study, the catalytic activity gradually decreased as the pH of the reaction mixture increased above 3, but the presence of common anions (e.g., nitrate, sulfate, and chloride) or organic compounds such as 4-nitrophenol (4-NP) did not significantly affect the catalytic activity.

[0066] The ability of a catalyst to achieve long-term stability without substantial loss of catalytic activity is one of the most important factors in assessing practical efficiency. Using a nanocomposite hydrogel-based heterogeneous catalyst, catalytic performance was evaluated through continuous catalytic reactions over time. As shown in Figure 8(b), the Cr(VI) conversion rate did not substantially decrease even after 10 hours of continuous reaction.

[0067] Figure 9 shows the results of performing a catalytic reaction using a nanocomposite hydrogel that was dried at room temperature, aged for a certain period of time, and then restored by swelling in water. As illustrated in Figure 9, even when the dried and aged nanocomposite hydrogel was restored and used, a Cr(VI) conversion rate almost identical to that of the nanocomposite hydrogel (fresh sample) that had not been dried or aged was obtained. These results demonstrate that the heterogeneous catalyst based on the nanocomposite hydrogel proposed in the present invention exhibits excellent stability when stored in a dry state and is easily reusable when swelled in water, making it highly suitable for practical applications.

[0068] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0069] The Pd-AuAg trimetallic hybrid nanocomposite manufactured according to the present invention can be utilized as a catalyst material having high catalytic activity as a catalyst in a reaction that chemically reduces toxic Cr(VI) ions into relatively less toxic Cr(III) ions in an aqueous solution.

Claims

1. A method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure, comprising a step of growing nanocrystals containing gold (Au) and silver (Ag) on ​​a specific location rather than the entire surface of a seed made of palladium (Pd) nanocrystals through a seed-mediated growth method.

2. In paragraph 1, A method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure, characterized in that the seed made of the above palladium (Pd) nanocrystals has the shape of a nanocube, nanoplate or nanorod.

3. In paragraph 2, By reacting a solution containing palladium (Pd) nanocubes and a reducing agent with a solution containing a gold (Au) precursor and a silver (Ag) precursor, A method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure, characterized by growing island-structured nanocrystals containing gold (Au) and silver (Ag) on ​​palladium (Pd) nanocubes.

4. In paragraph 3, A method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure, characterized in that the method comprises growing island-structured nanocrystals containing gold (Au) and silver (Ag) at each edge of the palladium (Pd) nanocube to synthesize a palladium-gold-silver trimetallic hybrid nanostructure having an octapod-like structure.

5. In paragraph 3, A method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure, characterized in that a palladium-gold-silver trimetallic hybrid nanostructure having a bumpy structure is synthesized by growing island-structured nanocrystals on each edge and each face of the palladium (Pd) nanocube.

6. In paragraph 3, A method for manufacturing a palladium-gold-silver trimetallic hybrid nanostructure, characterized in that a Janus-structured palladium-gold-silver trimetallic hybrid nanostructure is synthesized by growing island-structured nanocrystals on one side of the above palladium (Pd) nanocube.

7. In paragraph 1, A method for producing a palladium-gold-silver trimetallic hybrid nanostructure, characterized in that the gold (Au) precursor is chloroauric acid (HAuCl4), the silver (Ag) precursor is silver nitrate (AgNO3), and the reducing agent is polyvinylpyrrolidone (PVP).

8. A palladium-gold-silver trimetallic hybrid nanostructure manufactured according to the method described in any one of claims 1 to 7.

9. A catalyst for continuous flow chemical reaction comprising a hydrogel impregnated with the palladium-gold-silver trimetallic hybrid nanostructure described in Article 8.

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