KR102297995B1 - Iron oxide nanocube with open-mouthed cavity and methods for preparing the same - Google Patents

Abstract

The present invention relates to a method for manufacturing an iron oxide nanocube having an open cavity concave inward on its outer surface, and an iron oxide nanocube prepared thereby, and a use of the iron oxide nanocube, in a manufacturing method according to an embodiment According to the present invention, it is possible to prepare an iron oxide nanocube having an open cavity concave inward on the outer surface, and the catalyst for Fenton oxidation treatment including the iron oxide nanocube and the noble metal nanocrystal prepared by the above method has an asymmetric structure. It can be propelled and used to efficiently remove pollutants contained in wastewater.

Description

Iron oxide nanocube with open-mouthed cavity and methods for preparing the same

The present invention relates to a method for manufacturing an iron oxide nanoQ having an open cavity concave inwardly on an outer surface, an iron oxide nanocube prepared by the method, and a use of the iron oxide nanocube.

The synthesis of nanoparticles with a convex or flat surface surrounded by a face with a low refractive index with minimized energy is easy, whereas nanoparticles with a concave surface have been rarely synthesized so far. Nanoparticles with a concave surface (CS-NC) have a surface of high refractive index within a negative curvature, where low-coordinated atoms are densely packed. Nanoparticles with these concave surfaces have a wide range of applications in catalysis, plasmonics, medicine, and postsynthetic engineering that integrates multifunctionality into a single nanostructure. As a method for manufacturing CS-NCs, there are methods such as etching a specific set of faces in a pre-synthesized polygonal metal nanocrystal or overgrowth of atoms resulting from a metal precursor at a specific location, but these methods are A symmetrical CS-NC is formed by indiscriminately generating negative curvatures on all chemically equivalent faces in a dimensional nanocrystal. However, although a single concave pore is selectively formed on one surface and has an asymmetric Janus structure, there has been little research on how to synthesize it despite its high application potential due to its unique multifaceted structure and magnetic and catalytic properties. .

On the other hand, the Fenton oxidation reaction completely oxidizes organic substances present in wastewater or converts difficult-to-decompose organic substances to microbial decomposition in order to reduce the pollution load. It is a method of decomposing organic matter remaining in wastewater by generating free radicals (HO). If the catalyst for Fenton oxidation treatment is still in the fluid, it results in inefficient catalyst activity and long operating time, so it is important to improve the catalyst activity for the catalyst to operate dynamically. Therefore, in wastewater treatment, combining the function of a catalyst and autonomous movement is an effective strategy that can effectively increase the degree of water quality improvement.

Accordingly, the inventors of the present application have completed the present invention regarding a method for preparing nanoparticles having an asymmetric Janus structure capable of imparting dynamic movement to a catalyst.

Republic of Korea Patent Publication No. 10-2004-0052387

In one example of the present invention, when an iron oxide nanocube confined in a silica shell is heat-treated under oxidative and reductive conditions, iron ions selectively diffuse into the surrounding silica shell from the outer surface and the iron oxide nanocube of an asymmetric structure having concave pores It is to provide a method of manufacturing an iron oxide nanocube having an open cavity concave to the inside on one surface of the outside by using the thermal conversion.

Another example of the present invention relates to an iron oxide nanocube having an open cavity concave inwardly on the outer surface.

A further example of the present invention is an iron oxide nanocube and a noble metal nanocrystal having an open pore concave inward on the outer surface, which does not have an asymmetric structure and can exhibit superior pollutant decomposition efficiency than a catalyst without self-propelling force. It relates to a catalyst for Fenton oxidation treatment comprising a.

A further example of the present invention relates to a method for decomposing pollutants in water, comprising the step of adding the catalyst for Fenton oxidation treatment to wastewater containing pollutants.

Therefore, the present inventors have thermally treated iron oxide nanocubes confined in a silica shell under oxidative and reducing conditions into iron oxide nanocubes having an asymmetric structure having concave pores by selectively diffusing iron ions from the outer surface to the surrounding silica shell. By confirming the transformation, a method for manufacturing iron oxide nanocubes having an open cavity in the form of concave inward on the outer surface was completed.

An example of the present invention includes (1) a silica sol-gel reaction by adding an aqueous ammonia solution and a silica precursor to a microemulsion containing iron oxide nanocubes capped with an organic material, and comprising an iron oxide nanocube and a silica shell surrounding it preparing nanoparticles;

(2) heat-treating the nanoparticles obtained in step (1) at a temperature of 400° C. to less than 800° C. under oxidative conditions, thereby removing the organic material capped on the iron oxide nanocubes of the nanoparticles;

(3) by heat-treating the nanoparticles obtained in step (2) at a temperature of 400° C. or higher to less than 500° C. under reducing conditions, having an open cavity in the form of concave inward on the outer surface of the nanocube contained in the nanoparticles preparing nanoparticles; and

(4) treating the nanoparticles obtained in step (3) with a basic aqueous solution to remove the silica shell to obtain an iron oxide nanocube having an open pore concave inwardly on the outer surface,

It relates to a method for manufacturing an iron oxide nanocube having an open cavity concave inwardly on one external surface.

A further embodiment of the present invention relates to an iron oxide nanocube having an inwardly concave shape on the outer surface and having an open cavity having a diameter of 10 to 15 nm, preferably, the iron oxide nanocube is prepared in the steps (1) to (4). ) relates to a method for producing an iron oxide nanocube containing.

A further example of the present invention is a penton oxidation treatment comprising an iron oxide nanocube having an open cavity having an inner concave shape on the outer surface and having a diameter of 10 to 15 nm and a noble metal nanocrystal formed in the open cavity of the iron oxide nanocube It relates to a catalyst.

A further example of the present invention includes the step of decomposing pollutants by hydroxyl radicals generated by the Fenton oxidation reaction by adding _{hydrogen peroxide (H 2} O _{2 ), and the catalyst for Fenton oxidation treatment to wastewater containing pollutants.} It relates to a method for decomposing pollutants in water.

According to the manufacturing method according to the present invention, as a nanocube of an asymmetric structure, an iron oxide nanocube having an open pore concave inwardly on an external surface can be manufactured, and the nanocube of the asymmetric structure and the open cavities of the nanocube can be prepared. The catalyst for Fenton oxidation treatment including noble metal nanocrystals has a self-propelling force that moves in one direction in the presence of hydrogen peroxide and has excellent decomposition activity of pollutants.

As used herein, the term "iron oxide nanocube" refers to iron oxide nanoparticles having a hexahedral shape and having one side of the hexahedron having a nanometer size.

Hereinafter, the present invention will be described in detail.

An example of the present invention provides a method for manufacturing an iron oxide nanocube having an open pore concave inwardly on an external surface, comprising the following steps:

(1) performing a silica sol-gel reaction by adding an aqueous ammonia solution and a silica precursor to a microemulsion containing iron oxide nanocubes capped with an organic material, to prepare nanoparticles comprising iron oxide nanocubes and a silica shell surrounding them step;

(2) heat-treating the nanoparticles obtained in step (1) at a temperature of 400° C. to less than 800° C. under oxidative conditions, thereby removing the organic material capped on the iron oxide nanocubes of the nanoparticles;

(3) by heat-treating the nanoparticles obtained in step (2) at a temperature of 400° C. or higher to less than 500° C. under reducing conditions, having an open cavity in the form of concave inward on the outer surface of the nanocube contained in the nanoparticles preparing nanoparticles; and

(4) treating the nanoparticles obtained in step (3) with a basic aqueous solution to remove the silica shell, thereby obtaining an iron oxide nanocube having open pores concave inwardly on the outer surface.

The manufacturing method according to one embodiment can prepare an iron oxide nanocube having an open pore concave inwardly on one external surface using nanoparticles including an iron oxide nanocube and a silica shell surrounding the same as a starting material.

The method for manufacturing an iron oxide nanocube having open pores according to the present invention includes a step (step (1)) of preparing nanoparticles including a silica shell, specifically, a micro-cube including iron oxide nanocubes capped with an organic material. A silica sol-gel reaction is performed by adding an aqueous ammonia solution and a silica precursor to the emulsion to prepare nanoparticles comprising iron oxide nanocubes and a silica shell surrounding them.

The edge length of the iron oxide nanocubes capped with the organic material may be 10 to 30 nm, 12 to 28 nm, 14 to 26 nm, 15 to 25 nm, 16 to 24 nm, 18 to 24 nm, 20 to 25 nm, or 20 to 22 nm.

The microemulsion containing iron oxide nanocubes capped with an organic material in step (1) may be a water-in-oil microemulsion.

The microemulsion including iron oxide nanocubes capped with the organic material may be prepared by a known method, for example, organically through a thermal decomposition method (J. Am. Chem. Soc. 2009, 131, 454-455). After preparing iron oxide nanocubes capped with a material, it can be prepared by adding it to a microemulsion (or an organic solvent containing a surfactant).

The organic solvent may be a conventional organic solvent that can be used as an oil phase in the microemulsion, for example, at least one selected from the group consisting of cyclohexane, hexane, heptane, octane, isooctane, nonane, decane, and toluene. can

The surfactant is, for example, 4-biphenylcarboxylic acid, polyoxyethylene-5-nonylphenyl ether; for example, NP-5 or Igepal CO-520) , polyoxyethylene sorbitan (polyoxyethylene sorbitan; for example, Tween), poloxamer (poloxamer), and may be at least one selected from the group consisting of sorbitan ester (sorbitan ester).

The organic material serves as a stabilizing agent, and according to one embodiment, a microemulsion including iron oxide nanocubes capped with an organic material may be prepared only when the organic material is added.

The organic material may be at least one selected from the group consisting of an aliphatic amine containing a C ₄ to C ₃₀ fatty acid, including, to C ₄ aliphatic alcohol, and a C ₄ to C _30, including the C _30. The C ₄ to C ₃₀ fatty acids are lauric acid, myristic acid, linoleic acid, stearic acid, oleic acid, and palmitic acid ( palmitic acid) may be at least one selected from the group consisting of.

The silica precursor is, but not limited to, for example, tetraethyl ortho-silicate (TEOS), tetramethyl orthosilicate (TMOS), tetrabutyl orthosilicate (TBOS), and tetrapropyl orthosilicate (TBOS). It may be at least one selected from the group consisting of silicate (tetrapropyl orthosilicate).

The nanoparticles comprising the iron oxide nanocubes and the silica shell surrounding them are nanoparticles having a core@shell structure, including a nucleus including the iron oxide nanocubes and a silica shell surrounding the iron oxide nanocubes. can

The nanoparticles including the iron oxide nanocubes and the silica shell surrounding them may include iron oxide nanocubes capped with an organic material.

The iron oxide nanocubes may include magnetite (Fe ₃ O ₄ ), maghemite (γ-Fe ₂ O ₃ ), or a combination thereof. According to one embodiment, the iron oxide nanocubes capped with the organic material may be OA (Oleic acid)-Fe ₃ O ₄ . According to one embodiment, the nanoparticles including the iron oxide nanocubes _{and the silica shell surrounding them may be OA-Fe 3} O _{4 @SiO 2} .

The diameter of the nanoparticles comprising the iron oxide nanocube and the silica shell surrounding it is 10 to 60 nm, 15 to 55 nm, 20 to 50 nm, 20 to 45 nm, 25 to 45 nm, 30 to 45 nm, 30 to 40 nm, 35 to 40 nm, 40 to 45 nm, or 40 to 42 nm.

In the nanoparticles obtained in step (1), the silica shell and the iron oxide nanocube are in physical contact so that an empty space is not formed between the silica shell and the iron oxide nanocube.

The physical contact between the silica shell and the iron oxide nanocube, in the manufacturing method according to an embodiment, provides an important role for the movement of iron ions for the formation of an open pore structure concave inwardly on the outer surface of the nanocube. For example, even if the silica shell and the iron oxide nanocube are not in physical contact or the nanocube with minimal physical contact is subjected to heat treatment under oxidative conditions and heat treatment under reductive conditions, the pore structure on the outer surface of the nanocube does not appear, so it is impossible to prepare an iron oxide nanocube having an open cavity concave inwardly on the outer surface. The silica shell and the iron oxide nanocubes are not in physical contact or the nanocubes in which the physical contact is minimized may be those in which the iron oxide nanocubes are located inside the hollow silica shell.

The manufacturing method according to one embodiment can prepare an iron oxide nanocube having an open pore concave inwardly on an outer surface using nanoparticles including an iron oxide nanocube and a silica shell surrounding the same as a starting material. When the spherical iron oxide nanocrystals and nanoparticles containing the surrounding silica shell are subjected to heat treatment under reducing conditions, a concave pore structure is not observed in the nanoparticles (or spherical iron oxide nanocrystals), and the hollow silica shell and Iron oxide nanocrystals are formed on the outside of the silica shell.

The method for manufacturing an iron oxide nanocube having open pores according to the present invention includes the step (step (2)) of removing the organic material capped on the iron oxide nanocube of the nanoparticles, wherein the nanoparticles obtained in step (1) is heat-treated at a temperature of 400° C. or higher to less than 800° C. under oxidative conditions to remove the organic material capped on the iron oxide nanocubes of the nanoparticles.

The oxidative condition is air, oxygen (O ₂ ) gas, or more than 5 mol% of oxygen, more than 10 mol% of oxygen, more than 15 mol% of oxygen, more than 20 mol% of oxygen, more than 25 mol% of oxygen, more than 30 mol% of oxygen , 35 mol% or more of oxygen, 40 mol% or more of oxygen, or 50 mol% or more of oxygen may be a condition of using a mixed gas.

The heat treatment in the oxidative condition is 400 °C to less than 800 °C, 450 °C to less than 750 °C, 450 °C to less than 700 °C, 450 °C to less than 650 °C, 500 °C to less than 600 °C, or 500 It may be carried out for 1 to 30 hours, 5 to 20 hours, 10 to 15 hours, or 5 hours at a temperature of ℃.

The heat treatment in the oxidative condition may be performed at a heating rate of 1 to 10°C/min, or 5°C/min.

According to one embodiment, by heat-treating the nanoparticles obtained in step (1) at a temperature of 400° C. or higher to less than 800° C. under oxidative conditions, removing the organic material capped on the iron oxide nanocubes of the nanoparticles ((( When step 2) is included before the step (step (3)) of heat treatment under reducing conditions, the outer surface of the nanocube is concave inward than the method that does not include the step (step (2)) of removing the organic material. It is possible to increase the production yield of iron oxide nanocubes with an open pore shape. For example, when removing the organic material capped on the iron oxide nanocube of the nanoparticles by heat-treating the nanoparticles including the iron oxide nanocube and the silica shell surrounding it under oxidative conditions, the outer surface is concave inward. The iron oxide nanocubes having an open pore shape can be prepared in a yield of 80% or more, 85% or more, 90% or more, 95% or more, or 100%.

In the nanoparticles obtained in step (2), the iron oxide nanocubes may include _{maghemite (γ-Fe 2} O _{3 ).}

According to one embodiment, heat-treating the nanoparticles obtained in step (1) at a temperature of 400° C. to less than 800° C. under oxidative conditions to remove the organic material capped on the iron oxide nanocubes of the nanoparticles ((2) ) step), magnetite (Fe ₃ O ₄ ) included in the iron oxide nanocubes of the nanoparticles may be converted into maghemite (γ-Fe ₂ O _{3 ).}

According to an embodiment, the nanoparticles obtained in step (2) may be _{Fe 2} O ₃ @SiO _{2 .}

The method for manufacturing an iron oxide nanocube having open pores according to the present invention includes the step (step (3)) of preparing nanoparticles having open pores concave to the inside on the outer surface of the nanocube included in the nanoparticles Specifically, by heat-treating the nanoparticles obtained in step (2) at a temperature of 400° C. or higher to less than 500° C. under reducing conditions, an open cavity of a concave shape is formed on the outer surface of the nanocube contained in the nanoparticles. Nanoparticles with

The reducing conditions may be conditions using hydrogen (H ₂ ) gas, or a mixed gas containing 1 mol% or more of hydrogen. For example, hydrogen and an inert gas mixture may be used, for example, hydrogen 1 mol% or more, hydrogen 2 mol% or more, hydrogen 3 mol% or more, hydrogen 4 mol% or more, hydrogen 5 mol% or more, hydrogen 8 mol% or more, hydrogen 10 mol% or more, hydrogen 20 mol% or more, hydrogen 30 mol% or more, hydrogen 40 mol% or more, or a mixed gas containing 50 mol% or more hydrogen, argon (Ar) 96 mol% and hydrogen 4 A mixed gas containing mol%, or a mixed gas containing _{96 mol% of nitrogen (N 2} ) and 4 mol% of hydrogen may be used.

The heat treatment under the reductive conditions is 300 °C to less than 500 °C, 350 °C to less than 500 °C, 400 °C to less than 500 °C, 400 °C, or 450 °C for 1 to 30 hours, 5 to 20 hours. , 10 to 15 hours, or may be carried out for 5 hours.

According to one embodiment, when the nanoparticles obtained in step (2) are heat-treated at a temperature of 300° C. or higher under reducing conditions, maghemite contained in the iron oxide nanocubes of the nanoparticles (maghemite; γ-Fe ₂ O ₃ ) may be converted into magnetite (Fe ₃ O _{4 ).}

According to one embodiment, when the nanoparticles obtained in step (2) are heat-treated at a temperature other than the above range under the reductive conditions, an iron oxide nanocube having an open cavity in a concave shape on the outside cannot be prepared, By-products may be generated in addition to the nanoparticles to be produced (eg, iron oxide nanocubes having open pores concave inward on the outer surface). For example, as a by-product, the iron oxide nanocube inside the silica shell disappears, and a pore, a silica shell surrounding the cavity, and a nanosphere containing iron oxide on the outside of the silica shell may be formed. The magnetite phase may be converted to a ^{Fe 2+} -silicate phase (Fe ₂ SiO _{4 ).}

The heat treatment under the reducing conditions is 20 minutes to 48 hours, 20 minutes to 24 hours, 1 hour to 24 hours, 1 hour to 12 hours, 2 hours to 10 hours, 4 hours or 8 hours, 5 hours to 8 hours, 5 It may be carried out for hours to 10 hours, or 5 hours.

According to one embodiment, the yield of nanoparticles having open cavities concave inwardly on the outer surface is low during heat treatment under the reductive condition below the lower limit of the heat treatment time range, and the heat treatment time exceeds the upper limit of the heat treatment time range , the iron oxide nanocubes inside the silica shell may disappear, and nanospheres including cavities, silica shells surrounding the cavities and iron oxides on the outside of the silica shells may be formed.

The heat treatment in the reducing conditions may be performed at a heating rate of 1 to 10 °C / min, or 5 °C / min.

According to one embodiment, the nanoparticles obtained in step (3) may be conc -Fe ₃ O ₄ @SiO _{2 .}

The method for manufacturing an iron oxide nanocube having a cavity according to the present invention includes the step of obtaining an iron oxide nanocube having an open cavity concave inwardly on an outer surface (step (4)), specifically, in step (3) The obtained nanoparticles are treated with a basic aqueous solution to remove the silica shell to obtain an iron oxide nanocube having open pores concave to the inside on the outside surface.

The basic aqueous solution may be an aqueous solution containing at least one selected from the group consisting of ammonia (NH ₄ OH), sodium hydroxide (NaOH), and potassium hydroxide (KOH).

In step (4), the nanoparticles obtained in step (3) are treated with a basic aqueous solution and stirred at room temperature for 5 hours to 24 hours, 8 hours to 20 hours, 10 hours to 18 hours, or 12 hours to 16 hours. After the reaction, it can be obtained by precipitating iron oxide nanocubes having open pores concave to the inside on one external surface by centrifugation. The centrifugation may be performed in a conventional range that can be used in the art as long as it is a condition capable of precipitating an iron oxide nanocube having an open cavity concave inward on the outer surface, for example, 10,000 rpm to 15,000 rpm Centrifugation may be performed for 10 to 15 minutes under the conditions of to obtain iron oxide nanocubes having open pores concave to the inside on the outer surface.

The iron oxide nanocube having an open pore concave inwardly on the outer surface may have an open pore concave on only one surface of the six surfaces of the nanocube.

In the iron oxide nanocube having open pores concave inward on the outer surface, the diameter of the open pores may be 1 to 30 nm, 3 to 25 nm, 5 to 20 nm, 8 to 18 nm, 10 to 15 nm, or 10 to 12 nm.

The nanocubes obtained in step (4) may have an average diagonal length of 5 to 60 nm, 10 to 55 nm, 15 to 50 nm, or 20 to 45 nm. The diagonal length means the length of the diagonal of the iron oxide nanocube (hexahedron).

The nanocube obtained in step (4) may include magnetite (Fe ₃ O ₄ ).

In the manufacturing method according to an embodiment, between the steps (3) and (4), the nanoparticles obtained in the step (3) are heat-treated at a temperature of 400 ° C. to less than 800 ° C. After performing the step of converting to nanoparticles without It may be to further include the step of preparing the nanoparticles of the structure.

According to one embodiment, when the nanoparticles obtained in step (3) are heat-treated at a temperature of 400° C. to less than 800° C. under oxidative conditions (heat treatment under the same conditions as in step (2)), it does not have a pore structure The iron oxide nanocubes and nanoparticles comprising the surrounding silica shell are converted to nanoparticles, and the iron oxide nanocubes having no pore structure and the nanoparticles comprising the silica shell surrounding them are heated at a temperature of 400° C. or higher to less than 500° C. under reducing conditions. If the furnace heat treatment (heat treatment under the same conditions as in step (3) above), the nanoparticles can be converted into nanoparticles having open pores concave inwardly on the outer surface of the nanocube contained in the nanoparticles.

According to one embodiment, between steps (3) and (4), heat treatment under oxidative conditions and heat treatment under reductive conditions are additionally performed several times (eg, 1 to 100 times, 1 to 50 times, or 1 to 10 times), it is possible to prepare an iron oxide nanocube having an open cavity concave to the inside on one external surface.

According to one embodiment, the iron oxide nanocubes (nanoparticles obtained in step (4) above) having an open cavity concave inward on the outer surface may be conc -Fe ₃ O _{4 .}

The manufacturing method according to one embodiment comprises the steps of (5) treating the iron oxide nanocubes obtained in step (4) with an aqueous solution containing a reducing agent and a noble metal precursor, to prepare noble metal nanocrystals on the concave surface of the open pores of the nanocubes may further include.

The reducing agent is included without limitation as long as it can be used conventionally, for example, L-ascorbic acid (L-ascorbic acid), sodium borohydride (sodium borohydride), potassium borohydride (potassium borohydride), hydrazine (hydrazine) ), and/or hydrogen gas (H ₂ ).

The noble metal precursor is included without limitation as long as it can be conventionally used, for example, a platinum (Pt) precursor, a palladium (Pd) precursor, a rhodium (Rh) precursor, an iridium (Ir) precursor, a silver (Ag) precursor, and / or a ruthenium (Ru) precursor, for example, the palladium (Pd) precursor is Na ₂ PdCl ₄ , K ₂ PdCl ₄ , K ₂ PdCl ₆ , (NH ₄ ) ₂ PdCl ₄ , (NH ₄ ) ₂ PdCl ₆ , and/or PdCl ₂ may be, and the platinum (Pt) precursor is H ₂ PtCl ₆ ·6H ₂ O, H ₂ PtCl ₆ , K ₂ PtCl ₄ , K ₂ PtCl ₆ , Na ₂ PtCl ₄ ·xH ₂ O, and/or Na ₂ PtCl ₆ .6H ₂ O. Here, in the Na ₂ PtCl ₄ ·xH ₂ O, x is 3 to 6.

In step (5), the noble metal nanocrystals may be selectively formed on the concave surface of the open cavity of the nanocube, but not formed on the non-concave surface.

The manufacturing method according to one embodiment may further include (6) forming colloidal stability of the nanoparticles by PEGylating the nanoparticles obtained in step (5). For example, the nanoparticles may be PEGylated by mixing a suspension containing the nanoparticles obtained in step (5) with an aqueous mPEG-bisphosphonate solution.

Another example of the present invention provides an iron oxide nanocube manufactured by the above method according to the present invention, comprising an open pore having an inner concave shape on an outer surface and having a diameter of 10 to 15 nm. Regarding the iron oxide nanocube, it is the same as described for the iron oxide nanocube having an open cavity concave to the inside on one external surface.

The iron oxide nanocubes may include magnetite (Fe ₃ O ₄ ).

According to one embodiment, the iron oxide nanocubes may be used as a support for a catalyst, and a catalyst (eg, noble metal nanocrystals) or a catalyst precursor is located in an open cavity located on one side of the iron oxide nanocube by a physicochemical method It is possible to prepare nanoparticles of a Janus structure (eg, Pt@ conc -Fe ₃ O ₄ ) that are selectively supported so that the catalyst can be controlled in the open pores of the nanocube. The nanoparticles of the Janus structure have a dynamic movement in water or a solvent, and thus can be used as a nanoswimmer capable of efficiently removing contaminants.

Another example of the present invention is an iron oxide nanocube manufactured by the method according to the present invention, which is in the form of an inwardly concave shape on the outer surface and has an open pore having a diameter of 10 to 15 nm, and the iron oxide nanocube Provided is a catalyst for Fenton oxidation, comprising noble metal nanocrystals formed in open pores.

The Fenton oxidation reaction refers to a decomposition reaction of organic matter by hydroxyl radicals (OH·) generated when a mixture of hydrogen peroxide and iron salts react.

According to one embodiment, the Fenton oxidation reaction may oxidize an organic material (or a contaminant) by a mechanism such as Scheme 1 below.

[Scheme 1]

According to one embodiment, the iron oxide ions of the iron oxide nanocubes included in the catalyst for Fenton oxidation may react with hydrogen peroxide to form hydroxyl radicals that decompose organic pollutants.

The noble metal may be included without limitation as long as it catalyzes the decomposition of hydrogen peroxide into oxygen and water, and the noble metal is platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), silver (Ag), and ruthenium (Ru). ), and may be one selected from the group consisting of alloys thereof.

The diameter of the noble metal nanocrystals may be 0.5 to 10 nm, 0.7 to 8 nm, or 1 to 7 nm.

The noble metal nanocrystals included in the catalyst release oxygen (O _{2 ) in the presence of hydrogen peroxide (H 2} O ₂ ), so that the catalyst can move in one direction.

The noble metal crystals included in the catalyst for Fenton oxidation treatment decompose hydrogen peroxide in the presence of hydrogen peroxide and _{release O 2} to enable self-propelling to the catalyst for Fenton oxidation treatment, thereby increasing the decomposition effect of pollutants in the fluid. Can impart a kinetic catalytic effect. Since the catalyst for Fenton oxidation treatment has an asymmetric structure including noble metal nanocrystals formed in open cavities concave inward on the outer surface of the iron oxide nanocube, the noble metal nanocrystals formed on one surface of the nanocube decompose hydrogen peroxide to generate oxygen Therefore, oxygen is generated and/or released only from one side of the nanocube to give the nanoparticles mobility, so the catalyst for Fenton oxidation treatment may have a self-propelling force that moves in one direction in the presence of hydrogen peroxide.

The catalyst for Fenton oxidation treatment according to an embodiment does not have an asymmetric structure, and thus may exhibit superior pollutant decomposition efficiency than a catalyst without self-propelling force.

The catalyst for Fenton oxidation treatment according to an embodiment may exhibit catalytic activity by self-propulsion and Fenton oxidation reaction according to a mechanism as shown in Scheme 2 below.

[Scheme 2]

In another example of the present invention, hydrogen peroxide (H ₂ O ₂ ), and the catalyst for Fenton oxidation treatment of claim 17 are added to wastewater containing pollutants, and pollutants are decomposed by hydroxyl radicals generated by the Fenton oxidation reaction. It provides a method for decomposing pollutants in water, comprising the steps of.

The hydroxyl radical may be generated by reacting iron oxide ions of iron oxide nanocubes included in the catalyst for Fenton oxidation treatment with hydrogen peroxide.

The contaminant may be a recalcitrant organic material.

The hardly decomposable organic material may include an aromatic benzene ring compound or a halogenated organic compound.

According to the manufacturing method according to one embodiment, it is possible to prepare an iron oxide nanocube having an open pore concave inwardly on one external surface, and a catalyst for Fenton oxidation treatment comprising the iron oxide nanocube and the noble metal nanocrystal prepared by the above method Since it has an asymmetric structure, it can be propelled by itself and can be effectively used to remove pollutants contained in wastewater.

1 is a schematic view showing a method of manufacturing an iron oxide nanocube having an open cavity in the form of concave inward on the outer surface according to an embodiment.
2 a and b show TEM images and SEM images of _{OA-Fe 3} O _{4 , respectively.}
2 c shows a TEM image of OA-Fe ₃ O ₄ @SiO _{2 .}
2 d to h of 0A-Fe ₃ O ₄ @SiO ₂ Do not perform the step of heat treatment in air, and various temperatures (300 ℃ (d), 400 ℃ (e), 500 ℃ (f) under reducing conditions under reducing conditions. ), 600 °C (g), or 700 °C (h)) shows a TEM image of nanoparticles prepared by performing annealing heat treatment. 2 i to l are OA-Fe ₃ O ₄ @SiO ₂ at various temperatures (300 °C (i), 500 °C (j), 600 °C (k), or 700 °C (l)) under reducing conditions. A TEM image of nanoparticles prepared by performing annealing heat treatment is shown.
3a is a TEM image and HRTEM image (internal image) _{of nanoparticles (γ-Fe 2} O ₃ @SiO ₂ ) produced by annealing heat treatment of OA-Fe ₃ O _{4 @SiO 2} at a temperature of 500° C. in air. indicates 3 b is a TEM image and HRTEM image of nanoparticles ( conc -Fe ₃ O ₄ @SiO ₂ ) generated by annealing heat treatment of γ-Fe ₂ O ₃ @SiO ₂ at a temperature of 400° C. under reducing conditions ( internal image). 3 c shows a dark field STEM-EDS image for conc -Fe ₃ O ₄ @SiO ₂ , specifically, the upper left image is elemental mapping of Fe atoms, and the upper right image is Si The elemental mapping of atoms is shown, the lower left image shows the EDX line profile showing Fe distribution, and the lower right image shows the STEM image for conc -Fe ₃ O ₄ @SiO _{2 .}
3 d shows TEM and HRTEM images (internal images) for conc -Fe ₃ O _{4 .} Figure 3e shows the SEM image and SEM-EDX line profile (internal image) for conc -Fe ₃ O _{4 .} 3 f shows 3D structures and various BF-TEM images reconstructed from tomography at various inclinations for conc -Fe ₃ O _{4 .}
3 g is an XRD of nanoparticles (OA-Fe ₃ O ₄ @SiO ₂ , γ-Fe ₂ O ₃ @SiO ₂ , or Fe ₃ O ₄ @SiO ₂ ) before and after performing annealing heat treatment under various conditions. represents a pattern.
4 shows XRD patterns of _{nanoparticles (OA-Fe 3} O ₄ nanocrystals, or Fe ₃ O ₄ @SiO ₂ ) before and after performing annealing heat treatment under various conditions . 3 g and 4, the temperature in parentheses represents the annealing temperature, H ₂ represents the reductive condition in the annealing step, and Air represents the oxidative condition (air) in the annealing step.
Figure 5 shows the XPS spectrum for conc -Fe ₃ O ₄ @SiO _{2 .} Specifically, a to e and f to j in FIG. 5 are various temperatures (300°C (a and f), 400°C (b and g), 500°C (c and h), 600°C (d and i) under reducing conditions. ), or 700° C. (e and j)) for the nanoparticles prepared by performing annealing heat treatment, showing Fe 2p peaks ( FIGS. 5 a to 5 e ), and Si 2p peaks ( FIGS. 5 f to j ).
6 is OA-Fe ₃ O ₄ @SiO ₂ conc -Fe ₃ O ₄ @SiO ₂ prepared by annealing heat treatment in air and then heat-treating again at a temperature of 400° C. under reducing conditions for various times (0 to 30 minutes) TEM images for
7 is OA-Fe ₃ O ₄ @SiO ₂ conc -Fe ₃ O ₄ @SiO ₂ prepared by annealing heat treatment in air, and then heat treatment at a temperature of 400 ° C. under reducing conditions for various times (0 to 48 hours) The TEM image (upper image) and the diameter (nm) distribution of the pupil measured in the nanoparticles in which the pupil was observed (lower graph) are shown.
8 shows a TEM image of nanoparticles prepared by repeatedly performing thermal oxidation and reduction annealing of conc -Fe ₃ O ₄ @SiO ₂ by repeatedly switching a gaseous environment (air, or H _{2 +Ar).}
Figure 9 is Fe ₃ O ₄ @ h -SiO ₂ After annealing heat treatment in air, various temperatures (300 °C (a), 400 °C (b), 500 °C (c), 600 °C (d), or A TEM image of nanoparticles prepared by performing annealing heat treatment at 700° C. (e)) for 5 hours is shown.
Figure 10 is a spherical Fe ₃ O ₄ nanocrystals surrounded by silica at various temperatures (300 °C (a), 400 °C (b), 500 °C (c), 600 °C (d), or 700 °C) under reducing conditions. e)) shows a TEM image of nanoparticles (h -SiO ₂ -FeO) prepared by heat treatment for 5 hours.
11 shows MnO nanocubes surrounded by silica (MnO@SiO ₂ ) (a) and at various temperatures (300° C. (b), 400° C. (c), 500° C. (d), 600° C. (e) at reducing conditions. , or 700 ℃ (f)) shows a TEM image of the prepared nanoparticles by heat treatment for 5 hours.
Of Figure 12 is of a Pt @ conc -Fe ₃ O ₄ TEM image and HRTEM images indicate the (internal image), b of Figure 12 shows the STEM image of the Pt @ conc -Fe ₃ O _4, 12 for c is the deposition of the Pt @ conc -Fe ₃ O ₄ shows a STEM-EDS elemental mapping images of, in FIG. 12 d is Pt @ conc -Fe ₃ O ₄ synthesis (Pt nanocrystals in conc -Fe ₃ O ₄ of TEM image of nanoparticles over time (10 to 60 minutes) in the process) and a schematic diagram of the synthesis process.
13 shows a TEM image of nanoparticles over time (10 to 90 minutes) in the synthesis process of Pt@ conc -Fe ₃ O ₄ (the process of depositing Pt nanocrystals on conc -Fe ₃ O _{4 ).}
14 shows an XRD pattern for Pt@ conc -Fe ₃ O _{4 .}
15 a and b show the NTA size analysis results of Pt@ conc -Fe ₃ O ₄ nanoswimmers before (a) and after (b) the addition of _{fuel (H 2} O _{2 ), respectively.}
Figure 16a shows a schematic diagram of a process in which Rh6G is decomposed by Pt@ conc -Fe ₃ O ₄ , and Fig. 16 b is PEG-Pt@ conc -Fe ₃ O ₄ and _{after addition of H 2} O _{2 at various concentrations.} PEG- conc -Fe ₃ O average diffusion coefficient (D) denotes a (nm ² / s), in Figure 16 c of _{4 PEG-Pt @ conc -Fe 3 O} 4 , and the control particles (PEG-Fe ₃ O _4, PEG- conc -Fe ₃ O ₄ , PEG- conc -Fe ₃ O ₄ + Pt) shows the quantitative comparison results of the decomposition of Rh6G, d of FIG. 16 is H ₂ by PEG-Pt@ conc -Fe ₃ O ₄ Shows the Rh6G decomposition effect according to the O _{2 concentration.}
Figure 17 shows a standard curve (calibration curve) showing the serial dilution of rhodamine to various concentrations of 0 to 0.2mM (calibration curve).
Under the left graphs and the right graphs H ₂ O _2, each member of Figure 18 PEG-Pt @ conc -Fe ₃ O ₄ is added when the concentration of Rh6G with time, and PEG-Pt @ conc -Fe ₃ O ₄ according to the concentration of Represents the removal rate (%) of Rh6G.
19 shows the Rh6G decomposition effect of PEG-Pt@conc- Fe ₃ O ₄ under visible light under no catalyst (No catalyst), light (Light), or dark conditions (Dark).
A in FIG. 20 Fe ₃ O ₄ nano shows a TEM image of the symmetrical particles (PEG-Pt @ Fe ₃ O ₄₎ of Pt is deposited on all sides of the cube of Fig. 20 b are PEG-Pt @ Fe ₃ O ₄ shows the DLS size data, and in FIG. 20 c is PEG-Pt@ conc -Fe ₃ O ₄ , PEG-Pt@Fe ₃ O ₄ , or The results of Rh6G decomposition by PEG-Fe ₃ O _{4 are shown.}
21 shows the recycling potential of PEG-Pt@ conc -Fe ₃ O _{4 for Rh6G degradation.} Error bars in each figure were calculated from the results of three independent experiments.

Hereinafter, the present invention will be described in more detail through reference examples and examples. However, these Reference Examples and Examples are for illustrative purposes of the present invention, and the scope of the present invention is not limited to these Reference Examples and Examples.

Reference Example 1. Reagents and devices

Reference Example 1.1 Reagent

Iron (III) acetylaceonate (Strem), 4-biphenylcarboxylic acid (Acros), oleic acid (Aldrich), benzyl ether (Aldrich), IGEPAL CO-520 [ polyoxyethylene (5) nonylphenylether, Aldrich], NH ₄ OH (Samchun Chem.), TEOS (tetraethyl orthosilicate) (Acros), Na ₂ PdCl ₄ 3H ₂ O(Strem), NaOH (Samchun Chem.), L(+) All reagents including -ascorbic acid (L(+)-ascorbic acid) (Samchun Chem.) were used as purchased without further purification.

Reference Example 1.2 Device

Transmission electron microscopy (TEM) analysis was performed using JEOL JEM-2100 and JEM-2200FS. Elemental mapping and line profiling analyzes of scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (STEM-EDS) were performed using a JEOL JEM-2100F. Scanning electron microscopy (SEM) analysis was performed using a JSM 7800F Prime (JEOL) instrument. An X-ray diffraction (XRD) pattern was obtained using an X-ray diffraction apparatus (18 kW, Rigaku, Japan). The oxidation number of the samples was measured via X-ray photoelectron spectroscopy (XPS) with an X-ray source of monochromated Al Kα radiation (1486.6 eV) using theta probe AR-XPS system (Thermo Fisher, U.K.). A tilted 2D image was obtained using a Cs-corrected TEM (Libra 200 HT Mc, 200 kV, Carl Zeiss, Germany). The tilted 2D image was reconstructed into a 3D volume using a tomography program (JEOL, Japan). The 3D volume was visualized as a filled volume using the Amira program (Thermo Fisher Scientific, USA).

Reference Example 2. Fe capped with oleic acid ₃ O ₄ Nanocube (OA-Fe ₃ O ₄ ) manufacturing

In a Schrank flask of 500 ml volume, _{under N 2} atmosphere, 3.5 g of iron acetylacetonate (iron (III) acetylacetonate) was mixed with oleic acid (5.64 g), 4-biphenylcarboxylic acid (3.6 g), and benzyl It was dissolved by vigorous stirring in a solution containing benzyl ether (200 mL). While degassing, the solution was heated at a rate of 2° C./min at 50° C. for 2 hours. The reaction temperature was increased to 290° C. by heating at a rate of 25° C./min while stirring under a continuous N _{2 gas flow, followed by heating for 45 minutes.} The resulting black suspension was centrifuged and sonicated, washed repeatedly with a mixture of hexane and acetone in a volume ratio of 1:4, and _{a suspension in which OA-Fe 3} O ₄ nanocubes were dispersed in cyclohexane was prepared.

Reference Example 3. OA-Fe of nuclear @ shell structure ₃ O ₄ @SiO ₂ Nanoparticle Manufacturing

_{OA-Fe 3} O ₄ dispersed in cyclohexane prepared in Reference Example 2 in 1 ml of IGEPAL-CO-520 solution dispersed in 2 ml of cyclohexane in a glass vial (8 ml) 0.3 ml of the suspension (10 mg/ml) was added, and after shaking using a mechanical stirrer at room temperature for 4 hours (in _{a microemulsion containing OA-Fe 3} O ₄ ), 20 μl of a NH ₄ OH solution (28- 30%) and 20 μl of distilled water were successively added to the reaction solution to create a homogeneous reverse microemulsion system.

Then, it was further shaken at room temperature for 4 hours. 40 μl of TEOS was added to the suspension to initiate a silica sol-gel reaction, and the reaction was maintained at room temperature for 24 hours without stirring. In order to destroy the uniform reverse microemulsion system, methanol was added to the white suspension to separate a dark brown solid (OA-Fe ₃ O ₄ @SiO ₂ ) as a precipitate, which was centrifuged 3 times with ethanol and 1 time with distilled water. and repeated washing with sonication, followed by freeze-drying for further reaction.

Reference Example 4. OA-Fe ₃ O ₄ @SiO ₂ Oxidative and Reductive Annealing of

Reference Example 4.1 Annealing heat treatment under reductive conditions

In order to investigate thermal structural changes of Fe ₃ O ₄ nano-cube in an environment surrounded by silica, the reference by OA-Fe ₃ O _{4 2} @SiO the reductive conditions without performing the annealing step in air, prepared in Example 3 ( Ar + 4% H ₂ ) at various annealing temperatures (T _ann = 300° C. to 700° C.).

Reference Example 4.2 Performing annealing heat treatment under oxidative conditions and annealing heat treatment under pre-reduction conditions

In Reference Example 3, the freeze-dried OA-Fe ₃ O ₄ @SiO ₂ powder was gently pulverized with an agate mortar, and the obtained fine powder was transferred to an alumina tray. The alumina tray is put in a box-type furnace, heated slowly to 500°C at a rate of 5°C/min in the air, and then the temperature is maintained for 5 hours to completely remove organic residues in the nanoparticles, resulting in a red color (radish color) having a cube shape. ) of Fe ₂ O ₃ @SiO ₂ nanoparticles were prepared.

Fe ₂ O ₃ @SiO ₂ Powder is placed in a tubular furnace, _{heated slowly at a rate of 5 ℃ / min under Ar and 4% H 2} gas flow, and maintained at various temperatures of 300 ℃ to 700 ℃ for 5 hours by annealing heat treatment , _{Thermal conversion from Fe 2} O ₃ @SiO ₂ nanoparticles to conc -Fe ₃ O ₄ @SiO ₂ nanoparticles was performed.

Reference Example 4.3 Nanoparticle structure transformation according to annealing heat treatment under oxidative or reductive conditions

conc -Fe ₃ O ₄ @SiO ₂ Oxidation and reduction annealing were repeatedly performed for 5 hours at 400° C. under oxidative conditions (in air) or reductive conditions (Ar and 4% H _{2 ), respectively, to form a concave shape} The conversion between a cube structure with a pupil of , and a cube structure without a pupil of

Reference Example 5. conc -Fe ₃ O ₄ Preparation of nanoparticles

Before removing the silica shell, to prevent oxidation of conc -Fe ₃ O _{4 nanocrystals,} The internal gas was removed. 100 mL of 5M NaOH aqueous solution was heated at 100° C. for 2 hours while bubbling _{N 2 gas, and then cooled to 70° C.} In a glass vial (10 mg/ml), the conc -Fe ₃ O _{4 @SiO 2} powder prepared by the method of Reference Example 4.2 was placed in 100 ml of degassed 5M NaOH aqueous solution, and stirred at 70° C. for 24 hours, conc -Fe ₃ O ₄ nanocrystals were separated from the silica shell, and centrifugation and washing were performed three times.

Reference Example 6. Fe ₃ O ₄ @ h -SiO ₂ Synthesis and Reductive Annealing of

Fe ₃ O ₄ @ h -SiO ₂ was synthesized for control experiments. _{The OA-Fe 3} O ₄ @SiO ₂ nanoparticle powder prepared in Reference Example 3 was immersed in distilled water (1 mg/ml) and heated at 80° C. for 90 minutes _{to prepare Fe 3} O ₄ @ h -SiO ₂ nanoparticles, and , washed with distilled water through repeated centrifugation and sonication.

Fe ₃ O ₄ @ h -SiO ₂ Annealing heat treatment at a temperature of 500° C. in air for 5 hours, and then annealing heat treatment at a temperature of 300 to 700° C. under _{Ar + 4% H 2 flow for 5 hours (heating rate)} : 5°C/min).

Reference Example 7. Pt@ conc -Fe ₃ O ₄ Preparation of Janus Nanoparticles

330 μl of conc -Fe ₃ O ₄ colloidal suspension (1.5 mg/ml) dispersed in distilled water, 500 μl of ascorbic acid (20 mg/ml) dissolved in ethanol, and Na ₂ PtCl ₄ aqueous solution (25 mg/ml) 40 μl of a mixture of distilled water and ethanol (1:1 v/v) was continuously added to a glass vial to prepare a final volume of 1.5 ml. The reaction glass vial was shaken using a shaker at room temperature for 90 minutes. Centrifugation and washing were performed three times to remove excess reagent remaining in the solution, and Janus Pt@ conc -Fe ₃ O ₄ was separated from the reaction mixture. Pt@ conc -Fe ₃ O ₄ Janus nanoparticles are nanoparticles having an asymmetric structure in which Pt is formed in the pores of the iron oxide nanocube ( conc -Fe ₃ O ₄ ) having open pores concave inward on the outer surface of the nanocube. means particles.

Reference Example 8. Pt@ conc -Fe ₃ O ₄ PEGylation of Janus Nanoparticles

200 μl of Pt@ conc -Fe ₃ O ₄ nanoparticle suspension (3mg/ml) dispersed in water and 4ml of mPEG-bisphosphonate (1mg/ml) dispersed in water were successively added to a glass vial. After addition, the vial was shaken at room temperature for 30 minutes using a shaker to convert Pt@ conc -Fe ₃ O ₄ Janus nanoparticles into PEG (polyethylene glycol), and then used without washing.

Reference Example 9. Symmetrical Pt@Fe ₃ O ₄ Synthesis of nanoparticles

_{OA-Fe 3} O ₄ @SiO ₂ prepared in Reference Example 2 was treated with a basic aqueous solution in the same manner as in Reference Example 5 to obtain _{a Fe 3} O _{4 suspension dispersed in distilled water. 330 μl of Fe 3} O ₄ suspension (1.5 mg/ml) dispersed in distilled water, 500 μl of ascorbic acid (20 mg/ml) dispersed in ethanol, and _{40 μl of Na 2} PtCl ₄ aqueous solution (25 mg/μl ml) were mixed with distilled water and ethanol. The mixture (1:1 v/v) was added successively to the glass vial to make a final volume of 1.5 ml. The reaction glass vial was shaken using a shaker at room temperature for 90 minutes. The Fe ₃ O ₄ nano a symmetrical particle Pt is deposited on all surfaces of the cube (Pt @ Fe ₃ O ₄₎ from removing excess reagent and the reaction mixture remaining performed three times by centrifugation and washing in a solution was separated.

Reference Example 10. DLS (Dynamic Light Scattering; Dynamic Light Scattering) and Zeta Potential Measurement

The material synthesized above ( conc -Fe ₃ O ₄ @SiO ₂ , conc -Fe ₃ O ₄ , Pt@ conc -Fe ₃ O ₄ , PEG-Pt@ conc -Fe ₃ O ₄ ) was analyzed by DLS and Zeta potential was measured, and the data are shown in Table 1 below. Zeta potential represents the amount of surface charge of nanoparticles. After annealing, the size of the nanoparticles measured by DLS was much larger than the size confirmed by TEM, but this was due to agglomeration caused by the hydrophobicity of the material after heat treatment at high temperature. PEG-Pt@ conc -Fe ₃ O ₄ after being functionalized with a phosphate-polyethylene glycol ligand by the method of Reference Example 8 has greatly improved colloidal stability, compared to Pt@ conc -Fe ₃ O ₄ decreased DLS size.

[Table 1]

Reference Example 11. Pt@ conc -Fe ₃ O ₄ NTA-based diffusion studies of

To 1 ml of PEG-Pt@ conc- Fe ₃ O ₄ solution (1 mg/ml), 20 μl of various concentrations of hydrogen peroxide was added and diluted to a concentration range suitable for NTA measurement (10 μl in 2 ml of MilliQ water). - 2.2 x 10 ⁸ particles/ml). The movement of the nanoswimmer (PEG-Pt@conc- Fe ₃ O ₄ ) was recorded (25 frames per second) for 60 s at room temperature using Nanosight’s Nanoparticle Tracking Analysis (NTA 3.1), for a total of 1,498 13,332 particles in dog frames were used for NTA analysis. By analyzing the video, the x,y coordinates/position of each particle were determined as a function of the time interval. Diffusion constant (D) was derived for the concentration of _{H 2} O ₂ from the average for more than 438 particles.

When 1% to 5% of hydrogen peroxide was added, the diffusion of nanoswimmers (PEG-Pt@ conc -Fe ₃ O ₄ ) was observed to be high. The movement is proportional to the amount of hydrogen peroxide added, indicating that the nanoswimmers accelerated as the concentration of hydrogen peroxide increased. Because the nanoswimmers move fairly quickly due to their non-Brownian motion, the 'apparent' size of the moving nanoswimmers compared to the same structure before _{fuel (H 2} O _{2 ) was added.} was smaller Stokes-Einstein equation (D = TKB/3ðηd, where D is the diffusion constant of the particle, KB is the Boltzmann constant, η is the viscosity, T is the temperature, and d is the hydrodynamic diameter) ) because diffusion and (apparent) size are in inverse proportion to each other.

Reference Example 12. Pt@ conc - Fe ₃ O ₄ catalytic activity test

The catalytic activity of PEG-Pt@ conc -Fe ₃ O ₄ for the decomposition of Rh6G (Rhodamine 6G) in aqueous solution was evaluated through absorbance measurement. In a glass Petri dish, 1 mg/ml of catalyst (PEG-Pt@ conc -Fe ₃ O ₄ ) was mixed with 5 ml of Rh6G (0.1 mM) (the pH of the solution was adjusted to 4.2), and 5% hydrogen peroxide solution was added. . Aliquots samples of about 100 μl (diluted to 1 ml) were centrifuged at various time intervals. By measuring the absorbance of Rh6G at 550 nm, the concentration of the dye (Rh6G) in the filtered solution was analyzed. Figure 17 shows a standard curve (calibration curve) showing the serial dilution of rhodamine to various concentrations of 0 to 0.2mM (calibration curve).

Reference Example 13. Saturation Adsorption Test

By the addition of _{PEG-Pt @ conc -Fe 3 O} 4 to 10mg 100㎖ solution (pH 4.2) containing Rh6G of 10mg / L at room temperature for evaluating absorption rate of Rh6G for _{PEG-Pt @ conc -Fe 3 O} 4 did. The Rh6G concentration in the solution was measured by measuring the absorbance at 550 nm using a spectrophotometer.

When the amount of Rh6G added was increased to 25 mg/L, the degree of adsorption to PEG-Pt@ conc -Fe ₃ O ₄ did not improve, and the adsorption amount of PEG-Pt@ conc -Fe ₃ O _{4 of} Rh6G was very small (FIG. 18). . These results can be explained based on the weak electrostatic interaction between Pt@ conc -Fe ₃ O ₄ protected with polyethylene glycol ligands and cationic dye (Rh6G), and Rh6G reduction in solution is attributable to the nanoparticle surface. It can be seen that it is due to decomposition by catalytic reaction, not due to the physical adsorption of

Reference Example 14. Recyclability test

Recyclability for PEG-Pt@ conc -Fe ₃ O ₄ was performed as follows. In a glass Petri dish, 1 mg/ml of catalyst (PEG-Pt@ conc -Fe ₃ O ₄ ) was mixed with 5 ml of Rh6G (0.1 mM) (pH adjusted to 4.2), 5% hydrogen peroxide solution was added, and the reaction was completed. The catalyst was then recovered by magnetic separation. The recovered catalyst was centrifuged and washed three times to completely remove the adsorbed Rh6G, and the catalytic activity was evaluated as in the method of Reference Example 12 above.

Example 1. conc -Fe ₃ O ₄ Preparation of Nanocubes

Example 1.1 OA-Fe ₃ O ₄ @SiO ₂ Preparation of nanoparticles

An iron oxide nanocube capped with oleic acid (OA-Fe ₃ O ₄ ) was prepared as in the method of Reference Example 1, and X-ray diffraction (XRD) analysis of the prepared OA-Fe ₃ O _{4 , transmission electron microscopy (TEM)} ) and the results analyzed using a scanning electron microscope (SEM) are shown in FIGS. 2 a and b. As shown in the figure, OA-Fe ₃ O ₄ has an average edge length of 21 ± 1 nm.

Then, OA-Fe ₃ O ₄ @SiO _{2 was prepared by encapsulating OA-Fe 3} O ₄ with a silica shell using the reverse microemulsion method as in the method of Reference Example 2, and the prepared OA-Fe ₃ O ₄ A TEM image of @SiO ₂ is shown in FIG. 2 c. _{As shown in the figure, it shows that the diameter of OA-Fe 3} O ₄ @SiO ₂ nanoparticles (the diameter of silica nanospheres surrounding the nanocubes) surrounded by a soft silica shell with a thickness of 10 (± 1) nm is 41 ± 1 nm. . As shown in g of FIG. 3 , it was confirmed by XRD and HRTEM analysis that the _{Fe 3} O _{4 crystalline phase was preserved even after the encapsulation process by the silica shell.}

Example 1.2 OA-Fe under reductive conditions ₃ O ₄ @SiO ₂ Perform annealing heat treatment

_{In order to investigate the thermal nanocrystal change aspect of Fe 3} O ₄ in a spatially limited silica environment, as in the method of Reference Example 4.1, OA-Fe ₃ O ₄ @SiO ₂ was reduced without performing an annealing step in air. TEM images of nanoparticles produced by heat treatment at various annealing temperatures (T _ann = 300° C. to 700° C.) under conditions (flow of Ar and 4% H ₂ ) are shown in FIG. 2 d (300° C.), e (400° C.) ), f (500° C.), g (600° C.) and h (700° C.).

As shown in e of FIG. 2 , when OA-Fe ₃ O ₄ @SiO ₂ is heat-treated at an annealing temperature of 400° C. under reducing conditions without performing an annealing step in air, some nanoparticles (25% yield) outside On one side, pores having a concave shape (diameter of concave pore (d _conc ) = 4 to 11 nm) are formed, so that the asymmetrically concave Fe ₃ O ₄ ( conc -Fe ₃ O ₄ ) in silica contains a nanostructure ( conc ) -Fe ₃ O ₄ @SiO ₂ ) was observed. When the annealing temperature is increased from 400°C to 500°C, _{the conversion rate of OA-Fe 3} O ₄ @SiO ₂ to conc -Fe ₃ O ₄ @SiO ₂ increases from 25% to 45%, while the hollow silica nano A sphere [pupil diameter (d _hol ) = 20 (±2) nm] was additionally generated. As shown in the h of FIG. 2 , when OA-Fe ₃ O ₄ @SiO ₂ is heat-treated at an annealing temperature of 700° C. under reducing conditions without performing an annealing step in air, all nanostructures are collapsed and conc -Fe ₃ O ₄ @SiO _{2 It} was found that nanoparticles were aggregated in irregular shapes without further increase in yield.

Example 1.3 conc -Fe ₃ O ₄ @SiO ₂ Preparation of nanoparticles

In order to avoid interference from the oleate portion, as in the method of Reference Example 4.2, OA-Fe ₃ O ₄ @SiO ₂ was annealed at a temperature of 500° C. in air. After annealing OA-Fe ₃ O ₄ @SiO ₂ in air, TEM images of nanoparticles produced by annealing heat treatment at various temperatures (300° C. to 700° C.) under reducing conditions are i (300° C.) in FIG. 2, j (500° C.), k (600° C.), and l (700° C.).

3a shows a TEM image and an HRTEM image (internal image) of nanoparticles produced by annealing heat treatment of OA-Fe ₃ O _{4 @SiO 2 at a temperature of 500° C. in air.} As shown in a of FIG. 3 , in the product annealed in air at a temperature of 500° C., the shape and size of nanoparticles were maintained. However, as shown in g of FIG. 3 , the XRD patterns for nanoparticles prepared by annealing heat treatment of _{OA-Fe 3} O _{4 @SiO 2} at a temperature of 500° C. are three main ones appearing at 30°, 35.6° and 43°. (dominant) indicates that the Bragg peak is slightly shifted toward a higher angle, from which OA-Fe ₃ O ₄ @SiO ₂ in air annealing heat treatment at a temperature of 500 ° C., the oxidized γ-Fe ₂ O ₃ phase It can be seen that nanoparticles comprising

After that, as in the method of Reference Example 4.2, γ-Fe ₂ O ₃ @SiO ₂ was heat-treated at various temperatures (300° C. to 700° C.) under reducing conditions (Ar + 4% H _{2 ).} As shown in b, g and 4 of FIG. 3, from the results of XRD and HRTEM analysis, the crystalline phase γ-Fe ₂ O ₃ at a temperature of 300° C. or higher is superparamagnetic ( It was confirmed that it reverted to superparamagnetic) Fe ₃ O _{4 .} When annealing in air (under oxidative conditions) and then annealing at a temperature of 400° C. under reductive conditions, unlike the results of Example 1.2 above, Fe ₃ O ₄ nano a conc -Fe ₃ O ₄ @SiO ₂ was prepared having an open cavity on one side of the cube _{[d conc = 11 (± 1} ) nm].

As shown in Fig. 3c, elemental mapping and line profiling of conc -Fe ₃ O _{4 @SiO 2} single particles with a scanning transmission electron microscope (STEM-EDS) equipped with an energy-dispersive X-ray microscope, Fe atoms was uniformly distributed in the bright Z-contrast region except for the concave cavity region.

_{When γ-Fe 2} O ₃ @SiO ₂ is annealed at a temperature of 500°C or 600°C under reductive conditions , conc -Fe ₃ O ₄ @SiO ₂ [d _conc = 12 (±2)nm] together with by-products ( As a yield of about 20%), the nanocubes _{inside the SiO 2} disappear, and the pores inside [d _hol = 20 (±3) nm] and the nanospheres containing iron oxide on the outside of the silica shell [diameter (d) = 19 ( ±4) nm] of hollow silica nanoparticles ( h -SiO ₂ -FeO) are formed. As shown in FIG. 4, XRD and x-ray photoelectron spectroscopy (XPS) of by-products annealed at a temperature of 600° C. under reductive conditions showed new Bragg peaks at 36° and 42°, and as shown in FIG. 5 , , the Fe 2p area for Fe ²⁺ increased significantly at binding energy (BE) = 709.7 eV. This means that a crystalline FeO phase is generated from the by-product ( h -SiO _{2 -FeO).}

_{When the annealing heat treatment of Fe 3} O ₄ @SiO ₂ at a temperature of 700° C. under reducing conditions , the core @ shell and h -SiO ₂ -FeO were deformed and merged, and from the XRD pattern (g of FIG. It can be seen that the nanoparticles prepared by annealing at a temperature of 700° C. do _{not have a Fe 3} O ₄ phase, and ^{are composed of a crystalline Fe 2+} -silicate phase (Fe ₂ SiO _{4 ).}

Conc -Fe ₃ O ₄ @SiO ₂ From the above results it can be seen that the Fe ₃ O ₄ nano-cube is the middle of the process of converting the reduced FeO nano-sphere product. conc -Fe ₃ O ₄ Evolution of the recessed structure (concave structure) of @SiO ₂ is Fe ₃ O ₄ nano-cubes from Fe ²⁺ ions are released into the silica shell of the surrounding, for the growth of FeO on the outer shell surface of the nanocrystals It is expected to be an initial step to form an amorphous Fe ^{2+ -silicate phase supplying Fe 2+ ions.} In addition, as shown in FIG. 5 , in the deconvolution analysis of the high-resolution XPS spectrum of Si 2p ^{, a peak for the Fe 2+} -silicate phase (BE=709.7 eV) at 400° C. began to appear, which increased the annealing temperature. gradually increased with

In the initial stage of reductive annealing, Fe ²⁺ ions begin to migrate to the silica interface and are trapped at silicate anionic sites to form a thermodynamically stable Fe-silicate phase. This is a highly reactive part for the continuous movement of ^{Fe 2+ , and a nanoscopic defect is temporarily generated, and the surface on which Fe 2+} ions initially started to migrate evolves into a single cavity on the same surface. The pore-forming process is limited by the maximum amount of ^{Fe 2+} ions that can be accommodated by the surrounding silica shell.

Example 1.4 conc -Fe ₃ O ₄ Preparation of Nanocubes

As in the method of Reference Example 5, conc -Fe ₃ O ₄ @SiO ₂ By completely removing the silica shell from nanoparticles, conc -Fe ₃ O ₄ was prepared, and energy filtered for conc -Fe ₃ O _{4 TEM-} An accurate three-dimensional (3D) shape of a concave structure was reconstructed using a tomography method, and the result is shown in f of FIG. 3 . As shown in the BF-TEM projection images at different inclination angles (-72° to +68°) and the reconstructed 3D structure therefrom (Fig. 3f), the concave structure is a single facet of the nanocube. was selectively restricted to

Example 2. Changes in the pore structure according to annealing time

TEM for conc -Fe ₃ O ₄ @SiO ₂ prepared by annealing OA-Fe ₃ O ₄ @SiO ₂ in air, and then heat-treating it for various times (0 to 48 hours) at an annealing temperature of 400° C. under reductive conditions. The images are shown in FIGS. 6 and 7 , and the pore size distribution in the nanoparticles in which the pore structure is observed is shown in FIG. 7 . .

As shown in FIG. 6, a concave structure [d _{conc = 10 (±2) nm] in Fe 3} O ₄ of nanoparticles prepared by annealing heat treatment at 400° C. under reducing conditions began to appear 20 minutes after heat treatment, No observable intermediates were identified. In addition, as shown in FIG. 7 , the structure of the nanoparticles having pores on the outer surface was maintained even for 24 hours, because the surrounding silicate shell was saturated ^{with Fe 2+ ions.} After 48 h of heat treatment, the separation of the FeO- phase from the silicate shell was initiated through the sequential transfer ^{of Fe 2+} _{ions from the Fe 3} O ₄ core to the growing FeO nanocrystals (located on the outer shell surface), h -SiO ₂ -FeO with a hollow) silica shell was formed.

Example 3. conc -Fe ₃ O ₄ @SiO ₂ and Fe ₃ O ₄ @SiO ₂ conversion between

As in the method of Reference Example 4.3, conc -Fe ₃ O ₄ @SiO ₂ by repeatedly switching the _{gas environment (air, or H 2} +Ar) to the nanoparticles prepared by repeatedly performing thermal oxidation and reduction annealing A TEM image for the TEM image is shown in FIG. 8 .

conc -Fe ₃ O ₄ when the heat treatment for 5 hours at a temperature of 400 ℃ the @SiO ₂ in air, a concave cavity is recharged with Fe ₃ O ₄ crystalline phase (Fe ₃ O ₄ lattice-disconnected -crystalline phase) having a separate grid , forming separate small spherical domains, and the conc -Fe ₃ O ₄ core reverted to the nanocube-like structure of the initial Fe ₃ O _{4 @SiO 2} without pores, as shown in FIG. 8 , conc -Fe ₃ When O ₄ is repeatedly subjected to thermal oxidation (5 hours at 400°C) and reduction (5 hours at 400°C) annealing, it is reversible between a nanocube that does not have a concave pore structure and a nanocube structure that has concave pores on one surface. changed to The same dual domain crystal structure was shown in the TEM image of the nanoparticles after each oxidation step, confirming that Fe ions reciprocate at fixed positions at the iron oxide/silica interface.

Example 4. Control experiment

Example 4.1 Fe confined in a hollow silica shell ₃ O ₄ Nanocube (Fe ₃ O ₄ @ h -SiO ₂ ) of the thermal conversion control experiment

As in the method of Reference Example 6, Fe ₃ O ₄ is confined within the hollow silica shell, so Fe ₃ O ₄ and the silica shell are in minimal contact with Fe ₃ O ₄ @ h -SiO ₂ After annealing in air ( TEM images of nanoparticles prepared by performing annealing heat treatment at various temperatures (300° C. to 700° C.) under reductive conditions (for 5 hours at a temperature of 500° C.) are shown in FIG. 9 . As shown in Figure 9, Fe ₃ O ₄ @ h -SiO _{2 Asymmetric Fe 3} O ₄ concave in nanoparticles prepared by annealing heat treatment in air and then annealing heat treatment at a temperature of 400 to 700 ° C. under reducing conditions for 5 hours. No structure was observed, indicating that the close physical contact of _{Fe 3} O ₄ and silica shell plays an important role in the thermally induced migration of ^{Fe 2+ ions for concave structure formation.}

Example 4.2 Spherical Fe surrounded by silica shells ₃ O ₄ of thermal transformation control experiment

_{A TEM image of nanoparticles prepared by heat-treating spherical Fe 3} O ₄ nanocrystals [d = 5 (±1) nm] surrounded by silica at a temperature of 300 to 700° C. under reducing conditions for 5 hours is shown in FIG. indicated. After a heat treatment the Fe ₃ O ₄ nano-cube surrounded with silica in reductive conditions (Example 1) with differently, a rectangle surrounded by a silica Fe ₃ O ₄ nanocrystals as shown in FIG. 10 [d = 5 (± 1) nm] was not observed in the nanoparticles prepared by heat treatment in a reducing atmosphere, and hollow SiO ₂ and iron oxide nanocrystals ( h -SiO ₂ -FeO) escaping from the silica shell were found in the SiO ₂ outer shell. The formed nanoparticles ( h -SiO ₂ -FeO) were prepared. This is due to the isotropic morphology of the _{spherical Fe 3} O _{4 nanocrystals surrounded by silica.}

Example 4.3 MnO@SiO ₂ Thermal conversion control experiment using

For nanoparticles prepared by performing heat treatment at various annealing temperatures (300 to 700 ° C.) for 5 hours under reducing conditions (Ar+4% H ₂ ) using MnO nanocubes (MnO@SiO _{2 ) surrounded by silica.} A TEM image is shown in FIG. 11 .

_{Unlike the result of heat treatment of Fe 3} O ₄ nanocubes surrounded by silica under reducing conditions (Example 1), as shown in FIG. 11 , MnO nanocubes surrounded by silica (MnO@SiO ₂ ) were annealed under reducing conditions. In the heat treatment, when annealing at a temperature of 500°C, empty spaces began to form inside the MnO nanocubes, and when annealing at a temperature of 600°C, hollow inner cavities appeared in the nanostructure, and when annealing at a temperature of 700°C, hollow spaces were formed. Nanostructures are merged.

Example 5. Pt@ conc -Fe ₃ O ₄ Preparation and catalytic activity

Example 5.1 Janus Pt@ with asymmetric structure conc -Fe ₃ O ₄ catalyst preparation

Reference Example 5 to 7 and the method of, after disconnecting the conc -Fe ₃ O ₄ with a silica shell removed from conc -Fe ₃ O ₄ @SiO ₂ by basic hydrolysis, treatment with Na ₂ PtCl ₄ with ascorbic acid to Pt- to functionalize with nanocrystals to prepare Pt@ conc -Fe ₃ O ₄ , and for this, TEM images, HRTEM images, STEM images, STEM-EDS element mapping images, XRD patterns are shown in FIGS. 12, 13 and FIG. 14 is shown. As shown in the TEM image of Pt@ conc -Fe ₃ O ₄ and the XRD pattern of FIG. 14 over the course of reaction time in FIGS. 12 and 13 , Pt in the concave region of conc -Fe ₃ O _{4 with the lapse of reaction time} Nanocrystals were gradually deposited, and after 90 minutes of reaction, a Janus Pt@ conc -Fe ₃ O ₄ nanostructure having Pt nanocrystals with a diameter of 3.0 (±1) nm was prepared.

Example 5.2 Pt@ conc -Fe ₃ O ₄ rhodamine-degrading activity of

Scheme 3 below shows the catalytic activation mechanism by the self-propulsion and penton oxidation reaction of the Pt@ conc -Fe ₃ O _{4 catalyst.}

[Scheme 3]

Pt nanoparticles, because the decomposition of H ₂ O ₂ to H ₂ O and O ₂ from the catalyst H ₂ O _2, Pt @ conc -Fe ₃ O ₄ at one end of the catalyst of the aqueous H ₂ O ₂ by the Pt nanocrystals _{O 2} release by decomposition enables self-propellation of Pt@ conc -Fe ₃ O ₄ , resulting in a synergetic kinetic-catalytic effect that accompanies enhanced motion in the fluid and increases the decomposition effect of pollutants. give The iron oxide ions _{react with H 2} O ₂ to form hydroxyl radicals (OH·) that decompose organic pollutants.

For high colloidal stability, in the method of Reference Example 8, Pt@ conc -Fe ₃ O ₄ was first modified with phosphate-polyethylene glycol to prepare PEG-Pt@ conc -Fe ₃ O ₄ , and the method of Reference Example 11 Before and after the addition of H ₂ O ₂ as shown in Fig. 15 a and b, respectively, the NTA size analysis results for the Pt@ conc -Fe ₃ O _{4 nanoswimmers.} In the Stokes-Einstein equation, the size of nanoparticles (nanoswimmers) is inversely proportional to the diffusion coefficient (D), and the apparent size appears smaller as the diffusion coefficient (D) increases due to particle motion. As shown in a and b of FIG. 15 , when H ₂ O ₂ was added as a fuel, as a result of NTA size analysis, the size of Pt@ conc -Fe ₃ O ₄ was reduced, which was caused by decomposition of _{H 2} O _{2 O 2} This is because the motility of the particles is improved by the emission.

As a catalyst for decomposing rhodamine 6G (rhodamine 6G; Rh6G) via _{H 2} O ₂ , PEG-Pt@ conc -Fe ₃ O ₄ nanoswimmers were used. Of Figure 16 is a Pt @ by conc -Fe ₃ O ₄ shows a schematic diagram of a process in which the decomposition Rh6G, using the NTA for _{PEG-Pt @ conc -Fe 3 O} 4 , and PEG- conc -Fe ₃ O ₄ The diffusion coefficient (D) was measured according to the _{H 2} O ₂ ^{concentration, and the average D (nm 2} /s) was shown in FIG. 16 b . As shown in FIG. 16 b, when _{the concentration of H 2} O ₂ as a fuel is increased, the D of PEG-Pt@ conc -Fe ₃ O ₄ increases linearly, whereas in the absence of a Pt catalyst, PEG- conc D of -Fe ₃ O ₄ was not affected.

Quantitative comparison of Rh6G degradation effects by PEG-Pt@ conc -Fe ₃ O ₄ and control particles (PEG-Fe ₃ O ₄ , PEG- conc -Fe ₃ O ₄ , PEG- conc -Fe ₃ O _{4 + Pt)} Thus, it is shown in FIG. 16 c, and the Rh6G decomposition effect of Pt@ conc -Fe ₃ O _{4 according to the PEG-H 2} O ₂ concentration (0 to 4%) is shown in FIG. 16 d. As shown in FIG. 16 c , when PEG-Pt@ conc -Fe ₃ O ₄ (1 mg/ml) was used, Rh6G was decomposed to exceed 99% (>99%) within 30 minutes, whereas it was used as a control catalyst. PEG-Fe ₃ O ₄ , PEG- conc -Fe ₃ O _{4 ,} or a physical mixture of PEG -conc -Fe ₃ O ₄ and Pt nanocrystals (PEG- conc -Fe ₃ O ₄ + Pt) is 5 and 15, respectively. , showed an incomplete reaction with a conversion of 25%. Rh6G degrading activity of PEG- conc -Fe ₃ O ₄ is due to PEG-Fe ₃ O ₄ was shown to be slightly higher than the nano-cube, which is highly reactive pore (cavity) the interior of the Fe sites of conc -Fe ₃ O _4. In particular, the nonpropelling, physical mixture of Pt nanocrystals and PEG-conc -Fe ₃ O ₄ (PEG- conc -Fe ₃ O ₄ + Pt) showed inferior rhodamine degradation performance (conversion of 30%). . PEG-Pt@ conc -Fe ₃ O ₄ exhibited a synergistic Rh6G degradation effect due to the _{low-coordination Fe 3} O ₄ -Pt site and rapid self-propulsion at the interface with high reactivity in the cavity.

In the _{absence of H 2} O ₂ , the removal rate (%) of Rh6G according to the concentration of PEG-Pt@ conc -Fe ₃ O _{4 and} the concentration of PEG-Pt@ conc -Fe 3 O 4 over time when PEG-Pt@ conc -Fe ₃ O _{4 is added (%) is shown in FIG.} It is shown in a and b, respectively.

As shown in d of FIG. 16 , as _{the concentration of H 2} O ₂ increased, the Rh6G decomposition effect was improved, and as shown in FIGS. 18 a and b , PEG-Pt@ conc -Fe ₃ O in the _{absence of H 2} O _{2 . When 4} was treated with Rh6G solution for 160 minutes, only 6% of Rh6G was removed, so the PEG-Pt@ conc -Fe ₃ O ₄ nanoswimmer according to an embodiment of the present invention has excellent activity through H ₂ O _{2 .} can be used as a catalyst for decomposing Rh6G.

To investigate the effect of visible light on the decomposition of Rh6G, Rh6G in PEG-Pt@conc- Fe ₃ O ₄ under visible light (No catalyst), light (Light), or dark (Dark) conditions. The decomposition effect was measured and shown in FIG. 19 . As shown in FIG. 19 , there was no change in the concentration of Rh6G even after 30 minutes by visible light without the catalyst, and regardless of whether it was under light or dark conditions, Rh6G upon addition of a catalyst (PEG-Pt@ conc -Fe ₃ O _{4 )} was almost completely decomposed in 30 min.

Example 6. Control experiment using symmetrical nanoparticles with Pt deposited on all sides.

The method of Reference Example 9 to Fe ₃ O ₄ nano-manufacturing the symmetrical particles (Pt @ Fe ₃ O ₄₎ of Pt is deposited on all surfaces of the cube, and also a TEM image of the PEG-Pt @ Fe ₃ O ₄ 20 shown in a, and _{DLS size data for PEG-Pt@Fe 3} O ₄ is shown in FIG. 20 b, PEG-Pt@ conc -Fe ₃ O ₄ , PEG-Pt@Fe ₃ O ₄ , or The results of Rh6G decomposition by PEG- conc- Fe ₃ O ₄ are shown in FIG. 20 c . As shown in Fig. 20c , due to the asymmetric structure of _{PEG-Pt@Fe 3} O ₄ and the absence of Pt deposited on the concave surface of PEG-conc -Fe ₃ O ₄ , in both cases PEG-Pt@conc- Fe ₃ O ₄ showed inferior catalytic activity compared to that.

Example 7. Recyclability of catalysts

Recyclability of PEG-Pt@ conc -Fe ₃ O ₄ was performed in the same manner as in Reference Example 14. After each cycle, the catalyst was separated using magnetic properties and the Rh6G decomposition activity of the separated catalyst was tested. As shown in FIG. 21 , even after performing the Rh6G decomposition reaction 10 times, the catalyst was able to decompose Rh6G by ~90%.

Claims (23)

(1) performing a silica sol-gel reaction by adding an aqueous ammonia solution and a silica precursor to a microemulsion containing iron oxide nanocubes capped with an organic material, to prepare nanoparticles comprising iron oxide nanocubes and a silica shell surrounding them step;
(2) heat-treating the nanoparticles obtained in step (1) at a temperature of 400° C. to less than 800° C. under oxidative conditions, thereby removing the organic material capped on the iron oxide nanocubes of the nanoparticles;
(3) by heat-treating the nanoparticles obtained in step (2) at a temperature of 400° C. or higher to less than 500° C. under reducing conditions, having an open cavity in the form of concave inward on the outer surface of the nanocube contained in the nanoparticles preparing nanoparticles; and
(4) treating the nanoparticles obtained in step (3) with a basic aqueous solution to remove the silica shell to obtain an iron oxide nanocube having an open pore concave inwardly on the outer surface,
A method for manufacturing an iron oxide nanocube having an open cavity concave inwardly on an external surface. The method of claim 1, wherein the organic material is one selected from the group consisting of an aliphatic amine containing a C ₄ to aliphatic alcohols, and C ₄ to C _30, including fatty acids, C ₄ to C ₃₀ comprising a C ₃₀ The above, the manufacturing method. According to claim 2, wherein the C ₄ to C ₃₀ fatty acid containing lauric acid (lauric acid), myristic acid (myristic acid), linoleic acid (linoleic acid), stearic acid (stearic acid), oleic acid (oleic acid) , and at least one selected from the group consisting of palmitic acid, a manufacturing method. According to claim 1, wherein the iron oxide _{nanocubes magnetite (magnetite; Fe 3} O ₄ ), maghemite (maghemite; γ-Fe ₂ O ₃ ), or a combination thereof, the manufacturing method comprising. The method according to claim 1, wherein the silica shell and the iron oxide nanocubes in the nanoparticles obtained in step (1) are in physical contact so as not to form an empty space between the silica shell and the iron oxide nanocubes. The method according to claim 1, wherein the oxidative condition is a condition of using a mixed gas containing 10 mol% or more of oxygen. The method according to claim 1, wherein the iron oxide nanocubes in the nanoparticles obtained in step (2) include maghemite (γ-Fe ₂ O ₃ ). The method of claim 1, wherein the reducing condition is hydrogen gas (H ₂ ), or a condition using a mixed gas containing 1 mol% or more of hydrogen. The method according to claim 1, wherein the heat treatment under the reducing conditions is performed for 20 minutes to 24 hours. The method according to claim 1, wherein the diameter of the open pores in the nanocube obtained in step (4) is 10 to 15 nm. The method according to claim 1, wherein the nanocubes obtained in step (4) have an average diagonal length of 20 to 45 nm. According to claim 1, The nanocube obtained in step (4) is magnetite (magnetite; Fe ₃ O ₄ ), including a manufacturing method. The method according to claim 1, wherein, between steps (3) and (4), the nanoparticles obtained in step (3) are heat-treated at a temperature of 400° C. or higher to less than 800° C. under oxidative conditions to have a pore structure. After performing the step of converting to nanoparticles that do not have the same structure as the nanoparticles obtained in step (3) by heat-treating the nanoparticles without the pore structure at a temperature of 400° C. or higher to less than 500° C. under reducing conditions Further comprising the step of preparing nanoparticles, the manufacturing method. The method according to claim 1, wherein (5) treating the iron oxide nanocubes obtained in step (4) with an aqueous solution containing a reducing agent and a noble metal precursor to prepare noble metal nanocrystals on the concave surfaces of the open pores of the nanocubes. Including, a manufacturing method. 15. The iron oxide nanocube manufactured by the method of any one of claims 1 to 14, comprising an open pore having an inwardly concave shape on an outer surface and having a diameter of 10 to 15 nm. The iron oxide nanocube of claim 15 , wherein the iron oxide nanocube comprises magnetite (Fe ₃ O ₄ ). 15. The method of any one of claims 1 to 14, wherein the iron oxide nanocube, which is in the form of an inwardly concave shape on the outer surface and includes an open cavity having a diameter of 10 to 15 nm, and the open cavity of the iron oxide nanocube A catalyst for Fenton oxidation, comprising the formed noble metal nanocrystals. The method according to claim 17, wherein the noble metal is one selected from the group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), silver (Ag), ruthenium (Ru), and alloys thereof. , a catalyst for Fenton oxidation treatment. The catalyst according to claim 17, wherein the diameter of the noble metal nanocrystals is 1 to 7 nm. The method of claim 17, wherein the noble metal nanocrystals contained in the catalyst release oxygen (O _{2 ) in the presence of hydrogen peroxide (H 2} O ₂ ), so that the catalyst can move in one direction, for Fenton oxidation treatment catalyst. _{Hydrogen peroxide (H 2} O ₂ ), and the catalyst for the Fenton oxidation treatment of claim 17 are added to wastewater containing pollutants, and pollutants are decomposed by hydroxyl radicals generated by the Fenton oxidation reaction. Contaminants in water decomposition method. The method of claim 21, wherein the pollutant is a difficult-to-decompose organic material. The method of claim 22, wherein the hardly decomposable organic material comprises an aromatic benzene ring compound or a halogenated organic compound.

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