KR102385445B1 - β-FeOOH particles having a two-dimensional or three-dimensional structure, and a method for manufacturing the same - Google Patents

Abstract

The present invention comprises the steps of: a) preparing a reaction solution containing an iron precursor, polyethyleneimine and sulfate; And b) hydrothermal synthesis of the reaction solution; relates to a method for producing β-FeOOH particles comprising a;

Description

β-FeOOH particles having a two-dimensional or three-dimensional structure and a manufacturing method thereof {β-FeOOH particles having a two-dimensional or three-dimensional structure, and a method for manufacturing the same}

The present invention relates to β-FeOOH particles having a two-dimensional or three-dimensional structure and a method for preparing the same.

Compared to bulk materials, iron oxide nanomaterials have been widely used for environmental monitoring and decontamination of various inorganic pollutants due to their excellent performance such as high specific surface area, low cost, and eco-friendliness compared to bulk materials. Iron oxyhydroxide (FeOOH) nanomaterials are attracting great interest due to their broad applicability in catalysts, electrode materials and adsorption.

In addition, nanomaterials with different structures and crystal forms generally have various electrical and optical properties, so the two-dimensional (2D, two-dimension) or three-dimensional (3D, three-dimension) rule by assembling a one-dimensional nanostructure Techniques for transforming into superstructures are attracting great attention in the field of materials chemistry.

However, since FeOOH inherently has a non-layered crystal structure, nanowires can be formed into certain types of free-standing 2D nanostructures or free-standing 3D nanostructures. Self-assembly is still a difficult task.

On the other hand, as a similar prior document for producing FeOOH, Korean Patent Application Laid-Open No. 10-2017-0006627 is presented.

Republic of Korea Patent Publication No. 10-2017-0006627 (2017.01.18.)

The present invention for solving the above problems is a method for producing β-FeOOH particles having a specific type of free-standing 2D nanostructures or free-standing 3D nanostructures in which nanowires are self-assembled; and An object of the present invention is to provide β-FeOOH particles prepared therefrom.

Another object of the present invention is to provide an adsorbent comprising the β-FeOOH particles.

One aspect of the present invention for achieving the above object is a) preparing a reaction solution containing an iron precursor, polyethyleneimine and sulfate; And b) hydrothermal synthesis of the reaction solution; relates to a method for producing β-FeOOH particles comprising a.

In one aspect, the method for preparing the β-FeOOH particles comprises preparing β-FeOOH nanobundle particles having a two-dimensional structure from a reaction solution containing 0.0001 to 0.0010 moles of polyethyleneimine and 0.1 to 0.80 moles of sulfate per 1 mole of the iron precursor. It may be manufacturing.

In one aspect, the method for preparing the β-FeOOH particles is a three-dimensional structure of β-FeOOH nanospiky particles from a reaction solution containing 0.0011 to 0.0030 moles of polyethyleneimine and 0.85 to 1.50 moles of sulfate based on 1 mole of the iron precursor. may be manufactured.

In one aspect, the hydrothermal synthesis may be performed at a temperature of 150° C. or higher for 50 minutes or longer.

In addition, another aspect of the present invention relates to β-FeOOH particles prepared by the above-described method for preparing β-FeOOH particles.

In another aspect, the β-FeOOH particles may be β-FeOOH nanobundle particles having a two-dimensional structure or β-FeOOH nanospiky particles having a three-dimensional structure.

In another aspect, the β-FeOOH nanobundle particles having the two-dimensional structure may have a two-dimensional structure in which a plurality of nanowires having an average diameter of 1 to 3 nm are self-assembled.

In another aspect, the β-FeOOH nanospiky particles having the three-dimensional structure may have a three-dimensional sharp particle structure in which a plurality of nanowires having an average diameter of 1 to 3 nm are self-assembled.

In another aspect, the β-FeOOH particles may have a specific surface area measured by a nitrogen adsorption BET (Brunauer-Emmett-Teller) method of 80 m 2 /g or more.

In addition, another aspect of the present invention relates to a β-FeOOH adsorbent for removing heavy metal ions comprising the above-described β-FeOOH particles.

In another aspect, the β-FeOOH adsorbent may have an adsorption capacity of 50 mg/g or more.

In another aspect, the β-FeOOH adsorbent may satisfy the following relational formula (1).

[Relational Expression 1]

75 ≤ (Q _e5 /Q _e1 ) × 100

(In the above relation 1, Q _e1 is the adsorption capacity (mg/g) at the time of 1 cycle of adsorption, Q _e5 is the adsorption capacity (mg/g) at the time of 5 cycles of adsorption (mg/g). do.)

In another aspect, the β-FeOOH adsorbent may be for hexavalent chromium (Cr(VI)) removal.

In the method for producing β-FeOOH particles according to the present invention, β-FeOOH particles having a 2D nanobundle type or 3D nanospiky type can be easily prepared by hydrothermal synthesis of a reaction solution containing an iron precursor, polyethyleneimine and sulfate. .

In addition, the β-FeOOH particles having a 2D nanobundle type or 3D nanospiky type prepared by the above method have a high specific surface area, and when used as a heavy metal adsorbent, there is an advantage of having high adsorption capacity and recyclability.

1 shows a method for preparing β-FeOOH particles according to the present invention.
2 is a transmission electron microscopy (TEM) image of nanobundle-type β-FeOOH particles and nanospiky-type β-FeOOH particles prepared by varying the reaction time.
3 is a TEM image of nanobundle-type β-FeOOH particles and nanospiky-type β-FeOOH particles prepared by varying the reaction temperature.
4 is an X-ray diffraction pattern (XRD, X-ray diffraction) and TEM images of FeOOH particles prepared in Comparative Examples 1 to 3;
5 is a nitrogen adsorption/desorption isotherm of the nanobundle-type β-FeOOH particles (a) and the nanospiky-type β-FeOOH particles (b) prepared in Examples 1 and 2, respectively.
6 is an absorption spectrum (a) and a diffuse reflection spectrum (b) of the nanobundled β-FeOOH particles and the nanospiky β-FeOOH particles prepared in Examples 1 and 2, respectively.
7 is a TEM image (a, b) of nanobundle-type β-FeOOH particles and a high resolution transmission electron microscopy (HRTEM) image in a specific region of FIG. 7 b (region 1 b1, region 2 b2) )am.
FIG. 8 is a scanning electron microscopy (SEM) image (a) and an atomic force microscopy (AFM) image (b) of nanobundle-type β-FeOOH particles.
9 is a high-angle-dark field-scanning transmission electron microscope (HAADF-STEM, high-angle annular dark field, scanning transmission electron microscopy) image of a single nanobundle-type β-FeOOH particle (a) and energy dispersive spectroscopy ( Elemental mapping (b) measured by EDS, energy-dispersive X-ray spectroscopy.
10 is a TEM image of nanospiky-type β-FeOOH particles and an HRTEM image in a specific region.
11 is an adsorption isotherm of nanobundled β-FeOOH particles (a) and nanospiky β-FeOOH particles (b).
12 is an analysis result of adsorption capacity according to time of nano-bundled β-FeOOH particles.
13 is an analysis result of adsorption capacity according to pH of nanobundle-type β-FeOOH particles.
14 is an analysis result of adsorption capacity according to repeated adsorption and desorption of nanobundle-type β-FeOOH particles.
15 is a HAADF-STEM image (a) and TEM image (b) of nanobundled β-FeOOH particles after Cr(VI) adsorption.
16 is a TEM image of nanobundled β-FeOOH particles after Cr(VI) adsorption and an HRTEM image in a specific region.
17 is an EDS element mapping of nanobundled β-FeOOH particles after Cr(VI) adsorption.
18 is an X-ray photoelectron spectroscopy (XPS) spectrum of nanobundled β-FeOOH particles after Cr(VI) adsorption.

Hereinafter, β-FeOOH particles having a two-dimensional or three-dimensional structure according to the present invention and a manufacturing method thereof will be described in detail. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the technical field to which this invention belongs, and the summary of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

Although many methods for preparing β-FeOOH particles have been proposed, since β-FeOOH has an essentially non-layered crystal structure, self-assembled β-FeOOH particles into a specific type of stand-alone 2D nanostructure or 3D nanostructure can be prepared. It was difficult to do.

Accordingly, the present inventors have repeatedly studied to prepare β-FeOOH particles having a 2D or 3D structure, and can produce β-FeOOH particles having a 2D or 3D structure when an iron precursor, polyethyleneimine, and sulfate are hydrothermal synthetically reacted. It has been found that the present invention has been completed.

Specifically, the method for producing β-FeOOH particles according to an embodiment of the present invention comprises the steps of: a) preparing a reaction solution containing an iron precursor, polyethyleneimine and sulfate; and b) hydrothermal synthesis of the reaction solution.

As such, in the method for producing β-FeOOH particles according to the present invention, β-FeOOH particles having a 2D nanobundle type or 3D nanospiky type can be easily prepared by hydrothermal synthesis of a reaction solution containing an iron precursor, polyethyleneimine and sulfate. can

In addition, the β-FeOOH particles having a 2D nanobundle type or 3D nanospiky type prepared by the above method have a high specific surface area, and when used as a heavy metal adsorbent, there is an advantage of having high adsorption capacity and recyclability.

Hereinafter, each step and component elements of the method for producing β-FeOOH particles according to the present invention will be described in more detail.

First, a) a reaction solution containing an iron precursor, polyethyleneimine and sulfate may be prepared. As described above, self-assembled β-FeOOH particles into free-standing 2D nanostructures or 3D nanostructures can be prepared through the combination of an iron precursor, polyethyleneimine and sulfate. On the other hand, β-FeOOH particles self-assembled into stand-alone 2D nanostructures or 3D nanostructures cannot be prepared unless polyethyleneimine or sulfate is added. Specifically, when polyethyleneimine is not added, hierarchical β-FeOOH particles are prepared, when sulfate is not added, one-dimensional nanorod β-FeOOH particles are prepared, and when both compounds are not added β-FeOOH particles in the form of a one-dimensional spindle are prepared.

Meanwhile, in one embodiment of the present invention, the iron precursor may be used without particular limitation as long as it is used to prepare β-FeOOH particles, and specifically, any one or two selected from iron chloride (FeCl ₃ ) and its hydrates. may be more than

The polyethyleneimine is a polymer having a repeating unit composed of an amine group and an ethylene group spacer. The polyethyleneimine may be linear or branched, and preferably a branched polyethyleneimine in which a side branch is connected to a main branch. In addition, the weight average molecular weight of the polyethyleneimine may be 3,000 to 50,000 g/mol, more preferably 10,000 to 30,000 g/mol. In this range, 2D nanobundle β-FeOOH particles and 3D nanospiky β-FeOOH particles can be prepared more effectively.

The sulfate includes sulfate (SO ₄ ^2- ) and is not particularly limited as long as it does not inhibit the reaction, and specifically, for example, any one or two or more alkalized sulfuric acid selected from sodium sulfate, potassium sulfate and rubidium sulfate, and the like. , preferably sodium sulfate.

Furthermore, in the method for producing β-FeOOH particles according to the present invention, 2D nanobundle β-FeOOH particles or 3D nanospiky β-FeOOH particles can be prepared by controlling the concentrations of polyethyleneimine and sulfate.

As a specific example, the 2D nanobundle-type β-FeOOH particles may be prepared using a reaction solution containing 0.0001 to 0.0010 moles of polyethyleneimine and 0.1 to 0.80 moles of sulfate based on 1 mole of the iron precursor, and more preferably, polyethyleneimine It can be prepared using a reaction solution containing 0.0002 to 0.0006 moles and 0.3 to 0.7 moles of sulfate. When it is out of the above range, a one-dimensional particle may be manufactured or a three-dimensional nanospiky particle may be manufactured.

In addition, the 3D nanospiky-type β-FeOOH particles may be prepared using a reaction solution containing 0.0011 to 0.0030 moles of polyethyleneimine and 0.85 to 1.50 moles of sulfate based on 1 mole of the iron precursor, more preferably from 0.0012 to polyethyleneimine It can be prepared using a reaction solution containing 0.0020 moles and 0.88 to 0.95 moles of sulfate. When it is out of the above range, a one-dimensional particle may be manufactured or a two-dimensional nanospandle particle may be manufactured.

In addition, the reaction solution may be an aqueous solution, and the water may be deionized water or ultrapure water, and 5 to 20 l of water may be added per 1 mole of the iron precursor, preferably 7 to 15 l of water. can be In such a range, the hydrothermal synthesis reaction can be performed more effectively.

Next, when the reaction solution is prepared with the above combination and content, the reaction solution is rapidly ?g? After sealing, b) a hydrothermal synthesis reaction can be performed, and the reaction temperature and time are particularly important in preparing 2D nanobundle β-FeOOH particles or 3D nanospiky β-FeOOH particles.

As a specific example, the hydrothermal synthesis may be performed at a temperature of 150° C. or higher for 50 minutes or more, and preferably, the hydrothermal synthesis may be performed at a temperature of 160 to 180° C. for 60 to 120 minutes. In this range, 2D nanobundle-type β-FeOOH particles or 3D nanospiky-type β-FeOOH particles can be prepared. On the other hand, when the temperature is less than 150 °C or the reaction time is less than 50 minutes, as shown in FIGS.

In addition, the present invention relates to β-FeOOH particles prepared by the above-described method, wherein the β-FeOOH particles may be β-FeOOH nanobundle particles having a two-dimensional structure or β-FeOOH nanospiky particles having a three-dimensional structure. .

More specifically, the β-FeOOH nanobundle particles having the two-dimensional structure may have a plurality of nanowires self-assembled, and specifically, a two-dimensional structure in which a plurality of nanowires having an average diameter of 1 to 3 nm are self-assembled. there is. Furthermore, the β-FeOOH nanobundle particles having the two-dimensional structure have a very thin ultra-thin structure despite the nanowires having a self-assembled structure, and specifically, may have an average thickness of 5 to 20 nm.

In addition, the β-FeOOH nanospiky particles having the three-dimensional structure may also be self-assembled with a plurality of nanowires, and specifically, a three-dimensional pointed particle in which a plurality of nanowires having an average diameter of 1 to 3 nm are self-assembled. there is. Furthermore, the β-FeOOH nanospiky particles having the three-dimensional structure may have an average particle size of 50 to 200 nm.

Such β-FeOOH nanobundle particles having a two-dimensional structure or β-FeOOH nanospiky particles having a three-dimensional structure may have a high specific surface area, and specifically, the ratio measured by the nitrogen adsorption BET (Brunauer-Emmett-Teller) method. The surface area may be at least 80 m 2 /g, more preferably at least 90 m 2 /g. In this case, the upper limit of the specific surface area is not particularly limited, but may be, for example, 200 m 2 /g.

In addition, the β-FeOOH nanobundle particles of the two-dimensional structure or the β-FeOOH nanospiky particles of the three-dimensional structure may have a higher bandgap energy than the one-dimensional β-FeOOH nanorod particles (2.91 eV), specifically As a result, it may have a bandgap energy of 3 to 3.5 eV.

In addition, another aspect of the present invention relates to a β-FeOOH adsorbent for removing heavy metal ions comprising the above-described β-FeOOH particles.

That is, the above-described β-FeOOH nanobundle particles having a two-dimensional structure or β-FeOOH nanospiky particles having a three-dimensional structure may have a higher adsorption capacity as they have a high specific surface area, and thus heavy metal ions, especially 6 It may be particularly effective in adsorbing and removing chromium (Cr(VI)).

As a specific example, the β-FeOOH adsorbent may have an adsorption capacity of 50 mg/g or more, more preferably 55 mg/g, measured using 400 mg/L of a Cr(VI) ion solution at pH 2.5. At this time, the upper limit of the adsorption capacity is not particularly limited, but may be, for example, 200 mg/g.

In addition, the β-FeOOH adsorbent may satisfy Relational Equation 1 below.

[Relational Expression 1]

75 ≤ (Q _e5 /Q _e1 ) × 100

In the above relation 1, Q _e1 is the adsorption capacity (mg/g) at the time of one cycle of adsorption, Q _e5 is the adsorption capacity (mg/g) at the time of adsorption for 5 cycles (mg/g), and the cycle is between adsorption and desorption. . In addition, the adsorption capacity may be an adsorption capacity measured using 400 mg/L of a Cr(VI) ion solution at pH 2.5.

As such, the β-FeOOH nanobundle particles having a two-dimensional structure or the β-FeOOH nanospiky particles having a three-dimensional structure according to the present invention may have high recyclability.

Hereinafter, β-FeOOH particles having a two-dimensional or three-dimensional structure according to the present invention and a manufacturing method thereof will be described in more detail through examples. However, the following examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention. In addition, the unit of additives not specifically described in the specification may be weight %.

[Example 1] β-FeOOH particles in the form of 2D nanobundles

FeCl ₃ 5.0 mmol, Na ₂ SO ₄ 2.5 mmol, and polyethyleneimine (PEI, Mw 25,000 g/mol) 0.002 mmol were put into 50 ml of deionized water under stirring and mixed, then quickly transferred to an autoclave and sealed, 160° C. It was hydrothermally synthesized at a temperature of 1 hour.

After completion of the reaction, the product was separated by centrifugation, washed several times with a solvent (water:ethanol=5:45 volume ratio), and dried overnight at 25°C.

[Example 2] β-FeOOH particles in the form of 3D nanospiky

FeCl ₃ 5.5 mmol, Na ₂ SO ₄ 5.0 mmol and polyethyleneimine (PEI, Mw 25,000 g/mol) 0.008 mmol were put into 50 ml of deionized water under stirring and mixed, then quickly transferred to an autoclave and sealed, 160° C. It was hydrothermally synthesized at a temperature of 1 hour.

After completion of the reaction, the product was separated by centrifugation, washed several times with a solvent (water:ethanol=5:45 volume ratio), and dried overnight at 25°C.

[Comparative Example 1]

All processes were performed in the same manner as in Example 1 except that the hydrothermal synthesis reaction was performed without adding Na ₂ SO ₄ and polyethyleneimine.

[Comparative Example 2]

All processes were performed in the same manner as in Example 1 except that the hydrothermal synthesis reaction was performed without adding Na ₂ SO ₄ .

[Comparative Example 3]

All processes were carried out in the same manner as in Example 1 except that the hydrothermal synthesis reaction was performed without adding polyethyleneimine.

Reaction conditions for preparing the β-FeOOH particles are shown in Table 1 below.

Reaction solution (mmol) particle shape FeCl ₃ Na ₂ SO ₄ PEI Example 1 5.0 2.5 0.002 2D Nanobundle Example 2 5.5 5.0 0.008 3D Nanospiky Comparative Example 1 5.0 x x 1D spindle Comparative Example 2 (same as above) x 0.002 1D Nanorods Comparative Example 3 (same as above) 2.5 x hierarchy

[Characteristics analysis method]

1) Characterization of β-FeOOH particles:

XRD was measured with Cu K _β X-ray (λ = 1.54186 Å) radiation at a scanning speed of 5 ^o /min in the region of 2θ = 20-70 ^o (Rigaku Smartlab-9kW). The specific surface area and pore size distribution were measured by nitrogen (N ₂ ) adsorption-desorption test (Micromeritics Instrument ASAP 2420) at 77K. Surface morphology was observed by TEM, and HRTEM images were taken with a TALOS F200X electron microscope at an accelerating voltage of 200 kV. The binding energy was measured by XPS (K-alpha+). Magnetic properties were measured using a magnetic property measuring system (MPMS3-Evercool). The diffuse reflection spectrum and absorption spectrum were measured using a UV-VIS-NIR spectrophotometer (SolidSpec-3700). AFM images were measured using a Park system (PARK XE7). The Fourier transform infrared reflectance (FTIR) spectrum was measured using an ALPHA-P spectrometer. Inductively coupled plasma atomic emission spectrometer (ICP-AES) was measured using an OPTIMA 7300 DV.

Referring to Table 1 and FIGS. 1 to 10, in Examples 1 and 2, in which a hydrothermal synthesis reaction was performed by mixing both an iron precursor, sodium sulfate and polyethyleneimine according to the present invention, ultrathin nanowires were self-assembled (self-assembly) to prepare β-FeOOH particles in the form of 2D nanobundles or 3D nanospiky.

It is judged that such 2D nanobundles and 3D nanospiky β-FeOOH particles were prepared through a non-classical crystal growth route, not through a classical Ostwald ripening process.

Specifically, referring to FIG. 1 , crystal growth routes of 2D nanobundles and 3D nanospiky β-FeOOH particles are as follows. Nucleation occurs from the iron precursor to form β-FeOOH nanoparticles, and the β-FeOOH nanoparticles are reassembled and aggregated into spindle-shaped or spherical particles. Thereafter, recrystallization occurs on the surface of the aggregated particles and self-assembly is performed to prepare β-FeOOH particles in the form of 2D nanobundles or 3D nanospikes.

This can be confirmed more clearly through FIG. 2 . 2 is an image analyzed by TEM of the shape of particles according to the hydrothermal synthesis reaction time. After spindle-shaped or spherical particles are formed (20 minutes), recrystallization (40 minutes) occurs on the local surface, and gradually self-assembly (60 min) and it can be confirmed that a complete 2D nanobundle or 3D nanospiky β-FeOOH particle is prepared.

In addition, in order to examine the effect of the reaction temperature, hydrothermal synthesis was performed for 1 hour at different temperatures of 100°C, 120°C, and 140°C. As a result, as shown in FIG. 3, unlike the reaction performed at 160 °C, β-FeOOH particles in the form of 2D nanobundles and 3D nanospiky were not prepared at reaction temperatures of 100 °C, 120 °C, and 140 °C.

On the other hand, as shown in FIG. 4 , despite the hydrothermal synthesis reaction being performed under the same temperature and time conditions, Comparative Examples 1 to 3 had a one-dimensional spindle shape, not a 2D nanobundle and 3D nanospiky shape, One-dimensional nanorod (nanorod) form or hierarchy (hierarchy) form of β-FeOOH particles were prepared.

From this, it was confirmed that the addition of both polyethyleneimine and sodium sulfate is a very important component in preparing β-FeOOH particles in the form of 2D nanobundles and 3D nanospikes.

This is because the sulfate anion of sodium sulfate interacts with the amino group of polyethyleneimine, potentially reducing the positive surface charge and changing the surface charge of the β-FeOOH nanoparticles, resulting in different thermodynamic stabilization at the initial stage of the particle growth process. It is considered that this is because a different thermodynamically stable state was induced.

Meanwhile, the specific surface area of β-FeOOH particles was measured by nitrogen adsorption BET (Brunauer-Emmett-Teller) method. As a result, as shown in FIGS. 5 a and b, the specific surface area of the 2D β-FeOOH nanobundles was 90.07 m 2 /g, and the specific surface area of the 3D β-FeOOH nanospike was measured to be 101.3 m 2 /g.

6A and 6B are absorption spectra (a) and diffuse reflection spectra (b) of 1D nanorods, 2D nanobundles, and 3D nanospiky β-FeOOH particles. As shown in FIG. 6 a, the three particles are All showed an absorption band in the visible region due to the iron transition (2(6A1) → 2(4T1)). Also, as shown in FIG. 6b , the band gaps of 2.91 eV for 1D nanorods, 3.02 eV for 3D nanospiky, and 3.19 eV for 2D nanobundles were shown.

7 is a TEM image (a, b) of a 2D β-FeOOH nanobundle and an HRTEM image (region 1, region 2 b2) of a specific region in FIG. it's a pattern The SAED pattern showed five crystal planes (002), (521), (301), (310), and (211), which were consistent with the XRD results, and showed oriented growth along the <001> direction. Referring to the HRTEM image, one spacing of the lattice of 2D β-FeOOH nanobundles is measured to be 0.252 nm, which is consistent with the spacing of (211) facets, and another d-spacing of 0.151 nm is measured to be (002) facets. coincides with the spacing of In addition, it was confirmed from HRTEM that 2D β-FeOOH nanobundles were composed of ultra-thin, well-ordered nanowires with a diameter of about 2 nm.

8 a and b are SEM images (a) and AFM images (b) of 2D β-FeOOH nanobundles. It was confirmed that the measured thickness of 2D β-FeOOH nanobundles was about 9.3 nm, and also It was found that the 2D β-FeOOH nanobundles were composed of ultra-thin nanowire multilayers.

9a is a HAADF-STEM image of a single 2D β-FeOOH nanobundle, showing a relatively uniform contrast, suggesting that the nanowires self-assemble into a 2D nanobundle structure. The elemental mapping of a single 2D β-FeOOH nanobundle was measured by EDS and shown in Fig. 9b, showing the distribution of Fe and O elements).

10 is a TEM image of a single 3D nanospiky particle composed of ultra-thin nanowires with a diameter of about 2 nm.

2) Characterization of adsorbent:

Cr(VI) adsorption experiments were performed in a shaking incubator (JS research Inc. Korea) at 25°C and a shaking speed of 200rpm. A typical adsorption isotherm experiment was performed by adding 5 mg of adsorbent to 25 ml of Cr(VI) ion solution (20, 50, 100, 200, 300, 400 mg/L) at 30°C, and the pH was maintained at 2.5. . At this time, the adsorption capacity (Q _e , mg/g) was calculated using the following equation (1).

Equation (1):

(In the above formula (1), C _o is the initial concentration of the Cr(VI) ion solution (mg/L), C _e is the equilibrium concentration of the Cr(VI) ion solution (mg/L), and V is the Cr(VI) ion solution. The volume of the solution (L), m is the weight of the adsorbent (mg).)

In addition, the adsorption kinetics for Cr(VI) ions were investigated using a 2D β-FeOOH nanobundle adsorbent. In this experiment, 0.02 g β-FeOOH was carefully diffused into 100 ml of Cr(VI) solution (100 mg/L) with vigorous magnetic stirring. 5 ml solutions were extracted at different time intervals (10, 20, 30, 50, 100, 200 and 500 min), and the Cr(VI) ion concentration was monitored by ICP-AES.

Furthermore, the regeneration and reusability of the adsorbent were tested, and in order to reuse the adsorbent, the Cr-adsorbed 2D β-FeOOH nanobundle adsorbent was carefully washed with a NaOH + NaCl mixed solution to desorb chromium ions for the next experiment. , the adsorption and desorption processes were repeated through the adsorption method.

11 is data for evaluating the adsorption performance of the adsorbent, and FIG. 11 a is an adsorption isotherm of 2D β-FeOOH nanobundles. The adsorption capacity measured using a Cr(VI) ion solution of 400 mg/L is 55.9 mg/L was g. 11B is an adsorption isotherm of 3D β-FeOOH nanospiky, and the adsorption capacity measured using a 400 mg/L Cr(VI) ion solution was 83.4 mg/g. This is considered to be because the specific surface area of the nanospiky type is larger than that of the nanobundle type.

On the other hand, the contact time is an important effect factor in the adsorption process. The kinetic diagram in Fig. 12 shows that the adsorption process of 2D β-FeOOH nanobundles is very fast in the initial stage, gradually decreases and finally induces an adsorption equilibrium. During the first 10 minutes, the adsorption amount was a maximum of 55.7% of the adsorption capacity and equilibrium was reached at 100 minutes. This indicates that the 2D β-FeOOH nanobundles rapidly adsorbed Cr(VI) ions.

In addition, the effect of pH upon removal of Cr(VI) ions was investigated. As shown in FIG. 13 , the adsorption capacity gradually increased in the pH range of 1 to 2.5, and then the adsorption capacity decreased. This may be due to Cr(VI) species, such as H ₂ CrO ₄ , which exhibit a pH of 1.

Furthermore, the Cr(VI) ion removal efficiency according to the repeated adsorption and desorption of 2D β-FeOOH nanobundles was tested. When the adsorption and desorption were regarded as one cycle, the adsorption capacity calculated in the fifth adsorption cycle was 80.2% (FIG. 14) compared to the first adsorption cycle, and this cycling adsorption performance was significantly improved by the 2D β-FeOOH nanobundles. It has reusability and stability, indicating that it is a promising and effective adsorbent for Cr(VI) removal.

Finally, to investigate the Cr(VI) removal mechanism of 2D β-FeOOH nanobundles, the morphology, structure and chemical composition before and after Cr(VI) adsorption were studied.

After adsorption, the shape and structure of the 2D β-FeOOH nanobundles were first analyzed by HAADF-STEM (a) and TEM (b). As shown in FIGS. 15 a and b, the 2D nanobundle shape and structure were well maintained even after 12 hours of adsorption, which means that the structural and chemical stability are high. In addition, as shown in FIG. 16 , the crystal lattice of 2D β-FeOOH nanobundles after 12 hours of adsorption was the same as before Cr(VI) adsorption. In addition, referring to the EDS mapping shown in FIG. 17 , the presence of Cr element in the Cr-absorbed 2D β-FeOOH nanobundle sample can be clearly confirmed.

Furthermore, the reduction process from Cr(VI) to Cr(III) always occurred during adsorption. To further investigate the adsorption mechanism, 2D β-FeOOH nanobundles before and after Cr(VI) adsorption were analyzed using XPS spectra.

Referring to FIG. 18 , the peaks located at 284.8 eV and 530.83 eV are due to C _1S and O _1S , respectively. It can be seen that the binding energy (E) of N _1S shifts to a higher value after Cr-adsorption, but the strength of N _1S clearly decreases. The amine group is easily protonated to a positive charge in an acidic solution, and the protonation of the amine group has excellent binding ability to HCrO ₄ ^- and Cr ₂ O ₇ ² - through electrostatic interaction.

Also, looking at the XPS results of Cr _2p , two peaks are shown, Cr _2p1/2 and Cr _2p3/2 , Cr 2p1 _/ 2 of Cr(VI) is located at 587.78 eV and 578.58 eV, and Cr of Cr(III) _2p3/2 is located at 586.38 eV and 576.58 eV.

The above results indicate that the following reduction reaction occurred during Cr (VI) adsorption.

A. HCrO ₄ ^- + 7H ⁺ + 3e ^- → Cr ³⁺ + 4H ₂ O

B. Cr ₂ O ₇ ^2- + 14H ⁺ + 6e ^- → 2Cr ³⁺ + 7H ₂ O

In this case, the electron donor (e ⁻ ) comes from the amino group of polyethyleneimine. Therefore, it can be concluded that the adsorption process of Cr(VI) includes both redox reaction and chelation. Adsorption mechanism possible with two processes, namely Cr(VI) is first adsorbed on the surface of 2D β-FeOOH nanobundles by electrostatic interaction due to protonation of amino groups, and then Cr(VI) is reduced to Cr(III) .

Although the present invention has been described with reference to specific matters and limited examples as described above, these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and the present invention belongs to Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (13)

a) preparing a reaction solution containing an iron precursor, polyethyleneimine and sulfate; and b) hydrothermal synthesis of the reaction solution;
The method for preparing the β-FeOOH particles is to prepare β-FeOOH nanobundle particles having a two-dimensional structure from a reaction solution containing 0.0001 to 0.0010 moles of polyethyleneimine and 0.1 to 0.80 moles of sulfate with respect to 1 mole of the iron precursor,
Or, the method for preparing β-FeOOH nanospiky particles having a three-dimensional structure from a reaction solution containing 0.0011 to 0.0030 moles of polyethyleneimine and 0.85 to 1.50 moles of sulfate with respect to 1 mole of the iron precursor.
delete delete The method of claim 1,
The hydrothermal synthesis is carried out for at least 50 minutes at a temperature of 150 ° C. or higher, the method for producing β-FeOOH particles.
The β-FeOOH particles prepared by the method of claim 1,
The β-FeOOH particles are β-FeOOH nanospiky particles of a three-dimensional structure, and the β-FeOOH nanospiky particles of the three-dimensional structure are three-dimensional sharp self-assembled nanowires having an average diameter of 1 to 3 nm. What has a particle structure, β-FeOOH particles.
delete delete delete 6. The method of claim 5,
The β-FeOOH particles have a specific surface area measured by a nitrogen adsorption BET (Brunauer-Emmett-Teller) method of 80 m 2 /g or more, β-FeOOH particles.
A β-FeOOH adsorbent for removing heavy metal ions comprising the β-FeOOH particles of claim 5 .
11. The method of claim 10,
The β-FeOOH adsorbent has an adsorption capacity of 50 mg/g or more, a β-FeOOH adsorbent for heavy metal ion removal.
11. The method of claim 10,
The β-FeOOH adsorbent satisfies the following Relational Equation 1, β-FeOOH adsorbent for heavy metal ion removal.
[Relational Expression 1]
75 ≤ (Q _e5 /Q _e1 ) × 100
(In the above relation 1, Q _e1 is the adsorption capacity (mg/g) at the time of 1 cycle of adsorption, Q _e5 is the adsorption capacity (mg/g) at the time of 5 cycles of adsorption (mg/g). do.)
11. The method of claim 10,
The β-FeOOH adsorbent is for hexavalent chromium (Cr(VI)) removal, β-FeOOH adsorbent for heavy metal ion removal.

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