KR20190011549A - Zinc oxide/reduced graphene oxide nanocomposites photocatalytic controlled morphology with high photocatalytic performance and the preparation method thereof - Google Patents

Abstract

The present invention relates to a zinc oxide nanoparticle/reduced graphene oxide nanocomposite photocatalyst with a controlled shape having high photocatalytic properties and a method of preparing the same and, more specifically, to a reduced graphene oxide nanocomposite photocatalyst attached with a zinc oxide nanoparticle, which comprises: a reduced graphene oxide; and zinc oxide nanoparticles attached on the reduced graphene oxide. The zinc oxide nanoparticle/reduced graphene oxide nanocomposite photocatalyst with a controlled shape prepared according to the present invention exhibits dye removal efficiency of 98.8 and 97.7% for MB and RhB when being irradiated with UV at a low power of 40 W, and maintains the dye removal efficiency of the photocatalyst at 96.0% when dye decomposition is repeatedly performed 15 times, thereby exhibiting excellent reusability.

Description

TECHNICAL FIELD The present invention relates to a zinc oxide nanoparticle having a high photocatalytic property and a zinc oxide nanoparticle having a high photocatalytic property and a method for preparing the same,

The present invention can exhibit high photocatalytic activity against the decomposition of various dyes such as methylene blue (MB) and rhodamine B (RhB), and also has a high photocatalytic property The present invention relates to a zinc oxide nanoparticle / reduced graphene nanocomposite photocatalyst having a controlled shape and a method of manufacturing the same.

In recent years, demand for water treatment has increased significantly due to national economic development and increased water pollution in various countries.

Water treatment techniques that can remove pollutants from water include adsorption or solvent extraction; Chemical precipitation, ion exchange, ultrafiltration, reverse osmosis or electrochemical techniques; Biodegradation; And photocatalyst-based processes.

The method of removing contaminants through adsorption may exhibit a high recovery rate, reusability and separation rate, but has a problem of not being able to completely remove contaminants.

The method of removing contaminants by physicochemical methods is suitable only for treating heavy metals in wastewater and has serious drawbacks such as high energy consumption, ineffective removal and accumulation of harmful sludge after treatment.

Methods for removing contaminants through biodegradation techniques minimize the toxic organic compounds based on the metabolism of microorganisms, but biodegradation methods are extremely limited due to high concentration sensitivity of microorganisms, low rates of biodegradation at high concentrations, and high costs.

On the other hand, the photocatalytic decomposition method based on a semiconductor material is attracting attention as an effective decomposition method due to a low-cost, non-toxic process and an easy processing system.

Among the various semiconductor materials, titanium dioxide (TiO ₂ ) is being used as a photocatalytic semiconductor material for various applications such as self-cleaning, anti-bacterial, antireflective coating for solar cell, and corrosion inhibitor.

(TiO ₂ ) as a photocatalytic semiconductor material for a variety of applications, a variety of materials including photocatalysts such as sol-gel method, electrochemical synthesis, CVD, physical vapor deposition (PVD), sputtering and ion implantation Methods have been developed to produce TiO ₂ , but in general, there is a problem in that expensive and modern equipments and precursors are required and complex procedures are required.

In contrast, zinc oxide (ZnO) is attracting attention as a semiconductor useful in many applications such as photodetectors or sensors, energy storage materials, supercapacitors and photocatalysts due to its low cost, abundant solubility, electrochemical activity and environmental friendliness.

On the other hand, as a photocatalyst material, zinc oxide has disadvantages associated with recombination of photogenerated electron-hole pairs, photocorrosion effect, and photostability, which considerably reduce photocatalytic activity.

In order to overcome this problem, it has been found that a carbon compound doped with carbon nitride (C ₃ N ₄ ), fullerene (C ₆₀ ), chitosan, single layer polyaniline, or a nonmetal or metal element and zinc oxide are increased by forming a hybrid composite Several methods have been developed with specific surface area, improved catalytic activity, photo-deposition inhibition and effective electron-hole separation.

Among them, graphene belonging to the carbon series is an ideal material for improving the photocatalytic performance of the metal oxide due to its large specific surface area, high electron conductivity, chemical stability and excellent transport properties.

The combination of zinc oxide and graphene has attracted considerable interest in the field of photocatalytic material research.

The main purpose of the combination of the two materials is to obtain a high electron-hole isolation efficiency and freely transfer the charge generated by the photo-excitation process to the surface.

Recently, application of zinc oxide structures with various shapes of particles, rods, sculptures and flowers attached on a graphene sheet has been reported.

For example, there has been developed a process for producing a three-dimensional oxide graphene composite in which a zinc oxide rod has been grown by chemical vapor deposition and a hydrothermal treatment method for decomposing methyl orange (MO) using the complex as a photocatalyst, A complicated synthesis procedure of a three-dimensional oxidized graphene complex with a zinc rod grown and a decomposition efficiency of 92% for MO after 3 hours under UV irradiation have been reported.

Also, a method for producing a reduced graphene oxide (RGO) complex in which flower-shaped zinc oxide is adhered using hydrazine which is a highly toxic compound as a reducing agent under hydrothermal conditions has been developed, The highest rate constant for the methylene blue (MB) decomposition was 0.0395 min ^-1 .

Also, through the hydrothermal pathway, a process for producing reduced oxidized graphene complexes with zinc oxide nanoparticles, nano thin plates, nanospheres and nanorods for photocatalytic H ₂ production has been reported.

However, a number of studies have been reported on reduced oxidized graphene nanocomposite with zinc oxide and its applications. However, the comparison of photocatalytic efficiency of reduced graphene oxide graphene nanocomposite with various zinc oxide- .

Korea Patent No. 1212711

It is an object of the present invention to provide a process for producing zinc oxide seed nanoparticles having a short nanorod, nano hexagonal plate, and nanoparticle-shaped zinc oxide nanoparticles in a reduced oxidized state according to a solvent mixture ratio of anhydrous ethanol and deionized water, It is an object of the present invention to provide a method for manufacturing a zinc oxide nanoparticle / reduced graphene oxide nanocomposite photocatalyst having excellent photocatalytic properties and excellent reusability through a simple two-step method.

In order to achieve the above object, the present invention provides a photocatalyst comprising a reduced oxide graphene nanocomposite-attached photocatalyst having zinc oxide nanoparticles, which comprises reduced oxidized graphene and zinc oxide nanoparticles attached on the reduced oxidized graphene, to provide.

The present invention also relates to a method for preparing a silver halide emulsion, comprising the steps of: adding a zinc precursor to an oxidized graphene suspension, followed by stirring to prepare a first agitated material; Drying the first precipitate obtained by centrifuging the first agitate; Heat treating the dried first precipitate to prepare a reduced graphene graphene nanocomposite having zinc oxide seeds attached thereto; Adding the nanocomposite to anhydrous ethanol and a zinc oxide seed growth solvent; Adding a zinc precursor and a reducing agent to the zinc oxide seed growth solvent to which the nanocomposite is added and stirring to prepare a second agitated material; Subjecting the second agitator to heat treatment, cooling and centrifuging to obtain a second precipitate; And washing and drying the second precipitate to produce a reduced graphene graphene nanocomposite photocatalyst with zinc oxide nanoparticles, wherein the graphene oxide nanoparticle-adhered reduced graphene graphene nanocomposite photocatalyst ≪ / RTI >

The shape-controlled zinc oxide nanoparticles / reduced graphene oxide nanocomposite photocatalyst prepared according to the present invention exhibited dye removal efficiency of 98.8% and 97.7% for MB and RhB when UV was irradiated at a low power of 40 W And when the dye decomposition was repeated 15 times, the dye removal efficiency of the photocatalyst was 96.0%, which shows an excellent reusability.

FIG. 1 is a schematic diagram showing the synthesis of three different types of nanocomposite photocatalysts (sZG, dZG, rZG), such as spherical, hexagonal disc, rod-like shapes;
FIG. 2 is a graph showing the results of a comparison between graphite (a), oxidized graphene (b), reduced graphene graphene nanocomposite (c) with zinc oxide seeds attached thereto before heat treatment under argon gas, After the heat treatment, the reduced graphene graphene nanocomposite (e) having zinc oxide seeds adhered thereto, the reduced graphene graphene nanocomposite photocatalyst (f ', hereinafter referred to as' rZG nanocomposite ') having zinc oxide nanoparticles having nanorods' , Reduced oxidized graphene nanocomposite photocatalyst (g 'dZG nanocomposite') with zinc oxide nanoparticles in the shape of nano hexagonal plate, and reduced oxidized zinc oxide nanoparticles with nanospherical shape (Right) showing the XRD pattern (left) of the graphene nanocomposite photocatalyst (h) (hereinafter, 'sZG nanocomposite') and the (100), (002) and (101) crystal planes of the sample;
FIG. 3A shows FTIR spectra of oxidized graphene, reduced graphene oxide nanocomposite with zinc oxide seed, sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst, and rZG nanocomposite photocatalyst;
FIG. 3B is an enlarged image of a Raman spectrum and a rectangular dotted line region of the photocatalyst of oxide graphene and sZG nanocomposite; FIG.
4A is a scanning scan of a sZG nanocomposite photocatalyst;
Figure 4b shows a deconvoluted Zn 2p spectrum;
Figure 4c is a diagram illustrating the inverted line separated O1s spectrum;
Figure 4d shows a C 1s spectrum back-separated;
5 is a C 1s XPS spectrum of graphene oxide;
6 is a graph showing the results of measurement of the activity of zinc oxide nanoparticles synthesized during 24 hours using hexamethylenetetramine ((CH ₂ ) ₆ N ₄ , hexamethylenetetraamine (hereinafter referred to as 'HMTA' Fig. 3 is a SEM image of a reduced graphene oxide nanocomposite photocatalyst having a photocatalyst; Fig.
FIG. 7 shows an SEM image of a reduced oxidized graphene sheet to which zinc oxide nanoparticles having various shapes are adhered. FIG. 7 shows an SEM image of a reduced oxidized graphene nanocomposite (a), a rZG nanocomposite photocatalyst (b ), dZG nanocomposite photocatalyst (c), and sZG nanocomposite photocatalyst (d).
FIG. 8 is a graph showing the results of measurement of a photocatalyst of a nanocomposite (hereinafter referred to as 'sZG * nanocomposite photocatalyst') synthesized using a thin oxide graphene sheet instead of a reduced oxidized graphene sheet to which zinc oxide seeds are attached, a nanocomposite photocatalyst * Nanocomposite photocatalyst ') (b), nanocomposite photocatalyst (hereinafter' rZG * nanocomposite photocatalyst ') (c), and oxidized graphene sheet (d).
Fig. 9 shows TEM images (a1 to c1), HRTEM images (a2 to c2) of reduced oxidized graphene thin films to which zinc oxide nanoparticles having various shapes are attached, and reduced The SAED patterns (a3 to c3) corresponding to the oxidized graphene thin plate are shown. The rZG nanocomposite photocatalyst (a); dZG nanocomposite photocatalyst (b); sZG nanocomposite photocatalyst (c); And an EDX spectrum (d) of elemental mapping of the sZG nanocomposite photocatalyst;
10 shows SEM images of sZG nanocomposite photocatalysts prepared for 12 hours (a), 18 hours (b), 24 hours (c) and 36 hours (d);
11 shows TEM images of oxidized graphene sheet (a), reduced graphene graphene nanocomposite (b) and sZG nanocomposite photocatalyst (c to d) with various magnifications at various magnifications;
12 is a diagram showing a nitrogen adsorption-desorption isotherm of an sZG nanocomposite photocatalyst, a dZG nanocomposite photocatalyst, and an rZG nanocomposite photocatalyst;
13a shows UV-vis diffus reflectance spectra (UV-vis DRS) of i) sZG nanocomposite photocatalyst, ii) dZG nanocomposite photocatalyst, and iii) rZG nanocomposite photocatalyst drawing;
FIG. 13B shows a Tauc plot of an sZG nanocomposite photocatalyst, a dZG nanocomposite photocatalyst, and an rZG nanocomposite photocatalyst;
14 is a thermogravimetric analysis (hereinafter referred to as "TGA") profile of a sZG nanocomposite photocatalyst, a dZG nanocomposite photocatalyst, an rZG nanocomposite photocatalyst, and a reduced oxidized graphene nanocomposite with zinc oxide seeds;
15 shows PL spectra of sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst, and rZG nanocomposite photocatalyst excited at a wavelength of 325 nm at room temperature;
16A shows the photocatalytic decomposition of MB solution (10 ppm) under UV irradiation for several hours in the absence and presence of reduced oxidized graphene sheet, sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst and rZG nanocomposite photocatalyst (0.1 g / Fig.
FIG. 16B shows pseudo first order kinetics of photolysis of MB under UV irradiation; FIG.
FIG. 16C shows the photocatalytic decomposition of RhB solution (10 ppm) under UV irradiation for several hours in the absence and presence of reduced oxidized graphene sheet, sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst and rZG nanocomposite photocatalyst (0.1 g / Fig.
16D is a diagram showing a similar primary rate equation of photolysis of RhB under UV irradiation;
Figure 17 shows adsorption of the MB solution (10 ppm) onto the sZG nanocomposite photocatalyst after 3 hours under dark conditions;
Figure 18 shows a comparison of photocatalytic degradation of a 10 ppm MB solution in the presence of sZG nanocomposite photocatalyst, sZG * nanocomposite photocatalyst, dZG * nanocomposite photocatalyst and rZG * nanocomposite photocatalyst after 60 minutes under UV irradiation;
19 shows the dye decomposition efficiency of rZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst, and sZG nanocomposite photocatalyst after 60 minutes under UV irradiation (10 ppm dye solution, 0.1 g / L, 40 W);
20A is a photocatalytic decomposition curve of an aqueous solution of 10 ppm MB upon loading various catalysts (sZG nanocomposite photocatalyst) under UV irradiation;
20B shows photocatalytic decomposition of various concentrations of RhB aqueous solution under ultraviolet irradiation using 0.1 g / l of sZG nanocomposite photocatalyst under UV irradiation;
20C is a graph showing the results of trapping experiments on sZG nanocomposite photocatalyst (0.1 g / L) in a 10 ppm RhB dye solution;
20d shows the photocatalytic stability of the sZG nanocomposite photocatalyst (0.1 g / l) in 10 ppm MB dye under UV irradiation;
21 shows electron transfer between a reduced oxidized graphene sheet and zinc oxide nanoparticles of a reduced oxidized graphene nanocomposite photocatalyst adhered with zinc oxide nanoparticles under UV irradiation and dye photolysis mechanism;
22 is an SEM image of the sZG nanocomposite photocatalyst before and after use for measuring photocatalyst stability;
23A is a nyquist plot of an sZG nanocomposite photocatalyst, a dZG nanocomposite photocatalyst, and an electrode to which an rZG nanocomposite photocatalyst is applied;
FIG. 23B is a graph showing the photocurrent response of the sZG nanocomposite photocatalyst, the dZG nanocomposite photocatalyst, and the rZG nanocomposite photocatalyst; FIG.
24 is an SEM image of an sZG nanocomposite photocatalyst, a dZG nanocomposite photocatalyst, and an rZG nanocomposite photocatalyst manufactured under various reaction times (12 hours and 24 hours);
25 shows the sZG nano-structure synthesized without the HMTA for 12 hours (Sample-S1), 18 hours (Sample-S2), 24 hours (Sample-S3) and 36 hours (0.1 g / l) of the photocatalyst (sample-SO).

Hereinafter, zinc oxide nanoparticles / reduced graphene graphene nanocomposite photocatalyst having a high photocatalytic property and a method for producing the same will be described in detail.

The inventors of the present invention have found that zinc oxide nanoparticles having various shapes can be obtained according to the mixing ratio of the solvent of anhydrous ethanol and deionized water constituting the zinc oxide seed growth solvent and the reduced zinc oxide nanoparticles The present invention has been accomplished on the basis of the findings that it has high dye decomposition efficiency and excellent reusability when a composite photocatalyst is used.

The present invention provides a reduced oxidized graphene nanocomposite photocatalyst to which zinc oxide nanoparticles are attached, comprising reduced oxidized graphene and zinc oxide nanoparticles attached on the reduced oxidized graphene.

The zinc oxide nanoparticles may have any one of nanospheres, nano hexagons, and nanorods, but is not limited thereto.

The nanoporous zinc oxide nanoparticles having the nanoporous shape may have an average diameter of 5 to 30 nm, but are not limited thereto.

The nanoporous zinc oxide nanoparticles of the nano hexagonal plate may have an average diameter of 100 to 400 nm and an average thickness of 10 to 30 nm, but are not limited thereto.

The zinc oxide nanoparticles having the nanorods of the nanorods may have an average diameter of 20 to 200 nm, but are not limited thereto.

The present invention also relates to a method for preparing a silver halide emulsion, comprising the steps of: adding a zinc precursor to an oxidized graphene suspension, followed by stirring to prepare a first agitated material; Drying the first precipitate obtained by centrifuging the first agitate; Heat treating the dried first precipitate to prepare a reduced graphene graphene nanocomposite having zinc oxide seeds attached thereto; Adding the nanocomposite to anhydrous ethanol and a zinc oxide seed growth solvent; Adding a zinc precursor and a reducing agent to the zinc oxide seed growth solvent to which the nanocomposite is added and stirring to prepare a second agitated material; Subjecting the second agitator to heat treatment, cooling and centrifuging to obtain a second precipitate; And washing and drying the second precipitate to produce a reduced graphene graphene nanocomposite photocatalyst with zinc oxide nanoparticles, wherein the graphene oxide nanoparticle-adhered reduced graphene graphene nanocomposite photocatalyst ≪ / RTI >

The zinc precursor may be selected from the group consisting of zinc acetate, zinc nitrate, zinc sulfate, zinc phosphate, zinc fluoride, zinc chloride, and zinc iodide iodate), but the present invention is not limited thereto.

The step of drying the first precipitate obtained by centrifuging the first agitated product may include a step of drying the first precipitate obtained by centrifuging the first agitated product at 10,000 to 15,000 rpm at 20 to 30 ° C, But is not limited thereto.

The step of preparing the reduced graphene oxide nanocomposite with the zinc oxide seed may be a step of heat-treating the dried first precipitate at 250 to 350 ° C for 30 minutes to 90 minutes, but the present invention is not limited thereto.

The zinc oxide seed growth solvent may be anhydrous ethanol, deionized water, or a combination thereof, but is not limited thereto.

The zinc oxide seed growth solvent composed of the anhydrous ethanol and the deionized water may be an ethanol solution of anhydrous ethanol and deionized water at a volume ratio of 1: 0.25 to 1, but is not limited thereto.

The reducing agent may be hexamethylenetetramine (HMTA), but is not limited thereto.

The step of obtaining the second precipitate comprises heat-treating the second agitated material at 100 to 110 ° C for 12 to 36 hours, cooling, and centrifuging at 6,500 to 7,500 rpm for 3 to 10 minutes to obtain a second precipitate But is not limited thereto.

The zinc oxide nanoparticles may have any one of nanospheres, nano hexagons, and nanorods, but is not limited thereto.

The nanoporous zinc oxide nanoparticles having the nanoporous shape may have an average diameter of 5 to 30 nm, but are not limited thereto.

The nanoporous zinc oxide nanoparticles of the nano hexagonal plate may have an average diameter of 100 to 400 nm and an average thickness of 10 to 30 nm, but are not limited thereto.

The zinc oxide nanoparticles having the nanorods of the nanorods may have an average diameter of 20 to 200 nm, but are not limited thereto.

Hereinafter, zinc oxide nanoparticles / reduced graphene oxide nanocomposite photocatalyst having a high photocatalytic property and controlled in shape according to the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by these examples.

≪ Example 1 >

1. Preparation of materials

Graphite powder (99.9995%, Junsei Chemical Co., Ltd), zinc acetate dihydrate _{(Zn (CH 3 COO) 2} · 2H 2 O, 99.0%, Sigma Aldrich), hexamethylenetetramine ((CH _{2) 6} N ₄ , hexamethylenetetramine (hereinafter referred to as 'HMTA', 99 +%, solid, Alfa Aesar), methylene blue (hereinafter referred to as 'MB', high purity Alfa Aesar) and rhodamine B Gold) was used.

2. Synthesis of reduced oxidized graphene nanocomposite with zinc oxide seeds (ZnO seeds)

Referring to FIG. 1, the synthesis process has two steps.

The graphene oxide (GO, 50 mg) prepared by the Marcano-Tour method with a slight modification of the Hummers method was dispersed in anhydrous ethanol (1 mg / ml) with vigorous stirring to prepare an oxidized graphene suspension.

Subsequently, zinc acetate dihydrate ((Zn (CH ₃ COO) ₂ .2H ₂ O, 54.9 mg) was added to the oxidized graphene suspension and stirred at a stirring speed of 1,150 rpm for 60 minutes with a magnetic stirrer at room temperature, A stirrer was prepared.

The first agitator was separated into centrifuges (Beckman Coulter, Avanti J-E Centrifuge) at a rate of 12,000 rpm to obtain a first precipitate and dried overnight in a vacuum oven (room temperature).

Finally, the dried first precipitate was calcined in a quartz tube furnace under a stream of argon at 300 DEG C for 60 minutes (heating rate: 9 DEG C / min, operating pressure: 800 to 900 torr) And deposited on a reduced oxidized graphene sheet.

3. Reduced oxide graphene nanocomposite photocatalyst synthesis with nanoparticles of zinc oxide nanoparticles

Reduced graphene oxide graphene nanocomposite (15 mg) and anhydrous ethanol (15 ml) adhered with zinc oxide seeds were added to the vial (20 ml) and mixed for 2 hours.

Subsequently, zinc acetate dihydrate (Zn (CH ₃ COO) ₂ .2H ₂ O, 98.8 mg) and HMTA (63.1 mg) corresponding to a molar ratio of 1: 1 were added to the vial and further stirred for 30 minutes, A stirrer was prepared.

The second agitated material was transferred to a Teflon-lined stainless steel autoclave (30 ml) and heat treated in an oven at 105 ° C for 24 hours under autogenous pressure to obtain a reaction mixture .

The reaction mixture was then rapidly cooled to room temperature and centrifuged at 7,000 rpm for 5 minutes to obtain a second precipitate, which was washed five times with deionized water and then once with ethanol.

Finally, the washed second precipitate was slowly dried in a vacuum dryer at room temperature for 24 hours to synthesize a reduced graphene oxide nanocomposite photocatalyst with nanoparticle-shaped zinc oxide nanoparticles (hereinafter referred to as 'sZG nanocomposite photocatalyst' Respectively.

≪ Example 2 >

The sZG nanocomposite photocatalyst was synthesized under the same conditions as in Example 1 except that the heat treatment was performed in the oven for 12 hours.

≪ Example 3 >

The sZG nanocomposite photocatalyst was synthesized under the same conditions as in Example 1 except that the heat treatment was performed in the oven for 18 hours.

<Example 4>

The sZG nanocomposite photocatalyst was synthesized under the same conditions as in Example 1 except that the heat treatment was performed in the oven for 36 hours.

&Lt; Example 5 >

A thin layer of oxidized graphene grafted with zinc oxide nanoparticles having the shape of a nanosecond nanodisk was synthesized (hereinafter referred to as &quot; nanoparticles &quot;) by adding anhydrous ethanol (15 ml) and deionized water (3.75 ml) dZG nano-composite photocatalyst &quot;).

&Lt; Example 6 >

(15 mL) and deionized water (15 mL) were added at a volume ratio of 1: 1 to synthesize a reduced oxidized graphene sheet adhered with zinc oxide nanoparticles having a nanorod shape (hereinafter referred to as "dZG Nanocomposite photocatalyst &quot;) was used as the photocatalyst.

&Lt; Comparative Example 1 &

For comparison, a synthetic experiment was conducted according to the same procedure mentioned above by adding an oxidized graphene sheet instead of the reduced oxidized graphene nanocomposite with zinc oxide seeds.

Specifically, except that a thin oxide graphene sheet was used in place of the reduced oxidized graphene sheet to which zinc oxide seeds were adhered, a reduced oxidized graphene nanocomposite with zinc oxide nanoparticles attached thereto under the same conditions as in Example 1 (Hereinafter referred to as &quot; sZG * nanocomposite photocatalyst &quot;).

&Lt; Comparative Example 2 &

The reduced graphene oxide nanocomposite photocatalyst to which zinc oxide nanoparticles were attached was synthesized under the same conditions as in Example 5 except that the oxidized graphene sheet was used instead of the reduced oxidized graphene sheet to which zinc oxide seeds were attached (Hereinafter referred to as &quot; dZG * nanocomposite photocatalyst &quot;).

&Lt; Comparative Example 3 &

A reduced graphene oxide nanocomposite photocatalyst to which zinc oxide nanoparticles were attached was synthesized under the same conditions as in Example 5 except that the GO thin plate was used in place of the reduced oxide graphene thin plate to which zinc oxide seeds were attached &quot; rZG * nanocomposite photocatalyst &quot;).

&Lt; Comparative Example 4 &

A reduced oxidized graphene nanocomposite photocatalyst with zinc oxide nanoparticles was synthesized under the same conditions as in Example 1 except that HMTA was not added.

<Experimental Example 1> Morphology analysis of reduced oxidized graphene nanocomposite with zinc oxide nanoparticles

Scanning Electron Microscopy (SEM) was performed using a scanning electron microscope (Hitachi, S-4800, Japan) in order to analyze the shape of the reduced graphene nanocomposite photocatalyst with the prepared zinc oxide nanoparticles attached thereto. And a transmission electron microscope (TEM) was observed by accelerating a transmission electron microscope (Philips, CM-200) at 200 kV. High resolution transmission electron microscopy (TEM) X-ray diffraction (XRD ') was performed using Cu Kα (λ = 0.154 nm), which was observed by accelerating to 200 kV using a transmission electron microscope (TITAN G2 ChemiSTEM Cs Probe electron microscope) Ray diffractometer (XRD, PANalytical, X'Pert-PRO MPD) using a scanning electron microscope (SEM) was observed with an accelerating voltage of 40 kV, a applied current of 30 mA and a scanning speed (2θ) of 0.101 ˚ / s , Fourier transform infrared spectroscopy Raman spectroscopy was performed using a Raman spectroscope (HORIBA, XploRA plus) (532 nm laser) using a FT-IR spectrometer (Bio-Rad, Excalibur Series FTS 3000) X-ray photoelectron spectroscopy (XPS) was performed using Al Kα monochromatized radiation to examine the elemental composition and chemical state of the sample. And analyzed with a spectrophotometer (KRATOS, AXIS Nova).

Referring to FIG. 1, a process for synthesizing a reduced graft oxide nanocomposite photocatalyst having zinc oxide nanoparticles is performed in two steps.

After graphite flakes are oxidized and stripped to produce oxidized graphene, zinc oxide seeds are sprayed onto the reduced oxidized graphene sheet (first step), and then zinc oxide nanoparticles are grown under mild conditions (Second step).

It can be seen that a simple and efficient synthesis procedure is used to obtain the reduced graphene oxide nanocomposite photocatalyst with various forms of zinc oxide nanoparticles.

The reduced graphene graphene nanocomposite with zinc oxide seeds showed XRD with a broad zinc oxide peak at low intensity at 31.1, 33.5, 35.4, 46.8, 56.0, 62.3, Pattern (see Fig. 2 (e)) was observed.

This shows a low crystalline quality with a mean crystallite size (d) of 0.42 nm estimated from the (101) peak using the Debye-Scherrer equation represented by the following equation (1) .

[Formula 1]

Is the Cu K? Irradiation wavelength (? = 0.154 nm),? Is the full width at half maximum (FWHM) of the diffraction peak, and? Is the diffraction angle.

In the case of graphite, a sharp peak of 26.0 DEG 2 &amp;thetas; corresponding to the (002) crystal plane and a weak peak of 54.5 DEG 2 DEG relative to the (004) plane were assigned to hexagonal graphite (see FIG. 2A) .

The two peaks (26.0 deg. 2 and 54.5 deg. 2 theta) were not identified in the XRD pattern of the graphene oxide (see FIG. 2 (b) Respectively.

In the XRD pattern of the reduced graphene graphene nanocomposite with zinc oxide seeds before heat treatment in argon gas, zinc oxide peak did not appear (see Fig. 2 (c)).

The peak at 10.9 DEG 2 &amp;thetas; corresponding to the (001) plane of the graphene oxide disappears (see Fig. 2 (c)) as compared with the XRD pattern of the graphene oxide shown in Fig. 2 (b).

Due to the restacking of the oxidized graphene layer, the behavior is presumably due to the interaction between the Zn ²⁺ ions and the oxygen functional groups, resulting in a significantly narrower distance between the oxidized graphene layers, ) The peak can be seen to have disappeared.

In the process of zinc oxide seed formation, the reduction to oxidized graphene was progressed due to the presence of a wide peak at 23.3 ° 2θ, so that the oxidation of graphene oxide reduced in oxidized graphene (See Fig. 2 (d) and Fig. 2 (e)).

The reduced graphene graphene nanocomposite photocatalyst with zinc oxide nanoparticles prepared exhibits a (100), (002), (100), and (100) values in the wurtzite hexagonal structures of zinc oxide nanoparticles (JCPDS no. 36-1451) 101, 102, 110, 103, 200, 112, 201, 004, and 202, respectively, (See Figs. 2 (f) to 2 (h)).

Since the peak intensity of the graphene oxide reduced at 23.3 ° 2θ is very weak compared with the zinc oxide peak of the nanocomposite photocatalyst, the reduced oxidized graphene in the XRD pattern of the reduced graphene oxide graphene nanocomposite with zinc oxide nanoparticles prepared No peak of graphene was observed (see Figs. 2 (f) to 2 (h)).

In addition, the reduced graphene oxide nanocomposite photocatalyst to which zinc oxide nanoparticles are attached was successfully synthesized even in the absence of other crystalline impurities. However, referring to an enlarged view of a portion surrounded by a dotted line region in FIG. 2, (002) and (101) planes.

Peak migration towards the smaller Bragg's angle may be due to the effect of the solvent used during the reaction.

Specifically, when the amount of deionized water is reduced from 50% by volume to 20% by volume during the reaction, the peak moves further away from the reference peak.

These changes are due to changes in the size and structure of the zinc oxide nanoparticles as well as lattice strain as a result of the interaction between the zinc oxide nanoparticles and the reduced graphene oxide or lattice strain within the structure.

To reduce the abundance of oxygen-containing functional groups as reduced to oxidized graphene in oxidized graphene, pure oxide graphene, FT-IR spectroscopy at 4000-400 cm ^-1 , The characteristics of graphene oxide graphene nanocomposite and reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles were analyzed.

In the case of pure graphene grains, a broad absorption peak centered at 3209 cm ^-1 was assigned to the OH stretching vibration.

The pure graphene graphene has 1,730 cm ^-1 (C = O stretching vibration of carboxyl group -COOH at the edge of oxidized graphene sheet), 1,627 cm ^-1 (sp ² hybridized C = C group or carboxyl group -COOH or skeletal vibration of graphite domain of changeable vibration from the vibration strain OH), 1394 cm ^-1 (3 primary C-OH vibrations of the OH deformation), 1160 cm ^-1 (CO stretching vibration), 1043 cm ^-1 (CO alkoxy vibration), and 876 cm ^{- 1} (epoxy vibration).

The peak corresponding to the oxygen functional group disappeared from the spectrum of the reduced graphene graphene nanocomposite with zinc oxide seeds and the spectrum of the reduced graphene graphene nanocomposite photocatalyst with zinc oxide nanoparticles. It was confirmed that this was reduced to oxidized graphene reduced from oxidized graphene.

In addition, in the spectrum of pure graphene grains, a peak at 1627 cm ^-1 migrates to a reduced graphene graphene nanocomposite with zinc oxide seeds at 1551 cm ^-1 , and for the rZG nanocomposite photocatalyst and dZG nanocomposite photocatalyst 1565 cm ^-1 , and 1553 cm ^-1 for the sZG nanocomposite photocatalyst.

The change of the peak is due to the deformation of the? -Electron interaction in the aromatic ring capable of polarizing into the cation-? Interaction or the coordination between the hydroxyl group and the epoxy group present on the oxide graphene surface to which the zinc oxide nanoparticles are attached.

In addition, all samples containing zinc oxide nanoparticles assigned to CO-Zn bonds showed a new absorption peak at 1230 cm ^-1 .

Zn-O stretching vibration observed at 500 cm ^-1 or less was observed at 453, 403, and 300 nm in the reduced graphene oxide nanocomposite, rZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst, and sZG nanocomposite photocatalyst, respectively, 405 and 406 cm ^-1 A peak was observed.

The observed change may be due to the insertion of zinc oxide nanoparticles between oxidized graphene sheets reduced in the growth process of zinc oxide seeds.

Significant reduction in peak intensity, observed migration, disappearance of some of the peaks and formation of new peaks can be achieved by effective reduction of oxidized graphene to reduced graphene grains and reduction of the oxidized graphene nanocomposite photocatalyst with zinc oxide nanoparticles Lt; / RTI &gt;

Raman spectroscopy is another effective tool to identify structural changes in oxidized graphene and reduced oxidized graphene and the presence of zinc oxide nanoparticles in nanocomposite photocatalysts.

Referring to FIG. 3B, the Raman spectrum of the oxidized graphene has two characteristic peaks at 1366 cm ^-1 (D-band) and 1591 cm ^-1 (G-band).

The D-band corresponds to the breathing mode of the k-point phonon of the A _1g symmetry, which is assigned to the disorder and defect at the edge of the graphene sheet.

The G-band is related to the in-plane E _2g optical phonon mode of the sp ² bond of the carbon atom.

In addition, the peak intensity ratio (I _D / I _G ) was calculated so as to evaluate the degree of disorder in the oxide graphene and the reduced oxide graphene structure.

Zinc nanoparticles have a reduced oxidation graphene nanocomposite attached photocatalytic oxidation peak intensity ratio of the (sZG nanocomposite _{photocatalyst) (I D / I G =} 1.006) The ratio (I _D / I _G peak intensity for the oxidation graphene = 0.861) is due to the formation of the sp ² domain and the increase in the degree of disorder and defect of the reduced oxidized graphene structure, whereby the reduction to the oxidized graphene reduced in the oxidized graphene and the reduction of the reduced zinc oxide nanoparticles The presence of reduced oxidized graphene in the reduced graphene graphene nanocomposite photocatalyst can be confirmed.

sZG nanocomposite further confirmed the formation of a bond CO-Zn a blue shift (blue-shift) of the G- band of graphene oxide in confirmed by (at 1597.43 cm ^-1 moved to 1591.54 cm ^-1) in the photocatalytic nanocomposite photocatalyst sZG Respectively.

A blue shift of approximately 6 cm ^-1 indicates the formation of CO-Zn bonds in the nanocomposite photocatalyst and the strong chemical interaction between the zinc oxide nanoparticles and the reduced oxidized graphene.

Referring to the enlarged image surrounded by the dotted line area of FIG. 3B, it can be seen that at 2 8 2 (M) and 434 cm ^-1 at 328 cm ^-1 on wurtzite zinc oxide nanoparticles Shows the Raman spectrum of a sZG nanocomposite photocatalyst having two distinctive modes of oscillation including nonpolar optical phonon E2 (H).

XPS was performed to confirm the oxidation state and elemental composition of the sZG nanocomposite photocatalyst and to confirm that the oxide graphene was reduced to reduced graphene grains (see FIGS. 4A to 4D).

The survey spectrum of FIG. 4A shows the presence of the three major components Zn, O and C present in the reduced graphene oxide nanocomposite-adhered zinc oxide nanocomposite photocatalyst.

The Zn 2p core level high-resolution XPS spectrum shows Zn 2p _3/2 and Zn 2p _1/2 , and the two peaks have a spin-orbit splitting (ΔE) of 23.1 eV , And the main peak centered at 1021.4 eV and 1045.5 eV, respectively. This shows only the Zn (II) oxidation state in the nanocomposite photocatalyst.

The C 1s and O 1s spectra show the reduction of oxidized graphene and the formation of reduced oxidized graphene nanocomposite photocatalyst with zinc oxide nanoparticles attached during the synthesis of reduced oxidized graphene nanocomposite photocatalyst with zinc oxide nanoparticles The background correction was then adjusted using a Gaussian function to evaluate.

The core-level peak of O 1s is 530.9 eV (lattice oxygen bond with Zn; Zn-O bond), 532.2 eV (CO-Zn, CO, C = O bond or surface adsorption oxygen content) and 533.2 eV It is confirmed that the chemical bond between the zinc oxide nanoparticles and the reduced oxidized graphene is formed through three main peaks.

The deconvoluted C 1s spectrum showed four peaks at 284.5 eV, 285.4 eV, 288.3 eV, and 290.3 eV (see FIG. 4d).

The 284.5 eV, 285.4 eV, and 288.3 eV peaks were assigned to non-oxygenated C-C or C = C bonds, C-O-C (epoxy) bonds and C = O (carbonyl or carboxylate) bonds, respectively.

However, the 290.3 eV peak is assigned to the π-π ^* satellite peak, which can be self-healed in the synthesis process or transformed into another functional group (carboxylate, epoxide or hydroxyl group) It indicates recovery.

No 283.3 eV peak for carbon-metal (C-M) bonds was detected, confirming the absence of C-Zn bonds in the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles.

The degree of reduction of oxidized graphene to reduced oxidized graphene was confirmed by XPS.

Figures 5 and 6 (d) show typical C 1s XPS spectra of oxidized graphene and sZG nanocomposite photocatalyst, respectively.

In the case of oxidized graphene, the inverted-line separated spectrum has a CC and C = C bond at 284.4 eV, a CO bond at 285.3 eV, an OC = O (carboxylate) bond at 288.7 eV and an OCO (C = O) bond at 287.2 eV. And four Gaussian peaks corresponding to the binding (see FIG. 5).

On the other hand, the C 1 S spectrum of the sZG nanocomposite photocatalyst showed a significant increase in the peak intensity corresponding to the CC / C = C bond, a decrease in the relative area percentage of the OC = O bond, and a disappearance of the C = O bond at 287.2 eV , Which confirmed the reduction to oxidized graphene in the oxidized graphene (see Table 1).

sample sZG nanocomposite photocatalyst Oxidized graphene Combination C-C / C = C C-O O-C = O C-C / C = C C-O O-C = O O-C = O (C = O) Combined energy (eV) 284.5 285.4 288.3 284.4 285.3 288.7 287.2 Area 31302.2 52667.2 8173.6 15941.3 45942.4 18754.7 75500.8 Area ratio (%) 31.2 52.5 8.1 10.2 29.4 12.0 48.4

The results shown in Table 1 are consistent with FT-IR and Raman data results.

The morphology of the reduced graphene nanocomposite photocatalyst with zinc oxide nanoparticles was observed by SEM.

In the case of using zinc oxide seed growth solvent composed solely of anhydrous ethanol, the zinc oxide nanoparticles have a nanospherical shape and are uniformly distributed on the reduced graphene graphene surface and on the edge of the reduced oxidized graphene sheet, Insertion of nanoparticles could be observed (see Fig. 7 (d)).

When a zinc oxide seed growth solvent having a volume ratio of 1: 0.25 of anhydrous ethanol and deionized water is used, the zinc oxide nanoparticles have a shape of a nano hexagonal plate, and a structure such as a randomly arranged nano hexagonal plate is formed of a reduced oxidized graphene sheet (See Fig. 7 (c)).

In the case of using a zinc oxide seed growth solvent having a volume ratio of 1: 1 of anhydrous ethanol and deionized water, a short nanorod shaped zinc oxide nanoparticle having a larger particle size was obtained, and a short It was confirmed that the nanorods had a hexagonal wurtzite structure (see Fig. 7 (b)).

In contrast, SEM images of the sZG * nanocomposite photocatalyst (Comparative Example 1), dZG * nanocomposite photocatalyst (Comparative Example 2) and rZG * nanocomposite photocatalyst (Comparative Example 3) The attached zinc oxide nanoparticles did not show nanospheres, nano hexagonal plates, and nanorods (see FIG. 8).

When a thin oxide graphene sheet is used in place of the reduced graphene graphene nanocomposite with zinc oxide seeds (see Comparative Examples 1 to 3), the weak electrostatic force between the graphene oxide graphene surface and the positively charged zinc- The shortened nanorods, nano hexagonal plates and nanospheres are not formed on the reduced oxidized graphene sheet surface, indicating that the zinc oxide nanoparticles are not adhered in situ during the reaction.

In addition, when the reaction was carried out in the absence of HMTA (see Comparative Example 4), it was shown that the expression of the structure due to the growth of zinc oxide seeds on the surface of the reduced oxidized graphene can be prevented (see FIG. 6).

In addition to the characteristics of the solvent, there is a reduced graphene graphene nanocomposite with zinc oxide seeds attached thereto. On the surface of the oxidized graphene thin sheet using HMTA, zinc oxide seed crystals are formed on the surfaces of nanorods, nano hexagonal plates, It was confirmed that it can grow to spherical shape.

The proposed mechanism for the formation of the reduced graphene nanocomposite photocatalyst with zinc oxide nanoparticles is shown in Equations 2 to 6 below.

[Formula 2]

[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

In this case, the four-digit ligand is _{(CH 2) 6 N 4 (} 'HMTA') is a metal ion (Zn ²⁺⁾ binding coordination between pore 4s orbital and a lone pair of electrons of the nitrogen of the metal ion (Zn ²⁺⁾ to And plays an important role in forming a zinc-ammonium complex in medium with high concentration of ammonium.

The zinc-ammonium complex can interact with the reduced graphene graphene nanocomposite with zinc oxide seeds and can promote the formation of reduced graphene graphene nanocomposite photocatalyst with zinc oxide nanoparticles under hydrothermal reaction conditions have.

Hydrolysis of HMTA in the heated state leads to the formation of intermediates such as NH ₃ and [Zn (NH ₃ ) ₄ ] ^{2 +} (see Equation 3).

The complex of Zn ²⁺ and NH ₃ occurs at a slow rate in anhydrous ethanol which controls the growth of zinc oxide seeds on reduced oxidized graphene. However, the process takes place strongly in the presence of deionized water. Therefore, the rate of formation of NH ₃ and [Zn (NH ₃ ) ₄ ] ²⁺ greatly affects the particle size and morphology of the zinc oxide nanoparticles grown on the reduced graphene oxide.

In addition, the solvent is considered to be an important factor controlling the growth behavior of the structure of the zinc oxide nanoparticles. Here, the characteristics of the solvent in the reaction solution, such as dielectric constant and saturation vapor pressure as well as interfacial-solvent interactions related to the surface energy of the crystal, are also considered.

Specifically, increasing the deionized water content in the zinc oxide seed solvent increases the polarization of the solvent mixture, which results in a change in saturated vapor pressure in a mixed solvent of anhydrous ethanol and deionized water, It may be related to the formation of particles.

TEM and HRTEM were used to further analyze the morphology of the reduced graphene nanocomposite photocatalyst with zinc oxide nanoparticles.

The TEM image of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles shows that the short nanorods, nano hexagonal plates and nanoparticles of zinc oxide nanoparticles adhere to the opaque and thin reduced oxide graphene sheet (See Figs. 9 (a1) to 9 (c1)).

Specifically, the weak point of the rZG nanocomposite photocatalyst is that it has a wide particle size distribution (see FIG. 9 (a1)), and when the content of deionized water in the mixed solvent of anhydrous ethanol and deionized water increases, ₃ production rate can result in uncontrolled particle size.

Zinc oxide nanoparticles having the shape of a nano hexagonal plate having a lying orientation and a free-standing orientation on a reduced oxidized graphene sheet were clearly observed (see Fig. 9 (b1)), .

The TEM image of the sZG nanocomposite photocatalyst shows uniform nanocrystalline zinc oxide nanoparticles attached on the surface of the reduced oxidized graphene sheet (see FIG. 9 (c1), FIG. 10 and FIG. 11).

Further, when the HRTEM image is closely observed, the reduced graphene graphene nanocomposite photocatalyst to which the zinc oxide nanoparticles are attached is 0.25 corresponding to the interplanar spacing of the (101), (104), and (202) planes, Well-resolved lattice fringes including 0.13 and 0.12 nm (d-spacing) are seen (see Figs. 9 (a2) to 9 (c2)).

In addition, the interface between the reduced oxidized graphene sheet and the zinc oxide nanoparticle structure was clearly observed in the reduced graphene oxide and zinc oxide nanoparticles in the phase boundary region. As a result, zinc oxide nanoparticles And the reduced graphene grains.

Of the many factors that affect the activity of the photocatalytic material, such as its unique band structure, particle size and specific surface area, it has been found that the crystallinity of the catalyst is also beneficial for improving photocatalytic activity.

Specifically, excellent crystallinity of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles was confirmed by using selected area electron diffraction (SAED) (FIG. 9 (a3) to FIG. 9 9 (c3)).

In order to confirm the presence of elemental components in the sZG nanocomposite photocatalyst, energy-dispersive X-ray spectroscopy (EDX) mapping was performed (see FIG. 9 (d)), (C), oxygen (O) and zinc (Zn) in the limited field of view of the composite photocatalyst.

The existence of C, O and Zn in the sZG nanocomposite photocatalyst was confirmed by EDX spectrum. Specifically, a peak of about 8 eV in the EDX spectrum was assigned to copper (Cu) from a TEM grid (see Fig. 9 (d)).

<Experimental Example 2> BET surface area analysis

A Brunauer-Emmett-Teller (R) photocatalyst of reduced graphene oxide nanocomposite with zinc oxide nanoparticles attached thereto using a nitrogen adsorption-desorber (3Flex, Micromeritics Instruments Corp.) (Hereinafter referred to as 'BET') specific surface area (hereinafter referred to as 'S _BET ').

Before the adsorption-desorption experiment, the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles was degassed at 200 ° C for 24 hours.

S _BET was obtained by applying the BET equation.

The N ₂ adsorption-desorption isotherms of the sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst and rZG nanocomposite photocatalyst were analyzed (see FIG. 12).

According to the IUPAC classification, the sZG nanocomposite photocatalyst, the dZG nanocomposite photocatalyst and the rZG nanocomposite photocatalyst showed a type IV isotherm exhibiting a mesoporous structure (see FIG. 12).

The specific surface area (S _BET ) of the sZG nanocomposite photocatalyst, the dZG nanocomposite photocatalyst and the rZG nanocomposite photocatalyst were calculated as 84.6 m ² / g, 61.3 m ² / g and 38.6 m ² / g, respectively.

The calculated specific surface area (S _BET ) was determined by using a reduced graphene graphene nanocomposite photocatalyst (36.93 m ² / g) on which zinc oxide rod nanoparticles were adhered and a reduced graphene nano- Than the composite photocatalyst (23.6863 m ² / g and 23.8 m ² / g).

If the specific surface area of the catalyst is large, it means that there are many adsorption-reaction active sites capable of improving the resolution of the catalyst.

sample Apparent rate constant (k, min ^-1 ) Degradation efficiency (%) S _BET
(m ² / g) Band gap
(eV) rZG nanocomposite photocatalyst MB RhB MB RhB 0.0169 0.0141 68.6 61.7 38.6 3.06
dZG nanocomposite photocatalyst 0.0225 0.0224 79.9 77.8 61.3 2.93
sZG nanocomposite photocatalyst 0.0642 0.0610 98.8 97.7 84.6 2.85

< Experimental Example  3> UV- vis  Spectroscopy ( UV-vis  spectroscopy analysis

Visible light diffuse reflectance spectra (UV-vis-NIR spectroscopy) of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles in the wavelength range of 200 nm to 800 nm using a UV-vis-NIR spectrophotometer (Varian Cary 5000) vis diffus reflectance spectra (UV-vis DRS) and ultraviolet-visible spectra (UV-vis spectra).

Optical studies were performed using a UV / vis-NIR spectrophotometer to analyze the optical absorption of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles in the range of 200 nm to 800 nm at room temperature (see FIG. 13A).

The prepared sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst, and rZG nanocomposite photocatalyst showed strong absorption at a wavelength of 400 nm or less, which is an electron excitation from a valence band to a conduction band under UV excitation Is the result of the intrinsic band gap of zinc oxide nanoparticles.

Absorption tendency of visible light (400 ~ 800 nm) region was relatively stable for all sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst, and rZG nanocomposite.

On the other hand, the sZG nanocomposite photocatalyst among the sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst and rZG nanocomposite photocatalyst showed the strongest absorption in the UV-Vis spectrum.

Considering the above results, it can be concluded that the light utilization of the sZG nanocomposite photocatalyst is more effective than the dZG nanocomposite photocatalyst and the rZG nanocomposite photocatalyst.

The optical band gap of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles was calculated using the following equation 7 for Tauc plot.

[Equation 7]

Wherein hν is the photon energy (eV), α is the absorption coefficient, A is a proportional constant, E _g is the band gap (eV).

The exponent n depends on the nature of the electron transition. For direct permissible transitions n is 1/2, for direct prohibited transitions n is 3/2, for indirectly permissible transitions n is 2, and for indirectly prohibited transitions n is 3.

Zinc oxide nanoparticles belong directly to the direct semiconductor group with direct permissible transitions.

Therefore, Equation (7) can be expressed again by Equation (8).

[Equation 8]

The band gap of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles is extrapolating the linear region and the Tauc plot [(hνα) ² . hv).

The band gap of the sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst and rZG nanocomposite photocatalyst is estimated to be 2.85 eV, 2.93 eV and 3.06 eV, respectively, which is much lower than bulk zinc oxide nanoparticles (3.37 eV) (see FIG.

The results showed good correlation between the photonic band gap energy and photocatalytic activity.

&Lt; Experimental Example 4 >

Thermogravimetric analysis (hereinafter, referred to as "TGA") of the reduced graphene oxide nanocomposite photocatalyst with the prepared zinc oxide nanoparticles was carried out at a temperature of 10 ° C./min from room temperature to 900 ° C., (TA Instruments SDT Q600 thermogravimetric analyzer).

From the TGA curves of the sZG nanocomposite photocatalyst, the dZG nanocomposite photocatalyst and the rZG nanocomposite photocatalyst, the weight loss corresponding to the temperature range of 20 to 120 ° C., 120 to 250 ° C. and 250 to 500 ° C. is the loss of adsorbed water To 5%), gradual loss of oxygen-containing functional groups and burn-out of graphene (see FIG. 14).

TGA showed the weight of zinc oxide nanoparticles contained in the reduced graphene nanocomposite with rZG nanocomposite photocatalyst, sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst and zinc oxide seed, which were 78.6%, 77.8% , 74.2% and 43.2%, respectively.

Based on the small difference in zinc oxide nanoparticle content in rZG nanocomposite photocatalyst, sZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst, it can be suggested that this does not significantly affect the comparison of photocatalytic activity.

&Lt; Experimental Example 5 > Photoluminescence spectrum analysis

Photoluminescence (PL) spectrum analysis of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles was carried out using a photoluminescence spectrometer (HORIBA scientific) at 325 nm laser wavelength excitation at room temperature Respectively.

PL spectroscopy is an effective tool for evaluating recombination rates of photogenerated electron-hole pairs through recording of PL emission signals under excitation of room temperature and 325 nm laser.

In essence, the greater emission intensity of the PL spectrum reflects the high recombination rate of the charge carriers, which hinders the photocatalytic activity of the catalyst.

The emission intensity of the sZG nanocomposite photocatalyst was lower than that of the rZG nanocomposite photocatalyst and the dZG nanocomposite photocatalyst (see FIG. 15), resulting in the most effective charge separation by having the lowest emission intensity, Showed the highest photocatalytic activity.

<Experimental Example 6> Photocatalytic activity analysis

The reduced graphene oxide nanocomposite with zinc oxide nanoparticles prepared according to Examples and Comparative Examples under UV irradiation using a 40 W UV lamp having a center wavelength of 365 nm (UV light source,? = 365 nm) Photocatalytic activity was evaluated by dye decomposition of photocatalyst.

To determine the photodegradation efficiency of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles, MB and RhB were used as model sources in wastewater.

The photoreaction was carried out at room temperature in a photochemical reactor.

5 mg of a reduced graphene oxide graphene nanocomposite photocatalyst with zinc oxide nanoparticles prepared in 50 ml of a dye solution (0.1 g / l) was added in a usual manner.

To reach the adsorption-desorption equilibrium between the dye and the catalyst, the reaction mixture was stirred for 30 minutes under dark conditions before operating the UV lamp.

Thereafter, a UV lamp was operated, and 3 ml aliquots were recovered at a luminescence interval of 10 minutes and centrifuged at 13,000 rpm for 10 minutes to remove the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles .

The absorbance of the MB and RhB solutions was measured at 664 nm and 553 nm, respectively, during photolysis and the residual dye concentration was monitored with a spectrophotometer.

In order to compare the photocatalytic activities of the reduced graphene graphene nanocomposite photocatalyst and the reduced graphene oxide with the prepared zinc oxide nanoparticles, photodegradation of MB and RhB was carried out by irradiating UV at room temperature for 60 minutes (FIGS. 16d), a blank test was performed on the two dyes.

The background test results showed that the dye concentration did not change under UV irradiation and showed high chemical stability of MB and RhB dyes.

The reduced oxidized graphene samples showed strong adsorption of the dye due to negligible photodegradation. However, when rZG nanocomposite photocatalyst, sZG nanocomposite photocatalyst, and dZG nanocomposite photocatalyst were present, the concentrations of MB and RhB decreased significantly after 60 minutes of UV irradiation (see FIGS. 16A and 16C).

The photodegradation efficiencies of sZG nanocomposite, dZG nanocomposite, and rZG nanocomposite photocatalysts were 98.8%, 79.9% and 100%, respectively, when the same initial dye concentration (10 ppm) and catalyst input (0.1 g / 68.6%, and photodegradation efficiencies for RhB were 97.7%, 77.8%, and 61.7%, respectively.

The dye adsorption capacity plays an important role in promoting the photolytic ability of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles.

16A shows the dye adsorption ability of the sZG nanocomposite photocatalyst, the dZG nanocomposite photocatalyst, and the rZG nanocomposite photocatalyst. The sZG nanocomposite photocatalyst (FIG. 17) after 30 minutes of adsorption-desorption equilibrium in a 10 ppm solution in the dark (30.5%) was higher than that of dZG nanocomposite (20.5%) and rZG nanocomposite (13.2%).

The dye adsorption is due to the offset printing face-to-face orientation through the π-π conjugation in the interaction of MB molecules with the aromatic rings of the reduced oxidized graphene.

RhB molecules with higher molecular weight and more complex structure significantly inhibited the adsorption capacity of the reduced graphene graphene nanocomposite photocatalyst with zinc oxide nanoparticles, and the sZG nanocomposite photocatalyst, dZG nanocomposite Photocatalyst and rZG nanocomposite photocatalyst adsorbed 14.6%, 10.9% and 9.6%, respectively.

The above results can be explained in relation to the specific surface area of the nanocomposite photocatalyst.

The highest photocatalytic activity of the sZG nanocomposite photocatalyst is due to the large number of adsorption / reaction sites provided by large specific surface area.

For comparison, a photocatalytic test was performed on sZG * nanocomposite photocatalyst, dZG * nanocomposite photocatalyst and rZG * nanocomposite photocatalyst using a 10 ppm MB solution under UV irradiation (see FIG. 18).

After 60 minutes, the dZG * nanocomposite photocatalyst and rZG * nanocomposite photocatalyst showed very small MB photodegradation, but the sZG * nanocomposite photocatalyst was able to decompose 44.5% of MB (see FIG. 19).

Photocatalytic degradation kinetics of MB and RhB under UV irradiation follow pseudo-first-order kinetics (see Figs. 15 (b) and 15 (d)).

[Equation 9]

C is the residual concentration of the dye in the solution, C ₀ is the initial concentration of the dye after adsorption-desorption equilibrium, and k is the apparent rate constant (min ^-1 ).

Table 2 lists the rate constants calculated for photodegradation of 10 ppm MB and 10 ppm RhB. Among the listed values, the rate constants of MB (0.0642 min ^-1 ) and RhB (0.0610 min ^-1 ) were the highest when using the sZG nanocomposite photocatalyst under UV irradiation.

In order to investigate the photodegradation efficiency according to the amount of catalyst, MB (10 ppm) decomposition experiment was performed by changing the sZG nanocomposite photocatalyst to 0.1 g / ℓ, 0.2 g / ℓ, and 0.3 g / ℓ.

After irradiation with ultraviolet rays, 0.2 g / ℓ of sZG nanocomposite photocatalyst was used to obtain MB decomposition efficiency of 98.1% over 30 minutes, and the amount of injected sZG nanocomposite photocatalyst was increased to 0.3 g / ℓ. The decomposition efficiency of 97.8% was obtained.

As the amount of catalyst in the MB solution was increased, the adsorption capacity was also increased (see Fig. 20A).

When the amount of catalyst is increased, the total surface area and the number of active sites increase, and the adsorption and removal efficiency of MB increases in a shorter time.

The sZG nanocomposite photocatalyst (0.1 g / ℓ) was used under UV irradiation to investigate dye removal efficiency according to dye concentration.

RhB solutions with initial concentrations of 10, 15 and 20 ppm were used (see Fig. 20b).

When the concentration of RhB was increased, the photodegradation efficiency after 60 minutes decreased by 17.1% in 15 ppm of RhB solution and by 42.3% in 20 ppm of RhB solution.

The increase in RhB concentration not only increases the amount of dye adsorbed on the catalyst surface but also has a filtering effect at the interface between the bulk RhB solution and the adsorbed layer and the catalyst surface.

This effect prevents large quantities of incident UV light from reaching the catalyst surface through the bulk solution, thereby reducing photocatalytic activity.

&Lt; Experimental Example 7 > Photocatalytic reaction mechanism

In the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles, the conduction band and the valence band of the zinc oxide semiconductor can be determined using the following empirical formula.

[Equation 10]

[Equation 11]

E _CB and E _VB are the conduction band edge (E _CB ) and the valence band edge (E _VB ) of the semiconductor with a band gap of E _g , respectively, and χ is the electronegativity of the constituent atoms Mulliken electronegativity, geometric mean.

In the case of zinc oxide nanoparticles, when χ was 5.790, the conduction band and valence band obtained by the above equations 10 and 11 in the vacuum state were -4.36 eV and -7.21 eV, respectively.

Trapping or scavenging experiments were conducted to further investigate the photocatalytic mechanism and to identify the dominant active oxidizing species involved in the photolysis reaction.

The capture or capture experiments were carried out on scavengers, ie, hydroxyl radicals, hole and superoxide radicals, ie 0.2 M tert-butyl alcohol (TBA), 0.2 M sodium bicarbonate sodium hydrogen carbonate, NaHCO ₃ ) and 1 mM p-benzoquinone (BZQ) were added to the dye solution before UV irradiation.

In order to analyze the photocatalytic mechanism of the dye decomposition process, a reactive substance as a main component was confirmed by adding a capturing agent or a capturing agent.

TBA, NaHCO _3, and the addition of BZQ, especially BZQ (1 mM) and TBA (0.2 M) was the one after RhB decomposition deceleration of the addition, this second oxidation under UV irradiation (O ₂ ^{· -)} radicals and hydroxide It means that the radical (.OH) is the main active oxidizing species involved in the decomposition of RhB (see Fig. 19 (c)).

Further, the hole (h _VB ⁺ ) also plays a role in the photolysis process.

Based on the above results, the photodegradation mechanism of the dye for the sZG nanocomposite photocatalyst prepared according to the present invention can be expressed by the following formulas 12 to 20 (see FIG. 21).

[Equation 12]

[Formula 13]

[Equation 14]

[Formula 15]

[Formula 16]

[Formula 17]

[Formula 18]

[Formula 19]

[Formula 20]

The electron transfer process taking place at the surface of the catalyst under UV excitation has been described on the basis of the vacuum contrast energy level (E, eV vs. vacuum), and in part gives concrete evidence that the charged charge carriers are efficiently separated when graphene is present (See Fig. 21).

When the catalyst is exposed to UV, the electrons are excited into the conduction band from the valence band leaving a positive hole (see Equation 12).

Fundamentally, the photogenerated electrons and holes easily recombine to reach a stable energy state.

On the other hand, since the work function of reduced graphene graphene (-4.42 eV) is more negative than the potential of zinc oxide nanoparticles in the conduction band (E _CB = -4.36 eV vs. vacuum), the conduction band of zinc oxide nanoparticles The electron (e ^- _CB ) excited at the surface will be transferred to a reduced oxidized graphene sheet (see Equation 13).

Oxidation-reduction potential ^{_{(O 2 / O 2 · -}} ) [(E 0 (O 2 / O 2 · -) = -4.45 eV vs vacuum) is the work function of the graphene oxide and the reduction position of the zinc oxide nanoparticles conductive strip because than lower part of the electrons on the electron and surface zinc nanoparticle oxide on a reduced oxidation graphene surface is dissolved by second oxide reduce the oxygen (O ₂ ^{· -)} of an aqueous solution to form a radical (see equation 14, and equation 15) .

In addition, the redox potential (E _VB = -7.21 eV vs. vacuum) of the photo-generated holes in the valence band of the zinc oxide nanoparticles is more negative than the potential needed to oxidize the H ₂ O adsorbed on the surface Holes generated under photo-excitation directly convert dye molecules to non-toxic compounds such as CO ₂ , H ₂ O and other intermediates and interact with H ₂ O molecules in solution to assist in the decomposition process. OH radicals .

As a result, the separation of the mineralized electron-hole pairs has been significantly improved, increasing the number of electrons and holes participating in a series of reactions occurring in the photolysis process.

<Experiment 8> Analysis of reusability test

In order to evaluate the reusability of the photocatalyst, the sZG nanocomposite photocatalyst (1.0 g / ℓ) was added to the 10 ppm MB solution and the photocatalytic decomposition reaction was repeated 15 times to analyze the reusability.

After each photocatalytic decomposition reaction, the sZG nanocomposite photocatalyst was separated from the treated MB solution, washed with deionized water, and reused after drying in a vacuum oven at room temperature before the next photolysis reaction proceeded.

After the photocatalytic decomposition reaction was completed 15 times, the surface morphology and structure of the used sZG nanocomposite photocatalyst were investigated.

The degradation efficiency of 99.4% after one photodegradation reaction and 96.0% after 15 photodegradation reactions was obtained and it was found that the reduction of the photocatalytic decomposition efficiency after 15 times of use was insignificant. As a result, the sZG nanocomposite photocatalyst can be used for a long time (See FIG. 20D).

Referring to the SEM image showing the shape of the sZG nanocomposite photocatalyst after the photolysis reaction 15 times before and after the photolysis reaction, it remained relatively stable even though it was repeated 15 times (refer to FIG. 22).

In general, the limitation on the photostability of the zinc oxide catalyst in the dye decomposition reaction is related to the photocorrosion phenomenon according to Equation 21 below.

[Formula 21]

The reason why the reduced graphene oxide nanocomposite attached with zinc oxide nanoparticles has high stability even under prolonged UV irradiation is that the hole induced by the dye molecules adsorbed on the reduced oxidized graphene surface is a solid of zinc oxide nanoparticles - instead of moving to the solid-solution interface (see equation 21).

Therefore, introduction of reduced graphene graphene not only effectively separates electron-hole pairs for high photocatalytic performance but also improves the catalyst life due to strong synergistic action between zinc oxide nanoparticles and reduced graphene oxide.

<Experimental Example 9> Electrochemical Impedance Spectrum (EIS) Analysis

EIS analysis is a powerful tool for analyzing the photogenerated charges of a photocatalyst system and their migration behavior for their separation efficiency.

Electrochemical impedance spectroscopy (EIS) was performed in a conventional three-electrode cell system using an Autolab PGSTAT 302 N (Metrohm) instrument.

An Ag / AgCl electrode and a platinum (Pt) electrode were used as a reference electrode and a counter electrode, respectively, and an electrolyte solution containing 5 mM K ₃ [Fe (CN) ₆ ] and 0.5 M sodium sulfate was used.

The working electrode was prepared by drop-casting a reduced oxidized graphene nanocomposite photocatalyst with zinc oxide nanoparticles prepared in a fluorine-tin oxide (FTO) glass (active region, 1 cm x 1 cm) (drop-casting) method.

Specifically, 2 mg of the reduced graphene oxide nanocomposite photocatalyst with zinc oxide nanoparticles prepared was mixed with 1 ml of ethanol and 10 μl of Nafion (binder) to prepare a slurry (homogeneous).

Next, 15 μl of the homogeneous mixture was adhered onto the FTO glass by drop-casting method, and then dried for 24 hours under ambient conditions to prepare a working electrode.

The impedance spectrum of the sample was recorded in the frequency range of 10 ⁵ Hz (high frequency) to 0.01 Hz (low frequency).

Photocurrent was measured at 0.5 V (vs. SEC) on an Autolab PGSTAT302 N (Metrohm) instrument.

The reduced graft oxide nanocomposite photocatalyst with the prepared zinc oxide nanoparticles was treated with fluorine-tin oxide (FTO) glass (active region, 1 cm x 1 cm ) By a drop-casting method to prepare a working electrode.

A conventional three-electrode cell system was immersed in a 1 M Na ₂ SO ₄ electrolyte.

The photocurrent response under an on-off light irradiation cycle for several 300 seconds was measured using a 10 W UV lamp (? = 254 nm) as the light source.

The working electrode has the same illuminated area of 1 cm x 1 cm.

A Randles equilibrium circuit is used as the basis for the impedance characteristics, where Rs and Rct denote bulk solution resistance and charge transfer resistance, respectively.

In the Nyquist diagram, the semicircle at high frequencies is related to the resistance of the solid state interface and the charge transfer resistance.

The small semicircle represents the low resistance of the surface.

In the Nyquist plot of the sZG nanocomposite photocatalyst, the semicircle was smaller than the rZG nanocomposite photocatalyst and dZG nanocomposite photocatalyst. This means that the sZG nanocomposite photocatalyst has the smallest charge transfer resistance (Rct-sZG = 363.1 ?, Rct-dZG = 483.7? And Rct-rZG = 713?).

The sZG nanocomposite photocatalyst induces the fastest constant in the dye decomposition process as a result of the fastest interfacial movement of the photogenerated charge and the most effective recombination prevention of the electron-hole pairs at the interface of the nanocomposite photocatalyst.

By measuring the photocurrent transient response, the photocurrent transient response was measured, as well as the electronic interaction between the zinc oxide nanoparticles and the reduced graphene oxide, as well as the efficiency of photoinduced electron-hole pairs separation in each nanocomposite photocatalyst.

Photocurrent measurement was performed on the rZG nanocomposite photocatalyst, dZG nanocomposite photocatalyst and sZG nanocomposite photocatalyst under UV irradiation after adhering to the FTO electrode through on-off circulation (see FIG. 23B).

The photocurrent (2.03 μA) of the electrode with the sZG nanocomposite photocatalyst was about 3 times and 1.4 times higher than the electrode (0.75 μA) with the rZG nanocomposite photocatalyst and the electrode with the dZG nanocomposite photocatalyst (1.46 μA) This means that the efficiency of photoelectrolytic electron-hole separation is the highest, which is in good agreement with the results of EIS analysis and photocatalytic activity analysis as a result of electron interaction between zinc oxide nanoparticles and reduced graphene oxide.

Since the photocurrent is generated by the transfer of photoexcited electrons to the surface of the oxidized graphene and the FTO reduced in the semiconductor, it is believed that the spherical structure of the zinc oxide nanoparticles and the presence of the reduced oxidized graphene effectively separates the photo- Indicating that it plays an important role in promoting migration.

Improvement of separation efficiency and specific surface area of light absorption, charge transport, and charged carriers is a key factor contributing to improvement of the photocatalytic activity of the prepared catalyst, and it is believed that zinc oxide nanoparticles and reduced graphene graphene Can be achieved by an effective combination.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (14)

Reduced oxidized graphene; And
The zinc oxide nanoparticles attached on the reduced oxidized graphene
Wherein the photocatalyst is a grafted zinc oxide nanoparticle. The method according to claim 1,
The zinc oxide nano-
A reduced graphene graphene nanocomposite photocatalyst having zinc oxide nanoparticles attached thereto, characterized in that the graphene nanocrystal has a nano-shape of either a nanospherical shape, a nano hexagonal plate, or a nanorod. The method of claim 2,
Wherein the nanoporous zinc oxide nanoparticles have an average diameter of 5 to 30 nm. The photocatalyst of claim 1, wherein the zinc oxide nanoparticles have an average diameter of 5 to 30 nm. The method of claim 2,
Wherein the nano hexagonal zinc oxide nanoparticles have an average diameter of 100 to 400 nm and an average thickness of 10 to 30 nm. The zinc oxide nano- Composite photocatalyst. The method of claim 2,
Wherein the zinc oxide nanoparticles having the nano-shaped nanorods have an average diameter of 20 to 200 nm, and the reduced grafted oxide graphene nanocomposite photocatalyst to which the zinc oxide nanoparticles are attached. Adding a zinc precursor to the oxidized graphene suspension and stirring to prepare a first agitated material;
Drying the first precipitate obtained by centrifuging the first agitate;
Heat treating the dried first precipitate to prepare a reduced graphene graphene nanocomposite having zinc oxide seeds attached thereto;
Adding the nanocomposite to anhydrous ethanol and a zinc oxide seed growth solvent;
Adding a zinc precursor and a reducing agent to the zinc oxide seed growth solvent to which the nanocomposite is added and stirring to prepare a second agitated material;
Subjecting the second agitator to heat treatment, cooling and centrifuging to obtain a second precipitate; And
Preparing a reduced graphene graphene nanocomposite-coated reduced graphene graphene nanocomposite photocatalyst, comprising the steps of: washing the second precipitate and drying to form a reduced graphene graphene nanocomposite photocatalyst with zinc oxide nanoparticles attached thereto; Way. The method of claim 6,
Wherein the zinc precursor
It is composed of zinc acetate, zinc nitrate, zinc sulfate, zinc phosphate, zinc fluoride, zinc chloride and zinc iodate. Wherein the zinc oxide nanoparticles are selected from the group consisting of zinc oxide nanoparticles and zinc oxide nanoparticles. The method of claim 6,
The step of drying the first precipitate obtained by centrifuging the first agitated product comprises:
Wherein the first precipitate obtained by centrifuging the first agitated product at 10,000 to 15,000 rpm is dried at 20 to 30 占 폚, wherein the first precipitate is dried at 20 to 30 占 폚. The method of claim 6,
Wherein the step of preparing the reduced graphene oxide nanocomposite with the zinc oxide seeds comprises:
Treating the dried first precipitate at a temperature of 250 to 350 ° C for 30 to 90 minutes. The method of claim 6,
The zinc oxide seed growth solvent may include,
Wherein the zinc oxide nanoparticles are composed of anhydrous ethanol, deionized water or a combination thereof. The method of claim 10,
The zinc oxide seed growth solvent composed of the anhydrous ethanol and deionized water,
Characterized in that anhydrous ethanol and deionized water have a volume ratio of 1: (0 to?). The method of claim 6,
The reducing agent,
Wherein the zinc oxide nanoparticles are hexamethylenetetramine (HMTA). The method of claim 6,
The step of obtaining the second precipitate comprises:
Characterized in that the second agitated product is heat treated at 100 to 110 ° C for 12 to 36 hours and then cooled and centrifuged at 6,500 to 7,500 rpm for 3 to 10 minutes to obtain a second precipitate, Reduced photocatalytic oxide graphene nanocomposite. The method of claim 6,
The zinc oxide nano-
A method for producing a reduced graphene graphene nanocomposite photocatalyst having a zinc oxide nanoparticle attached thereto, characterized in that the graphene nanocrystal has a nano shape of any one of a nanospherical shape, a nano hexagonal plate, and a nanorod.

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