KR101830575B1 - Ag-ZnFe2O4@rGO Nanocomposite Photocatalyst for Efficient Treatment of Organic Wastes under Ultraviolet and Visible Light and the Preparation Method Thereof - Google Patents

Abstract

The present invention relates to Ag-ZnFe_2O_4@rGO nanocomposite photocatalyst capable of treating organic wastes effectively under UV light and visible light, and a preparation method of the same. More specifically, the present invention provides Ag-ZnFe_2O_4@rGO nanocomposite photocatalyst which comprises: reduced graphene oxide (rGO); and zinc ferrite (hereinafter referred to as ′ZnFe_2O_4′) nanoparticles and silver (Ag) nanoparticles attached to the rGO. The Ag-ZnFe_2O_4@rGO nanocomposite photocatalyst and the preparation method according to the present invention have effects of reducing aggregation of nanoparticles through a synergistic effect among Ag nanoparticles, ZnFe_2O_4 nanoparticles, and rGO, and enlarging the surface area of the catalyst, thereby causing better absorption under both UV light and visible light. Thus, the Ag-ZnFe_2O_4@rGO nanocomposite photocatalyst shows a high photocatalytic activity with respect to decomposition of various dyes including MB, RhB, and MO.

Description

(Ag-ZnFe2O4 @ rGO Nanocomposite Photocatalyst for Efficient Treatment of Organic Wastes under Ultraviolet and Visible Light and the Preparation Method Thereof) which can efficiently treat organic wastes in ultraviolet and visible light,

Disclosure of Invention Technical Problem The present invention relates to a dye-sensitized solar cell having excellent adsorption characteristics and capable of decomposing various dyes such as methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) (Hereinafter referred to as " rGO ") nanocomposite photocatalyst (hereinafter referred to as " Ag-ZnFe ₂ O ₄ ") capable of effectively treating organic wastes in ultraviolet and visible light, &Quot; Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst ") and a method for producing the same.

Organic dye effluents and dyes from the textile and dyeing industries are one of the largest pollutants emitted from each production site without proper treatment.

Conventional biological, physical and chemical methods for wastewater treatment have been established, but in this case the pollutant only changes from the liquid phase to the solid phase and further treatment is needed to purify the resulting sludge. Also, very low concentrations of pollutants are still difficult to remove from the wastewater.

Therefore, the advanced oxidation processes (AOPs) proposed to solve the above problems have been used to remove a wide range of organic pollutants from water and air.

In this respect, heterogeneous photocatalysis is considered one of the most potent AOPs because of its potential applicability in the degradation of organic pollutants.

Although semiconductors such as titanium dioxide (TiO ₂ ), zinc oxide (ZnO) and tin dioxide (SnO ₂ ) have been extensively studied as photocatalysts, these semiconductors have a wide band gap (3.0 To 3.8 eV), there is a problem that the photocatalytic activity is limited under visible light irradiation. However, many spinel-type oxides exhibit photocatalytic activity in the visible region.

Among these spinel oxides, spinel zinc ferrite (hereinafter referred to as 'ZnFe ₂ O ₄ ') has a narrow band gap (1.9 eV), low toxicity, natural richness, excellent ferromagnetic property for magnetic separation from suspension, Is a potential candidate for photocatalytic action in the environment.

Recently, ZnFe ₂ O ₄ A study was conducted by Cai et al. To evaluate the photocatalytic activity of orange Ⅱ (orange Ⅱ) dyes by producing nanoparticles and producing highly reactive OH radicals by decomposition of H ₂ O ₂ under visible light irradiation .

However, due to the low valence-band potential of pure ZnFe ₂ O ₄ and the accompanying poor photo-electron conversion properties, rapid recombination of electron-hole pairs generated by light occurs, so Orange II is a pure ZnFe ₂ O ₄ There is a problem in that it can not be disassembled.

In the present invention, a new path has been developed in order to solve the above-mentioned problems and achieve excellent performance.

Graphene has attractive properties such as large surface area, good mechanical flexibility, high chemical stability and unique electronic properties. Graphene fixes nanoparticles on the surface of the layer due to the enhanced adsorptivity of the catalyst, the non-aggregation of the nanoparticles, the increased optical absorption range and the significantly less recombination of the photogenerated electron-hole pairs, It is regarded as an ideal substrate for making pin-based nanocomposite photocatalyst.

Furthermore, silver (Ag) nanoparticles strongly absorb visible light due to surface plasmon resonance (SPR). Ag nanoparticles act as an electron sink to facilitate the charge separation of the photogenerated electron-hole pairs, thereby improving the photocatalytic activity of the nanocomposite.

Various metal ferrite-graphene nanocomposite photocatalysts have been reported. Yao et al. Evaluated the activity of nanocomposite catalysts through the decomposition of orange Ⅱ on photocatalysts of magnetic ZnFe ₂ O ₄ - graphene nanocomposite under visible light when peroxymonosulfate was present. Fu and Wang also studied the synthesis of ZnFe ₂ O ₄ - graphene nanocomposites and the removal of methylene blue (MB) by irradiating visible light in the presence of H ₂ O ₂ . Zu et al. Prepared a Ag / MFe ₂ O ₄ catalyst (M = Zn, Cu, Co and Ni) using conventional wet impregnation techniques and performed photolysis reaction of 4-chlorophenol under visible light irradiation Respectively.

Microwave-assisted synthesis is regarded as an attractive method for nanocomposite photocatalyst production. Microwaves excite molecular dipoles to enhance rotation and vibration to increase friction between molecules, and to dissipate the heat generated thereby uniformly and rapidly throughout the reactor. Thus, the reaction mechanism of the microwave-assisted manufacturing method is more closely related to the molecular structure and properties than the conventional heating method.

Highly monodisperse oxide nanoparticles such as ZnFe ₂ O ₄ -grapein, rGO / Ag ₃ PO ₄ and graphene-TiO ₂ nanocomposites have been produced through the microwave method. Under microwave irradiation, the volume of graphene oxide (GO) expanded and a large amount of gas evolution was observed from the pyrolysis process. After pyrolysis reaction, GO with high oxygen content was converted into pyrogenic graphene oxide and deoxidized under microwave irradiation. Microwave heating is more efficient in terms of energy used, takes less time to synthesize, and provides homogeneous high temperatures in the reactor, producing particles of 15-35 nm size.

In addition, the magnetic properties of ZnFe ₂ O ₄ nanoparticles allow the nanocomposite photocatalyst to be more easily separated from the process, thus avoiding environmental contamination during processing, and the presence of Ag nanoparticles can result in light generation in the ultraviolet and visible regions Hole pairs can be prevented and the decomposition rate of the organic compound can be accelerated by improving the separation.

Therefore, it is necessary to develop a nanocomposite photocatalyst capable of having high photocatalyst stability and expandability by using GO, ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles, thus completing the present invention.

Korea Patent No. 1683059

It is an object of the present invention to provide a photocatalyst having high photocatalytic activity for decomposing dyes such as MB, RhB and MO through a simple single container hydrothermal synthesis using a microwave at a low temperature and in a short time without using a surfactant or a template, ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst capable of effectively separating organic wastes from ultraviolet rays and visible rays and having excellent reusability, and a method for manufacturing the same.

In order to achieve the above object, And Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst comprising ZnFe ₂ O ₄ nanoparticles and silver (Ag) nanoparticles attached on rGO.

The present invention also provides a method for preparing a ferroelectric film, comprising: preparing a first mixed solution by dissolving an iron precursor and a zinc precursor in deionized water; Dispersing the GO in deionized water and sonicating to prepare a GO dispersion; Adding the first mixed solution to the GO dispersion and stirring to prepare a second mixed solution; Adding a silver precursor to the second mixed solution and stirring to prepare a third mixed solution; Adding a reducing agent to the third mixed solution and stirring to prepare a suspension; The suspension is irradiated with microwaves, heated, cooled to room temperature, and centrifuged to collect nanocomposites containing ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles attached to rGO. And preparing a nanocomposite photocatalyst comprising ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles adhered to rGO by washing the collected nanocomposite and vacuum drying the nanocomposite, wherein Ag-ZnFe ₂ O ₄ @rGO A nanocomposite photocatalyst production method is provided.

The Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst capable of effectively treating organic wastes in ultraviolet and visible light according to the present invention and its manufacturing method can produce a synergistic effect between Ag nanoparticles, ZnFe ₂ O ₄ nanoparticles and rGO To reduce aggregation of nanoparticles and increase the surface area of the catalyst to induce better absorption in both UV light and visible light and to prevent recombination of photogenerated electron- By enhancing the separation, there is an effect of exhibiting high photocatalytic activity against decomposition of various dyes MB, RhB and MO.

FIG. 1 is a schematic view showing a process for producing Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst by a microwave-assisted self-assembly synthesis method for a short time;
Figure 2 is prepared according to comparative example 1 The pure ZnFe ₂ O ₄ nanoparticles photocatalyst (a), comparing a ZnFe ₂ O ₄ @rGO photocatalytic nanocomposite (b) prepared according to Example 2 prepared in accordance with, and in Example 1 X-ray diffraction pattern of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst (c);
FIG. 3 is an FE-SEM image (a and b) and a TEM image (c) of a Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1, and a high-resolution TEM image of FIG.
FIG. 4 shows XPS spectra of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1. The XPS spectrum of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 is shown in FIG. ), O 1s (e) and C 1s (f) energy regions;
5 shows a C 1s XPS spectrum of GO;
6 shows FT-IR spectra (a) and Raman spectrum (b) of the GO and the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1;
7 is a N ₂ adsorption-desorption isotherm of an Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1. FIG. The drawing shows a pore size distribution;
8 is a graph showing the TGA and DSC curves of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 in air and nitrogen atmosphere;
FIG. 9 is a graph showing the relationship between the ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1, the ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Comparative Example 2, and the Ag-ZnFe ₂ O ₄ @rGO UV-vis absorption spectrum (a) and EIS spectrum (b) of the nanocomposite photocatalyst; UV absorption spectrum (c) and EIS spectrum (d) of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Examples 1 to ₄ ;
FIG. 10 is a graph showing the relationship between the ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1, the ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Comparative Example 2, the Ag-ZnFe ₂ O ₄ @rGO Decomposition of MB (20 ppm) by UV (? = 365 nm) on a nanocomposite photocatalyst, and decomposition of visible light for comparison purposes on the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 gt; (20 ppm) < / RTI >
Fig. 11 is a comparative diagram (comparative diagram of photocatalytic decomposition of MB under ultraviolet (a) and visible light (b) using Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst is easily separated by magnetism);
12 is a graph showing changes in adsorption (a) and photocatalytic degradation performance (b) of MB on the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Examples 1 to ₄ ;
13 is a graph showing changes in UV (a) and visible light (b) of an aqueous solution of three dyes (MO, RhB and MB) at 10 ppm using Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 ≪ / RTI >
14 is a graph showing the similar primary rate constants (k (k)) for photodegradation of ultraviolet and visible light of MB, RhB and MO (all in an aqueous solution of 10 ppm) by Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 FIG.
15 shows the photolysis of MB (20 ppm) of a Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst (0.5 g cat L ^{- 1} ) prepared according to Example 1 using a 40 W UV lamp (λ = 365 nm) Of a reusability test;
16 is a graph showing the results of photocatalytic decomposition of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 using p-benzoquinone (BZQ), sodium bicarbonate (NaHCO 3) collecting (trapping) of a), the hole (h _VB ⁺⁾ and hydroxyl ^{_{(· OH) - · O 2}} : 3 '), and isopropyl alcohol (isopropyl alcohol: hereinafter' IPA ') reaction species acetate weapon (superoxide radical by Fig. And
17 is a schematic view showing the MB decomposition mechanism of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 under UV or visible light irradiation.

Hereinafter, Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst capable of effectively treating organic wastes in ultraviolet rays and visible rays according to the present invention and a method for producing the same will be described in detail.

The inventors of the present invention have found that by synergy between Ag nanoparticles, ZnFe ₂ O ₄ nanoparticles, and rGO by using a low temperature, microwave assisted, self-assembly precipitation method, the agglomeration of nanoparticles is reduced and the surface area of the catalyst is increased To induce better absorption in both UV light and visible light, to prevent recombination of photogenerated electron-hole pairs, and to improve their separation, thereby to improve the separation of various dyes such as MB, RhB and MO And can exhibit high photocatalytic activity against decomposition. The present invention has been completed based on this finding.

The present invention relates to rGO; And Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst comprising ZnFe ₂ O ₄ nanoparticles and silver (Ag) nanoparticles attached on rGO.

The ZnFe ₂ O ₄ nanoparticles may have an average diameter of 10 to 20 nm, but are not limited thereto.

The Ag nanoparticles may have an average diameter of 30 to 40 nm, but are not limited thereto.

The nanocomposite photocatalyst may be composed of 55 to 65 wt% of ZnFe ₂ O ₄ nanoparticles, 20 to 30 wt% of Ag nanoparticles, and 10 to 20 wt% of rGO, but is not limited thereto.

The present invention also provides a method for preparing a ferroelectric film, comprising: preparing a first mixed solution by dissolving an iron precursor and a zinc precursor in deionized water; Dispersing the GO in deionized water and sonicating to prepare a GO dispersion; Adding the first mixed solution to the GO dispersion and stirring to prepare a second mixed solution; Adding a silver precursor to the second mixed solution and stirring to prepare a third mixed solution; Adding a reducing agent to the third mixed solution and stirring to prepare a suspension; The suspension is irradiated with microwaves, heated, cooled to room temperature, and centrifuged to collect nanocomposites containing ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles attached to rGO. And preparing a nanocomposite photocatalyst comprising ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles adhered to rGO by washing the collected nanocomposite and washing the nanocomposite with Ag-ZnFe ₂ O ₄ @rGO nano A method for producing a composite photocatalyst is provided.

The iron precursor may be selected from the group consisting of ferric nitrate nonahydrate (Fe (NO ₃ ) ₃ ), ferrous chloride (FeCl ₂ ), ferric chororide (FeCl ₃ ) ferrous sulfate: FeSO ₄ , ferric sulfate: Fe ₂ (SO ₄ ) ₃ and ferrous acetate: Fe (CO ₂ CH ₃ ) ₂ ) But is not limited thereto.

Wherein the zinc precursor is zinc acetate _{(zinc acetate: Zn (CH 3} COOH) 2), zinc sulfate (zinc sulfate: ZnSO _4), zinc chloride (zinc chloride: ZnCl _2), zinc nitrate _{(zinc nitrate: Zn (NO 3} ) ₂ ), zinc bromide (ZnBr ₂ ) and zinc iodide (ZnI ₂ ), but the present invention is not limited thereto.

The step of preparing the first mixed solution may be prepared by dissolving the iron precursor and the zinc precursor in deionized water in a molar ratio of 1: 0.5 to 3, but is not limited thereto.

The GO dispersion may have a concentration of 0.2 to 3 mg / ml, but is not limited thereto.

Wherein the precursor is silver nitrate (silver nitrate: AgNO _3), silver sulfate _{(silver sulfate: Ag 2 SO 4} ), acetic acid (silver acetate: AgCOOCH _3), silver chloride (silver chloride: AgCl) and carbonate (silver carbonate: Ag ₂ CO ₃ ), but is not limited thereto.

The reducing agent is selected from the group consisting of hydrazine (N ₂ H ₄ ), sodium borohydride (NaBH ₄ ), ethylene glycol (C ₂ H ₄ (OH) ₂ ), thiourea ₂ ) ₂ CS) and thiourea dioxide (NH 3) (NH ₂ ) CSO ₂ H), but the present invention is not limited thereto.

In the step of collecting the nanocomposite comprising ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles attached to the rGO, the suspension is irradiated with a microwave of 50 to 400 W, heated to 60 to 150 ° C, and then irradiated for 3 to 20 minutes The temperature may be maintained, then cooled to room temperature and centrifuged, but is not limited thereto.

The step of preparing the nanocomposite photocatalyst including the ZnFe ₂ O ₄ nanoparticles and the Ag nanoparticles attached to the rGO may be performed by washing the collected nanocomposite and then vacuum drying at 20 to 100 ° C for 30 minutes to 5 hours , But is not limited thereto.

Hereinafter, Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst capable of effectively treating organic wastes in ultraviolet and visible light 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 > Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst synthesis

All reagents purchased from Alfa Aesar are analytical grade and used as received without further purification.

GO was synthesized by oxidation of graphite powder under acidic conditions according to Tour method.

The Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst of the present invention was synthesized by a low-temperature, microwave-assisted, self-assembly precipitation method.

Figure 1 shows the synthesis mechanism of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst.

The first mixed solution was prepared by dissolving 2 mmol of FeCl ₃ .6H ₂ O and 1 mmol of Zn (CH ₃ COOH) ₂ .2H ₂ O in 10 ml of deionized water. Then, 80 mg of GO (hereinafter referred to as 'G80' ) Was dispersed in 60 ml of deionized water and ultrasonicated for 1 hour to prepare a GO dispersion.

A first mixed solution containing Fe ³⁺ and Zn ²⁺ was added to the GO dispersion and stirred for 30 minutes to prepare a second mixed solution.

Next, 10 ml of 0.1 M AgNO ₃ was added to the second mixed solution, and the mixture was stirred for 30 minutes to prepare a third mixed solution.

To the third mixed solution, 5 ml of N ₂ H ₄ .H ₂ O 4 ml was added and stirred for 30 minutes to prepare a suspension.

The resulting suspension was transferred to a 2.45 GHz microwave reactor (CEM Discover), heated to 100 < 0 > C (150 W) at atmospheric pressure, held at temperature for 10 minutes and then cooled to room temperature.

Finally, the sample was collected by centrifugation, repeatedly washed with deionized water and anhydrous ethanol, and then dried in a vacuum oven at 60 ° C for 2 hours to prepare an Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst.

≪ Example 2 > Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst synthesis

Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was prepared under the same conditions as in Example 1, except that 20 mg of GO (hereinafter referred to as 'G20') was used.

≪ Example 3 > Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst synthesis

Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was prepared under the same conditions as in Example 1, except that 40 mg of GO (hereinafter referred to as 'G40') was used.

≪ Example 4 > Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst synthesis

Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was prepared under the same conditions as in Example 1 except that 100 mg of GO (hereinafter referred to as 'G100') was used.

≪ Comparative Example 1 > Pure ZnFe ₂ O ₄ Manufacture of nanoparticle photocatalyst

A ZnFe ₂ O ₄ nanoparticle photocatalyst was prepared under the same conditions as in Example 1 without adding AgNO ₃ and GO.

≪ Comparative Example 2 > ZnFe ₂ O ₄ @ rGO nanocomposite photocatalyst manufacture

A ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was prepared under the same conditions as in Example 1 without adding AgNO ₃ .

≪ Experimental Example 1 > Ag-ZnFe ₂ O ₄ Analysis and morphology of @rGO nanocomposite photocatalyst

X-ray diffraction (hereinafter, referred to as 'XRD') was performed using X-ray diffraction (XRD) using Cu Kα irradiation in order to analyze the phase structure and morphology of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite prepared in Example 1 Field-emission scanning electron microscopy (hereinafter, referred to as 'FE-SEM') was performed using a field emission scanning electron microscope (Hitachi, S-4800 Transmission Electron Microscope (TEM) was observed at 200 kV using a transmission electron microscope (Philips, CM-200). Fourier transform infrared spectroscopy (Fourier transform infrared spectroscopy) was used. Raman spectroscopy was performed using a Raman spectroscope (HORIBA, XploRA plus), and X-ray photoelectron spectroscopy (FT-IR) was performed using an FT-IR spectroscopic analyzer (Bio- Rad, Excalibur Series FTS 3000) X-ray photoelectron spectroscopy (XPS) Monochromatic Al Kα were analyzed by irradiation (monochromatized radiation) an XPS (KRATOS, AXIS Nova) with for use.

FIG. 2 is a graph showing the relationship between the pure ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1, the ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Comparative Example 2 and the Ag-ZnFe ₂ O ₄ @ The XRD pattern of the rGO nanocomposite photocatalyst is shown.

In the case of such an XRD pattern, 30.1, 35.3, 43.0 (corresponding to (220), (311), (400), (422), (511) and (440) crystal faces of spinel ZnFe ₂ O ₄ , 53.5, 56.3 and 62.4 [deg.] 2 [theta].

For the ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst, an additional weak broad peak was observed at 18-22 ° 2θ, which is associated with rGO.

The pure rGO showed a characteristic peak (002) in the 18-25 ° 2θ range, but no XRD peak for rGO was detected in the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst.

rGO is a spacer, which attaches Ag nanoparticles and ZnFe ₂ O ₄ nanoparticles to effectively minimize restacking of the rGO thin sheet after reduction.

In addition, in the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst, 38.12, 44.28, 64.43 and 77.47 corresponding to the (111), (200), (220) and (311) crystal faces of the Ag nanoparticles (JCPDS 04-0783) An additional XRD peak was assigned at ˚ 2θ.

3 (a) to 3 (c) show FE-SEM images and TEM images of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1. FIG.

FIGS. 3 (b) and 3 (c) show that the sizes of ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles are approximately 10 to 20 nm and 30 to 40 nm.

This means that the interaction between the ZnFe ₂ O ₄ nanoparticles and the flexible layered graphene sheet can limit the aggregation of crystalline ZnFe ₂ O ₄ nanoparticles to some extent.

3 (c) is a TEM image showing an essential hybrid structure of a photocatalyst adhered to the surface of a large rGO thin plate with ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles.

A high-resolution TEM (hereinafter referred to as HRTEM) image of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 (refer to the upper right diagram of FIG. 3 (c) (Black) and the smaller ZnFe ₂ O ₄ particles (gray) adjacent to it.

The structures of rGO edge, ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles were clearly observed in high magnification TEM images.

Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst can provide efficient chemical properties because of strong interaction between ZnFe ₂ O ₄ nanoparticles, Ag nanoparticles and graphene sheets.

FIG. 4 shows the surface chemical composition and electronic state of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst by XPS spectrum.

The survey spectra of FIG. 4 (a) showed the presence of Zn 2p, Fe 2p, Ag 3d, O 1s and C 1s energy regions.

4 (b) shows a high-resolution Zn 2p spectrum showing two major fitting peaks centered at 1044.8 eV and 1021.7 eV, assigned to Zn 2p _1/2 and Zn 2p _3/2 , ₂ O ₄ shows the oxidation state of Zn (II).

In the Fe 2p spectrum of FIG. 4 (c), the binding energies of Fe 2p _3/2 were 713.1 eV and 711.4 eV, respectively, which correspond to the tetrahedral site and the octahedral site, respectively. On the other hand, the binding energy peak at 725.6 eV corresponds to Fe 2p _1/2, and two shakeup satellite signals (719.3 eV and 732.8 eV) were observed in the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst with ZnFe ^Suggesting that only Fe ³⁺ (Fe ²⁺ element) exists in ₂ O ₄ . The oxidation state of Fe (III) in ZnFe ₂ O ₄ was confirmed by this analysis.

The high-resolution XPS spectrum of Ag 3d in Fig. 4 (d) shows Ag 3d _5/2 and Ag 3d _3/2 , and these two peaks exhibit binding energies of 368.1 eV and 374.1 eV, respectively. In the diagram, the spacing of the Ag 3d double lines is 6.0 eV, which indicates the formation of metallic Ag in the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst. Detailed deconvolution of the Ag 3d peak was performed to better understand the chemical nature of the Ag nanoparticles. The binding energies of Ag 3d _5/2 core levels for Ag and AgO were 368.4 eV and 367.6 eV, respectively. According to reverse-line separation analysis, about 65.7% of the Ag nanoparticles were in the Ag ⁰ (metal) state, while about 33.4% were in the Ag ⁺ chemical state.

The O1s spectrum of Figure 4 (e) could be inversely separated at 530.4, 531.8, and 532.8 eV to three different peaks, and the O1s binding energy of 530.4 eV was due to lattice oxygen (Fe-O and 0.0 > Zn-O). ≪ / RTI > Also, the peaks with binding energies of 531.8 eV and 532.8 eV, respectively, have surface absorbed oxygen species such as O ₂ ^- _ads and O ^- _ads and residual oxygen containing groups (CO and C = O) bonded with C atoms of graphene, . Ag-ZnFe ₂ O ₄ @rGO nanocomposite Oxygen chemically adsorbed on the photocatalyst surface is the most active oxygen in the oxidation reaction.

The degree of reduction of rGO from XPS was also confirmed.

FIG. 4 (f) shows a typical C 1s XPS spectrum of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst and GO, respectively.

The peaks for the C 1s signal of the original GO were inverted to multiple signals, which were 284.7 eV each for CC and C = C bonds without oxygen, 285.4 eV for CO and 287.4 eV, 287.4 eV C = O bonds, and OC = O bonds representing carboxylates at 288.9 eV.

Comparing FIG. 4 (f) with FIG. 5, the peak intensities of C-C and C = C bond significantly decreased while the peak intensities of C-C and C = O bond significantly decreased.

The degree of reduction of GO was calculated based on XPS results.

The content of oxygen-containing carbon (C-O, C = O, and O-C = O) was 87.4% in GO but decreased to 69.8% in nanocomposite photocatalyst, indicating that GO was reduced to rGO under microwave irradiation.

The amount of Ag in the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was quantified to about 25 wt% by ICP-AES.

The reason why a large amount of Ag particles can be attached is because the oxygen-containing group of the GO thin plate acted as an anchor point of the Ag nanoparticles.

Figure 6 (a) shows the FT-IR spectrum of GO and Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst to confirm evidence of reduction of oxygen-containing groups on the GO surface.

In the FT-IR spectrum of the GO, the characteristic peak of the oxygen-containing group on the GO, namely the C = O stretching vibration (1721.04 cm ^-1 ) of the COOH group and the OH vibration deformation (1625.31 cm ^-1 ), the OH strain vibration (1398.49 cm ^-1 ) of the tertiary C-OH and the CO stretching vibration (1056.81 cm ^-1 ) of the epoxy group were observed.

Also, the wide absorption peak over a wide range from 3100 to 3700 cm ^-1 is due to OH stretching vibration.

On the other hand, after the microwave-assisted hydrothermal reaction, the peak for C = O disappeared and the peak intensity for O-H and C = O decreased. This indicates that the partial reduction of the GO, that is, the removal of oxygen-containing groups, resulted in the formation of rGO in the nanocomposite photocatalyst.

In addition, two strong absorption peaks in the spectrum of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalysts were observed at low frequencies (about 570.9 cm ^-1 and 416.6 cm ^-1 ), and Fe-O bonds and Zn-O Lt; / RTI >

Figure 6 (b) is shown as GO, and a Raman spectrum of the Ag-ZnFe ₂ O ₄ @rGO photocatalytic nanocomposite, two characteristic peaks are derived from the defect of a carbon material (defect) and disorder (disorder) of about 1350 cm ^{- 1} (D-band) and 1589 cm ^-1 (G-band) peak due to the oscillation of the sp ² -bonded carbon atom.

Ag-ZnFe ₂ O ₄ @rGO peak intensity ratio of the photocatalytic nanocomposite _{(I D / I G = 1.102} ) is shown larger than the intensity ratio _{(I D / I G = 0.906} ) for the GO sp ² domain (sp ² domains) and an increase in disorder and degree of association.

It was confirmed that GO was deoxidized and reduced to rGO by increasing the I _D / I _G ratio.

In the case of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst, the Raman spectrum exhibits one peak in the low frequency region (660 cm ^-1 ) consistent with previous studies on the ZnFe ₂ O ₄ / graphene nanocomposite photocatalyst .

Experimental Example 2 Ag-ZnFe ₂ O ₄ Analysis of BET surface area and pore size distribution of @rGO nanocomposite photocatalyst

Zn-Fe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Examples 1 to 4 using a nitrogen adsorption-desorbing machine (Micromeritics 3Flex Surface Characterization Analyzer, Micromeritics Instruments) at -196 ° C. (BET) specific surface area (hereinafter referred to as 'SBET') and a pore-size distribution (hereinafter referred to as 'PSD').

Before the adsorption-desorption experiment, the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 was degassed at 180 ° C for 12 hours.

SBET was obtained by applying the BET equation and PSD was obtained using the Barrett-Joyner-Halenda (BJH) method.

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 were carried out at 10 K / min with a thermogravimetric analyzer (TA Instruments SDT Q600 thermogravimetric analyzer) in an air and nitrogen atmosphere.

In order to analyze the Ag content of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst, inductively coupled plasma-atomic emission spectrometry (ICP-AES, PerkinElmer) was used.

Referring to FIG. 7, the N ₂ adsorption-desorption isotherm of Ag-ZnFe ₂ O ₄ @rGO and the corresponding PSD are shown.

According to the IUPAC classification, the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst exhibits an IV isotherm showing porosity.

The shape of the hysteresis loop is H2 type and forms a slit-like pore structure.

The SBET of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was calculated to be 178.77 m ² / g.

7 shows BJH and PSD corresponding to the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst and shows a sharp maximum value at about 3.6 nm (see Table 1), and Ag-ZnFe ₂ O ₄ @rGO nano It can be confirmed that the composite photocatalyst is porous.

During the photocatalytic reaction, more adsorption / reaction space can be provided through the larger surface area, which can contribute to the improvement of the photocatalytic activity.

Figure 8 shows two apparent weight losses from a TGA profile with a total weight loss of 19% in the air between 20 and 120 < 0 > C and two temperature ranges of 250-400 DEG C, Loss (3.8 wt%) and combustion of graphene (15.2 wt%).

Based on this, the rGO content was estimated to be about 15.2 wt% of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst.

In addition, a strong exothermic peak at 320 ° C was observed in the DSC curve, which was assigned to the combustion and decomposition of the carbon skeleton.

Under nitrogen flow, the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst showed high thermal stability without rapid weight loss up to 800 ° C.

This is consistent with the thermal behavior of graphene itself under a nitrogen atmosphere as already known.

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

UV-vis diffuse reflectance spectra (hereinafter referred to as &quot; UV-vis diffuse reflectance spectra &quot;) of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Examples 1 to 4 using a UV-vis-NIR spectrophotometer (Varian Cary 5000) 'DRS').

FIG. 9 (a) shows the ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1, the ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Comparative Example 2, and the Ag prepared according to Examples 1 to 4 -ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst.

Pure ZnFe ₂ O ₄ nanoparticles exhibited broad absorption in the visible region with an absorption edge at about 700 nm, which corresponds to a band gap of about 1.9 eV.

The absorption of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was significantly increased by the introduction of rGO.

Ag-ZnFe ₂ O ₄ @rGO Nanocomposites The increase in visible absorption of photocatalysts is mainly caused by the background absorption of rGO as well as the effect of the Ag nanoparticles on the SPR.

On the other hand, referring to FIG. 9 (c), as the rGO content increases, there is almost no change in the end position of the absorption band, which means that the introduction of rGO has little effect on the band gap of ZnFe ₂ O ₄ .

EXPERIMENTAL EXAMPLE 4 Electrochemical Impedance Spectrum (EIS) and Photocurrent Response Analysis

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

The working electrode was prepared by adding an active material (ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1, prepared according to Comparative Example ² ) to a fluorine-tin oxide (FTO) glass (active region 1 cm ² ) (ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst or Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1) was prepared by drop-casting.

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 0.1 M KCl in 5 mM K ₃ [Fe (CN) ₆ ] was used.

EIS measurements were made at a potential window of 0 V to 0.6 V at a scan rate of 25 mV / s and the impedance spectrum of the samples was recorded in the frequency range of 100 kHz to 0.01 Hz.

Photocurrent was measured with an Autolab PGSTAT302 N (Metrohm) instrument.

The working electrode was an active material (ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1, or Ag-ZnFe ₂ O ₄ @rGO ₂ prepared according to Examples 1 to ₄ ) to FTO glass (active area 0.5 cm ² ) Nanocomposite photocatalyst) was prepared by drop-casting method and a 10 W UV lamp (λ = 254 nm) was used as the light source.

Graphene acts as an electron acceptor and an electron transfer path, and plays an important role in promoting the separation and migration of the generated electrons.

Referring to Fig. 9 (b), the semicircle of the EIS diagram becomes smaller with the introduction of reduced graphene and Ag nanoparticles, which exhibit solid interface-layer resistance and reduced charge transfer resistance at the surface.

Overall, the electron acceptance and transfer characteristics of graphene in the nanocomposite photocatalyst can contribute to the suppression of charge recombination, resulting in a faster photocatalytic reaction rate.

The EIS Nyquist plot of G80 and G100 (see Figure 9 (d)) shows a much smaller semicircle, indicating that the charge transfer resistance of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst is significantly reduced.

Since G80 shows the smallest semicircle, it can be seen that the optimal GO content for the best charge transfer is 80 mg.

The high charge transfer resistance of G100 is due to the excessive addition of rGO, which can act as a new recombination center for photogenerated electrons and holes that interfere with the movement of photogenerated electrons from the inside to the nanocomposite surface.

Also, excessive introduction of black rGO shields the active site of the catalyst surface and reduces the intensity of light passing through the reaction solution.

After attaching to the FTO electrode through several on-off cycles, the pure ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1 and the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 Photocurrent measurement was performed.

Photocurrent transient response was measured under UV light irradiation and in the dark at potentials of 0.5 M Na ₂ SO ₄ aqueous solution and 0 V (vs SCE).

The photocurrent of the electrode with Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst (190 nA) was about 8 times higher than that of the electrode with pure ZnFe ₂ O ₄ nanoparticles (24 nA) The efficiency of separation of the photo-generated electrons and holes is remarkably improved as a result of the electron interaction between the particles, the ZnFe ₂ O ₄ nanoparticles and the graphene thin plate.

Experimental Example 5 Ag-ZnFe ₂ O ₄ @ rGO Nanocomposite Photocatalytic Activity and Stability Analysis

Photocatalytic activity of Ag-ZnFe ₂ O ₄ @rGO nanocomposite was evaluated by photocatalytic decomposition of Ag-ZnFe ₂ O ₄ @rGO nanocomposite of MB under UV and visible light irradiation.

The reaction was carried out at a temperature of about 25 ° C in a photoreactor and 25 mg of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst was dispersed in 50 ml of MB aqueous solution (20 ppm) and then adsorbed-desorption equilibrium was achieved And stirred for 30 minutes in the dark state.

A 40 W UV lamp (UV light source,? = 365 nm) and an overhead projector lamp (OHP) (visible light source,?> 420 nm) were used for the photoreaction.

At a predetermined time interval, 3 ml of the liquid was taken out from the reaction liquid and separated by a centrifuge (13000 rpm, 10 minutes).

To investigate the universality of the samples obtained as an example for the degradation of organic pollutants, the same set of procedures was performed separately, especially for 50 ml of MB, RhB and MO aqueous solutions (10 ppm), which are various types of dyes.

The concentrations of MB, RhB and MO in the solution were measured with a UV-vis spectrophotometer at wavelengths of 663, 553 and 460 nm, respectively.

MB is a model source of photocatalytic decomposition and a representative organic dye of textile wastewater.

10 and 11, a pure ZnFe ₂ O ₄ nanoparticle photocatalyst prepared according to Comparative Example 1 under UV irradiation was used, and MB was decomposed by about 9% after 30 minutes.

On the other hand, the photocatalytic activity of ZnFe ₂ O ₄ nanoparticles was remarkably improved to 85% after 30 minutes by the introduction of rGO.

Similarly, by introducing Ag nanoparticles into the ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst, the degradation rate of MB was improved to 99.8% due to the SPR effect of Ag nanoparticles under UV and visible light irradiation.

The specific catalytic properties of Ag nanoparticles are directly related to the size of the Ag nanoparticles and the degree of dispersion on the graphene sheet.

The effect of Ag dose was studied.

Specifically, when the amount of 0.1 M AgNO ₃ is increased to 10 ㎖, the photocatalytic activity is increased. However, when the AgNO ₃ solution is further added, the photocatalytic activity decreases because the Ag nanoparticles aggregate into larger particles.

The Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst showed an increase in adsorption characteristics with increasing rGO content (see FIG. 12 (a)).

During the adsorption, the dye molecules migrated from the bulk solution to the surface of the nanocomposite photocatalyst and adsorbed in the offset-plane orientation through the π-π bond between MB and the aromatic region of the graphene sheet.

FIG. 12 (b) shows the change in the concentration of MB during the photolysis process under UV irradiation.

While UV irradiation, the light excited electrons is yes may be rapidly injected between the pin layer, well react with the adsorbed O ₂ molecules on the surface of the pinned layer · O ₂ ^- it may generate a radical.

In this way, prepared nanocomposite photocatalysts can generate more electrons and holes as well as more superoxide anions.

O ₂ ^- radicals cause the dye to be oxidized to H ₂ O, CO ₂ and other minerals.

Electron transfer inhibits charge recombination in the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst, thus greatly improving the photocatalytic property efficiency.

Applying the parameters used in the present invention, the photocatalytic performance was measured to be about 99.8% under UV irradiation for a maximum of 30 minutes when the rGO content was about 15.2 wt% (G80).

13 (a) and 13 (b) show the universality of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst prepared according to Example 1 for the photolysis of various types of dyes (MB, RhB and MO) .

Plot concentration versus time indicates that using Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst under UV can remove dyes faster than using Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst under visible light Respectively.

MB can be completely decomposed in 15 minutes and 30 minutes under UV and visible light, respectively.

RhB was degraded by 95.5% and MO was decomposed by 77% after 30 minutes of UV irradiation.

Also, RhB and MO were decomposed by about 95% and 72%, respectively, after 30 minutes of visible light irradiation.

Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst showed better photocatalytic decomposition performance for cationic dyes (MB and RhB) than anionic dyes (MO).

This is because cationic dyes are much easier to adsorb onto nanocomposite photocatalysts that are negatively charged than anionic dyes.

In addition, the photocatalytic activity of RhB was smaller than that of MB because of the larger and more complex structure of RhB molecules.

The photocatalytic decomposition rate of MB follows a pseudo-first-order behavior.

The rate constant (k) for photocatalytic decomposition of MB, RhB and MO under UV and visible light irradiation at 25 ° C can be calculated using the following equation (1).

[Equation 1]

Where k is the apparent rate constant, C ₀ is the initial concentration of the contaminant after adsorption-desorption equilibrium, C _t is the residual concentration of the contaminant in the solution collected at constant time intervals under UV and visible light irradiation to be.

Figure 14 shows a similar primary rate constant for photodegradation of 10 ppm MB, RhB and MO using Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst under UV and visible light.

Among the calculated values, the MB decomposition rate constant under UV irradiation was the highest (k = 0.415 min ^-1 ), 2.3 times higher than the case of visible light irradiation.

Experimental Example 6 Analysis of Reusability Test

In order to investigate the photocatalyst stability and reusability of the sample, the aforementioned photocatalytic activity was repeatedly measured five times using MB aqueous solution (20 ppm).

After each cycle, the used photocatalyst was separated from the treated MB solution, washed with deionized water, dried in an oven and again used for the next photolytic cycle.

Photocatalytic decomposition follows pseudo-first-order kinetics, which is expressed in Equation (1) above.

To further investigate the photocatalytic mechanism, trapping experiments were conducted to determine the dominant reactive species involved in photodecomposition of MB dyes.

The capture experiments were carried out using scavenger compounds such as 0.001 M p-benzoquinone (BZQ), 0.1 M isopropyl alcohol (IPA) or 0.1 M sodium bicarbonate , &Lt; / RTI &gt; NaHCO ₃ &apos;). &Lt; / RTI &gt;

In addition to photocatalytic activity, photocatalytic stability is another important factor in determining the use of catalysts in practical applications.

Through repeated tests using the photocatalyst of the magnetic Ag-ZnFe ₂ O ₄ @rGO photocatalytic nanocomposite was analyzed photocatalytic stability of Ag-ZnFe ₂ O ₄ @rGO nanocomposite.

FIG. 15 shows that the photocatalytic decomposition efficiency of Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst did not decrease much after 5 times of use.

This shows the possibility of using Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst for a long time.

The structure of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst maintained a relatively stable state as shown by FE-SEM and TEM images of the catalyst.

The FT-IR spectrum of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst used showed a characteristic absorption band similar to the new catalyst.

The only difference was observed in the range of 1000 to 1300 cm ^-1 , which is due to the precipitation of some organic material on the surface of the catalyst used.

Likewise, the diffraction pattern of the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst used after the fifth use showed no significant difference from the diffraction pattern of the new nanocomposite photocatalyst.

From these results, it was confirmed that the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst of the present invention has excellent long-term stability and reusability.

<Experimental Example 7> Analysis of photocatalytic reaction mechanism

To understand the photocatalytic mechanism, the main active oxidant should be identified in the photocatalytic reaction.

The oxidant produced in the photocatalytic reaction can be measured by addition of a scavenging reagent.

Isopropyl alcohol (IPA), NaHCO ₃ and p-benzoquinone (BZQ) were used as trapping agents for hydroxyl group (-OH), hole (h _VB ⁺ ) and acetic acid group (O ₂ ^- ).

16 shows that decomposition of MB is decelerated after addition of NaHCO ₃ (0.1 M) or BZQ (0.001 M) in a photocatalytic system, which shows that the hole (h _VB ⁺ ) and the pyrogenic acid (O ₂ ^- Is the major active species involved in the oxidation of MB.

Addition of IPA (0.1 M) had negligible effect on MB decomposition.

This indicates that the hydroxyl group (-OH) makes a very small contribution to the photocatalytic reaction.

Based on the above results, the mechanism of the photocatalytic activity enhanced on the prepared Ag-ZnFe ₂ O ₄ @rGO nanocomposite was proposed as follows (refer to FIG. 17).

[Chemical Formula 1]

(2)

(3)

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

(7)

Ag-ZnFe ₂ O ₄ @rGO Nanocomposite When UV or visible light is irradiated to a photocatalyst in the presence of an organic compound aqueous solution (eg MB dye), ZnFe ₂ O ₄ nanoparticles are excited by photons to form electron-hole pairs (1)).

The photogenerated electrons can easily migrate from the conduction band (CB) of ZnFe ₂ O ₄ nanoparticles to the surface of graphene nanotubes. This is because the conduction band of graphene (-0.75 V vs. normal hydrogen electrode (NHE ')) is larger than CB (-1.54 V vs NHE) of ZnFe ₂ O ₄ nanoparticles ) (See Chemical Formula 2).

At the same time, the Ag nanoparticles can absorb light and generate electrons due to the SPR effect. Due to the lower CB of negative graphene, which is smaller than ZnFe ₂ O ₄ nanoparticles, the plasmon- Can flow into CB of graphene instead of ZnFe ₂ O ₄ nanoparticles (see Formula 3), and Ag nanoparticles can accept electrons from CB of ZnFe ₂ O ₄ nanoparticles to improve charge separation.

Some Ag ⁺ nanoparticles change to Ag nanoparticles due to the tendency of the CB electrons on the ZnFe ₂ O ₄ nanoparticles to migrate to positive Ag ⁺ nanoparticles (see Chemical Formula 4). On the other hand, other electrons are removed by O ₂ in water to form a superoxide anion radical (see Chemical Formula 5), and react with an organic dye MB and a main activating species (O ₂ ^- ) (Chemical Formula 6 ).

Also, ZnFe ₂ O ₄ the valence band of the nanoparticles; there reactive in (valence band than 'VB') holes can be oxidized directly to the MB, which ZnFe ₂ O ₄ of the electric potential VB of the nanoparticles (0.38V vs. NHE) (E · OH / H ₂ O = 2.87 V vs. NHE) required to generate OH by oxidizing the adsorbed H ₂ O on the surface (Formula 7).

As a result, the efficiency of the photo-generated charge carriers can be effectively improved at the interface of the nanocomposite photocatalyst, allowing more holes to participate in the photocatalytic reaction.

While the present invention has been described with reference to the exemplary embodiments and the drawings, it is to be understood that the present invention is not limited thereto and that various changes and modifications will be apparent to those skilled in the art. It is to be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (13)

Reduced graphene oxide (hereinafter 'rGO'); And
Zinc ferrite (hereinafter referred to as 'ZnFe ₂ O ₄ ') nanoparticles and silver (Ag) nanoparticles attached to the rGO;
Lt; / RTI &gt;
The Ag nano-
An average diameter of 30 to 40 nm,
The nanocomposite photocatalyst,
Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst, characterized in that it consists of 55 to 65 wt% of ZnFe ₂ O ₄ nanoparticles, 20 to 30 wt% of Ag nanoparticles and 10 to 20 wt% of rGO. The method according to claim 1,
The ZnFe ₂ O ₄ nano-
Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst characterized by an average diameter of 10 to 20 nm. delete delete Preparing a first mixed solution by dissolving an iron precursor and a zinc precursor in deionized water;
Dispersing the oxidized graphene in deionized water and subjecting it to ultrasonic treatment to prepare a GO dispersion;
Adding the first mixed solution to the GO dispersion and stirring to prepare a second mixed solution;
Adding a silver precursor to the second mixed solution and stirring to prepare a third mixed solution;
Adding a reducing agent to the third mixed solution and stirring to prepare a suspension;
The suspension was irradiated with a microwave of 50 to 400 W, heated to 60 to 150 ° C., maintained at the temperature for 3 to 20 minutes, cooled to room temperature, and centrifuged to obtain rGO-attached ZnFe ₂ O ₄ nanoparticles and Ag Collecting a nanocomposite comprising nanoparticles; And
Washing the collected nanocomposite and vacuum drying to prepare a nanocomposite photocatalyst comprising ZnFe ₂ O ₄ nanoparticles and Ag nanoparticles attached to rGO;
, Ag-ZnFe ₂ O ₄ @rGO photocatalytic nanocomposite production method comprising a. The method of claim 5,
The iron precursor,
Ferric nitrate nonahydrate (Fe (NO ₃ ) ₃ ), ferrous chloride (FeCl ₂ ), ferric chororide (FeCl ₃ ), ferrous sulfate ₄ ), ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) and ferrous acetate (Fe (CO ₂ CH ₃ ) ₂ ) Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst production method. The method of claim 5,
Wherein the zinc precursor
Acid zinc _{(zinc acetate: Zn (CH 3} COOH) 2), zinc sulfate (zinc sulfate: ZnSO _4), zinc chloride (zinc chloride: ZnCl _2), zinc nitrate _{(zinc nitrate: Zn (NO 3} ) 2), bromide ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst characterized in that it is selected from the group consisting of zinc bromide (ZnBr ₂ ) and zinc iodide (ZnI ₂ ). The method of claim 5,
Wherein the step of preparing the first mixed solution comprises:
ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst is prepared by dissolving an iron precursor and a zinc precursor in deionized water at a molar ratio of 1: (0.5 to 3). The method of claim 5,
The GO dispersion may contain,
Wherein the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst has a concentration of 0.2 to 3 mg / ml. The method of claim 5,
The silver precursor,
Silver nitrate (AgNO ₃ ), silver sulfate (Ag ₂ SO ₄ ), silver acetate (AgCOOCH ₃ ), silver chloride (AgCl) and silver carbonate (Ag ₂ CO ₃ ) Wherein the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst is selected from the group consisting of Ag-ZnFe ₂ O _{4 and} rGO nanocomposite. The method of claim 5,
The reducing agent,
Hydrazine _{(hydrazine: N 2 H 4)} , sodium borohydride _{(sodium boro hydride: NaBH 4)} , ethylene glycol _{(ethylene glycol: C 2 H 4} (OH) 2), thiourea (thiourea: (NH _{2) 2} CS) and thiourea dioxide ((NH) (NH ₂ ) CSO ₂ H). _{2. The method according} to claim 1, wherein the Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst is selected from the group consisting of: delete The method of claim 5,
The step of preparing the nanocomposite photocatalyst including the ZnFe ₂ O ₄ nanoparticles and the Ag nanoparticles attached to the rGO,
Wherein the collected nanocomposite is washed and then vacuum-dried at 20 to 100 ° C for 30 minutes to 5 hours to prepare a Ag-ZnFe ₂ O ₄ @rGO nanocomposite photocatalyst.

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