Graphene/BaCrO₄ Nanocomposites Catalyzed Photodegradation and Kinetics Study of Organic Dyes

Graphene/BaCrO ₄ Nanocomposites Catalyzed Photodegradation and Kinetics Study of Organic Dyes

Keun Hyung Kim and Weon Bae Ko ^†

Department of Chemisty, Sahmyook University, Seoul 139-742, Korea

(Received December 2, 2014, Revised December 30, 2014, Accepted January 7, 2015)

Abstract: The BaCrO

nanoparticles were synthesized from a 0.1 M K

CrO

and 0.1 M BaCO

solution with stirring for 10 h. The product was washed several times with acetone and heated to 700°C for 6 h. At that time, the color of mixture was a greenish yellow. The graphene/BaCrO

nanocomposites were prepared with graphene and BaCrO

nanoparticles by stirring in tetrahydrofuran and heated in an electric furnace at 700°C for 2 h. The BaCrO

nanoparticles, graphene/BaCrO

and heated graphene/BaCrO

nanocomposites were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The graphene/BaCrO

nanocomposites and heated graphene/BaCrO

nanocomposites were evaluated as a photocatalyst and discussed about kinetics study for the degradation of organic dyes, such as methylene blue and rhodamine B under ultraviolet light irradiation at 254 nm.

Keywords: BaCrO

nanoparticles, Graphene, Methylene blue, Rhodamine B, Photodegradation

Introduction

Organic wastewater causes serious worldwide environmen- tal problems.

Semiconductor photocatalysis has attracted increasing attention over the past two decades as an effective technique for reduction of pollutants in organic dyes, air and wastewater.

Semiconductor oxides and other inorganic compounds can exhibit high photocatalytic activity for the synthesis, reforming, degradation, and other reactions of organic compounds.

Photocatalytic reactions using semi- conductors for purification, such as water splitting and the decomposition of waste materials, have attracted particular attention because of their possible applications to the con- version of solar energy to chemical energy as well as to pol- lution remediation using solar energy.

The band gap of BaCrO

nanoparticles is 2.63 eV, making them an attractive candidate for photocatalysis, such as an oxidizing agent in organic reactions and an efficient photocatalyst with a response to visible light irradiation.

Two dimensional graphene is one atom thick sheet of carbon atoms bound together in an aromatic structure (sp

bond) and is the basic building block of zero dimensional fullerenes, one dimen- sional carbon nanotubes and three dimensional graphite.

This one atom thick pseudo-infinite nanocrystal is charac- terized by its large theoretical conductivity, and excellent optical transmittance,

such as nanoelectronic devices, energy storage materials and polymer composites, owing to the high mobility of charge carriers, specific surface area and Young’s modulus.

Experiment Details

1. Chemicals

Organic dyes, such as methylene blue (MB), rhodamine B (RhB) were purchased from Sigma-Aldrich. K

CrO

, BaCO

, acetone and tetrahydrofuran (THF) were obtained from Sam- chun Chemicals. Graphene was supplied by ENano Tec.

2. Instruments

An electric furnace (Ajeon Heating Industry Co., Ltd.) was used to heat the sample. A UV lamp (8 W, 254 nm, 77202 Marne La Valee-Cedex1 France) was used as an ultraviolet light irradiation source.

The surfaces of the BaCrO

nanoparticles, graphene/

BaCrO

nanocomposites and heated graphene/BaCrO

nano- composites were observed by scanning electron microscopy

†

Corresponding author E-mail: [email protected]

(SEM, JEOL Ltd, JSM-6510) at an accelerating voltage of 0.5 to 15 kV. The morphology and crystallite size of the sam- ples were examined by transmission electron microscopy (TEM, JEM-2010, JEOL Ltd.) at an acceleration voltage of 200 kV. The crystal structure of the nanomaterials was exam- ined by X-ray diffraction (XRD, Bruker, D8 Advance) using Cu Kα radiation and a secondary monochromator (V = 40 kV, A = 40 mA, Ni filter). The properties and photocatalytic activity of the nanomaterials were assessed by ultraviolet-vis- ible (UV-vis, Shimazu UV-1601PC) spectroscopy.

Synthesis

1. Synthesis of BaCrO

nanoparticles

BaCrO

nanoparticles were synthesized from a 0.1 M K

CrO

and 0.1 M BaCO

solution with stirring for 10 h. The product was washed several times with acetone and heated to 700

C for 6 hrs. At that time, the color of mixture was greenish yellow.

2. Synthesis of graphene/BaCrO

nanocomposites

In a typical experiment, the graphene/BaCrO

nanocom- posites were prepared from graphene and BaCrO

nanopar- ticles at a mixing ratio of 1:1. The mixture was dissolved in 10 ml of THF with constant stirring to produce the graphene/

BaCrO

nanocomposites. The mixture was then dried at room temperature.

3. Synthesis of heated graphene/BaCrO

nanocomposites

In a typical experiment, the heated graphene/ BaCrO

nanocomposites were prepared from graphene and BaCrO

nanoparticles at a mixing ratio of 1:1. The mixture was dis- solved in 10 ml of THF with constant stirring to produce the graphene/BaCrO

nanocomposites and heated in an electric furnace at 700°C for 2 h.

4. Photocatalytic degradation of organic dyes with hybrid nanocomposites

The photocatalytic activity of graphene/BaCrO

nanocom- posites and heated graphene/BaCrO

nanocomposites were examined using MB and RhB solution as the model pollut- ant. 5 mg of either graphene/BaCrO

nanocomposites or

heated graphene/BaCrO

nanocomposites were dispersed in 10 ml of water containing 0.01 mM MB or RhB. All of the mixture solution were irradiated with ultraviolet light at 254 nm. The MB and RhB solution degraded by each nanoma- terial as a photocatalyst under ultraviolet light at 254 nm were observed by UV-vis spectrophotometry.

Results and Discussion

Figure 1 shows SEM images of (a) BaCrO

nanoparticles,

Figure 1. SEM images of the (a) BaCrO

nanoparticles, (b) graphene/BaCrO

nanocomposites and (c) heated graphene/

BaCrO

nanocomposites.

(b) graphene/BaCrO

nanocomposites and (c) heated graph- ene/BaCrO

nanocomposites. The shape of the BaCrO

nanoparticles were irregular hexahedron and barite structure.

The BaCrO

nanoparticles in both the unheated graphene/

BaCrO

nanocomposites and heated graphene/BaCrO

nano- composites were located above the graphene nanoparticles.

Figure 2 shows TEM images of (a) BaCrO

nanoparticles, (b) graphene/BaCrO

nanocomposites and (c) heated graph- ene/BaCrO

nanocomposites. The BaCrO

nanoparticles exhibited a barite structure with an average crystallite size of 30~100 nm. The BaCrO

nanoparticles in both the unheated graphene/BaCrO

nanocomposites and heated graphene/

BaCrO

nanocomposites showed an agglomerate state and the graphene sheets were decorated with BaCrO

nanopar- ticles.

Figure 2. TEM images of the (a) BaCrO

nanoparticles, (b) graphene/BaCrO

nanocomposites and (c) heated graphene/

BaCrO

nanocomposites.

Figure 3. XRD patterns of the (a) BaCrO

nanoparticles, (b) graphene/BaCrO

nanocomposites and (c) heated graphene/

BaCrO

nanocomposites.

Figure 3 shows XRD patterns of (a) BaCrO

nanoparticles, (b) graphene/BaCrO

nanocomposites and (c) heated graph- ene/BaCrO

nanocomposites. The BaCrO

nanoparticles showed XRD peaks at 20.1°, 22.36°, 24.24°, 25.33°, 26.16°, 28.13°, 30.83°, 32.37°, 35.34°, 38.06°, 40.07°, 41.51°, 41.54°, 41.89°, 41.92°, 42.94°, 46.08°, 47.72°, 50.73°, 50.81°, 53.55°, 53.63° and 58.85° 2θ, which were assigned to the (0 1 1),

(1 1 1), (0 0 2), (2 1 0), (1 0 2), (2 1 1), (1 1 2), (0 2 0), (2 1 2), (2 2 0), (2 2 1), (4 0 1), (1 1 3), (2 0 3), (3 1 2), (4 1 0), (3 2 1), (3 0 3), (1 0 4), (1 2 3), (1 1 4), (2 3 0) and (3 2 3) planes of the BaCrO

nanoparticles, respectively.

The XRD peaks at 26.54°, 42.32°, 44.51°, 50.65° and 54.66°

Figure 4. UV-vis spectra of the degradation of MB with the (a) graphene/BaCrO

nanocomposites, (b) heated graphene/BaCrO

nanocomposites and (c) kinetics of MB under ultraviolet irradiation at 254 nm.

Figure 5. UV-vis spectra of RhB with the (a) graphene/BaCrO

nanocomposites, (b) heated graphene/BaCrO

nanocomposites

and (c) kinetics of RhB under ultraviolet irradiation at 254 nm.

2θ were assigned to the (0 0 2), (1 0 0), (1 0 1), (1 0 2) and (0 0 4) planes of graphene.

Figure 4 shows the UV-vis spectra of methylene blue pho- todegradation with the (a) graphene/BaCrO

nanocomposites, (b) heated graphene/BaCrO

nanocomposites and (c) kinetics of MB under ultraviolet irradiation at 254 nm. The UV-vis spectra and kinetics showed that the heated graphene/BaCrO

nanocomposites were more effective in degrading the MB solution than the graphene/BaCrO

nanocomposites. The kinetics of the organic dyes followed a first-order equation, ln(C/C

) = –kt, where C is the concentration at the reaction time, C

is the initial concentration, within – kt, k is the first- order rate constant, and t is the reaction time.

Figure 5 shows the UV-vis spectra of rhodamine B pho- todegradation with the (a) graphene/BaCrO

nanocomposites, (b) heated graphene/BaCrO

nanocomposites as well as (c) kinetics of RhB under ultraviolet irradiation at 254 nm. As a result, the UV-vis spectra and kinetics showed that heated graphene/BaCrO

nanocomposites were more effective in the degradation of the RhB solution than the graphene/BaCrO

nanocomposites.

The order of the kinetics of the photocatalytic degradation of the organic dyes was MB > RhB.

Conclusion

BaCrO

nanoparticles were prepared by heat treatment at 700

C for 6 h. The graphene/BaCrO

nanocomposites and heated graphene/BaCrO

nanocomposites were synthesized as a catalyst for the degradation of MB and RhB under ultra- violet irradiation at 254 nm for 20 min. The photocatalytic degradation of MB and RhB followed first-order reaction kinetics according to the kinetics equation: ln(C/C

) = –kt, where C is concentration according to the reaction time, C

is the initial concentration, k is the apparent first-order rate constant, and t is the reaction time. The heated graphene/

BaCrO

nanocomposites were more efficient in degrading the MB and RhB solution than the graphene/BaCrO

nanocom- posites. The heated graphene/BaCrO

nanocomposites under ultraviolet irradiation at 254 nm were more efficient in the degradation of the MB solution than the RhB solutions.

Acknowledgments

This study was supported by Sahmyook University funding in Korea.

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