Synthesis of graphene-based nanomaterials: their applications in - - PowerPoint PPT Presentation

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Synthesis of graphene-based nanomaterials: their applications in electrochemical detection of organic molecules

Stela Pruneanu

INCDTIM Cluj-Napoca

NANOGENTOOLS Autumn School October 2017

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TOPICS

• 1. Graphene synthesis
• TEM/HRTEM characterization
• XRD and UV-Vis characterization
• 2. Electrochemical detection of catechol
• 3. Photo-degradation of pollutants with graphene-TiO2 based materials
• 4. Conclusions

NANOGENTOOLS Autumn School October 2017

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 Single layer of sp2 hybridized carbon atoms  High mobility of charge carriers: 200.000 cm2V−1s−1  Surface area of a single graphene sheet is 2630 m2/g Graphene is resistant to attack by powerful acids and alkalis (hydrofluoric acid, ammonia)

• 1. Graphene synthesis

NANOGENTOOLS Autumn School October 2017

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 Au(x)/MgO- catalyst, where x = 1, 2 or 3 wt%  Ag(x)/MgO-catalyst, where x = 1,2 or 3 wt%  Pt(x)/MgO-catalyst, where x = 1,2 or 3 wt%  AuAg(x)/ MgO-catalyst, where x = 1:1 or 1.5:1.5 wt%  AuPd (x)/ MgO-catalyst, where x = 1:1 or 1.5:1.5 wt%  AuCu (x)/ MgO-catalyst, where x = 1:1 or 1.5:1.5 wt%  AuPt (x)/ MgO-catalyst, where x = 1:1 or 1.5:1.5 wt% Methane; (carbon source) 1000 oC- synthesis temperature (60 minutes) Purification in HCl (30 minutes) Drying - 120 oC (overnight)

A) Chemical Vapor Deposition (CVD)-bottom up

NANOGENTOOLS Autumn School October 2017

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2 6

TEM/HRTEM images (3 wt.% metal)

Graphene-gold nanoparticles (5-35 nm; 22 nm) Graphene-silver nanoparticles (5-200 nm; 35 nm) Graphene-platinum nanoparticles (2-10 nm; 8 nm) NANOGENTOOLS Autumn School October 2017

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XRD patterns of Gr-Au-x nanocomposites

d-spacing: Graphite = 0.335 nm Gr-Au-3 = 0.349 nm Gr-Au-2 = 0.358 nm

XRD study

Gr-Au-3 τ (graphene): 2.2 nm (6 graphitic layers) Gr-Au-2 τ (graphene): 1.6 nm (4 graphitic layers)

S Pruneanu et al, International Journal of Nanomedicine 2013(8) 1429–1438

10 20 30 40 50 60 70 80 90 200 400 600 800

Gr(100)

2 (degrees)

Gr-Au-1 Gr-Au-2 Gr-Au-3

Intensity (a.u.)

(111) (200) (220) (311) (222) Gr(002)

Bragg’s law: nλ = 2d sinϴ

where K is the shape factor, λ is the x-ray wavelength, β is the line broadening at half the maximum intensity (FWHM) in radians, and θ is the Bragg angle τ = the mean size of the crystalline domains

Scherrer equation: τ = Kλ/βcosθ

NANOGENTOOLS Autumn School October 2017

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B) Chemical synthesis (top-down)

Thermal reduction 300o Ar

• C. Socaci et al., Sensors and Actuators B 213 (2015) 474–483

Chemical reduction

1. 2. NANOGENTOOLS Autumn School October 2017

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d-spacing: GO = 0.75 nm RGO = 0.36 nm N-Gr = 0.35 nm

ε228 nm = 0.88 mL·mg-1·cm-1 ε700 nm = 0.04 mL·mg-1·cm-1 A(λ) = εm(λ)·d·C

NANOGENTOOLS Autumn School October 2017

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Graphene-metallic nanoparticles starting from graphite

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Graphene/AuNPs (10 – 40 nm) Graphene/PtNPs (5 – 10 nm) Graphene/Au-PdNPs (5 – 20 nm)

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• Electrochemical exfoliation of graphite- in acidic solution
• Electrolyte: mixture of strong acids (sulfuric : nitric)
• low voltage (2-3 V)
• few hours
• wash, filtrate and dry

TEM images of graphene

NANOGENTOOLS Autumn School October 2017

• C. Electrochemical graphene/graphene-porphyrin synthesis (top-down)

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5 10 15 20 25 30 35 10 20 30 40 50

Intensity (a.u.) 2  (degrees)

Measured spectra FLG MLG 21.28 25.99 21.28 25.99

• No. of layers

3 15 % 77 23

Gr 22a 5 10 15 20 25 30 35 10 20 30 40

Measured spectra FLG MLG

Intensity (a.u.) 2  (degrees)

21.23 26.26

• No. of layers

3 27 % 93 7 26.26 21.23

Gr 35

0.5 M electrolyte 1 M electrolyte

XRD pattern of graphene XRD pattern of graphene

XRD study

immediately after preparation: mixture of few-layer and multi-layer graphene

NANOGENTOOLS Autumn School October 2017

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after few days: mixture of graphene oxide, few-layer and multi-layer graphene

5 10 15 20 25 30 35 10 20 30 40 50 60 70 80 90 100

Measured GO FLG MLG

Intensity (a.u.) 2degrees)

11.95 22.89 26.04 11.95 22.89 26.04

• No. of layers

3 4 14 % 55 23 22

21L

GO GO GR

XRD pattern of the mixt material TEM image of the mixt material d-spacing: GO = 0.75 nm (insulating; good biocompatibility with living systems) GR = 0.36 nm (highly conductive; poor biocompatibility with living systems)

NANOGENTOOLS Autumn School October 2017

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• Electrochemical exfoliation of graphite - in neutral solution

XRD pattern of EGr-TPyP composite TEM/AFM images of EGr-TPyP composite

67 % 33 %

NANOGENTOOLS Autumn School October 2017

6 x 10-6 M TPyP in 0.2 M KCl Bias: 9 V

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200 300 400 500 600 700 800 0.32 0.40 0.48 0.56 0.64 0.72 0.80

200 300 400 500 600 700 800

• 0.02
• 0.01

0.00 0.01 0.02 0.03 0.04

740

10-6 M TPyP Absorbance (a.u.)  (nm)

413 511 657 Q-bands Soret band

413

 (nm)

Absorbance (a.u.)

268 EGr-TPyP graphene-acidic solution

UV-Vis spectrum of EGr-TPyP composite UV-Vis spectrum of porphyrin Soret band Q bands

• Porphyrins display extreme intense bands, the so-called Soret or B-bands in the 380–500 nm

range with molar extinction coefficients of 105 M -1 cm -1

• In the 500–750 nm range, their spectra contain a set of weaker, but still considerably intense

Q bands with molar extinction coefficients of 104 M -1 cm -1

UV-Vis characterization

NANOGENTOOLS Autumn School October 2017

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• 2. Electrochemical detection of catechol

 Increases the active surface area (50 - 100 %)  Improves the transfer of electrons EGr-TPyP/GC Screen-printed electrode

CE WE RE NANOGENTOOLS Autumn School October 2017

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• catechol undergoes reversible oxidation to quinone by a

transfer of two electrons and two protons

• Phenolic compounds are a class of chemical compounds consisting of a hydroxyl functional group (–OH)

attached to an aromatic ring

• Phenols can have two or more hydroxyl groups bonded to the aromatic ring(s) in the same molecule
• Phenol, catechol, and hydroquinone, are urinary end-products of the metabolism of benzene, nutrients,

drugs, and endogenous substances.

• Phenol, catechol, and hydroquinone may have a role in the carcinogenicity of benzene and in mechanisms

that lead to leukemia.

Phenols

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• CAT and HQ are widely used in industrial applications such as cosmetics, pesticides, flavoring agents,

antioxidant, dyes and pharmaceutics

• They are highly toxic to both the environment and humans, even at very low concentrations.
• The high toxicity and low degradability has made CAT and HQ important contaminants, which are

considered as environmental pollutants by the US Environmental Protection Agency (EPA) and the European Union (EU)

• Therefore, it is very important to develop simple and rapid analytical methods for the determination of CT

and HQ.

• In this respect there is the need of rapid, low-cost, and possibly direct methods to quantify these phenolic

metabolites.

NANOGENTOOLS Autumn School October 2017

According to Romanian regulations, CAT concentrations < 4.5 x 10-7 M are normal Alert values: > 10-5 M

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Optimization of experimental conditions

• 0.2

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10-4 M CAT pH 3.6 pH 4.4 pH 5.0 pH 6.0 pH 7.0 pH 8.0

I (A) E (V) vs Ag/AgCl

CVs recorded with EGr-TPyP/GC electrode in pH varying solutions (from 3.6 to 8); Optimum pH was selected to be pH 6 SWVs recorded with GC electrodes modified with various volumes of EGr-TPyP solution in pH 6 PBS solution containing 10-4 M catechol; scan rate 10 mVs-1. NANOGENTOOLS Autumn School October 2017

0.0 0.2 0.4 0.6 0.8 0.0 1.0x10

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E (V) vs Ag/AgCl

8 L 10 L 15 L

I (A)

graphene dispersion in DMF 1 mg/mL

Icap = C x dV/dt- 3 x 10-5 - 6 x 10-5 A

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• 0.2

0.0 0.2 0.4 0.6 0.8

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10-4 M CAT pH 6 PBS

i (A/cm

2)

E (V) vs Ag/AgCl

0.21 V 0.15 V EGr-TPyP/GC electrode

b.

Glassy carbon vs EGr-TPyP/Glassy carbon Active area (GC) = 0.028 cm2 Active area (EGr-TPyP/GC) = 0.081 cm2

• 0.2

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TPyP/GC

i (A/cm

2)

E (V) vs Ag/AgCl

pH 6 PBS 10-4 M CAT 10-4 M CAT

GC 0.46 V 0.1 V

a.

quasi-reversible redox process ΔEpeak = 380 mV (>> 60 mV) Ipa >>Ipc reversible redox process ΔEpeak = 60 mV Ipa = Ipc

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0.0 0.2 0.4 0.6 0.8 8.0x10

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1.6x10

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pH6 PBS 10-6 M 3x10-6 M 6x10-6 M 10-5 M 3x10-5 M 6x10-5 M 10-4 M

I (A) E(V) vs Ag/AgCl

EGr-TPyP/GC electrode

0.26 V b.

EGR-TPyP/GC electrode

• 0.2

0.0 0.2 0.4 0.6 0.8 0.0 1.5x10

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3.0x10

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pH 6 PBS 3x10-6M 6x10-6 M 10-5 M 3x10-5 M 6x10-5 M 10-4 M

I (A) E (V) vs Ag/AgCl

a. GC electrode

GC electrode EGR-TPyP/GC electrode GC electrode Linear range: 10-5 - 10-4 M Sensitivity: 6 mA/M LOD = 1.42 x 10-5 M Linear range: 10-6 - 10-4 M Sensitivity: 242 mA/M LOD = 2.09 x 10-6 M

SWV recorded in the presence of CAT SWV recorded in the presence of CAT

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GC electrode Ipeak (A) CCAT (M) y = - 3.71 x 10-8 + 0.006 x CCAT LOD = 1.42 x 10-5 M

EGr-TPyP/GC y = - 5.22 x 10-7 + 0.242 x CCAT LOD = 2.09 x 10-6 M

Ipeak (A) CCAT (M)

c.

NANOGENTOOLS Autumn School October 2017

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• The reactivity of the aromatic ring activated with an OH group > when the OH group is

in the ortho or para positions (the highest electron density is located on both ortho and para positions).

• Hydroquinone and catechol have the aromatic ring activated, while the resorcinol ring is

not activated.

SWV recorded in the presence of HQ and CAT SWV recorded in the presence of REZ and CAT

EGR-TPyP/GC electrode

0.0 0.2 0.4 0.6 0.8 1.0x10

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HQ

0.26 V

CAT

pH 6 PBS 10-6 M 3x10-6 M 6x10-6 M 10-5 M 3x10-5 M 6x10-5 M 10-4 M

I (A) E (V) vs Ag/AgCl

a. 0.16 V

Hydroquinone: 5 x 10-5 M

0.0 0.2 0.4 0.6 0.8 1.0x10

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0.65 V

pH 6 PBS 10-6M 3x10-6M 6x10-6M 10-5M 3x10-5M 6x10-5M 10-4 M

I (A) E (V) vs Ag/AgCl

CAT

0.27 V

REZ

c.

Resorcinol: 5 x 10-5 M

NANOGENTOOLS Autumn School October 2017

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Interfering species Hydroquinone: 5 x 10-5 M Linear range: 10-6 - 10-4 M Sensitivity: 110 mA/M LOD = 9.4 x 10-6 M Resorcinol: 5 x 10-5 M Linear range: 10-6 - 10-4 M Sensitivity: 290 mA/M LOD = 1.22 x 10-6 M No Interfering species

0.0 3.0x10

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LOD = 1.22 x 10

• 6 M

LOD = 9.4 x 10

• 6 M

LOD = 2.09 x 10

• 6 M

y = 9.29 x 10-8 + 0.29 x CCAT y = - 5.52 x 10-7 + 0.11 x CCAT y = - 5.22 x 10-7 + 0.242 x CCAT

EGr-TPyP/GC

b.

5 x 10-5 M HQ interferent 5 x 10-5 M REZ interferent No interfering species

CCAT (M) Ipeak (A)

Linear range: 10-6 - 10-4 M Sensitivity: 242 mA/M LOD = 2.09 x 10-6 M

NANOGENTOOLS Autumn School October 2017

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Analysis of CAT in a relevant environment two drinking water sources:

• tap water (the pH was adjusted to pH 6)
• commercial mineral water (pH 5.9) containing known quantities (mg/L) of interfering species:

23.59 Na+; 4.75 K+; 60.14 Mg2+; 191.2 Ca2+; 11.12 Cl-; 13.57 SO4

2-.

0.0 0.2 0.4 0.6 0.8 5.0x10

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mineral water

0.2 M KCl 3x10-7M 6x10-7M 10-6M 3x10-6M 6x10-6M 10-5M 3x10-5M 6x10-5M 10-4M

I (A) E(V) vs Ag/AgCl

No interfering species Linear range: 10-6 - 10-4 M Sensitivity: 242 mA/M LOD = 2.09 x 10-6 M In mineral water: Linear range: 6 x 10-6 - 10-4 M Sensitivity: 115 mA/M LOD = 1.82 x 10-6 M In tap water: Linear range: 6 x 10-6 - 10-4 M Sensitivity: 90 mA/M LOD = 4.19 x 10-6 M

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y = -3.51 x 10-7 + 0.09 x CCAT LOD = 4.19 x 10

• 6

M

in tap water

y = - 5.22 x 10-7 + 0.242 x CCAT LOD = 2.09 x 10-6 M

Ipeak (A) CCAT (M)

y = -1.437 x 10-7 + 0.115 x CCAT LOD = 1.82 x 10

• 6

M

in mineral water

in PBS pH 6

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EGr-TPyP/GC Added (M) Found (M) Recovery % RSD (%)

Mineral water 10-5 0.95 x 10-5 95 7.21 3 x 10-5 3.3 x 10-5 110 7.22 10-4 1.04 x 10-4 104 3.15 Tap water 10-5 0.97 x 10-5 97 4.49 3 x 10-5 2.96 x 10-5 98 5.07 10-4 1.03 x 10-4 103 6.48 Table 2. Determination of catechol in mineral and tap water

NANOGENTOOLS Autumn School October 2017

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Sensor device is under construction…

For detection of:

• heavy metal ions (Pb2+)
• phenols (catechol, hydroqinone)
• neurotransmitters (dopamine)

SLIDE 27

• 3. Photodegradation of pollutants with graphene-TiO2 based materials

200 300 400 500 600 700 800 0.0 0.5 1.0 1.5 2.0

Eg Absorbance (a.u.) Wavelength (nm) TiO2 TA TA-GO TA-GR TA-GT Eg

Graphene-TiO2/Ag composites

3.26 eV – wide band-gap semiconductor 3.09 eV 3.06 eV 3.04 eV 3.05 eV TiO2 TA- TiO2/Ag TA- GO TA- GR TA - GT

Shift of the absorption edge towards visible range UV-Vis spectra of graphene-TiO2 based materials

NANOGENTOOLS Autumn School October 2017

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TEM/EDS mapping of TiO2/Ag TEM images of graphene-TiO2/Ag c d e

NANOGENTOOLS Autumn School October 2017

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• Is a purple azo dye used to color: food, cosmetics, paper, wood, leather
• Coloring agent for jam, jellies (E123- food additive)
• In USA it is legally prohibited (since 1976)
• In Romania is legally used (since 2002)
• Prolonged intake can result in tumors and allergy

Amaranth

NANOGENTOOLS Autumn School October 2017

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200 300 400 500 600 700 800 0.0 0.2 0.4 0.6 0.8 1.0 1.2

sun light

Absorbance (a.u.) Wavelenght (nm) AM 2 x 10

• 5 M

AM TA TA-GO TA-GR TA-GT

200 300 400 500 600 700 800 0.0 0.2 0.4 0.6 0.8 1.0 1.2

day light

AM 2 x 10

• 5 M

AM TA TA-GO TA-GR TA-GT Absorbance (a.u.) Wavelenght (nm)

4 mg of photo-catalysts (TA, TA-GO, TA-GR and TA-GT) - in 20 ml of amaranth solution (2 x 10-5 M)

200 300 400 500 600 700 800 0.0 0.2 0.4 0.6 0.8 1.0 1.2

UV light

AM 2 x 10

• 5 M

AM TA TA-GO TA-GR TA-GT Absorbance (a.u.) Wavelenght (nm)

60 W

UV-Vis investigation After two hours

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• r

50 100 150 200 250

• 5
• 4
• 3
• 2
• 1

AM TA TA-GO TA-GR TA-GT ln Ct/C0 UV irradiation time (min)

UV

50 100 150 200 250

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AM TA TA-GO TA-GR TA-GT ln Ct/C0 Sun light irradiation time (min)

Sun

50 100 150 200 250

• 3
• 2
• 1

AM TA TA-GO TA-GR TA-GT ln Ct/C0 Daylight irradiation time (min)

Day

First order reaction- the rate depends linearly on the concentration of only one reactant (a unimolecular reaction)

Reaction kinetics

the reaction rate; k is the first order rate constant

NANOGENTOOLS Autumn School October 2017

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Sun light 30 min 2 h 4 h TA 77% 12.8% 0.04% TA-GO 69 7.3 TA-GR 55 2 TA-GT 59.2 3.2

HPLC analysis

Samples k (min-1) k (min-1) k (min-1) AM 0.0010 0.0052 0.0006 TA 0.0168 0.0347 0.0050 TA-GO 0.0191 0.0552 0.0063 TA-GR 0.0204 0.0583 0.0122 TA-GT 0.0173 0.0505 0.0070

UV Sun Day first order rate constant

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Conclusions

• Novel method for graphene/graphene-porphyrin synthesis – electrochemical exfoliation
• f graphite
• Substrates modified with graphene-TPyP- highly sensitive to the electrochemical

detection of catechol – but NOT selective

• Additional work - to eliminate the influence of interfering species
• Graphene-TiO2 nanoparticles composite – excellent material for pollutants degradation

Funding Projects Partnership-230/2014 TE- 5/2015 PED 101/2017 PED 102/2017 PED 103/2017 CETATEA - 623/11.03.2014- for TEM/HRTEM investigation

NANOGENTOOLS Autumn School October 2017

SLIDE 34

Working TEAM

• Dr. Florina Pogacean
• Dr. Eng. Stefan Gergely
• Dr. Maria Coros
• Eng. Mirel Valentin
• Dr. Lidia Magerusan
• Dr. Marcela Rosu
• Dr. Crina Socaci
• Dr. Alexandru Biris

PhD student Alex Turza PhD student Alin Porav

Thank-you