Stabilization of Phenolic Radicals on Graphene Oxide: An XPS and

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Stabilization of Phenolic Radicals on Graphene Oxide:An XPS and EPR Study Panagiota Stathi, Dimitrios Gournis, Yiannis Deligiannakis, and Petra Rudolf Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b01248 • Publication Date (Web): 17 Aug 2015 Downloaded from http://pubs.acs.org on September 10, 2015

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Stabilization of Phenolic Radicals on Graphene

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Oxide: An XPS and EPR Study

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Panagiota Stathi1*, Dimitrios Gournis2, Yiannis Deligiannakis3, Petra Rudolf1*

1) Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747AG Groningen, The Netherlands. 2) Department of Material Science and Engineering, University of Ioannina, GR-45110 Ioannina, Greece 3) Department of Environmental and Natural Resources Management, University of Patras, Seferi 2, GR-30100, Agrinio, Greece KEYWORDS: Graphene Oxide, Gallic Acid, Free Radicals, XPS, EPR.

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ACS Paragon Plus Environment

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ABSTRACT

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A Graphene Oxide-Gallic Acid hybrid material was synthesized by immobilization of Gallic

4

Acid (3,4,5trihydroxobenzoic acid) on Graphene Oxide. The grafting was achieved via formation

5

of amide bonds between the amine groups on the organo-functionalized Graphite Oxide surface,

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and the carboxyl groups of the Gallic Acid molecules. The EPR signal of the Gallic Acid radicals

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in this hybrid material remained almost unaltered over at least 500 days, with less than 3% signal

8

decay over that period, pointing to a truly remarkable stability of these radicals. The produced

9

material was characterized by Fourier Transform Infrared, X-ray photoelectron and Electron

10

Paramagnetic Resonance spectroscopies, as well as by thermogravimetric analysis and Kaiser

11

test. The stability of the radicals in the material was studied in powder form and in aqueous

12

solution vs. pH. We demonstrate that in the Graphene Oxide-Gallic Acid hybrid materiala radical

13

is favorably stabilized on the ring-O, while the oxidation of the second OH is precluded, and this

14

result in long-term stabilization of the Gallic Acid radicals in solid hybrid material. Thus in

15

applications where it will be used in O2-free and humidity-free conditions, the Graphene Oxide-

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Gallic Acid hybrid material is a reliable spintronics scaffold.

17 18 19

Introduction

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Among the different types of building blocks for hybrid materials, Graphite or Graphene Oxide

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(GO) attracts a growing interest due to its specific characteristics, such as stability to both strong

22

acidic and basic media1-3 and stability at high temperatures2-3.GO has the additional advantage


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that the chemical properties of the surface can be modified to control its polarity and

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hydrophobicity. GO is decorated by a large number of oxygen moieties, like carboxyl, hydroxyl

3

and epoxy groups3,4; these oxygen groups can react with organic molecules and polymers

4

allowing for an organic functionalization of GO. Moreover, GO has a 2D planar structure with a

5

high specific area, which can play a crucial role for the properties of the material. Furthermore,

6

graphene oxide has the advantage over other support materials such asSiO2 particles that it is

7

highly stable in a wide range of chemical conditions, such as extreme pH conditions.

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During the last half decade chemically modified graphite oxide has been studied in a context of

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many applications such as polymer composites5, energy-related materials6,7, sensors4.5, and

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biomedical applications6, due to its excellent electrical, mechanical and thermal properties1.

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Several types of oxygen-containing functional groups on the basal plane and at the sheet edges

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allow GO to interact with a wide range of organic and inorganic components through non-

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covalent, covalent and/or ionic interactions, so that functional hybrids and composites with

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unusual properties can be readily synthesized1. Furthermore, for what its electronic structure is

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concerned, GO features both sp2and sp3hybridized carbon atoms4.

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Gallic Acid (3,4,5-trihydroxybenzoicacid, GA) is a naturally occurring polyphenolic

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molecule, which can be harnessed for antibacterial, antiviral, anti-inflammatory, anticancer and

18

antioxidant

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have a lifetime of less than 20 min in aqueous solution13.Recently, we have demonstrated that

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covalent immobilization of GA on a SiO2 surface13 stabilizes the GA radicals for more than 2

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hours. The covalent attachment of GA on solid surfaces precludes the deactivation of the GA

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radicals via GA-GA polymerization. Moreover, H-bonding between neighboring OH of GA

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prevents quinone formation by a second OH oxidation on the same GA molecule8. Thus grafting

8-12

applications. GA radicals, which are responsible for most of these properties,


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of GA on a solid matrix such as SiO2 or GO has a double beneficial protective effect that

2

stabilizes the GA radicals13, 8.

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Here a novel hybrid material (GO-GA) was prepared by covalent grafting of Gallic Acid on GO

4

surface, with the aim to develop a novel hybrid material with controlled spintronic properties.

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GO-GA material was characterized with Fourier transform infrared (FTIR) spectroscopy,

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thermogravimetric analysis (TGA),X-ray photoelectron spectroscopy (XPS), powder X-ray

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diffraction (XRD) and electron paramagnetic resonance (EPR)spectroscopy.

8 9 10

Materials and Methods

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Preparation of Materials

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Graphite Oxide was synthesized using a modified Staudenmaier'smethod14. 10 g of powdered

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Graphite (purum, powder≤0.2 mm, Fluka) were added to a mixture of 400 mL of 95–97% H2SO4

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and 200 mL of 65%HNO3 while cooling in an ice water bath. 200 g of powdered KClO3 were

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added to the mixture in small portions under continuous stirring and cooling. The reaction was

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quenched after 18 h by pouring the mixture into distilled water and the oxidation product was

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washed until the pH reached 6.0;thefinal product was left to dry in air at room temperature.

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The preparation protocol of the GO-GA hybrid consisted of two main steps. First GO modified

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with amine groups was prepared; the immobilization of amine was achieved by the nucleophilic

21

attack of the –NH2 end group of diamine on the epoxide groups of GO, as detailed in reference

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15. For the preparation of GO-modified with amine groups, which we call GO-NH2,1g of GO

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were dispersed in 250mL of Milli-Q water and the suspension was stirred for 12h. 300mg of


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hexamethylenediamine in 100mL of Milli-Q water were then added tothe GO dispersion and the

2

mixture was allowed to react under vigorous stirring for 24h at room temperature. GO-NH2 was

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then separated by centrifugation, washed several times with Milli-Q water and acetone and

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finally left to dry in air. In a second step, the immobilization of GA was achieved by formation

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of an amide bond between the amine groups of the organo-functionalized GO and the carboxyl

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group of the GA activated by N-(3-Dimethylaminopropyl)-N2-ethylcarbodiimide (commonly

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known as EDC). This method was successfully applied previously for GA immobilization on a

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silica matrix13. In detail, 500mg of the amino-functionalized GO were suspended in 50mLof

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toluene, and 100mg GA and 33mg EDC were added to the suspension. The mixture was refluxed

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for 12h at 80°Cand then centrifuged, rinsed several times with toluene, methanol, Milli-Q water

11

and acetone and finally dried under ambient conditions. This final product is called GO-GA

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hereafter.

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Characterization Techniques

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Thermogravimetric analysis. TG analyses were performed on a TGA Q500, TA Instruments.

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Samples of approximately 0.5 mg were heated at a rate of 10 °C/min under Nitrogen (N2,

18

99.9 %)17.

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Kaiser test :For the quantification test of amino groups a Kaiser test was carried outas described

20

in the literature

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this suspension 1mL of sodium acetate/acetic acid buffer solution (pH= 5.5) was added. Asa next

22

step 1mL of KCN and 1mL phenol solution were added and the suspension heated for 10min at

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120°C. Thereafter 1 mL of ninhydrine solution was added and the suspension heated for again

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. Briefly 0.2 g of the samplewas suspended in1mL of Milli-Q water and to


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for 10minat 120°C. After the cooling the sample, 5 mL of ethanol were added. The suspension

2

centrifuged, and the UV-Vis spectrum of the supernatant recorded (568 nm). A calibration curve

3

with benzyl amine as an NH2 source was obtained following the same protocol. The

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hexamethyllenedimine loading was calculated from the UV-vis absorbance at 561nm taking into

5

account that the secondary amines formed during the reaction of hexamethylenediamine with

6

epoxy groups of the GO were not detected via the Kaiser test.

7 8

Atomic force microscopy.AFM images were recorded in tapping mode with a Bruker Multimode

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3D Nanoscope, using a silicon micro-fabricated cantilever type TAP-300G, with a tip radius

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8.For the

3

SiO2-GA hybrid the detailed study of the radical stabilization showed that the phenolic radical

4

stabilizes for at least 2 h on the SiO2 surface. Here we present analogous results for GA

5

immobilized on the GO surface; Figure 7a presents the EPR spectra of GA in solution at various

6

pH after exposure to ambient O2 for 10min. At acidic and natural pH values below 8 no EPR

7

signal was detected. At alkaline pH instead, an EPR signal with g=2.0040 and ∆Η= 3.5±0.1G

8

was found. The pH dependence of the GA radical is a well-documented phenomenon13 and can

9

be attributed to the oxidation of GA to the semiquinone form when the phenolic OH of GA

10

isdeprotonated. Taking into account the phenolic pKa of GA13, radical formation can take place

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only at pH>8.

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pH dependence of GO radicals: Figure 7bdisplays the EPR spectra for a suspension of GO in

14

H2O at various pH. The EPR lineshape and intensity for GO were pH independent; this shows

15

that the GO radicals are not affected by the pH of the suspension32.

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pH dependence of GO-GA radicals: Figure 7c shows the EPR spectra of a GA-GO suspension in

18

H2O at various pH(after the subtraction of the GO radicals).In contrast to GO, in the case of GO-

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GA different pH values caused changes of the EPR signal intensity on changing to alkaline pH,

20

the EPR signal gradually increases. The percentage of radicals vs. pH for GA, GO and GO-GA is

21

presented in figure 7d.Table S3 presents the concentration of the GA radicals detected vs. the pH

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of the suspension. Importantly, in GO-GA suspensions stable GA radicals were detected even at

23

pH=5;the latter represent 25% of the maximum amount of GA radicals. Overall these data show


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that GO-GA comprises two types of spins [i]pH-independent spins attributed to the electrons on

2

GO and[ii] pH-dependent spins which show the same pH profile as GA, and can therefore be

3

attributed to the GA molecules on the GO surface.

4

Stability of the radicals in the powder material: Figure 8a shows the EPR of GO-GA as a

5

function of time. The signal showed a truly remarkable stability since it remained almost

6

unaltered over at least 500 days, with less than 3% signal decay over that period.

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Stability of the radical in water: Figure 8b shows the stability of the radicals of GO and GO-GA

8

in an aqueous suspension at pH=12. The EPR signal of GO was unaltered after incubation in

9

aqueous suspension for at least 9 h. When GO-GA was incubated in aqueous solution at pH=12,

10

the intensity of the EPR spectra decreased with time. More precisely, the signal diminished by

11

20% in ca. 9 h. This is in a striking contrast with the much lower stability of the GA radicals in

12

solution, which disappear completely after 20min13.Consideringthat the GO spins remained

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stable over this period, we can conclude that the decrease of the EPR signal is due to GA on the

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GO surface. An analogous phenomenon was observed for GA immobilized on SiO213,where the

15

GA radicals remained stable for 2 h. The disappearance of the GA radicals on GO-GA cannot be

16

due to GA-GA polymerization since GA is anchored to the GO matrix. Instead, as detailed in

17

reference 8, the formation of a quinine ,i.e. a 2-electron oxidation of two phenolic OHs in the

18

same GA14, is the reason for the disappearance of the GA spins. More precisely, at alkaline pH,

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one OH on the ring is converted to O- , which can then be oxidized by ambient O2 thus forming

20

one radical on the GA ring14. When a second OH on the same GA ring is deprotonated, the ring-

21

O- can be easily oxidized by O2, thus forming a second radical on GA. These two radicals then

22

rapidly rearrange14 to form two C=O groups on the ring, resulting in a quinone structure that is

23

EPR silent since it has no unpaired spin. Thus the key-factor is the deprotonation of the OH next


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to the O-radical on the GA ring. In GA-GO, as in the case of SiO2-GA13, 14, the second OH has a

2

high dissociation constant due to Hydrogen bonding between neighboring GA8, 13. In GO-GA an

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analogous beneficial effect is concluded :the attachment of GA on the GO matrix and H-bonding

4

between adjacent GA inhibit the deprotonation/oxidation of the second OH, thus inhibiting the

5

radical quenching phenomenon in aqueous solutions. In the solid GO-GA, the first radical is

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favorably stabilized on the ring-O, while the oxidation of the second OH is prevented, and this

7

results in the eternal stabilization of the GA radicals in the GO-GA material. Thus in applications

8

where itwill be used in O2-free and humidity-free conditions, GO-GA is a reliable spintronics

9

scaffold.

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Conclusion

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The present study demonstrates the stabilization of the phenolic radical in a GO-GA hybrid. The

13

radicals in GO-GA are more stable compared toSiO2-GA and this can be attributed to the

14

remarkable stability of GO as well as to the immobilization of the GA molecules between the

15

GO layers. The basic physicochemical factors responsible for the decay of GA radicals are i)

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GA polymerization; ii)auto-oxidation of GA radicals with the formation of quinones with rate

17

limiting step the deprotonation of the phenoxyl group of GA. The grafting of GA on GO

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prevents GA-GA polymerization. Moreover, the attachment of GA to the GO surface allows for

19

the formation of H-bonds between neighboring GA molecules, which in turnprevents the

20

deprotonation of GA and the formation quinones.

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Figure1.X-ray diffraction patterns of (a) GO, (b) GO-NH2, (c) GO-GA (left panel); schematics of

10

GO-NH2 and GO-GA (right panel). Next to the schematics of GO-GA the dimensions of Gallic

11

Acid are shown;Insetin the left panel: AFM image of GO-GA.

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Figure 2 X-ray photoelectron spectra of the C1s core level region of graphene oxide (GO), of

5

graphene oxide functionalized with hexamethylenediamine (GO-NH2) and additionally

6

functionalizedwith Gallic Acid(GO-GA); fits to the experimental lines are also shown.

7 C-C

GO

9 10 11

Intensity (arb. units)

8

C-O

C=O(O)

12 GO-NH2

14


13

C-C

C-N/C-O C=O

15 C1s

16 17 18 19


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GO-GA

C-N/C-O C=O

20 21

C-C

300

295

290

285

280

275

270

Binding Energy (eV)


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Figure 3. X-ray photoelectron spectra of the N1s core level region of graphene oxide

3

functionalized with hexamethylenediamine (GO-NH2) and additionally functionalized with

4

Gallic Acid (GO-GA); black: Experimental, colored lines: theoretical deconvolutionof the

5

experimental lines are also shown.

6 7

9 10


8

GO-NH2

Neutral Amines (59.9 %)

Protonated Amines (40.1 %)

11

GO-GA 12 13 14


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Protonated Amines (40 %)

Neutral Amines (38.5 %)

Amide Bond (21.5 %)

15 410 408 406 404 402 400 398 396 394 392 390

16

Binding Energy (eV)

17 18


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Figure 4.FTIR spectra of a) graphene oxide (GO) b) graphene oxide functionalized with

5

hexamethylenediamine (GO-NH2) and c) GO-NH2functionalized with Gallic Acid (GO-GA)

6

a) GO

Absorbance

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b) GO-NH2 c) GO-GA

v(C=N) amide II v(C=O) amide I

3500 7

3000

2500

2000

1500

1000

500

Wavenumbers (cm-1)

8


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Figure 5. Continuous wave EPR spectra of pure GO (red line), GA (green line) and GO-GA

2

(black line); the difference between GO-GA and GO is also presented (blue line). Experimental

3

conditions: microwave frequency 9.49GHz, temperature 77K, modulation amplitude 4.00Gpp,

4

microwave power 2mW.

5 6

GO g=2.0026

7 8 9 10 11 12 13

dx"/dH (arb. un.)

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GO-GA g=2.0036 Subtraction g=2.0040

GA in solution g=2.0040

14 15 16

3370

3380

3390

3400

3410

Magnetic Field (G)

17 18 19 20 21 22 23 24


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Figure 6.Progressive power saturation of EPR spectra of GO, GA, GO-GA and GA immobilized

3

on GO-GA a) at room temperature and b) at 77K.Characteristic EPR spectra of GO-GA recorded

4

with different power, c) at room temperature d) at 77K. 1,0

5

7 8 9 10 11

GO-GA P1/2=1.16mW

0,8

GA in solution P1/2=0.20mW

0,6

GA on GO-GA P1/2=0.64mW

0,4

0,2

0,0

a)

GO P1/2=0.40mW

-0,2 1E-3

0,01

12

0,1

1

10

100

Log(intensity/Sqrt(P))

6

1,0

Log(intensity/Sqrt(P))

1000

0,5

GO-GA P1/2=0.92mW

0,0

GA on GO-GA P1/2=0.06mW

-0,5

GO P1/2=0.27mW

b)

GA in solution P1/2=0.03mW

-1,0 1E-3

0,01

0,1

13

15 16 17 18 19

10

100

1000

8dB

8dB

dx"/dH (arb. units)

14

1

Microwave (mW)

Microwave (mW)

dx"/dH (arb. units)

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22dB

c)

3370

3380

3390

3400

3410

22dB

d)

3370

Magnetic Field (G)

3380

3390

3400

3410

Magnetic Field (G)


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Figure 7. Continuous wave EPR signal at different pH a) GA, b) GO, c) GO-GA after

3

subtraction of the GO signal d) Percentage of radical formation vs.pH.

4

dx"/dH (arb. units)

7

pH=12

pH=9

pH=12

pH=9

pH=7

pH=5

b)

pH=7 pH=5

3370 3380 3390 3400 3410

3370 3380 3390 3400 3410

Magnetic Field (G)

Magnetic Field (G)

100

pH=12 pH=9 pH=7 pH=5

C)

% Radical Fomation

6

a)

dx"/dH (arb. units)

5

dx"/dH (arb. units)

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GO

80

GO-GA

60 40

d)

20 0

GA in Solution 4

5

6

3370 3380 3390 3400 3410

7

8

9

10

11

12

13

pH

Magnetic Field (G)


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1 2

Figure 8.Spin concentrations of GO and GO-GA vs. time (a) powder exposed to ambient

3

conditions (b) GO and GO-GA incubated in aqueous solution at pH=12. Insert: percentage of

4

radicals in a GA solution at pH=12.

17

2,8x10

17

2,8x10

GO-GA

7 8

2,6x10

17

2,6x10

17

2,4x10

17

2,2x10

17

60 40 20 0 0

17

2,2x10

2

4

6

8

10

time (min)

2,0x10

(a)

GO

17

9

17

2,4x10

80

17

2,0x10

1,8x10

100

GO-GA

17

Spins/gr

6

% Radical Formation

5

Spins/gr

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(b)

GO 17

0

100

200

300

400

500

1,8x10

0

2

Time (days)

4

6

8

10

12

Time (hours)

10


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Scheme1.Schematic representation of the synthetic steps forGO-NH2and GO-GA.

3 4


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1 2 3 4 5 Table 1. EPR Parameters and Spin Quantification Analysis

Sample

g

∆Η(±0.1) [Gauss]

spins/g

(±0.0005) GO-radicals in GO(powder)

2.0026

GO+GA radicals inGO-GA(powder) Gallic-Radicals in GO-GA(powder) GA (In solution)

µmol spins/ g

6 lineshape factor κ

7 3.0

2.0x10

17

3.3

2.65 /Lorentzian

2.0026

4.3

2.5x10 17

4.1

1.66 /Gaussian

2.0040

3.5

0.5x10 17

0.3

1.33/Gaussian

2.0040

3.0

8 9 10

1.20/Gaussian

11 12 13 14 15 16 17


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1

ASSOCIATED CONTENT

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SupportingInformation.SurveyXPS spectra of materials, results of the Kaiser test and

3

thermographs of materials.

4

AUTHOR INFORMATION

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Corresponding Authors

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P. Stathi, P. Rudolf

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*[email protected] ; [email protected]

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Present Addresses

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†P.S. now works at the Department of Chemistry, University of Ioannina, GR-45110 Ioannina,

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Greece.

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ACKNOWLEDGMENT

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P.S. acknowledges E.U. support through the PIEF-GA-2009-255129 Marie Curie fellowship.

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This project received financial support from the“Graphene-based electronics” research program

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of the Foundation for Fundamental Research on Matter (FOM), part of the Netherlands

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Organization for Scientific Research (NWO), and the University of Ioannina (UOI).

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REFERENCES

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(1) Dreyer, D. R.; Park, S.; Bielawski, C.W.; Ruoff, R.S. The Chemistry of Graphene Oxide. Chem. Soc.Rev. 2010, 39, 228-240. (2) Geim, A. K.; Novoselov, K.S. The Rise of Graphene. Nat.Nanotechnol.2007 ,6, 183-191.


28

Page 29 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3 4 5

Langmuir

(3) Park, S.; Ruoff, R.S. The Chemical Methods for the Production of Graphenes.Nat.Nanotechnol.2009,4, 217-224. (4) Ping Loh, K.; Bao Q.; Eda G.; Chowalla, M. Graphene Oxide as a Chemically Tunable Platform for Optical Applications.Nat.Chem..2010, 2, 1015-1024. (5) Cao, Y.; Feng, L.J.; Wu, P. Graphene Oxide Sheets Covalently Functionalized With Block

6

Copolymers via Click Chemistry as Reinforcing Fillers. J. Mater. Chem. 2010, 21, 9271-

7

9278.

8 9 10 11 12

(6) Zhu, Y.; Murali, S.; Cai, W.; Li, X.; Suk, J.W.; Potts J.R.; Ruoff, R.S. Graphene and Graphene Oxide: Synthesis, Properties and Applications. Adv.Mat.,2010, 22, 3906-3924. (7) Radich, J. R.; Kamat, P.V. Origin of Reduced Graphene Oxide Enhancements in Electrochemical Energy Storage. ACS Catal.2012, 2, 807-816. (8) Deligiannakis, Y.; Sotiriou G.A.; Pratsinis, S.A . Antioxidant and Antiradical SiO2

13

Nanoparticles Covalently Functionalized With Gallic Acid. Appl. Mater. Inter. 2012, 4,

14

6609-66017.

15 16 17

(9) Becker, L. Final Report on the Amended Safety Assessment of Propyl Gallate, Int. J. Toxicol. 2007, 26, 89−118. (10) Lu, Z. B.; Nie, G. J.; Belton, P. S.; Tang, H. R.; Zhao, B. L. Identification of Three

18

Novel Polyphenolic Compounds, Origanine A-C, With Unique Skeleton from

19

Origanumvulgare L. Using the Hyphenated LC-DAD-SPE-NMR/MS

20

Methods.Neurochem. Int. 2006, 48, 263−274.

21

(11) Dwibedy, P.; Dey, G. R.; Naik, D. B.; Kishore, K.; Moorthy, P. N. Pulse Radiolysis

22

Studies on Redox Reactions of Gallic Acid: One Electron Oxidation of Gallic Acid by

23

Gallic Acid–OH Adduct. Phys. Chem. Chem. Phys.1999, 1, 1915−1918.


29

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

(12) Saeki, K.; Yuo, A.; Isemura, M.; Abe, I.; Seki, T.; Noguchi, H. Apoptosis-Inducing

2

Activity of Lipid Derivatives of Gallic Acid. Biol. Pharm. Bull. 2000, 23, 1391−1394

3

(13) Stathi, P.; Louloudi, M.; Deligiannakis Y. EPR Study of Phenolic Radical Stabilization

4

by Grafting on SiO2. Chem.Phys.Lett. 2009, 472, 85-89.

5

(14) Stergiou, D.V.; Diamanti, E.K.; Gournis, D.; Prodromidis M.I. Comparative Study of

6

Different Types of Graphenes as Electrocatalysts for Ascorbic Acid. Electrochemistry

7

Comm., 2010, 12, 1307-1309.

8 9 10 11

(15) Kaiser, E.; Colescott, R.L.; Bossinger, C.D.; Cook, P.I.Color Test for Detection of Free Terminal Amino Groups in the Solid-phase Synthesis of Peptides. Anal. Biochem.,1970 , 34, 595598.

(16) Jarre, G.; Heyer, S.; Memmel, E.; Meinhardt, T.; Krueger A. Synthesis of Nanodiamond

12

Derivatives Carrying Amino Functions and Quantifications by Modified Kaiser Test. J.

13

Organ. Chem. 2014,10, 2729-2737.

14

Page 30 of 33

(17) Bourlinos, A. B.; Gournis D.; Petridis D.; Szabo T.; Szeni A.; Dekany I. Graphite

15

Oxide; Chemical Reduction to Graphite and Surface Modification With Primary Aliphatic

16

Amines. Langmuir, 2003, 19, 6050-6055.

17

(18) Ivashenko, O.; Logtenberg, H.; Areephong, J.; Coleman, A. C.; Wesenhagen, P. V.;

18

Geertsema, E. M.; Heureux, N.; Feringa, B. L.; Rudolf, P.; Browne, W. R. Remarkable

19

Stability of High Energy Conformers in Self-Assembled Monolayers of a Bistable

20

Electro- and Photoswitchable Overcrowded Alkene. J. Phys. Chem. C 2011, 115, 22965–

21

22975.

22 23

(19) Moulder J.F.; Stickle W.F.; Sobol P.E.; Bomben K.D. Handbook of X-Ray Photoelectron Spectroscopy, Physical Electronics, Inc. Eden Prairie, MN, USA,1995.


30

Page 31 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3 4 5

Langmuir

(20) Chang T.; The Calibration Methods and Reference Materials in ESR Spectroscopy Magn. Reson. Rev. 1984, 9, 65-124. (21) Decani, I.; Kruger –Grasser, R.; Weiss, A. Selective Liquid Sorption Properties of Hydrophobized Graphite Oxide Nanostructures.ColloidPolym. Sci. 1998,276, 570-576. (22) Enotiadis, A.; Angjeli, K.; Baldino, N.; Nicotera, I.; Gournis, D.Graphene-Based

6

NafionNanocomposite Membranes: Enhanced Proton Transport and Water Retention by

7

Novel Organo-Functionalized Graphene Oxide Nanosheets. Small2012, 5,3338-3349.

8 9 10 11 12 13 14 15 16

(23) Quintana, M.; Spyrou, K.; Grzelczak, M.; Browne, W. R.; Rudolf, P.; Prato, M. Functionalization of Graphenevia 1,3-Dipolar Cycloaddition. ACS Nano2010, 4, 3527– 3533. (24) Jansen, R.J.J.; van Bekkum, H.XPS of Nitrogen-Containing Functional Groups on Activated Carbon. Carbon, 1995, 33, 1021-1027. (25) Nakamoto, K.; Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York, 1997. (26) Poole, C.P.; Farach, H.A.; Handbook of Electron Paramagnetic Resonance, Springer, Heidelberg,1999.

17

(27) Christoforidis,K.C.; Un, S.; Deligiannakis, Y. Effect of Metal Ions on the Indigenous

18

Radicals of Humic Acids: High Field Electron Paramagnetic Resonance Study. Environ.

19

Sci. Technol., 2010, 44,7011-7016.

20

(28) Eslani, A.C.; Pasanphan, W.;Wagner, B. A.; Buettner, G. R.; Free Radicals Produced by

21

the Oxidation of Gallic Acid: An Electron Paramagnetic Resonance Study. Chem. Central

22

J. 2010, 4, 15-19.


31

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3

(29) Hyde J. S.;Rao, K.V.S. Spin-lattice Relaxation of the Pheophytin, Pheo-, Radical of Photosystem II. Biochemistry1996, 35, 11239-11246. (30) Blum, H.;Ohnishi, T. Electron Spin Relaxation of the Electron Paramagnetic

4

Resonance Spectra of Cytochrome c.Biochimica et BiophysicaActa1980, 621, 9-18.

5

(31) Galli, C.; Innes, J.B.; Hirsh, D.J.; Brudvig, G.W.Effects of Dipole-Dipole Interactions

6

on Microwave Progressive Power Saturation of Radicals in Proteins. J.ofMagn. Reson.

7

B1996, 110, 284-287.

8 9

Page 32 of 33

(32) Morita, Y.; Suzuki, S.; Sato, K.; Takui, T. Synthetic Organic Spin Chemistry for Structurally Well-Defined Open–Shell Graphene Fragments. Nat. Chem.2011, 3, 197-204.

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Table of Contents/Abstract Graphics

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Stabilization of Phenolic Radicals on Graphene Oxide: An XPS and

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