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Degradation of Graphene by Hydrogen Peroxide

July 2014
Particle and Particle Systems Characterization 31(7):745-750

DOI:10.1002/ppsc.201300318

Authors:

Weiliang Xing

Stony Brook University

Gaurav Lalwani

Stony Brook University

Balaji Sitharaman

Millennial Scientific

Graphene, the 2D carbon nanomaterial, is suitable for diverse applications, ranging from electronics and telecommunication, to energy and healthcare. Despite its tremendous technological and commercial prospects, its interactions with biological and environmental constituents still require thorough examination. Here, we report that pristine multilayered graphene degrades in the presence of the naturally occurring, ubiquitous compound hydrogen peroxide (H 2 O 2 ) at physiologically and environmentally relevant concentrations (1–10 000 × 10 −6 M ) at various time points (0–25 h).

Representative TEM images of multilayered graphene treated with A) deionized water, B) 1 × 10−6 m H2O2, C) 100 × 10−6 m H2O2, and D) 10 000 × 10−6 m H2O2 for 10 h. Arrows in (B) indicate the formation of holes on graphene sheets, and arrows in (C) indicate the formation of lighter (few graphene layers) and darker regions (multiple graphene layers) suggesting the degradation of multilayered graphene. It should be noted that the arrows in (B–D) only point to a few representative holes.

…

Representative AFM images of multilayered graphene on Ni wafer. A,C,E) are topographical scans of pristine graphene samples (incubated with DI water) and B,D,E) are graphene after 25 h of H2O2 treatment (10 000 × 10−6 M). Insets in images C and D correspond to the line height profile. Images E and F are 3D representations of images C and D, respectively.

…

Figures - uploaded by Gaurav Lalwani

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Content uploaded by Gaurav Lalwani

Content may be subject to copyright.

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and >1 × 10

−3 M cause necrosis.

[ 22 ] Thus, given the widespread

presence of H

2 O 2 in the body and environment, and the future

impact graphene may have on human health and environment,

systematic studies need to be performed to investigate the direct

chemical interaction between H

2 O 2 and graphene. As a ﬁ rst

step, in this communication, we examine the effects of H

2 O 2

on multilayered pristine graphene at physiologically and envi-

ronmentally relevant concentrations (1–10 000 × 10

−6 M ). [ 19,22,23 ]

Pristine multilayered graphene deposited on nickel wafer

(wafer size = 1 cm × 1 cm, Graphene Supermarket, Calverton,

NY, USA) or directly onto TEM grids was placed in petri dishes

and treated with H

2 O 2 solution at concentrations of 1 × 10

−6 ,

100 × 10

−6 , or 10 000 × 10

−6 M ( n = 4 per group). Graphene incu-

bated with distilled water (DI) served as the control. As H

2 O 2

solutions gradually deteriorate,

[ 22 ] the solutions were aspirated

out every hour and exchanged with fresh solutions. The experi-

ments were terminated after 10 or 25 h. At these time points,

solutions were completely removed, and graphene substrates

were air-dried. Graphene samples before (time t = 0 h) and after

2 O 2 treatment (time t = 10 and 25 h) were examined with

transmission electron microscopy (TEM), atomic force micros-

copy (AFM), and confocal Raman spectroscopy (laser excitation

of 532 nm).

Figure 1 shows representative TEM images of graphene-

coated TEM grids incubated with various concentrations of

2 O 2 for 10 h. Figure 1 A shows the control graphene sheet

incubated with DI water with no holes or defects, and has

the basic hexagonal lattice of graphene, possessing 0.142 nm

carbon–carbon bond length, occupying ≈0.17 nm

2 area. [ 24 ]

Compared with the control group (Figure 1 A), graphene

with 1 × 10

−6 M H 2 O 2 treatment after 5 h showed the pres-

ence of randomly distributed small holes as seen in Figure 1 B

(arrows point to few representative holes). The diameter dis-

tribution of holes on graphene was measured by analyzing

multiple ( n = 20) TEM images. Incubation of graphene with

1 × 10

−6 M H 2 O 2 for 10 h resulted in the formation of holes

ranging from 1 to 15 nm diameter (representing an area

up to 175 nm

2 ). Thus, these visible holes indicate a “cluster

effect,” i.e., the holes, or defect sites are generated initially by

random attack of H

2 O 2 followed by progressive attraction of

more H

2 O 2 to destroy carbon–carbon bonds around the ini-

tial defect sites. This effect is dependent on the concentration

of H

2 O 2 , and enhanced by higher concentrations of H

2 O 2 .

Upon treatment with 100 × 10

−6 M H 2 O 2 , formation of larger-

sized holes (10–15 nm) was observed (Figure 1 C). Addition-

ally, Figure 1 C also shows formation of lighter (few graphene

layers) and darker regions (multiple graphene layers) indi-

cating the degradation of multilayered graphene. Figure 1 D

shows graphene after incubation with 10 000 × 10

−6 M H 2 O 2 .

Large-defect sites (10–30 nm) and few graphene layers were

observed corresponding to the degradation of majority of the

graphene sheets.

W. Xing, G. Lalwani, Prof. B. Sitharaman

Department of Biomedical Engineering

Stony Brook University

Stony Brook , New York 11794–5281, USA

E-mail: balaji.sitharaman@stonybrook.edu

Dr. I. Rusakova

Texas Center for Superconductivity

and Advanced Materials

University of Houston Science Center

Houston, Texas 77004–5002 , USA

DOI: 10.1002/ppsc.201300318

Degradation of Graphene by Hydrogen Peroxide

WeiLiang Xing , Gaurav Lalwani , Irene Rusakova , and Balaji Sitharaman *

Graphene, the 2D carbon nanomaterial, is suitable for diverse

applications, ranging from electronics and telecommunication,

to energy and healthcare. Despite its tremendous technological

and commercial prospects, its interactions with biological and

environmental constituents still require thorough examination.

Here, we report that pristine multilayered graphene degrades in

the presence of the naturally occurring, ubiquitous compound

hydrogen peroxide (H

2 O 2 ) at physiologically and environmen-

tally relevant concentrations (1–10 000 × 10

−6 M ) at various time

points (0–25 h).

Graphene, a 2D sheet comprised of sp

2 -hybridized carbon

possessing exciting electrical, mechanical, thermal, and optical

properties,

[ 1 ] has been investigated as enabling components in

fuel cells,

[ 2,3 ] sensors, [ 2,4 ] photocatalysis, [ 5 ] electronics, [ 6 ] compos-

ites,

[ 7 ] electrical and optical biosensors,

[ 8 ] drug delivery,

[ 9 ] tissue

engineering,

[ 10,11 ] and imaging probes.

[ 12 ] Recent reports predict

that graphene may overtake carbon nanotubes in commercial

applications.

[ 13 ] The development of potential graphene-based

commercial technologies for applications in material and bio-

medical sciences has raised concerns about its short-term and

long-term effects on human health and the environment,

[ 14 ]

and leads to multiple investigations to assess and evaluate these

effects.

[ 15 ]

An important attribute to be examined while investigating

graphene's effect on human health and environment is its

bio- and environmental-degradation properties. Several studies

have investigated the biodegradation of carbon nanotubes,

[ 16,17 ]

wherein enzymes such as horseradish peroxidase (HRP) and

human myeloperoxidase (hMPO) were employed to catalyze

oxidative degradation of these nanomaterials. A recent study

has used a similar strategy on graphene oxide, and exploits the

catalytic activity of HRP enzyme.

[ 18 ] H 2 O 2 is a component of

this degradation process.

H 2 O 2 is a naturally occurring, ubiquitous compound and a

strong oxidizing agent, found in rain and surface water, and

biota.

[ 19,20 ] Its concentration in natural water sources has been

determined to be 1–7 × 10

−3 M . [ 19,21 ] In normal living cells,

diverse cellular pathways synthesize H

2 O 2 in tightly regulated

concentrations varying between 1 × 10

−9 and 700 × 10

−9 M . H 2 O 2

steady-state concentrations >1 × 10

−6 M cause oxidative stress,

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AFM was performed (using a previously described proce-

dure)

[ 11 ] to assess the surface topography of graphene sheets

before and after H

2 O 2 treatment. Samples were incubated

with DI water and 10 000 × 10

−6 M H 2 O 2 for 25 h. Pristine

graphene sheets ( Figure 2 A,C,E) appeared smooth, without

any topographical defects. Randomly distributed holes in

graphene sheets were observed after incubation with H

2 O 2

(Figure 2 B,D,E). The diameter of holes ranged from 5.3 to

13.5 nm. Compared with the height of single graphene sheet

(≈0.34 nm),

[ 18 ] the depth of the holes (9.4–13.5 nm, inset

Figure 2 D) was greater by several folds suggesting the attack of

2 O 2 on the inner layers of graphene. Once superﬁ cial defect

sites are generated, H

2 O 2 may pass through these defect sites

attacking the underlying C–C bonds, and accelerating the deg-

radation of graphene at higher concentrations of H

2 O 2 .

Raman spectroscopy was used to characterize the graphene

samples before and after treatment with H

2 O 2 at every time

point ( Figure 3 ). The ratio of D-band and G-band intensities

( I D / I G ) at all-time points before and after H

2 O 2 treatment are tab-

ulated in Table 1 . The D band indicating the degree of disorder

in sp

2 -hydridized carbon system was observed between 1335 and

1350 cm

−1 , and the G band, indicating stretching of graphitic

carbon, was observed between 1570 and 1580 cm

−1 . [ 25 ] Table 1

shows decrease in the intensity of D and G bands for all groups

treated with various concentration of H

2 O 2 for 25 h, suggesting

a gradual structural degradation of graphene.

[ 26 ] For groups

treated with 1 × 10

−6 and 100 × 10

−6 M H 2 O 2 , the I D / I G ratio

increased within 10 h of incubation, and decreased at later time

points. Increase in I D / I G ratio during initial time points can be

attributed to increase in the number of defects on graphene, and

is consistent with previous reports on enzymatic degradation of

graphene.

[ 17,18,26 ] The decrease in I D / I G ratio at later time points

can be attributed to disintegration of the multiple layers of gra-

phene due to progressive increase in the defect sizes, exposing

the underlying pristine graphene layers.

[ 26 ] The Raman spectra

from these underlying pristine graphene layers would have an

intense G band, reducing the I D / I G ratio. For the group treated

with 10 000 × 10

−6 M H 2 O 2 , I D / I G ratio progressively decreased

at all time points, unlike 1 × 10

−6 and 100 × 10

−6 M H 2 O 2 treat-

ment groups, which showed an initial increase in the I D / I G ratio

within the ﬁ rst 10 h. After 25 h, both D and G bands almost dis-

appeared for the 10 000 × 10

−6 M H 2 O 2 treatment group.

G ′ band, a characteristic of layered graphene, was observed

at ≈2750 cm

−1 for all treatment groups.

[ 27 ] The intensity of

G′ band increased during the ﬁ rst 10 h of H

2 O 2 treatment,

decreased, and became negligible at later time points. The

G′ band became progressively narrow and down shifted at

increasing time points. Several reports have shown the rela-

tion of G′ band with the number of layers of graphene in which

wider, higher intensity, and an upshift of G′ band corresponds

to increasing number of graphene layers.

[ 25,27,28 ] In this study,

as the degradation progressed, decrease in the width, intensity,

and downshift of G′ band corresponds to progressive, layer-

by-layer degradation of graphene. A layer-by-layer degradation

phenomenon was observed during degradation of multiwalled

carbon nanotubes by HRP.

[ 17,29 ] Furthermore, differences in G′

band peak intensity and width between various H

2 O 2 treatment

groups imply the dependence of graphene degradation rate on

Figure 1. Representative TEM images of multilayered graphene treated with A) deionized water, B) 1 × 10

−6 M H 2 O 2 , C) 100 × 10

−6 M H 2 O 2 , and

D) 10 000 × 10

−6 M H 2 O 2 for 10 h. Arrows in (B) indicate the formation of holes on graphene sheets, and arrows in (C) indicate the formation of lighter

(few graphene layers) and darker regions (multiple graphene layers) suggesting the degradation of multilayered graphene. It should be noted that the

arrows in (B–D) only point to a few representative holes.

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the concentration of hydrogen peroxide, i.e., graphene treated

with 1 × 10

−6 M H 2 O 2 may degrade at a slower rate compared to

treatment with 10 000 × 10

−6 M H 2 O 2 .

The above results taken together clearly indicate the deg-

radation of multilayered pristine graphene at a wide range of

2 O 2 concentrations found in living systems and environment.

Previous studies report that metal ions such as nickel (Ni), iron

(Fe), and copper (Cu) can catalyze the degradation of H

2 O 2 to

form reactive hydroxyl radicals via the Haber–Weiss reaction.

[ 30 ]

Ni, Fe, or Cu-based substrates or catalysts are used for graphene

Figure 2. Representative AFM images of multilayered graphene on Ni wafer. A,C,E) are topographical scans of pristine graphene samples (incubated

with DI water) and B,D,E) are graphene after 25 h of H

2 O 2 treatment (10 000 × 10

−6 M). Insets in images C and D correspond to the line height proﬁ le.

Images E and F are 3D representations of images C and D, respectively.

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synthesis using the chemical vapor deposition method.

[ 31 ] Thus,

in this study, the presence of trace amounts of Ni used during

the CVD synthesis of the graphene may be catalyzing the deg-

radation of graphene during H

2 O 2 treatment. The results also

indicate that rate of degradation of graphene is dependent

on H

2 O 2 exposure concentration; increase in concentration

accelerates graphene’s degradation. The visible holes indicate a

“cluster effect,” i.e., the holes, or defect sites are generated ini-

tially by random attack of H

2 O 2 followed by progressive attrac-

tion of more H

2 O 2 to destroy the carbon–carbon bond around

initial defect sites. Furthermore, reaction temperature may also

inﬂ uence the degradation rate. Additional studies are necessary

Figure 3. Representative Raman spectra of graphene treated with A) 10 000 × 10

−6 M H 2 O 2 , B) 100 × 10

−6 M H 2 O 2 , and C) 1 × 10

−6 M H 2 O 2 for a period

of 0, 10, and 25 h. Decrease in the D and G band intensities can be observed after 25 h. Figures D–F show the corresponding I D / I G intensity ratio at

every time point .

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Table 1. I D / I G ratio of multilayered graphene samples before and after

incubation with H

2 O 2 for 25 h.

2 O 2 incubation

concentration

I D / I G

ratio

Before incubation After incubation (25 h)

10 000 × 10

−6 M 0.2312 0.1706

100 × 10

−6 M 0.2312 0.1519

1 × 10

−6 M 0.2312 0.1499

Received: September 25, 2013

Revised: December 12, 2013

Published online: February 24, 2014

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vide better understanding of chemical mechanism of H

2 O 2 -

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2 O 2 concen-

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the presence of H

2 O 2 still needs to be determined.

Acknowledgements

This work was supported by the National Institutes of Health (grants no.

1DP2OD007394–01).

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Nanotechnology has increased the release of nanoparticles into the environment, which poses a risk to human health and the ecosystem. Therefore, finding ways to eliminate these hazardous particles from the environment is crucial. This research studied the ability of Trametes versicolor fungi to remove carboxylated multi-walled carbon nanotubes. The study analyzed the impact of pH, MWCNT-COOH concentration, and initial fungal growth time on the removal process. The properties of the adsorbent were measured before and after the biosorption process using SEM, FTIR, and EDS techniques. The results showed that the live biomass of T. versicolor was more effective in removing nanoparticles than dead biomass at 30 °C and pH 7. An increase in carbon nanotube concentration from 5 to 20 mg. mL⁻¹ decreased biosorption potential from 100% to 28.55 ± 1.7%. The study also found that an increase in initial fungal growth time led to higher biomass production and adsorption capacity, increasing biosorption ability for concentrations > 5mg. ml⁻¹. The biosorption kinetics followed a pseudo-second-order model and corresponded most closely to the Freundlich isotherm model. The adsorption capacity of live fungal biomass to remove multi-walled carbon nanotubes was 945.17 mg. g⁻¹, indicating that T. versicolor fungi have significant potential for removing carbon nanostructures from the environment.

Ultra-Broadband THz Absorbers Based on 3D Graphene

Article

Full-text available

Sep 2023
J PHYS D APPL PHYS

We use terahertz and multi-terahertz spectroscopy to investigate optical properties of 3D graphene across a wide frequency range of 0.15–10 THz. We explore the electromagnetic shielding, stealth, and absorber capabilities of 3D graphene samples annealed at various temperatures up to 1300 °C. We show that the tradeoff between the transmitted, absorbed and reflected power of the materials can be controlled by the annealing temperature through a fine broadband tuning of the refractive and absorptive indices of the material. This ultralight system (with a specific mass of ∼7 mg cm^(-3)) is capable of acting as a stealth element (non-annealed sample, R<1%), THz absorber (annealing at 750 °C, A>85%) or a shielding coating (annealing at 1300 °C, T<0.1%) within an ultrabroadband range of 0.2–7 THz. All these properties can be combined by stacking these materials on top of each other, which provides unique opportunities for THz applications.

Investigation on electrocatalytic performance and material degradation of an N-doped graphene-MOF nanocatalyst in emulated electrochemical environments

Article

Full-text available

Aug 2023

To develop graphene-based nanomaterials as reliable catalysts for electrochemical energy conversion and storage systems (e.g. PEM fuel cells, metal–air batteries, etc.), it is imperative to critically understand their performance changes and correlated material degradation processes under different operational conditions. In these systems, hydrogen peroxide (H2O2) is often an inevitable byproduct of the catalytic oxygen reduction reaction, which can be detrimental to the catalysts, electrodes, and electrolyte materials. Here, we studied how the electrocatalytic performance changes for a heterogeneous nanocatalyst named nitrogen-doped graphene integrated with a metal–organic framework (N-G/MOF) by the effect of H2O2, and correlated the degradation process of the catalyst in terms of the changes in elemental compositions, chemical bonds, crystal structures, and morphology. The catalyst samples were treated with five different concentrations of H2O2 to emulate the operational conditions and examined to quantify the changes in electrocatalytic performances in an alkaline medium, elemental composition and chemical bonds, crystal structure, and morphology. The electrocatalytic performance considerably declined as the H2O2 concentration reached above 0.1 M. The XPS analyses suggest the formation of different oxygen functional groups on the material surface, the breakdown of the material's C–C bonds, and a sharp decline in pyridinic-N functional groups due to gradually harsher H2O2 treatments. In higher concentrations, the H2O2-derived radicals altered the crystalline and morphological features of the catalyst. Keywords: Nitrogen-doped graphene-based electrocatalyst; Metal–organic framework; Hydrogen peroxide effect on catalyst; Electrocatalytic performance; Material degradation.

Nanomaterial-Based Scaffolds for Tissue Engineering Applications: A Review on Graphene, Carbon Nanotubes and Nanocellulose

Article

Apr 2023
TISSUE ENG REGEN MED

Nanoscale biomaterials have garnered immense interest in the scientific community in the recent decade. This review specifically focuses on the application of three nanomaterials, i.e., graphene and its derivatives (graphene oxide, reduced graphene oxide), carbon nanotubes (CNTs) and nanocellulose (cellulose nanocrystals or CNCs and cellulose nanofibers or CNFs), in regenerating different types of tissues, including skin, cartilage, nerve, muscle and bone. Their excellent inherent (and tunable) physical, chemical, mechanical, electrical, thermal and optical properties make them suitable for a wide range of biomedical applications, including but not limited to diagnostics, therapeutics, biosensing, bioimaging, drug and gene delivery, tissue engineering and regenerative medicine. A state-of-the-art literature review of composite tissue scaffolds fabricated using these nanomaterials is provided, including the unique physicochemical properties and mechanisms that induce cell adhesion, growth, and differentiation into specific tissues. In addition, in vitro and in vivo cytotoxic effects and biodegradation behavior of these nanomaterials are presented. We also discuss challenges and gaps that still exist and need to be addressed in future research before clinical translation of these promising nanomaterials can be realized in a safe, efficacious, and economical manner.

Article

Full-text available

Mar 2023

This paper builds on the context and recent progress on the control, reproducibility, and limitations of using graphene and graphene-related materials (GRMs) in biomedical applications. The review describes the human hazard assessment of GRMs in in vitro and in vivo studies, highlights the composition–structure–activity relationships that cause toxicity for these substances, and identifies the key parameters that determine the activation of their biological effects. GRMs are designed to offer the advantage of facilitating unique biomedical applications that impact different techniques in medicine, especially in neuroscience. Due to the increasing utilization of GRMs, there is a need to comprehensively assess the potential impact of these materials on human health. Various outcomes associated with GRMs, including biocompatibility, biodegradability, beneficial effects on cell proliferation, differentiation rates, apoptosis, necrosis, autophagy, oxidative stress, physical destruction, DNA damage, and inflammatory responses, have led to an increasing interest in these regenerative nanostructured materials. Considering the existence of graphene-related nanomaterials with different physicochemical properties, the materials are expected to exhibit unique modes of interactions with biomolecules, cells, and tissues depending on their size, chemical composition, and hydrophil-to-hydrophobe ratio. Understanding such interactions is crucial from two perspectives, namely, from the perspectives of their toxicity and biological uses. The main aim of this study is to assess and tune the diverse properties that must be considered when planning biomedical applications. These properties include flexibility, transparency, surface chemistry (hydrophil–hydrophobe ratio), thermoelectrical conductibility, loading and release capacity, and biocompatibility.

Application of Nanomaterials in the Production of Biomolecules in Microalgae: A Review

Article

Full-text available

Nov 2023
MAR DRUGS

Nanomaterials (NMs) are becoming more commonly used in microalgal biotechnology to empower the production of algal biomass and valuable metabolites, such as lipids, proteins, and exopolysaccharides. It provides an effective and promising supplement to the existing algal biotechnology. In this review, the potential for NMs to enhance microalgal growth by improving photosynthetic utilization efficiency and removing reactive oxygen species is first summarized. Then, their positive roles in accumulation, bioactivity modification, and extraction of valuable microalgal metabolites are presented. After the application of NMs in microalgae cultivation, the extracted metabolites, particularly exopolysaccharides, contain trace amounts of NM residues, and thus, the impact of these residues on the functional properties of the metabolites is also evaluated. Finally, the methods for removing NM residues from the extracted metabolites are summarized. This review provides insights into the application of nanotechnology for sustainable production of valuable metabolites in microalgae and will contribute useful information for ongoing and future practice.

rGO outperforms GO in generating oxidative stress and DNA strand breaks in Zebrafish liver cells

Article

Jul 2023
AQUAT TOXICOL

Graphene oxide (GO) and reduced graphene oxide (rGO) are both widely applicable and there is a massive production throughout the world which imply in inevitable contamination in the aquatic environment by their wastes. Nevertheless, information about their interaction at the cellular level in fish is still scarce. We investigated the metabolic activity, reactive oxygen species (ROS) production, responses of antioxidant defenses, and total antioxidant capacity (TAC) as well as oxidative stress and DNA integrity in zebrafish liver cells (ZFL) exposed to (0.001, 0.01, 0.1 and 1 µg mL-1) of GO and rGO after two exposure period (24 and 72 h). Higher ROS production and no significant changes in the antioxidant defenses resulted in lipid peroxidation in cells exposed to rGO. Cells exposed to GO increased the activity of antioxidant defenses sustaining the TAC and avoiding lipid peroxidation. Comet assay showed that both, GO and rGO, caused DNA strand breaks after 24 h of exposure; however, only rGO caused DNA damage after 72 h of exposure. The exposure to rGO was significantly more harmful to ZFL cells than GO, even at very low concentrations. The cells showed a high capacity to neutralize ROS induced by GO preventing genotoxic effects and metabolic activity, thus sustaining cell viability. The time of exposure had different impacts for both nanomaterials, GO caused more changes in 24 h showing recovery after 72 h, while cells exposed to rGO were jeopardized at both exposure times. These results indicate that the reduction of GO by removal of the oxygen functional groups (rGO) increased toxicity leading to adverse effects in the cells, even at very low concentrations.

Graphene oxide degradation by a white-rot fungus occurs in spite of lignin peroxidase inhibition

Article

Full-text available

Jan 2023

This study investigated the degradation of graphene oxide (GO) by the white-rot fungus Phanerochaete chrysosporium . Axenic fungal suspensions were inoculated in malt extract glucose medium enriched with various concentrations of...

Biodegradable Sensors: A Comprehensive Review

Article

Jul 2023

Graphene-based contrast agents for photoacoustic and thermoacoustic tomography

Article

Full-text available

Dec 2013

In this work, graphene nanoribbons and nanoplatelets were investigated as contrast agents for photoacoustic and thermoacoustic tomography (PAT and TAT). We show that oxidized single- and multi-walled graphene oxide nanoribbons (O-SWGNRs, O-MWGNRs) exhibit approximately 5–10 fold signal enhancement for PAT in comparison to blood at the wavelength of 755 nm, and approximately 10–28% signal enhancement for TAT in comparison to deionized (DI) water at 3 GHz. Oxidized graphite microparticles (O-GMPs) and exfoliated graphene oxide nanoplatelets (O-GNPs) show no significant signal enhancement for PAT, and approximately 12–29% signal enhancement for TAT. These results indicate that O-GNRs show promise as multi-modal PAT and TAT contrast agents, and that O-GNPs are suitable contrast agents for TAT.

Physicochemical characterization of a novel graphene-based magnetic resonance imaging contrast agent

Article

Full-text available

Aug 2013
INT J NANOMED

We report the synthesis and characterization of a novel carbon nanostructure-based magnetic resonance imaging contrast agent (MRI CA); graphene nanoplatelets intercalated with manganese (Mn(2+)) ions, functionalized with dextran (GNP-Dex); and the in vitro assessment of its essential preclinical physicochemical properties: osmolality, viscosity, partition coefficient, protein binding, thermostability, histamine release, and relaxivity. The results indicate that, at concentrations between 0.1 and 100.0 mg/mL, the GNP-Dex formulations are hydrophilic, highly soluble, and stable in deionized water, as well as iso-osmolar (upon addition of mannitol) and iso-viscous to blood. At potential steady-state equilibrium concentrations in blood (0.1-10.0 mg/mL), the thermostability, protein-binding, and histamine-release studies indicate that the GNP-Dex formulations are thermally stable (with no Mn(2+) ion dissociation), do not allow non-specific protein adsorption, and elicit negligible allergic response. The r 1 relaxivity of GNP-Dex was 92 mM(-1)s(-1) (per-Mn(2+) ion, 22 MHz proton Larmor frequency); ~20- to 30-fold greater than that of clinical gadolinium (Gd(3+))- and Mn(2+)-based MRI CAs. The results open avenues for preclinical in vivo safety and efficacy studies with GNP-Dex toward its development as a clinical MRI CA.

Two-Dimensional Nanostructure-Reinforced Biodegradable Polymeric Nanocomposites for Bone Tissue Engineering

Article

Full-text available

Feb 2013
BIOMACROMOLECULES

This study investigates the efficacy of two-dimensional (2D) carbon and inorganic nanostructures as reinforcing agents for cross-linked composites of the biodegradable and biocompatible polymer polypropylene fumarate (PPF) as a function of nanostructure concentration. PPF composites were reinforced using various 2D nanostructures: single- and multiwalled graphene oxide nanoribbons (SWGONRs, MWGONRs), graphene oxide nanoplatelets (GONPs), and molybdenum disulfide nanoplatelets (MSNPs) at 0.01-0.2 weight% concentrations. Cross-linked PPF was used as the baseline control, and PPF composites reinforced with single- or multiwalled carbon nanotubes (SWCNTs, MWCNTs) were used as positive controls. Compression and flexural testing show a significant enhancement (i.e., compressive modulus = 35-108%, compressive yield strength = 26-93%, flexural modulus = 15-53%, and flexural yield strength = 101-262% greater than the baseline control) in the mechanical properties of the 2D-reinforced PPF nanocomposites. MSNP nanocomposites consistently showed the highest values among the experimental or control groups in all the mechanical measurements. In general, the inorganic nanoparticle MSNP showed a better or equivalent mechanical reinforcement compared to carbon nanomaterials, and 2D nanostructures (GONPs, MSNPs) are better reinforcing agents compared to one-dimensional (1D) nanostructures (e.g., SWCNTs). The results also indicated that the extent of mechanical reinforcement is closely dependent on the nanostructure morphology and follows the trend nanoplatelets > nanoribbons > nanotubes. Transmission electron microscopy of the cross-linked nanocomposites indicated good dispersion of nanomaterials in the polymer matrix without the use of a surfactant. The sol-fraction analysis showed significant changes in the polymer cross-linking in the presence of MSNP (0.01-0.2 wt %) and higher loading concentrations of GONP and MWGONR (0.1-0.2 wt %). The analysis of surface area and aspect ratio of the nanostructures taken together with the above results indicated differences in nanostructure architecture (2D vs 1D nanostructures), and the chemical compositions (inorganic vs carbon nanostructures), number of functional groups, and structural defects for the 2D nanostructures may be key properties that affect the mechanical properties of 2D nanostructure-reinforced PPF nanocomposites and the reason for the enhanced mechanical properties compared to the controls.

Graphene for environmental and biological applications

Article

Jul 2012

The latest addition to the nanocarbon family, graphene, has been proclaimed to be the material of the century. Its peculiar band structure, extraordinary thermal and electronic conductance and room temperature quantum Hall effect have all been used for various applications in diverse fields ranging from catalysis to electronics. The difficulty to synthesize graphene in bulk quantities was a limiting factor of it being utilized in several fields. Advent of chemical processes and self-assembly approaches for the synthesis of graphene analogues have opened-up new avenues for graphene based materials. The high surface area and rich abundance of functional groups present make chemically synthesized graphene (generally known as graphene oxide (GO) and reduced graphene oxide (RGO) or chemically converted graphene) an attracting candidate in biotechnology and environmental remediation. By functionalizing graphene with specific molecules, the properties of graphene can be tuned to suite applications such as sensing, drug delivery or cellular imaging. Graphene with its high surface area can act as a good adsorbent for pollutant removal. Graphene either alone or in combination with other materials can be used for the degradation or removal of a large variety of contaminants through several methods. In this review some of the relevant efforts undertaken to utilize graphene in biology, sensing and water purification are described. Most recent efforts have been given precedence over older works, although certain specific important examples of the past are also mentioned.

Observation of Raman Band Shifting with Excitation Wavelength for Carbons and Graphites

Article

Jul 1981

The Raman spectra of crystalline graphite, graphite damaged by ion-etching, and structurally disordered pyrolytic and glassy carbons were examined as a function of excitation wavelength λ over the range 488.0 to 647.1 nm. The bands located at 1360, 2720 and 2950 cm 1 with λ = 488.0 nm undergo a progressive red-shift as λ increases, while the positions of the other major bands (1580 and 1620 cm 1) are invariant. The significance of these observations is briefly discussed.

Upconversion-P25-Graphene Composite as an Advanced Sunlight Driven Photocatalytic Hybrid Material

Article

May 2012
J MATER CHEM

Herein, a new nanocomposite consisting of up-conversion (UC) material (YF3:Yb3+,Tm3+), TiO2 (P25) and graphene (GR) has been prepared and shown to be an advanced sunlight activated photocatalyst. During the facile hydrothermal method, the reduction of graphene oxide and loading of YF3:Yb3+,Tm3+ and P25 were achieved simultaneously, and the functionalities of each part were integrated together. The as-prepared ternary UC–P25–GR nanocomposite photocatalyst exhibited great adsorptivity of dyes, a significantly extended light absorption range, efficient charge separation properties and superior durability. Indeed, the photocatalytic activity of this novel ternary nanocomposite under sunlight was improved compared with those of P25–GR nanocomposites and bare P25. Overall, this work could provide new insights into the fabrication of ternary composites as high performance photocatalysts and facilitate their application in environmental protection issues.

In vitro and in vivo behaviors of dextran functionalized graphene

Article

Oct 2011
CARBON

Development of biocompatible surface coating is critical to engineer various functional nanomaterials for biomedical applications. Here, we present a new surface chemistry of graphene by covalently conjugating graphene oxide (GO) with dextran (DEX), a biocompatible polymer widely used for surface coating of biomaterials. Compared with GO, the graphene–dextran (GO–DEX) conjugate shows reduced sheet sizes, increased thickness and significantly improved stability in physiological solutions. Cellular experiments uncover that DEX coating on GO offers remarkably reduced cell toxicity. We further label GO–DEX with a radioactive isotope, 125I, for in vivo tracking in animal studies. It is found that GO–DEX accumulates in the reticuloendothelial system (RES) including liver and spleen after intravenous injection, and importantly, shows obvious clearance from the mouse body within a week without causing noticeable short-term toxicity to the treated animals. Our results suggest that this DEX coating method on GO may potentially be useful to the further development of novel graphene-based bioconjugates for various biomedical applications.

Making Graphene Holey. Gold-Nanoparticle-Mediated Hydroxyl Radical Attack on Reduced Graphene Oxide

Article

May 2013
ACS NANO

Graphene oxide (GO) and reduced graphene oxide (RGO) have important applications in the development of new electrode and photocatalyst architectures. Gold nanoparticles (Au NP) are employed as catalyst to assist generation of hydroxyl radicals (OH•) in a UV-peroxide system and further promote the oxidation of RGO. The oxidation of RGO is marked by pores and wrinkles within the 2-D network. Nanosecond flash photolysis used in conjunction with competition kinetics to elucidate the oxidative mechanism and calculate rate constants for the Au NP-catalyzed and direct reaction between RGO and OH• radicals. Through Au NP-mediated oxidation reaction it is possible to tune the properties of RGO through the degree of oxidation and/or functional group selectivity in addition to the nanoporous and wrinkle facets. The ability of Au NP to catalyze the photolytic decomposition of H2O2 as well as the OH• radical-induced oxidation of RGO raises new issues concerning graphene stability in energy conversion and storage (photocatalysis, fuel cells, Li-ion batteries, etc). Understanding RGO oxidation by free radicals will aid in maintaining the long-term stability of RGO-based functional composites where intimate contact with radical species is inevitable.

Fabrication and Characterization of Three-Dimensional Macroscopic All-Carbon Scaffolds

Article