Chapter 8

CARBON NANOMATERIALS (CNM)FROM Euglena tuba AND STUDY OFITS ANTIOXIDANT ACTIVITY

CARBON NANOMATERIALS (CNM) FROM Euglena tuba ANDSTUDY OF ITS ANTIOXIDANT ACTIVITY

Nanostructured materials have been the subject of intense scientific research due to their

characteristic properties that are distinctly different from their bulk counterparts (Weller,

1993). The report from Royal Society and The Royal Academy of Engineering, UK,

defined nanoscience and nano technology as Nanoscience is the study of phenomena and

manipulation of materials at atomic, molecular and macro molecular scales, where

property differs significantly from those at a larger scale (The Royal Acad. of Engg.,

2004).

Design, characterization, production and application of structures, devices and systems

by controlling shape and size on the nano scale is an attractive option for current research

(Pitkethly,2004; Holister and Harper, 2002; Jones and Mitchell, 2001; Rittner, 2001). A

vast body of knowledge of synthesis, physical and chemical properties has been

accumulated and is thoroughly reviewed (Shen et al., 2006; Wang and Xie, 2006; Wang

et al., 2006). Their technological potentials apart, such materials are also interesting

systems for basic scientific investigation. The combination of low dimensionality and the

contribution from the surface area are responsible for the unique properties of

nanomaterials. Though physical methods are quite extensively used, chemical synthesis

mechanisms over other methods are preferred owing to enhanced chemical homogeneity.

It offers mixing at molecular level and is thus considered to be versatile tool for

nanomaterial synthesis. Chemical methods are by and large less expensive and easy to

scale up. Template based approaches for nano-material synthesis are also quite popular

(Hung and Whang, 2003; Li et al., 2004). Sol-gel process is another commonly adopted

strategy of synthesis of such materials (Deng and Chen, 2004). Hydrothermal process in

another promising preparative method and ensures better morphology control of the

resultant products by carefully selecting appropriate reaction environment, precursor,

reducing and coordinating agents and reaction time(Cao et al., 2003).

Nanomaterials of different dimensions have many applications, e.g., 1-10nm particles are

ideal in tunneling effect, molecular recognition, catalysis whereas in superconductivity

studies, 0.1-100nm particles are of interest (Murday, 2002).

Discovery of fullerene by Smalley, Kroto and coworkers in 1985, a new form of nano

sized carbon, led to the Nobel Prize in Chemistry in 1997. Besides diamond, graphite and

C60, quasi one-dimensional nanotube is another form of carbon first reported by Ijima in

1991 when he discovered multi-walled carbon nano tubes (MWCNT) and later single-

walled carbon nano tubes (SWCNTs) (Pitkethly, 2004). Since then, nanotubes have

captured the attention of researchers worldwide. Various methods of preparing carbon

nano tubes includes

Electric Arc Discharge Method(EAD)

Laser Ablation Method(LA)

Chemical Vapour Deposition Method(CVD)

In the present work CVD technique for synthesis of carbon nanomaterial(CNM) were

adopted. CVD method was developed by Cheng et al (1998) using hydrocarbons as

precursor. Using the same technique in gas phase, Smalley’ group made SWNT by using

carbon monoxide as a source of carbon. Carbon nanomaterials are at the verge of creating

a revolution in all fields like pharmaceuticals, agriculture, medicinal, transport, fast

moving consumer goods (FMCG) products etc. (Yang et al., 2020; Semete et al., 2010;

Sharon and Sharon, 2006). In general, organic chemicals like acetylene, methane,

benzene, cyclohexane etc are used as precursor for the synthesis of CNM . Apart from

being expensive, all of these precursors are related to fossil fuels that are nonrenewable.

Thus, there is a global search for alternative sources like plants that provide numerous

fibrous materials, seeds and oils which could be a potential source for commercial access

to nanomaterials (Xie et al., 2009; Myers et al., 2000). Different parts of plants or whole

of it as precursors can be directly employed in Chemical Vapour Deposition (CVD)

technique as the plant materials contain various metals and that may act as a catalyst (Xie

et al., 2009; Ebbesen and Ajayan, 1992). Moreover, plant tissues contain different types

of oils, lipids, carbohydrates, cellulose, lignin etc. which are rich source of carbon

rendering them excellent raw material for CNM synthesis (Kumar and Ando, 2008).

These substances may play specific role in synthesis of some unique useful carbon nano

materials. Pyrolysis of plant derived materials in open air/inert atmosphere lead to some

very interesting porous or channel like structures (Heinlann et al., 2008). It is almost

certain that CVD technique would be most suitable for the production of large quantity of

CNM and is being explored by many research groups for the synthesis of CNM as it is

truly a low-cost and scalable technique for mass production of CNT (Xie et al., 2009).

Of the large number of varieties of nano forms of carbon, carbon nano tubes (CNT,

SWCNT, MWCNT) have emerged as an important material in nanoscale science (Biro et

al., 2005). Antioxidant activity of carbon nano materials, among other biological

applications, are receiving lot of current attention (Zhang et al., 2005).

Different methods employ atomistic, molecular, chemical and particulate processing in

vacuum or liquid medium (Daniel & Astruc, 2004), however, such techniques are

expensive and energetically not viable. . Synthetic approaches that relies on minimal

environmental and human health risks offer clean, nontoxic, and environmentally benign

synthetic protocol. Previous studies utilised biomolecules (proteins, amino acids,

carbohydrates, and sugars etc.) and different types of whole cell microorganisms or plant

parts (roots,leaves, flowers, bark powders, seeds, roots, and fruits)for the synthesis of

metal nanoparticles (Semete et al., 2010; Sharon et al, 2006; Che et al., 1998; Xie, 2009;

Myers, 2000). Plant species are important source of phytochemicals that are

environmentally benign reservoirs for the production of nanoparticles.

Micrcroorganisms such as bacteria, fungi and algae, also serve as eco-friendly nano-

factories for the biosynthesis of metal nanoparticles. Laminaria japonica, a brown macro

algae is documented for their role in food, medicine, industries (Kumar and Ando, 2008;

Ebbesen and Ajayan, 1992). Rich in biologically active compounds, such as

polysaccharides (alginate, laminaran, fucoidan), polyphenols, carotenoids, fiber, protein,

vitamins,and minerals(Samant et al., 2007; Afolabi et al., 2007; Zhang et al., 2005) such

species can serve both as effective metal-reducing agents and as capping agents coating

the metal nanoparticle surface in a single step. Biological approaches to nanoparticle

synthesis are thus beginning to be appreciated as viable alternatives to the existing

physical and chemical methods (Shen et al. 2006; Tessonnier, 2011).

Algae primarily comprises of proteins, carbohydrates, fats and nucleic acids in varying

proportions. Their cell walls are largely made up of polysaccharides, which can be

hydrolyzed to sugar. Being a whole cell organism the composition of an alga is generally

much more uniform and consistent than biomass from terrestrial plants, because algae

lack specific functional parts such as roots and leaves.

In addition to synthesis, carbon nanomaterials, CNT and / or CNFs as macromolecular

scaffolds are considered to behave as radical traps in chain reaction( Zeynalov &

Friedrich, 2008).Their significance as biosensors, diagnostic tools, drugs, and

therapeautics have triggered intense current research on synthesis and application of

carbon nanomaterials ( Tessonnier, 2011)

In light of the aforementioned discussion and potential significance of these materials,

synthesis and characterization of carbon nanomaterials from Euglena biomass using CVD

technique and assessment of antioxidant activity of the CNM constituted the primary

goal of this chapter.

8.2 Material and Methods

8.2.1 Protocol for synthesis of carbon nanomaterials from Euglena algae

The synthesis of CNMs from Euglena biomass was carried out in a CVD furnace. The

process involved pyrolytic degradation of the mass at suitable temperature in oxygen free

atmosphere.

A quartz boat loaded with 10g of dry algal biomass (also known as CVD precursor) was

taken inside the horizontal quartz tube (1m long with an inner diameter of 25 mm), which

was mounted inside a reaction furnace (300 mm long). The outer part of the quartz tube

was attached with a water bubbler. The reaction parameters such as argon flow,

temperature and duration of heating were set as per the requirement. In a typical

experiment, the horizontal quartz tube containing quartz boats was first flushed with Ar

gas in order to eliminate air from the tube. Then the gas was allowed to flow with a flow

rate of 6ml/min. Furnace was then switched on to attain the set temperature of 9000C at

the rate of 70C/min. When the desired temperature is reached, furnace was left on for a

set time of 2 hours and then allowed to cool. After cooling the furnace, carbon materials

were taken out and powdered and then purified by heating at 4000C in an muffle furnace

for half an hour to remove the amorphous carbon from the synthesised material and yield

was recorded.

The schematic representation of the synthetic strategy:

Precursor (algae)

CVD 9000 C, 2 h

(Ar atm)

Carbon Nanomaterials (CNMs)

4000 C

30 min

Nanoflakes

8.2.1 Synthetic method for carbon nanomaterials

Carbon nanomaterials(CNMs) synthetic methods have gone through a great evolution

since the first discovery of CNTs by Iijima in 1991. In general, there are three major

routes such as Electric-Arc-Discharge (EAD), Laser Ablation (LA) and Chemical Vapour

Deposition (CVD) methods are used for the synthesis of CNMs. The CVD method is

believed as the most suitable carbon nanomaterial synthetic method in terms of product

purity and large scale production

The CVD method is believed to be the most suitable carbon nanomaterials synthesis in

terms of product purity and large scale production. Compared to arc-discharge and laser

methods, this method is simple and economic for synthesizing CNMs at low temperature

and ambient pressure. CVD allows the experimenter to avoid the process of separating

nanomaterials of particular morphology from the carbonaceous particulate that often

accompanies the other two methods of synthesis. Excellent alignment, as well as

positional control on the nanometer scale, can be achieved by the use of CVD. Control

over the diameter, as well as the growth rate of the nanomaterials can also be maintained.

In a typical CVD process, a mixture of gases passing over a hot surface undergoes

chemical reactions which lead to solid deposit on the surface. It is a complex

phenomenon and is extremely versatile. Small changes in the experimental parameters

cause a drastic change in the results and hence lead to different branches of CVD.There

are different branches of CVD are Thermal CVD, plasma assisted CVD, Atmospheric

pressure CVD (APCVD), Low-pressure CVD (LPCVD), Laser Chemical Vapour

Deposition (LCVD), Photochemical Vapour Deposition (PCVD), Metal-Organic

Chemical Vapour Deposition (MOCVD) etc., The CVD is so rich and versatile because

of its adaptability to new technologies. Virtually, it is a homemade recipe that offers

creativity and credibility. The present synthesis of CNM is conducted with the help of

thermal CVD.

8.3.2 CVD Setup

A thermal chemical vapour deposition unit and its different accessories are is shown in

Fig 8.1

Fig. 8.1: A schematic diagram of CVD apparatus

A thermal CVD apparatus consists of several basic components as detailed below.

Gas delivery system – For the supply of precursors to the reactor chamber.

Reactor chamber – Chamber within which deposition takes place.

Substrate loading mechanism – A system for introducing and removing substrates,

mandrels etc

Energy source – Provide the energy/heat that is required to get the precursors to

react/decompose.

Vacuum system – A system for removal of all other gaseous species other than those

required for the reaction/deposition.

Exhaust system – System for removal of volatile by-products from the reaction

chamber.

Exhaust treatment systems – In some instances, exhaust gases may not be suitable for

release into the atmosphere and may require treatment or conversion to safe/harmless

compounds.

Process control equipment – Gauges, controls etc to monitor process parameters such

as pressure, temperature and time. Alarms and safety devices would also be included

in this category.

Fig.8.2.: A typical thermal CVD apparatus used for the synthesis of CNM

8.3.3 CVD parameters

A CVD reaction is almost always a heterogeneous process. The nature of the chemical

reaction taking place depends on the nature of the raw materials that liberates the CVD

precursor. CVD reactions are strongly affected by the experimental parameters, such as

reactor temperature, pressure, precursor composition and concentration and flow rate.

The reactor geometry is also an important parameter. Various forms of CNMs are

obtained depending on the catalyst, temperature, carrier gas and raw material used.

However, the main parameters for CNM growth are carbon precursor (raw materials),

catalyst, support materials and growth temperature. These parameters are needed to be

carefully optimized on a particular experimental set up. With proper optimization of all

the parameters, CNM can be grown in a variety of forms, such as, powder, thick or thin

films, straight or coiled, aligned or entangled, or a desired architecture of nanomaterials

on predefined sites of a patterned substrate.

8.3.4 Carbon Precursor

The precursor for carbon nanotubes is fed into the system in the gaseous state at some

specific conditions. To avoid oxidation of the carbon, the chamber is kept free of oxygen

during the production process. Generally continuous inert gas flow is supplied to the

reaction chamber. Nitrogen and argon are the most extensively used inert gases.

Sometimes inert gas is changed with hydrogen gas to reduce the oxygen content in the

reaction environment. Precursors obtained from fossil fuel and petroleum products have

been mostly used for this purpose. Generally, hydrocarbon is catalytically decomposed

to liberate carbon atoms and that constitute CNMs. A plenty of hydrocarbons (methane,

ethane, ethylene, acetylene, benzene, xylene etc.) have been used as a carbon source for

growing CNMs. However some other raw materials such as carbon monoxide, ethanol,

camphor, naphthalene, turpentine oil, kerosene, ferrocene have also been successful in

producing CNMs. Hence it is believed that any carbon containing material can produce

CNMs, though the optimum experimental conditions (temperature, pressure, catalyst etc.)

are quite different for different starting materials. Since CVD is a vapour phase reaction,

it is the vapour pressure of the raw materials that dictates the deposition conditions which

need to be carefully optimized. Very recently, the attempts were successful in

synthesizing CNTs from plant derived precursors by CVD. The plant derived precursors

can yield CNM of similar and sometime even better quality than one would normally get

by using fossil fuel material and products derived from petroleum product.[r] The

advantage of using plant-derived precursors is that unlike fossil fuel they can be

cultivated in required quantity as and when needed without any fear of depletion. In the

present work, Euglena algal biomass is used as the precursor for carbon nanomaterial.

8.3.5 Temperature

In thermal CVD, carbon nanomaterials especially carbon nanotubes can be grown in a

limited temperature range. Generally, the growth temperature is between 5500C and

12000C, and the reaction temperature may vary according to the catalyst-support material

pair. General experience is that low temperature CVD yields multiwalled carbon

nanotubes(MWNTs,) nano beads spheres whereas higher temperature reaction favours

singlewalled carbon nanotubes(SWNT) growth indicating that the latter have a higher

energy of formation. The reaction temperature also plays an important role in the

alignment properties and diameter of the synthesized nanomaterials. Within the

temperature range of 600-9000C, diameter distribution of MWNTs increases with the

increasing temperature. The lower is the CVD temperature the narrower is the diameter

distribution.

The lower temperatures also result in lower yield of carbon nanomaterials. At low growth

temperatures, only a carbon layer is formed on the graphite fiber surface whereas at high

temperatures, the diffusion rate of catalyst particles into carbon fibers was enhanced and

the nanomaterials growth possibility reduced. In the present experiment, the

temperature is maintained at 9000C.

8.3.6 Catalyst

Most of CNM synthesis techniques require the introduction of catalyst in the form of gas

particulates or as a solid support. The selection of a metallic catalyst may affect the

growth and morphology of the nanomaterials. Generally, transition metals are catalyst of

choice for the CNM growth as the phase diagram of carbon and metals suggests finite

solubility of carbon in transition metals at high temperature. Solid organo metallocenes

are widely used catalyst because they liberate metal particles in – situ that efficiently

catalyses CNM growth. It is experienced that the catalyst particle- size dictates that tube

diameter.

The studies on catalytic effects of several coatings with M(NO3)n. mH2O, where M = Al,

Mg, Mn, Cu, Zn, Fe, Co, and Ni, in terms of yield of nanotube formation showed that the

yield significantly depends on M and this can be explained in terms of reducing tendency

of the catalyst and their relative sizes. The work on the effect of selected catalysts

(nickel, iron and cobalt) on the synthesis of CNMs revealed that the rate of respective

nanotube growth is dependent on the catalyst type in the order of Ni >Co > Fe. The

widely used catalyst materials are cobalt, iron titanium, nickel, a couple of zeolites and

combinations of these metals and/or oxides. The metal nano particles of controlled size

are also used to grow CNMs of controlled diameter. In the present work, no external

catalyst was used as the plant precursor contains different inorganic materials that might

have catalysed the carbon nanomaterial formation.

A little change in the experimental parameters such as temperature and catalyst leads to

different morphologies of CNM derived from the same precursor. For example, methane

on chemical vapour deposition at 5500C in presence of catalyst NiO supported on SiO2

yields carbon nano fibres whose outer diameter distributed in the wide range from 10 –

100 nm and their hollow cores were completely filled while the CNMs grown on

CoO/SiO2 catalyst exhibited hollow cores. The diameters of the CNMs produced over

CoO/SiO2 catalyst were quite uniform i.e. the outer diameters were within 10 - 45 nm.

The diameter CNMs are further decreased on changing the support of the catalyst and

reaction temperature. The pyrolytic temperature and duration were prefixed and self

catalyzing property of the precursor ensured the desired product.

8.3.7 Characterization of synthesized carbon nanomaterials

SEM Analysis

Scanning Electron Micrographs were obtained on a JEOL, JSM 6360 scanning electron

microscope (SEM) at SAIF, NEHU, Shillong.

The scanning electron microscope (SEM) uses a focused beam of high-energy electrons

to generate a variety of signals at the surface of solid specimens. The signals that derive

from electron-sample interactions reveal information about the sample including external

morphology, chemical composition and crystalline structure and orientation of materials

making up the sample. In most applications, data are collected over a selected area of the

surface of the sample, and a 2-dimensional image is generated that displays spatial

variations in these properties. Areas ranging from approximately 1 cm to 5 microns in

width can be imaged in a scanning mode using conventional SEM techniques

(magnification ranging from 20X to approximately 30,000X, spatial resolution of 50 to

100 nm). The SEM is also capable of performing analyses of selected point locations on

the sample; this approach is especially useful in qualitatively or semi-quantitatively

determining chemical compositions using EDS (Energy Dispersive Spectra).

Principle of Scanning Electron Microscopy (SEM)

Accelerated electrons in an SEM carry significant amounts of kinetic energy, and this

energy is dissipated as a variety of signals produced by electron-sample interactions when

the incident electrons are decelerated in the solid sample. These signals include

secondary electrons that produce SEM images and heat. Secondary electrons and

backscattered electrons are commonly used for imaging samples: secondary electrons are

most valuable for showing morphology. SEM analysis is considered to be "non-

destructive"; that is, X-rays generated by electron interactions do not lead to volume loss

of the sample, so it is possible to analyze the same materials repeatedly.

Fig.8.3: Schematic diagram of Scanning Electron Microscope (SEM).

Essential components of Scanning electron Microscope include the following:

Electron gun

Magnetic lens & scanning lens

Vacuum chamber (Sample chamber)

Detectors & image recorders

Sample Preparation in SEM

Sample preparation can be minimal or elaborate for SEM analysis, depending on the

nature of the samples and the data required. Minimal preparation includes acquisition of a

sample that will fit into the SEM chamber and some accommodation to prevent charge

build-up on electrically insulating samples. Most electrically insulating samples are

coated with a thin layer of conducting material, commonly carbon, gold, or some other

metal or alloy. The choice of material for conductive coatings depends on the data to be

acquired: carbon is most desirable if elemental analysis is a priority, while metal coatings

are most effective for high resolution electron imaging applications. Alternatively, an

electrically insulating sample can be examined without a conductive coating in an

instrument capable of "low vacuum" operation. In our case, the sample to be examined is

allowed to adhere over the sample holder with the help of doubled sided tape. To make

the sample conductive it is coated with a thin film of gold with the help of fine coat ion

sputter.

TEM Analysis

Transmission electron microscopy images were obtained on a JEOL, 9JSM-100CX

transmission electron microscope (TEM) with an accelerating voltage of 100kV. The

sample powders were dispersed in ethanol, under sonication and TEM grids were

prepared using a few of the dispersion followed by drying in air.

Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of

electrons is transmitted through an ultra thin specimen, interacting with the specimen as it

passes through. An image is formed from the interaction of the electrons transmitted

through the specimen; the image is magnified and focused onto an imaging device, such

as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such

as a CCD camera.

TEMs are capable of imaging at a significantly higher resolution than light microscopes,

owing to the small de Broglie wavelength of electrons. This enables the instrument's user

to examine fine detail—even as small as a single column of atoms, which is tens of

thousands times smaller than the smallest resolvable object in a light microscope. TEM

forms a major analysis method in a range of scientific fields, in both physical and

biological sciences. TEMs find application in cancer research, virology, materials science

as well as pollution, nanotechnology, and semiconductor research.

At smaller magnifications TEM image contrast is due to absorption of electrons in the

material, due to the thickness and composition of the material. At higher magnifications

complex wave interactions modulate the intensity of the image, requiring expert analysis

of observed images. Alternate modes of use allow for the TEM to observe modulations in

chemical identity, crystal orientation, electronic structure and sample induced electron

phase shift as well as the regular absorption based imaging.The first TEM was built by

Max Knoll and Ernst Ruska in 1931, and later the same group developed the first

commercial TEM in 1939. .

Fig.8.4: Schematic diagram of Transmission Electron Microscope (TEM).

Sample preparation in TEM

Sample preparation in TEM can be a complex procedure. TEM specimens are required to

be at most hundreds of nanometers thick. High quality samples will have a thickness that

is comparable to the mean free path of the electrons that travel through the samples,

which may be only a few tens of nanometers. Preparation of TEM specimens is specific

to the material under analysis and the desired information to obtain from the specimen.

As such, many generic techniques have been used for the preparation of the required thin

sections.

Materials that have dimensions small enough to be electron transparent, such as powders

or nanotubes, can be quickly prepared by the deposition of a dilute sample containing the

specimen onto support grids or films. In material science and metallurgy the specimens

tend to be naturally resistant to vacuum, but still must be prepared as a thin foil, or etched

so some portion of the specimen is thin enough for the beam to penetrate. Constraints on

the thickness of the material may be limited by the scattering cross-section of the atoms

from which the material is comprised.

Results and Discussion

The yield of the synthesized carbon nanomaterials was recorded to be 30%. The materials

are black and air and moisture stable. The tapping density of the material is found to be

0.35 g/cm3. The physical characteristics of the synthesized carbon nanomaterials are

given in the Table 8.1.

Table 8.1: Reaction profile and physical characteristics

Precursor Reaction Profile Yield Density Appearance

Pyrolysis Temp(0C) Time

(hr)

Flow Gas % g/cm3

Euglena tuba 900 2 Ar 30 0.35 Black

fibrous

Scanning Electron Microscopic (SEM) Studies

The external morphology of the synthesized materials was investigated through the SEM

studies. The carbon from Green algae (Euglena tuba) indicates cluster of particles of

different dimension and orientation. The average particle size is observed to be in the

range of 50-100 nm. (Plate 8.1).

Transmission Electron Microscopic (TEM) Studies

The morphology and internal structure of the synthesized materials were investigated

through the TEM studies. The High resolution transmission electron micrograph

(HRTEM) shows particle size as well as the lattice spacing of the materials (Plate 8.2).

TEM image of the nanomaterial obtained from Euglina tuba clearly shows the

nanoflakes consisted of rhombohedral and spherical shaped paricles with average size

in the range of 40 to 50 nm. The HRTEM image shows the lattice spacing to be ~

0.2nm which is corresponds to graphitic nature of the material. The SAED pattern shows

a set of spots instead of rings due to the random orientation of the nanoparticles (Plate

8.3).

Antioxidant activity of the synthesized Carbon Nanomaterials

8.2.2 Antioxidant activity:

UV-Vis spectrometer (Shimadzu 1800 PC) was used to determine the variation in DPPH

concentrations photometrically at 517nm. Since carbon nanomaterials, are insoluble in

methanol, a modified DPPH method for insoluble materials as reported by Serpen et al.,

2009 was used to determine antioxidant activities of the synthesized carbon nano

materials

One of the important and basic studies in molecular biology and biotechnology is the

study of antioxidant potency of different materials and compounds. The antioxidants

play a signi during

the biological processes. The study of antioxidant property gives an insight about the

behavior and interaction of these materials with biomolecules inside a living system.

The antioxidant behaviour of the synthesized materials was studied with the help of

DPPH scavenging. The carbon nanomaterials obtained from Euglena tuba has shown

profound antioxidant activity.

Free radical scavenging assay

Carbon nanomaterial + DPPH

(2, 4, 6, 8, 10, 15 and 20 mg) (3 ml, 100 µm)

Sonication, Centrifugation

Absorbances were measured at 517 nm at an interval of 15, 30, 45 and 60 mins with a

UV-vis spectrophotometer.

The scavenging percentage was calculated using the formula:

DPPH scavenging (%)Ac As

AcX 100

where, Ac and As are absorbance of DPPH (control) and DPPH with nanomaterial at 517

nm, respectively. The SC-50 (the scavenging concentration needed to scavenge 50% of

DPPH) value was calculated graphically.

It has been found that with increase in concentration of nanomaterials there was an

increase in DPPH scavenging. The observed antioxidant property might be due to the

neutralization of free radical character of DPPH• that ocurred by the transfer of an

electron between the reactants.

The carbon nanomaterial from Euglena tuba showed pronounced antioxidant property at

SC-50 concentration of 15.13 mg.

SC50=15.13 mg

Fig.8.6: Time dependent UV-vis absorbance of the carbon nanoflakes

Conclusion

Carbon nano flakes consisting of spheres and rhombohedrals were obtained by pyrolysis

of algae, an unconventional inexpensive natural precursor, as a carbon source. The

dimension of the carbon nanoflakes are in the range 50-100 nm. These materials could

provide an inexpensive ecofriendly renewable alternative resource for carbon nanotubes

in their different mechanical and biochemical properties. The carbon nanomaterials

(CNM) from Euglena tuba shows a pronounced antioxidant property at SC-50 value of

15.13 mg. Carbon nanomaterials (CNM) are used mainly in advanced composite

materials to improve strength, stiffness, durability, electrical conductivity, or heat

resistance CNM production cost are substantially less than carbon nanotubes (CNT) and

therefore offer significant advantages over nanotubes for certain applications, providing a

high performance to cost ratio.

0 20 40 60 80 100

40

50

60

70

80

90

100

Sample weight (mg)

15.13mg

Plate 8.1: SEM micrographs of carbon nanomaterials from Euglena tuba at

different magnifications (a & b)

Plate 8.2: TEM image of the carbon nanomaterial obtained from Euglena tuba atdifferent magnification (a, b & c)

Plate 8.3: High Resolution TEM and Selected Area Electron diffraction (SAED)

pattern of carbon nanomaterial from Euglena tuba

Sample weight=10mg Sample weight=20mg

Sample weight=30mg Sample weight=50mg

Sample weight=10mg

Sample weight=70 mg Sample weight=100 mg

Fig. 8.5: Time dependent UV-vis spectra of the nanoflakes obtained Euglena

tuba at different weight of the sample.

400 450 500 550 600

-0.2

0.0

0.2

0.4

0.6

Wavelength (nm)

Control15 mins30 mins45 mins60 mins

400 450 500 550 600

-0.2

0.0

0.2

0.4

0.6Control15 mins30 mins45 mins60 mins

Wavelength (nm)

400 450 500 550 600

-0.2

0.0

0.2

0.4

0.6Control15 mins30 mins45 mins60 mins

Wavelength (nm)400 450 500 550 600

-0.2

0.0

0.2

0.4

0.6Control15 mins30 mins45 mins60 mins

Wavelength (nm)

400 450 500 550 600

-0.2

0.0

0.2

0.4

0.6Control15 mins30 mins45 mins60 mins

Wavelength (nm)400 450 500 550 600

-0.2

0.0

0.2

0.4

0.6Control15 mins30 mins45 mins60 mins

Wavelength (nm)