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24 Biosynthesis of Nanoparticles Using Agriculture and Horticulture Waste

24.4.2

Fourier-Transform Infrared Spectroscopy (FTIR)

The extract obtained from the agriculture and horticulture waste contains func-

tional groups taking part in the reduction process and capped on the surface of

synthesized nanoparticles. In order to identify these functional groups present in

the relevant extract and on the surface of nanoparticles, Fourier-transform infrared

spectroscopy (FTIR) analysis is carried out. The mid infrared spectrum is divided

into four regions in the absorption verses wave number data. The wave number

2500–4000 cm⁻¹ corresponds to the single bond region, 2000–2500 cm⁻¹ to triple

bond region, 1500–2000 cm⁻¹ to double region, and 600–1500 cm⁻¹ to finger print

region, respectively [14].

24.4.3

Dynamic Light Scattering (DLS) and Zeta Potential

Size distribution of the nanoparticles in colloidal suspension is measured based on

its Brownian motion using dynamic light scattering (DLS) technique. The measure-

ments are recorded by maintaining uniform temperature. The technique is noninva-

sive in nature. DLS measures the hydrodynamic diameter of the particle and relates

to diffused light particles scattered in the carrier fluid. The fluctuations in scattered

light intensity are measured with respect to time. Fluctuations in intensity arise due

to the random Brownian motion of the nanoparticle. Larger particles diffuse more

slowly than small particles, wherein particle size can be related to the measured

fluctuation in light scattering intensity.

The stability of the colloidal nanoparticles is decided based on the zeta potential

measurement. The colloidal particles suspended in the solution are electrically

charged due to the dipolar characteristics and ionic attributes. This leads to net

electric charges at the surface of nanoparticles that causes the accumulation of

counter ions (opposite charges) around them to form an electrical double layer.

The ion with a set of counter ions forms a fixed part of the double layer. Under the

applied electric field, the particles are attracted toward electrodes depending on

their polarity. The potential at which the fixed part of the double layer along with

a part of the mobile layer move toward an electrode is termed as zeta potential.

The particle in solution with large positive or negative zeta values will repel each

other. However, with low zeta values, there is no force to prevent the nanoparticles

from coagulation. Greater the zeta value, greater will be the stability, wherein the

threshold zeta potential value is ±30 mV.

24.4.4

Scanning Electron Microscope (SEM) and Transmission Electron

Microscope (TEM) with Energy-Dispersive X-ray (EDX)

To determine the shape and size of the nanoparticles, scanning electron microscope

(SEM) and transmission electron microscope (TEM) are considered to be most suit-

able. Both methods adopt different principles of working. The resolution of SEM and

TEM is less than 5 and 1 nm, respectively. Generally, SEM is suitable for the analysis.

TEM is recommended prior to proceeding with a critical step in research.