Characterization Techniques

Material characterization is a significant microscopic technique to provide the information of morphology, crystal structures, optical properties and elemental compositions. In the present research work, the formation of CMG-Ag nanocomposites was confirmed by UV-Vis spectra, and HRTEM analysed the surface morphology. The crystalline structure and elemental composition of samples were confirmed using XRD and XPS analyses, respectively while the molecular structure analyses of the samples depended on the peaks obtained from the spectrum of Raman analysis.

3.5.1 Ultraviolet-Visible (UV-Vis) Spectroscopy

UV-Vis absorption spectrophotometer confirmed the chemical change of nanosized materials by examining the shift in the wavelength of the intensity. Different molecules were involved with different absorption wavelength. The optical absorption properties in the spectral region of 200–800 nm was evaluated using Thermoscientific Evolution

300 UV-vis absorption spectrophotometer. The absorption spectroscopy served as a preliminary study to confirm the formation of Ag NPs based on the appearance of

characteristic surface plasmon resonance (SPR) band at ~400 nm. Throughout the measurement, the molecules of each sample underwent electronic transition under the excitation of the electromagnetic spectrum. The absorption spectrum measurement reflected the transition from the lower to the excited state that produced an absorbance spectrum via software which displayed on the monitor.

3.5.2 High Resolution Transmission Electron Microscopy (HRTEM)

The HRTEM technique studied the interaction of energetic electrons with the sample and provided morphological, compositional and crystallographic information. The technique provided high-resolution images and enabled more magnification, thus allowing for direct imaging of the atomic structure of the sample compared to SEM. High-resolution transmission electron microscope functioned on the principle of electron diffraction and used both the transmitted and the scattered beams to create an interference image. It is a phase contrast image and can be as small as the unit cell of a crystal. The analysis accurately confirmed the formation of nanocomposites in the sample.

This research study used JEM-2100F-HRTEM for analyzing the morphology, compositional, crystal structure and lattice imperfections on an atomic resolution of CMG-Ag nanocomposite. Prior to sample analysis, the prepared nanocomposite samples are homogeneously dispersed by sonication for 30 minutes, followed by drop- casting onto the carbon-coated copper grid and afterwards dried at room temperature. The thickness of the specimen must be tremendously thin (<10 nm) to get the highest resolution and relatively beam insensitive.

3.5.3 X-Ray Diffraction (XRD)

X-Ray Diffraction is a non-destructive analytical technique which can yield the unique fingerprint of Bragg reflections associated with a crystal structure. It is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. By scanning the sample through a range of 2θ angles, all possible diffraction directions of the lattice would be attained, thus providing a unique “fingerprint” of different phases due to the random orientation of the material/sample. From the “fingerprint,” we can construe the peaks value by

comparing them to the standard reference pattern. The as-prepared GO and CMG-Ag nanocomposite was placed in a holder, and the XRD characterization was performed using a Siemens D5000 XRD Diffractometer. The diffraction patterns were collected using a fixed wavelength of CuKα radiation (λ = 1.4506 Å) by employing a scanning

rate of 0.033°s-1 over the 2θ range of 5o to 80o in 0.1o or 0.05o intervals.

3.5.4 Raman Spectroscopy

Raman spectroscopy is a spectroscopic technique based on inelastic scattering of monochromatic light, and it provides information about molecular vibrations useful for

sample identification and quantitation.The technique involves shining a monochromatic

light source, usually from a laser source on a sample and detecting the scattered light. This spectroscopy is a useful technique for characterization of graphene. In this research study, the prepared GO and CMG-Ag nanocomposites were characterized using Renishaw inVia Raman microscope system excited with 514 nm (green laser).

Measurements scanning were from wavenumber 100 to 2000 cm-1. It is important to

note that selection of a wrong laser power may cause the destruction of the sample.

3.5.5 X-ray Photoelectron Spectroscopy (XPS)

X-ray Photoelectron Spectroscopy is the most widely used surface analysis technique for analyzing the surface chemistry of material. It functions on a broad range of materials and measures the elemental composition, empirical formula, chemical state and electronic state of the elements within a material. A photoelectron spectrum recording counts the ejected electrons over a range of electron kinetic energies and peaks that appear in the spectrum from atoms emitting electrons of a characteristic energy. The energies and intensities of the photoelectron peaks provide identification and quantification of all surface elements (except hydrogen). In this research study, XPS

measurements were performed using synchrotron radiation from beamline no. 3.2 at the Synchrotron Light Research Institute, Thailand.

3.5.6 Fourier Transform Infrared Spectroscopy (FT-IR)

Fourier Transform Infrared spectroscopy is an important technique in organic and inorganic chemistry which identifies chemical bonds in a molecule by creating an infrared absorption spectrum. The spectrum produces a profile of the sample and a distinctive molecular fingerprint which can be used to screen and scan samples for many different components. This technique is useful for identifying the chemical bonds on the surface of graphene oxide. When graphite flakes oxidized due to strong oxidizing agents, the carbon atom’s layer of graphite is decorated by oxygen-containing groups. FTIR spectroscopy can identify these oxygen-containing groups. In this research study, FTIR spectroscopy analysis of GO was conducted using a Fourier transform infrared

spectrometer (FTIR; Perkin Elmer System 2000 series spectrophotometer, USA). A small drop of GO was placed on one of the Potassium bromide (KBr) plates. The

second plate was placed on top of that and a quarter turn was made to obtain a nice even film. The plate was then placed into the sample holder and the spectrum was observed.