A Guide to the Characterization of Nanoparticles: Key Techniques

A Guide to the Characterization of Nanoparticles: Key Techniques

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Introduction

Creating nanoparticles through innovative methods like green synthesis is just the first step. To ensure these particles are effective and safe for medical or industrial use, scientists must perform a rigorous analysis to understand their properties. This process is known as the characterization of nanoparticles.

This research excerpt provides a detailed look into the essential analytical techniques used to confirm the synthesis, determine the size and shape, and identify the composition of gold and silver nanoparticles, ensuring they meet the required standards for advanced applications.

Original Excerpt: A Deep Dive into Nanoparticle Analysis

Why the Characterization of Nanoparticles is Crucial

Nanoparticles can be characterized using various techniques including UV-vis spectrophotometric analysis, XRD, SEM, and FTIR. This multi-step characterization of nanoparticles is essential for validating their synthesis and understanding their physical and chemical properties.

UV-vis spectrophotometric analysis detects the synthesis of NPs due to the Surface Plasmon Resonance (SPR) characteristics of NPs. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) give information about nanocrystallite size and shape.

Finally, Fourier Transformed Infrared Spectroscopy (FTIR) identifies the molecules involved in the reduction of metal to synthesize the nanoparticles.

Techniques for the Characterization of Nanoparticles

UV-vis Spectrophotometric Analysis: The First Confirmation

The synthesis of gold (AuNPs) and silver (AgNPs) nanoparticles was first monitored and confirmed visually by a color change in the solution, then verified with UV-vis spectrophotometric analysis. This technique is fundamental to the characterization of nanoparticles.

• Surface Plasmon Resonance (SPR): Free electrons present in AuNPs and AgNPs produce a phenomenon called Surface Plasmon Resonance. The vibrations of these free electrons interacting with light create a resonance, resulting in the absorption of light at a specific wavelength.
• Detection: A UV-vis spectrophotometer detects this absorption and produces a characteristic peak. For AuNPs, this peak appears in the 500nm-600nm range, while for AgNPs, it is in the 400nm-500nm range. The intensity of this peak depends on the concentration of nanoparticles in the solution.
• In this study, AuNPs showed peak absorbance between 529nm and 544nm, while AgNPs showed peaks between 411nm and 434nm, confirming their successful synthesis.

X-Ray Diffraction (XRD) Analysis: Understanding Crystalline Structure

The characterization of nanoparticles continued with XRD analysis to determine the nature and nanocrystallite size of the synthesized AuNPs and AgNPs. A fine powder of the nanoparticles was smeared uniformly on a glass slide for analysis.

• Crystalline Nature: Analysis of the XRD results for AuNPs revealed Bragg’s reflections corresponding to the face-centered cubic (fcc) structure bands of gold. Similarly, the XRD patterns for AgNPs indicated characteristic peaks corresponding to the fcc structure of silver. This proved that the nanoparticles produced by this green synthesis method were highly crystalline in nature.
• Size Calculation: By determining the Full Width Half Maximum (FWHM) of the most intense reflection peaks and applying the Scherrer equation, the average size of the nanocrystallites was calculated. For AuNPs, the average size ranged from 6.23nm to 12.00nm. For AgNPs, the average nanocrystallite size ranged from 7.43nm to 14.12nm. The sharpness of the peaks clearly indicated that the synthesized particles were in the nano-region.

Scanning Electron Microscopy (SEM): Visualizing Size and Shape

Morphological characterization of nanoparticles, including their size and shape, was studied using a high-resolution SEM. Liquid nanoparticle samples were coated on an ultraclean carbon grid and evaporated at room temperature for analysis.

• Shape: SEM results confirmed that both the synthesized AuNPs and AgNPs were uniform and spherical in shape. The particles were described as nanospheres.
• Average Size:
  • AuNPs: The average sizes were 36nm (A. jacquemontii tubers), 29nm (H. nepalensis leaves), 32nm (H. nepalensis stem), 24nm (V. jatamansi shoot), and 25nm (V. jatamansi root).
  • AgNPs: The average sizes were 30nm (A. jacquemontii tubers), 30nm (H. nepalensis leaves), 35nm (H. nepalensis stem), 32nm (V. jatamansi shoot), and 49nm (V. jatamansi root).

Fourier-Transform Infrared (FTIR) Spectroscopy: Identifying Capping Agents

FTIR spectroscopic analysis was performed to identify the possible functional groups from the plant extracts that were involved in the bio-reduction of the metal salt and the stabilization (capping) of the nanoparticles. The disappearance of certain absorption bands present in the pure plant extract from the spectra of the nanoparticles indicates their involvement in the synthesis.

• Functional Groups in AuNP Synthesis: For AuNPs, the disappearance of bands corresponding to Carboxylic acid/Phenols and tertiary alcohol functional groups confirmed their role in reducing the gold chloride.
• Functional Groups in AgNP Synthesis: For AgNPs, the analysis revealed that groups like carboxylic acid, ethers, alkenes, esters, and aromatic rings were mainly identified as the reducing and capping agents responsible for the synthesis and stabilization of the silver nanoparticles.

Conclusion

The successful characterization of nanoparticles relies on a complementary suite of advanced analytical techniques.

As this research demonstrates, UV-vis spectroscopy confirms their formation, XRD reveals their crystalline structure and size, SEM provides direct visual evidence of their morphology, and FTIR identifies the crucial plant-based compounds responsible for their synthesis.

Together, these methods provide a complete picture, verifying the success of green synthesis and ensuring the production of high-quality, well-defined nanoparticles for future applications.

Source Citation

• Researcher: Madiha Iqbal
• Thesis Title: BIOGENIC SYNTHESIS, CHARACTERIZATION AND PHARMACOLOGICAL EVALUATION OF NANO-PARTICLES PREPARED BY USING THE EXTRACTS OF Arisaema jacquemontii, Hedera nepalensis AND Valeriana jatamansi
• Guide: Prof. Dr. Jehan Bakht (Chairman, Supervisory Committee)
• University: The University of Agriculture, Peshawar, Pakistan
• Completion Date: August, 2017
• Excerpt Source Pages: 23, 27, 38, 43, 59, 79, 174, 177-181, 184-187.

Disclaimer

Some sentences have been lightly edited for SEO and readability. For the complete and original research, please refer to the full thesis PDF above.

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