14. Metal NPs (Au, Ag, and Cu): Synthesis, Stabilization, and Their Role in Green Chemistry and Drug Delivery

Nature is very powerful and strategic and has tailored various materials with sizes in nanometers. This phenomenon is observed with the passage of time. In the current picture, the most important thing is to control the changes in biological processes at the nanoscale. Due to this behavior of nature, scientists and academicians have been inspired and encouraged towards nanoscience and nanotechnology and reproducing the manufacture and controlled synthesis of nanomaterials in bulk. Nanoscience is the interdisciplinary science where basics and the advancement of the discipline of the fundamental principles of atoms and molecules have been discussed regarding their structures in various dimensions where the particle size is less than 100 nm. Nanoparticles are popular due to their high specific surface area and good dispersion in various solvents. Therefore, metal nanoparticles (NPs) have been applied in different areas of science including medicine, electronics, electrical, and catalysis, among others. The synthesis of metal NPs in bulk is a challenge to researchers due to their aggregation behavior. Thus, the stabilization of metal nanoparticles becomes a challenging job. But in the last decade ionic liquids (ILs) were found to be potent alternatives for the stabilization of metal nanoparticles.

As per the literature, ionic liquids are organic salts. They are based on the ammonium or phosphonium cation and different anions. Ionic liquids melt at low temperature, that is, 100°C. Their hydrophobicity or polarity can be tuned easily via changing the alkyl part of the ammonium or phosphonium cation as well as the anion together or independently. ILs have low vapor pressure and are preferred over conventional organic solvents. Gold, silver, and copper NPs can be synthesized in ionic liquid (FIL) as a solvent and stabilizer. Synthesized metal NPs can be used in the synthesis of composite materials of PANI, gelatin, and triblock copolymers to explore their conducting and biomedical applications. Synthesized metal NPs were used to catalyze various organic reactions including the Knoevenagel reaction, oxidation of thiols, and acetylation of alcohol and amines. The products obtained are in high yields and of short duration using metal NPs in ionic liquids as catalytic media. This methodology is much cheaper than the others and also does not require high temperature. Hence, ILs serve in a green and efficient method. Further catalytic applications of metal nanoparticles for various reactions are currently under investigation.