Thathan Premkumar

Facile synthesis of silver nanoparticles using unmodified cyclodextrin and their surface-enhanced Raman scattering activity

A simple and one-pot approach to synthesise silver nanostructures of different sizes and shapes in aqueous medium at room temperature is reported. The reduction of the silver salt and the stabilization of the as-prepared silver nanostructures are achieved using a macrocycle, the unmodified β-cyclodextrin, under alkaline conditions at room temperature. This green approach, which utilizes water as a benign solvent and the non-toxic and biocompatible β-cyclodextrin as both the reducing and the protecting agent at room temperature, does not need any additional reducing agents and external energy under ambient experimental conditions. Furthermore, we are able to prepare silver nanostructures of different sizes and shapes by simply altering the reaction conditions such as the concentration or temperature. The results show that spherical, polygonal, rod-, flower-, wire- and ant-like silver nanostructures are achieved by using an alkaline solution of unmodified β-cyclodextrin under different experimental conditions without adding additional agents. Furthermore, we demonstrate that the as-prepared silver nanostructures can be used as efficient surface-enhanced Raman scattering active substrates, and p-aminothiophenol is used as a Raman probe to evaluate their enhancement ability. It was found that the enhancement ability of the agglomerated silver nanostructures is higher than that of the well-dispersed and smaller sized silver nanoparticles. The reason for this is discussed from the point of electromagnetic and chemical mechanisms in addition to the agglomeration behaviour of silver nanoparticles, which gain a stronger surface-enhanced Raman scattering effect than the isolated silver nanoparticles because of the coupling between the silver nanoparticles.

Isomorphic metal malonates with N-aminoguanidine: MCo2O4 (M = Ni & Zn) nanoparticle synthesis via a (AmgH)2[M1/3Co2/3(mal)2(H2O)2] precursor solid solution

Divalent metal complexes of malonate with aminoguanidine possessing (AmgH)2[M(mal)2(H2O)2] [M = Co (1), Ni (2) or Zn (3); mal = malonate anion and AmgH = aminoguanidinium cation] stoichiometry and their solid solutions, (AmgH)2[Ni0.5Co0.5(mal)2(H2O)2] (4) and (AmgH)2[M1/3Co2/3(mal)2(H2O)2] [where M = Ni (5) or Zn(6)], were prepared and characterized by analytical, thermal and powder X-ray diffraction studies. The crystal and molecular structures of both cobalt and nickel compounds were isomorphic, crystallizing in the triclinic space group P. The complexes exhibit similar modes of endo-followed by exothermic decomposition to produce respective metal oxides below 550 °C. Metal cobaltites, MCo2O4 where M = Ni and Zn, were obtained from the above solid solutions as decomposition residues by heating at 600, 700 and 800 °C in a silica crucible for 3 h. Spinel oxides nanoparticles were characterized by infrared spectra, powder X-ray diffraction patterns, scanning electron microscope coupled with energy dispersive X-ray analysis and transmission electron microscope studies.

A General Approach to Synthesize Metal Nanostructures by Using Cucurbit[7]uril

Various metal (iron, copper, zinc, platinum)-based nanostructures were synthesized by a simple, green, and one-pot reaction of respective metal precursor and a cucurbit[7]uril (CB7) in an aqueous alkaline mixture at room temperature. The metal nanostructures (MNS) were obtained without adding any additional traditional reducing or protecting agents and/or external energy sources. Further, we could be able to tune the size and shape of the MNS just by varying the experimental conditions such as reaction concentration. Depending on the metal salts and reaction conditions, we could be able to produce different sizes and shapes of nanostructures. For example, the diameter of the CuO and iron nanoparticles (NP) was observed as ∼1nm (even <1nm) which suggests the inclusion mechanism. However, the particle size of zinc and platinum was over 2nm which suggests the capping mechanism for the well-dispersed nanoparticles. It is worth mentioning that the CB7 acts as both reducing and protecting agent for the preparat...

Binaphthyl-incorporated π-conjugated polymer/gold nanoparticle hybrids: a facile size- and shape-tailored synthesis

Size- and shape-tailored metal nanoparticles and π-conjugated polymer hybrids are applied in various fields such as surface-enhanced Raman scattering, sensors, heterogeneous catalysis, solar cells, and memory devices. For such applications, it is important to precisely control the morphology of the polymer–metal nanoparticle hybrids. In our study, we utilized binaphthyl-incorporated conjugated polymers to simultaneously reduce auric ions (Au3+) to gold nanoparticles and stabilize them, which resulted in nanoparticle and π-conjugated polymer hybrids. Interestingly, we found that the size and shape of the gold nanoparticles were controlled by the solvents utilized and molecular weights of the binaphthyl-containing π-conjugated polymers. We attributed this to the difference in the coverage of the gold nanoparticle facets by the polymers, which was dictated by the conformation of the polymers and reduction rates in different solvents. In addition, the hybrid materials showed enhanced electrochemical properties compared to the polymers.