Synthesis and characterization of noble metal nanoparticles

Skozi celotno zgodovino je zanimanje za žlahtne kovine temeljilo na njihovih estetskih lastnostih. Zlato in srebro, na primer, sta bila vedno del okrasja in nakita. V preteklem stoletju in predvsem v zadnjih nekaj desetletjih so se pojavile revolucionarne raziskave na področju nanomaterialov. Veliko je bilo odkritega o njihovih optičnih, katalitičnih, električnih in biomedicinskih lastnostih. Te lastnosti predstavljajo namreč ogromen potencial za uporabo na več področjih, kot so kataliza, pretvorba energije in biomedicina. Nanodelci imajo edinstvene lastnosti, ki se pogosto močno razlikujejo od njihovega makroskopskega materiala. Ko so delci manjši od 100 nm se pokaže veliko zanimivih lastnosti. Veliko razmerje med specifično površino in prostornino, ki je značilno za nanodelce, spreminja toplotne, mehanske in kemijske lastnosti materialov. Lastnosti nanodelcev so močno odvisne od njihove velikosti, oblike, trdne ali votle notranjosti in sestave. Z uravnavanjem in kontroliranjem parametrov pri sintezi lahko tako spremenimo ali optimiziramo želeno lastnost za ciljno aplikacijo. Na primer pri katalizi površina, velikost in oblika močno vplivajo na katalitsko aktivnost in selektivnost, zato moramo imeti naštete lastnosti v mislih, ko načrtujemo sintezo. Obstaja več načinov sinteze nanodelcev, ki jih na splošno razdelimo na “top-down” in “bottom-up” pristope. Pri prvih makroskopski material, na primer, postopoma meljemo, da dosežemo nano dimenzije delcev. Zato se imenujejo pristopi od zgoraj navzdol. V drugi kategoriji kemijskih pristopov se tvorba nanodelcev začne iz atomov, ki nastanejo iz ionov, v raztopini. Zato se ti pristopi imenujejo od spodaj navzgor. V tekoči fazi se nanodelci kemijsko sintetizirajo v koloidni raztopini, ki vsebuje prekurzorje, reducirana sredstva, surfaktante in topilo. “Bottom-up” pristopi omogočajo proizvodnjo velikih količin nanodelcev z dobrim nadzorom velikosti, oblike, morfologije in sestave nanodelcev po razmeroma nizkih stroških.The ancient interest in noble metals was based on their aesthetic properties. Gold and silver, for example, were employed in the composition of ornaments and jewelry. In the past century and especially in the past few decades, revolutionary developments occurred in the field of nanoscience. A lot was studied about their optical, catalytic, electronic and biomedical properties. These unique properties hold enormous potential for applications in several areas such as catalysis, energy conversion and biomedicine. Nanoparticles have unique properties that are significantly different from their bulk counterparts. When the dimension of a particle decreases below 100nm, it exhibits many intriguing properties. High surface-to-volume ratio alters the thermal, mechanical and chemical properties of materials. The properties of nanoparticles are strongly dependent on their size, shape, solid or hollow interiors and composition. By tuning and controlling the parameters of synthesis, one can alter and optimize the desired property for a target application. For instance, in the case of catalysis, surface area, size and shape strongly affect catalytic activities and selectivity. Various nanoparticle synthesis approaches are available, which can be broadly classified into top-down and bottom-up approaches. In the first category, nanoparticles can be obtained by techniques such as milling which generates small particles from corresponding bulk materials. In the second category, nanoparticles can be formed atom-by-atom, which are obtained from ions in a solution. In the liquid phase, nanoparticles are chemically synthesized in colloidal solution containing precursors, a reducing agent, surfactants and a solvent. Bottom-up approaches have the potential to produce large quantities of nanoparticles with good control of size, shape, morphology and composition at reasonably low cost