Università degli Studi di Trieste Dipartimento di Ingegneria e Architettura A.A. 2016-2017 Scienza e Tecnologia dei Materiali Ceramici Modulo 2: Materiali Nanostrutturati - Lezione 10 - Vanni Lughi vlughi@units.it 040 558 3769 Dipartimento di Ingegneria e Architettura Università degli Studi di Trieste
Previous lecture: Review Nanoparticles: characterization
This lecture: Content Metallic nanoparticles
Metallic nanoparticles
Synthesis of metallic nanoparticles Riduzione di complessi metallici in soluzioni diluite Tipicamente: -bassa concentrazione del soluto (precursore del metallo) - stabilizzanti polimerici
Synthesis of metallic nanoparticles
Gold NCs: synthesis Riduzione HAuCl 4 da parte di Na 3 C 6 H 5 O 7 Si dissolve HAuCl 4 in acqua in modo da avere 20 ml di soluzione di concentrazione 2.5x10-4 M. Si porta ad ebollizione (in riflusso) e si aggiunge 1 ml di soluzione acquosa di Na 3 C 6 H 5 O 7 allo 0.5%. La soluzione viene mantenuta a 100 C finché non diventa rossa.
Gold NCs: synthesis and properties
Gold Nanoparticles - homogeneous Electron Micrograph of 15 nm Au Particles solution Faraday s gold sol In Royal Institution in London
Surface Plasmons Control Metal Nanocrystal Colour Gold Nanocrystals grown by Romans in glass - the red colour is observed only for particles 5-25nm in size. The size distributions must be very narrow. The growth kinetics must be carefully controlled. Lycurgus Cup ~50AD - British Museum
Silver NCs: synthesis
Silver NCs: synthesis and properties
Silver NCs: other syntheses
Synthesis of amorphous silver NPs
Rhodium NPs: synthesis
Stabilization of metal colloids Typically: electrosteric stabilization
Effects of synthesis parameters: size distribution Concentration influences size and size distribution
Effects of synthesis parameters: size distribution Concentration influences size and size distribution Generalmente un agente riducente forte favorisce una reazione molto veloce e quindi la formazione di nanoparticelle più piccole. Il contrario per agenti riducenti deboli. Tuttavia una reazione lenta può portare sia ad una distribuzione delle dimensioni molto stretta che molto larga. Infatti se la lenta reazione porta alla continua formazione di nuclei secondari, si avrà una distribuzione allargata, mentre se tale reazione lenta non porta alla formazione di nuclei secondari, si avrà semplicemente una crescita controllata da processi di diffusione limitata e quindi si avrà una distribuzione più uniforme delle dimensioni delle nanoparticelle
Effects of synthesis parameters: shape Reducing agents influence morphology
Effects of synthesis parameters: shape Reducing agents influence morphology
Effects of synthesis parameters: stabilizer Stabilizing agents influence morphology
Effects of synthesis parameters: shape Reducing agents influence morphology
Effects of synthesis parameters Chloride ions influence size distribution
Optical properties of metallic nanoparticles Band structure of metals
Optical properties of metallic nanoparticles Color of metals
Surface Plasmon Oscillations Assume a slab of electrons in one dimension. The concentration is N. An electric field E app pushes the electrons to one side a distance x, leaving positive charges at the other end. These charges cause restoring force (field) E s E s x + + + E app N x - - -
Surface Plasmon Oscillations The Electric field E app creates a force F = -ee. The charges move a distance x, which makes a surface charge density s = Nex at each end. Gauss Law says the field created between two planes of surface charge is E s = s/ e o. This creates an opposing force F s = -ee s = -Ne 2 x/ e o So the electrons move according to F = md 2 x/dt 2 = -Ne 2 x/e o, or d 2 x/dt 2 = -Ne 2 /me o x. The solution is x = A cos w t, with w = Ne 2 /me o. So electrons oscillate at a definite frequency, the plasma frequency.
Optical properties of metallic nanoparticles The optical properties of small metal nanoparticles are dominated by the collective oscillation of conduction electrons resulting from the interaction with electromagnetic radiation. These properties are mainly observed in Au, Ag, and Cu, because of the presence of free conduction electrons. The electric field of the incoming radiation induces the formation of a dipole in the nanoparticle. A restoring force in the nanoparticle tries to compensate for this, resulting in a unique resonance wavelength.
Optical properties of metallic nanoparticles
Optical properties of metallic nanoparticles
Optical properties of metallic nanoparticles
Proprietà ottiche di nanoparticelle metalliche Per particelle sferiche piccole (2R<<l), con una funzione dielettrica complessa e=e +ie dipendente dalla frequenza w (cioè da l) immerse in un mezzo con costante dielettrica e m : The origin of the strong color changes displayed by small particles lies in the denominator of previous equation, which predicts the existence of an absorption peak when e (w) = -2 e m (e small or weakly dependent from w) l=2pc/w
Optical properties of metallic nanoparticles
Optical properties of metallic nanoparticles
Optical properties of metallic nanoparticles
Overview of Novel Effects in Metal Nanocrystals Surface plasmon changes due to electron density. Surface plasmon changes due to shells or adsorbates e.g. biomolecules. Surface plasmon changes with particle size. Surface plasmon changes with particle shape.
Applications of metal nanoparticles Main fields of application Remediation Catalysis Antibacterial (Ag) Theranostics