Photo-promoting Fabrication of Silver Nanoparticles in the Presence of Anthracenyl-Focal PAMAM Dendrons

Abstract

ABSTRACT:Silver nanoparticles protected by first to third generation poly(amido amine) dendrons with an anthracenyl-focal point were fabricated by photo-promotion of silver ions in aqueous dendron solutions. The reaction solutions colored from light to deep brown and displayed a broad plasmon band at 450 nm, indicating the formation of silver nanoparticles. The formation of particles progressed with time, although it slowed down at the light-shielding (dark) condition. The light-promoted electron transfer from amine groups of dendron to silver ions through anthracenyl moiety might concern to the formation of silver nanoparticles. According to the images of transmission electron microscopy, the shape of nanoparticles was not only spherical (15-20 nm in size) but also polygonal (20-35 nm in size). It was confirmed from the crystallographic analysis of electron diffraction patterns that the polygon was a hexagonalclose-packing (hcp) single crystal, whereas the crystal structure of spherical nanoparticles was face-centered-cubic (fcc). The reaction was fastest when the second generation dendron was used, indicating the competition of increasing number of amine groups and reducing efficiency of photo-promoted electron transfer with generation. [DOI 10.1295/polymj.38.44] KEY WORDS Poly(amido amine) Dendron / Anthracene / Anthracenyl-focal Poly(amido amine) Dendron / Silver Nanoparticle / Nanoparticle / Photo-induction / Photo-fabrication / Transmission Electron Microscopy / Electron Diffraction / Hexagonal-close-packing / Face-centered-cubic / Dendrimers are synthesized stepwise through branching points and spacers, resulting in the spherical shape. From their structural characteristics like a lot of terminal groups and internal voids, the unique applications of dendrimers are prospective. Especially, poly(amido amine) (PAMAM) dendrimers with simple hydrophilic terminal groups are water-soluble and nontoxic, indicating bio-compatible. Utilizing the PAMAM dendrimers as a protector, metal and metalderivative nanoparticles with small size and narrow size distribution were synthesized. [1][2][3][4][5][6][7][8][9][10][11][12] Then the protection by PAMAM dendrimers may develop the advanced application of nanoparticles as medical materials like therapeutic reagents besides industrial materials.Water-dispersible gold and silver nanoparticles with small sizes (less than 10 nm) were synthesized by the reduction of metal ions in the presence of PAMAM dendrimers.3-9 While in almost of investigations, metal nanoparticles were reduced with the aid of reducer, gold and silver nanoparticles were prepared by reducing the metal salt in PAMAM dendrimer solutions under UV, X-ray, or laser irradiation or heating. 3,4,[6][7][8] Particle sizes and their dispersion in water depended on the generation of dendrimers and the mixing ratio of metal ion and dendrimer.In the present work, the fabrication of silver nanoparticles without coexistence of common reducer has been reported. The silver nanoparticles were prepared with a photochemical me...

Generation of Ag Nanoparticles by PAMAM Dendrimers and their Size Dependence on the Aggregation Behavior of Dendrimers

“…Since metal nanoparticles possess characteristic plasmon absorption peaks in the visible region of the electromagnetic spectrum, UV–Vis absorption spectroscopy has been utilized as one of the initial methods for confirming the formation of metal nanoparticles in the system. For example, silver nanoparticles in the size range up to 35 nm results in an absorption peak around 450 nm 23. Upon stirring and ageing the system containing AgNO 3 and zero generations PAMAM or PPI dendrimers for 24 h in a dark chamber, an absorption peak in the range of 420–450 nm was observed.…”

Experimental and Theoretical Studies of the Photoreduction of Metal Ion−Dendrimer Complexes: Observation of a Delocalized Organic Radical

“…Dendrimers are also useful photochemical reaction media, as they can be modified with chromophores at the core (the inner tertiary amine sites), the focal point (the outer tertiary amine sites), and the periphery . There are a number of reports of the formation of metallic nanoparticles by photochemical reduction involving dendrimers. − Au, Ag, Pt, and Cu nanoparticles have been prepared by ultraviolet (UV) irradiation (λ > 200 nm) following complexation of precursor metal ions with the PAMAM dendrimer. On the PAMAM dendrimer, only the amide and amine groups in PAMAM can absorb photons at wavelengths longer than 200 nm .…”

“…19 There are a number of reports of the formation of metallic nanoparticles by photochemical reduction involving dendrimers. [20][21][22][23][24] Au, Ag, Pt, and Cu nanoparticles have been prepared by ultraviolet (UV) irradiation (λ > 200 nm) following complexation of precursor metal ions with the PAMAM dendrimer. On the PAMAM dendrimer, only the amide and amine groups in PAMAM can absorb photons at wavelengths longer than 200 nm.…”

Photochemical synthesis of crown-shaped platinum nanoparticles using aggregates of G4-NH2PAMAM dendrimer as templates

“…UV irradiation yielded not only spherical but also polygonal silver nanoparticles in the presence of PAMAM dendrons with an anthracenyl focal point. 17 The transformation from spherical gold nanoparticles to polygonal microplates with time was observed under UV irradiation in the presence of PAMAM dendrimers at a low content. 18 In this report, we describe the synthesis of crown-shaped platinum nanoparticles under the UV irradiation in the presence of fourth generation NH 2 -terminal (G4-NH 2 ) PAMAM dendrimers.…”