Bimetallic core–shell nanocomposites using weak reducing agent and their transformation to alloy nanostructures

Abstract

An in situ seeding growth methodology towards the preparation of core-shell nanoparticles composed of noble metals has been developed by employing trimethylamine borane (TMAB) as the reducing agent. Being a weak reducing agent, TMAB is able to distinguish the smallest reduction potential window of any two metals which renders selective reduction of metal ions thus affording a core-shell architecture of the nanoparticles. A dramatic effect of solvent was noted during the reduction of Ag(+) ions: an immediate reduction took place at room temperature when dry THF was used as solvent however, usage of wet THF (THF used directly from the bottle) brings out the reduction only at reflux conditions. In the case of Au and Pd nanoparticles, preparation was found to be independent of the quality of solvent used. Au nanoparticles are realized at room temperature whereas reflux conditions are required in the case of Pd nanoparticles. This difference in behavior of the monometallic nanoparticles was successfully exploited to construct different noble metal nanoparticles with core-shell architectures such as Au@Ag, Ag@Au, and Ag@Pd. Transformation of these core-shell nanoparticles to their thermodynamically stable alloy counterparts is also demonstrated under very mild conditions reported to date.

Heterogeneous PdAg alloy catalyst for selective methylation of aromatic amines with formic acid under an additive-free and solvothermal one-pot condition

“…26 Moreover, the surface chemistry of the multicomponent catalyst was determined by X-ray photoelectron spectroscopy (see ESI † Supplementary Figure S3). Doublet X-ray photoelectron spectroscopy peaks of Pd 3d (336 and 341 eV) and Ag 3d (368 and 374 eV) confirmed the metallic features of Pd 0 and Ag 0 (see ESI † Supplementary Figure S4e and S4f), 30 whereas the ratio of Pd/Ag (0.31 at %/0.33 at % = 0.94, Supplementary Table S5) in the surface composition was similar to the compositional Pd/Ag ratio (2.40 wt%/2.72 wt% = 0.89) measured by inductively coupled plasma-atomic emission spectroscopy, which is additional evidence of alloy structure. Three N1s peaks at~399, 400 and 402 eV were assigned to the pyridinic, pyrolic and graphitic or quaternary N (see ESI † Supplementary Figure S4c).…”

Role of PdAg interface in Pd-Ag/SiO2 bimetallic catalysts in low-temperature oxidation of carbon monoxide

“…Note that the plasmon absorption of silver indicates the occurrence of an individual phase of silver rather than bimetallic PdAg alloys, which are not characterized by plasmon absorption [21]. The observed shift of the absorption maximum from 460 to 430 nm for the PdAg samples can be a consequence of the interaction of the electron densities of silver and palladium, including that due to the partial transfer of palladium atoms into the structure of silver nanoparticles [41]. Figure 3 presents the catalytic properties of the syn thesized Ag, Pd, and PdAg of catalysts in CO oxidation after oxidative pretreatment at 500°C (Fig.…”

“…The formation of bimetallic alloys and intermetallic or nanocomposite structures, including core-shell structures, structured bimetallic nanoparticles, nanodendrites, etc., is possi ble [14]. Various structures of bimetallic particles, including alloys [14,21], core-shell structures [22], and dendrimer bimetallic alloys [14] were described for PdAg catalysts, which are interesting for hydrogenation reactions [15,16] and the selective [17][18][19] and deep oxidation of organic substances [20]. However, a com mon special feature of the majority of PdAg catalysts is the concentration of silver on the surface of the particles under the action of a reaction mixture or high tempera tures, which leads to a decrease in activity due to the lower activity of silver in comparison with palladium [23].…”

Deposition of Au nanoshells on thermally grown patterned Ag nanoparticles from the block copolymer micelle thin films by seeding method

“…Upon Au nanoshell growth, a 0.5-eV shift in these binding energies to the higher energy is recorded. The result clearly indicates that the dipolar interaction indeed occurred between Au and Ag NPs [49]. The change of the characteristic binding energies of Ag to the higher energy level is attributed to the relative charging of electrons on the surface of Ag NPs.…”