In Situ Atomic-Level Tracking of Heterogeneous Nucleation in Nanocrystal Growth with an Isocyanide Molecular Probe

Abstract

We report the use of 2,6-dimethylphenyl isocyanide (2,6-DMPI) as a spectroscopic probe to study the heterogeneous nucleation and deposition of Pd on Ag nanocubes under different conditions by surface-enhanced Raman scattering. As a major advantage, the spectroscopic analysis can be performed in situ and in real time with the nanoparticles still suspended in the reaction solution. The success of this method relies on the distinctive stretching frequencies (ν) of the isocyanide group in 2,6-DMPI when it binds to Ag and Pd atoms through σ donation and π-back-donation, respectively. Significantly, we discovered that ν was sensitive to the arrangement of Pd adatoms on the Ag surface. For example, when the isocyanide group bound to one, two, and three Pd atoms, we would observe the atop, bridge, and hollow configurations, respectively, at different ν frequencies. As such, the ν band could serve as a characteristic reporter for the Pd adatoms being deposited onto different types of facets on Ag nanocubes with atomic-level sensitivity. When 2,6-DMPI molecules were introduced into the reaction solution, we further demonstrated in situ tracking of heterogeneous nucleation and early stage deposition of Pd on Ag nanocubes by monitoring the evolution of ν bands for both Ag and Pd surface atoms as a function of reaction time. This in situ technique opens up the opportunity to investigate the roles played by reaction temperature and the type of Pd(II) precursor in influencing the heterogeneous nucleation and growth of bimetallic nanocrystals. The sensitivity of isocyanide group to Pd atoms helps elucidate some of the details on the reduction, deposition, and diffusion processes involved in heterogeneous nucleation.

Surface Capping Agents and Their Roles in Shape‐Controlled Synthesis of Colloidal Metal Nanocrystals

“…Taken together, it is highly desirable to have a quantitative measure and understanding of the capping agent involved in a synthesis. This can be achieved through the development of in situ tracking methods such as synchrotron X‐ray diffraction and surface‐enhanced Raman scattering (SERS) while including computational modeling with an emphasis on the dynamic aspects …”

Ag Nanocrystals with Nearly Ideal Optical Quality: Synthesis, Growth Mechanism, and Characterizations

“…In general, silver nanocrystals are considered as the best material for LSPR in the visible-light window because of their smallest imaginary part of permittivity among all metal materials. Although synthetic chemistry and growth mechanisms for Ag nanocrystals have been extensively studied, − there is still a gap between their theoretical and experimental optical properties. Quality factor ( Q )also known as an index of LSPR strengthis a key intrinsic optical property of LSPR nanocrystals, which is calculated by Q = E R /Γ ( E R and Γ being respectively the resonance energy and full width at half-maximum of the LSPR spectrum) .…”

Probing Single‐Atom Catalysts and Catalytic Reaction Processes by Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy

“…PIC can be adsorbed on the surface of Pd via Pd-CN interactions by adopting top or bridge configurations. [18] In the case of atomically dispersed Pd, only top adsorption can be observed in Raman spectra. [19] Otherwise, when Pd exists in the form of NPs, the adsorption of PIC is dominated by bridge adsorption.…”