Encapsulation of Silicon Nanoclusters in Zeolite Y

Abstract

Luminescent silicon clusters have been synthesized by the chemical vapor deposition of Si2H6 into the α-cages of H32Na24Y zeolite. The synthetic process was monitored by FTIR, TGA-MS, and 29Si and 1H solid-state NMR spectroscopies. In the initial step at 100 °C, Si2H6 reacts with the Brønsted acid sites to produce anchored ZO−Si2H5. Si2H6 is also chemisorbed at Na+ cation sites to give Si2H6/NaHY and is possibly physically trapped within the α-cage by the anchored disilyl groups. Multiple quantum 1H NMR spin counting shows that each α-cage contains 38 H atoms. This is equivalent to 14 Si atoms present as a combination of disilyl and disilane. Subsequent thermal treatment of the entrapped disilane precursors leads, via H2 and SiH4 elimination, to the formation of Si clusters. The formation of Si clusters is complete at 550 °C. These clusters are capped by up to 5 H atoms (determined by 1H NMR spin counting) and attached to the zeolite framework through SiO x linkages (determined by Si K-edge XANES). The average size of the resulting silicon clusters is 12 ± 2 Si atoms (determined by XPS and Si K-edge XANES). The encapsulated Si clusters are air-stable and exhibit a room-temperature photoluminescence in the green-yellow region with a peak energy at ∼2.2 eV. The HOMO−LUMO energy gap in the Si cluster is estimated to be 2.2 eV, from a comparison of the band edges of the Si clusters and bulk Si (c-Si) (determined by synchrotron photoabsorption (Si K-edge XANES) and photoemission spectroscopies). The close correspondence of the HOMO−LUMO energy gap and the photoluminescence peak energy confirms the origin of luminescence from the Si cluster as a predominantly electron−hole radiative recombination process.

Theoretical prediction of Ni(I)‐catalyst for hydrosilylation of pyridine and quinoline

“…These findings indicate that 1 is the active species. This is consistent with the fact that only monomeric (bpy)Ni I H was reported by Zhu and coworkers [31] Also, the investigation of the solvation effects on the stability of monomer (bpy)Ni I H suggested that such a polar (coordinating) solvent as acetonitrile and THF are useful for the stabilization of the monomeric (bpy)Ni I H species. [37] With continuing our interest in the catalysis of Ni(I) species, we wish to demonstrate here that (bpy)Ni I H (bpy = 2,2 0 -bipyridine) 1 is indeed a good catalyst for hydrosilylation of pyridine and quinoline.…”

“…Very recently, Lee and Yoo [30] synthesized a T-shaped nickel(I) complex using a rigid acridanebased pincer ligand and suggested that sterically exposed halffilled d x 2 −y 2 orbital of Ni(I) provided unique open-shell reactivity toward such substrates containing double bond as C 2 H 4 and CO 2 . Zhu and coworkers [31] recently succeeded catalytic arylation of remote and proximal double bonds using nickel(I)-hydride catalyst. Chirik and coworkers [32] succeeded the reductive arylation of alkene by dimeric nickel(I)-hydride catalyst, in which alkene insertion into Ni─H bond occurred rapidly.…”

Oligo- and poly(fullerene)s for photovoltaic applications: Modeled electronic behaviors and synthesis

“…To decide whether or not PFs are suitable for OPV use, we determined their electronic properties compared to benchmark materials, namely: PCBM, 33,34 bis-PCBM, [35][36][37][38] mono-indene-C 60 (ICMA), and the indine bisadduct ICBA. [38][39][40] , with the structures detailed in Figure 1. PCBM is a successful acceptor due to its appropriate LUMO level (ca., 24.3 eV), 41 good solubility, 36 high electron affinity (EA), and ability to form semi-crystalline domains that act as as percolation channels.…”

Double Resonance NMR Echo Spectroscopy of Aluminosilicates

“…The framework of aluminosilicate molecular sieves (zeolites) have been explored as nanoreactors for synthesizing threedimensional arrays of size-controlled semiconductive clusters with photoluminescent properties. [12] The zeolite framework is made up of corner-and edge-sharing SiO 4 and AlO 4 tetrahedra, with a balancing positive charge for each Al in the structure. Dehydrated NaHY zeolite has Na + and H + as charge-balancing species, and the latter, as…”