Introduction Of Br Research Articles

Toward the Synthesis of Sub-15 nm Ag Nanocubes with Sharp Corners and Edges: The Roles of Heterogeneous Nucleation and Surface Capping.

We report a polyol method for the facile synthesis of Ag nanocubes having sharp corners and edges, together with edge lengths below 15 nm. The rapid nucleation of Ag atoms was facilitated through the addition of a trace amount of SH(-) to generate Ag2S clusters while the corners and edges of the nanocubes were sharpened through the introduction of Br(-) as a regulator of the growth kinetics and a capping agent for the Ag(100) surface. Because of their much smaller size relative to the more commonly used capping agent based on poly(vinylpyrrolidone), Br(-) ions are more effective in passivating the {100} facets on very small Ag nanocubes. The mechanistic roles of these additives, along with the effects of their interactions with other species present in the reaction solution, were all systematically investigated. The concentration of SH(-) was found to be a particularly effective parameter for tuning the edge length of the nanocubes. As a result of the understanding gained during the course of this study, Ag nanocubes with uniform edge lengths controllable in the range of 13-23 nm could be reliably produced. The nanocubes of 13.4 ± 0.4 nm in edge length constitute the smallest nanocrystals of this kind reported to date; they also possess sharper corners and edges relative to the limited examples of sub-20 nm Ag nanocubes reported in the literature. The availability of such small and sharp Ag nanocubes will open the door to an array of applications in plasmonics, catalysis, and biomedicine.

LiMn(2)O(4-y)Br(y) Nanoparticles Synthesized by a Room Temperature Solid-State Coordination Method.

LiMn2O4–yBrynanoparticles were synthesized successfully for the first time by a room temperature solid-state coordination method. X-ray diffractometry patterns indicated that the LiMn2O4–yBrypowders were well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiMn2O4–yBrypowders consisted of small and uniform nanosized particles. Synthesis conditions such as the calcination temperature and the content of Br−were investigated to optimize the ideal condition for preparing LiMn2O4–yBrywith the best electrochemical performances. The optimized synthesis condition was found in this work; the calcination temperature is 800 °C and the content of Br−is 0.05. The initial discharge capacity of LiMn2O3.95Br0.05obtained from the optimized synthesis condition was 134 mAh/g, which is far higher than that of pure LiMn2O4, indicating introduction of Br−in LiMn2O4is quite effective in improving the initial discharge capacity.

1‐(bromoacetyl)pyrene and its arsonium salt as novel photoinitiators for styrene polymerization

AbstractThe photopolymerization of styrene (Sty) in DMSO induced by pyrene (Py), 1‐Acetylpyrene (AP), 1‐(Bromoacetyl) pyrene (BP), and 1‐Acetylpyrene triphenyl arsonium bromide (APAS) has been investigated. Under all conditions employed, Py was completely ineffective. Incorporation of a chromophoric (COCH3) moiety introduces photoinitiating activity into Py. It was observed that introduction of Br into AP markedly accelerated the rate of UV irradiation‐induced polymerization. BP was further modified to its arsonium salt (APAS). The kinetics and mechanism of polymerization using BP and APAS as initiators have been investigated in detail. The polymerization with BP followed nonideal kinetics (Rp ∝ [BP]0.8 [Sty]1.1) with respect to initiator concentration whereas ideal kinetics (Rp ∝ [APAS]0.48 [Sty]1.1) was observed when APAS was used as initiator. Degradative transfer is thought to be mainly responsible for this unusual kinetic behavior for BP–Sty system. The kinetic data proved that BP was more effective and faster initiator than APAS. In both the cases, the mechanism of polymerization was free radical as evident by inhibiting the effect of hydroquinone and ESR studies. IR and NMR spectra showed the atactic nature of polystyrene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1793–1798, 2006

Synthesis and conformational studies of tetrahydroxy[3.1.3.1]metacyclophanes and electrophilic aromatic substitution of their tetramethoxy derivatives

Base-catalysed condensation of 1,3-bis(5-tert-butyl-2-hydroxyphenyl)propane 5 with formaldehyde in xylene has been carried out to form the novel propane-bridged calixarene-type macrocyclic compound, tetrahydroxy[3.1.3.1]metacyclophane 6. The optimum yield (90%) of 6 is obtained with NaOH as the base, the use of other alkali-metal hydroxides giving lower yields. AlCl 3 –MeNO 2 -catalysed trans-tert-butylation of 6 in benzene affords 7 in 80% yield. Intramolecular hydrogen bonding has been observed in the tetraols 6 and 7 as comparable to calix[4]arene. Methylation of 7 with MeI affords the tetramethoxy derivative 11a. The stability of multi-membered carbon skeletons permits the interconversion of functional groups at the lower and upper rims without special regard to ring-opening side-reactions on the upper rim. For example, the introduction of Br, formyl and acetyl substituents has been achieved by electrophilic aromatic substitution of the tetramethoxy derivative 11a. The 1 H NMR spectral behaviour of these macrocyclic metacyclophanes is also discussed.

Counterion specific interactions in dioctadecyldimethylammonium bromide monolayers at the monolayer/subphase interface

We have investigated the influence of halogen counterions on the molecular organization characteristics of dioctadecyldimethylammonium bromide (DOMA) monolayers at the air/water interface. Surface pressure- and surface potential-area isotherms and Brewster angle microscopy were used to characterize the head group-counterion interactions. The counterions used were F −, Cl −, Br − and I −. The presence of halogen ions in the subphase leads to compression of the π-A and a decrease in the surface potential. The effects of counterions on the microscopic features of molecular organization are, however, the most dramatic. DOMA at the air/water interface shows a homogeneous and featureless morphology during the whole compression process. The presence of F − and Cl − ions in the subphase does not lead to any significant changes. However, the introduction of Br − ions results in the appearance of dendritic structures in the liquid/solid coexistence region. The I − ions have an even greater effect on the morphology, in that solid domains are formed immediately after spreading. The influence of counterions on DOMA isotherms and morphology may be rationalized in terms of the degree of hydration of the various ions.

Mechanism of halide conversion process of colloidal AgCl microcrystals by Br − ions : I. Observation of the dynamic changes in shape, structure, and composition

The mechanism of the halide conversion process in suspension of AgCl microcrystals by bromide ions was studied by electron microscopy, X-ray diffractometry, and electron-beam diffractometry. The typical conversion process after the introduction of Br − was found to consist of more than three distinctive steps. The first step was an almost instantaneous reaction within a few seconds for a surface conversion without apparent morphological change of the original particles. The second step was a very rapid epitaxial growth process of virtually pure AgBr crystals on every corner and partly on the edges of the AgCl cubic microcrystals with dissolution of their own {100} faces, which was finished in about 1 min at 25°C. The third step was a much slower process of about 2 h at 25°C (ca. 5 min at 45°C) for the formation of an AgCl 0.5Br 0.5 solid solution developing from the joints of AgBr guest and AgCl host by simultaneous dissolution of the guests and the hosts. After the complete dissolution of the AgBr guests, a further recrystallization process that formed a solid solution richer in chloride content followed. Finally, the conversion virtually stopped midway to yield double-structured particles of Ag(Cl, Br) shell/AgCl core. However, when the initial molar ratio of [Br −] 0 [AgCl] 0 was so high as to exceed unity, the original AgCl particles were totally decomposed into about eightfold AgBr particles in number. In this case the steps later than the second one were missing. Also, it was suggested from the subsidiary study on open systems, where bromide ions were added continuously, that the kinetics was basically controlled by the deposition rate of the solute of the AgBr component of the growing parts, though it was switched to being limited by the dissolution rate of the host AgCl crystals when their open surface area for dissolution was extremely diminished.