Solute-solvent halogen bonding during adsorption on silver nanostructures.

We offer here evidence for halogen bonding induced by silver nanoparticles (SNPs) in a multilayer containing 4-iodobenzoate ion (4IBI) and CCl(4). SERS experiments show in the monolayer that CCl(4) does not adsorb and 4-iodobenzoic acid (4IBA) adsorbs as 4IBI. SEIRA experiments reveal that 4IBI forms in the multilayer during deposition from CCl(4) on SNPs. Further infrared experiments on clean BaF(2) prove that 4IBI formation caused by underlying SNPs was necessary for CCl(4) inclusion in a 4IBI multilayer. Several potential scenarios involving intermolecular attraction between CCl(4) and 4IBI are proposed to explain the results. Although halogen bonding involving solvents has been theoretically and experimentally demonstrated in solution phase chemistry, in bulk crystals, and at the monolayer level, here it is shown that halogen bonding interactions can also be significant in multilayer films. Results from this work will likely impact a range of applications across diverse fields where halogen bonding in thin films and nucleation chemistry are important.

Adsorption analysis of nitrophenol isomers on silver nanostructures by surface-enhanced spectroscopy.

SEIRA, SERS, TPD and DFT were used to study 4-nitrophenol (4NP), 3-nitrophenol (3NP) and 2-nitrophenol (2NP) adsorption on nanoscale silver films/powder. SERS and DFT demonstrated that 4NP adsorbed as the 4-nitrophenolate ion. SEIRA results revealed that a 4NP multilayer condensed differently using deposition solvents with and without polar bonds. 3NP and 2NP adsorption were not altered by the polar properties of the solvent. The nanoscale properties of the silver films/powder were shown to impact how the polar properties of the deposition solvent altered nitrophenol adsorption. In the SEIRA spectra of 4NP and 3NP a C=O stretch was observed above 1700cm(-1) using a highly volatile n-pentane deposition solvent. No other solvent yielded such a peak for 4NP or 3NP adsorption including n-heptane. 2NP had a C=O stretch regardless of deposition solvent. A C=O stretch confirmed nitrophenol ionization in the monolayer and pointed toward the significance of resonance in NP adsorption. 2NP never formed a multilayer at high exposures as demonstrated using TPD and SEIRA. Results of this work will have environmental implications and will aid biochemical and industrial applications where phenolic compounds are employed.