Differentiation of carbon black from black carbon using a ternary plot based on elemental analysis.

Carbon black (CB) is composed of engineered nanoparticles that are commercially produced by partial combustion of hydrocarbons. It is mainly used as a reinforcing agent in vehicle tires. Although the potential health effects of CB have been investigated extensively, some toxicological reports interchange CB with black carbon (BC), which has similar features, thereby misusing the term. BC is an undesirable byproduct of the incomplete combustion of fuels. Therefore, there is a need to differentiate CB from the unintentionally produced nanomaterials (BC) in nano-toxicity, environmental, and human health studies. To distinguish clearly CB from BC, it is important to find the key parameters from several characteristics of two substances. The fundamental physicochemical properties of commercial CB and naturally formed BC were conducted. Based on the elemental analysis, we found three key factors, which could be used to differentiate the CB from BC. And thus, herein, we propose a ternary plot of the aH/C-log(C/b)-1/H combination for use in differentiating CB from BC. The plot of the 100H/C-log(C/10)-1/H combination of elemental ratios separated the CB domain from the BC domain symmetrically. The effectiveness of the ternary chart was validated using 37 samples (nine samples in this work, 25 sample results taken from references studies, and three samples from the field). Therefore, the ternary plot could be used as a prescreening tool for distinguishing CB from BC.

Changes in the Enantiomeric Composition of Chiral Mixtures Upon Adsorption on a Non-Chiral Surface.

The adsorption of propylene oxide, a chiral molecule, on a Pt(111) single-crystal surface was studied as a function of enantiomeric composition by temperature programmed desorption (TPD) and molecular beams. Two opposing trends were observed leading to variations in the enantiomeric excess (ee) of the chemisorbed layers with respect to the composition of the gas-phase mixtures: a kinetic effect dominant during the initial uptake, with a preference toward the formation of enantiopure layers, and a steady-state effect seen after approximately monolayer half-saturation, at which point the preference is toward racemization. These effects may account for important phenomena such as the bias toward one chirality in biological systems and the selective crystallization of some chiral compounds, and may also be used in practical applications for chemical separations and catalysis.

Interference of the surface of the solid on the performance of tethered molecular catalysts.

The catalytic performance of cinchonidine in the promotion of thiol additions to conjugated ketones was used as a probe to assess the tethering of molecular functionality onto solid surfaces using well-known "click" chemistry involving easy-to-react linkers. It has been assumed in many applications that the tethered molecules retain their chemical properties and dominate the chemistry of the resulting solid systems, but it is shown here that this is not always the case. Indeed, a loss of enantioselectivity was observed upon tethering, which could be accounted for by a combination of at least three effects: (1) the nonselective catalytic activity of the surface of the solid itself; (2) the activity of the OH species generated by hydrolysis of some of the Si-alkoxy groups in the trialkoxy moieties used to bind many linkers to oxide surfaces; and (3) the bonding of the molecule to be tethered directly to the surface. Several ideas were also tested to minimize these problems, including the silylation of the active OH groups within the surface of the oxide support, the selection of solvents to optimize silane polymerization and minimize their breaking up via hydrolysis or alcoholysis reactions, and the linking at defined positions in the molecule to be tethered in order to minimize its ability to interact with the surface.