Langmuir type adsorption was observed for two systems:  methylene blue (MB) on TX titania and acid blue 40 (AB40) on P25 titania at an ambient temperature of (23 ± 2) °C and ambient pH initially at 4.6 ± 0.2 for P25 titania and 7.8 ± 0.2 for TX titania. Based on a Langmuir analysis, values for maximum surface coverage, N max, and adsorption intensity, b, are 1.6 × 10-5 mol MB·g-1 and 3.6 × 104 L·mol-1, respectively, for TX titania. An N max value of 5.0 × 10-5 mol AB40·g-1 was determined for P25 titania. The TX titania adsorption surface area is estimated to be 12 m2·g-1 based on maximum adsorption of methylene blue. Results of gel electrophoresis on both dyes at pH values of 4 and 9 indicate that methylene blue remains cationic and acid blue 40 remains anionic in this pH range. Single-point adsorption experiments at selected pH values other than ambient were performed. Experimental evidence clearly indicates that electrostatic attraction is a reasonable explanation for the observed adsorption process in the MB/TX system. Although the evidence is less conclusive, electrostatic attraction may also influence the adsorption process of the AB40/P25 system.

No abstract

Viscosity experiments using Ostwald-type gravity flow viscometers are not new to the physical chemistry laboratory. Several physical chemistry laboratory texts (1 - 3) contain at least one experiment studying polymer solutions or other well-defined systems. Several recently published articles (4 - 8) indicated the continued interest in using viscosity measurements in the teaching lab to illustrate molecular interpretation of bulk phenomena. Most of these discussions and teaching experiments are designed around an extensive theory of viscous flow and models of molecular shape that allow a full data interpretation to be attempted. This approach to viscosity experiments may not be appropriate for all teaching situations (e.g., high schools, general chemistry labs, and nonmajor physical chemistry labs). A viscosity experiment is presented here that is designed around common seed and vegetable oils. With the importance of viscosity to foodstuffs (9) and the importance of fatty acids to nutrition (10), an experiment using these common, recognizable oils has broad appeal.

The pressure dependence of the luminescence lifetimes of Ru(bpy)3Cl2 and Ru(phen)3Cl2 (bpy = bipyridine; phen = phenanthroline) in H20 and D20 is reported in the 0.1-300-MPa range at several temperatures (2-70 °C). The observed activation volumes for electronic relaxation are analyzed in terms of a small, negative AVf (-2 mL/mol) for the CT -> GS nonradiative process and a large, positive AVf (10 mL/mol) for the CT -*• LF decay channel. The observed magnitudes for the two intrinsic activation volumes are consistent with the changes expected from the calculated metal-nitrogen bonds of the complex in the ligand field (LF), charge transfer (CT), and ground (GS) electronic states. Superimposed on these principal trends is a small deuterium isotope effect in AV2 and a small ligand effect in AVf.

No abstract