Micellar-enhanced ultrafiltration for the solubilization of various phenolic compounds with different surfactants.

Micellar-enhanced ultrafiltration (MEUF) was applied to the separation of phenolic compounds p-nitrophenol (PNP), p-chlorophenol (PCP), p-cresol (PC) and phenol (P) from effluents using a hydrophilic polyethersulfone ultrafiltration membrane. Cationic cetylpyridinium chloride (CPC), nonionic TX-100 and anionic sodium dodecyl benzene sulfonate (SDBS) were chosen as the surfactants. Several important parameters, i.e. the separation efficiency, the distribution coefficient of phenolic compounds and the removal ratio of surfactants, were investigated. It was shown that the separation efficiency and the distribution coefficient of phenolic compounds ascended with the increasing surfactant concentration and could be arranged as the following order: PNP>PCP>PC>P. Moreover, in the case of phenolic compound separation, CPC achieved the highest treatment efficiency, and the separation efficiency of SDBS was a little lower than that of TX-100. The removal ratios of the same surfactant when treating different phenolic effluents were nearly similar. However, when treating the same phenolic compound, the sequence of the surfactant rejection was in the following order: TX-100>CPC>SDBS. These results indicate that CPC has a distinct superiority in the treatment of phenolic effluents via the MEUF process, and PNP easily solubilizes in the surface of the micelles.

Effect of low-concentration rhamnolipid on adsorption of Pseudomonas aeruginosa ATCC 9027 on hydrophilic and hydrophobic surfaces.

The effects of low-concentration monorhamnolipid (monoRL) on the adsorption of Pseudomonas aeruginosa ATCC 9027 grown on glucose or hexadecane to glass beads with hydrophobic or hydrophilic surfaces was investigated using batch adsorption experiments. Results showed that adsorption isotherms of the cells on both types of glass beads fitted the Freundlich equation better than the Langmuir equation. The Kf of the Freundlich equation for adsorption of hexadecane-grown cell to glass beads with hydrophobic surface was remarkably higher than that for adsorption of hexadecane-grown cell to glass beads with hydrophilic surface, or glucose-grown cell to glass beads with either hydrophilic or hydrophobic surface. Furthermore, it decreased with the increasing monoRL concentration. For both groups of cells, the zeta potential was close to each other and stable with the increase of monoRL concentration. The surface hydrophobicity of hexadecane-grown cells, however, was significantly higher than that of the glucose-grown cells and it decreased with the increase of monoRL concentration. The results indicate the importance of hydrophobic interaction on adsorption of bacterial cells to surfaces and monoRL plays a role in reducing the bacterial adsorption by affecting cell surface hydrophobicity.

Local and nonlocal contributions to molecular first-order hyperpolarizability: a Hirshfeld partitioning analysis.

Based on first-principles calculations, a decomposition scheme is proposed to investigate the molecular site-specific first-order hyperpolarizability (ß) responses by means of Hirshfeld population analysis and finite field method. For a molecule, its ß is decomposed into local and nonlocal contributions of individual atoms or groups. The former describes the response within the atomic sphere, while the latter describes the contributions from interatomic charge transfer. This scheme is then applied to six prototypical donor-acceptor (D-A) or D-π-A molecules for which the local and nonlocal hyperpolarizabilities are evaluated based on their MP2 density. Both the local and nonlocal parts exhibit site-specific characteristics, but vary differently with molecular structures. The local part depends mainly on the atomic attributes such as electronegativity and charge state, as well as its location in the molecule, while the nonlocal part relates to the ability and distance of charge delocalization within the molecule, increasing rapidly with molecular size. The proposed decomposition scheme provides a way to distinguish atomic or group contributions to molecular hyperpolarizabilities, which is useful in the molecular design for organic nonlinear optical materials.

Theoretical investigation of adsorption of molecular oxygen on small copper clusters.

Adsorption of molecular oxygen on Cu(N) (N = 2-10) clusters is investigated using density functional theory under the generalized gradient approximation of Perdew-Burke-Ernzerhof. An extensive structure search is performed to identify low-energy conformations of Cu(N)O(2) complexes. Optimal adsorption sites are assigned for low-energy isomers of the clusters. Among these are some new arrangements unidentified heretofore. Distinct size dependences are noted for the ground state Cu(N)O(2) complexes in stability, adsorption energy, Cu-O(2) bond strength, and other characteristic quantities. Cu(N)O(2) with odd-N tend to have larger adsorption energies than their even-N neighbors, with the exception of Cu(6)O(2), which has a relatively large adsorption energy resulting from the adsorption-induced 2D-to-3D structural transition in Cu(6). The energetically preferred spin-multiplicity of all the odd-N Cu(N)O(2) complexes is doublet; it is triplet for N = 2 and 4 and singlet for N = 6, 8, and 10.