Biexcitonic fine structure of CdSe nanocrystals probed by polarization-dependent two-dimensional photon echo spectroscopy

The spectroscopy of colloidal CdSe nanocrystals is investigated using two-dimensional photon echo (2DPE) spectroscopy with copolarized and cross-polarized pulse sequences. Clearly resolved excited state absorption features are observed to beat at the frequency of the longitudinal-optical phonon, and the phase of this beating is found to be polarization-dependent. A simulation is performed using the excitonic and biexcitionic fine structure states predicted by theory, and the polarization-dependent beating allows each feature to be assigned to a particular excited state absorption pathway. Owing to their circularly polarized selection rules, the polarization-dependent 2DPE technique provides valuable insights into the spectroscopy of quantum dots. In particular, transient absorption features observed in pump-probe studies of CdSe quantum dots can now be assigned to specific fine structure transitions to the ground state biexciton.     

The application of TiO2 photocatalysis for disinfection of water contaminated with pathogenic micro-organisms: a review

The use of semiconductor photocatalysis for treatment of water and air has been the topic of intense research activity over the past 20 years. This powerful process has also been extended to the disinfection of environments contaminated with pathogenic micro-organisms. This review summarizes recent developments concerned with the photocatalytic treatment of water contaminated with pathogenic micro-organisms presenting a potential hazard to animals and human beings.     

Measurement of Void Size Correlation in Inhomogeneous Porous Media

In previous works, we have described a void space reconstruction method based on non-wetting fluid intrusion, wetting fluid drainage, and image analysis data. The method has been applied to a wide range of substances, including sandstone, compressed and sintered powders, paper substrates and coatings, soil and fibrous mats. We have also demonstrated in a previous work that the spatial correlation of similarly sized voids within inhomogeneous porous media has a huge effect on permeability. We therefore describe a method of measuring such correlation, suitable for use in our void space reconstructions. The method involves a cubic spline smoothing of a variogram of the void sizes in a binary image of the porous medium. It has been successfully tested on an artificially correlated void network, comprising two sintered glass discs of different void size ranges. Stereological effects, caused by the off-centre sectioning of voids, can interfere with the variogram features. Our method is sh own to be insensitive to artificially generated stereological interference. The method is also applied to sandstone samples.     

New chemosensory materials based on disubstituted polyacetylene with strong green fluorescence

A new imidazole‐containing disubstituted polyacetylene ( P1 ) with strong green fluorescence was successfully prepared through polymer reaction, which was nearly impossible to be obtained from the direct polymerization of its corresponding monomer. The polymer was soluble in common organic solvents, and its strong green fluorescence could be quenched completely by the Cu²⁺ and Co²⁺ ions, at the concentrations as low as 1.33 and 1.67 × 10⁻⁵ mol/L (0.85 and 0.92 ppm), respectively. Because of the high stability of the complex formed by cyanide and copper ions, the quenched green fluorescence of P1 by copper ions could be turned on upon the addition of trace cyanide (as low as 2.70 × 10⁻⁵ mol/L, 0.70 ppm), making P1 a new sensitive cyanide chemosensor. The results thus provided a new opportunity to develop anion chemosensors based on good cation chemosensors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8070–8080, 2008     

Achieving Rapid Absorption and Extensive Liquid Uptake Capacity in Porous Structures by Decoupling Capillarity and Permeability: Nanoporous Modified Calcium Carbonate

Porous media with rapid absorption properties are greatly sought after in the fields of super absorbers and catalysts. Natural materials, such as diatomite, or synthetic zeolite feature strongly in industrial reaction processes. Most, or all, of such materials, however, are surface acidic. A novel rapidly absorbing alkaline porous structure, with a high absorption capacity, is presented here. As in the case of diatomite or zeolite, the pigment design incorporates strong capillarity within a highly permeable packed medium. A model is proposed for general use with highly absorbing media that can be proven microscopically to have separate domains of micro- or nano-capillarity embedded within a permeable matrix. The new pigment morphology, based on natural ground calcium carbonate (gcc), exhibits this property using special surface structure modifications. It is contrasted with standard gcc by using consolidated tablet blocks made from a suspension of the pigment and chosen mixtures thereof. The blocks are characterised after drying by mercury porosimetry, and the absorption dynamic of a selected liquid is studied. It is shown that using a self-assembly method of discrete pore structures provides a much faster absorption rate and a liquid capacity for up to 10 times more fluid than a conventional homogeneously distributed pore concept. In such unique discrete network systems, the mercury intrusion curve provides a separable analysis of permeability and capillarity in respect to the inflection point of the cumulative intrusion curve. The discrete decoupled properties each follow the absorption behaviour predicted by previous modelling (Ridgway and Gane, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 206(1–3), 2002). The absorption driving force is shown to be determined by the proportion of fine pores present up to a size equal to a Bosanquet inertially-defined optimum within the timescale of absorption. Combining the wetting force, from the capillarity-controlled fine pore structure, with the experimental flow resistance of the sample, consisting of the assembly of particles, it is possible to predict the trends in absorption dynamic using the pore and throat model Pore-Cor.* Use of this model allows existing materials as well as new synthetic designs to be modelled prior to manufacture. The novel alkaline material is compared with independent absorption data for diatomite and shown to be comparable. *Pore-Cor is a software product name of the Environmental and Fluid Modelling Group, University of Plymouth, Devon PL4 8AA, U.K.     

Backscatter effects of surfaces composed of dry biological particles

We present the backscattering of particulate surfaces consisting of dry biological particles using two laboratory photopolarimeters that measure intensity and degree of linear polarization in a phase-angle range 0.2-60°. We measure scattering properties from three samples composed of dry biological particles, Bacillus subtilis var. niger (BG) spores and samples of fungi Aspergillus terreus and Sporisorium cruentum spores. We find that the surfaces display a prominent brightness opposition effect and significant negative polarization near backscattering angles. The brightness and polarimetric phase curves are different for B. subtilis and the fungi.