A general method for entrapment of hydrophobically coated nanocrystals in micrometer and submicrometer composite silica spheres, nano@micro, was developed. The method employs two starting solutionshydrophobic solvent containing the sol−gel precursor, a polymer, and the nanocrystals, and an emulsifying hydrophilic phase which catalyzes the sol−gel process. The use of a hydrophobic polymer, polystyrene, serves to encapsulate the nanocrystals inside the spheres while maintaining many of their original properties. The obtained nano@micro spheres were characterized structurally by transmission electron microscopy and scanning electron microscopy, chemically by energy dispersive X-ray spectroscopy, and optically by ensemble and single-particle fluorescence spectroscopy. It is possible to control the size of the microspheres from the 100 nm scale to the micrometer scale, with good monodispersivity and with good separation between the microspheres. The method is demonstrated for encapsulating a wide variety of nanocrystals, primarily semiconductors covering different spectral bands, and of different shapes including spheres and rods. The semiconductor nanocrystals impart widely tunable emission to the microspheres. A similar encapsulation technique was also applied to thiol-coated Au particles. The technique is generally applicable to other hydrophobic nanocrystal systems of magnetic, oxide, and other materials.

The creation of new materials systems for lightweight and flexible displays is an extremely active research field. Electrochromic displays possess a keen advantage over other technologies because it is possible for a single electrochromic pixel to produce multiple colors in addition to white, depending on applied potential. This possibility has proven quite challenging to achieve in practice. Here we present the successful fabrication of a multiply colored electrochromic electrode using layer-by-layer (LBL) assembly. The electrode films are created by exploiting intrinsic electrostatic attraction between the polycation poly(aniline) (PANI) and a negatively ionized Prussian Blue (PB) nanoparticle dispersion. The resultant organic/inorganic nanocomposites exhibit excellent smoothness and a classical linear increase in film thickness with assembly exposure steps. Electrochemical and spectrophotometric characterization confirms the distinct and noninteracting contributions from PANI and PB and reveals that both are fully electrochemically accessible even in thick, high contrast films. Switching speed is accelerated due to the incorporation of electronically conducting PANI. The PANI/PB nanocomposite undergoes an uncolored to green to blue transition over the potential range from −0.2 to 0.6 V vs K-SCE. These results validate an LBL-assembly-based intermixing strategy for the design of multiple-hue electrochromic electrode films. Future horizons include extension to other materials, with the eventual goal of creating a single electrode film or electrochemical cell capable of displaying any visible color on demand.

The chemical synthesis of polyaniline (PANI) is explored using tetrachloroaurate, AuCl₄^-. These studies provide a simple method for the oxidation of aniline by AuCl₄^- and simultaneous formation of bulk quantities of a PANI/Au composite. In situ UV/vis spectroscopy indicates that the rate of formation of gold colloids and intermediate (short-chain) PANI species is rapid in comparison to that of the long-chain PANI. Longer PANI chains are produced at a slower rate, at the expense of short-chain intermediate species. The gold particles act as nucleation sites for the oxidative formation of PANI, encapsulating the metal in the form of a polymer/metal composite. Results from the elemental analysis and the FTIR spectra of the composite material are consistent with PANI produced using only ammonium persulfate as the oxidant. In addition, XPS, optical microscopy, and TEM diffraction show that the gold particles are polycrystalline with relatively constant diameter (0.8−1 μm). Finally, the PANI/Au/HBF₄ conductance does not change significantly with the introduction of Au particles, relative to that of PANI/HBF₄ without Au particles. These studies provide a new method for growth of PANI/metal composites where the presence of the metal in the polymer does not adversely affect the electronic structure.

A titania−acrylic composite reactor was constructed with a coil geometry. The presence of multiple titania layers within the reactor increases the titania surface area while making maximum use of the illumination provided. Both compact fluorescent blacklight (CFL) and ultraviolet light emitting diodes (LEDs) were used as illumination sources. An external pump was used to recirculate 650−800 mL of water containing organic, metallic, or bacterial contamination through the coil reactor. Complete purification of the water was achieved within 300 min with 10 ppm methylene blue, 10 ppm methyl orange, 20 ppm Pb²⁺, and 2200 colony forming units per milliliter (CFU/mL) of E. coli respectively using the CFL source. The effectiveness, low cost, durability, ruggedness, and energy efficiency of this reactor are advantageous for both portable and fixed-base applications.

Fully oxidized α-Al^IIIW₁₂O₄₀^5- (1_ox), and one-electron-reduced α-Al^IIIW₁₂O₄₀^6- (1_red), are well-behaved (stable and free of ion pairing) over a wide range of pH and ionic-strength values at room temperature in water. Having established this, ²⁷Al NMR spectroscopy is used to measure rates of electron exchange between 1_ox (²⁷Al NMR: 72.2 ppm relative to Al(H₂O)₆³⁺; ν_1/2 = 0.77 Hz) and 1_red (74.1 ppm; ν_1/2 = 0.76 Hz). Bimolecular rate constants, k, are obtained from line broadening in ²⁷Al NMR signals as ionic strength, μ, is increased by addition of NaCl at the slow-exchange limit of the NMR time scale. The dependence of k on μ is plotted using the extended Debye−Hückel equation: log k = log k₀ + 2αz₁z₂μ^1/2/(1 + βrμ^1/2), where z₁ and z₂ are the charges of 1_ox and 1_red, α and β are constants, and r, the distance of closest contact, is fixed at 1.12 nm, the crystallographic diameter of a Keggin anion. Although not derived for highly charged ions, this equation gives a straight line (R² = 0.996), whose slope gives a charge product, z₁z₂, of 29 ± 2, statistically identical to the theoretical value of 30. Extrapolation to μ = 0 gives a rate constant k₁₁ of (6.5 ± 1.5) × 10^-3 M^-1 s^-1, more than 7 orders of magnitude smaller than the rate constant [(1.1 ± 0.2) × 10⁵ M^-1 s^-1] determined by ³¹P NMR for self-exchange between P^VW₁₂O₄₀^3- and its one-electron-reduced form, P^VW₁₂O₄₀^4-. Sutin's semiclassical model reveals that this dramatic difference arises from the large negative charges of 1_ox and 1_red. These results, including independent verification of k₁₁, recommend 1_red as a well-behaved electron donor for investigating outer-sphere electron transfer to molecules or nanostructures in water, while addressing a larger issue, the prediction of collision rates between uniformly charged nanospheres, for which 1_ox and 1_red provide a working model.

The radiation field in an annular photocatalytic reactor is simulated using a Monte Carlo method (MC) for two TiO₂ suspensions in water. Simulations are performed by using both the spectral distribution and the wavelength-averaged scattering and absorption coefficients. The Henyey−Greenstein phase function is adopted to represent forward, isotropic, and backward scattering modes. It is assumed that the UV lamp reflects the backscattered photons by the slurred medium. Photoabsorption rates using MC simulations and spectral distribution of the optical coefficients agree closely with experimental observations from a macroscopic balance. It is found that the scattering mode of the probability density function is not a critical factor for a consistent representation of the radiation field. MC simulation for the optimal catalyst concentration reveals that the maximum LVREA is reached at a concentration of 0.14 g L⁻¹ for TiO₂ Degussa P25. From this concentration, the apparent optical thickness is determined to be 2.8476 which is in agreement with the optimal one previously reported. This concentration is comparable to that determined experimentally for phenol photocatalytic degradation.