A simple and facile template-free method has been developed for the fabrication of CdS hollow nanospheres via hydrothermal treatment of aqueous solutions of cadmium acetate and thiourea. Based on the detailed investigation on the influences of experimental parameters including the precursor chemical concentrations, reaction time, and reaction temperature, the formation mechanism of the hollow interiors by an Ostwald ripening process was the first time proposed for CdS hollow nanospheres. In particular, it was found that molar ratio of thiourea:Cd2+ in the starting solutions affected the sizes of the nanospheres and the hollowing process. At a high ratio of 25:1, hollow nanospheres with an average diameter of ca. 100 nm were obtained. In the presence of a large excess of thiourea, isotropic growth of CdS nanocrystallites occurred with their domain sizes in [100] and [001] directions similar at ca. 20 nm. At the same time, the hollowing process was promoted because of a fast mass transport. At lower molar ratios at 10:1 and 5:1, hollow interiors were not observed and the diameters of the nanospheres increased to 200 and 280 nm. The nanocrystallites in these larger nanospheres grew preferentially in [001] direction to ca. 40 nm. All the nanospheres formed have a hexagonal wurtzite structure and exhibit good size uniformity and regularity. Furthermore, the as-prepared hollow nanospheres demonstrated a good photocatalytic activity for methylene blue degradation by complete oxidation under visible light.

Uniform NiO, α-Fe2O3, ZnO, CuO and Ga2O3 hollow nanospheres consisting of a shell of closely packed nanoparticles with a shell wall thickness of a few tens of nanometers have been successfully synthesized on a large scale by controlled precipitation of metal cations with urea in the presence of carbonaceous saccharide nanospheres as hard templates. In addition, it is interesting to find that the single-phase transition metal oxides of NiO and α-Fe2O3 can form ball-in-ball hollow nanoarchitectures by this simple approach. Furthermore, it is demonstrated that direct size control of the oxide hollow nanospheres can be achieved by using carbon templates of different diameters. This method could be extended to the synthesis of many other metal oxide hollow nanospheres. The hollow nanostructured metal oxides might be found to have potential applications in many fields such as catalyst supports, catalysis, drug delivery, chemical/biological separation, sensing, etc.

Monodispersed single crystalline R-GaOOH spindles have been prepared via a simple wet-chemical route at 60 °C, in which GaCl 3 was used as the gallium source and ammonia as the alkali. The R-GaOOH spindles obtained at pH values of 10.0 and 11.0 have a hierarchical layered nanostructure and are comprised of many nanoplatelets. The investigation of the products formed at early growth stages indicates that the spindles are formed by a self-assembly process via oriented attachment. During this process, the pH value and the ammonia molecule have great influence on the morphology of the final products. Smooth prism-like R-GaOOH crystals were obtained at a lower pH value of 8.0 when ammonia was used or when ammonia was replaced by ethylenediamine at pH values of 8.0 and 10.0. The single-phase R-Ga 2 O 3 and β-Ga 2 O 3 spindles can be obtained by thermal treatment of the R-GaOOH spindles at 600 and 900 °C, respectively. The morphological characteristics of the pristine R-GaOOH spindles are well maintained in the oxide products in terms of good dispersion, size uniformity and layered nanostructure. The β-Ga 2 O 3 spindle product exhibits a strong blue luminescence emission under the excitation wavelength of 250 nm.

Cationic gemini surfactant homologues alkanediyl-alpha,omega-bis(dodecyldiethylammonium) bromide, [C12H25(CH3CH2)2N(CH2)SN(CH2CH3)2C12H25]Br2, where S = 4, 6, 8, 10, or 12, referred to as C12CSC12(Et), and cationic bolaamphiphiles BPHEAB (biphenyl-4,4'-bis(oxyhexamethylenetriethylammonium) bromide), PHEAB (phenyl-4,4'- bis(oxyhexamethylenetriethylammonium) bromide) were synthesized, and their aggregation behaviors in aqueous solution were studied and compared by means of dynamic light scattering, fluorescence entrapment, and transmission electron microscopy. Spherical vesicles were found in the aqueous solutions of these gemini and bola surfactants, which can be attributed to the increase of the hydrocarbon parts of the polar headgroup of the surfactants. In combination with the result of the other gemini with headgroup of propyl group, the increase of the hydrophobic parts of the surfactant polar headgroup will be beneficial to enhance the aggregation capability of the gemini and bola surfactants. Both of the vesicles formed in the gemini and bola systems showed good stabilities with time and temperature, but different stability with salt due to the different membrane conformations of surfactant molecules in the vesicles.

Separating azeotrope-forming solvent−water mixtures by conventional distillation poses technical, economic, and environmental challenges. Pervaporation and vapor permeation membrane technologies using water-permselective membranes provide an efficient alternative for water removal from solvents. We present here new water-selective materials, based on 1,2polybutadiene, that address two problems reported for traditional hydrophilic membrane materials under high water activities: swelling and hydrolysis. Exposure to UV radiation and/or heat converted portions of the vinyl groups in the polybutadiene to cross-links and hydrophilic functional groups, including alcohols, ketones, and carboxylic acids. In testing with a series of alcohols, such materials displayed high water permeabilities and stable performance over several months even at the extremes of 100% water, low water (2%), and an ethanol/water vapor at 115 °C and 2.5 bar.

The polysiloxane of greatest commercial importance and scientific interest is poly(dimethylsiloxane) (PDMS), [Si(CH3)2 –O –]x, a member of the symmetrical dialkyl polysiloxanes, with repeat unit [SiR2 –O –]x. This polymer is discussed extensively in the following chapters, particularly in chapter 5. Other members of this series are poly(diethylsiloxane) [Si(C2H5) –O–]x, and poly(di-n-propylsiloxane) [SiC3H7)2–O–]x. An example of an aryl member of the symmetrically substituted series is poly(diphenylsiloxane), with repeat unit [Si(C6H5)2–O–]x. This polymer is unusual because of its very high melting point and the mesophase it exhibits. The closely related polymer, poly(phenyl/tolylsiloxane), has also been prepared and studied. The unsymmetrically substituted polysiloxanes have the repeat unit [SiRR’O–]x, and are exemplified by poly(methylphenylsiloxane) [Si(CH3) (C6H5) –O–]xand poly(methylhydrosiloxane) [Si(CH3)(H) –O–]x. In some cases, one of the side chains has been unusually long, for example C6H13, C16H33, and C18H37, including a branched side chain—CH(CH3– (CH2)m–CH3. Another example has methoxy-substituted aromatic fragments as one of the two side chains in the repeat unit. Such chains have stereochemical variability in analogy with the vinyl polymers such as polypropylene [CH(CH3) –CH2–]xand vinylidene polymers such as poly(methyl methacrylate) [C(CH3)(C = OOCH3) –CH2–]xOne can also introduce optically active groups as side chains, the simplest example being the secondary butyl group—CH(CH3)(C2H5). Another example involves redox-active dendritic wedges containing ferrocenyl and carbonylchromium moieties. Other substituents have included phenylethenyl groups, cyclic siloxane groups, and Cr-bound carbazole chromophores. In a reversal of roles, some polymers were prepared to have PDMS side chains on a poly(phenylacetylene) main chain. Siloxane-terminated solubilizing side chains are used to improve the properties of thin-film transistors. Silalkylene polymers have methylene groups replacing the oxygen atoms in the backbone. Poly(dimethylsilmethylene) is an example, [Si(CH3)2–CH2]x. A variation on this theme is to include aryl groups, for example, in poly(dimethyldiphenylsilylenemethylene) [Si(CH3)2CH2Si(C6H5)2]x. Other aryl substituents, specifically tolyl groups, have also been included as side chains. It is also possible to insert a silphenylene group [Si(CH3)2–C6H4–] into the backbone of the polysiloxane repeat unit to give [Si(CH3)2–C6H4– Si(CH3)2O–], in which the phenylene can be para or ortho or meta. A specific example is poly(tetramethyl-p-silphenylene-siloxane).

The ability of homogeneous and mixed matrix membranes prepared using standard silicone rubber, poly(dimethylsiloxane) (PDMS), and fluorosilicone rubber, poly(trifluoropropylmethylsiloxane) (PTFPMS), to dehydrate ethanol by pervaporation was evaluated. Although PDMS is generally considered to be the benchmark hydrophobic membrane material in pervaporation, water/ethanol molar permselectivity of a pure PDMS membrane was found to be 0.89 for a feed containing 80/20 w/w ethanol/water at 50 C, indicating a slight selectivity for water. Fluorinated groups in PTFPMS improved the water-ethanol permselectivity to 1.85, but decreased the water permeability from 9.7 Â 10 À12 kmol Á m/m 2 Á s Á kPa in PDMS to 5.1 Â 10 À12 kmol Á m/m 2 Á s Á kPa (29,000 and 15,200 Barrer, respectively). These water permeabilities are attractive, particularly since the rubbery materials should not experience the steep declines in water permeability observed with most standard dehydration membranes as water concentration in the feed decreases. However, the water selectivity is lower than desired for most applications. Particles of hydrophilic zeolite 4A were loaded into both PDMS and PTFPMS matrices in an effort to boost water selectivity and further improve water permeability. Water-ethanol permselectivities as high as 11.5 and water permeabilities as high as 23.2 Â 10 À12 kmol Á m/m 2 Á s Á kPa were observed for the PTFPMS/zeolite 4A mixed matrix membranesÀ6 times higher than for the unfilled PTFPMS membrane.

Molecularly imprinted microspheres for recognition of chlorpyrifos were prepared by thermal initiation and precipitation polymerization, and were characterized using scanning electron microscope and infrared spectroscopy. Binding characteristics of the microspheres were also investigated. Sensitive film electrode of chlorpyrifos was prepared using the microspheres above on the surface of gold electrode by spin coating. Electrochemical sensor was constructed with the electrode prepared above as recognition element, and the response characteristics of the sensor to chlorpyrifos in water were investigated based on constant-current potentiometry. It was shown that a reasonable linear response curve between potential and concentration was obtained from 1.0×10-12mol/L to 2.0×10-8mol/L, with a detection limit of 1.0×10-13mol/L. The suitable pH was 2.2~3.4,and response time was 10 min. The imprinted electrode showed relatively high selectivity to chlorpyrifos and was applied to the analysis of chlorpyrifos in the simulated river samples with recovery rates ranging from 89% to 105%.