Search

Abstract: The photo-induced reactivity of three nanostructured titanium dioxides including TiO2 nanoparticles (i.e., nano-TiO2), titania–silica aerogel and nanotextured TiO2 film, were investigated for gas phase photocatalytic oxidation of trichloroethylene and inactivation of Bacillus subtilis and Escherichia coli microbial cells. A correlation was observed between photoreactivity for TCE conversion and bactericidal activity within TiO2 of similar nanostructures and composition (i.e., elemental and phase). This indicates that the photogenerated radical species from UV-irradiated TiO2 responsible for TCE photo-oxidation also play a major role in the inactivation of microbial cells. The superb bactericidal activities of titania–silica aerogels (i.e., up to 6log reductions in viable B. subtilis) and nanotextured TiO2 film (3.4log reduction) compared to commercial Degussa P25 TiO2 (0.64log reduction) and optimum nano-TiO2 (1.3log reduction) far exceeds the observed activity enhancement for TCE photo-oxidation. This implies that nanoscale chemical and structural environment also contribute towards the bactericidal activities. [Copyright &y& Elsevier]

Abstract: A multichannel membrane microreactor for continuous selective oxidation of aniline by hydrogen peroxide on TS-1 nanoparticles was successfully demonstrated. The high surface area to volume ratio that can be attained in the microreactor (3000m2/m3) facilitates the selective removal of water by-product, which reduces the effect of catalyst deactivation during the reaction. An improvement in the product yield and selectivity towards azoxybenzene was also observed. Azobenzene was obtained as by-product and its formation was attributed to homogeneous reaction of nitrosobenzene with aniline. Increasing temperature was beneficial for both yield and selectivity, but beyond 340K, microreactor operation was ineffective due to bubble formation and hydrogen peroxide decomposition. [Copyright &y& Elsevier]

Abstract: Mesoporous silica MCM-41 was successfully prepared by flow synthesis in a microreactor at shorter reaction times (i.e., minutes versus day) at high yield (i.e., 60% calcined sample) to give particles of more uniform size and shape compared to MCM-41 prepared by conventional batch synthesis. Magnetic iron oxide nanoparticles were incorporated and organic amines (i.e., propylamine and propyl diethylene amine) were grafted to obtain magnetic mesoporous catalysts for the Knoevenagel condensation reactions of benzaldehyde with ethyl cyanoacetate, ethyl acetoacetate and diethyl malonate. The incorporation of magnetic nanoparticles and large organic amines can hinder reactants access to the catalyst resulting in lower reactivity. NH2-magMCM-41 showed superb catalyst activity and selectivity for the all three Knoevenagel condensation reactions studied. The catalyst can be easily dispersed into solution and rapidly removed by a magnet for recovery and reuse. [Copyright &y& Elsevier]

Abstract: Chromium (VI) oxyanions were removed selectively from various aqueous systems using magnetic MCM-41 nanosorbents of large surface area (>550m2 g−1) and high magnetization (≥8.0emug−1). 10nm magnetic iron oxide nanoparticles were embedded within 250±50nm MCM-41 to obtain a highly dispersible magnetic material, magMCM-41 that can be easily removed by a magnetic field. A highly selective nanosorbent was obtained by grafting aminopropyls and adsorbing Fe3+ on the pores of the magMCM-41. Chromium oxyanions were selectively removed over the pH range of 2–7 with high adsorption capacity of ca. 1.9mmolg−1 (ca. 100mgg−1) and K d >25,000mLg−1 for single and binary component adsorptions from distilled, tap, mountain stream and river waters. The presence of calcium in the tap and natural waters as well as humic compounds in mountain stream and river waters resulted in a slightly lower chromium adsorption, but did not affect its superb selectivity (ca. 97%). The adsorption and separation of the chromium oxyanions were adequately described by Freundlich and LeVan–Vermeulen equations. [Copyright &y& Elsevier]

Abstract: Freestanding blocks of binary oxides, TiO2–SiO2 aerogel containing highly ordered mesophase structures were successfully prepared by a new synthesis method involving partial solvent evaporation followed by supercritical extraction and drying. The new method allows the routine preparation of large, crack-free aerogels of high titanium content (i.e., Ti/Si⩽0.75 or up to 50wt.% Ti), ordered mesopores (i.e., 2–20nm), large surface area (i.e., 400–900m2 g−1) and pore volume (i.e., 0.7–2.6cm3 g−1). Aerogels with well-ordered mesopores were obtained for Ti/Si atom ratios of 0.04–0.08. The size of ordered mesopore domains decreases with increasing titanium loading, and TS75 aerogels with Ti/Si=0.75 display discontinuous microdomains of ordered mesoporosity within disordered phases interspersed with crystalline anatase TiO2. The greater permeability of the TS75 pore network resulted in fifteen times better activity for photocatalytic oxidation of airborne trichloroethylene compared to commercial Degussa P25 TiO2 and more than twice that TiO2–SiO2 aerogel (TS100) of similar titanium loading but with disordered and tortuous pore network. [Copyright &y& Elsevier]

We demonstrate the preparation of sandwich structured microspheres containing Fe 3 O 4 cores, inner silica shells, supported Pd nanoparticles and outer ZIF-8 shells. The synthesis involved first deposition of silica layer on magnetic cores through traditional Stöber method and subsequent immobilization of Pd nanoparticles on the silica surface via grafting techniques, followed by the assembly of ZIF-8 shells over the Pd nanoparticles. Uniquely, the noble metal nanoparticles are sandwiched between the silica shell and porous ZIF-8 shell and such a configuration allows the metal nanoparticles to remain stable against aggregation and leaching while at the same time they are selectively accessible to the external environment outside of the ZIF-8 shells. Also, the resulting core@double-shell microspheres exhibit a superparamagnetic behavior with a high saturation magnetization of ~36.7 emu/g inheriting from the magnetic Fe 3 O 4 cores. It is believed that the designed microspheres could find potential uses in heterogeneous catalysis and adsorption fields with excellent reusability and high efficiency. [ABSTRACT FROM AUTHOR]

Abstract: A monolayer of zeolite nanoparticles was deposited uniformly on SiO2 beads’ surface by a new seeding method based on the combined use of organic linker and dip-coating procedure. The seeds were transformed into a well-intergrown TS-1 zeolite film and characterizations by SEM and XRD indicated that the film has a preferred (011) orientation. EDXS, XPS and UV–vis spectroscopies confirmed the successful preparation of egg-shell TS-1/SiO2 catalysts. Thin shell catalysts (i.e., <11μm) were more active for styrene oxidation. Conversion reaction rate of 8.9mmolg−1 h−1 and turnover frequency of 28h−1 were obtained with aromatic aldehydes (i.e., benzaldehyde and phenyl acetaldehyde) being the main products. Greater mass transfer resistance made thick shell catalysts less efficient with lower specific conversion rate of 6.9mmolg−1 h−1 and turnover frequency of 25h−1. Also, the extra-framework titanium resulting from the longer synthesis led to poorer selectivity. Egg-shell TS-1/SiO2 catalyst beads were shown to be resistant to attrition and were easier to separate and recover from reaction. [Copyright &y& Elsevier]

Abstract: Titanium silicalite-1 (TS-1) zeolites and films supported on porous α-Al2O3 tubes were prepared using TS-1 and silicalite-1 (Sil-1) seeds by hydrothermal synthesis. The structure and catalytic properties of the TS-1 powders and films were characterized by SEM, XRD, FT-IR, UV–vis and styrene partial oxidation by hydrogen peroxide. The results showed that TS-1 prepared from Sil-1 seeds were as active as TS-1 from nucleated and TS-1 seeded syntheses, in spite of the concerns about nonuniformity and dilution caused by the use of pure silica Sil-1 seeds. The Ti atoms were successfully incorporated as tetra-coordinated titanium in the zeolite framework and the phenylacetaldehyde selectivity correlates well with the infrared band for Ti–O–Si of the TS-1. Reaction over TS-1 film indicates that reactions occurred at the topmost layer of the film due to the slow diffusion in the zeolite pores. [Copyright &y& Elsevier]