Multiple Bridging Groups Aid Absorption Properties of Ordered Porous Organic-Inorganic Hybrids
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notable innovation of the work is then achieved by simultaneous application of the FD and BD control beams. This produces an interference pattern that causes the Rb atoms to act like tiny mirrors, effectively trapping the light pulse inside the medium. The pulse is then released in the forward direction by turning off the BD beam. In this fashion, the researchers brought light to a halt. ANDY FRANCIS
Multiple Bridging Groups Aid Absorption Properties of Ordered Porous Organic–Inorganic Hybrids Organic–inorganic hybrid polymers in the form of periodic mesoporous organosilicas (PMOs) have highly ordered pore networks and large internal surface areas. Although similar in morphology, they are more mechanically and hydrothermally stable than ordered mesoporous silicas. One way to tailor the pore size in PMOs for specific applications (e.g., sorbents, sensors, and catalysts) is to vary the organic groups that bridge the inorganic moieties. Toward this end, a team of researchers at the Center for Bio/Molecular Science and Engineering within the Naval Research Laboratory, Washington, D.C., has synthesized and characterized a class of ordered PMOs with more than one type of organic group. In an article published in the December 17, 2003, issue of Chemistry of Materials, investigator M.A. Markowitz and coworkers used a versatile surfactant templating technique to synthesize PMOs in which the organic bridging group was an ethylene homopolymer, a phenylene homopolymer, or an ethylene phenylene copolymer. In the current study, PMOs with organic copolymers were prepared with ratios of phenylene and ethylene precursor ratios of 3:1, 1:1, and 1:3. Analyses by the researchers of solid-state 13C and 29Si cross-polarization/magic angle spinning nuclear magnetic resonance (CP/ MAS NMR) spectra confirmed that the C–Si and Si–O bonds were stable during synthesis for all PMO polymers. In addition, the NMR spectra showed that extraction of the surfactant was complete. The researchers showed that powder x-ray diffraction patterns are consistent with
hexagonally packed arrays of round cylindrical voids (i.e., the pores), surrounded by the polymer matrix. The researchers found that the pore size distribution was very narrow and centered at 4 nm. Although the researchers note a trend in pore size based on precursor ratio, the differences in pore size are small. Nitrogen sorption measurements obtained classic Type IV isotherms with large nitrogen capacities (0.9–1.1 cm3/g at STP). The absorption capacity of the PMO prepared from a 1:1 ethylene phenylene precursor ratio is about 75% greater than the phenylene-bridged PMO and about twice that of the ethylene-bridged PMO. The researchers said this demonstrates that the phenylene–ethylene combination results in improved performance. A diphenylene-bridged organosilica was also previously reported to have high absorption capacity, but that material has an amorphous pore structure, which is disadvantageous for some applications. The researchers attribute this lack of pore order to the flexible natu
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