Molecularly imprinted silica as a selective SPE sorbent for triazine herbicides

A molecularly imprinted organically modified silica was prepared through a simple sol‐gel procedure and evaluated as a specific sorbent for SPE of triazine herbicides. The material proved to be highly selective for the template molecule, atrazine, as well as for other structurally related species such as simazine and propazine. The performance of this material was shown to be comparable with commercial acrylate‐based molecularly imprinted polymers. The molecularly imprinted silica was applied for the determination of trace levels of the target triazine analytes in sugar cane juice (locally called “garapa”).     

Poly(methyloctylsiloxane) immobilized on silica as a sorbent for solid-phase extraction of some pesticides

A laboratory-made sorbent for solid-phase extraction (SPE) was obtained by thermal immobilization of poly(methyloctylsiloxane) (PMOS) onto silica. Cartridges packed with the new sorbent were used for the simultaneous determination of imazethapyr, nicosulfuron, diuron, linuron and chlorimuron-ethyl in water. These pesticides were separated and quantified using high-performance liquid chromatography with diode array detection (HPLC-DAD). The recoveries achieved with the laboratory-made PMOS cartridges were compared with those of some commercially available silica-based and polymer-based cartridges having C18, C8 and NH(2) pendant groups. Method validation using the laboratory-made sorbent was performed for the five pesticides at three fortifications levels (1x, 2x and 10x the limit of quantification of each pesticide). The laboratory-made PMOS cartridge has low cost preparation and showed good recoveries (72-111%) for all pesticides. Repeatability and intermediate precision were lower than 15%. Its performance was similar or even better, in some cases, than those of the commercial cartridges.     

Post-irradiation time effects on the graft of poly(ethylene-alt-tetrafluoroethylene) (ETFE) films for ion exchange membrane application

Grafting of styrene followed by sulfonation onto poly(ethylene-alt-tetrafluoroethylene) (ETFE) was studied for synthesis of ion exchange membranes. Radiation-induced grafting of styrene onto ETFE films was investigated after simultaneous irradiation (in post-irradiation condition) using a ⁶⁰Co source. The ETFE films were irradiated at 20 kGy dose at room temperature and chemical changes were monitored after contact with styrene for grafting. The post-irradiation time was established at 14 days when the films were remained in styrene/toluene 1:1 v/v. After this period the grafting degree was evaluated in the samples. The grafted films were sulfonated using chlorosulfonic acid and 1, 2-dichloroethane 20:80 (v/v) at room temperature for 5 h. The membranes were analyzed by infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), thermogravimetric measurements (TG) and degree of grafting (DOG). The ion exchange capacity (IEC) of membranes was determined by acid–base titration and the values for ETFE membranes were achieved higher than Nafion^® films. Preliminary single cell performance was made using pure H₂ and O₂ as reactants at a cell temperature of 80 °C and atmospheric gas pressure. The fuel cell performance of ETFE films was satisfactory when compared to state-of-art Nafion^® membranes.     

Self-immobilization of poly(methyloctylsiloxane) on high-performance liquid chromatographic silica

Poly(methyloctylsiloxane) (PMOS) was deposited on HPLC silica by a solvent evaporation procedure and this material was then extracted, using a good solvent for the PMOS, after different time periods, to remove unretained liquid polymer. Solvent extraction data reveal changes which occur at ambient temperature as a function of the time interval between particle loading and extraction. The quantity of PMOS remaining on the silica after extraction, as determined by elemental analysis for carbon, is attributed to strongly adsorbed polymer. This phenomenon is termed self-immobilization. Solid-state 29Si NMR spectra indicate the formation of a silicon species with a different chemical shift than the original PMOS. These new signals are attributed to a combination of different adsorbed and chemically bonded groups.     

From Ynamides to Highly Substituted Benzo[b]furans: Gold(I)‐Catalyzed 5‐endo‐dig‐Cyclization/Rearrangement of Alkylic Oxonium Intermediates

A series of arylynamides with alkyloxy groups at the ortho position of the aryl group was prepared through a short alkylation/cross‐coupling/amidation sequence. The gold‐catalyzed conversion of these substrates combined both C? O and C? C formation steps, thus providing benzofurans with amine functionalities at the 2‐position and alkyl groups at the 3‐position. Cross‐over experiments showed that the alkyl‐migration step was an intermolecular process. X‐ray crystal‐structure analysis of two of the products supported our structural assignment. In some cases, the corresponding benzofurans without the alkyl group at the 3‐position were obtained as side‐products, which were formed through a competing protodeauration process.     

催化:古老却富有挑战性的石墨烯基材料(英文)

An assessment is offered regarding the progress made, and the remaining challenges, in the field of carbocatalysis. The fundamental principles that govern the preparation and performance of sp2-hybridized carbon materials in heterogeneous catalysis have been known for decades, and the level of understanding of key issues – especially the importance of textural and ion-exchange properties (i.e., surface area, pore size distribution, and proton transfer) – remains quite satisfactory. The opportunities for novel catalytic materials – especially graphene nanosheets and carbon nanotubes– are tremendous, especially when it comes to taking advantage of their structural order, such that electron transfer can be both better understood and controlled to enhance catalytic activity and selectivity.