UV Raman spectroscopic study on the synthesis mechanism of zeolite X

The synthesis of zeolite X is characterized by UV Raman spectroscopy, NMR spectroscopy, and X-ray diffraction. UV Raman spectra of the liquid phase of the synthesis system indicate that AI(OH); species are incorporated into silicate species, and the polymeric silicate species are depolymerized into monomeric silicate species during the early stage of zeolite formation. An. intermediate species possessing Raman bands at 307, 503, 858 and 1020 cm(-1) is detected during the crystallization ill the solid phase transformation. The intermediate species is attributed to the beta cage, the secondary building unit of zeolite X. A model for the formation of zeolite X is proposed, which involves four-membered rings connecting to each other via six-membered ring to form beta cages, then the beta cages interconnect via double six-membered rings to form the framework of zeolite X. (C) 2001 Elsevier Science B.V. All rights reserved.

Phenylurea herbicides-selective polymer prepared by molecular imprinting using N-(4-isopropylphenyl)-N'-butyleneurea as dummy template

A phenylurea herbicides-selective molecularly imprinted polymer (MIP) was prepared using N-(4-isopropylphenyl)-N'-butyleneurea as a dummy template and toluene as a porogen. The experimental results showed that the optimum molar ratio of template, functional monomer (MAA) and cross-linker (EDMA) was 1:8:20. Scatchard analysis showed that two classes of binding sites were formed in the imprinted polymer with dissociation constants of 26.81 mu L mol l(-1) and 1.428 mmol l(-1). The affinity and selectivity of MIP for phenylurea herbicides were studied. Among the 14 phenylurea herbicides tested, the MIP prepared showed obviously high affinity and selectivity for 10 chemicals (monuron, diuron, isoproturon, fenuron, chlortoluron, difenoxuron, metoxuron, neburon, buturon and fluometuron) with dichloromethane containing 10% hexane as mobile phase while non-imprinted polymer showed very low affinity for all the phenylurea herbicides tested. The experimental and calculated results also indicated that the size and property of the group at the N' position of phenylurea molecules have great influence on the affinity of MIP for them and the recognition site is mainly located at the N' position of phenylurea herbicides. (c) 2005 Elsevier B.V. All rights reserved.