Studies On Preparation And Property Of Functionalized Magadiite-Based Heterostructures

Clay minerals are widely ultilized in designing catalysts, adsorbents and novel functionalized materials due to their cation-exchangable and interlamellar expandable properties. In the present work, porous magadiite heterostrctures (PMH) and aluminated derivatives of PMH (xAl-PMH) were prepared using 2-D interlayer cosurfactants-directing TEOS hydrolysis-condensation-polymerization upon a synthetic magadiite and postgrafting of Al into the interlayer silica framework of PMH. The combinational characterization techniques including XRD, SEM/EDS, HRTEM, BET,27A1 and 29Si MAS NMR, NH3-TPD and pyridine FT-IR were employed to study the structure, composition, morphology and surface acidity of the catalysts. The Friedel-Crafts alkylation reactivities of the catalysts were deeply discussed. Novel magadiite-immobilized selective Hg2+"OFF-ON" fluorescent and colormetric chemosensors were prepared by grafting Rhodamine B derived luminophore onto the interlayer surface of cetyltrimethylammounium (CTMA+) intercalated magadiite. The main results and highlights of the thesis are as follows:(1) Porous magadiite heterostructures (PMH) was prepared upon 2-D interlayer cosurfactants-directing TEOS hydrolysis-condensation-polymerization from synthetic magadiite, which was characterized with high surface area (729 m2/g), high thermal stability and unique supermicro-mesoporous structure (0.80-1.96 nm) upon effective assembly of interlayer mesostructured silica and clay layers. Post-synthesis Al-grafting on PMH from NaAlO2 resulted in a series of aluminated PMH derivatives (xAl-PMH, x refers to Al/Si molar ratio, x=0.2,0.4,0.6) compared with staring Al-magadiite derived porous Al-magadiite heterostructures PAMH (Al/Si molar ratio=0.03). xAl-PMH samples exhibit dominant tetra-coordinated Al in the interlayer silica framework with significantly increased Lewis acidity and newly formed Bronsted acidity in comparison with extremely weak Lewis-acidic PMH, while PAMH shows a more pronounced octa-coordinated Al in the layered framework, leading to slightly enhanced Lewis acidity and trace Bronsted acidity.(2) The obtained xAl-PMH catalysts exhibit greatly enhanced liquid-phase Friedel-Crafts alkylation of catechol (CAT) with tert-butyl alchol (TBA) compared with PMH and PAMH. The influence of various reaction parameters on Friedel-Crafts reactivity is discussed with optimum reaction conditions being reaction temperature of 138℃ TBA/CAT molar ratio of 2.0 and reaction time of 4 h. Among all the catalysts,0.4A1-PMH exhibits 93.4% CAT conversion, the highest 4-tert-butyl-catechol (4-TBC) selectivity of 80.4% and the highest 4-TBC yield of 75.1% under optimum reaction conditions due to its strong synergy between the relative large surface area, the lowest microporous volume, the highest Bronsted acid concentration and well-kept supermicro-mesoporosity.(3) Novel magadiite-immobilized selective Hg2+"OFF-ON" fluorescent and colormetric chemosensors (SRhB-maga-X, X refers to SRhB-IPTS/CTAM-maga molar ratio, X-1 or 6) were prepared by grafting luminophore (SRhB-IPTS) (derivative of RhB-ethylenediamine spirolactam and 3-(triethoxysilyl) propylisocyanate) onto the interlay er surface of CTMA intercalated magadiite (CTAM-maga).(4) SRhB-maga-X clearly exhibits high Hg2+ sensitivity by naked-eye. Colorless SRhB-maga-6 fluorescent sensor converts to pink in the prescence of Hg2+ with the fluorescence detection limitation for Hg2+in MeCN-H2O solution (9:1, v/v) being 6.2×10-8 M, and exhibits effectively fluorescent response within a broad pH span (5-12) in 2 minutes and excellent Hg2+ selectivity over various competitive cations including alkali and earth, the first-row transition metals and heavy metals. SRhB-maga-6 can be regenerated by treatment with tetrapropyl- ammonium hydroxide solution. The analytical process is entirely visualized by naked-eye.This excellent Hg2+ detection properties of SRhB-maga-6 can be ascibed to the high SRhB-IPTS content and the ordered Si-O-Si linkage between the luminophore and CTMA-maga substrate as well as the open gallery of the sample.