Showing papers by "Lingxia Zhang published in 2007"

Preparation of multi-amine-grafted mesoporous silicas and their application to heavy metal ions adsorption

Abstract: Single amine-, double amine- and trinal amine-grafted mesoporous silica SBA-15 (denoted as 1N-SBA-15, 2N-SBA-15 and 3N-SBA-15) have been synthesized by refluxing SBA-15 and γ-aminopropyltriethoxysilane (APTS), N-[3-(trimethoxysilyl)-propylethylene]diamine (TPED) and trimethoxysilyl propyl diethylenetriamine (TPDT), respectively, in dry toluene under nitrogen atmosphere. These adsorbents could remove the metal ions of Pb2+, Cu2+, Cd2+, Zn2+ as well as Hg2+ rather completely. Thus these adsorbents will be a better choice when more than one kind of metal ions needs to be removed. From 1N-SBA-15 to 3N-SBA-15, their adsorption capacities for Hg2+ increase from 382 mg/g to 726 mg/g , which can be attributed to not only the large content of amino groups but also the rather increased steric freedom and accessibility of the functional groups in the large pore channels of SBA-15. The Hg/N ratio decreases with the increase of N numbers. A decrease about 20–47% of adsorption capacity of regenerated samples has been obtained and could be attributed to the N loss in concentrated acid. In addition, the fresh dry samples were found to show much higher adsorption capacity than the aged ones due to the competitive adsorption between atmosphere moisture and the metal ions on the amino groups.

Synthesis and Characterization of Uniform Spindle-Shaped Microarchitectures Self-Assembled from Aligned Single-Crystalline Nanowires of Lanthanum Phosphates

Abstract: A new synthetic approach using the Pluronic P123-assisted hydrothermal reaction of lanthanum phosphate and europium-doped lanthanum phosphate has been developed, which results in the formation of uniform spindle-shaped microarchitectures most probably by a self-assembly process. Our results reveal that the obtained spindle-shaped microarchitectures consist of several tens of aligned single-crystalline nanowires with smooth, well-defined facets and highly uniform morphologies. These well-defined spindle-shaped microarchitectures show greatly enhanced photoluminescence in these compounds when compared to their counterparts of disordered arrangements. A possible formation mechanism for these spindle-shaped microarchitectures is presented and discussed.

Preparation of highly ordered Fe-SBA-15 by physical-vapor-infiltration and their application to liquid phase selective oxidation of styrene

Abstract: A simple physical-vapor-infiltration (PVI) method was applied to prepare highly ordered Fe-containing mesoporous silica SBA-15. The loading amount of Fe in SBA-15 was very high (up to 24 mol%) and can be tuned by using different PVI time. The liquid phase selective oxidation of styrene with H 2 O 2 has been used to characterize their catalytic properties, the major product is benzaldehyde and the minor is styrene oxide. Independent of the Fe contents and the heat treatment temperature, the selectivity for benzaldehyde in the reaction at a mild temperature of 50 °C are all above 91%. At elevated temperature of 70 °C, the conversion rate of styrene increases beyond 36% and more significantly the selectivity for benzaldehyde can reach as high as 99%. Comparatively, another two different schemes (simple wet impregnation and incorporation using silane coupling agent) have been also applied to synthesize Fe-containing SBA-15 samples. Under the same condition, the styrene conversion on these two samples are both very low with minor product of phenylacetaldehyde and other styrene oxides.

Synthesis of periodic mesoporous organosilicas with chemically active bridging groups and high loadings of thiol groups

Abstract: Chemically active isocyanurate-bridged periodic mesoporous organosilica materials with high loadings of pendant thiol groups have been synthesized via co-condensation under acidic conditions, using the triblock copolymer EO20PO70EO20 (P123) as template and a mixture of mercaptopropyl-containing silane and isocyanurate-containing silsesquioxane to form the framework. The obtained SH–ICS–PMOs were characterized by XRD, transmission electron microscopy (TEM), solid state 13C and 29Si MAS NMR spectroscopy, and N2 physical sorption. The data show that well-ordered SH–ICS–PMOs were obtained with 40% of the framework Si atoms bearing the thiol pendant groups. Interestingly, the introduction of the thiol groups improved the mesostructural ordering and favored the cross-linking of the pore walls. The determination of Hg2+ uptake from aqueous solution as a test case showed that both the bridging ICS groups and the pendant thiol groups in the SH–ICS–PMOs are active in adsorbing Hg2+. Our study demonstrated that well-ordered periodic mesoporous organosilicas are capable of supporting both chemically active bridging groups and active pendant groups with high loadings.

Facile one-step synthesis of highly ordered bimodal mesoporous phosphosilicate monoliths.

Abstract: Highly ordered bimodal mesoporous phosphosilicate monoliths were synthesized in a facile one-step sol−gel route, whose mesostructures were tuned via optimizing the addition time of trimethxyl phosphate. After the removal of surfactant, the bulk monoliths are glassy and present vitreous luster and fibrous patterns. The monoliths have a dual mesoporosity, consisting of two kinds of 20 hexagonal mesostructures with narrow pore size distributions. Their mesopores are partially connected together to form 3D pore networks and joints. These were examined and confirmed by small-angle X-ray diffraction, N2 sorption, and transmission electron microscopy. The monoliths may find applications in catalysis, separation, and electrochemical devices.