| 1. |
- Bai, Licheng, et al.
(författare)
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Explaining the Size Dependence in Platinum-Nanoparticle-Catalyzed Hydrogenation Reactions
- 2016
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55:50, s. 15656-15661
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogenation reactions are industrially important reactions that typically require unfavorably high H-2 pressure and temperature for many functional groups. Herein we reveal surprisingly strong size-dependent activity of Pt nanoparticles (PtNPs) in catalyzing this reaction. Based on unambiguous spectral analyses, the size effect has been rationalized by the size-dependent d-band electron structure of the PtNPs. This understanding enables production of a catalyst with size of 1.2 nm, which shows a sixfold increase in turnover frequency and 28-fold increase in mass activity in the regioselective hydrogenation of quinoline, compared with PtNPs of 5.3 nm, allowing the reaction to proceed under ambient conditions with unprecedentedly high reaction rates. The size effect and the synthesis strategy developed herein may provide a general methodology in the design of metal-nanoparticle-based catalysts for a broad range of organic syntheses.
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| 2. |
- Gao, Chuanbo, 1981-
(författare)
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Formation Mechanism of Anionic Surfactant-Templated Mesoporous Silica
- 2006
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Ingår i: Chemistry of Materials. - : ACS. - 0897-4756 .- 1520-5002. ; 18, s. 3904-3914
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis mechanism of anionic surfactant-templated mesoporous silica (AMS) is described. A family of highly ordered mesoporous silica structures have been synthesized via an approach based on the self-assembly of anionic surfactants and inorganic precursors by using aminopropylsiloxane or quaternized aminopropylsiloxane as the co-structure-directing agent (CSDA), which is a different route from previous pathways. Mesophases with differing surface curvatures, varying from cage type (tetragonal P42/mnm; cubic Pm-3n with modulations; cubic Fd-3m) to cylindrical (two-dimensional hexagonal p6mm), bicontinuous (cubic Ia-3d and Pn-3m), and lamellar have been obtained by controlling the charge density of the micelle surfaces by varying the degree of ionization of the carboxylate surfactants. Changing the degree of ionization of the surfactant results in changes of the surfactant packing parameter g, which leads to different mesostructures. Furthermore, variation of the charge density of positively charged amino groups of the CSDA also gives rise to different values of g. Mesoporous silicas, functionalized with amino and quaternary ammonium groups and with the various structures given above, have been obtained by extraction of the surfactant. This report leads to a deeper understanding of the interactions between the surfactant anions and the CSDA and provides a feasible and facile approach to the mesophase design of AMS materials.
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| 3. |
- Gao, Chuanbo, 1981-
(författare)
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Formation mechanism of anionic-surfactant-templated mesoporous silica (AMS)
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation is focused on synthesis, characterization and formation mechanism of anionic-surfactant-templated mesoporous silica (AMS). Structural control mechanisms of AMS are investigated. First, different ionization degree of anionic surfactant affected by the acidity or alkalinity of the synthesis system gives rise to different charging density of micelles and therefore determines the organic/inorganic interface curvature, producing mesophases from cage-type to cylindrical, bicontinuous and lamellar. Second, mesocage/mesocage electrostatic repulsive interaction affects the formation of cage-type mesostructure, which is derived from a full-scaled synthesis-field diagram of AMS. The mesocage/mesocage interaction changes with charge density of mesocages and gives rise to their different packing manners. Third, the structural properties of AMS materials could be tuned by molecular features of surfactant and co-structure-directing agent (CSDA). The pore size of AMS is found to be controlled by alkyl chain length, ionization degree of surfactant and the CSDA/surfactant ratio. Alkyl chain length of surfactant determines size of micelles and thus mesopores. Larger ionization degrees of anionic surfactant give rise to smaller pore sizes due to thermodynamic coiling of alkyl chains of surfactant. The hydrophobic interactions between the pendant organic groups of CSDA on the silica wall and the hydrophobic core of the micelles drive a contraction of the mesopores. A mesoporous silica with novel bicontinuous cubic Pn-3m structure has been prepared using a diprotic anionic surfactant. 3d-reconstruction of the structure shows that it is bicontinuous composed of an enantiomeric pair of 3d mesoporous networks that are interwoven with each other, divided by a D surface. Inverse replication suggests the possible presence of ordered complimentary micropores in the material.
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| 4. |
- Gao, Chuanbo, 1981-, et al.
(författare)
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Formation of Diverse Mesophases Templated by a Diprotic Anionic Surfactant
- 2008
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley-VCH Verlag GmbH&Co. KGaA. - 0947-6539 .- 1521-3765. ; 14:36, s. 11423-11428
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis system for mesophase formation, using the diprotic anionic surfactant N-myristoyl-l-glutamic acid (C14GluA) as the structuredirecting agent (SDA) and N-trimethoxylsilylpropyl-N,N,N-trimethylammonium chloride (TMAPS) as the co-structure-directing agent (CSDA), has been investigated and a full-scaled synthesis-field diagram is presented. In this system we have obtained mesophases including three-dimensional (3D) micellar cubic Fm-3m, Pm-3n, Fd-3m, micellar tetragonal P42/mnm, two-dimensional (2D) hexagonal p6mm and bicontinuous cubic Pn-3m, by varying the C14GluA/NaOH/TMAPS composition ratios. From the diagram it can be concluded that the mesophase formation is affected to a high degree by the organic/inorganicinterface curvature and the mesocage–mesocage electrostatic interaction. Bicontinuous cubic and 2D-hexagonalphases were found in the low organic/inorganic-interface curvature zones, whereas micellar cubic and tetragonal mesophases were found in the high organic/inorganic-interface curvature zones. Formation of cubic Fm-3m and tetragonal P42/mnm was favoured in highly alkaline zones with strong mesocage–mesocage interactions, and formation of cubic Pm-3n and Fd-3m was favoured with moderate mesocage–mesocage interactions in the less alkaline zones of the diagram.
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| 5. |
- Gao, Chuanbo, 1981-
(författare)
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Formation of mesoporous Co3O4 replicas of different mesostructureswith different pore sizes
- 2009
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 123, s. 314-323
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous metal oxides Co3O4 are prepared via hard templating synthesis method by using various mesoporous silicas with different pore size as templates. The pore size of the mesoporous silicas with the symmetry of two-dimensional (2d)-hexagonal p6mm, bicontinuous cubic Ia-3d and Pn-3m have been controlled in the range of 6.6–10.7, 4.2–7.5 and 5.1–6.7 nm, respectively, by choosing different surfactants and co-surfactants and by adjusting either the aging temperature or the ionization degree of the surfactant. The pore size of the silica template has been considered to be an important factor that determines the mesostructure of the resulting metal oxides. It has been found that for p6mm, it is easier to replicate the mesoporous symmetry at large size of mesopores. For Ia-3d, at large-pore size two sets of bicontinuous meso-channels are replicated into mesoporous Co3O4, while small-pore Ia-3d leads to replication of both one set and two sets of meso-channels. Co3O4 can replicate both one set and two sets of bicontinuous Pn-3m meso-channels at all pore sizes that can be obtained (5.1–6.7 nm), indicating the existence of ordered complementary micropores within the silica walls.
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| 6. |
- Gao, Chuanbo, et al.
(författare)
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Mesostructured silica based delivery system for a drug with a peptide as a cell-penetrating vector
- 2009
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 122:1-3, s. 201-207
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Tidskriftsartikel (refereegranskat)abstract
- A drug delivery system using mesostructured silica as a reservoir has been developed for the storage and controlled release of a drug with a cell-penetrating peptide (CPP) as a vector. We use fluorescein isothiocyanate (FITC) as the drug model and octaarginine (R8) as a vector to endow the drug with cell-penetrating property. The mesostructured silica reservoir system was prepared by using a one-pot liquid?crystal templating method, which is suitable for the encapsulation of intact FITC-R8 conjugates and sustained release of drugs without hampering their properties. The hydrophobic poly(propyl oxide) (PPO) shell of the pore-filling Pluronic F127 and the electrostatic interaction between R8 and siloxide ions on the pore walls act as the diffusion-limiting factors of the FITC-R8 conjugate. A sigmoidal in vitro release of FITC-R8 from mesostructured silica into phosphate buffered saline (PBS, pH 7.4) was observed and the typical release duration was 5 days at 37 ‹C. Release from the reservoir yielded significant elongation in duration of the FITC signals in DU145 cells by confocal microscopic analysis, compared with a single administration of FITC-R8.
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| 7. |
- Gao, Chuanbo, 1981-
(författare)
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Molecular design of AEC tri-block anionic surfactant towards rational synthesis of targeted thick-walled mesoporous silica
- 2009
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Ingår i: Journal of Materials Chemistry. - United Kingdom : The Royal Society of Chemistry. - 0959-9428 .- 1364-5501. ; 19, s. 3404-3411
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Tidskriftsartikel (refereegranskat)abstract
- Here we report a new synthesis strategy to synthesize thick-walled two dimensional hexagonal mesoporous silicas, using tri-block surfactant fatty alcohol ether carboxylate [AEC: CnH2n+1O(CH2CH2O)mCH2COONa] with two different hydrophilic head groups of (EO)x-block and anionic carboxylate. The unique formation of double-layer silica wall arose from two types of hydrophilic head groups via the silica source condensation led to an obvious increase in the wall thickness. The successful carbon replication proved the existence of micropores formed by imbedded (EO)x-block and electrostatic bonding of carboxylate head group and organic group of co-structuredirecting agent. The template-free mesoporous silica showed a high hydrothermal stability due to the thick wall.
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| 8. |
- Gao, Chuanbo, 1981-
(författare)
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Molecular design of the surfactant and the co-structure-directing agent (CSDA) toward rational synthesis of targeted anionic surfactant templatedmesoporous silica
- 2007
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Ingår i: Journal of Materials Chemistry. - United Kingdom : The Royal Society of Chemistry. - 0959-9428 .- 1364-5501. ; 17, s. 3591-3602
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Tidskriftsartikel (refereegranskat)abstract
- The formation of anionic surfactant templated mesoporous silica (AMS) is investigated from the perspective of the geometrical molecular design of the surfactant and the co-structure-directing agent (CSDA) toward the rational synthesis of the targeted mesostructure. Increasing the geometrical size of two types of head group of the anionic surfactant in the order (i) sulfonate, sulfate and phosphate, and (ii) carboxylate, N-acylalanate/N-acylglycinate and N-acylglutamate, resulted in the mesophase changing from a disordered or lamellar phase to two-dimensional (2D) hexagonal (p6mm) and three-dimensional (3D) cage-type (hexagonal and a modulated cubic phase) with increasing order of the organic/inorganic interface curvature. A change in the chain length of the surfactant also led to different surfactant packing and mesophase interfacial curvatures, and resulted in a change in mesophase from a modulated cage-type mesophase to cubic Fd-3m, cubic Pm-3n and a disordered cage-type mesophase. The geometrical change in the CSDA resulted in an increasing micellar curvature in the order: aminopropyl , N-methylaminopropyl, N,N-dimethylaminopropyl trimethoxysilane, which led to a change of mesophase from bicontinuous cubic Pn-3m to 2D-hexagonal p6mm. An increase in the CSDA/surfactant ratio in the synthesis gave rise to the mesophase change from a disordered cage-type mesophase to cubic Fm-3m or from lamellar to 2D-hexagonal p6mm, and elemental analysis results showed that the mesoporous silicas have an increased loading of organic moieties using the CSDA method.
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| 9. |
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| 10. |
- Liu, Kai, et al.
(författare)
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Porous Au-Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis
- 2016
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:6, s. 3675-3681
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au-Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of similar to 1.3 x 10(7) on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications.
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| 11. |
- Wei, Xinyu, et al.
(författare)
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Holey Au-Ag alloy nanoplates with built-in hotspots for surface-enhanced Raman scattering
- 2016
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 8:34, s. 15689-15695
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic noble metal nanocrystals with interior nanogaps have attracted great attention in surface-enhanced Raman scattering (SERS) applications due to the presence of built-in hotspots. Herein, we report a synthesis route to holey Au-Ag alloy nanoplates by controlled galvanic replacement with Ag nanoplates as the sacrificial template, a sulfite-coordinated Au(I) salt as the Au source, and polyvinylpyrrolidone (PVP) as the capping agent. PVP helps regulate the anisotropic growth of nanopores on the Ag nanoplates to afford a highly holey nanostructure, and the monovalent Au(I) salt plays a critical role in stabilizing these holey nanoplates by rapidly enriching Au in the alloy nanostructures. Numerical simulations and experimental results suggest that these holey Au-Ag alloy nanoplates possess enormous internal hotspots for high sensitivity in the SERS analysis, and high stability for excellent reliability of the analysis under many harsh conditions. We believe that this strategy is potentially applicable to the synthesis of many other types of plasmonic nanostructures with inherent nanogaps for many sensing and imaging applications.
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