Showing papers by "Nanjing Tech University published in 2010"

Enhancement of Pt and Pt-alloy fuel cell catalyst activity and durability via nitrogen-modified carbon supports

Abstract: Insufficient catalytic activity and durability are key barriers to the commercial deployment of low temperature polymer electrolyte membrane (PEM) and direct-methanol fuel cells (DMFCs). Recent observations suggest that carbon-based catalyst support materials can be systematically doped with nitrogen to create strong, beneficial catalyst-support interactions which substantially enhance catalyst activity and stability. Data suggest that nitrogen functional groups introduced into a carbon support appear to influence at least three aspects of the catalyst/support system: 1) modified nucleation and growth kinetics during catalyst nanoparticle deposition, which results in smaller catalyst particle size and increased catalyst particle dispersion, 2) increased support/catalyst chemical binding (or “tethering”), which results in enhanced durability, and 3) catalyst nanoparticle electronic structure modification, which enhances intrinsic catalytic activity. This review highlights recent studies that provide broad-based evidence for these nitrogen-modification effects as well as insights into the underlying fundamental mechanisms.

Folate-Conjugated Fe3O4@SiO2 Hollow Mesoporous Spheres for Targeted Anticancer Drug Delivery

Abstract: Herein we developed a targeted anticancer drug delivery system based on folate-conjugated rattle-type Fe3O4@SiO2 hollow mesoporous spheres combining receptor-mediated targeting and magnetic targeting. Folic acid (FA) ligands were successfully grafted onto rattle-type Fe3O4@SiO2 hollow mesoporous spheres via amide reaction. The magnetization saturation value of folate-conjugated Fe3O4@SiO2 spheres (Fe3O4@SiO2−FA) was about 1.6 emu/g, and these spheres could be targeted under an external magnetic field. On the other hand, in vitro cytotoxicity and cell uptake of these Fe3O4@SiO2−FA spheres to Hela cells were evaluated. These Fe3O4@SiO2−FA spheres were nontoxic up to a concentration of 150 μg/mL, and further can be specifically taken up by Hela cells via FA receptor-mediated endocytosis. Doxorubicin hydrochloride (DOX), an anticancer drug, was introduced into Fe3O4@SiO2−FA spheres. The release of DOX from Fe3O4@SiO2−FA spheres had a sustained release pattern, and the DOX-loaded Fe3O4@SiO2−FA spheres exhibite...

Hierarchical ZnO Nanowire-Nanosheet Architectures for High Power Conversion Efficiency in Dye-Sensitized Solar Cells

Abstract: We present a two-step synthesis process to produce hierarchical ZnO nanoarchitectures that involves the preparation of ZnO nanosheet arrays by the pyrolysis of the precursor Zn5(OH)8Cl2 electrodeposited on conductive glass substrates, followed by the aqueous chemical growth (ACG) of dense ZnO single-crystalline nanowires on the surfaces of the primary ZnO nanosheets. The dye-sensitized solar cell (DSSC) based on the hierarchical ZnO nanowire−nanosheet architectures showed a power conversion efficiency of 4.8%, which is nearly twice as high as that of the DSSC constructed using a photoanode of bare ZnO nanosheet arrays. The better photovoltaic performance of hierarchical ZnO nanoarchitecture DSSC was due to a better dye loading and light harvesting as a consequence of the enlargement of the internal surface area within the photoanode. Moreover, the improved performance for the DSSC with the hierarchical ZnO nanowire−nanosheet architectures may be also ascribed to more light scattering behavior through exte...

Five 3D metal–organic frameworks constructed from V-shaped polycarboxylate acids and flexible imidazole-based ligands

Abstract: Five new metal–organic frameworks, namely, Cd2(SA)(obix) (1), Zn2(SA)(bimb) (2), Cd(SDBA)(timb)·3H2O (3), Co(SDBA)(bimb) (4), and Co(SDBA)(obix) (5) (H4SA = 3,3′,4,4′-diphenylsulfonetetracarboxylate acid, H2SDBA = 4,4′-dicarboxybiphenyl-sulfone, obix = 1,2-bis(imidazol-1-ylmethyl)benzene, timb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene and bimb = 4,4′-bis(imidazol-1-ylmethyl)biphenyl), have been synthesized under hydrothermal conditions by employing mixed ligands of various imidazole-based ligands with H4SA or H2SDBA. The networks exhibit a variety of topologies and coordination modes at the metal centers. Complex 1 features a novel (5,7)-connected seh net consisting of one-dimensional inorganic chains which are bridged by carboxylate groups of SA4− ligands, whereas complex 2 possesses a unique 4-connected 3D framework with (62·82·102)(62·83·10)(62·83·9) topology. Complex 3 exhibits a rare (3,5)-connected 3D framework with gra topology. Complex 4 shows 4-connected MOFs with (65·8) CdSO4-type topology, while in 5, the SDBA and obix ligands linked the Co(II) atoms into a deeply corrugated 2D sheet. The corrugated 2D sheets polycatenate each other in a parallel manner yielding a rare 2D → 3D parallel polycatenation net. The photoluminescence properties of 1–3 were studied in the solid state at room temperature. Moreover, the second-harmonic-generation (SHG) activity of 2–5 have also been investigated.

A Molecular Simulation Probing of Structure and Interaction for Supramolecular Sodium Dodecyl Sulfate/Single-Wall Carbon Nanotube Assemblies

Abstract: Here we report a larger-scale atomic-level molecular dynamics (MD) simulation for the self-assembly of sodium dodecyl sulfate (SDS) surfactant on single-walled carbon nanotube (SWNT) surfaces and the interaction between supramolecular SDS/SWNT aggregates. We make an effort to address several important problems in regard to carbon nanotube dispersion/separation. At first, the simulation provides comprehensive direct evidence for SDS self-assembly structures on carbon nanotube surfaces, which can help to clarify the relevant debate over the exact adsorption structure. We also, for the first time, simulated the potential of mean force (PMF) between two SWNTs embedded in SDS surfactant micelles. A novel unified PMF approach has been applied to reveal various cooperative interactions between the SDS/SWNT aggregates, which is different from the previous electrostatic repulsion explanation. The unique role of sodium ions revealed here provides a new microscopic understanding of the recent experiments in the electrolyte tuning of the interfacial forces on the selective fractionation of SDS surrounding SWNTs.

Development of a stepwise aeration control strategy for efficient docosahexaenoic acid production by Schizochytrium sp.

Abstract: The effect of aeration on the performance of docosahexaenoic acid (DHA) production by Schizochytrium sp. was investigated in a 1,500-L bioreactor using fed-batch fermentation. Six parameters, including specific growth rate, specific glucose consumption rate, specific lipid accumulation rate, cell yield coefficient, lipid yield coefficient, and DHA yield coefficient, were used to understand the relationship between aeration and the fermentation characteristics. Based on the information obtained from the parameters, a stepwise aeration control strategy was proposed. The aeration rate was controlled at 0.4 volume of air per volume of liquid per minute (vvm) for the first 24 h, then shifted to 0.6 vvm until 96 h, and then switched back to 0.4 vvm until the end of the fermentation. High cell density (71 g/L), high lipid content (35.75 g/L), and high DHA percentage (48.95%) were achieved by using this strategy, and DHA productivity reached 119 mg/L h, which was 11.21% over the best results obtained by constant aeration rate.

Ball milling pretreatment of corn stover for enhancing the efficiency of enzymatic hydrolysis.

Abstract: Ethanol can be produced from lignocellulosic biomass with the usage of ball milling pretreatment followed by enzymatic hydrolysis and fermentation. The sugar yields from lignocellulosic feed stocks are critical parameters for ethanol production process. The research results from this paper indicated that the yields of glucose and xylose were improved by adding any of the following dilute chemical reagents: H2SO4, HCl, HNO3, CH3COOH, HCOOH, H3PO4, and NaOH, KOH, Ca(OH)2, NH3·H2O in the ball milling pretreatment of corn stover. The optimal enzymatic hydrolysis efficiencies were obtained under the conditions of ball milling in the alkali medium that was due to delignification. The data also demonstrated that ball milling pretreatment was a robust process. From the microscope image of ball milling-pretreated corn stover, it could be observed that the particle size of material was decreased and the fiber structure was more loosely organized. Meanwhile, the results indicate that the treatment effect of wet milling is better than that of dry milling. The optimum parameters for the milling process were ball speed of 350 r/min, solid/liquid ratio of 1:10, raw material particle size with 0.5 mm, and number of balls of 20 (steel ball, Φ = 10 mm), grinding for 30 min. In comparison with water milling process, alkaline milling treatment could increase the enzymatic hydrolysis efficiency of corn stover by 110%; and through the digestion process with the combination of xylanase and cellulase mixture, the hydrolysis efficiency could increase by 160%.

High performance cobalt-free perovskite cathode for intermediate temperature solid oxide fuel cells

Abstract: Bi doping of SrFeO3−δ results in the formation of a structure with high symmetry and extraordinary electrochemical performance for Bi0.5Sr0.5FeO3-δ, which is capable of competing effectively with the current Co-based cathode benchmark with additional advantages of lower thermal expansion and cost.

Engineering Klebsiella oxytoca for efficient 2, 3-butanediol production through insertional inactivation of acetaldehyde dehydrogenase gene

Abstract: Ethanol was a major byproduct of 2,3-butanediol (2,3-BD) fermentation by Klebsiella oxytoca ME-UD-3. In order to achieve a high efficiency of 2,3-BD production, K. oxytoca mutants deficient in ethanol formation were successfully constructed by replace the aldA gene coding for aldehyde dehydrogenase with a tetracycline resistance cassette. The results suggested that inactivation of aldA led to a significantly improved 2,3-BD production. The carbon flux to 2,3-BD was enhanced by eliminating the byproducing ethanol and at the same time reducing the accumulation of another byproduct acetoin. At last, by fed-batch culturing of the mutant, the final 2,3-BD titer up to 130 g/l with the productivity of 1.63 g/l.h and the 2,3-BD yield relative to glucose of 0.48 g/g was obtained.

Nanoporous Metal Membranes with Bicontinuous Morphology from Recyclable Block‐Copolymer Templates

Abstract: [*] Prof. Y. Wang, Prof. W. Xing, F. Li, L. Tong, Z. Chen, X. Liao, X. Liao State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology Nanjing 210009, Jiangsu (P. R. China) E-mail: yongwang@njut.edu.cn; xingwh@njut.edu.cn Fax: 0086-25-8317-2292 Dr. C. He College of Chemistry, Beijing Normal University Beijing, 100875 (P. R. China)

Experimental Study on the Stability of Railroad Silt Subgrade with Increasing Train Speed

Abstract: The comfort and safety of a moving train is largely determined by the dynamic response of the railway track and its foundation (i.e., subgrade). To study the dynamic stability of a silt subgrade subjected to train traffic loading with increasing speed, cyclic triaxial tests were conducted for compacted silt specimens with varying dry density, water content, dynamic stress, and load frequency. The laboratory test results and field measurements of the subgrade dynamic stress under train loading indicate that with increasing train speed, an increase in dynamic stress and load frequency does not impair the stability of the silt subgrade, provided the subgrade is in sound physical condition (i.e., its natural water content approximates the optimal water content) and the relative compaction is at least 90%. However, if the relative compaction is 85%, the subgrade is stable only at a dynamic stress level that is below 70 kPa, and the subgrade may suffer shear failure at a higher dynamic stress level. The elastic deformation of the subgrade linearly increases with an increase in train speed. However, if the degree of saturation of the silt subgrade increases, the thresholds of both the dynamic stress and resilient modulus decrease markedly, accompanied by sharp increases in elastic deformation and cumulative deformation and can even result in the shear failure of the subgrade. These conditions are unfavorable for the high speeds and stability needed for trains; therefore, train speeds should be limited in wet conditions to reduce subgrade dynamic stress and load frequency.

Reusable and efficient polystyrene-supported acidic ionic liquid catalyst for esterifications

Abstract: Polystyrene (PS)-supported 1-(propyl-3-sulfonate) imidazolium hydrosulfate acidic ionic liquid (PS-CH 2 -[SO 3 H-pIM][HSO 4 ]) catalyst was prepared by supporting the ionic liquid onto highly cross-linked chloromethylated polystyrene (PS-CH 2 Cl). FT-IR, SEM and TG-DSC were employed to characterize the structure and property of the catalyst. Results suggested that acidic ionic liquid was supported onto the surface of PS-CH 2 Cl by covalent bond. The original rough surface of PS-CH 2 Cl was covered with acidic ionic liquid, forming a compact and thin surface layer, and its size had no obvious change. Moreover, the PS-CH 2 -[SO 3 H-pIM][HSO 4 ] catalyst showed a better thermal stability than that of PS-CH 2 Cl support. It also exhibited high catalytic activity for a series of esterifications. After the catalyst was reused for 13 times in the synthesis of n-butyl acetate, the yield only decreased 7.3%. A reaction mechanism of esterification over this new catalyst was proposed as well.

Adsorptive desulfurization by copper species within confined space.

Abstract: Copper species were incorporated into SBA-15 by solid-state grinding precursor with as-prepared mesoporous silica (SPA). The obtained materials (CuAS) were well-characterized by XRD, TEM, N(2) adsorption, H(2)-TPR, IR, and TG and compared with the material derived from calcined SBA-15 (CuCS). Surprisingly, CuO up to 6.7 mmol·g(-1) can be highly dispersed on SBA-15 by use of SPA strategy. Such CuO forms a smooth layer coated on the internal walls of SBA-15, which contributes to the spatial order and results in less-blocked mesopores. However, the aggregation of CuO takes place in CuCS material containing 6.7 mmol·g(-1) copper, which generates large CuO particles of 21.4 nm outside the mesopores. We reveal that the high dispersion extent of CuO is ascribed to the abundant silanols, as well as the confined space between template and silica walls provided by as-prepared SBA-15. The SPA strategy allows template removal and precursor conversion in one step, avoids the repeated calcination in conventional modification process, and saves time and energy. We also demonstrate that the CuAS material after autoreduction exhibits much better adsorptive desulfurization capacity than CuCS. Moreover, the adsorption capacity of regenerated adsorbent can be recovered completely.