Ever since the discovery of carbon nanotubes (CNTs), it has long been a challenging goal to create macroscopically ordered assemblies, or crystals, of CNTs that preserve the one-dimensional quantum properties of individual CNTs on a macroscopic scale.Recently, a simple and well-controlled method was reported for producing wafer-scale crystalline films of highly aligned and densely packed CNTs through spontaneous global alignment that occurs during vacuum filtration [Nat. Nanotechnol. 11, 633 (2016)].However, a full understanding of the mechanism of such global alignment has not been achieved. Here, we report results of a series of systematic experiments that demonstrate that the CNT alignment direction can be controlled by the surface morphology of the filter membrane used in the vacuum filtration process. More specifically, we found that the direction of parallel grooves pre-existing on the surface of the filter membrane dictates the direction of the resulting CNT alignment. Furthermore, we intentionally imprinted periodically spaced parallel grooves on a filter membranes using a diffraction grating, which successfully defined the direction of the global alignment of CNTs in a precise and reproducible manner.
In this study, different nano-particles were used to modify recycled aggregates concrete (RAC) containing recycled clay brick aggregates (RCBAs) to improve the RAC properties. Two stages of experimental works were performed. In the first stage, various nano-particle mixtures produced by different mixing methods, i.e. the use of surfactant and ultrasonication, were examined by optical microscope to evaluate the dispersion of the nano-particles in water liquid. The nano-particles modified cement mortar specimens were further evaluated by flexural tensile test to check how these mixing methods affect the properties of the nano-particle modified cement mortar. In the second experimental stage, the effects of four replacement ratios of recycled aggregates, three type of nano-particles, two mixing methods of RAC, additional surfactant and ultrasonication process used in the mix of nano-particle liquid, and the dosages of the nano-particles on the workability, compressive and split tensile properties of the nano-particle modified RAC were investigated.
The biogeochemical cycling of antimony (Sb) is often coupled with sulfur and sulfate-reducing bacteria (SRB). The biogenic sulfide is usually assumed to facilitate Sb immobilization via Sb 2 S 3 precipitation. Here, on the contrary, we discovered that SRB mobilize adsorbed Sb(V). When Sb V (OH) 6 −bearing goethite was incubated anaerobically with Desulfovibrio vulgaris DP4, an elevated level of antimony was released due to the formation of thioantimonate, which is the dominant Sb species in solution. Our Fourier transform ion cyclotron resonance mass spectrometry analysis revealed multiple six-or five-coordinate thioantimonate intermediates, suggesting stepwise ligand exchange of hydroxyl groups on Sb V (OH) 6− by biogenic sulfide. Direct H 2 S elimination reactions resulted in four-coordinate thioantimonate species as the stable end product, which was confirmed by our density functional theory calculations. The thiolation of antimonate is pH-dependent and occurs in neutral environments. The thiolation changed Sb(V) from a six-coordinate octahedral coordination to a four-coordinate tetrahedral coordination, weakening its affinity for iron oxides and thus facilitating its release into the aquatic environment. The results of this study highlight the importance of biogenic sulfide produced by SRB for the fate and transport of Sb.
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