Nanofluidic Ion Transport through Reconstructed Layered Materials

Electrolytes confined in nanochannels with characteristic dimensions comparable to the Debye length show transport behaviors deviating from their bulk counterparts. Fabrication of nanofluidic devices typically relies on expensive lithography techniques or the use of sacrificial templates with sophisticated growth and processing steps. Here we demonstrate an alternative approach where unprecedentedly massive arrays of nanochannels are readily formed by restacking exfoliated sheets of layered materials, such as graphene oxide (GO). Nanochannels between GO sheets are successfully constructed as manifested by surface-charge-governed ion transport for electrolyte concentrations up to 50 mM. Nanofluidic devices based on reconstructed layer materials have distinct advantages such as low cost, facile fabrication, ease of scaling up to support high ionic currents, and flexibility. Given the rich chemical, physical, and mechanical properties of layered materials, they should offer many exciting new opportunities for studying and even manufacturing nanofluidic devices

Effect of Sheet Morphology on the Scalability of Graphene-Based Ultracapacitors

Graphene is considered a promising ultracapacitor material toward high power and energy density because of its high conductivity and high surface area without pore tortuosity. However, the two-dimensional (2D) sheets tend to aggregate during the electrode fabrication process and align perpendicular to the flow direction of electrons and ions, which can reduce the available surface area and limit the electron and ion transport. This makes it hard to achieve scalable device performance as the loading level of the active material increases. Here, we report a strategy to solve these problems by transforming the 2D graphene sheet into a crumpled paper ball structure. Compared to flat or wrinkled sheets, the crumpled graphene balls can deliver much higher specific capacitance and better rate performance. More importantly, devices made with crumpled graphene balls are significantly less dependent on the electrode mass loading. Performance of graphene-based ultracapacitors can be further enhanced by using flat graphene sheets as the binder for the crumpled graphene balls, thus eliminating the need for less active binder materials

Dated estimate of phylogeny for species of the subgenus <i>Megabombus</i>.

<p>From Bayesian analysis of COI barcodes, using single samples selected to represent each of the species from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.g002" target="_blank">Fig 2</a> and using the birth-death process for speciation on the tree. The tree is dated in Ma by setting the date for the divergence with the <i>Mendacibombus</i> outgroup to 34 Ma [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.ref033" target="_blank">33</a>]. Values at each node: posterior probability / age in Ma. Nodes with support <i>p</i>≥0.8 show 95% confidence limits for the date estimate as grey bars; nodes with support <i>p</i><0.8 have the values shown in grey; nodes with support <i>p</i><0.66 are shown collapsed. The vertical gray line show the 1.3 Ma position to distinguish between the two time periods. The extreme food specialization species name with under dashed line.</p

Relationship of number of food-plant species recorded per bumblebee species to number of bee records per bumblebee species.

<p>For species of the subgenera <i>Megabombus</i> (black spots), <i>Pyrobombus</i> (triangles), <i>Melanobombus</i> (circles), and <i>Bombus s</i>. <i>str</i>. (squares). Species with few food-plant-species records relative to the number of bee records are interpreted as more specialised in their fewer food-plant choices (Data from North China [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.ref014" target="_blank">14</a>]).</p

Map of sites sampled across China for bumblebees.

<p>Grey spots, all bumblebee records; black spots, records of species of the subgenus <i>Megabombus</i>. Map was created using a free computer program DIVA-GIS(<a href="http://www.diva-gis.org/download" target="_blank">http://www.diva-gis.org/download</a>) and free spatial data (<a href="http://www.diva-gis.org/Data" target="_blank">http://www.diva-gis.org/Data</a>).</p

Growing degree days of collecting site for six <i>Megabombus</i> species (Boxplots show the median, upper and lower quartiles, 99% confidence limits and outliers).

<p>Growing degree days of collecting site for six <i>Megabombus</i> species (Boxplots show the median, upper and lower quartiles, 99% confidence limits and outliers).</p

Earlier estimate of phylogeny for species of the subgenus <i>Megabombus</i>.

<p>From combined Bayesian analysis of five genes: (mitochondrial) 16S, and (nuclear) opsin, ArgK, EF-1α, and PEPCK [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.ref011" target="_blank">11</a>]. Values at each node: posterior probability / age in Ma. Redrawn with nodes with support <i>p</i><0.66 shown collapsed. Date estimates in millions of years before the present (Ma) are taken from Hines (her <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.g002" target="_blank">Fig 2</a>) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.ref033" target="_blank">33</a>]. Species concepts and names are adjusted according to the interpretations of the present study.</p

Diversity from different phases of speciation of the subgenus <i>Megabombus</i>.

<p>Data sources and grid map as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.g005" target="_blank">Fig 5</a>. Richness in the species <i>B</i>. <i>hortorum</i> to <i>B</i>. <i>sushkini</i> and ‘unnamed’ from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132358#pone.0132358.g004" target="_blank">Fig 4</a>.</p

Distribution of diversity for the subgenus <i>Megabombus</i> among equal-area grid cells.

<p>Data for China are updated from the review by Williams 1998 using the IAB collection, and exclude records for known introductions (New Zealand, South America, Iceland). The grid is based on longitudinal intervals of 10°, which are used to calculate graduated latitudinal intervals to provide equal-area cells (each cell of area approximately 611,000 km²). Grey scale (right) with equal-interval richness classes. Cylindrical orthomorphic projection (excluding Antarctica) with north at the top of the map.</p

GMYC analysis to recognise species of <i>Megabombus</i>.

<p>Values at the nodes are Bayesian posterior probabilities for groups (values <0.8 are shown in grey). The scale bar represents 0.02 substitutions per nucleotide site. The single threshold of GMYC model result is shown by the vertical grey bar. Each tip is labelled with: the length of COI barcode sample sequence; the taxon name; the GenBank or BOLD ID; the sample COUNTRY and for larger countries, province.</p