A nanofluidic membrane for ion regulation with aligned cellulose nanofibers was directly obtained from wood.

Solid-state nanofluidic devices have proven to be ideal systems for studying the physics of ionic transport at the nanometer length scale. When the geometrical confining size of fluids approaches the ionic Debye screening length, new transport phenomena occur, such as surface mediated transport and permselectivity. Prior work has explored these effects extensively in monovalent systems (e.g., predominantly KCl and NaCl). In this report, we present a new characterization method for the study of divalent ionic transport and have unambiguously observed divalent charge inversion at solid/fluid interfaces. This observation has important implications in applications ranging from biology to energy conversion.

Nanochannels remain at the focus of growing scientific and technological interest. The nanometer scale of the structure allows the discovery of a new range of phenomena that has not been possible in traditional microchannels, among which a direct field effect control over the charges in nanochannels is very attractive for various applications, since it offers a unique opportunity to integrate wet ionics with dry electronics seamlessly. This review will focus on the voltage gated ionic and molecular transport in engineered gated nanochannels. We will present an overview of the transport theory. Fabrication techniques regarding the gated nanostructures will also be discussed. In addition, various applications using the voltage gated nanochannels are outlined, which involves biological and chemical analysis, and energy conversion.

yield orders of magnitude higher gas permeances because of its atomic thickness and low cross-membrane transport resistance. [3,4] Because perfect single-layer graphene is almost impermeable to gases, [5,6] in-plane pores, which are vacancy defects in the graphene lattice, are necessary for gas permeation. To realize the enormous potential of porous graphene for gas separation, the areal pore density in graphene should be considerably high. Our group theoretically predicted that the pore density needs to exceed 10 14 m −2 for a graphene membrane to surpass the Robeson upper bound for polymers. [7,8] Further, to enable selective gas transport, the pore sizes in the graphene membrane should be precisely controlled such that they are commensurate with the gas molecular sizes. In fact, the pore sizes in porous graphene are typically widely distributed and fitted by a lognormal distribution, where a small fraction of larger pores determine the total gas permeance. [9][10][11][12] As a result, an even higher pore density is needed for porous graphene to achieve a high gas permeance with enough competitiveness. Etching away atoms from pristine graphene has been the most widely applied strategy to increase the pore density in a graphene membrane. High-energy ion or electron bombardment was used to perforate graphene in some early studies. [12][13][14][15] Later, chemical oxidative etching was developed as a more scalable graphene perforation method. [16][17][18] For example, He et al. used O 2 plasma to perforate as-synthesized graphene from chemical vapor deposition (CVD) and measured a H 2 /CH 4 selectivity > 15. [11] Zhao et al. exposed pristine graphene to O 2 plasma for a short pore nucleation burst, and then to mild O 3 etching for controllable pore expansion, in order to partially decouple the pore nucleation and growth and to obtain a narrow pore size distribution. [19] However, despite the efforts made to decouple the pore nucleation and growth, the correlation between them still exists for those etching-based methods. Because the nucleation and growth of the pores are both triggered by etching (e.g., O 2 plasma), one needs to raise the energy intensity of the etching reaction to increase the pore density, which in turn generates larger, less selective pores. This Single-layer graphene containing molecular-sized in-plane pores is regarded as a promising membrane material for high-performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching-based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade-off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. In this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are ...

Although the structure and properties of water under conditions of extreme confinement are fundamentally important for a variety of applications, they remain poorly understood, especially for dimensions less than 2 nm. This problem is confounded by the difficulty in controlling surface roughness and dimensionality in fabricated nanochannels, contributing to a dearth of experimental platforms capable of carrying out the necessary precision measurements. In this work, we utilize an experimental platform based on the interior of lithographically segmented, isolated single-walled carbon nanotubes to study water under extreme nanoscale confinement. This platform generates multiple copies of nanotubes with identical chirality, of diameters from 0.8 to 2.5 nm and lengths spanning 6 to 160 μm, that can be studied individually in real time before and after opening, exposure to water, and subsequent water filling. We demonstrate that, under controlled conditions, the diameter-dependent blue shift of the Raman radial breathing mode (RBM) between 1 and 8 cm–1 measures an increase in the interior mechanical modulus associated with liquid water filling, with no response from exterior water exposure. The observed RBM shift with filling demonstrates a non-monotonic trend with diameter, supporting the assignment of a minimum of 1.81 ± 0.09 cm–1 at 0.93 ± 0.08 nm with a nearly linear increase at larger diameters. We find that a simple hard-sphere model of water in the confined nanotube interior describes key features of the diameter-dependent modulus change of the carbon nanotube and supports previous observations in the literature. Longer segments of 160 μm show partial filling from their ends, consistent with pore clogging. These devices provide an opportunity to study fluid behavior under extreme confinement with high precision and repeatability.