Yaping Feng

Electrokinetic Energy Conversion in Self‐Assembled 2D Nanofluidic Channels with Janus Nanobuilding Blocks

Inspired by the microstructure of nacre, material design, and large-scale integration of artificial nanofluidic devices step into a completely new stage, termed 2D nanofluidics, in which mass and charge transportation are confined in the interstitial space between reconstructed 2D nanomaterials. However, all the existing 2D nanofluidic systems are reconstituted from homogeneous nanobuilding blocks. Herein, this paper reports the bottom-up construction of 2D nanofluidic materials with kaolinite-based Janus nanobuilding blocks, and demonstrates two types of electrokinetic energy conversion through the network of 2D nanochannels. Being different from previous 2D nanofluidic systems, two distinct types of sub-nanometer- and nanometer-wide fluidic channels of about 6.8 and 13.8 Å are identified in the reconstructed kaolinite membranes (RKM), showing prominent surface-governed ion transport behaviors and nearly perfect cation-selectivity. The RKMs exhibit superior capability in osmotic and hydraulic energy conversion, compared to graphene-based membranes. The mineral-based 2D nanofluidic system opens up a new avenue to self-assemble asymmetric 2D nanomaterials for energy, environmental, and healthcare applications.

Bioinspired Energy Conversion in Nanofluidics: A Paradigm of Material Evolution

Well-developed structure-function relationships in living systems have become inspirations for the design and application of innovative materials. Building artificial nanofluidic systems for energy conversion undergoes three essential steps of structural and functional development with the uptake of separate biological inspirations. This research field started from the mimicking of the bioelectric function of electric eels, wherein a transmembrane ion concentration gradient is converted into ultrastrong electrical impulses via membrane-protein-regulated ion transport. On a small scale, solid-state nanopores are transformed from cylindrical to cone-shaped to acquire asymmetric ion-transport properties; they also further gain versatile responsiveness via chemical modification. These features mimic the rectifying and gating functions of the biological ion channels. Toward large-scale integration and real-world applications, the structure of the nanofluidic system evolves from a one-dimensional straight-channel to a two-dimensional layered membrane, inspired by the layered microstructure of nacre. The research progress, current challenges, and future perspectives of this growing field are highlighted and discussed from the viewpoint of material evolution.

On the Origin of Ionic Rectification in DNA-Stuffed Nanopores: The Breaking and Retrieving Symmetry

The discovery of ionic current rectification (ICR) phenomena in synthetic nanofluidic systems elicits broad interest from interdisciplinary fields of chemistry, physics, materials science, and nanotechnology; and thus, boosts their applications in, for example, chemical sensing, fluidic pumping, and energy related aspects. So far, it is generally accepted that the ICR effect stems from the broken symmetry either in the nanofluidic structures, or in the environmental conditions. Although this empirical regularity is supported by numerous experimental and theoretical results, great challenge still remains to precisely figure out the correlation between the asymmetric ion transport properties and the degree of symmetry breaking. An appropriate and quantified measure is therefore highly demanded. Herein, taking DNA-stuffed nanopores as a model system, we systematically investigate the evolution of dynamic ICR in between two symmetric states. The fully stuffed and fully opened nanopores are symmetric; therefore, they exhibit linear ion transport behaviors. Once the stuffed DNA superstructures are asymmetrically removed from one end of the nanopore via aptamer-target interaction, the nanofluidic system becomes asymmetric and starts to rectify ionic current. The peak of ICR is found right before the breakthrough of the stuffed DNA forest. After that, the nanofluidic system gradually retrieves symmetry, and becomes non-rectified. Theoretical results by both the coarse-grained Poisson-Nernst-Planck model and the 1D statistic model excellently support the experimental observations, and further establish a quantified correlation between the ICR effect and the degree of asymmetry for different molecular filling configurations. Based on the ICR properties, we develop a proof-of-concept demonstration for sensing ATP, termed the ATP balance. These findings help to clarify the origin of ICR, and show implications to other asymmetric transport phenomena for future innovative nanofluidic devices and materials.

A general strategy to simulate osmotic energy conversion in multi-pore nanofluidic systems

As a type of clean energy resource, salinity gradient power between seawater and river water is important to satisfy the ever-growing energy demand on earth. In the recent years, the use of reverse electrodialysis in biomimetic nanofluidic systems has become a promising way for large-scale and high-efficiency harvesting of the salinity gradient power and surpasses the conventional polymeric ion-exchange membrane-based process. With regard to practical applications, significant efforts have been made towards the design and fabrication of high-performance and economically viable materials and devices. However, while extrapolating from single nanopores to multi-pore membrane materials, the commonly used linear amplification method causes severe deviation from the actual experimental value obtained on nanoporous membranes, particularly at a high pore density. An appropriate simulation method is therefore highly demanded and a great challenge. Herein, we present a general strategy for multi-pore nanofluidic systems by taking the influence of neighbouring nanopores into consideration. We have found that the fourth nearest-neighbor approximation is sufficiently precise for simulation in nanoporous systems. The simulation data are in good agreement with the experimental results. The simulation method provides insights for understanding the pore–pore interaction in porous nanofluidic systems and for the design of high-performance devices.

Simulation of osmotic energy conversion in nanoporous materials: a concise single-pore model

Salinity difference in ionic solutions is considered as a potential candidate for clean energy. Nowadays, nanofluidic reverse electrodialysis systems have received renewed attention for harnessing salinity gradient power. Towards practical applications, great efforts have been made in the fabrication of membrane-scale nanoporous materials. From a theoretical point of view, however, state-of-the-art simulation methods for multi-pore nanofluidic systems consume huge amounts of computational resources that frequently preclude simulation on lab-used computers. Here, we present a concise single-pore model to simulate the osmotic energy conversion in nanoporous materials. By regulating the geometric size of the solution reservoir, we show that the single-pore model is sufficiently accurate to simulate diffusive ion transport in multi-pore nanofluidic systems. More importantly, it largely reduces the computational scale by more than one order of magnitude. A benefit of this feature is that the model can incorporate more physical processes, such as the motion of fluid and heat conduction, which greatly expands the scope of the simulation method for understanding charge and mass transport behavior through nanoporous materials.