Modulating Water Slip Using Atomic-Scale Defects: Friction on Realistic Hexagonal Boron Nitride Surfaces

Seal, Aniruddha; Rajan, Ananth Govind

doi:10.1021/acs.nanolett.1c02208

Cited by 22 publications

(31 citation statements)

References 66 publications

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“…Yet others have used the density-derived electrostatic and chemical (DDEC) method and electrostatic potential fitting (ESP) method (e.g., Jafarzadeh et al) to calculate partial charges. In previous work, we showed that ESP-based charges are not able to predict correctly the electrostatic potential above defects in hBN . In Section S10, we show that DDAP (using default parameters), Hirshfeld, Mulliken, and DDEC partial charges are also not suitable for predicting the electrostatic potential above nanopores in hBN.…”

Section: Results and Discussionmentioning

confidence: 99%

How Grain Boundaries and Interfacial Electrostatic Interactions Modulate Water Desalination via Nanoporous Hexagonal Boron Nitride

Sharma

Rajan

2022

J. Phys. Chem. B

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To fulfill the increasing demand for drinking water, researchers are currently exploring nanoporous two-dimensional materials, such as hexagonal boron nitride (hBN), as potential desalination membranes. A prominent, yet unsolved challenge is to understand how such membranes will perform in the presence of defects or surface charge in the membrane material. In this work, we study the effect of grain boundaries (GBs) and interfacial electrostatic interactions on the desalination performance of bicrystalline nanoporous hBN using classical molecular dynamics simulations supported by quantum−mechanical density functional theory (DFT) calculations. We investigate three different nanoporous bicrystalline hBN configurations, with symmetric tilt GBs having misorientation angles of 13.2, 21.8, and 32.2°. Using lattice dynamics calculations, we find that grain boundaries alter the areas and shapes of nanopores in bicrystalline hBN, as compared to the nanopores in monocrystalline hBN. We observe that, although bicrystalline nanoporous hBN with a misorientation angle of 13.2°shows an improved water flow rate by ∼30%, it demonstrates reduced Na + ion rejection by ∼6%, as compared to monocrystalline hBN. We also uncover the role of the nanopore shape in water desalination, finding that more elongated pores with smaller sizes (in 21.8-and 32.2°-misoriented bicrystalline hBN) can match water permeation through less elongated pores of slightly larger sizes, with a concomitant ∼3−4% decrease in Na + rejection. Simulations also predict that the water flow rate is significantly affected by interfacial electrostatic interactions. Indeed, the water flow rate is the highest when altered partial charges on B and N atoms were determined using DFT calculations, as compared to when no partial charges or bulk partial charges (i.e., charged hBN) were considered. Overall, our work on water/ion transport through nanopores in bicrystalline hBN indicates that the presence of GBs and surface charge can lead, respectively, to a decrease in the ion rejection and water permeation performance of hBN membranes.

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Section: Results and Discussionmentioning

confidence: 99%

How Grain Boundaries and Interfacial Electrostatic Interactions Modulate Water Desalination via Nanoporous Hexagonal Boron Nitride

Sharma

Rajan

2022

J. Phys. Chem. B

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“…Overall, these results consolidate the picture of dipolar environment-tuned defects, whose properties are affected by changes in the sensing hemisphere with volume ∼ 2/3π 3 dip , which encloses fewer than 100 molecules in the case of acetonitrile. Beyond passive diffusion and dielectric sensing of confined liquids, tracking defect activation dynamics in confinement may be used to directly image nanoscale flow and study its interplay with defects 54 . While a macroscopic control over the ensemble surface charge of nanofluidic devices with light was found to be useful for biomolecule detection 55 and energy harvesting applications 56,57 , the possibility to address single charges in confinement suggested by our results may reveal fundamentally new phenomena such as correlated ion transport 52 .…”

Section: Integration In Single-digit Nanofluidic Systemsmentioning

confidence: 99%

Liquid-activated quantum emission from native hBN defects for nanofluidic sensing

Ronceray¹,

You²,

Glushkov³

et al. 2022

Preprint

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Nanostructures made of two-dimensional (2D) materials have become the flagship of nanofluidic discoveries in recent years 1,2 .By confining liquids down to a few atomic layers, anomalies in molecular transport 3-5 and structure 6, 7 have been revealed.Currently, only indirect and ensemble averaged techniques have been able to operate in such extreme confinements, as even the smallest molecular fluorophores are too bulky to penetrate state-of-the-art single-digit nanofluidic systems 8 . This strong limitation calls for the development of novel optical approaches allowing for the direct molecular imaging of liquids confined at the nanoscale. Here, we show that native defects present at the surface of hexagonal boron nitride 9 (hBN) -a widely used 2D material -can serve as probes for molecular sensing in liquid, without compromising the atomic smoothness of their host material. We first demonstrate that native surface defects are readily activated through interactions with organic solvents and confirm their quantum emission properties. Vibrational spectra of the emitters suggest that their activation occurs through the chemisorption of carbon-bearing liquid molecules onto native hBN defects. The correlated activation of neighboring defects reveals single-molecule dynamics at the interface, while defect emission spectra offer a direct readout of the local dielectric properties of the liquid medium. We then harvest these effects in atomically smooth slit-shaped van der Waals channels, revealing molecular dynamics and increasing dielectric order under nanometre-scale confinement. Liquid-activated native defects in pristine hBN bridge the gap between solid-state nanophotonics and nanofluidics and open up new avenues for nanoscale sensing and optofluidics. MainFluorescent defect centers in wide band-gap materials like diamond, silicon carbide or boron nitride have received increasing attention in recent years as they allow to probe nanoscale matter through interactions with their dipoles and electron spins 10,11 . In particular, a variety of point defects with energy levels well within the 6 eV band gap of hexagonal boron nitride (hBN) were

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“…Hexagonal boron nitride (hBN) is an inorganic two-dimensional (2D) material − that has found applications in seawater desalination, , osmotic power harvesting, and biological sensors . Understanding the wetting and fluidic properties of 2D materials is essential in such applications because of the resultant intimate contact between liquids and the solid surface. − In this regard, the interfacial properties of a solid surface can be impacted by any defects or roughness present in it. − For example, the equilibrium contact angle and slip length for fluid flow can depend on the nanoscale structure of the solid. However, there is a lack of understanding of the wetting and frictional behavior of solids containing atomic-scale defects and/or roughness.…”

Section: Introductionmentioning

confidence: 99%

“…The wetting and slip behavior of water on 2D materials such as graphene and hBN have been both experimentally ,,− and theoretically ,,,− determined. These studies have shown that water’s wetting and flow properties can significantly depend on the surface’s chemical composition , and morphology, ,,, as these affect the electrostatic and dispersion forces operative between the solid and water .…”

Section: Introductionmentioning

confidence: 99%

“…Theoretical studies have also examined the wettability and slippage of water on graphene ,,,− and hBN, − ,,,− with molecular dynamics (MD) simulations offering a robust methodology to quantify the wetting and frictional behavior of contamination-free surfaces. These investigations have been carried out with a number of force fields for describing hBN–water and water–water interactions.…”

Section: Introductionmentioning

confidence: 99%

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Surface Roughness Explains the Observed Water Contact Angle and Slip Length on 2D Hexagonal Boron Nitride

Verma

Rajan

2022

Langmuir

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Hexagonal boron nitride (hBN) is a two-dimensional (2D) material that is currently being explored in a number of applications, such as atomically thin coatings, water desalination, and biological sensors. In many of these applications, the hBN surface comes into intimate contact with water. In this work, we investigate the wetting and frictional behavior of realistic 2D hBN surfaces with atomic-scale defects and roughness. We combine density functional theory calculations of the charge distribution inside hBN with free energy calculations using molecular dynamics simulations of the hBN−water interface. We find that the presence of surface roughness, but not that of vacancy defects, leads to remarkable agreement with the experimentally observed water contact angle of 66°on freshly synthesized, uncontaminated hBN. Not only that, the inclusion of surface roughness predicts with exceptional accuracy the experimental water slip length of ∼1 nm on hBN. Our results underscore the importance of considering realistic models of 2D materials with surface roughness while modeling nanomaterial−water interfaces in molecular simulations.

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Modulating Water Slip Using Atomic-Scale Defects: Friction on Realistic Hexagonal Boron Nitride Surfaces

Cited by 22 publications

References 66 publications

How Grain Boundaries and Interfacial Electrostatic Interactions Modulate Water Desalination via Nanoporous Hexagonal Boron Nitride

How Grain Boundaries and Interfacial Electrostatic Interactions Modulate Water Desalination via Nanoporous Hexagonal Boron Nitride

Liquid-activated quantum emission from native hBN defects for nanofluidic sensing

Surface Roughness Explains the Observed Water Contact Angle and Slip Length on 2D Hexagonal Boron Nitride

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