Interaction of Nanodiamonds with Water: Impact of Surface Chemistry on Hydrophilicity, Aggregation and Electrical Properties.

Maria Carmen Valsania,Alfio Battiato,Paolo Olivero,Lorenzo Mino,Sofia Sturari,Veronica Varzi,Pietro Aprà,Federico Picollo

doi:10.3390/nano11102740

Maria Carmen Valsania, Alfio Battiato + Show 6 more

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https://doi.org/10.3390/nano11102740

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Abstract

In recent decades, nanodiamonds (NDs) have earned increasing interest in a wide variety of research fields, thanks to their excellent mechanical, chemical, and optical properties, together with the possibility of easily tuning their surface chemistry for the desired purpose. According to the application context, it is essential to acquire an extensive understanding of their interaction with water in terms of hydrophilicity, environmental adsorption, stability in solution, and impact on electrical properties. In this paper, we report on a systematic study of the effects of reducing and oxidizing thermal processes on ND surface water adsorption. Both detonation and milled NDs were analyzed by combining different techniques. Temperature-dependent infrared spectroscopy was employed to study ND surface chemistry and water adsorption, while dynamic light scattering allowed the evaluation of their behavior in solution. The influence of water adsorption on their electrical properties was also investigated and correlated with structural and optical information obtained via Raman/photoluminescence spectroscopy. In general, higher oxygen-containing surfaces exhibited higher hydrophilicity, better stability in solution, and higher electrical conduction, although for the latter the surface graphitic contribution was also crucial. Our results provide in-depth information on the hydrophilicity of NDs in relation to their surface chemical and physical properties, by also evaluating the impacts on their aggregation and electrical conductance.

Highlights

Nanodiamonds (NDs) are attracting ever-increasing interest for their appealing physical, chemical, and optical properties for a broad range of technological applications
The results were consistent with the expectations provided by diffuse-reflectance infrared Fourier-transform (DRIFT)
Nanodiamonds with different size distributions were investigated in terms of water interaction, both from environmental moisture and in solution

Summary

Introduction

Nanodiamonds (NDs) are attracting ever-increasing interest for their appealing physical, chemical, and optical properties for a broad range of technological applications. Due to the extreme hardness and the low friction coefficient of diamond, NDs were mainly employed in tribology [5] Over time, they turned out to be interesting for a much wider variety of applications, in the context of nanocomposites, sensing, quantum emitters, and energy storage and conversion [6]. One of the most documented and natively present defects of the synthesis processes is the nitrogen-vacancy (NV) defect [10], consisting of a substitutional nitrogen atom near to a vacancy defect This system possesses two optically active states—namely, the negatively charged NV− center, with a zero-phonon line (ZPL) spectrally located at 638 nm, and the neutral-charge-state NV0 center, with a ZPL emission spectrally located at 575 nm. The electronic structure of the NV− center shows peculiar spin-dependent radiative transitions that can be exploited as a high-sensitivity magnetometer and thermometer, by means of optically detected magnetic resonance (ODMR), with appealing prospects in high-sensitivity and high-resolution sensing applications [11,12,13,14,15]

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