Article Cite This: Langmuir 2017, 33, 11180-11188
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Water Adsorption Property of Hierarchically Nanoporous Detonation Nanodiamonds Elda-Zoraida Pina-Salazar,†,‡ Koki Urita,§ Takuya Hayashi,∥ Ryusuke Futamura,† Fernando Vallejos-Burgos,† Jerzy Włoch,⊥ Piotr Kowalczyk,# Marek Wiśniewski,○,□ Toshio Sakai,‡ Isamu Moriguchi,§ Artur P. Terzyk,○ Eiji Osawa,△ and Katsumi Kaneko*,† †
Center for Energy and Environmental Science, ‡Department of Materials Chemistry, Faculty of Engineering, and ∥Department of Electrical Engineering, Shinshu University, Nagano 380-8553, Japan § Division of Chemistry and Materials Science, Graduate School of Engineering, Nagasaki University, Nagasaki 852-8521, Japan ⊥ Faculty of Chemistry, Synthesis and Modification of Carbon Materials Research Group, Nicolaus Copernicus University in Toruń, Gagarin Street 7, 87-100 Toruń, Poland # School of Engineering and Information Technology, Murdoch University, Murdoch 6150, WA, Australia ○ Faculty of Chemistry, Physicochemistry of Carbon Materials Research Group, Nicolaus Copernicus University in Toruń, Gagarin Street 7, 87-100 Toruń, Poland □ INVEST-TECH R&D Center, Plaska Street 32-34, 87-100 Toruń, Poland △ Nano-Carbon Research Institute, Ltd., Ueda, Nagano 386-8567, Japan S Supporting Information *
ABSTRACT: The detonation nanodiamonds form the aggregate having interparticle voids, giving a marked hygroscopic property. As the relationship between pore structure and water adsorption of aggregated nanodiamonds is not well understood yet, adsorption isotherms of N2 at 77 K and of water vapor at 298 K of the well-characterized aggregated nanodiamonds were measured. HR-TEM and Xray diffraction showed that the nanodiamonds were highly crystalline and their average crystallite size was 4.5 nm. The presence of the graphitic layers on the nanodiamond particle surface was confirmed by the EELS examination. The pore size distribution analysis showed that nanodiamonds had a few ultramicropores with predominant mesopores of 4.5 nm in average size. The water vapor adsorption isotherm of IUPAC Type V indicates the hydrophobicity of the nanodiamond aggregates, with the presence of hydrophilic sites. Then the hygroscopic nature of nanodiamonds should be associated with the surface functionalities of the graphitic shell and the ultramicropores on the mesopore walls.
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oxides.13−15 Osawa et al. succeeded to obtain highly pure detonation nanodiamonds.13 Although the properties of nanodiamonds depend on the production method, precursors, and applied conditions, nanodiamonds can be generally described as polyhedral particles of sp3 hybridized carbon atoms, which can be obtained as colloidal individual particles as small as 4−5 nm in diameter.1,2,13 Such materials have chemically active surfaces, while its core remains inert. Nanodiamonds present a unique
INTRODUCTION Diamond nanoparticle (nanodiamond)s were first discovered in the 1960s as a product of detonation processes.1,2 Nanodiamonds are also found in nature as part of protoplanetary disks of certain types of stars.3,4 Nowadays, nanodiamonds are produced by several routes such as plasma-assisted chemical vapor deposition (CVD),5 autoclave synthesis from supercritical fluids,6 electron irradiation of carbon “onions”,7 ion irradiation of graphite,8 chlorination of carbides,9 ultrasound cavitation,10 laser ablation,11 and high-energy ball milling of high-pressure and high-temperature (HPHT) diamond crystals.12 The most popular nanodiamonds are the ones prepared by the detonation method.1 This is because of the multistep oxidation-purification procedure, which has been actively studied for detonation soots consisting of diamond particles (up to wt. 75%), other carbon allotropes, metal impurities, and © 2017 American Chemical Society
Special Issue: Tribute to Keith Gubbins, Pioneer in the Theory of Liquids Received: June 15, 2017 Revised: July 31, 2017 Published: August 9, 2017 11180
DOI: 10.1021/acs.langmuir.7b02046 Langmuir 2017, 33, 11180−11188
Article
Langmuir surface structure coming from the mixture of diamond-like sp3 and graphitic sp2 carbon atoms.14−16 The graphitic or amorphous carbon layers, consisting of sp2 hybridized carbon, wrap the surface of each nanodiamond particle.17 Nanodiamond particles tend to aggregate at the nanometer scale of 50−500 nm due to their high surface energy.18 The aggregates have intergranular gaps, which accounts mainly for mesoporosity.19−21 Moreover, exceptional properties of nanodiamonds are reported as mechanical and optical properties, fluorescence, high thermal conductivity and electrical resistivity, chemical stability, and resistance to harsh environments and biocompatibility. In addition, water adsorption on the surfaces of diamonds and detonation nanodiamonds induces negative electron affinity22 and giant electric permittivity,23 respectively. Nanodiamonds are expected to be mechanical enhancers and highly sensitive photodetectors. Furthermore, nanodiamonds are described as the most biocompatible materials among all the carbon-based materials because of their low toxicity, and thereby, the nanodiamonds are excellent candidates in biochemical and medical fields.24−26 Wettability well defines the hydrophilic (or hydrophobic) character of a material. The water wettability is described by contact angle for liquid water. The air−water contact angles of polished diamond faces of a single crystal are 75.9° (for the diamond face [111]) and 71.0° (for the diamond face [110]).27 Therefore, the surfaces of the diamond are not hydrophilic, but rather hydrophobic. Although the wettability of nanodiamonds has not been fully explored, the water contact angle of a nanodiamond film was 73 ± 3° in air at room temperature.28 Besides, low water affinity of nanodiamond powders is reported.29 The contact angles of nanodiamonds synthesized by chemical vapor deposition are 32° after oxidation and 93° after reduction.30 Nanodiamond surfaces without oxidation treatment are also hydrophobic. However, no reports were found on the contact angle of detonation nanodiamonds due to difficult measurements through the hygroscopic nature.31 Accordingly, water adsorption studies were carried out to evaluate the affinity of the detonation nanodiamonds for water,23,32,33 giving no clear understanding yet. For example, powder of detonation nanodiamonds containing a small amount of large mesopores (>15 nm) was able to adsorb a small amount (
