Research Article www.acsami.org
Salt-Assisted Ultrasonic Deaggregation of Nanodiamond K. Turcheniuk,† C. Trecazzi,† C. Deeleepojananan,† and V. N. Mochalin*,†,‡ †
Missouri University of Science and Technology, Schrenk Hall, 400 West 11th Street, Rolla, Missouri 65409, United States Department of Materials Science & Engineering, Missouri University of Science and Technology, 1400 North Bishop, Rolla, Missouri 65409, United States
‡
S Supporting Information *
ABSTRACT: We report a new facile, inexpensive, and contaminant-free technique of salt-assisted ultrasonic deaggregation (SAUD) of nanodiamond into single-digit particles stable in aqueous colloidal solution in a wide pH range. The technique utilizes the energy of ultrasound to break apart nanodiamond aggregates in sodium chloride aqueous slurry. In contrast to current deaggregation techniques, which introduce zirconia contaminants into nanodiamond, the single-digit nanodiamond colloids produced by SAUD have no toxic or difficult-to-remove impurities and are therefore well-suited to produce nanodiamonds for numerous applications, including theranostics, composites, and lubrication, etc. Requiring only aqueous slurry of sodium chloride and standard horn sonicator, and yielding highly pure well-dispersed nanodiamond colloids, the technique is an attractive alternative to current nanodiamond deaggregation protocols and can be easily implemented in any laboratory or scaled up for industrial use. KEYWORDS: salt-assisted ultrasonic deaggregation, nanodiamond, nanoparticle, salt, ultrasound, colloidal solution
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nanoparticles.2,11−18 At the same time, biomedical applications are very sensitive to the presence of any impurities in the material. Since traditional dispersion techniques are ineffective for ND, specific deaggregation methods have been developed (Table 1). These include zirconia microbead-assisted wet ball milling,2,11 salt- and sugar-assisted dry attrition and ball milling,19−21 and bead-assisted sonic disintegration (BASD).2,11,22 Although each technique is capable of significantly reducing the size of ND agglomerates and even yielding single-digit NDs, they have crucial disadvantages and deficiencies that prevent their use in certain applications, especially in biology and medicine. In addition, some of these deaggregation methods significantly increase the cost of single-digit NDs. Among the mentioned ND deaggregation techniques, those using zirconia micrometer-sized beads (ZrO2 microbeadassisted wet milling and BASD) are now most common. In particular, BASD-derived ND colloids have been used in development of biomedical applications, particularly for adsorption and delivery of insoluble anticancer therapeutics.23,24 In BASD, the dense zirconia microbeads, propelled by the energy of cavitation, collide and crush the nanodiamond aggregates trapped in between. BASD yields stable single-digit ND colloidal solutions of up to 10 wt % concentration with up to 80% yield relative to initial ND mass.22 However, zirconia
INTRODUCTION Nanoparticles in dry powder state tend to form agglomerates, in this way reducing their high surface energy. This property represents a significant obstacle for certain applications. Detonation nanodiamond particles (nanodiamonds, NDs) are particularly known to form agglomerates that cannot be destroyed by traditional means such as sonication, milling, and so on.1,2 This is generally explained by the rich surface chemistry of ND.3 The presence of diverse functional groups on ND surface, such as carboxyl, hydroxyl, lactone, etc., may result in formation of multiple hydrogen and even covalent bonds between the adjacent ND particles, making it difficult to separate them. Strong agglomeration severely limits potential of NDs in many applications. For example, good dispersion and interfacing of ND to polymer or metal matrix are the greatest challenges in developing ND−polymer and ND−metal composites.4−6 The nanocomposites benefit from a large amount of the interphase achieved with small concentrations of well-dispersed nanoparticles, which in contrast to larger fillers or agglomerates, do not compromise the valuable properties of the matrix. Additionally, well-dispersed nanoparticles maximize the nanoparticle−matrix interactions while minimizing the unfavorable nanoparticle−nanoparticle interactions. Biomedical applications of NDs provide another example where small and uniform particle size is crucial. Recent progress made in dispersion of NDs in aqueous media,1,2,7 along with control of their purity and surface chemistry,3,8−10 have dramatically propelled research on biomedical applications of these least toxic of all known carbon © 2016 American Chemical Society
Received: July 8, 2016 Accepted: September 2, 2016 Published: September 2, 2016 25461
DOI: 10.1021/acsami.6b08311 ACS Appl. Mater. Interfaces 2016, 8, 25461−25468
Research Article
ACS Applied Materials & Interfaces Table 1. ND Deaggregation Techniques method bead-assisted sonic disintegration (BASD) bead-assisted ball milling salt-assisted attrition milling ultracentrifugation salt-assisted ultrasound deaggregation (SAUD)
additive
ultrasound power, W
ZrO2, SiO2 microbeads
400−450
ZrO2 microbeads NaCl crystals
NaCl crystals
500 150
ND diameter, nm
workup
comments
ref
dissolution of ZrO2 contaminants in strong base or acid
4−5
difficult-to-remove contamination from microbeads
2, 11, 13, 22, 25
dissolution of ZrO2 contaminants in strong base or acid acid treatment to remove Fe and other metals followed by pH adjustment to 11 centrifugation at 18000g washing/centrifugation steps (×2)
