Control of sp2/sp3 carbon ratio and surface chemistry of nanodiamond powders by selective oxidation in air.
ABSTRACT The presence of large amounts of nondiamond carbon in detonation-synthesized nanodiamond (ND) severely limits applications of this exciting nanomaterial. We report on a simple and environmentally friendly route involving oxidation in air to selectively remove sp(2)-bonded carbon from ND. Thermogravimetric analysis and in situ Raman spectroscopy shows that sp(2) and sp(3) carbon species oxidize with different rates at 375-450 degrees C and reveals a narrow temperature range of 400-430 degrees C in which the oxidation of sp(2)-bonded carbon occurs with no or minimal loss of diamond. X-ray absorption near-edge structure spectroscopy detects an increase of up to 2 orders of magnitude in the sp(3)/sp(2) ratio after oxidation. The content of up to 96% of sp(3)-bonded carbon in the oxidized samples is comparable to that found in microcrystalline diamond and is unprecedented for ND powders. Transmission electron microscopy and Fourier transform infrared spectroscopy studies show high purity 5-nm ND particles covered by oxygen-containing surface functional groups. The surface functionalization can be controlled by subsequent treatments (e.g., hydrogenization). In contrast to current purification techniques, the air oxidation process does not require the use of toxic or aggressive chemicals, catalysts, or inhibitors and opens avenues for numerous new applications of nanodiamond.
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ABSTRACT: Hybrid nanocarbon, comprised of a diamond core and a graphitic shell with a variable sp(2) -/sp(3) -carbon ratio, is controllably obtained through sequential annealing treatment (550-1300 °C) of nanodiamond. The formation of sp(2) carbon increases with annealing temperature and the nanodiamond surface is reconstructed from amorphous into a well-ordered, onion-like carbon structure via an intermediate composite structure-a diamond core covered by a defective, curved graphene outer shell. Direct dehydrogenation of propane shows that the sp(2) -/sp(3) -nanocomposite exhibits superior catalytic performance to that of individual nanodiamond and graphitic nanocarbon. The optimum catalytic activity of the diamond/graphene composite depends on the maximum structural defectiveness and high chemical reactivity of the ketone groups. Ketone-type functional groups anchored on the defects/vacancies are active for propene formation; nevertheless, once the oxygen functional groups are desorbed, the defects/vacancies alone might be active sites responsible for the CH bond activation of propane.Chemistry 04/2014; · 5.93 Impact Factor
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ABSTRACT: Nanodiamonds are a class of carbon-based nanoparticles that are rapidly gaining attention, particularly for biomedical applications, i.e., as drug carriers, for bio imaging, or as implant coatings. Nanodiamonds have generally been considered biocompatible for a broad variety of eukaryotic cells. We show that, depending on their surface composition, nanodiamonds kill Gram-positive and -negative bacteria rapidly and efficiently. We investigated six different types of nanodiamonds exhibiting diverse oxygen-containing surface groups that were created using standard pretreatment methods for forming nanodiamond dispersions. Our experiments suggest that the antibacterial activity of nanodiamond is linked to the presence of partially oxidized and negatively charged surfaces, specifically those containing acid anhydride groups. Furthermore, proteins were found to control the bactericidal properties of nanodiamonds by covering these surface groups, which explains the previously reported biocompatibility of nanodiamonds. Our findings describe the discovery of an exciting property of partially oxidized nanodiamonds as a potent antibacterial agent.ACS Nano 05/2014; · 12.03 Impact Factor
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ABSTRACT: Hybrid composite nanomaterials provide an attractive and versatile material platform for numerous emerging nano- and biomedical applications by offering the possibility to combine diverse properties which are impossible to obtain within a single material. In this work, we present the fabrication of novel hybrid diamond and amorphous diamond-like carbon (DLC) coated nanoporous alumina materials that exhibit multiple functionalities, such as high surface area, quasi-ordered nanopore structure, tunable surface chemistry and electrical conductivity, excellent biological, chemical and corrosion resistance. These multifunctional nanohybrid materials are fabricated using the plasma-induced carbonization method that effectively modifies the surface and the inside of the nanopores of anodic alumina, producing a homogenous ultrathin DLC protecting layer over the whole external and internal surfaces of the membranes. We demonstrate that the interplay between internal and external carbon supply is a critical factor for the formation of the ultrathin sp3-bonded carbon layer in the nanopores. This study brings new insights in the DLC growth mechanisms in confined nanospaces and opens new avenues to fabricate hybrid, chemically resistant and biocompatible carbon-coated nanoarchitectures on other inorganic supports.Carbon 08/2014; 75:452-464. · 5.87 Impact Factor