Instructor: Instructor:

Dr. Marinella SandrosDr. Marinella Sandros

1

NanochemistrNanochemistryy

NAN 601NAN 601

Lecture 16: Nanodiamonds

Detonation nanodiamond (DND), often also called ultradispersed diamond (UDD), is diamond that originates from a detonation.

When an oxygen-deficient explosive mixture of TNT/Hexogen is detonated in a closed chamber, diamond particles with a diameter of ca. 5 nm are formed at the front of detonation wave in time of several microseconds.

http://en.wikipedia.org/wiki/Detonation_nanodiamond

The discovery of nanodiamond synthesis in 1963, followed by a prolonged suspension of active study.

For several reasons, including the security measures in place in the USSR and a lack of industrial interest in nanotechnology at the time, them application of this nanodiamond (ND) remained unreported and under-exploited until very recently.

Rediscovery of the synthesis in 1982–1993, with intensified study and production of nanodiamonds simultaneously at several research centers in the USSR. In this period, production potential exceeded the scale of application.

Unprofitable production of small batches of nanodiamonds in 1993–2003, leading to the closure of a number of research centers and the termination of production.

Ice or water shell

Inert gas

Explosives:

O2N NO2

NO2

CH3

N

N

NO2N NO2

NO2

TNT Hexogen

+

Wet product collector

Dry product collector

Further acid purification

Scheme of explosive technology

The detonation of carbon-containing explosives at high temperature and pressure with a negative oxygen balance results in the condensation of the free atomic carbon products as diamond or liquid carbon.

Phys. Sol. State, 2004 46, 611–615

•Theoretical calculations show that conditions for diamond stability during this process are only conserved for a very short time (sub-microsecond) and are closely followed by conditions where graphite is the more stable phase.

•This is due to a fast decrease in pressure while the system is still at a high temperature, which favours a diamond-to-graphite transformation.

•To obtain diamond, it is therefore important to control the rate at which the system cools—faster cooling at relatively high pressure results in a higher diamond yield.

(i) Rapid decrease in pressure at high temperatures facilitates the diamond-to-graphite transition.

(ii) Rapid cooling ensures that diamond remains the most stable phase and results in higher yields of detonation ND.

Phys. Sol. State, 2004 46, 611–615

The most commonly used explosives for this process are mixtures of trinitrotoluene (TNT) and hexogen or octogen. Explosion commonly takes place in a sealed stainless steel chamber in the absence of oxygen.

Diamond yield increases with the quantity of coolant present in the system; gases such as argon are commonly used, as well as water, water-based foams and ice.

Optimal cooling rates after detonation are found to be 3000–4000 K min-1. The products of detonation are a complex mix of ND particles of an average size of 5 nm and other graphitic carbon forms, hence rigorous cleaning stages are then employed to remove the nondiamond material.

The extent and method of cleaning depends on the source of the ND powder, but generally includes either gaseous ozone treatment or solution phase nitric acid oxidation to remove sp2 carbon and metallic impurities.

Produced by detonation from carbon-containing precursors such as TNT and hexogen, resulting in nanoparticles with 2 wt% nitrogen and 1wt% of hydrogen.

Nanodiamonds are unique structures that have diverse electronic properties depending on their size and morphology.

The powder contains diamond particles of very narrow size distribution averaging 5 nm but, as is clear from the image, the particles readily agglomerate to form aggregates up to several micrometres in dimension.

Kulakova, I. I. 2004 Surface chemistry of nanodiamonds. Phys. Solid State 46, 636–643.

The exact nature of the outer layer remains unclear, but two general modelshave emerged:

(i) an amorphous shell with significant sp2 carbon content or

(ii) an sp2 graphene-type sheet, of a fullerene structure, giving rise to a structure described as ‘bucky-diamond’. Heating ND particles to above 1000 K

in vacuum does result in laminates of fullerene shells being formed around the diamond core and ultimately to the formation of ‘carbon onions’.

The nature of the bonding sites of nitrogen in ND is still the subject of debate; in some studies, FTIR spectroscopy has shown the presence of NH2 groups on the surface of the ND, while others demonstrate that nitrogen atoms are only present within the core of the ND.

It is probable that nitrogen groups present on the surface have been introduced during the acid cleaning stage, whereas substitutional core nitrogen impurities come about during the detonation process, as nitrogen is a component of most explosives used.

The hydrogenated surface is part of a 0.6 nm-thick shell of seven partially disordered carbon layers that contain 61% of all C and mostly produce higher-field 13C NMR signals. Unpaired electrons (indicated by red arrows) occur with a density of 40 per particle and are located 0.4–1 nm from the surface.

J. Am. Chem. Soc., 2009, 131, 1426–1435

Krueger A,Chem. Eur. J.14,1382–1390 (2008).

Nitrogen is the most common impurity in diamond , and is present in natural specimens in various forms.

Nitrogen may be atomically incorporated either as single isolated (substitutional) impurities known as C centres, as pairs of adjacent impurities known as A centres, or in groups such as four substitutional nitrogen atoms surrounding a vacancy known as B centres.

In addition to this, diamond can contain a variety of other ‘color centres’ based on the combination of impurity atoms and their vacancy complexes

NDs defect comprises of a single nitrogen impurity in a substitutional position directly adjacent to a lattice vacancy.

This defect is of interest in the field of

nanomedicine as it is fluorescent, with an unusually high quantum yield.

The energy level structure of the N–V defect in diamond has a ground state and excited states forming an electron spin triplet with 3A and 3E, and due to the spin–spin interaction in the diamond crystal, the ground state is split into (ms = 0) and (ms = ±1) sub-levels. A transition between these states may be excited with light of ultraviolet wavelength (<400 nm).

One of the attractive properties of ND is its ability to fluoresce when excited with light of ultraviolet wavelength (< 400 nm).

The emission of 5 nm detonation diamond is dominated by a broad band in the visible region, from 390 to 650 nm.

The mechanism of photoluminescence has been variously assigned to the emission from impurity sites (e.g. dopants) within the core, defects in the diamond lattice or sp2 clusters on the ND surface.

Some lower energy (red) emissions were found to vary between ND samples and also to decrease after heating, indicating an association with the amount of sp2 carbon on the surface of the ND.

However, when thicker layers of graphite were formed on the surface, photoluminescence intensity was found to decrease dramatically, demonstrating that graphite itself was not responsible for this emission and it was conjectured that sp2 clusters embedded in a sp3 matrix may be responsible

Schematic of available energy levels within the diamond band gap capable of undergoing excitation and

photoluminescence.

Holt K B Phil. Trans. R. Soc. A 2007;365:2845-2861

©2007 by The Royal Society

Another ND fluorescence process of note is that resulting from excitation of the negatively charged nitrogen–vacancy (N–V)− centre, which absorbs strongly at 560 nm and emits efficiently at 700 nm.

This type of fluorescence has been reported in 1b (nitrogen-containing) diamond particles of 35 and 100 nm that have been irradiation damaged to create defects.

Irradiation with an electron beam creates a vacancy in the lattice and the sample is then annealed to bring the vacancy close to the nitrogen atom; this (N–V)− centre acts as an ion embedded in a solid matrix. As this fluorescence arises from defects deep within the ND core, it is unaffected by the surface chemistry of the ND.

Diamond Relat. Mater., 2009, 18, 567–573

(A) bright-field image(B) epifluorescence image(C) time traces of the

nanodiamonds and 100 nm green fluorescent polystyrene beads excited under the same conditions (mercury lamp: λex = 450–490 nm) and the resulting fluorescence was collected over the wavelength range of 505–545 nm.

Diamond Relat. Mater., 2009, 18, 567–573

Scheme for separation and purification of the recombinant protein from Escherichia coli cells using adsorption of proteins onto detonation ND (using the procedure described by Bondar et al. 2004).

Holt K B Phil. Trans. R. Soc. A 2007;365:2845-2861

©2007 by The Royal Society

Nanodiamonds easily internalized into cells for drug release. A – E. Confocal images of fluorescently (FITC)-labeled nanodiamonds incubated with RAW 264.7 macrophages. F. Transmission electron microscope image of ND–DOX complexes within the cytoplasm of macrophage cells. Scale bars represent 20 nm.

Layer-by-layer deposition process: sequential 2 x 2 μm AFM scans of (A) glass, (B) poly-l-lysine and (C) ND thin film layer.

ACS Nano, 2008, 2(2), 203-12.

A. Schematic depiction of the construction of nanodiamond-parylene microfilms. Nanodiamonds are sandwiched between a thick base layer and thin variable non-conformal layer of parylene, which allows for controllable release.

B. Resultant microfilms can be of varied size and are flexible.

A. Fluorescence spectra of 35-nm FNDs suspended in water (1 mg ml- 1 each), prepared with either 40-keV He+ or 3-MeV H+ irradiation. Inset: Fluorescence image of a 35-nm FND suspension excited by 532-nm laser light.

B. Fluorescence intensities of FNDs as a function of particle size at three different laser powers. Inset: Fluorescence time trace (intensity normalized) of a 25-nm FND.

Helium atoms are chemically inert, and embedding these atoms in a diamond lattice through neutralization of the stopped He+ ions does not appreciably change the photophysical properties of the FNDs produced.

40-keV He+ ion can create 40 vacancies as it penetrates diamond

high-fluence 40-keV He+ beams can be readily generated by radio-frequency ion sources. The current is more than two orders of magnitude higher than that of a 3-MeV H+ beam emanating from a tandem particle accelerator.

(A) Bright-field and epifluorescence (red pseudocolour) images of the cell after fluorescent nanodiamond uptake.

(B) Three-dimensional reconstruction (left panel), showing the boundaries of the nucleus and the cytoplasm of the cell. Three-dimensional trajectory (shown in pseudo-colour, right panel) and displacements of a single fluorescentnanodiamond (labeled with a yellow box in (A)) inside the cell over a time span of 200 s.

1. How are NDs made?

2. NDs emission at 700 nm is attributed to what?

1. NDs are made from the detonation of carbon-containing precursors such as TNT and hexogen under inert atmosphere in a closed chamber.

1. Arise from the N–V defect.