Iodine-mediated high-pressure high-temperature carbonization of hydrocarbons and synthesis of nanodiamonds

doi:10.1016/j.materresbull.2020.111189

Materials Research Bulletin

Volume 137, May 2021, 111189

https://doi.org/10.1016/j.materresbull.2020.111189 Get rights and content

Highlights

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The synthesis of nanodiamonds from 1-iodoadamantane occurs above 800 °C at 8 GPa.
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Only graphite was synthesized in adamantane-I system at 3.5 and 8 GPa.
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No diamonds were synthesized in adamantane-GeI₄ system at 3.5 and 8 GPa.
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Iodination of hydrocarbons is crucial for mass formation of nanodiamonds.
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GeI₄ is thermally stable up to 1250 °C at 8 GPa.

Abstract

Carbonization behavior of iodinated adamantane, adamantane and naphthalene in mixtures with germanium iodide or iodine was studied at pressures of 3.5 and 8 GPa to elucidate diamond-forming catalytic activity of iodine. Using XRD, Raman spectroscopy and TEM as characterization methods, we have found that pyrolysis of iodinated adamantane at 8 GPa is accompanied with formation of nanodiamonds at temperatures exceeding 800 °C. Post-pyrolysis growth of nanodiamonds points out the diamond-forming catalytic activity of iodine. In the samples obtained from precursor mixtures, only graphite was detected as a pyrolysis product, which means that hydrocarbon iodination is a prerequisite for iodine-mediated synthesis of nanodiamonds.

Graphical abstract

Introduction

The synthesis of diamonds at high pressures from organic compounds becomes a hot topic due to the possibility of obtaining color centers in nanodiamonds with high structure perfection [[1], [2], [3]]. Color centers in nanodiamonds can be used as nanoscale sensors of magnetic and thermal fields, fluorescent biolabels, and as effective single photon emitters [4,5]. Successful synthesis of nanodiamonds from halogenated adamantanes (C₁₀H₁₄Br, C₁₀H₁₅Cl) at static pressures of 8−9 GPa and temperatures 700−1700 °C has initiated research of controlled production of nanodiamonds in halogen-containing hydrocarbon growth systems [6,7].

The recent report on germanium iodide-mediated synthesis of nanodiamonds from hydrocarbons at 3.5 GPa and 500 °C in diamond anvil cell raises questions of whether mass synthesis of nanodiamonds can be realized at such extremely mild conditions, and whether germanium iodide and iodine possess catalytic ability in formation of diamonds from hydrocarbons [8]. Elucidation of catalytic activity of elemental iodine in “organic” synthesis of nanodiamonds deserves close attention, since one can expect reduction or thermal decomposition of germanium iodide in hydrocarbon environment [9]. The mixtures of saturated hydrocarbons were used in germanium iodide-mediated synthesis of nanodiamonds, while adamantane molecules were considered as "seeds" for the diamond nucleation [8]. It is known, that initial structure of hydrocarbon precursors has great impact on nucleation of diamonds [10,11]. In this regard, use of unsaturated hydrocarbons, such as naphthalene in iodine-mediated synthesis of diamonds seems very important for explanation of mechanism of catalysis. We assume that saturation of carbon bonds with iodine can play a key role in formation of diamond nuclei from unsaturated hydrocarbons, whereas in case of saturated hydrocarbon, for example, adamantane, iodine atoms can prevent formation of graphite during its pyrolysis in diamond stability region. It should be noted, that in some reports on HPHT synthesis of nanodiamonds from hydrocarbons, halogen-containing compounds were included into the growth systems, but their influence on the nucleation and growth of nanodiamonds was not considered [12,13]. For instance, chlorinated hydrocarbons were added into reaction volume to assist dissolving of 2-azaadamantane hydrochloride “seeds” in nonpolar carbon “sources” [12]. The question on the catalytic activity of iodine as a halogen is also interesting for understanding the diamond origin in nature. Increased content of halogens in kimberlite rocks, as well as detection of Cl, Br, and I inclusions in some varieties of natural diamonds, may indicate that halogen-containing fluids participate in the diamonds formation in mantle [14,15].

The purpose of this work is to elucidate catalytic activity of iodine in formation of nanodiamonds from hydrocarbons under pressure, as well as to explore the feasibility of mass synthesis of nanodiamonds from iodinated adamantane, double mixtures of adamantane and naphthalene with germanium iodide or iodine.

Section snippets

Experimental

1-Iodoadamantane, C₁₀H₁₅I (98 %, Aldrich), Adamantane C₁₀H₁₅ (99 %, Aldrich), Naphtalene (99.9 %, Aldrich), Germanium iodide GeI₄ (99.99 %, Aldrich) and Iodine (99.99 %, Aldrich) were used as starting materials for obtaining samples. Mixtures of adamantane or naphthalene with iodine or germanium iodide were prepared by grinding the reagents in jasper mortar with pest for 5 min. The mass of reagents for preparation of mixtures was selected to provide an atomic ratio of carbon to iodine 10:1 as

Results and discussion

Fig. 2 shows X-ray diffraction patterns of samples obtained from iodinated adamantane at pressure of 8 GPa and temperatures of 800−1250 °C. Appearance of three wide diamond peaks in diffraction pattern of the sample synthesized at 1100 °C clearly shows formation of nanodiamonds. The average size calculated by (111) diffraction peak using the Scherrer’s formula is about 3 nm, which is consistent with direct measurements of diamond grains in TEM images (Fig. 3). Nanodiamonds are equiaxial with

Conclusions

The possibility of obtaining nanodiamonds from adamantane and naphthalene with addition of iodine or germanium iodide, as well as from 1-iodoadamantane was studied on bulk samples synthesized at pressures of 3.5 and 8 GPa and temperatures up to 1250 °C. We observed mass formation of nanodiamonds in the synthesis from 1-iodoadamantane at 8 GPa and temperatures above 800 °C, while adamantane pyrolysis in mixtures with iodine and germanium iodide resulted in graphitization only. Our experiments

CRediT authorship contribution statement

E.A. Ekimov: Conceptualization, Methodology, Investigation, Data curation, Writing - original draft, Writing - review & editing. K.M. Kondrina: Investigation, Data curation. I.P. Zibrov: Investigation, Data curation. S.G. Lyapin: Investigation, Data curation. M.V. Lovygin: Investigation, Data curation. P.R. Kazanskiy: Investigation, Data curation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by Russian Science Foundation (Grant No.19-12-00407). Authors thank Yu. B. Lebed for technical assistance.

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Iodine-mediated high-pressure high-temperature carbonization of hydrocarbons and synthesis of nanodiamonds

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

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