Pyrolytic formation and photoluminescence properties of a new layered carbonaceous material with graphite oxide-mimicking characteristics
Introduction
Layered carbonaceous materials (LCMs) with long-range lamellar ordering are built up from stacks of two-dimensional covalent networks containing predominantly carbon as well as varying amounts of heteroatoms such as H, F, N and O. Well-known examples include graphite, graphite fluoride, graphite fluoroxide, graphitic carbon nitride, graphite oxide and graphite epoxide [1], [2], [3], [4], [5], [6]. Because of their properties these 2D functional materials undoubtedly play a significant role in carbon science and technology. Nevertheless, graphite oxide is the only member that exhibits distinct ion-exchange and colloidal properties [7], features that have enabled a wealth of experimental studies including intercalated derivatives, catalysis, polymer composites, flexible membranes, single graphenes and thin films [8], [9], [10], [11], [12], [13]. On the other hand, LCMs, including graphite oxide, are derived from relatively inert graphitic lattices under rather aggressive reaction conditions using extremely hazardous reagents. In addition, due to the large lateral size of the starting graphitic particles (>1 μm) the resulting covalent derivatives are generally of microscale dimensions, which limits their potential in certain applications (e.g., drug delivery or cell studies).
In this respect, the development of nanoscale LCMs with tailored composition, structure, morphology and size using a simple and safe chemical approach is very appealing. Additionally, the combination of ion-exchange and colloidal properties would further broaden the spectrum of potential applications by improving processability and allowing fine-tuning of their physicochemical properties by intercalation, similarly to graphite oxide. To that end, the carbonization of suitable molecular precursors [14] represents a convenient synthetic approach offering the following advantages: (i) it proceeds under normal conditions in a simple and safe manner, (ii) enables control of size in the nanoregime, (iii) inserts heteroatoms in the final composition, (iv) directly introduces functional groups in the solid and, thus, it eliminates the need for chemical post-treatment of the relatively inert graphitic lattice, and (v) allows for additional functionality to be introduced (e.g., magnetic or optical).
In this context, we present here the synthesis of a new LCM derived from thermal carbonization of the molecular precursor bis(2-chloroethyl)amine hydrochloride and discuss in detail its properties. The solid possesses a layered structure with small lateral dimensions, disperses easily in water and exhibits ion-exchange properties. The material, despite its different structure and composition, essentially shares similar features with graphite oxide [5], [7]. In addition, it strongly fluoresces in the visible providing a new class of carbon-based emitters.
Section snippets
Experimental
About 1 g bis(2-chloroethyl)amine hydrochloride powder [, Aldrich 98%] was heated in air at 260 °C for 2 h at a heating rate of 10 °C min−1. The solid residue was extracted with 15 ml warm water followed by filtration through a large-pore filter paper. The filtrate was then centrifuged twice at 4000 rpm for 5 min to give a clear deep-brown colloid. The as-prepared LCM was isolated by water evaporation at 90 °C. Yield: 20%. Color: brown. LCM is effectively dispersible in water providing
Results and discussion
LCM is derived from bis(2-chloroethyl)amine hydrochloride simply via thermal carbonization in air (Fig. 1). The molecular precursor incorporates both the source for the carbonaceous layers, through the alkyl chloride tails, and the functional ammonium chloride groups. It is suggested that the layers consist of carbonized intermediates with a highly defected structure of co-existing aromatic and aliphatic regions, in analogy with the carbonaceous networks of graphite oxide or coal compounds [5],
Conclusions
In summary, mild thermal carbonization of bis(2-chloroethyl)amine hydrochloride affords a functional carbonaceous material that is layered, hydrophilic and exhibits ion-exchange properties. In addition, the material strongly emits light in the visible when stimulated with different excitation wavelengths. The method described here provides an alternative, simple way to synthesize functional layered carbonaceous materials from molecular precursors.
Acknowledgements
This work was supported by CFCI funded by DOE, the Project ΠENEΔ-Contract 03EΔ581, and the Projects of the Ministry of Education of the Czech Republic (1M6198952901 and MSM6198959218).
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