Bulk graphanes synthesized from benzene and pyridine

Abstract

We report a high-pressure high-temperature synthesis of several millimeter-sized samples of bulk graphanes with the composition C–H(D) from benzene and graphene-derivative C–H–N_0.2 from pyridine. X-ray diffraction, transmission electron microscopy, and infrared spectroscopy of the new materials reveal relatively large (several nanometers in size) crystalline grains of an sp³-bonded graphane lattice (3-cycle-4-step, the orthorhombic structure (Pbca) with the parameters a = 9.5–9.8 Å, b = 8.9–9.1 Å, and c = 17.1–17.3 Å). The main hydrogen groups in the samples are C–H groups connected by aliphatic bonds. The synthesized graphanes at atmospheric pressure are stable up to 500 °C. The macroscopic density of CH samples is 1.5–1.57 g cm⁻³ and the refractive index is 1.78–1.80. The absorption spectra of samples with a high degree of crystallization exhibit a weak absorption maximum at 2.8 eV, which is responsible for the yellow-orange color, the large absorption maximum at 4 eV and an absorption edge associated with the width of the optical gap at 5.2 eV. The bulk modulus (30–37 GPa) and shear modulus (15–18 GPa) of the fabricated samples, as well as their hardness (1–1.5 GPa), are about twice as high as the respective values for polycrystalline graphite. The dissolution of metalorganic complexes in benzene and pyridine makes it possible to obtain doped graphanes, which can have extraordinary electron transport and magnetic properties.