Anisotropic Carbon Phases Prepared from Fullerite C70 under High Pressure

Abstract

We present the structural and ultrasonic study of carbon phases prepared by quenching after heating of fullerite C₇₀ in the temperature range 300–1100°C at pressures 4 and 7.5 GPa. The main aspect of the work concerns the structural and elastic anisotropy of samples resulted as consequence of quasi hydrostatic pressure with an additional pressure component along the axis of pressure load. Structural anisotropy correlates with anisotropy of the tensor of effective elastic constants taken for the medium with single axis of anisotropy. Comparison of the data obtained with anisotropy effects, earlier observed in the phases synthesized from C₆₀ in the similar quasi hydrostatic conditions, clarifies the role of non‐spherical symmetry of C₇₀ molecule.     

Special features of structural transformations of fullerite C<Subscript>60</Subscript> at high pressures and temperatures

The results of experimental studies of special features of fullerite C₆₀ structural transformations at high pressures and temperatures are discussed. It has been found that under the action of a pressure of ∼ 7.0 GPa and a temperature of 2000–2200 K on fullerite graphite forms and with the liquid phase present diamond forms.     

Hard and superhard carbon phases synthesized from fullerites under pressure

A review has been presented on the structural and mechanical properties of hard carbon phases synthesized from fullerite C₆₀ under pressure. The density and nanostructure have been recognized as the key parameters defining the mechanical properties of hard carbon phases. By suggesting a version of the transitional high-pressure diagram of C₆₀ (developed up to 20 GPa), the three areas of the formation of hard carbon phases have been highlighted. The corresponding phases of superhard carbon are (1) disordered sp₂-type atomic structures at moderate pressures and high temperatures (> 1100 K), (2) three-dimensionally polymerized C₆₀ structures at moderate temperatures and high pressures (> 8 GPa), and (3) sp₃-based amorphous and nanocomposite phases at high pressures and temperatures. First region can be in turn separated into 2 subparts with different peculiarities of sp² structures and properties: low pressure part (0.1–2 GPa) and high-pressure part (2–8 GPa). Temperature can be recognized as a factor responsible for the formation of nanostructures by the partial destruction of molecular phases, whereas pressure is a factor responsible for stimulating the formation of rigid polymerized structures consisting of covalently bonded C₆₀ molecules, whereas the combination of both factors leads to the formation of atomic-based phases with dominating sp³ bonding.     

Photoluminescence Study of the Two‐Dimensional Tetragonal and Rhombohedral Polymers of C60 at High Pressure

Abstract

The pressure behavior of the photoluminescence (PL) spectra of the planar polymeric phases of C₆₀ have been studied at pressure up to 4 GPa. The PL spectra and the pressure‐induced shift of the principal bands differ considerably for the pristine C₆₀, two‐dimensional tetragonal (2D‐T) and rhombohedral (2D‐R) polymers of C₆₀. The changes in the PL spectra may be related with the transformation of the electron energy spectrum of polymers.     

Kinetic Properties of Orientational Phase Transition in Polymerized States of Fullerites C60

Abstract

In the present work, we have shown that at early stages of dimerization, which occur during synthesis of C₆₀ fullerite T _syn = 10–40°C and P _syn = 1.5–8 GPa, kinetics of the sc→fcc phase transition, may be well described by Avrami law with Avrami's exponent n _Avr = 3 (i.e., in this case we are dealing with martensite‐like transformation). Fullerite's samples produced at higher temperatures (40°C < T _syn < 120°C) exhibit different kinetics with lower Avrami‐exponent. This behavior we attribute to the transformation switching to diffusion‐controlled kinetics.     

Equilibrium Phase Diagram of Polymerized C60 and Kinetics of Decomposition of the Polymerized Phases

Abstract

Equilibrium phase diagram (T=0–1000 K; p=0–8 GPa) of pressure‐temperature polymerized C₆₀ has been constructed. It included rhombohedral; orthorhombic and tetragonal polymerized phases of C₆₀ along with fcc monomeric phases of C₆₀. The isothermal kinetics of depolymerization (T=373–513 K) of the O‐, R‐, T‐ and D‐phases was studied by means of the IR‐spectroscopy. The isothermal rate of decomposition goes up along the series: (T‐)<(O‐)<(R‐)<(D‐).     

Synthesis,Spectral Investigations,and Thermal Stability of [60]Fullerene Complexes with TMTSF: 2(C60) · 2(TMTSF) · (C6H6), C60 · TMTSF · 2(CS2), and 2(C60) · 2(TMTSF) · (C6H5Cl)

Abstract

Molecular complexes of [60]fullerene with tetramethyltetraselenafulvalene (TMTSF): C₆₀ · (TMTSF) · 2(CS₂) (1), 2(C₆₀) · (2(TMTSF) · (C₆H₆) (2), and 2(C₆₀) · (2(TMTSF) · (C₆H₅Cl) (3) have been synthesized and their thermal stability and IR spectra vs. light polarization and temperature have been performed.     

C60 and C70 pressure-and-temperature transformations into fullerene-related forms

A two-stage pressure-and-temperature treatment of the C₆₀ and C₇₀ fullerites was carried out. C₆₀ and C₇₀ molecules collapsed at the first-stage hot-isostatic-pressing (HIP; 220 MPa, argon) and transformed into some fullerene-related form in the 900–1750°C temperature range. These materials were used at the second stage of the high-pressure-high-temperature (HPHT; 7.7 GPa/1400°C) treatment to produce the bulk samples that had: a specific weight of about 2.0 g/cm³, 40/110 GPa Young modulus, 6.0/12.5 GPa, and elastic recovery above 81%. Transformations under the treatments were investigated with the X-ray and transmission electron microscopy techniques. The mechanism of the pressure-and-temperature transformations is discussed.     

Low temperature heat capacity and sound velocity in fullerite C60 orientational glasses

The nature of the linear term in the heat capacity of fullerite C₆₀ has been investigated. The low-temperature dependence of the sound velocity has been determined from the data of the heat capacity at temperatures below 4 K. A model of the dynamic configuration excitations (DCE) is proposed to describe the contribution of the linear term in heat capacity and calculate the dependence of sound velocity. It is shown that this model, apparently, adequately describes the dynamics of cluster formations of the short-range order in fullerite C₆₀ by taking into account excitations of both the atomic and electronic subsystems. In the framework of this model, it is shown that low-energy tunnel states that are located at the boundaries of C₆₀ domains make a dominant contribution to the low-temperature effects in the heat capacity and sound velocity of C₆₀.     

Diamond synthesis from C<Subscript>60</Subscript> fullerite using boron and titanium diboride

Boron-doped diamond has been synthesized from C₆₀ fullerite at 7 GPa and 2000–2050 K using unconventional solvents for carbon: boron and titanium diboride.     

Raman Modes and Stability at High Pressure of the Two‐Dimensional Rhombohedral Polymer of C60

Abstract

Phonon modes and stability of the planar rhombohedral polymer of C₆₀ have been studied at pressure up to ～30 GPa by means of in situ Raman scattering. At P ～ 15 GPa the phonon frequencies show an irreversible transition to a new phase related with random covalent bonding between the molecules in adjacent polymeric sheets.     

Highly efficient metal–organic-framework catalysts for electrochemical synthesis of ammonia from N<Subscript>2</Subscript> (air) and water at low temperature and ambient pressure

Metal–organic-frameworks (MOFs) (i.e., MOF(Fe), MOF(Co) and MOF(Cu)) were synthesized by a hydrothermal process. The prepared MOFs were characterized using X-ray diffraction, Fourier transform infrared spectroscopy and N₂ adsorption–desorption. The catalytic activities of the MOFs for the electrochemical synthesis of ammonia were evaluated when using N₂ (air) and water as raw materials at low temperature and ambient pressure. The results indicated that the prepared MOFs have fine crystalline structures, abundant micropores, and large specific surface areas. The prepared MOFs showed excellent catalytic activity for the electrochemical synthesis of ammonia at low temperature and ambient pressure. Among these MOFs, the MOF(Fe) displayed the best catalytic activity, and the highest ammonia formation rate and the highest current efficiency reached 2.12 × 10^?9 mol s^?1 cm^?2 and 1.43%, respectively, at 1.2 V and 90 °C, when using pure N₂ and water as raw materials. The prepared MOFs in this work showed remarkable catalytic activities for the electrochemical synthesis of ammonia at low temperature and ambient pressure among the non-noble metal catalysts. It was the first exploration to apply MOFs as the electrocatalysts for the electrochemical synthesis of ammonia at low temperature and ambient pressure.     

Synthesis of bipyramidal gold nanoparticle-[C60]fullerene nanowhisker composites and catalytic reduction of 4-nitrophenol

The seed solution was prepared by dissolving hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O), trisodium citrate dihydrate (C₆H₅Na₃O₇·2H₂O), and sodium borohydride (NaBH₄) in distilled water. The resulting reddish-purple seed solution was stirred for 3 h at room temperature. The growth solution was prepared by mixing hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O), cetyltrimethylammonium bromide (CTAB, (C₁₆H₃₃)N(CH₃)₃Br), silver nitrate (AgNO₃), hydrochloric acid (HCl), and ascorbic acid (C₆H₈O₆) in distilled water. Subsequently, 100 μL of this seed solution was transferred into 10 mL of the growth solution. The mixed solution was maintained at 30 °C for 3 h to obtain a solution of bipyramidal gold nanoparticles. The bipyramidal gold nanoparticle-[C₆₀] fullerene nanowhisker composites were synthesized by applying the liquid-liquid interfacial precipitation (LLIP) method to a saturated solution of C₆₀ in toluene, the solution of bipyramidal gold nanoparticles, and isopropyl alcohol. The prepared bipyramidal gold nanoparticle-[C₆₀] fullerene nanowhisker composites were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The catalytic activity of these composites was confirmed in the reduction of 4-nitrophenol by UV-Vis spectroscopy.     

Quantum Chemical ab initio Investigations of Non-Covalent Bonding Derivatives of Fullerene C60 and Li Atom or Cs2, C6H6 Molecules

Abstract

Quantum chemical ab initio investigations of the stability of the non-covalent fullerene complexes: C₆₀ molecule + Li atom, two C₆₀, two C₆₀ + CS₂, C₆₀ + CS₂, C₆₀ + C₆H₆ were performed using Hartree-Fock (HF) and Density Functional Theory (DFT) methods in various basis sets. The inclusion of electron correlation effect calculated by using DFT B3PW91 model during the optimization of Li atom position above hexagonal of C₆₀ gives the smaller distance from the centre of C₆₀ equal to 7.75 Å and large positive energy of formation equal to 4.452 kcal/mol in comparison with HF calculated distance 8.39 Å and energy of formation 1.810 kcal/mol. The positive energy of formation equal to 0.483 kcal/mol for optimized complex two C₆₀ + one CS₂ was found by HF. The presence of CS₂ molecule stabilises this complex with the energy equal to 0.281 kcal/mol. Complexes: C₆₀ + CS₂, C₆₀ + C₆H₆ do not possess the positive energy of formation.     

Photo‐Induced Polymerization and Stress Effects in Fullerite C60

Abstract

Modifications of the structure and hardness of fullerite C₆₀ crystals under stresses generated during photo‐induced polymerization are investigated.     

Anisotropic Nanoclustered Carbon Phases Prepared from Fullerite C60 Under Non‐hydrostatic High Pressure

Abstract

We show that application of the non‐hydrostatic pressure to the cluster‐based molecular material, like fullerite C₆₀, provides a new opportunity to create elastically and structurally anisotropic carbon materials, including 2D polymerized rhombohedral C₆₀ and graphite‐type (sp ²) disordered atomic‐based phases. The elastic anisotropy, detected by the difference in the ultrasound velocities propagating along and across the loading axis, is directly confirmed by the results of x‐ray diffraction.     

ESR Studies on C60.OX and C60.HMTTEF

Abstract

The electron spin resonance (esr) of C₆₀.O_x and C₆₀.HMTTEF (hexamethylentetratellurafulvalene) has been investigated at 9.36 GHz as a function of temperature. T (298 T 4 K). C₆₀.O_x shows an esr absorption of equal ‘g’ value to that of C₆₀ exposed to O₂ and light but is more intense. The C₆₀ in its pure form is in a singlet state. The impurity sites introduced by O₂ produce the esr absorption. The Curie - Weiss plots of inverse esr absorption intensity versus temperature indicate an antiferromagnetic TH = 50 for air exposed C₆₀ and 90K for C₆₀O_x. From the esr intensity at room temperature, the calculated number of free spins (S = 1/2) is =1/3 per mole of C_60-O_x. In case of C₆₀.HMTTEF, there is a very weak esr absorption at room temperature suggesting that the room temperature form is diamagnetic with very small charge transfer between C₆₀ and HMTTEF. This conclusion is consistent with the structure and magnetic susceptibility of this cocrystal. As the temperature is lowered, the equilibrium: AD <=> A?^? + D?⁺ is displaced towards the formation of free radical species, A?^? and D?⁺.     

Study of Undersaturated C60 Solutions in Cs2 by Small Angle Neutron Scattering

Abstract

We measured precisely, using the Small Angle Neutron Scattering (SANS) technique, the radius of the carbon nuclei shell of the C₆₀ molecule, in spite of its small value. For this purpose, controlled undersaturated solutions of C₆₀ in CS₂, where theC₆₀ molecules are individually distributed, were studied in the room temperature range. Absolute measurements also allowed us to extract from the contrast in scattering length the partial molecular volume of the molecule C₆₀ in solution in CS2.     

A new superhard carbon allotrope: tetragonal C<Subscript>64</Subscript>

A novel superhard carbon allotrope C₆₄ is predicted which is composed of C28 cages. It is porous and exhibits distinct topologies including zigzag 5, 6, 8, 10 and 12-fold carbon rings. The elastic constants and phonon calculations reveal that C₆₄ is mechanically and dynamically stable at ambient pressure. The hardness of C₆₄ is 60.2 GPa. The tensile and shear strength calculations indicate that the lowest tensile and shear strengths have the almost same value of 48.1 GPa. For the electronic properties, the band structure calculations show that C₆₄ is a quasi-direct band gap semiconductor with a band gap of 1.32 eV.     

Preparation and characterization of fullerene (C60)-modified BiVO4/Fe3O4 nanocomposite by hydrothermal method and study of its visible light photocatalytic and catalytic activity

In this study, BiVO₄/Fe₃O₄/C₆₀ nanocomposite has been synthesized for the first time using a facile and feasible hydrothermal method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), vibrating sample magnetometer (VSM), and N₂ adsorption-desorption analysis were utilized to analyze the structure, morphology, size, and the magnetic property of the synthesized nanocomposite. The photocatalytic activity of the magnetic BiVO₄/Fe₃O₄/C₆₀ nanocomposite was investigated for the degradation of methylene blue. The results showed that 84% degradation of methylene blue (MB) (25 mg/L) solution within 5 h with a rate constant equal to 0.0049 min^?1 in the presence of BiVO₄/Fe₃O₄/C₆₀ nanocomposite and H₂O₂ (1 mL, 30%) under visible light irradiation. The effects of BiVO₄/Fe₃O₄/C₆₀ dosage, H₂O₂ amount dye initial concentration and C₆₀ amount on the efficiency of degradation process were investigated. Furthermore, the catalytic activity of the magnetic BiVO₄/Fe₃O₄/C₆₀ nanocomposite was investigated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using sodium borohydride (NaBH₄) in the aqueous solution and at room temperature. The results showed that BiVO₄/Fe₃O₄/C₆₀ nanocomposite exhibited an excellent performance for the reduction of 4-NP with 97% conversion into its corresponding amino derivative within 38 min with a constant rate equal to 0.0775 min^?1. As indicated by the results, the magnetic BiVO₄/Fe₃O₄/C₆₀ nanocomposite exhibited much higher photocatalytic and catalytic activity than BiVO₄/ C_60, BiVO₄/Fe₃O_4, and pure BiVO₄. Moreover, the BiVO₄/Fe₃O₄/C₆₀ nanocomposite could be magnetically separated from the reaction mixture due to the presence of the Fe₃O₄ and reused without any change in structure.