Turbostratic Structure Research Articles

Enabling high-quality carbon fiber through transforming lignin into an orientable and melt-spinnable polymer

Compared to carbon fibers made from conventional petroleum-based precursors, lignin-based carbon fibers can lower the production cost while enabling cleaner manufacturing. The use of lignin-based carbon fibers is currently hindered by their poor mechanical properties that are mainly attributed to the lack of orientability in lignin structure. Herein, we demonstrated a novel method of producing high-quality carbon fiber, by which lignin is first transformed into a new precursor polymer with a linear molecular orientation, and the precursor is subsequently melt-processed. Specifically, a raw red oak lignin bio-oil consisting of multifunctional compounds with distributed molecular weights was converted into a lightly branched, acrylate polymer via a hybrid functionalization followed by controlled radical polymerization. By carefully investigating different synthesis parameters and determining the effects of the intrinsic properties of the crude lignin bio-oil have on the polymerization, a melt-spinnable thermoplastic polymer could be obtained in high yield. The new polymer was then used to produce carbon fiber with average tensile strength of 1.70 GPa and tensile modulus of 182 GPa. Our analysis results indicated that the new precursor structure can improve the degree of graphitization and reduce structural defects in the resulting carbon fiber. Structural analyses showed that the carbon fiber contains a highly ordered and well-stacked turbostratic structure. Overall, this study presents a promising approach to produce low-cost, high-quality carbon fiber that may have applications in the automobile industries.

Nano-Confinement Effects on Structural Development and Organic Solvent-Induced Swelling of Ultrathin Carbon Molecular Sieve Films.

Successful implementation of carbon molecular sieve (CMS) membranes in large scale chemical processes inevitably relies on fabrication of high performance integrally skinned asymmetric or thin-film composite membranes. In principle, to maximize separation efficiency the selective CMS layer should be as thin as possible which requires its lateral confinement to a supporting structure. In this work, we studied pyrolysis-induced structural development as well as ethanol vapor-induced swelling of ultrathin CMS films made from a highly aromatic polyimide of an intrinsic microporosity (PIM–PI) precursor. Utilization of a light polarization-sensitive technique, spectroscopic ellipsometry, allowed for the identification of an internal orientation within the turbostratic amorphous CMS structure driven by the laterally constraining support. Our results indicated a significant thickness dependence both in the extent of pyrolytic collapse and response to organic vapor penetrant. Thinner, substrate-confined films (∼30 nm) collapsed more extensively leading to a reduction of microporosity in comparison to their thicker (∼300 nm) as well as self-supported (∼70 μm) counterparts. The reduced microporosity in the thinner films induced changes in the balance between penetrant-induced dilation (swelling) and filling of micropores. In comparison to thicker films, the initial lower microporosity of the thinner films was accompanied by slightly enhanced organic vapor-induced swelling. The presented results are anticipated to generate the fundamental knowledge necessary to design optimized ultrathin CMS membranes. In particular, our results reinforce previous findings that excessive reduction of the selective layer thickness in amorphous microporous materials (such as PIMs or CMS) beyond several hundred nanometers may not be optimal for maximizing their fluid transport performance.

Novel Stimuli‐Responsive Turbostratic Oxides/Hydroxides for Material‐Driven Robots

Herein, a novel class of high‐performing actuating oxides/hydroxides with turbostratic crystal structures is reviewed. These materials, including nickel hydroxide/oxyhydroxide, cobalt oxides/hydroxides, nickel‐doped cobalt oxides/hydroxides, and manganese oxides, exhibit a volume‐changing redox reaction, rendering them an electrochemical actuation behavior. Also, due to their turbostratic crystal structures, they typically exhibit light‐driven actuation due to water deintercalation from the crystal structure induced by light. Compared with other actuating materials, these oxides/hydroxides actuate with high stress and strain at fast rates, under very low stimuli requirements. Furthermore, they are easily printable on different substrates, thus allowing flexible robots with demodularized muscle‐skeletal designs to be made.

Rapid In Situ Polymerization of Polyacrylonitrile/Graphene Oxide Nanocomposites as Precursors for High-Strength Carbon Nanofibers.

Graphene oxide (GO) has been widely used as an additive of polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) to optimize its crystal structure and improve the mechanical performances of nanofibers. However, the homogeneous dispersion of GO nanosheets among entangled PAN molecular chains is always challenging, and the poor dispersion of GO severely limits its positive effects on both the structure and performances of CNFs. Considering this issue, this paper provides for the first time an effective solution to achieve rapid and uniform introduction of GO in PAN-based nanofibers via in situ polymerization, and the optimization of the nanofiber structure by GO is systematically studied in three consecutive stages (polymerization, electrospinning, and carbonization) of the production process. During in situ polymerization, PAN is tightly attached on GO nanosheets to form PAN/GO nanocomposites, and this interaction is maintained throughout the spinning process. Not only the arrangement of PAN molecular chains but also the crystal size of the final turbostratic structure of CNFs is considerably improved by the interaction between PAN and GO. Besides, the direct proof that GO nanosheets promote the crystallization and orientation of the nanofiber matrix is presented. As a result, the tensile strength of CNFs is remarkably increased by 2.45 times with 0.5 wt % addition of GO. In summary, this paper provides a method for efficiently introducing nanoscale additives into PAN-based nanofibers and gives insights into the production of high-performance CNFs with the addition of GO.

Improved performance of Ni/Al2O3 catalyst deriving from the hydrotalcite precursor synthesized on Al2O3 support for dry reforming of methane

Exploiting Ni-based catalysts with excellent catalytic activity and anti-coking ability is significant for dry reforming of CH4 with CO2 (DRM) which is a promising route to CO2 utilization. In this work, the Ni/Al2O3 catalyst with hydrotalcite precursor (NiAl-LDH) was synthesized by a facile in-situ growth method. And the effect of the NiAl-LDH structure on the catalytic activity and anti-coking ability of Ni/Al2O3 catalyst was revealed. The H2-temperature programmed desorption (H2-TPD) revealed that better Ni dispersion and more Ni–Al2O3 interface could be obtained by the NiAl-LDH precursor, which were vital for the activation of CH4 and CO2. Moreover, the NiAl-LDH precursor with non-LDH phase or turbostratic structure was also created by insufficient or extra amount of urea, and the obtained catalysts exhibited a poor catalytic stability, further confirming the importance of the LDH structure. In comparison with the Ni-IMP catalyst prepared by the conventional impregnation method, the CH4 conversion increased by 16% and the carbon deposition decreased by 75% over Ni-6 catalyst with well-organized LDH precursor under the same reaction conditions. Hence, this work represents an important step toward developing Ni-based catalysts with excellent catalytic activity and anti-coking ability for DRM with the LDH precursor.

Preferential Elimination of Ba2+ through Irreversible Biogenic Manganese Oxide Sequestration

Biogenic manganese oxides (BMOs) formed in a culture of the Mn(II)-oxidizing fungus Acremonium strictum strain KR21-2 are known to retain enzymatic Mn(II) oxidation activity. Consequently, these are increasingly attracting attention as a substrate for eliminating toxic elements from contaminated wastewaters. In this study, we examined the Ba2+ sequestration potential of enzymatically active BMOs with and without exogenous Mn2+. The BMOs readily oxidized exogenous Mn2+ to produce another BMO phase, and subsequently sequestered Ba2+ at a pH of 7.0, with irreversible Ba2+ sequestration as the dominant pathway. Extended X-ray absorption fine structure spectroscopy and X-ray diffraction analyses demonstrated alteration from turbostratic to tightly stacked birnessite through possible Ba2+ incorporation into the interlayer. The irreversible sequestration of Sr2+, Ca2+, and Mg2+ was insignificant, and the turbostratic birnessite structure was preserved. Results from competitive sequestration experiments revealed that the BMOs favored Ba2+ over Sr2+, Ca2+, and Mg2+. These results explain the preferential accumulation of Ba2+ in natural Mn oxide phases produced by microbes under circumneutral environmental conditions. These findings highlight the potential for applying enzymatically active BMOs for eliminating Ba2+ from contaminated wastewaters.

Waste tire carbon in synergetic interaction with spent gamma radioactive source for efficient radiocatalytic degradation of organic dye

Enhanced degradation of organic dye was achieved using two different kinds of waste materials: waste tire granules and spent sealed radioactive sources. Waste tire granules were used as raw material for the production of waste tire char (WTC), which was further utilized as an adsorbent matrix for synergetic adsorption/irradiation degradation of organic dye. The spent radioactive sources were radiographic sealed sources that originate from the industry which generate the high energy radiation. Methylene Blue (MB) was used as an organic model compound. Synthesized WTC has turbostratic structure, irregular shaped particles and developed mesoporous surface. Complete degradation of 0.02 dm3 of 100 mg dm−3 MB solution, having WTC dose of 1.25 g dm−3, was achieved with delivered doze of only 60 Gy. The applied doses were 100 times smaller than those presented in the literature. Degradation pathway was determined: OH radicals that originate from radiolysis of water and from the surface of WTC played the crucial role in the radiocatalytic degradation of MB. Breakage of the aromatic ring of MB appeared by the scission of the double C‒S+˭C bond as a result of the attack of OH species on adsorbed and electronically reorganized MB molecule.

Graphene‐Based Hybrid Carbons: Ultrahigh Strength and Modulus Graphene‐Based Hybrid Carbons with AB‐Stacked and Turbostratic Structures (Adv. Funct. Mater. 50/2020)

In article number 2005381, Sunghwan Jin, Rodney S. Ruoff, Seongwoo Ryu, and co-workers show a graphene-based hybrid carbon film composed of AB-stacked and turbostratic structure by heat-treating graphene/poly(catecholamine) composites. The graphene/poly(catecholamine) composites have a brick-mortar structure that the composite films are transformed to have both AB-stacked (mainly from graphene oxide) and turbostratic (mainly from poly(catecholamines)) structures.

Synthesis of metal-free nitrogen-enriched porous carbon and its electrochemical sensing behavior for the highly sensitive detection of dopamine: Both experimental and theoretical investigation

In this study, a nitrogen-inherited foam-like porous carbon was sequestered from the starch of Artocarpus heterophyllus seeds. The obtained carbon material was used as a sustainable electrode for the electrochemical detection of dopamine biomolecule. The material exhibited a turbostratic structure, high degree of graphitization, strong carbon-nitrogen bonding, high surface area, and porous architecture. It showed good catalytic activity with a low onset potential (80 mV), wide linear responses (30–90 μM and 200–400 μM), a low limit of detection (2.74 nM), and superior sensitivity (4.64 μA μM −1cm −2). The results indicated that the porous architecture and organic functionalities on the surface provided fast electron transfer at the electrode/electrolyte interface. Moreover, it offered superior stability, reproducibility, and biocompatibility toward dopamine sensing in real samples. Furthermore, first-principle calculations were performed in both the gas and aqueous phase to determine the molecular-level interaction between the porous carbon and dopamine. The results indicated that the interaction between dopamine and the nitrogen-enriched carbon sheet was stronger (−0.64 eV) than the oxygen-rich sheet. The atoms-in-molecules analysis, charge density difference analysis, and Fukui function plots indicated a charge transfer from the biomolecules to the carbon sheet. Overall, the theoretical findings confirmed the observed experimental results.

Recycling of graphite and metals from spent Li-ion batteries aiming the production of graphene/CoO-based electrochemical sensors

This work describes the synthesis of hybrid materials based on reduced graphene oxide (rGO) and cobalt oxide (CoO) from recycled Li-ion batteries. A hydrometallurgical route was employed in the recycling process, with citric acid and nitric acid used as the leaching agents for the cathode and anode materials, respectively. Graphene oxide (GO) was prepared from the recycled graphite by a modified Hummers method; the hybrid material was produced by mixing GO and the recycled metal oxides (mostly CoO) using a sol-gel route followed by heat treatment at 450 °C during 2 h. The physicochemical characterization of the hybrid material was conducted by X-ray diffraction, scanning electron microscopy and solid-state 7Li and 13C nuclear magnetic resonance (NMR) spectroscopy; the results indicated the formation of crystalline CoO (with face centered cubic structure) and rGO (with turbostratic structure), whereas lithium and manganese were also identified as minor components. The performance of this product as electrochemical sensor was evaluated by cyclic voltammetry. The study of the electrocatalytic oxidation of ascorbic acid using the hybrid material as electrode showed good linearity in the relationship between the oxidation current and the acid concentration. These results showed that the hybrid material produced from the recycled batteries is promising for applications as an enzyme-free electrochemical sensor.

Investigation of the carbon structure of naturally graphitized coals from Central Hunan, China, by density-gradient centrifugation, X-ray diffraction, and high-resolution transmission electron microscopy

A suite of six naturally graphitized coals were separated by density-gradient centrifugation (DGC). The density profiles of anthracite and meta-anthracite samples show an average density increase from 1.50 g/mL to 1.93 g/mL with increased rank. Components of partially graphitized coals were separated into two distinct density peaks: a low-density peak at ~1.82 g/mL, and a high-density peak at ~2.0 g/mL; sample SL-3 also showed a shoulder at around 2.14 g/mL. The separated density fractions of the partially graphitized samples were examined by X-ray diffraction (XRD) and optical microscopy. This revealed that the lower density portions contain vitrinite and inertinite, whereas microcrystalline graphite along with needle and flake graphite are the primary components of the higher density portions, demonstrating that DGC can be used to separate components in metamorphosed coals. Carbon phases including local molecular oriented domains (LMODs) and turbostratic layers are observed in the partially graphitized coals under high-resolution transmission electron microscopy (HRTEM). The average density of the most graphitized coal is 2.18 g/mL, which together with the XRD pattern suggests a carbon structure close to that of graphite. In anthracite, basic structural units (BSUs) are distributed throughout the disordered carbon structure matrix; whereas graphitic lamellae are the primary constituent in the most graphitized coals, indicating the transformation of the carbon structure from amorphous-like anthracite to ordered graphite during natural graphitization. The co-occurrence of different carbon phases and structural units in the same sample demonstrates the heterogeneous nature of graphitized coals. The presence of novel carbon structures (such as BSUs, LMODs, turbostratic structure, and onion-like carbon, etc.) in the naturally graphitized coal series suggests potential use in the future development of new coal-based carbon materials.

High-quality laser-assisted biomass-based turbostratic graphene for high-performance supercapacitors

Preparing high-quality graphene-like structures and materials in a consistent and environmentally friendly way is still elusive. Recent advances have revealed that laser irradiation of proper precursors presents great potential and versatility towards realizing high-quality growth of graphene-like materials at low cost. Here, we present a detailed study of the laser-assisted transformation of homogenized dried Corinthian raisins (Vitis vinifera L., var. Apyrena) to graphene-like material. This is a one-step process, as the transformation of the raw biomass material takes place at ambient conditions. Diffraction, Raman scattering and electron microscopy have revealed that the structure of the laser-irradiated product is found to differentiate significantly from that of Bernal stacked graphitic carbon. This is the first demonstration of a laser-assisted growth of turbostratic phase via the decomposition of an organic compound. XPS analysis show a very high C/O ratio, i.e. 19, after the decomposition of a raw biomass material. The combination of turbostratic structure and almost complete oxygen species removal results in an ultralow sheet resistance of 10 Ω·sq−1, confirming the successful modification of the raw material to a graphene-like structure with high sp2 hybridization degree. An additional merit of the current approach is that the process can induce both the growth of graphene-like structures on the irradiated target and in addition yields high-quality graphene-like powders. The latter have been used to prepare electrodes for symmetrical supercapacitors demonstrating superior performance compared to supercapacitors based on graphene prepared by other laser-assisted techniques.

Maximizing the rate capability of carbon-based anode materials for sodium-ion batteries

Maximizing the rate capability of carbon materials optimizes sodium ion battery (SIB) performance. This study develops nanoscale nitrogen-doped carbon material (NNCM), in which nano-sized primary particles aggregate. These aggregates form a meso–macro-hierarchical porous structure, which facilitates Na+ diffusion from outside the aggregates into the primary nanoparticles. The large specific surface area of carbon black improves Na+ accessibility by forming large interfaces, and Na+ is easily solvated through defect sites and pores on the primary particle surfaces. Furthermore, primary nanoparticles have short Na+ diffusion pathways, while turbostratic structures provide broad pathways aiding Na+ diffusion. Nitrogen improves the electrical conductivity of the carbon matrix and provides abundant active sites by creating extrinsic defects. Together, these factors afford NNCM good capacity retention (38% at 100 A/g vs. 1 A/g), reversible capacity (~101 mAh/g at 100 A/g), ultrahigh cycling stability (11,000 cycles at 100 A/g), high initial coulombic efficiency (80%), and remarkable rate capability.

Ultrahigh Strength and Modulus Graphene‐Based Hybrid Carbons with AB‐Stacked and Turbostratic Structures

AbstractGraphene‐based hybrid carbons composed of a mix of AB‐stacked and turbostratic regions are reported. Macroscopic graphene films consisting of stacked graphenes are prepared using a liquid crystal graphene oxide dispersion. The graphene films are then infiltrated with bioinspired adhesives, catecholamines, and polymerized to obtain graphene/poly(catecholamine) composites. After heat treatment up to 3000 ºC, the composite films are transformed to have both AB‐stacked (mainly from graphene oxide) and turbostratic (mainly from poly(catecholamines)) structures, and exhibit significantly improved mechanical properties compared to the films having a predominant AB‐stacked structure made from only graphene oxide. They have almost twice the fracture strength (1012 ± 146 MPa) and ≈1.5× increase of both Young's modulus (21.87 ± 2.24 GPa) and strain‐to‐failure (8.91 ± 0.50%). In addition, the films have an in‐plane electrical conductivity as high as 1320 ± 159 S cm−1. Such hybrid‐carbon films with the indicated mechanical and electrical properties have many promising uses, such as for light‐weight structural materials, and in flexible electronics such as for wearable heaters or in sensing electrodes.

Insight into the aromatic ring structures of a low-rank coal by step-wise oxidation degradation

Aromatic skeleton structure of Naomaohu (NMH) coal was investigated by a step-wise oxidation degradation and XRD, Raman and XPS characterization. Coal was first oxidized with H2O2 to result in breakage of only bridged bonds and side chains, then the oxidation residue was further degraded through controlling alkali-oxygen (A-O) oxidation to avoid ring-open of polyaromatics and the conversion of coal sample exceeded 97.4 wt%. Synchronous fluorescence spectrometry (SFS) analysis of the oxidation products inferred that the aromatic structures in NMH coal mainly involve 1–4 rings compounds, among which single-ring structures are dominant accounting for 54.4 mol%. The results of XRD, Raman and XPS showed that NMH coal has a turbostratic structure, an intermediate state between the amorphous state and graphite, comprised by amorphous carbons and orderly aromatic clusters. The heteroatoms mainly exist in the forms of carbonyl, hydroxyl, pyrrolic nitrogen, mercaptan or thiophenol, thiophene, sulfoxide and sulfone. A simplified model of coal skeleton structure was proposed based on the complementary information from various techniques. Moreover, SFS analysis of A-O oxidation products clearly exhibits the gradual cracking process of polyaromatics, which provides an efficient method for controllable production of benzene carboxylic acids by preventing excessive or incomplete oxidation.

Functionalized nanoporous graphene membrane with ultrafast and stable nanofiltration

Herein, a functionalized nanoporous graphene (FNG) membrane was developed to mitigate the contemporary issues affecting graphene oxide (GO) membranes, such as the low flux induced by its long tortuosity and poor membrane stability in aqueous solvents. GO was thermally activated at 650 °C to prepare a nanoporous carbon sheet with a turbostratic structure (pore size < 4 nm). Thereafter, the nanoporous graphene (NG) was consecutively functionalized with oxygen-containing groups by KMnO4 treatment and re-dispersed in water to deposit an FNG layer on a porous polymeric support. The FNG membrane exhibited ultrafast water permeance (586 Lm-2h-1bar-1) and precise molecular separation (molecular weight cut off: 269 Da). The membrane performance surpasses the upper bound of previously reported polymers and two dimensional-material-based nanofiltration membranes by the synergistic effect of nanopores and oxygen-containing groups. Furthermore, the practical operation of the FNG membrane is feasible under cross-flow, and water-flux decline by filtered molecules is highly suppressed by the presence of abundant nanopores as compared to conventional GO membranes.

Multiscale characterization of exhaust and crankcase soot extracted from heavy-duty diesel engine and implications for DPF ash

Engine-dynamometer bench tests were performed to evaluate the severity of engine operation resulting in oil degradation, set limits for drain intervals and provide recommendations for oil formulators to develop an additive package offering enhanced engine hardware protection. Engine oil was sampled at specified intervals to monitor depletion of additives, changes in viscosity, soot agglomerates and wear elements. A myriad of characterization techniques such as temperature resolved XRD, TEM, EDS, BET, Raman, DLS, TGA and ICP-OES are employed to develop a holistic understanding of crankcase soot interaction with lubricant additives influencing soot-induced wear, and oxidative properties of exhaust soot trapped in the DPF. XRD phase analysis of residue left behind after crankcase soot oxidation showed the presence of crystalline compounds embedded in the soot structure (CaSO4, Ca3(PO4)2, and Zn3(PO4)2); exhaust soot showed no crystalline compounds and had 85 wt% less residue after oxidation compared to crankcase soot. The residue inevitably forms ash precursors that are trapped in the DPF (Diesel Particulate Filter) affecting the filtration performance and fuel efficiency of the vehicle in the longer run. The turbostratic structure of both soot samples remains the same prior to oxidation; however, the embedded crystalline and amorphous species in the crankcase soot structure are different compared to exhaust soot. Ex-situ experiments were performed on soot-ash mixture with heated microscopy stage to allow for better visualization of ash formation, sintering and transport properties in the DPF channels. Findings in the study help in developing a comprehensive insight into ‘soot ecosystem’ in diesel engine vehicles.

The effect of boron nitride interphase on the thermal stability of SiC fibers

The SiC fibers were coated with uniform boron nitride interphase by chemical vapor infiltration (CVI). The as-received and BN-coated fibers were heat-treated in flowing nitrogen for 2 h to investigate the effect of BN interphase on the thermal stability of fibers. Tensile strengths of as-received and BN-coated fibers have been measured at room temperature. The effects of heat-treatment on the tensile strengths of fibers were investigated using Weibull distribution. The results showed the deposited BN interphase has turbostratic structure, with nano crystallites of h-BN randomly orientated. Heat-treatment improved the crystallization degree of BN interphase. The as-received fibers had a tensile strength of 2.56 GPa and a Weibull modulus of 5.39. The BN-coated fibers showed lower tensile strength than the as-received fibers, on account of the increased diameter and soft nature of BN. The average strengths of fibers decreased, and BN-coated fibers showed higher strength retention than as-received fibers at the same heat-treatment temperature due to the protection of BN interphase. The BN interphase acts as a compliant layer, which reduces the thermal damage to SiC fibers during heat-treatment.

Visible-Light-Driven, Nickel-Doped Cobalt Oxides/Hydroxides Actuators with High Stability.

Material-based, light-driven actuators have been a recent research focus for the development of untethered, miniaturized devices and microrobots. Recently introduced nickel hydroxide/oxyhydroxide (Ni(OH)2/NiOOH) and cobalt oxides/hydroxides (CoOx(OH)y) are promising light-driven actuators, as they exhibit large and rapid actuation response and are inexpensive to fabricate by fast electrodeposition. However, as their actuation is due to the volume change accompanying the light-induced desorption of intercalated water in their turbostratic structures, their actuation reduces over time as crystallization takes place slowly, which lowers the amount of water held. Here, we introduce nickel-doped cobalt oxides/hydroxides (NiCoOx(OH)y) actuator that exhibits similar turbostratic crystal structures and actuation magnitude as CoOx(OH)y, but with much slower crystallization and hence significantly more stable actuation than CoOx(OH)y or Ni(OH)2/NiOOH. The new actuator exhibits much better applicability than the Co and Ni counterparts, and the present work shows that a stabilized turbostratic structure is a key for achieving high light-driven actuation in transition-metal oxide/hydroxide actuators.

Role of graphite crystal structure on the shock-induced formation of cubic and hexagonal diamond

During shock wave compression at about 500,000 atm of pressure and of about 100 nanoseconds duration, graphite is transformed into either hexagonal diamond or cubic diamond, depending on the crystal structure of the graphite crystallites that make up the sample. The figure shows x-ray diffraction data for two types of graphite: (a) and (b) show data for graphite crystallites having hexagonal structure, while (c) and (d) show data for graphite crystallites having turbostratic structure.