Structure Of Carbon Skeleton Research Articles

The unique interconnected structure of hollow carbon skeleton doped by F and N facilitating rapid Li ions diffusion in lithium-sulfur batteries

Hollow carbons are considered as one of promising host materials applied in lithium-sulfur batteries because sulfur can be well encapsulated in these hollow units. However, the ineffective contact among these discrete units tends to cause high lithium ions diffusion barrier and interunit resistance, thus reducing sulfur conversion kinetics and utilization. Herein, a hollow carbon skeleton (NFHC) with interconnected tubular cavity is fabricated by successfully replicating the nanostructure complementary to attapulgite fiber bundle templates. The unique interconnected structure and introduction of polar F and N sites facilitate lithium ions diffusion and inhibit the shuttle effect of polysulfides through chemisorption. The NFHC/S cathode delivers a reversible capacity of 675.3 mAh g−1 at 0.5 C after 500 cycles with a low capacity decay rate of 0.05% per cycle. Its lithium ions diffusion rate is 2–3 times as that of dispersed carbon nanotubes. Therefore, NFHC/S delivers an improved capacity with 546.8 mAh g−1 at 4 C. Further increasing the sulfur loading to 4.7 mg cm−2, the NFHC/S cathode exhibits a reversible capacity of 530.0 mAh g−1 with a low E/S ratio of 6 μL mg−1 after 300 cyles. This work provides new insights into the structural optimization of hollow functional materials.

Sub/supercritical CO2-induced benign fabrication of magnetic hybrid using waste halogenated plastics and its performance for Cr(Ⅵ) stabilization

• Carbonization and crystallization of feedstock can be achieved by one step in Sc-CO 2. • Iron salt enhanced depolymerization of plastics significantly via catalytic effect. • Sc-CO 2 favored formation of oxygen-rich functional groups on magnetic hybrid surface. • Magnetic Fe 3 O 4 was in-situ anchored in formed carbonaceous pore of bulk char. • Halogen-free magnetic hybrid exhibited excellent capacity for Cr(VI) immobilization. A huge amount of waste halogenated plastics is a considerable resource pool but how to transform these wastes into functional products is always a great technical challenge due to potential release of halogenated dioxin during process. In this study, one type of benign reaction medium-sub/supercritical carbon dioxide (Sc-CO 2 ) was used for converting halogenated plastics into magnetic carbon-based hybrid along with simultaneous dehalogenation. It was found that Sc-CO 2 treatment coupled with subsistent iron salt adjuvant advantageously inhibited the generation of benzene derivatives with high molecular weight and facilitated growth of pore structure of carbon skeleton with limited production of coke tars. Meanwhile, magnetic Fe 3 O 4 particles were gradually crystallized and eventually encapsulated in ordered mesoporous carbonaceous product to enhance the further carbonization of plastics without any halide residues. Cr(Ⅵ) immobilization tests indicated that as-obtained magnetic hybrid exhibited great adsorption capacity above 157 mg g −1 and the immobilization process was well fit for Langmuir model and pseudo-second-order kinetic model. This study provides a new insight into a cost-effective process for fabrication of magnetic functional hybrid using waste halogenated plastics without release of second pollutants and its versatile application as adsorbents or catalysts.

Microwave pyrolysis coupled with conventional pre-pyrolysis of the stalk for syngas and biochar

The study presented a novel approach microwave pyrolysis coupled conventional pre-pyrolysis (MCCP) to dispose of the stalk for syngas and biochar. Impacts of preheating temperature (250 ∼ 450 °C) on pyrolysis property and products characteristics were investigated. Compared with microwave-assisted pyrolysis (MAP), the initial time for rapid temperature ramp in MCCP was distinctly advanced from 124 s to within 20 s; the biochar yields significantly increased from 24.19% to 33.24%, and the H2 content of syngas in the second stage reached up to 64.65%. The biochar from MCCP had higher carbon content (greater than 70%), carbon retention (greater than 50%), and BET surface area (141.69 m2/g) than MAP. A high degree of aromatization and complete carbon skeleton structure was observed in the biochar from MCCP. Finally, a mobile application system based on MCCP was proposed, increasing the energy efficiency from 13.5 ∼ 27% (MAP) to 58.5 ∼ 76.5%.

Structural characterization of high fidelity for bituminous and semi-anthracite: Insights from spectral analysis and modeling

Although molecular structure evolution in response to coalification process has been reported to be prevalent recently, their characterization accuracy for coals of different ranks still needs to be enhanced. In this paper, the occurrence information of the carbon skeleton structure, functional groups, and nitrogen and sulfur heteroatoms in coals of different ranks (Ro, max = 0.99% for XZ-02, 1.39% for YT-09, 1.63% for YT-11, 2.29% for ZC-15) were extracted via ultimate and spectrum analysis. Then four molecular structure models were created using computer-aided molecular design (CAMD). Results show that the oxygen atoms in coal primarily exhibit phenolic hydroxyl groups, ether groups, and carbonyl groups. The nitrogen heteroatoms are present as pyrrole and protonated pyridine, and the sulfur heteroatoms mainly served as thiophene. The content of aliphatic structures gradually decreased as coalification continued. Their length first decreased (Ro, max ≤ 1.9%) and subsequently increased (Ro, max > 1.9%). The content of aromatic structures gradually increased accompanied by the gradually cleaving of oxygen functional groups and alkyl side chain from the aromatic clusters. Hence, the degree of aromatization gradually increased, and condensation reactions dominated in the late stage of coalification. The initial molecular formulas and structural models were determined for the four coals. Also, the bonding modes among the aromatic clusters, aliphatic side chains, and oxygen functional groups within the molecular structure were adjusted based on the comparison between experiment and calculation spectra, finally creating the following molecular representations: C174H128O8N2 (XZ-02), C167H114O5N2S2 (YT-09), C151H96O7N2 (YT-11), and C146H80O4N2 (ZC-15). The fitting carbon spectra of these molecular representations were consistent with the experimental carbon spectra whose error is within the allowable range (relative error < 15%), verifying the applicability of the molecular structure model and the above method. Furthermore, the mechanism of coalification was discussed based on the variations of the side chains and chemical bonds. The above research can provide a theoretical reference for the molecular structural evolution for coals of different ranks and a high fidelity method to create molecular structure representation.

Construction of three-dimensional electronic interconnected Na3V2(PO4)3/C as cathode for sodium ion batteries

The NASICON (Sodium super ion conductor)-type of Na3V2(PO4) (NVP) has a great potential for energy storage application due to its high voltage plateau, three-dimensional (3D) ionic diffusion channel, perfect thermal stability, and high structural robustness. Here, Na3V2(PO4)-based composites with 3D porous carbon skeleton structure were synthesized via hydrothermal methods. After a series of hydrolysis and polymerization processes, transparent colloid mainly containing (NH4)4Na2V10O28 phase was formed. The 3D porous hydrogel with the (NH4)4Na2[V10O28]·10H2O phase was produced by adjusting the reaction time. The product has a lamellar structure, and its ion is suitable to grow the nanosheets, and the present PO43- groups may be distributed in the (NH4)4Na2[V10O28]·10H2O phase of the interlayer structure, leading to the enhanced electronic conductivity. The 3D porous Na3V2(PO4)/C (NVP/C) with the size of 100–200 nm particles can be used as cathode for sodium ion batteries. The NVP/C delivers a specific capacity of 62.1 mAh g−1 at 10 C. The excellent stability of NVP/C can be obtained with 98% capacity retention after 140 cycles at 1 C. After 2000 cycles (5 C), the capacity is still 80.4 mAh g−1, with the capacity retention of about 86%. Our encouraging results may boost further studies of SIBs device by smart engineering of the electrode materials.

Effect of pressure on the structure and reactivity of demineralized coal during O2/H2O thermal conversion process

Pressure can strongly affect the thermal conversion characteristics of coal. This work used a pressurized horizontal furnace to study the pyrolysis (Ar) and O2/H2O (10 vol%/25 vol%) thermal conversion characteristics of demineralized coal under different pressure (0.1–1.5 MPa) and at 1000 °C. The changes of carbon conversion, pore structure, carbon skeleton structure, and surface functional group structure of different pressure pyrolysis char and its combustion residual char were obtained by using N2 adsorption, Raman and X-ray Photoelectron Spectroscopy (XPS) test methods. A micro fluidized bed reaction analyzer was then used to test the reactivity of the char to explore the influence of pressure. Pressure can increase the yield of pyrolysis char from 64.81% to 68.78% and promote the conversion of char in O2/H2O conditions from 27.78% to 78.58%. For the pore structure of char, pressure and O2/H2O atmosphere have a positive promotion effect, and have a similar effect on the degree of graphitization and the relative content of C–C and C–H bonds. Largest BET area of char is 234.72 m2/g at 1.5 MPa of pyrolysis and 793.43 m2/g at 1.0 MPa of O2/H2O combustion, respectively. For the reactivity of char prepared in O2/H2O combustion, the pore structure is dominant compared to chemical structure.

Fuel molecular structure influences the polycyclic aromatic hydrocarbons formation of butanol/butane isomers: A ReaxFF molecular dynamics study

This work explores the influence differences in the molecular structure of butanol/butane isomers, particularly the hydroxyl (OH) group binding site, on polycyclic aromatic hydrocarbon (PAH) formation by using ReaxFF MD. Visualization of the fuel molecule decomposition and PAH formation processes revealed that OH bonded to interior carbon atoms could lead to earlier PAH formation onset in t-butanol and s-butanol. When OH groups were bonded to interior carbon atoms, these groups were easily abscised via simple fission, and the adjacent CC bonds showed less cleavage. Thus, abundant i-C4Hx (2-methylallyl) species were detected from t-butanol with a branched carbon skeleton structure and specific OH binding sites. s-Butanol produced more n-C4Hx species than t-butanol. Visualization of the formation of mono-aromatic ring molecules directly revealed that dehydrodimerization and dehydroaromatization by i-C4Hx lead to the earliest onset of mono-aromatic ring formation in t-butanol. Mono-aromatic ring formation via cyclization and condensation by polyyne radicals occurred later in i-butanol than the upper pathway and dominated straight fuels at a higher temperature of 2500 K. The drastic decay of C2H2 and visualization of HACA-like pathways in the simulation trajectories for n-butanol revealed the close concentration of the larger PAHs for straight-chain butanol isomers with the branched-chain isomers.

Study on the thermal conversion characteristics of demineralized coal char under pressurized O2/H2O atmosphere

The pressurized O2/H2O combustion technology can achieve nearly zero CO2 emissions during coal-fired power generation. In order to explore the influence of pressurized O2/H2O conditions on the thermal conversion characteristics of pulverized coal, Zhundong demineralized coal was used as raw material to prepare pyrolyzed char at 0.5 MPa and then the O2/H2O combustion experiments with different H2O concentration (0–40%), temperature (850-1000℃) and residence time (100–250 s) were carried out under the same pressure by a pressurized horizontal furnace. The carbon transformation, pore structure, carbon skeleton structure, and surface functional group structure of char under different experimental conditions were obtained by weighing method, Nitrogen adsorption test, Raman, and X-ray photoelectron spectroscopy methods, respectively. In addition, the reactivity of char was tested by thermogravimetric analyzer and micro fluidized bed reaction analyzer (MFBRA) to explore the relationship between the char structure and reactivity.

An electrochemical immunosensor for the detection of carcinoembryonic antigen based on Au/g-C3N4 NSs-modified electrode and CuCo/CNC as signal tag.

Carcinoembryonic antigen levels in the human body reflect the conditions associated with a variety of tumors and can be used for the identification, development, monitoring, and prognosis of lung cancer, colorectal cancer, and breast cancer. In this study, an amperometric immunosensor with CuCo/carbon nanocubes (CuCo/CNC) as the signal label is constructed. The bimetal-doped carbon skeleton structure has a high specific surface area and exhibits good electrocatalytic activity. In addition, Au/g-C3N4 nanosheets (Au/g-C3N4 NSs) are used to modify the substrate platform, facilitating the loading of more capture antibodies. The reaction mechanism was explored through electrochemical methods, X-ray powder diffraction, X-ray photoelectron spectroscopy, and other methods. Kinetic studies have shown that CuCo/CNC have good peroxidase-like activity. In addition, the electrocatalytic reduction ability of CuCo/CNC on hydrogen peroxide can be monitored using amperometric i-t curve (- 0.2V, vs. SCE), and the response current value is positively correlated with the CEA antigenconcentration. The prepared electrochemical immunosensor has good selectivity, precision, and stability. The dynamic range of the sensor was 0.0001-80ng/mL, and the detection limit was 0.031pg/mL. In addition, the recovery and relative standard deviation in real serum samples were 97.7-103% and 3.25-4.13%, respectively. The results show that the sensor has good analytical capabilities and can provide a new method for the clinical monitoring of CEA.

Honeycomb-like biomass carbon with planted CoNi3 alloys to form hierarchical composites for high-performance supercapacitors

It is a significant challenge to combine a large pseudocapacitive material with conductive honeycomb-like carbon frameworks for long-term stable supercapacitors. Herein, hierarchical composite materials are manufactured by using biomass carbon, ZIF-67, and a mild pore former (Ni(CH3COO)2) to generate alloy-type CoNi3 nanoparticles planted into conductive honeycomb-like carbon frameworks (C@ZIF-67-T). Meanwhile, the effect of carbonization temperature on the honeycomb-like pore size and the structure of composite materials is systematically investigated. As the honeycomb-like carbon skeleton structure guarantees good ionic and electronic conductivities and a large contact area, whereas the alloy nanoparticles provide a rich redox reaction for Faradaic capacitance. Therefore, the as-obtained C@ZIF-67–600 electrode presents a remarkable specific capacitance of 1044.8 F · g−1 at 1.0 A · g−1 and an ultra-long cycling stability with 30,000 cycles at 5.0 A · g−1 in a three-electrode system. In addition, the assembled C@ZIF-67–600//activated carbon asymmetrical supercapacitor exhibit a high specific capacitance of 274.4F · g−1 at 1.0 A · g−1 and a long-term stable lifespan with a capacitance retention of 87% after 20,000 cycles at 5.0 A · g−1. Besides, the asymmetrical supercapacitor also presents a maximum energy density of 85.13 Wh · kg−1 at a power density of 750 W · kg−1. Such superior electrochemical performance demonstrate that the designed electrode material provides a promising energy storage application.

Similar chemical composition with different tribological properties: Influences of C[sbnd]F bond strength and carbon-skeleton structure on fluorinated graphene and PTFE

Taking fluorinated graphene (FG) and polytetrafluorethylene (PTFE) as the typical models, this work aims to clarify the influences of carbon-skeleton structure and CF bond strength on their tribological performance and lubrication mechanism under extreme-pressure condition. As oil additives, the load-bearing capacity of PAO-6 increases from 300 N to 600 N with FG and 400 N with PTFE. Compared with the situation with the PTFE sub-microspheres, the wear rate of PAO-6 with FG nanosheets reduces by about 40%. Proved by the apparent difference in tribofilm formation ability of FG and PTFE, it is believed that the higher reactivity of the CF bond and adsorption ability of two-dimensional carbon-skeleton play a crucial role in FG’s excellent tribological performance.

Quantum Mechanical Investigation of the Oxidative Cleavage of the C-C Backbone Bonds in Polyethylene Model Molecules.

Recalcitrant plastic waste has caused serious global ecological problems. There is an urgent need to develop environmentally friendly and efficient methods for degrading the highly stable carbon skeleton structure of plastics. To that end, we used a quantum mechanical calculation to thoroughly investigate the oxidative scission of the carbon-carbon (C–C) backbone in polyethylene (PE). Here, we studied the reaction path of C–C bond oxidation via hydroxyl radical in PE. The flexible force constants and fuzzy bond orders of the C–C bonds were calculated in the presence of one or more carbocations in the same PE carbon chain. By comparison, the strength of the C–C bond decreased when carbocation density increased. However, the higher the density of carbocations, the higher the total energy of the molecule and the more difficult it was to be generated. The results revealed that PE oxidized to alcohol and other products, such as carboxylic acid, aldehyde and ketone, etc. Moreover, the presence of carbocations was seen to promote the cleavage of C–C backbones in the absence of oxygen.

Combined impacts of intrinsic alkali and alkaline earth metals and chemical structure on reactivity of low-rank coal char: New explanation for the role of water-soluble AAEMs during pyrolysis and gasification

The char reactivity generally determines the overall efficiency of the whole gasification process of coal, so it is of great significance to deeply understand the factors influencing the char reactivity and the coupling mechanism between them. This study aims to investigate the combined impacts of intrinsic alkali and alkaline earth metals (AAEMs) and chemical structure of organic matter on char reactivity, and provide new evidence for confirming the controversial role of water-soluble AAEMs during char gasification. Four series of char samples prepared from Zhundong coal containing different forms of intrinsic AAEMs were isothermally gasified by air in TGA, obtaining the specific reaction-rate curves, and a reasonable evaluation index of char reactivity was established. The carbon skeleton structure of char surfaces was analyzed by Raman spectroscopy. The comprehensive discussion of chemical structure, AAEMs state and char reactivity indicates that the water-soluble AAEMs reduce the char reactivity in the early part of gasification process, which is due to the catalytic cracking of aromatic CH caused by these substances on char surfaces during pyrolysis, while improving the char reactivity in the later part because of the original catalysis of these substances on gasification; the ion-exchangeable AAEMs significantly catalyze the opening of aromatic rings in char during gasification, especially the small rings, which weakens the reaction priority of aliphatic structures; the increasing pyrolysis temperature results in the ordering of chemical structure and the enrichment of ion-exchangeable AAEMs, and the former reduces the char reactivity, while the latter has the opposite effect; at the pyrolysis temperature of 400–600°C, the enrichment of ion-exchangeable AAEMs is the main factor controlling the char reactivity, while at 700–1000°C, the ordering of chemical structure plays a dominant role.

Interconnected SnO2/graphene+CNT network as high performance anode materials for lithium-ion batteries

As a metal oxide with a high theoretical capacity, SnO2 is considered to be one of the promising alternative anode materials in lithium-ion batteries. However, the pulverization of electrodes caused by the large volume expansion of SnO2 during repeated charge/discharge hinders its practical application. Here, SnO2 nanoparticles decorated on a 3D carbon network structure formed by the interconnection of graphene and CNT (SnO2/G + CNT), which is designed and successfully synthesized via in situ chemical synthesis and thermal treatment. In this structure, the SnO2 with nanosized can increase energy storage points and decrease the ions transport length, the carbon network can build a high conductive network that facilitates electron transport and alleviate the volume expansion to prevent electrode pulverization. In addition, graphene has a high specific surface area effect that facilitates lithium-ion storage, and the CNT also supports the graphene frame to make the carbon skeleton structure more stable, and provides a large number of ion transport channels, increasing the active sites of the reaction. Due to this excellent structure with synergistic effects, the SnO2/G + CNT electrode exhibits superior reversible capacity (1227.2 mAh g-1 at 0.1 A g-1 after 200 cycles), superior rate capacity (549.3 mAh g-1 at 3.0 A g-1) and long cycle stability (1630.1 mAh g-1 at 0.5 A g-1 after 1000 cycles).

Comparative Analysis of 3D Graphene–LiOH·H2O Composites by Modification with Phytic Acid and Ascorbic Acid for Low‐Grade Thermal Energy Storages

3D Graphene (3D‐GF) modified with different additive concentrations (phytic acid [PA] and ascorbic acid [AA]) is developed and then combined with different LiOH contents by the hydrothermal method to obtain composite materials. It can be found that the addition of PA and AA will not destroy the carbon skeleton structure of 3D‐GF. With increasing additive content, the thermal conductivities of modified 3D‐GF first increase and reach their maximum values at 8 mg mL−1. The modified 3D‐GF with the highest thermal conductivity is selected to be combined with different LiOH contents. The addition of PA and AA can broaden the charging temperature range from 60–110 to 30–200 °C and improve the LiOH hydration rate and heat storage density. Compared with the PA‐modified composite, the AA‐modified composite shows smaller (about 7.6 nm) and more uniform LiOH·H2O particles (the particles size standard deviation of 3D‐GF‐AA‐LiOH·H2O is 1.1503), a larger specific surface area (119 m2 g−1), higher heat storage density (the highest value of 2763 kJ kg−1 for LiOH⋅H2O, which can be about 4.2 times of pure LiOH), and less influenced by the change of LiOH content (the thermal conductivity standard deviation of 3D‐GF‐AA‐LiOH·H2O is 0.123).

C5 and C6 Polymerizations by Anion Migrated Ring-Opening of 1-Cyclopropylvinylbenzene and 1-Cyclobutylvinylbenzene

As an emerging method, anion migrated ring-opening polymerization (AMROP) can effectively regulate the carbon skeletons of polymer backbones with specific vinyl monomers. As reported here, polymers with C5 and C6 skeletons were synthesized by AMROP of 1-cyclopropylvinylbenzene (CPVB) and 1-cyclobutylvinylbenzene (CBVB). Moreover, C4 polymerization of 1-phenyl-1,3-butadiene (1-PB) was also conducted (in a general anionic polymerization process) for comparison with C5 and C6 polymerizations. Among the three base polymers prepared with the C4, C5, and C6 polymerizations, PCBVB exhibited the most flexible carbon skeleton structure and the lowest glass transition temperature (Tg = −18.8 °C). Then, the resultant base polymers with different carbon skeletons were hydrogenated and cyclized. The hydrogenation of P(1-PB), PCPVB, and PCBVB resulted in the formation of products with unique alternating styrene/ethylene (alt-SE), periodic styrene/ethylene/methylene (pd-SEM), and periodic styrene/ethylene/ethylene (pd-SEE) structures. Moreover, pd-SEM and pd-SEE can be considered as sequence-defined template polymers, and these structures cannot be synthesized through general copolymerization of styrene and ethylene. Owing to the specific carbon skeletons exhibited in alt-SE, pd-SEM, and pd-SEE, their Tg values showed significant differences (24.6, 10.9, and −6.0 °C, respectively). Additionally, the specific carbon skeletons of the base polymers resulted in the formation of cyclized polymers with different annular substituents. Moreover, diverse annular substitutes endowed the cyclized polymers with prominent thermal resistance and luminescence properties. Through the above investigations, it is clearly demonstrated that small changes in carbon skeleton structure can remarkably affect the polymer properties. Moreover, AMROP provides a new strategy to design novel polymers with C5 and C6 skeleton structures.

The structural characteristics of waste tire chars at different pyrolysis temperatures

Pyrolysis was a promising technology to achieve waste tire (WT) dispose and utilization. However, large quantities of low quality waste tire chars (WTCs) would remain after pyrolysis and they could be employed to various applications. Further understanding the structural characteristics of WTCs at different pyrolysis temperatures would benefit to guide their utilizations. Herein, pyrolysis experiments were systematically conducted at 400 °C, 600 °C, 800 °C, and 1000 °C respectively to collect WTCs, whose structural characteristics were detailed analyzed. It was found that higher temperature can promote decrease of large and small aromatic ring systems, alkyl-aryl C-C bonds, defects with ordered arrangements of carbon skeleton structure. Pyrolysis can significantly promote pores formation, higher temperature would promote formation of micropores, while mesopores+macropores destroy before 600 °C and then gradually form. Higher temperature can promote decomposition of pyrrolic nitrogen and sulfur bridge with enrichment of oxidised nitrogen and sulphone bridge. Higher temperature would assist in generation of pyridinic nitrogen before 800 °C and quaternary nitrogen before 600 °C.

Investigation on Structure and Reactivity of Demineralized Coal Under Pressurized O &lt;sub&gt;2&lt;/sub&gt;/H &lt;sub&gt;2&lt;/sub&gt;O Conditions

Pressure strongly affects the pyrolysis of coal and the subsequent combustion process. In this paper, a pressurized horizontal furnace was used to conduct pyrolysis experiments of demineralized coal at 1000 ℃ under different pressure (0.1-1.5 MPa). And then use pyrolysis char as the initial experimental sample, a combustion experiment at 1000 ℃ with 10 vol% of O2 and 25 vol% of H2O was performed at corresponding pyrolysis pressure. Using N2 adsorption, Raman and X-ray Photoelectron Spectroscopy (XPS) test methods, the changes of carbon conversion and pore structure, carbon skeleton structure and surface functional group structure of different pressure pyrolysis char and its combustion residual char were obtained. A micro fluidized bed reaction analyzer was then used to test the reactivity of char to explore the influence of pressure on the reactivity of char. Pressure can increase the yield of pyrolysis char and promote the conversion of char in O2/H2O conditions. For the pore structure of char, pressure and O2/H2O atmosphere have a positive promotion effect, and have a similar effect on the chemical structure of char. And for the reactivity of char prepared in O2/H2O combustion, the pore structure is dominant.

Synthesis and characterization of a twisted tri-sulfur-doped polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbons (PAHs) generally refer to aromatic compounds containing two or more fused benzene rings. PAHs have excellent optical, electronic and self-assembly properties, and have important applications in organic light-emitting diodes (OLED), organic field effect transistors (OFET), organic solar photovoltaic cells (OPVC) and other fields. The introduction of heteroatoms to PAHs can adjust the electronic structure, dipole moment, and the self-assembly behavior. Among them, sulfur-doped PAHs have been widely studied. Due to the proper energy level and bonding mode of sulfur atom, the sulfur-doped PAHs have stronger dipole-dipole interactions, electron donating ability, and weakened aromaticity. Sulfur-doped PAHs usually exhibit unique redox characteristics and better hole transporting, so they are widely used as p-type organic semiconductor and electronic donor in photoelectric conversion, and donation unit in donor-acceptor conjugated molecules. Doping PAHs with sulfur is mainly through two ways: post-modification and fusing the sulfur-containing heterocyclic unit. On the other hand, regarding the regulation of geometric structure of carbon skeleton, non-hexagonal ring is introduced to transform the molecular structure from planar to curved structure. The structural distortion can be achieved by the peripherial stereo-hindrance. For example, the PAHs containing helicene units have a highly distorted structure, thus showing a unique optical, electric and assembly properties. In order to construct novel PAHs, this article combines heteroatom doping and geometric control of carbon skeleton. A twisted tri-sulfur-doped PAH C36S3H10(C9H11)6 (molecule 1 ) was synthesized by oxidative cyclodehydrogenation of an oligophenylene precursor, which contains three thiophene rings. X-ray single crystal diffraction exactly characterized the structure of molecule 1 . Because the ring is not completely fused, molecule 1 contains two [5]helicene units, which leads to a twisted molecular structure. In crystalline state, molecule 1 forms dimers through C−H···π and weak π-π interactions, which further packs into one-dimensional columnar stacking through the weak interactions of C−H···π and C−H···S. Different from the planar PAHs, the twisted molecule 1 is not easy to aggregate in solution. Molecule 1 exhibits a yellow photoluminescence, but its quantum yield is low. Combined with the study of transient fluorescence spectroscopy, it is speculated that its twisted molecular structure may be the reason for its low quantum yield. The synthesis of molecule 1 enriches the family of sulfur-doped PAHs, and the derivatives with alkyl chains of molecule 1 can be synthesized in the future and be used as organic semiconductors or electron donors in solar cells and organic electronic devices, etc.

Experimental and modeling studies of quadricyclane and 2-ethylnorbornane pyrolysis from atmospheric to high pressure

To improve the understanding of cyclopentadiene-based high-density liquid hydrocarbon fuels combustion chemistry, the pyrolysis experiments of 1,3-cyclopentadiene (c-C5H6), quadricyclane (QC) and ethylnorbornane (EthNB, reported in our recent work: Wang et al.,2020), were performed in a flow reactor at atmospheric and high pressure over 348–1173 K. The mole fraction profiles of products in three fuels pyrolysis were obtained using online GC–MS/FID. Based on theoretical calculations and literature research, a universal kinetic model (397 species and 1522 reactions) of QC and EthNB, incorporating the sub-mechanisms of c-C5H6 and polycyclic aromatics, was constructed in this work. It was validated against the present data and pyrolysis data of c-C5H6 as well as norbornane in literature with reasonable reproducibility. The rate of production analysis shows that the retro-Diels-Alder reaction to c-C5H6 plus C2H2 is always the dominant path to 2,5-norbornadiene (NBD, the only isomer product of QC) consumption at atmospheric and high pressures, whereas the contribution of isomerization to 1,3,5-cycloheptatriene increases with the increasing pressure and is almost equal to that of the former at high pressure and low conversion. The aromatics formation channels in QC pyrolysis are affected by the presence of C2H2 and different from those of c-C5H6 pyrolysis, especially under high pressure. For EthNB decomposition, the open-ring and H-abstraction reactions play a dominant role. The C2-C6 alkene products are formed via the decomposition of ethylnorbornyl radicals and the further reactions of these alkenes are the precursors of aromatics in EthNB pyrolysis. Although QC and EthNB have a similar U-shaped carbon skeleton structure, the difference is that the former has an extra four-membered ring with more strain energy, which leads a lower initial decomposition temperature. Similarly, the extra CC double bonds, in NBD compared to EthNB, result in more c-C5H6 and C2H2 formation and further increase the growing tendency of initial PAH.