Aromatic Sheets Research Articles

Staged evolutionary features of the aromatic structure in high volatile A bituminous coal (hvAb) during gold tube pyrolysis experiments

Low-temperature pyrolysis of coal is a crucial step in the coal thermal conversion process and involves very complex physical and chemical reactions that can have different effects on the coal's structure. The thermal evolution behavior and transformation mechanism of the coal microstructure are not yet fully understood, which also limits the efficient utilization of coal to a certain extent. The aromatic structural features (including size, molecular ordering, nematic symmetry, stacking, and curvature) of the char produced from low-temperature pyrolysis of high volatile A bituminous coal (hvAb) from the Xutuan coal mine, China, were quantitatively assessed via high-resolution transmission electron microscopy (HRTEM) image processing and analytical techniques. The thermal transformation process and the mechanisms controlling it were explored. The results show that, except for the unexpected slight growth of aromatic sheets at 440 °C, the lower pyrolysis temperature (< 521 °C) contributed weakly to their size growth, whereas at higher temperatures (561–600 °C), it significantly increased their size. The aromatic molecular ordering tended to gradually change in three stages: increasing between 340 and 440 °C, decreasing between 440 and 521 °C and increasing again between 521 and 600 °C. The nematic symmetry strength of aromatic fringes also followed a similar pattern with temperature at different scales. Additionally, in addition to a very minor development trend at 440 °C, the stacking did not significantly change at temperatures below 521 °C but developed appreciably further with increasing temperatures at 561–600 °C; however, the average spacing of the stacks did not appear to be significantly reduced at all temperatures. The curvature of the aromatic sheets also varied in different temperature stages, i.e., initially slightly increasing (340–380 °C), then gradually decreasing (380–480 °C), later increasing again (480–521 °C), and eventually decreasing (521–600 °C). The properties of the chemical composition and structure of the initial coal play important roles in the thermal reaction behavior, and the physical and chemical reactions that dominate at the different temperature stages may be responsible for such wiggly trends in the evolution of the aromatic structure. Notably, the properties of the mesophase (approximately 440 °C) strongly influence the subsequent structural transformation. These findings could provide useful information for the microstructure–property relationships and preparation of coal-based carbon materials.

Crystal structure of asphaltene under mechanical stress of ball milling

This work aims to investigate the structural behaviour of asphaltene under mechanical stress using ball milling. Asphaltene samples were collected and separated from Kuwait export crude using n-heptane and subsequently ball milled for up to 24 h. X-ray diffraction was used to provide an insight into asphaltene macrostructure properties, which subsequently utilised to determine crystallite parameters. The results showed that the mechanical stress has a great influence on these structural parameters, with an increase of the aromatic sheet's inter-layer distance from 3.6 Å to 3.9 Å. While the height of stacked aromatic sheets per cluster and the number of stacked aromatic sheets per cluster decreased from 24.6 Å to 9.3 Å and 8 to 3.2, respectively. A significant increment in the aromaticity value was also observed after the ball milling experimentations, indicating mechanical stress induces cyclisation and aromatisation. The XRD profiles of the higher milling time samples reveals a high background intensity. This suggests a formation and/or increasing the proportion of highly disordered materials. In addition, the effects magnitude on asphaltene crystal parameters between the mechanical stress against heat stress was compared. The results showed core structural parameters are more sensitive to mechanical stress over heat stress.

Mesoscopic Simulation of Aggregate Characteristics of Asphaltene Molecules Under Shear Fields.

Behaviors of asphaltene molecules in toluene under a shear force field were investigated by dissipative particle dynamics (DPD). The results showed that asphaltene molecules aggregated into nanoaggregates (NAs) in three forms, mainly in the face-to-face type, which contained up to 7 asphaltene molecules. In the aggregates, the distance between aromatic sheets (ASes) of adjacent asphaltene molecules was about 6 Å, and the minimum was 5.49 Å. The composition of NAs changed dynamically. In the absence of shear, the aggregates lasted for more than 3000 ps and up to 8000 ps. The asphaltene molecules in an aggregate might reaggregate once dispersed. Both the number and size of the aggregates decreased under the shear force field, and the duration decreased to less than 1000 ps. The direction of the ASes was distributed randomly when the shear rate was zero. Once sheared, the angle between the ASes and the shear force field plane decreased while the range of it expanded. The ASes tended to be parallel to the shear field and the angle between the two concentrated below 40°. As the shear rate increased, the angle decreased and the distribution was more concentrated.

Microstructural alterations of coal induced by interaction with sequestered supercritical carbon dioxide

A total of four samples with different coal ranks were exposed to supercritical CO2 (SC–CO2) fluids for one week at 313.15 K and 12 MPa. FTIR and X-ray diffraction were combined to explore the changes in functional groups, mineral compositions and aromatic microcrystallite structures of coal samples before and after SC-CO2 interaction. The results indicate that a great number of aliphatic hydrocarbons in coal are extracted and the content is reduced by 47.83–83.08 %, whereas the oxygen-containing groups are slightly changed within 8 %. The content of carbonate minerals is decreased by 29.05–46.11 % after SC-CO2 saturation, while quartz content is enhanced. The changes in coal crystalline structures are attributed to the mineral dissolution and hydrocarbon extraction during SC-CO2 saturation. Numerous voids are generated among aromatic layers after mineral dissolution, which directly enlarges the layer spacing of aromatic sheets. The extraction of aliphatic hydrocarbons can not only further increase layer spacing, but also loosen the coal macromolecular structure. Consequently, the directional alignment of aromatic microcrystallites is reduced within coal, leading to the decline of stacking height and aromatic layers. These findings are of significance for assessing both the recovery of CO2-enhanced coalbed methane and the trapping of CO2 in coal reservoirs.

Modifying improved-Hummer’s method to synthesize graphene derivatives from waste asphaltene

A method for synthesizing graphene derivatives from asphaltene is proposed in this work. The method is based on chemical treatment on which the asphaltene molecules are dispersed in liquid intercalating agents to remove the alkyl side chains, functionalize the aromatic core, and expand the inter-layer distance between the aromatic sheets to facilitate their exfoliation. In this intercalation process, the graphitic surface of asphaltene was oxidized to form asphaltene oxide and then graphene derivative. The results designate that the chemical treatment has caused considerable changes in aliphaticity, aromaticity, oxidation level, sulfonation range, and condensation degree. The novelty in the proposed method is envisaged by the fact that it has been tailored to selectively oxidize the asphaltene molecules and maintain its aromatic moiety. The results also confirmed that the conventional graphite oxidation treatments, such as Hummers’ Method and its subsequent improvements, are not suitable because asphaltene is far more susceptible to oxidation than graphite. The method proposed in this study, in comparison with graphite conventional oxidation methods, has less effluents of undesirable chemicals, less time, lower degree of oxidation, less weight losses, and subsequently higher yield.

Mechanistic insight into the coke formation tendency during upgradation of crude oil in slurry phase batch reactor using MoS2 and its various oil soluble catalysts

This work intends to provide a deep insight on how can the MoS2 and its oil soluble analogues synthesized using various organic acid ligands (oleate, palmitic acid, lauric acid, stearic acid) efficiently fits well into the landscape of refinery and petrochemical integrations. The slurry phase hydroprocessing of crude oil has been efficiently carried out at 420 °C temperature and 120 bar H2 pressure. The hydroprocessing of crude oil presents the prominent results by increasing the lighter and more valuable fractions in the crude oil, as obtained from SARA analysis result, boiling point distribution, viscosity, sulfur and MCR data. The oil soluble MoS2 catalyst (MLT) synthesized from sodium oleate presented better hydroprocessing activity (65 % VR conversion) than other catalysts due to the small crystallite size, greater hydrophobic interaction, low stacking number and slab length. In this study, the comprehensive analysis of the solid coke obtained from both thermal and catalytic reactions are conducted using the XRD to get various structural parameters (average layer distance between two aromatic sheets (dm), average inter-chain layer distance (dλ), average perpendicular height of stack of aromatic sheets (Lc), average diameter of aromatic sheet (La), and average number of stacked aromatic sheets (M)) to elucidate the coke formation mechanism. These findings highlight the crucial role of catalysts in activating supplied hydrogen gas and promoting the hydrocracking reactions.

The effect of low-temperature oxidation on asphaltene structure and properties during air injection

Air injection is a promising method to enhance light crude oil recovery. To effectively utilize this technology, understanding the oxidation behaviour and interactions of SARA components during low-temperature oxidation (LTO) is crucial. In this study, the SARA components of two light crude oils from the Xinjiang oilfield were characterized during LTO under air and nitrogen atmospheres, respectively. Firstly, our results revealed that the oxidation behaviour under air significantly affected crude oil stability at temperatures above 150 °C. Secondly, asphaltene component exhibited the highest oxidative activity, leading to the introduction of more oxygen and further oxidation of C–O groups and sulphoxides on the asphaltene surface. This resulted in stronger intermolecular forces among asphaltene molecules. Furthermore, the polarity characterization showed increased polarity difference between asphaltenes and resins. Structural parameters changes were observed in asphaltene aggregates, with enhanced aromaticity and accumulation of aromatic sheets after LTO reactions. Finally, these findings contribute to a deeper understanding of SARA component oxidation and interactions during LTO process, which is valuable for future air injection applications.

Structural Organization of Asphaltenes and Resins and Composition of Low Polar Components of Heavy Oils

Comparative characteristics of resins, asphaltenes, and low polar components of heavy oils from the Ashalchinskoye (I) and Nurlatskoye (II) oil fields (Republic of Tatarstan, Russia) are given. These oils differ in the age of host rocks (Permian and Devonian, respectively) and the content of their components and heteroatoms. An X-ray phase analysis and scanning and transmission electron microscopy reveal that, in contrast to smooth surface asphaltenes of oil I, asphaltenes of oil II are characterized by a loose and porous surface and smaller sizes of nanoaggregates. Nanoaggregates form a disorderly tangled structure because of the alkyl side-chain configuration, which makes it difficult to stack aromatic sheets. The crystallites of nanoaggregates of asphaltenes of oil II are smaller than the crystallites of nanoaggregates of asphaltenes of oil I. The application of the method of structural-group analysis based on the use of the measured indicators of the elemental composition, average molecular weights, and the results of 1H NMR spectroscopy made it possible to establish that overall sizes of mean molecules of resins and asphaltenes of heavy oil I are larger due to the increased content of aromatic and naphthenic cycles in the naphthenoaromatic system. A feature of the structure of the resin–asphaltene components of oil II is a greater number of alkyl substituents in the side chains. According to gas chromatography–mass spectrometry (GC–MS) analysis, the low polar components under study are characterized by a similar set of saturated hydrocarbons (n-alkanes, mono-, and polycycloalkanes) but differ in the composition of identified aromatic hydrocarbons and heteroorganic compounds. A feature of the low polar components of oil II is the presence of a wider range of n-alkyl- and phenylalkyl-substituted benzenes and nitrogen- and oxygen-organic compounds in their composition.

Solubility and structural parameters of asphaltene subfractions separated from bitumen via an improved method

Asphaltene is an important component of bitumen, and it is closely related to the performance of bitumen. Asphaltene is a complex mixture, and it is obviously not accurate to simply regard it as the heptane-insoluble part in bitumen. In this paper, an improved reduced pressure column precipitation device was developed to separate the asphaltene sub-fractions in 2 kinds of road petroleum bitumen which had the same Performance Grade (PG) and almost free of wax, but significantly different physical aging degree. The separation process is strictly based on the solubility of asphaltene subfractions in different polar solvents. Based on the extended Hansen solubility parameter (HSP) model, 6 kinds of isolated asphaltenes were tested by turbidimetric titration test to determine their structural stabilities in three solubility directions: dispersion interaction, polar interaction and hydrogen bonding. Furthermore, the structural characteristic parameters (aromatic sheet diameters and aromaticity) of 6 kinds of asphaltenes were obtained using Raman spectroscopy and Fourier-transform infrared spectroscopy. The research showed that asphaltenes exhibited lower dispersion and stronger hydrogen bonding with the increasing of polarity. The aromatic hydrocarbon size and aromaticity also increased with polarity. The research results can explain bitumen phase imbalance (such as thermoreversible aging) caused by the change of asphaltene components.

Asphaltene inhibitor performance as a function of the asphaltene molecular/aggregate characteristics: Evaluation by interfacial rheology measurement and bulk methods

Asphaltene precipitation/deposition in well tubing and porous media is categorized as asphaltene damage. Addressing this issue, this study offers an asphaltene inhibitor (namely BZSS-012) and highlights the mutual dependence of the inhibitor-asphaltene molecular structure/functional groups for a successful inhibition performance. Asphaltenes were extracted from two dead oil samples, designated as A- and F- oil, characterized well and dissolved in n-hexane/toluene mixture to prepare A- and F-model oil. Interfacial rheology measurements, in addition to conventional asphaltene dispersant test (ADT), was introduced as a new test approach to evaluate the inhibitor performance. The dynamic interfacial tension (IFT) and dilational elasticity of the model oils-water interface were measured. In addition, the standard deviation from the Young-Laplace drop shape (YL-STD) during a high-amplitude compression-expansion of the interface was calculated. Compared to the F-asphaltene, the A-asphaltene molecules have a larger aromatic sheet size, shorter peripheral chains, higher heteroatom content, and higher density of hydroxyl groups, leading to a higher self-association tendency. However, the aggregates size of the F-asphaltene is larger than that of the A-asphaltene in the model oil. Despite its larger aggregates, the F-asphaltene has an enough extent and strength of interactions with the inhibitor, leading to the efficiency of 99.2% in the ADT test, much higher than 66.7% efficiency for the A-model oil. In addition, compared to the A-model oil, the F-model oil exhibits lower IFT values with a slower dynamic in-line with the F-asphaltene larger aggregates and revealing their outward functional groups. The addition of the inhibitor accelerates the dynamic of the IFT and results in lower IFT values. No sharp peak in the YL-STD of the F-model oil dosed with 50 ppmv of the inhibitor is observed. This reflects the inhibitor efficiency for controlling the association and networking of the asphaltene aggregates to inhibit interfacial asphaltenic film evolution. Monitoring the YL-STD seems to be an appropriate method to screen asphaltene inhibitors.

Synthesis of graphene derivatives from asphaltenes and effect of carbonization temperature on their structural parameters.

A method for synthesizing graphene derivatives from asphaltene is proposed in this work. The graphene derivatives are mainly composed of few-layer graphene-like nano-sheets of randomly distributed heteroatoms; mainly sulfur and nitrogen. The proposed method is based on a thermal treatment in which asphaltene is carbonized in a rotating quartz-tube furnace under an inert atmosphere at a temperature in the range of 400-950 °C. Asphaltenes from different origins were employed to verify the synthesis method. The results indicate that graphene derivatives obtained at high carbonization temperature have similar structural parameters, despite the evident differences in parent asphaltenes structures and compositions. The transformation of asphaltene to graphene derivatives mainly occurred due to three factors: the reduction in the average number of aromatic layers (n), the expansion in aromatic sheet diameter (L a), and the elimination of alkyl side chains. The reduction in the number of aromatic sheets per stack is primarily ascribed to thermal exfoliation, while the increase in the aromatic sheet diameter is attributed to secondary reactions in the aromatic core of asphaltene. The elimination of side chains, on the other hand, is mainly credited to thermal cracking. The quantification of defect density (L D) in the graphene derivatives suggests an association between defects and heteroatoms presence.

The study on interactions between stabilizers and asphaltenes

Asphaltene stabilizers are the main means to inhibit the flocculation and sedimentation of asphaltenes in crude oil exploitation, transportation, and refining operations. In this work, the interactions between asphaltenes and 2-dodecyl benzene sulfonic acid, 4-dodecyl benzene sulfonic acid, 4-dodecyl aniline, 4-dodecyl phenol, polyisobutylene succinic imide benzene boric acid and polyisobutylene succinic imide benzene sulfonic acid were studied by XPS, XRD, DLS, TEM and SEM methods. The aggregation behavior of asphaltenes in the absence and presence of stabilizers was characterized by analyzing asphaltene’s particle size, surface composition, and aggregate microstructure. It was observed that the interactions between asphaltene and stabilizers decreased asphaltene aggregate size in solution, and that the polymeric stabilizer with an acidic group was superior to the small-molecule stabilizer with an acidic group, but both better than chemicals with basic groups. It was found that stabilizer adsorption on asphaltenes affected the O, N, S contents of asphaltene surface and prompted formation of protonated pyridinic N+ and nitrogen-oxide -R-N+-O-, which further revealed that an acid-base reaction was the most effective at stabilizing asphaltene-stabilizer complexes, followed by π-π interactions and hydrogen bonds. We also found that the synergistic effects of π-π and acid-base reactions stimulated the transformation of 2-dodecyl benzene sulfonic acid adsorbed on asphaltene from the vertical state at low concentrations to the tiled arrangement at high concentrations. XRD results showed that adsorption of stabilizers on asphaltene increased the distance of asphaltene aromatic sheets and decreased the aggregation number of asphaltene to below the critical aggregation number of asphaltene tactoids.

Chemical characterization of asphaltenes deposits from Hassi Messaoud field

The precipitation and deposition of asphaltenes are complex phenomena that reduce the efficiency in oil production operations. In this study, spectroscopic and thermal methods were used for the characterization of asphaltene samples extracted from deposits belonging to different locations in the Hassi Messaoud field. Structural parameters and the chemical structure of the studied asphaltenes were determined using 13C solid nuclear magnetic resonance (NMR), X-ray diffraction and Raman spectroscopy. The thermal behavior of the asphaltenes studied was examined using differential scanning calorimetry. The results obtained suggest that island is the predominent architecture for the asphaltenes studied with an average of 7 to 8 fused rings and aliphatic length chain of about 3–4 carbons. The number of aromatic sheets in a stacked cluster (N) is between 7 and 8 sheets. The aromatic sheet diameter of the four samples ranges from 12.18 to 15.52 Å with an average interlayer distance between aromatic sheets of 3.52 Å and an average interchain layer distance of 4.48 Å.

Effect of Temperature on Asphaltene Precipitation in Crude Oils from Xinjiang Oilfield.

During the production of crude oil, asphaltenes are prone to precipitate due to the changes of external conditions (temperature, pressure, etc.). Therefore, a series of research studies were designed to investigate the effect of temperature on asphaltene precipitation for two Xinjiang crude oils (S1, S2) so as to reveal the mechanism of asphaltene dissolution. First, the changes of asphaltene precipitation were intuitively observed by using a microscope. The results demonstrated that the asphaltene solubility increased with the increase of temperature and the dispersion rate of asphaltene particles increased with the decrease of particle size. Second, the variation of asphaltene precipitation with temperature was quantified by a gravimetric method. The results suggested that the different asphaltenes showed different sensitivity to temperature within the temperature range 25–120 °C. Third, a hypothesis was proposed to explain these results and proved that the asphaltene aggregate structure was an important factor for asphaltene stability. The crystallite parameters of asphaltenes were obtained by X-ray diffraction (XRD) to describe the structural characteristics. The results revealed that the layer distance between aromatic sheets (dm) of asphaltenes derived from S1 oil and S2 oil were 0.378 and 0.408 nm, respectively, which implied that the asphaltene aggregates derived from S2 oil were looser than those of S1 oil. Therefore, high temperature could facilitate the penetration of resins into asphaltene aggregates and ultimately improve the dispersion of asphaltenes. Finally, molecular dynamics (MD) simulation was used to verify the conclusions. Based on the molecular dynamics method, asphaltene aggregate models were developed. The compactness and internal energy of each model were calculated. The results showed that the asphaltene dispersion capability was proportional to the porosity and internal energy.

Synthesizing few-layer carbon materials from asphaltene by thermal treatment

Few-layer carbon materials were synthesized from asphaltene by a top-down approach using a thermal treatment. Asphaltene was carbonized in a rotating quartz-tube furnace under inert atmosphere at a temperature range of 400–950 °C. The carbonization process converted asphaltene molecules into few-layer carbon materials by eliminating the alkyl side chains, exfoliating the aromatic layers (n), and expanding the aromatic sheet diameter (La). The elimination of the alkyl side chains was confirmed by the FTIR analysis; while the exfoliation of aromatic layers was verified by the XRD, Raman, and TEM analyses. The XRD, Raman, and TEM results also revealed an increase in the aromatic sheet diameter as the carbonization temperature increased, which would suggest secondary reactions in the aromatic core of asphaltene. The elemental analysis indicated insignificant changes in sulfur and nitrogen contents for all samples, indicative of the existence of these heteroatoms within the intact aromatic sheets. The density of defect in aromatic sheets was quantified by measuring the average distance between defects (LD), which showed an almost constant value (~13 Å). The consistent trends between the LD measurements and the sulfur and nitrogen contents would infer that the observed defects are mainly associated with the presence of heteroatoms in the aromatic layers.

Structural Model Construction and Optimal Characterization of High-Volatile Bituminous Coal Molecules

The structural characteristics of coal at the molecular level are important for its efficient use. Bituminous coal from the Baozigou Coal Mine is investigated, using elemental analysis, 13C nuclear magnetic resonance, X-ray photoelectron spectroscopy, and Fourier transform infrared. The molecular structure was determined. The aromatic compounds of bituminous coal molecules are primarily two- and three-ring structures, and the aliphatic structures are primarily in the form of methyl, ethyl side chains, and naphthenic hydrocarbons. The ratio of aromatic bridge carbon to peripheral carbon in the molecular structure is 0.279. Oxygen atoms in the form of carbonyl, phenolic hydroxyl and C–O, and nitrogen atoms in pyrroles. Thus, the average structure model of bituminous coal macromolecules was constructed; the molecular formula was C169H128O10N2S, and the molecular weight was 2378. The aromatic structural units in the macromolecular structure of coal include four naphthalenes, three anthracenes, two tetracenes, and heteroatoms in the form of three carbonyl groups, one phenolic hydroxyl group, one pyrrole, and one pyridine. The structure optimization and annealing kinetic simulation of a single macromolecular structure model were performed. Chemical bonds such as bridge bonds and aliphatic bonds were found to be twisted, and π–π interactions between the aromatic sheets in the molecule produced adjacent aromatic sheets. This arrangement tends to be approximately parallel, and the total energy decreases from 6713.401 to 2667.595 kJ/mol, among which the bond stretching energy and van der Waals energy dominate. We used 20 bituminous coal macromolecular models to construct aggregated structural models. After optimization by molecular dynamics simulation, the macromolecules were constrained by the surrounding molecules, and the sheet-like aromatic carbon structures that were originally approximately parallel were distorted. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant.

In-depth characterization of light, medium and heavy oil asphaltenes as well as asphaltenes subfractions

Asphaltenes, and their related issues, have been the focus of many literature investigations. However, in-depth analysis of asphaltenes structure and its relation to asphaltenes stability has been considered by fewer studies. In this research, extensive analysis of the structure of asphaltenes extracted from light, medium, and heavy oils is provided, together with analysis of three subfractions of the medium oil asphaltene having the least, intermediate, and highest solubilities. To this end, elemental analysis, EDX, mass spectroscopy, FTIR, NMR, XRD, and SEM results were collected. Higher hydrogen content and hydrogen/carbon atomic ratio, lower aromatic nature and olefinic entities were observed in heavy oil asphaltenes as well as the most soluble subfraction. Moreover, the molecular structure of heavy oil asphaltenes and the most soluble subfraction displayed broader mass to charge (m/z) distribution range, longer alkyl side chains as well as higher number of stacked aromatic sheets within their nanoclusters. Asphaltenes hydrogens in α position followed similar trend as their heteroatom content, which was higher for the less soluble subfraction and medium oil asphaltenes. Generally, heavy oil asphaltenes possessed a molecular structure that was closer to the most soluble asphaltenes subfraction, whereas light oil asphaltenes possessed a molecular structure similar to the least soluble subfraction. Asphaltenes precipitation/destabilization was attributed to primarily higher attractive π-π interactions coupled with lower steric hindrance.

Selective and Cooperative Photocycloadditions within Multistranded Aromatic Sheets

A series of aromatic helix-sheet-helix oligoamide foldamers composed of several different photosensitive diazaanthracene units have been designed and synthesized. Molecular objects up to 7 kDa were straightforwardly produced on a 100 mg scale. Nuclear magnetic resonance and crystallographic investigations revealed that helix-sheet-helix architectures can adopt one or two distinct conformations. Sequences composed of an even number of turn units were found to fold in a canonical symmetrical conformation with two helices of identical handedness stacked above and below the sheet segment. Sequences composed of an odd number of turns revealed a coexistence between a canonical fold with helices of opposite handedness and an alternate fold with a twist within the sheet and two helices of identical handedness. The proportions between these species could be manipulated, in some cases quantitatively, being dependent on solvent, temperature, and absolute control of helix handedness. Diazaanthracene units were shown to display distinct reactivity toward [4 + 4] photocycloadditions according to the substituent in position 9. Their organization within the sequences was programmed to allow photoreactions to take place in a specific order. Reaction pathways and kinetics were deciphered and product characterized, demonstrating the possibility to orchestrate successive photoreactions so as to avoid orphan units or to deliberately produce orphan units at precise locations. Strong cooperative effects were observed in which the photoreaction rate was influenced by the presence (or absence) of photoadducts in the structure. Multiple photoreactions within the aromatic sheet eventually lead to structure lengthening and stiffening, locking conformational equilibria. Photoproducts could be thermally reverted.

HRTEM analysis of the aggregate structure and ultrafine microporous characteristics of Xinjiang Zhundong coal under heat treatment

Understanding the change in coal structure during heat treatment is the basis of efficient and clean utilization of coal. In this study, high-resolution transmission electron microscopy (HRTEM) was used to analyse the changes in the aggregate structure and ultramicropores of Zhungdong coal samples (Xinjiang, China) that were heated from ambient temperature to 800 °C respectively. Then, the relationship between their HRTEM characteristics and the corresponding reaction activation energy were also analyzed. The results show that the length, curvature, order, layer spacing and stacking height of the aromatic layers of the coal sample vary with an increasing temperature, and are related to the activation energy of the reaction. As the temperature reaches 300 °C, the HRTEM characteristics of the heated coal samples are obviously different from those of the raw coal sample. It is shown that the length of lattice fringes is in the range of 0.3–1.15 nm which accounts for approximately 95% of the total number of fringes. The overall orientation of lattice fringes is not good, but there are two main directions. After heating, the number of naphthalenes in the coal samples decreased, while the number of larger aromatic layers increased. The distance between the aromatic layers of the coal sample decreased with an increasing stacking height, the order of the aromatic layers was enhanced, and the number of aromatic sheets with a larger curvature increased. The coal ultramicropores are mainly concentrated from 0.4 to 0.7 nm. Heat treatment reduces the total number of ultramicropores, but the maximum number of pores is increased. The non-six-membered ring and lattice defects lead to the bending of the fringes, the distribution of fatty structures affects the orientation of the fringes, and the relationship between the pore and molecular structure does not exist independently. After heat treatment, the aggregate structure and ultramicropore size of coal have a high correlation with the activation energy. The activation energy is closely related to the 0.6 nmultramicropores. However, the current experiment could not explain the underlying causes of these relationships. The aggregated state in coal is the macromolecular group formed between different aromatic structures, fat structures and other molecules, which is formed by the interaction of internal defects and pores in the molecular group. The structural differences at different temperatures therefore reflect the interaction of different macromolecules in coal.

Bioinspired synthesis of thermally stable and mechanically strong nanocomposite coatings

An innovative biomimetic method has been developed to synthesize layered nanocomposite coatings using silica and sugar-derived carbon to mimic the formation of a natural seashell structure. The layered nanocomposites are fabricated through alternate coatings of condensed silica and sugar. Sugar-derived carbon is a cost-effective material as well as environmentally friendly. Pyrolysis of sugar will form polycyclic aromatic carbon sheets, i.e., carbon black. The resulting final nanocomposite coatings can survive temperatures of more than 1150 °C and potentially up to 1650 °C. These coatings have strong mechanical properties, with hardness of more than 11 GPa and elastic modulus of 120 GPa, which are 80% greater than those of pure silica. The layered coatings have many applications, such as shielding in the form of mechanical barriers, body armor, and space debris shields.Graphical abstract