Aromatic Structures Research Articles

Processing of Pinus sylvestris L. into a heat-insulating, thermally stable, and flame-retarded material by combining the flame-retardant impregnation and densification treatment

Abstract Flame-retardant impregnation and densification are two major modification techniques to improve the fire safety of wood. Here, these two techniques were combined to prepare flame-retarded wood, aiming at further fire hazard reduction. The delignated Pinus sylvestris L. was impregnated with boric acid (BA) and graphene oxide (GO) solutions, then densified to prepare densified flame-retarded wood named BGO-DW sample. The results revealed that the BGO-DW sample obtained a limiting oxygen index (LOI) value of 47.4 %. Its backside temperature after 1200 s heating was 49 % lower than that of unmodified wood. Besides, the peak heat release rate (PHRR) and total heat release (THR) values of BGO-DW sample were 72 and 62 % lower than those of unmodified wood due to its shorter pyrolysis interval and lower peak mass loss rate (PMLR), as supported by thermogravimetric (TG) analysis. The flame retardancy of BGO-DW sample could be attributed to the formation of compatible char containing C=C aromatic structure, C–O–C cross-linked structure, and boron trioxide (B2O3) structure. These features of BGO-DW sample offer a new method to improve thermal stability, heat insulation, and flame retardancy for wood and wood-based products.

A Design Strategy for Multiple Resonance‐Induced Pure Violet Thermally Activated Delayed Fluorescence Emitters with a Narrow Emission Band

AbstractThis study proposes a novel approach to develop highly efficient, narrow‐emitting violet materials based on boron and oxygen polycyclic aromatic hydrocarbon multiple resonance structure. Herein, B‐2OCz is developed by fusing indole with a 5,9‐dioxa‐13bboranaphtho[3,2,1‐de]anthracene (DOBNA) core to enhance its thermally activated delayed fluorescence (TADF) properties and molecular rigidity. On the other hand, the B‐2OCz‐Si is decorated with a bulky tetraphenylsilyl substituent. B‐2OCz‐Si exhibits exceptional features such as violet emission at 397 nm, a very small full width at half maximum of 16 nm, and 82% of photoluminescence quantum yield. The B‐2OCz‐Si devices achieve a high external quantum efficiency of over 15%, violet emission with a peak wavelength of 423 nm, and color coordinates of (0.156, 0.037). Furthermore, the B‐2OCz‐Si is used as an electron transport type host material for phosphorescent organic light‐emitting diodes (PhOLEDs), based on its high triplet energy and TADF properties. As compared to the conventional triazine based host materials, these newly developed DOBNA‐based materials display superior device lifetime performance. All these potential aspects corroborate that this new class of DOBNA‐based materials can work as a promising host material for PhOLEDs and violet‐emitting fluorescent devices.

From Lignins to Renewable Aromatic Vitrimers based on Vinylogous Urethane.

During the last decades, Covalent Adaptable Networks (CANs) have proven to be an important new class of polymer materials combining the main advantages of thermoplastics and thermosets. For instance, materials can undergo reprocessing cycles by incorporating dynamic covalent bonds within cross-linked network. Due to their versatility, renewable resources can be easily integrated into these innovative systems to develop sustainable materials, which can be related to the context of the recent development of circular bioeconomy. Lignins, the main renewable sources of aromatic structures, is a major candidate in the design of novel and biobased stimuli-responsive materials such as vitrimers due to their high functionality and specific chemical architectures. In the aim of developing recyclable lignin-based vinylogous urethane (VU) networks, an innovative strategy was elaborated in which lignin was first modified into liquid polyols, and then into polyacetoacetates. Resulting macromonomers were integrated into aromatic VU networks and fully characterized through thermal, mechanical, and rheological experiments. Viscoelastic behaviors of the different aromatic vitrimers exhibited fast stress-relaxations (e.g., 39s at 130°C) allowing easy and fast mechanical reprocessing. A thermomechanical recycling study was successfully performed. Then, the developed strategy enabled the fabrication of healing biobased aromatic vitrimers with tunable structural design and properties.

Structural characterization analysis and macromolecular model construction of coal from Qinggangping coal mine

Understanding the molecular structure characteristics of coal at the molecular level is of great significance to realize the rational utilization and efficient conversion of coal. This paper gives insights into the acquisition of characterization parameters of coal molecular microstructure by testing and analyzing the long flame coal from Qinggangping (QGP) Coal Mine through proximate analysis, ultimate analysis, vitrinite reflectance determination, fourier transform infrared Spectroscopy test (FTIR), X-ray photoelectron epectroscopy test (XPS), carbon nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The results show that benzene rings in the QGP coal are mainly connected in a disubstituted way, accounting for 36.48%. Oxygen atoms mainly exist in the oxygen-containing functional groups such as the ether C–O, C=O and –COO. Aliphatic hydrocarbons in the aliphatic group are mainly of symmetrical -CHx stretching vibration. Hydroxyl groups are mainly composed of OH–OH and OH–O hydrogen bonds, accounting for 29.21% and 21.53%, respectively. Nitrogen atoms exist in the form of C4H5N. The coal molecular is mainly of aromatic carbon structure, where the ratio of bridge aromatic carbon to peripheral carbon is 0.198. There are benzene, naphthalene and anthracene in the coal molecular structure, and the former two chemicals play a dominating role. According to the analysis results, the molecular formula of the QGP coal is finally determined as C205H181O29N3S. On this basis, the two-dimensional and three-dimensional macromolecular models are constructed with the assistance of simulation software. In addition, the 13C-NMR spectra and densities of the constructed molecular models are calculated, which verifies the rationality of the models. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant.

Functional Lignin‐based Polymers: Isolation, Synthetic Methods and High‐valued Applications

AbstractAs a major component of lignocellulosic biomass, lignin has lots of fascinating properties, such as regeneration, biocompatibility, antioxidant, hydrophilicity, unique aromatic structure, and various functional groups, which make them become interesting natural polymer raw material, and attracted more and more attention. In particular, the rich functional groups of lignin can be easily functionalized through various synthesis methods, which can endow lignin‐based polymers with new structure and function. These functional lignin‐based polymers are widely used in environmental remediation, smart hydrogel materials, catalysis, biomedical, etc. However, its various sources and types, the complex structure, relatively weak chemical reactivity, the unstable processing property, and few high value‐added products limited their practical applications. With the development of lignin varieties, modified reagent, synthesis methods, and polymerization process, many works had been published for the synthesis and application of lignin‐based polymers. In this review, the lignin isolation, modification strategies, polymerization method and process, and the promising applications were summarized and analyzed in recent years. Specially, the recent advances in the preparation of high excellent adsorbents from deconstructed lignin products are highlighted from the synthesis methods and adsorption mechanism perspective. Finally, we discussed these challenges in the green and controllable synthesis of lignin‐based polymers, and prospected their functional applications.

Electronic spectroscopy of 1-cyanonaphthalene cation for astrochemical consideration

Context. Polycyclic aromatic hydrocarbons (PAHs) are believed to be the carriers of the aromatic infrared bands and have been proposed as candidates to explain other astronomical phenomena such as diffuse interstellar bands (DIBs). The first aromatic structures possessing more than one ring, 1- and 2-cyanonaphthalene (CNN), were recently detected by rotational spectroscopy in the dense molecular cloud TMC-1. Laboratory investigations have indicated that due to fast and efficient relaxation through recurrent fluorescence (RF), CNN+ may be photostable in the harsh conditions of the lower density, more diffuse regions of the interstellar medium (ISM) exposed to ultraviolet (UV) radiation. As a result, it has been suggested that the widely held belief that small PAHs present in these regions are dissociated may need to be revisited. If 1-CNN+ is able to survive in the diffuse ISM it may contribute to the population of 1-CNN observed in TMC-1. To investigate the abundance of 1-CNN+ in diffuse clouds, laboratory spectroscopy is required. The present work concerns the electronic spectroscopy of 1-CNN+ in absorption and the search for its spectroscopic fingerprints in diffuse clouds. Aims. The aim is to obtain laboratory data on the electronic transitions of gas-phase 1-CNN+ under conditions appropriate for comparison with DIBs and assess abundance in diffuse clouds. Methods. Spectroscopic experiments are carried out using a cryogenic ion trapping apparatus in which gas-phase 1-CNN+ is cooled to temperatures below 10 K through buffer gas cooling. Calculations are carried out using time-dependent density-functional theory. Results. Experimental and theoretical data on the D2 ← D0 and D3 ← D0 electronic transitions of 1-CNN+ are reported. The former transition has a calculated oscillator strength of f = 0.075 and possesses a pattern dominated by its origin band. The origin band is located at 7343 Å and has a full width at half maximum of 28 Å. In observational data, this falls in a region polluted by telluric water lines, hindering assessment of its abundance. Conclusions. Space-based observations are required to search for the spectroscopic signatures of 1-CNN+ and evaluate the hypothesis that this small aromatic system, stabilised by RF, may be able to survive in regions of the ISM exposed to UV photons.

CHEMICAL-PHARMACOLOGICAL STUDY OF COAL HUMIC SUBSTANCES FOR APPLICATION IN FOOD AND PHARMACEUTICAL INDUSTRIES

Physicochemical and pharmacological properties of the humic substances from coal of the Kansk-Achinsk coal basin, the Pereyaslovskoe deposit, have been studied. The presence of polycyclic aromatic structures and aliphatic fragments with various functional groups as substituents (carboxyl, carbonyl and quinoid, phenolic, alcoholic, ether and ester, amino and amide) was established by means of UV, IR, 13C NMR spectroscopy, fluorimetry, and elemental analysis. It has been determined by HPLC that coal humic substances are highly hydrophilic polydisperse biopolymers with medium molecular weights. According to the indicator of microbiological purity (category 3B), the content of microorganisms does not exceed the indicators required by the State Pharmacopeia of the Russian Federation (SPh XIV edition). The content of radionuclides, toxic metals (lead, cadmium, mercury, arsenic) corresponds to the norms (according to SPh XIV edition). The presence of 11 essential elements has been established. The studied humic substances belong to the V class of hazard (low-hazard substances, according to GOST 32644-2014), do not have allergising properties and cytotoxic effect within a broad concentration range. Antioxidant, immunotropic, cytoprotective properties were established in the studies of specific pharmacological activity with various experimental models. The ability to inhibit free radicals such as hydroxyl radicals (HO•) and superoxide-anion radical (O2-• should be stressed, as these radicals are able to bypass the endogenous antioxidant defense systems of the body. It is concluded that the studied humic substances of the Kansk-Achinsk coal basin, the Pereyaslovskoe deposit, are safe and effective biologically active substances of natural origin for use as a promising biologically active substance in the food and pharmaceutical industries.

Research on the Optimization for Acidification Modification Scheme Considering Coal's Wettability Based on the AHP-TOPSIS Method.

Acidification technology is an important measure for enhancing the extraction of coalbed methane from seams with low permeability and abundant minerals, and the acidification scheme is the key to the success of acidification treatment. To determine the optimal acidification modification scheme, an improved AHP-TOPSIS method is proposed to decide on the optimal conditions for wettability modification. This method constructs an evaluation index system, taking the wettability of coal as the target layer and the pro/hydrophobic functional groups in coal as the index layer. Meanwhile, it innovatively takes the adsorption energy of each functional group when absorbing a single water molecule as the basis for assigning weights to the evaluation indexes. Then, nine acidification modification schemes are evaluated and selected by the improved AHP-TOPSIS method based on the test results of different schemes to get the optimal one. The optimal scheme selected by the AHP-TOPSIS method is validated by water adsorption tests and isothermal adsorption tests. The results showed that the significance of each evaluation index is ranked as follows: aromatic structures > hydroxyl groups > aliphatic functional groups > oxygen-containing functional groups. The optimal acidification modification scheme is selected by the AHP-TOPSIS method with a HF concentration of 4% and a reaction time of 6 h. The ranking of acidification modification schemes obtained by the AHP-TOPSIS method is in high agreement with the ranking of water adsorption tests. When compared with raw coal, the coal samples treated with the optimal scheme have lower adsorption capacity for gas, which indicates that the aforementioned method could be used to evaluate and select the optimal acidification modification scheme, and the selected optimal scheme has the potential to increase the output of coalbed methane.

Van der Waals Interaction Mediated Redox on Graphene Electrode

Graphene, unlike (defective) graphene oxide, is generally not considered to be a highly efficient electrochemical electrode except for activity at the edges. This is because, graphene forms a highly stable hydration bilayer that screens the electric field emanating from the electrode to drive the electrochemical process. A remarkable electrochemical electrode property of graphene is discovered and explored. The property emerges from graphene’s single crystal, aromatic structure. The redox behavior of an aromatic compound, methylene blue (MB) and non-aromatic compounds, such as , potassium ferric cyanide are compared. The electrochemical behavior on monolayer of graphene is quantitatively measured by a novel opto-electrochemical instrument for both electrochemical and structural information. The instrument called, the Scanning Electrometer for electrical Double-layer (SEED) allows local measurement of redox on a 10 micron laser spot to exclusively measure redox signal away from the edges of graphene. Two distinct peaks for both reduction and oxidation during conventional cyclic voltametric (CV) waveform are observed by SEED (Figure 1). The two peaks were attributed to two distinct orientation of MB chemisorption on graphene and subsequent electron transfer. One of the peak depended on precise orientation of the MB on single crystal graphene surface indicating pi-pi interaction mediated chemisorption (Figure 2). The other peak is independent of graphene orientation. MB redox on Au showed a single peak (Figure 1) and was independent of orientation (Figure 2). The effect of the two modes of chemisorption on ionic strength was studied and compared with MB redox on pure gold performed on the same chip. The two peaks were not distinguishable by CV or differential pulse voltammetry (DPV) measured on the same sample under similar conditions. This indicated the sensitivity of SEED to obtain structural information and its ability to measure electrochemical activity on micro-spot. All the three measurements, SEED, DPV and CV were performed without taking the sample out of the solution. The redox of non-aromatic compounds showed no orientation effect. The distinct van der Waals interaction mediated chemisorption by pi-pi stacking on graphene electrode may have distinct advantage to design highly sensitive and specific sensors and biosensors in future, for example, in DNA and RNA sensing. Figure 1

(Invited) Advanced Organic Electrode Materials for High-Performance and Sustainable Na-Ion Batteries

Na-ion batteries (NIBs) are promising alternatives to Li-ion batteries (LIBs) due to the low cost, abundance, and high sustainability of sodium resources. However, the high performance of inorganic electrode materials in LIBs does not extend to NIBs because of larger ion size of Na+ than Li+ and more complicated electrochemistry. Therefore, it is vital to search for high-performance electrode materials for NIBs. To this end, organic electrode materials (OEMs) with the advantages of high structural tunability and abundant structural diversity show great promise in developing high-performance NIBs. To achieve advanced OEMs for NIBs, a fundamental understanding of the structure–performance correlation is desired for rational structure design and performance optimization. Tailoring molecular structures of OEMs can enhance their performance in Na-ion batteries, however, the substitution rules and the consequent effect on the specific capacity and working potential remain elusive. Herein, we explored the electrochemical performances and reaction mechanisms of various carboxylate-based anode materials, including halogenated sodium carboxylates, N-doped sodium carboxylates, etc. By examining sodium carboxylates with different functional groups, selective N substitution, and extended conjugation structure, we exploited the correlation between structure and performance to establish substitution rules for high-capacity OEMs. Our results show that substitution position and types of functional groups are essential to create active centers for uptake/removal of Na+ and thermodynamically stabilize organic structures. Furthermore, rational host design and electrolytes modulation were performed to extend the cycle life. In addition to sodium carboxylate-based anode materials, we also designed and synthesized novel organic cathode materials based on azo and carbonyl groups for NIBs. The electrochemical performance of the organic cathode materials with an extended conjugated structure such as a naphthalene backbone structure is better than that with benzene and biphenyl structures due to faster kinetics and lower solubility in the electrolyte. It unravels the rational design principle of extending π-conjugation aromatic structures in redox-active polymers to enhance the electrochemical performance. To further optimize the organic cathodes, nitrogen-doped or single layer graphene is employed to increase the conductivity and mitigate the dissolution of organic materials in the electrolytes. The resulting organic cathodes deliver high specific capacity, long cycle life, and fast-charging capability. Post-cycling characterizations were employed to study the chemical structure and morphology evolution upon cycling, demonstrating that the active centers (azo and carbonyl groups) in the organic cathode materials can undergo reversible redox reactions with Na+ for sustainable NIBs. Our work provides a valuable guideline for the design principle of high-capacity and stable OEMs for sustainable energy storage.

Molecular insight into DOM fate using EEM-PARAFAC and FT-ICR MS and concomitant heavy metal behaviors in biologically treated landfill leachate during coagulation: Al speciation dependence

Various combined processes with pre-coagulation have been developed for biologically treated landfill leachate, but the microscopic-level processes occurring during coagulation remain largely unknown. Herein, dissolved organic matter (DOM) fate using fluorescence excitation emission matrix spectroscopy combined with parallel factor analysis and electrospray ionization coupled Fourier transform-ion cyclotron resonance mass spectrometry and concomitant heavy metal (HM) behaviors were explored at the molecular level. In addition, AlCl3 and two polyaluminum chloride (PACl) species (dominated by [AlO4Al12(OH)24(H2O)12]7+ and [(AlO4)2Al28(OH)56(H2O)26]18+, respectively) were used. The results show that all coagulants are efficient at removing DOM. PACl was found to be advantageous over AlCl3 in overcoming pH fluctuation, which is ascribed to the different dominant mechanisms, namely, entrapment and sweep flocculation for AlCl3 and charge neutralization for PACl. Consequently, PACl was more effective at removing humic substances, usually high-molecular-weight, oxygen-rich and unsaturated, than protein substances. For HM removal, PACl was likewise better and more stable, where As, Cu, Ni, Co and Hg were removed predominantly via adsorption, and Cr, Zn, Pb, Cd and Mn were removed via coprecipitation. Correlation analysis showed that humic substances tended to complex with HMs and be removed synergistically due to the ubiquitous occurrences of aromatic structures and oxygen-containing functional groups.

Metal catalyst-free selective acetosyringone synthesis from rice straw lignin.

In recent decades, due to abundance (second most abundant natural polymer after cellulose) and sustainability, lignin has attracted much interest from different researchers to use as a raw material for producing various value-added materials such as polymer and fuel. In addition to that, the aromatic structure of lignin makes it a suitable candidate for producing platform chemicals with aromatic rings. As a result, lignin depolymerization has become an interesting process to derive different phenolic monomers like vanillin, acetosyringone, and guaiacol. Among them, due to the bioactive characteristics and efficiency of acetosyringone in plant regulatory systems, the production of acetosyringone from lignin has been presented in this work. A green and cost-effective method was developed for the selective formation of acetosyringone via depolymerization of isolated rice straw lignin (RSL) by using metal catalyst-free conditions in the biphasic medium and described. The RSL was characterized with various spectroscopic techniques such as FT-IR, solid-state 13C NMR, XPS, and TGA. The selectivity of synthesized acetosyringone during depolymerization of RSL was checked from GC-MS analysis. The molecular structure and purity of acetosyringone isolated from preparative thin layer chromatography (TLC) were confirmed with the help of 1H NMR and HRMS, respectively.

Theoretical analysis of OLED performances of some aromatic nitrogen-containing ligands.

It is well-known that tris(8-hydroxyquinoline) aluminum (Alq3) complex and N,N'diphenyl-N,N'-bis(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine compound (TPD) are widely used as electron transfer material (ETL) and hole transfer material (HTL) in organic light emitting diode (OLED) structure, respectively. Considering the reference materials, in the present work, the OLED performances of some cyclic aromatic structures such as 4,4'azopyridine [AZPY], 4,4'-bipyridine [BIPY], 1,2-bis[4'-(4-methylphenyl)2,2':6'2″-terpyridin6-yl]ethyne (BISTERPY), 5,5'-diamino-2,2'-bipyridine (DABP), dipyrido[3,2-a:2',3'c]phenazine (DPP), 4,7-phenanthroline (PHEN) including nitrogen atom have been theoretically analyzed. It is important to note that B3LYP/6-31G(d) and B3LYP/TZP levels of the theory were taken into account for the calculations about monomeric and dimeric structures, respectively. Additionally, the calculations of the mentioned monomeric form were performed at B3LYP-D3/6-31G, CAM-B3LYP/6-31G and ωB97X-D/6-31G(d) levels. For a detailed theoretical analysis, the reorganization energies (λe and λh), adiabatic and vertical ionization potentials and electron affinities, the effective transfer integrals (Ve and Vh), and the charge transfer rates (We and Wh) of all compounds were computed by means of computational chemistry tools. In the light of calculated parameters, it is determined that these mentioned aromatic cyclic structures will be used in which layers of OLED structure. The results obtained in this study will be helpful in the design and applications of new molecules as OLED materials in the future.

Molecular Modelling of Polychlorinated Dibenzo-p-Dioxins Non-Covalent Interactions with β and γ-Cyclodextrins.

Polychlorinated dibenzo-p-dioxins (PCDD) are persistent organic pollutants which result as byproducts in industrial or combustion processes and induce toxicity in both wildlife and humans. In this study, all seven PCDD, tetrachlorinated dibenzo-p-dioxins (TCDD), pentachlorinated dibenzo-p-dioxins (P5CDD), hexachlorinated dibenzo-p-dioxins (H6CDD), heptachlorinated dibenzo-p-dioxins (H7CDD), and octachlorinated dibenzo-p-dioxins (OCDD) were studied in interaction with two cyclodextrins, β-CD and γ-CD, resulting in a total of 40 host-guest complexes. The flexibility of the cyclodextrins was given by the number of glucose units, and the placement of the chlorine groups on the dioxins structure accounted for the different complex formed. Various geometries of interaction obtained by guided docking were studied, and the complexation and binding energy were calculated in the frame of MM+ and OPLS force fields. The results show that the recognition of the PCDD pollutants by the CD may be possible through the formation of PCDD:CD inclusion complexes. This recognition is based on the formation of Coulombic interactions between the chlorine atom of the PCDD and the primary and secondary hydroxyl groups of the CD and van der Waals interaction of the CD hydrophobic cavity with PCDD aromatic structures. Both MM+ and OPLS calculus resulted in close values for the complexation and binding energies. Molecular mechanics calculations offer a proper insight into the molecular recognition process between the PCDD compounds and CD molecules, proved by a good description of the C-H···O bonds formed between the guest and host molecules. It was shown for the first time that CD may efficiently trap PCCDs, opening the way for their tremendous potential use in environmental remediation.

Unveil the mechanism of photosensitized fluoroquinolones enhancing chlortetracycline photodegradation under simulated sunlight: Batch experiments and DFT calculation

Fluoroquinolones (FQs), as the most commonly used antibiotics, are ubiquitous in the aquatic environment. The FQs' self-sensitization process could generate reactive oxygen species (ROS), which could react with other coexisting organic pollutants, impacting their transformation behaviors. However, the FQs’ influences and mechanisms on the photochemical transformation of coexisting antibiotics are not yet revealed. In this study, we found ofloxacin (OFL) and norfloxacin (NOR), the two common FQs, can obviously accelerate chlortetracycline (CTC) photodegradation. In the presence of OFL and NOR (i.e., 10 μM), CTC photodegradation rate constants increased by 181.1% and 82.9%, respectively. With the help of electron paramagnetic resonance (EPR) and quenching experiments, this enhancement was attributed to aromatic ketone structure in FQs, which absorbed photons to generate ROS (i.e., 3OFL*, 3NOR*,1O2, and •OH). Notably, 3OFL* or 3NOR* was dominantly contributed to the enhanced CTC photodegradation, with the contribution ratios of 79.9% and 77.3% in CTC indirect photodegradation, respectively. Compared to CTC direct photodegradation, some new photodegradation products were detected in FQs solution, suggesting that 3OFL* or 3NOR* may oxide CTC through electron transfer. Moreover, the higher triple-excited state energy of OFL and NOR over DFT calculation implied that energy transfer from 3OFL* or 3NOR* to CTC was also theoretically feasible. Therefore, the presence of FQs could significantly accelerate the photodegradation of coexisting antibiotics mainly via electron or energy transfer of 3FQs*. The present study provided a new insight for accurately evaluating environmental behaviors and risks when multiple antibiotics coexist.

Soil microbial community, dissolved organic matter and nutrient cycling interactions change along an elevation gradient in subtropical China

To identify possible dominating processes involved in soil microbial community assembly, dissolved organic matter (DOM) and multi-nutrient cycling (MNC) interactions and contribute to understanding of climate change effects on these important cycles, we investigated the interaction of soil chemistry, DOM components and microbial communities in five vegetation zones - ranging from evergreen broad-leaved forest to alpine meadow - along an elevation gradient of 290–1960 m in the Wuyi Mountains, Fujian Province, China. Soil DOM composition and microbial community assembly were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and Illumina MiSeq high-throughput sequencing, respectively. Sloan's neutral model and the modified stochasticity ratio were used to infer community assembly processes. Key microbial drivers of the soil MNC index were identified from partial least squares path models. Our results showed that soil DOM composition is closely related to the vegetation types along an elevation gradient, the structure and composition of the microbial community, and soil nutrient status. Overall, values of the double bond equivalent (DBE), modified aromaticity index (AImod) increased, and H/C ratio and molecular lability boundary (MLBL) percentage decreased with elevation. Lignins/CRAM-like structures compounds dominated soil DOM in each vegetation type and its relative abundance decreased with elevation. Aliphatic/protein and lipids components also decreased, but the relative abundance of aromatic structures and tannin increased with elevation. The alpha diversity index of soil bacteria gradually decreased with elevation, with deterministic processes dominating the microbial community assembly in the highest elevation zone. Bacterial communities were conducive to the decomposition of labile degradable DOM compounds (H/C ≥ 1.5) at low elevation. In the cooler and wetter conditions at higher-elevation sites the relative abundance of potentially resistant soil DOM components (H/C < 1.5) gradually increased. Microbial community diversity and composition were important predictors of potential soil nutrient cycling. Although higher elevation sites have higher nutrient cycling potential, soil DOM was assessed to be a more stable carbon store, with apparent lower lability and bioavailability than at lower elevation sites. Overall, this study increases understanding of the potential linkage between soil microbial community, multiple nutrient cycling and DOM fate in subtropical mountain ecosystems that can help predict the effect of climate change on soil carbon sequestration and thus inform ecosystem management.

Elucidating the electronic synergetic effects in heteroatomic doped FeN4-C-N-R (R= -F, -Cl, -Br) oxygen reduction catalysts

The structural and electronic characteristics of FeN4 are the determining factors in the catalytic performance of heat-treated Fe-N-C materials, as they serve as active sites. The insertion of heteroatoms as co-dopants (B, S, halogens) can induce electronic effects in the carbon matrix that improves their ORR catalytic activity. Therefore, it has become essential to combine experimental studies with DFT approaches to rationally design this type of catalyst. In this work, we evaluated by means of first principle DFT approaches, the ORR activity for the Fe(phen)2N2 moiety including atoms/functionalities with different atomic radii and electronegativity, to resemble co-doped Fe-N-C-R catalysts. The results showed that the inclusion of halogens heteroatoms (-F, -Cl, and -Br) in the graphitic NC surrounding the FeN4 core could improve its ORR activity in terms of Fe-O2 binding energy that is related to the Fe(III)/Fe(II) formal potential and, in consequence, with the on-set potential for the ORR. The high expected ORR activity is obtained for bromide co-doped FeN4 catalyst (FeN4-C-Br) since -Br atoms act synergistically, inducing long- and short-range electronic effects over both the FeN4 unit and N-pyridinic-like functions that change the electronic distribution over the aromatic NC structure modulating the Fe acidity, Fe-O2 binding, and Fe-O2 orbital interaction.

Investigation of the synergistic effect of O2/H2O pretreatment and Na addition on the NO-semichar reaction

The surface physicochemical features of semichar play a crucial role in determining its reactivity, dominating the subsequent reaction between semichar and NO. Therefore, the synergistic effect of O2/H2O pretreatment and Na addition on the microstructural characteristics of semichar and NO reduction characteristics is revealed through experimental and density functional theory (DFT) methods. Experimental results indicate that O2/H2O pretreatments with Na addition promote the development of pores. Micropores are considered the major pore structures in semichar. Based on Raman and laser-induced breakdown spectroscopy (LIBS) results, the combined effect of O2/H2O pretreatments and Na promotes the formation of small aromatic rings, exhibiting a positive correlation with molecular emissions. Temperature-programmed reduction experiments (TPR) demonstrate that the inclusion of Na in O2/H2O pretreatments enhances the reduction ability of NO. The reduction mechanism of NO-semichar is determined using the DFT method. The simulation results indicate that the adsorption of H2O during O2/H2O pretreatment is chemisorption and independent of Na atom. The additional Na reduces the energy gap of the NO-semichar, facilitating the decomposition of N2 by weakening the conjugated components of the aromatic structures.

Analysis of Molecular Structure Changes in Humic Acids from Manure-Amended Soils over 17 Years Using Elemental Analysis and Solid-State 13C Nuclear Magnetic Resonance Spectroscopy

Soil organic matter (SOM) plays an important role in regulating plant nutrient availability. Here, the effects of the long-term application of different forms of processed swine manure on the SOM structure are explored through the analysis of humic acid (HA) using elemental analysis and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. The HAs from soils amended with liquid swine manure (LSM) and swine manure compost (SMC) are found to be more humified compared to the soils treated with solid swine manure (SSM) and the control (CK). The H/C and O/C molar ratios suggest that carboxyl-rich aliphatic structures are the most important class of biomolecules contributing to the LSM- and SMC-HA structures, while lignin-like structures are the most important biomolecules contributing to the CK- and SSM-HAs. SSM promoted the formation of aliphatic polar structures, which are more susceptible to aerobic biodegradation, whereas the CK facilitated the inclusion of condensed aromatic structures into the HA. Apart from the LSM-HA, the proportion of carboxylic acid functional groups reduced with manure application, while the proportion of phenolic acid functional groups increased. LSM-HA has the highest potential to enhance plant nutrient availability.

Synthesis and characterization of metal oxide dopped beaded sugarcane bagasse fly ash for direct red 28 dye removal

The direct red 28 (DR28) dye discharging into the water body creates toxicity to aquatic organisms because of its aromatic structure with difficult degradation and accumulation in the organisms, so DR28 dye-contaminated wastewater is required to be treat before release. This study aimed to synthesize and characterize sugarcane bagasse fly ash beads (SBFB), sugarcane bagasse fly ash beads doped with titanium dioxide (SBFBT), aluminum oxide (SBFBA), zinc oxide (SBFBZ), and magnesium oxide (SBFBM) for removing DR28 dye, and their DR28 dye removal efficiencies were studied by batch experiments, effect of ionic strength, adsorption isotherms, kinetics, thermodynamic studies, and desorption experiments. SBFBM had higher surface area and pore volume than others. They were rough surfaces with irregular structures and consisted of carbon, oxygen, silica, calcium, chloride, sodium, Si–OH, C = O, T − O − T (T = Al or Si), C − O − C, and Si − H. They could remove DR28 dye by more than 82%, whereas SBFBM demonstrated the highest DR28 dye removal efficiency at 98.31%. The ionic strength had little effect on their DR28 dye adsorptions. They corresponded to Freundlich model except for SBFB, and they corresponded to pseudo-second-order kinetic model. They were favorable DR28 dye adsorption with increasing temperatures, and they could reuse more than 5 cycles.