Spontaneous Oxidation Research Articles

Electrocatalytic Oxidation of Carbohydrates via Surface-Immobilized Viologen

Electricity produced directly from renewable carbohydrates—Earth’s most abundant biomolecules—offers tremendous potential if it can be done cheaply, efficiently, and practically. Previous work demonstrated that the viologen-mediated process accelerates carbohydrate oxidation but also results in incomplete oxidation products reducing the efficiency of electricity production. Subsequent studies suggested that soluble polymeric viologen compounds improved oxidation efficiency by increasing the local concentration of the viologen mediators. In the present study, the utility of surface-immobilized viologen mediators for the oxidation of simple carbohydrates was investigated. Self-assembled monolayers of thiolated viologen derivatives were prepared on gold anodes to enhance the electrocatalytic oxidation of dihydroxyacetone, fructose, and glucose. The thiolated viologen mediators formed surface-adsorbed films on gold electrodes that were consistent with incomplete monolayers, as characterized by quartz crystal microbalance and cyclic voltammetry. Monolayers formed from dialkylated viologens enhanced the spontaneous electrooxidation of carbohydrates in an unoptimized alkaline electrochemical cell. These results indicate that immobilized mediators can be used to enhance the spontaneous oxidation of carbohydrates to generate electricity from renewable sources. The same tethered-mediator strategy could be used for other mediators to increase the electrochemical cell efficiency and enable long-lasting anodes in carbohydrate fuel cells.

Oxidation-enhanced thermoelectric efficiency in a two-dimensional phosphorene oxide

We performed density functional theory calculations to investigate the thermoelectric properties of phosphorene oxide (PO) expected to form by spontaneous oxidation of phosphorene. Since thermoelectric features by nature arise from the consequences of the electron-phonon interaction, we computed the phonon-mediated electron relaxation time, which was fed into the semiclassical Boltzmann transport equation to be solved for various thermoelectric-related quantities. It was found that PO exhibits superior thermoelectric performance compared with its pristine counterpart, which has been proposed to be a candidate for the use of future thermoelectric applications. We revealed that spontaneous oxidation of phosphorene leads to a significant enhancement in the thermoelectric properties of n-doped phosphorene oxide, which is attributed to the considerable reduction of lattice thermal conductivity albeit a small decrease in electrical conductivity. Our results suggest that controlling oxidation may be utilized to improve thermoelectric performance in nanostructures, and PO can be a promising candidate for low-dimensional thermoelectric devices.

Influence of Magnetite Nanoparticles Shape and Spontaneous Surface Oxidation on the Electron Transport Mechanism.

The spontaneous oxidation of a magnetite surface and shape design are major aspects of synthesizing various nanostructures with unique magnetic and electrical properties, catalytic activity, and biocompatibility. In this article, the roles of different organic modifiers on the shape and formation of an oxidized layer composed of maghemite were discussed and described in the context of magnetic and electrical properties. It was confirmed that Fe3O4 nanoparticles synthesized in the presence of triphenylphosphine could be characterized by cuboidal shape, a relatively low average particle size (9.6 ± 2.0 nm), and high saturation magnetization equal to 55.2 emu/g. Furthermore, it has been confirmed that low-frequency conductivity and dielectric properties are related to surface disordering and oxidation. The electric energy storage possibility increased for nanoparticles with a disordered and oxidized surface, whereas the dielectric losses in these particles were strongly related to their size. The cuboidal magnetite nanoparticles synthesized in the presence of triphenylphosphine had an ultrahigh electrical conductivity (1.02 × 10−4 S/cm at 10 Hz) in comparison to the spherical ones. At higher temperatures, the maghemite content altered the behavior of electrons. The electrical conductivity can be described by correlated barrier hopping or overlapping large polaron tunneling. Interestingly, the activation energies of electrons transport by the surface were similar for all the analyzed nanoparticles in low- and high-temperature ranges.

Temperature rise characteristics of spontaneous combustion and oxidation ofcoal with different particle sizes under the effect of thermal-stress coupling

Temperature rise characteristics of spontaneous combustion and oxidation ofcoal with different particle sizes under the effect of thermal-stress coupling

Investigation into engine performance of a hydrogen-dimethyl ether spark-ignition engine under various dimethyl ether fractions

Spark-ignition combustion mode could be used to widen the operation range of homogeneous charge compression ignition combustion mode on a hydrogen-dimethyl ether (DME) engine. To improve power output and reduce nitrogen oxides emissions, this study investigated the combustion and emissions properties of a hydrogen-DME spark-ignition engine under various DME fractions (αDME). The result showed that flame development and propagation periods were extended after DME blended. The increases of both periods were 1.7 and 2.0 °CA when αDME various from 1.4% to 3.0%, respectively. However, when αDME increased to 3.4%, flame propagation period had a 1.7 °CA reduction because of the spontaneous high-temperature oxidation of a few end unburned mixtures. Blending DME could improve power output of the neat hydrogen engine. The maximum improvement of indicated mean effective pressure could achieve 18.3%, after DME addition. Because of the weakened flame kernel and flame propagation process, when αDME lower than 3.0%, blending DME increased cyclic variation yet the variations were in 0.13%. Nitrogen oxides emissions could be reduced significantly, when DME was added into the neat hydrogen engine. The maximum reduction could achieve 49.9%, based on neat hydrogen fuel-supply mode. Hydrocarbon and carbon monoxide emissions were increased after DME addition. When αDME increased from 1.4% to 3.4%, the enhancement of hydrocarbon emissions was about two-third lower than that of carbon monoxide emission.

Flexible and Stretchable Liquid Metal Electrodes Working at Sub-Zero Temperature and Their Applications.

We investigated characteristics of highly flexible and stretchable electrodes consisting of Galinstan (i.e., a gallium-based liquid metal alloy) under various conditions including sub-zero temperature (i.e., <0 °C) and demonstrated solar-blind photodetection via the spontaneous oxidation of Galinstan. For this work, a simple and rapid method was introduced to fabricate the Galinstan electrodes with precise patterns and to exfoliate their surface oxide layers. Thin conductive films possessing flexibility and stretchability can be easily prepared on flexible substrates with large areas through compression of a dried suspension of Galinstan microdroplets. Furthermore, a laser marking machine was employed to facilitate patterning of the Galinstan films at a high resolution of 20 μm. The patterned Galinstan films were used as flexible and stretchable electrodes. The electrical conductivity of these electrodes was measured to be ~1.3 × 106 S m−1, which were still electrically conductive even if the stretching ratio increased up to 130% below 0 °C. In addition, the surface oxide (i.e., Ga2O3) layers possessing photo-responsive properties were spontaneously formed on the Galinstan surfaces under ambient conditions, which could be solely exfoliated using elastomeric stamps. By combining Galinstan and its surface oxide layers, solar-blind photodetectors were successfully fabricated on flexible substrates, exhibiting a distinct increase of up to 14.7% in output current under deep ultraviolet irradiation (254 nm wavelength) with an extremely low light intensity of 0.1 mW cm−2, whereas no significant change was observed under visible light irradiation.

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines.

In-situ-generated N-aryl nitrile imines derived from trifluoroacetonitrile efficiently react with polycyclic 1,4-quinones, yielding fused pyrazole derivatives as the exclusive products. The reactions proceed via the initially formed [3 + 2]-cycloadducts, which undergo spontaneous aerial oxidation to give aromatized heterocyclic products. Only for 2,3,5,6-tetramethyl-1,4-benzoquinone, the expected [3 + 2]-cycloadduct exhibited fair stability and could be isolated in moderate yield (53%). The presented method offers a straightforward access to hitherto little known trifluoromethylated polycyclic pyrazoles. All products were isolated as pale colored solids with medium-intensity absorption maxima in the range of 310–340 nm for naphthoquinone-derived products and low-intensity bands in the visible region (≈400 nm) for the anthraquinone series.

Вивчення кінетики просочення базальтових, вуглецевих, оксидних волокон розплавами алюмінію та його сплавами

Wetting studies were performed by the sessile drop method using the capillary purification method of melt during the experiment in a vacuum of 2·10-3 Pa in the temperature range of 600–700 oC. The use of a dropper allows separate heating of the melt and the substrate, capillary and thermo vacuum cleaning of the melt, as well as thermo vacuum cleaning of the coatings surface. This is a model scheme of the impregnation process of non-metallic frames with matrix melts in the manufacture of composite materials by spontaneous free impregnation. Vanadium, copper and nickel metals were chosen for the coatings, which were sprayed on the materials by electron beam evaporation of metals in vacuum, and titanium, nickel powders for the coatings were used. The nature of the wetting angle dependence on the film thickness is a linear decrease in the angle with increasing film thickness. Studies have shown the possibility of using double films vanadium–copper, vanadium–nickel for the manufacture of composite materials from basalt fibers. The process of impregnation of basalt, carbon and oxide fibers with aluminum melts and its alloy with silicon in the temperature range 650–700 oC has been studied. The metal titanium, nickel powder coatings and films vanadium–copper, vanadium–nickel for the method of spontaneous free impregnation were used. Speciments of the composite material were obtained and the limit of destruction of these samples was determined. The bend strength of composites (basalt fiber 200 μm) is 270 MPa. Keywords: spontaneous free impregnation, composites, aluminium melts, basalt, carbon, oxide fibers, wetting, metal coatings and coverings.

The Catecholaldehyde Hypothesis for the Pathogenesis of Catecholaminergic Neurodegeneration: What We Know and What We Do Not Know.

3,4-Dihydroxyphenylacetaldehyde (DOPAL) is the focus of the catecholaldehyde hypothesis for the pathogenesis of Parkinson’s disease and other Lewy body diseases. The catecholaldehyde is produced via oxidative deamination catalyzed by monoamine oxidase (MAO) acting on cytoplasmic dopamine. DOPAL is autotoxic, in that it can harm the same cells in which it is produced. Normally, DOPAL is detoxified by aldehyde dehydrogenase (ALDH)-mediated conversion to 3,4-dihydroxyphenylacetic acid (DOPAC), which rapidly exits the neurons. Genetic, environmental, or drug-induced manipulations of ALDH that build up DOPAL promote catecholaminergic neurodegeneration. A concept derived from the catecholaldehyde hypothesis imputes deleterious interactions between DOPAL and the protein alpha-synuclein (αS), a major component of Lewy bodies. DOPAL potently oligomerizes αS, and αS oligomers impede vesicular and mitochondrial functions, shifting the fate of cytoplasmic dopamine toward the MAO-catalyzed formation of DOPAL—destabilizing vicious cycles. Direct and indirect effects of DOPAL and of DOPAL-induced misfolded proteins could “freeze” intraneuronal reactions, plasticity of which is required for neuronal homeostasis. The extent to which DOPAL toxicity is mediated by interactions with αS, and vice versa, is poorly understood. Because of numerous secondary effects such as augmented spontaneous oxidation of dopamine by MAO inhibition, there has been insufficient testing of the catecholaldehyde hypothesis in animal models. The clinical pathophysiological significance of genetics, emotional stress, environmental agents, and interactions with numerous proteins relevant to the catecholaldehyde hypothesis are matters for future research. The imposing complexity of intraneuronal catecholamine metabolism seems to require a computational modeling approach to elucidate clinical pathogenetic mechanisms and devise pathophysiology-based, individualized treatments.

SnO2/SnSe2 Heterostructures for NO2 and H2 Sensing

SnO2/SnSe2 Heterostructures for NO2 and H2 Sensing

Screen-Printed Carbon Electrode with Self-Assembled Aunps@Mxene for High Sensitive Electrochemical Gas Detection

Introduction Gas sensors have been received extensive attentions due to the critical roles of various gases in industry, environmental monitoring and agriculture. A variety of gas sensing approaches has been developed such as gas chromatography, optical sensing, metal oxide semiconductor-based sensing and electrochemical sensing. Compared to other methods, electrochemical method features high sensitivity, low detection limit, good reproducibility and wide detection range, which has been explored for applications in real world. As a typical electrochemical device, screen printed electrodes (SPEs) can be easily and massively fabricated with good integration and low cost. Also, the easily tunable ink composition is another intriguing feature for specific applications. However, screen printed carbon electrodes (SPCEs) have inferior electrochemical catalysis to noble metal-based sensors despite of its low cost. To further improve the electrochemical performance of SPCEs for gas sensing, nanomaterials are considered as a promising alternative due to its high catalysis, fast electron transfer and large active surface area. MXene is a new class of two-dimensional materials such as Ti3C2X, in which X indicates oxygen- and fluorine-containing functional groups. MXene demonstrates outstanding electrochemical features with excellent catalytic ability. However, MXene materials can easily induce spontaneous oxidation reaction with oxygen and water due to its inherent feature. Therefore, nanocomposites with MXene and metal nanostructures are introduced to improve the stability and further enhance the catalytic performance. In this paper, a screen-printed carbon electrode (SPCE) with self-assembled AuNPs@MXene modification was developed for high sensitive electrochemical gas detection. The sensor performance was compared and evaluated with different concentrations of oxygen using cyclic voltammetry and chronoamperometry. Experimental Compressed air (21% O2) and nitrogen were used as the target gas and balancing gas, respectively. Room temperature ionic liquids 1-butyl-1-methylpyrrolidinium bis-(trifluoromethylsulfonyl)-imide ([C4mpy][NTf2], Aladdin, China) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6], Acros Organics, USA) were used as the supporting electrolyte by drop-casting on the sensor surface. Ti3C2X powders were synthesized by using HF to etch Ti3AlC2 particles as reported in the literature [1]. Gold nanoparticles were synthesized by using trisodium citrate and chloroauric acid as reported in the literature [2]. All chemicals were used as received without further purification. Screen-printed carbon electrodes were purchased from Zensor R&D Inc. A gas blender (MCQ100, Italy) was used for gas mixing, and the total gas flow rate was set constant as 200 standard cubic centimeter per minute (SCCM).An electrochemical analyzer CHI 1030 was used for electrochemical tests using cyclic voltammetry (CV) and constant potential chronoamperometry. Results The bare SPCE was first tested in 21% O2 and nitrogen using cyclic voltammetry, and a pair of reduction peak and oxidation peak can be apparently observed, validating the catalytic ability of carbon-based sensors for gas sensing. Two different RTILs were tested using as the electrolyte, and the results indicate that the sensor using [C4mpy][NTf2] presents higher current response and sensitivity. The sensing performance of bare SPCE, MXene modified SPCE and AuNPs@MXene modified SPCE was compared using CV and chronoamperometry, and AuNPs@MXene modified SPCE exhibits the highest current response and sensitivity due to the synergetic catalytic effect of MXene and AuNPs. The AuNPs@MXene modified SPCE was tested with different oxygen concentration, validating that the sensor has very high sensitivity, wide linear range, low detection limit and good reproducibility. Thus, the sensor can be a promising device for practical gas sensing applications in the real world.

Intensity of free-radical reactions in metastasizing cervical cancer.

e17508 Background: Cervical cancer (CC) is one of the main causes of death among patients with gynecological tumors. As a rule, patients die from relapses and metastases which rates reach 30-45%. According to research data, treatment of patients with distant metastases is ineffective, and half of them die within 9.7 months, while the average survival is 15.9±0.26 months. The development of many pathological processes is considered to be associated with an increase in free-radical reactions leading to oxidative damage to various biomolecules. The purpose of the study was to analyze some characteristics of the free-radical oxidation and antioxidant defence in metastasizing CC. Methods: The study included 56 patients aged 29-73 years with stage IIB-IV CC after antitumor treatment. The main group – 27 patients who developed metastases within 4 months to 8 years after the CC diagnosis; controls – 29 patients with non-metastatic CC; donors – 19 healthy women aged 27-61 years. The accumulation of carbonyl derivatives in blood plasma proteins was detected in the reaction with 2, 4-dinitrophenylhydrazine. The induced oxidative modification of proteins was stimulated with Fenton's reagent. Free-radical processes was evaluated by the intensity of peroxide-induced luminol-dependent plasma chemiluminescence and the content of nitric oxide metabolites; the intensity of lipid peroxidation - by the content of malondialdehyde (MDA); the activity of catalase and ceruloplasmin was also studied. Results: CC progression was accompanied by increasing lipid peroxidation and spontaneous oxidation of blood plasma proteins. MDA levels in patients with metastases increased by 57.8% compared to donors and by 34.3% compared to patients without metastases (p &lt; 0.05). The concentration of 2, 4-dinitrophenylhydrozones increased on average by 4 times compared to donors and by almost 2 times compared to patients without metastases. Patients with metastasizing CC demonstrated elevated levels of products of the interaction of nitric oxide and its derivatives with proteins and peptides - 3-nitrotyrosine and nitrosoglutathione, compared to both donors (by 31.4% and 55.3%) and patients in remission (by 38.1% and 34.5%). Chemiluminescence activity increased by 54.5% compared to donors (p &lt; 0.05) and by 93% (p &lt; 0.01) compared to controls. Catalase activity in the blood plasma of patients with metastases increased by 54.1% compared to donors, but was lower than the values in the control group (by 22.1%). Ceruloplasmin activity was increased only in patients without metastases (by 33%). Conclusions: The process of CC metastasis is accompanied by a greater intensity of oxidative processes of both proteins and lipids, as well as depletion of the adaptive capabilities of the body's antioxidant system.

Recovery of Iron from Mill Scale by Reduction with Carbon Monoxide

The mill scale is a waste from the iron and steel industry. Due to the high content of iron in the form of oxides, it is an attractive material for the recovery of metallic iron by reduction. The product of mill scale reduction is an iron with a very extended surface and a high affinity for oxygen. The smaller iron particles are, the easier it is for spontaneous rapid oxidation, which can be linked to pyrophoricity. This article presents results of experiments using the TG/DTA thermal analysis method aimed at verifying the possibility of recovering iron from the mill scale by a reduction with carbon monoxide at 850 °C, 950 °C, and 1050 °C, taking into account the phenomenon of secondary oxidation in contact with oxygen from air at temperatures of 300 °C, 350 °C, and 400 °C. Two forms of mill scale were used for tests, in the original state and after grinding to develop the surface.

Water-Air Interfaces as Environments to Address the Water Paradox in Prebiotic Chemistry: A Physical Chemistry Perspective.

The asymmetric water-air interface provides a dynamic aqueous environment with properties that are often very different than bulk aqueous or gaseous phases and promotes reactions that are thermodynamically, kinetically, or otherwise unfavorable in bulk water. Prebiotic chemistry faces a key challenge: water is necessary for life yet reduces the efficiency of many biomolecular synthesis reactions. This perspective considers water-air interfaces as auspicious reaction environments for abiotic synthesis. We discuss recent evidence that (1) water-air interfaces promote condensation reactions including peptide synthesis, phosphorylation, and oligomerization; (2) photochemistry at water-air interfaces may have been a significant source of prebiotic molecular complexity, given the lack of oxygen and increased availability of near-ultraviolet radiation on early Earth; and (3) water-air interfaces can promote spontaneous reduction and oxidation reactions, potentially providing protometabolic pathways. Life likely began within a relatively short time frame, and water-air interfaces offer promising environments for simultaneous and efficient biomolecule production.

Explorative study on the antibacterial effects of 3D-printed PMMA/nitrides composites

Following the rising interested on 3D-printing technologies, this research explores the possibility to apply nitride-polymethylmethacrylate composite coatings on 3D printed parts in order to increase their resistance to bacteria colonization. Four different nitrides were tested: silicon, zirconium, hafnium and aluminum. Trans-micrometric particles of hafnium nitride (average size 1 µm) could be dispersed better than the other three nitrides (average size between 8 and 10 µm), but the chemical analysis confirmed that the former, due to the higher surface area, are more prone to spontaneous oxidation in air. After deposition, the surface of the various coatings contained between 40% (silicon nitride) and 90% (hafnium nitride) of exposed ceramic particles. All composite materials showed antibacterial effects when compared to standard polymethylmethacrylate, with hafnium nitride being the most effective against E. coli and aluminum nitride against S. epidermidis. It has been postulated that while Si3N4 long-term antibacterial effects are granted by the constant dissolution of the SiO2 surface layer, zirconium and hafnium composites are effective because they possess antibacterial properties both in their nitride and oxide forms.

Grain Boundary Engineering of Cu-Ag Thin-Film Catalysts for Selective (Photo)Electrochemical CO2 Reduction to CO and CH4.

We investigated the relationship between grain boundary (GB) oxidation of Cu-Ag thin-film catalysts and selectivity of the (photo)electrochemical CO2 reduction reaction (CO2 RR). The change in the thickness of the Cu thin film accompanies the variation of GB density, and the Ag layer (3 nm) has an island-like morphology on the Cu thin film. Therefore, oxygen from ambient air penetrates into the Cu thin film through the GB of Cu and binds with it because the uncoordinated Cu atoms at the GBs are unstable. It was found that the Cu thin film with a small grain size was susceptible to spontaneous oxidation and degraded the faradaic efficiency (FE) of CO and CH4. However, a relatively thick (≥80 nm) Cu layer was effective in preventing the GB oxidation and realized catalytic properties similar to those of bulk Cu-Ag catalysts. The optimized Cu (100 nm)-Ag (3 nm) thin film exhibited a unique bifunctional characteristic, which enables selective production of both CO (FECO = 79.8%) and CH4 (FECH4 = 59.3%) at a reductive potential of -1.0 and -1.4 VRHE, respectively. Moreover, the Cu-Ag thin film was used as a cocatalyst for photo-electrochemical CO2 reduction by patterning the Cu-Ag thin film and a SiO2 passivation layer on a p-type Si photocathode. This novel architecture improved the selectivity of CO and CH4 under light illumination (100 mW/cm2).

Sulfide induces physical damages and chemical transformation of microplastics via radical oxidation and sulfide addition

Transformation of microplastics in aquatic environments and engineered systems (e.g., wastewater treatment plants) significantly affects their transport, fate and effects. Here, we present the counterintuitive finding that sulfide, a prevalent nucleophile and reductant, can result in oxidation of microplastics, in addition to sulfide addition. Treating four model microplastics (thermoplastic polyurethane, polystyrene, polyethylene terephthalate and polyethylene) with 0.1 mM sulfide in a Tris-buffer solution (pH 7.2, 25 °C) resulted in physical damages (embrittlement and cracking) and chemical transformation (increased O/C ratio and formation of C–S bonds) of the materials. Pre-aging of the microplastics with O3 or UV treatment had varied effects on their reactivities toward sulfide, depending on the specific structural and surface chemistry properties of the polymers. Electron paramagnetic resonance and radical trapping/quenching experiments showed that sulfide underwent spontaneous oxidation to form •OH radicals, which acted as the primary oxidant to attack the carbon atoms in the polymer chains, leading to surface oxidation and chain scission. Notably, sulfide addition, verified with X-ray photoelectron spectroscopy and 13C-nuclear magnetic resonance spectroscopy analyses, likely contributed to the physicochemical transformation of microplastics together with radical oxidation in a synergistic manner. The findings unravel an important transformation route (and a potential source) of microplastics in the environment.

Lead-free tin perovskite solar cells

Summary The development of efficient and stable lead-free perovskite solar cells (PSCs) is crucial for addressing the concern of environmental pollution from the toxic element lead. In recent years, tin PSCs have emerged as a promising candidate for high-performance, eco-friendly photovoltaic technology with a high certified power conversion efficiency (PCE) of more than 11%, indicating a great potential for future applications. Here, we review the recent efficiency progress of tin PSCs based on the equivalent circuit model of solar cells. We then discuss approaches toward efficiency improvement from the device viewpoint, such as optimizing the band gap, increasing the light-harvesting efficiency and carrier diffusion length, surface passivation, and regulating the interface energy-level alignment. Finally, we point out the possibility of reaching 20% PCE for tin PSCs and issues regarding enlarging the cell size and realizing scalable production in the future. We expect that these perspectives will be helpful for accelerating the commercialization of tin PSCs.

Elucidating oxidation-based flavour formation mechanism in the aging process of Chinese distilled spirits by electrochemistry and UPLC-Q-Orbitrap-MS/MS

The oxygen-based oxidation process is leading toward the understanding of the flavour formation mechanism of aged Baijiu. However, the oxygen-based oxidation process in Baijiu aging is difficult to explore because of (1) the composition of Baijiu produced in different batches varies a lot and (2) the spontaneous oxidation needs several years or even decades to occur. Hence, the flavour formation mechanism of Baijiu aging was investigated using electrochemistry and UPLC-Q-Orbitrap-MS/MS, which enabled us to solve the two difficulties above. The oxidation reaction on gold surface could accelerate Baijiu aging by catalyzing the transformation from alcohols to acids. Although natural aging contributed more diverse compound changes to Baijiu, the oxygen-based oxidation process during natural aging was similar to that in the electrochemical oxidation as a whole. This study provides new insights to flavour formation mechanism of aged liquors and provides a new way for liquor-related enterprises to optimise the aging process.

Oxidation Characteristics of Functional Groups in Relation to Coal Spontaneous Combustion.

To investigate and better understand the mechanism of coal spontaneous combustion, the distributions, evolution, and oxidation characteristics of functional groups in different coal samples were characterized using in situ Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) experiments. The macroscopic characteristics of coal spontaneous combustion in relation to functional groups were also analyzed using the thermogravimetric/differential scanning calorimetry–FTIR coupling technique. The experimental results indicated that −OH was the most active groups of coal spontaneous combustion. It not only could react with the absorbed oxygen spontaneously but also found to be the main product of the chemisorption. Consequently, −OH was believed to contribute most both for the loss and increase of coal mass during the process of spontaneous combustion. Aliphatic hydrocarbons were the main components to form −C–O–O• and could be further oxidized into C=O. However, reactions between aliphatic hydrocarbons and oxygen were nonspontaneous. EPR experiments suggested that the tendency of coal spontaneous combustion acutely depended on the stability and survival time of free radicals. The more the stable and longer survival time of free radicals are, the lower the tendency of coal spontaneous combustion is.