Low-temperature Carbon Research Articles

Interplay between remote single-atom active sites triggers speedy catalytic oxidation

•We propose an electron-delocalized mechanism (EDM) universally present in catalysis •EDM is an electron-transfer-based dynamic interplay between catalytic sites in action •EDM provides a fundamental design strategy to rationally develop efficient catalysts Understanding interaction between active sites in heterogeneous catalysis is a grand challenge, owing to difficulty in extracting information from different active sites. We report a solution to this problem by showing that electron conduction can facilitate direct interplay of distant active sites. By fabricating two single-atom site catalysts (manganese dioxide-encapsulated metallic silver atomic wires) with one or two ending silver atoms of each wire exposed on surfaces, we find that only the catalyst with both ending silver atoms exposed can trigger low-temperature carbon monoxide oxidation, which provides unequivocal evidence that interaction between active sites is possible upon eligible electron conducting. This result indicates that the interaction between active sites might be universally present in catalysis reactions when there is effective communication between the active sites. Understanding interaction between active sites in heterogeneous catalysis is a grand challenge, owing to difficulty in extracting information from different active sites. We report a solution to this problem by showing that electron conduction can facilitate direct interplay of distant active sites. By fabricating two single-atom site catalysts (manganese dioxide-encapsulated metallic silver atomic wires) with one or two ending silver atoms of each wire exposed on surfaces, we find that only the catalyst with both ending silver atoms exposed can trigger low-temperature carbon monoxide oxidation, which provides unequivocal evidence that interaction between active sites is possible upon eligible electron conducting. This result indicates that the interaction between active sites might be universally present in catalysis reactions when there is effective communication between the active sites.

Effects of stabilization on structures and properties of Electrospun Polyacrylonitrile based carbon nanofibers as a binder free electrode for supercapacitor application

Electrospun nanofibers were produced with Polyacrylonitrile (PAN) precursor using the Electrospinning technique. Stabilization is an important heat treatment process before carbonization. A total of 2 samples were considered for the carbonization process. Electrospun Pure PAN nanofiber mat was used with aluminium foil substrate for the heat treatment process in a tube furnace. The first sample was stabilized at 290 °C temperature at a 2 °C/min heating rate and constant heating for 3 h. The second sample was directly used for carbonization without stabilization. Fibers were carbonized at 500 °C under a nitrogen atmosphere with a dwell time of 1 h. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to study the influence on structures and properties of carbon fibers of both samples. To investigate elemental concentration in samples Energy-dispersive X-ray spectroscopy (EDX) was used. EDX results showed 45 % and 60 % carbon atom non stabilized and stabilized carbon nanofibers respectively. An SEM result reveals a drastic fiber diameter reduction in a sample that was not stabilized before carbonization as compared with the sample which was stabilized before the carbonization process. FTIR results showed the complete conversion of CN to CN at a stabilization temperature of 290 °C. Also, FTIR results reveal that 500 °C temperature is too low for complete carbonization as some peaks are still there after the carbonization. Low temperature carbonization is necessary to avoid the melting of aluminium foil substrate during the carbonization process. Further CNF mat will be peeled off from the substrate and will be used directly as electrode material for electrochemical characterization.

Low-temperature hydrothermal carbonization of pectin enabled by high pressure

Pectin is an important component of biomass waste widely existing in the plant cell wall. Hydrothermal carbonization of pectin can produce carbon materials for energy storage, adsorption, and catalysis. However, pressure is generally the self-generated pressure in the hydrothermal reaction, which changes with temperature during the heating process. The independent effect of pressure on the hydrothermal reaction of pectin is unclear and has not been investigated before, especially the effect of high pressure at a low temperature. In this study, by performing the hydrothermal treatment of pectin under different pressures (up to 20 MPa) at a fixed temperature of 200 °C, we found that high pressure could effectively promote carbonization. To understand the mechanism of pressure effect on hydrochar properties, the produced hydrochars were characterized by elemental analysis, scanning electron microscopy (SEM), N2 adsorption/desorption, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), while pyrolysis and combustion behaviors were analyzed using the thermogravimetric analyzer (TGA). The mechanism of high pressure was cleaving the hydroxyl groups, ester carbonyl groups, and aliphatic structures with the process of dehydration and decarboxylation. More aromatic structures were formed in hydrochars with higher carbon content, resulting in a structure with better thermal stability. Carbon spheres with a larger diameter could be formed under higher pressure. The promoting effect was strongest in the range of 2–8 MPa and weaker under higher pressures (8–20 MPa). Future studies may improve the degree of hydrothermal carbonization of pectin by applying an appropriate high pressure.

Stellite Weld Overlay Qualification on the Body of a Dual Plate Check Valve in Low-Temperature Carbon Steel in the Offshore Oil and Gas Industry

Stellite Weld Overlay Qualification on the Body of a Dual Plate Check Valve in Low-Temperature Carbon Steel in the Offshore Oil and Gas Industry

Water vapor sorption properties on coals affected by hydrophilic inorganic minerals and pore fissures

It is essential to understand the law by which coal adsorbs water to prevent coal and rock disasters in the mining process. However, the hydration of coal containing inorganic minerals is seldom studied. In this study, X-ray diffraction (XRD), low-pressure nitrogen adsorption (LPNA), and low-temperature carbon dioxide adsorption (TCA) experiments were performed on coal samples to obtain inorganic mineral compositions and pore structure characteristics. Then, vacuum vapor sorption analyzer (VVS) experiments were carried out on coal samples. GAB and Freundlich models were used to classify the strong adsorption region, weak adsorption region, and critical humidity for monolayer adsorption. The relationship between the amount of adsorbed water and the coal's pore structure and surface chemical properties was discussed. Then, the reason for the difference in specific surface area between N2 and H2O adsorbents was elucidated. Finally, we discuss the significance of coal-water adsorption by pyrite and clay minerals in preventing coal and dynamic rock disasters.

Influence of Acid Modification of Natural Phlogopite on Catalytic Activity of Supported Pd(II)-Cu(II) Complexes in the Reaction of Oxidation of Carbon Monoxide by Atmospheric Oxygen

The paper presents original results on the of nitric acid concentrations effect on structure, morphology, protolytic properties and the activity of low-temperature carbon monoxide oxidation catalysts based on acid-modified phlogopite (Н-Phl-1) and K2PdCl4, Cu(NO3)2, KBr base components. The obtained samples were characterized by XRD, SEM, FT-IR spectroscopy and pH metric method. The obtained catalyst Pd(II)-Cu(II)/8H-Phl-1 can be recommended for use in respiratory devices.

Preparation and characterization of W@WCx composite powder by oxidation-vacuum carbonization process

In the present work, the W@WCx composite powder was successfully prepared through oxidation-vacuum carbonization process. Firstly, the acetone was used to oxidize W particles, leading to the formation of needle-like WO2.72 phase, which is uniformly distributed on the surface of the W particles (W@W2.72). Then through low-temperature vacuum carbonization of the W@W2.72 composite powder, the ultrafine WC and W2C particles generated on the surface of the W particles, and the W@WCx composite powder was obtained. Finally, the as-prepared W@WCx composite powder was used to fabricated W–Cu composite.

Highly Durable Pt–Ru-Doped Ce0.9Zr0.1O2 as an Effective Dual Catalyst for Low-Temperature Simultaneous Propane and Carbon Monoxide Oxidation

Highly Durable Pt–Ru-Doped Ce_0.9Zr_0.1O₂ as an Effective Dual Catalyst for Low-Temperature Simultaneous Propane and Carbon Monoxide Oxidation

Adsorption Behaviors of Cationic Methylene Blue and Anionic Reactive Blue 19 Dyes onto Nano-Carbon Adsorbent Carbonized from Small Precursors.

In this work, an innovative nano-carbon material (N-CM) adsorbent was reported for exploring its adsorption behaviors toward cationic methylene blue (MB) and anionic reactive blue 19 (RB19) pollutants. The proposed N-CM was synthesized by a one-step solvothermal treatment of citric acid and zinc gluconate small precursors. N-CM consists of nanosheets that have an advantageous specific surface area, large sp2/sp3 hybridized domains, and abundant nitrogen/oxygen-containing surface functional groups. The synergistic effects of these features are conducive to the MB and RB19 adsorption. Different from anionic RB19 adsorption (79.54 mg/g) by the cooperative π-π stacking and hydrogen bonding, cationic MB adsorbed onto N-CM mainly by the electrostatic attraction at the natural pH solution (> pHpzc), with an adsorption capacity up to 118.98 mg/g. Interestingly, both MB and RB19 adsorption conformed to the pseudo-second order kinetic (R2 ≥ 0.995) and Langmuir isothermal (R2 ≥ 0.990) models, accompanied by similar maximum monolayer adsorption capacities of 120.77 and 116.01 mg/g, respectively. Their adsorption processes exhibited spontaneously endothermic characteristics. Moreover, N-CM showed superior selective capability toward MB in different mixed dye systems, with high removal efficiencies of 73–89%. These results demonstrate that the high-performance carbon adsorbent prepared from small precursors via low-temperature carbonization shows great potentials in wastewater treatment.

Kinetic triplet from low-temperature carburization and carbon deposition reactions

Kinetic triplet from low-temperature carburization and carbon deposition reactions

MOF-derived hollow Co/C with order macropores prepared at low pyrolysis temperature as high-performance microwave absorber

Herein, a new kind of metal organic framework (MOF)-based magnetic metal nanoparticle/carbon composite, hollow porous Co/C composite (HP-Co/C) with ordered macroporous (∼60 nm) embedded in shell has been fabricated by low-temperature carbonization (500 °C) of ZIF-8@ZIF-67/SiO2 core@shell precursor and subsequent HF etching process. Compared with its control sample of hollow Co/C (H-Co/C), HP-Co/C composite displays significantly improved microwave absorbing properties in matter of both reflection loss (RL) and effective microwave absorbing bandwidth (EAB, RL < −10 dB). Especially, the corresponding EAB is up to7.64 GHz with filler loading of only 15 wt%. This superior microwave absorbing performance is ascribed to the stronger attenuation capability and better impedance matching characteristics induced by the ordered macropores in the hollow Co/C shell. It is believed that this structural design strategy can be extended to prepare other MOFs-derived lightweight and broadband microwave absorbents at relatively low pyrolysis temperature.

Carbon diffusion in bcc- and bct-Fe: Influence of short-range C–C pair interactions studied from first-principles calculations

Identifying the mechanisms of interstitial diffusion in iron is important to understanding the low-temperature ageing of Fe–C ferritic and martensitic alloys. In spite of the low solubility of carbon in ferrite at equilibrium, carbon-rich areas are often found at segregated grain boundaries and in Cottrell atmospheres around dislocations. Carbon-rich areas also form by spinodal decomposition in martensite. In those cases, carbon atoms experience short-range interactions, susceptible to modify their migration behaviour. We performed first-principles calculations to study the influence of these C–C interactions on the migration of interstitial carbon in body-centered iron. The ab initio energy database was introduced in kinetic Monte Carlo simulations to compute the thermodynamic and kinetic parameters. We found that the migration energies of carbon are largely affected by the presence of a neighbouring carbon atom. We explain the evolution of these energies by the relative stability of the C–C configurations corresponding to stable and transition-state positions. The C–C pair interactions slightly modify the ferrite/martensite transition conditions and significantly change the carbon atomic migration path. The latter leads to an increase of the diffusivity up to 10 times and an important kinetic correlation at low temperature (<300 K) and high carbon contents (>1 at.%).

Low-temperature supercritical activation enables high-performance detection of cell-free DNA by all-carbon-nanotube transistor

Biosensors based on carbon nanotube (CNT) thin-film transistors (TFTs) have drawn intense interests for their exhibiting great potential in ultrasensitive and label-free DNA detection. However, the inevitable defects in the dielectric and channel of CNT-based TFTs may induce noisy or unreliable output signals. Here, we propose a low-temperature supercritical carbon dioxide (SCCO2) fluid activation method to enhance the performance of transistor-based biosensors. An activation model of SCCO2 treatment is proposed to elaborate that the SCCO2 treatment can repair the dangling bonds of SiO2 dielectric facilely and passivate the hydroxyl groups effectively. Furthermore, a cell-free DNA detection platform is built up based on all-carbon-nanotube TFTs (AC-TFTs) modified by the CW-Peptide probe. By adopting the SCCO2 treatment, the response of AC-TFT biosensors to AKT2 gene related to triple-metastatic negative breast cancer can be enhanced by more than 114% with high uniformity, and a broad detection range of six orders of magnitude is yielded with a theoretical limit of detection of 42 fM. Additionally, the response has a linear correlation with the length of DNA targets. The nondestructive and eco-friendly SCCO2 activation method provides a promising and universal strategy for achieving highly accurate and sensitive transistor-based biosensors in future clinical applications.

Lignin-based sulfonated carbon as an efficient biomass catalyst for clean benzylation of benzene ring compounds

Low-temperature carbonization–sulfonation two-step process or one-step sulfonation process was employed to draft sodium lignosulfonate (SLS), the primary biological macromolecule ingredient of papermaking black liquor, into lignin-based sulfonated carbon. The two-step lignin-based sulfonated carbon named SLC400,1S was found to be an efficient catalyst for clean Benzyl-alcohol (BA) route Friedel-Crafts (F-C) benzylation of benzene ring compounds. FT-IR, XRD, Raman spectra, XPS, SEM with EDX-mapping, TGA-DSC, acid-base titration, and n-butylamine–acetonitrile titration characterizations demonstrated that the specific two-step process could introduce porous properties and a large number of surface sulfonic, hydroxyl, and carboxyl active groups into the structure of the prepared material, which was found to account for the good catalytic performance for benzylation. Similar to that of hierarchical mesoporous ZSM-5 under optimal conditions, the apparent activation energy for benzylation of paraxylene (PX) with BA over SLC400,1S was estimated to be 119 kJ·mol−1. The common by-product of BA route benzylation, dibenzyl ether (DBE), was almost inhibited because of the extraordinary activity of SLC400,1S and the optimized reaction conditions. A 12-run recycling test demonstrated easy recovery and steady reusability of the above lignin-based sulfonated carbon catalyst.

Employing 2D‐Perovskite as an Electron Blocking Layer in Highly Efficient (18.5%) Perovskite Solar Cells with Printable Low Temperature Carbon Electrode

AbstractInterface engineering and passivating contacts are key enablers to reach the highest efficiencies in photovoltaic devices. While printed carbon–graphite back electrodes for hole‐transporting material (HTM)‐free perovskite solar cells (PSCs) are appealing for fast commercialization of PSCs due to low processing costs and extraordinary stability, this device architecture so far suffers from severe performance losses at the back electrode interface. Herein, a 2D perovskite passivation layer as an electron blocking layer (EBL) at this interface to substantially reduce interfacial recombination losses is introduced. The formation of the 2D perovskite EBL is confirmed through X‐ray diffraction, photoemission spectroscopy, and an advanced spectrally resolved photoluminescence microscopy mapping technique. Reduced losses that lead to an enhanced fill factor and VOC are quantified by electrochemical impedance spectroscopy and JSC–VOC measurements. This enables reaching one of the highest reported efficiencies of 18.5% for HTM‐free PSCs using 2D perovskite as an EBL with a significantly improved device stability.

Wool-Based Carbon Fiber/MoS2 Composite Prepared by Low-Temperature Catalytic Hydrothermal Method and Its Application in the Field of Gas Sensors.

Under the background of the Paris Agreement on reducing greenhouse gases, waste wools were converted into wool carbon fiber (WCF) and WCF–MoS2 composites by low-temperature catalytic hydrothermal carbonization. Their structures and gas-sensing performances were studied for the first time. Due to the existence of heterojunctions, the responses of the WCF–MoS2 composite to the five analytes were 3–400 times those of MoS2 and 2–11 times those of WCF. Interestingly, because of the N, P, and S elements contained in wools, the WCF prepared by the hydrothermal method was realized the doping of N, P, and S, which caused the sensing curves of WCF to have different shapes for different analytes. This characteristic was also well demonstrated by the WCF–MoS2 composite, which inspired us to realize the discriminative detection only by a single WCF–MoS2 sensor and image recognition technology. What’s more, the WCF–MoS2 composite also showed a high sensitivity, a high selectivity, and a rapid response to NH3. The response time and the recovery time to 3 ppm NH3 were about 16 and 5 s, respectively. The detection of limit of WCF–MoS2 for NH3 was 19.1 ppb. This work provides a new idea for the development of sensors and the resource utilization of wool waste.

Research on dynamic microwave low-temperature carbonization of high performance carbon fiber

Polyacrylonitrile precursor was obtained by one-step method of polymerization and spinning. After conventional pre-oxidation at 180–280 °C in air, the polyacrylonitrile pre-oxidized fiber was carbonized at 600–1000 °C by microwave heating and conventional heating in nitrogen. An infrared thermometer is used to detect the surface temperature of the fiber in real time. The dielectric loss tangent (tanδ) increases first and then decreases with increasing temperature. The intensity of the A line of the MCF-1000 sample increases, the G line gradually separates from the D line, and the ID/IG value decreases. Compared with CCF-700, the tensile strength of MCF-700 is increased by 10.06%. The microwave carbonization method creates excellent carbon fiber tensile strength at a temperature of 200 °C lower than the conventional carbonization temperature. The initial modulus of MCF-700 is 51.33% higher than that of CCF-700. Microwave carbonization can obtain carbon fiber with a higher initial modulus at a lower carbonization temperature.

Preparation of nanoscale WC powders by sol-gel synthesis and carbon monoxide carbonization

In this study, tungsten carbide (WC) nanopowders with an average size of about 10 nm were synthesized by a three-step process: the sol-gel preparation of nanoscale WO3, reduction and carbonization in carbon monoxide (CO) atmosphere and short time high-energy ball milling. The average particle size of the sol-gel synthesized WO3 precursor is about 31 nm. Through low-temperature reduction and carbonization at 700 °C in CO, spherical and dendritic WC powders were obtained. After high-energy ball milling at 800 rpm for 10 min and 20 min, the average particle size of WC decreases to 16 nm and 10 nm, respectively. This method provides a facile method for the preparation of nanoscale WC powders with the advantages of low cost, simple process and suitability for industrial production.

Tailoring sub-3.3 Å ultramicropores in advanced carbon molecular sieve membranes for blue hydrogen production.

Carbon molecular sieve (CMS) membranes prepared by carbonization of polymers containing strongly size-sieving ultramicropores are attractive for high-temperature gas separations. However, polymers need to be carbonized at extremely high temperatures (900° to 1200°C) to achieve sub-3.3 Å ultramicroporous channels for H2/CO2 separation, which makes them brittle and impractical for industrial applications. Here, we demonstrate that polymers can be first doped with thermolabile cross-linkers before low-temperature carbonization to retain the polymer processability and achieve superior H2/CO2 separation properties. Specifically, polybenzimidazole (PBI) is cross-linked with pyrophosphoric acid (PPA) via H bonding and proton transfer before carbonization at ≤600°C. The synergistic PPA doping and subsequent carbonization of PBI increase H2 permeability from 27 to 140 Barrer and H2/CO2 selectivity from 15 to 58 at 150°C, superior to state-of-the-art polymeric materials and surpassing Robeson’s upper bound. This study provides a facile and effective way to tailor subnanopore size and porosity in CMS membranes with desirable molecular sieving ability.

Copper nanoparticles decorated N-doped mesoporous carbon with bimodal pores for selective gas separation and energy storage applications

• Mesoporous N & Cu doped carbon materials with enhanced physico-chemical features. • Materials display redox, conducting, basic, adsorption and porous characteristics. • N/Cu doped carons show ordered structure with a bimodal pores size distribution. • High gas adsorption capacity and selectivity in a mixture of CO 2 /H 2 and CO 2 /CH 4. • High values for supercapacitance with good cyclic ability and capacitance retention. We demonstrate a synthesis of copper nanoparticles decorated over nitrogen-doped mesoporous carbon with different N and Cu contents which exhibit conducting, redox, basic, adsorption, and excellent textural properties. These materials are prepared through a nanotemplating approach by simultaneously encapsulating sucrose, guanidine hydrochloride, and Cu(NO 3 ) 2 into the porous channels of mesoporous SBA-15 at a low carbonization temperature of 600 °C. The prepared materials exhibit an ordered mesoporous carbon framework with bimodal pores, decorated with nitrogen and Cu functionalities on the surface of the pores and in the wall structure. The presence of nitrogen functionalities in the porous carbon matrix not only helps to reduce the Cu ions but also stabilizes the nanoparticles and offers redox sites, which are beneficial for adsorption and electrochemical applications. The optimized sample exhibits the highest adsorption capacity of different gases such as CO 2 – 22.5 mmol/g at 273 K, H 2 −13.5 mmol/g at 77 K at 30 bar and CH 4 − 5 mmol/g at 298 K and 50 bar. We also demonstrate that the prepared material shows a high selectivity of adsorption towards CO 2 in a mixture of CO 2 /H 2 and CO 2 /CH 4 and it also registers a high supercapacitance of 209 F g −1 at a current density of 1 A g −1 with excellent cyclic stability.