A comparative study on characterizations of biomass derived activated carbons prepared by both normal and inert atmospheric heating conditions

In the present study, cost effective activated carbon from wasteland biomass of Calotropis gigantea stem was prepared at 400 °C, 600 °C, 750 °C and 900 °C carbonization temperatures in normal atmosphere (NA) and at 600 °C, 750 °C in inert atmosphere (IA) of nitrogen by using Potassium Carbonate (K₂CO₃) as chemical activating agent in the impregnation ratios of 0.5, 1 and 2. Activated carbons prepared under NA and IA were characterized and compared. Field Emission Scanning Electron Microscopy (FESEM) study confirmed presence of micropores and mesopores. While Xray Diffraction (XRD) analysis confirmed presence of both disordered amorphous carbon humps and graphitic crystallite peaks. Presences of functional groups were more prominent in NAC; found from Fourier Transform Infra-Red Spectroscopy (FTIR) analysis. BET surface area at 750 °C at chemical impregnation ratio 1 under NA was recorded highest containing both micropores and mesopores. Disordered carbon structure was confirmed from RAMAN spectroscopic analysis and nanoporous structure of activated carbon was confirmed from HRTEM analysis. NA activated carbons processed from wasteland weed can be preferred for different adsorption related applications as they are reasonable with improved properties.     

Syngas Production from Lignite Coal Using K2CO3 Catalytic Steam Gasification with Controlled Heating Rate in Pyrolysis Step

Gasification uses steam increases H2 content in the syngas. Kinetics of gasification process can be improved by using K₂CO₃ catalyst. Controlled heating rate in pyrolysis step determines the pore size of charcoal that affects yield gas and H₂ and CO content in the syngas. In previous research, pyrolisis step was performed without considering heating rate in pyrolysis step. This experiment was performed by catalytic steam gasification using lignite char from pyrolysis with controlled heating rate intended to produce maximum yield of syngas with mole ratio of H₂/CO ≈ 2. Slow heating rate (3 °C/min) until 850 °C in the pyrolysis step has resulted in largest surface area of char. This study was performed by feeding Indonesian lignite char particles and K₂CO₃ catalyst into a fixed bed reactor with variation of steam/char mole ratio (2.2; 2.9; 4.0) and gasification temperature (750 °C, 825 °C, and 900 °C). Highest ratio of H₂/CO (1.682) was obtained at 750 °C and steam/char ratio 2.2. Largest gas yield obtained from this study was 0.504 mol/g of char at 900 °C and steam/char ratio 2.9. Optimum condition for syngas production was at 750 °C and steam/char mole ratio 2.2 with gas yield 0.353 mol/g of char and H₂/CO ratio 1.682.     

Fast pyrolysis (ultrapyrolysis) of cellulose

A fast pyrolysis process, termed ultrapyrolysis, has been developed at the University of Western Ontario in order to exploit the high heating rates, short residence times high temperatures and rapid quenching, which are required to produce valuable non-equilibrium intermediates (i.e. ethylene and acetylene) from finely divided biomass. Hot solids(Thermo-for) are used to carry and transfer heat to the biomass particles in a very turbulent vortical contactor (Thermovortactor). This turbulence creates an ideal environment for fast thorough mixing and extremely rapid heat transfer. Cold solids (Cryofor) are then used to quickly quench the products. Trials with cellulose were conducted at temperatures between 750 and 900°C and residence times between 250 and 450 ms. Ethylene yields, expressed as a mass fraction of the product gas, varied from 6.8 to 8.2% for temperatures ranging from 750 to 900°C. The total hydrocarbon yield, also expressed as amass fraction of the product gas, was 18.8% at 900°C. The conversion of cellulose to a permanent non-condensible gaseous product was estimated to be 98% by mass at 900°C.     

Mg-induced g-C3N4 synthesis of nitrogen-doped graphitic carbon for effective activation of peroxymonosulfate to degrade organic contaminants

The nitrogen-doped carbon derived from graphitic carbon nitride （g-C₃N₄） has been widely deployed in activating peroxymonosulfate （PMS） to remove organic pollutants.However,the instability of g-C₃N₄at high temperature brings challenges to the preparation of materials.The nitrogen-doped graphitic carbon nanosheets （N-GC750） were synthesized by magnesium thermal denitrification.Magnesium undergoes the displacement reaction with small molecules produced b...     

Pyrolytic conversion of an Al?Si?N?C precursor prepared via hydrosilylation between [Me(H)SiNH]4 and [HAlN(allyl)]m[HAlN(ethyl)]n

An iminoalane‐silazane polymer (ISP), an Al? Si? N? C precursor, has been synthesized via Pt‐catalyzed hydrosilylation between poly(allyl iminoalane‐co‐ethyl iminoalane) {[HAlN(allyl)]_m[HAlN (ethyl)]_n, AE‐alane} and 1,3,5,7‐tetrahydro‐1,3,5,7‐tetramethylcyclotetrasilazane {[Me(H)SiNH]₄, TCS}. The IR and ¹H NMR spectra of ISP indicate that the relative amounts of the allyl groups decrease slightly in comparison with those of AE‐alane, suggesting that hydrosilylation occurs partially. TG analysis up to 900 °C reveals that the ceramic yield of ISP is 83.1 mass%. It is suggested that the high ceramic yield can be ascribed to cross‐linking reactions occurring during pyrolysis. Possible reactions during pyrolysis are hydrosilylation, polymerization of the C?C bonds in the allyl groups and dehydrocoupling among the SiH groups, NH groups and AlH groups in ISP. The pyrolyzed residue at 1700 °C contains crystalline AlN, 2H‐SiC, β‐SiC and β‐Si₃N₄ and amorphous carbon, as revealed by solid‐state nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy and X‐ray diffraction (XRD) analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of annealing temperature on titania thin films prepared by spin coating

Essentially fully dense titania thin films were spin coated on fused quartz substrates under identical conditions and subjected to annealing over the range 750°–900°C. The films were of a consistent ~400 nm thickness. The anatase → rutile phase transformation temperature was between 750°C and 800°C, with first-order kinetics; annealing at 900°C yielded single-phase rutile. Silicon contamination from the fused quartz substrate was considered to be critical since it suppressed both titania grain growth (maintaining constant grain size) and the phase transformation (occurring at an unusually high temperature); its presence also was considered to be responsible for the formation of lattice defects, which decreased the transmittances and the band gaps.     

Evaluation of the porous structure development of chars from pyrolysis of rice straw: Effects of pyrolysis temperature and heating rate

The effects of pyrolysis temperature and heating rate on the porous structure characteristics of rice straw chars were investigated. The pyrolysis was done at atmospheric pressure and at temperatures ranging from 600 to 1000 °C under low heating rate (LHR) and high heating rates (HHR) conditions. The chars were characterized by ultimate analysis, field emission scanning electron microscope (FESEM), helium density measurement and N₂ physisorption method. The results showed that temperature had obvious influence on the char porous characteristics. The char yield decreased by approximately 16% with increasing temperature from 600 to 1000 °C. The carbon structure shrinkage and pore narrowing occurred above 600 °C. The shrinkage of carbon skeleton increased by more than 22% with temperatures rising from 600 to 1000 °C. At HHR condition, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum porosity development appeared at 900 °C. The total surface area (S_total) and micropore surface area (S_micro) reached maximum values of 30.94 and 21.81 m²/g at 900 °C and decreased slightly at higher temperatures. The influence of heating rate on S_total and S_micro was less significant than that of pyrolysis temperature. The pore surface fractal dimension and average pore diameter showed a good linear relationship.     

Monitoring of N-doped organic xerogels pyrolysis by TG–MS

Pyrolysis of N-doped organic xerogels prepared from different N-containing precursors has been studied by TG–MS. The pyrolytic process has been ascertained to consist of three steps. The first step (up to cca. 250 °C) has been interpreted as water loss (humidity, fixed water from pores) and in some cases as formaldehyde loss. The second step has been connected with volatile substances evolution (cca. 250–450 °C) with predominant release of NH₃, CO₂ and products of melamine (M) or urea decomposition. Reaction/pore water and formaldehyde have also been detected in this step. The third step of pyrolysis (450–1,000 °C) has been ascribed to carbonization reaction when the other releases of NH₃, CO₂, reaction/pore water and M decomposition products have continued. This was accompanied with evolution of H₂ and 3-hydroxypyridine. On the basis of TG measurements, it was found that increasing time of condensation of organic xerogels and amount of used catalyst lead to higher yield of carbonaceous products. In addition, adsorption experiments of Pb(II) on N-doped carbon xerogels proved that relationship between adsorption properties of xerogels and nitrogen loss during pyrolysis exists. When the sample contains only amino groups, they are lost during pyrolysis as ammonia and the adsorption ability is low, while nitrogen comprised in the aromatic rings of N-precursors stays in the structure and causes enlarging of adsorption capacity.     

Effect of mineral matter on the formation of NOX precursors during biomass pyrolysis

Formation of NO_X precursors during pyrolysis of three typical kinds of biomass (wheat straw, rice straw and corn cob) was studied using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer in argon atmosphere. Two pretreatment methods, including deionized water washing and acid washing were utilized to investigate the effect of included minerals on the distribution of nitrogen containing species during wheat straw pyrolysis. KOH and CaO were loaded onto the demineralized (dem) wheat straw to study the effect of excluded minerals on nitrogen release. The residues of the samples after pyrolysis were characterized by X-ray diffraction (XRD) analysis. The results show that different kinds of biomass have distinctive formation characteristics of N-containing species. HCN and HNCO are the main N-containing species for rice straw, while NH₃ and HCN are the main N-containing species for wheat straw and corn cob.The existence of minerals influences the formation of N-containing species during biomass pyrolysis. Both the included potassium and excluded potassium promote N-conversion to NH₃, HCN, NO and HNCO at lower temperature, but decrease the total yields of N-containing species. The included calcium decreases N-conversion to HCN, NH₃ and HNCO at lower temperature (<about 330 °C), while favors the total yields of N-containing species. However, the presence of added calcium restrains N-conversion to HCN, NH₃, NO and HNCO.     

Agar-derived nitrogen-doped porous carbon as anode for construction of cost-effective lithium-ion batteries

Balancing cost and performance of porous carbon (PC) as anode for lithium-ion battery (LIBs) is the key to effectively promote commercial application. Herein, low-cost N-doped PC (NPC-Ts, T = 600, 750 and 900 °C) were facilely prepared in batches via one-pot pyrolysis of agar with different carbonization temperature. The NPC-750 with specific surface area of 2914 m²/g and N content of 2.84% exhibits an ultrahigh reversible capacity of 1019 mAh/g at 0.1 A/g after 100 cycles and 837 mAh/g at 1 A/g after 500 cycles. Remarkably, the resulting LIBs exhibit an ultrafast charge-discharge feature with a remarkable capacity of 281 mAh/g at 10 A/g and a superlong cycle life with a capacity retention of 87% after 5000 cycles at 10 A/g. Coupling with LiFePO₄ cathode, the fabricated lithium-ion full cells possess high capacity, excellent rate and cycling performances (125 mAh/g at 100 mA/g, capacity retention of 95%, after 220 cycles), highlighting the practicability of this NPC-750 as the anode materials.     

Surface Chemistry and Structure of Silicon Oxycarbide Gels and Glasses

In this study, the surface chemistry and structure of methyl-substituted silica gels and porous oxycarbide glasses were investigated. FTIR was used to measure the relative concentration of Si−CH₃ and Si−OH as a function of the degree of methyl-substitution and the pyrolysis temperature. The gels and glasses were further heated, dehydrated or hydrated, in situ, within the FTIR spectrometer. In the temperature range of 800–850°C, high surface area oxycarbide glasses were created with no detectable surface hydroxyl groups. Oxycarbide glasses synthesized in argon at 700°C displayed a weak band for surface hydroxyl groups and reversible physisorption of water, while those synthesized at 850/900°C showed a complete absence of surface hydroxyl groups and the formation of vicinal silanols upon chemisorption of water. Isolated silanols were observed upon heat treatment in vacuum. Formation of aromatic carbon species was found to correlate with the decomposition of the methyl groups. The oxycarbide surface is quite stable to densification (presumably due to elemental carbon on the pore surfaces). In the absence of oxygen, porous silicon oxycarbide glass powders maintain surface areas >200 m²/g at 1200°C. However, oxidizing species in the atmosphere deplete the aromatic carbon species, and the glasses lose surface area.     

A simple routine method for the rapid determination of organic and inorganic carbon in oil shale

A procedure for the rapid determination of organic and inorganic carbon in oil shale samples is proposed. Oil shale samples are decomposed in an oxygen stream at three different temperatures (450°C, 550°C, 900°C). The resulting CO₂ is determined after absorption in 0.02 M NaOH in a relative conductometric detection unit. Temperature. differentiated carbon analysis was used to establish the decomposition temperatures of the organic material (450°C) and the inorganic fractions (550°C and 900°C). The method was tested for samples weighing 2–4 mg. Oil shales with organic carbon contents of 8–20% were determined with good reproducibility (r.s.d. 0.4–1.3%). The accuracy was tested with a standard oil shale sample. One determination requires 8 min.     

Upconversion luminescence of Er3+/Yb3+ co-doped nanolangasite synthesized by a modified Pechini route

Nanopowders of langasite (La₃Ga₅SiO₁₄) doped with 1 at.% Er³⁺ and 3 at.% Yb³⁺ were synthesized for the first time by a modified Pechini route and annealed in air at 700, 750, 800, 900, and 1,000?°C. The langasite powders were characterized by XRD, FTIR and luminescence techniques. Crystallization began at 750?°C and pure langasite phase was obtained for the samples annealed at 800 and 900?°C. Traces of LaGaO₃ and Ga₂O₃ were observed in the sample annealed at 1,000?°C. Bright green and red luminescence was observed for pumping at 973?nm whose intensity increased with annealing temperature due to the removal of the adsorbed impurities and the improvement of crystallinity.     

Cobalt‐based Catalysts Modified Cathode for Enhancing Bioelectricity Generation and Wastewater Treatment in Air‐breathing Cathode Microbial Fuel Cells

To seek an efficient way to enhance the power output and wastewater treatment of microbial fuel cell (MFC), several cobalt‐based composites are successfully synthesized by a facile hydrothermal method under different pyrolysis temperature, and these composites are used as electrocatalyst in air‐breathing cathode of MFC. Different species of nitrogen atom are successfully grafted on the cobalt‐based composites and confirmed by physical and electrochemical analyses. In MFC tests, the maximum power density increases from 577.8 mW m^?2 to 931.1 mW m^?2 with pyrolysis temperature (except for 1000 °C). These electrochemical tests and high COD removal show that Co/N/C‐900 can rapidly transfer electron via a 2×2 e^? transfer pathway, mainly due to the exposure of large electrochemical active area and introduction of the defects of pyridinic?N and abundant oxygen vacancies. Although the power density of MFC with Co/N/C‐900 is 81.1 % of that of commercial Pt/C, the MFC with Co/N/C‐900 is more stable than that of Pt/C, and the power density for Co/N/C‐900 has only a 2.8 % decrease during 25‐cycles operation. The great electrocatalytic activity of the novel Co/N/C‐900 composite exhibits a superior outlook for scale‐up application of MFC in the future.     

Vanadium/cobalt oxides–anchored flexible carbon nanofibers with tunable magnetism as recoverable peroxidase-like catalysts

High-efficiency peroxidase-like catalysts that can be easily recycled are desperately needed for the rapid and accurate detection of H₂O₂. Herein, a novel flexible membrane composed of vanadium/cobalt oxides–anchored carbon (VCoO/C) nanofibers has been purposely designed and fabricated by electrospinning and subsequent carbonization, where there are processing temperature-dependent morphology, composition, and versatile properties. As the carbonization temperature increases from 600°C to 900°C, the saturation magnetization of the as-prepared VCoO/C nanofibers rises gradually. When treated at 750°C under Ar protection, the resultant VCoO/C-750 nanofibers yield superior peroxidase-like catalytic activity toward H₂O₂ with a low limit of detection of 0.44 μM (signal-to-noise ratio = 3). The combination of magnetic behavior and flexibility enables the effective recovery of catalysts. It is believed that our results will open a new avenue for the controlled preparation of flexible nanofiber materials, which are endowed with multiple functions.     

Single Cobalt Atoms with Precise N‐Coordination as Superior Oxygen Reduction Reaction Catalysts

A new strategy for achieving stable Co single atoms (SAs) on nitrogen‐doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal–organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X‐ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as‐generated N‐doped porous carbon. Surprisingly, the obtained Co‐N_x single sites exhibit superior ORR performance with a half‐wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non‐precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.     

Elimination of carbon monoxide by electron impact on quinoline N-oxide,carbostyril and 8-hydroxyquinoline

Under electron impact, the molecular ions of quinoline N-oxide, carbostyril and 8-hydroxyquinoline lose carbon monoxide giving a fragment ion C₈H₇N (m/z 117), which was shown by collision-activated dissociation in each case to have the structure of the molecular ion of indole. Its formation from 8-hydroxyquinoline requires an unusual rearrangement. Isoquinoline N-oxide loses HCN rather than CO and gives a fragment which has the structure of the molecular ion of benzofuran. When the first three compounds were subjected to flash vacuum pyrolysis, quinoline N-oxide at 500–700°C gave carbostyril and indole was detected by gas chromatography/mass Spectrometry. At 900°C carbostyril and 8-hydroxyquinoline both gave indole in small amounts, detected by gas chromatography/mass Spectrometry.     

Thermal degradation and evolved gas analysis of N,N′-bis(2 hydroxyethyl) linseed amide (BHLA) during pyrolysis and combustion

The thermal degradation of N,N′-bis(2 hydroxyethyl) linseed amide (BHLA) was investigated by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy and mass spectroscopy (TG–FTIR–MS). Thermogravimetric analysis revealed that the thermal degradation process can be subdivided into three stages: sample drying (<200 °C), main decomposition (200–500 °C), and further cracking (>500 °C) of the polymer. The compound reached almost 800 °C during pyrolysis and combustion. The activation energy at the second step during combustion was slightly higher than that of pyrolysis emissions of carbon dioxide, aliphatic hydrocarbons, carbon monoxide, and hydrogen cyanide, and other gases during combustion and pyrolysis were detected by FTIR and MS spectra. It was observed that the intensities of CO₂, CO, HCN, and H₂O were very high when compared with their intensities during pyrolysis, and this was attributed to the oxidation of the decomposition product.     

Pyrolysis of methane on a heat-treated FeCrAl coil heated with electric current

We studied methane pyrolysis of at 750 to 1100°C on a heat-treated FeCrAl wire heated by electric current both in the absence of oxygen and at CH₄ : O₂ = 15 : 1 and 9 : 1. The process proceeds in two temperature ranges differing in pyrolysis product selectivity. In the transition region, intensive carbon deposition occurs on the wire surface. The presence of oxygen shifts the methane conversion versus temperature and product selectivity versus temperature curves to higher temperatures. We believe that the existence of two process regions is due to the coking of the catalyst surface.     

TG-FTIR, Py-two-dimensional GC–MS with heart-cutting and LC–MS/MS to reveal hydrocyanic acid formation mechanisms during glycine pyrolysis

To elucidate the formation process of HCN from the pyrolysis of glycine, the small molecule gaseous pyrolysates, H₂O, NH₃, CO₂, CO, HNCO, and HCN, were analyzed in real-time by TG-FTIR. The appearance of the volatile pyrolysis products and the solid residue was determined in real-time at their corresponding formation temperatures by online Py-two-dimensional GC–MS with heart-cutting and LC–MS/MS. The pyrolysis of 2,5-diketopiperazine, a thermolytic by-product of glycine pyrolysis, was also studied. The results showed that: (1) the pyrolysis of glycine can be divided into three temperature ranges 200–300, 300–440, and 440–900 °C; HCN forms in each range with three peaks appearing at 273, 422, and 763 °C, respectively. (2) The mechanistic pathways of HCN formation from glycine in the low- and high-temperature heating stages are different. Below 273 °C, glycine undergoes a decarboxylation reaction to produce methylamine, which subsequently forms HCN by means of dehydrogenation. Above 300 °C, glycine gives relatively large amounts of HCN via 2,5-diketopiperazine and subsequent HNCO or methylenimine formation.