Calcination In Air Research Articles

High efficient trifunctional electrocatalyst based on bimetallic oxide with rich oxygen vacancies towards electrochemical oxidation of small molecules at high current density

Exploiting low-cost, high-activity and robust-stability catalysts has become a meaningful and challenging research topic in the development of hydrogen production via electrochemical water splitting, meanwhile the as-synthesized materials exhibiting multi-functional electrocatalytic performance is highly desirable, but remains tremendous difficulty. Herein, a facile and scalable strategy is developed to synthesize nanowire-like NiCo2O4 arrays with space group Fd3¯m in-situ grown on cobalt foam (denoted as NiCo2O4/CF) via hydrothermal approach and air calcination treatment. The as-prepared nanoporous NiCo2O4/CF electrode possesses a high specific surface area, multiple redox couples and rich oxygen vacancies, thus displaying excellent tri-profitable catalytic activities towards hydrazine oxidation reaction (HzOR), urea oxidation reaction (UOR) and methanol oxidation reaction (MOR). Experimental results show that affording current densities of 10 and 100 mA cm−2 needs potentials of −0.172 and −0.149 V for HzOR, delivering 100 and 500 mA cm−2 current densities merely requires low potentials of 1.343 and 1.440 V for UOR. Impressively, for MOR, a potential of only 1.5 V is required to achieve a high current density of 1058 mA cm−2, outperforming most of the reported electrocatalysts. What's more, the NiCo2O4/CF electrode exhibits exceptional stability at a high current density of 100 mA cm−2 over 20 h for all of the three small molecules electro-oxidation. The current work provides a promising application opportunity for the nanowire-like NiCo2O4 in the aspect of energy-saving hydrogen generation with the assistance of small molecule electro-oxidation reaction.

Significantly enhancing CO2 adsorption on Amine-Grafted SBA-15 by boron doping and acid treatment for direct air capture

Among the most studied adsorbents for CO2 capture is amine-grafted mesoporous silica SBA-15. In this work, boron, a heteroatom, was incorporated into the SBA-15 framework and removed by acid treatment to increase the amount of surface hydroxyl groups. It was discovered that the removal of boron resulted in the formation of silanol nests, with four silanol groups in each nest. Compared with the common method of air calcination for SBA-15, acid-treated boron doped SBA-15, exhibited higher silanol density, as well as higher amine loading after amine grafting. This work is the first to study the use of the silanol nests to graft amines and interact with CO2 directly; the results show more than doubling of the CO2 adsorption capacity for direct air capture.

Simple Fabrication of ϵ‐Fe2O3 Nanoparticles Containing Silica Monoliths with Enhanced Coercivity

AbstractMost of large‐size permanent room‐temperature hard magnets contain rare‐earth elements. Here, we present the preparation of a large‐size rare‐earth free hard magnet based on the loading of the ordered mesoporosity of a preformed ordered mesoporous silica monolith obtained by a sol‐gel route with the Fe(NO3)3 salt, followed by a simple calcination in air. The investigation of the influence of the thermal treatment temperature as well as the Fe/Si ratio on the microstructure of the ϵ‐Fe2O3/SiO2 nanocomposites reveals well‐controlled ϵ‐Fe2O3 particles size and size distribution. Their magnetic study allows us i) to specify the size of the particles with an enhanced coercivity and ii) to show a linear correlation between the magnetic coercivity of the materials and the mass percent of these particles in the nanocomposites. A ϵ‐Fe2O3 based bulk hard magnet with the highest coercive field of 18 kOe at room temperature was obtained by this synthesis process.

Enhanced Structural Control of Soft-Templated Mesoporous Inorganic Thin Films by Inert Processing Conditions.

Mesoporous thin films are widely used for applications in need of high surface area and efficient mass and charge transport properties. A well-established fabrication process involves the supramolecular assembly of organic molecules (e.g., block copolymers and surfactants) with inorganic materials obtained by sol-gel chemistry. Typically, subsequent calcination in air removes the organic template and reveals the porous inorganic network. A significant challenge for such coatings is the anisotropic shrinkage due to the volume contraction related to solvent evaporation, inorganic condensation, and template removal, affecting the final porosity as well as pore shape, size, arrangement, and accessibility. Here, we show that a two-step calcination process, composed of high-temperature treatment in argon followed by air calcination, is an effective fabrication strategy to reduce film contraction and enhance structural control of mesoporous thin films. Crucially, the formation of a transient carbonaceous scaffold enables the inorganic matrix to fully condense before template removal. The resulting mesoporous films retain a higher porosity as well as bigger pores with extended porous order. Such films present favorable characteristics for mass transport of large molecules. This is demonstrated for lysozyme adsorption into the mesoporous thin films as an example of enzyme storage.

Composite materials based on a ceramic matrix of polycarbosilane and iron-containing nanoparticles

Composite materials comprised of a ceramic matrix with metal-containing nanoparticles were prepared by sintering iron (II) oxalate and polycarbosilane. The chemical composition of the material can be controlled by a sintering process. Sintering in inert atmosphere leads to reduction of the sample and metal iron formation (a-Fe, carbide). Formation of iron oxides requires calcination procedure in series (argon and air) for removing by products. The air-sintering materials consist mainly of oxide phases, but also contain metal iron. The prepared samples were characterized by the: SEM, TEM, XRD and EMR techniques and the Mössbauer spectroscopy. It was shown unique behavior that iron containing particles after calcination in air decreased from 5-30 nm to 2–5 nm due to interaction with matrix under air atmosphere.

Characterization, Calcination and Pre-Reduction of Polymetallic Manganese Nodules by Hydrogen and Methane

A polymetallic manganese nodule was characterized and further calcined and pre-reduced by H2, CH4, and H2-CH4 mixtures at elevated temperatures. It was found that the main Mn and Fe elements coexisted in the ore in different minerals, and the Mn/Fe ratio varies in the ore. Moreover, Cu, Ni and Co are distributed with Mn and Fe, and no known minerals of these elements were identified. The calcination of the ore was carried out through calcination in air in a muffle furnace, and under Ar in a thermogravimetry (TG) furnace. It was found that manganese and iron oxides are evolved from a variety of oxide and hydroxides in the ore during calcination. The pre-reduction of the calcined ore particles by H2 gas in the TG furnace indicated fast reduction by hydrogen. The pre-reduction of the calcined ore by H2, CH4, and H2-CH4 mixtures in a stationary bed reactor and further characterization of the products indicated the same products. It was found that the pre-reduction by all the applied gases at elevated temperatures yield a pre-reduced ore that contains metallic Fe, Cu, Ni, and Co, while MnO co-exist as the dominant phase.

Visible-Light-Active N-Doped TiO2 Photocatalysts: Synthesis from TiOSO4, Characterization, and Enhancement of Stability Via Surface Modification

This paper describes the chemical engineering aspects for the preparation of highly active and stable nanocomposite photocatalysts based on N-doped TiO2. The synthesis is performed using titanium oxysulfate as a low-cost inorganic precursor and ammonia as a precipitating agent, as well as a source of nitrogen. Mixing the reagents under a control of pH leads to an amorphous titanium oxide hydrate, which can be further successfully converted to nanocrystalline anatase TiO2 through calcination in air at an increased temperature. The as-prepared N-doped TiO2 provides the complete oxidation of volatile organic compounds both under UV and visible light, and the action spectrum of N-doped TiO2 correlates to its absorption spectrum. The key role of paramagnetic nitrogen species in the absorption of visible light and in the visible-light-activity of N-doped TiO2 is shown using the EPR technique. Surface modification of N-doped TiO2 with copper species prevents its intense deactivation under highly powerful radiation and results in a nanocomposite photocatalyst with enhanced activity and stability. The photocatalysts prepared under different conditions are discussed regarding the effects of their characteristics on photocatalytic activity under UV and visible light.

Design of Ni(OH)2 Nanosheets@NiMoO4 Nanofibers' Hierarchical Structure for Asymmetric Supercapacitors.

Transition-metal-based materials show great promise for energy conversion and storage due to their excellent chemical properties, low cost, and excellent natural properties. In this paper, through simple strategies such as classical electrospinning, air calcination, and the one-step hydrothermal method, a large area of Ni(OH)2 nanosheets were grown on NiMoO4 nanofibers, forming NiMoO4@Ni(OH)2 nanofibers. The one-dimensional nanostructure was distributed with loose nanosheets, and this beneficial morphology made charge-transfer and diffusion more rapid, so the newly developed material showed good capacitance and conductivity. Under the most suitable experimental conditions, the optimal electrode exhibited the highest specific capacitance (1293 F/g at 1 A/g) and considerable rate capability (56.8% at 10 A/g) under typical test conditions. Most interestingly, the corresponding asymmetrical capacitors exhibited excellent electrochemical cycle stability, maintaining 77% of the original capacitance. NiMoO4@Ni(OH)2 nanofibers were verified to be simple to prepare and to have good performances as energy-storage devices within this experiment.

Effects of Processing Strategies and La + Sm Co-Doping on the Thermoelectric Performance of A-Site-Deficient SrTiO3-δ Ceramics

The effect of calcining in either air (VSTO-A) or 5% H2/N2 (VSTO-H) on the thermoelectric performance of La and Sm co-doped A-site-deficient Sr1-3x/2Lax/2Smx/2TiO3-δ ceramics is reported. All calcined powders were sintered 6 h in 5% H2/N2 at 1773 K to ≥96% relative density. All peaks in X-ray diffraction patterns indexed as a cubic perovskite phase. Scanning electron microscopy revealed grain sizes ~14 and ~10 μm for VSTO-A and VSTO-H ceramics, respectively. x = 0.30 showed the lowest k (2.99 W/m.K at 973 K) for VSTO-A, whereas x = 0.20 had the lowest (2.67 W/m.K at 973 K) for the VSTO-H ceramics. x = 0.30 VSTO-A showed a thermoelectric figure of merit, ZT = 0.25 (at 973 K), whereas the maximum ZT = 0.30 (at 973 K) was achieved for x = 0.20 VSTO-H ceramics, demonstrating that thermoelectric properties are optimized when all processing is carried out in 5% H2/N2.

Kinetics and optimization of biodiesel production from rapeseed oil over calcined waste filter cake from sugar beet processing plant

A low-cost, highly active CaO-based catalyst was prepared from waste filter cake (WFC) from a sugar beet processing factory by calcination in air at 900 °C for 2 h, referred to as the calcined filter cake (CFC). It was used to catalyze the rapeseed oil transesterification with methanol under mild reaction conditions (methanol-to-oil molar ratio of 9:1, catalyst loading of 4–10 %, and reaction temperature of 40–60 °C). Rapeseed oil was characterized regarding the physicochemical properties and fatty acid profile. Low free fatty acid content (about 2.0 mg KOH/g) allowed the direct use of the base CFC catalyst for rapeseed oil transesterification. Rapeseed oil has more unsaturated fatty acids (about 93 %), with oleic acid as the most abundant, than saturated fatty acids (about 7 %). A simplified model combining the changing mechanism of the reaction and the triacylglycerols mass transfer limitation successfully describes the kinetics of transesterification. A good agreement between the model and the experiment was proved by the mean relative percentage deviation for the conversion degree of only ± 7.43 % (based on 42 data). The apparent reaction rate constant follows the Arrhenius equation with the activation energy of 51.9 kJ mol−1. The FAME content higher than 96.5 % can be obtained in wide ranges of the catalyst amount (4–10 %) and the reaction time (about 45–70 min). The following conditions were optimum: the reaction temperature of 59.2 °C, the catalyst loading of 9.1 % (based on the oil weight), and the reaction time of 47 min.

Improving the stability of La-exchanged zeolite Y catalysts in the vapor-phase isomerization of endo-tetrahydrodicyclopentadiene by co-feeding steam

• La 3+ exchanged zeolite Y is more effective than HY catalyst for isomerizing endo-THDCPD to its exo isomer in vapor phase. • LaY catalyst has more Brönsted acidity and more moderate acid sites than HY catalyst. • Deactivated LaY catalyst could be completely recovered after calcination in air. • Improved stability of LaY catalyst was observed in the presence of a small amount of steam. The activities of La-exchanged zeolite Y (LaNaY) catalysts were investigated and compared with that of HNaY catalyst for the vapor-phase isomerization of endo-tetrahydrodicyclopentadiene (endo-THDCPD) to exo-THDCPD. HNaY and LaNaY catalysts were characterized by means of X-ray diffraction (XRD), nitrogen adsorption, NH 3 -TPD, pyridine-adsorbed Fourier Transformation Infrared Spectroscopy (FTIR). The LaNaY catalysts with La loading of 2-5 wt% showed better catalytic performance than the HNaY catalyst. All catalysts deactivated gradually with number of run. The activity of the deactivated LaNaY catalyst could be completely recovered after calcination in air for 4 h at 550 °C. The effect of steam co-feeding on the stability of the LaNaY catalyst was investigated. The results show that the stability of the LaNaY catalyst was improved by co-feeding steam compared to those in the absence of steam, which was attributed to the replacement of adamantane adsorbed on the active sites of the catalyst by competitive adsorption of water. In the presence of 5 % steam, the effect of temperature on the stability of the LaNaY catalyst was also studied. A high and stable activity was observed at 185 °C.

Phase transformation and hydrogen reduction behavior of nanoscale W-Y2O3 powders synthesized by nano in-situ composite method

Powder plays an important role in the performance of tungsten composites. In this work, the nano-scaled W-Y2O3 powder was successfully synthesized by two-stage process of nano in-situ composite method: the calcination in air and hydrogen reduction. The phase transformation and microstructure evolution of powder were investigated and observed by the XRD, SEM, EDS and TEM technologies. Besides, the reaction and refining mechanisms for hydrogen reduction have initially proposed as well. Results showed that the phase transformation processes went through two stages of dehydration and deamination and finally forms complete tungsten oxide during the calcination stage. While, in the reduction stage, WO3 phase was mainly reduced to different WOX (1/3 ≤ x < 3) intermediate phase, especially the formation of W3O phase. The morphology of reduction of W-Y2O3 powder evolves from hollow spheres to slices, fragments and nano-irregular polygon as the reduction temperature increases. Simultaneously, the average particle size of W-Y2O3 powder decreases significantly with the increase of reduction temperature, while the reduction temperature is 800 °C, the change trend is opposite, but it's still much lower than pure tungsten. The addition of Y2O3 significantly affected the phase transition and microstructure evolution behavior of composite powders. The reduction was started from the surface region of powder, and then in the form of cracks or porous structures extend into the interior of the powder until all the nano-particles were formed, which was able to be explained by “shrinkage fissure - particle rupture” and “nucleation - evaporation - sedimentation” model. Moreover, the core-shell structure and Y2WO6 phase formed by addition of Y2O3 can hamper the chemical vapor transport (CVT) and the formation of WO2(OH)2 phase, thus significantly refining the reduced W-Y2O3 powder(115 nm).

Surface engineering towards high-energy carbon cathode for advanced aqueous zinc-ion hybrid capacitors

Opportunities coexist with challenges for the development of carbon-based cathodes with a high energy density applied for zinc ion hybrid capacitors (ZIHCs). In the present study, a facile and effective surface engineering approach is demonstrated to greatly improve the energy storage ability of commercial carbon paper (CP) in ZIHC. Benefiting from the introduced oxygen functional groups, larger surface area and improved surface wettability upon air calcination, the assembled aqueous ZIHC with the functionalized carbon paper (FCP) exhibits a much higher areal capacity of 0.22 mAh/cm2 at 1 mA/cm2, outperforming the counterpart with blank CP by over 5000 times. More importantly, a superior energy density and power density of 130.8 µWh/cm2 and 7460.5 µW/cm2, are respectively delivered. Furthermore, more than 90% of the initial capacity is retained over 10000 cycles. This surface engineering strategy to improve the energy storage capability is potentially applicable to developing a wide range of high-energy carbon electrode materials.

Facilely controlled synthesis of porous ZnO nanotubes with rich oxygen vacancies for highly sensitive and selective detection of NO2 at low temperature

In this work, biomorphic ZnO materials were prepared by simple and controllable zinc salt immersion plus air calcination method using waste willow catkins as biomass template, which present high sensing ability to trace NO2 at low energy consumption. The ZnO hollow nanotube calcined at 500 ℃ was assembled by cross-linkage of small-size nanoparticles with uniform mesoporous distribution and rich oxygen vacancies. The synergistic effect of these microstructure characteristics can not only dramatically promote the rapid gas diffusion on sensing layer, but also greatly increase active sites for surface adsorption and chemical reaction, thus enhancing gas-sensing performance. At low operating temperature of 92 °C, its fabricated sensor exhibits high response of 100.4–10 ppm NO2, which is separately 2.3, 5.6 and 12.1 times larger than those of ZnO hollow nanotube calcined at 600 ℃, thin nanorods (ZnO-TRs) and columnar nanorods (ZnO-CRs). And it is also higher than that of most reported 1-D nanostructured ZnO-based sensors. Meanwhile, this sensor also exhibits high selectivity and satisfactory response-recovery characteristics, as well as excellent humidity resistance and long-term stability. In addition, the enhanced sensing mechanism was also explored in great detail.

Solid Fe Resources Separated from Rolling Oil Sludge for CO Oxidation.

The efficient recycling of valuable resources from rolling oil sludge (ROS) to gain new uses remains a formidable challenge. In this study, we reported the recycling of solid Fe resources from ROS by a catalytic hydrogenation technique and its catalytic performance for CO oxidation. The solid Fe resources, after calcination in air (Fe2O3-H), exhibited comparable activity to those prepared by the calcinations of ferric nitrate (Fe2O3-C), suggesting that the solid resources have excellent recycling value when used as raw materials for CO oxidation catalyst preparation. Further studies to improve the catalytic performance by supporting the materials on high surface area 13X zeolite and by pretreating the materials with CO atmosphere, showed that the CO pretreatment greatly improved the CO oxidation activity and the best activity was achieved on the 20 wt.%Fe2O3-H/13X sample with complete CO conversion at 250 °C. CO pretreatment could produce more oxygen vacancies, facilitating O2 activation, and thus accelerate the CO oxidation reaction rate. The excellent reducibility and sufficient O2 adsorption amount were also favorable for its performance. The recycling of solid Fe resources from ROS is quite promising for CO oxidation applications.

Psyllium-Husk-Assisted Synthesis of ZnO Microstructures with Improved Photocatalytic Properties for the Degradation of Methylene Blue (MB).

Wastewater from the textile industry is chronic and hazardous for the human body due to the presence of a variety of organic dyes; therefore, its complete treatment requires efficient, simple, and low cost technology. For this purpose, we grew ZnO microstructures in the presence of psyllium husk, and the role of psyllium husk was to modify the surface of the ZnO microstructures, create defects in the semiconducting crystal structures, and to alter the morphology of the nanostructured material. The growth process involved a hydrothermal method followed by calcination in air. Additionally, the psyllium husk, after thermal combustion, added a certain value of carbon into the ZnO nanomaterial, consequently enhancing the photocatalytic activity towards the degradation of methylene blue. We also investigated the effect of varying doses of photocatalyst on the photocatalytic properties towards the photodegradation of methylene blue in aqueous solution under the illumination of ultraviolet light. The structure and morphology of the prepared ZnO microstructures were explored by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. The degradation of methylene blue was monitored under the irradiation of ultraviolet light and in the dark. Also, the degradation of methylene blue was measured with and without photocatalyst. The photodegradation of methylene blue is highly increased using the ZnO sample prepared with psyllium husk. The photodegradation efficiency is found to be approximately 99.35% for this sample. The outperforming functionality of psyllium-husk-assisted ZnO sample is attributed to large surface area of carbon material from the psyllium husk and the synergetic effect between the incorporated carbon and ZnO itself. Based on the performance of the hybrid material, it is safe to say that psyllium husk has high potential for use where surface roughness, morphology alteration, and defects in the crystal structure are vital for the enhancing the functionality of a nanostructured material. The observed performance of ZnO in the presence of psyllium husk provides evidence for the fabrication of a low cost and efficient photocatalyst for the wastewater treatment problems.

Ammonia Decomposition over Ru/SiO2 Catalysts

Ammonia decomposition is a key step in hydrogen production and is considered a promising practical intercontinental hydrogen carrier. In this study, 1 wt.% Ru/SiO2 catalysts were prepared via wet impregnation and subjected to calcination in air at different temperatures to control the particle size of Ru. Furthermore, silica supports with different surface areas were prepared after calcination at different temperatures and utilized to support a change in the Ru particle size distribution of Ru/SiO2. N2 physisorption and transmission electron microscopy were used to probe the textural properties and Ru particle size distribution of the catalysts, respectively. These results show that the Ru/SiO2 catalyst with a high-surface area achieved the highest ammonia conversion among catalysts at 400 °C. Notably, this is closely related to the Ru particle sizes ranging between 5 and 6 nm, which supports the notion that ammonia decomposition is a structure-sensitive reaction.

Effects of furanic compounds from biomass pyrolysis on ketonization reaction: The role of oxygenated side groups

Ketonization of biomass-derived oxygenates is promising for sustainable production of platform chemicals, but the catalyst activity will be severely inhibited by furanic compounds. To investigate the mechanism of the inhibition effect, furanic compounds with different side functional groups were chosen for co-ketonization with propanoic acid over CeO2. Results from 12 h continuous reaction showed that conversion of propanoic acid changed slightly when furan was co-fed with propanoic acid, while decreased significantly from 100 % for sole propanoic acid feeding to <55 % when co-feeding with furfural and furfuralcohol. Therefore, the inhibition ability followed the order of furfural ≈ furfuralcohol ≫ furan, which agreed well with the coke yield on the spent catalysts (51 %, 47 %, and 22 %, respectively). DFT calculation indicated that furfural and furfuralcohol, with the adsorption energy of 17–19 kJ·mol−1, were much easier to adsorb on the catalyst than furan (11 kJ·mol−1). However, the lack of α-H of these furanic compounds led to their conversion into aromatic coke components. It is evidenced that the oxygenated side groups, rather than the furan ring, are responsible for the inhibition effect. Successive ketonization-combustion-ketonization tests revealed that simple air calcination can hardly recover the activity of the spent CeO2. This investigation gives new insights into the inhibitory impact of furans on the ketonization activity.

Two-dimensional NiO nanosheets for efficient Congo red adsorption removal

Strategies for developing new adsorbents are necessary for more efficient processes to remove contaminants from wastewater. Thus, it is essential to adjust the synthesis parameters of the adsorbent nanomaterial to control the surface area and morphology and, therefore, enhance the adsorption performance. Herein, α-Ni(OH)2 nanosheets were synthesized via a simple and fast microwave-assisted solvothermal method and converted to NiO nanostructures by calcination in air. The effect of different calcination temperatures (range of 300–600 °C) on the morphology, crystal structure, and adsorption performance of Congo red (CR) was evaluated. The calcination of α-Ni(OH)2 at 300 °C resulted in 2D NiO nanosheets, which showed the best performance to remove CR dye due to the increased surface area and porosity provided by the 2D morphology. The nanosheet-like structure is lost with increasing the calcination temperature and the nanoparticles become bigger, consequently, the CR adsorption capacities are significantly reduced. The 2D NiO nanosheets can adsorb a significant amount of CR quickly, reaching equilibrium after only 120 min, indicating a high affinity between the adsorbate species and the surface of the adsorbent. Additionally, the adsorption isotherm was compatible with the Langmuir model, which provides a maximum calculated adsorption capacity of 259.74 mg g−1. Thus, our findings showed how to adequate the synthesis parameters to obtain NiO nanosheets and improve the adsorption parameters to CR, which can be extended to the fabrication of new materials to promote advances in sustainable technologies.

An aluminum-grafted SBA-15-catalyzed conversion of glucose to 5-hydroxymethylfurfural

Environmentally friendly processes for preparing catalysts and converting glucose into 5-hydroxymethylfurfural (HMF) were studied under water-based conditions. A series of aluminum-grafted SBA-15 mesoporous silica with Si/Al molar ratios of 1.5–20 was prepared by tuning aluminum precursors, solvents, and the pH values in grafting. Among them, the 3Al-S15-w-pH 8 catalyst with high acid capacity and mixed acid sites of Lewis and Brønsted acids was fabricated by adjusting the pH value of the water-soluble aluminum precursor to 8 in a water medium. Thus, it converted 87% of glucose at 160 °C for 5 h in the water medium with 33% HMF selectivity. Moreover, the used 3Al-S15-w-pH 8 catalyst was easily regenerated by calcination in air, which was further used for converting glucose to HMF without losing its performance. Our findings provide new ideas for environmentally friendly catalyst preparation and biomass conversion methods, which can be readily applied to catalysis and bio-refining processes.