Two-step Calcination Research Articles

Effect of SiO2 Coating on Microstructure and Electrochemical Properties of LiNi0.5Mn1.5O4 Cathode Material

Abstract We present a simple method for producing SiO2-modified LiNi0.5Mn1.5O4 (LNMO) cathode materials. Manganese carbonate was directly mixed with nickel nitrate and lithium hydroxide, and a spherical structure LNMO cathode material was prepared by two-step calcination, then ethyl orthosilicate and LNMO powder were simply mixed in solid and liquid phases to prepare SiO2-coated LNMO material. The effect of SiO2 coating on the structure of LNMO was studied by diffraction of X-rays, scanning electron microscope (SEM), transmission electron microscope (TEM), and thermogravimetric analysis and differential scanning calorimetry. An amorphous SiO2 coating layer developed on the surface of the LNMO particles in the modification and this could alleviate the strike of hydrogen fluoride (HF) caused by electrolyte decomposition as well as the development of a solid electrolyte interphase. The electrochemical performance of the coated material was as follows: when the amount of SiO2 was 0 wt%, 1 wt%, 2 wt%, and 3 wt%, the initial discharge capacity of the sample was 98.2, 84.1, 101.3, and 89.8mAh/g, respectively. After 50 charge−discharge cycles, the capacity retention rates are 92.7%, 66.8%, 97.9%, and 93.8%, respectively. The cyclic stability of the samples can be significantly improved when the SiO2 coating amount is 2 wt% and 3 wt%, indicating that SiO2 coating can not only improve the discharge-specific capacity of the material but also improve its cyclic stability.

Ceria-based quantum dots/nanorods supported metallic cobalt for efficient photocatalytic hydrogen production

The concentration of photogenerated electrons on support surface has a significant impact on the photocatalytic performance of the corresponding catalyst. Herein, the CeO2-based homojunction support consisted of quantum dots/nanorods (QDs/NRs) was fabricated by two-step calcination with assistance of KCI and NaCl. Based on CeO2-QDs/NRs support, the Co-based catalyst exhibited excellent catalytic performance for photocatalytic hydrogen evolution from Ammonia Borane (NH3BH3). The catalysts exhibited the highest activity with TOF 96.15 min−1 under optimized conditions, which was significantly improved compared Co/CeO2 NRs (68.5 min−1). Detailed structure characterizations revealed that the QDs with size range from 2 to 5 nm grow on the surface of NRs, which had capacity to transfer more photogenerated electrons from the bulk to surface compared with pristine CeO2 NRs. Meanwhile, work function was upshifted from CeO2 NRs to CeO2-QDs/NRs. The synergy of two factors drove more electrons transfer from CeO2-QDs/NRs to active metal Co, accelerating the adsorption and activation of NH3BH3. In addition, the forming mechanization QDs by inducing the morphological evolution of CeO2 nanoparticles was also investigated. This work not only provides efficient photocatalyst for H2 evolution from NH3BH3 but also provides new insights into the design and preparation efficient QDs-based homojunction catalyst.

Selective degradation of organic micropollutants by activation of peroxymonosulfate by Se@NC: Role of Se doping and nonradical pathway mechanism

In this study, Se@NC-x decorated with Se was successfully prepared via two-step calcination with zeolitic imidazole framework (ZIF) as a precursor. Mechanistic studies show that PMS would be adsorbed onto the surface of Se@NC-900 to form an active complex (Se@NC-900/PMS*), and the active Se@NC-900/PMS* could oxidize phenol by the rapid decomposition of PMS. Specifically, electrons are extracted by Se@NC-900/PMS* and then transferred to the surface of Se@NC-900, which can trigger the degradation of phenol. Notably, it is found that the local charge redistribution caused by the doping of Se can activate the catalytic potential of the intrinsically inert carbon skeleton through density flooding theory (DFT) calculations. The XLogP, ΔE, VIP, and ELUMO (Se@NC/PMS)-HOMO (pollutants) and degradation rate constants of different micropollutants were correlated well linearly. This indicates that the Se@NC-900/PMS system has a great selectivity for the degradation of pollutants. Overall, these findings not only illustrate the role of Se in tuning the electronic structure of Se@NC-x to enhance the activation of PMS, but also bridge the gap in our knowledge about the physicochemical properties and degradation performance of Se@NC catalysts.

Selective hydrodeoxygenation of guaiacol to cyclohexanol over core-shell Cox@C@Ni catalysts under mild condition

Guaiacol, a typical lignin-derived phenolic compound, can be converted to high value-added cyclohexanol through hydrodeoxygenation (HDO). In this work, a series of core-shell Cox@C@Ni catalysts were prepared via two-step hydrothermal and calcination treatments, and applied to catalyze guaiacol to cyclohexanol. Compared with Co@C catalyst, core-shell Cox@C@Ni catalysts exhibited much better catalytic performance. Almost 100% guaiacol conversion and 90% cyclohexanol selectivity were achieved over Co1.2@C@Ni catalyst at 220 °C, 0 MPa N2 for 2 h using isopropanol as H-donor solvent, which was carried out under much milder conditions compared with previous research. The structure feature of core-shell Cox@C@Ni catalysts were analyzed by BET, XRD, SEM, TEM, HRTEM, etc. The catalyst compositions and acidities played a significant role on hydrodeoxygenation of guaiacol via ICP and NH3-TPD analysis. The influences of reaction temperature, reaction time and initial nitrogen pressure were also investigated to explore the optimal reaction condition. Moreover, the possible reaction pathways and reaction mechanism was deduced based on the product distributions and physicochemical properties.

In Situ Growth of Mo2C Crystals Stimulating Sodium-Ion Storage Properties of MoO2 Particles on N-Doped Carbon Nanobundles

Sodium-ion batteries (SIBs) are considered as the candidate for the upcoming large-scale energy storage systems. However, transition-metal oxides still have the problem of insufficient utilization of active sites, mainly signified by the low practical capacity in long cycles. Here, the composite (MoO2@Mo2C/C) of Mo2C crystals in situ grown in N-doped carbon nanobundles (N-CNBs) with MoO2 particles on their surface is designed by self-polymerization and two-step calcination. Through a series of characterizations and tests, it is found that the N-CNBs endow the composite with improved conductivity and reinforced structural stability and effectively alleviates the volume expansion and structural collapse of MoO2 particles. The high integration of Mo2C crystals with MoO2 particles/N-CNBs (Mo2C/C) further enhances the charge-transfer ability and structural stability for the composite. Importantly, the storage sites of MoO2 particles and Mo2C crystals are gradually activated during sodium-ion storage, significantly improving the effective capacity in the long cycles. After 8000 cycles at 5.0 A g–1, the reversible capacity of MoO2@Mo2C/C as a SIB anode gradually increases from 126.2 to 419.1 mAh g–1, with a capacity retention of up to 332.4%. This study fully demonstrates the potential advantages of metal carbides in energy storage and can provide a good reference for the development of metal ion batteries.

Simultaneous removal of Cr(VI) and phenol in a dual-chamber photocatalytic microbial fuel with NiCo2O4/MoS2/GF photocathode

Efficient treatment and resource utilization of sewage are of great value for global sustainability. In this study, a composite photocathode was prepared by loading NiCo2O4 nanosheets and MoS2 nanoflowers to a graphite felt (GF)-based electrode through a two-step hydrothermal and calcination method. A photocatalytic microbial fuel cell (PMFC) was constructed using the NiCo2O4/MoS2/GF photocathode and carbon felt (CF) anode in a dual-chamber H-type battery. Cr(VI) and phenol were employed as target pollutants in the cathode chamber. The photoelectric performance of the NiCo2O4/MoS2/GF photocathode and the removal efficiency of the battery system were studied systematically. When a mixed solution of Cr(VI) and phenol was used, the removal rates of Cr(VI) and phenol after 24 h of light exposure were 8.13 % and 12.65 % higher than those when Cr(VI) or phenol was used alone, respectively. At the same time, the output power density of the battery in the mixed pollutants was 362.7 mW/m3, which was 45.78 % higher than that in the single Cr(VI) solution (248.8 mW/m3). The excellent performance of the PMFC was attributed to three reasons: (1) NiCo2O4 and MoS2 were simultaneously excited as two narrow-bandgap semiconductors, and the utilization rate of light energy was increased; (2) The Z-scheme heterojunction between NiCo2O4 and MoS2 improved the separation efficiency of the photoelectric carriers and retained the high valence band of NiCo2O4 and low conduction band of MoS2 to the greatest extent, which is crucial for the PMFC to achieve electronic export and double contaminant removal; and (3) the NiCo2O4 nanosheet and MoS2 nanoflower structures enhanced the contact between the catalysts and the pollutants.

Methanation of CO2 over High Surface Nickel/Aluminates Compounds Prepared by a Self-Generated Carbon Template

Catalytic gas-phase hydrogenation of CO2 into CH4 was tested under three different nickel/aluminate catalysts obtained from precursors of hexaaluminate composition (MAl16O19, M = Mg, Ca, Ba). These catalysts were prepared using a carbon template method, where carbon is self-generated from a sol-gel that contains an excess of citric acid and the Al and M salts (Ba2+, Ca2+, Mg2+) by two-step calcination in an inert/oxidizing atmosphere. This procedure yielded Ni particles decorating the surface of a porous high surface area matrix, which presents a typical XRD pattern of aluminate structure. Ni particles are obtained with a homogeneous distribution over the surface and an average diameter of ca 25–30 nm. Obtained materials exhibit a high conversion of CO2 below 500 °C, yielding CH4 as a final product with selectivity >95%. The observed trend with the alkaline earth cation follows the order NiBaAlO-PRx > NiCaAlO-PRx > NiMgAlO-PRx. We propose that the high performance of the NiBaAlO sample is derived from both an appropriate distribution of Ni particle size and the presence of BaCO3, acting as a CO2 buffer in the process.

Manipulating electronic structure and light absorption of carbon nitride via P-doping and local crystallization for efficient photocatalytic reduction of CO2

Graphitic carbon nitride (g-C3N4, CN) with high light harvesting and suppressed charge recombination is desired in photocatalytic reactions. Herein, locally crystalline CN (KP/CN) with photoresponse edge of 648 nm was synthesized by a two-step calcination method. First step was P-doping via calcining phytic acid and nitrogen-containing precursor. Another was local crystallinity tailoring via calcining with KSCN. The obtained KP/CN facilitated the n → π* electronic transition, exhibited improved light utilization and charge mobility. Theoretical calculations confirmed that CO2 adsorption and activation became easy on KP/CN-2. The yields of CO and CH4 under KP/CN catalysis were 58.7 and 29.0 μmol g−1, respectively, after 5 h in the presence of 0.5 mL water. This work demonstrated the synergistic enhancement of light absorption and charge carrier dissociation via doping and partial crystallization.

The influence of B heteroatom concentrations on the physiochemical properties of N, B-co-doped biochar for peroxymonosulfate activation in ciprofloxacin removal

N, B-co-doped biochars with varying boric acid (BA):urea mass ratio were prepared by two-step calcination of sawdust (NB-BC-x, where x = 1, 2, and 3 corresponds to the BA:urea mass ratio of 0.025:1, 0.05:1, and 0.1:1, respectively) and characterized. Generally, B doping prior to N doping can improve N doping because the presence of oxidized B during N doping can interact with NH3, facilitating N doping. The performance of NB-BCs in PMS activation for ciprofloxacin (CIP) removal was evaluated and it was found that the kapp increased in the order of: N-BC (0.010 min−1) < B-BC (0.016 min−1) < NB-BC-2 (0.031 min−1) < NB-BC-3 (0.039 min−1) < NB-BC-1 (0.053 min−1). Due to its large specific surface area and synergistic interaction between N and B moieties, NB-BC-1 presented the best PMS activator, achieving CIP removal of ∼45 and ∼80 % by adsorption and degradation in 60 min, respectively. Further performance study using NB-BC-1 revealed that the kapp increased with increasing catalyst loading and PMS dosage. Meanwhile, higher pH can reduce the CIP removal efficiency due to the electrostatic repulsion between NB-BC-1 and PMS. It was also demonstrated that NB-BC-1 can be reused and regenerated after deactivation using thermal treatment at 500 °C. From the chemical scavengers and electrochemical studies, it can be deduced that NB-BC-1 activates PMS through both radical and nonradical pathways. Lastly, the degradation pathway of CIP was also proposed by identifying the degradation intermediates and their toxicity were accessed. Overall, this study showed that NB-BC-1 can potentially be used as a PMS activator for wastewater treatment.

Effect of Fe3+ and/or PO43– Doping on the Electrochemical Performance of LiNi0.5Mn1.5O4 Cathode Material for Li-Ion Batteries

An Fe3+/PO43– codoped LiNi0.5Mn1.4667Fe0.02P0.0133O4 sample has been prepared by a coprecipitation–hydrothermal method followed by two-step calcination. A novel wet chemical route, using FeSO4 rather than Fe2(SO4)3 as the Fe3+ source and NaH2PO4 as the PO43– source, is adopted to obtain uniform codoping of Fe3+ and PO43– ions in a carbonate precursor according to the precipitation–dissolution–transformation mechanism. For comparison, Fe3+-doped and PO43–-doped samples have been also synthesized via the same route. The effects of Fe3+/PO43– codoping and single doping on the crystalline structure, morphology, and electrochemical performance of LiNi0.5Mn1.5O4 are investigated. Compared with pristine and single doped samples, the codoped sample shows better electrochemical performance, with a specific discharge capacity of 125.2 mAh g–1 at 10 C and a capacity retention rate of 85.9% after 200 cycles at 1 C, under the synergy of Fe3+/PO43– codoping, including enhanced crystallinity, decreased Mn3+ content, significantly reduced primary particle size and secondary agglomeration, as well as the appearance of (110) surfaces in truncated octahedral primary particles.

Impact of two-step calcination on microstructure, phase, electronic, and dielectric properties of KCa2Nb3O10 bulk layered perovskite

ABSTRACT The effects of varying calcination temperature, K content, and the number of calcination steps in the dielectric performance of KCa2Nb3O10 synthesized via solid-state reaction are investigated. Adding an extra calcination step at 500°C followed by another calcination at 1100°C suppressed the formation of secondary phases while maximizing the relative density (95%) and the average grain area (2.12 μm2). The first calcination at 500°C ensures the formation of intermediate phases (KNbO3 and Ca2Nb2O7), which are prerequisites for single-phase KCa2Nb3O10 synthesis. A significantly high dielectric constant of 352 at 100k Hz is achieved in the two-step calcined sample despite the low sintering temperature of 1250°C. The highest resistivity of the two-step calcined sample (2 × 108 Ω cm) obtained from complex impedance analysis supports its lowest dielectric loss (0.034 at 100k Hz). When the two-step calcined KCa2Nb3O10 powder is exfoliated, much higher dielectric properties of Ca2Nb3O10 nanosheets are expected.

Effect of Two-Step Calcination on Specific Surface Area and Morphology of Graphitic Carbon Nitride

Effect of Two-Step Calcination on Specific Surface Area and Morphology of Graphitic Carbon Nitride

Ultrahigh-performance hybrid supercapacitors based on sodium sulfate template-derived electrodes with surface modulation

Exploring efficient and durable electrode materials is crucial for the mature application of high-performance hybrid supercapacitors. Herein, the Fe3O4/Fe nanoparticles with surface phosphate ions modulation (P-Fe3O4/Fe) are successfully deposited on the two-dimensional carbon nanosheets (CNS) through a solid-state sodium sulfate template-directed two-step calcination strategy. Benefiting from the synergistic effect of each component and the unique two-dimensional architecture, the prepared P-Fe3O4/Fe/CNS delivers excellent energy storage features with splendid specific capacitance (427.4 F g−1 at 1 A g−1) and outstanding cycling stability at 15 A g−1 (90.8% retention after 10,000 cycles). Following, phosphate functionalized Co9S8/CoS (P-Co9S8/CoS) nanoparticles anchored on CNS are also fabricated by the same synthesis route, which deliver a maximum specific capacity of 544.6 C g−1 at 1 A g−1 and long cyclic retention of 91.6% after 10,000 cycles at 15 A g−1. By coupling with P-Fe3O4/Fe/CNS and P-Co9S8/CoS/CNS electrodes, the assembled P-Co9S8/CoS/CNS//P-Fe3O4/Fe/CNS hybrid supercapacitor depicts an admirable energy density of 73.4 Wh kg−1 at 1041.7 W kg−1 in alkaline electrolyte and ultralong cycling stability up to 20,000 cycles with only 10.5% capacitance decay. Furthermore, the red light-emitting diode (LED) can be successfully operated for up to 45 min by the series connection of the two devices. This work proposes an efficient strategy to construct ultrahigh-performance hybrid supercapacitors with advanced sodium sulfate template-derived electrodes by phosphate functionalization.

Fabrication of BaTiO3 nanopowders with high tetragonality via two-step assisted rotary furnace calcination for MLCC applications

Ultrafine ceramic powders with high tetragonality are essential for next-generation multi-layer ceramic capacitors (MLCC). The solid-state reaction synthesis commonly used in industry is challenging to prepare ultra-fine BaTiO3 powders due to issues of the coarse crystallization at high temperature calcinations. In this study, a two-step calcination combining with the rotary furnace was innovatively used to synthesize ultra-fine BaTiO3 powders with uniform particle and high tetragonality. Through the reaction kinetics study, it was found that the rotary furnace increases the point contact area of Ba2+ and Ti4+ by improving the heat transfer efficiency of the solid-phase reaction and decreases the diffusion rate of both, so that the diffusion-nucleation-growth rate is greater than the decomposition rate of BaCO3 to improve the tetragonality of BaTiO3 powders. The optimal process parameters were determined and the reaction mechanism was studied. Particularly, the optimized two-step assisted rotary furnace calcination had succeeded in preparing finer powders with an average particle size of 250 nm and tetragonality (c/a) of 1.0096. The BaTiO3 ultrafine powders sintered at 1200 °C has a ceramic density of 96%, dielectric constant of 9173 at the Curie temperature point (131 °C) and a grain activation energy of 0.821 eV, representing excellent dielectric properties and reliability.

ZIF-L-derived C-doped ZnO via a two-step calcination for enhanced photocatalytic hydrogen evolution

Metal organic frameworks (MOFs) are considered as desirable precursors for the preparation of photocatalyst to improve photocatalytic hydrogen evolution efficiency due to the maintained special morphology. Herein, C-doped rod-like ZnO with porous structure has been successfully prepared by using ZIF-L as precursor via an optimized two-step calcination strategy, which is applied for photocatalytic hydrogen evolution reaction from water splitting. The results show that ZnO-350-450 exhibits the best photocatalytic activity with a hydrogen production rate of 0.35 mmol·g−1·h−1, which is 1.9 times higher than that of ZnO-400 (0.184 mmol·g−1·h−1) under simulated sunlight illumination. The enhanced photocatalytic performance is attributed to the fact that the two-step calcination provides the regular porous rod-like structure (ZIF-L) and the inclusion of carbon in ZnO photocatalyst. C-doped ZnO with regular morphology offers faster charge transfer rate and higher charge separation efficiency, and the C-doped expands a wider range of light absorption. Overall, the presented work could provide a new idea for designing and preparing of photocatalysts with high efficiency for photocatalytic hydrogen production.

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.

Highly Enhanced Photocatalytic Hydrogen Production Performance of Heterostructured Ti3C2/TiO2/rGO Composites.

There has been a dire need for the exploration of renewable clean hydrogen energy recourses in recent years. In this work, we investigated the photocatalytic hydrogen production of heterostructured Ti3C2/TiO2/rGO composites. Ti3C2/TiO2/rGO heterojunction nanocomposites were synthesized using two-step calcination and hydrothermal methods, and the optimum in situ growth ratio of TiO2 of 71.8% (nTi-O/nTi) and rGO mass ratio (mRGO/mTiO2/mTi3C2) of 12% were obtained. The target photocatalyst presented an outperforming photocatalytic hydrogen production performance of 1671.85 μmol·g-1 hydrogen production capacity in 4 h, with the maximum hydrogen production rate of 808.11 μmol·g-1·h-1 in the first hour being 3.08 times the maximum hydrogen production rate of bare TiO2 (262.66 μmol·g-1·h-1). The excellent hydrogen production performance was due to the formed rutile TiO2 and the constructed heterojunction of Ti3C2/TiO2/rGO, where rGO provided different electron transport channels, and made charge transfer easier, and restrained the recombination efficiency of electrons and holes.

Synergistic Engineering of Defects and Architecture in a Co@Co3O4@N-CNT Nanocage toward Li-Ion Batteries and HER.

The design and synthesis of hollow and porous nanostructured electrode materials is an effective strategy to improve the electrochemical performance of lithium-ion batteries and the hydrogen evolution reaction (HER). Herein, we synthesize hollow and porous Co@Co3O4 nanoparticles embedded in N-doped CNTs (N-CNTs) with rich surface defects through a two-step calcination strategy. The formation mechanism is explored. The influence of oxygen vacancies regulated by the nanoscale Kirkendall effect on the electrochemical performance of the electrode is elucidated. The Co@Co3O4@N-CNTs exhibit remarkable activity for catalyzing the HER with a low onset overpotential of 296 mV (a low Tafel slope of 116.2 mV dec-1), much better than Co3O4@N-CNTs (315 mV for overpotential and 124.2 mV dec-1 for Tafel slope). Significantly, the Co@Co3O4@N-CNTs deliver a high discharge capacity of 990 mA h g-1 after 600 cycles at 0.1 A g-1. Our nanostructure strategy can provide new insights into the strategy for high-rate and highly stable energy storage systems.

Functional partition of Fe and Ti co-doped g-C3N4 for photo-Fenton degradation of oxytetracycline: Performance, mechanism, and DFT study

In this study, we synthesized Fe and Ti co-doped graphitic carbon nitride (FTCN) with high catalytic ability by a two-step calcination method. The photoelectrochemical results indicated that FTCN possessed a reduced bandgap and promoted photocarrier transfer efficiency, which enables FTCN excellent performance on oxytetracycline (OTC) degradation (90 % within 10 min). The main reactive oxygen species and the intermediates of OTC in the photo-Fenton process were obtained. Experimental data and density functional theory (DFT) were combined to explore the mechanism in depth. Interestingly, it was found that Fe and Ti respectively act as the main activation centers of H2O2 and O2, while few oxygen-containing metal active sites participate in the activation process. The synergistic effect of bimetallic doping plays a significant role in enhancing the photo-Fenton catalytic performance. Hopefully, a new approach to design highly efficient multifunctional catalysts or dual single-atom catalysts can be developed.

In-situ growth and excellent corrosion protection properties of molybdenum dioxide/boron nitride heterojunction composites

Molybdenum dioxide has been widely applied in various fields. Constructing novel molybdenum-dioxide-based heterojunction is prospective to expand the applications in metal corrosion protection. Herein, the novel molybdenum dioxide/boron nitride heterojunction composites were synthesized with a two-step calcination method. MoO2 nanoparticles were in-situ loaded on the surface of BN and formed a heterojunction structure. The total impedance values of MoO2/BN-1 (synthesized with melamine and boric acid) and MoO2/BN-2 (synthesized with urea, melamine and boric acid) coatings respectively increased to 314.7 % and 163.6 % of that of epoxy coating. It was attributed to synergistic effects consisted of the physical barrier effect, electron transport blocking effect and photo-induced corrosion protection effect. Synthesizing stabilized molybdenum oxide heterojunction with boron nitride carrier exhibited feasibility for practical corrosion protection application.