Facile Heat Treatment Research Articles

Hollow CuCo-based trimetallic oxides derived from ZIF-67 as enhanced electrocatalysts for OER

Multimetallic oxide configuration and hollow structure construction are effective strategies for the design of efficient electrocatalysts, which can regulate the intrinsic properties of the active sites, enlarge the specific surface areas and expose more active sites. In this work, hollow-structured CuCo-based ternary metal oxides supported nitrogen-carbon networks (HS-CuMCoOx, M = Fe/Zn/Ni) derived from ZIF-67 hollow spheres were fabricated through facile ion exchange and heat treatment. The prepared composites possess hollow configurations with homogeneously dispersed trimetallic active species on the shells. Among all the ternary metallic derivatives, hollow spheres supporting Cu, Fe, and Co oxides (HS-CuFeCoOx) exhibited highest electrocatalytic activity towards oxygen evolution reaction (OER). The improved OER performance ascribed to the inherent electrocatalytic properties of the ternary metal active species and microstructure by hollow structure design and heat treatment, which offered an effective synthetic strategy for the fabrication of trimetallic oxide composites for as OER electrocatalysts.

Reconstructing delocalized π electron structure of C3N4 nanosheets for enhanced visible light photocatalytic hydrogen evolution

For improving the essential photocatalytic H2 evolution activity of C3N4, strategies via simultaneously modulating the delocalized π electron structure and defects are feasible but challenging. Herein, a C3N4 nanosheets material defined as C3N4-NS-RN with expansive delocalized π electron structure and enriched N vacancies was synthesized successfully via a facile post heat treatment. Firstly, a precursor of C3N4 nanosheets defined as C3N4-NS-PN with corrugate tri-s-triazine basal plane and abundant NHx groups in aromatic conjugate system was prepared. Fourier transform infrared spectra, X-ray photoelectron spectroscopy and nuclear magnetic resonance demonstrated C3N4-NS-PN had an enhanced delocalized π electron configuration via van der Waals coupling effect. However, the delocalization of π electrons across the basal plane was disturbed due to the corrugate conjugate plane. For further reconstructing delocalized π electron structure of C3N4-NS-PN, C3N4-NS-RN was synthesized via eliminating NHx groups and introducing enriched N vacancies in the conjugate system. Photoluminescence spectroscopy and electron paramagnetic resonance verified C3N4-NS-RN had an enhanced delocalized π electrons structure than C3N4-NS-PN. The photocatalytic H2 evolution activity of C3N4-NS-RN was steady and was about 1.8 and 6.1 times of C3N4-NS-PN and the bulk C3N4, respectively.

The mechanism of intrinsic peroxidase (POD)-like activity of attapulgite.

Natural attapulgite (ATP) is a promising substitute for existing artificial nanozymes due to its intrinsic enzymatic activity. However, the active center of ATP's inherent enzymatic activity has not yet been revealed, which limits its further design and activity optimization. Studying the active center of mineral materials can be extremely challenging due to their complexity. Here, we demonstrated that Fe is the primary element in ATP responsible for peroxidase (POD)-like activity through theoretical speculation and experimental verification. More importantly, we found that the ratio of Fe2+/Fe3+ is responsible for the district POD-like activity of ATP from different regions with the same Fe content. Additionally, three facile strategies, including grinding, heat treatment, and acid treatment, were demonstrated to increase the relative Fe content and thus optimize the POD-like activity of ATP. Finally, ATP was used to detect the concentration of H2O2, enabling the detection of low concentrations (0.11-1.76mM) of H2O2. This study serves as a novel reference for the future design and performance optimization of nanozymes that are based on ATP and clay minerals.

Local spatial polarization induced efficient electron transfer in fluorinated borocarbonitride for boosting CO2 photoreduction

CO2 photoreduction into highly value-added chemicals over metal-free h-BCN has emerged as a promising strategy to address the issue of global warming. However, the serious carrier recombination caused by disordered charger transfer has limited its practical application. To circumvent this issue, fluorine modified h-BCN were synthesized using a facile heat treatment method. The surface halogenation created local spatial polarized electric field, which facilitated the local charge separation and transmission efficiency. Among them, BCN-F-4 exhibited the best photocatalytic CO2 reduction activitiy with CO and CH4 yield of 25.38 and 14.11 µmol g−1h−1, respectively. The turnover number (TON) of BCN-F-4 reached up to 163.6 μmol g−1h−1, 4.4 times that of BCN. Both theoretical simulation and experimental analysis demonstrated a strong covalent interaction between the F atoms and the h-BCN matrix, which gain deep understanding of the mechanism of prominent photocatalytic CO2 reduction activity boosted by surface halogenation.

Molecular-level manipulation of polyamide membranes for high-performance H2/CO2 separation

The preparation of high-performance H2/CO2 polymer separation membranes is an urgent need to reduce the global greenhouse effect. Here, polyamide (PA) membranes with excellent H2/CO2 separation performance are produced using a facile interfacial polymerization (IP) plus heat treatment approach. The synergistic effect of the substrate-confinement and the control of the d-spacing and crosslinking degree of PA membranes creates sufficient H2 selective channels. The effects of test parameters such as feed temperature and feed pressure on membrane performance were investigated. The ultra-high H2/CO2 selectivity of 110 with excellent H2 permeance of 180 GPU is observed at 150 °C and feed pressure of 2 bar. In addition, PA membranes have high-pressure resistance (16 bar), high-temperature resistance (300 °C), and attractive durability (210 h). The excellent performance and facile preparation process make them expected to be one of the most promising membranes for H2/CO2 separation.

Three-dimensional cage based on porous Ni–Co–Cu phosphide as efficient and stable bifunctional electrocatalysts for overall water splitting

The development of cheap and high-performance dual electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an electrolyte is of great importance. Tuning the electronic structure through heteroatom doping and increasing the catalytic sites through designing the morphology of nanostructures are the most popular approaches to enhance electrocatalytic performance. In recent years, with the development of nanotechnology and interface engineering, significant progress has been made in this field, but it is still challenging. Here three-dimensional porous NiCoCu–P cage were synthesized using a quick and easy method with the help of 26-face Cu2O as a sacrificial template, then it was phosphidated by a facile phosphidation heat treatment in N2 atmosphere and then for the electrochemical evaluations, the glassy carbon electrode surface (GCE) surface was modified with it. Taking advantage of these strategies, NiCoCu–P cage offer large surface area, fast electron/mass transfer and open channels for efficient gas release, which show improved electrochemical performance in alkaline environment and achieved an overpotential of −210 mV at 10 mA cm−2 for HER and 240 mV at 50 mA cm−2 for OER. Also, an overall water splitting device is assembled by two symmetric NiCoCu–P cage/carbon cloth as cathode and anode, that can provide a current density of 100 mA cm−2 at a cell voltage of less than 1.6 V.

Chitosan-Pd0 nanoparticles encapsulated in Al, Co-pillared montmorillonite by one-pot process

Chitosan-Pd0 (CS-Pd0) nano particles encapsulated in Al, Co-pillared montmorillonite (MMt) nanocomposites were synthesized by a facile one-pot heat treatment method. The MMt was impregnated with Al, Co pillaring reagent, protonated chitosan solution, and Na2PdCl4 solution, followed with a controlled low-temperature (200 °C) heat treatment, resulting in Pd@CS/Al, Co-MMt nanocomposites. Al, Co pillaring effectively expanded the basal spacing of MMt layers from 1.24 nm to 1.82 nm, and generated numerous mesopores in interlayer space, resulting in increase of surface area from 11.8 m2/g to 198.3 m2/g. Due to the well encapsulation of CS chains in the interlayer nano-spaces, the specific surface area of the hybrid nanocomposite underwent a reasonably decrease as the CS content increase. Most of nano-sized Pd species (2–3 nm) chelated with CS chains dispersed well in the interlayer space of the porous Al, Co pillared MMt matrix. The resultant nanocomposite prepared by such facial one-pot process method have similar high comprehensive catalytic performances as applied in coupling reactions to that prepared by regular divided-multistep method. Moreover, it is confirmed that Al pillaring doped with Co and encapsulation of CS chains have synergistic improving effects on the comprehensive catalytic performance of the nanocomposites.

Constructed electron-dense Mn sites in nitrogen-doped Mn3O4 for efficient catalytic ozonation of pyrazines: Degradation and odor elimination

In this study, N-doped Mn3O4 catalysts (Mn-nN) with electron-dense Mn sites were synthesized and employed in heterogeneous catalytic ozonation (HCO). These catalysts demonstrated excellent performance in pyrazines degradation and odor elimination. The synthesis of Mn-nN was achieved through a facile urea-assisted heat treatment method. Experimental characterization and theoretical analyses revealed that the MnN structures in Mn-nN, played a crucial role in facilitating the formation of electron-dense Mn sites that served as the primary active sites for ozone activation. In particular, Mn-1N exhibited excellent performance in the HCO system, demonstrating the highest 2,5-dimethylpyrazine (2,5-DMP) degradation efficiency. •OH was confirmed as the primary reactive oxygen species involved in the HCO process. The second-order rate constants for 2,5-DMP degradation with O3 and •OH, were determined to be (3.75 ± 0.018) × 10−1 and (6.29 ± 0.844) × 109 M−1 s−1, respectively. Seventeen intermediates were identified through GC-MS analysis during the degradation of 2,5-DMP via HCO process with Mn-1N. The degradation pathways were subsequently proposed by considering these identified intermediates. This study introduces a novel approach to synthesize N-doped Mn3O4 catalysts and demonstrates their efficacy in HCO for the degradation of pyrazines and the elimination of associated odors. The results show that the catalysts are promising for addressing odor-related environmental issues and provide valuable insights about the broader significance of catalytic ozonation processes.

Synthesis and broadband electromagnetic wave absorption for lightweight porous SiC/Si3N4 composite nanowires

As contemporary aerospace and radar-detecting technologies evolve, hypersonic vehicle components must avoid electromagnetic wave (EMW) detection in extremely harsh environments. In this study, lightweight porous SiC/Si3N4 composite nanowires (SiC/Si3N4 NWs), exhibiting excellent performance of broadband electromagnetic wave absorption (EWA), were successfully prepared via a facile electrostatic spinning and heat treatment in nitrogen atmosphere using phenol-formaldehyde resin (PR) and silica solution as precursors. The nanowire (NW) was composed of carbon-rich SiC and Si3N4 nanograins, and its microstructure and phase composition were regulated by carbon thermal reduction temperature. The EWA performance of the nanowires obtained through carbothermal reduction at 1300 °C, 1400 °C，and 1500 °C was investigated. The nanowires with 15 wt% obtained at 1500 °C were added to a paraffin matrix and the effective absorption bandwidth (EAB) was observed to cover almost the entire C, X, and Ku bands (4.2–18 GHz). Moreover, for a coating thickness of only 2.1 mm, the EAB was as high as 7.12 GHz (10.88–18 GHz), covering the entire Ku-band and achieving a minimum value of reflection loss (RLmin) of - 48 dB at 6.5 GHz. The 3D network structure of SiC/Si3N4 NWs with large specific surface areas and numerous mesopores extended the electromagnetic wave (EMW attenuation route and effectively improved the EWA performance through interfacial synergy between the carbon-rich SiC and Si3N4 nanograins). The strong absorption and wide EAB of the porous SiC/Si3N4 NWs rendered them highly suitable lightweight EMW absorbers in harsh, high-temperature environments.

Facile Preparation of Dense Polysulfone UF Membranes with Enhanced Salt Rejection by Post-Heating.

Polysulfone (PSf) membranes typically have a negligible rejection of salts due to the intrinsic larger pore size and wide pore size distribution. In this work, a facile and scalable heat treatment was proposed to increase the salt rejection. The influence of heat treatment on the structure and performance of PSf membranes was systematically investigated. The average pore size decreased from 9.94 ± 5.5 nm for pristine membranes to 1.18 ± 0.19 nm with the increase in temperature to 50 °C, while the corresponding porosity decreased from 2.07% to 0.13%. Meanwhile, the thickness of the sponge structure decreased from 20.20 to 11.5 μm as the heat treatment temperature increased to 50 °C. The MWCO of PSf decreased from 290,000 Da to 120 Da, whereas the membrane pore size decreased from 5.5 to 0.19 nm. Correspondingly, the water flux decreased from 1545 to 27.24 L·m-2·h-1, while the rejection ratio increased from 3.1% to 74.0% for Na2SO4, from 1.3% to 48.2% for MgSO4, and from 0.6% to 23.8% for NaCl. Meanwhile, mechanism analysis indicated that the water evaporation in the membranes resulted in the shrinkage of the membrane pores and decrease in the average pore size, thus improving the separation performance. In addition, the desalting performance of the heat-treated membranes for real actual industrial wastewater was improved. This provides a facile and scalable route for PSf membrane applications for enhanced desalination.

Microstructural evolution during annealing of a powder metallurgical TiAl–Nb composite and its effect on mechanical properties

Ductile Nb particles have been applied to toughen TiAl-based intermetallic alloys due to the positive effects of the Nb element on their mechanical and processing properties. However, the room-temperature (RT) fracture toughness of powder metallurgical (PM) TiAl–Nb composites needs further improvement to avoid micro-cracks in complex components prepared by PM near-net shape technologies. Herein, a facile heat treatment—annealing in the (α+γ) phase region for a short duration and air-cooling—was applied to strengthen and toughen a PM TiAl–Nb composite. The phase and microstructure evolution of the PM composite during annealing, and their effects on mechanical properties and fracture behaviors, were investigated specifically. It is found that after annealing, the volume fraction of α2 phase increased markedly, while that of the B2 phase decreased significantly, and the Nb solid solution (Nbss) phase almost completely disappeared; the microstructures of the TiAl–Nb composite became significantly finer and more uniform overall, and the microstructure type of the TiAl matrix transformed from near-gamma (NG) to duplex (DP). Both the RT tensile strength and fracture toughness of the TiAl–Nb composite improved markedly after annealing. The strengthening mechanisms for the as-annealed composite were primarily based on the phase and microstructure evolution. The toughening mechanisms for the as-annealed composite included the generation of shear ligaments, delaminations, crack deflection and branching. The improvement in tensile strength and the reduction in work-hardening exponent made the composite tougher through facile annealing. The incorporation of Nb particles and further heat treatment can efficiently facilitate the improvement in fracture toughness of PM TiAl-based alloy.

Oxygen vacancies-dominated reactive species generation from peroxymonosulfate activated by MoO3−x for pollutant degradation

Interface oxygen vacancies (OVs) are commonly used to improve the catalytic performance of activators in persulfate-based advanced oxidation processes, but the underlying mechanism was not fully explored. This work reports a facile heat treatment method to regulate OVs in MoO3−x to elucidate the mechanism of peroxymonosulfate (PMS) activated by OVs to degrade 2,4,4-Trichlorobiphenyl (PCB28). Electron spin resonance, free radical quenching, X-ray photoelectron spectroscopy, and Raman spectroscopy confirmed that both reducing Mo species and OVs of MoO3−x surface were responsible for PMS activation. Further experiments and Density Function Theory (DFT) calculation suggest that OVs in MoO3−x induced the formation of superoxide radical (O2•−), and then O2•− was transformed into singlet oxygen (1O2) or mediated PMS activation to generate radicals, which contritbued to 70.2% of PCB28 degradation. The steady-state concentrations of free radical calculated with the kinetics model show that OVs were more favorable to mediate PMS to generate hydroxyl radicals (•OH) under oxic conditions, while reducing Mo species would like to induce PMS to produce sulfate radicals (SO4•−). Overall, this study is dedicated to a new insight into the in-depth mechanism of PMS activation by OVs-rich catalysts and provides a novel strategy for reactive species regulation in PMS based oxidation process.

Thermal treatment effect on electrochemical properties of silicon alloy anodes with poly(ether imide) binder for lithium-ion batteries

The development of silicon-based anodes with high capacity and good cycling stability for next-generation Li+ batteries (LIBs) is a very challenging task due to the large volume expansion of the electrodes during repeated cycling, which leads to fading in capacity. In this study, the electrochemical performance of Si alloy-based anodes with poly (ether imide) (PEI) binder is evaluated after thermal treatment at various temperatures. The systematic study revealed that the thermal treatment of the anodes with PEI binder at above 500 °C results in the partial carbonization of the PEI and remarkably enhances the electrochemical performance, such as cycle life and high rate capabilities. The partially carbonized PEI acts as both a binder and conductive additive for the Si-alloy anodes. This superior electrochemical performance is attributed to the strong adhesion of the partially carbonized PEI binder resulting from enhanced secondary interactions, which maintained good electrical contacts between the active materials, electronic conductors, and current collector during cycling. The partial carbonization strategy can be readily scaled up due to the facile heat treatment process, offering a new approach for developing next-generation high-capacity batteries.

Construction of new conductive networks for expandable graphite-based cement composites via a facile heat treatment process

Electro-thermal applications of cement composites are restricted by their poor conductivity. This study expands the homogeneously distributed graphite inside the matrix via a facile heat treatment process to form new conductive networks, thus endowing the cement composites with excellent conductivity. The obtained cement composites exhibit excellent electro-thermal performance and reliable cyclic heating properties. The average surface temperature of the composite is approximately 417 °C under 20 V, with uniform heat distribution. The surface temperature of the composites can be controlled by the expanded graphite content and applied voltage. Furthermore, the obtained cement composite melts 150 g ice cubes in 12 min under 12 V, thus exhibiting excellent deicing performance. The excellent electro-thermal performance facilitates the usage of cement composite in Joule heating applications, such as indoor climate control, pavement deicing, and cooking, thus considerably broadening the applications of cement and concrete composites for a sustainable and resilient future.

Biomimetic and flexible high-performance carbon paper prepared by welding three-dimensional carbon fiber network with polyphenylene sulfide spherical sites for fuel cell gas diffusion layer

High-performance carbon fiber paper (CFP) is usually an important part of the fuel cell gas diffusion layer (GDL). However, the preparation of CFP for GDL is still a challenge due to its arduous preparation process. Here, inspired by the structure of bird's nest in nature, we present the original design of PPS spherical sites welding three-dimensional (3D) carbon fiber network to produce high-performance CFP by facile wet papermaking and heat treatment. With a 3D CF network as the skeleton and PPS spherical sites as the welding points, CFs/PPS composite paper exhibits good mechanical strength and outstanding flexibility. Meanwhile, the excellent conductivity (6.8 S/cm) is integrated with super-hydrophobic performance, electrothermal performance (Tmax = 365 °C), heat resistance (DTGmax>575 °C), and corrosion resistance, becoming a high-performance multifunctional CFP. The mythical combination of these properties makes CFs/PPS composite paper an ideal candidate in the field of fuel cell GDL. In addition, the evolution of chemical structure of CF/PPS during carbonization is emphasized, which is of great significance for the properties of composite paper. This work presents a leap forward in the preparation of multi-property high-performance CFP in a simple method and is a key step toward exploring how the structural changes of CFs/PPS composite paper can be understood during carbonization.

Nickel cobaltite nanowire arrays grown on nitrogen-doped carbon nanotube fiber fabric for high-performance flexible supercapacitors

Flexible supercapacitors have received considerable attention for their potential application in flexible electronics, but usually suffer from relatively low energy density. Developing flexible electrodes with high capacitance and constructing asymmetric supercapacitors with large potential window has been considered as the most effective approach to achieve high energy density. Here, a flexible electrode with nickel cobaltite (NiCo2O4) nanowire arrays on nitrogen (N)-doped carbon nanotube fiber fabric (denoted as CNTFF and NCNTFF, respectively) was designed and fabricated through a facile hydrothermal growth and heat treatment process. The obtained NCNTFF-NiCo2O4 delivered a high capacitance of 2430.5 mF cm−2 at 2 mA cm−2, a good rate capability of 62.1 % capacitance retention even at 100 mA cm−2 and a stable cycling performance of 85.2 % capacitance retention after 10,000 cycles. Moreover, the asymmetric supercapacitor constructed with NCNTFF-NiCo2O4 as positive electrode and activated CNTFF as negative electrode exhibited a combination of high capacitance (883.6 mF cm−2 at 2 mA cm−2), high energy density (241 μW h cm−2) and high power density (80175.1 μW cm−2). This device also had a long cycle life after 10,000 cycles and good mechanical flexibility under bending conditions. Our work provides a new perspective on constructing high-performance flexible supercapacitors for flexible electronics.

Improved barrier effect of hierarchical micro-nano precipitate framework in magnesium-aluminum alloy for corrosion mitigation

The galvanic effect of second phases in Mg alloys often does harm to corrosion resistance. Here, a hierarchal micro-nano β phase framework is proposed to improve the barrier effect of the second phase in high-aluminum-containing Mg-Al alloy, which can be achieved through facile heat treatment. Compared to pristine and solid-solution-processed β phases, this designed β phase framework effectively mitigates the corrosion in 0.6 M NaCl solution because of the formation of a brick-and-mortar structured corrosion product layer.

Facile synthesis of C, N, P co-doped SiOx as anode material for lithium-ion batteries with excellent rate performance

SiOx has high specific capacity for lithium-ion batteries, but the rate and the cycling performances need to be further improved to satisfy the needs of the future. In this study, the C, N, P doping SiOx/G@CNP anodes are prepared by a facile ball milling and heat treatment process. The electrochemical performances of SiOx are improved by the synergistic effect of C, N, P doping. The SiOx/G@CNP-2 anode with the addition of 20 wt% phytate shows the best electrochemical performances and maintains a specific capacity of 77.45% after 150 cycles at 0.2 A·g−1. Importantly, it exhibits a remarkable rate performance with specific capacities of 528.2 mAh·g−1 and 370.0 mAh·g−1 even at 3.0 and 5.0 A·g−1, respectively. Artificial graphite and the carbon shell formed by the thermal decomposition of citric acid contribute to the structural stability of SiOx and improve the cycling performance of the material. Moreover, the addition of P element and high content of pyridine N accelerates the rate of Li+ deintercalation, and the conductivity and ion diffusion coefficient of the material are effectively promoted, thus greatly improving the rate performance of the material. This work presented herein provides a simple and feasible method for the preparation of high-performance anode materials.

Electronic interconnected CoV2O6 to induce boosted reaction kinetics for highly stable sodium-ion half/full batteries

It is one of the most common methods to improve the performance of sodium-ion batteries (SIBs) by improving the anodes. Vanadium metal oxides, including cobalt vanadate, are potential substitute as new anode material for SIBs due to their high theoretical capacity, variable crystal structure, synergistic effect and interfacial effect between multiple metals. However, although the specific capacity of such anode material is high, the irreversible capacity is often caused by the phase transition process in the charging and discharging process, which leads to a large amount of capacity attenuation. In addition, poor conductivity also limits the rate performance. In this work, bimetallic CoV2O6 (CVO) nanoparticles were modified by using two-dimensional (2D) reduced graphene oxide (rGO) with facile hydrothermal and heat treatment method. Via this construction, the CVO-rGO owns the advantage of porous electronic interconnected network structure, favoring the Na ions/electrons transportation, and suppressing the phase transition during Na+ (de)insertion. Benefiting from the built structure of CVO-rGO, it exhibits excellent performance in SIBs half and full cells. Specifically, CVO-rGO delivers stable 980 mAh g−1 at 0.1 A g−1 after 500 cycles and 98% capacity retention after 1000 cycles at 1 A g−1. Moreover, as anode in SIBs pouch cell, 84.7 mAh g−1 at 2 A g−1 after 1000 cycles (specific capacity retention: 90.3%) can be achieved. Such superior sodium storage of CVO-rGO is confirmed by reaction kinetics analysis and ex-situ XPS/Raman characterization. This work provides a reference for cobalt vanadium oxide to be used as anode material for high performance SIBs.

Interface engineering of crystalline/amorphous Pt/TeOx nanocapsules for efficient alkaline hydrogen evolution

Hydrogen evolution reaction (HER) is an important process in electrochemical energy technology, and efficient electrocatalysts are of great significance for renewable and sustainable energy conversion. Here, we report a facile hydrothermal and heat treatment process to synthesize a series of Pt-based nanocapsules (NCs) as an effective hydrogen evolution catalyst. The Pt/TeOx NCs exhibit excellent HER activity in an alkaline medium. The Pt/TeOx NCs only need the overpotential of 33 mV to achieve the current density of 10 mA cm−2, and the Tafel slope was as low as 29 mV dec−1, which was even better than that of commercial Pt/C. Detailed experimental characterizations demonstrate that the interface between the crystalline Pt/amorphous TeOx and the strong electron transfer contribute to alkaline HER activity. This work opens up a new direction for the preparation of efficient catalysts for electrocatalytic reactions or other conversion filed.