Two-step Thermal Treatment Research Articles

A Versatile Synthesis Platform Based on Polymer Cubosomes for a Library of Highly Ordered Nanoporous Metal Oxides Particles.

Polymer cubosomes (PCs) have well-defined inverse bicontinuous cubic mesophases formed by amphiphilic block copolymer bilayers. The open hydrophilic channels, large periods, and robust physical properties of PCs are advantageous to many host-guest interactions and yet not fully exploited, especially in the fields of functional nanomaterials. Here, the self-assembly of poly(ethylene oxide)-block-polystyrene block copolymers is systematically investigated and a series of robust PCs is developed via a cosolvent method. Ordered nanoporous metal oxide particles are obtained by selectively filling the hydrophilic channels of PCs via an impregnation strategy, followed by a two-step thermal treatment. Based on this versatile PC platform, the general synthesis of a library of ordered porous particles with different pore structures , tunable large pore size (18-78nm), high specific surface areas (up to 123.3m2g-1 for WO3) and diverse framework compositions, such as transition and non-transition metal oxides, rare earth chloride oxides, perovskite, pyrochlore, and high-entropy metal oxides is demonstrated. As typical materials obtained via this method, ordered porous WO3 particles have the advantages of open continuous structure and semiconducting properties, thus showing superior gas sensing performances toward hydrogen sulfide.

Bimetallic sulfide/N-doped carbon composite derived from Prussian blue analogues/cellulose nanofibers film toward enhanced oxygen evolution reaction.

Exploiting effective, stable, and cost-efficient electrocatalysts for the water oxidation reaction is highly desirable for renewable energy conversion techniques. Constructional design and compositional manipulation are widely used approaches to efficaciously boost the electrocatalytic performance. Herein, we designed a NiFe-bimetallic sulfide/N-doped carbon composite via a two-step thermal treatment of Prussian blue analogues/cellulose nanofibers (PBA/CNFs) film. The NiFe-bimetallic sulfide/N-doped carbon composite displayed enhanced OER performance in an alkaline environment, with an overpotential of 282 mV at 10 mA cm-2, a Tafel slope of 59.71 mV dec-1, and good stability, making the composite a candidate electrocatalyst for OER-related energy equipment. The introduction of CNFs in the precursor prevented the aggregation of PBA nanoparticles (NPs), exposed more active sites, and the resulting carbon substrate enhanced the electroconductivity of the composite. Moreover, the synergistic effect of Ni and Fe in the bimetallic sulfide could modulate the configuration of electrons, enrich the catalytically active sites, and augment the electric conductivity, thus ameliorating the OER performance. This study broadens the application of MOF-CNF composites to construct hierarchical structures of metal compounds and provides some thoughts for the development of cost-effective precious-metal-free catalysts for electrocatalysis.

Peroxymonosulfate conversion to singlet oxygen over π-electron delocalized carbon nitride for selective degradation of emerging contaminants

Graphitic carbon nitride is a promising catalyst for peroxymonosulfate (PMS) activation towards removal of emerging contaminants in water environment. However, the dependence on light and the non-selectivity of PMS activation pathway limit its practical applications. In this work, a two-step thermal treatment process was developed to modulate the π-electron delocalization degree of carbon nitride. The obtained modified carbon nitride (TCN) showed excellent capability on PMS activation without light, and simultaneously achieved high selectivity on the generation of non-radical species 1O2. Based on the results of quenching and probe experiments, isotopic solvent effect, as well as in-situ capture technique, the dominant contribution of 1O2 to the degradation of pollutants was clarified. The TCN/PMS system showed highly selective degradation of electron-donating pollutants, further demonstrating the dominant role of 1O2. Combining the control experimental results, PMS was speculated to be catalytically activated mainly through the spontaneous decomposition pathway. Further, according to the characterizations results and density functional theoretical calculations, it was the delocalized π-electrons at modified C-N heterocycles that accelerated the self-decomposition reactions of PMS. The high selectivity towards 1O2 endowed good resistance of TCN/PMS system in complex water matrices, achieving efficient removal of a number of emerging contaminants.

A Facile Two-Step Thermal Process for Producing a Dense, Phase-Pure, Cubic Ta-Doped Lithium Lanthanum Zirconium Oxide Electrolyte for Upscaling

An inorganic solid electrolyte is the most favorable candidate for replacing flammable liquid electrolytes in lithium batteries. Lithium lanthanum zirconium oxide (LLZO) is considered a promising solid electrolyte due to its safe operating potential window (0–5 V) combined with its good electrochemical stability. In this work, 250 g batches of pre-sintered Ta-doped LLZO (Li7La3Zr1.6Ta0.4O12, Ta-LLZO) were synthesized for bulk production of a dense LLZO electrolyte. A simple two-step thermal treatment process was developed. The first thermal step at 950 °C initiates nucleation of LLZO, with carefully controlled process parameters such as heating atmosphere, temperature, and dopant concentration. In the second thermal step at 1150 °C, sintered discs were obtained as solid electrolytes, with relative densities of 96%. X-ray diffraction analysis confirmed the phase purity of the sintered Ta-LLZO disc, and refined data were used to calculate the lattice parameter (12.944 Å). Furthermore, the presence of the Ta dopant in the disc was confirmed through X-ray photoelectron spectroscopy (XPS) analysis. The ionic and electronic conductivity values of the Ta-LLZO disc were 10−4 S cm−1 and 10−10 S cm−1, respectively. These values confirm that the prepared (Ta-LLZO) discs exhibit ionic conductivity while being electronically insulating, being suitable for use as solid electrolytes with the requisite electrical properties.

Acetic acid production by the two-step thermal treatment of tobacco filter

The thermolysis of waste tobacco filters (WTFs) was carried out and characterized by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/ mass spectrometry (Py-GC/MS). The WTFs showed four distinctive derivative TG (DTG) peaks. Such distinctive DTG curves were indicative of the thermal desorption of triacetin (< 220°C), thermal desorption of glycerol tricaprylate (221–270°C), decomposition of cellulose acetate (CA, 281–400°C), and char stabilization (> 400°C). The activation energy (E<sub>a</sub>) (223–279 kcal kg<sup>-1</sup>) in the additives desorption region (220–270°C) were higher than those (169 ± 5.1 kcal kg<sup>-1</sup>) from the WTFs at the main decomposition region of CA (281–400°C). Py-GC/MS suggested that a large amount of acetic acid (AA, 33.0 wt.%) was recovered as the major pyrogenic product stemming from WTF. An increase in AA purity up to 76.2% (except for CO<sub>2</sub>) was achieved in the 2<sup>nd</sup> Py step at 400°C after eliminating the non-target chemicals (nicotine, triacetin, glycerol tricaprylate, and 2-(decanoyloxy)propane-1,3-diyl dioctanoate) through the 1<sup>st</sup> thermal desorption (TD) step to 300°C.

Well-designed glucose precursor carbon/g-C3N4 nanocomposite for enhanced visible light photocatalytic CO2 reduction activity

Fabrication of glucose precursor carbon-doped g-C3N4 nanocomposite (C/g-C3N4) for enhancing photocatalytic CO2 reduction into syngas (CO, CH4) has been investigated. The samples were successfully synthesized via a two-step thermal treatment and tested in a fixed bed reactor under visible light. The 0.2 % glucose precursor carbon-doped over g-C3N4 photocatalyst has demonstrated excellent activity in converting CO2 to CO and CH4 under visible light. The main product yield, CO of 898.9 μmol g-cat−1 was produced over 0.2 % C/g-C3N4, which is 4.6 folds the amount of CO obtained over the g-C3N4 (196.8 μmol g-cat−1). The XPS results confirmed the formation of a C-O-C bond between carbon and g-C3N4, resulting in a strong interaction between carbon and g-C3N4. Carbon-doped g-C3N4 possesses a narrow energy band and the ability to effectively absorb solar light, which enables efficient transportation of electrons generated by photon excitation. Possible reaction mechanisms for photoreduction of CO2 over carbon-doped g-C3N4 photocatalyst were proposed in order to understand the movement of electrons and holes. This work provides a simple method for designing highly efficient carbon-based photocatalysts for potential application in photocatalytic CO2 reduction using solar energy.

Alkaline metal derived secondary thermal polymerization for superior thin g-C3N4 nanosheets with efficient photocatalytic performance

The thermal polymerization controlled the thickness and composition of graphic carbon nitride (g-C3N4) to affect the photocatalytic performance. In this paper, potassium and sodium ions were firstly incorporated in bulk g-C3N4 prepared using melamine through a mechano-chemical pre-reaction. After a two-step thermal polymerization treatment at 500 and 550 °C, respectively, superior thin g-C3N4 nanosheets were created because K or Na ions implanted between g-C3N4 layers, in which activated cites were remained in the nanosheets. The results revealed that potassium or sodium ion doping revealed an important impact on the photocatalytic activity of g-C3N4. With an optimized K loading of 3%, the hydrogen evolution rate of potassium doped g-C3N4 superior thin nanosheets was 18.1 times of that of bulk g-C3N4. For the degradation of the degradation rate of Rhodamine B (Rh B), K-doped g-C3N4 sample revealed 3.8 times increase compared with pure g-C3N4. To indicate the role of alkaline metal ions, Na-doped samples were also used for H2 generation and Rh B degradation. Meanwhile, the hydrogen generation and Rh B degradation rate of sodium doped g-C3N4 nanosheets improved to 3.6 and 1.75 times higher than those of pure g-C3N4, respectively. The result suggested a mechano-chemical pre-treatment helped K and Na ions to improve the microstructure of g-C3N4 nanosheets and increase activated cites for photocatalysis.

Synergistic effect on the improved lithium ion storage performance in the porous Fe2O3@Fe3C@C composite

The porous Fe2O3@Fe3C@C composite was synthesized by a simple two-step thermal treatment and its structure, morphology, lithium ion storage performance and diffusion kinetics were discussed. Benefitting from the high theoretical capacity of Fe2O3 and fast kinetics of Fe3C, the Fe2O3@Fe3C@C composite exhibits a stable cycling capacity of 800.3 mAh g−1 after 100 cycles at 0.1 A g−1 with superior rate capability. The CV and in-situ EIS analysis results reveal that the Fe2O3@Fe3C@C composite has reversible redox reaction, stable solid electrolyte interphase films and low charge transfer resistance during the discharging and charging process. In addition, the lithium ion diffusion coefficients of the Fe2O3@Fe3C@C composite at different voltage states are investigated by GITT measurement. This work can provide an effective strategy for synthesis of metal oxide@metal carbide composite for lithium-ion batteries.

Two-step thermal treatment of electrochemical graphene oxide films for high-performance electrical heating and electromagnetic interference shielding

Electric heaters have attracted growing interest due to their wide applications in healthcare, smart wear, and aerospace. Contrarily, conventional heaters fail to meet the expectations of flexibility, high temperature, and efficiency. The current protocol focus on the fabrication of a flexible, high-temperature, and high-performance heater through a multi-step strategy. The modified two-step electrochemical exfoliation approach facilitated the formation of electrochemical graphene oxide (EGO). The simple two-step thermal treatment of EGO produced graphene film. The EGO structure exhibits excellent flexibility, good electrical conductivity, and thermal stability after thermal treatment. Consequently, graphene film showed good flexibility and efficient electric heating performance. It only required 13 s to reach 401.2 °C at 3.5 V. Additionally, graphene film displays sufficient heating reliability, stability, and repeatability under heating cycles and prolonged heating. Moreover, it demonstrates electromagnetic interference shielding effectiveness of up to 30383.6 dB cm2/g. Therefore, graphene film has emerged as a promising alternative for developing intelligent clothes, wearable devices, and healthcare devices.

Highly exfoliated graphitic carbon nitride for efficient removal of wastewater pollutants: Insights from DFT and statistical modelling

The present work entails the synthesis of thermally modified graphitic carbon nitride (GCN) using a two-step thermal treatment procedure and its subsequent use in the photocatalytic reduction of toxic pollutants such as rhodamine B dye (RhB) and chromium (VI) (Cr(VI)) from aquatic environments. The as-synthesised exfoliated GCN (GCNX) is characterised by X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), Brunauer–Emmett–Teller analysis (BET), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). These characterisations helped to elucidate the phase formation, chemical structure, composition, surface area, optical properties, and morphology of the sample. With assistance from a visible light source, GCNX can degrade RhB dye within 30 min in the presence of hydrogen peroxide (H2O2) and reduce Cr(VI) to Cr(III) in under 2 h in the presence of formic acid (FA/HCOOH). Variations in different catalytic parameters, including catalyst amount, pH of the solution, initial RhB or Cr(VI) concentration, and variation in H2O2 or FA concentration, are performed to inspect their effects on the photodegradation activity of GCNX. Moreover, the GCNX catalyst exhibits impressive stability and reusability. A thorough statistical evaluation follows the response surface methodology to understand the complex interaction between the factors contributing to the catalytic activity. The band alignment of differently functionalised GCN blocks in their pristine form and their H2O2/FA-adsorbed states is investigated using first-principles calculations to provide a further understanding of the RhB and Cr(VI) reduction mechanisms. The modified GCN can thus be effectively employed as a low-cost material for removing contamination from aquatic environments.

A Stable and Reusable Supported Copper Catalyst for the Selective Liquid-Phase Hydrogenation of 5-Hydroxymethylfurfural to 2,5-Bis(hydroxymethyl)furan

Synthesis of 2,5-bis(hydroxymethyl)furan (BHMF) by selective 5-hydroxymethylfurfural (HMF) hydrogenation is ecofriendly and industrially important since HMF is obtained from renewable sources, and BHMF is a raw material used for production of biodegradable polymers. Four copper-based catalysts were prepared by incipient wetness impregnation (Cu/SiO2-I, Cu/Al2O3-I), precipitation–deposition (Cu/SiO2-PD) and coprecipitation (CuMgAl), and then tested in the liquid-phase hydrogenation of HMF. Metallic phases with large copper particles were obtained by incipient wetness impregnation, while precipitation methods gave highly dispersed metal copper nanoparticles. The pattern found for the concentration and strength of surface acid sites was: CuMgAl > Cu/Al2O3-I > Cu/SiO2-PD > Cu/SiO2-I. The copper-based catalysts active in HMF hydrogenation are all highly selective to BHMF, but the intrinsic activity and stability depend on metallic copper dispersion and support nature. The catalyst stability becomes poorer in the cases that the metallic phase is formed by large copper particles or interacts with high-acidity supports. Therefore, the catalyst with the highest activity, BHMF yield and stability was Cu/SiO2-PD. Furthermore, it was found that Cu/SiO2-PD is reusable in the selective liquid-phase HMF hydrogenation after being submitted to a two-step thermal treatment: (1) calcination under air flow at 673 K; (2) reduction under H2 flow at 523 K.

Porous Carbon-Carbon Composite Materials Obtained by Alkaline Dehydrochlorination of Polyvinyl Chloride.

Porous carbon-carbon composite materials (PCCCM) were synthesized by the alkaline dehydrochlorination of polyvinyl chloride solutions in dimethyl sulfoxide containing the modifying additives of a nanostructured component (NC): graphite oxide (GO), reduced graphite oxide (RGO) or nanoglobular carbon (NGC), with subsequent two-step thermal treatment of the obtained polyvinylene-NC composites (carbonization at 400 °C and carbon dioxide activation at 900 °C). The focus of the study was on the analysis and digital processing of transmission electron microscopy images to study local areas of carbon composite materials, as well as to determine the distances between graphene layers. TEM and low-temperature nitrogen adsorption studies revealed that the structure of the synthesized PCCCM can be considered as a porous carbon matrix in which either carbon nanoglobules (in the case of NGC) or carbon particles with the "crumpled sheet" morphology (in the case of GO or RGO used as the modifying additives) are distributed. Depending on the features of the introduced 5-7 wt.% nanostructured component, the fraction of mesopores was shown to vary from 11% to 46%, and SBET-from 791 to 1115 m2 g-1. The synthesis of PCCNC using graphite oxide and reduced graphite oxide as the modifying additives can be considered as a method for synthesizing a porous carbon material with the hierarchical structure containing both the micro- and meso/macropores. Such materials are widely applied and can serve as adsorbents, catalyst supports, elements of power storage systems, etc.

Preparation of N-doped carbon materials from cellulose:chitosan blends and their potential application in electrocatalytic oxygen reduction

Carbon-based electrocatalysts for oxygen reduction reaction (ORR) are prepared by a direct pathway including a two-step thermal treatment process applied to porous spheres of natural biopolymer blends. Cellulose blends with chitosan are first thermally treated at moderate temperatures (e.g., 200 °C), then pyrolyzed at elevated temperature (800–1000 °C), both steps under a constant nitrogen flow. By blending of cellulose with chitosan, the nitrogen content in the final carbon-based catalyst can be considerably increased. The influence of the composition of the precursor biopolymer blend on the ORR electrocatalytic activity is analyzed in correlation with the elemental composition and other structural features of the catalyst. The polymer blend containing cellulose:chitosan = 75:25, thermally treated 1 h at 200 °C and pyrolyzed 1 h at 800 °C under nitrogen atmosphere, shows the highest electrocatalytic ORR activity. This is attributed to an increased surface area combined with relatively high nitrogen content and a higher pyridinic/pyrrolic species ratio.

New nitrogen-doped graphitic carbon nanosheets with rich structural defects and hierarchical nanopores as efficient metal-free electrocatalysts for oxygen reduction reaction in Zn-Air batteries

Carbon materials are highly promising alternative metal-free catalysts for oxygen reduction reaction (ORR), an important element reaction involved in various energy storage/conversion processes, while controllable and fine structural and morphological tunning is key for maximizing the catalytic performance. Here, we report the rational design of hierarchical porous graphitic carbon nanosheets with rich defects (d-pGCS) based on a facile two-step thermal treatment route, delivering superior catalytic ORR performance in alkaline electrolytes. The second thermal treatment is critical in creating such structural defects and nanopores. Through optimizing synthesis parameters, d-pGCS-1000 exhibits outstanding electrocatalytic ORR performance in terms of positive onset potential (0.95 V), half-wave potential (0.82 V), and limiting current density (6.02 mA cm−2). As a proof-of-concept, the obtained Zn-air battery delivers a large open-circuit voltage (1.42 V), high peak power density (182.8 mW cm−2), high specific capacity (773 mAhgZn−1), and good rate performance. Such results are comparable to or even better than the Pt/C-based Zn-air battery.

Enhanced visible light photocatalytic hydrogen evolution by intimately contacted Ni2P decorated Ni-doped CdS nanospheres

Ni-doped cadmium sulfide (CdS) nanospheres with nickel phosphide (Ni2P) loading (Ni2P@CdS-Ni) were successfully prepared via the two-step thermal treatment growth and chemical reduction method in this work. Firstly, the thermal treatment method was applied to introduce the Ni2+ into the lattice of CdS and induce the Ni-precursor loaded on surface of the CdS intimately. Then, the Ni-precursor was reduced into Ni(OH)2 by using the chemical reduction process. Furthermore, the Ni2P were loaded on the CdS via the second thermal phosphorization reaction. The loaded Ni2P would evidently accelerate the transfer of photo-generated electrons between CdS-Ni and Ni2P and meanwhile effectively decrease the charges recombination. Moreover, the results of UV–vis DR spectra and density functional theory (DFT) calculations confirmed that Ni cations doped in the lattice of CdS lead to a doping level at the bottom of the conduct band, which narrowed the bandgap. The work function indicated that doped Ni2+ helps to enhance the migration and separation of the photo-induced charge. Based on the synergistic effects, 3.7% Ni2P@CdS-Ni-3 presented a relatively high hydrogen evolution rate of 176.6 mmol h−1 g−1 under visible light irradiation (λ ≥ 420 nm), which is 63 times of the common CdS.

Rational design of hierarchical Ni-Mo bimetallic Selenide/N-doped carbon microspheres toward high–performance potassium ion batteries

Potassium ion batteries (KIBs) have received a lot of attention in large-scale energy storage applications because of abundant potassium resources. However, owing to the poor structural durability of electrode materials and sluggish reaction kinetics, the commercialization of KIBs is challenging. Herein, we design a hierarchically structured Ni–Mo bimetallic selenide/N-doped carbon microsphere (NMSe/NC) as an advanced anode material for KIBs. The hierarchical Ni-Mo/polydopamine microsphere precursor, obtained from the spontaneous chemical reaction of NiMoO4 nanorods with dopamine hydrochloride, is converted into heterostructured-Ni–Mo selenide crystals confined in a hierarchical NC matrix via a two-step thermal treatment. The unique hierarchical surface structure and the synergistic effect of Mo and Ni species provide sufficient electrochemical reaction sites and promote the reaction kinetics. Furthermore, the proximate contact between the active materials and the N-doped carbon matrix can facilitate electron transportation and enhance the structural robustness of the electrode. Consequently, the resulting NMSe/NC hierarchical microspheres delivered a high reversible capacity of 332 mA h g−1 after 200 cycles (current density: 0.5 A g−1) and a remarkable rate capability of 206 mA h g−1 (current density: 2.0 A g−1). The excellent electrochemical performance of NMSe/NC indicates their potential for KIB commercialization in large-scale energy storage systems in the future.

Platinum-Tin/Tin Oxide/CNT Catalysts for High-Performance Electrocatalytic Ethanol Oxidation.

Ethanol is a promising liquid clean energy source in the energy conversion field. However, the self-poisoning caused by the strongly adsorbed reaction intermediates (typically, CO) is a critical problem in ethanol oxidation reaction. To address this issue, we proposed a joint use of two strategies, alloying of Pt with other metals and building Pt/metal-oxide interfaces, to achieve high-performance electrocatalytic ethanol oxidation. For this, a well-designed synthetic route combining wet impregnation with a two-step thermal treatment process was established to construct PtSn/SnOx interfaces on carbon nanotubes. Using this route, the alloying of Pt-Sn and formation of PtSn-SnOx interfaces can simultaneously be achieved, and the coverage of SnOx thin films on PtSn alloy nanoparticles can be facilely tuned by the strong interaction between Pt and SnOx . The results revealed that the partial coverage of SnOx species not only retained the active sites, but also enhanced the CO anti-poisoning ability of the catalyst. Consequently, the H-PtSn/SnOx /CNT-2 catalyst with an optimized PtSn-SnOx interface showed significantly improved performances toward the ethanol oxidation reaction (825 mA mgPt -1 ). This study provides deep insights into the structure-performance relationship of PtSn/metal oxide composite catalysts, which would be helpful for the future design and fabrication of high-performance Pt-based ethanol oxidation reaction catalysts.

Bifunctional tin modified SnO2 nanospheres embedded biomass-derived carbon network for polysulfides adsorption-conversion in lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have been intensively studied as promising candidates of energy storage devices due to the high theoretical specific capacity. Unfortunately, the insulating nature and shuttling effect of sulfur are crucial obstacles. In this study, a “network-sphere” structure of in-situ reduced Sn modifying SnO2 nanospheres embedded in carbonized bacterial cellulose (CBC) porous nanofiber network (CBC@SnO2-Sn) is designed via two-step thermal treatment as 3D sulfur host material for LSBs to overcome these issues. The CBC exerts a positive role in alleviating the volume change as well as accelerating the electron and ion transfer. More significantly, the uniformly distributed SnO2 nanospheres with in-situ reduced Sn not only provide numerous active sites for chemisorption of polysulfides, but also accelerate the redox kinetics by catalyzing the polysulfides conversion, coordinately alleviating the shuttle effect during cycling. The CBC@SnO2-Sn/S cathode delivers an outstanding electrochemical performance with a high initial discharge capacity of 1573.6 mA h g−1 at 0.1 A g−1 and superior cycling stability (564.6 mA h g−1 after 500 cycles at 3 A g−1 with the coulombic efficiency kept above 99%). The novel structure, with synergy effect between conductive network and polysulfide adsorption-conversion, creates a promising strategy in improving the electrochemical performance for LSBs and other energy storage applications.

A two-step thermal treatment method to produce reduced graphene oxide with selectively increasing electrochemically active carbonyl group content for high-performance supercapacitor electrode

The variation of oxygen functional groups (OFGs) is extremely complicated during the thermal treatment of graphene oxide (GO). Selectively improving the content of electrochemically active OFGs through multi-step thermal treatment is a promising strategy to enhance the charge storage capability of graphene-based supercapacitor electrodes. In this work, a two-step thermal treatment method was used to produce reduced graphene oxide (RGO) with selectively increasing the content of electrochemically active quinone-type carbonyl groups (C˭O). The first step is thermal reduction at 500 °C in Ar atmosphere, during which GO is exfoliated into separated sheets with porous structure and larger surface area; the second step is air oxidation at 400 °C, which facilitates the selective formation of quinone-type C˭O groups and enhances the mesoporous fraction. Due to the pseudocapacitive behavior of quinone-type C˭O groups and low ion diffusion resistance, the electrode prepared by RGO exhibits a high specific capacitance of 303 F g−1 at 0.2 A g−1 with excellent rate capability (202 F g−1 at 10 A g−1) and notable cycling performance (~ 116% capacitance retention after 1500 cycling at 1 A g−1). The present work proposed a facile and environmentally friendly two-step thermal treatment strategy in effectively controlling the surface property and microstructure of graphene materials, which has significant implications for mass producing graphene materials for supercapacitor electrodes.

Controllable preparation and microwave absorption properties of shape anisotropic Fe3O4 nanobelts

To substantially prevent electromagnetic threatens, microwave absorbing materials (MAMs) are required to eliminate surplus electromagnetic waves. As a typical MAM, Fe3O4 particles with complex permittivity and permeability have been widely applied due to the coexistence of magnetic loss and dielectric loss. However, the necessary high mass fraction significantly limited its applications, thus Fe3O4 nanostructures have been extensively investigated to overcome this problem. In this work, uniform Fe3O4 nanobelts were prepared by electrospinning and two-step thermal treatment. By controlling the composition and viscosity of the electrospinning precursor solution, Fe3O4 nanobelts with tunable lateral sizes (200 nm–1 μm) were obtained. The samples with low content (only 16.7 wt%) Fe3O4 exhibited wide maximum effective absorbing bandwidths (EAB) over 3 GHz, and Fe3O4 nanobelts with smaller lateral sizes showed a maximum EAB of 4.93 GHz. Meanwhile, Fe3O4 nanobelts with smaller lateral sizes presented superior reflection loss properties, the lowest reflection loss reached −53.93 dB at 10.10 GHz, while the maximum EAB was up to 2.98 GHz. The excellent microwave reflection loss of Fe3O4 nanobelts was contributed to the enhanced synergistic effect of magnetic loss, dielectric loss, and impedance matching, originated from the hierarchically cross-linked networks and shape anisotropies. This study could broaden the practical applications of magnetic absorbers, and provided an approach for the development of shape anisotropic magnetic materials.