Fe3O4/biocarbon composites with superior performance in supercapacitors

Detection of Cd2+ based on Nano-Fe3O4/MoS2/Nafion/GCE sensor

It is necessary to detect cadmium ions in seawater with high sensitivity because the pollution of cadmium ions seriously endangers the health and life of human beings. Nano-Fe3O4/MoS2/Nafion modified glassy carbon electrode was prepared by a drop coating method. The electrocatalytic properties of Nano-Fe3O4/MoS2/Nafion were measured by Cyclic Voltammetry (CV). Differential Pulse Voltammetry (DPV) was used to study the stripping Voltammetry response of the modified electrode to Cd2+. The optimal conditions were determined: In 0.1 mol/L HAc-NaAc solution, the solution pH was 4.2, the deposition potential was - 1.0 V, and the deposition time was 720 s, the membrane thickness was 8 μL. Under the optimum condition, the linear relation of Cd2+ concentration was found in the range of 5-300 μg/L, and the detection limit was 0.053 μg/L. The recovery of Cd2+ in seawater ranged from 99.2 to 102.9%. A composite material with simple operation, rapid response and high sensitivity was constructed for the determination of Cd2+ in seawater.

Ball-milled magnetic sludge biochar enables fast aerobic granulation in anoxic/oxic process for the treatment of coal chemical wastewater

Coal chemical wastewater (CCW) containing toxic and hazardous matters requires to be treated prior to discharge. Promoting the in-situ formation of magnetic aerobic granular sludge (mAGS) in continuous flow reactor process has a great potential for CCW remediation. However, long granulation time and low stability limit the application of AGS technology. In this study, Fe₃O₄/sludge biochar (Fe₃O₄/SC) with biochar matrix derived from coal chemical sludge were applied to facilitate the aerobic granulation in two-stage continuous flow reactors, containing separated anoxic and oxic reaction units (abbreviated as A/O process). The performance of A/O process was evaluated at various hydraulic retention times (HRTs) (42 h, 27 h, and 15 h). Magnetic Fe₃O₄/SC with porous structures, high specific surface area (BET = 96.69 m²/g), and abundant functional groups was successfully prepared by ball-milled method. Adding magnetic Fe₃O₄/SC to A/O process could promote aerobic granulation (85 days) and the removal of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N)_, and total nitrogen (TN) from CCW at all tested HRTs. Since the formed mAGS had high biomass, good settling ability, and high electrochemical activities, mAGS-based A/O process had high tolerance to the decrease of HRT from 42 h to 15 h for CCW treatment. The optimized HRT for A/O process was 27 h, at which Fe₃O₄/SC addition can result in the increase of COD, NH₄⁺-N and TN removal efficiencies by 2.5 %, 4.7 % and 10.5 %, respectively. Based on 16S rRNA genes sequencing, the relative abundances of genus Nitrosomonas, Hyphomicrobium/Hydrogenophaga and Gaiella in mAGS accounting for nitrification, denitrification as well as COD removal were increased during aerobic granulation. Overall, this study proved that adding Fe₃O₄/SC to A/O process was effective for facilitating aerobic granulation and CCW treatment.

Three-Dimensional Hybrid Nanostructures of Fe3O4 Nanoparticles/Vertically-Aligned Carbon Nanotubes for High-Performance Supercapacitors

A three-dimensional (3D) hybrid nanostructure of Fe3O4 nanoparticles uniformly anchored on vertically-aligned carbon nanotubes (VACNTs) was fabricated by a facile two-step method. Assisted by supercritical carbon dioxide (SCCO2), the Fe precursor was firstly absorbed on CNT surface and then transformed into Fe3O4 nanoparticles by vacuum thermal annealing. Owing to the synergetic effects of well-distributed Fe3O4 nanoparticles (~7 nm) and highly conductive VACNTs, the hybrid electrode exhibits a high specific capacitance of 364.2 F g−1 at 0.5 A g−1 within the potential range from −0.9 to +0.1 V in Na2SO3 electrolyte and an excellent cycling stability of 84.8% capacitance retention after 2000 cycles at a current density of 4 A/g. This 3D hybrid architecture consisting of aligned CNTs and pseudocapacitive metal oxide may be a promising electrode for high-performance supercapacitors.

Metal-Supported Biochar Catalysts for Sustainable Biorefinery, Electrocatalysis and Energy Storage Applications: A Review

Biochar (BCH) is a carbon-based bio-material produced from thermochemical conversion of biomass. Several activation or functionalization methods are usually used to improve physicochemical and functional properties of BCHs. In the context of green and sustainable future development, activated and functionalized biochars with abundant surface functional groups and large surface area can act as effective catalysts or catalyst supports for chemical transformation of a range of bioproducts in biorefineries. Above the well-known BCH applications, their use as adsorbents to remove pollutants are the mostly discussed, although their potential as catalysts or catalyst supports for advanced (electro)catalytic processes has not been comprehensively explored. In this review, the production/activation/functionalization of metal-supported biochar (M-BCH) are scrutinized, giving special emphasis to the metal-functionalized biochar-based (electro)catalysts as promising catalysts for bioenergy and bioproducts production. Their performance in the fields of biorefinery processes, and energy storage and conversion as electrode materials for oxygen and hydrogen evolutions, oxygen reduction, and supercapacitors, are also reviewed and discussed.

Advanced asymmetric supercapacitors with a squirrel cage structure Fe3O4@carbon nanocomposite as a negative electrode

Carbon materials have been used as negative electrodes for supercapacitor applications; nevertheless, owing to the low capacitance, they have limited ability to enhance the supercapacitor electrochemical properties.

Preparation of Chitosan/Magnetic Porous Biochar as Support for Cellulase Immobilization by Using Glutaraldehyde

In this work, porous biochar was obtained from sugarcane bagasse by alkali activation and pyrolysis and then magnetized with γ-Fe₂O₃ by calcination. After functionalization with chitosan and activation with glutaraldehyde, the as-prepared chitosan/magnetic porous biochar served as a support to immobilize cellulase by covalent bonds. The immobilization amount of cellulase was 80.5 mg cellulase/g support at pH 5 and 25 °C for 12 h of immobilization. To determine the enzymatic properties, 1% carboxymethyl cellulose sodium (CMC) (dissolved in 0.1 M buffer) was considered as a substrate for hydrolysis at different pH values (3–7) and temperatures (30–70 °C) for 30 min. The results showed that the optimum pH and temperature of the free and immobilized cellulase did not change, which were pH 4 and 60 °C, respectively. The immobilized cellulase had a relatively high activity recovery of 73.0%. However, it also exhibited a higher Michaelis–Menten constant (K_m) value and a slower maximum reaction velocity (V_max) value compared to the free enzyme. In the reusability assay, the immobilized cellulase showed initial glucose productivity of 330.9 mg glucose/g CMC and remained at 86.0% after 10 uses. In conclusion, the chitosan/magnetic porous biochar has great potential applications as a support for enzyme immobilization.

Toward fiber-, paper-, and foam-based flexible solid-state supercapacitors: electrode materials and device designs

Flexible solid-state supercapacitors possess promising safety performance and intrinsic fast charging-discharging properties, enabling them to accomplish the requirements of lightweight and multifunctional wearable electronics that have recently become fairly popular. Because electrode materials are the core component of flexible solid-state supercapacitors, we exhaustively review the recent investigations involving electrode materials that have used carbons, metal oxides, and conductive polymers. The principles and methods of optimizing and fabricating electrodes for use in flexible supercapacitors are discussed through a comprehensive analysis of the literature. In addition, we focused on three types of flexible solid-state supercapacitors (fiber-, paper-, and porous foam-based structures) to satisfy the requirements of flexible electronic devices. Further, we summarize the practical applications of flexible solid-state supercapacitors, including energy conversion/collection devices and energy storage/detection devices. Finally, we provide the developmental direction for flexible solid-state supercapacitors in the future.

Fe3O4 nanospheres in situ decorated graphene as high-performance anode for asymmetric supercapacitor with impressive energy density

Unique nanostructure, high electrical conductivity, satisfactory energy density, and extraordinary cycling stability are important evaluation criteria for high-efficient energy storage devices. Herein, Fe₃O₄ nanospheres are successfully in situ decorated on graphene nanosheets through an environmentally benign and facile solvothermal procedure. When utilized as an electrode for supercapacitor, the graphene/Fe₃O₄ nanocomposite exhibits a notably enhanced specific capacity (268 F·g^-1 at 2 mV·s^-1) and remarkable cycling performance with 98.9% capacity retention after 10,000 cycles. Furthermore, the fabricated graphene/MnO₂//graphene/Fe₃O₄ asymmetric supercapacitor device displays a desirable energy density (87.6 Wh·kg^-1) and superior cycling stability (93.1% capacity retention after 10,000 cycles).

Towards magnetic responsive chalcogenides for efficient separation in water treatment: facile synthesis of magnetically layered chalcogenide Fe3O4/KMS-1 composite adsorbents and their zinc removal application in water

A novel easily separated magnetic chalcogenide based composite, Fe₃O₄/KMS-1, was successfully synthesized under vigorous stirring of a mixture in ethanol solution.