Ultrafine Fe3O4 Nanoparticles Research Articles

A Stable Fe3O4-Based Hybrid Anodes for High Performance Li-Ion Batteries

There is an increasing demand for high-performance Li-ion batteries especially due to environmental concerns. To meet the high-performance requirements of the Li-ion batteries, conversion-type anodes stand out with their capacities. The crystal structure of magnetite (Fe3O4) benefits from its empty interstitial sites which hinders volume changes during the insertion and extraction of lithium ions. Combined with its high theoretical lithium storage capacity and abundance, Fe3O4 has great potential as an alternative anode. Yet in its practical use, the material suffers from severe capacity degradation, mainly due to the formation of a passive metallic iron layer on the electrode [1]. Another suggested mechanism responsible for the deterioration of the performance is the formation of electrochemically inactive FeO-based side products upon delithiation process [2].In this study, we utilize reduced graphene oxide (rGO) as a substrate for the ultrafine Fe3O4 nanoparticles to form a two-dimensional hybrid material with improved characteristics. Under a mild hydrothermal condition, nanoparticles were deposited by a simple redox process in an interconnected porous network of graphene. Graphene aids in improving the Fe3O4 performance not only by reducing the charge transfer resistance, buffering the volume change induced stresses and facilitating the ion transport but also by forming an effective interface with the delocalized electrons of Fe3O4 to further result in the increase of battery capacitance by the interfacial conjugation mechanism, as confirmed by in-situ EIS measurements. The Fe3O4 particles have been effectively stabilized on the rGO surface, becoming less prone to agglomeration during cycling. Consequently, the deliverable specific capacity of the hybrid material was gradually improved upon extended cycling, reaching from 1500 mAh/g up to 2200 mAh/g at 0.5 A/g at the end of 100 cycles of operation. The increase of the specific capacity during the extended cycling was attributed to the chemical and structural changes of the electrode material evaluated by TEM and ex-situ EELS measurements. It was confirmed that the particle size is greatly reduced to 1-2 nm scale, improving the lithium-ion diffusion kinetics by the increased surface area and reversibility of the redox reaction upon graphene contribution. Moreover, the aged cells were observed to still deliver around 1100 mAh/g capacity upon more than 250 times cycling at 1 A/g, indicating the great potential of the ultrafine Fe3O4 decorated reduced graphene hybrids as superior performance Li-ion battery anode materials.

Sepiolite-metal organic framework-iron oxide catalyst for degradation of Rhodamine B using Fenton-like process

BackgroundThe catalytic degradation of harmful organic pollutants, i.e., Rhodamine B (RhB), is very valuable from the environmental viewpoint. In this way, the design and fabrication of an effective heterogeneous catalyst has a prospect in the treatment of dye containing effluents. MethodsThe magnetic catalyst was prepared by first successfully deposition of the MOF(801) material on clay substrate using a solvothermal process to form Sep-MOF(801) and subsequent formation of ultrafine Fe3O4 nanoparticles via a simple chemical precipitation route on the surface of Sep-MOF(801) to prepare Sep-MOF(801)-Fe3O4. The morphological and structural characters of the Sep-MOF(801)-Fe3O4 nanocomposite were explored using FT-IR, BET, XRD, TEM, SEM, EDX, VSM and XPS methods. Significant findingsExperimentally, the RhB degradation efficiencies at various Fenton-like systems abided by the order of Sep-MOF(801)-Fe3O4/H2O2+NH2OH > Fe3O4/H2O2+NH2OH > Sep-MOF(801)/H2O2+NH2OH > Sep/H2O2+NH2OH > MOF(801)/H2O2+NH2OH > H2O2+NH2OH. The presence of NH2OH as reducing agent can further improve the RhB degradation performance and led to less consumption of H2O2. Under the optimum experimental conditions, 50 mg L−1 RhB was completely degraded in 12 min. In addition, the reusability of the Sep-MOF(801)-Fe3O4 catalyst was investigated after six repeated catalytic cycles.

Highly sensitive and selective serotonin (5-HT) electrochemical sensor based on ultrafine Fe3O4 nanoparticles anchored on carbon spheres

Neurotransmitter serotonin (5-HT) is involved in various physiological and pathological processes. Therefore, its highly sensitive and selective detection in human serum is of great significance for early diagnosis of disease. In this work, employing iron phthalocyanine as Fe source, ultrafine Fe3O4 nanoparticles anchored on carbon spheres (Fe3O4/CSs) have been prepared, which exhibits an excellent electrochemical sensing performance toward 5-HT. With carbonecous spheres turned into conductive carbon spheres under the heat treatment in N2 atmosphere, iron phthalocyanine absorbed on their surfaces are simultaneously pyrolysised and oxidized, and finally transformed into ultrafine Fe3O4 nanoparticles. Electrochemical results demonstrate a high sensitivity (5.503 μA μM−1) and a low detection limit (4 nM) toward 5-HT for as-prepared Fe3O4/CSs. In combination with the morphology and physicochemical property of Fe3O4/CSs, the enhanced sensing mechanism toward 5-HT is disscussed. In addition, the developed electrochemical sensor also displays a good sensing stability and an anti-interferent ability. Further applied in real human serum samples, a satisfactory recovery rate is achieved. Promisingly, the developed electrochemical sensor can be employed for the determination of 5-HT in actual samples.

Encapsulating ultrafine Fe3O4 nanoparticles into interconnected 3D multiporous carbon for superior Li-ion energy storage

Although Fe3O4 has low cost and high theoretical capacity, its low electrical conductivity and significant volume changes during the reaction process result in poor electrochemical performance, particularly cycling performance, which limit its application as anode materials. To overcome these limitations, this study created Fe3O4@3D cellular carbon composites (Fe3O4@3D cellular carbon: Fe3O4@3D-CC) by homogeneously embedding ultrafine Fe3O4 nanoparticles of size around 10 nm in a three-dimensional cellular carbon skeleton using a template-assisted method. The porous structure enables for large volumes of electrolyte to be stored and features a dual continuous transport channel for ions and electrons, which can considerably improve the conductivity of the Fe3O4. Furthermore, 3D cellular carbon locks Fe3O4 nanoparticles, allowing them to adapt to volume changes during charge-discharge process and preventing structural degradation. Due to the aforementioned structural properties, this material has a first discharge-specific capacity of 2534 mA h g−1 at a rate of 0.1 C and can still reach 1011 mA h g−1 after 400 cycles at a high rate of 2 C. This keeps the theoretical capacity at 109 % and distinctly enhances the electrochemical performance of Fe3O4, particularly the cycling performance.

Facile premixed flame synthesis C@Fe2O3/SWCNT as superior free-standing anode for lithium-ion batteries

Premixed flame configuration is considered as an effective method for the synthesis of carbon materials. In this work, flexible single-walled carbon nanotube network decorated by carbon-encapsulated Fe2O3 nanoparticles (C@Fe2O3/SWCNT) membrane was in-situ fabricated via a facile floating catalyst premixed ethanol flame method, and followed by annealing treatment. In this process, low-cost ethanol and ferrocene were used as carbon source and catalyst precursor for the synthesis of C@Fe2O3/SWCNT, respectively. Benefiting from the interconnected conductive network, the as-fabricated C@Fe2O3/SWCNT membrane was used as a free-standing anode for lithium-ion batteries. Structural characterization revealed that the ultrafine Fe2O3 nanoparticles homogeneously anchored on the SWCNT network, which facilitates the fast diffusion for electron. Furthermore, the carbon layers uniformly enwrap on Fe2O3 can effectively suppress the aggregation and buffer the volume change of Fe2O3 during the lithiation/delithiation process. Consequently, this material delivered an excellent lithium storage performance with a high reversible capacity of 1294.7 mAh g−1 at 50 mA g−1, and an excellent cyclability of 82.5% retention is obtained after cycles at 2 A g−1. This study provides a novel low-cost and fast method for preparing flexible advanced electrode for next-generation rechargeable batteries.

TEA driven C, N co-doped superfine Fe3O4 nanoparticles for efficient trifunctional electrode materials

Poor conductivity is an obstacle that restricts the development of the electrochemistry performance of Fe3O4. In this work, a novel carbon and nitrogen co-doped ultrafine Fe3O4 nanoparticles (CN-Fe3O4) have been synthesized by triethylamine (TEA) induction and subsequent calcination. The addition of TEA could not only regulate the size of Fe3O4 nanoparticles, but also promote the formation of amorphous carbon layer. Well-designed CN-Fe3O4 heterostructures provide a highly interconnected porous conductive network, large heterogeneous interface area, large specific surface area and a large number of active sites, which greatly improve conductivity and promote electron transfer and electrolyte diffusion. The prepared CN-Fe3O4 electrode exhibits a high specific capacitance of 399.3 mF cm−2 and good cycling stability. Meanwhile, CN-Fe3O4 catalyst exhibits excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities, with overpotentials of 136 and 281 mV at the current density of 10 mA cm−2, respectively. This work provides a promising approach for the design of high-performance anode materials for supercapacitors and provides profound implications for the development of catalysts with bifunctional catalytic activity.

In-situ dispersing ultrafine Fe2O3 nanoparticles in mesoporous silicas for efficient peroxymonosulfate-activated degradation of tetracycline over a broad pH range

The supported ultra-small Fe2O3 nanoparticles, as conventional functional materials for versatile applications, are scarcely investigated for their catalytic properties in peroxymonosulfate-activated reactions to deal with the ever-growing environment issues. In this work, highly dispersed ultrafine Fe2O3 nanoparticles are successfully generated in framework of mesoporous silicas (such as Fe/Si-3, with 3.01 wt% of Fe content) through an in-situ approach with iron phthalocyanine as Fe source. The formation of Fe-N or Fe-C bonds exerted remarkable isolation effect on the generation of the nanoparticles. Fe/Si-3 gave superior activity to other Fe catalysts analogs including bulk Fe2O3 in peroxymonosulfate-triggered degradation of tetracycline. Fe/Si-3 has a wide working pH window of 3–11. It can be recycled for 3 times without significant loss of the degradation activity. The radicals of SO4⋅−, ⋅OH, O2⋅− and 1O2 all contributed to the degradation reaction. The factors for high degradation efficiency and broad working pH range of Fe/Si-3, the mechanism for formation of various radicals, as well as the transformation pathway of tetracycline molecules were proposed.

Electronic structure modulation with ultrafine Fe3O4 nanoparticles on 2D Ni-based metal-organic framework layers for enhanced oxygen evolution reaction

Two-dimensional (2D) metal organic frameworks (MOFs) are emerging as low-cost oxygen evolution reaction (OER) electrocatalysts, however, suffering aggregation and poor operation stability. Herein, ultrafine Fe3O4 nanoparticles (diameter: 6 ± 2 nm) are homogeneously immobilized on 2D Ni based MOFs (Ni-BDC, thickness: 5 ± 1 nm) to improve the OER stability. Electronic structure modulation for enhanced catalytic activity is studied via adjusting the amount of Fe3O4 nanoparticles on Ni-BDC. The optimal Fe3O4/Ni-BDC achieves the best OER performance with an overpotential of 295 mV at 10 mA cm−2, a Tafel slope of 47.8 mV dec-1 and a considerable catalytic durability of more than 40 h (less than 5 h for Ni-BDC alone). DFT calculations confirm that the active sites for Fe3O4/Ni-BDC are mainly contributed by Fe species with a higher oxidation state, and the potential-determining step (PDS) is the formation of the adsorbed O* species, which are facilitated in the composite.

Microwave-Assisted Facile Hydrothermal Synthesis of Fe3O4–GO Nanocomposites for the Efficient Bifunctional Electrocatalytic Activity of OER/ORR

A challenging task is to develop and improve the efficiency of the electrocatalysts for bifunctional oxygen reaction activities for the higher generation of current with lower overpotential. In the present work, ultrafine Fe₃O₄ nanoparticles were uniformly decorated on the layered surface of graphene oxide (GO) sheets using the microwave-assisted hydrothermal method and successfully tested for bifunctional oxygen reaction activities for the first time. This heterostructure composites were used as a promising candidate for highly efficient bifunctional material for oxygen evolution/reduction reactions (ORR/OER) in both KOH and H₂SO₄ solutions. The composite structure and morphology were characterized by scanning and high-resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. These heterostructure composites show a very low onset potential value for ORR (0.975 V vs RHE) and OER (1.25 V vs RHE) in the presence of KOH solution. Additionally, the composites exhibit superior performance activity for ORR (0.92 V vs RHE) and OER (1.2 V vs RHE) in sulfuric acid solution. Interestingly, the pure GO showed a better result than the previously reported work that supported the superior electrocatalytic performance of the hybrid composites. This coupling of techniques provides a higher density of Fe–C–O crystalline sites and ultrafine Fe–O particles as boosting higher charge transferability in the composites. This physicochemical behavior facilitates in breaking the functional groups on the surface and providing more active transfer sites that are influenced by microwave and hydrothermal processing. This study may provide useful insights into the Fe-enabled high bifunctional activity to guide the design of an efficient catalyst for many potential electrochemical activities.

Superior lithium-storage properties derived from a g-C3N4-embedded honeycomb-shaped meso@mesoporous carbon nanofiber anode loaded with Fe2O3 for Li-ion batteries.

In this work, a honeycomb-shaped meso@mesoporous carbon nanofiber material incorporating homogeneously dispersed ultra-fine Fe2O3 nanoparticles (denoted as Fe2O3@g-C3N4@H-MMCN) is synthesised through a pyrolysis process. The honeycomb-shaped configuration of the meso@mesoporous carbon nanofiber material derived from a natural bio-carbon source (crab shell) acts as a support for an anode material for Li-ion batteries. Graphitic carbon nitride (g-C3N4) is produced via the one-step pyrolysis of urea at high temperature under an N2 atmosphere without the assistance of additives. The resulting favorable electrochemical performance, with superior rate capabilities (1067 mA h g-1 at 1000 mA g-1), a remarkable specific capacity (1510 mA h g-1 at 100 mA g-1), and steady cycling performance (782.9 mA h g-1 after 500 cycles at 2000 mA g-1), benefitted from the advantages of both the host material and the Fe2O3 nanoparticles, which play an important role due to their ultra-fine particle size of 5 nm. The excellent cycle life and high capacity demonstrate that this strategy of strong synergistic effects represents a new pathway for pursuing high-electrochemical-performance materials for lithium-ion batteries.

Construct of Carbon Nanotube-Supported Fe2O3 Hybrid Nanozyme by Atomic Layer Deposition for Highly Efficient Dopamine Sensing.

The Fe2O3 nanozyme has been identified as the most promising alternative for the Fe3O4 nanozyme due to its relatively low toxic risk and good chemical stability. However, its enzyme-like activity is relatively low enough to meet specific application requirements. Furthermore, previous synthesis approaches have difficulties in fabricating ultra-small Fe2O3 nanoparticles with tunable size and suffer from agglomeration problems. In this study, atomic layer deposition (ALD) was used to deposit Fe2O3 on surfaces of carbon nanotubes to form hybrid nanozymes (Fe2O3/CNTs). ALD enables the preparation of ultrafine Fe2O3 nanoparticles with precise size control <1 nm, while CNTs could be served as promising support for good dispersibility and as an effective activity activator. Hence, the formed Fe2O3/CNTs exhibit excellent peroxidase-like activity with a specific peroxidase activity of 24.5 U mg−1. A colorimetric method for sensing dopamine (DA) was established and presented good sensitivity with a limit of detection (LOD) as low as 0.11 μM. These results demonstrated that, in virtue of meticulous engineering methods like ALD, carbon nanomaterial-based hybrids can be developed as talented enzyme mimetic, thus paving a way for nanozyme design with desired activity and broadening their applications in biosensing and other fields.

Three-Phase Boundary in Cross-Coupled Micro-Mesoporous Networks Enabling 3D-Printed and Ionogel-Based Quasi-Solid-State Micro-Supercapacitors.

The construction of advanced micro-supercapacitors (MSCs) with both wide working-voltage and high energy density is promising but still challenging. In this work, a series of nitrogen-doped, cross-coupled micro-mesoporous carbon-metal networks (N-STC/Mx Oy ) is developed as robust additives to 3D printing inks for MSCs fabrication. Taking the N-STC/Fe2 O3 nanocomposite as an example, both experimental results and theoretical simulations reveal that the well-developed hierarchical networks with abundantly decorated ultrafine Fe2 O3 nanoparticles not only significantly facilitate the ion adsorption at its three-phase boundaries (Fe2 O3 , N-STC, and electrolyte), but also greatly favor ionic diffusion/transport with shortened pathways. Consequently, the as-prepared N-STC/Fe2 O3 electrode delivers a high gravimetric capacitance (267 F g-1 at 2 mV s-1 ) and outstanding stability in a liquid-electrolyte-based symmetric device, as well as a record-high energy density of 114 Wh kg-1 for an asymmetric supercapacitor. Particularly, the gravimetric capacitance of the ionogel-based quasi-solid-state MSCs by 3D printing reaches 377 F g-1 and the device can operate under a wide temperature range (-10 to 60 °C).

N-doped honeycomb-like carbon networks loaded with ultra-fine Fe2O3 nanoparticles for lithium-ion batteries

N-doped honeycomb-like carbon networks (N–HCN) loaded with ultra-fine Fe2O3 nanoparticles (Fe2O3/N–HCN) are proposed as anode materials for lithium-ion batteries (LIBs). The Fe2O3/N–HCN nanocomposites are prepared by freeze-drying of glucose-Fe(NO3)3 solution, following by grinding it with urea, and finally annealing treatment. The N–HCN with dozen micrometer-sized macropores is composed of carbon nanosheets with a thickness of about 33 nm. A large number of 2–7 nm-sized ultra-fine Fe2O3 nanoparticles with an average size of 4.4 nm are uniformly arrayed on the wall of N–HCN. The Fe2O3/N–HCN nanocomposites exhibit good performances as anode materials for LIBs. After 500 cycles under a large current density of 5 A g−1, the Fe2O3/N–HCN nanocomposites still show a reversible capacity of 408 mAh g−1. The good performance can be ascribed to the uniformly dispersed ultra-fine Fe2O3 nanoparticles and unique honeycomb-like structure of N–HCN which provides a continuous conductive network to greatly promote the rapid transfer of ions and electrons, and effectively alleviate the volume fluctuation effect of Fe2O3 during charging and discharging. More importantly, the cheap and environmentally friendly glucose as raw materials provides possibility for green energy applications.

Metal-organic framework derived amorphous VOx coated Fe3O4/C hierarchical nanospindle as anode material for superior lithium-ion batteries.

Lithium-ion batteries (LIBs) are widely regarded as a promising electrochemical energy storage device, due to their high energy density and good cycling stability. To date, the development of anode materials for LIBs is still confronted with many serious problems, and much effort is required for constructing more ideal anode materials. Herein, starting with metal-organic frameworks (MOFs), an amorphous VOx coated Fe3O4/C hierarchical nanospindle has been successfully synthesized. The obtained Fe3O4/C@VOx nanospindle has a uniform particle size of ∼100 nm in diameter and ∼400 nm in length and consists of ultrafine Fe3O4 nanoparticles (∼5 nm) embedded in a porous carbon matrix as the core and an amorphous VOx layer as the shell. Notably, as the anode material for LIBs, Fe3O4/C@VOx delivers a high coulombic efficiency (74.2%) and a large capacity of 845 mA h g-1 after 500 cycles at 1000 mA g-1. A prominent discharge reversible capacity of 340 mA h g-1 is also still retained at 5000 mA g-1. More importantly, the presented facile MOF-derived route could be easily extended to other functional materials for widespread applications.

Enhanced catalytic performance on the thermal decomposition of TKX-50 by Fe3O4 nanoparticles highly dispersed on rGO

Fe3O4/reduced graphene oxide (Fe3O4/rGO) nanocomposite has been successfully fabricated using a modified interface solvothermal method and characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. In the preparation procedure, graphene oxide was reduced and ultrafine Fe3O4 nanoparticles (NPs) were uniformly loaded on reduced graphene oxide (rGO) carrier. Scanning electron microscope, transmission electron microscope images and Brunauer–Emmett–Teller specific surface area revealed that the aggregation of Fe3O4 NPs was greatly reduced by introducing rGO as a substrate. The average size of the Fe3O4 NPs anchored on the graphene sheets was 100 nm, which is much smaller than 1-μm bare Fe3O4. The DSC results showed that Fe3O4/rGO nanocomposite reduces the first decomposition temperature of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) by 44.9 °C and decreases the apparent activation energy of TKX-50 by 26.2 kJ mol−1, which exhibits higher catalytic performance than its individual components and their physical mixture (hybrid). Hence, Fe3O4/rGO nanocomposite can be a promising additive for insensitive solid propellants based on TKX-50.

Retraction of "Hierarchical Nanosheet-Built CoNi2S4 Nanotubes Coupled with Carbon-Encapsulated Carbon Nanotubes@Fe2O3 Composites toward High-Performance Aqueous Hybrid Supercapacitor Devices".

A hybrid supercapacitor system was designed with ternary Ni–Co sulfides (CoNi2S4) as cathode materials and Fe-based composites [carbon nanotubes (CNTs)@Fe2O3@C] as anode materials to achieve excellent overall electrochemical performance with high energy and power density as well as long lifespan. Here, hierarchical CoNi2S4 nanotubes were synthesized by a solvothermal route followed by sulfidation reaction for the first time, in which nanotubes were composed of interconnected ultrathin nanosheets. Consequently, such a unique nanosheet-built nanoarchitecture enables the CoNi2S4 cathode with multidimensional synergistic effect from one-dimensional nanotubes, two-dimensional nanosheets, and three-dimensional frameworks. Profiting from its structural merits, the as-prepared CoNi2S4 nanotubes deliver a high capacitance of 2552 F g–1 at 1 A g–1 with a high rate capacity of 81% at 25 A g–1. In addition, the CNTs@Fe2O3@C anode materials—incorporating carbon-encapsulated ultrafine Fe2O3 nanoparticles into CNT matri...

Hierarchical Nanosheet-Built CoNi2S4 Nanotubes Coupled with Carbon-Encapsulated Carbon Nanotubes@Fe2O3 Composites toward High-Performance Aqueous Hybrid Supercapacitor Devices.

A hybrid supercapacitor system was designed with ternary Ni-Co sulfides (CoNi2S4) as cathode materials and Fe-based composites [carbon nanotubes (CNTs)@Fe2O3@C] as anode materials to achieve excellent overall electrochemical performance with high energy and power density as well as long lifespan. Here, hierarchical CoNi2S4 nanotubes were synthesized by a solvothermal route followed by sulfidation reaction for the first time, in which nanotubes were composed of interconnected ultrathin nanosheets. Consequently, such a unique nanosheet-built nanoarchitecture enables the CoNi2S4 cathode with multidimensional synergistic effect from one-dimensional nanotubes, two-dimensional nanosheets, and three-dimensional frameworks. Profiting from its structural merits, the as-prepared CoNi2S4 nanotubes deliver a high capacitance of 2552 F g-1 at 1 A g-1 with a high rate capacity of 81% at 25 A g-1. In addition, the CNTs@Fe2O3@C anode materials-incorporating carbon-encapsulated ultrafine Fe2O3 nanoparticles into CNT matrices-were achieved by atomic layer deposition and acetylene thermal decomposition, which realize excellent electrochemical properties (678 F g-1 at 1 A g-1 and capacity retention of 82% at 25 A g-1) that matched well with CoNi2S4 cathode materials. With the well-designed nanostructure and matching of materials and properties, the corresponding aqueous hybrid device exhibits a wide output voltage window of 0-1.75 V with a maximum energy density of 90.5 W h kg-1 at a power density of 1.84 kW kg-1. Meanwhile, a high energy density of 73.1 W h kg-1 can be retained at an ultrahigh power density of 26.9 kW kg-1. Moreover, the hybrid device has a stable cycling ability with 82.1% retention over 5000 cycles. This coordinative design strategy integrating the cathode and anode electrodes developed in this work provides a novel way to manufacture next-generation energy-storage device with high performance and safety.

Recyclable Fenton-like catalyst based on zeolite Y supported ultrafine, highly-dispersed Fe2O3 nanoparticles for removal of organics under mild conditions

A versatile wet impregnation method was employed to conveniently and controllably deposit Fe2O3 nanoparticles on zeolites including commercial Y, mordenite and ZSM-5 with the similar framework Si/Al ratios and crystal sizes, respectively. The ultrafine Fe2O3 nanoparticles in size of 5nm can be highly dispersed on zeolite Y matrix due to its much better wettability than ZSM-5 and mordenite. By using the obtained Fe2O3/zeolite composite as the heterogeneous Fenton-like catalysts, the degradation of phenol as a model reaction was systematically investigated, including the zeolite supports, particle size and dispersion of Fe2O3, and reaction conditions of H2O2 concentration, temperature, and pH value. The catalyst based on zeolite Y with Fe loading of 9% exhibited the best phenol degradation efficiency (> 90%) in neutral pH within 2h. Its high catalytic activity in Fenton reaction can be attributed to the bifunctional properties of strong surface Brønsted acidity and high reactivity of octahedral Fe3+ in the highly-dispersed ultrafine Fe2O3 nanoparticles in size of 5nm, which were the primary active centers to quickly decompose H2O2 into hydroxyl radicals. Since phenol degradation can be performed under mild conditions of ambient temperature (283–323K) and a wide pH range (4.0–7.0), the catalysts can be easily recovered for recyclable use with stable degradation activity, which own the immense potential in deep treatment of organic pollutants in industrial wastewater.

Aptamer-based sensor for diclofenac quantification using carbon nanotubes and graphene oxide decorated with magnetic nanomaterials

In this contribution, a novel label-free electrochemical biosensor for diclofenac (DCF) detection was developed using the unique properties of acid-oxidized carbon nanotubes (CNT), graphene oxide (GO), and Fe3O4 magnetic nanomaterials. The GO sheets and CNT were interlinked by ultrafine Fe3O4 nanoparticles forming three-dimensional (3D) architectures. The characterization of the nanocomposite was studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDS), and wavelength-dispersive X-ray (WDX) spectroscopy. Initially, aminated detection probe (aptamer) was surface-confined on the CNT/GO/Fe3O4 nanocomposite via the covalent amide bonds formed by the carboxyl groups on the CNT/GO and the amino groups on the oligonucleotides at the 5′ end. Our constructed folding-based electrochemical sensor was used for detection of target molecule utilizing structure-switching aptamers. Signaling arose from changes in electron transfer efficiency upon target-induced changes in the conformation of the aptamer probe. These changes were readily monitored using differential pulse voltammetry technique. This sensor exhibited binding affinities ranging from 100 to 1300 pM with a low detection limit of 33 pM.

An Impedimetric Sensor Comprising Magnetic Nanoparticles–Graphene Oxide and Carbon Nanotube for the Electrocatalytic Oxidation of Salicylic Acid

An effective and facile electrocatalytic oxidation approach for the determination of salicylic acid (SA) on the surface of Ni-2,3-pyrazine dicarboxylic acid (Ni-PDA)/Fe3O4 magnetic nanoparticles/graphene oxide (GO)/carbon nanotube (CNTs) modified carbon paste electrode was demonstrated in this article. The GO sheets and CNTs were interlinked by ultrafine Fe3O4 nanoparticles forming three dimensional (3D) architectures. The characterization of the nanocomposites was studied by scanning electron microscopy, energy-dispersive X-ray, X-ray diffraction, and wavelength-dispersive X-ray spectroscopy. The electrochemical performance of the Ni-PDA film and the parameters affecting its activity were also investigated by cyclic voltammetry, and electrochemical impedance spectroscopy. The data revealed that the modified electrode present considerable electrocatalytic activity toward SA oxidation. The effects of some parameters such as the different scan rates, pH, and SA concentrations were also evaluated to provide catalysis mechanism for SA oxidation at the surface of modified electrode. Furthermore, impedimetric studies showed that the fabricated electrode as the sensing element has a detection capability of 900 nM allowing the quantitative analysis of SA in the concentration range from 5.00 to 155 µM. Remarkable advantages of the prepared modified electrode such as low detection limit, wide linear range of concentration and high sensitivity make it as good sensor for the selective determination of SA.