FeOOH Nanorods Research Articles

Colloidal Surface Engineering: Growth of Layered Double Hydroxides with Intrinsic Oxidase‐Mimicking Activities to Fight Against Bacterial Infection in Wound Healing

Colloidal surface engineering is of particular importance to impart modular functionalities to the colloidal systems. Here, a layer of Mn/Ni layered hydroxides (Mn/Ni(OH)x LDHs) can be successfully coated on various colloidal particles, such as silica spheres, silica rods, ferrite nanocrystal supraparticles, as well as FeOOH nanorods. Such layered hydroxides have intrinsic oxidase-mimetic activities, as demonstrated by catalytic oxidation of tetramethyl benzidine in the presence of oxygen. Furthermore, Mn/Ni(OH)x LDHs structure seems to capture bacteria (both Gram positive and Gram negative) and exhibit antibacterial properties in vitro. Moreover, local delivery of Mn/Ni-LDH structure fights against infection and reverses delayed wound healing procedures in mice models. Importantly, such hierarchical structures may have strong adhesive properties to the bacteria, which may maximize the contact between Mn/Ni(OH)x LDHs and the bacteria's surface. Overall, the present versatile colloidal surface engineering strategy will bring new insights in the field of antibiotics for its high efficiency toward antibacterial activity.

Conductive FeOOH as Multifunctional Interlayer for Superior Lithium-Sulfur Batteries.

The commercial course of Li-S batteries (LSBs) is impeded by several severe problems, such as low electrical conductivity of S, Li2 S2 , and Li2 S, considerable volume variation up to 80% during multiphase transformation and severe intermediation lithium polysulfides (LiPSs) shuttle effect. To solve above problems, conductive FeOOH interlayer is designed as an effective trapper and catalyst to accelerate the conversion of LiPSs in LSBs. FeOOH nanorod is effectively affinitive to S that Fe atoms act as Lewis acid sites to capture LiPSs via strong chemical anchoring capability and dispersion interaction. The excellent electrocatalytic effect enables that reduced charging potential barrier and enhanced electron/ion transport is realized on the FeOOH interlayer to promote LiPSs conversion. Significantly, Li2 S oxidation process is improved on the FeOOH interlayer determined as a combination of reduced Li2 S decomposition energy barrier and enhanced Li-ion transport. Therefore, the multifunctional FeOOH interlayer with conductive and catalytic features show strong chemisorption with LiPSs and accelerated LiPSs redox kinetics. As a result, LSBs with FeOOH interlayer displays high discharge capacity of 1449 mAh g-1 at 0.05 C and low capacity decay of 0.05% per cycle at 1 C, as well as excellent rate capability (449 mAh g-1 at 2 C).

Template-free fabrication of BiFeO3 nanorod arrays: multiferroic and photo-electrochemical performances

BiFeO3 (BFO) has been widely investigated in many forms and morphologies because of its combined multiferroic and photovoltaic properties. However, direct growth of vertically aligned BFO nanorods on an underlying substrate has remained a challenge. In this work, we report template free growth of BiFeO3 nanorod arrays on fluorine doped tin oxide coated glass substrate. This has been achieved by a two-step process, in which FeOOH nanorods are grown by chemical bath deposition and converted into BFO using bismuth (Bi) coating by physical vapour deposition (PVD). Both DC sputtering and thermal evaporation are attempted under PVD and the results suggest that Bi deposited by DC sputtering leads to well-defined BFO nanorods, which show superior performance in both multiferroic and photoelectrochemical studies. Piezoelectric force microscopy data shows the signature butterfly loop that confirms piezoelectric behaviour with a d33 value of 8 pmV−1 in the BFO nanorods grown by DC sputtering. Further, the M-H hysteresis curve for the same samples reveals a remanent magnetization (Mr) value of 0.54 emu cc−1 and antiferromagnetic nature at room temperature. Finally, a stable photocurrent density of 0.05 mA cm−2 is achieved at 0.8 V vs Ag/AgCl under 1 Sun illumination. This work opens up new avenues for BFO in applications involving 1D nanostructures.

Synthesis, characterization, and gas sensing properties of Fe3O4/FeOOH nanocomposites for a mass-type gas sensor

Fe3O4/FeOOH nanocomposites were synthesized by a simplistic precipitation method for high-performance gas sensing applications. A spray-coating method was used to deposit a sensitive film of Fe3O4/FeOOH nanocomposites on a quartz crystal microbalance (QCM). The structural and morphological characteristics were analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS), Fourier transforms infrared (FTIR) spectroscopy, and a vibrating sample magnetometer (VSM). The average diameter and length of the FeOOH nanorods were 30 and 100 nm, respectively. The maximum saturation magnetization of the prepared Fe3O4/FeOOH nanocomposites obtained a value ~30 emu g−1. The QCM sensor based on the Fe3O4/FeOOH nanocomposites was measured with various concentrations of toxic gases (CO, NO2, SO2) at room temperature. The gas sensing results indicated that the developed sensor had a considerable potentiality to apply for toxic gas sensors with a high detection sensitivity, repeatability, and good stability.

NiMnCr layered double hydroxide-carbon spheres modified Ni foam: An efficient positive electrode for hybrid supercapacitors

New electrode composite materials, consisting of NiMnCr layered double hydroxides (LDHs) coated on carbon spheres (CS) supported on nickel foam (NiMnCr LDHs@CS/NF), were synthesized using a two step hydrothermal process. The obtained binder-free NiMnCr LDHs@CS/NF composite was investigated as a positive electrode for supercapacitors and achieved a high specific capacity of 569 C g−1 at 3 A g−1; this value was ~6.5 times that of CS/NF (87.9 C g−1 at 3 A g−1) and ~3.3 times that of NiMnCr LDHs/NF composite (173.2 C g−1 at 3 A g−1). The NiMnCr LDHs@CS/NF composite retained ~76% of its original capacity after 10,000 cycles, much better than ~54% achieved by NiMnCr LDHs/NF composite, suggesting good reversibility and stability. Furthermore, a hybrid supercapacitor was fabricated using NiMnCr LDHs@CS/NF as the positive electrode and FeOOH nanorods deposited on NF (FeOOH/NF) as the negative electrode. The hybrid supercapacitor displayed an energy density of 48 Wh kg−1 at a power density of 402.7 W kg−1. A home-designed windmill device was successfully driven by the as-fabricated supercapacitor device for about 25 s. Additionally, two as-fabricated hybrid supercapacitor cells in series were used to light up a yellow LED and a red LED in parallel for ~111 s and ~343 s, respectively. Taken together, these results indicate that the developed electrodes hold a promising potential in energy storage application.

Preparation of monodisperse SiO2 nanorods with hollow structure and parameters affecting the length-diameter ratio

Monodisperse SiO2 nanorods with hollow structure were prepared using FeOOH as a template. Powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption isotherms were utilized to characterize the products. With a FeCl3 concentration of 0.1 M, the average length and width of the prepared hollow SiO2 nanorods were 397 nm and 116 nm, respectively, and the average length-diameter ratio was calculated as 3.4. The average size of the nanopores of the amorphous SiO2 shell were measured as 2.5 nm. Furthermore, increasing the concentration of Cl− ions improved length-diameter ratios of the FeOOH nanorod template and hollow SiO2 nanorods.

Identifying Phase-Dependent Electrochemical Stripping Performance of FeOOH Nanorod: Evidence from Kinetic Simulation and Analyte-Material Interactions.

Metal hydroxide nanomaterials are widely applied in the energy and environment fields. The electrochemical performance of such materials is strongly dependent on their crystal phases. However, as there are always multiple factors relating to the phase-dependent electrochemistry, it is still difficult to identify the determining one. The well-defined crystal phases of α- and β-FeOOH nanorods are characterized through the transmission electron microscopy by a series of rotation toward one rod, where the cross-section shape and the growth direction along the [001] crystalline are first verified for 1D FeOOH nanostructures. The electrosensitivity of the two materials toward Pb(II) is tested, where α-FeOOH performs an outstanding sensitivity whilst it is only modest for β-FeOOH. Experiments via Fourier transform infrared spectroscopy, X-ray absorption fine structure (XAFS), etc., show that α-FeOOH presents a larger Pb(II) adsorption capacity due to more surficial hydroxyl groups and weaker PbO bond strength. The reaction kinetics are simulated and the adsorption capacity is found to be the determining factor for the distinct Pb(II) sensitivities. Combining experiment with simulation, this work reveals the physical insights of the phase-dependent electrochemistry for FeOOH and provides guidelines for the functional application of metal hydroxide nanomaterials.

Nanoporous 6H-SiC Photoanodes with a Conformal Coating of Ni-FeOOH Nanorods for Zero-Onset-Potential Water Splitting.

A surface-nanostructured semiconductor photoelectrode is highly desirable for photoelectrochemical (PEC) solar-to-fuel production due to its large active surface area, efficient light absorption, and significantly reduced distance for charge transport. Here, we demonstrate a facile approach to fabricate a nanoporous 6H-silicon carbide (6H-SiC) photoanode with a conformal coating of Ni–FeOOH nanorods as a water oxidation cocatalyst. Such a nanoporous photoanode shows significantly enhanced photocurrent density (jph) with a zero-onset potential. A dendritic porous 6H-SiC with densely arranged holes with a size of ∼40 nm on the surface is fabricated by an anodization method, followed by the hydrothermal deposition of FeOOH nanorods and electrodeposition of NiOOH. Under an illumination of AM1.5G 100 mW/cm2, the Ni–FeOOH-coated nanoporous 6H-SiC photoanode exhibits an onset potential of 0 V versus the reversible hydrogen electrode (VRHE) and a high jph of 0.684 mA/cm2 at 1 VRHE, which is 342 times higher than that of the Ni–FeOOH-coated planar 6H-SiC photoanode. Moreover, the nanoporous photoanode shows a maximum applied-bias-photon-to-current efficiency (ABPE) of 0.58% at a very low bias of 0.36 VRHE, distinctly outperforming the planar counterpart. The impedance measurements demonstrate that the nanoporous photoanode possesses a significantly reduced charge-transfer resistance, which explains the dramatically enhanced PEC water-splitting performance. The reported approach here can be widely used to fabricate other nanoporous semiconductors for solar energy conversion.

Polyphenol-metal manipulated nanohybridization of CNT membranes with FeOOH nanorods for high-flux, antifouling and self-cleaning oil/water separation

Carbon nanotube (CNT) membranes with nano-enhanced superwettability show great potential in high-efficient oil/water separation. In this study, we present a novel polyphenol-metal manipulated nanohybridization strategy to prepare CNT nanohybrid membranes embedded with FeOOH nanorods (NRs). The polyphenol-metal manipulated nanohybridization strategy lies in the assembly of polyphenol-metal (chitosan/tannic acid-Fe3+) complex primer on the CNT membranes followed by in situ FeOOH NRs mineralizating. The polyphenol-metal complex modulates the uniform distribution of in situ mineralized FeOOH NRs in the as-prepared CNT@CS/TA-FeOOH nanohybrid membrane, which endows the CNT nanohybrid membrane with both superhydrophilicity and underwater superoleophobicity. By integrating the high permeability of CNT membranes and the hydrophilicity and photo-degradation activity of FeOOH NRs, the CNT@CS/TA-FeOOH nanohybrid membrane possesses achieved a high water permeability above 8000 Lm-2h-1bar-1 and greatly elevated flux recovery ratio above 97% for oil/water separation. Both hydration-induced antifouling property and photo-induced self-cleaning capability contributed to the robust flux recovery for highly efficient oil/water separation. The CNT@CS/TA-FeOOH nanohybrid membrane is promising for oily wastewater treatment applications, and the proposed polyphenol-metal manipulated nanohybridization strategy shows great potential for engineering various multifunctional nanohybrid membranes.

Construction of 1D/2D α-Fe2O3/SnO2 Hybrid Nanoarrays for Sub-ppm Acetone Detection.

Exhaled acetone is one of the representative biomarkers for the noninvasive diagnosis of type-1 diabetes. In this work, we have applied a facile two-step chemical bath deposition method for acetone sensors based on α-Fe2O3/SnO2 hybrid nanoarrays (HNAs), where one-dimensional (1D) FeOOH nanorods are in situ grown on the prefabricated 2D SnO2 nanosheets for on-chip construction of 1D/2D HNAs. After annealing in air, ultrafine α-Fe2O3 nanorods are homogenously distributed on the surface of SnO2 nanosheet arrays (NSAs). Gas sensing results show that the α-Fe2O3/SnO2 HNAs exhibit a greatly enhanced response to acetone (3.25 at 0.4 ppm) at a sub-ppm level compared with those based on pure SnO2 NSAs (1.16 at 0.4 ppm) and pure α-Fe2O3 nanorods (1.03 at 0.4 ppm), at an operating temperature of 340°C. The enhanced acetone sensing performance may be attributed to the formation of α-Fe2O3–SnO2 n-n heterostructure with 1D/2D hybrid architectures. Moreover, the α-Fe2O3/SnO2 HNAs also possess good reproducibility and selectivity toward acetone vapor, suggesting its potential application in breath acetone analysis.

The structure-directing role of graphene in composites with porous FeOOH nanorods for Li ion batteries.

Graphene sheets that contain porous iron oxides including Fe2O3 and FeOOH nanorods were synthesized via a one-step hydrothermal route. A novel mechanism for controlling the structure of graphene-based composites was developed. Porous FeOOH nanorods with a high capacity for electron- and ion-transport were synthesized by controlling the composition of GO dispersion. The synthesized graphene/FeOOH composite anode exhibited an excellent electrochemical performance in which a reversible capacity of 304 mA h g−1 was reached with nearly 100% coulombic efficiency after 1000 cycles of charge and discharge under a high current rate of 5 A g−1.

Colorimetric and electrochemical arsenate assays by exploiting the peroxidase-like activity of FeOOH nanorods.

The authors describe an electrochemical and an optical method for the determination of As(V) by using iron oxyhydroxide (FeOOH) nanorods that display peroxidase-mimicking activity. The nanorods catalyze the oxidation of substrate ABTS by H2O2 to form a green product with an absorption maximum at 418nm. If, however, As(V) is electrostatically adsorbed on the nanorods, the oxidation is gradually inhibited. A colorimetric assay was worked out based on these findings. Response is linear in the 0 to 8ppb and 8 to 200ppb As(V) concentration range, and the detection limit is 0.1ppb. Even higher sensitivity is achieved in an electrochemical method which is based on the excellent electrical conductivity of FeOOH nanorods. Electrochemical analysis of As(V) was achieved by first adsorbing As(V) on the nanorods. This inhibits the ABTS reduction current signal, best measured at a potential of 150mV (vs. Ag/AgCl). The linear range extends from 0.04 to 200ppb, and the detection limit is as low as 12ppt. Graphical abstract Schematic representation of FeOOH nanorod-based colorimetric and electrochemical assays for arsenate (As(V)). As(V) adsorbed on FeOOH nanorods inhibits the peroxidase-mimicking activity of nanorods, and a colorimetric and electrochemical dual-signal assay was constructed to achieve sensitive determination of As(V).

Vertically aligned nanostructured FeOOH@MnO2 core shell electrode with better areal capacitance

Present work focuses on hydrothermal preparation of FeOOH@MnO2 core shell as a vertically aligned 1-D nanostructure and improvement in electrochemical charge storage by utilizing MnO2 nanostructure as an active electrode material and vertically aligned FeOOH nanorods for one dimensional electron transfer paths. A FeOOH@MnO2 core shell thin film electrode gives maximum capacitance of 0.252 Fcm−2 for the applied current density of 1 mAcm−2 and maintains 99.5% capacitance retention for 2000 charge discharge cycles at 5 mAcm−2 that attributes to better capacitive charge storage in the material. Assembled solid state symmetric electrochemical capacitor of FeOOH@MnO2 electrode yields maximum of 0.05 mWhcm−2 energy density with power delivery of 1.5 mWcm−2.

Tuning MnO2 to FeOOH replicas with bio-template 3D morphology as electrodes for high performance asymmetric supercapacitors

Controlled synthesis of tunable Mn-iron-oxide (Mn-FeOx) hybrids with unique three-dimensional (3D) porous structure based on diatoms for high performance supercapacitors is demonstrated. Successful transition process from MnO2 to FeOOH on diatomite was performed by two-step hydrothermal method and resultant replicas with 3D diatom morphology were obtained via etching process. The fabricated MnFeOx-0 diatom replica without transition was composed by MnO2 nanosheets and exhibited a high specific capacitance (228.6 F g−1 at 1 A g−1), good rate capability (74.6% retention after current density were increased to 10 A g−1), high coulombic efficiency (about 93.1% at 10 A g−1), and steady cycling performance (94.3% capacitance retention after 4000 cycles). MnFeOx-110 replica with FeOOH nanorods owned 224.6 F g−1 at 1 A g−1, high coulombic efficiency about 80% at 10 A g−1 and steady cycling performance about 92.5% retention after 4000 cycles. Finally, an asymmetric supercapacitor was assembled based on MnO2 nanosheets as the positive electrode and FeOOH nanorods as the negative electrode, which delivered a wide potential of 2 V with maximum energy density of 51.5 Wh kg−1 and power density of 9.1 kW kg−1. Considering that the two replicas owned great energy storage property, it opens an opportunity for rational design of the diatom morphology samples applied to high-performance supercapacitors.

Fe3C/Fe2O3 heterostructure embedded in N-doped graphene as a bifunctional catalyst for quasi-solid-state zinc–air batteries

The development of nonprecious metal catalysts with highly efficient and durable activities is of great importance for high performances of zinc–air batteries. Herein, the N-doped graphene wrapped Fe3C/Fe2O3 heterostructure has been designed as a bifunctional oxygen catalyst for zinc–air batteries. In the synthesis process of the catalyst, graphene oxide (GO) can assemble with graphitic carbon nitride (g-C3N4) and FeOOH nanorods by the π−π stacking and hydrogen bonds, respectively. The assembly of GO, g-C3N4 and FeOOH nanorods results in nanostructure of carbon layers coated iron species and leads to outstanding durability in both alkaline and acidic media. The synergistic effect of nitrogen doping and Fe3C/Fe2O3 heterostructure allows the catalyst (Fe3C/Fe2O3@NGNs) to display high oxygen reduction and evolution reaction activities. The liquid zinc–air battery assembled with the catalyst presented a remarkable peak power density (139.8 mW cm−2), large specific capacity (722 mAh g−1) and excellent charging–discharging cycling performance. The quasi-solid-state zinc–air battery with the catalyst exhibited an impressive open-circuit voltage and a peak power density. Therefore, the Fe3C/Fe2O3@NGNs catalyst is expected to have a bright future for practical applications in energy conversion devices.

Facile thermochemical conversion of FeOOH nanorods to ZnFe2O4 nanorods for high-rate lithium storage.

We successfully prepared ZnFe2O4 nanorods (ZFO-NRs) by a simple thermochemical reaction of FeOOH nanorods with Zn(NO3)2 to use as an anode material in lithium-ion batteries. The FeOOH nanorod shape was well maintained after conversion into ZFO-NR with the formation of porous structures. The nanorod structure and porous morphology facilitate Li+ transport, improve the reaction rates owing to the larger contact area with the electrolyte, and reduce the mechanical stress during lithiation/delithiation. The ZFO-NR electrode exhibited a reversible capacity of 725 mA h g−1 at 1 A g−1 and maintained a capacity of 668 mA h g−1 at 2 A g−1; these capacities are much higher and more stable than those of ZFO nanoparticles prepared by a hydrothermal method (ZFO-HT) (216 and 117 mA h g−1 at 1 and 2 A g−1, respectively). Although ZFO-NRs exhibited high, stable capacities at moderate current densities for charging and discharging, the capacity rapidly decreased under fast charging/discharging conditions (>4 A g−1). However, carbonized ZFO-NR (C/ZFO-NR) exhibited an improved reversible capacity and rate capability resulting from an increased conductivity compared with ZFO-NRs. The specific capacity of C/ZFO-NRs at 1 A g−1 was 765 mA h g−1; notably, a capacity of 680 mA h g−1 was maintained at 6 A g−1.

Amorphous FeOOH nanorods and Co3O4 nanoflakes as binder-free electrodes for high-performance all-solid-state asymmetric supercapacitors

We have built a high-performance supercapacitor anode based on carbon fabric (CF), vertically aligned graphene nanosheets (VAGN) and FeOOH nanorods.

FeOOH nanorods array and its application in the photoreduction of Cr(VI)

FeOOH nanorod array was synthesized utilizing a facile hydrothermal method. The photoreduction efficiency to Cr(VI) is 70% after 4 h illumination at pH < 3. The Mott-Schottky plots confirmed the n-type behavior and the donor density is calculated to be 6.91 × 1016 cm−3. The best anodic photo-current is 90 nA/cm2 under illumination of light with intensity of 0.02 W/cm2. The onset potential of photo-current is −0.2 V (vs. Ag/AgCl (Sat. KCl)), which indicates the FeOOH nanorods array has an active interface.

Facile-fabricated iron oxide nanorods as a catalyst for hydrogenation of nitrobenzene

β-FeOOH nanorods were prepared by a poly ethylene glycol (PEG) assisted precipitation of FeCl3 ∙ 6H2O aqueous solution with urea. Na2CO3 aqueous solution was introduced to maintain their shapes under annealing. The one-dimensional porous iron oxide nanorods were synthesized successfully. The as-prepared catalysts were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption isotherms and X-ray photoelectron spectroscopy. The hydrogenation of nitrobenzene to aniline was taken as probe reaction to evaluate their catalytic performance. FeOOH (iron oxides hydroxide) nanorods, fabricated by annealing β-FeOOH nanorods at 250°C in Ar atmosphere for 4h, exhibited high catalytic activity for the transfer hydrogenation of nitrobenzene to aniline with hydrazine hydrate as hydrogen donors.

Quasi-Topotactic Transformation of FeOOH Nanorods to Robust Fe2O3 Porous Nanopillars Triggered with a Facile Rapid Dehydration Strategy for Efficient Photoelectrochemical Water Splitting.

A facile rapid dehydration (RD) strategy is explored for quasi-topotactic transformation of FeOOH nanorods to robust Fe2O3 porous nanopillars, avoiding collapse, shrink, and coalescence, and compared with a conventional treatment route. Additionally, the so-called RD process is capable of generating a beneficial porous structure for photoelectrochemical water oxidation. The obtained RD-Fe2O3 photoanode exhibits a photocurrent density as high as 2.0 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE) and a saturated photocurrent density of 3.5 mA cm-2 at 1.71 V versus RHE without any cocatalysts, which is about 270% improved photocurrent density over Fe2O3 with the conventional temperature-rising route (0.75 mA cm-2 at 1.23 V vs RHE and 1.48 mA cm-2 at 1.71 V vs RHE, respectively). The enhanced photocurrent on RD-Fe2O3 is attributed to a synergistic effect of the following factors: (i) preservation of single crystalline nanopillars decreases the charge-carrier recombination; (ii) formation of long nanopillars enhances light harvesting; and (iii) the porous structure shortens the hole transport distance from the bulk material to the electrode-electrolyte interface.