α-Fe2O3 Nanorods Research Articles

Synthesis of ZnO/α-Fe2O3 heterojunction nanocomposites for ultra-sensitive acetone detection

ZnO/α-Fe2O3 nanocomposites with ultra-sensitive response to acetone were successfully prepared by hydrothermal and solvothermal methods. The synthesized materials were characterized by SEM, TEM, XPS and other means, and the results indicated that a good heterojunction was constructed between α-Fe2O3 nanorods and ZnO nanosheet particles. The results obtained by gas sensing tests show that compared with pure α-Fe2O3 and pure ZnO, ZnO/α-Fe2O3(S-2) sensor has superior performance, and it exhibits high response (Ra/Rg = 62.8), fast response and recovery time (4 s and 10 s) to 100 ppm acetone at 220 °C. The n-n heterojunction effect and structural characteristics are the main reasons for the performance improvement. The nanocomposites have broad application prospects in the field of acetone detection.

Exploring novel p-n core/shell structure in single α-Fe2O3 nanorods of hierarchical hollow microspheres for ultrasensitive acetone gas sensor

Fabricating metal oxide sensors with super-sensitivity and good distinguishing properties for gases is a challenge due to the difficulties in controlling vacancy-type structural defects of nanomaterials and the data processing. In this paper, we reported the fabrication of hierarchical α-Fe2O3 hollow microsphere (HFHM)-based sensor using a facile and scalable method with uniform-micro spherical carbon templates, as well as the data analysis using artificial intelligence (AI). The shell of the unique hollow microspheres was built by connecting many α-Fe2O3 nanorods, so the superstructures have 0D, 1D, and 3D structural features. In these α-Fe2O3 nanorods, positron annihilation measurements revealed abundant oxygen-vacancy clusters (11 atoms), nanopores (0.53 nm) and p-n core/shell structure. The HFHM-based sensors, hence, exhibited an extremely high sensitivity toward acetone (Response = 320 (200 ppm), limited detection (DL) ∼ 250 ppt) and ethanol (Response = 300 (200 ppm), DL ∼ 500 ppt), as well as a super-fast response time (1–2 s). In particular, by using the Principal Component Analysis (PCA), an applied AI tool, we were able to significantly improve the distinguishing and selective abilities of acetone and ethanol (high-response gas groups) as well as H2, CO and NH3 (low-response gas groups).

In-situ hydrothermal synthesis of oriented hematite nanorods for sub-ppm level detection of ozone gas

The development of simple and reproducible synthesis techniques for obtaining one-dimensional semiconducting nanostructures is essential for the advancement of gas sensor devices. We report a facile and versatile approach for the in-situ growth of vertically oriented hematite nanorods to be applied as a resistive ozone gas sensor. The α-Fe2O3 nanorods were grown via a hydrothermal treatment directly onto an Al2O3 substrate with interdigitated Pt electrodes, thus facilitating the integration of nanorods into the sensing platform. At 150 °C, the gas-sensing experiments revealed a good sensitivity of these nanorods to different ozone concentrations (10–570 ppb), besides a fast response time and repeatable response–recovery cycles. The present study offers a promising way for designing high-performance gas sensors based on hematite nanorods.

Oxygen vacancy modified α-Fe2O3 nanorods provide an environment-friendly and efficient anti-corrosion passive film into polymer coating

Oxygen vacancy modified Fe2O3 (OV-Fe2O3) nanorods were fabricated and then used as epoxy coating fillers. The OV-Fe2O3 fillers passivates the steel substrate, because oxygen atoms can be stored in the vacancies to form a metastable state. Electrochemical impedance spectroscopy showed the impedance modulus of OV-Fe2O3 coatings was about 105 times higher than general α-Fe2O3 coatings after O2-high pressure and high-temperature corrosion. X-ray photoelectron spectroscopy and scanning vibrating electrode technique confirm OV-Fe2O3 can continuously transport oxygen from the oxygen-rich environment to the substrate surface (oxygen-deficient environment) before the permeation of the corrosive medium, eventually achieving efficient passivation.

Role of oxygen vacancies and porosity in enhancing the electrochemical properties of Microwave synthesized hematite (α-Fe2O3) nanostructures for supercapacitor application

Herein, we report a green and cost-effective microwave-assisted synthesis of oxygen vacancy-rich porous α-Fe2O3 nanorods and α-Fe2O3 nanospheres for supercapacitor applications. The synthesized samples were characterized using Field emission scanning electron microscopy (FESEM) coupled with Energy Dispersive X-Ray (EDX), X-ray diffraction (XRD), Raman Spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analysis. The synthesized α-Fe2O3 nanorods have a high specific surface area of 133.6 m2g-1 and a pore size of around 15.2 nm. With the use of cyclic voltammetry (CV), galvanostatic charge-discharge experiments, and electrochemical impedance spectroscopy, the electrochemical characteristics of α-Fe2O3 nanorod and nanosphere-based electrodes were studied and compared. In contrast to hematite nanospheres, which displayed a specific capacitance of only 715.05 Fg-1, hematite nanorods exhibited the highest specific capacitance of 1253.02 Fg-1 and excellent capacitance retention of 93% after a long life of 3000 cycles in 3 M KOH electrolyte with a potential window of −0.2 to 0.55 V. The enhancement in electrochemical properties could be attributed to its porous nature and the presence of oxygen vacancies which provided more active sites for redox reactions and high electrical conductivity. The results demonstrate that oxygen vacancy-rich and porous α-Fe2O3 nanorods synthesized via the green approach can serve as an ideal electrode material for supercapacitors.

Cobalt-doped double-layer α-Fe2O3 nanorod arrays for enhanced photoelectrochemical reduction of Cr(VI)

Element doping is an important method for improving the performance levels of photoelectrochemical (PEC) cells. Nevertheless, to date, the PEC conversion efficiency and photocurrent characteristics of the available photoanodes remain very low. In this study, cobalt (Co) was selectively doped into the bottom and/or top layers of double-layered α-Fe2O3 nanorod arrays grown on conductive transparent substrates (F:SnO2, FTO) via a two-step hydrothermal method; this process was performed to enhance the charge transfer ability and thus significantly improve the PEC performance. The light response capabilities of all α-Fe2O3 films were evaluated by an electrochemical workstation under dark or visible light irradiation conditions. The sample of Co doped in the bottom layer exhibited a high photoelectrochemical performance, achieving a current density of 1.37 mA/cm2 at + 1.0 V versus saturated calomel electrode (SCE); additionally, the sample exhibited a photoelectric synergistic ability to reduce Cr(VI) in an aqueous solution, with 84.85% reduction in 180 min. Under the influence of the electric field inside the double-layer electrode, the photoexcited electrons and holes are transferred to the surfaces of the FTO substrate and the photoanode, increasing the current density and enhancing Cr(VI) reduction. The results of this study offer an alternative approach for designing novel photoanodes with improved PEC performance levels by engineering the electron density distribution and band structure for efficient carrier separation; the results may provide new solutions in heavy metal reduction and contaminant degradation projects.

Clay-derived Synthesis of Supported α-Fe2O3 Nanoparticles: Shape, Adsorption, and Photo-catalysis

Background: This paper reports a versatile bentonite clay-mediated growth method for selectively synthesizing zero-dimensional α-Fe2O3 nanoparticles and one-dimensional α-Fe2O3 nanorods. Method: In such a growth process without any other surfactant or additive, the bentonite clay is not only used as the supporter, but also as a shape mediator for α-Fe2O3 nanocrystals. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results: The as-prepared products were used to investigate their promising adsorptive and photocatalytic applications in water treatment. According to the Langmuir equation, the maximum adsorption capacity of the α-Fe2O3/bentonite composite for Congo red (CR) is calculated to be 96.9 mg·g-1. Furthermore, the α-Fe2O3/bentonite nanocomposites also show an excellent photocatalytic property in the degradation of methyl orange (MO). Conclusion: This facile and novel synthesis method has the potential to be applied to prepare the low-cost α-Fe2O3/bentonite nanocomposite for the removal of CR and MO.

Sea urchin-like SnO2/α-Fe2O3 heterostructural microspheres for enhanced acetone gas sensing: Materials preparation, performance evaluation, and mechanism investigation

Herein, sea urchin-like SnO2/α-Fe2O3 (SU-SnO2/α-Fe2O3) heterostructural microspheres was prepared successfully by two-steps hydrothermal treatment, and used as semiconductor for acetone gas sensing. SEM and TEM characterizations showed that as-prepared composites exhibited sea urchin-like morphology with microstructures of inner SnO2 microspheres and outer vertically grown α-Fe2O3 nanorods. SnO2/α-Fe2O3 microspheres presented higher and faster response / recovery for acetone in comparison to pure SnO2. At the optimum temperature of 300 °C, response value of SU-SnO2/α-Fe2O3 sensor reached 18.7 towards acetone vapor with concentration of 100 ppm. The response time was 8 s, and recovery time was 2 s. Moreover, the proposed method displayed an excellent linearity for measuring acetone vapor with concentration range of 1–200 ppm. The improvement of gas sensing properties for SnO2/α-Fe2O3 microspheres was ascribed to the unique microstructures, formation of heterojunction, and abundant adsorbed oxygen. To further demonstrate the promoted mechanism, adsorption behavior of as-prepared composites for acetone molecule was investigated by density-functional theory (DFT), with results that Fe sites on the hetero-interface possessed strong interaction with acetone molecule, which enhanced the gas sensing properties towards acetone. This study confirmed the gas sensor performance of SnO2/α-Fe2O3 microspheres towards acetone, and supplemented the promotion mechanism by DFT calculations.

Synergy of Ultrathin CoOx Overlayer and Nickel Single Atoms on Hematite Nanorods for Efficient Photo-Electrochemical Water Splitting.

To solve surface carrier recombination and sluggish water oxidation kinetics of hematite (α-Fe2 O3 ) photoanodes, herein, an attractive surface modification strategy is developed to successively deposit ultrathin CoOx overlayer and Ni single atoms on titanium (Ti)-doped α-Fe2 O3 (Ti:Fe2 O3 ) nanorods through a two-step atomic layer deposition (ALD) and photodeposition process. The collaborative decoration of ultrathin CoOx overlayer and Ni single atoms can trigger a big boost in photo-electrochemical (PEC) performance for water splitting over the obtained Ti:Fe2 O3 /CoOx /Ni photoanode, with the photocurrent density reaching 1.05mA cm-2 at 1.23V vs. reversible hydrogen electrode (RHE), more than three times that of Ti:Fe2 O3 (0.326 mA cm-2 ). Electrochemical and electronic investigations reveal that the surface passivation effect of ultrathin CoOx overlayer can reduce surface carrier recombination, while the catalysis effect of Ni single atoms can accelerate water oxidation kinetics. Moreover, theoretical calculations evidence that the synergy of ultrathin CoOx overlayer and Ni single atoms can lower the adsorption free energy of OH* intermediates and relieve the potential-determining step (PDS) for oxygen evolution reaction (OER). This work provides an exemplary modification through rational engineering of surface electrochemical and electronic properties for the improved PEC performances, which can be applied in other metal oxide semiconductors as well.

3D Porous Compact 1D/2D Fe2 O3 /MXene Composite Aerogel Film Electrodes for All-Solid-State Supercapacitors.

2D MXene nanoflakes usually undergo serious restacking, that easily aggravates during the traditional vacuum-assisted filtration process; and thus, hinders the electrochemical performance of the corresponding film electrodes. Herein, 3D porous compact 1D/2D Fe2 O3 /MXene aerogel film electrode with an enhanced electrochemical performance is fabricated by freeze-drying assisted mechanical pressing. An introduction of 1D α-Fe2 O3 nanorods can not only alleviate the restacking of 2D MXene but also provide additional pseudocapacitance for the composite film system. Thus, the resulting Fe2 O3 /MXene aerogel film electrode shows an enhanced specific capacitance of 182 F g-1 (691 mF cm-2 ) at a current density of 1 A g-1 in 3 m H2 SO4 electrolyte as well as with 81.74% capacitance retention after 10000 charge-discharge cycles. Besides, the addition of 1D α-Fe2 O3 nanorods has a significant contribution in the volumetric capacitance of the composite aerogel film (150 F cm-3 ), which is 2.68 times that of the pure MXene aerogel film (56 F cm-3 ). Moreover, the fabricated all-solid-state symmetric supercapacitor (SSSC) delivers a superior areal energy density of 3.61 µWh cm-2 at a power density of 119.04 µW cm-2 . This rapid-forming 3D porous, binder-free, and freestanding aerogel film provides a progressive strategy for the fabrication of MXene-based electrode for supercapacitors.

Investigation of photoelectrocatalytic degradation mechanism of methylene blue by α-Fe2O3 nanorods array

Efficiently and thoroughly degrading organic dyes in wastewater is of great importance and challenge. Herein, vertically oriented mesoporous α-Fe2O3 nanorods array (α-Fe2O3-NA) is directly grown on fluorine-doped tin oxide (FTO) glass and employed as the photoanode for photoelectrocatalytic degradation of methylene blue simulated dye wastewater. The Ov sites on the α-Fe2O3-NA surface are the active sites for methylene blue (MB) adsorption. Electrons transfer from the adsorbed MB to Fe-O is detected. Compared with electrocatalytic and photocatalytic degradation processes, the photoelectrocatalytic (PEC) process exhibited the best degrading performance and the largest kinetic constant. Hydroxyl, superoxide free radicals, and photo-generated holes play a jointly leading role in the PEC degradation. A possible degrading pathway is suggested by liquid chromatography-mass spectroscopy analysis. This work demonstrates that photoelectrocatalysis by α-Fe2O3-NA has a remarkable superiority over photocatalysis and electrocatalysis in MB degradation. The in-depth investigation of photoelectrocatalytic degradation mechanism in this study is meaningful for organic wastewater treatment.

Modulation of Magnetism and Optical Properties of Hematite (α-Fe2O3) Nanorods Fabricated via Thermal Conversion of Hydrothermally Synthesized Akaganeite (β-FeOOH)

A simple hydrothermal approach was used to effectively synthesize high-quality single crystal hematite (α-Fe2O3) nanorods with an average diameter of ∼59.40 nm. Rietveld refinement analysis was used to examine the crystal structure and phase purity of hematite that displayed a hexagonal crystal structure with a single phase in the R-3c space group. Unit cell and other reliability parameters were also determined using Rietveld refinement. In addition, magnetic measurements using a vibrating sample magnetometer (VSM) have been conducted at room temperature from which magnetic hysteresis loops reveal that the material is weakly ferromagnetic with lowered magnetic parameter values. In the synthesized sample, both ferromagnetic (FM) and antiferromagnetic (AFM) contributions were observed and separated by applying a theoretical modification of the measured M-H loop.

Photocatalytic performance of an α-Fe2O3 electrode and its effects on the growth and metabolism of Citrobacter freundii.

Electronic exchanges occur between semiconductor minerals and microorganisms. However, researchers have focused on the photocatalytic degradation of pollutants by semiconductor minerals, and there is a limited amount of studies on semiconductor photogenerated electrons that influence the growth and energetic mechanisms of bacteria. Bioelectrochemical systems (BES) are important new bioengineering technologies for investigating the mechanisms by which bacteria absorb electrons. In this work, we built a BES that used α-Fe2O3 nanorods as a photoanode and Citrobacter freundii as bio-cathode bacteria to explore the effect of photoelectrons on C. freundii growth and metabolism. The photoanode was prepared by a hydrothermal synthesis method. As confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the photoanode was made of α-Fe2O3. Corresponding scanning electron microscope (SEM) images showed that α-Fe2O3 nanorod arrays formed with a diameter of 50nm, and the band gap was 2.03eV, as indicated by UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The C. freundii growth metabolism changed significantly because of photoelectrons; under light conditions, the growth rate of C. freundii significantly accelerated, and as inferred from the three-dimensional fluorescence spectrum, the protein, humic acid, and NADH concentrations were significantly higher at 72h. According to the changes in the organic acid content, photoelectrons participated in the reductive tricarboxylic acid cycle (rTCA) to enhance growth and metabolism. The results of the study have broad implications for advancing fields that study the effects of semiconductor minerals on electroactive microorganisms and the semiconductor-photoelectronic transport mechanisms of electroautotrophic microorganisms. KEY POINTS: • For the first time, A BES was built that used α-Fe2O3 nanorods as a photoanode and C. freundii as a bio-cathode bacteria. • Photoelectrons produced by α-Fe2O3 photoelectrode promote the growth of C. freundii. • Effects of photoelectrons on C. freundii metabolism were conjectured by the changes of organic acids and NADH.

Vertically Aligned CdO-Decked α-Fe2O3 Nanorod Arrays by a Radio Frequency Sputtering Method for Enhanced Photocatalytic Applications.

Green hydrogen production is one of the most desirable sustainable goals of the United Nations. Thus, for that purpose, we developed hematite (α-Fe2O3), an n-type semiconductor, a desirable candidate for photoelectrochemical (PEC) water splitting, enabling hydrogen evolution. High recombination losses, low efficiency, and large-scale production hinder its potential. To address these issues, we have fabricated optimized bare and cadmium oxide (CdO)-decorated hematite thin film nanorod arrays using a throughput radio frequency (RF) sputtering with efficient water splitting behavior. To the best of our knowledge, no work has been done so far on the synthesis of CdO/α-Fe2O3 via RF sputtering for PEC application. Bare α-Fe2O3 samples, with a morphology of vertically aligned nanorods, were fabricated with optimized parameters such as as-deposited 70 nm of Fe, an angle of deposition of 70°, and an annealing temperature of 600 °C, which showed a photocurrent density of 0.38 mA/cm2 at 1.65 V vs reversible hydrogen electrode (RHE). Characterizations depicted that this unique morphology with high crystallinity directly enhanced the performance of hematite photoanodes. Further, deposition of 30 nm of cadmium (CdO) on the α-Fe2O3 nanorods produced a corn-like morphology with CdO nanoparticles (∼2 nm), resulting in 4-times enhancement of the PEC performance (1.2 mA/cm2 at 1.65 V vs RHE). CdO acted as a co-catalyst, responsible for satisfactory suppression of recombination and facilitating the hole transfer, directly enhancing the overall photocurrent density. This photoanode showed an extremely stable behavior over a period of 26 h when kept under constant illumination. Furthermore, the CdO-modified photoanode showed a better dye degradation (98% in 40 min) than the bare hematite (60% in 40 min), proving to be an efficient photoanode.

α-Fe2O3 based nanotherapeutics for near-infrared/dihydroartemisinin dual-augmented chemodynamic antibacterial therapy

Due to the negligible bacterial resistance, chemodynamic therapy (CDT) is a promising treatment for bacterial infection. However, it is severely impeded by the constant body temperature, shortage of Fe(Ⅱ) ions and insufficient H2O2 level in infected tissue. To enhance the therapeutic efficiency of CDT, improved strategies are urgently needed to tackle these problems. Herein, we exploited an infection microenvironment-responsive nanotherapeutics for near-infrared (NIR)/dihydroartemisinin (DHA) dual-augmented antibacterial CDT. The convenient encapsulation of DHA-loaded α-Fe2O3 nanorods with metal-polyphenol networks (MPN) led to the generation of an antibacterial nanoagent Fe2O3@DHA@MPN (FDM). Afterwards, its photothermal and peroxidase-like activities were intensively studied. Furthermore, the bactericidal efficacy of FDM was evaluated through both in vitro and in vivo antibacterial assays. Firstly, FDM showed both satisfactory photothermal and NIR/DHA dual-augmented peroxidase-like activities. Besides, it exhibited a pH-responsive release behavior of both Fe(Ⅱ) ions and DHA. Moreover, it presented tannic acid-mediated bacterial adhesion effect. In vitro experiments demonstrated that FDM could achieve a satisfactory efficiency against both planktonic bacteria and biofilms. In vivo assays illustrated both the extraordinary synergistic antibacterial effect and efficient anti-inflammatory ability of FDM. The outcomes indicated that the exploited antibacterial agent could offer new insight on developing intelligent nanotherapeutics for clinical use in the future. Statement of significanceThe antibacterial efficiency of chemodynamic therapy (CDT) is seriously limited by the constant body temperature, shortage of Fe(Ⅱ) ions and insufficient H2O2 level at the mildly acidic inflammatory microenvironment. To address these issues, we have developed a pH-responsive nanoagent (Fe2O3@DHA@MPN) for near-infrared (NIR)/dihydroartemisinin (DHA) dual-augmented CDT. Through the NIR-induced photothermal effect of exterior Fe(Ⅲ)/tannic acid complex, the increased local temperature led to a photothermal enhanced CDT. Besides, a continuous supply of Fe(Ⅱ) ions could be achieved by tannic acid-mediated Fe(Ⅲ) reduction. Moreover, DHA was adopted as a substitute for H2O2 to initiate DHA-mediated CDT. Both in vitro and in vivo assays demonstrated its outstanding bactericidal efficiency. Therefore, the developed nanotherapeutics could be a promising candidate for clinical trials.

Effect of O2 on Selective Catalytic Reduction of NO by C3H6 over Fe Catalysts Supported on Porous Clay Heterostructures (Fe-PCH)

K10 montmorillonite was used as the raw clay to prepare porous clay heterostructures (PCH) by organic template intercalation and tetraethylorthosilicate (TEOS) was used as silicone source. Fe was load on the PCH support by impregnation method to prepare Fe-PCH catalysts. The catalytic activity tests were carried out in a fixed bed micro-reactor in the atmosphere of 0.1% C3 H6 , 0.1%NO, 0~10%O2 in N2 balance. The total flow rate was 100ml/min and corresponding gas hourly space velocity (GHSV) was 15000h-1. The mircro-reaction pathways were studied by Diffuse Reflection Infrared Fourier Transform Spectrometer (DRIFTS). The influence of O2 on the SCR-C3 H6 reactivity over Fe-PCH was analyzed. The results showed that FePCH catalyst exhibited the best catalytic performance without oxygen, which reached the maximum NO conversion of 100% at 4000 C. When the concentration of O2 is below a critical value, [O2 ]crit, the catalytic activity gradually decreased with the increasing concentration of O2 . When the concentration of O2 is above [O2 ]crit, the NO conversion was only 20%~30%. Fe-PCH catalysts were characterized by transmission electron microscope (TEM), N2 adsorption/desorption and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that Fe-PCH had supermicroporous and mesoporous structures. The active components on Fe-PCH catalyst were mainly α-Fe2 O3 nanorods, exposing (024) and (104) planes. The in situ DRIFTS technique was used to detect the reactive intermediates over the surface of Fe-PCH catalyst, which could help analyze the mechanism of the influence of oxygen on catalytic activity. The results presented that oxygen could inhibit the formation of isocyanate species over Fe-PCH catalyst during C3 H6 -SCR, which might be the reason for the decrease of NO conversion. Finally, a reasonable reaction path of C3 H6 -SCR over Fe-PCH catalyst was proposed.

Influence of erbium doping on the structural, magnetic and optical properties of hematite (α-Fe2O3) nanorods

Pure and Er-doped hematite (α-Fe2O3) nanorods were prepared by a two-step method involving hydrothermal synthesis and calcination of pure and Er-doped goethite (α-FeOOH) nanorods. Substitution of Fe3+ by Er3+ in the crystal structure of hematite caused morpho-structural changes such as expansion of the unit cell and gradual shortening and rounding of hematite nanorods towards formation of nanoellipsoids. These changes induced modification of magnetic and optical properties suggesting the possibility of a systematic control of physical properties via rare earth substitution. A decrease in the hyperfine magnetic field, coercive field and Morin transition temperature, as well as an increase of the magnetic susceptibility and a narrowing of the optical band gap were observed by substitution. Intimate mechanisms related to the formation of more and more defect-like hematite phases with decreased temperatures for the transition to the low temperature antiferromagnetic phase at increased doping level were evidenced via temperature dependent Mössbauer spectroscopy.

Regulating Sn self-doping and boosting solar water splitting performance of hematite nanorod arrays grown on fluorine-doped tin oxide via low-level Hf doping

Hematite (α-Fe2O3) nanorod arrays grown on fluorine-doped tin oxide (FTO) substrate exhibit outstanding solar water splitting efficiency, benefiting from Sn self-doping induced by high-temperature annealing. However, this Sn self-doping couldn’t be freely controlled without changing the optimized annealing conditions, which limits the further improvement of their photoelectrochemical (PEC) properties. Here, we report a facile hydrothermal synthesis with subsequent annealing approach to regulate the Sn diffusion via hafnium (Hf) doping as well as enhance the PEC performance of hematite photoanode. Upon increasing the Hf doping concentration, the Sn self-doping content was continuously suppressed. The very low doping-level of Hf (i.e., atomic Hf/Fe = 0.13 ∼ 1.54%) was sufficient for enhancing the electrical conductivity. The Hf-doped α-Fe2O3 with the optimized dopant concentration (Hf/Fe = 1.34%, denoted as 0.25-Hf-Fe2O3) showed a photocurrent density of 1.79 mA/cm2 at 1.23 V vs. RHE, 70% higher than that of the Sn self-doped one (Pristine-Fe2O3). The donor density of 0.25-Hf-Fe2O3 increased 2.5 times compared to Pristine-Fe2O3 while its space-charge resistance and charge transfer resistance declined by 40% and 22%, respectively, verifying Hf doping improves the charge carrier density and accelerates the charge transfer for solar water oxidation. We offered here a prospective dopant alternative for preparing superior hematite-based photoanode.

Synthesis of core-shell ZIF-8@α-Fe2O3 nanorods and improvement of selectivity for ammonia gas

Uniform and dense α-Fe2O3 nanorods were directly synthesized on the ceramic tube substrate by hydrothermal method, and then a layer of porous and dense ZIF-8 film was hydrothermally grown and coated on the surface of α-Fe2O3 nanorods after immersion in ligand solution and high-temperature treatment. Then the core-shell ZIF-8 @ α-Fe2O3 nanorods were obtained. The elements, composition, surface morphology, and crystal structure of the samples were analyzed by XPS, SEM, TEM, and XRD. These results indicate that the width of the rod-shaped α-Fe2O3 was between 20 and 40 nm while the rod-shaped α-Fe2O3 coated with a layer of dense porous ZIF-8 was between 50 and 80 nm. The gas sensing results reveal that compared with pure α-Fe2O3 nanorods, ZIF-8 @ α-Fe2O3 had a great improvement in gas selectivity (11.7), response value (136.9 for ammonia gas of 50 ppm at 280 ℃). The working process and gas sensing mechanism of the ZIF-8 @ α-Fe2O3 were discussed and it demonstrates that ZIF-8 not only plays a screen role in the gas-sensitive response process, but also increases the sensitivity by adsorbing oxygen molecules. It proved that the direct growth of ZIF-8 @ α-Fe2O3 on the ceramic tube provides a more effective way to improve the gas response and selectivity.

Criss-crossed α-Fe2O3 nanorods/Bi2S3 heterojunction for enhanced photoelectrochemical water splitting

In this research work, α-Fe2O3/Bi2S3 heterojunction photoelectrodes for improved photoelectrochemical water splitting have been successfully fabricated on FTO substrate by applying hydrothermal and solvothermal approaches. A seed layer approach is also applied before the solvothermal step for the homogeneous distribution of Bi2S3 over α-Fe2O3 nanorods to obtain a uniform heterojunction. The physicochemical and optical techniques results of α-Fe2O3/Bi2S3 indicate high crystallinity, presence of two distant phases with different bandgap positions. Linear sweep voltammetry (LSV) results indicate that the optimized α-Fe2O3/Bi2S3 photoanode performs a maximum photocurrent density of 2.550 mA cm−2 at 1.23 VRHE which is almost 20 times higher than pristine α-Fe2O3 (0.123 mA cm−2 at 1.23 V RHE). Electrochemical Impedance Spectroscopy (EIS) entirely shows α-Fe2O3/Bi2S3.6 h is the lowest Rp (180.9 Ω cm2) compare to pristine Fe2O3 (5810 Ω cm2), indicating enhanced photocatalytic performance on OER and S2-/S22- cycle followed under 100 mW cm−2 solar irradiation. This significant upsurge in the photocurrent density and applied biased photon-to-current conversion efficiency shown by the heterojunction is attributed to the improved light-harvesting efficiency, enhanced conductivity, and effective charge separation at the α-Fe2O3/Bi2S3 interface.