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Introduction of oxygen vacancies into hematite in local reducing atmosphere for solar water oxidation
摘要： Sn Doping and creation of oxygen vacancies have been adopted universally to overcome the poor electric conductivity and unfavorable hole diffusion length of α-Fe2O3 photoanodes. Generally, Sn doping is realized via longitudinal migration of tin element from FTO (fluorine-doped tin oxide) substrates into α-Fe2O3 at high temperature. To introduce oxygen vacancies along with Sn into hematite for further promoting its electric conductivity, we have created a local reducing atmosphere via partial oxidation of graphite while doping hematite with Sn. The donor density of the resultant Fe2O3 photoanode annealed on graphite (G-Fe2O3) at 770 °C for 20 min is increased to ～1.7 times that of the counterpart annealed on SiO2 powders (S-Fe2O3), indicating that the electric conductivity of hematite is improved after introduction of oxygen vacancies. Moreover, oxygen vacancies have been demonstrated to significantly reduce the charge transfer resistance of Sn doped hematite. Consequently, the photocurrent density of G-Fe2O3 is enhanced remarkably (～70%) compared with S-Fe2O3. However, the improvement in photocurrent density due to oxygen vacancies becomes less significant when more Sn is doped into hematite. The strategy for creation of oxygen vacancies reported here can be extended to other photoanodes for better understanding the effect of oxygen vacancies on PEC performance.
关键词： Oxygen vacancies,Sn doping,Solar water oxidation,Hematite
更新于2025-09-23 15:23:52
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Novel design of photocatalyst coaxial ferromagnetic core and semiconducting shell microwire architecture
摘要： We report a novel design of coaxial core-shell magnetic-semiconductor microwire, as a catalyst under sunlight irradiation. The nano/micro hierarchical architecture-like device is comprised of a coaxial core-shell microwire where the core is the ferromagnetic Fe metal and the shell is formed by a semiconducting hematite layer. The fabrication process of our substrate-free device is simply based on controlled thermal oxidation process revealing a simple and low-cost method. The hematite outer microlayer has a mesoporous structure decorated with nanowires. The ferromagnetic and metallic core assume fundamental importance as to mechanical stability, collect the generated photoelectrons, and to be removed back from the dye solution by a magnetic field gradient or simply a magnet. This nano/micro device has exhibited photocatalytic activity to degrade the methylene blue dye under simulated sunlight irradiation. Additionally, the coaxial magnetic/semiconducting can also be designed as a photoanode to drive water oxidation reaction. The coaxial magnetic/semiconducting photoanode response has shown good chemical stability and long activity under simulated sunlight radiation. In fact, this designed architecture gives novel perspective in the development of substrate free photocatalyst.
关键词： Photoelectrochemical performance,Hematite photoanodes,Photodegradation,Micro/nano architecture,Core-shell microstructures,Thermal oxidation
更新于2025-09-23 15:23:52
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Modulated anodization synthesis of Sn-doped iron oxide with enhanced solar water splitting performance
摘要： Modulated anodization synthesis is introduced here for the fabrication of porous Sn-doped iron oxide. Continuous square-wave modulation consisting of highly positive (+50 to +80 V range) and slightly negative potentials (-2 to -10 V range) at 100 Hz allowed the etching anodization of the metallic Fe foil and incorporation of Sn-dopant from the fluoride anion-containing electrolyte, respectively. Compared with the undoped iron oxide, the surface-enriched Sn-dopant (in the form of Sn4+) alleviates the trapping and recombination of surface holes, while enhancing the hole transfer at the surface states. As such, the overpotential for photoelectrochemical (PEC) water oxidation was reduced by 110 mV and photocurrent density doubled. The incorporation of Co-Pi co-catalyst further improved the hole transfer efficiency, resulting in further reduction in overpotential by another 330 mV with respect to the bare Sn-doped iron oxide and significant improvement in photocurrent density at potentials below +1.23 V vs. reversible hydrogen electrode. Lastly, the iron oxide electrodes exhibit highly stable PEC water oxidation with no degradation in activity throughout the 10 h assessment under simulated solar irradiation and Faradaic efficiency of 90%. We envisage that the modulated anodization technique can be conveniently incorporated for a wide range of other dopants in search of efficient solar water splitting electrodes.
关键词： Doping,Hematite,Hydrogen,Photoelectrochemical water splitting,Charge transport
更新于2025-09-23 15:23:52
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The Fine Characterization and Potential Photocatalytic Effect of Semiconducting Metal Minerals in Danxia Landforms
摘要： The Danxia landform is representative of the Cretaceous continental red sediment. The careful identi?cation and potential environmental effects of minerals in Danxia red beds have yet to be clearly reported. In this work, reddish sandstone samples were collected from Lang Mountain Danxia landform in Xinning, Hunan province, China, and their mineral phases, element distribution, microstructure, and the spatial relationship of different minerals were investigated using polarizing optical microscope, environmental scanning electron microscopy, energy-dispersive X-ray analysis, electron probe microanalysis, micro-Raman spectra, micro- X-ray diffraction, X-ray ?uorescence spectroscopy, and high-resolution transmission electron microscopy. The results revealed that iron oxide (mainly hematite) and titanium oxide (mainly anatase) were the dominant minerals in Danxia red layers. Microcrystalline hematite was suggested as being the coloring mineral. Anatase, reported here for the ?rst time in Danxia red beds, constituted the content of titanium in the red layer (0.17–0.57%) and was present in a signi?cantly higher amount than the adjacent limestone formation (0.13%). Over 95% of Fe/Ti oxides served as a cementation agent along the framework of coarse-grain minerals (quartz and feldspar). The hematite and anatase were visible-light-responsive semiconductors, with a band gap of 2.01 eV and 3.05 eV, respectively. Photoelectrochemical experiments were performed on synthetic hematite, anatase, and their coupled material. The inactive hematite displayed an enhanced 23-fold photocurrent at 0.8 V (vs. Ag/AgCl) when coupled with anatase. Furthermore, in a photodegradation experiment using methyl orange dye under simulated sunlight, the coupled material showed decolorizing ef?ciency 2.4 times that of hematite. The anatase, therefore, prominently improved the photocatalytic activities of hematite. It is proposed that these semiconducting minerals in red beds produce oxygen reactive species and have signi?cant environmental effects, which is of great importance.
关键词： photocatalysis,anatase,hematite,environmental effect,Danxia landform
更新于2025-09-23 15:22:29
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Acid-treated Ti4+ doped hematite photoanode for efficient solar water oxidation—Insight into surface states and charge separation
摘要： Acid-treatment has been proved to be an efficient approach to improve the photoelectrochemical (PEC) performance of hematite. However, efforts to optimize hematite photoanode have been limited by an inadequate understanding of the semiconductor surface. Here we make efforts to understand the microscopic charge separation processes of Ti4+ doped Fe2O3 photoanode before and after acid-treatment. Surface photovoltage (SPV) transient and the work function measurements directly reveal that acid-treatment leads to passivation of the surface states. Surface photovoltage (SPV) spectroscopic studies coupled to open-circuit photovoltage (OPV) measurements indicate that the surface states of hematite photoanode before acid-treatment result in the pinning of the Fermi level, which reduce the intensity of interfacial electric field at the semiconductor-electrolyte interface.
关键词： Water oxidation,Charge separation,Surface states,Hematite,Acid-treatment
更新于2025-09-23 15:22:29
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New method for improving the bulk charge separation of hematite with enhanced water splitting
摘要： Due to its poor bulk charge separation efficiency, the photoelectrochemical (PEC) performance of pristine hematite prepared directly from an electrodeposited Fe film is limited. Au-modification of hematite via a simple immersion method improves the PEC performance two-fold to 0.31 mA cm?2. The Au nanoparticles deposited from HAuCl? act as plasmonic photosensitizers and electron collectors to improve the light absorption and bulk charge separation efficiency of the photoanode. In addition, the increase in the (110) plane and specific surface area induced by HAuCl? enhances the bulk charge separation efficiency. After further modification with Ti, the photocurrent response of the resulting Ti/Au/α-Fe?O? photoanode improves to 0.51 mA cm?2; this increase is attributed to its increased light absorption, bulk charge separation efficiency (η_bulk), and surface charge injection efficiency (η_surface). In this work, the effect of Au and Ti on the crystalline structure, morphology and PEC performance of the novel electrodeposited hematite photoanode are investigated by systematical characterization.
关键词： Cathodic electrodeposition,Hematite,Charge separation,Modification,Au nanoparticles
更新于2025-09-23 15:22:29
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Ti, Zn co-doped hematite photoanode for solar driven photoelectrochemical water oxidation
摘要： Although there have been many reports of metal doping to ameliorate the drawbacks of hematite as the photoanode for water oxidation, most of them focused on monometallic doping, and only a few of them payed attention to bimetallic doping. What is worse, the synergetic mechanism between two metal dopants was not su?ciently studied, especially the density functional theory (DFT) calculation. In this work, the n-type hematite was synthesized by introducing Ti dopant into hematite through the hydrothermal method, and dipping-sintering treatment was employed to further introduce homogeneously dispersed Zn dopant into that, forming the Ti, Zn co-doped hematite. Under the optimal condition, Ti-doped hematite photoanode reached approximately 2-times enhancement of the photocurrent density compared with the pristine one at 1.23 V vs. RHE, while Ti, Zn co-doped hematite anode obtained another 25% elevation. UV –Vis spectroscopy, Mott –Schottky plots, EIS analysis, photo-oxidation of hole scavenger (H 2 O 2 ), and DFT calculation were employed to understand the role of Ti, Zn dopant. Based on the obtained results, the synergetic mechanism of two dopants was discussed, i.e., the improvement of PEC performance of Ti, Zn co-doped hematite photoanode was possibly attributed to greater carrier density and improved charge separation e?ciency at the surface of hematite. This work provides new strategy and understanding of the improvement of PEC performance of hematite by doping engineering.
关键词： Photoelectrochemical water oxidation,Zn co-doping,Ti,DFT calculation,Hematite
更新于2025-09-23 15:21:01
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Design of an inherently-stable water oxidation catalyst
摘要： While molecular water-oxidation catalysts are remarkably rapid, oxidative and hydrolytic processes in water can convert their active transition metals to colloidal metal oxides or hydroxides that, while quite reactive, are insoluble or susceptible to precipitation. In response, we propose using oxidatively-inert ligands to harness the metal oxides themselves. This approach is demonstrated by covalently attaching entirely inorganic oxo-donor ligands (polyoxometalates) to 3-nm hematite cores, giving soluble anionic structures, highly resistant to aggregation, yet thermodynamically stable to oxidation and hydrolysis. Using orthoperiodate (at pH 8), and no added photosensitizers, the hematite-core complex catalyzes visible-light driven water oxidation for seven days (7600 turnovers) with no decrease in activity, far exceeding the documented lifetimes of molecular catalysts under turnover conditions in water. As such, a fundamental limitation of molecular complexes is entirely bypassed by using coordination chemistry to harness a transition-metal oxide as the reactive center of an inherently stable, homogeneous water-oxidation catalyst.
关键词： visible-light driven,hematite,polyoxometalates,water oxidation,catalyst
更新于2025-09-23 15:21:01
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Semiconductor α-Fe <sub/>2</sub> O <sub/>3</sub> Hematite Fabricated Electrode for Sensitive Detection of Phenolic Pollutants
摘要： Hematite (α-Fe2O3) semiconductor is an abundant and non-toxic catalyst for different (photo)electrochemical reactions. In this work, a selective p-nitrophenol sensor was developed by fabricating a thin-layer of a glassy carbon electrode (GCE) with 5% nafion coating binders onto α-Fe2O3 thin film synthesized by a simple and inexpensive process. High sensitivity including long-term stability, and enhanced linear dynamic range, electrochemical performance towards p-nitrophenol were achieved by a reliable current-voltage method. A linear calibration curve was observed over a wide range of p-nitrophenol concentrations. Very low detection limit (0.6 ? 0.02 nM), good limit of quantification (2.0 nM) and high sensor sensitivity (K = 74.1 μA?cm(cid:0) 2) are calculated based on noise to signal ratio of ～ 3 N/S. Very importantly, the detection range covers over 7 orders of magnitude concentrations, from nM to mM. Figures of merits are comparable with best reported results whilst using a very simple device configuration. We show that hematite is an excellent material for the development of chemical sensors to detect hazardous compounds for environmental safety in a broad scale of concentrations.
关键词： Environmental safety,Sensitivity,p-Nitrophenol sensor,Hematite α-Fe2O3,Glassy carbon electrode
更新于2025-09-23 15:21:01
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Tuning of opto-electrical properties of hematite thin films using Co2+ doping
摘要： Hematite thin films have attracted widespread interest in recent years because of their advanced electronic and optical properties. Optical and electronic properties of hematite thin films can be enhanced/tuned using doping or additive-based strategies. An application oriented sol–gel method is used for the synthesis of cobalt (Co) doped hematite sol with variation in Co concentration in the range of 0–10 wt%. Hematite phase is observed in undoped thin films annealed at 300 °C under 500 Oe magnetic field for 60 min. Strengthening of hematite phase is observed with increase in Co concentration up to a value of 8 wt%. Bond angle with +ive tilt (i.e. ~ 19.74°) was observed in refined structural parameters for thin films prepared with Co concentration in the range of 0–8 wt%. Higher Co concentration, i.e. 10 wt%, results in decrease in crystallinity of the films along with smaller +ive tilt in bond angle (i.e. ~ 8.82°). High transmission (~ 88%) is observed for thin film prepared using dopant concentration of 8 wt% in the visible and infrared regions. The energy band gap varies from 2.42 to 2.25 eV with variation in Co concentration from 0 to 10 wt%. Relatively smaller band gap values are correlated with defect induced states in the band gap. Spectroscopic ellipsometry is used for calculation of refractive index and high values are indication of high density of thin films. Relatively higher value of dielectric constant (~ 183, log f = 5.0) along with lower value of tangent loss is observed at Co concentration of 8 wt%. Higher grain boundary resistance (1.88 × 105 ?) was observed at 8 wt% Co concentration. Variation in d.c. conductivity with dopant concentration is studied in detail using Jonscher’s power law. The value of frequency exponent (n) lies in the range of 0.88–0.98 (< 1) with variation in dopant concentration signifying that motion of charge carriers involves translational motion along with sudden hopping process. It is important to mention here that combined tuning of optical and electrical properties are observed in the present study with no change in phase pure hematite crystallographic structure.
关键词： Hematite thin films,Optical properties,Sol-gel method,Electrical properties,Dielectric constant,Transmission,Band gap,Cobalt doping
更新于2025-09-19 17:15:36