Search Results (8)

This study explores the enhancement of α-Fe₂O₃ (hematite) nanorod arrays for photoelec-trochemical applications by constructing a Cu₂ZnSnS₄ (CZTS) heterojunction. While α-Fe₂O₃ offers good stability, a low cost, and environmental benefits, its efficiency is limited by slow oxygen evolution kinetics, high carrier recombination rates, and low conductivity. By introducing CZTS, a material with strong light absorption and charge transport properties, we enhance the separation of photogenerated charge carriers, reduce charge transfer resistance, and increase the carrier concentration, thereby boosting the overall photoelectrochemical performance. The experimental results show that a modified FC-15 photoanode achieves a photocurrent density of 3.40 mA/cm² at 1.60 V vs. RHE, a substantial increase compared to 0.40 mA/cm² for unmodified α-Fe₂O₃. Band gap analysis reveals a reduced band gap in the FC-15 material, enhancing light absorption and boosting the photoelectrocatalytic performance. In photoelectrochemical water-splitting tests, the FC-15 photoanode achieves a hydrogen production rate of 41.6 μmol/cm²/h, which is significantly improved over the unmodified sample at 5.64 μmol/cm²/h. These findings indicate that the CZTS/α-Fe₂O₃ heterojunction effectively promotes charge separation, enhances charge transport, and improves light absorption, substantially increasing photocatalytic efficiency. This heterojunction approach offers new insights and technical strategies for developing photocatalytic materials with potential applications in renewable energy. Full article

Hematite (α-Fe₂O₃) is one of the most promising and widely used semiconductors for application in photoelectrochemical (PEC) water splitting, owing to its moderate bandgap in the visible spectrum and earth abundance. However, α-Fe₂O₃ is limited by short hole-diffusion lengths. Ultrathin α-Fe₂O₃ films are often used to limit the distance required for hole transport, therefore mitigating the impact of this property. The development of highly controllable and scalable ultrathin film deposition techniques is therefore crucial to the application of α-Fe₂O₃. Here, a plasma-enhanced atomic layer deposition (PEALD) process for the deposition of homogenous, conformal, and thickness-controlled α-Fe₂O₃ thin films (<100 nm) is developed. A readily available iron precursor, dimethyl(aminomethyl)ferrocene, was used in tandem with an O₂ plasma co-reactant at relatively low reactor temperatures, ranging from 200 to 300 °C. Optimisation of deposition protocols was performed using the thin film growth per cycle and the duration of each cycle as optimisation metrics. Linear growth rates (constant growth per cycle) were measured for the optimised protocol, even at high cycle counts (up to 1200), confirming that all deposition is ‘true’ atomic layer deposition (ALD). Photoelectrochemical water splitting performance was measured under solar simulated irradiation for pristine α-Fe₂O₃ deposited onto FTO, and with a α-Fe₂O₃-coated TiO₂ nanorod photoanode. Full article

Magnetite nanorods (MNRs) are synthesized based on the use of hematite nanoparticles of the desired geometry and dimensions as templates. The nanorods are shown to be highly monodisperse, with a 5:1 axial ratio, and with a 275 nm long semiaxis. The MNRs are intended to be employed as magnetic hyperthermia and photothermia agents, and as drug vehicles. To achieve a better control of their photothermia response, the particles are coated with a layer of gold, after applying a branched polyethyleneimine (PEI, 2 kDa molecular weight) shell. Magnetic hyperthermia is performed by application of alternating magnetic fields with frequencies in the range 118–210 kHz and amplitudes up to 22 kA/m. Photothermia is carried out by subjecting the particles to a near-infrared (850 nm) laser, and three monochromatic lasers in the visible spectrum with wavelengths 480 nm, 505 nm, and 638 nm. Best results are obtained with the 505 nm laser, because of the proximity between this wavelength and that of the plasmon resonance. A so-called dual therapy is also tested, and the heating of the samples is found to be faster than with either method separately, so the strengths of the individual fields can be reduced. Due to toxicity concerns with PEI coatings, viability of human hepatoblastoma HepG2 cells was tested after contact with nanorod suspensions up to 500 µg/mL in concentration. It was found that the cell viability was indistinguishable from control systems, so the particles can be considered non-cytotoxic in vitro. Finally, the release of the antitumor drug doxorubicin is investigated for the first time in the presence of the two external fields, and of their combination, with a clear improvement in the rate of drug release in the latter case. Full article

In this work, we report the effect of zinc (Zn) and nickel (Ni) co-doping of hydrothermally synthesized hematite nanorods prepared on fluorine-doped tin oxide (FTO) substrates for enhanced photoelectrochemical (PEC) water splitting. Seeded hematite nanorods (NRs) were facilely doped with a fixed concentration of 3 mM Zn and varied concentrations of 0, 3, 5, 7, and 9 mM Ni. The samples were observed to have a largely uniform morphology of vertically aligned NRs with slight inclinations. The samples showed high photon absorption within the visible spectrum due to their bandgaps, which ranged between 1.9–2.2 eV. The highest photocurrent density of 0.072 mA/cm² at 1.5 V vs. a reversible hydrogen electrode (RHE) was realized for the 3 mM Zn/7 mM Ni NRs sample. This photocurrent was 279% higher compared to the value observed for pristine hematite NRs. The Mott–Schottky results reveal an increase in donor density values with increasing Ni dopant concentration. The 3 mM Zn/7 mM Ni NRs sample produced the highest donor concentration of 2.89 × 10¹⁹ (cm⁻³), which was 2.1 times higher than that of pristine hematite. This work demonstrates the role of Zn and Ni co-dopants in enhancing the photocatalytic water oxidation of hematite nanorods for the generation of hydrogen. Full article

The hematite-based nanomaterials are involved in several catalytic organic and inorganic processes, including water decontamination from organic pollutants. In order to develop such species, a series of bimetallic hematite-based nanocomposites were obtained by some goethite composites-controlled calcination. Their composition consists of various phases such as α-FeOOH, α-Fe₂O₃ or γ-Fe₂O₃ combined with amorphous (Mn₂O₃, Co₃O₄, NiO, ZnO) or crystalline (CuO) oxides of the second transition ion from the structure. The component dimensions, either in the 10–30 or in the 100–200 nm range, together with the quasi-spherical or nanorod-like shapes, were provided by Mössbauer spectroscopy and powder X-ray diffraction as well as transmission electron microscopy data. The textural characterization showed a decrease in the specific area of the hematite-based nanocomposites compared with corresponding goethites, with the pore volume ranging between 0.219 and 0.278 cm³g⁻¹. The best catalytic activity concerning indigo carmine removal from water in hydrogen peroxide presence was exhibited by a copper-containing hematite-based nanocomposite sample that reached a dye removal extent of over 99%, which correlates with both the base/acid site ratio and pore size. Moreover, Cu-hbnc preserves its catalytic activity even after four recyclings, when it still reached a dye removal extent higher than 90%. Full article

Ion doping in transition metal oxides is always considered to be one of the most effective methods to obtain high-performance electrochemical supercapacitors because of the introduction of defective surfaces as well as the enhancement of electrical conductivity. Inspired by the smelting process, an ancient method, quenching is introduced for doping metal ions into transition metal oxides with intriguing physicochemical properties. Herein, as a proof of concept, α-Fe₂O₃ nanorods grown on carbon cloths (α-Fe₂O₃@CC) heated at 400 °C are rapidly put into different aqueous solutions of alkaline earth metal salts at 4 °C to obtain electrodes doped with different alkaline earth metal ions (M-Fe₂O₃@CC). Among them, Sr-Fe₂O₃@CC shows the best electrochemical capacitance, reaching 77.81 mF cm⁻² at the current of 0.5 mA cm⁻², which is 2.5 times that of α-Fe₂O₃@CC. The results demonstrate that quenching is a feasible new idea for improving the electrochemical performances of nanostructured materials. Full article

Co-doped and Ni-doped hematite (α-Fe₂O₃) nanorod arrays were prepared on fluorine-doped tin oxide (FTO) conductive glass via aqueous chemical growth, in which the doping and the formation of nanorods occurred simultaneously (i.e., in situ doping). These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet (UV)–visible spectrophotometry, linear sweep voltammetry and Mott–Schottky (M–S) measurement. Results showed that the introduction of 5% Co or Ni into α-Fe₂O₃ (the molar ratio of dopant to Fe is 1:20) did not change its crystal phase, morphology, energy gap and flat band potential. Both the undoped and the doped α-Fe₂O₃ showed a direct band gap of 2.24 eV, an indirect band gap of 1.85 eV, and a flat band potential of −0.22 V vs. saturated calomel electrode (SCE). At an applied potential of 0.2 V vs. SCE, the Co-doped and the Ni-doped α-Fe₂O₃ exhibited a photocurrent of 1.28 mA/cm² and 0.79 mA/cm², respectively, which were 2.1 times and 1.3 times that of the undoped α-Fe₂O₃. After the Co or Ni doping, the charge carrier concentration increased from 1.65 × 10²⁵ m⁻³ to 3.74 × 10²⁵ m⁻³ and 2.50 × 10²⁵ m⁻³, respectively. Therefore, the increase in the photocurrent of the doped α-Fe₂O₃ was likely attributed to their enhanced conductivity. Full article

Hematite is a low band gap, earth abundant semiconductor and it is considered to be a promising choice for photoelectrochemical water splitting. However, as a bulk material its efficiency is low because of excessive bulk, surface, and interface recombination. In the present work, we propose a strategy to prepare a hematite (α-Fe₂O₃) photoanode consisting of hematite nanorods grown onto an iron oxide blocking layer. This blocking layer is formed from a sputter deposited thin metallic iron film on fluorine doped tin oxide (FTO) by using cyclic voltammetry to fully convert the film into an anodic oxide. In a second step, hematite nanorods (NR) are grown onto the layer using a hydrothermal approach. In this geometry, the hematite sub-layer works as a barrier for electron back diffusion (a blocking layer). This suppresses recombination, and the maximum of the incident photon to current efficiency is increased from 12% to 17%. Under AM 1.5 conditions, the photocurrent density reaches approximately 1.2 mA/cm² at 1.5 V vs. RHE and the onset potential changes to 0.8 V vs. RHE (using a Zn-Co co-catalyst). Full article