Photoelectrochemical Sensing of Hydrogen Peroxide on Hematite

Effect of Shape and Size on Synthesized Triple (Co/Ni/Zn)-Doped α-Fe2O3 Nanoparticles on their Photocatalytic and Scavenging Properties

Co/Ni/Zn triple doped [Formula: see text]-Fe2O3 nanoparticles (NPs) have been synthesized via polyvinylpyrrolidone (PVP)/Azadirachta indica (A. Indica) leaf extract coating. XRD, UV–Vis, SEM, TEM, EDS, Raman spectroscopy, FTIR, VSM were used to characterize the synthesized NPs. XRD pattern revealed that the crystallite size of NPs ranges from 14[Formula: see text]nm to 21[Formula: see text]nm. Spherical NPs were found by SEM/TEM examination ranging from 16[Formula: see text]nm to 26[Formula: see text]nm of doped [Formula: see text]-Fe2O3 NPs. Analysis of the magnetic properties of [Formula: see text]-Fe2O3 NPs revealed antiferromagnetic characteristics, convergence between magnetization curves (MS), and switching field distribution dM/dh below an irreversible temperature of [Formula: see text][Formula: see text]K. Produced catalyst was used for the degradation of anionic azo dye Malachite green (MG) and Rhodamine blue (RhB) dyes under the influence of UV radiation. RhB and MG were reduced as a result of the doped [Formula: see text]-Fe2O3 catalyzing the conversion of dissolved O2 to hydroxyl radicals (OH) when exposed to visible light. This shows that the main active radical specifically engaged in the photo-catalytic breakdown of dyes is OH. The most effective photo-catalyst was determined by investigating the proposed doped [Formula: see text]-Fe2O3 NPs reusability over three cycles. The catalyst was retrieved and utilized three times after the reaction without suffering a substantial loss of catalytic activity. The plant-mediated [Formula: see text]-Fe2O3 NPs have significant antioxidant activity due to their higher phenolic content. These have a promising future with potential applications in health, aging, food preservation, cosmetics, agriculture and environmental protection.

Insights into the multirole CoAl layered double hydroxide on boosting photoelectrochemical activity of hematite: Application to hydrogen peroxide sensing

As an important compound in many industrial and biological processes, hydrogen peroxide (H₂O₂) would cause harmfulness to human health at high concentration level. It thus is urgent to develop highly sensitive and selective sensors for practical H₂O₂ detection in the fields of water monitoring, food quality control, and so on. In this work, CoAl layered double hydroxide ultrathin nanosheets decorated hematite (CoAl-LDH/α-Fe₂O₃) photoelectrode was successfully fabricated by a facile hydrothermal process. CoAl-LDH/α-Fe₂O₃ displays the relatively wide linear range from 1 to 2000 μM with a high sensitivity of 132.0 μA mM^-1 cm^-2 and a low detection limit of 0.04 μM (S/N ≥ 3) for PEC detection of H₂O₂, which is superior to other similar α-Fe₂O₃-based sensors in literatures. The (photo)electrochemical characterizations, such as electrochemical impedance spectroscopy, Mott-Schottky plot, cyclic voltammetry, open circuit potential and intensity modulated photocurrent spectroscopy, were used to investigate the roles of CoAl-LDH on the improved PEC response of α-Fe₂O₃ toward H₂O₂. It revealed that, CoAl-LDH could not only passivate the surface states and enlarge the band bending of α-Fe₂O₃, but also could act as trapping centers for holes and followed by as active sites for H₂O₂ oxidation, thus facilitated the charge separation and transfer. The strategy for boosting PEC response would be help for the further development of semiconductor-based PEC sensors.

PEC thrombin aptasensor based on Ag-Ag2S decorated hematite photoanode with signal-down effect of precipitation catalyzed by G-quadruplexes/hemin

A photoelectrochemical (PEC) aptasensor for thrombin detection was rationally designed based on the photoanode of one-dimensional hematite nanorods (α-Fe₂O₃ NRs) with several steps of modifications. Uniform α-Fe₂O₃ NRs were grown vertically on the surface of fluorine-doped tin oxide (FTO) conductive glass through a one-step hydrothermal method; then Ag was grown on the surface of α-Fe₂O₃ NRs through a photoreduction method followed by a partial in-situ transformation into Ag₂S, conferring an improvement on the initial photocurrent. Two main critical factors, namely, the steric hindrance of thrombin, benzoquinone (BQ) precipitation oxidized by H₂O₂ under the catalysis of G-quadruplexes/hemin, contributed to the sensitive signal-down response toward the target. Photocurrent signals related with thrombin concentration was established for thrombin analysis due to the non-conductive complex as well as their competitive consumption of electron donors and irradiation light. The excellent initial photocurrent was combined with the signal-down amplification in the design of the biosensor, conferring a limit of detection (LOD) as low as 40.2 fM and a wide linear range from 0.0001 nM to 50 nM for the detection of thrombin. The proposed biosensor was also assessed in terms of selectivity, stability, and applicability in human serum analyses, which provided an appealing maneuver for the specific analysis of thrombin in trace amount.

Photoelectrochemical sensing and mechanism investigation of hydrogen peroxide using a pristine hematite nanoarrays

In this paper, a facile hydrothermal combined with subsequent two-step post-calcination method was used to fabricate hematite (α-Fe₂O₃) nanoarrays on fluorine-doped SnO₂ glass (FTO). The morphology, crystalline phase, optical property and surface chemical states of the fabricated α-Fe₂O₃ photoelectrode were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet visible spectroscopy and X-ray photoelectron spectroscopy correspondingly. The α-Fe₂O₃ photoelectrode exhibits excellent photoelectrochemical (PEC) response toward hydrogen peroxide (H₂O₂) in aqueous solutions, with a low detection limit of 20 μM (S/N = 3) and wide linear range (0.01-0.09, 0.3-4, and 6-16 mM). Additionally, the α-Fe₂O₃ photoelectrode shows satisfying reproducibility, stability, selectivity and good feasibility for real samples. Mechanism analysis indicates, comparing with H₂O, H₂O₂ possesses much more fast reaction kinetics over α-Fe₂O₃ surface, thus the recombination of photogenerated charges are reduced, followed by much more photogenerated electrons are migrated to the counter electrode via external circuit. The insight on the enhanced photocurrent, which is corelative to the concentration of H₂O₂ in aqueous solution, will stimulate us to further optimize the surface structure of α-Fe₂O₃ to gain highly efficient α-Fe₂O₃ based sensors.

An unprecedented polyoxometalate-based 1D double chain compound with opposite charges enables conductivity improvement

A POM-based one-dimensional (1D) chain compound, {BW₁₂O₄₀[Cu(2,2'-bipy)₂]₂[Cu(2,2'-bipy)(H₂O)]}{BW₁₂O₄₀[Cu(2,2'-bipy)₂][Cu(2,2'-bipy)(H₂O)₂]}·7H₂O, has been synthesized and structurally characterized, which represents an unprecedented 1D double chain structure with opposite charges. In contrast to common POMs, this compound exhibits a relatively high electrical conductivity of 1.17 × 10^-9 S cm^-1 at 25 °C. In addition, its semiconducting properties have also been investigated by application of photoelectrochemical sensing of H₂O₂.

Design and fabrication of cost-effective and sensitive non-enzymatic hydrogen peroxide sensor using Co-doped δ-MnO2 flowers as electrode modifier

The development of a cost-effective and highly sensitive hydrogen peroxide sensor is of great importance. Electrochemical sensing is considered the most sensitive technique for hydrogen peroxide detection. Herein, we reported a cost-effective and highly sensitive hydrogen peroxide sensor using Co-doped δ-MnO₂ (Co@δ-MnO₂) flower-modified screen-printed carbon electrode. The δ-MnO₂ and Co@δ-MnO₂ flowers were synthesized by employing a hydrothermal approach. Advanced techniques such as PXRD, SEM, FTIR, Raman, UV, EDX, BET, and TEM were utilized to confirm the formation of δ-MnO₂ and Co-doped δ-MnO₂ flowers. The fabricated sensor exhibited an excellent detection limit (0.12 μM) and sensitivity of 5.3 μAμM^-1 cm^-2.Graphical abstract.