Sacrificial Interlayer for Promoting Charge Transport in Hematite Photoanode

Target Recognition-Triggered Interfacial Electron Transfer Model: Toward Signal-On Photoelectrochemical Aptasensing for Efficient Detection of Staphylococcus aureus Using Ti3C2Tx-Au NBPs/ZnO NR Composites

Staphylococcus aureus (S. aureus) is one of the most common foodborne pathogens worldwide, which poses a great threat to public health. It is of utmost importance to develop rapid, simple, and sensitive methods for the determination of S. aureus. A signal-on photoelectrochemical (PEC) aptasensor is constructed herein based on titanium carbide (Ti3C2Tx)-Au nanobipyramids (NBPs)/ZnO nanoarrays (NRs). The reliability and capability of the PEC aptasensor make it suitable for the sensitive and selective determination of S. aureus. First, the electrostatically self-assembled Ti3C2Tx-Au NBP nanomaterial was coated on the ZnO NR surface by a spin-coating method. On the one hand, Ti3C2Tx-Au NBPs can broaden the spectral absorption of ZnO NRs, resulting in Ti3C2Tx-Au NBPs/ZnO NR composites that exhibit a wide range of absorption from the ultraviolet to the infrared region. On the other hand, Ti3C2Tx can reduce the agglomeration of nanoparticles, while Au NBPs can effectively fix the aptamer through the Au-S bond. Specifically, the experimental results show that when S. aureus is present, the Au NBPs-aptamer-S. aureus complex is shed from the electrode surface, altering the interfacial electron transfer model and reducing the steric hindrance. Consequently, an amplified photocurrent signal for the quantitative determination of S. aureus is obtained. Under optimal experimental conditions, a linear correlation is observed between the current response of the aptasensor and the logarithm of the S. aureus concentration (ranging from 1.0 to 1.0 × 106 CFU/mL), with an impressive detection limit as low as 0.5 CFU/mL. Furthermore, the aptasensor has been successfully employed for the detection of S. aureus in milk, with the recovery of 93.0%-99.0%. Hence, this research offers a novel approach for the detection of foodborne pathogens and other noxious substances.

The Role of Photo in Oxygen Evolution Reaction: A Review

Photo enhanced oxygen evolution reaction has recently emerged as an advanced strategy with great application prospects for highly efficient energy conversion and storage. In the course of photo enhanced oxygen evolution reactions, the other works focus has predominantly centered on catalysts while inadvertently overlooking the pivotal role of photo. Consequently, this manuscript embarks upon a comprehensive review of recent advancements in photo-driven, aiming to illuminate this critical dimension. A detailed introduction to the photothermal effect, photoelectronic effect, photon-induced surface plasmon resonance, photo and heterojunction, photo-induced reversible geometric conversion, photo-induced energy barrier reduction, photo-induced chemical effect, photo-charging, and the synthesis of laser/photo-assisted catalysts, offering prospects for the development of each case is provided. A detailed introduction to the photothermal effect, photoelectronic effect, photon-induced surface plasmon resonance, photo and heterojunction, photo-induced reversible geometric conversion, photo-induced energy barrier reduction, photo-induced chemical effect, photo-charging, and the synthesis of laser/photo-assisted catalysts is provided. At the same time, the overpotential and Tafel slope of some catalysts mentioned above at 10 mA cm-2 is collected, and calculated the lifting efficiency of light on them, offering prospects for the development of each case.

Interface Engineering of CoFe-LDH Modified Ti: α-Fe2O3 Photoanode for Enhanced Photoelectrochemical Water Oxidation

Effectively regulating and promoting the charge separation and transfer of photoanodes is a key and challenging aspect of photoelectrochemical (PEC) water oxidation. Herein, a Ti-doped hematite photoanode with a CoFe-LDH cocatalyst loaded on the surface was prepared through a series of processes, including hydrothermal treatment, annealing and electrodeposition. The prepared CoFe-LDH/Ti:α-Fe2O3 photoanode exhibited an outstanding photocurrent density of 3.06 mA/cm2 at 1.23 VRHE, which is five times higher than that of α-Fe2O3 alone. CoFe-LDH modification and Ti doping on hematite can boost the surface charge transfer efficiency, which is mainly attributed to the interface interaction between CoFe-LDH and Ti:α-Fe2O3. Furthermore, we investigated the role of Ti doping in enhancing the PEC performance of CoFe-LDH/Ti:α-Fe2O3. A series of characterizations and theoretical calculations revealed that, in addition to improving the electronic conductivity of the bulk material, Ti doping also further enhances the interface coupling of CoFe-LDH/α-Fe2O3 and finely regulates the interfacial electronic structure. These changes promote the rapid extraction of holes from hematite and facilitate charge separation and transfer. The informative findings presented in this work provide valuable insights for the design and construction of hematite photoanodes, offering guidance for achieving excellent performance in photoelectrochemical (PEC) water oxidation.

Influence of CoOx surface passivation and Sn/Zr-co-doping on the photocatalytic activity of Fe2O3 nanorod photocatalysts for bacterial inactivation and photo-Fenton degradation

Hydrothermal and wet impregnation methods are presented in this study for synthesizing CoO_x(1 wt%)/Sn-Zr codoped-Fe₂O₃ nanorod photocatalysts for the degradation of organic pollutants and deactivation of bacteria. A hydrothermal route was used to synthesize self-assembled rod-like hierarchical structures of Sn(0-6%) doped Zr-Fe₂O₃ NRs. Additionally, a wet impregnation method was used to load CoO_x onto the surface of photocatalysts (Sn(0-6%)-doped Zr-Fe₂O₃ NRs). A series of 1 wt% CoO_x modified Sn(0-6%)-doped Zr-Fe₂O₃ NRs were synthesized, characterized, and utilized for the photocatalytic decomposition of organic contaminants, along with the killing of E. coli and S. aureus. In comparison with 0, 2, and 6% Sn co-doped Zr-Fe₂O₃ NRs, the CoO_x(1 wt%)/4%Sn/Zr-Fe₂O₃ NRs photocatalyst exhibited an E. coli and S. aureus inactivation efficiencies (90 and 98%). A bio-TEM study of treated and untreated bacterial cells revealed that the CoO_x(1 wt%)/4%Sn/Zr-Fe₂O₃ NRs photocatalyst led to considerable changes in the bacterial cell membranes' morphology. The optimal CoO_x(1 wt%)/Sn(4%) co-doped Zr-Fe₂O₃ NRs photocatalyst achieved degradation efficiencies of 98.5% and 94.6% for BPA and orange II dye. As a result, this work will provide a facile and effective method for developing visible light-active photocatalysts for bacterial inactivation and organic pollutants degradation.

A portable solar light-driven biophotoelectrocatalytic system for pollutant removal powered by photovoltaic cells

Photoelectrocatalytic (PEC) technology has been considered as one of the most efficient advanced oxidation processes for wastewater treatment, but the necessity of external electric power supply limits the portability of PEC system for on-field applications. Herein, a portable solar-powered biophotoelectrocatalytic system driven by photovoltaic (PV) cells was explored for degradation of pollutant by coupling BiVO₄/Fe₂O₃-deposited photoanode and horseradish peroxidase (HRP)-immobilized cathode. The integration of PV cells in this PEC device could not only avoid the necessary introduction of external electric power supply, but also improve the utilization of solar irradiation. The characterization of BiVO₄/Fe₂O₃ photoanode demonstrates that ultrathin Fe₂O₃ layer on BiVO₄ electrode could facilitate the holes transfer to the surface efficiently and thus avoid charge recombination. After HRP was immobilized on the cathode, the removal efficiency for 2,4-dichlorophenol (2,4-DCP) was obviously promoted, attributed to the efficient HRP-catalyzed oxidation reaction by in-situ generated H₂O₂ from PEC process. Under natural solar irradiation, the proposed portable biophotoelectrocatalytic device exhibited a satisfying removal efficiency of 92.0% for 100 ppm of 2,4-DCP after 3-h treatment. The intermediate products formed during the degradation process were identified by liquid chromatography-mass spectrometry, and possible 2,4-DCP degradation pathway was also proposed.

Simple electrodeposition to synthesize a NiFeSx-modified Ti-Fe2O3 photoanode: an effective strategy to improve the photoelectrochemical water oxidation reaction

Decorating a high-efficiency oxygen evolution reaction (OER) electrocatalyst as a cocatalyst on an α-Fe₂O₃ photoanode is known to be one of the most efficient methods to improve the photoelectrochemical (PEC) water oxidation activity. In our work, different from traditional methods of transition metal sulfide cocatalyst synthesis, an NiFeS_x-decorated Ti-Fe₂O₃ photoanode is synthesized through a simple one-step electrodeposition method, which benefits the interface between Ti-Fe₂O₃ and NiFeS_x. With the help of this excellent OER electrocatalyst, the photocurrent density of the NiFeS_x-Ti-Fe₂O₃ photoanode rises to 3 mA cm^-2 at 1.23 V vs. RHE, which is 2.5 times greater than the photocurrent of Ti-Fe₂O₃. Moreover, the onset potential of NiFeS_x-Ti-Fe₂O₃ shifts negatively by 170 mV compared with that of pure Ti-Fe₂O₃. Furthermore, surface photovoltage spectroscopy (SPV) and transient photovoltage (TPV) techniques and photoelectrochemical impedance spectroscopy (PEIS) were used to analyze the true effects of NiFeS_x as an efficient cocatalyst for enhancing the PEC performance of the NiFeS_x-Ti-Fe₂O₃ photoanode. This work provides a simple method for loading a low-cost and efficient cocatalyst to modify a Ti-Fe₂O₃ photoanode for the PEC water oxidation reaction.

Simultaneous Enhancement of Charge Separation and Hole Transportation in a W:α-Fe2O3/MoS2 Photoanode: A Collaborative Approach of MoS2 as a Heterojunction and W as a Metal Dopant

In this study, a facile approach has been successfully applied to synthesize a W-doped Fe₂O₃/MoS₂ core-shell electrode with unique nanostructure modifications for photoelectrochemical performance. A two-dimensional (2D) structure of molybdenum disulfide (MoS₂) and tungsten (W)-doped hematite (W:α-Fe₂O₃) overcomes the drawbacks of the α-Fe₂O₃ and MoS₂ semiconductor through simple and facile processes to improve the photoelectrochemical (PEC) performance. The highest photocurrent density of the 0.5W:α-Fe₂O₃/MoS₂ photoanode is 1.83 mA·cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE) under 100 mW·cm² illumination, which is higher than those of 0.5W:α-Fe₂O₃ and pure α-Fe₂O₃ electrodes. The overall water splitting was evaluated by measuring the H₂ and O₂ evolution, which after 2 h of irradiation for 0.5W:α-Fe₂O₃/MoS₂ was determined to be 49 and 23.8 μmol.cm^-2, respectively. The optimized combination of the heterojunction and metal doping on pure α-Fe₂O₃ (0.5W:α-Fe₂O₃/MoS₂ photoanode) showed an incident photon-to-electron conversion efficiency (IPCE) of 37% and an applied bias photon-to-current efficiency (ABPE) of 26%, which are around 5.2 and 13 times higher than those of 0.5W:α-Fe₂O₃, respectively. Moreover, the facile fabrication strategy can be easily extended to design other oxide/carbon-sulfide/oxide core-shell materials for extensive applications.

Tuning of oxygen vacancy-induced electrical conductivity in Ti-doped hematite films and its impact on photoelectrochemical water splitting

Titanium (Ti)-doped hematite (α-Fe₂O₃) films were grown in oxygen-depleted condition by using the spray pyrolysis technique. The impact of post-deposition annealing in oxygen-rich condition on both the conductivity and water splitting efficiency was investigated. The X-ray diffraction pattern revealed that the films are of rhombohedral α-Fe₂O₃ structure and dominantly directed along (012). The as-grown films were found to be highly conductive with electrons as the majority charge carriers (n-type), a carrier concentration of 1.09×10²⁰ cm⁻³, and a resistivity of 5.9×10⁻² Ω-cm. The conductivity of the films were reduced upon post-deposition annealing. The origin of the conductivity was attributed firstly to Ti⁴⁺ substituting Fe³⁺ and secondly to the ionized oxygen vacancies (V_O) in the crystal lattice of hematite. Upon annealing the samples in oxygen-rich condition, V_O slowly depleted and the conductivity reduced. The photocurrent of the as-grown samples was found to be 3.4 mA/cm⁻² at 1.23 V vs. RHE. The solar-to-hydrogen efficiency for the as-grown sample was calculated to be 4.18% at 1.23 V vs. RHE. The photocurrents were found to be significantly stable in aqueous environment. A linear relationship between conductivity and water-splitting efficiency was established.

Improving the Water Oxidation Efficiency with a Light-Induced Electric Field in Nanograting Photoanodes

Severe charge recombination in solar water-splitting devices significantly limits their performance. To address this issue, we design a frustum of a cone nanograting configuration by taking the hematite and Au-based thin-film photoanode as a model system, which greatly improves the photoelectrochemical water oxidation activity, affording an approximately 10-fold increase in the photocurrent density at 1.23 V versus the reversible hydrogen electrode compared to the planar counterpart. The surface plasmon polariton-induced electric field in hematite plays a dominant role in efficiency enhancement by facilitating charge separation, thus dramatically increasing the incident photon-to-current efficiency (IPCE) by more than 2 orders of magnitude in the near band gap of hematite. And the relatively weak electric field caused by light scattering in the nanograting structure is responsible for the approximate maximum 20-fold increase in IPCE within a broadband wavelength range. Our scalable strategy can be generalized to other solar energy conversion systems.

In situ synthesis of FeP-decorated Ti–Fe2O3: an effective strategy to improve the interfacial charge transfer in the photoelectrochemical water oxidation reaction

The unprecedented FeP/Ti–Fe₂O₃ possesses the advantages of efficient charge transfer in the bulk photoanode and at the interface of the photoanode and the electrolyte.

Dual-Axial Gradient Doping (Zr and Sn) on Hematite for Promoting Charge Separation in Photoelectrochemical Water Splitting

One of the crucial challenges to enhance the photoelectrochemical water-splitting performance of hematite (α-Fe₂ O₃ ) is to resolve its very fast charge recombination in bulk. Herein, we describe the design and fabrication of dual-axial gradient-doping on 1D Fe₂ O₃ nanorod arrays with Zr doping for x-axial and Sn doping for y-axial directions to promote the charge separation. This dual-axial gradient-doping structure fulfills the requirements of a greater electron-carrier concentration for increasing conductivity as well as a higher charge-separation efficiency across the dual-axial direction of Fe₂ O₃ nanorods, ultimately showing an excellent photocurrent density of 1.64 mA cm^-2 at 1.23 V vs. RHE, which is 26.3 times more than that of the bare Fe₂ O₃ . Furthermore, the remarkably improved photocurrent density, when comparing the uniform Zr-doped Fe₂ O₃ nanorod arrays (1.0 mA cm^-2 at 1.23 V vs. RHE) with dual-axial gradient-doped (Zr and Sn) Fe₂ O₃ nanorod arrays, highlights the additional charge-separation effect resulting from gradient codoping of Zr and Sn. Hence, this promising design may provide guidelines for dual-axial gradient doping into photoelectrodes to realize efficient PEC water splitting.

Vertically Aligned Porous Organic Semiconductor Nanorod Array Photoanodes for Efficient Charge Utilization

Because of inefficient charge utilization caused by localized π-electron conjugation and large exciton binding energy, the photoelectrochemical water-splitting efficiency of organic polymers is seriously limited. Taking the graphitic carbon nitride (g-CN) polymer as an example, we report a novel photoanode based on a vertically aligned g-CN porous nanorod (PNR) array prepared in situ, using a thermal polycondensation approach, with anodic aluminum oxide as the template. The g-CN PNR array exhibits an excellent photocurrent density of 120.5 μA cm^-2 at 1.23 V_RHE under one sun illumination, the highest reported incident photon-to-current efficiency of ∼15% at 360 nm, and an outstanding oxygen evolution reaction stability in 0.1 M Na₂SO₄ aqueous solution, which constitutes a benchmark performance among the reported g-CN-based polymer photoanodes without any sacrificial reagents. When compared with its planar counterpart, the enhanced performance of the PNR array results principally from its unique structure that enables a high degree of aromatic ring π-electron conjugation for higher mobility of charge carriers, provides a direct pathway for the electron transport to the substrate, produces a large portion of hole-accepting defect sites and space charge region to promote exciton dissociation, and also withstands more strain at the interface to ensure intimate contact with the substrate. This work opens a new avenue to develop nanostructured organic semiconductors for large-scale application of solar energy conversion devices.

Influence of Sb5+ as a Double Donor on Hematite (Fe3+) Photoanodes for Surface-Enhanced Photoelectrochemical Water Oxidation

To exploit the full potential of hematite (α-Fe₂O₃) as an efficient photoanode for water oxidation, the redox processes occurring at the Fe₂O₃/electrolyte interface need to be studied in greater detail. Ex situ doping is an excellent technique to introduce dopants onto the photoanode surface and to modify the photoanode/electrolyte interface. In this context, we selected antimony (Sb⁵⁺) as the ex situ dopant because it is an effective electron donor and reduces recombination effects and concurrently utilize the possibility to tuning the surface charge and wettability. In the presence of Sb⁵⁺ states in Sb-doped Fe₂O₃ photoanodes, as confirmed by X-ray photoelectron spectroscopy, we observed a 10-fold increase in carrier concentration (1.1 × 10²⁰ vs 1.3 × 10¹⁹ cm^-3) and decreased photoanode/electrolyte charge transfer resistance (∼990 vs ∼3700 Ω). Furthermore, a broad range of surface characterization techniques such as Fourier-transform infrared spectroscopy, ζ-potential, and contact angle measurements reveal that changes in the surface hydroxyl groups following the ex situ doping also have an effect on the water splitting capability. Theoretical calculations suggest that Sb⁵⁺ can activate multiple Fe³⁺ ions simultaneously, in addition to increasing the surface charge and enhancing the electron/hole transport properties. To a greater extent, the Sb⁵⁺- surface-doped determines the interfacial properties of electrochemical charge transfer, leading to an efficient water oxidation mechanism.

Facile Integration between Si and Catalyst for High-Performance Photoanodes by a Multifunctional Bridging Layer

Designing high-quality interfaces is crucial for high-performance photoelectrochemical (PEC) water-splitting devices. Here, we demonstrate a facile integration between polycrystalline n⁺p-Si and NiFe-layered double hydroxide (LDH) nanosheet array by a partially activated Ni (Ni/NiO_x) bridging layer for the excellent PEC water oxidation. In this model system, the thermally deposited Ni interlayer protects Si against corrosion and makes good contact with Si, and NiO_x has a high capacity of hole accumulation and strong bonding with the electrodeposited NiFe-LDH due to the similarity in material composition and structure, facilitating transfer of accumulated holes to the catalyst. In addition, the back illumination configuration makes NiFe-LDH sufficiently thick for more catalytically active sites without compromising Si light absorption. This earth-abundant multicomponent photoanode affords the PEC performance with an onset potential of ∼0.78 V versus reversible hydrogen electrode (RHE), a photocurrent density of ∼37 mA cm^-2 at 1.23 V versus RHE, and retains good stability in 1.0 M KOH, the highest water oxidation activity so far reported for the crystalline Si-based photoanodes. This bridging layer strategy is efficient and simple to smooth charge transfer and make robust contact at the semiconductor/electrocatalyst interface in the solar water-splitting systems.

A photo-responsive electrocatalyst: CdSe quantum dot sensitized WS2 nanosheets for hydrogen evolution in neutral solution

Under visible light irradiation, the photoinduced electrons help CdSe QD/WS₂ electrocatalysts to achieve a notable HER activity enhancement.