Nanotextured Spikes of α-Fe2O3/NiFe2O4 Composite for Efficient Photoelectrochemical Oxidation of Water

Peracetic acid activated by nickel cobaltite as effective oxidizing agent for BPA and its analogues degradation

The presented research concerns the use of nickel cobaltite nanoparticles (NiCo2O4 NPs) for the heterogeneous activation of peracetic acid and application of NiCo2O4-PAA system for degradation 10 organic micropollutants from the group of bisphenols. The bisphenols removal (initial concentration 1 μM) process was optimized by selecting the appropriate process conditions. The optimal amount of catalyst (115 mg/L), peracetic acid (PAA) concentration (7 mM) and pH (7) were determined using response surface analysis in the Design of Experiment. Then, NiCo2O4 NPs were used to check the possibility of reuse in subsequent oxidation cycles. The work also attempts to explain the mechanism of oxidation of the studied micropollutants. The participation of the sorption process on the catalyst was excluded and based on the experiments with radical scavengers it can be concluded that the oxidation proceeds in a radical pathway, mainly with participation of O2•- radicals. Experiments conducted in real water matrices exhibit low impact on degradation efficiency. Toxicity tests with green alga Acutodesmus obliquus and aquatic plant Lemna minor showed that post-reaction mixture influenced growth and the content of photosynthetic pigments in concentration dependent manner.

Three-Dimensional Hierarchical HRP-MIL-100(Fe)@TiO2@Fe3O4 Janus Magnetic Micromotor as a Smart Active Platform for Detection and Degradation of Hydroquinone

A novel multifunctional Janus magnetic micromotor was designed and constructed by using MIL-100(Fe)@TiO₂@Fe₃O₄ multicore-shells modified with horseradish peroxidase (HRP) as a smart active platform to realize detection and degradation of hydroquinone (HQ). The obtained micromotor showed a unique three-dimensional (3D) hierarchical architecture with highly exposed active sites and could autonomously move at a speed of 140 ± 7.0 μm·s^-1 by O₂ bubbles generated from the catalytic decomposition of H₂O₂ fuel. Benefiting from the combination of active self-propulsive motion, high peroxidase-like activity, tuned heterojunctions with matching band structures, and a 3D hierarchical structure, an effective platform involving dynamically sensitive detection and quick removal of HQ from water was established by using the multifunctional HRP-integrated MIL-100(Fe)@TiO₂@Fe₃O₄ Janus micromotor. The proposed multifunctional Janus magnetic micromotor had advantages of simple and feasible fabrication, sensitive detection and effective photo-Fenton degradation of HQ in a wide pH range of 4-7, and magnetic recycling, revealing potential for environmental remediation applications.

Elevating the charge separation of MgFe2O4 nanostructures by Zn ions for enhanced photocatalytic and photoelectrochemical water splitting

Magnesium ferrites (MgFe₂O₄) are important class of ferrites that have been receiving greater attention as promising excellent photocatalyst due to its low cost, wide light spectrum response and environment-friendly nature. However, its poor electronic conductivity and fast charge carrier recombination hinders its electrocatalytical applications. Hence, accelerating charge carriers separation efficiency is important to modify the photoelectrochemical performance of MgFe₂O₄. Herein, novel Zn ions doped MgFe₂O₄ nanospheres are fabricated for the first time. Zn ions are doped into MgFe₂O₄ nanostructures from surface to enhance their charge separation efficiency. The doped MgFe₂O₄ nanostructures show significant photocatalytic activity and enhanced photocurrent density than that of pristine MgFe₂O₄.The improved photoelectrocatalytic performance is attributed to doping effect, were Zn ions actually enhance the conductivity. Zn ions enhance the activity of MgFe₂O₄ and accelerate the charge transfer properties in MgFe₂O₄. The results highlight that Zn doped MgFe₂O₄ nanospheres could be a potential candidate for photocatalytic and photoelectrochemical applications.

Ordered nanostructures arrays fabricated by anodic aluminum oxide (AAO) template-directed methods for energy conversion

Clean and efficient energy conversion systems can overcome the depletion of the fossil fuel and meet the increasing demand of the energy. Ordered nanostructures arrays convert energy more efficiently than their disordered counterparts, by virtue of their structural merits. Among various fabrication methods of these ordered nanostructures arrays, anodic aluminum oxide (AAO) template-directed fabrication have drawn increasing attention due to its low cost, high throughput, flexibility and high structural controllability. This article reviews the application of ordered nanostructures arrays fabricated by AAO template-directed methods in mechanical energy, solar energy, electrical energy and chemical energy conversions in four sections. In each section, the corresponding advantages of these ordered nanostructures arrays in the energy conversion system are analysed, and the limitation of the to-date research is evaluated. Finally, the future directions of the ordered nanostructures arrays fabricated by AAO template-directed methods (the promising method to explore new growth mechanisms of AAO, green fabrication based on reusable AAO templates, new potential energy conversion application) are discussed.

Solvothermal phase change induced morphology transformation in CdS/CoFe2O4@Fe2O3 hierarchical nanosphere arrays as ternary heterojunction photoanodes for solar water splitting

The design of efficient heterojunction photoanodes with appropriate band alignment and ease of charge separation has been one of the most highly focused research areas in photoelectrodes.

Earth abundant transition metal ferrite nanoparticles anchored ZnO nanorods as efficient and stable photoanodes for solar water splitting

Poor light absorption, severe surface charge recombination and fast degradation are the key challenges with ZnO nanostructures based electrodes for photoelectrochemical (PEC) water splitting. Here, this study attempts to design an efficient and durable nano-heterojunction photoelectrode by integrating earth abundant chemically stable transition metal spinel ferrites MFe₂O₄ (M = Co and Ni) nano-particles on ZnO Nanorod arrays. The low band gap magnetic ferrites improve the solar energy harvesting ability of the nano-heterojunction electrodes in ultraviolet-visible light region resulting in a maximum increase of 105% and 190% in photocurrent density and applied bias photon-to-current efficiency, respectively, compared to pristine ZnO nanorods. The favourable type-II band alignment at the ferrites/ZnO nano-heterojunction provides significantly enhanced photo-generated carrier separation and transfer, endowing the excellent solar H₂ evolution ability (743 and 891 μmol cm^-2 h^-1for ZnO/CoFe₂O₄ and ZnO/NiFe₂O₄, respectively) of the photoanodes by using sacrificial agent. The hybrid nanostructures deliver long term stability of the electrode against photocorrosion. This work demonstrates an easy but effective strategy to develop low-cost earth abundant ferrites-based heterojunction electrodes, which offers excellent PEC activity and stability.

Electrocoagulants Characteristics and Application of Electrocoagulation for Micropollutant Removal and Transformation Mechanism

Predominantly, the removal of dissolved contaminates via the Fe electrocoagulation (EC) process depends on the electrocoagulants stability, specific area, porosity, dissolution rate, and phase transformation kinetics. The present investigation elucidates the role of applied currents and electrolyte counteranions on the crystalline phase and surface topography of electrocoagulants generated from Fe EC. Moreover, the dissolved contaminant micropollutant removal efficiency was also evaluated by electrochemically produced coagulants. This study confirms that mixed-phase iron (oxyhydr) oxide nanostructures were consistently produced from Fe EC with predominant formation of the goethite phase. The applied current controls the morphology of the coagulants, with flake-like morphology observed with currents at and below 100 mA and spherical morphology observed with currents above 100 mA. The counteranions in the electrolyte also impacted the morphology with spherical, nanosheet, and nanorod morphologies produced by Cl^- or SO₄^2-, CO₃^2-, and HCO₃^- counteranions, respectively. BET analysis revealed the formation of electrocoagulants with micro-, meso-, and macropores. Surface area was markedly reduced from 142.85 to 41.96 m² g^-1 by incident coagulation resulting from increased anodic dissolution. Applicability of the electrocoagulant was examined by different micropollutants (acetaminophen (AC), antipyrine (AT), and atenolol (AT)). Results suggest that >90% and >80% TOC reduction were achieved with Na₂CO₃ and NaHCO₃ as electrolyte media. The lower TOC reduction was rationalized by the identified intermediate products, and possible micropollutant degradation pathways were proposed based on LC-MS/MS analysis.

Current progress in developing metal oxide nanoarrays-based photoanodes for photoelectrochemical water splitting

Solar energy driven photoelectrochemical (PEC) water splitting is a clean and powerful approach for renewable hydrogen production. The design and construction of metal oxide based nanoarray photoanodes is one of the promising strategies to make the continuous breakthroughs in solar to hydrogen conversion efficiency of PEC cells owing to their owned several advantages including enhanced reactive surface at the electrode/electrolyte interface, improved light absorption capability, increased charge separation efficiency and direct electron transport pathways. In this Review, we first introduce the structure, work principle and their relevant efficiency calculations of a PEC cell. We then give a summary of the state-of the-art research in the preparation strategies and growth mechanism for the metal oxide based nanoarrays, and some details about the performances of metal oxide based nanoarray photoanodes for PEC water splitting. Finally, we discuss key aspects which should be addressed in continued work on realizing high-efficiency metal oxide based nanoarray photoanodes for PEC solar water splitting systems.

Facile construction of a novel NiFe2O4@P-doped g-C3N4 nanocomposite with enhanced visible-light-driven photocatalytic activity

Construction of a Z-scheme-based photocatalyst, i.e., NiFe₂O₄@P-g-C₃N₄ nanocomposite, was successfully fabricated by coupling phosphorus-doped g-C₃N₄ with spinel structure NiFe₂O₄. The structural, morphological, and spectroscopic data of the as-synthesized photocatalyst was successfully characterized through XRD, FTIR, SEM, TEM, UV-Vis DRS, PL, and XPS techniques. It was found that NiFe₂O₄@P-g-C₃N₄ had an increased light-absorption capacity, high exciton separation, low photogenerated electron-hole recombination, and showed better photocatalytic activity toward phenol oxidation and hydrogen energy production than the neat materials. Photocatalytic phenol oxidation by 20 wt% NFO@P-CN was also superior and could achieve a 96% conversion, which was 2 and 3 times higher than that by P-CN and NFO, respectively. The 20 wt% NFO@P-CN showed excellent photostability and was able to evolve 904 μmol h^-1 H₂ under visible-light irradiation. The enhanced photocatalytic activity of NiFe₂O₄@P-g-C₃N₄ was in good agreement with the photocurrent results. The synergistic effect between P-CN and NFO could accelerate photogenerated charge separation and, moreover, the distinctive magnetism of NiFe₂O₄@P-g-C₃N₄ aided the collection and recycling of the photocatalyst.

Rational Design and Construction of Cocatalysts for Semiconductor-Based Photo-Electrochemical Oxygen Evolution: A Comprehensive Review

Photo-electrochemical (PEC) water splitting, as an essential and indispensable research branch of solar energy applications, has achieved increasing attention in the past decades. Between the two photoelectrodes, the photoanodes for PEC water oxidation are mostly studied for the facile selection of n-type semiconductors. Initially, the efficiency of the PEC process is rather limited, which mainly results from the existing drawbacks of photoanodes such as instability and serious charge-carrier recombination. To improve PEC performances, researchers gradually focus on exploring many strategies, among which engineering photoelectrodes with suitable cocatalysts is one of the most feasible and promising methods to lower reaction obstacles and boost PEC water splitting ability. Here, the basic principles, modules of the PEC system, evaluation parameters in PEC water oxidation reactions occurring on the surface of photoanodes, and the basic functions of cocatalysts on the promotion of PEC performance are demonstrated. Then, the key progress of cocatalyst design and construction applied to photoanodes for PEC oxygen evolution is emphatically introduced and the influences of different kinds of water oxidation cocatalysts are elucidated in detail. Finally, the outlook of highly active cocatalysts for the photosynthesis process is also included.

The effect of fluorine doping on the photocatalytic properties of hematite for water splitting

Fluorine-doped hematite samples with different concentrations were successfully synthesized through a hydrothermal method to improve the water splitting properties.