Tailoring surface morphology of heterostructured iron-based Fenton catalyst for highly improved catalytic activity

Fe/Au galvanic nanocells to generate self-sustained Fenton reactions without additives at neutral pH

The generation of reactive oxygen species (ROS) via the Fenton reaction has received significant attention for widespread applications. This reaction can be triggered by zero-valent metal nanoparticles by converting externally added H2O2 into hydroxyl radicals (˙OH) in acidic media. To avoid the addition of external additives or energy supply, developing self-sustained catalytic systems enabling onsite production of H2O2 at a neutral pH is crucial. Here, we present novel galvanic nanocells (GNCs) based on metallic Fe/Au bilayers on arrays of nanoporous silica nanostructures for the generation of self-sustained Fenton reactions. These GNCs exploit the large electrochemical potential difference between the Fe and Au layers to enable direct H2O2 production and efficient release of Fe2+ in water at neutral pH, thereby triggering the Fenton reaction. Additionally, the GNCs promote Fe2+/Fe3+ circulation and minimize side reactions that passivate the iron surface to enhance their reactivity. The capability to directly trigger the Fenton reaction in water at pH 7 is demonstrated by the fast degradation and mineralization of organic pollutants, by using tiny amounts of catalyst. The self-generated H2O2 and its transformation into ˙OH in a neutral environment provide a promising route not only in environmental remediation but also to produce therapeutic ROS and address the limitations of Fenton catalytic nanostructures.

Annealing and electrochemically activated amorphous ribbons: Surface nanocrystallization and oxidation effects enhanced for oxygen evolution performance

Annealing and cyclic voltammetry (CV) are essential for the activation of amorphous alloy ribbons. Various amorphous alloy ribbons have been activated in the fields of environmental catalysts using either annealing or CV. However, the combination of the two methods for improving the oxygen evolution reaction (OER) performance has rarely been reported. This combination is expected to significantly improve the OER performance of amorphous ribbons. Here, we developed an "annealing +CV-activation" integrated strategy to treat a free-standing NiFeBSiP ribbon, which as an efficient and stable oxygen-evolving electrode. The "annealing +CV-activation" strategy induces the nanocrystallization and oxidation effects on the surface of the NiFeBSiP ribbon. The effects significantly increase the electron transfer ability, the Ni/Fe/P oxidation state and the surface area of the NiFeBSiP ribbon, which consequently leads to enhancing the OER performance. As a result, the treated ribbon exhibits a low overpotential of 269 mV at 10 mA cm^-2 and a small Tafel slope of 40.5 mV dec^-1, which are much better than the OER performance of the as-spun ribbon. The enhanced OER performance of the NiFeBSiP ribbon demonstrates the significant and promising effect of the "annealing +CV-activation" integrated strategy for designing high-efficiency amorphous alloy ribbons electrocatalysts.

Copper Nanocomposites In Situ Formed from Metallic Glasses for an Efficient Catalytic Performance

Metallic glasses (MGs) with the unique long-range disordered and short-range ordered atomic structure have attracted extensive attention in the field of environmental catalysis due to their advanced catalytic capability. Herein, CuZr-based MGs are first proven to exhibit superior catalytic performance toward the degradation of organic pollutants compared to the annealed ribbons with different crystal structures; many Cu nanocomposites are gradually in situ precipitated on the surface of the ribbons. The enhanced catalytic behavior is mainly attributed to the random atomic packing structure accelerating electron transport and providing sufficient active sites. On the other hand, the active species, for example, ·OH, ·O₂^-, and Cu(III), are generated through an activation reaction between Cu/Cu₂O nanocomposites and H₂O₂ molecules for the catalytic degradation process. Additionally, further investigation indicated that CuZr-based MGs also present superior stability and durability along with an approximate 96% degradation efficiency within 10 min at the 10th run. This research can successfully explain why MGs have a little higher catalytic reactivity than their crystalline counterparts, and more importantly, it will provide a new strategy for the preparation of catalytic materials for wastewater treatment.

Preparation, characterization, and applications of Fe-based catalysts in advanced oxidation processes for organics removal: A review

Fe-based catalysts as low-cost, high-efficiency, and non-toxic materials display superior catalytic performances in activating hydrogen peroxide, persulfate (PS), peracetic acid (PAA), percarbonate (PC), and ozone to degrade organic contaminants in aqueous solutions. They mainly include ferrous salts, zero-valent iron, iron-metal composites, iron sulfides, iron oxyhydroxides, iron oxides, and supported iron-based catalysts, which have been widely applied in advanced oxidation processes (AOPs). However, there is lack of a comprehensive review systematically reporting their synthesis, characterization, and applications. It is imperative to evaluate the catalytic performances of various Fe-based catalysts in diverse AOPs systems and reveal the activation mechanisms of different oxidants by Fe-based catalysts. This work detailedly summarizes the synthesis methods and characterization technologies of Fe-based catalysts. This paper critically evaluates the catalytic performances of Fe-based catalysts in diverse AOPs systems. The effects of solution pH, reaction temperature, coexisting ions, oxidant concentration, catalyst dosage, and external energy on the degradation of organic contaminants in the Fe-based catalyst/oxidant systems and the stability of Fe-based catalysts are also discussed. The activation mechanisms of various oxidants and the degradation pathways of organic contaminants in the Fe-based catalyst/oxidant systems are revealed by a series of novel detection methods and characterization technologies. Future research prospects on the potential preparation means of Fe-based catalysts, practical applications, assistive technologies, and impact in AOPs are proposed.

Fe3O4@N-doped carbon derived from dye wastewater flocculates as a heterogeneous catalyst for degradation of methylene blue

The study used wastewater to mitigate pollution, wherein the catalyst was derived from MG dye wastewater flocculates produced by electrocoagulation.

A novel ball-milled aluminum-carbon composite for enhanced adsorption and degradation of hexabromocyclododecane

Hexabromocyclododecane (HBCD) is one of the priority persistent organic pollutants (POPs), yet a cost-effective technology has been lacking for the removal and degradation of HBCD. Zero-valent aluminum (ZVAl) is an excellent electron donor. However, the inert and hydrophilic surface oxide layer impedes the release of the electrons from the core metallic Al, resulting in poor reactivity towards HBCD. In this research, a new type of modified mZVAl particles (AC@mZVAl^bm/NaCl) were prepared through ball milling mZVAl in the presence of activated carbon (AC) and NaCl, and tested for adsorption and reductive degradation of HBCD in water. AC@mZVAl^bm/NaCl was characterized with a metallic Al core with newly created reactive surface coated with a thin layer of crushed carbon nanoparticles. AC@mZVAl^bm/NaCl was able to rapidly (within 1 h) adsorb HBCD (C₀ = 2 mg L^-1) and thus effectively enriched HBCD on the carbon surface of AC@mZVAl^bm/NaCl. The pre-enriched HBCD was subsequently degraded by the electrons from the core Al, and ∼63.44% of the pre-sorbed HBCD was completely debrominated after 62 h of the contact. A notable time lag (∼12 h) from the onset of the adsorption to the debromination was observed, signifying the importance of the solid-phase mass transfer from the initially adsorbed AC particles to the reactive Al-AC interface. Overall, AC@mZVAl^bm/NaCl synergizes the adsorptive properties of AC and the high reactivity of metallic Al, and enables a novel two-step adsorption and reductive degradation process for treating HBCD or likely other POPs.

Design and perspective of amorphous metal nanoparticles from laser synthesis and processing

Amorphous metal nanoparticles (A-NPs) have aroused great interest in their structural disordering nature and combined downsizing strategies (e.g. nanoscaling), both of which are beneficial for highly strengthened properties compared to their crystalline counterparts. Conventional synthesis strategies easily induce product contamination and/or size limitations, which largely narrow their applications. In recent years, laser ablation in liquid (LAL) and laser fragmentation in liquid (LFL) as "green" and scalable colloid synthesis methodologies have attracted extensive enthusiasm in the production of ultrapure crystalline NPs, while they also show promising potential for the production of A-NPs. Yet, the amorphization in such methods still lacks sufficient rules to follow regarding the formation mechanism and criteria. To that end, this article reviews amorphous metal oxide and carbide NPs from LAL and LFL in terms of NP types, liquid selection, target elements, laser parameters, and possible formation mechanism, all of which play a significant role in the competitive relationship between amorphization and crystallization. Furthermore, we provide the prospect of laser-generated metallic glass nanoparticles (MG-NPs) from MG targets. The current and potential applications of A-NPs are also discussed, categorized by the attractive application fields e.g. in catalysis and magnetism. The present work aims to give possible selection rules and perspective on the design of colloidal A-NPs as well as the synthesis criteria of MG-NPs from laser-based strategies.

Enhanced Fenton-like catalytic activity and stability of g-C3N4 nanosheet-wrapped copper phosphide with strong anti-interference ability: Kinetics and mechanistic study

Metal-based Fenton-like catalysts usually activate H₂O₂ to produce free radicals (^•OH and O₂^•-) for the degradation of organic pollutants. However, a catalytic reaction dominated by free radicals is easily interfered with by various inorganic anions and water matrices. Herein, g-C₃N₄-wrapped copper phosphide (Cu_xP), as a highly efficient Fenton-like catalyst, was successfully synthesized by a simple low-temperature phosphidation method. The Cu_xP/g-C₃N₄ catalyst exhibited excellent catalytic ability for the removal of various organic contaminants over a wide pH range of 3-11. In addition, the catalyst exhibited strong anti-interference ability toward various inorganic anions (Cl^-, SO₄^2-, NO₃^-, F^-, H₂PO₄^-, HCO₃^- and CO₃^2-) and water matrices (lake water, river water, tap water and simulated water matrix). The reasons for this performance were analyzed by verifying the mechanism of the catalytic reaction. Compared to the pure Cu_xP catalyst, the Cu_xP/g-C₃N₄ composite possessed good catalytic stability. The enhanced and deactivated mechanisms of the Cu_xP/g-C₃N₄ catalyst were systematically analyzed by a series of characterization techniques. A possible reaction mechanism was also proposed based on the experimental results. This work provides new insights into designing highly efficient metal-based Fenton-like catalysts with strong anti-interference ability to practically treat wastewater.