Unveiling the role of inorganic nanoparticles in Earth's biochemical evolution through electron transfer dynamics

This article explores the intricate interplay between inorganic nanoparticles and Earth's biochemical history, with a focus on their electron transfer properties. It reveals how iron oxide and sulfide nanoparticles, as examples of inorganic nanoparticles, exhibit oxidoreductase activity similar to proteins. Termed "life fossil oxidoreductases," these inorganic enzymes influence redox reactions, detoxification processes, and nutrient cycling in early Earth environments. By emphasizing the structural configuration of nanoparticles and their electron conformation, including oxygen defects and metal vacancies, especially electron hopping, the article provides a foundation for understanding inorganic enzyme mechanisms. This approach, rooted in physics, underscores that life's origin and evolution are governed by electron transfer principles within the framework of chemical equilibrium. Today, these nanoparticles serve as vital biocatalysts in natural ecosystems, participating in critical reactions for ecosystem health. The research highlights their enduring impact on Earth's history, shaping ecosystems and interacting with protein metal centers through shared electron transfer dynamics, offering insights into early life processes and adaptations.

Structural Fe(II)-induced generation of reactive oxygen species on magnetite surface for aqueous As(III) oxidation during oxygen activation

Magnetite is a reductive Fe(II)-bearing mineral, and its reduction property is considered important for degradation of contaminants in groundwater and anaerobic subsurface environments. However, the redox condition of subsurface environments frequently changes from anaerobic to aerobic owing to natural and anthropogenic disturbances, generating reactive oxygen species (ROS) from the interaction between Fe(II)-bearing minerals and O2. Despite this, the mechanism of ROS generation induced by magnetite under aerobic conditions is poorly understood, which may play a crucial role in As(III) oxidation. Herein, we found that magnetite could activate O2 and induce the oxidative transformation of As(III) under aerobic conditions. As(III) oxidation was attributed to the ROS generated via structural Fe(II) within the magnetite octahedra oxygenation. The electron paramagnetic resonance and quenching tests confirmed that O2•-, H2O2, and •OH were produced by magnetite. Moreover, density function theory calculations combined with experiments demonstrated that O2•- was initially formed via single electron transfer from the structural Fe(II) to the adsorbed O2; O2•- was then converted to •OH and H2O2 via a series of free radical reactions. Among them, O2•-and H2O2 were the primary ROS responsible for As(III) oxidation, accounting for approximately 52 % and 19 % of As(III) oxidation. Notably, As(III) oxidation mainly occurred on the magnetite surface, and As was immobilized further within the magnetite structure. This study provides solid evidence regarding the role of magnetite in determining the fate and transformation of As in redox-fluctuating subsurface environments.

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology

Oxidoreductases play crucial roles in electron transfer during biological redox reactions. These reactions are not exclusive to protein-based biocatalysts; nano-size (<100 nm), fine-grained inorganic colloids, such as iron oxides and sulfides, also participate. These nanocolloids exhibit intrinsic redox activity and possess direct electron transfer capacities comparable to their biological counterparts. The unique metal ion architecture of these nanocolloids, including electron configurations, coordination environment, electron conductivity, and the ability to promote spontaneous electron hopping, contributes to their transfer capabilities. Nano-size inorganic colloids are believed to be among the earliest 'oxidoreductases' to have 'evolved' on early Earth, playing critical roles in biological systems. Representing a distinct type of biocatalysts alongside metalloproteins, these nanoparticles offer an early alternative to protein-based oxidoreductase activity. While the roles of inorganic nano-sized catalysts in current Earth ecosystems are intuitively significant, they remain poorly understood and underestimated. Their contribution to chemical reactions and biogeochemical cycles likely helped shape and maintain the balance of our planet's ecosystems. However, their potential applications in biomedical, agricultural, and environmental protection sectors have not been fully explored or exploited. This review examines the structure, properties, and mechanisms of such catalysts from a material's evolutionary standpoint, aiming to raise awareness of their potential to provide innovative solutions to some of Earth's sustainability challenges.

In situ doping lignin-derived carbon quantum dots on magnetic hydrotalcite for enhanced degradation of Congo Red over a wide pH range and simultaneous removal of heavy metal ions

A new N, S-CQDs@Fe₃O₄@HTC composite was prepared by loading N, S carbon quantum dots (N, S-CQDs) derived from lignin on magnetic hydrotalcite (HTC) via an in-situ growth method. The characterization results showed that the catalyst had a mesoporous structure. These pores facilitate the diffusion and mass transfer of pollutant molecules inside the catalyst, allowing them to approach the active site smoothly. The catalyst performed well in the UV degradation of Congo red (CR) over a wide pH range (3-11), with efficiencies over 95.43 % in all cases. Even at a high NaCl content (100 g/L), the catalyst showed extraordinary CR degradation (99.30 %). ESR analysis and free radical quenching experiments demonstrated that OH and O₂^- were the main active species governing CR degradation. Besides, the composite had outstanding removal efficiency for Cu²⁺ (99.90 %) and Cd²⁺ (85.08 %) simultaneously due to the electrostatic attraction between the HTC and metal ions. Moreover, the N, S-CQDs@Fe₃O₄@HTC had excellent stability and recyclability during five cycles, making it free of secondary contamination. This work provides a new environment-friendly catalyst for the simultaneous removal of multiple pollutants and a waste-to-waste strategy for the value-added utilization of lignin.

Defective Fe3 O4- x Few-Atom Clusters Anchored on Nitrogen-Doped Carbon as Efficient Oxygen Reduction Electrocatalysts for High-Performance Zinc-Air Batteries

It remains a challenge to develop cost-effective, high-performance oxygen electrocatalysts for rechargeable metal-air batteries. Herein, zinc-mediated zeolitic imidazolate frameworks are exploited as the template and nitrogen and carbon sources, onto which is deposited a Fe₃ O₄ layer by plasma-enhanced atomic layer deposition. Controlled pyrolysis at 1000 °C leads to the formation of high density of Fe₃ O_{4- x} few-atom clusters with abundant oxygen vacancies deposited on an N-doped graphitic carbon framework. The resulting nanocomposite (Fe₃ O_{4- x} /NC-1000) exhibits a markedly enhanced electrocatalytic performance toward oxygen reduction reaction in alkaline media, with a remarkable half-wave potential of +0.930 V versus reversible hydrogen electrode, long-term stability, and strong tolerance against methanol poisoning, in comparison to samples prepared at other temperatures and even commercial Pt/C. Notably, with Fe₃ O_{4- x} /NC-1000 as the cathode catalyst, a zinc-air battery delivers a high power density of 158 mW cm^-2 and excellent durability at 5 mA cm^-2 with stable 2000 charge-discharge cycles over 600 h. This is ascribed to the ready accessibility of the Fe₃ O_{4- x} catalytic active sites, and enhanced electrical conductivity, oxygen adsorption, and electron-transfer kinetics by surface oxygen vacancies. Further contributions may arise from the highly conductive and stable N-doped graphitic carbon frameworks.

Novel and Green Synthesis of Nitrogen-Doped Carbon Cohered Fe3O4 Nanoparticles with Rich Oxygen Vacancies and Its Application

A one-pot and green synthesis methodology was successfully designed to prepare nitrogen-doped carbon (NC) cohered Fe3O4 nanoparticles with rich oxygen vacancies (Fe3O4-OVs/NC). The preparation was achieved via cold-atmospheric-pressure air plasma using Fe2O3 nanoparticles as the only precursor, and pyridine as the carbon and nitrogen source. Systematic characterization results of the as-prepared Fe3O4-OVs/NC confirmed the transition from Fe2O3 to Fe3O4, along with the generation of oxygen vacancies, while preserving the original needle-like morphology of Fe2O3. Moreover, the results indicated the formation of the NC attaching to the surface of the formed Fe3O4 nanoparticles with a weight percent of ~13.6%. The synthesized nanocomposite was further employed as a heterogeneous Fenton catalyst to remove phenol from an aqueous solution. The material has shown excellent catalytic activity and stability, demonstrating a promising application for wastewater treatment.

Microstructural Analysis and Mechanical Properties of a Hybrid Al/Fe2O3/Ag Nano-Composite

This work aims to define the microstructure and to study the mechanical properties of an Al matrix incorporated with various amounts of Fe2O3 (3, 6, 9, 12 and 15 wt.%) with a constant amount of Ag at 1 wt.%. Al/Fe2O3 + Ag hybrid nano-composite samples are manufactured using powder metallurgy. An aluminum matrix is considered an important alloy, owing to its properties such as being lightweight, strong and corrosion and wear resistant, which enable it to be used in many applications, such as electronics, aerospace and automotive purposes. Various examinations have been performed for the samples of this work, such as Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD) analysis to estimate the microstructure and phases of manufactured nano-composites. Mechanical testing is also carried out, such as micro-hardness testing, compressive testing and wear testing, to estimate the mechanical properties of the hybrid nano-composites. The results of FESEM and XRD demonstrate that Fe2O3 and Ag nanoparticles are uniformly distributed and dispersed into the Al matrix, whereas the mechanical tests show that enhancement t micro-hardness, compressive strength of 12 wt.% Fe2O3 + 1Ag and wear rate decrease to a minimum value of 12 wt.% of Fe2O3 + 1Ag.

Development of chitosan decorated Fe3O4 nanospheres for potential enhancement of photocatalytic degradation of Congo red dye molecules

Fe₃O₄ nanospheres (Nsps) and chitosan (Cts)/Fe₃O₄ Nsps were prepared using a one-pot hydrothermal method and subsequently used as photocatalysts against the degradation of Congo red (CR) dye molecules. The sphere-shaped Fe₃O₄ nanoparticles were heterogeneously decorated by the Cts matrix, which was confirmed by powder X-ray diffraction, scanning and transmission electron microscopies. The Cts/Fe₃O₄ Nsps demonstrated 98% efficient photocatalytic activity against CR dye molecules upon 60 min exposure to visible light compared to Fe₃O₄ Nsps (77% for 60 min). When compared to Fe₃O₄ Nsps, the visible light photocatalytic efficiency of Cts/Fe₃O₄ Nsps against CR dye molecules was significantly improved.

On the Interplay Between Oxygen Vacancies and Small Polarons in Manganese Iron Spinel Oxides

Ternary spinel oxides are promising materials due to their potentially versatile properties resulting from the disorder inherent in their crystal structure. To fully unlock the potential of these materials, a deeper understanding of their electronic structures, both as pristine and defective crystals, is required. In the present work, we investigate the effects of oxygen vacancies on the electronic structure and charge transport properties of the ternary spinel oxide Mn _x Fe_3-x O₄, modeled on epitaxial thin films of the material, using density functional theory + U (DFT + U). The formation energy of a single oxygen vacancy in the spinel cell is found to be large and unaffected by changes in stoichiometry, in agreement with experimental results. We find that the immediate vicinity of the vacancy has a marked impact on the formation energy. In particular, Mn cations are found to be preferred over Fe as sites for charge localization around the vacancy. Finally, we examine the charge transport in the defective cell using the formalism of Marcus theory and find that the activation barrier for electron small-polaron hopping between sites not adjacent to the vacancy is significantly increased, with a large driving force toward sites that reside on the same (001) plane as the vacancy. Hence, vacancies delay charge transport by increasing the activation barrier, attributed to a rearrangement of vacancy-released charge on the cations immediately neighboring the vacancy site. These results highlight the impact of oxygen vacancies on charge transport in spinel oxides.

Enhanced dielectric properties with a significantly reduced loss tangent in (Mg2+, Al3+) co-doped CaCu3Ti4O12 ceramics: DFT and experimental investigations

CaCu₃Ti₄O₁₂ and CaCu_2.95Mg_0.05Ti_3.95Al_0.05O₁₂ ceramics were fabricated via a solid-state reaction method. A single-phase of CaCu₃Ti₄O₁₂ was found in these two ceramics. Very great grain size expansion was produced by co-doping with Mg²⁺ and Al³⁺. DFT results indicate that both Mg and Al atoms preferentially occupy Cu sites, creating liquid-phase sintering decomposition at grain boundary layers. Very high dielectric permittivity of ∼58 397 and low loss tangent of about 0.047 were achieved in a CaCu_2.95Mg_0.05Ti_3.95Al_0.05O₁₂ ceramic. Additionally, the temperature stability of the dielectric response was improved. Better dielectric properties in the co-doped ceramic have possible origins from enhanced grain boundary responses, especially from the influences of metastable phases and oxygen enrichment at the grain boundaries. Experimental and computational results indicate that the colossal dielectric properties in CaCu₃Ti₄O₁₂ ceramics might be correlated with an internal barrier layer capacitor structure.

Mg and Al atoms preferentially occupy Cu sites, creating liquid-phase sintering decomposition at grain boundary layers. This results in very high dielectric permittivity and a low loss tangent of the CaCu_2.95Mg_0.05Ti_3.95Al_0.05O₁₂ ceramic.

Controllable design of defect-rich hybrid iron oxide nanostructures on mesoporous carbon-based scaffold for pseudocapacitive applications

The controllable design of functional nanostructures for energy and environmental applications represents a critical yet challenging technology. The existing fabrication strategies focus mainly on increasing the number of accessible active sites. However, these techniques generally necessitate complex chemical agents and suffer from limited experimental conditions delivering high costs, low yields, and poor reproducibility. The present work reports a new strategy for controllable synthesis of a hybrid system including mixed iron oxide nanostructures enriched with non-stoichiometric Fe21.34O32 and Fe3+[Fe5/33+□1/32+]O4 phases, which possess a high concentration of oxygen and Fe2+ vacancies, and a mesoporous carbon-based scaffold (MCS), which was dervied from coffee residues, with graphitic surface and perforated architecture. The nanoperforates acted as trapping sites to localise the FexOy nanoparticles, thereby boosting the density of accessible active sites. Additionally, at the interfacial regions between the FexOy crystallites, a high density of oxygen vacancies with an oriented pattern was shown to create superlattice structures. The energy storage functionality of the defect-rich MCS/FexOy nanostructure with nanoperforated architecture was investigated, where the results exhibited a high gravimetric capacitance of 540 F g-1 at a current density of 1 A g-1 with outstanding capacitance retention of 73.6% after 14 000 cycles.

Adsorption mechanism of NH3, NO, and O2 molecules over the FexOy/AC catalyst surface: a DFT-D3 study

The surface model of the Fe_xO_y/AC catalyst was constructed and the adsorption mechanism of gas molecules on its surface was revealed.