Surface Oxidation State Research Articles

Fast smoothing on diamond surface by inductively coupled plasma reactive ion etching

Abstract

Multi-modal and multi-scale non-local means method to analyze spectroscopic datasets

A multi-modal and multi-scale non-local means (M3S-NLM) method is proposed to extract atomically resolved spectroscopic maps from low signal-to-noise (SNR) datasets recorded with a transmission electron microscope. This method improves upon previously tested denoising techniques as it takes into account the correlation between the dark-field signal recorded simultaneously with the spectroscopic dataset without compromising on the spatial resolution. The M3S-NLM method was applied to electron energy dispersive X-ray and electron-energy-loss spectroscopy (EELS) datasets. We illustrate the retrieval of the atomic scale diffusion process in an Al1-xInxN alloy grown on GaN and the surface oxidation state of perovskite nanocatalysts. The improved SNR of the EELS dataset also allows the retrieval of atomically resolved oxidation maps considering the fine structure absorption edge of LaMnO3 nanoparticles.

Tracing the initial state of surface oxidation in black phosphorus

Black phosphorus has emerged as a class of two-dimensional semiconductors, but its degradation caused by surface oxidation upon exposure to ambient conditions has been a serious issue. A key to understanding the mechanism of surface oxidation is the initial-state structure that has remained elusive. We study the initial state of surface oxidation in black phosphorus by low-temperature core-level photoelectron spectroscopy with the in situ dosage of O2 in the ultrahigh-vacuum condition. Our high-resolution P 2p core-level spectra show two clearly distinct initial-state components of P atoms that have one and two neighboring O atoms, respectively. It is followed by the rapid growth of other higher binding-energy components originating from incomplete P2O5 bonded to black phosphorus with one or two less bonds to O atoms. The variation in the proportion of these components reveals the initial-state structure of dissociative adsorption and its evolution to the final form of phosphorus oxides.

Interplay between Activation Processes, Physicochemical Properties and Electrochemical Performance of “Core-Shell” Carbon Nitride Pt-Ni ORR Electrocatalysts Based on Hierarchical Graphene Supports

The sluggishness of the kinetics of the oxygen reduction reaction (ORR) is one of the most relevant phenomena curtailing the operation capability of proton-exchange membrane fuel cells (PEMFCs)[1]. Hence, the development of advanced ORR electrocatalysts (ECs) is one of the main goals of the research in this field. The ECs described here exhibit a “core-shell” morphology: a hierarchical graphene-based support (H-GR) “core” is covered by a carbon nitride “shell” stabilizing the active sites in “coordination nests” [2]. The “core” comprises highly defected graphene nanoplatelets [3] and carbon black nanoparticles; the latter act as spacers and facilitate the charge and mass transport phenomena that take place during the EC operation. The ECs proposed here are characterized by a very low loading of platinum, on the order of ca. 5 wt%, that is the “active metal”; Ni is introduced as the “co-catalysts” to improve the ORR performance [2]. An extensive post-synthesis activation process (A) is applied to the ECs, significantly affecting their chemical composition, structure and morphology. The ORR performance of the “activated” ECs is much improved in comparison with state-of-the-art Pt/C reference ECs. This work is aimed at investigating the effect of different activation parameters on the ORR performance and reaction mechanism, aiming at a robust and reliable upscaling of the preparation process [4]. The proposed ECs are extensively characterized both before and after A to study the complex interplay between the synthetic/activation parameters, the physicochemical properties, and the electrochemical ORR performance both “ex-situ” and in single PEMFC. The bulk chemical composition of the ECs is determined by means of Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and CHNOS microanalyses; the structure is investigated through wide-angle X-ray diffraction (WAXD) and vibrational spectroscopies (e.g., confocal micro-Raman); the surface composition and oxidation states are probed with X-ray photoelectron spectroscopy (XPS); morphology is observed by high-resolution transmission electron microscopy (HR-TEM); the details of the ORR performance and reaction pathway as a function of the pH of the environment are elucidated by cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE). Finally, the ECs are used to fabricate membrane-electrode assemblies (MEAs) that are tested in single PEMFC in operating conditions. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219, and from the BIRD 2018 program of UNIPD.

Assessing the Surface Oxidation State of Free-Standing Gold Nanoparticles Produced by Laser Ablation.

The surface chemistry of gold nanoparticles produced by the pulsed laser ablation in liquids method is investigated by X-ray photoelectron spectroscopy (XPS). The presence of surface oxide expected on these systems is investigated using synchrotron radiation in conditions close to their original state in solvent but free from substrate or solvent effects which could affect the interpretation of spectroscopic observations. For that purpose we performed the experiment on a controlled free-standing nanoparticle beam produced by combination of an atomizer and an aerodynamic lens system. These results are compared with those obtained by the standard situation of deposited nanoparticles on silicon substrate. An accurate analysis based on Bayesian statistics concludes that the existence of oxide in the free-standing conditions cannot be solely confirmed by the recorded core-level 4f spectra. If present, our data indicate an upper limit of 2.15 ± 0.68% of oxide. However, a higher credence to the hypothesis of its existence is brought by the structureless valence profile of the free-standing beam. Moreover, the cross-comparison with the deposited nanoparticles case clearly evidences an important misleading substrate effect. Experiment with free-standing nanoparticles is then demonstrated to be the right way to further investigate oxidation states on Au nanoparticles.

On the Oxidation State of Cu2 O upon Electrochemical CO2 Reduction: An XPS Study.

The encouraging selectivity of copper oxides for the electroreduction of CO2 into ethylene and alcohols has led to a vivid debate on the possible relation between their operando (sub-)surface oxidation state (i. e. fully reduced or partially oxidized) and this distinct reactivity. The high roughness of the Cu oxides used in previous studies on this matter adds complexity to this controversy and motivated us to prepare quasi-planar Cu2 O thin films that displayed a CO2 reduction selectivity similar to that of oxide-derived copper catalysts reported in previous studies. Most importantly, when the post-mortem thin films were transferred for characterization in an air-free environment, X-ray photoelectron spectroscopy measurements confirmed their complete reduction in the course of the CO2 reduction reaction. Thus, our results indicate that the selectivity of the Cu oxides featured in previous studies stems from their enhanced roughness, highlighting the importance of controlled sample transfer upon post-mortem characterization with ex situ techniques.

Correlation Between Reactivity and Oxidation State of Cobalt Oxide Catalysts for CO Preferential Oxidation

Catalytic performance is known to be influenced by several factors, with the catalyst surface oxidation state being the most prominent of all. However, in the great majority of industrial heterogen...

Immobilization of elemental mercury in non-ferrous metal smelting gas using ZnSe1−xSx nanoparticles

Gaseous elemental mercury (Hg0) in non-ferrous smelting gas is generally accompanied by a high concentration of SO2. Traditional sorbents for Hg0 removal often suffer from SO2 poisoning. To develop a sorbent that has high mercury removal efficiency and excellent sulfur resistance, Zn-Se-S composites were selected. The experimental results indicated that the ZnSe0.7S0.3 composite had the best Hg0 removal performance, achieving an Hg0 removal efficiency higher than 99% after 120 min of reaction at 150 °C. A “hump” was observed in the adsorption breakthrough curve. This phenomenon is due to the activation of surface Se0, with reduction in surface oxidation state (from Se2+ to Se0) by Hg0 or SO2. This composite has multiple adsorption sites (Se0 and active S) for mercury uptake from smelting gas. Moreover, this specific Zn-Se-S composite had excellent SO2 resistance. Even high concentrations (1000 or 2000 ppm) of SO2 barely influenced Hg0 removal performances. The Zn-Se-S composite exhibited potential for Hg0 removal from non-ferrous smelting gas.

Effect of Small Molecular Organic Acids on the Structure and Catalytic Performance of Sol–Gel Prepared Cobalt Cerium Oxides towards Toluene Combustion

Cobalt cerium oxide catalysts with small molecular organic acids (SOAs) as chelating agents were prepared via the sol–gel method and investigated for the complete oxidation of toluene. Four kinds of natural SOAs, i.e. malic acid (MA), citric acid (CA), glycolic acid (GA), and tartaric acid (TA), were selected. The effect of organic acids on the composition, structure, morphology and catalytic performance of metal oxides is discussed in details. The cobalt cerium oxides catalysts were characterized by various techniques, including TG–DSC, XRD, SEM–EDS, N2–adsorption and desorption, XPS, and H2–TPR analyses. The results show that the nature of organic acids influenced the hydrolysis, condensation and calcination processes, as well as strongly affected the textural and physicochemical properties of the metal oxides synthesized. The best catalytic activity was obtained with the CoCe–MA catalyst, and the toluene conversion reached 90% at 242 °C. This outstanding catalytic activity could be related to its textural, redox properties and unique surface compositions and oxidation states. In addition, the CoCe–MA catalyst also showed excellent stability in long–time activity test.

Structural, morphological and optomagnetic properties of GO/Nd/Cu-Mn ferrite ternary nanocomposite

Graphene oxide (GO)/neodymium (Nd)/Cu 0·5 Mn 0·5 Fe 2 O 4 ternary nanocomposite was prepared by sonochemical method and modified Hummer's method. The crystal structure and structural parameter of Cu 0·5 Mn 0·5 Fe 2 O 4 (CMF) nanoferrites were changed with the addition of Nd 3+ and GO. Raman active modes of the GO and ferrite system were observed from Raman spectra. The surface oxidation state (C 1s, O 1s, Cu 2p, Mn 2p, Fe 2p, and Nd 3 d) and their respective binding energies of the prepared nanocomposite were discussed. Different surface morphologies were acquired for CMF, Cu 0·5 Mn 0·5 Fe 1.85 Nd 0.15 O 4 (CMNF), GO, and GO/Cu 0·5 Mn 0·5 Fe 1.85 Nd 0.15 O 4 (GCMNF) ferrite nanocomposites. The absorption of the Cu-Mn nanoferrite (red region) shifted into the blue region with the addition of Nd 3+ and GO. The magnetic parameters were changed with doping of Nd into CMF and GO in CMNF nanoferrite. It was found that the high anisotropy energy values of the CMNF and GCMNF ferrite nanocomposites could be used for electromagnetic wave-absorbing application.

Simultaneous O2 plasma and thermal treatment for improved surface conductivity of Cu-Doped SnO2 films

Cu-doped SnO2 thin films were deposited on a glass substrate using radio frequency magnetron sputtering. The effects of varying the O2 partial pressure during the deposition process and post-O2 plasma treatment at 420 °C were investigated. Bulk and surface oxidation states were measured by X-ray absorption near-edge structure spectroscopy and X-ray photoelectron spectroscopy. The as-deposited films exhibited oxygen deficient compositions and Cu+ or Cu2+ ions, which depend on the deposited O2 partial pressure. After the post-plasma treatment, the films changed from an amorphous structure into a low crystalline film. X-ray diffraction results indicated substitutional doping, wherein some Sn4+ ions were replaced with Cu+ or Cu2+ ions. The O2 plasma treatment can remove Cu2+ and O2− from the film surface. The oxygen deficiency defects and Cu+- or Cu2+- doped present at the surface are the key factors in controlling the sheet resistance of the Cu-doped SnO2 film. The minimum sheet resistance was obtained after the plasma treatment of the films deposited at a 2% O2 partial pressure.

Role of Additive Structure on Controlling Ceria/Substrate Interactions Relevant to Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP)

Chemical Mechanical Polishing (CMP) has emerged as a critical process step for achieving global planarization in advanced integrated circuit manufacturing and has lead to the extension of Moore’s Law. Specifically, Shallow Trench Isolation (STI) CMP is used in the electrical isolation of the active components in an integrated circuit by actively removing TEOS and stopping on Si3N4 to achieve angstrom level uniformity and limit defectivity. Planarization of the overburden material is achieved through a balance of an applied mechanical force and the delivery of a colloidal dispersion (slurry) containing ceria (CeO2) nanoparticles, complexing additives, and rheology modifiers to the substrate surface. Currently, STI slurries contain chemical additives that selectively boost material removal rate (MRR) as well as enhance selectivity via non-covalent passivation films formed at the polishing substrate surface. A crucial factor in maintaining a high MRR is the presence of CeO2 surface oxygen vacancies, commonly associated with Ce3+surface oxidation state, which can be achieved either from pre-dispersion particle processing or though additive/nanoparticle surface reactions present in the slurry formulation. This study probed the impact of the slurry additive functionality, such as carboxylic acids, amines, and phenols, on the removal rate and post-CMP defectivity. Results suggest that the Ce3+ oxidation state is critical to performance but the Ce4+ oxidation state is also a viable reaction site as long as it remains uncomplexed and free of any site-blocking additives. The additive adsorption to the CeO2 surface will result in altering the dynamic interplay of the abrasive particle/chemistry at the substrate surface shifting CMP performance. Employing and correlating a suite of modified analytical methods, such as atomic force microscopy (AFM), electrochemical quartz crystal nanobalance (EQCN), dynamic contact angle measurements, fluorescence microscopy, pre/post characterization of particle properties (size and zeta potential), and dynamic contact angle, a strong correlation between surface energy and CMP performance metrics has been uncovered.

Oxides of Manganese As Efficient Bifunctional Electrocatalysts

The electrolysis of water, or water splitting reaction is one of the cleanest ways of producing hydrogen and oxygen gas for fuel. Electrochemical devices employing these reactions include regenerative fuel cells and rechargeable metal-air batteries, which have the highest theoretical energy density. Considerable efforts have been dedicated towards improving the energy conversion efficiency of these devices. However, the single main obstacle for achieving this has been the lack of suitable bifunctional oxygen electrocatalysts that show simultaneous high activity for both oxygen reduction (ORR) and oxygen evolution (OER) reactions during charge/discharge cycles. The overpotential and slow kinetics of oxygen reactions are limiting parameters in the advancement of electrochemical storage devices. Taking inspiration from nature’s photosynthetic process that uses a Mn4O4Ca cluster in photosystem II to catalyze water splitting, we studied the efficiency of various phases of manganese oxide (MnOx) as electrocatalysts for OER and ORR process, including the role of defects on bifunctionality. Cyclic voltammetry was used to prove that Mn2O3 is a bifunctional catalyst by showing high activity for OER and ORR. Next, in-situ UV-Vis absorbance spectroscopy was conducted to track changes in the surface oxidation state as a result of occurring reactions. Finally, we use electrochemical quartz crystal microbalance to track ion intercalation into the material. Results from these studies were used to obtain a structure-defect-function correlation that can improve the design of electrocatalysts with bifunctional properties. Acknowledgements: The authors would like to thank Rensselaer Polytechnic Institute (RPI) and National Science Foundation, CBET award (No: 1511733), for the partial financial support and Nicholas Smieszek for his assistance with the preparation of this manuscript. I.R, and Q.W also gratefully acknowledge the partial support of Howard P. Isermann fellowship provided by the Department of Chemical and Biological Engineering at RPI.

Exploring oxygen electrocatalytic activity and pseudocapacitive behavior of Co3O4 nanoplates in alkaline solutions

Cobalt-based materials are regarded as important materials for oxygen reduction and evolution reactions (ORR and OER) in metal-air batteries and supercapacitors. However, the activity of oxygen electrocatalysis and the pseudocapacitive performance of cobalt oxide (Co3O4) in the reported works are usually inconsistent. To explore this issue, a series of Co3O4 nanoplates are fabricated using different calcination temperatures, and their morphologies, microstructures, and electrochemical behaviors in alkaline solutions are systemically characterized. It is found that the high calcination temperature destroys the hexagonal nanoplate morphology and leads to decreased surface areas and pore volumes. In addition, the activity of Co3O4 nanoplates toward the ORR and OER and the capacitance values decrease with an increase of the calcination temperature. From the ORR/OER activity and the specific capacitance normalized by the specific and electrochemical surface area, the intrinsic electrochemical performance may be correlated to the surface oxidation states of Co and O. The high calcination temperature leads to the high amounts of adsorbed oxygen species and Co3+ atoms on the surface, which may be the key for the high intrinsic ORR and OER activity based on the electrochemical surface area. However, the apparent performance is insufficient due to the greatly reduced surface area. For the pseudocapacitive performance, on the contrary, the greater amount of Co2+ on the surface is favorable. Hence, the inconsistent electrochemical performance of Co3O4 may originate from different geometries and surface oxidation states on the surface, which are affected by the calcination temperature in the synthesis process. This work provides insights into the design and optimization of non-precious materials in electrochemical systems, and offers a feasible strategy to improve the performance by using a low-temperature calcination method.

Reactions at noble metal contacts with methylammonium lead triiodide perovskites: Role of underpotential deposition and electrochemistry

Chemical reactivity of halide perovskites coupled with a low energy of formation makes it a challenge to characterize material properties and achieve long-term device stability. In this study, we elucidate electrochemical reactions occurring at the methylammonium lead triiodide (MAPbI3)/Au interface. X-ray photoemission spectroscopy is used to identify a type of reduction/oxidation reaction termed underpotential deposition (UPD) involving lead, iodine, and hydrogen occurring at interfaces with noble metals. Changes in surface compositions and oxidation states suggest that UPD derived adsorbates at MAPbI3/Au interfaces lower the energy barrier for release of volatile HI and/or I2 catalyzing degradation at exposed contacts. Additionally, comparison to PbI2/Au interfaces demonstrates that the presence of methylammonium/methylamine accelerates the formation of a Pb0 adlayer on the Au. Reactions involving UPD Pb0 can transform the typically anodic (hole collecting) Au to a cathode in a photovoltaic measurement. Cyclic voltammetry reveals electrochemical reaction peaks in indium tin oxide (ITO)/MAPbI3/Au devices occurring within voltage ranges commonly used for perovskite characterization. The electrochemical stability window of this device architecture is measured to be between −0.5 V and 0.9 V. Voltage induced interfacial reactions contribute to reversible electrochemical peaks, hysteresis, switchable perovskite diode polarity, and permanent degradation at larger voltages. These types of surface reactions alter the interface/interphase composition beyond ion accumulation, provide a source for the diffusion of defects, and contribute to electrode material dependent current-voltage hysteresis. Moreover, the results imply fundamental limitations to achieving high device stability with noble metals and/or methylammonium containing perovskites.

H4SiO4 sorption and polymerization at the magnetite - aqueous interface: The influence of interfacial redox state

Many aspects of the behaviour of iron oxide phases are influenced significantly by the interaction with H4SiO4 which is a ubiquitous solute in aquatic systems. This interaction can involve H4SiO4 sorption and interfacial oligomerization and has a dependence on the structures present on the oxide surface. In this work the sorption and oligomerization of H4SiO4 on the surface of magnetite (Fe3O4) was studied as a function of the particle surface oxidation state. Magnetite samples were prepared from FeCl2:FeCl3 or FeSO4:FeCl3 and were characterised by Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Raman and infrared (IR) spectroscopy. Magnetite from FeCl2:FeCl3 was pure magnetite by XRD but Raman spectra indicated ferrihydrite was present on the “as prepared” surface. Raman also indicated that the ferrihydrite layer was decreased following reduction with hydrazine but was increased following treatment with dilute H2O2. In situ Attenuated Total Reflectance Infrared Spectroscopy (ATRIR) showed the propensity of H4SiO4 oligomerization on magnetite was enhanced following hydrazine reduction and was not influenced by H2O2. In all cases the proportion of oligomers to monomers was significantly greater on the surface of magnetite than on ferrihydrite. The inference is that both the as prepared and the H2O2 oxidised magnetite have a ferric oxide layer that has a local environment similar to ferrihydrite, as indicated by the Raman, however on the magnetite surface this phase does not have the high surface curvature of the ferrihydrite prepared directly from Fe(NO3)3 hydrolysis. The high surface curvature inherent with very small sized particles such as ferrihydrite (≈2 nm), has been linked with a low propensity of H4SiO4 oligomerization on these surfaces. The results from this study support the association between surface curvature and propensity for interfacial H4SiO4 oligomerization. Magnetite prepared from FeSO4:FeCl3 had minor amounts of goethite and was found to promote the formation of a higher degree of 3 dimensional H4SiO4 polymerization on this oxide which is attributed to the nature of the (021) goethite faces.

Dynamic Reorganization of Bimetallic Nanoparticles under Reaction Depending on the Support Nanoshape: The Case of RhPd over Ceria Nanocubes and Nanorods under Ethanol Steam Reforming

Bimetallic catalysts exhibit high performance compared to that of their monometallic counterparts in a wide range of catalytic reactions. Both geometric and electronic phenomena yield unique properties that cannot be reproduced by other means. Bimetallic nanoparticles reorganize dynamically under reaction conditions, usually forming complex core–shell distributions of metals and oxidation states. This reorganization is even more complex in the presence of a reducible support. Here we show by operando ambient pressure X-ray photoelectron spectroscopy (AP-XPS) that the shape of the support also plays a crucial role in the reorganization of bimetallic nanoparticles, which has important consequences for catalytic performance. We have monitored the surface composition and oxidation states of preformed Rh0.5Pd0.5 model nanoparticles of 4 nm in size supported over CeO2 nanocubes and CeO2 nanorods during the catalytic steam reforming of ethanol (ESR) at 823 K. Over Rh0.5Pd0.5/CeO2-nanocubes, both rhodium and pall...

X-ray induced vanadium L3M23M45 auger electron spectra as tool to trace vanadium oxidation state: Study of surface stoichiometry recovery of V2O3 film

Ratio of two peaks in X-ray induced vanadium L3M23M45 Auger electron spectra has been used to monitor oxidation state of V2O3 thin film surface followed by vacuum annealing. The V2O3 film was grown with sol-gel method on the Al2O3 (0001) substrate. The O 1s, V 2p core-level X-ray photoelectron spectra and V L3M23M45 Auger electron spectra were measured from the film as function of annealing temperature. Brief exposure of the film to the air turned surface vanadium to 4+ oxidation state. Annealing in UHV at 455 K completely converted vanadium to 3+. The binding energy (BE) difference between O 1s and V 2p3/2 core-level changed from 14.0 eV to 14.9 eV as annealing temperature increased from room temperature to 455 K. Intensity ratio of the two peaks in V L3M23M45 Auger electron spectra, peak originated from O 2p region to that from V 3d region, changes from 0.91 to 0.63. In combination with measurement from VO2 film, relation between intensity ratio of V L3M23M45 doublet and the oxidation state of vanadium was established by comparison with BE difference between O 1s and V 2p3/2 core-level. V L3M23M45 Auger electron spectra can be useful tool for scanning Auger microscope (SAM) to get high spatial resolution vanadium ion distribution. A few points to consider for application toward SAM mapping have been discussed.

The characteristics of sediment pollution and the identification of oxidation layer under long-term operation of large-scale surface flow constructed wetlands

研究湿地底泥污染特性及水-土界面边界层性质是明确大型人工湿地长期运行下底泥内源污染问题的关键.本文以典型人工湿地为例，通过综合布点垂向分层监测湿地底泥理化性质，明确底泥污染特性，分析水-土界面边界氧化层现象、性质及形成机理，探讨其性质成因.结果表明：与湖泊类似，长期运行人工湿地底泥也会产生氧化层，垂向由上到下分为氧化层、污染层、过渡层和健康层；运行6年的湿地底泥可形成厚约1 cm、无明显臭味、棕黄色可塑状的氧化层；与污染层相比，氧化层色味变淡、流动性减弱，含水率、d（0.9）、亚铁、总有机碳和总氮含量分别降低7.20%、54.04%、54.59%、17.89%和7.00%，氧化还原电位和总磷含量分别升高150.41%和18.17%；氧化层是由氧化、沉降协同作用下形成的底泥表层氧化态微环境，其中上覆水溶解氧水平越高越有利于提高氧化层致密程度，降低氧化层有机质、总氮含量，上覆水悬浮物浓度越高、水深越深越有利于增加氧化层厚度.;The study on the characteristics of sediment pollution and the boundary layer of water-soil interface is the key to identify the problem of sediment pollution under the long-term operation of large constructed wetlands. This paper takes a typical surface flow constructed wetland as an example, through comprehensive vertical layered monitoring of the physicochemical properties of the wetland sediment, to clarify the pollution characteristics of the sediment and analyzed the phenomenon, nature and formation mechanism of the boundary oxidation layer of the water-soil interface. The results show that, similar to lakes, the sediment of constructed wetland in long-term operation also generates oxidation layer, which is divided into oxidation layer, pollution layer, transition layer and health layer from top to bottom. After 6 years of operation, the wetland sediment can form an oxidation layer, which is about 1 cm thick, brown-yellow, malleable, with no obvious odor. Compared with the pollution layer, the color and smell of the oxidation layer are weakened, and its fluidity is weakened. Meanwhile, the water content, d(0.9), diatomic iron, total organic carbon and total nitrogen are decreased by 7.20%, 54.04%, 54.59%, 17.89% and 7.00%. Eh and total phosphorus are increased by 150.41% and 18.17%, respectively. Oxidation layer is a micro-environment of surface oxidation state formed under the synergistic action of oxidation and settlement. The higher the dissolved oxygen level of overlying water is, the more favorable it is to increase the density of the oxidation layer and reduce the organic matter and total nitrogen content of the oxidation layer. In addition, the higher the concentration of overlying water suspended substance and the deeper the water depth, the more favorable it is to increase the thickness of the oxidation layer.

Redox-dependent catalase mimetic cerium oxide-based nanozyme protect human hepatic cells from 3-AT induced acatalasemia.

Recently, CeNPs have emerged as an effective therapeutic agent due to their redox-active nature encompassing the ability to switch between +4 or +3 oxidation states of surface "Ce" atoms. CeNPs with predominantly high Ce +4 oxidation state have been shown to exhibit biological catalase enzyme-like activity. Catalase enzyme is naturally present in mammalian cells and facilitates the protection from reactive oxygen species (ROS), generated due to decomposition of hydrogen peroxide (H2O2). Inactivation of cellular catalase enzyme is known to cause several diseases such as acatalasemia, type 2 diabetes mellitus, and vitiligo. In this study, we have artificially inhibited the activity of cellular catalase enzyme from human liver cells (WRL-68) using 3-Amino-1,2,4-Triazole (3-AT). Further, CeNPs was used for imparting protective effect against the deleterious effects of elevated cellular H2O2 concentration. Our results suggest that CeNPs (+4) can protect hepatic cells from cytotoxicity and genetic damage from the high concentrations of H2O2 in the absence of functional catalase enzyme. CeNPs were efficiently internalized in WRL-68 cells and effectively scavenge the free radicals generated due to elevated H2O2 inside the cells. Additionally, CeNPs were also shown to protect cells from undergoing early apoptosis and DNA damage induced due to the 3-AT exposure. Moreover, CeNPs did not elicit the natural antioxidant defense system of the cells even in the absence of functional catalase enzyme, suggesting that the observed protection was due to the H2O2 degradation activity of CeNPs (+4). Our finding substantiates the reinforcement of CeNPs as pharmacological agents for the treatment of diseases related to nonfunctional biological catalase enzyme in the mammalian cells.