Nanoscale anti-ferromagnetic (AFM) NiO exhibits intriguing magnetic anomalies influenced by factors such as size, stoichiometry, surface chemistry, and lattice strain. In the present work, black-coloured NiO nanoparticles were synthesized by combustion method, incorporating cationic Ni2+ vacancies and Ni3+ species on their surface. Annealing NiO at high temperatures (400–800 °C) led to a colour change from black to green, indicating the transition from a non-stoichiometric to a stoichiometric state. The formation of Ni2+ vacancies disrupted AFM ordering between Ni2+ and O2− ions, while the presence of Ni3+ promoted double exchange interactions between Ni3+ and neighbouring Ni2+ ions, contributing to ferromagnetism (FM) in AFM NiO. The spin exchange interaction at AFM-FM core–shell interface in NiO resulted in an exchange bias effect. Notably, the NiO nanoparticles with smaller average crystallite size ( 5 nm) and higher cationic Ni2+ vacancies on the surface exhibited strong ferromagnetism and higher coercivity values. In particular, the as-prepared NiO (N) and N-4 samples showed remarkable improvement in exchange bias field, measuring 2.5 kOe and 2.1 kOe, respectively, due to the reinforced spin-exchange interaction within the FM-AFM core–shell structure of NiO.

This paper reports the synthesis and magnetic properties of NiF2 assisted growth of multi-walled carbon nanotubes. Ni-Multi-Walled Carbon Nanotubes (Ni-MWCNT) were synthesized by catalytic decomposition of Xylene (C8H10) and NiF2 (as a precursor for metallic Ni) using Chemical Vapor Deposition (CVD). The presence of graphitic carbon crystallization and a dominant metallic nickel phase is confirmed by XRD and Raman analysis. The in-situ formation of Ni nanoparticles from NiF2 precursor successfully aids the growth of Ni-MWCNTs. The diameter of synthesized Ni-MWCNT was measured to be around 100 nm. Ni-MWCNT exhibit a weak ferromagnetic property due to the presence of metallic Ni residues. Copyright (C) 2022 Elsevier Ltd. All rights reserved.

Glioblastoma multiforme (GBM) is a lethal and the most common type of primary brain tumor. Extensive hypoxic regions in GBMs turn these tumors highly malignant and worsen the prognosis and clinical outcomes of the patients. Tumor cells residing in hypoxic regions exhibit high ROS levels and resistance to chemo- and radiation therapies. This facilitates the cancer stem cell niche to expand and contribute to cell proliferation and further tumor growth. Therapeutic approaches targeting hypoxia-induced factors, such as the anti-VEGF monoclonal antibody, bevacizumab have shown promising results in stabilizing the disease. Glioblastomas are predominantly glycolytic and hypoxia-induced factors are useful in the metabolic reprogramming of these tumors. Hence, developing therapeutic approaches that counter hypoxia may hold the key to improving the prognosis and clinical outcome of GBMs. In this work, we report that cerium oxide nanoparticles (CNPs) hold therapeutic potential for the treatment of GBM. CNPs of size 6 nm (CNP-6) and 12 nm (CNP-12) were used for this study. Our results show that CNP-6 exhibits short-term mitigation of ROS levels (up to 24 h) and are able to modulate the TMZ IC50 in tumor microenvironment-like conditions. CNP-12, on the other hand, mitigated ROS levels for up to 72 h, but the mitigation proved to be too lethal for the cells to survive given the important role played by basal-level ROS inside cells. Also, CNP-6 was better at altering metabolic gene expression profile compared to CNP-12 under tumor microenvironment-like conditions. These results indicate that CNPs of size < 10 nm may hold potential for development as nano-therapeutic modalities for tumor treatment. Graphic Abstract Cerium oxide nanoparticles modulate the metabolic gene expression in GBM derived cell lines

The defect association modifies the energy barrier for oxygen ion hopping between the vacancies, which is sensitive to the dopant ionic size in the CeO2-delta. Here, the work focuses on the co-dopant strategy of M0.1Sm0.1Ce0.8O2-delta (M = Yb, Gd, Sm, Nd, La) to study the defect association energy, and its subsequent effect on ionic conduction and power density. The electrolyte material with different co-dopants modifies the lattice parameter and bond length of cation-anion, which changes the defect-dopant interactions. Among the tested dopant, Nd0.1Sm0.1Ce0.8O2-delta exhibits the highest ionic conductivity of 34 mS cm1 at 550 ?C, which is nearly 2.3 times higher than the conventional Sm0.2Ce0.8O2-delta. This experimental observation validates the theoretically proposed concept of the balanced defect-dopant interactions at different sites leading to the reduction in defect association enthalpy. The experimental results were rationalized by calculating the defect association enthalpy for the co-doped system using density functional theory via one-cell method. The cell with Nd0.1Sm0.1Ce0.8O2-delta as an electrolyte shows a peak power density of 466 mW cm-2 at 550 ?C, which is twice higher than the cell containing standard Sm0.2Ce0.8O2-delta electrolyte (212 mW cm? 2). The results confirm that Nd0.1Sm0.1Ce0.8O2-delta is the potential electrolyte for low temperature SOFC operation. Superscript/Subscript Available

Elemental diffusion in ceramics can modulate the conductivity as well as fuel cell performance. Here, we report the effect of diffusion on NiO coated samarium doped ceria (SDC) with temperature and correlated with conductivity. NiO thin film was deposited using electron beam physical vapor deposition over the pre-sintered SDC substrate and subsequently treated at 800 degrees C, 1000 degrees C, and 1200 degrees C. Depth profiling analysis across NiO-SDC hetero-interface using FESEM-EDAX revealed that the width of the diffusion zone increased with temperature. All the constituent ions like Ni, Sm and Ce diffuse mutually without forming any impurity phases at the NiO-SDC interface. The estimated diffusivity values demonstrated that the nickel predominantly diffuses through the grain boundary of SDC. The constituent cations were found to diffuse several hundred nanometers through grain boundaries at a temperature of 1200 degrees C. An increase in the electrical conductivity was observed in proportion to the width of the diffusion layer. The diffusion of nickel predominantly along the grain boundary reduced the grain boundary resistance by altering the space charge potential at the NiO-SDC interface. Our study demonstrates that the modification of grain boundary through the controlled diffusion of metal ions reduce the resistance for oxygen ion transport in NiO-SDC electrolyte.

The current study focus on the exchange bias properties of Ni/NiO ferromagnetic-antiferromagnetic nanocomposite by fabricating Ni (FM) using a one-step solution combustion method. The prepared Ni nanoparticles were oxidized at 400 degrees C for different time durations (tau = 3, 6, 12, 24, 48, 72, 96, 120, 144 and 168 h) in the ambient atmosphere to grow NiO (AFM). The X-ray diffraction pattern of the Ni/NiO nanocomposite indicate good crystallinity of the samples. Raman spectroscopy exhibited a short-range magnon excitation around 1400 cm(-1) that indicate the contribution of AFM exchange energy between the Ni2+-O-2(-)-Ni2+ chain in the composites. The presence of Ni and NiO phases were confirmed by room temperature magnetization measurement. For the better understanding of the exchange bias of the Ni/NiO nanocomposite subjected to heat treatment for several hours (0-168 h), zero-field cooled and field cooled M-H and M-T measurements were made. The hysteresis loop shift along the field axis and enhanced coercivity values shows the exchange bias effect in the Ni/NiO structure in the controlled oxidation process. The Ni and NiO interfacial effect and phase fraction have significant effect on the observed exchange bias. Moreover, finite size effects contribution on the antiferromagnetic exchange and spin glass features observed at a temperature of 24 K of the Ni/NiO system contribute to the large exchange bias and enhanced coercivity. (C) 2018 Elsevier B.V. All rights reserved.

The antioxidant activity of cerium oxide nanoparticles (CNPs) depends on the concentration of oxygen vacancies and Ce3+ active sites. In the present work, we report the impact of 5 mol % trivalent rare-earth-doped (RE3+ = Eu3+, Nd3+, Pr3+, and La3+) CNPs on the oxidation state modulation and antioxidant property with respect to ionic radii. An increase in the lattice parameter, strain, and oxygen vacancy concentration was observed as a function of ionic radii. Among the various dopants in CNPs, La3+ with higher ionic radii having smaller crystallite size (7.9 nm) and higher vacancy displayed better peroxidase, oxidase, and hydroxyl radical (HO center dot) scavenging activities. The kinetic parameters for the peroxidase and oxidase activities were found to be superior with K-m = 0.217 and 0.261 mM, respectively, for 5 mol % La3+-doped CNPs. To divulge the role of dopant concentration on the structural properties, we also explored using 10 and 20 mol % La3+ doping in CNPs. Because of the smaller crystallite size (6.7 nm) and higher defect level (3.12 X 10(21) cm(-3)), 20% La3+ doping showed superior peroxidase and oxidase activities, as shown by the low K-m values. CNPs exhibit both peroxidase and oxidase activities in a concentration-dependent manner. Moreover, CNPs exhibit concentration-dependent peroxidase and oxidase activities that can be selectively activated for various theranostic applications. Thus, our results demonstrate the crucial role of ionic radii and the concentration of RE3+ dopants on defect formation in CNPs for improved antioxidant properties of ceria.

Cerium oxide nanoparticles exhibit selective cytotoxic and biomimetic antioxidant activity due to the redox transformation between Ce3+ ↔ Ce4+ states under tumor-like conditions.

Improved enzymatic activity and concentration-dependent selective activation of peroxidase and oxidase activity of combustion-synthesized nanoceria.

The structural, electrical and optical property of nickel oxide thin films deposited by electron beam physical vapour deposition were investigated with respect to substrate temperature (Ts = 100, 300, and 450°C). In spite of the amorphous nature of the substrate (quartz), depending on the substrate temperature either a preferred or polycrystalline NiO growth was observed. A (200) preferential orientation resulted at 100°C while at 300 and 450°C the NiO films were oriented along (111) and (220) planes. The NiO films obtained at Ts = 100°C was highly transparent compared to the polycrystalline films due to the low light scattering of (200) film. The conductivity of NiO films measured at 100°C was found to be three orders higher than the films obtained at Ts = 450°C. Thus, the orientation was found to be influencing optical and electrical properties of NiO films.

Rare earth phosphates have been used extensively in luminescent phosphors, bio-imaging, catalysis, and sensors. However, there is a need to correlate the structural-chemical changes associated with stability and performance. In the present work, hydrothermally synthesized CePO4:Smx (x = 0, 5 and 10 mol%) nanorods were annealed at different temperatures to understand the modulations in structure as well as optical and enzyme mimetic properties. As prepared samarium doped cerium phosphate (SCP) nanorods crystallized in a hydrated hexagonal structure transformed into an anhydrous hexagonal and a monoclinic structure on annealing at 400 °C and 800 °C, respectively. Though temperature did not affect the rod-like morphology of the SCP, the lattice strain changed from compressive to tensile. Monoclinic SCP exhibited excellent emission until 5% Sm3+ doping while the quenching effect dominated at 10% Sm3+. Monoclinic SCP samples demonstrated higher peroxidase-like enzymatic activity in comparison to natural enzyme HRP and hexagonal SCP. A mechanism for the enhanced peroxidase-like activity of the monoclinic structure was proposed based on the fluorescence property of terephthalic acid and the surface peroxo complex using Raman spectroscopy. Fluorimetric detection based on the luminescent quenching effect of the monoclinic SCP nanorods treated with different concentrations of hydrogen peroxide showed a linear response from 0 to150 μM concentration with a detection limit (LOD) of 3.17 μM H2O2. Our results demonstrate the importance of structure for enzyme mimetic activity.

In the present work, we focus on the development of CePO4-CeO2 composite nanorods with peroxidase mimetic activity for the sensitive detection of hydrogen peroxide and glucose. The Ce3+/PO43- molar ratio (CP10:1, CP5:1, CP2:1) in the hydrothermal reaction controlled the formation of pure CePO4, CePO4-CeO2 composite nanozymes with different percentages of CeO2, and its crystal structure. A higher Ce3+/PO43- molar ratio (CP10:1 or CP5:1) was required to obtain CePO4-CeO2 composite nanostructure, while a lower Ce3+/PO43- molar (CP2:1) ratio was sufficient to fabricate pure CePO4 nanorods. In the presence of hydrogen peroxide, the prepared nanozymes catalyze the oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB). Steady state kinetic analysis based on the Michaelis-Menten model revealed that CP10:1 showed excellent affinity toward the TMB ( Km = 0.236 mM and Vmax = 8.78 × 10-8 M s-1) in comparison to the catalytic activity of CP5:1 and CP2:1 and horseradish peroxidase ( Km = 0.434 mM and Vmax = 10.0 × 10-8 M s-1). The superior peroxidase activity of CePO4-CeO2 composite nanozymes can be ascribed to the enhanced redox switching between Ce3+ ↔ Ce4+ sites from the CePO4 and CeO2 lattice, respectively. The colorimetric detection of hydrogen peroxide and glucose showed a linear response around 150 μM concentration with the limits of detection (LOD) of 2.9 and 4.1 μM, respectively.

Influential role of fuel to oxidizer ratio (F/O) as the controlling parameter in combustion synthesis of europium doped cerium oxide was studied in terms of defect chemistry, optical property and antioxidant capacity. Europium (5 mol%) doped cerium oxide nanoparticles synthesized by solution combustion in fuel deficient (F/O=0.6, 1.1) and stoichiometric (F/O=1.6) conditions resulted in size ranging from 6 to 25 nm while excess fuel (F/O=2.1) lead to the lower size of 17 nm. Raman spectroscopic analysis showed the formation of intrinsic and europium ion induced extrinsic oxygen vacancies and the defect concentration was found to be decreasing with F/O ratio. Photoluminescence emission was dominated by magnetic dipole transition in F/O=0.6, 1.1 and electrical dipole in F/O=1.6, 2.1 which resulted in a persistent luminescence. Fenton reaction generated hydroxyl radical scavenging activity was influenced by the surface oxygen vacancy concentration and crystallites size. In addition to size and defect, morphology of the nanoparticle plays a significant role in determining the antioxidant efficacy.

Gold-coated cerium oxide nanoparticles enhance the catalytic activity towards nitrophenol degradation.