Growth Of CeO2 Research Articles

Cascade enzyme-mimicking with spatially separated gold-ceria for dual-mode detection of superoxide anions

Metal-semiconductor nanozyme of dumbbell Au-CeO2 with spatially separated heterostructure has cascade superoxide dismutase (SOD)-like and peroxidase (POD)-like activities for superoxide anions detection. It was synthesized by selective growth of CeO2 at the ends of Au nanorod (Au NR). Taking advantage of the excellent local surface plasmon resonance (LSPR) effect of Au NR, the spatially separated Au-CeO2 has a higher photothermal effect than the continuously growing core-shell structure of Au@CeO2. Meanwhile, the hot electrons of Au NR could transfer to CeO2 under 808 nm laser irradiation, changing the ratio of Ce3+/Ce4+ redox couples over CeO2 and facilitating H2O2 decomposition thus enhancing POD-like activity. Based on the SOD-like activity of Au-CeO2, superoxide anion (O2·−) can be transformed into hydrogen peroxide (H2O2). Dual-mode including absorbance and temperature sensing detection of O2·−, with the detection range from nM to μM i.e., 0.1–150 μM and LOD of 0.033 μM (S/N = 3) was achieved through the cascade catalysis and photothermal effect. The as-proposed method was applicable to both cancer and normal cell samples with satisfactory accuracy and recovery.

In-situ growth of CeO2 on biofilms: Innovative nanoparticles for photothermal therapy & multi-pronged attack on Alzheimer’s disease

Alzheimer’s disease (AD) is complex and multifactorial, and its pathogenesis involves multiple factors and processes. This study pioneered the in situ growth of cerium oxide nanoparticles on macrophage membranes (Ce-RAW). Further, carbon quantum dots (CQD) were biomimetically modified by Ce-RAW, leading to the synthesis of a multifunctional nanocomposite (CQD-Ce-RAW). Within the framework of this research, CQD-Ce-RAW was strategically combined with photothermal therapy (PTT), aiming to achieve a more significant therapeutic effect. The macrophage membrane confers the system with anti-phagocytic and anti-inflammatory biological functions. More importantly, the ultra-small size of cerium oxide grown on the membrane acts as a reactive oxygen species (ROS) scavenger and alleviates the degree of oxidative stress. Meanwhile, CQD as a photosensitizer helps dissociate amyloid-β (Aβ) aggregates and chelates excess copper ions, thus further inhibiting Aβ aggregation. Cell experiments showed that CQD-Ce-RAW combined with PTT could effectively degrade and inhibit the aggregation of Aβ, remove ROS, and improve cell survival rate. The results of in vivo photothermal experiments demonstrated that near-infrared light enhanced the efficiency of drug penetration through the blood-brain barrier and facilitated its accumulation in brain tissue. This comprehensive therapeutic approach can intervene in the disease progression from multiple pathways, providing a new prospect for treating AD.

Evaluation of laser cladding of Ti6Al4V-ZrO2-CeO2 composite coating on Ti6Al4V alloy substrate

A titanium metal matrix composite (Ti6Al4V-ZrO2-CeO2) cladding is performed on Ti6Al4V alloy by irradiating a pulsed wave fibre laser source. A varying weight percentage of ceria (CeO2) is added to the composite to study its effect on cladding microstructure, hardness, and wear properties. A detailed microstructure and phase identification study is made using FESEM, XRD, XPS, and EBSD. The presence of CeO2 in the composite refines the microstructure of the clad. It promotes the in-situ formation of ceramic compounds such as Ce1-xO2Zrx, Al2O3, Ti6O, and ZrO2 and restricts acicular α‑titanium growth by favouring equiaxed CeO2 growth. Due to grain refinement and the presence of hard ceramic compounds, the microhardness, COF, fracture toughness, and wear resistance is significantly affected with the variation of CeO2 in the cladding. The lowest coefficient of friction (COF) and highest hardness value of 0.21 and 700HV300 were obtained with samples containing 5 wt% of CeO2. Also, the indicative parameters of wear resistance, such as H/E and H3/E2 computed from the nano-indentation test, are highest in the samples containing 5 wt% of CeO2. The novelty lies in graded grain size and in-situ formed hard and rugged cladding without vertical cracks.

Fenton-like degradation of methyl orange over CeO2 loaded on porous Al2O3: Catalyst preparation, efficiency and mechanism

In this work, the CeO2/Al2O3 composites were prepared by in situ growth method and developed as the heterogeneous Fenton-like catalyst for efficiently catalytic degradation of methyl orange (MO). Porous Al2O3 was firstly prepared by an evaporation-sintering method, and then the CeO2/Al2O3 composites were constructed by the in situ growth of CeO2 onto porous Al2O3. The phases and morphologies of the porous Al2O3 and CeO2/Al2O3 composites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and specific surface area and pore size analyzer. The results indicated that the higher amount of the porogenic agent (NH4Cl) could make the specific surface area of porous Al2O3 larger and the Fenton-like reaction efficiency of CeO2/Al2O3 better. Free radical trapping experiments showed that the singlet oxygen (1O2) was the main reactive oxygen species responsible for the MO degradation. Finally, the possible mechanism of the Fenton-like reaction catalyzed by CeO2/Al2O3 was proposed and discussed.

Non-classical crystallization of CeO2 by means of in situ electron microscopy.

During in situ liquid-phase electron microscopy (LP-EM) observations, the application of different irradiation dose rates may considerably alter the chemistry of the studied solution and influence processes, in particular growth pathways. While many processes have been studied using LP-EM in the last decade, the extent of the influence of the electron beam is not always understood and comparisons with corresponding bulk experiments are lacking. Here, we employ the radiolytic oxidation of Ce3+ in aqueous solution as a model reaction for the in situ LP-EM study of the formation of CeO2 particles. We compare our findings to the results from our previous study where a larger volume of Ce3+ precursor solution was subjected to γ-irradiation. We systematically analyze the effects of the applied irradiation dose rates and the induced diffusion of Ce ions on the growth mechanisms and the morphology of ceria particles. Our results show that an eight orders of magnitude higher dose rate applied during homogeneous electron-radiation in LP-EM compared to the dose rate using gamma-radiation does not affect the CeO2 particle growth pathway despite the significant higher Ce3+ to Ce4+ oxidation rate. Moreover, in both cases highly ordered structures (mesocrystals) are formed. This finding is explained by the stepwise formation of ceria particles via an intermediate phase, a signature of non-classical crystallization. Furthermore, when irradiation is applied locally using LP scanning transmission electron microscopy (LP-STEM), the higher conversion rate induces Ce-ion concentration gradients affecting the CeO2 growth. The appearance of branched morphologies is associated with the change to diffusion limited growth.

Strong Ru-CeO2 interaction boosts catalytic activity and stability of Ru supported on CeO2 nanocube for soot oxidation

Cerium oxide based catalysts are active for soot oxidation, while serious catalyst deactivation feasibly occurs due to thermal sintering. In this study, Ru and Ag supported on CeO2 were prepared and their catalytic performances as well as thermal durability for soot oxidation were evaluated. Characterization results show that thermal treatment at 800 °C leads to substantial crystalline growth of CeO2 and Ag particles in Ag/CeO2. In contrast, crystalline growth of CeO2 is remarkably alleviated and high dispersion of Ru particles is effectively maintained on Ru/CeO2 owing to the formation of RuOCe bonds. As a result, catalyst recycling and thermal pretreatment at 800 °C lead to remarkably catalyst deactivation of CeO2 and Ag/CeO2, but slightly declined activity on Ru/CeO2. The combination of experiments and DFT calculations clearly indicates that the strong interactions between Ru and CeO2 account for the high catalytic activity and strong thermal duration of Ru/CeO2 for soot oxidation.

The growth of CeOx(111) thin films on Ru(0001)

Ceria has attracted great attention in recent years in the catalysis community. Metal catalysts supported on ceria exhibit a promising catalytic activity due to the ceria’s unique redox properties and oxygen storage capacity. The purpose of this paper is to look at the fundamental aspect of CeOx(111) thin films on Ru(0001). The investigation presented in this paper utilizes the surface science method to understand the properties of CeOx(111). In one component, through a series of XPS studies, it is shown that the deposition of Ce in the presence of oxygen on Ru(0001) can produce ceria thin films. Fully oxidized CeO2 can be obtained with an oxygen pressure of 2 x 10−7 Torr. With the decrease in the oxygen pressure, partially reduced CeOx films can be prepared. Moreover, STM images are collected from the CeO2 growth in the presence of 2×10−7 Torr of oxygen and partially reduced ceria with oxygen pressures of 8×10−8 Torr. These films can completely cover the Ru(0001) substrate. The measured step height is about 0.3 nm, which is consistent with the 0.313 nm spacing of O-Ce-O tri-layers in the CeO2(111) fluorite bulk structure.

Controlled Fabrication of the Biomass Cellulose–CeO2 Nanocomposite Membrane as Efficient and Recyclable Adsorbents for Fluoride Removal

The biomass cellulose nanocomposite membrane is regarded as one of the most promising adsorbents for resource recovery and pollution control owing to the unique physicochemical properties. Herein, a recyclable biomass cellulose–CeO₂ nanocomposite membrane (BCCM) is fabricated by in situ growth of CeO₂ on the cellulose membrane (CM) surface and then employed for the elimination of fluoride from industrial wastewater. Structural characteristics of the BCCM were characterized by XRD and SEM. The adsorption experiment indicated that the maximum fluoride adsorption capacity of the BCCM was 48.0 mg/g. Kinetic and isotherm results elucidated that multilayer chemisorption dominated the BCCM adsorption process. Besides, the adsorption mechanism was also investigated by the energy-dispersive X-ray, FT-IR, and XPS analysis. More importantly, the BCCM has strong acid–base adaptability and can be used in extreme environments. This work provides an effective and environmentally friendly strategy to prepare other biomass nanocomposite membranes, which shows great potential for environmental remediation and chemical separation.

Highly Enhanced Visible‐light Photocatalytic Activity via a Novel Surface Structure of CeO2/g−C3N4 toward Removal of 2,4‐dichlorophenol and Cr(VI)

AbstractPhotocatalysis is an efficient and eco‐friendly method of solving the environmental problems, but the low charge separation efficiency of photocatalysts limits their application. Herein, we report the fabrication of CeO2/g−C3N4 composites via an in‐situ growth of CeO2 on the dispersed g−C3N4 sheets (CN−OH) in an strong KOH condition, and the resultant CeO2/CN−OH composites set up a new interface structure, which demonstrate a dramatically boosted the photocatalytic activity compared with CeO2/g−C3N4 composites by conventional two‐step combination method. The decomposition efficiency of CeO2/CN−OH for 2,4‐dichlorophenol (2,4‐DCP) degradation comes up to 6 times of bare CeO2 or g−C3N4. Compared to conventional CeO2/g−C3N4, the CeO2/CN−OH showed 65.9 % and 23.2 % improvement for 2,4‐DCP and Cr(VI) removal, respectively. The significantly enhanced photodegradation ascribe to the alkaline modified CN−OH and the fabrication of CeO2/CN−OH n–n type heterojunction, both can improve the charge separation efficiency and increase the reaction active sites. Furthermore, the probable pathway and concreted photocatalytic mechanism for 2,4‐DCP degradation are proposed based on the detected intermediate products.

In-situ ion irradiation induced grain growth in nanocrystalline ceria

Irradiation grain growth of CeO2 was studied using in-situ ion irradiation with transmission electron microscopy (TEM). Thin films of ceria were produced by electron beam physical vapor deposition (EB-PVD) and then irradiated at the Intermediate Voltage Electron Microscope (IVEM) with 1 MeV Kr2+ ions at temperatures of 400°C, 600°C, and 800°C. During irradiation at the elevated temperatures, the CeO2 phase remained stable and its grains grew with irradiation. Grain growth was only weakly dependent on irradiation temperature between 400°C and 800°C. The grain growth kinetics were evaluated by a thermal spike model that was used to calculate the activation energy for grain growth.

Are CEOs Overpaid? A Brief Look at CEO Incentive Pay and Compensation in the US

According to statistics, CEO-to-worker compensation ratio for large publicly traded firms in the U.S. has surged almost fifteen times since the 1960’s. There is also a significant difference between CEO compensation and that of the average earner in the top 0.1 percent category (of around 5.5-to-1). However, the growth in CEO pay does not necessarily reflect correspondingly higher output or better firm performance, nor can the difference between CEO pay and that of the top 0.1 percent earners be explained by greater productivity or more talent. Some argue that, this growth is a form of rent-seeking behavior by CEOs who use their power to extract concessions and set their own pay by virtue of their positions and their control over the board of directors. But, why is this rent-seeking behavior permitted by stakeholders, especially the shareholders? Does this suggest weaknesses in the corporate governance structure which fails to discipline growth of CEO pay, or is the legal framework too weak or ineffective to really matter? Assuming that such high levels of inequality in pay are undesirable from a corporate governance and societal perspective, how can this issue be best tackled?

Sales Growth, CEO Pay, and Corporate Governance in India

Although stock return-based performance metrics are common in CEO compensation contracts in the United States, similar CEO pay arrangements may not be appropriate in India given higher stock return volatility and lower liquidity. Instead, sales growth as a performance metric could be useful in incentivizing Indian CEOs to pursue earnings growth consistent with shareholder value maximization. In this study, we examine the use of sales growth as a performance metric in extant Indian CEO pay arrangements and whether the usage is consistent with efficiency. Our findings suggest that the weight placed on sales growth in determining CEO compensation in India is positive and is higher for more powerful CEOs. We also find that board vigilance is effective in moderating the weight placed on sales growth in CEO pay arrangements. Finally, we show that the weight placed on sales growth in assessing CEO pay negatively impacts future firm performance, particularly for firms that are in the later stages of the firm life cycle, are less profitable, and have weaker shareholder monitoring. Collectively, our findings are consistent with inefficiency (efficiency) in CEO pay contracting in the use of sales growth as a performance metric in later (early) stage firms, less (more) profitable firms, and weaker (stronger) shareholder monitoring firms. More broadly, our findings albeit India-specific are of potential interest to CEO pay arrangement debates in the United States and elsewhere where sales growth is an important performance metric in determining CEO compensation.

Role of SiO2 in synthesis of SiO2-supported CeO2 composites

Pure and SiO2-supported CeO2 samples were prepared by Ce(NO3)3 decomposition, precipitation, and sol–gel methods in an attempt to study the role of SiO2 in the synthesis of these materials. During synthesis process, SiO2 support uniformly adsorbed cerium ions in aqueous solution, preventing nucleation and crystal growth of CeO2 during the subsequent water evaporation and calcination steps. Uniform adsorption and inhibition were enhanced by NH4+ and, to a larger extent, C5H7O5COO-. Despite the dispersion of cerium ions on SiO2 reduced the temperature at which CeO2 was formed, crystal size and crystallinity of CeO2 in composites were significantly lower than that of pure CeO2 sample prepared by the same synthesis method and at the same temperature. Composites were quite stable upon increasing the temperature from 400 to 800 °C. Visible light absorption, reduction, and photocatalytic activity characteristics of CeO2 were improved upon dispersion on SiO2. This work can help synthetize supported oxides with high activity and thermal stability.

CeO2 nanoparticles growth by chemical bath and its thermal annealing treatment in air atmosphere

A novel synthesis of CeO2 powder by using chemical bath (CB) as green method is presented. The process was completed by thermal annealing (TA) at 1000°C during 2 h. CeO2 growth was confirmed by: X-ray diffraction (XRD), UV–vis spectra, Energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Raman spectra. By FTIR, bands associated with CO32−and OH− ions were identified, disappearing with the TA process. The X-ray diffraction (XRD) patterns of the as grown and CeO2 TA samples showed the reflection characteristic of CeO2 structure with a cubic symmetric pattern. By XRD diffractograms the grain size calculated were ∼2.7nm and ∼28.5nm for as-grown and CeO2 TA samples, respectively. The grain size of ∼2.7nm is the smallest among the reported values for CeO2. Absorbance of as-grown spectra showed three bands located at ∼382, ∼357 and ∼271nm while the CeO2 TA sample displayed only two bands at ∼271 and ∼320nm. Direct optical energy gap were Eg=4.4 eV and Eg=4.3 eV for as-grown and CeO2 TA samples, respectively, showing quantum size effect of CeO2 nanoparticles. Raman spectra indicated that the as-grown and CeO2 samples have the fluorite structure.

Influence of graphene oxide on photocatalytic enhancement of cerium dioxide

Graphene oxide (GO) was prepared by oxidizing purified natural flake graphite via modified Hummers method. The suspension of GO particles and cerium-based precursors were treated hydrothermally in order to prepare CeO2/GO composites. The disappearance of the [001] GO diffraction peak was observable in the XRD pattern for CeO2/GO composites because the crystal growth of CeO2 between the interlayer of GO destroyed the regular layer stacking of GO phase. However XPS spectra of O 1s core level and oxygen vacancies defect in CeO2 caused the decrease in degree of crystallinity. Composite of CeO2 with GO not only prevented the formation of extrinsic vacancies in the oxygen sub-lattice, but also prevented the switching from the major photoactive species Ce4+ to Ce3+.The photocatalytic activity measurements demonstrated that the CeO2/GO composites exhibited much higher photocatalytic activity than CeO2 for degradation of methylene blue (MB) under visible light irradiation. The enhancement of photocatalytic activity could be attributed to the excellently elevated absorption ability for the MB dye through π–π conjugation. As reported in PL results, the effective inhibition of the recombination of photogenerated electron–hole pairs due to the charge interaction between CeO2 and GO.

High performance super-hydrophobic ZrO2-SiO2 porous ceramics coating with flower-like CeO2 micro/nano-structure

The super-hydrophobic (SH) porous ceramics material with good stability was successfully prepared via the hydrothermal growth of CeO2 micro/nano-structure and the subsequent dip-coating of low surface energy substance 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) over the surfaces of ZrO2-SiO2 porous ceramics substrate. The surface morphology, chemical composition and wettability of material were investigated by means of SEM, EDS, XRD, FT-IR, and contact angle measurement. It was found that a layer of CeO2 nano-flowers had been attached over the surfaces of ZrO2-SiO2 porous ceramics substrate, using the optimized concentration of CeNO3 precursor, and after the grafting of PFDTES, the super hydrophobicity of the obtained material was achieved, with the water contact angle being as high as 162° and sliding angle being approximately 0°. Particularly, the super hydrophobicity was found to occur also in the pores of the obtained material. The obtained material was found to possess the significantly large thermal and chemical stabilities.

The preparation of continuous CeO2/CuO/Al2O3 ultrafine fibers by electro-blowing spinning (EBS) and its photocatalytic activity

CeO2/CuO/Al2O3 catalyst has attracted considerable attention due to its higher activity and better selectivity at lower reaction temperature in comparison with commercial catalysts, and it has exhibited potential applications in water gas shift reaction and exhaust gas treatment. In this paper, the continuous CeO2/CuO/Al2O3 ultrafine fibers were prepared by electro-blown spinning method followed by a calcination process. The as-spun fibers were formed with solvent evaporation under the drawing of air flow and electrostatic force. The diameters of fibers could be regulated by changing the parameters, such as PVP content, gas pressure, voltage and injection rate, etc. These fibers could be subsequently converted into CeO2/CuO/Al2O3 ultrafine fibers via calcination in air at 400 °C. The presence of Al2O3 made the more flexibility of CeO2/CuO/Al2O3 fibers and well inhibited the crystal growth of CeO2 and CuO during the calcination process. Most importantly, CuO could be highly dispersed into CeO2, which provide a higher content of surface oxygen vacancies and should empirically benefit the catalytic process. Therefore, CeO2/CuO/Al2O3 composite fibers exhibited the excellent catalytic efficiency in dye degradation, and the utilization efficiency of solar light was effectively enhanced by the loading CuO into the materials. In addition, the mass production of CeO2/CuO/Al2O3 ultrafine fiber catalysts might be realized by this novel method.

Remuneration committees, shareholder dissent on CEO pay and the CEO pay–performance link

AbstractWe provide evidence on whether the adoption of the full Australian Securities Exchange recommendations for remuneration committee formation and structure are associated with a lower shareholder dissenting vote or a stronger CEO pay–performance link. We find some evidence that a minority‐ and majority‐independent remuneration committee and a committee size of at least the recommended three members are associated with lower shareholder dissent. Companies with an independent committee have a stronger CEO pay–performance link. In addition, a majority‐independent committee strengthens the link between performance and growth in CEO pay.

Ultrasmooth Ru(0001) Films as Templates for Ceria Nanoarchitectures

Single crystalline magnetron sputter-deposited Ru(0001) epitaxial thin films on c-plane sapphire were prepared and used as a template for reactive CeO2 growth. Low-energy electron microscopy and diffraction, as well as transmission electron microscopy and atomic force microscopy, experiments were performed to investigate the crystallinity and morphology of the prepared films. Multiple cycles of Ar+ sputtering and high-temperature annealing produces films of exceptional surface quality. High-temperature reactive ceria growth leads to perfectly aligned triangular single-crystalline CeO2(111) islands of extraordinary morphological and structural homogeneity. At the chosen growth conditions, ceria nucleation takes place only at V-shaped surface defects on the otherwise atomically flat Ru terraces, opening up the possibility to influence the nucleation by introducing artificial surface defects using standard etching techniques. Due to their high crystallinity and extraordinary surface quality, these substrates...

Perfect Separation of Hybrid Orientation Structure of CeO2(100) and (110) Regions Grown on SOI Substrates with Lithographically Formed Trenches

Using magnetron sputtering with low energy electron beam irradiation, epitaxial growth of CeO2 layers on Si(100) substrates has been studied for the application to microelectronics. We have found that orientation selective epitaxial (OSE) growth of CeO2(100) and (110) layers on Si(100) is capable by controlling surface potential distribution. With the aim of application to hybrid orientation technology for higher speed CMOS devices, we are studying the hybrid orientation structure of the CeO2(100) and (110) regions on Si(100) substrates using electron beam-induced OSE growth by reactive magnetron sputtering. Two separate areas of growth are seen, with CeO2(100) layers found to grow in areas irradiated by electrons during the growth process, and the CeO2(110) layers growing in the areas without irradiation. The lateral orientation mapping by X-ray diffraction measurements reveal the existence of transition regions between these two orientation areas. The width of the transition region is found to be considerably large and decrease proportionally as the logarithm of the underlying Si substrate resistivity. To make a breakthrough in the limitation in reduction of the transition region width, we propose a new method of OSE growth on silicon on insulator (SOI) substrates with lithographically formed trenches. The trenches prevent spread of the potential distribution to the neighboring Si islands. We report the experimental results showing perfect isolation between OSE grown regions having different crystallographic orientations, optimizing the Si layer thickness of SOI and the cross-sectional geometry of the trenches. Figure 1