Coexistence Of Ce Research Articles

Bimetallic metal organic frameworks-based nanozyme for colorimetry/fluorescence dual-mode uremic toxin detection

Chronic kidney disease (CKD) can greatly increase the mortality risk for clinical patients, with a major challenge being the accurate detection of uremic toxins. Metal organic frameworks (MOFs)-based colorimetry/fluorescence dual-mode probe have shown great potential for bio-detection. However, one of the challenges for MOFs-based nanoprobe is to effectively improve the activity of mimetic enzymes for colorimetric assays while maintaining their outstanding luminescence response for fluorescence sensing. Here, we developed a novel bimetallic Zr/Ce-MOFs, which possesses high catalytic activity and excellent luminescence properties for dual-mode sensing of uremic toxins. The co-existence of Ce and Zr in the MOFs improves the catalytic activity for colorimetric detection of phosphate ions (one type of uremic toxins) and the strong coordinate covalent interaction between phosphate ions and Zr/Ce leads to a significant fluorescence enhancement of the MOFs. Furthermore, we achieved high sensitivity phosphate ions analysis in serum samples. This strategy provides an easy and reliable platform for the detection of uremic toxins in complicated physiological environment.

Synergistic effect of Cerium and Niobium enhances the low-temperature NH3-SCR activity of Fe-containing solid waste

To develop environment-friendly low temperature NH3-SCR catalyst and realize the resource utilization of industrial solid waste, this research prepared a series NH3-SCR catalysts by using Fe-containing solid waste loading CeO2 and Nb2O5. It was found that the Ce2Nb1/Fe-Si catalyst exhibited the highest NH3-SCR activity, reaching about 93 % NOx conversion and 99 % N2 selectivity at 300 °C due to the synergistic effect between Ce and Nb species. The characterization results showed that the interaction between Ce and Nb was stronger than that between Nb and Fe species, promoting the NH3 adsorption and redox cycle of Ce4+ + Nb4+ ↔ Ce3+ + Nb5+, Ce3+ + Fe3+ ↔ Fe2+ + Ce4+, which increased the contents of Fe2+ and surface adsorbed oxygen. Moreover, the co-existence of Ce and Nb species would increase the NOx adsorption ability and promote the oxidation of NO to NO2, which was beneficial for “Fast SCR” reaction. Finally, the introduction of CeO2 and Nb2O5 did not changed the reaction mechanism, followed by a Langmuir-Hinshelwood mechanism.

Multifunctional cerium doped carbon dots nanoplatform and its applications for wound healing

Oxidative stress, which is induced by the overproduced free radicals around inflammation, is one of the most important factors to delay the wound healing process. Much efforts have been focused on wound repair with an emphasis on exploring novel biomaterials which have prominent antioxidant activity and good biocompatibility. In this work, cerium-doped carbon nanodots (Ce-CNDs) are fabricated by a simple hydrothermal method. The as-prepared Ce-CNDs have monodispersed and ultrasmall sizes ranging from 2 to 4 nm with unique photoluminescence, good photostability and certain antibacterial property. MTT assays reveal that Ce-CNDs exhibit superior biocompatibility, and the nanoscale of Ce-CNDs is very helpful for the penetration of cell membranes for cell imaging. The most remarkable point is that the coexistence of Ce(III)/Ce(IV) in Ce-CNDs endows them with attractive antioxidant property to resist the excessive inflammation and accelerate the wound healing process thereby. In consequence, this finding explores the beneficial effect of Ce-CNDs in wound healing for the first time and develops the potential applications of Ce-CNDs as visualization and treatment integrated nanoplatform in oxidative-related diseases.

A strategy for constructing highly efficient yolk-shell Ce@Mn@TiOx catalyst with dual active sites for low-temperature selective catalytic reduction of NO with NH3

In this work, Ce@MnOx catalysts with core-shell structure were obtained via simple hydrothermal treatment, and the redox capacity can be effectively improved through co-existence of Ce and Mn. Since the strong oxidation capacity of MnOx can lead to the peroxidation of ammonia, the redox capacity can be suppressed with the decrease of manganese content. However, in the case of low manganese content, it is discovered that the surface acidity is very weak and the ammonia adsorption behavior on the catalyst is limited, which is detrimental to the NH3-SCR process. To solve this problem, a series of yolk-shell structured Ce@Mn@TiOx were accordingly constructed, where the TiO2 shell can provide more surface acid sites to promote the adsorption and activation of ammonia. As expected, the Ce@Mn@TiOx exhibits excellent catalytic performance for NH3-SCR at low temperature and possesses a relatively wide working temperature window. More importantly, the TiO2 shell could protect the active sites from water vapor competitive adsorption as well as sulfur attack. Thus, the Ce@Mn@TiOx-10% catalyst exhibited satisfied water vapor resistance in the SCR process, and its sulfur tolerance was also improved to a certain extent. In situ DRIFTs analysis demonstrated that the Ce@Mn@TiOx-10% catalyst mainly follows the L-H reaction mechanism. Consequently, the separation of acid and redox sites has been successfully accomplished by the construction of Ce@Mn@TiOx with yolk-shell structure, where the outer shell (TiO2) mainly enhanced the adsorption capacity of ammonia and protected active centers from attacking by moisture and even sulfur species, while the MnOx interlayer enhanced the interfacial electronic interaction of Ce/Mn and ensured efficient redox cycle during the NH3-SCR process.

The effect of composite configurations of Fe ionic spins on the dielectric properties in Sm-doped CeFeO3 ceramics

The Sm-doping effect on the crystal structure, dielectric and magnetic properties of CeFeO3 ceramics are systemically investigated. A giant dielectric response with high dielectric constant and low dielectric loss at room temperature (RT) is observed in Ce0.5Sm0.5FeO3 compounds. The increase of the dielectric constant is attributed to the increase of the ratio of Fe2+/Fe3+ ionic contents due to the charge transfer between Ce3+ and Fe3+ ions induced by Sm doping. Besides, the starting temperature T1 of spin-reorientation transition from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz) increases with Sm doping, and even reaches to a higher one than RT. Meanwhile, composite spin configurations of Fe3+ ions containing Γ1 and/or Γ2 (Fx, Cy, Gz) are found at RT in 0.2≤x ≤ 0.5 samples (x is Sm doping level), besides Γ4 state, whose formation originates from the strengthening of the anisotropic exchange interactions between Fe3+ and Ce3+/Sm3+ spins and the coexistence of Ce- and Sm-rich regions caused by Sm doping. It is suggested that the combining and competing functions of the Fe2+-Fe3+ ferromagnetic double-exchange interaction related to the Fe2+ ionic content and the composite spin configurations of Fe3+ ions containing Γ1 and/or Γ2 dominate the dielectric loss of Ce1-xSmxFeO3 ceramics. The results provide a different view for the physical theory and adjustment of the dielectric properties for applications.

Sampling oxygenated Archean hydrosphere: Implications from fractionations of Th/U and Ce/Ce* in hydrothermally altered volcanic sequences

Hydrothermally altered Archean igneous suites erupted in the submarine environment record variable excursions of Ce/Ce* and Th/U from primary magmatic values of 1 and ~4 respectively. Rhyolites of the 2.96Ga bimodal basalt–rhyolite sequence of the Murchison Domain, Yilgarn Craton, Western Australia, hosting the Golden Grove VMS deposit, are enriched in MnO up to ten fold over primary values. Th/U ratios span 2.6–4.7, Ce/Ce*=2.5–16, and Eu/Eu*=1.3–3. The 2.8Ga Lady Alma ultramafic–mafic subvolcanic complex of the same domain features highly dispersed MREE and LREE due to intense hydrothermal alteration. Th/U ratios span 0.005–0.16 from preferential addition of U, with Ce/Ce*=0.6–2.2, and Eu/Eu*=1–1.4. The eastern Dharwar Craton, India, includes greenstone terranes dominantly 2.7–2.6Ga. Adakites of the Gadwal terrane preserve near primary magmatic Th/U, Ce/Ce*, and Eu/Eu*. In contrast, igneous lithologies of the Hutti greenstone terrane are characterized by total ranges of Th/U=2–5.8, Ce/Ce*=1.01–1.28, and Eu/Eu*=0.82–1.26, and counterparts of the Sandur terrane have Th/U=0.4–6.0, Ce/Ce*=0.9–1.25, and Eu/Eu*=0.8–1.8. Coexistence of Ce and Eu anomalies may reflect a two-stage process: low-temperature hydrothermal alteration at high water–rock ratios by oxidizing fluids, with evolution of the hydrothermal systems to high temperature, low water–rock ratios, under reducing conditions. Uranium is dominantly added to these lithologies over Th in common with Recent altered ocean crust. Iron-rich shales in the Sandur terrane record U-enrichment where Th/U=2–4. Three shales record true negative Ce anomalies and Eu/Eu*=0.8–2.4: true negative Ce anomalies, present in some other Archean iron formations, are interpreted as a signature of precipitates from the ocean water column whereas Eu anomalies are hydrothermal in origin. Volcanic flows of the 2.7Ga Blake River Group, Abitibi greenstone terrane, Canada, preserve Th/U=1.5–8.5, the conjunction of low Th/U values with Ce/Ce*=1.4 in two samples, and Eu/Eu*=0.15–1.3. Mobility of U and Ce in these hydrothermally altered Archean lithologies is in common with their mobility in Phanerozoic counterparts by oxygenated fluids.

Characterization of ceria–yttria stabilized zirconia plasma-sprayed coatings

Ceria–yttria stabilized zirconia (CYSZ) coatings were prepared by air plasma-sprayed on the nickel alloy. The as-sprayed CYSZ coatings and heat-treated CYSZ coatings were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The XPS data indicated the coexistence of Ce 3+, Ce 4+, Y 3+ and Zr 4+ ions near the surface of the as-sprayed CYSZ coatings and the disappearance of Ce 3+ ions in the CYSZ coatings after thermal treatment at 1000 °C for 15 h. From the XRD patterns, the solid solution of CeO 2–Y 2O 3–ZrO 2 formed in the CYSZ coatings because of the lack of any features from Y 2O 3 and ZrO 2 single phases. After thermal treatment, the main phases of all the samples were consistent with the characteristic peaks of cubic ZrO 2.

Role of redox couples of Rh 0/Rh δ+ and Ce 4+/Ce 3+ in CH 4/CO 2 reforming over Rh–CeO 2/Al 2O 3 catalyst

The interaction between Rh and CeO 2 over the Rh–CeO 2/Al 2O 3 catalyst was investigated for the reaction of methane reforming with CO 2. It was shown that the activity and coke resistance of Rh/Al 2O 3 were enhanced by the addition of CeO 2, which greatly depend on the interaction between rhodium and ceria under the reaction atmosphere. In situ electrical conductivity results showed that the reducing agents (CH 4, H 2) in the reaction system could be activated and dissociated on Rh 0, releasing electrons to CeO 2 in close contact with Rh 0 and generating the Ce 4+/Ce 3+ redox couple. Meanwhile, it was found from XPS measurements that the electron transfer could also happen from Rh 0 to CeO 2, creating the Rh 0/Rh δ+ couple. Thus, the very coexistence of Ce 4+/Ce 3+ and Rh 0/Rh δ+ redox couples facilitated the activation of CH 4 and CO 2 and further enhanced the catalytic activity and coke resistance of Rh/Al 2O 3. For CH 4 activation, the electron-deficient state of Rh δ+ had higher ability to accept σ electrons of CH 4 to promote CH 4 adsorption and C–H bond cleavage, while CO 2 activation was mainly facilitated by accepting free electrons of Ce 3+ species, which resulted in the enhancement of carbon elimination to yield CO. Finally, a cycle mechanism of redox couples over Rh–CeO 2/Al 2O 3 in CH 4/CO 2 reforming was proposed.

Preparation and adsorption mechanism of rare earth-doped adsorbent for arsenic(V) removal from groundwater

Several types of rare earth metal-doped iron oxide adsorbents were prepared and their arsenic(As(V)) removal performance was evaluated. The cerium(Ce(IV))-doped adsorbent (CFA4) has the highest adsorption capacity. The crystalline properties (XRD), surface charge, FTIR and X-ray photoelectron spectroscopy (XPS) were determined for CFA. Based on the results of XRD, introduction of Ce(IV) ions into Fe(II)/Fe(III) systems results in the co-existence of Ce and Fe with the formation of minicrystals. The pHzpc (the pH value at which surface charge is zero) of CFA is 5.8 by the measurement of the acid-base titration method. By FTIR measurements, it is shown that the substitution of M-OH groups at CFA surface by As(V) ions plays an important role in the adsorption mechanisms of CFA. XPS spectra of CFA before and after adsorption of As demonstrate that Fe atom might be activated for As removal as a result of rare earth metal (Ce) doping.

Thermal decomposition of cerium(III) acetate studied with sample-controlled thermogravimetric–mass spectrometry (SCTG—MS)

Abstract Thermal decomposition of cerium(III) acetate hydrate, Ce(CH 3 CO 2 ) 3 ·1.5H 2 O, to cerium(IV) oxide, CeO 2 , in helium has been successfully investigated by sample-controlled thermogravimetry combined with evolved gas analysis by mass-spectrometry (SCTG–MS). Cerium(III) anhydrous acetate decomposed to cerium (IV) oxide through four decomposition steps in the temperature range of 250–800 °C. SCTG–MS was very useful to distinguish the successive decomposition accompanying the formation of the intermediate products to identify simultaneous gas evolution during the mass losses. The decomposition intermediates quenched from SCTG were characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES). The XANES revealed clearly the coexistence of Ce(III) and Ce(IV) and the valence change from cerium(III) to cerium(IV). The three decomposition intermediate products were presumed to be Ce 2 O(CH 3 CO 2 ) 4 , Ce 2 O 2 (CH 3 CO 2 ) 2 and Ce 2 O 2 CO 3 . A detailed thermal decomposition mechanism of Ce(CH 3 CO 2 ) 3 ·1.5H 2 O is discussed.

Reaction of Nitrogen Oxides with Potassium-doped Carbons Modified with Ce and Mn under Simulated Exhaust Gases.

Reduction of NO was examined over the potassium-doped active carbon modified with Ce and Mn (K, Ce, Mn/C) in the presence and/or absence of O2. NO is reduced at temperatures above 473K even in the absence of O2, while the reduction of NO is enhanced at 473K in the presence of O2. Twenty-five percent of NO was steadily reduced at 473K in the reaction of NO with K, Ce, Mn/C under simulated exhaust gas containing oxygen (2%). The NO conversions on both K, Ce/C and K, Mn/C were less than 10% under the same condition. Therefore, co-existence of Ce and Mn acts attractively for the steady reduction of NO to N2 with carbon.

Selective catalytic reduction of nitric oxide by methane over cerium and silver ion-exchanged ZSM-5 zeolites

A new catalyst comprising cerium and silver ion-exchanged ZSM-5 zeolite is reported in this paper, for the reduction of nitric oxide by methane in the presence of excess oxygen. The bi-cation exchanged Ce—Ag-ZSM-5 catalyst was very active for this reaction, while either Ce-ZSM-5 or Ag-ZSM-5 alone showed low activity. The presence of oxygen in the feed gas mixture enhanced the activity of the catalyst and the NO conversion to N 2 increased with the CH 4/NO ratio and Ag loading of the zeolite. The presence of water vapor had a small adverse effect on the catalyst activity. The coexistence of Ce and Ag ions in the zeolite is crucial for achieving high NO conversion to N 2. A small amount of cerium is adequate to promote the selective catalytic reduction of NO. The two main functions of Ce ions are (i) to provide the Ag ion sites with NO 2 by catalyzing the oxidation of NO to NO 2 and (ii) to suppress the direct CH 4 oxidation to CO 2. The Ag sites are the active centers where the reaction of NO 2 with CH 4 takes place.