Revealing the Dynamic Structure of Complex Solid Catalysts Using Modulated Excitation X‐ray Diffraction

X‐ray diffraction (XRD) is typically silent towards information on low loadings of precious metals on solid catalysts because of their finely dispersed nature. When combined with a concentration modulation approach, time‐resolved high‐energy XRD is able to provide the detailed redox dynamics of palladium nanoparticles with a diameter of 2 nm in 2 wt % Pd/CZ (CZ=ceria–zirconia), which is a difficult sample for extended X‐ray absorption fine structure (EXAFS) measurements because of the cerium component. The temporal evolution of the Pd(111) and Ce(111) reflections together with surface information from synchronous diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements reveals that Ce maintains Pd oxidized in the CO pulse, whereas reduction is detected at the beginning of the O₂ pulse. Oxygen is likely transferred from Pd to Ce³⁺ before the onset of Pd re‐oxidation. In this context, adsorbed carbonates appear to be the rate‐limiting species for re‐oxidation.     

Growth and Electronic Properties of Ag Nanoparticles on Reduced CeO2-x(111) Films

Ag nanoparticles grown on reduced CeO_2-x thin films have been studied by X-ray photoelec-tron spectroscopy and resonant photoelectron spectroscopy of the valence band to understand the effect of oxygen vacancies in the CeO_2-x thin films on the growth and interfacial elec-tronic properties of Ag. Ag grows as three-dimensional particles on the CeO_2-x(111) surface at 300 K. Compared to the fully oxidized ceria substrate surface, Ag favors the growth of smaller particles with a larger particle density on the reduced ceria substrate surface, which can be attributed to the nucleation of Ag on oxygen vacancies. The binding energy of Ag3d increases when the Ag particle size decreases, which is mainly attributed to the final-state screening. The interfacial interaction between Ag and CeO_2-x(111) is weak. The resonant enhancement of the 4f level of Ce³⁺ species in RPES indicates a partial Ce⁴⁺→Ce³⁺ re-duction after Ag deposited on reduced ceria surface. The sintering temperature of Ag on CeO_1.85(111) surface during annealing is a little higher than that of Ag on CeO₂(111) surface, indicating that Ag nanoparticles are more stable on the reduced ceria surface.     

Study on the oxygen exchange capacities of Ce<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> pyrochlore

Ce₂Sn₂O₇ pyrochlore was synthesized by a hydrothermal method. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the composition and valence state of the sample. The oxygen exchange property of the Ce₂Sn₂O₇ phase was measured by an oxidation reaction in sealed air atmosphere and a followed reduction reaction in 5% H₂-95% N₂ atmosphere. Gas chromatography (GC) was used to analyze the oxygen change in the reaction. The results show that Ce₂Sn₂O₇ sample has excellent oxygen absorption capacity at 250°C as Ce³⁺ ions are oxidized to Ce⁴⁺ ions. The oxidized sample can be reduced by 5% H₂-95% N₂. The refreshed sample remains the capacity of oxygen absorption, while the oxygen exchange capacity degrades with the reduction times.     

On the sol–gel synthesis and catalytic activity of Ce1−xAxO2−δ (A = Pr, Sm, Gd) SOFCs anode materials for reforming of methane

A sol–gel route to synthesize nanocrystalline praseodymium-, samarium- and gadolinium-doped ceria powders for solid oxides fuel Cells SOFCs is presented. The method involves metal nitrates with propionic acid (both as chelating ligand and solvent), gel formation, liquid nitrogen quenching, drying at 150 °C/24 h, and finally decomposition at 450 °C in nitrogen followed by calcination at 650 °C in air. TG–DTA, BET, XRD, FTIR, UV–vis and catalytic tests were used to characterize the samples. Ce_0.8Pr_0.2O_2?δ sample exhibited the best catalytic performance in methane steam reforming under water deficient conditions, closely followed by Ce_0.9Gd_0.1O_2?δ, Ce_0.8Sm_0.2O_2?δ and Ce_0.8Gd_0.2O_2?δ catalysts. The superior catalytic performance of Ce_0.8Pr_0.2O_2?δ sample was attributed to the existence of praseodymium species (Pr⁴⁺/Pr³⁺) strongly interacting with ceria. The two systems act synergistically in the catalytic steam reforming of methane.     

The Vital Role of Buffer Anions in the Antioxidant Activity of CeO2 Nanoparticles

Cerium oxide (CeO₂) nanoparticles display excellent antioxidant properties by scavenging free radicals. However, some studies have indicated that they can cause an adverse response by generating reactive oxygen species (ROS). Hence, it is important to clarify the factors that affect the oxidant/antioxidant activities of CeO₂ nanoparticles. In this work, we report the effects of different buffer anions on the antioxidant activity of CeO₂ nanoparticles. Considering the main anions present in the body, Tris‐HCl, sulfate, and phosphate buffer solutions have been used to evaluate the antioxidant activity of CeO₂ nanoparticles by studying their DNA protective effect. The results show that CeO₂ nanoparticles can protect DNA from damage in Tris‐HCl and sulfate systems, but not in phosphate buffer solution (PBS) systems. The mechanism of action has been explored: cerium phosphate is formed on the surface of the nanoparticles, which interferes with the redox cycling between Ce³⁺ and Ce⁴⁺. As a result, the antioxidant activity of CeO₂ nanoparticles is greatly affected by the external environment, especially the anions. These results may provide guidance for the further practical application of CeO₂ nanoparticles.     

A New Class of Blue‐LED‐Excitable NIR‐II Luminescent Nanoprobes Based on Lanthanide‐Doped CaS Nanoparticles

Lanthanide (Ln³⁺)‐doped luminescent nanoparticles (NPs) with emission in the second near‐infrared (NIR‐II) biological window have shown great promise but their applications are currently limited by the low absorption efficiency of Ln³⁺ owing to the parity‐forbidden 4f→4f electronic transition. Herein, we developed a strategy for the controlled synthesis of a new class of NIR‐II luminescent nanoprobes based on Ce³⁺/Er³⁺ and Ce³⁺/Nd³⁺ co‐doped CaS NPs, which can be effectively excited by using a low‐cost blue light‐emitting diode chip. Through sensitization by the allowed 4f→5d transition of Ce³⁺, intense NIR‐II luminescence from Er³⁺ and Nd³⁺ with quantum yields of 9.3 % and 7.7 % was achieved, respectively. By coating them with a layer of amphiphilic phospholipids, these NPs exhibit excellent stability in water and can be exploited as sensitive NIR‐II luminescent nanoprobes for the accurate detection of an important disease biomarker, xanthine, with a detection limit of 32.0 nm .     

CO2 Reduction by Hydrogen Pre-Reduced Acceptor-Doped Ceria

The reactivity of H₂ pre-reduced acceptor-doped ceria materials Gd_0.10Ce_0.90O_2-δ (GDC10) and Sm_0.15Ce_0.85O_2-δ (SDC15) was tested with respect to the reduction of CO₂ to CO in the context of the reverse water-gas shift reaction. It was demonstrated that not only oxygen vacancies, but also dissolved hydrogen is a reactive species for the reduction of CO₂. Dissolved hydrogen must be considered upon discussion of the mechanism of the reverse water-gas shift reaction on ceria-derived materials apart from oxygen vacancies and formates. The reduction of CO₂ is preceded by the formation of carbonate species of different thermal stability and reactivity. The stability of these carbonates was directly demonstrated by in situ infrared spectroscopy and revealed the largely reversible nature of CO₂ ad- and desorption. In comparison to pre-reduced samples, decreased carbonate coverage is obtained after oxidative treatments of GDC10 and SDC15. No significant effect of the sample treatment (O₂ oxidation or H₂ reduction) on the surface carbonate stability was noticed. Mono-dentate carbonates and carboxylates appear to be more easily formed on pre-reduced (i. e. defective) samples. Ce⁴⁺ reduction to Ce³⁺ (by H₂) and re-oxidation to Ce⁴⁺ (by CO₂) on GDC10/SDC15 were directly monitored by infrared spectroscopic analysis of a distinct, IR-active electronic transition of Ce³⁺. These results show the complex interplay of oxygen vacancy/dissolved hydrogen reactivity and surface chemical aspects in acceptor-doped ceria materials.     

A Detailed Insight into the Effects of Morphologies of Cerium Oxide on Fenton-like Reactions for Different Applications

As an exceptional Fenton-like reagent, cerium oxide (CeO₂) finds applications in biomedical science and organic pollutants treatment. The Fenton-like reaction catalyzed by CeO₂ typically encompasses two distinct processes: one resembling the classical Fenton reaction, wherein cerium (Ce³⁺) triggers the decomposition of hydrogen peroxide (H₂O₂) to yield reactive oxygen species (ROS), and the other involves the complexation of H₂O₂ on the Ce³⁺ surface, leading to the formation of peroxides. However, the influence of diverse CeO₂ morphologies on these two reaction pathways has not been comprehensively explored. In this study, CeO₂ exhibiting three typical morphologies, rods, cubes, and spheres, were prepared. The generation of ROS and peroxides was evaluated using the 3,3,5,5-tetramethylbenzidine (TMB) oxidation reaction and the reduction current of H₂O₂, respectively. Moreover, the impacts of pH variations and CeO₂/H₂O₂ concentrations on the production and conversion of these two reaction products were investigated. To corroborate the distinctions between the resultant products and their applicability, apoptosis assays and acid orange 7 (AO7) degradation analyses were performed. Notably, CeO₂ rods exhibited the highest proportion of Ce³⁺, predominantly engaging in complexation with H₂O₂ to foster peroxide formation, thereby facilitating the robust degradation of AO7. However, the generated peroxides appeared to occupy Ce³⁺ sites, thereby impeding the H₂O₂ decomposition process. Conversely, Ce³⁺ species on the surface of CeO₂ cubes were primarily involved in H₂O₂ decomposition, leading to heightened ROS production, and thus showcasing substantial potential for damaging A549 tumor cells. It is worth noting that the ability of these Ce³⁺ species to form peroxides through complexation with H₂O₂ was comparatively reduced. In summation, this study sheds light on the intricate interplay between distinct CeO₂ morphologies and their divergent impacts on Fenton-like reactions. These findings expand our comprehension of the influences on its reactivity of CeO₂ morphologies and open new insights for applications in diverse domains, from organic dye degradation to tumor therapy.     

Ce4+替代Pu4+的模拟固化体(Gd1-xCex)2Zr2O7+x的合成及结构演变

Gd₂Zr₂O₇中Gd具有很大的中子吸收截面, 其烧绿石结构-缺陷萤石结构的转变能较低, 使其成为理想的核废料固化基材. 使用硝酸盐为原料, 添加少量NaF作助熔剂, 在较低温度下(和传统高温固相反应相比), 合成了烧绿石型Gd₂Zr₂O₇. 以Ce⁴⁺模拟Pu⁴⁺, 研究了Gd₂Zr₂O₇对锕系核素的固化, 并合成了系列模拟固化体(Gd_1-xCe_x)₂Zr₂O_7+x (0≤x≤0.6). 采用粉末X射线衍射(XRD)对系列样品进行了表征. 结果表明: 随着x值的增大,样品从烧绿石结构向缺陷萤石结构转变, 且晶胞大小基本保持恒定, 但当x=0.6时, 衍射峰明显宽化, 晶格畸变比较严重, 晶格稳定性降低. 当x=1时, 即用Ce⁴⁺完全取代Gd³⁺进行合成, 不能得到Ce₂Zr₂O₈, 产物发生了相分离, 为四方结构的(Zr_0.88Ce_0.12)O₂和萤石结构的(Ce_0.75Zr_0.25)O₂的混合物. 模拟固化体的浸出率测试表明: 当x≤0.2时, 各元素浸出率均很低, 但当x≥0.4时, 各元素的浸出率明显升高, 说明以Gd₂Zr₂O₇作为固化Pu⁴⁺的基材, Pu⁴⁺掺入量不宜高于40%.     

Synthesis and crystal structure of two new cerium rhodium oxides: Ce2/3−xRh2O4 (x∼0.12) with Ce mixed valency and CeRh2O5

The new compounds Ce_2/3−xRh₂O₄ (x∼0.11-0.14) and CeRh₂O₅ have been prepared. Their structures were determined from single crystal X-ray diffraction data. Electrical and magnetic properties were also evaluated. Based on the structural analysis and physical properties, oxidation states for CeRh₂O₅ can be assigned as Ce⁴⁺Rh³⁺₂O₅. A small variation in x was detected for Ce_2/3−xRh₂O₄ indicating a formula ranging from Ce^3.64+_0.55Rh³⁺₂O₄ to Ce^3.81+_0.525Rh³⁺₂O₄.     

Apoptosis induced by NaYF<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles in liver cells via mitochondria damage dependent pathway

As lanthanide-doped sodium yttrium flouride (NaYF₄) nanoparticles have great potential in biomedical applications, their biosafety is important and has attracted significant attention. In the present work, three different sized NaYF₄:Eu³⁺ nanoparticles have been prepared. Liver BRL 3A cell was used as a cell model to evaluate their biological effects. Cell viability and apoptosis assays were used to confirm the cytotoxicity induced by NaYF₄:Eu³⁺ NPs. Apart from the elevated malondialdehyde (MDA), the decrease of superoxide dismutase (SOD), glutathione peroxidase (GSH-PX) and catalase (CAT) activity indicated reactive oxygen species (ROS) generation, which were associated with oxidative damage. The decrease of mitochondrial membrane potential (MMP) value demonstrated the occurrence of mitochondria damage. Then, release of cytochrome c from mitochondria and activation of caspase-3 confirmed that NaYF₄:Eu³⁺ NPs induced apoptosis was mitochondria damage-dependent.     

Magnetism and Afterglow United: Synthesis of Novel Double Core–Shell Eu2+-Doped Bifunctional Nanoparticles

Afterglow–magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core–shell strategy is presented, uniting co-precipitation with combustion synthesis routes to combine an Fe₃O₄ magnetic core (≈15 nm) with an afterglow SrAl₂O₄:Eu²⁺,Dy³⁺ outer coat (≈10 nm), and applying a SiO₂ protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe₃O₄@SiO₂@SrAl₂O₄:Eu²⁺,Dy³⁺ NPs emit green light attributed to the 4f⁶5d¹→4f⁷(⁸S_7/2) transition of Eu²⁺ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules.     

Study of magnetic ferrite nanoparticles labeled with <Superscript>99m</Superscript>Tc-pertechnetate

This study examined the applications of novel non-polymer magnetic ferrite nanoparticles (Fe₃O₄ NPs) labeled with ^99mTc-pertechnetate (^99mTcO₄ ⁻). The radiochemistry, chemistry, and biodistribution of Fe₃O₄ NPs labeled with ^9mTcO₄ ⁻ were analyzed. This paper employed instant thin layer chromatography and magnetic adsorption to evaluate the labeling efficiency and stability of ^99mTc-Fe₃O₄ at various reaction conditions. A scanning electron microscope, X-ray diffractometer, Fourier transform infrared spectrometer, laser particle size analyzer, and superconducting quantum interference device magnetometer were used to analyze the physical and chemical properties of the Fe₃O₄ and ⁹⁹Tc-Fe₃O₄ nanoparticles. The biodistribution and excretion of ^99mTc-Fe₃O₄ were also investigated. Radiochemical analyses showed that the labeling efficiency was over 92% after 1 min in the presence of a reducing agent. Hydroxyl and amine groups covered the surface of the Fe₃O₄ particles. Therefore, ⁹⁹Tc (VII) reduced to lower oxidation states and might bind to Fe₃O₄ NPs. The sizes of the ⁹⁹Tc-Fe₃O₄ NPs were about 600 nm without ultrasound vibrations, and the particle sizes were reduced to 250 nm under ultrasound vibration conditions. Nonetheless, Fe₃O₄ NPs and ⁹⁹Tc-Fe₃O₄ NPs exhibited superparamagnetic properties, and the saturation magnetization values were about 55 and 47 emu/g, respectively. The biodistribution showed that a portion of the ^99mTc-Fe₃O₄ nanoparticles might embolize in a pulmonary capillary initially; the embolism radioactivity was cleared from the lungs and was then taken up by the liver. ^99mTc-Fe₃O₄ metabolized very slowly only 1–2% of the injected dose (ID) was excreted in urine and about 2.37% ID/g was retained in the liver 4 h after injection. Radiopharmaceutically, ^99mTc-Fe₃O₄ NPs displayed long-term retention, and only ^99mTc-Fe₃O₄ NPs that dissociated to free pertechnetate could be excreted in urine. This research evaluated the feasibility of non-polymer magnetic ferrite NPs labeled with technetium as potential radiopharmaceuticals in nuclear medicine.     

Master sintering curve for Gd-doped CeO<Subscript>2</Subscript> solid electrolytes

The sintering behavior of gadolinia-doped ceria powders was studied by the master sintering curve (MSC). Dilatometric analyses of powders produced by a soft chemical method were performed to provide the experimental data set for the construction of the MSC. The assumed model provided good fittings of the MSC and the activation energy for the sintering of Ce_1−x Gd _x O_3−δ, with x = 0, 0.05, 0.1, and 0.2 were found to be in the 218–325 KJ/mol range, depending on the dopant content. The results supported that both the nanometric size of the particles and the difference in ionic radii between Gd³⁺ and Ce⁴⁺ affects the sintering of Gd-doped CeO₂.     

Structural and catalytic properties of lanthanide (La, Eu, Gd) doped ceria

Ce_0.9M_0.1O_2−δ mixed oxides (M=La, Eu and Gd) were synthesized by coprecipitation. Independent of the dopant cation, the obtained solids maintain the F-type crystalline structure, characteristic of CeO₂ (fluorite structure) without phase segregation. The ceria lattice expands depending on the ionic radii of the dopant cation, as indicated by X-ray diffraction studies. This effect also agrees with the observed shift of the F_2g Raman vibrational mode. The presence of the dopant cations in the ceria lattice increases the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce⁴⁺/Ce³⁺. All synthesized materials show higher catalytic activity for the CO oxidation reaction than that of bare CeO₂, being Eu-doped solid the one with the best catalytic performances despite of its lower surface area.     

Preparation and radioluminescent characteristics of Li<Subscript>2</Subscript>O-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-CaF<Subscript>2</Subscript> glasses doped with Ce(III) and Gd(III)

A method has been developed for the preparation of homogeneous moisture-resistant glasses with the composition Li₂O-B₂O₃-P₂O₅-CaF₂ : Ce³⁺-Gd³⁺. Energy transfer from Gd³⁺ to Ce³⁺ was noted in a study of the radioluminescence spectra of these samples using ²⁴¹Am as the excitation source (60 keV). The decay time of the Ce³⁺ radioluminescence in the glasses obtained was 20-25 ns.     

Simultaneous Fenton‐like Ion Delivery and Glutathione Depletion by MnO2‐Based Nanoagent to Enhance Chemodynamic Therapy

Chemodynamic therapy (CDT) utilizes iron‐initiated Fenton chemistry to destroy tumor cells by converting endogenous H₂O₂ into the highly toxic hydroxyl radical (^.OH). There is a paucity of Fenton‐like metal‐based CDT agents. Intracellular glutathione (GSH) with ^.OH scavenging ability greatly reduces CDT efficacy. A self‐reinforcing CDT nanoagent based on MnO₂ is reported that has both Fenton‐like Mn²⁺ delivery and GSH depletion properties. In the presence of HCO₃^?, which is abundant in the physiological medium, Mn²⁺ exerts Fenton‐like activity to generate ^.OH from H₂O₂. Upon uptake of MnO₂‐coated mesoporous silica nanoparticles (MS@MnO₂ NPs) by cancer cells, the MnO₂ shell undergoes a redox reaction with GSH to form glutathione disulfide and Mn²⁺, resulting in GSH depletion‐enhanced CDT. This, together with the GSH‐activated MRI contrast effect and dissociation of MnO₂, allows MS@MnO₂ NPs to achieve MRI‐monitored chemo–chemodynamic combination therapy.     

Magnetically recyclable nano copper/chitosan in O‐arylation of phenols with aryl halides

Interaction of chitosan (CS) with Fe₃O₄, followed by embedding Cu nanoparticles (NPs) on the magnetic surface through adsorption of Cu²⁺, and its reduction to Cu^o via NaBH₄, offers a reusable efficient catalyst (Fe₃O₄/CS‐Cu NPs) that is employed in cross‐coupling reactions of aryl halides with phenols, which affords the corresponding diaryl ethers, with good to excellent yields. The catalyst is completely recoverable from the reaction mixture by using an external magnet. It can be reused four times, without significant loss in its catalytic activity.     

Synthesis and photoluminescence properties of tunable emission phosphors Ca4Si2O7F2:Ce3+

The Ce³⁺ activated phosphors Ca₄Si₂O₇F₂:Ce³⁺ are prepared by a solid state reaction technique. The UV–vis luminescence properties as well as fluorescence decay time spectra are investigated and discussed. The results revealed that there were two kinds of Ce³⁺ luminescence behavior with 408 and 470 nm emissions, respectively. Under 355 nm excitation, the Ce(1) emission (408 nm) is dominant at low doping concentration, and then the Ce(2) emission (470 nm) get more important with increasing of Ce³⁺ concentrations in the host. The phosphors Ca₄Si₂O₇F₂:xCe³⁺ show tunable emissions from blue area to green-blue area under near-ultraviolet light excitation, indicating a potential application in near-UV based w-LEDs.     

Oxidation of Reduced Ceria by Incorporation of Hydrogen

The interaction of hydrogen with reduced ceria (CeO_2?x) powders and CeO_2?x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce³⁺ species to hydrogen, which results in the formation of Ce⁴⁺, and thus in oxidation of ceria.