CeO2 Nanospheres Research Articles

Substrate-Switched Dual-Signal Self-Powered Sensing System Based on Dual-Nanozyme Activity of Bimetal-Doped CeO2 Nanospheres for Electrochemical Assay of Aflatoxin B1.

The long-term operation feature of enzymatic biofuel cell-based self-powered biosensor (EBFC-SPB) endows them with the potential to execute dual-signal biosensing without having to integrate an extra signal acquisition device. Herein, cobalt and manganese codoped CeO2 nanospheres (CoMn-CeO2 NSs) with glucose-oxidase-like and peroxidase-like activities have been developed as substrate-switched dual-channel signal transduction components in EBFC-SPB for a dual-signal assay of aflatoxin B1 (AFB1). The CoMn-CeO2 NSs modified with aptamer are anchored to a complementary DNA-attached bioanode of EBFC-SPB by base complementary pairing, which catalyze the glucose oxidation together with the glucose oxidase (GOx) on the bioanode. Once the AFB1 appears, CoMn-CeO2 NSs will be released from the bioanode due to the binding specificity of the aptamer, resulting in a decreased catalytic efficiency and the first declining stage of EBFC-SPB. Accompanied by the introduction of H2O2, the residual CoMn-CeO2 NSs on the bioanode switch to peroxidase-like activity and mediate the production of benzo-4-chlorohexadienone (4-CD) precipitate, which increases the steric hindrance and yields another declining stage of EBFC-SPB. By assessing the variation amplitudes during these two declining stages, the dual-signal assay of AFB1 has been realized with satisfying results. This work not only breaks ground in dual-signal bioassays but also deepens the application of nanozymes in EBFC-SPB.

Oxygen vacancy-engineered cerium oxide mediated by copper-platinum exhibit enhanced SOD/CAT-mimicking activities to regulate the microenvironment for osteoarthritis therapy

Cerium oxide (CeO2) nanospheres have limited enzymatic activity that hinders further application in catalytic therapy, but they have an “oxidation switch” to enhance their catalytic activity by increasing oxygen vacancies. In this study, according to the defect-engineering strategy, we developed PtCuOX/CeO2-X nanozymes as highly efficient SOD/CAT mimics by introducing bimetallic copper (Cu) and platinum (Pt) into CeO2 nanospheres to enhance the oxygen vacancies, in an attempt to combine near-infrared (NIR) irradiation to regulate microenvironment for osteoarthritis (OA) therapy. As expected, the Cu and Pt increased the Ce3+/Ce4+ ratio of CeO2 to significantly enhance the oxygen vacancies, and simultaneously CeO2 (111) facilitated the uniform dispersion of Cu and Pt. The strong metal-carrier interaction synergy endowed the PtCuOX/CeO2-X nanozymes with highly efficient SOD/CAT-like activity by the decreased formation energy of oxygen vacancy, promoted electron transfer, the increased adsorption energy of intermediates, and the decreased reaction activation energy. Besides, the nanozymes have excellent photothermal conversion efficiency (55.41%). Further, the PtCuOX/CeO2-X antioxidant system effectively scavenged intracellular ROS and RNS, protected mitochondrial function, and inhibited the inflammatory factors, thus reducing chondrocyte apoptosis. In vivo, experiments demonstrated the biosafety of PtCuOX/CeO2-X and its potent effect on OA suppression. In particular, NIR radiation further enhanced the effects. Mechanistically, PtCuOX/CeO2-X nanozymes reduced ras-related C3 botulinum toxin substrate 1 (Rac-1) and p-p65 protein expression, as well as ROS levels to remodel the inflammatory microenvironment by inhibiting the ROS/Rac-1/nuclear factor kappa-B (NF-κB) signaling pathway. This study introduces new clinical concepts and perspectives that can be applied to inflammatory diseases.Graphical

CeO2 nanospheres incorporated with Bi2MoO6/g-C3N4 enhanced photocatalysis towards environmental pollutant Rhodamine B removal.

We have adopted a novel CeO2/Bi2MoO6/g-C3N4-based ternary nanocomposite that was synthesized via hydrothermal technique. The physiochemical characterization of as-prepared samples was examined through various analytical techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy TEM, photoluminescent spectra (PL), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and ultraviolet diffuse reflectance spectroscopy (UV-DRS) technique. In addition, the photocatalytic performance was carried out by degradation of Rhodamine B dye under visible light irradiation using this nanocatalyst. The ternary nanocomposite achieved 94% of the degradation efficiency within 100min which is higher than the pristine and binary composites under the predetermined condition pH = 7, Rhodamine B dye = 5mg/L, and catalyst concentration = 150mg/L. The experimental synergetic effect of CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite has been ascribed to the interfacial charge carrier migration between CeO2, Bi2MoO6, and g-C3N4. The optical absorption range of CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite was enhanced, and the band gap was reduced up to 2.2eV. In addition, scavenger trapping experiment proves that the super oxide anions (O2-.) and photogenerated holes are the major active species. The reusability and stability experiment proved the CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite keeps good durability during the photocatalytic degradation process after the five successive cycles. Furthermore, based on the results, the charge carrier transfer photocatalytic mechanism was also discussed. This CeO2/Bi2MoO6/g-C3N4 ternary nanocomposite may offer the cheapest material and extend the great opportunity for clean and environmental remediation approach under the visible light irradiation.

Manipulating dual effects of morphology and oxygen vacancies through the incorporation of CuO onto CeO2 nanospheres for electrochemical CO2 reduction

Despite significant advancements in the investigation of catalyst morphology in electrochemical CO2 reduction (ECR), achieving precise control over multi-carbon (C2+) products selectivity remains challenging. Thus, a sequence of catalysts with incorporation of CuO onto three-dimensional (3D) spherical CeO2 were synthesized using a hydrothermal and calcination two-step method. The molar ratios of Cu(NO3)2·H2O to Ce(NO3)3·6H2O can manipulate morphology and oxygen vacancies (Ov) of CuxCey catalysts, further influencing their product distribution in ECR. Materials characterization and electrochemical testing demonstrate that dual effects of spherical morphology and Ov in the CuxCey catalysts can enhance the activity and C2H4 selectivity in ECR. To elaborate further on the topic, the pure CeO2 exhibits excellent Faradaic efficiency (FE) of CH4 with the value of 54.3 %. Cu7Ce3, among all CuxCey catalysts, reaches a maximum value of 37.22 % at −1.2 V vs. RHE, possibly attributed to its highest Ov concentration. More significantly, the possible reaction pathway was monitor by ATR-FTIR technique for CuxCey during ECR is: CO2 → *COOH →*CO → *CHO → *OCCOH → C2H4. The concept of dual tuning strategy by morphology and Ov opens up a wide range of possibilities for the development of effective Cu-based catalysts for ECR.

Direct and specific detection of methyl-paraoxon using a highly sensitive fluorescence strategy combined with phosphatase-like nanozyme and molecularly imprinted polymer

Methyl paraoxon (MP) is a highly toxic, efficient and broad-spectrum organophosphorus pesticide, which poses significant risks to ecological environment and human health. Many detection methods for MP are based on the enzyme catalytic or inhibition effect. But natural biological enzymes are relatively expensive and easy to be inactivated with a short service life. As a unique tool of nanotechnology with enzyme-like characteristics, nanozyme has attracted increasing concern. However, a large proportion of nanozymes lack the intrinsic specificity, becoming a main barrier of constraining their use in biochemical analysis. Here, we use a one-pot reverse microemulsion polymerization combine the gold nanoclusters (AuNCs) with molecularly imprinted polymers (MIPs), polydopamine (PDA) and hollow CeO2 nanospheres to synthesize the bright red-orange fluorescence probe (CeO2@PDA@AuNCs-MIPs) with high phosphatase-like activity for selective detection of MP. The hollow structure possesses a specific surface area and porous matrix, which not only increases the exposure of active sites but also enhances the efficiency of mass and electron transport. Consequently, this structure significantly enhances the catalytic activity by reducing transport distances. The introduced MIPs provide the specific recognition sites for MP. And Ce (III) can excite aggregation induced emission of AuNCs and enhance the fluorescent signal. The absolute fluorescence quantum yield (FLQY) of CeO2@PDA@AuNCs-MIPs (1.41 %) was 12.8-fold higher than that of the GSH-AuNCs (0.11 %). With the presence of MP, Ce (IV)/Ce (III) species serve as the active sites to polarize and hydrolyze phosphate bonds to generate p-nitrophenol (p-NP), which can quench the fluorescent signal through the inner-filter effect. The as-prepared CeO2@PDA@AuNCs-MIPs nanozyme-based fluorescence method for MP detection displayed superior analytical performances with wide linearities range of 0.45–125 nM and the detection limit of 0.15 nM. Furthermore, the designed method offers satisfactory practical application ability. The developed method is simple and effective for the in-field detection.

Polyvinyl alcohol-encapsulated cerium oxide nanospheres composite nanofiber membrane for enhanced antioxidant and antibacterial applications☆

Cerium oxide (CeO2) has attracted much attention in recent years owing to its reversible switch ability in Ce3+/Ce4+ redox to produce improved antioxidation properties for biomedical applications. Here, we report to embed the CeO2 nanospheres into the organic polymer network using electrostatic spinning technology to prepare polyvinyl alcohol (PVA)-encapsulated CeO2 nanospheres composite nanofibrous membranes (PVA-CeO2) for the first time, which is beneficial to improving the dispersion and biocompatibility of CeO2 nanosphere without altering the original antioxidant properties of CeO2. Detailed characterization of the as-prepared composite nanofibrous membranes reveals that CeO2 was successfully introduced into the PVA fibers with strong interactions, thus enhancing the thermal stability and fracture toughness of the nanofibers. As a result, PVA-CeO2 exhibits superior UV shielding performance, antioxidant performance and bacteriostatic performance. Meaningfully, PVA-CeO2 has strong absorbance in both UVA and UVB bands when the CeO2 concentration in the nanofiber membrane reaches 1.5 wt%, and shows an excellent scavenging effect on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals with a scavenging rate of 86.52%. Moreover, the Kirby-Bauer (K-B) method of agar diffusion test further confirms that PVA-CeO2 has antimicrobial ability against three types of representative strains, including Gram-positive bacteria (Staphylococcus aureus), Gram-negative bacteria (Escherichia coli) and fungi (Candida albicans). Importantly, no obvious cytotoxicity is observed for PVA-CeO2 even though the amount of embedded CeO2 nanosphere reaches as high as 1.5 wt%. This study reveals new avenues for improving the future smart design of CeO2-based nanofiber membrane composite materials for biological antioxidants.

Boosting catalytic hydrolysis of carbonyl sulfide over K+ modified CeO2 nanospheres at low-temperature

Carbonyl sulfide (COS) as one of typical atmospheric sulfur-containing pollutants widely emitted from various industrial processes, which has a significant impact on human health and environmental safety. Currently, developing highly efficient catalysts to eliminate COS is of great significance for both fundamental catalytic research and actual industrial application. Here we report a series of K+ doping spherical cerium oxide (CeO2-S) that showing promote activity for catalytic hydrolysis of COS. The research results demonstrated that the K+-doped CeO2-S formed more Ce3+ and oxygen vacancies than CeO2-S. The hydrolysis activity and stability of CeO2-S for COS were significantly improved by the introduction of K+. Among them, the 0.2 K/CeO2-S showed the optimal performance. Further in-situ DRIFTS results revealed that a slight increase in alkalinity could enhanced the activation of H2O over 0.2 K/CeO2-S, and the generated surface active hydroxyl groups reacted with adsorbed COS to produce the intermediate species (HSCO2-), leading to the formation of H2S and CO2. The catalysts prepared in this paper exhibited promoted activity with low-temperature and high stability for COS hydrolysis, which is beneficial for practical industrial scale-up applications and provides novel insights into designing efficacious catalysts with efficient low-temperature activity and superior stability for removing COS.

Influence of Particle Size of CeO2 Nanospheres Encapsulated in SBA-15 Mesopores on SO2 Tolerance during NH3-SCR Reaction

Ce-based selective catalytic reductions with an NH3 (NH3-SCR) catalyst have emerged as a focal point in denitrification catalyst research. However, the correlation between the structural characteristics of Ce-based catalysts and the influence of CeO2 nanoparticle size on SO2 resistance remains unclear. CeO2 nanospheres with different sizes of less than 10 nm were synthesized, and a series of supported CeO2/SBA-15 catalysts were prepared according to the 10 nm pore size of SBA-15. These catalysts were used to explore the influence of the size of the CeO2 nanospheres on these catalysts, specifically on their SO2 resistance in NH3-SCR reactions. With the increase in size, their SO2 resistance became stronger. The results of NH3-TPD, H2-TPR, and XPS indicated that the catalyst with the largest particle size had the lowest adsorption of SO2, which was attributed to more acid sites and a mutual effect between Si and Ce, resulting in the best SO2 resistance. It was also observed that there was less sulfate deposition on the catalyst by thermogravimetric analysis. In situ DRIFTs revealed that after SO2 poisoning, the NH3-SCR reaction on the catalyst predominantly follows the E-R mechanism. This study offers recommendations for the development of Ce-based SO2-resistant NH3-SCR catalysts, specifically focusing on the synthesis and interaction of nanomaterials.

Enhanced Interface with Strong Charge Delocalization toward Ultralow Overpotential CO2 Electroreduction

The construction of an interface has been demonstrated as one of the most insightful strategies for designing efficient catalysts toward electrochemical CO2 reduction (CO2RR). However, the weak interfacial interaction and inherent instability inevitably hinder a further performance enhancement in CO2RR attributable to the interface effect. Herein, 2 nm Ag nanoclusters (Ag NCs) are embedded onto CeO2 nanospheres (CeO2 NSs) with highly interconnected porosity (Ag NCs@CeO2 NSs) to exclusively study the pure interface effect toward CO2RR. The enhanced Ag–CeO2 pure interface endows Ag NCs@CeO2 NSs with a remarkably larger current density, significantly higher Faraday efficiency (FE), and energy efficiency as compared to Ag NCs, CeO2 NSs, and the one with Ag NCs dispersed on CeO2 nanoparticles. More importantly, an impressively high CO FE of over 70.0% is achieved at an ultralow overpotential (η) of 146 mV. The free energy and differential charge calculations, coupled with X‐ray photoelectron spectroscopy results jointly imply that the effective initiation of CO2RR to CO at a lower η over Ag NCs@CeO2 NSs derives from the enhanced interface‐induced charge delocalization, which enhances the electron transfer ability toward *COOH intermediate, thus overcoming the energy barrier demanded for the rate‐determining step.

Morphological optimized CeO2 and Cu-doped CeO2 nanocrystals for hydrogen production by solar photo-thermochemical water splitting based on surface photoinduced oxygen vacancies

Photo-thermochemical (PTC) reaction produces hydrogen by water splitting through the consumption of surface photoinduced oxygen vacancies (VOs). In this study, CeO2 and Cu-doped-CeO2 were synthesized with typical different morphologies of nanorods and nanospheres and different crystallite sizes. These factors, i.e. microstructure, crystalline size and Cu doping were proven to influence the physical properties and photoresponse performance of CeO2 which affected the generation of surface photoinduced VOs and their reactions of hydrogen production in PTC. Cu-doped CeO2 nanospheres with smaller crystallite size demonstrated the best catalytic activity with the largest H2 yield of 18.4 μmol g-1h−1. The electron paramagnetic resonance and Ultraviolet–visible diffuse reflection spectroscopy analysis showed that the VOs generation of nanospheres was strengthened compared to nanorods when the physical characteristics were similar. The positive correlation between the change in physical properties and yield supports its importance in VOs consumption in the thermochemical process. The smaller crystallite size of the nanospheres exhibited better porous properties and specific surface area, which facilitated thermochemical reaction. The doping significantly reduces the band gap of the sample, enhances the light absorption capacity and significantly increases the H2 yield of CeO2.

Room-Temperature Triethylamine Sensor Based on Reduced Graphene Oxide/CeO2 Nanocomposites

Triethylamine (TEA) detection has been widely performed by using chemoresistive sensors. Nevertheless, chemoresistive sensors still exhibit limitations to be addressed in terms of power consumption and humidity interference, and developing efficient TEA sensors operated at low temperatures and humid conditions remains a challenge. Here, we present the effect of reduced graphene oxide (RGO) on the TEA-sensing performance of CeO2 nanospheres at room temperature and a relative humidity (RH) range of 34–70%. We show that CeO2 is a suitable sensing material for TEA detection at room temperature and humidity conditions; however, the modification with RGO greatly improves the TEA-sensing performance. The RGO/CeO2 nanocomposite has higher sensitivity and selectivity to TEA than the bare CeO2-based sensor, in addition to the low theoretical detection limit of 1 ppm at 70% RH. Moreover, we elucidate that humidity plays a positive role in the detection of TEA. Our findings elucidate that RGO positively affects the sensing performance of CeO2 nanospheres, which can be attributed to the improvements in the baseline electrical resistance and enhancement of the active sites for TEA adsorption due to the RGO modification. This work provides a promising strategy for developing sensitive TEA sensors with practical applications.

Engineering an Enzymatic Cascade Catalytic Smartphone-Based Sensor for Onsite Visual Ratiometric Fluorescence-Colorimetric Dual-Mode Detection of Methyl Mercaptan.

Precise and reliable onsite detection of methyl mercaptan (CH3SH) is of great significance for environmental surveillance. Here, we synthesized a novel blue fluorescence nanozyme CeO2@TPE with high peroxidase-like activity by employing aggregation-induced emission (AIE) tetraphenylethene (TPE) to embed into hollow CeO2 nanospheres. In the presence of ethanol oxidase (AOX) and o-phenylenediamine (OPD), we engineered an enzymatic cascade activation ratiometric fluorescence-colorimetric dual-mode system AOX/CeO2@TPE + OPD toward CH3SH. In this design, CH3SH initiated AOX catalytic activity to convert it into H2O2 for activating the peroxidase-like activity of CeO2@TPE, producing •OH for oxidizing the naked-eye colorless OPD into deep yellow 2,3-diaminophenazine (DAP) with an absorption enhancement at ∼425 nm, companied by a new emission peak at ∼550 nm to match with the intrinsic emission at ∼441 nm for observing ratiometric fluorescence response, enabling a ratiometric fluorescence-colorimetric dual-mode analysis. Interestingly, both the ratiometric fluorescence and colorimetric signals could be gathered for being converted into the hue parameter on a smartphone-based sensor, achieving the onsite visual fluorescence-colorimetric dual-mode detection of CH3SH in real environmental media with acceptable results. This study gave a novel insight into designing target-responsive enzymatic cascade activation system-based efficient and reliable dual-mode point-of-care sensors for safeguarding environmental health.

Construction of a direct Z-scheme CeO2/UiO-66-NH2 heterojunction for boosting photocatalytic organic pollutant degradation and H2 evolution performance.

In this study, hollow CeO2 nanospheres were grown on UIO-66-NH2 nanosheets to form a novel CeO2/UiO-66-NH2 (abbreviation, CUx) Z-scheme heterojunction photocatalyst by calcination and hydrothermal method for hydrogen production and photocatalytic degradation of organic pollutants. Under visible light, the H2 generation rate of the CU0.50 composite was 5662.1 μmol g-1 h-1, which was 22 and 7 fold than that of pure CeO2 and pure UiO-66-NH2, respectively. In addition, compared with CeO2 and UiO-66-NH2, the as-prepared CUx composites exhibited enhanced photo-degradation efficiencies for tetracycline (TC) and 2,4-dichlorophenol (DCP) under simulated solar light irradiation. Among them, the CU0.50 composite demonstrated the highest photocatalytic performance and reached 91.5% for TC, and 94.3% for DCP. In addition, a logical solid-state Z-type electron transfer mechanism is presented with the results of radical scavenging and ESR experiments to illustrate the intensive decomposed ability of the photocatalytic system. The enhanced photocatalytic performance of CUx heterostructures can be attributed to the formation of a band-position-matched hollow structure heterojunction between CeO2 and UIO-66-NH2, which can effectively inhibit the recombination of carriers and increase the specific surface area as well as the light absorption. Moreover, the oxidation and reduction ability of the charge carriers was also increased. This work resulted in a feasible idea for removing organic pollutants and hydrogen production by traditional inorganic semiconductor/MOF-based heterostructured photocatalysts.

Structural, optical, and photocatalytic properties of La3+ doped CeO2 nanospheres for enhanced photodegradation of tetracycline

This work reports the structural, optical, and photocatalytic properties of Ce1−xLaxO2 nanospheres (x = 0, 0.04, 0.06, 0.08, and 0.10) for the photodegradation of organic pollutants. The Ce1−xLaxO2 samples with particle sizes of ∼ 9–30 nm were prepared by a solution method using polyvinyl pyrrolidone (PVP) as a polymer precursor. The prepared Ce1−xLaxO2 samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results of XRD and TEM with selected area electron diffraction (SEAD) show that the prepared Ce1−xLaxO2 nanospheres have a cubic fluorite structure without secondary phase. The XPS shows the presence of oxygen vacancies on the surfaces of all samples. The Ce0.90La0.10O2 sample shows the highest concentration of oxygen vacancies, causing a decrease in Eg, and thus resulting in an enhancement of its photocatalytic activity. The photocatalytic activities of the CeO2 and Ce1−xLaxO2 photocatalysts were studied by the degradation of TC solution under visible light irradiation. Pure CeO2 shows poor photocatalytic activity with about 43 % of TC degraded in 40 min, while Ce1−xLaxO2 exhibits significantly higher photocatalytic efficiency, which increases with La-doping concentration. It is proposed that photogenerated holes are the main active species for photochemical degradation of the TC via Ce0.90La0.10O2 upon irradiation with visible light, while superoxide radicals and hydroxyl radicals are the less active species. Our results indicate that, with excellent photocatalytic performance, the Ce1−xLaxO2 nanospheres can be further developed for photocatalytic applications.

Nanoceria as an Electron Reservoir: Spontaneous Deposition of Metal Nanoparticles on Oxides and Their Anti-inflammatory Activities.

Designing metal-metal oxide heteronanostructures with synergistic and superior activities (unattainable in the case of a single entity) is of great interest for a wide range of technological applications. Traditional synthetic strategies typically require reducing agents, stabilizing ligands, or high temperature reductive treatment to produce oxide-supported metals. Herein, a facile noble metal deposition strategy is developed to produce silver, gold, and platinum nanocrystals on the surface of hollow mesoporous cerium oxide nanospheres without any pretreatment. Unlike the galvanic replacement reaction, the developed protocol employs the innate reductive potential of CeO2 to produce a high density of ultrafine noble metal nanocrystals homogeneously immobilized onto the surface of CeO2 nanospheres. The multienzyme-like activities (i.e., superoxide dismutase-like and catalase-like) of CeO2@metal nanostructures, originating from CeO2 and metal nanoparticles, were effectively utilized for anti-inflammatory therapies in two in vivo models. This oxygen vacancy-mediated reduction strategy can be generalized to produce diverse metal-metal oxide nanostructures for a wide range of applications.

Enhanced electrocatalytic water splitting by Sm and Gd-doped ceria electrocatalysts on Ni foam substrate

CeO2 is attractive for water splitting due to its various valence oxidation states, however, its catalytic performance in alkaline medium is challenging. In this study, we synthesized novel ceria-based electrocatalysts: Gd-doped CeO2 nanocrystals (GDC) and Sm-doped CeO2 nanospheres (SDC) on Ni foam using sol–gel and one-step hydrothermal methods, respectively. These ceria-based electrocatalysts, GDC and SDC, depict excellent activity in the OER and HER, respectively. The GDC/NF showed promising OER performance, achieving an exceptional overpotentials of 300 and 420 mV to keep current densities of 10 and 100 mA cm−2, respectively. In addition, SDC/NF exhibited excellent HER activity with overpotentials of 117 and 325 mV to reach current densities of 10 and 100 mA cm-2, respectively. Furthermore, both GDC and SDC were ultra-stable at a fixed current density of 50 mA cm−2 for 25 h. Moreover, the complete anion-exchange membrane (GDC/NF||SDC/NF) demonstrated 1.6 Vcell to accomplish 10 mA cm-2 current density, with ultra-durability for 40 h at 50 mA cm-2. The versatile electrochemical performance of ceria-based catalysts is attributed to diverse-valence Ce3+/Ce4+ redox states and positive entropy contribution of the f0–f1 transition. Notably, doping with Gd and Sm led to an easy and strong reduction owing to the oxygen voids created and hydroxyls. Moreover, dopants stabilized ceria and assisted the generation of metal–H groups, which improved the kinetic activity of ceria for electrochemical water splitting.

Regulation of Third‐Order NLO Properties by Central Metal Exchange of Heterogeneous MOFs@CeO2

AbstractChanging the chemical composition and generating heterogeneous structures have a synergistic effect on the third‐order nonlinear optical (NLO) properties of metal–organic frameworks (MOFs) materials. In this work, it is demonstrated that the transformations from a parent‐MOF [Zn4(dcpp)2(DMF)3(H2O)2]n (1, dcpp = 3,4‐bis(4‐carboxyphenyl)phthalate) into two child‐MOFs, [Cu4(dcpp)2(DMF)3(H2O)2]n (2) or [Zn2.5Co1.5(dcpp)2(DMF)3(H2O)2]n (3), via central metal exchange can regulate the third‐order NLO properties of the parent‐MOF, especially its third‐order NLO absorption signal can change from the reverse saturable absorption (RSA) to the saturable absorption (SA) when Cu2+ are introduced. Heterogeneous 1@CeO2 materials are further engineered by depositing CeO2 nanospheres onto the whole surface of 1, and are surprisingly still able to be exchanged into 2@CeO2 or 3@CeO2. Analyses on these MOFs@CeO2 indicate that the interfacial interaction between metal oxide particles and MOFs surface can effectively tune the charge transfer efficiency of the material which leads to their third‐order NLO refraction signals. The interface inducement of CeO2‐shell to the MOF‐core also significantly changes their third‐order NLO properties compared to pure MOFs. This work provides new insights and efficient strategies for the development of new third‐order NLO materials with potential practical usage.

L-asparagine Assisted Synthesis of Pt/CeO2 Nanospheres for Toluene Combustion

Pt1/CeO2 nanospheres (Pt/CeO2-NS) were synthesized by the bath oiling method with L-asparagine as a necessary additive. Owing to the morphology control effect and coordination interaction of L-asparagine, CeO2 nanospheres can retain their nanosphere structure and show stronger electronic metal-support interaction with highly dispersed Pt. Moreover, the toluene catalytic combustion performance of Pt/CeO2-NS was investigated. The structure-performance relationship is analyzed according to the coordination state of Pt. The Pt/CeO2-NS catalyst exhibited superior catalytic activity than the commercial CeO2-supported Pt catalyst, which is attributed to its higher oxygen vacancy and Pt4+.

Development of Cu-doped CeO2 nanospheres mimic nanozyme-based immunoassay for the specific screening of Bacillus cereus.

Due to the highly similar genetic background, it is difficult to distinguish Bacillus cereus (B. cereus) with other members of B. cereus group. Herein, an antibody-based colorimetric immunoassay using Cu-doped CeO2 nanospheres as peroxidase mimics was developed for the detection of B. cereus in food. First, monoclonal antibodies (mAbs) and polyclonal antibody (pAb) with good specificity to B. cereus were prepared and characterized. Second, the regular-shaped hollow Cu/CeO2 nanospheres with highly catalytic activity and biocompatibility were synthesized as mimic nanozymes to capture secondary antibody. Finally, a sandwich colorimetric immunoassay for the specific and sensitive detection of B. cereus was developed, showing linear detection range from 3.2 × 102 to 1 × 105CFU/mL and a limit detection of 1.7 × 102CFU/mL. The developed immunoassay holds great potential as an effective tool for detecting B. cereus in food poisoning.

CO2 Activation over Nanoshaped CeO2 Decorated with Nickel for Low-Temperature Methane Dry Reforming.

Dry reforming of methane (DRM) is a promising way to convert methane and carbon dioxide into H2 and CO (syngas). CeO2 nanorods, nanocubes, and nanospheres were decorated with 1–4 wt % Ni. The materials were structurally characterized using TEM and in situ XANES/EXAFS. The CO2 activation was analyzed by DFT and temperature-programmed techniques combined with MS-DRIFTS. Synthesized CeO2 morphologies expose {111} and {100} terminating facets, varying the strength of the CO2 interaction and redox properties, which influence the CO2 activation. Temperature-programmed CO2 DRIFTS analysis revealed that under hydrogen-lean conditions mono- and bidentate carbonates are hydrogenated to formate intermediates, which decompose to H2O and CO. In excess hydrogen, methane is the preferred reaction product. The CeO2 cubes favor the formation of a polydentate carbonate species, which is an inert spectator during DRM at 500 °C. Polydentate covers a considerable fraction of ceria’s surface, resulting in less-abundant surface sites for CO2 dissociation.