Highly efficient and selective heterogeneous catalytic reduction of 2-nitroaniline by cerium oxide nanocatalyst under microwave irradiation.

Efficient nanocatalyst with incredible performance is highly demanding in a heterogeneous catalysis system. Herein, we report the facile fabrication of uniform and highly stable Cerium Oxide nanoparticles (CeO2 NPs), through chemical precipitation method using sodium hydroxide as reducing agent. The synthesized material is characterized through highly sophisticated techniques including UV-Visible, FT-IR, SEM, AFM, XRD, and Zeta Sizer- Potential to check the particle formation, surface morphology, topography, crystalline nature, size, and surface potential. The heterogeneous catalytic performance of CeO2 NPs has been accomplished for the reduction of 2-nitroaniline from the aqueous media. The CeO2 nanocatalyst displayed excellent reusability, while the reduction in several repetitive catalytic cycles against 2-nitroaniline under optimized conditions. The CeO2 nanocatalyst shows 99.12% efficiency within 60s reaction time under a greener source of microwave radiation.

Novel Ag/cellulose-doped CeO2 quantum dots for efficient dye degradation and bactericidal activity with molecular docking study.

In the present study, the novel Ag/cellulose nanocrystal (CNC)-doped CeO2 quantum dots (QDs) with highly efficient catalytic performance were synthesized using one pot co-precipitation technique, which were then applied in the degradation of methylene blue and ciprofloxacin (MBCF) in wastewater. Catalytic activity against MBCF dye was significantly reduced (99.3%) for (4%) Ag dopant concentration in acidic medium. For Ag/CNC-doped CeO2 vast inhibition domain of G-ve was significantly confirmed as (5.25-11.70 mm) and (7.15-13.60 mm), while medium- to high-concentration of CNC levels were calculated for G + ve (0.95 nm, 1.65 mm), respectively. Overall, (4%) Ag/CNC-doped CeO2 revealed significant antimicrobial activity against G-ve relative to G + ve at both concentrations, respectively. Furthermore, in silico molecular docking studies were performed against selected enzyme targets dihydrofolate reductase (DHFR), dihydropteroate synthase (DHPS), and DNA gyrase belonging to folate and nucleic acid biosynthetic pathway, respectively to rationalize possible mechanism behind bactericidal potential of CNC-CeO2 and Ag/CNC-CeO2.

Novel CoFe2O4@ZnO-CeO2 ternary nanocomposite: Sonochemical green synthesis using Crataegus microphylla extract, characterization and their application in catalytic and antibacterial activities.

In this study, CoFe2O4@ZnO-CeO2 magnetic nanocomposite (CoFe@Zn-Ce MNC) was successfully prepared by facile sonochemical method for the first time. CoFe@Zn-Ce MNC was obtained by green and cost-effective process in the presence of Crataegus microphylla (C. microphylla) fruit extract. Influence of some parameters like capping agents (C. microphylla, SDS and CTAB), sonication time (10, 30 and 60 min) and sonication power (40, 60 and 80 W) were studied to achieve optimum condition. The as-obtained products were characterized by FT-IR, FESEM, TEM, DRS, VSM, EDS, TGA and XRD analysis. Results showed that high magnetic properties (20.38 emug-1), 70-80 nm size and spherical morphology were unique characteristics of synthesized nanocomposite. Antibacterial activity of CoFe@Zn-Ce MNC was examined against E. coli, P. aeruginoss and S. aureus bacteria. Among theme, S. aureus as gram-positive bacteria showed excellent antibacterial activity. Furthermore, photocatalytic performance of the CoFe@Zn-Ce MNC was investigated by degradation of humic acid (HA) molecules under visible and UV light irradiations. The influence of morphology of products and incorporation of cerium oxide with CoFe2O4@ZnO on photocatalytic activity of CoFe2O4@ZnO was performed. After 100 min illumination, the decomposition of HA pollutant by magnetic nanocomposite were 97.2% and 72.4% under exposure of UV and visible light irradiations, respectively. Also, CoFe@Zn-Ce MNC demonstrated high stability in the cycling decomposition experiment after six times cycling runs.

Survey of cytotoxic and UV protection effects of biosynthesized cerium oxide nanoparticles.

Cerium oxide nanoparticles (CeO2 NPs) are among the important nanoparticles that are extensively utilized in cosmetics, automotive industries, ultraviolet (UV) filtration, gas sensors, and pharmaceutical products. In this study, CeO2 NPs were synthesized using an aqueous extract of Ziziphus jujube fruit. The synthesized nanoparticles were characterized using UV-visible spectroscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive spectroscopy, field energy scanning electron microscopy, and Raman methods. The results indicated that the size of synthesized nanoparticles is between 18 and 25 nm, and they have a spherical shape. UV absorbance of the synthesized nanoparticles was measured through spectrophotometric method in the range of 290 to 320 nm. The cytotoxic activity of synthesized CeO2 NPs against colon (HT-29) cancer cell line was surveyed through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The results showed that synthesized nanoparticles are nontoxic on HT-29 cells under 400 µg/mL concentrations after 24 hours of treatment time periods. The increase in treatment time cases increases cytotoxic activity of synthesized nanoparticles. Sun protection factor of CeO2 NPs, as a criterion for amount of sunlight radiation protection, was determined by applying Mansur equation. The results demonstrated that synthesized CeO2 NPs have excellent UV protection and sunscreen physical absorption properties.

Enhanced visible-light photocatalytic degradation of tetracycline by a novel hollow BiOCl@CeO2 heterostructured microspheres: Structural characterization and reaction mechanism.

A high-efficiency hollow BiOCl@CeO2 heterostructured microspheres with type-II staggered-gap type was successfully synthesized by precipitation-hydrothermal process loaded with BiOCl nanoparticles on CeO2 microspheres. XRD, FT-IR, EDS, SEM, HRTEM and XPS results show that the prepared materials have good crystallization, morphology and retain hollow spherical structure of CeO2. Batch experiments indicate that the photocatalytic performance of BiOCl@CeO2 towards Tetracycline (TC) is superior to pure BiOCl or CeO2 owing to the distinctive hollow structures and the formed heterostructure between BiOCl and CeO2. Cyclic experiment exhibits that the optimal BiOCl@CeO2 photocatalyst can still photodegrade more than 80% of TC in 120 min after 4 cycles. Additionally, the reactive oxidation species (ROS) trapping experiments reveal that the critical ROS include photogenerated holes (h+) and superoxide radical anions (O2-). Finally, the possible degradation pathways of TC and enhanced photodegradation mechanism was systematically discussed. On this basis, the hollow BiOCl@CeO2 heterostructured microspheres provide a new alternative with great potential in efficient visible-light-driven photodegradation of persistent organic pollutants.

Sonophotocatalytic treatment of rhodamine B using visible-light-driven CeO2/Ag2CrO4 composite in a batch mode based on ribbon-like CeO2 nanofibers via electrospinning.

CeO2/Ag2CrO4 composite photocatalyst was successfully fabricated using electrospinning and calcination and chemical precipitation method based on CeO2 ribbon-like fibers and characterized by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS) and Fourier-transform infrared spectroscopy (FT-IR). The as-obtained CeO2/Ag2CrO4 composite used photocatalytic performance in the sonophotodegradation of rhodamine B in aqueous solution under visible-light (LED) irradiation. DRS analysis illustrates that CeO2/Ag2CrO4 composite exhibited enhanced absorption in the visible region-attributed CeO2 nanofibers. The effect of four effective parameters including initial concentration of rhodamine B (RhB), photocatalyst dosage, pH, and irradiation time was studied and optimized using central composite design. The kinetic studies confirmed ability of pseudo first-order reaction based on the Langmuir-Hinshelwood model for fitting empirical data, while its rate constant (kobs), L-H rate constants (kr), and L-H adsorption constants (KA) were 0.0449 min-1, 11.66 mg L-1 min-1 and 1.09E-3 mg L-1, respectively. The enhanced photocatalytic activity could be ascribed to the ultrasound field and formation of a heterojunction system among CeO2 and Ag2CrO4, which lead to a better mass transfer and higher efficiency of charge electron-hole separation, respectively.

Organic Fluorophore Coated Polycrystalline Ceramic LSO:Ce Scintillators for X-ray Bioimaging.

The current effort demonstrates that lutetium oxyorthosilicate doped with 1-10% cerium (Lu2SiO5:Ce, LSO:Ce) radioluminescent particles can be coated with a single dye or multiple dyes and generate an effective energy transfer between the core and dye(s) when excited via X-rays. LSO:Ce particles were surface modified with an alkyne modified naphthalimide (6-piperidin-1-yl-2-prop-2-yn-1-yl-1 H-benzo[ de]isoquinoline-1,3-(2 H)-dione, AlNap) and alkyne modified rhodamine B ( N-(6-diethylamino)-9-{2-[(prop-2-yn-1-yloxy)carbonyl]phenyl}-3 H-xanthen-3-ylidene)- N-ethylethanaminium, AlRhod) derivatives to tune the X-ray excited optical luminescence from blue to green to red using Förster Resonance Energy Transfer (FRET). As X-rays penetrate tissue much more effectively than UV/visible light, the fluorophore modified phosphors may have applications as bioimaging agents. To that end, the phosphors were incubated with rat cortical neurons and imaged after 24 h. The LSO:Ce surface modified with AlNap was able to be successfully imaged in vitro with a low-output X-ray tube. To use the LSO:Ce fluorophore modified particles as imaging agents, they must not induce cytotoxicity. Neither LSO:Ce nor LSO:Ce modified with AlNap showed any cytotoxicity toward normal human dermal fibroblast cells or mouse cortical neurons, respectively.

A versatile CeO2/Co3O4 coated mesh for food wastewater treatment: Simultaneous oil removal and UV catalysis of food additives.

Food waste water is one of the most urgent environmental problems for the close connection between food and our daily life. Herein, we use a simple hydrothermal method to prepare a highly efficient catalyst-CeO2/Co3O4 compound on the stainless steel mesh, aiming for food waste water treatment. Possessing the superhydrophilic property and catalytic ability under ultraviolet light, CeO2/Co3O4 coated mesh has successfully processed three representative contaminants in food wastewater, which are soybean oil (food oil), AR (food dye) and VA (food flavor) simultaneously with an one-step filtration. Besides, the mesh is stable in a wide pH range and performs well in reusability. Therefore, such a multifunctional material with simple preparation method, high processing efficiency and facile operation shows a promising prospect for practical production and application for food wastewater treatment.

Size controlled ultrafine CeO2 nanoparticles produced by the microwave assisted route and their antimicrobial activity.

Cerium oxide (CeO2) nanoparticles (NPs) have a wide range of biological and biomedical applications. This work describes a new methodology for producing ultrafine, highly uniform NPs with controlled sizes using the chemical microwave assisted route. The size of CeO2-NPs decreased from 10 to 5 nm by increasing the molar ratio of cerium nitrate Ce(NO3)3.(6H2O) to that of hexamethylenetetramine (C6H12N) from 1:20 to 20:20. Detailed information about their structural characterization was obtained from the XRD, UV-visible, photoluminescence, Raman spectroscopy, SEM, TEM and AFM. These CeO2-NPs were tested as antimicrobial agent against Gram-negative (Escherichia.coli), Gram-positive (Bacillus.subtilis) bacteria and yeast (Saccharomyces cerevisiae). The obtained results showed significant inhibition of these strain even at low concentration of CeO2-NPs. The CeO2-NPs with the molar ratio 5:20 had the most effective inhibition against E.coli (~70%) at a concentration of 20 µL. The CeO2-NPs with the ratio 12:20 were found to be the most effective against B.subtilis (inhibition ~68%). On the other hand, CeO2-NPs synthesized with the 20:20 molar ratio caused the highest inhibition for S. cerevisiae (~60%). It is observed that at higher NPs concentration (i.e., >20 µL) the inhibition of these strains decreased. The antimicrobial activity may be attributed to the penetrating power of CeO2-NPs size beside the generated oxygen species radicals that caused inhibition of bacterial growth.

Microwave synthesis of pure and doped cerium (IV) oxide (CeO2) nanoparticles for methylene blue degradation.

Cerium (IV) oxide (CeO2), samarium (Sm) and gadolinium (Gd) doped CeO2 nanoparticles were prepared using microwave technique. The effect of microwave irradiation time, microwave power and pH of the starting solution on the structure and crystallite size were investigated. The prepared nanoparticles were characterized using X-ray diffraction, FT-Raman spectroscopy, and transmission electron microscope. The photocatalytic activity of the as-prepared CeO2, Sm and Gd doped CeO2 toward degradation of methylene blue (MB) dye was investigated under UV light irradiation. The effect of pH, the amount of catalyst and the dye concentration on the degradation extent were studied. The photocatalytic activity of CeO2 was kinetically enhanced by trivalent cation (Gd and Sm) doping. The results revealed that Gd doped CeO2 nanoparticles exhibit the best catalytic degradation activity on MB under UV irradiation. For clarifying the environmental safety of the by products produced from the degradation process, the pathways of MB degradation were followed using liquid chromatography/mass spectroscopy (LC/MS). The total organic carbon content measurements confirmed the results obtained by LC/MS. Compared to the same nanoparticles prepared by another method, it was found that Gd doped CeO2 prepared by hydrothermal process was able to mineralize MB dye completely under UV light irradiation.

Measurement of intrinsic rise times for various L(Y)SO and LuAG scintillators with a general study of prompt photons to achieve 10 ps in TOF-PET.

The coincidence time resolution (CTR) of scintillator based detectors commonly used in positron emission tomography is well known to be dependent on the scintillation decay time (τd) and the number of photons detected (n'), i.e. CTR proportional variant √τd/n'. However, it is still an open question to what extent the scintillation rise time (τr) and other fast or prompt photons, e.g. Cherenkov photons, at the beginning of the scintillation process influence the CTR. This paper presents measurements of the scintillation emission rate for different LSO type crystals, i.e. LSO:Ce, LYSO:Ce, LSO:Ce codoped Ca and LGSO:Ce. For the various LSO-type samples measured we find an average value of 70 ps for the scintillation rise time, although some crystals like LSO:Ce codoped Ca seem to have a much faster rise time in the order of 20 ps. Additional measurements for LuAG:Ce and LuAG:Pr show a rise time of 535 ps and 251 ps, respectively. For these crystals, prompt photons (Cherenkov) can be observed at the beginning of the scintillation event. Furthermore a significantly lower rise time value is observed when codoping with calcium. To quantitatively investigate the influence of the rise time to the time resolution we measured the CTR with the same L(Y)SO samples and compared the values to Monte Carlo simulations. Using the measured relative light yields, rise- and decay times of the scintillators we are able to quantitatively understand the measured CTRs in our simulations. Although the rise time is important to fully explain the CTR variation for the different samples tested we determined its influence on the CTR to be in the order of a few percent only. This result is surprising because, if only photonstatistics of the scintillation process is considered, the CTR would be proportional to the square root of the rise time. The unexpected small rise time influence on the CTR can be explained by the convolution of the scintillation rate with the single photon time resolution (SPTR) of the photodetector and the photon travel spread (PTS) in the crystal. The timing benefits of prompt photons at the beginning of the scintillation process (Cherenkov etc) are further studied, which leads to the conclusion that the scintillation rise time, SPTR and PTS have to be lowered simultaneously to fully profit from these fast photons in order to improve the CTR significantly.

Sub-100 ps coincidence time resolution for positron emission tomography with LSO:Ce codoped with Ca.

The coincidence time resolution (CTR) becomes a key parameter of 511 keV gamma detection in time of flight positron emission tomography (TOF-PET). This is because additional information obtained through timing leads to a better noise suppression and therefore a better signal to noise ratio in the reconstructed image. In this paper we present the results of CTR measurements on two different SiPM technologies from FBK coupled to LSO:Ce codoped 0.4%Ca crystals. We compare the measurements performed at two separate test setups, i.e. at CERN and at FBK, showing that the obtained results agree within a few percent. We achieve a best CTR value of 85 ± 4 ps FWHM for 2 × 2 × 3 mm(3) LSO:Ce codoped 0.4%Ca crystals, thus breaking the 100 ps barrier with scintillators similar to LSO:Ce or LYSO:Ce. We also demonstrate that a CTR of 140 ± 5 ps can be achieved for longer 2 × 2 × 20 mm(3) crystals, which can readily be implemented in the current generation PET systems to achieve the desired increase in the signal to noise ratio.

Synthesis, characteristics and thermoluminescent dosimetry features of γ-irradiated Ce doped CaF2 nanophosphor.

Nanoparticles of cerium doped calcium fluoride (CaF2:Ce) were synthesized for the first time using the hydrothermal method. The formation of nanostructures was confirmed by X-ray diffraction (XRD) patterns, indicating cubic lattice structure for the particles produced. Their shape and size were observed by scanning electron microscopy (SEM). Thermoluminescence characteristics were studied by having the samples irradiated by gamma rays of (60)Co source. The optimum thermal treatment of 400 °C for 30 min was found for the produced nanoparticles. The Tm-Tstop and computerized glow curve deconvolution (CGCD) methods, used to determine the number of component glow peaks and kinetic parameters, indicated seven overlapping glow peaks on the TL glow curve at approximately 394, 411, 425, 445, 556, 594 and 632 K. A linear dose response of up to 2000 Gy, was observed for the prepared nanoparticles. Maximum TL sensitivity was found at 0.4 mol% of Ce impurity. Other TL dosimetry features, including reusability and fading, were also presented and discussed.

Chemical effect on the K shell x-ray fluorescence parameters of some Ce compounds.

Chemical effects on the Kß/Kα x-ray intensity ratios, fluorescence yields wK and vacancy transfer probabilities ηKL for some Ce compounds were investigated. In this study, the samples were excited by 59.54 keV γ-rays from a 5Ci (241)Am annular radioactive source. K x-rays emitted by samples were counted by an HPGe detector with a resolution of 182 eV at 5.9 keV. The experimental values were compared with the theoretical and other experimental values. The aim of these measurements was to characterize the dependence of the line position and line width with the chemical environment changes.

Wet-chemical preparation of Ce3+-activated K2LaX5 (X = Cl, Br or I) phosphors.

There has been a renewed interest in Ce(3+) -activated halide phosphors due to applications as scintillation detectors, especially for positron emission tomography. For K(2) LaCl(5), the light yield increases and the energy resolution (FWHM) improves with increasing Ce(3+) doping. K(2) LaX(5) compounds are also important as laser hosts for the mid-IR range. K(2) LaCl(5):Nd crystals show bright mid-IR luminescence, which makes them a candidate for IR laser materials. Efficient emission in the IR range has also been reported in K(2) LaCl(5):U(3+). A one-step, wet chemical process for preparing Ce(3+)-activated K(2) LaCl(5) phosphor is described. Intense luminescence of Ce(3+) can be observed in the as-prepared powders without any heat treatment. The availability of such powders opens up several exciting possibilities, such as growing single crystals without going to the high temperatures required for melting the constituent chlorides, or even obtaining processed, transparent, Ce(3+)-activated materials without taking recourse to crystal growth.

Room temperature synthesis of crystalline CeO2 nanopowder: advantage of sonochemical method over conventional method.

In the present study, nano-sized ceria (CeO(2)) powders were prepared using conventional and sonochemically assisted precipitation method, without any stabilizers, using cerium nitrate as a starting material and sodium hydroxide as a precipitating agent. The synthesized ceria powders were characterized by XRD, TGA and SEM to determine crystallite size, % crystallinity, thermal weight loss and shape respectively. It was found that the crystallite size obtained in both the synthesis methods were below 30 nm. It was also found that sonochemical synthesis method is energy efficient method saving more than 92% of energy as compared to that utilized by the conventional synthesis method. There was also a significant reduction in the reaction duration.

Surface damages of zirconia by Nd:YAG dental laser irradiation.

The purpose of this study was to characterize the surface damages of zirconia by Nd:YAG dental laser irradiation through a systematic evaluation of the associated microstructural changes. Disk specimens of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/Al2O3 nanocomposite) were irradiated by Nd:YAG dental laser. The specimens were characterized using scanning electron microscopy, X-ray diffractometry, and wavelength dispersive X-ray spectroscopy. Every single irradiated spot was indicated by a circular black pit surrounded by a circular raised rim with a sunken depression at the center. On surface changes, many cracks were formed inside each irradiated pit. On changes in elemental composition, the concentration of oxygen decreased while that of zirconium increased. After heating in air, the assembly of circular black pits turned white, although the depression and raised rim remained. This study showed that Nd:YAG dental laser irradiation induced cracking and reduced oxygen content on the surface of zirconia. Consequently, these phenomena reduced the mechanical strength of zirconia. Therefore, Nd:YAG dental laser welding should not be performed on tetragonal zirconia.

Color stability of pigmented maxillofacial silicone elastomer: effects of nano-oxides as opacifiers.

OBJECTIVES: This study evaluated the effects of nano-oxides on the color stability of pigmented silicone A-2186 maxillofacial prosthetic elastomers before and after artificial aging. METHODS: Each of three widely used UV-shielding nano-sized particle oxides (TiO(2), ZnO, CeO(2)), based on recent survey of the industry at 1%, 2%, 2.5% concentrations were combined with each of five intrinsic silicone pigment types (no pigments, red, yellow, blue, and a mixture of the three pigments). Silicone A-2186 without nano-oxides or pigments served as control, for a total of 46 experimental groups of elastomers. In each group of the study, all specimens were aged in an artificial aging chamber for an energy exposure of 450kJ/m(2). CIE L*a*b* values were measured by a spectrophotometer. The 50:50% perceptibility (ΔE*=1.1) and acceptability threshold (ΔE*=3.0) were used in interpretation of recorded color differences. Color differences after aging were subjected to three-way analysis of variance. Means were compared by Fisher's PLSD intervals at the 0.05 level of significance. RESULTS: Yellow pigments mixed with all three nano-oxides at all intervals increased ΔE* values significantly from 3.7 up to 8.4. When mixed pigment groups were considered, TiO(2) at 2%, and 2.5% exhibited the smallest color changes, followed by ZnO and CeO(2), respectively (p<0.001). At 1%, CeO(2) exhibited the smallest color changes, followed by TiO(2) and ZnO, respectively (p<0.001). The smallest color differences, observed for nano-oxides groups, were recorded for CeO(2) at 1%, and TiO(2) at 2% and 2.5%. When the nano-oxides were tested at all concentrations, CeO(2) groups overall had the most color changes, and TiO(2) groups had the least. All ΔE* values of the mixed pigment groups were below the 50:50% acceptability threshold (ΔE*=1.2-2.3, below 3.0) except 2% CeO(2) (ΔE*=4.2). CONCLUSION: 1% nano-CeO(2) and 2% and 2.5% nano-TiO(2) used as opacifiers for silicone A-2186 maxillofacial prostheses with mixed pigments exhibited the least color changes when subjected to artificial aging at 450kJ/m(2). Yellow silicone pigment mixed with all three nano-oxides significantly affected color stability of A-2186 silicone elastomer.

A resonant photoemission applied to cerium oxide based nanocrystals.

Cerium 4f level occupation determines the properties of cerium oxide based catalysts in a significant way. The Ce 4f level of nanosized cerium oxide particles was investigated with the use of resonant photoelectron spectroscopy in the Ce 4d-4f photoabsorption region. A strong interaction of ceria with different additives, e.g. Pd and Sn, led to a partial Ce4+-->Ce3+ transition that was observed as a significant resonance enhancement of 4f photoemission intensity. Increases of the CO oxidation catalytic activity were observed simultaneously. The ratio of resonance enhancement of Ce photoemission intensity DCe(3+)/DCe(4+) was used to monitor Ce(3+) and Ce(4+) state occupation. The relative parameter DCe(3+)/DCe(4+) was found to be particularly useful in the case of photoemission studies of nanopowder ceria catalysts.

Synthesis, characterization and computational study of nitrogen-doped CeO2 nanoparticles with visible-light activity.

Nitrogen-doped CeO2 nanoparticles were synthesized through a wet-chemical route. Nitrogen has been successfully incorporated into CeO2 nanoparticles and the nitrogen-doping level was also successfully controlled. The optical properties due to the different N-doping levels in CeO2 nanoparticles were characterized by UV-Vis diffuse reflectance spectroscopy (DRS), which showed a visible-light absorbance shift. The resulting nanoparticles show enhanced visible-light sensitivity and photocatalytic activity compared to undoped CeO2 nanoparticles. DFT calculations were performed to explore the effect of nitrogen doping versus oxygen vacancies. The calculations show that the change of the electronic structure upon N-doping CeO2 is quite different from that of N-doped TiO2, which has been studied extensively.