A comparison between Ce(Ⅲ) and Ce(Ⅳ) ions in photocatalytic degradation of organic pollutants

Nano cerium oxides are efficient photocatalysts for pollutants degradation with highly dispersed Ce(III) ions as the suggested active species to promote the reaction, while Ce(IV) species do not behave as a catalyst. In this paper, to understand the mechanism of Ce-based photocatalysts, we studied the comparison of simple cerium ions, Ce(III) and Ce(IV) in aqueous solution for organic pollutants degradation under UV irradiation. Orange II(AOII), methyl orange, and p-nitrophenol were selected as the target pollutants. The formation and contribution of reactive oxygen species, the kinetics of Ce(IV) photoreduction and Ce(III) photooxidation, and the influence of solution p H were investigated in detail. It was found that at low p H Ce(IV) ions showed a higher activity for hydroxyl radicals production and AOII degradation than Ce(III) ions, which could be attributed to its fast reduction rate to Ce(III). However, its activity dramatically decreased when solution p H increased, and was also strongly influenced by the type of pollutants; while Ce(III) exhibited high degradation efficiency of all the tested pollutants over a wide pH range.     

Pairs of Ln(Ⅲ) dopant ions in crystalline solid luminophores: an ab initio computational study

Formation of dopant ions clusters in solid(glass) luminophores may affect efficiency of non-radiative energy transfer processes between dopant(photoactivator) ions via shortening of the effective distance between them. This study was based on the assumption that the distance between the dopant ions affects the energy of crystal volume at proximity. According to this idea, semi-empirical and ab initio density functional theory(DFT) calculations were performed on various supercells of YVO_4:Eu~(3+) as a model system. It was noted that a shorter Eu–Eu distance resulted in lower total energy of the system, compared to an analogous structure with distant Eu~(3+) ions. As lower energy configurations are preferred, the observed phenomenon was considered to be related to dopant ions clusters formation. Additionally, the values of energies obtained from DFT calculations were used to estimate the percentage of dopant ions occurring as pairs, for different dopant concentrations. The estimation agreed quite well with the available literature data.     

Chemical State, Site, Solid Solubility, and Magnetism of Fe in the Ferropericlase (Mg1–x Fe x )O Produced by Ball Milling of MgO and Fe

Ferropericlase (Mg_1–x Fe _x )O solid solution was prepared by ball milling of the mixture of MgO with a rock-salt structure and metal Fe powders in atmosphere and at room temperature. Differing from (Mg_1–x Fe _x )O prepared at high temperature by using MgO and FeO as starting materials, the solution of Fe in MgO is not continuous but limited in the ball milling process, and the solubility limit is less than 30 at. pct. About 92 pct of the Fe ions occupy the site of tetrahedral oxygen coordination in trivalent Fe (Fe³⁺) with high spin, whereas about 8 pct of the Fe ions occupy the site of octahedral oxygen coordination in bivalent Fe (Fe²⁺) with high spin. The Fe³⁺ and Fe²⁺ ions do not show a ferromagnetic but show a paramagnetic state. The as-milled (Mg_1–x Fe _x )O is metastable and decomposes to ferropericlase (Mg_1–y Fe _y )O (where y < x) and MgFe₂O₄ with spinel structure as annealed above 773 K (500  °C), and the content of Fe in the (Mg_1–y Fe _y )O increases with increasing annealing temperature. A bulk (Mg_1–x Fe _x )O was fabricated by annealing the as-milled (Mg_1–x Fe _x )O powders at 973 K (700  °C). It shows n-type conductivity, which is attributed to an electronic small polaron with an activation energy of 0.135 eV.     

Calorimetric Studies of the Synergistic Effect: The Reaction of RE(TTA)_3 with N503 in Toluene

Titration calorimetry has been used to study the thermodynamics of reaction in toluene solution of2-thenoyltriflueroacetone(TTA)complexes of rare earths(RE=Y,Nd,Eu,Yb)with N,Ndimethylheptyl-acetamide(N503)at 298.15 K.The heat of the reaction was determined with a TRONACModel 1250 automatic isoperibol calorimeter.The data and figures of titration curve were recorded by the com-puter automatically.An iterative technique of least-square analysis was used to calculate the equilibrium con-stants and the thermodynamic functions including the entropy and free energy changes,minimizing the errorsquare sum by a computer program.     

First-Principles Calculations on Stabilization of Iron Carbides (Fe3C, Fe5C2, and η-Fe2C) in Steels by Common Alloying Elements

The control of carbide formation is crucial for the development of advanced low-alloy steels. Hence, it is of great practical use to know the (de)stabilization of carbides by commonly used alloying elements. Here, we use ab initio density functional theory (DFT) calculations to calculate the stabilization offered by common alloying elements (Al, Si, P, S, Ti, V, Cr, Mn, Ni, Co, Cu, Nb, Mo, and W) to carbides relevant to low-alloy steels, namely cementite $(\hbox{Fe}_{3}\hbox{C}),$ H?gg $(\hbox{Fe}_{5}\hbox{C}_{2}),$ and eta-carbide $(\eta{\text{-}}\hbox{Fe}_{2}\hbox{C})$ . All alloying elements are considered on the Fe sites of the carbides, whereas Al, Si, P, and S are also considered on the C sites. To consider the effect of larger supercell size on the results of (de)stabilization, we use both 1?×?1?×?1 and 2?×?2?×?2 supercells in the case of $\hbox{Fe}_{3}\hbox{C}.$      

Effect of Nitrogen Concentration in a Gas Mixture on the Structure and Properties of Zr–B–(N) Coatings Obtained by the HIPIMS Methods

Russian Journal of Non-Ferrous Metals - Zr–B–N сoatings have been obtained by high-power impulse magnetron sputtering (HIPIMS) in Ar, Ar + 15% N2, and N2 gaseous media using a...     

Promoter of (Ce-Zr)O_2 Solid Solution Modified by Praseodymia in Three-Way Catalysts

CeO2 ispresentinthemajorityoftheformulationsofthethree waycatalystsduetoitswell knownmulti pleeffectssuchas :(1)stabilizationofthepreciousmetalsdispersionandthealuminasupport[1] ,(2 )pro motionofwatergasshiftreactionandsteamreformingreaction[2 ] andsoon .TheprimaryfunctionofCeO2 intheTWCsistoprovideoxygenstoragecapacity(OSC) ,actingasanefficient“oxygenbuffer”toun dergoeffectivereduction/oxidationcyclesbyshiftingbetweenCeO2 underoxidizingconditions (oxygenstor age)andCe2 O3underreducingco…     

Effect of Mn Substitution on Microstructure Evolution and Magnetic Phase Transition in La(Fe1−x Mn x )10.8Co0.7Si1.5 Compounds

The influences of Mn substitution for Fe on microstructures of La(Fe_1?x Mn _x )_10.8Co_0.7Si_1.5 (x = 0, 0.01, 0.02, 0.03) alloys in both the as-cast state and the annealed state have been studied. The results show that Mn substitution promotes the fining of the as-cast microstructure and increases the formation of 1:13 phase significantly when annealed. An almost single 1:13 phase is obtained for x = 0.01 when annealed at 1373 K (1100 °C) for 3 days, while a large amount of impurity phases is still present for x = 0. By increasing the amount of Mn to x = 0.02, a more purified annealed microstructure can be obtained. However, further substitution of Mn up to x = 0.03 is harmful for the formation of 1:13 phase. The Curie temperature T _C of the annealed La(Fe_1?x Mn _x )_10.8Co_0.7Si_1.5 (x = 0, 0.01, 0.02, 0.03) varies monotonously with Mn content x, decreasing from ~279 K (6 °C) for x = 0 to ~236 K (?37 °C) for x = 0.03. When x = 0.01, a higher maximum entropy change (?ΔS)_max of 5.3 J/(kgK) and relative cooling power (RCP) of 166 J/kg can be obtained under a magnetic field of 2T. Further substitution of Mn (x = 0.02) results in a slight decrease of (?ΔS)_max, whereas a larger RCP can still be kept.     

A smart nanoprobe based on luminescent terbium metal-organic framework coated gold nanorods for monitoring and photo-stimulated combined thermal-chemotherapy

Real-time monitoring and accurate treatment are of great significance for reducing the side effects during the cancer therapy.In this work,we rationally prepared a smart nanoprobe based on core-shell terbium metal-organic gramework(MOF) with highly effective photothermal conversion capacity and drug release efficiency under near-infrared light irradiation for real-time fluorescence imaging-guided multimodal therapy.The nanoprobe can achieve prominent photothermal therapy and controllable drug re...     

Effective regulation of electronic structures and luminescence properties of LiGd9(SiO4)6-x(GeO4)xO2:Dy3+ phosphors by tetrahedral substitution

A series of Dy³⁺-activated phosphors with the general formula LiGd₉(SiO₄)_6-x(GeO₄)_xO₂:Dy₃₊(0 ≤ x≤ 3)characterized by an apatite-type structure were successfully synthesized via a simple solid-state technique involving a partial substitution of [SiO₄]^4-with [GeO₄]^4- species.The effects of homovalent[GeO₄]^4--[SiO₄]^4- substit...     

Effect of excitation wavelength (blue vs near UV) and dopant concentrations on afterglow and fast decay of persistent phosphor SrAl2O4:Eu2+,Dy3+

The persistent phosphor SrAl₂O₄:Eu²⁺,Dy³⁺ is the subject of numerous investigations. One often neglected aspect is that in this phosphor, as well as in Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺, there are two different Sr²⁺ sites which can be occupied by the dopant Eu²⁺ ions. We first introduce a general scheme of possible energy transfers in these persistent phosphor materials including explicitly both europium ions. This scheme is used as a generic starting point to study experimentally specific pathways. We illustrate this application with the study of the effect of excitation wavelength (444 and 382 nm) on the afterglow of differently doped SrAl₂O₄:Eu²⁺,Dy³⁺ samples, as well as on the emission decay curves. With the same excitation intensity under 444 nm excitation, the resulting afterglow intensity is stronger than under near UV excitation. At 382 nm, Eu²⁺ ions on both Sr²⁺ sites in SrAl₂O₄ are excited, but at room temperature the blue emission is quenched, leading to a loss of photons. The observed effects can further be associated with the ratio of Eu²⁺ ions and trap states which are modulated by the concentrations of Eu²⁺ and Dy³⁺ in SrAl₂O₄, as well as by temperature. Increasing the nominal Dy³⁺ content from 0.1 mol% to 0.5 mol% with respect to Sr results in the doubling of the integrated afterglow intensity and confirms thus that Dy³⁺ ions are indeed involved in the trapping process. The concentration of trap states is much lower than the concentration of Eu²⁺ ions, as even with low excitation densities, a plateau of integrated afterglow intensity (corresponding to the total number of accessible traps) is reached. We postulate that an important fraction of excited Eu²⁺ ions can potentially transfer their energy to trap states. Once that all traps are filled or in a dynamical filling-depletion process under illumination (with thermal and/or optical depletion processes), for the remaining Eu²⁺ a “normal” steady-state emission is observed. The luminescence decay curves at 520 nm measured at 77 K show a mono-exponential decay with a common lifetime of about 1140 ns for all 5 samples under 437 nm excitation, while under 375 nm excitation, a feed process originating from the energy transfer between Eu²⁺ ions is demonstrated. Under 375 nm excitation, the non-exponential decay observed at 440 nm can be quantitatively associated to a Förster energy transfer process with R₀ = 1.58 (8) nm. For the overall understanding of the afterglow processes, it appears that one has to consider the individual contributions of all active ions on different lattice sites.