Improvement of coercivity and thermal stability of Nd-Fe-B sintered magnets by intergranular addition of Tb80Fe20 alloy

To improve the coercivity and temperature stability of Nd-Fe-B sintered magnets for high-temperature applications, the eutectic Tb₈₀Fe₂₀ (wt%) alloy powders were added into the Nd-Fe-B sintered magnets by intergranular method to enhance the coercivity (H_cj) and thermal stability. The microstructure, magnetic properties and thermal stability of the Nd-Fe-B magnets with different Tb₈₀Fe₂₀ contents were studied. The experimental results demonstrate that the coercivity (H_cj) of the sintered Nd-Fe-B magnet is significantly enhanced from 14.12 to 27.78 kOe, and the remanence (B_r) decreases not obviously by introducing 4 wt% Tb₈₀Fe₂₀ alloy. Meanwhile, the reversible temperature coefficients of coercivity (β) and remanence (α) of the Nd-Fe-B magnets are increased from ?0.5634%/℃ to ?0.4506%/℃ and ?0.1276%/℃ to ?0.1199%/℃ at 20–170 ℃, respectively. The Curie temperature (T_C) of the Nd-Fe-B magnet is slightly enhanced with the increase of Tb₈₀Fe₂₀ content. Moreover, the irreversible flux magnetic loss (h_irr) is obviously reduced as Tb₈₀Fe₂₀ addition increases. Further analysis of the microstructure reveals that a modified microstructure, i.e. clear and continuous RE-rich grain boundary layer, is acquired in the sintered magnets by introducing Tb₈₀Fe₂₀ alloy. The associated mechanisms on improved coercivity and thermal stability were comprehensively researched.     

Hydroxyl-and-carboxyl ligand concatenating multi-lanthanide substituted tellurotungstates and electrochemical detection of noradrenaline

Developing and exploring organic–inorganic hybrid multi-lanthanide (Ln) implanted heteropolyoxometalates (HPOMs) has bloomed into an emerging research field. In this article, two neoteric d-gluconic acids (H₆GA) concatenating multi-Ln^III implanted heteropolytungstates K₁₄H₁₀[Ln₄(H₂O)₄W₆(H₂GA)₄O₁₂(B-α-TeW₉O₃₃)₄]·60H₂O (Ln = La³⁺ (1), Pr³⁺ (2)) were obtained in acidic aqueous system. Attractively, in the polyanion structure of 1 and 2, six W^VI and four Ln^III centers are connected by four flexible H₂GA^4? ligands via carboxyl and hydroxyl groups, resulting in the heterometallic [Ln₄(H₂O)₄W₆(H₂GA)₄O₁₂]⁸⁺ cluster and then the heterometallic cluster is surrounded by four [B-α-TeW₉O₃₃]^8– segments. Electrochemical measurements for the 1@CFMCN/GCE sensor (CFMCN = carboxyl-functionalized multiwalled carbon nanotube; GCE = glass carbon electrode) demonstrate that 1@CFMCN/GCE shows benign recognition response to detecting noradrenaline (NDA). This research expands the structural diversity of Ln-implanted HPOMs and presents an electrochemical platform of recognizing NDA in the field of biosensors.     

Catalytic feasibility of Ce-doped LaCoO3 systems for chlorobenzene oxidation: An analysis of synthesis method

A family of Ce-doped LaCoO₃ perovskites are presented as possible catalysts for Cl–VOCs elimination. These materials with different contents of Ce were obtained through the citrate and the reactive grinding methods. The insertion of Ce in the original perovskite structure favours the presence of Co²⁺/Co³⁺ and Ce³⁺/Ce⁴⁺ redox pairs and a higher content of oxygen vacancies that enhances the catalytic performance in chlorobenzene combustion based on differential kinetics studies. The family obtained by the grinding method presents a performance as high as that synthesized by citrate method. Thus, the reactive grinding is a feasible green chemistry alternative to obtain a catalyst with the same performance as that obtained from traditional methods. Finally, the stability of samples was evaluated under total combustion reaction conditions showing an excellent activity during 45 h time on stream.     

In-situ generation of platinum nanoparticles on LaCoO3 matrix for soot oxidation

The LaCo_0.94Pt_0.06O₃ catalyst is reduced under 5% H₂/Ar at different temperatures to get Pt/LaCoO₃ with high catalytic activity for soot oxidation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR), O₂-temperature programmed desorption (O₂-TPD) and thermogravimetric analysis (TGA) were used to study the physicochemical properties of the catalyst. SEM and TEM results indicate that Pt nanoparticles (<10 nm) are grown homogeneously on the surface of the LaCoO₃ matrix after in-situ reduction. XRD shows that the reduced catalyst has a high symmetrical structure. TGA results indicate that all reduced catalysts exhibit an excellent activity, especially the catalyst reduced at 350 °C (T₁₀ = 338 °C, T₅₀ = 393 °C, T₉₀ = 427 °C). And perovskite is the primary active component. According to XPS study, the high symmetrical structure benefits the mobility of oxygen vacancy, and Pt nanoparticles induce the oxygen vacancy to move to its adjacent situation, resulting in more adsorbed oxygen on the surface of the reduced catalyst and increasing the activity. The possible reaction principle is also proposed.     

Sm-MnOx catalysts for low-temperature selective catalytic reduction of NOx with NH3: Effect of precipitation agent

A series of Sm–Mn mixed oxide catalysts were prepared via precipitation using various precipitants, namely Na₂CO₃ (NH₄)₂CO₃, and NH₃·H₂O, and evaluated for the selective catalytic reduction (SCR) of NO_x with NH₃ at low temperatures. Various characterisation techniques were used to determine the physicochemical properties of the catalysts, and it is found that their catalytic performance is greatly influenced by the nature of the precipitation agent used. It is found that Sm_0.1Mn–Na₂CO₃ and Sm_0.1Mn-(NH₄)₂CO₃ exhibit superior catalytic performance in the SCR reaction to that of Sm_0.1Mn–NH₃·H₂O due to an abundance of surface acid sites, high surface concentration of Mn⁴⁺, and high NO oxidation capacity. From in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) analysis, we conclude that the Sm–Mn catalysts follow both Eley-Rideal and Langmuir–Hinshelwood mechanisms, and that the Eley-Rideal mechanism is dominant at elevated temperatures.     

Fluorescent lamp promoted formaldehyde removal over CeO2 catalysts at ambient temperature

Exploring an alternative strategy with high efficiency and low cost to abate formaldehyde (HCHO) in indoor environment, is of increasing significance for people's health. CeO₂ catalysts prepared by hydrothermal, precipitation and calcination methods were investigated for HCHO removal at ambient temperature. It is found that indoor fluorescent light visibly boosts the catalytic performance of CeO₂ catalysts for HCHO decomposition at ambient temperature. Among the CeO₂ catalysts, CeO₂ prepared from hydrothermal method (CeO₂–H) exhibits a superior catalytic performance and an excellent durability by eight recycle times. Based on the characterization and analysis, the excellent catalytic performance of CeO₂–H is mainly contributed by its abundance of surface oxygen vacancies, and photogenerated electrons and hole activated by fluorescent light. This work shows a potential practicability in HCHO pollution elimination by taking full advantage of the existing lighting in indoor environments.     

Preparation of M/Ce1–xTixO2 (M=Pt,Rh, Ru) from sol-gel method and their catalytic oxidation activity for diesel soot

A series of Ce_1–xTi_xO₂ mixed oxide catalysts were synthesized by sol-gel method and then loading of noble metal (M = Pt, Rh, Ru) was used for soot oxidation. Ti-doped Ce_1–xTi_xO₂ catalysts (x is the molar ratio of Ti/(Ti + Ce) and ranges from 0.1 to 0.5) exhibit much better oxidation performance than CeO₂ catalyst, and the Ce_0.9Ti_0.1O₂ catalyst calcined at 500 °C has the best catalysis activity. Each noble metal (1 wt%) was supported on Ce_0.9Ti_0.1O₂ (M/C9T1) and the properties of the catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, Brunauer–Emmett–Teller (BET) method, and H₂-temperature programmed reduction (H₂-TPR) results. Results show that the introduction of Ti into CeO₂ forming Ti-O-Ce structure enhances the catalytic activity and increases the number of oxygen vacancies at the catalyst surface. The noble metal is highly dispersed over Ce_0.9Ti_0.1O₂, and M/C9T1 catalysts present enhanced activity in comparison to Ce_0.9Ti_0.1O₂. It is found that noble metals can greatly increase the activity of the catalyst and the corresponding oxidation rate of soot can enhance the electron transfer capacity and oxygen adsorption capacity of the catalyst. A small amount of Ti doping in CeO₂ can significantly improve the activity of the catalyst, while a large amount of Ti reduces the performance of the catalyst because a large amount of Ti is enriched on the surface of the catalyst, which hinders the contact and reaction between the catalyst and the soot.     

A dual-stimuli-responsive intelligent layered lanthanide hydroxide for application in information security and latent fingerprint identification

With the rapid changes in the field of information, the research and development of optical storage materials with high security and large storage capacity are particularly important in the development of contemporary society. However, conventional memory materials with static fluorescent outputs have the disadvantages of easy simulation and forgery, which limits their practical application in the protection of confidential information. In this research, a dual-stimuli-responsive intelligent fluorescent material based on Tb³⁺ and Eu³⁺ ions doped layered lanthanide hydroxide (LYH:Eu_xTb_1–xDPA) was fabricated, which can realize reversible multi-color luminescence conversion (from green to red) by varying the pH and temperature. Combined with the Morse code and security pattern, the multiple encryption and decryption of confidential information and anti-counterfeiting can also be realized. Therefore, the obtained intelligent fluorescent material has a great application prospect for information security. In addition, due to the excellent color tunability, the material can provide the possibility to obtain potential fingerprints with high contrast and no background interference on different color substrates. The unique dual-stimuli-responsive behavior of this material provides more ingenious design inspiration for the design of multi-color intelligent fluorescent devices.     

Highly dispersed CeO2–x nanoparticles with rich oxygen vacancies enhance photocatalytic performance of g-C3N4 toward methyl orange degradation under visible light irradiation

CeO₂/g-C₃N₄ photocatalysts have attracted tremendous attention in the photocatalytic degradation of organic pollutants. The design and construction of highly active CeO₂/g-C₃N₄ photocatalysts without harsh conditions are still challenging. Herein, highly dispersed CeO_2–x nanoparticles with rich oxygen vacancies were successfully precipitated on the surface of g-C₃N₄ under mild conditions. The fabricated CeO_2–x/g-C₃N₄ exhibits remarkable activity and stability for photocatalytic degradation of MO pollutant. The optimal rate constant of MO degradation over CeO_2–x/g-C₃N₄ is about 0.031 min^?1, which is three times higher than that of g-C₃N₄. A negligible activity decrease is observed after three cycling runs. The enhanced catalytic performance can be ascribed to the excellent dispersion of CeO_2–x with rich oxygen vacancies that benefit O₂ adsorption and visible light absorption. In addition, the proper band alignment between CeO_2–x and g-C₃N₄ is conducive to the highly efficient separation of photogenerated electron–hole pairs.     

Synthesis of NaYF4:20% Yb3+,2% Er3+,2% Ce3+@NaYF4 nanorods and their size dependent uptake efficiency under flow condition

Lanthanide doped fluorescent nanoparticles have gained considerable attention in biomedical applications. However, the low uptake efficiency of nanoparticles by cells has limited their applications. In this work, we demonstrate how the uptake efficiency is affected by the size of nanoparticles under flow conditions. Using the same size NaYF₄:20% Yb³⁺,2% Er³⁺,2% Ce³⁺ (the contents of rare earths elements are in molar fraction) nanoparticles as core, NaYF₄:20% Yb³⁺,2% Er³⁺,2% Ce³⁺@NaYF₄ core–shell structured nanorods (NRs) with different sizes of 60–224 nm were synthesized by thermal decomposition and hot injection method. Under excitation at 980 nm, a strong upconversion green emission (541 nm, ²H_11/2 → ⁴I_15/2 of Er³⁺) is observed for all samples. The emission intensity for each size nanorod was calibrated and is found to depend on the width of NRs. Under flow conditions, the nanorods with 96 nm show a maximum uptake efficiency by endothelial cells. This work demonstrates the importance of optimizing the size for improving the uptake efficiency of lanthanide-doped nanoparticles.