The rare earth elements (REEs) extraction by chemical leaching from ion-adsorption type rare earth ores (IAREO) has led to serious ecological and environmental risks. Conversely, demand of bioleaching is on the rise with the advantage of being environmental-friendly. As one of the organic acids produced by biological metabolism, citric acid was used to leach RE and explore the performance and process. The results demonstrate that citric acid exhibits higher leaching efficiency (96.00%) for REEs at relatively low concentration of 0.01 mol/L compared with (NH4)2SO4 (84.29%, 0.1 mol/L) and MgSO4 (83.99%, 0.1 mol/L). Citric acid shows a preference for leaching heavy rare earth elements, with 99% leaching efficiency in IAREO, which shows higher capacity than (NH4)2SO4 and MgSO4 (as inorganic leaching agents). Kinetic analysis indicates that the leaching process of REEs with citric acid is controlled by both the internal diffusion kinetics and chemical reaction kinetics, which is different with inorganic leaching agent. Visual Minteq calculations confirm that RE-Citrate are the main constituents of extract solution in the leaching process of the IAREO, thereby enhancing the leaching efficiency of REEs from the IAREO. It suggests that citric acid may be used as a promising organic leaching agent for the environmental-friendly extraction of REEs from IAREO.

The technology of solid-state lighting has developed for decades in various industries. Phosphor, as an element part, determines the application domain of lighting products. For instance, blue and red-emitting phosphors are required in the process of plant supplementing light, arrow-band emitting phosphors are applied to backlight displays, etc. In this work, a Bi3+-activated blue phosphor is obtained in a symmetrical and compact crystal structure of Gd3SbO7 (GSO). Then, the co-doping strategy of alkali metal ions (Li+, Na+, and K+) is used to optimize the performance. The result shows that the photoluminescence intensity is increased by 2.1 times and 1.3 times respectively by introducing Li+ and K+ ions. Not only that, it also achieves narrow-band emitting with the full width of half-maximum (FWHM) reaching 42 nm through Na+ doping, and its excitation peak position also shifts from 322 to 375 nm, which can be well excited by near-ultraviolet (NUV) light emitting diode (LED) chips (365 nm). Meanwhile, the electroluminescence spectrum of GSO:0.6 mol%Bi3+,3 wt%Na+ matches up to 93.39% of the blue part of the absorption spectrum of chlorophyll a. In summary, the Bi3+-activated blue phosphor reported in this work can synchronously meet the requirements of plant light replenishment and field emission displays.

The microstructure of (Nd, Ce)–Fe–B sintered magnets with different diffusion depths was characterized by a magnetic force microscope, and the relationship between the magnetic properties and the local structure of grain boundary diffused magnets is discussed. The domains perpendicular to the c-axis (easy magnetization direction) show a typical maze-like pattern, while those parallel to the c-axis show the characteristics of plate domains. The significant gradient change is shown in the concentration of Dy with the direction of diffusion from the surface to the interior. Dy diffuses along grain boundaries and (Dy, Nd)2Fe14B layer with a high anisotropy field formed around the grains. Through in-situ electron probe micro-analysis/magnetic force microscopy (EPMA/MFM), it is found that the average domain width decreases, and the proportion of single domain grains increases as diffusion depth increases. This is caused by both the change of concentration and distribution of Dy. The grain boundary diffusion process changes the microstructure and microchemistry inside the magnet, and these local magnetism differences can be reflected by the configuration of the magnetic domain structure.

As a promising optical and piezoelectric crystal, efficient growth of LGN single crystal is crucial for its practical applications. Herein, a langanite (La3Ga5.5Nb0.5O14, LGN) crystal with high quality was successfully grown by the Bridgman method along the Z direction. In order to prepare high-purity polycrystalline precursors for LGN crystal growth, the sintering conditions of LGN polycrystalline precursors were studied in detail. The melting point of LGN was also measured to provide a reference for the crystal growth temperature. For the 001 oriented wafer, the full width at half maximum (FWHM) value of the high-resolution X-ray diffraction (HRXRD) analysis is 38.52″, demonstrating that the LGN crystal exhibits excellent crystalline quality. In addition, we also measured the thermal properties and transmission spectrum of the as-grown LGN crystal. It is found that the absorption peak at 1.85 μm of the LGN crystal grown in air using the Bridgman method disappears compared with previous reports (grown in N2 + (1–3) vol% O2 atmosphere), which is attributed to the oxygen-enriched growth environment. Similar phenomenon also occurs in other LGS-type disordered crystals. It is believed that these findings may expand the potential applications of LGS series crystals at 1.85 μm.

Grain boundary diffusion technology is pivotal in the preparation of high-performance NdFeB magnets. This study investigates the factors that affect the efficiency of grain boundary diffusion, starting from the properties of the diffusion matrix. Through the adjustment of the sintering process, we effectively prepared magnets with varied densities that serve as the matrix for grain boundary diffusion with TbHx diffusion. The mobility characteristics of the Nd-rich phase during the densification stage are leveraged to ensure a more extensive distribution of heavy rare earth elements within the magnets. According to the experimental results, the increase in coercivity of low-density magnets after diffusion is significantly greater than that of relatively high-density magnets. The coercivity values measured are 805.32 kA/m for low-density magnets and 470.3 kA/m for high-density magnets. Additionally, grain boundary diffusion notably enhances the density of initial low-density magnets, addressing the issue of low density during the sintering stage. Before the diffusion treatment, the Nd-rich phases primarily concentrate at the triangular grain boundaries, resulting in an increased number of cavity defects in the magnets. These cavity defects contain atoms in a higher energy state, making them more prone to transition. Consequently, the diffusion activation energy at the void defects is lower than the intracrystalline diffusion activation energy, accelerating atom diffusion. The presence of larger cavities also provides more space for atom migration, thereby promoting the diffusion process. After the diffusion treatment, the proportion of bulk Nd-rich phases significantly decreases, and they infiltrate between the grains to fill the cavity defects, forming continuous fine grain boundaries. Based on these observations, the study aims to explore how to utilize this information to develop an efficient technique for grain boundary diffusion.

The magnetization dynamics of lanthanide coordination compounds are fundamentals governing their potential applications such as information storage or molecular switches. Herein, two two-dimensional coordination polymers [Er(CA)1.5(bpy) (DMF)]n (1) and [Er(CA)1.5(phen) (DMF)]n (2) (H2CA = 2,5-dichloro-3,6-dihydroxy-p-quinone, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) were synthesized and fully characterized. By the irradiation of ultraviolet light, 1 and 2 were converted to 1a and 2a which contain light-generated radicals, inducing an increase of χMT at room temperature. A detailed study of the dynamic magnetic property shows that the magnetization dynamics observed for 1 and 1a are dominated by Raman process, but Orbach and Raman processes are observed in 2 and 2a. The structural factors influencing the magnetic properties of this photomagnetic system are discussed.

Transformation of glycerol into value-added chemicals via electro-oxidation using the green electricity is considered as a sustainable and promising process. Whereas, the synthesis of specific C3 products such as glyceric acid (GLA) from electro-oxidation of glycerol still suffers from poor catalytic performance. Here, we used a two-step deposition strategy to prepare Au-CeO2/CNT catalyst for highly efficient electrosynthesis of GLA from glycerol oxidation under alkaline conditions. Upon treating 0.5 mol/L glycerol at 1.12 V (vs. RHE) for 12 h in 1.0 mol/L KOH solution, the glycerol conversion and GLA selectivity over Au-CeO2/CNT achieve 99.7% and 50.0%, respectively. The glycerol conversion doubles when an optimal amount of CeO2 is introduced to the Au/CNT catalyst. Au-CeO2/CNT provides numerous active sites at ternary junctions of Au-CeO2-CNT, which effectively suppress the adsorption of GLA on the surface of Au nanoparticles and prevent the nanoparticles from serious agglomeration, thereby facilitate the glycerol-to-GLA conversion with considerable cyclability. This study provides valuable insight into the rational design of high-performance catalysts for alcohol electro-oxidation.

The influence of the growth of rare earth on the viscosity during the uniform cooling of CaO-SiO2-CaF2-Ce2O3 slag was investigated by the high temperature viscometer. The results show that Ce2O3 affects the viscosity variedly before and after the break temperature. At higher temperatures Ce2O3 reduces the viscosity. When the temperature is below the break temperature, at a Ce2O3 content of ≥3 mol%, a rare-earth crystalline phase is observed during the slag cooling process, and the break temperature progressively increases with the increase of Ce2O3 concentration. There are no crystallized rare earths in the slag under the condition of Ce2O3 concentration lower than 3 mol%. Too low or too high CaF2 content is found to be unfavorable for rare-earth crystallisation. The increase of Ce2O3 content facilitates the depolymerization of silica-oxygen tetrahedral structure. Ca‒F bond exists between structural units, weakening the flow resistance of structural units and lowering the viscosity of slag.

Cerium-based materials are widely used in various applications such as photocatalytic environmental remediation, CO2 photoreduction and photocatalytic hydrogen production due to their unique optical properties and special oxygen vacancy formation mechanisms. The special external electronic structure of cerium (4f15d16s2f15d16s2), the highly electronic 4f orbital, promotes the formation of oxygen vacancies through Ce4+/Ce3+ conversion, thereby improving the optical properties of the catalyst. Consequently, the application of cerium-based materials in the field of photocatalysis has been of great interest to researchers. In this paper, we briefly review the synthesis of cerium-based photocatalysts and their applications in pollutant removal, CO2 reduction, and hydrogen production, as well as their promising applications.

Metal-organic frameworks (MOFs) and their derivatives have gained significant attention in recent years for their ability to catalyze the advanced oxidation of persulfates. Cerium-doped MOFs, in particular, have shown promise due to their high catalytic efficiency, practical applicability, and cost-effectiveness. However, their structure, catalytic properties, and mechanisms are not yet fully understood. ZIF-8 was chosen as the raw material to prepare cerium-doped hollow carbon nanofibers (Ce-HCNFs) using the electrostatic spinning-calcination method. The objective is to investigate the structure, catalytic performance, and catalytic mechanism of Ce-HCNFs. The results show that Ce-HCNFs catalyzed the degradation of tetracycline (TC) by persulfate up to 76.9%. Quenching experiments and electron paramagnetic resonance experiments indicate the dominant role of single-linear oxygen. Furthermore, the experiments on the influence factor and cycling demonstrate the exceptional stability and recycling capability of Ce-HCNFs in real-world water environments.

The integration of surface filtration and catalytic decomposition functions in catalytic bags enables the synergistic removal of multiple pollutants (such as dust, nitrogen oxide, acid gases, and dioxins) in a single reactor, thus effectively reducing the cost and operational difficulties associated with flue gas treatment. In this study, Mn–Ce-Sm-Sn (MCSS) catalysts were prepared and loaded onto high-temperature resistant polyimide (P84) filter through ultrasonic impregnation to create composite catalytic filter. The results demonstrate that the NO conversion rates of the composite catalytic filter consistently achieve above 95 % within the temperature range of 160–260 °C, with a chlorobenzene T90 value of 230 °C. The ultrasonic impregnation method effectively loaded the catalyst onto the filter, ensuring high dispersion both on the surface and inside the filter. This increased exposure of catalyst active sites enhances the catalytic activity of the composite catalytic filter. Additionally, increasing the catalyst loading leads to a gradual decrease in permeability, an increase in pressure drops and the long residence time of the flue gas, thereby improving catalytic activity. Compared to ordinary impregnation methods, ultrasonic impregnation improves the bonding strength between the catalyst and filter, as well as the permeability of the composite catalytic filter under the same loading conditions. Overall, this study presents a novel approach to prepare composite catalytic filter for the simultaneous removal of NO and chlorobenzene at low temperatures.

In this study, to enhance the coercivity and high-temperature stability of hot-deformed PrNd-Fe-B magnets, the NdHoAlGa alloy was utilized as a diffusion source and a dual-alloy diffusion process was employed to enhance the room temperature coercivity from 1.72 to 2.28 T. For the magnet doped with 7 wt% Nd72.3Ho13.8Al2.3Ga11.7, within the temperature range from 20 to 200 °C, the remanence temperature coefficient α increases from −0.16 %/°C to −0.14 %/°C, and the coercivity temperature coefficient β increases from −0.49 %/°C to −0.43 %/°C. By controlling grain boundary (GB) phases and optimizing the main phase simultaneously, Ga was induced to motivate the formation of non-ferromagnetic GB phases, reducing the size of grains and intergranular exchange coupling. Additionally, Ho was diffused into the main phase, forming (Pr,Nd,Ho)-Fe-B phase, which enhances the magnetic crystalline anisotropy field of the main phase grains at high temperatures.

Neodymium-iron-boron (Nd-Fe-B) sludge is an important secondary resource of rare-earth elements (REEs). However, the state-of-the-art recycling method, i.e., HCl-preferential dissolution faces challenges such as slow leaching kinetics, excessive chemical consumption and wastewater generation. In this work, the in situ anodic leaching of Nd-Fe-B sludge was developed to selectively recover REEs with high efficiency. The leaching rates of the REEs are 2.4–9.0 times higher using the in situ anodic leaching at the current density from 10 to 40 mA/cm2 than using conventional chemical leaching under the maintained pH of 3.7. Mechanism studies reveal that the anode-generated H+ plays the key role during the in situ anodic leaching process that locally increases the H+ concentration at the interface of sludge particles, accelerating the leaching kinetics. By achieving a total leaching efficiency of Nd-Fe-B sludge close to 100% and the Fe deposition efficiency in the range of 70.9%–74.3%, selective leaching of REEs is successfully realized and thus largely reduces chemical consumption. Additionally, a two-step recycling route involving electrolysis-selective precipitation was proposed that enables a stable REEs recovery of 92.2% with recyclable electrolyte. This study provides a novel and environmentally-friendly strategy for the efficient recovery of REEs from secondary resources.

The successful control of hydrocarbon and CO emissions from low-temperature diesel exhausts requires the use of highly active co-oxidation catalysts. In this study, Sn was used to enhance the catalytic performance of Pd/CeO2 in CO and C3H6 co-oxidation conditions. CeO2 with added stannum (Sn) was prepared as a support using the co-precipitation method, and Pd was loaded onto the support using the impregnation method. After Sn addition (the optimal Ce/Sn ratio is 0.75:0.25), the T50 values of CO and C3H6 are reduced by 20 and 32 °C, respectively. A series of characterization methods indicates that the addition of Sn to the support greatly enhances its lattice oxygen mobility and increases the proportion of PdO. During the co-oxidation process, stronger lattice oxygen mobility allows CO to react faster through the Mars–van Krevelen mechanism, weakening the competition with C3H6 for O2. A higher PdO content enhances the C3H6 oxidation capability. Moreover, CO can more readily reduce PdO than Pd2+ in solid solution with the support, which consequently further enhances co-oxidation activity. Therefore, the addition of Sn is a simple and effective strategy for enhancing the performance of Pd/CeO2 catalysts in CO and C3H6 co-oxidation reactions. Furthermore, the promotional effect of CO achieved in this study contributes to a deeper understanding of the interactions that occur during the co-oxidation of C3H6 and CO.