Rare Earth Metal Ions Research Articles

Multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column for separation of rare earth elements

Multistep pH-peak-focusing liquid chromatography with a column packed with a hydrophilic polymer gel (a cross-linked hydroxylated methacrylic polymer gel) was developed for separation of rare earth metal ions. Metal ions in a sample solution introduced to the column are chromatographically extracted into the stationary gel phase at the top of the column equilibrated with a basic solution used as the first mobile phase containing acetylacetone and 1,10-phenanthroline by synergistic extraction effect. After the sample solution is introduced, the mobile phases are delivered into the column by stepwise gradient elution in order of decreasing pH. Each metal ion is concentrated at a pH border formed between the zones of different pH in the column and moves toward the outlet of the column with the pH border. Mutual separation of La(III), Ce(III), Nd(III), Eu(III), Y(III), Tb(III), and Yb(III) was achieved by the present method for an 1-mL sample injection with the column of which the inner volume is 11.8 mL. The multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column developed in this study has great potential as a useful method for the separation of rare earth metal ions on a preparatory scale.

Influence of ionic radius on the degree of extraction of rare earth metals during sorption by the interpolymer system AMBERLITE IR-120 –AВ-17-8

Studies have been carried out on the sorption of rare earth metal ions in solution using the interpolymer system Amberlite IR-120:AB-17-8. The purpose of the work is to search for conditions for maximum sorption of rare earth elements (Dy, Tb, Gd, Eu and Sm) from aqueous solutions using the effect of remote interaction of ion exchange resins. Methodology. The residual concentrations of rare earth ions were determined using an Optima 8300DV Duo inductively coupled plasma spectrometer. Results. The best sorption characteristics were determined by the interpolymer system at a ratio of 3:3. The residual concentration of rare earth elements in the solution was: Dy – 4.64 mg/l, Tb – 4.16 mg/l, Gd – 4.21 mg/l, Eu – 4.16 mg/l, Sm – 4.56 mg/l. The variations in the ionic radius of the ions chosen for the study are Dy3+<Tb3+<Gd3+<Eu3+<Sm3+. The degree of sorption of interpolymer system increased with increasing ionic radius of the metals. For dysprosium with the smallest ionic radius, the degree of sorption was η – 52%, and for terbium, gadolinium and europium it increased to η – 58%. For individual Amberlite IR-120 (6:0), the degree of sorption of terbium ions was 47%. Conclusion. The results of the study showed that the interpolymer system with a ratio of 3:3 has the best sorption activity. It has been established that the degree of sorption of interpolymer pairs increases with increasing order of the ionic radius of metals (Tb3+< Gd3+< Eu3+).

Highly Selective and Portable Fluorescence Turn-On Detection of Sc3+ in Ore and Water Based on Strong Lewis Acid-Base Coordination.

Detecting scandium (Sc) with high selectivity and sensitivity is a challenging task due to its chemical similarity to other rare earth ions. Our findings show that the fluorescence of the complex fluorescent indicator calcein (CL) is quenched under acidic conditions (pH = 2), and Sc3+ strongly inhibits this process. The results demonstrate that CL forms multimers and precipitates out of the solution under acidic conditions, while Sc3+ causes a significant decrease in the scattering intensity of the solution. Additional experiments revealed that the strong Lewis acid nature of Sc3+ complexes with the carboxyl groups of CL leads to increased dispersion of CL even under acidic conditions, thus enhancing its absorption and fluorescence. The complexation ratio of Sc3+ and CL was investigated through spectral titrations and theoretical calculations. The interaction between Sc3+ and CL is the strongest among rare earth and common metal ions due to the smallest ionic radius, resulting in high selectivity. The fluorescence turn-on strategy had a linear range of 0.04 to 2.25 μM under optimal conditions, with a detection limit of 20 nM for Sc3+. The combination of 3D printing and a smartphone program allows for portable on-site analysis of Sc3+. Mineral and water samples were used to demonstrate the potential of this strategy for the rapid, selective, and sensitive analysis of low levels of Sc3+.

Review of novel approach and scalability forecast of ZnSe and Perovskite/Graphene based thin film materials for high performance solar cell applications

Abstract In the recent years, the using of fossil energy source-based fuels are delivering to the predetermined nature, health and environmental exposure, there is a universal necessitate prepared to well improvement and consumption of renewable energy source and apparatus. With the rapid growth of human life, energy is more essential. The explosive growth of population and energy consumption demands are the exclusive issue of the present world. In response to the energy demands, the growth of highly efficient energy conversion and storage devices. With increasing energy demands and environmental pollution, there is a requirement of the world to great some novel conducting materials consist of Perovskite solar cells (PSCs) which is delivered that excellent photoconversion efficiencies (PCE) compare with the other silicon supported photovoltaics, and also semiconducting materials for the conversion of substitute energy sources and preparation of high high-performance semiconductor devices. Semiconducting thin films play an indispensable role in fashionable science and electronic technology. Among them, the II–VI compound semiconductor thin films are an important class of materials, and they are generally comprehensive wide-band gap materials. In addition, the un-doped and rare-earth metal ions doped zinc selenide (ZnSe) thin films are currently the most demanding and technologically important materials, which have the potential for optoelectronic devices (solar cells, photoelectrochemical cell and light emitting diodes) and are active throughout the entire visible spectrum extending into the infrared wavelengths. Various techniques for depositing thin coatings on these substances are utilized to a greater extent. In this review, the most recent advanced techniques in the application of semiconducting materials-based thin films were produced in various energy-generated fields, particularly solar cells, with a major focus on a review of recent progress in the development of various types of ZnSe thin film-based material for high-performance semiconducting thin film material for solar cell application. Lastly, the advantages and material challenges of semiconductor-based thin films for future sanitary energy device process are described.

Exploring sulfur donor atom coordination chemistry with La(II), Nd(II), and Tm(II) using a terphenylthiolate ligand.

To expand the range of donor atoms known to stabilize 4fn5d1 Ln(II) rare-earth metal (Ln) ions beyond the C, N, and O first row main group donor atoms, the Ln(III) sulfur donor terphenylthiolate iodide complexes, LnIII(SAriPr6)2I (AriPr6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2, Ln = La, Nd) were reduced to form LnII(SAriPr6)2 complexes. These Ln(II) species were structurally characterized, analyzed by density functional theory (DFT) calculations, and compared to Tm(SAriPr6)2, which was synthesized from TmI2(DME)3.

Structure and optical properties of stable Bi/Eu codoped borophosphate La7O6(BO3)(PO4)2 phosphors for application in wLEDs

Rare-earth (RE) and/or transition metal (TM) ions (co)doped phosphors have garnered much attention for promoting development in the fields of solid state lighting (SSL) and displays. It is a meaningful work to design high-quality phosphor via intelligent assembling from wide variety of compounds with RE/TM ions. Herein, the lanthanum borophosphate La7O6(BO3)(PO4)2 (LOBP) and Bi/Eu were selected as host and dopants for constructing the phosphor LOBP: Bi/Eu via solid phase synthetic method due to simple synthesis, chemical/thermal stability, rich cationic sites, appropriate bandgap, and controllable optical tuning from synergistic effect of cyan (Bi) and red (Eu) emissions, respectively. The structure and site occupations were analysed via XRD and Rietveld refinements, showing Bi3+ ions were only resided in La3+ sites within the monoclinic matrix (P21/n) and appeared greater inclination towards the La sites with coordinate number (CN) = 8 as compared with CN = 7 due to the closer ion radius ratio. While Eu3+ ions entered into the two distinct La sites with almost the same probability. The morphology and elemental mapping were obtained via SEM/EDS, exhibiting irregular particle shape with micron-level size, and the chemical composition met expectation. Through energy transfer (ET) from Bi to Eu under n-UV excitation, the adjustable photoluminescence (PL) from cyan traversing white and finally to red could be achieved. The concentration quenching for both singly- (Bi) and co-doped (Bi/Eu) phosphors were charged by the d-d interactions. Finally, the stable as-fabricated n-UV pumped wLED via coupling the composition-optimized white-emitting LOBP: 2%Bi, 7%Eu to a commercial 305 nm n-UV LED chip shows splendid performances.

Chelation of [111In]In3+ with the dual-size-selective macrocycles py-macrodipa and py2-macrodipa.

Indium-111 (111In) is a diagnostic radiometal that is important in nuclear medicine for single-photon emission computed tomography (SPECT). In order to apply this radiometal, it needs to be stably chelated and conjugated to a targeting vector that delivers it to diseased tissue. Identifying effective chelators that are capable of binding and retaining [111In]In3+in vivo is an important research area. In this study, two 18-membered macrocyclic chelators, py-macrodipa and py2-macrodipa, were investigated for their ability to form stable coordination complexes with In3+ and to be effectively radiolabeled with [111In]In3+. The In3+ complexes of these two chelators were characterized by NMR spectroscopy, X-ray crystallography, and density functional theory calculations. These studies show that both py-macrodipa and py2-macrodipa form 8-coordinate In3+ complexes and attain an asymmetric conformation, consistent with prior studies on this ligand class with small rare earth metal ions. Spectrophotometric titrations were carried out to determine the thermodynamic stability constants (log KML) of [In(py-macrodipa)]+ and [In(py2-macrodipa)]+, which were found to be 18.96(6) and 19.53(5), respectively, where the values in parentheses are the errors of the last significant figures obtained from the standard deviation from three independent replicates. Radiolabeling studies showed that py-macrodipa and py2-macrodipa can quantitatively be radiolabeled with [111In]In3+ at 25 °C within 5 min, even at ligand concentrations as low as 1 μM. The in vitro stability of the radiolabeled complexes was investigated in human serum at 37 °C, revealing that ∼90% of [111In][In(py-macrodipa)]+ and [111In][In(py2-macrodipa)]+ remained intact after 7 days. The biodistribution of these radiolabeled complexes in mice was investigated, showing lower uptake in the kidneys, liver, and blood at the 24 h mark compared to [111In]InCl3. These results demonstrate the potential of py-macrodipa and py2-macrodipa as chelators for [111In]In3+, suggesting their value for SPECT radiopharmaceuticals.

Synthesis and catalytic activity of tetradentate β-diketiminato rare-earth metal monoalkyl complexes in tandem Oppenauer oxidation and cross-aldol condensation.

A series of unsymmetric tetradentate β-diketiminato rare-earth metal monoalkyl complexes were synthesized, and their catalytic behavior has been well developed. Indole-incorporated β-diketiminato proligands H2L (L = MeC(NDipp)CHC(Me)NCH2CH2-3-(1-R-C8H4N), R = CH2-(2-C4H7O), L1; R = (CH2)2OMe, L2; Dipp = 2,6-iPr2C6H3) were prepared by the reaction of an arylamino-enone with 1-substituted-tryptamine in good yields. Treatment of the proligands with the rare-earth metal trialkyl complexes RE(CH2SiMe3)3(THF)2 generated the corresponding unsymmetric N,N,C,O-tetradentate β-diketiminato rare-earth metal monoalkyl complexes LRE(CH2SiMe3) (L1, RE = Y (1a), Gd (1b), Yb (1c), Lu (1d); L2, RE = Y (2a), Gd (2b), Yb (2c), and Lu(2d)). During the process, the activation of the sp2 C-H bond at the 2-position of the indole ring led to the formation of an unprecedented β-diketiminato dianion L2-, bonding to the rare-earth metal ions in a chelating N,N,C,O-tetradentate manner. Further studies indicated that these tetradentate rare-earth metal complexes could initiate the Oppenauer oxidation of secondary alcohols into the corresponding ketones in high yields. In the case of primary alcohols, a tandem Oppenauer oxidation and cross-aldol condensation occurred unexpectedly. Various α-mono-substituted benzylidene acetones, α,α'-bis-substituted benzylidene acetones and cyclohexanones were obtained under mild conditions only by controlling the molar ratio of alcohols to ketones. Notably, all these alkenylation ketones exhibited exclusive E configuration.

β-Diketone functionalized covalent organic framework for detection of europium(III) and successive detection of tetracycline antibiotics

A new covalent organic framework (M-TT-COF) was designed and prepared by grafting Meldrum’s acid on the scaffold of TT-COF via esterification. M-TT-COF retained the crystal structure and high thermal stability of TT-COF. M-TT-COF as a “turn-on” fluorescence sensor can selectively identify and detect Eu3+ and tetracycline antibiotics in successive mode, the other metal ions, anions and antibiotics did not exert an obvious influence on the selective detection performance. The sensing performance has high sensitivity with low detection limits, 3.94 μM of M-TT-COF for Eu3+ and 0.56 μM of Eu@M-TT-COF for tetracycline antibiotics (oxytetracycline). In addition, both M-TT-COF and Eu@M-TT-COF have satisfactory recovery in the detection of Eu3+ and tetracycline antibiotics in the practical water samples, respectively. The mechanism of the fluorescence enhancement is attributed to the energy transfers from the β-diketone structure to Eu3+. This work successfully exploits a covalent organic framework as a “turn-on” fluorescence sensor in the identification and detection of rare earth metal ions and antibiotics.

Rare earth metals ion intercalated hydrated vanadium oxides for high-performance aqueous zinc-ion batteries

Hydrated vanadium oxide (V2O5·nH2O) is promising cathode candidates for aqueous rechargeable Zn-ion batteries (ZIBs) owing to its high theoretical specific capacity, abundant resources and environmentally friendly. However, the higher charge density of Zn2+ lead to its structural instability, cyclic degradation and sluggish Zn2+ diffusion kinetics. Herein, rare earth metal ions intercalated into the interlayer of V2O5·nH2O materials (abbreviated as RE-VOH) are successfully synthesized to expand interlayer spacing and stabilize the layered structure via a simple sol-gel method, among, the yttrium ion intercalated V2O5·nH2O (Y–VOH) exhibits a honeycomb porous microstructure and a remarkably enlarged interlayer distance (13.6 Å), which can not only increase the contact area between the electrode material and the electrolyte but also offer rapid diffusion channel for Zn2+. Meanwhile, the problem of vanadium dissolution of cathode materials is inhibited by the electrolyte additive strategy through adding suitable vanadium oxide sol to aqueous electrolyte, furthermore, the zinc anode modification strategy in electroplating process inhibits the formation of zinc dendrites. Benefitting from the synergistic effect of modification design for the ZIBs systems of cathode, electrolyte and anode, the overall electrochemical performance of Y–VOH electrode is significantly improved, delivering a large specific capacity of 337 mAh g−1 at the current density of 500 mA g−1 and excellent rate capability of 170 mAh g−1 at 10 A g−1, along with an outstanding capacity retention of 90 % over 3000 cycles. Additionally, systematical ex situ characterizations prove the (de)intercalation reversibility of Zn2+ storage mechanism for the Y–VOH cathode. This research may provide a new way for exploiting high performance vanadium-based materials for aqueous ZIBs.

Separation of rare earth elements using chelating agent-assisted electrodialysis: Phenomenological modeling and comparison with experimental data

The study presented here focuses on the development of a phenomenological model based on the Nernst-Planck equation for the separation of neodymium (Nd) and praseodymium (Pr) from a mixture containing cerium (Ce) and lanthanum (La) using chelated-assisted electrodialysis with hydroxyethylethylenediaminetriacetic acid (HEDTA) tri disodium salt as the chelating agent. This model considers solution selectivity, membrane selectivity, and ion migration within the membrane. The model is then used to study the optimal concentration of the chelating agent and pH conditions. It is demonstrated that the efficiency of the separation process could be enhanced through a multistage approach where the chelating agent concentration is maintained below the stoichiometric ratio of the elements to be masked. The model's predictive capabilities were evaluated by comparing its results with experimental data obtained at a HEDTA/Nd molar ratio of 1 and pH 3. The model showed an error of less than 26% for removal efficiency for all rare earth elements (REEs), and error values of 3% for purity and 9% for yield. These results indicate that the model can reasonably predict experimental outcomes with an acceptable level of accuracy. The developed model has the potential to be expanded for investigating chelation chemistry and electrodialysis operations involving various combinations of REEs and concentrations. It can be used to design experimental setups to study the effect of chelating agent to REE ratios and pH on key performance factors such as purity, yield, and separation factor. The versatility of the model makes it a valuable tool in the field of electrodialysis for the separation of rare earth metal ions using chelating agents.

Charge compensators achieve controlled self-reduction of Europium in BaMgP2O7

The exploitation of ecofriendly luminescent materials is crucial for advancing phosphor applications. Herein, Eu3+ self-reduction was performed using the energy-saving high-temperature solid-phase method in air environment. Achieving controllable self-reduction is challenging for high-valent rare-earth and transition metal ions. Therefore, we incorporate charge compensators, such as Li+/K+ to control the reaction and obtain hetero-valent Eu2+/Eu3+. Experimental results indicate that charge compensators can eliminate vacancies, suppress self-reduction, and affect luminescence properties. Moreover, a nonequivalent substitution mechanism about self-reduction using a charge compensation model is discussed here. Notably, Eu2+ shows a strong blue narrow-band emission peak at 410 nm with a full width at half maxima of 34 nm, overlapping well with that of chlorophyll. The phosphors are nontoxic and exhibit high contrast under ultraviolet light, which can be utilized for forensic science detection. The precisely controllable self-reduction of phosphors can contribute to the development of next-generation smart and green materials. Advanced applications of the phosphors for plant growth, fingerprint visualization, and screen printing are also explored.

Removal of heavy metal ions from acidic wastewater by constructing positively charged hollow fiber nanofiltration separating-layer based on Fe (III)/co deposition-quaternization

A surface positively charged nanofiltration (NF) membrane was successfully constructed to effectively remove heavy metal ions by co-deposition and quaternization strategy. The combination between Fe3+ and H2O2 accelerated the co-deposition of tannic acid (TA) and polyvinyl amine (PVAM) on the membrane surface. The mechanism by which metal ions accelerated co-deposition process to regulate membrane surface structure was elucidated. The convenient quaternary ammonium modification was carried out by reacting glycidyl trimethyl ammonium chloride (GTMAC), which significantly increased the potential and density of the membrane surface. The membrane had a high retention rate for heavy metal ions (1000 ppm (mg· L−1), Cr3+ (94.6 %), Fe3+ (93.7 %), Cu2+ (92.1 %), Ni2+ (90.2 %)), while maintaining an excellent water permeance (27.8 L m−2 h−1 bar−1). The membrane also presented outstanding separation performance for rare earth metal ion. In particular, the retention rate for 500 ppm (mg·L−1) Ce3+ was 95.3 %. The relationship between membrane surface potential, pore size and rejection of heavy metal revealed the removal mechanism. Furthermore, the membrane exhibited excellent acid-base resistance and long-term operation stability. This study supplies an effective surface modification method for preparing hollow fiber NF membranes used for removing heavy metal and recovering rare earth metal from wastewater.

Highly luminescent ultra-thin films with rare earth for plasmonic applications

Amphiphilic complexes with luminescent rare earth metal ions suitable for Lanmuir-Blodgett (LB) deposition have been synthesized. LB monolayers with closely packed Eu complexes deposited directly on silver demonstrate significant far-field emission in contrast to the theoretical predictions of full quenching. Angular radiation and polarization patterns of the electric and magnetic dipole emission of Eu3+ point to a high excitation efficiency of surface plasmon polaritons. Different luminescent behavior of closely packed emitters in comparison to diluted systems is tentatively attributed to the collective state of emitters in LB layers formed via near-field coupling with surface plasmons.

Sorption suction of lanthanum ion with new modified sorbents

In this article, a new modified synthetic high-molecular organic ionite is proposed for the sorption of rare-earth metal ions from water bodies. Concentrated citric acid (C6H8O7) is used as a modifier. The article shows an increase in the volume of La3+ extraction from the concentration of the C6H8O7 modifier. During the sorption extraction experiment, the concentration of La3+ extraction increases at 90 min. heating. AB-17-8 is referred to as strongly basic anionites, which work effectively at pH 2-14. Rare earth metals (REM) are widely used in various industries: electrical engineering, catalysts, permanent magnets and phosphors. All this causes anthropogenic pollution of the environment, living organisms, so it is necessary to study potential threats. To do this, we must be able to detect small amounts of REM in the environment and water. REM in wastewater is often determined by separation and concentration methods, such as co-precipitation, ion exchange, liquid-liquid extraction, electrolysis, etc. However, these methods have disadvantages, such as the duration and complexity of the study, as well as material costs.

SORPTION SUCTION OF LANTHANUM ION WITH NEW MODIFIED SORBENTS

In this article, a new modified synthetic high-molecular organic ionite is proposed for the sorption of rare-earth metal ions from water bodies. Concentrated citric acid (C6H8O7) is used as a modifier. The article shows an increase in the volume of La3+ extraction from the concentration of the C6H8O7 modifier. During the sorption extraction experiment, the concentration of La3+ extraction increases at 90 min. heating. AB-17-8 is referred to as strongly basic anionites, which work effectively at pH 2-14. Rare earth metals (REM) are widely used in various industries: electrical engineering, catalysts, permanent magnets and phosphors.All this causes anthropogenic pollution of the environment, living organisms, so it is necessary to study potential threats. To do this, we must be able to detect small amounts of REM in the environment and water.REM in wastewater is often determined by separation and concentration methods, such as co-precipitation, ion exchange, liquid-liquid extraction, electrolysis, etc. However, these methods have disadvantages, such as the duration and complexity of the study, as well as material costs.

Fabrication of magnesium oxide–calcium alginate hydrogel for scaffolding yttrium and neodymium from aqueous solutions

In this research, the possibility of using sustainable nano-MgO/Ca-alginate beads for efficient sorption of some rare earth metal ions such as neodymium(III) and yttrium(III) from an aqueous acidic solution was explored. The nano-MgO/Ca-alginate beads adsorbent was characterized before and after sorption of Nd(III) and Y(III) using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) techniques. Batch sorption parameters were investigated, such as contact time, initial metal ion concentration, and adsorbent dose (V/m). The calculated experimental results showed that the suitable selected sorption conditions were carried out using 100 mg/L of Nd(III) and Y(III) with nano MgO/Ca-alginate beads (contact time = 90 min, pH = 2, V/m = 0.05 L/g). The maximum sorption capacity of 0.1 g of nano MgO/Ca-alginate was found to be 7.85 mg/g and 5.60 mg/g for Nd(III) and Y(III), respectively. The desorption of Nd(III) and Y(III) from the loaded nano MgO/Ca-alginate was achieved with 1.0 M sulfamic acid and found to be 51.0% and 44.2%, respectively. The calculated thermodynamic parameters for the nano MgO/Ca-alginate/Nd/Y system show that the positive charge of ΔHo confirmed the endothermic nature of the sorption process, ΔSo (positive) indicates an increase in reaction system disordering, and ΔGo (negative) indicates a spontaneous process. These kinetic results indicate that the sorption process of Nd(III) and Y(III) on nano MgO/Ca-alginate beads is performed by the chemisorption process.

A Synergistic Three-Phase, Triple-Conducting Air Electrode for Reversible Proton-Conducting Solid Oxide Cells.

Reversible proton-conducting solid oxide cells (R-PSOCs) have the potential to be the most efficient and cost-effective electrochemical device for energy storage and conversion. A breakthrough in air electrode material development is vital to minimizing the energy loss and degradation of R-PSOCs. Here we report a class of triple-conducting air electrode materials by judiciously doping transition- and rare-earth metal ions into a proton-conducting electrolyte material, which demonstrate outstanding activity and durability for R-PSOC applications. The optimized composition Ba0.9Pr0.1Hf0.1Y0.1Co0.8O3-δ (BPHYC) consists of three phases, which have a synergistic effect on enhancing the performance, as revealed from electrochemical analysis and theoretical calculations. When applied to R-PSOCs operated at 600 °C, a peak power density of 1.37 W cm-2 is demonstrated in the fuel cell mode, and a current density of 2.40 A cm-2 is achieved at a cell voltage of 1.3 V in the water electrolysis mode under stable operation for hundreds of hours.

Rare earth Gd-doped NiFe2O4 @2D layered carbonaceous composite: Synthesis, structural evaluation and photocatalytic parameters studies

NiFe2O4 (F-1) and rare earth metal (Gd) doped NiFe2O4 (F-2) were prepared via a co-precipitation approach. Gd-NiFe2O4@rGO (F-3) was prepared via an ultrasonication route for the degradation of pendimethalin under sunlight. The structural confirmation of as-fabricated samples was done via XRD. The Tauc plot of F-1 showed a bandgap energy of 2.79 eV and F-2 exhibited a bandgap energy of 2.63 eV. The optical band gap was lowered due to the presence of rare-earth metal ions. NiFe2O4 and Gd-NiFe2O4 showed 48.88 %, and 61.11 % degradation of pendimethalin. Gd-NiFe2O4@rGO nanocomposite showed the highest degradation efficiency. It exhibited 84.44 % degradation of pendimethalin in 140 min at the rate of 0.01 min−1. The reason for the greater activity is due to the insertion of rare earth (Gd) ions and rGO sheets in the nickel ferrite. The doping with rare earth metal ions lowers the recombination of electrons and holes which was further supported by the addition of carbonaceous material. The surface area of the nickel ferrite was improved by rGO sheets and in turn more active sites were formed on the surface of the catalyst which fastens the rate of reaction.

Preparation of rare earth metal ions promoted MnOx@halloysite catalyst for highly efficient catalytic oxidation of toluene

Halloysite with nanotube structure is a potential functional support to prepare high-performance catalysts for the oxidation of volatile organic compounds (VOCs) at low temperatures. In this work, rare earth metal ions promoted MnOx@halloysite system were synthesized and demonstrated improved toluene oxidation. The obtained catalyst exhibits excellent catalytic performance, including toluene conversion efficiency (T90 = 232 °C), CO2 selectivity (100%), super long-term stability and water resistance under the condition of toluene concentration with 1000 ppm. It has been demonstrated that the La-promoted halloysite-supported MnOx catalyst increased the ratio of Mn3+ and the number of surface oxygen vacancies, facilitating the formation of active oxygen species and enhancing low-temperature catalytic activity. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy confirmed the intermediates generated during toluene oxidation. Toluene oxidation occurred via the benzyl alcohol → benzoate → anhydride reaction pathway over the obtained catalysts. This work provides a considerable experimental basis for understanding the catalytic performance and reaction mechanism of rare earth metal ions promoting the manganese oxides supported by clay minerals for toluene oxidation and paves the way for the development of high-performance catalysts toward toluene oxidation.