Grafting of terbium(iii) complexes onto layered rare-earth hydroxide nanosheets to fabricate novel optical fiber temperature sensors

Two-dimensional nanomaterials based on rare earth elements for biomedical applications

As a kind of star materials, two-dimensional (2D) nanomaterials have attracted tremendous attention for their unique structures, excellent performance and wide applications. In recent years, layered rare earth-based or doped nanomaterials have become a new important member of the 2D nanomaterial family and have attracted significant interest, especially layered rare earth hydroxides (LREHs) and layered rare earth-doped perovskites with anion-exchangeability and exfoliative properties. In this review, we systematically summarize the synthesis, exfoliation, fabrication and biomedical applications of 2D rare earth nanomaterials. Upon exfoliation, the LREHs and layered rare earth-doped perovskites can be dimensionally reduced to ultrathin nanosheets which feature high anisotropy and flexibility. Subsequent fabrication, especially superlattice assembly, enables rare earth nanomaterials with diverse compositions and structures, which further optimizes or even creates new properties and thus expands the application fields. The latest progress in biomedical applications of the 2D rare earth-based or doped nanomaterials and composites is also reviewed in detail, especially drug delivery and magnetic resonance imaging (MRI). Moreover, at the end of this review, we provide an outlook on the opportunities and challenges of the 2D rare earth-based or doped nanomaterials. We believe this review will promote increasing interest in 2D rare earth materials and provide more insight into the artificial design of other nanomaterials based on rare earth elements for functional applications.

Recovery of terbium by Lysinibacillus sp. DW018 isolated from ionic rare earth tailings based on microbial induced calcium carbonate precipitation

Microbial induced calcium carbonate precipitation (MICP) is considered as an environmentally friendly microbial-based technique to remove heavy metals. However, its application in removal and recovery of rare earth from wastewaters remains limited and the process is still less understood. In this study, a urease-producing bacterial strain DW018 was isolated from the ionic rare earth tailings and identified as Lysinibacillus based on 16S rRNA gene sequencing. Its ability and possible mechanism to recover terbium was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and fourier transform infrared spectroscopy (FTIR). The results showed that the urease activity of DW018 could meet the biomineralization requirements for the recovery of Tb3+ from wastewaters. The recovery rate was as high as 98.28% after 10 min of treatment. The optimal conditions for mineralization and recovery were determined as a bacterial concentration of OD600 = 1.0, a temperature range of 35 to 40°C, and a urea concentration of 0.5%. Notably, irrespective of CaCO3 precipitation, the strain DW018 was able to utilize MICP to promote the attachment of Tb3+ to its cell surface. Initially, Tb3+ existed in amorphous form on the bacterial surface; however, upon the addition of a calcium source, Tb3+ was encapsulated in calcite with the growth of CaCO3 at the late stage of the MICP. The recovery effect of the strain DW018 was related to the amino, hydroxyl, carboxyl, and phosphate groups on the cell surface. Overall, the MICP system is promising for the green and efficient recovery of rare earth ions from wastewaters.

Recyclable and flexible Bi(Ho3+-Yb3+)OBr/g-C3N4 composite porous fiber for efficient water purification and real-time temperature sensing

Herein, an electrospinning porous nanofiber with large specific surface area, excellent flexibility, remarkable tensile strength, and high stability of thermal degradation has been developed by loading Ho3+/Yb3+ co-doped BiOBr/g-C3N4 (BHY/CN) heterojunction photocatalysts on polyacrylonitrile (PAN) nanofibers. The optimized BHY/CN-2 nanofiber demonstrates outstanding photocatalytic activity for the degradation of 98.83% tetracycline (TC, 60 min) and 99.06% rhodamine B (RhB, 90 min) under simulated sunlight irradiation, and maintains a high level of reusability and recycling stability in three cycles. In addition, temperature monitoring of the catalytic degradation process can be feedback by (5F4, 5S2) → 5I8 and 5F5 → 5I8 radiation transitions of Ho3+ with excellent sensitivity. More importantly, the nanofiber luminescence performance is enhanced by the doping of g-C3N4, which maintain the effective upconversion luminescence properties even in water, providing a reliable reference for real-time monitoring and feedback of the operating temperature, and further expanding the application fields of photocatalysts.

A self-powered wearable brain-machine-interface system for real-time monitoring and regulating body temperature

Heat stroke that may cause acute central nervous system dysfunction, multiple organ dysfunction and even death has become a typical health problem in tropical developing countries. The primary goal of heat stroke treatment is to lower core body temperature, which necessitates physical or medical cooling in time. Here, we design a new self-powered wearable brain-machine-interface system for real-time monitoring and regulating body temperature. This system can monitor body temperature in real time and transmit neural electrical stimulation signals into specific brain regions to lower the body temperature. The whole system can work without an external power supply and be powered by the body itself through the piezoelectric effect. The system comprises a temperature detecting unit, a power supply unit, a data processing module, and a brain stimulator. Demonstration of the system with stimulation electrodes implanted in the median preoptic nucleus brain region in mice reveals an evident decrease in body temperature (1.0 °C within 15 min). This self-powered strategy provides a new concept for future treatment of heat stroke and can extend the application of brain-machine-interface systems in medical care.

Facile Preparation of YVO4: RE Films and the Investigation of Photoluminescence

Facile preparation of YVO4 films was hydrothermally achieved within 1 h by using layered yttrium hydroxide (Y2(OH)5NO3·nH2O) films as the sacrificial precursor in the presence of excess NaVO3 at pH~8, without subsequent heat treatment. Detailed structures and optical properties of the products were obtained by using a combination of XRD, FT-IR, FE-SEM, HR-TEM, and PLE/PL techniques. The phase and morphological evolution from Y2(OH)5NO3·nH2O to YVO4 was unveiled by varying the reaction time. Photoluminescence spectra showed that the Eu3+ doped YVO4 films exhibited the characteristic emission of Eu3+, with the transition 5D0–7F2 (614 nm, red) being the dominant; while Dy3+ activator doped YVO4 films exhibited the characteristic emission of Dy3+, with the transition 4F9/2–6H13/2 (575 nm, green) being the most dominant.

Eroding the Surface of Rare Earth Microcrystals through Vanadate Ions for Considerable Improvement of Luminescence

Developing an efficient approach to improve the luminescence of the phosphors without heating processing is a challenge, but attracts much attention. In the present paper, prismatic microcrystals of RE4O(OH)9NO3 (RE = Y, Eu) were synthesized by a hydrothermal reaction at 180 °C for 24 h. The reaction with VO3− did not change the crystal structure of the microcrystals and VO3− substituting for NO3− anions did not take place. However, it contributed to the formation of amorphous particles containing VO3− on the surface of a prism, which is similar to the surface corrosion of a metal, called “surface eroding”. Therefore, surface modification was successfully achieved by eroding the surface of the microcrystals through the reaction with vanadate ions. As a result of VO3−→Eu3+ energy transfer and the light-harvesting ability of VO3−, the red emission intensity at 617 nm of the modified microcrystals greatly increased. Eroding the surface of rare earth microcrystals recommends a new paradigm for luminescence improvement of rare earth compounds.

Low-temperature synthesis of NaRE(WO4)2 films via anion exchange from Layered rare-earth hydroxides (LRHs) films, phase/morphology evolution and photoluminescence

Alkaline lanthanide tungstates NaRE(WO4)2 (RE = La-Ho, and Y) films were hydrothermally synthesized via anion exchange using the electrodeposited layered rare-earth hydroxide (RE2(OH)5NO3·nH2O) films as precursor template in the presence...

Fabrication of REVO4 films via sacrificial conversion from Layered rare-earth hydroxides (LRHs) films: the investigation of the transition mechanism and their photoluminescence

The rare-earth orthovanadate REVO4 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Y) films were directly synthesized within 2 hours by sacrificial conversion from the electrodeposited...

General Synthesis of Layered Rare-Earth Hydroxides (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, Y) and Direct Exfoliation into Monolayer Nanosheets with High Color Purity

Layered rare-earth hydroxides (LREHs) are promising optical and magnetic materials, while it is hard to obtain monolayer nanosheets through a direct exfoliation. In this study, organic dodecyl sulfate (C₁₂H₂₅SO₄^-, DS^-) was used to prepare LREHs. In-plane lattice parameters of the LREHs decreased from Sm³⁺ to Er³⁺, correlating well with the monotonically decreasing ionic radius. Conversely, the interlayer spacing slightly increased with the increase of host layer charge density and corresponding intercalated DS^- contents. By a direct sonication of the LREHs in formamide, nanosheets were obtained with a thickness of ∼1 nm and size of ∼500 nm. Compared to the bulk crystals, exfoliation resulted in a slight elongation of in-plane lattice constants and a more asymmetric coordination environment. The suspension of europium hydroxide nanosheets exhibited a remarkably high red-light emission purity (91.4%). This work demonstrated an important strategy toward an efficient synthesis of well-defined LREH nanosheets with high color purity.

Layered terbium hydroxides for simultaneous drug delivery and imaging

Layered rare-earth hydroxides have begun to gather increasing attention as potential theranostic platforms owing to their extensive intercalation chemistry combined with magnetic and fluorescent properties. In this work, the potential of layered terbium hydroxide (LTbH) as a platform for simultaneous drug delivery and fluorescence imaging was evaluated. LTbH-Cl ([Tb2(OH)5]Cl·yH2O) was loaded with three nonsteroidal anti-inflammatory drugs (diclofenac, ibuprofen, and naproxen) via ion-exchange. Drug release studies in phosphate buffered saline (pH = 7.4) revealed all three formulations release their drug cargo rapidly over the course of approximately 5 hours. In addition, solid state fluorescence studies indicated that fluorescence intensity is strongly dependent on the identity of the guest anion. It was postulated that this feature may be used to track the extent of drug release from the formulation, which was subsequently successfully demonstrated for the ibuprofen loaded LTbH. Overall, LTbH exhibits good biocompatibility, high drug loading, and a strong, guest-dependent fluorescence signal, all of which are desirable qualities for theranostic applications.

Superlattice films of semiconducting oxide and rare-earth hydroxide nanosheets for tunable and efficient photoluminescent energy transfer

Europium and terbium doped layered gadolinium hydroxides were prepared by microwave assisted hydrothermal precipitation. They were subsequently exfoliated into nanosheets by sonication treatment in formamide. The thickness of the nanosheets (LGdH:Eu and LGdH:Tb) was found to be approximately 1 nm, exemplifying a single-layer feature. Multilayer and superlattice films were prepared through layer-by-layer (LbL) deposition of exfoliated hydroxide nanosheets with a polyanionic electrolyte (polystyrene sulfonate, PSS) and heteroassembly with semiconducting oxide nanosheets (Ti0.87O20.52- and TaO3-), respectively. Compared to the multilayers of (LGdH:Eu/PSS)n and (LGdH:Tb/PSS)n, the superlattices of (LGdH:Eu/Ti0.87O20.52-)n and (LGdH:Tb/TaO3-)n exhibited significantly enhanced photoluminescence intensity, ∼14 times and ∼5 times, respectively. The photoenergy absorbed by the semiconducting nanosheets can be transferred to the excited states of rare-earth hydroxide nanosheets for enhanced photoluminescence emission. Further investigation on the stacking sequence of the nanosheets revealed that direct neighboring and energy level matching with semiconducting nanosheets was essential for realizing efficient energy transfer across the nanosheet interface. Annealing at 600 °C could further enhance the emission intensity of the superlattice structured films. The current work demonstrates an important strategy for hetero-assembling nanosheets at the molecular level with a carefully designed interface for tunable and enhanced functionalities.

A groundbreaking strategy for fabricating YAG:Ce3+ transparent ceramic films via sintering of LRH nanosheets on a sapphire substrate

Here, we proposed a groundbreaking strategy for fabricating YAG:Ce3+ transparent ceramic films via a novel interface reaction of LRH nanosheets with a sapphire substrate without a tedious process. The incorporation of Gd3+ greatly enhanced the emission intensity of the ceramic film by ∼11.3 times. The prepared transparent ceramic film with a high transmittance of ∼97% is a promising photo-converter for WLEDs.

Nanoscale light-matter interactions in metal-organic frameworks cladding optical fibers

The utilization of refractive index (RI) change due to guest-host interactions between the guest volatile organic compound vapor and porous metal-organic frameworks (vapor-MOF interactions) is promising in photonic vapor sensors. Therefore, the study of light-matter interactions in nanoporous metal-organic frameworks (MOFs) is fundamental and essential for MOF-based photonic devices. In this work, the manipulation of light in MOFs to investigate the vapor-MOF interactions by using optical fiber devices is demonstrated. The vapor-MOF interactions and the light-vapor interactions (light in MOFs to sense the RI changes resulting from the vapor-MOF interactions) are investigated. The cladding mode is excited by a long-period fiber grating (LPFG) for evanescent field sensing in a ZIF-8 sensitive coating. The experimental results combining quantum chemical calculations and optical simulations reveal the relationships between the microscopic energy of vapor desorption, RI changes and evanescent field enhancement in ZIF-8 during the vapor-MOF interactions. With exceptionally large RI changes, the evanescent field of cladding mode in ZIF-8 is greatly enhanced to sense the vapor-MOF interactions. As a proof-of-concept, a LPFG sensor with ZIF-8 coating showed a high sensitivity of 1.33 pm ppm-1 in the linear range from 9.8 ppm to 540 ppm for the sensing of ethanol vapor. The investigation of light-matter interactions in ZIF-8 provides a useful guideline for the design and fabrication of MOF-based optical waveguide/fiber sensors.