Preparation,Fabrication And Properties Of Layered Rare-earth Hydroxide Nanosheets

Layered rare-earth hydroxides(LREHs,RE₂（OH）_6-m[A^x?]_m/x?n H₂O)possess facile ion exchangeability and can be exfoliated into ultra-thin nanosheets,has promising applications in the fields of multicolor displayers and biochemistries.As the host layers of LREHs possess a high density of positive charges and a strong non-covalent bond between the layers,resulting in difficulty in the efficient preparation of single-layer nanosheets.Thus,in this thesis,the controllable exfoliation of LREHs was systematically studied,the obtained LREHs nanosheets were assembled into superlattice structures,moreover,the relationship between the superlattice structures and properties was further investigated.The main innovative research results of this work are as follows.（1）A facile method of exfoliation and preparation of LREHs nanosheets was proposed.A series of LREHs were synthesized,by direct sonication of the as-prepared LREHs in formamide,LREHs（RE=Sm—Er,and Y）monolayer nanosheets were obtained with a thickness of～1 nm and size of～500 nm.The suspension of nanosheet exhibited a more asymmetric coordination environment,resulting in a remarkably high red-light emission purity.The red-light emission purity of LEu H nanosheet increased from 87.0%to 91.4%.（2）The energy transfer process in the superlattice structure was revealed.Superlattice structured films of LREHs and transition metal oxides（TMOs）nanosheets were prepared through layer-by-layer（Lb L）method.Results show that the energy transfer between oxide nanosheets and hydroxide nanosheets is closely related to stacking sequence and energy matching in the multilayer films.In the superlattice structured film of LREH/TMO,the efficient energy transfer from TMO nanosheet to LREH nanosheet results in an enhanced photoluminescent property.The emission intensity of（Gd Eu/Ti O）₁₀and（Gd Tb/Ta O）₁₀ superlattice film was14 times and 5 times higher than that of（Gd Eu/PSS）₁₀and（Gd Tb/PSS）₁₀film,respectively.（3）Color-controllable photoluminescence in the component-fixed self-standing membrane was achieved.Drastically enhanced emission and color tunable self-standing LREH/TMO membranes were fabricated by filtrating corresponding suspensions.The efficient energy transfer from TMO nanosheet to LREH nanosheet is the main energy transfer in the LREH/TMO self-standing membran.The superlattice membrane Gd Eu/Ti O and Gd Tb/Ta O showed drastically enhanced emission intensity,21.5 and 38.6 times,higher than that of Gd Eu and Gd Tb,respectively,as well as a higher color purity and longer lifetime.The（Gd Eu/Ti O）/（Gd Tb/Ta O）integrated membrane exhibited tunable color under different excitation wavelengths which changed from green to green-blue,then to red-pink,and finally to yellow-rose.Moreover,the superlattice membrane exhibited strong and stable cathodoluminescence（CL）under continuous cathode-ray radiation.The CL intensity of Gd Tb/Ta O membrane increased to as high as 180%after 40 minutes of radiation.（4）Bifunctional material with photothermal and MRI properties was prepared.The hybrid material LGd H/Ti₃C₂（LGd H/TC）with LGd H and Ti₃C₂（TC）nanosheets was prepared through electrostatic adsorption method.The LGd H/TC exhibited enhanced near infrared（NIR）photothermal property and magnetic resonance imaging（MRI）performance.The mass absorption coefficient?of LGd H/TC was 50.0 L g?¹ cm?¹ at 805 nm.Under irradiation for 10 min,the temperature increased from room temperature up to 67.2°C.Moreover,the LGd H/TC shows good T1-weight MRI performance.