Mengjiao Li

Superior adsorption and photoinduced carries transfer behaviors of dandelion-shaped Bi 2 S 3 @MoS 2 : experiments and theory

The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi2S3 microsphere compactly decorated with wing-shaped few layered MoS2 lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi2S3 and MoS2. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi2S3 to MoS2, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with Ilight/Idark ratio 567).

Copper ferrites@reduced graphene oxide anode materials for advanced lithium storage applications

Copper ferrites are emerging transition metal oxides that have potential applications in energy storage devices. However, it still lacks in-depth designing of copper ferrites based anode architectures with enhanced electroactivity for lithium-ion batteries. Here, we report a facile synthesis technology of copper ferrites anchored on reduced graphene oxide (CuFeO2@rGO and Cu/CuFe2O4@rGO) as the high-performance electrodes. In the resulting configuration, reduced graphene offers continuous conductive channels for electron/ion transfer and high specific surface area to accommodate the volume expansion of copper ferrites. Consequently, the sheet-on-sheet CuFeO2@rGO electrode exhibits a high reversible capacity (587 mAh g−1 after 100 cycles at 200 mA g−1). In particular, Cu/CuFe2O4@rGO hybrid, which combines the advantages of nano-copper and reduced graphene, manifests a significant enhancement in lithium storage properties. It reveals superior rate capability (723 mAh g−1 at 800 mA g−1; 560 mAh g−1 at 3200 mA g−1) and robust cycling capability (1102 mAh g−1 after 250 cycles at 800 mA g−1). This unique structure design provides a strategy for the development of multivalent metal oxides in lithium storage device applications.

Exploring optoelectronic properties and mechanisms of layered ferroelectric K 4 Nb 6 O 17 nanocrystalline films and nanolaminas

Two-dimensional layered K4Nb6O17 (KN) was easily formed as a secondary phase caused by the volatilization of alkali metal ions, when preparing ferroelectric KxNa1−xNbO3 based ceramics and films. In this work, it was believed that KN film is with weak ferroelectricity and has a little effect on the ferroelectric properties of KxNa1−xNbO3 based films. Moreover, temperature dependent (77–500 K) dielectric functions of KN film have been firstly extracted by fitting ellipsometric spectra with the Adachi dielectric function model and a four-phase layered model. The high-frequency dielectric constant linearly increases and optical band gap slightly decreases with increasing the temperature. We also research its photoelectrochemical properties and its application in high-efficient light-induced H2 evolution. In addition, X-ray photoelectron spectroscopy, Raman scattering, temperature dependent transmittance and infrared reflectance spectra, and first-principles calculation were conjointly performed to further reveal the intrinsic optoelectronic features and relevant mechanisms of KN.

Free-anchored Nb2O5@graphene networks for ultrafast-stable lithium storage

Orthorhombic Nb2O5 (T-Nb2O5) has structural merit but poor electrical conductivity, limiting their applications in energy storage. Although graphene is frequently adopted to effectively improve its electrochemical properties, the ordinary modified methods cannot meet the growing demands for high-performance. Here, we demonstrate that different graphene modified routes play a vital role in affecting the electrochemical performances of T-Nb2O5. By only manual shaking within one minute, Nb2O5 nano-particles can be rapidly adsorbed onto graphene, then the free-anchored T-Nb2O5@graphene three-dimensional networks can be successfully prepared based on hydrogel method. As for the application in lithium-ion batteries, it performs outstanding rate character (129 mA h g-1 (25C rate), 110 mA h g-1 (50C rate) and 90 mA h g-1 (100C rate), correspond to 79%, 67% and 55% capacity of 0.5C rate, respectively) and excellent long-term cycling feature (∼70% capacity retention after 20000 cycles). Moreover, it still maintains similar ultrafast-stable lithium storage performances when Cu foil is substituted by Al foil as current collector. In addition, relevant kinetics mechanisms are also expounded. This work provides a versatile strategy for the preparation of graphene modified Nb2O5 or other types of nanoparticles.

Boosted adsorption–photocatalytic activities and potential lithium intercalation applications of layered potassium hexaniobate nano-family

Two-dimensional layered K4Nb6O17 (KN) possesses two different types of interlayer regions, which is of great interest for applications in energy conversion, environmental purification, etc. Although the photocatalytic properties of KN have been extensively studied, there still remain some pivotal problems that need to be clarified for future applications. Here we demonstrate that the KN nano-family (including KN nanolaminas and nano hollow spheres) can be derived from the same Nb2O5-based hydrothermal reaction. Different morphologies of KN show unique microstructures and optoelectronic properties. Remarkably, the initial pH of a dye solution has been proven to play a vital role in affecting the adsorption and photocatalytic performances of KN. Due to the effects of dye sensitization, KN shows superior photodegradation performance under both ultraviolet and visible light. Based on these crucial results, a highly-efficient and feasible scheme has been proposed to deal with dye wastewater. In addition, KN as a potential anode material for lithium ion batteries has been investigated for the first time. The present work could be helpful in broadening the multifunctional applications of KN and other layered niobate materials.

Interband electronic transitions and phase diagram of PbZr1−x Ti x O3 (0.05 ≤ x ≤ 0.70) ceramics: ellipsometric experiment and first-principles theory

The thermal evolutions of optical properties and phase transitions of PbZr1−x Ti x O3 (PZT) ceramics as the functions of Ti compositions have been systemically explored by means of temperature dependent ellipsometric spectra and first-principles calculations. Two interband electronic transitions have been obtained by fitting the second derivatives of the complex dielectric functions and the physical origins can be explained with the aid of theoretical calculations. Based on the interband transitions, the phase diagram of PZT ceramics can be well-established. Importantly, dramatic Zr-rich ion clusters at 70 K and two intermediate regions are captured. The Zr-side intermediate phase is attributed to the tilting competitions of high [FER(HT)] and low [FER(LT)] temperature rhombohedral structures. Moreover, a wider range of the monoclinic (M) region from x = 0.28 to 0.50 has been determined than previously reported. Interestingly, one can conclude that a more superior performance of PZT may be obtained with the larger M domains relying on external strains or fields.

Controllable interlayer space effects of layered potassium triniobate nanoflakes on enhanced pH dependent adsorption-photocatalysis behaviors

Despite the extensive study of two-dimensional layered KNb3O8 (KN), there still remains some vital problems need to be clarified for future applications in environmental purification. Here we demonstrated the successful preparation of interlayer-controlled KN nanoflakes using alkaline hydrothermal conditions by adjusting the amount of thiourea in the reaction. This process resulted in KN nanoflakes with a larger specific surface area than previously reported. Moreover, the initial pH of dye solution and discrepant preferential orientation of interlayer peak have been proved to significantly influence the adsorption and photocatalysis performances of KN. In addition, relevant photocatalysis mechanisms have been expounded, by combined the first-principles calculation. The present work could be helpful in revealing the intrinsic adsorption-photocatalysis features of KN and other similar niobates.

Facile fabrication of 3D porous MnO@GS/CNT architecture as advanced anode materials for high-performance lithium-ion battery

To overcome inferior rate capability and cycle stability of MnO-based anode materials for lithium-ion batteries (LIBs), we reported a novel 3D porous MnO@GS/CNT composite, consisting of MnO nanoparticles homogeneously distributed on the conductive interconnected framework based on 2D graphene sheets (GS) and 1D carbon nanotubes (CNTs). The distinctive architecture offers highly interpenetrated network along with efficient porous channels for fast electron transfer and ionic diffusion as well as abundant stress buffer space to accommodate the volume expansion of the MnO nanoparticles. The MnO@GS/CNT anode exhibits an ultrahigh capacity of 1115 mAh g-1 at 0.2 A g-1 after 150 cycles and outstanding rate capacity of 306 mAh g-1 at 10.0 A g-1. Moreover, a stable capacity of 405 mAh g-1 after 3200 cycles can still be achieved, even at a large current density of 5.0 A g-1. When coupled with LiMn2O4 (LMO) cathode, the LMO [Formula: see text] MnO@GS/CNT full cell characterizes an excellent cycling stability and rate capability, indicating the promising application of MnO@GS/CNT anode in the next-generation LIBs.