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Facile synthesis of biocompatible magnetic titania nanorods for T-1-magnetic resonance imaging and enhanced phototherapy of cancers
No full textCancer treatment has been recently energized by nanomaterials that simultaneously offer diagnostic and therapeutic effects. Among the imaging and treatment modalities in frontline research today, magnetic resonance imaging (MRI) and phototherapy have gained significant interest due to their noninvasiveness among other intriguing benefits. Herein, Fe(iii) was adsorbed on titanium dioxide to develop magnetic Fe-TiO2 nanocomposites (NCs) which leverage the Fe moiety in a double-edge-sword approach to: (i) achieve T-1-weighted MRI contrast enhancement, and (ii) improve the well-established photodynamic therapeutic efficacy of TiO2 nanoparticles. Interestingly, the proposed NCs exhibit classic T-1 MRI contrast agent properties (r(1) = 1.16 mM(-1) s(-1)) that are comparable to those of clinically available contrast agents. Moreover, the NCs induce negligible cytotoxicity in traditional methods and show remarkable support to the proliferation of intestine organoids, an advanced toxicity evaluation system based on three-dimensional organoids, which could benefit their potential safe application for in vivo cancer theranostics. Aided by the Fenton reaction contribution of the Fe component of the Fe-TiO2 NCs, considerable photo-killing of cancer cells is achieved upon UV irradiation at very low (2.5 mW cm(-2)) intensity in typical cancer PDT. It is therefore expected that this study will guide the engineering of other biocompatible magnetic titania-based nanosystems with multi-faceted properties for biomedical applications
Increasing Accessible Subsurface to Improving Rate Capability and Cycling Stability of Sodium-Ion Batteries
No full textNumerous studies have reported that the enhancement of rate capability of carbonaceous anode by heteroatom doping is due to the increased diffusion-controlled capacity induced by expanding interlayer spacing. However, percentage of diffusion-controlled capacity is less than 30% as scan rate is larger than 1 mV s(-1), suggesting there is inaccuracy in recognizing principle of improving rate capability of carbonaceous anode. In this paper, it is found that the heteroatom doping has little impact on interlayer spacing of carbon in bulk phase, meaning that diffusion-controlled capacity is hard to be enhanced by doping. After synergizing with tensile stress, however, the interlayer spacing in subsurface region is obviously expanded to 0.40 nm, which will increase the thickness of accessible subsurface region at high current density. So SRNDC-700 electrodes display a high specific capacity of 160.6 and 69.5 mAh g(-1) at 20 and 50 A g(-1), respectively. Additionally, the high reversibility of carbon structure insures ultralong cycling stability and hence attenuation of SRNDC-700 is only 0.0025% per cycle even at 10 A g(-1) for 6000 cycles. This report sheds new insight into mechanism of improving electrochemical performance of carbonaceous anode by doping and provides a novel design concept for doping carbon
Flexible high-energy and stable rechargeable vanadium-zinc battery based on oxygen defect modulated V2O5 cathode
No full textThe development of earth-abundant, high-capacity and stable cathode materials for robust aqueous Zn-ion batteries (ZIBs) is an ongoing challenge. With the merits of suitable operating voltage window and highly reversible redox reaction, vanadium oxide has recently emerged as an attractive cathode material. Herein, an oxygen defect modulated binder-free V2O5 nanorods (named as PVO@C) was constructed for aqueous/quasi-solid-state Zn ion battery. Accompanying the fast electron transport ability, increased concentration of oxygen defect and enhanced active sites, the aqueous PVO@C//Zn battery delivers an excellent high capacity of 385.34 mAh g(-1) at 0.13 A g(-1) and robust long-term life span of 86.7% capacity retention after 5000 cycles with nearly 100% coulomb efficiency. In particular, the assembled quasi-solid-state ZIBs exhibited the high voltage of 1.3 V, yielding an admirable energy density of 10.5 mWh cm(3) at a power density of 33.4 mW cm(3) and admirable cycling performance. What's more, the solid-state ZIB exhibits extremely high safety, wettability and wear-ability over the lithium ion batteries. It performs well even at a variety of severe hazardous conditions, such as punctured, soaked, bent, sewed, washed, cut, and hammered conditions. This work innovatively proposes the synergistic effect of oxygen defect modulation and phosphorus doping to optimize reaction kinetics, which will lead to further improvements in the performance of metal oxides electrode. This strategy can be extended to electrode materials of other battery systems for the construction of highly efficient flexible energy storage devices and accelerated the commercialization of wearable electronics technology
The origin of the 500 nm luminescence band related to oxygen vacancies in ZrO2
No full textIn this paper, ion-beam-induced luminescence (IBIL) spectra of raw ZrO2 irradiated with 2 MeV H+ ions and photoluminescence (PL) spectra of annealed (200, 500 and 800 degrees C in air, nitrogen or oxygen) ZrO2 were investigated. The luminescence intensity decreased with increasing fluence, which indicated that the concentration of luminescence centers decreased during irradiation. The PL spectral results show that, with increasing partial pressure of oxygen during annealing, the intensity of luminescence decreases due to the decrease in oxygen vacancies. First-principles calculations were used to study the formation energy and transition level for oxygen vacancies (Vo), Ti-substituted Zr (Ti) and Ti adjacent to the nearest Vo (Ti-Vo) complex. The binding energies of Ti3+ and Vo(+) are 2.10 eV, which indicates that oxygen vacancies benefit the formation of Ti3+. The calculated configuration coordinate diagram and IBIL results indicated that Vo is not the luminescence origin. A new light-emitting structure of the Ti-Vo complex (F-A center) structure was proposed based on our calculations and previous studies. The calculated results of the luminescence model match the PL and IBIL spectra remarkably. The emission band of ZrO2 at approximately 500 nm was assigned to the F-A center or Ti3+ (the e(g) to t(2g) transition) adjacent to Vo(+)
Tailoring Highly Ordered Graphene Framework in Epoxy for High-Performance Polymer-Based Heat Dissipation Plates
No full textAs the power density and integration level of electronic devices increase, there are growing demands to improve the thermal conductivity of polymers for addressing the thermal management issues. On the basis of the ultrahigh intrinsic thermal conductivity, graphene has exhibited great potential as reinforcing fillers to develop polymer composites, but the resultant thermal conductivity of reported graphenebased composites is still limited. Here, an interconnected and highly ordered graphene framework (HOGF) composed of high-quality and horizontally aligned graphene sheets was developed by a porous film-templated assembly strategy, followed by a stress-induced orientation process and graphitization post-treatment. After embedding into the epoxy (EP), the HOGF/EP composite (24.7 vol %) exhibits a record-high in-plane thermal conductivity of 117 W m(-1) K-1, equivalent to similar to 616 times higher than that of neat epoxy. This thermal conductivity enhancement is mainly because the HOGF as a filler concurrently has high intrinsic thermal conductivity, relatively high density, and a highly ordered structure, constructing superefficient phonon transport paths in the epoxy matrix. Additionally, the use of our HOGF/EP as a heat dissipation plate was demonstrated, and it achieved 75% enhancement in practical thermal management performance compared to that of conventional alumina for cooling the high-power LED
Hyperbranched flame retardant to simultaneously improve the fire-safety, toughness and glass transition temperature of epoxy resin
No full textIt is highly desired yet very challenging to overcome the flammability and brittleness of epoxy resin without compromising its glass transition temperature (T-g). Herein, an epoxy-terminated hyperbranched flame retardant (EHBFR) was designed and synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and renewable protocatechualdehyde as well as guaiacol. When the synthesized EHBFR was taken to modify diglycidyl ether of bisphenol A (DGEBA), it is found that the incorporation of EHBFR remarkably improved its fire safety, endowing it with a UL-94 V-0 rating and a limiting oxygen index (LOI) of 33.0 vol%. Meanwhile, the notched impact strength of modified DGEBA at 25 and -196 degrees C (quenched by liquid nitrogen) exhibited significant increment by 135% (from 3.39 to 7.97 KJ/m(2)) and 114% (from 2.34 to 5.01 KJ/m(2)), respectively. Moreover, the T-g of modified epoxy resin did not show any decrease, and even increased from 172 to 194 degrees C when the content of EHBFR was 10 wt%, due to the synergistic effect of rigid DOPO-containing groups and high crosslink density. This work offers an efficient strategy for constructing high-performance epoxy thermosets with excellent flame retardancy, superior toughness and strength, as well as elevated T-g
Surface reinforcement doping to suppress oxygen release of Li-rich layered oxides
No full textLi-rich layered oxides can deliver ultrahigh capacities which stem from a blend of cationic redox and mostly lattice oxygen redox. However, the oxygen redox reaction often leads to structure transition and oxygen release from the material surface. Herein, the surface doping of B is conducted via a molten salt method, which creates a thin reinforcement layer containing stable B-O bonds. X-ray photoelectron spectroscopy reveals that the doping of B only acts on the material surface and cannot inhibit oxygen redox in the bulk. Differential electrochemical mass spectroscopy measurement demonstrates that the surface protective layer effectively reduces the oxygen release of LLOs. A combination of X-ray diffraction and transmission electron microscope analyses confirm the enhanced structural stability. As a consequence, the target material displays a high reversible capacity of 275 mAh g-1 at 0.1C and a suppressed voltage decay rate of 2.5 mV per cycle during the first 80 cycles (at 0.2C, 2.0-4.8V). The findings highlight the essential role of stable surface oxygen framework in cycling stability, and demonstrate the effectiveness of surface reinforcement doping in reducing oxygen release
Single Atom-Modified Hybrid Transition Metal Carbides as Efficient Hydrogen Evolution Reaction Catalysts
No full text2D transition metal carbides and nitrides (MXenes) are promising hydrogen evolution reaction (HER) catalysts owing to their metallic conductivity, abundant surface active sites, and high specific surface area. The introduction of a single transition metal atom (TM) at the surface is a good way to improve the HER performance of MXenes. However, the effect of TM on MXenes in previous theoretical studies focused on pure functional groups, and ignored the hybrid-functionalized ones, which are mostly observed in experiments. Herein, the HER performance of four O/F ratios stable hybrids MXenes, Ti2CTx (T = -O, -F), is explored. Ti2CO1.33F0.67 exhibits superior HER catalytic activity, comparable to that of platinum metals. Further combinatorial screening of approximate to 200 TMs based on Ti2CTx structures suggests that Rh, Ti, Ir, and Pt are optimal TM candidates that enhance the sensitivity to strain modulation and reduce the activation barrier for hydrogen generation. A descriptor psi is used to quantify HER performance and reveals the role of the electron filling of TM to the antibonding orbitals. These findings propose feasible candidates with high HER performance through single-atom modification for hybrid-functional MXenes, and a useful descriptor to screen for MXenes with desirable catalytic properties
Indication of Strongly Correlated Electron Transport and Mott Insulator in Disordered Multilayer Ferritin Structures (DMFS)
No full textElectron tunneling in ferritin and between ferritin cores (a transition metal (iron) oxide storage protein) in disordered arrays has been extensively documented, but the electrical behavior of those structures in circuits with more than two electrodes has not been studied. Tests of devices using a layer-by-layer deposition process for forming multilayer arrays of ferritin that have been previously reported indicate that strongly correlated electron transport is occurring, consistent with models of electron transport in quantum dots. Strongly correlated electrons (electrons that engage in strong electron-electron interactions) have been observed in transition metal oxides and quantum dots and can create unusual material behavior that is difficult to model, such as switching between a low resistance metal state and a high resistance Mott insulator state. This paper reports the results of the effect of various degrees of structural homogeneity on the electrical characteristics of these ferritin arrays. These results demonstrate for the first time that these structures can provide a switching function associated with the circuit that they are contained within, consistent with the observed behavior of strongly correlated electrons and Mott insulators
Kinetostatic Modeling of Dual-Drive H-Type Gantry With Exchangeable Flexure Joints
No full textThe flexure joints are proposed to replace the rigid assembly between the cross-arm and the moving carriages of dual-drive H-type gantry (DHG) for higher reliability and fine rotational alignments. In the literature, the flexure joint of the DHG is modeled as an ideal linear torsional spring, resulting in an inaccurate estimation of the cross-arm's angle. In this study, a generalized analytical kinetostatic model of flexure-linked DHG is built by considering the geometric nonlinearities. The expressions of beam coefficients in the model are obtained from either beam constraint model (BCM) or Timoshenko BCM (TBCM) according to the given criterion of length-to-thickness ratio. The model is capable to accurately estimate any two variables among the rotation angle of the cross-arm, the misalignment of two carriages, and the net driving force, as long as the other is known. Simulations and experiments on the testbed validate the accuracy and show practical appeals of the proposed model