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  • Mo-V-Nb-O-based catalysts for low-temperature selective oxidation of C α -OH lignin model compounds
    Front. Mater. Sci. (IF 1.701) Pub Date : 2020-01-23
    Lu-Lu Zhang, Kun Hao, Rui-Kai Wang, Xiu-Qiang Ma, Tong Liu, Liang Song, Qing Yu, Zhong-Wei Wang, Jian-Min Zeng, Rong-Chang Zeng

    Abstract Mo-V-Nb tri-component oxide catalysts were prepared and firstly used for the selective oxidation of Cα-OH lignin compounds. The catalytic performance of the composite oxides was obviously enhanced due to the synergistic effects of Mo and V elements. Mo5-xVxO14 phase with a variable Mo/V ratio provided suitable active sites for the oxidative dehydrogenation (ODH) of Cα-OH lignin model compound. The optimized Mo-V-Nb molar composition was confirmed as Mo0.61V0.31Nb0.08Ox/TiO2, which exhibited the prominent catalytic activity with the turnover frequency of 1.04×10-3 mmol·g(cat)-1·s-1. Even at room temperature, the catalysts showed highly-efficient ODH reaction activities. The active phase for selective oxidation reaction and the inhibiting effect of α-MoO3 phase were also discussed in the study.

  • Corrosion resistance and hydrophobicity of myristic acid modified Mg-Al LDH/Mg(OH) 2 steam coating on magnesium alloy AZ31
    Front. Mater. Sci. (IF 1.701) Pub Date : 2020-01-08
    Zai-Meng Qiu, Fen Zhang, Jun-Tong Chu, Yu-Chao Li, Liang Song

    A hydrophobic surface was successfully fabricated on the Mg-Al-layered double hydroxide (Mg-Al LDH)/Mg(OH)2-coated AZ31 magnesium alloy via an in-situ steam coating (SC) process and a subsequent surface modification with environment-friendly myristic acid (MA). The microstructure, composition and hydrophobicity of SC/MA composite coating were investigated by XRD, SEM, EDS, FTIR, and contact angle (CA) measurement. The corrosion behavior of the hybrid coating was evaluated by potentiodynamic polarization, EIS and hydrogen evolution test in 3.5 wt.% NaCl solution. The results showed that the LDH coating had nano-flake microstructure, which remained unchanged after modification with MA. The CA of the MA-modified coating surface reached up to 129°± 3.5°, and the corrosion current density of SC/MA-2 coating decreased about three orders of the magnitude compared to that of the substrate. It is proven that the modified surface has an effective anti-corrosion effect on AZ31 alloy. The formation mechanism and the corrosion mechanism of the coating were also discussed.

  • Investigation of post-thermal annealing-induced enhancement in photovoltaic performance for squaraine-based organic solar cells
    Front. Mater. Sci. (IF 1.701) Pub Date : 2020-01-04
    Rui Zhu, Feiyang Liu, Zixing Wang, Bin Wei, Guo Chen

    In this work, we have systematically investigated the post-thermal annealing-induced enhancement in photovoltaic performance of a 2,4-bis[4-(N, N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIBSQ)/C60 planar heterojunction (PHJ) organic solar cells (OSCs). An increased power conversion efficiency (PCE) of 3.28% has been realized from a DIBSQ/C60 device with thermal annealing at 100 °C for 4 min, which is about 33% enhancement compared with that of the as-cast device. The improvement of the device performance may be mainly ascribed to the crystallinity of the DIBSQ film with post-thermal annealing, which will change the DIBSQ donor and C60 acceptor interface from ^PHJ to hybrid planar-mixed heterojunction. This new donor-acceptor heterojunction structure will significantly improve the charge separation and charge collection efficiency, as well as the open circuit voltage (Voc) of the device, leading to an enhanced PCE. This work provides an effective strategy to improve the photovoltaic performance of SQ-based OSCs.

  • Synthesis, characterization, antibacterial and photocatalytic performance of Ag/AgI/TiO 2 hollow sphere composites
    Front. Mater. Sci. (IF 1.701) Pub Date : 2020-01-03
    Zhihong Jing, Xiue Liu, Yan Du, Yuanchun He, Tingjiang Yan, Wenliang Wang, Wenjuan Li

    Dispersed TiO2 hollow spheres were successfully prepared which was obtained via Ostwald ripening under solvothermal conditions without any templates or surfactants. Then, the AgI/TiO2 was synthesized by the deposition-precipitation process. Finally, Ag/AgI/TiO2 was obtained by a photocatalytic reduction way. Their characteristics were analyzed by XRD, SEM, HRTEM, N2 adsorption-desorption measurements and UV-vis absorption spectra. To demonstrate the potential applications of such composites, their antibacterial activity against Escherichia coli (E. coli) was studied by microcalori-metry for the first time, and their photocatalytic performance for degradation of different organic dyes under simulated UV and visible light was discussed. The results indicated that Ag/AgI/TiO2 hollow spheres revealed elevated antibacterial and photocatalytic activity because of their unique morphology, hollow structure and high surface area. The mechanism of the excellent antibacterial and photocatalytic activity of Ag/AgI/TiO2 hollow spheres are discussed which are attributed to the synergetic effect of Ag, AgI and TiO2. It suggested that the new Ag/AgI/TiO2 photocatalyst has broad application prospects in solar cell, sensor, antibacterial, catalysis and nanotechnology.

  • Hydrothermal growth of hydroxyapatite and ZnO bilayered nanoarrays on magnesium alloy surface with antibacterial activities
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-12-28
    Mengke Peng, Fenyan Hu, Minting Du, Bingjie Mai, Shurong Zheng, Peng Liu, Changhao Wang, Yashao Chen

    Abstract Magnesium alloy (MgA) has been extensively used as orthopedic and cardiovascular scaffolds in virtue of its good biocompatibility, unique biodegradability and excellent mechanical properties. However, poor corrosion resistance and easy infection after implantation seriously limit the potential applications of MgA in the biomedical field. Herein, we fabricated bilayered nanoarrays of hydroxyapatite nanorods (HANRs) and ZnO nanorods (ZnONRs) onto the surface of MgA (MgA-MgO-HANRs-ZnONRs) via micro-arc oxidation (MAO) treatment, microwave-assisted hydrothermal and hydrothermal methods. The morphology and chemical composition of MgA-MgO-HANRs-ZnONRs was characterized by FE-SEM, XRD and EDS, indicating that HANRs-ZnONRs bilayered nanoarrays were fabricated on the surface of MgA-MgO. The surface of MgA-MgO-HANRs-ZnONRs exhibited excellent hydrophilicity as evidenced by the low water contact angle of 3°. Compared with the original MgA, the corrosion resistance of MgA-MgO-HANRs-ZnONRs was obviously improved with decreasing the corrosive current density (icorr) of 2 orders of magnitude. The MgA-MgO-HANRs-ZnONRs performed excellent antibacterial properties with the bactericidal rate of 96.5% against S. aureus and 94.3% against E. coli.

  • Preparation and visible photocatalytic dye degradation of Mn-TiO 2 /sepiolite photocatalysts
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-12-27
    Pengfei Zhu, Zhihao Ren, Ruoxu Wang, Ming Duan, Lisi Xie, Jing Xu, Yujing Tian

    Abstract The performance of Mn-TiO2/sepiolite photocatalysts prepared by the solgel method and calcinated at different temperatures was studied in the photocatalytic degradation of direct fast emerald green dye under visible light irradiation, and a series of analytical techniques such as XRD, SEM, FTIR, TG-DSC, XPS, UV-vis-DRS and Raman spectroscopy were used to characterize the morphology, structure and optical properties of the photocatalysts. It is found that the anatase TiO2 was formed in all photocatalysts. Mn4+ might incorporate into the lattice structure of TiO2 and partially replace Ti4+, thus causing the defects in the crystal structure and the broadening of the spectral response range of TiO2. At the same time, TiO2 particles were dispersed on the surface of the sepiolite, which immobilized TiO2 particles with sepiolite via the bond of Ti-O-Si. Mn-TiO2/sepiolite calcined at 400 °C exhibits the highest photocatalytic activity and the degradation rate of direct fast emerald green is up to 98.13%. Meanwhile, it also shows good stability and universality.

  • Enhancement of red emission assigned to inversion defects in ZnAl 2 O 4 :Cr 3+ hollow spheres
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-12-27
    Dong Zhang, Jingxin Chen, Chunyu Du, Bingjun Zhu, Qingru Wang, Qiang Shi, Shouxin Cui, Wenjun Wang

    Abstract ZnAl2O4:Cr3+ hollow spheres composed of secondary nanoparticles with single spinel phase were fabricated using carbon templets. Monitoring the emission of 687 nm, two wide excitation bands attributed to the electrons of Cr3+ transiting from 4A2g (4F) → 4T1g (4F) and 4A2g (4F) → 4T2g (4F) were observed. The broad excitation band at about 397 nm was asymmetric and consisted of two peaks, indicating that there was a trigonal distortion existing in the lattices. The intensity of all emitting peaks revealed sharp increasing trend with the sintering temperature increase, and the intensity of emission at 698 nm assigned to inversion defects was more intense than that of emission at 687 nm assigned to octahedral Cr3+ ions in the undistorted spinel lattice. The samples with higher synthesized temperature revealed longer decay time, and the relative weightage of shorter decay time component decreased with the increase of sintering temperature, indicating that the surface defects decreased.

  • Microwave hydrothermal synthesis of lanthanum oxyfluoride nanorods for photocatalytic nitrogen fixation: Effect of Pr doping
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-12-27
    Xiangyu Yan, Da Dai, Kun Ma, Shixiang Zuo, Wenjie Liu, Xiazhang Li, Chao Yao

    Abstract Photocatalytic fixation of nitrogen has been recognized as a green and promising strategy for ammonia synthesis under ambient conditions. However, the efficient reduction of nitrogen remains a challenge due to high activation energy of nitrogen and low utilization of solar energy. Herein, lanthanum oxyfluoride with different doping content of Pr3+ (LaOF:xPr3+) upconversion nanorods were synthesized by microwave hydrothermal method. Results indicated that the doping of Pr3+ generated considerable defects on the surface of LaOF which acted as the adsorption and activation center for nitrogen. Meanwhile, the Pr3+ ion narrowed the band gap and broadened the light response range of LaOF because LaOF:Pr3+ can upconvert visible light into ultraviolet light, which excite LaOF nanorods and improve the utilization of solar light. The doping amount of Pr3+ had critical effect on the photocatalytic nitrogen fixation performance which reached as high as 180 μmol·L−1·ho1 when the molar ratio of Pr3+ to LaOF was optimized to be 2%.

  • Synthesis of poly(ethylene glycol)-SS-poly(ε-caprolactone)-SS-poly(ethylene glycol) triblock copolymers via end-group conjugation and self-assembly for reductively responsive drug delivery
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-05
    Junbo Li, Junting Jiang, Biyu Zhou, Chaohuang Niu, Wendi Wang, Wenlan Wu

    In this study, we describe a simple synthesis route to prepare triblock copolymers with disulfide-linkers, poly(ethylene glycol)-SS-poly(ε-caprolactone)-SS-poly (ethylene glycol) (PEG-SS-PCL-SS-PEG) for application in the reductively responsive release of doxorubicin (DOX). To synthesize PEG-SS-PCL-SS-PEG, two end-groups of PCL-diol were first modified with cystamine to introduce disulfide bonds and subsequently conjugated with PEG-NHS via carbodiimide chemistry. PEG-SS-PCL-SSPEG fabricated into polymeric micelles with stable structure and different nanoscale sizes via adjusting the PCL chain length, showing obvious reductive responsiveness and fast drug release of encapsulated DOX in the presence of glutathione (GSH). Moreover, DOX-loaded PEG-SS-PCL-SS-PEG micelles exhibited higher therapeutic efficacy than reduction-insensitive PEG-b-PCL micelles in vitro. Thus, end-groups conjugation is a simple and straightforward strategy to introduce intelligent responsiveness in biocompatible block copolymers and improve their therapeutic efficacy.

  • Upconversion optical nanomaterials applied for photocatalysis and photovoltaics: Recent advances and perspectives
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-15
    Timur Sh. Atabaev, Anara Molkenova

    Upconversion (UC) lanthanide nanomaterials have attracted enormous attention in the last two decades thanks to their unique ability to convert low-energy infrared photons into high-energy photons. In this mini-review, we briefly discussed the recent achievements related to the direct utilization of UC optical nanomaterials for photocatalysis and photovoltaic applications. In particular, selected examples of UC-containing devices/nanocomposites with improved performance were covered. In addition, we outlined some challenges and future trends associated with the widespread usage of UC nanomaterials.

  • An approach to prepare uniform graphene oxide/aluminum composite powders by simple electrostatic interaction in water/alcohol solution
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-10-12
    Wei Sun, Rui Zhao, Tian Wang, Ke Zhan, Zheng Yang, Bin Zhao, Ya Yan

    The homogenous dispersion of graphene in Al powders is a key challenge that limits the development of graphene-reinforced metal matrix composites with high performance. Here, uniform distribution of graphene oxide (GO) coated on flake Al powders were obtained by a simply stirring and ultrasonic treatment in the water/alcohol solution. The effect of water volume content on the formation of GO/Al composite powders was investigated. The results showed that GO adsorbed with synchronous reduction on the surface of Al powders, but when the water content was higher than 80% in the solution, Al powders were totally changed into Al(OH)3. With optimizing the water content of 60% in the solution, reduced GO was homogenously coated onto the surface of flake Al powders. The formation mechanism can be ascribed to the balance control between the liquid/solid interaction and the hydrolysis reaction.

  • Synthesis and characterization of lanthanide-doped sodium holmium fluoride nanoparticles for potential application in photothermal therapy
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-15
    Kaushik Das, G. A. Kumar, Leonardo Mirandola, Maurizio Chiriva-Internati, Jharna Chaudhuri

    Upconversion nanoparticles (UC NPs) in combination with plasmonic materials have great potential for cancer photothermal therapy. Recently, sodium holmium fluoride (NaHoF4) is being investigated for luminescence and magnetic resonance imaging (MRI) contrast agent. Here, we present successful synthesis of excellent quality doped NaHoF4 NPs for possible UC luminescence application and coated for possible photothermal therapy application. Synthesized NaHoF4 nanocrystals were doped with Yb/Er and coated with gold, gold/silica, silver and polypyrrole (PPy). XRD, XPS and TEM were used to determine structure and morphology of the NPs. Strong UC photoluminescence (PL) emission spectra were obtained from the NPs when excited by near-infrared (NIR) light at 980 nm. Cell viability and toxicity of the NPs were characterized using pancreatic and ovarian cancer cells with results showing that gold/ silica coating produced least toxicity followed by gold coating.

  • SrTiO 3 /TiO 2 heterostructure nanowires with enhanced electron-hole separation for efficient photocatalytic activity
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-05
    Liuxin Yang, Zhou Chen, Jian Zhang, Chang-An Wang

    Heterostructure is an effective strategy to facilitate the charge carrier separation and promote the photocatalytic performance. In this paper, uniform SrTiO3 nanocubes were in-situ grown on TiO2 nanowires to construct heterojunctions. The composites were prepared by a facile alkaline hydrothermal method and an in-situ deposition method. The obtained SrTiO3/TiO2 exhibits much better photocatalytic activity than those of pure TiO2 nanowires and commercial TiO2 (P25) evaluated by photocatalytic water splitting and decomposition of Rhodamine B (RB). The hydrogen generation rate of SrTiO3/TiO2 nanowires could reach 111.26 mmol·g−1·h−1 at room temperature, much better than those of pure TiO2 nanowires (44.18 mmol·g−1·h−1)and P25 (35.77 mmol·g−1·h−1). The RB decomposition rate of SrTiO3/TiO2 is 7.2 times of P25 and 2.4 times of pure TiO2 nanowires. The photocatalytic activity increases initially and then decreases with the rising content of SrTiO3, suggesting an optimum SrTiO3/TiO2 ratio that can further enhance the catalytic activity. The improved photocatalytic activity of SrTiO3/TiO2 is principally attributed to the enhanced charge separation deriving from the SrTiO3/TiO2 heterojunction.

  • Corrosion resistance of a silane/ceria modified Mg-Al-layered double hydroxide on AA5005 aluminum alloy
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-04
    Wei Wu, Fen Zhang, Yu-Chao Li, Yong-Feng Zhou, Qing-Song Yao, Liang Song, Rong-Chang Zeng, Sie Chin Tjong, Dong-Chu Chen

    The present work aimed at assessing the electrochemical behavior and the corrosion inhibition performance of Mg-Al-layered double hydroxide (LDH) coatings modified with methyltrimethoxysilane (MTMS) and cerium nitrate on AA5005 aluminum alloy. The chemical compositions and surface morphologies of the coatings were investigated by XRD, FT-IR and FE-SEM, while their corrosion resistance was evaluated by electrochemical and immersion tests. An optimum corrosion resistance of the composite coatings was obtained by adding 10−2 mol·L−1 cerium nitrate. An excess addition of cerium nitrate resulted in a loose structure and poor corrosion resistance of the coating. The corrosion mechanism of the composite coatings was proposed and discussed.

  • Electrochemical performances of NiO/Ni 2 N nanocomposite thin film as anode material for lithium ion batteries
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-23
    Yanlin Jia, Zhiyuan Ma, Zhicheng Li, Zhenli He, Junming Shao, Hong Zhang

    Despite the high specific capacities, the practical application of transition metal oxides as the lithium ion battery (LIB) anode is hindered by their low cycling stability, severe polarization, low initial coulombic efficiency, etc. Here, we report the synthesis of the NiO/Ni2N nanocomposite thin film by reactive magnetron sputtering with a Ni metal target in an atmosphere of 1 vol.% O2 and 99 vol.% N2. The existence of homogeneously dispersed nano Ni2N phase not only improves charge transfer kinetics, but also contributes to the one-off formation of a stable solid electrolyte interphase (SEI). In comparison with the NiO electrode, the NiO/Ni2N electrode exhibits significantly enhanced cycling stability with retention rate of 98.8% (85.6% for the NiO electrode) after 50 cycles, initial coulombic efficiency of 76.6% (65.0% for the NiO electrode) and rate capability with 515.3 mA·h·g−1 (340.1 mA·h·g−1 for the NiO electrode) at 1.6 A·g−1.

  • Influence of temperature on preparing mesoporous mixed phase N/TiO 2 nanocomposite with enhanced solar light photocatalytic activity
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-18
    Elias Assayehegn, Ananthakumar Solaiappan, Yonas Chebudie, Esayas Alemayehu

    Nitrogen-doped titanium dioxide (N/TiO2) nanophotocatalysts were successfully synthesized in the presence of environmentally benign nitrogen dopant source, guanidinium chloride, by the sol-gel method. The effect of calcination temperature (300–600 °C) on their physicochemical properties was investigated by means XRD, XPS, FESEM, HRTEM, Raman spectroscopy, UV-vis DRS, PL and BET. Moreover, their photocatalytic activities were evaluated against rhodamine B (RhB) degradation under direct sun light. Results showed that the crystal phase of spheroidal N/TiO2 nanoparticles was changed from anatase (300 °C) to rutile (600 °C) via an intermediate anatase/rutile (A/R) mixed phase (400–500 °C), and the RhB photodegradation performance was increased with the decrease of the calcination temperature. Notably, N/TiO2 prepared at 400 °C demonstrated the best degradation performance (99%) after 5 h irradiation. The enhanced performance with high photostability was mainly attributed to its higher surface area and pore volume, stronger light absorption, and lower recombination rate. Such nanomaterials have practical applications for environmental remediation.

  • Preparation and thermal properties of layered porous carbon nanotube/epoxy resin composite films
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-05
    Jun Zhao, Hang Zhan, Hai Tao Chen, Jian Nong Wang

    A floating-catalyst spray pyrolysis method was used to synthesize carbon nanotube (CNT) thin films. With the use of ammonium chloride as a pore-former and epoxy resin (EP) as an adhesive, CNT/EP composite films with a porous structure were prepared through the post-heat treatment. These films have excellent thermal insulation (0.029–0.048 W·m−1·K−1) at the thickness direction as well as a good thermal conductivity (40–60 Wm−1·K−1) in the film plane. This study provides a new film material for thermal control systems that demand a good thermal conductivity in the plane but outstanding thermal insulation at the thickness direction.

  • Ca 2+ doping effects in (K, Na, Li)(Nb 0.8 Ta 0.2 )O 3 lead-free piezoelectric ceramics
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-28
    Lei Tang, Tengfei Liu, Jinxu Ma, Xiaowen Zhang, Linan An, Kepi Chen

    Lead-free (K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3 (KNLNT) and (K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3 (KNLNT-Ca) ceramics were prepared by a conventional ceramic processing. Structural analysis shows that the Ca2+ doping takes the A site of ABO3 perovskite and decreases the phase transition temperature. Property measurements reveal that as a donor dopant, the Ca2+ doping results in higher room-temperature dielectric constant, lower dielectric loss, and lower mechanical quality factor. In addition, the Ca2+ doping does not change the positive piezoelectric coefficient d33, but increases the converse piezoelectric coefficient d33* significantly. This is likely due to the increase in the relaxation, as well as the appearance of (CaNa/K·-VNa/K’) defect dipoles.

  • Upconversion luminescence Ca–Mg–Si bioactive glasses synthesized using the containerless processing technique
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-11-27
    Qin Li, Min Xing, Lan Chang, Linlin Ma, Zhi Chen, Jianrong Qiu, Jianding Yu, Jiang Chang

    In this study, a series of Er3+/Yb3+ co-doped Ca–Mg–Si glasses were prepared via the containerless processing. Phase composition and luminescent properties of the prepared materials were investigated through XRD and spectrometry, and bioactivity, biocompatibility and cytotoxicity were evaluated. The XRD patterns indicated that akermanite (AKT) ceramic powders were completely transformed into the glassy phase (AKT-G, EYA) through the containerless processing, which exhibit upconversion luminescence, and the luminescence intensity increased with the increase of the doping amount of Er3+ and Yb3+. High amount of Yb3+ doping and existence of Ca2+ in glasses resulted in more intensive red-light emission. The SEM observation, combined with EDS analysis, and cell culture experiments showed that the as-prepared glasses were nontoxic, biocompatible and bioactive. All these results demonstrated that the containerless processing is a facile method for preparing homogeneous luminescent bioactive glasses. Furthermore, this luminescent Ca–Mg–Si glasses may be used as bone implant materials to study the in vivo distribution of degradation products of bone implants, which may be of great significance for the development and clinical application of new bone grafting materials.

  • Facile preparation of acid/CO 2 stimuli-responsive sheddable nanoparticles based on carboxymethylated chitosan
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-07-30
    Weiwei Fan, Jilu Wang, Jiajun Feng, Yong Wang

    The present study describes the facile preparation of acid/CO2 stimuli-responsive sheddable nanoparticles based on carboxymethylated chitosan (CMCS). Commercially available CMCS was grafted with monomethoxy polyethylene glycol (mPEG) chains via an acid/CO2 responsive linker, i.e., benzoic-imine, and then was used for the cross-linking with CaCl2. With a high CMCS concentration up to 7 mg/mL, stable nanoparticles were successfully prepared. The particle size grew slightly with increasing the molecular weight of mPEG. When the concentration of CaCl2 and the feed ratio of CMCS to mPEG increased, the particle size decreased at first and then increased after reaching a minimum size. When the particles were stimulated by CO2 or acid, benzoicimine cleaved quickly, and mPEG fell off the nanoparticles simultaneously, and then flocculation and precipitation occurred. These sheddable nanoparticles might have potential application in the biomedical field including the intelligent drug delivery system.

  • Electric-field-induced microstructure modulation of carbon nanotubes for high-performance supercapacitors
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-07-31
    Chengzhi Luo, Guanghui Liu, Min Zhang

    The growth direction, morphology and microstructure of carbon nanotubes (CNTs) play key roles for their potential applications in electronic and energy storage devices. However, effective synthesis of CNTs in high crystallinity and desired microstructure still remains a tremendous challenge. Here we introduce an electric field for controlling the microstructure formation of CNTs. It reveals that the electric field not only make CNTs aligned parallel but also improve the density of CNTs. Especially, the microstructures of CNTs gradually change under electrical field. That is, graphite sheets are transformed from the “herringbone” structure to a highly crystalline structure, facilitating the transportation of electrons. Due to the improved aligned growth direction, high density and highly crystalline microstructure, the electrochemical performance of CNTs is greatly improved. When the CNTs are applied in supercapacitors, they present a high specific capacitance of 237 F/g, three times higher than that of the CNTs prepared without electrical field. Such microstructure modulation of CNTs by electric field would help to construct high performance electronic and energy storage devices.

  • Ag-assisted CeO 2 catalyst for soot oxidation
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-09-07
    Lirong Zeng, Lan Cui, Caiyun Wang, Wei Guo, Cairong Gong

    In this work, the Ag loaded Ce-based catalyst was synthesized (by the sol-gel method) and its performance was studied by TG, H2-TPR, XRD, SEM, TEM, BET and XPS. The results show that Ag nanoparticles be successfully loaded onto the CeO2 surface and the relative content of Ag nanoparticles is about 10.22 wt.% close to the theoretical value (10%). XPS shows that Ag nanoparticles induce a great number of oxygen vacancies in the CeO2 lattice through the electronic transfer, and H2-TPR indicates that the Ag-assisted CeO2 catalyst exhibits a better reduction performance and Ag nanoparticles can promote O- transform into O2-. The catalytic activity for soot oxidation was studied by TG under air atmosphere and the activity was found to be obviously enhanced when Ag nanoparticles be load on the surface of CeO2 (T10 = 386 °C, T90 = 472.5 °C, Tm = 431 °C). The reaction mechanism was also presented and O 2 - species is regarded as the determinant factor for the catalytic activity.

  • Progress in synthesis and application of zwitterionic Gemini surfactants
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-09-07
    Yuqiao Cheng, Yang Yang, Chunrong Niu, Zhe Feng, Wenhui Zhao, Shuang Lu

    Zwitterionic Gemini surfactants have the Gemini molecular structure in which there are both multiple lipophilic groups and multiple hydrophilic groups. However, their hydrophilic groups have different charges. Due to the special molecular structure, this kind of surfactants possesses excellent properties, including high surface activities, isoelectric point (IP), low critical micelle concentration (CMC), less toxicity, low irritating, biodegradability, bioactive, interface modification, and so on. In this review, synthetic strategies of three kinds of zwitterionic Gemini surfactants, i.e., anioniccationic, cationic-nonionic and anionic-nonionic Gemini surfactants, are discussed, and their potential applications in life sciences, chemical industry and enhanced oil recovery (EOR) are illustrated. Their future development is also prospected.

  • Preparation and optimization of freestanding GaN using low-temperature GaN layer
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-07-01
    Yuan Tian, Yongliang Shao, Xiaopeng Hao, Yongzhong Wu, Lei Zhang, Yuanbin Dai, Qin Huo, Baoguo Zhang, Haixiao Hu

    In this work, a method to acquire freestanding GaN by using low temperature (LT)-GaN layer was put forward. To obtain porous structure and increase the crystallinity, LT-GaN layers were annealed at high temperature. The morphology of LT-GaN layers with different thickness and annealing temperature before and after annealing was analyzed. Comparison of GaN films using different LT-GaN layers was made to acquire optimal LT-GaN process. According to HRXRD and Raman results, GaN grown on 800 nm LT-GaN layer which was annealed at 1090 °C has good crystal quality and small stress. The GaN film was successfully separated from the substrate after cooling down. The self-separation mechanism of this method was discussed. Cross-sectional EBSD mapping measurements were carried out to investigate the effect of LT-buffer layer on improvement of crystal quality and stress relief. The optical property of the obtained freestanding GaN film was also determined by PL measurement.

  • Micromagnetic investigation by a simplified approach on the demagnetization field of permanent magnets with nonmagnetic phase inside
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-08-22
    Wei Li, Lizhong Zhao, Zhongwu Liu

    A simplified analysis method based on micromagnetic simulation is proposed to investigate effects of nonmagnetic particles on the demagnetizing field of a permanent magnet. By applying the additivity law of the demagnetizing field, the complicated demagnetizing field of the real magnet could be analyzed by only focusing on the stray field of the reserved magnet. For a magnet with nonmagnetic particles inside, the particle size has no significant effect on the maximum value of the demagnetization field, but the area of the affected region by the particle is proportional to the particle size. A large particle produces a large affected area overlapped with those influenced by other particles, which leads to the large demagnetization field. With increasing the length of the particle along the magnetization direction, the demagnetization field on the pole surface increases. The pole surface with a convex shape will increase the demagnetization field. The demagnetizing field near the nonmagnetic particle will be further increased by the large macroscopic demagnetizing field near the pole surface. This work suggests some practical approaches to optimize the microstructure of permanent magnets.

  • Fabrication of carboxylic graphene oxide-composited polypyrrole film for neurite growth under electrical stimulation
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-07-19
    Chaoyuan Liu, Zhongbing Huang, Ximing Pu, Lei Shang, Guangfu Yin, Xianchun Chen, Shuang Cheng

    An aligned composite film was fabricated via the deposition of carboxylic graphene oxide (C-GO) and polypyrrole (PPy) nanoparticles on aligned poly(L-lactic acid) (PLLA) fiber-films (named as C-GO/PPy/PLLA), which has the core (PLLA)-sheath (C-GO/PPy) structure, and the composition of C-GO (∼4.8 wt.% of PPy sheath) significantly enhanced the tensile strength and the conductivity of the PPy/PLLA film. Especially, after 4 weeks of immersion in the PBS solution, the conductivity and the tensile strength of C-GO/PPy/PLLA films still remained ∼6.10 S/cm and 28.9 MPa, respectively, which could meet the need of the sustained electrical stimulation (ES) therapy for nerve repair. Moreover, the neurite length and the neurite alignment were significantly increased through exerting ES on C-GO/PPy/PLLA films due to their sustained conductivity in the fluid of cell culture. These results indicated that C-GO/PPy/PLLA with sustained conductivity and mechanical property possessed great potential of nerve repair by exerting lasting-ES.

  • LaNiO 3 modified with Ag nanoparticles as an efficient bifunctional electrocatalyst for rechargeable zinc–air batteries
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-09-23
    Pengzhang Li, Chuanjin Tian, Wei Yang, Wenyan Zhao, Zhe Lü

    No-precious bifunctional catalysts with high electrochemical activities and stability were crucial to properties of rechargeable zinc-air batteries. Herein, LaNiO3 modified with Ag nanoparticles (Ag/LaNiO3) was prepared by the co-synthesis method and evaluated as the bifunctional oxygen catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Compared with LaNiO3, Ag/LaNiO3 demonstrated the enhanced catalytic activity towards ORR/OER as well as higher limited current density and lower onset potential. Moreover, the potential gap between ORR potential (at −3 mA·cm−2) and OER potential (at 5 mA·cm−2) was 1.16 V. The maximum power density of the primary zinc-air battery with Ag/LaNiO3 catalyst achieved 60 mW·cm−2. Furthermore, rechargeable zinc-air batteries operated reversible charge-discharge cycles for 150 cycles without noticeable performance deterioration, which showed its excellent bifunctional activity and cycling stability as oxygen electrocatalyst for rechargeable zinc-air batteries. These results indicated that Ag/LaNiO3 prepared by the co-synthesis method was a promising bifunctional catalyst for rechargeable zinc-air batteries.

  • Graphene-based bipolar plates for polymer electrolyte membrane fuel cells
    Front. Mater. Sci. (IF 1.701) Pub Date : 2019-09-23
    Ram Sevak Singh, Anurag Gautam, Varun Rai

    Bipolar plates (BPs) are a major component of polymer electrolyte membrane fuel cells (PEMFCs). BPs play a multifunctional character within a PEMFC stack. It is one of the most costly and critical part of the fuel cell, and hence the development of efficient and cost-effective BPs is of much interest for the fabrication of next-generation PEMFCs in future. Owing to high electrical conductivity and chemical inertness, graphene is an ideal candidate to be utilized in BPs. This paper reviews recent advances in the area of graphene-based BPs for PEMFC applications. Various aspects including the momentous functions of BPs in the PEMFC, favorable features of graphene-based BPs, performance evaluation of various reported BPs with their advantages and disadvantages, challenges at commercial level products and future prospects of frontier research in this direction are extensively documented.

  • Bio-inspired supramolecular self-assembly towards soft nanomaterials.
    Front. Mater. Sci. (IF 1.701) Pub Date : 2011-10-08
    Yiyang Lin,Chuanbin Mao

    Supramolecular self-assembly has proven to be a reliable approach towards versatile nanomaterials based on multiple weak intermolecular forces. In this review, the development of bio-inspired supramolecular self-assembly into soft materials and their applications are summarized. Molecular systems used in bio-inspired "bottom-up self-assembly" involve small organic molecules, peptides or proteins, nucleic acids, and viruses. Self-assembled soft nanomaterials have been exploited in various applications such as inorganic nanomaterial synthesis, drug or gene delivery, tissue engineering, and so on.

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上海纽约大学William Glover