Frontiers of Materials Science


ISSN 2095-025X (Print)
ISSN 2095-0268 (Online)
CN 11-5985/TB
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Synthesis, characterization, antibacterial and photocatalytic performance of Ag/AgI/TiO2 hollow sphere composites
Zhihong JING, Xiue LIU, Yan DU, Yuanchun HE, Tingjiang YAN, Wenliang WANG, Wenjuan LI
Front. Mater. Sci.    2020, 14 (1): 1-13.
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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 microcalorimetry 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.

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Honeycomb-like polyaniline for flexible and folding all-solid-state supercapacitors
Ge JU, Muhammad Arif KHAN, Huiwen ZHENG, Zhongxun AN, Mingxia WU, Hongbin ZHAO, Jiaqiang XU, Lei ZHANG, Salma BILAL, Jiujun ZHANG
Front. Mater. Sci.    2019, 13 (2): 133-144.
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Porous polyaniline (PANI) was prepared through an efficient and cost-effective method by polymerization of aniline in the NaCl solution at room temperature. The resulting PANI provided large surface area due to its highly porous structure and the intercrossed nanorod, resulting in good electrochemical performance. The porous PANI electrodes showed a high specific capacitance of 480 F∙g−1, 3 times greater than that of PANI without using the NaCl solution. We also make chemically crosslinked hydrogel film for hydrogel polymer electrolyte as well as the flexible supercapacitors (SCs) with PANI. The specific capacitance of the device was 234 F∙g−1 at the current density of 1 A∙g−1. The energy density of the device could reach as high as 75 W∙h∙kg−1 while the power density was 0.5 kW∙kg−1, indicating that PANI be a promising material in flexible SCs.

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Application of BIB polishing technology in cross-section preparation of porous, layered and powder materials: A review
Rongrong JIANG, Ming LI, Yirong YAO, Jianmin GUAN, Huanming LU
Front. Mater. Sci.    2019, 13 (2): 107-125.
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For the accuracy of experimental results, preparing a high quality polished surface and cross-section of the materials for further analysis using electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA), and scanning probe microscopy (SPM) is extremely important. Broad ion beam (BIB) polishing, a method based on the principle of ion bombardment, has irreplaceable advantages. It makes up for the drawbacks and limitations of traditional polishing methods such as mechanical polishing, electrochemical polishing, and chemical polishing. The ions will not leave the bombardment area during polishing, which makes the BIB method suitable for porous materials. The energy of the ion beam can be adjusted according to the sample to reduce the deformation and strain of the polishing area, especially for fragile, soft, and hard materials. The conditions that need to be controlled during BIB polishing are simple. This paper demonstrated the unique advantages of BIB polishing technology in porous, layered and powder materials characterization through some typical application examples, and guided more researchers to understand and utilize BIB polishing technology in the development of new applications.

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Preparation of sulfur-doped graphene fibers and their application in flexible fibriform micro-supercapacitors
Bin CAI, Changxiang SHAO, Liangti QU, Yuning MENG, Lin JIN
Front. Mater. Sci.    2019, 13 (2): 145-155.
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A novel type of sulfur-doped graphene fibers (S-GFs) were prepared by the hydrothermal strategy, the in situ interfacial polymerization method and the annealing method. Two S-GFs were assembled into an all-solid-state fibriform micro-supercapacitor (micro-SC) that is flexible and has a high specific capacitance (4.55 mF·cm−2) with the current density of 25.47 μA·cm−2. The cyclic voltammetry (CV) curve of this micro-SC kept the rectangular shape well even when the scan rate reached 2 V·s−1. There is a great potential for this type of S-GFs used in flexible wearable electronics.

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Sprayable and rapidly bondable phenolic-metal coating for versatile oil/water separation
Heling GUO, Xiaolin WANG, Xie LI, Xiulan ZHANG, Xinghuan LIU, Yu DAI, Rongjie WANG, Xuhong GUO, Xin JIA
Front. Mater. Sci.    2019, 13 (2): 193-205.
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Phenolic-metal complexation coatings have been discovered to be a universal route for the deposition of multifunctional coatings. However, most complexation coatings have been prepared by the immersion method, which limits their practical large-scale application. Herein, we describe a facile and green engineering strategy that involves spraying phenolic compound and metal ions on substrate to form in-situ complexation coating with different coordination states. The coating is formed within minutes and it can be achieved in large scale by the spray method. The pyrogallol-FeIII complexation coating is prepared at pH 7.5, which consists predominantly of bis-coordination complexation with a small amount of tris-coordination complexation. It displays that the water contact angle is near zero due to the generation of rough hierarchical structures and massive hydroxyl groups. The superhydrophilic cotton resulting from the deposition of the pyrogallol-FeIII complexation can separate oil/water mixtures and surfactant-stabilized oil-in-water emulsions with high separation efficiency. The formation of the phenolic-metal complexation coating by using spray technique constitutes a cost-effective and environmentally friendly, strategy with potential to be applied for large-scale surface engineering processes and green oil/water separation.

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Synthesis of nitrogen-doped carbon spheres using the modified Stöber method for supercapacitors
Meng LIU, Lei LIU, Yifeng YU, Haijun LV, Aibing CHEN, Senlin HOU
Front. Mater. Sci.    2019, 13 (2): 156-164.
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Nitrogen-doped carbon spheres (NCSs) with uniform and regular morphology were facilely prepared by the modified Stöber method. Hexamethylenetetramine (HMT) was selected as the starting material, which decomposed to provide nitrogen and carbon sources for the synthesis of NCSs. The decomposition product formaldehyde polymerized to form carbon skeleton with resorcinol after carbonization, and the in-situ nitrogen doping was achieved with the decomposed nitrogen source. NCSs were obtained with regular spherical morphology, high specific surface area, and suitable nitrogen doping. When used as the electrode material, NCSs exhibited good capacitance and electrochemical stability, indicating that NCSs be the promising candidate for the electrode material of high-performance supercapacitors.

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Biocompatible, small-sized and well-dispersed gold nanoparticles regulated by silk fibroin fiber from Bombyx mori cocoons
Chengzhi YANG, Shikun CHEN, Huilan SU, Haoyue ZHANG, Jianfei TANG, Cuiping GUO, Fang SONG, Wang ZHANG, Jiajun GU, Qinglei LIU
Front. Mater. Sci.    2019, 13 (2): 126-132.
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Biocompatible, small-sized but well-dispersed gold nanoparticles (Au NPs) remain a major challenge for their synthesis. Here a convenient solution impregnation technique is developed to prepare such Au NPs under the regulation of degummed silk fibroin fibers (SFFs) extracted from Bombyx mori cocoons. SFFs play multiple roles in the formation of Au NPs such as reactive substrate to capture AuCl4 ions by the chelation of −C=O, reducing agent for Au(0) by the reduction of −OH, and modifiers to render biocompatible Au NPs by some functional groups and biomolecules. The as-prepared Au NPs with a size of 7–10 nm are embedded in the solid SFF substrate, and can disperse well in the liquid system by the disintegration of SFFs into silk fibroin (SF) in a certain CaCl2 solution. The biocompatible Au NPs exhibit uniform small size and distribute stably in both solid and solution states, which have distinctive properties and functional advantages, and bring great convenience to their storage and transportation.

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Upconversion optical nanomaterials applied for photocatalysis and photovoltaics: Recent advances and perspectives
Front. Mater. Sci.    2019, 13 (4): 335-341.
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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.

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SnO2 nanoparticles anchored on graphene oxide as advanced anode materials for high-performance lithium-ion batteries
Ruiping LIU, Ning ZHANG, Xinyu WANG, Chenhui YANG, Hui CHENG, Hanqing ZHAO
Front. Mater. Sci.    2019, 13 (2): 186-192.
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Lithium-ion batteries (LIBs) with high energy density have attracted great attention for their wide applications in electric vehicles, and the exploration of the next-generation anode materials with high theoretical capacity is highly desired. In this work, SnO2 nanoparticles with the particle size of 200 nm uniformly anchored on the surface of graphene oxide (GO) was prepared by combination of the ultrasonic method and the following calcination process. The SnO2/GO composite with the weight ratio of SnO2 to GO at 4:1 exhibits excellent electrochemical performance, which originates from the synergistic effects between GO and SnO2 nanoparticles. A high discharge capacity of 492 mA·h·g−1 can be obtained after 100 cycles at 0.2C, and after cycling at higher current densities of 1C and 2C, a discharge capacity of 641 mA·h·g−1 can be restored when the current density goes back to 0.1C. The superior electrochemical performance and simple synthesis process make it a very promising candidate as anode materials for LIBs.

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Preparation of carbon nanotube/epoxy composite films with high tensile strength and electrical conductivity by impregnation under pressure
Heng CHEN, Yun CHEN, Hang ZHAN, Guang WU, Jian Ming XU, Jian Nong WANG
Front. Mater. Sci.    2019, 13 (2): 165-173.
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Based on the production of a carbon nanotube (CNT) assembly, a new technique is developed for preparing CNT/epoxy (EP) composite films with high tensile strength and electrical conductivity. CNTs are synthesized by floating catalyst spray pyrolysis. After self-assembling into a hollow cylindrical assembly, CNTs are drawn and wound on a rotating drum to form a uniform CNT film. EP resin solutions of different concentrations are used to fill into the pores within the film under different pressures and form composite films after hot-press curing. The permeability of the EP resin and thus the interfacial bonding between the CNT and the EP resin are studied by varying the concentration of the EP resin solution and the pressure used for impregnation. Under optimal preparation conditions, the composite film contains CNTs of a high content of 59 wt.%, and shows a high tensile strength of 1.4 GPa and a high electrical conductivity of 1.4×105 S·m−1, 159% and 309% higher than those of the neat CNT film, respectively.

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Pr-doped In2O3 nanocubes induce oxygen vacancies for enhancing triethylamine gas-sensing performance
Chao WANG, Wu WANG, Ke HE, Shantang LIU
Front. Mater. Sci.    2019, 13 (2): 174-185.
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Nanocubes derived from pure In2O3 and xPr-In2O3 (x= 1, 2, 3 and 5 mol.%) were synthesized using a facile hydrothermal method, followed by calcination. The morphological and structural characterization demonstrated that as-synthesized samples presented regular cubes that decreased in size with the increase of the Pr doping. The data showed that the sensing performances of sensors based on In2O3 were notably improved after the Pr doping. Among them, the sensor based on 2 mol.% Pr-In2O3 had the best sensing performance towards the triethylamine (TEA) gas, including a high response (Ra/Rg = 260 to 100 ppm TEA gas, which is about 12 times higher than that of the sensor based on pure In2O3), a short response time (2 s), and a low detection limit (0.2 ppm) at 350 °C. The mechanism responsible for the enhancement of sensing performance was attributed to the improvement of the vacancy content of 2 mol.% Pr-In2O3, which promoted the oxidation–reduction reaction with the TEA gas that occurred on the materials surface.

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Structural whiteness of the multi-component glaze dependence on amorphous photonic crystals
Hongquan ZHAN, Chuanqi WU, Ce DENG, Xiaohong LI, Zhipeng XIE, Changan WANG
Front. Mater. Sci.    2019, 13 (2): 206-215.
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A kind of enhancing mechanism of structural whiteness dependence on amorphous photonic crystal (APC) structure is introduced in this paper. In the glaze system composed of albite, kaolin, talc, calcite, quartz, titanium dioxide and zinc oxide, the APC structure will be produced by using quartz as a variable to induce the phase separation. Under different polarities between Ti, Zn etc. and Si ion, the separated spheres with the core–shell structure can be obtained and then make up opal-like APCs in the glaze layer. In addition to inner and outer layers of core–shell spheres, the calculated results of refractive indices clearly show the great difference between the particles and the matrix. As a result of different refractive indices, the multiple scatting of visible light plays a key role in the structural whiteness. However, due to the decrease of the cationic content, APCs with the reverse opal structure would be formed in the interface between glaze and body. Ultimately, the glaze appearance reveals extremely high structural whiteness due to the special APC structure.

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Tailoring properties of reticulated vitreous carbon foams with tunable density
Front. Mater. Sci.    2016, 10 (2): 157-167.
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Reticulated vitreous carbon (RVC) foams were manufactured by multiple replications of a polyurethane foam template structure using ethanolic solutions of phenolic resin. The aims were to create an algorithm of fine tuning the precursor foam density and ensure an open-cell reticulated porous structure in a wide density range. The precursor foams were pyrolyzed in inert atmospheres at 700°C, 1100°C and 2000°C, and RVC foams with fully open cells and tunable bulk densities within 0.09–0.42 g/cm3 were synthesized. The foams were characterized in terms of porous structure, carbon lattice parameters, mechanical properties, thermal conductivity, electric conductivity, and corrosive resistance. The reported manufacturing approach is suitable for designing the foam microstructure, including the strut design with a graded microstructure.

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Graphene-based bipolar plates for polymer electrolyte membrane fuel cells
Ram Sevak SINGH, Anurag GAUTAM, Varun RAI
Front. Mater. Sci.    2019, 13 (3): 217-241.
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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.

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SrTiO3/TiO2 heterostructure nanowires with enhanced electron--hole separation for efficient photocatalytic activity
Liuxin YANG, Zhou CHEN, Jian ZHANG, Chang-An WANG
Front. Mater. Sci.    2019, 13 (4): 342-351.
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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.

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Hydrothermal growth of hydroxyapatite and ZnO bilayered nanoarrays on magnesium alloy surface with antibacterial activities
Mengke PENG, Fenyan HU, Minting DU, Bingjie MAI, Shurong ZHENG, Peng LIU, Changhao WANG, Yashao CHEN
Front. Mater. Sci.    2020, 14 (1): 14-23.
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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.

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Fabrication of carboxylic graphene oxide-composited polypyrrole film for neurite growth under electrical stimulation
Chaoyuan LIU, Zhongbing HUANG, Ximing PU, Lei SHANG, Guangfu YIN, Xianchun CHEN, Shuang CHENG
Front. Mater. Sci.    2019, 13 (3): 258-269.
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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.

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Corrosion resistance and hydrophobicity of myristic acid modified Mg--Al LDH/Mg(OH)2 steam coating on magnesium alloy AZ31
Zai-Meng QIU, Fen ZHANG, Jun-Tong CHU, Yu-Chao LI, Liang SONG
Front. Mater. Sci.    2020, 14 (1): 96-107.
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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.

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The multifunctional wound dressing with core–shell structured fibers prepared by coaxial electrospinning
Qilin WEI,Feiyang XU,Xingjian XU,Xue GENG,Lin YE,Aiying ZHANG,Zengguo FENG
Front. Mater. Sci.    2016, 10 (2): 113-121.
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The non-woven wound dressing with core–shell structured fibers was prepared by coaxial electrospinning. The polycaprolactone (PCL) was electrospun as the fiber’s core to provide mechanical strength whereas collagen was fabricated into the shell in order to utilize its good biocompatibility. Simultaneously, the silver nanoparticles (Ag-NPs) as anti-bacterial agent were loaded in the shell whereas the vitamin A palmitate (VA) as healing-promoting drug was encapsulated in the core. Resulting from the fiber’s core–shell structure, the VA released from the core and Ag-NPs present in the shell can endow the dressing both heal-promoting and anti-bacteria ability simultaneously, which can greatly enhance the dressing’s clinical therapeutic effect. The dressing can maintain high swelling ratio of 190% for 3 d indicating its potential application as wet dressing. Furthermore, the dressing’s anti-bacteria ability against Staphylococcus aureus was proved by in vitro anti-bacteria test. The in vitro drug release test showed the sustainable release of VA within 72 h, while the cell attachment showed L929 cells can well attach on the dressing indicating its good biocompatibility. In conclusion, the fabricated nanofibrous dressing possesses multiple functions to benefit wound healing and shows promising potential for clinical application.

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Progress in synthesis and application of zwitterionic Gemini surfactants
Yuqiao CHENG, Yang YANG, Chunrong NIU, Zhe FENG, Wenhui ZHAO, Shuang LU
Front. Mater. Sci.    2019, 13 (3): 242-257.
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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., anionic– cationic, 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.

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LaNiO3 modified with Ag nanoparticles as an efficient bifunctional electrocatalyst for rechargeable zinc--air batteries
Pengzhang LI, Chuanjin TIAN, Wei YANG, Wenyan ZHAO, Zhe LÜ
Front. Mater. Sci.    2019, 13 (3): 277-287.
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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.

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An approach to prepare uniform graphene oxide/aluminum composite powders by simple electrostatic interaction in water/alcohol solution
Wei SUN, Rui ZHAO, Tian WANG, Ke ZHAN, Zheng YANG, Bin ZHAO, Ya YAN
Front. Mater. Sci.    2019, 13 (4): 375-381.
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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.

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Preparation and visible photocatalytic dye degradation of Mn-TiO2/sepiolite photocatalysts
Pengfei ZHU, Zhihao REN, Ruoxu WANG, Ming DUAN, Lisi XIE, Jing XU, Yujing TIAN
Front. Mater. Sci.    2020, 14 (1): 33-42.
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The performance of Mn-TiO2/sepiolite photocatalysts prepared by the sol-gel 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.

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Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31
Lan-Yue CUI,Rong-Chang ZENG,Xiao-Xiao ZHU,Ting-Ting PANG,Shuo-Qi LI,Fen ZHANG
Front. Mater. Sci.    2016, 10 (2): 134-146.
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Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)5/AZ31. Then, the (PAH/PSS)5/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)5/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)5/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca–P compounds including Ca3(PO4)2 and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.

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Cited: Crossref(19) WebOfScience(17)
Electrochemical performances of NiO/Ni2N nanocomposite thin film as anode material for lithium ion batteries
Yanlin JIA, Zhiyuan MA, Zhicheng LI, Zhenli HE, Junming SHAO, Hong ZHANG
Front. Mater. Sci.    2019, 13 (4): 367-374.
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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.

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Microwave hydrothermal synthesis of lanthanum oxyfluoride nanorods for photocatalytic nitrogen fixation: Effect of Pr doping
Xiangyu YAN, Da DAI, Kun MA, Shixiang ZUO, Wenjie LIU, Xiazhang LI, Chao YAO
Front. Mater. Sci.    2020, 14 (1): 43-51.
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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·h−1 when the molar ratio of Pr3+ to LaOF was optimized to be 2%.

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Dynamic recrystallization behavior of AZ31 magnesium alloy processed by alternate forward extrusion
Feng LI, Yang LIU, Xu-Bo LI
Front. Mater. Sci.    2017, 11 (3): 296-305.
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One of the important factors that affect the microstructure and properties of extruded products is recrystallization behavior. Alternate forward extrusion (AFE) is a new type of metal extrusion process with strong potential. In this paper, we carried out the AFE process experiments of as-cast AZ31 magnesium alloy and obtained extrusion bar whose microstructure and deformation mechanism were analyzed by means of optical microscopy, electron backscattered diffraction and transmission electron microscopy. The experimental results indicated that homogeneous fine-grained structure with mean grain size of 3.91 μm was obtained after AFE at 573 K. The dominant reason of grain refinement was considered the dynamic recrystallization (DRX) induced by strain localization and shear plastic deformation. In the 573–673 K range, the yield strength, tensile strength and elongation of the composite mechanical properties are reduced accordingly with the increase of the forming temperature. Shown as in relevant statistics, the proportion of the large-angle grain boundaries decreased significantly. The above results provide an important scientific basis of the scheme formulation and active control on microstructure and property for AZ31 magnesium alloy AFE process.

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Cited: Crossref(3) WebOfScience(2)
Three-dimensional numerical analysis and experimental investigation of grain refinement in multi-pass equal channel angular pressing for round-workpieces
XU Shubo, ZHAO Guoqun, WU Xin, MA Xinwu, GUAN Yanjin
Front. Mater. Sci.    2007, 1 (2): 187-196.
Abstract   PDF (680KB)
Equal channel angular pressing (ECAP) has the capability of producing ultra fine-grained (UFG) materials bellow the dimension of 1 μm. At present, it is one of the most important methods to get bulk UFG materials. Multi-pass ECAP processes for round workpieces are investigated by using numerical simulations and experimental studies in this paper. The deformation mechanism of ECAP for grain refinement is obtained. Three processing routes A, B and C are simulated in order to study the influence of the processing routes to the deformation uniformity of the workpiece. The finite element (FE) analysis results of the multi-pass ECAP process show that the different processing routes result in the different deformation distributions. The grain in the workpiece is refined obviously after multi-pass pressing. The microstructures of the processed material are more different than that of the microstructure of the annealing initial equiaxed grains. The microstructure evolution of the workpiece can be changed via different processing routes. It is found that route B can get a high angle grain boundaries distribution in the workpiece than other routes. The results of the analysis show that the process of grain refinement can be described as a continuous dynamic recovery and recrystallization. The microstructure evolutions of the grain refinement mechanisms and micro-structural characteristics for different multi-pass ECAP processing routes are verified by using OM (optical model) and TEM (transmission electron microscope) analysis. In addition, the experimental microstructure results are also consistent with FE analysis results.
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Wearable gas/strain sensors based on reduced graphene oxide/linen fabrics
Xia HE, Qingchun LIU, Jiajun WANG, Huiling CHEN
Front. Mater. Sci.    2019, 13 (3): 305-313.
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Multifunctional wearable e-textiles have been a focus of much attention due to their great potential for healthcare, sportswear, fitness, space, and military applications. Among them, electroconductive textile yarn shows great promise for use as the next-generation flexible sensors without compromising properties and comfort of usual textiles. Recently, a myriad of efforts have been devoted to improving performance and functionality of wearable sensors. However, the current manufacturing process of metal-based electroconductive textile yarn is expensive, unscalable, and environmentally unfriendly. In this work, we report the preparation of multifunctional reduced graphene oxide/linen (RGO/LN) fabrics through the reduction and the followed suction filtration. As-prepared RGO/LN fabric could serve as the methane gas sensor, which exhibited high sensitivity, remarkable reliability and feasibility. Furthermore, the RGO/LN fabric sensor exhibited good moisture permeability and air permeability. The present work reveals that RGO/LN fabric has great potential as wearable smart devices in personal healthcare applications.

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Influence of temperature on preparing mesoporous mixed phase N/TiO2 nanocomposite with enhanced solar light photocatalytic activity
Front. Mater. Sci.    2019, 13 (4): 352-366.
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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.

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