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.
Abstract   HTML   PDF (3445KB)

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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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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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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Large-sized nano-TiO2/SiO2 mesoporous nanofilm-constructed macroporous photocatalysts with excellent photocatalytic performance
Zhiyu ZHANG, Lixia HU, Hui ZHANG, Liping YU, Yunxiao LIANG
Front. Mater. Sci.    2020, 14 (2): 163-176.
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Novel large-sized mesoporous nanofilm-constructed macroporous SiO2 (LMNCMS) with two sets of well-defined 3D continuous pass-through macropores (pore size of 0.5–1.0 μm, wall thickness of 40–50 nm) was prepared through a dual-templating approach, and used as an advanced support for TiO2 nanocrystalline photocatalyst. The structural and optical properties of the as-prepared materials were investigated by various characterization techniques in order to explore the connections between catalysts’ features and catalytic performance. The photocatalytic activities were evaluated by degradations of methylene blue (MB) and phenol under the simulated sunlight irradiation. To gain insight into the impact of preparation and operation conditions on photocatalytic degradation processes, experiments were conducted at wide ranges of the TiO2 loading content, calcination temperature, solution pH, and photocatalyst dosage. Nano-TiO2/LMNCMS exhibited high photocatalytic activity and stability. Rapid matter transport, good accessibility of pollutants to TiO2 and high light harvesting could mainly account for the superior photocatalytic performance. The trapping experiments were performed to identify the main reactive species in the catalytic reactions.

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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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Double core---shell nanostructured Sn---Cu alloy as enhanced anode materials for lithium and sodium storage
Luoyang LI, Tian CHEN, Fengbin HUANG, Peng LIU, Qingrong YAO, Feng WANG, Jianqiu DENG
Front. Mater. Sci.    2020, 14 (2): 133-144.
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Sn-based alloy materials are considered as a promising anode candidate for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), whereas they suffer from severe volume change during the discharge/charge process. To address the issue, double core–shell structured Sn–Cu@SnO2@C nanocomposites have been prepared by a simple co-precipitation method combined with carbon coating approach. The double core–shell structure consists of Sn–Cu multiphase alloy nanoparticles as the inner core, intermediate SnO2 layer anchored on the surface of Sn–Cu nanoparticle and outer carbon layer. The Sn–Cu@SnO2@C electrode exhibits outstanding electrochemical performances, delivering a reversible capacity of 396 mA·h·g−1 at 100 mA·g−1 after 100 cycles for LIBs and a high initial reversible capacity of 463 mA·h·g−1 at 50 mA·g−1 and a capacity retention of 86% after 100 cycles, along with a remarkable rate capability (193 mA·h·g−1 at 5000 mA·g−1) for SIBs. This work provides a viable strategy to fabricate double core–shell structured Sn-based alloy anodes for high energy density LIBs and SIBs.

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Injectable hydrogel wound dressing based on strontium ion cross-linked starch
Yuxuan MAO, Mingming PAN, Huilin YANG, Xiao LIN, Lei YANG
Front. Mater. Sci.    2020, 14 (2): 232-241.
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Severe skin wounds cause great problems and sufferings to patients. In this study, an injectable wound dressing based on strontium ion cross-linked starch hydrogel (SSH) was developed and evaluated. The good inject-ability of SSH made it easy to be delivered onto the wound surface. The good tissue adhesiveness of SSH ensured a firm protection of the wound. Besides, SSH supported the proliferation of NIH/3T3 fibroblasts and facilitated the migration of human umbilical vein endothelial cells (HUVECs). Importantly, SSH exhibited strong antibacterial effects on Staphylococcus aureus (S. aureus), which could prevent wound infection. These results demonstrate that SSH is a promising wound dressing material for promoting wound healing.

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Preparation and enhanced properties of ZrMOF@CdTe nanoparticles with high-density quantum dots
Xin LIU, Xiangling REN, Longfei TAN, Wenna GUO, Zhongbing HUANG, Xianwei MENG
Front. Mater. Sci.    2020, 14 (2): 155-162.
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ZrMOF@CdTe nanoparticles (NPs) with high fluorescence were synthesized by hydrothermal method. The morphology, particle size distribution, compositions, fluorescence properties and stability of the synthesized ZrMOF@CdTe were analyzed via the characterization by TEM, ICP-AES and fluorescence spectrophotometry, and the effects of the reaction time and pH value on the fluorescent property of ZrMOF@CdTe NPs were discussed. The results show that ZrMOFs could maintain its morphology and structure well during the process of loading CdTe quantum dots. With the increase of the loading reaction time, the red-shifted emission peaks of ZrMOF@CdTe NPs appear, and their fluorescence gradually changes from green to red color. With the increase of the pH value and temperature of the hydrothermal reaction, the fluorescence of ZrMOF@CdTe NPs was also consistent with the red-shifted change. The fluorescent property of ZrMOF@CdTe NPs could be remained for more than 3 months. Therefore, ZrMOF@CdTe NPs synthesized by the hydrothermal method have the characteristics of simple operation, adjustable fluorescent color and high stability, and the potential application in the fields of biological detection and sensing is expected.

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Two-step preparation of carbon nanotubes/RuO2/polyindole ternary nanocomposites and their application as high-performance supercapacitors
Danhua ZHU, Qianjie ZHOU, Aiqin LIANG, Weiqiang ZHOU, Yanan CHANG, Danqin LI, Jing WU, Guo YE, Jingkun XU, Yong REN
Front. Mater. Sci.    2020, 14 (2): 109-119.
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A ternary single-walled carbon nanotubes/RuO2/polyindole (SWCNT/RuO2/PIn) nanocomposite was fabricated by the oxidation polymerization of indole on the prefabricated SWCNT/RuO2 binary nanocomposites. The nanocomposite was measured by FTIR, XRD, SEM, TEM, EDS and XPS, together with the electrochemical technique. The electrochemical results demonstrated that the symmetric supercapacitor used SWCNT/RuO2/PIn as electrodes presented 95% retention rate after 10000 cycles, superior capacitive performance of 1203 F·g−1 at 1 A·g−1, and high energy density of 33 W·h·kg−1 at 5000 W·kg−1. The high capacitance performance of SWCNT/RuO2/PIn nanocomposite was mainly ascribed to the beneficial cooperation effect among components. This indicated that the SWCNT/RuO2/PIn nanocomposite would be a good candidate for high-performance supercapacitors.

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Fabrication of Cu/graphite film/Cu sandwich composites with ultrahigh thermal conductivity for thermal management applications
Rui ZHAO, Weikai LI, Tian WANG, Ke ZHAN, Zheng YANG, Ya YAN, Bin ZHAO, Junhe YANG
Front. Mater. Sci.    2020, 14 (2): 188-197.
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Effective thermal management of electronic integrated devices with high powder density has become a serious issue, which requires materials with high thermal conductivity (TC). In order to solve the problem of weak bonding between graphite and Cu, a novel Cu/graphite film/Cu sandwich composite (Cu/GF/Cu composite) with ultrahigh TC was fabricated by electro-deposition. The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electro-deposition. TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated. The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content, and the strong texture orientation of deposited Cu resulted in high TC. Under the optimizing preparing condition, the highest in-plane TC reached 824.3 W·m−1·K−1, while the ultimate tensile strength of this composite was about four times higher than that of the graphite film.

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One-step functionalization of graphene via Diels--Alder reaction for improvement of dispersibility
Jinxing ZHANG, Kexing HU, Qi OUYANG, Qilin GUI, Xiaonong CHEN
Front. Mater. Sci.    2020, 14 (2): 198-210.
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Good dispersibility of graphene in a medium or matrix is a critical issue in practical applications. In this work, graphene was functionalized using N-(4-hydroxyl phenyl) maleimide (4-HPM) via the Diels–Alder (DA) reaction by a one-step catalyst-free approach. The optimal reaction condition was found to be 90 °C for 12 h using dimethylformamide (DMF) as the solvent. FTIR, Raman spectroscopy, XPS and EDS proved that 4-HPM moieties were successfully grafted onto the surface of graphene. UV-vis and TGA confirmed that the grafting amount of 4-HPM was 3.75%–3.97% based on the mass of graphene. Functionalized graphene showed excellent dispersion stability when dispersed in common solvents such as ethanol, DMF, water, tetrahydrofuran and p-xylene. Meanwhile, functionalized graphene also exhibited pH sensitivity in aqueous due to the phenolic hydroxyls from the 4-HPM moieties. As a result of good dispersion stability and pH sensitivity, compared with graphene, functionalized graphene had better adsorption capacity for methylene blue (MB) from aqueous solution.

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Facile preparation of low swelling, high strength, self-healing and pH-responsive hydrogels based on the triple-network structure
Zhicun WANG, Xiaoman HAN, Yixi WANG, Kenan MEN, Lin CUI, Jianning WU, Guihua MENG, Zhiyong LIU, Xuhong GUO
Front. Mater. Sci.    2019, 13 (1): 54-63.
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A polyacrylic acid (PAA)/gelatin (Gela)/polyvinyl alcohol (PVA) hydrogel was prepared by copolymerization, cooling, and freezing/thawing methods. This triple-network (TN) structure hydrogel displayed superior mechanical properties, low swelling ratio and self-healing properties. The superior mechanical properties are attributed to the triple helix association of Gela and PVA crystallites by reversible hydrogen bonding. The characterization results indicated that the fracture stress and the strain were 808 kPa and 370% respectively, while the compression strength could reach 4443 kPa and the compressive modulus was up to 39 MPa under the deformation of 90%. The hydrogen bonding in PVA contributed to maintain and improve the self-healing ability of hydrogels. Every type of hydrogels exhibited a higher swelling ratio under alkaline conditions, and the swelling ratios of PAA, PAA/PVA and PAA/Gela hydrogels were 27.71, 12.30 and 9.09, respectively. The PAA/Gela/PVA TN hydrogel showed the lowest swelling ratio (6.57) among these hydrogels. These results indicate that the novel TN hydrogels possess good environmental adaptability and have potential applications in the biomedical engineering and sensor field.

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Cited: Crossref(1) WebOfScience(1)
Facile solvothermal synthesis of NiFe2O4 nanoparticles for high-performance supercapacitor applications
Meenaketan SETHI, U. Sandhya SHENOY, Selvakumar MUTHU, D. Krishna BHAT
Front. Mater. Sci.    2020, 14 (2): 120-132.
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We report a green and facile approach for the synthesis of NiFe2O4 (NF) nanoparticles with good crystallinity. The prepared materials are studied by various techniques in order to know their phase structure, crystallinity, morphology and elemental state. The BET analysis revealed a high surface area of 80.0 m2·g−1 for NF possessing a high pore volume of 0.54 cm3·g−1, also contributing to the amelioration of the electrochemical performance. The NF sample is studied for its application in supercapacitors in an aqueous 2 mol·L−1 KOH electrolyte. Electrochemical properties are studied both in the three-electrode method and in a symmetrical supercapacitor cell. Results show a high specific capacitance of 478.0 F·g−1 from the CV curve at an applied scan rate of 5 mV·s−1 and 368.0 F·g−1 from the GCD analysis at a current density of 1 A·g−1 for the NF electrode. Further, the material exhibited an 88% retention of its specific capacitance after continuous 10000 cycles at a higher applied current density of 8 A·g−1. These encouraging properties of NF nanoparticles suggest the practical applicability in high-performance supercapacitors.

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Synthesis of hollow Prussian blue cubes as an electrocatalyst for the reduction of hydrogen peroxide
Qinglin SHENG, Dan ZHANG, Yu SHEN, Jianbin ZHENG
Front. Mater. Sci.    2017, 11 (2): 147-154.
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A cubic Prussian blue (PB) with the hollow interior was successfully synthesized by direct dissociation followed by a controlled self-etching process. The etching process also made hollow Prussian blue (HPB) a porous structure. SEM, TEM and XRD were employed to confirm the structure and morphology of the prepared materials. Then HPB and chitosan (CS) were deposited on a glassy carbon electrode (GCE), used to determine H2O2. The amperometric performance of HPB/CS/GCE was investigated. It was found that the special structure of HPB exhibits enhanced performance in the H2O2 sensing.

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On the Taylor principles for plastic deformation of polycrystalline metals
Weimin MAO
Front. Mater. Sci.    2016, 10 (4): 335-345.
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Grain orientation evolutions and texture formation based on the Taylor principles offer important references to reveal crystallographic mechanisms of deformation behaviors. Strain equilibrium between grains is achieved in Taylor theory, however, stress equilibrium has not yet been reached perfectly even in many modifications of the theory though the textures predicted become very close to those of experimental observations. A reaction stress model is proposed, in which mechanical interactions between grains are considered in details and grain deformation is conducted by penetrating and non-penetrating slips. The new model offers both of the stress and strain equilibria and predicts the same textures indicated by Taylor theory. The rolling texture simulated comes very close to the experimental observations if the relaxation effect of the non-penetrating slips on the up-limits of reaction stresses is included. The reaction stress principles open theoretically a new field of vision to consider deformation behaviors of polycrystalline materials, whereas the Taylor principles become unnecessary both theoretically and practically. Detailed engineering conditions have to be included in simulations if the deformation textures of industrial products should be predicted.

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Cited: Crossref(7) WebOfScience(6)
Graphene-induced enhanced anticorrosion performance of waterborne epoxy resin coating
Huan-Yan XU, Dan LU, Xu HAN
Front. Mater. Sci.    2020, 14 (2): 211-220.
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In this work, waterborne epoxy resin E44 and graphene were employed as the matrix and nanofiller, respectively, to construct composite coatings with enhanced anticorrosion performance. XRD pattern and TEM observation indicated that the obtained graphene had a stacked structure of few-layer graphitic sheets with numbers of wrinkles. SEM observations revealed that no defects or microcracks existed on the surface of graphene/epoxy coatings and the internal micropores and microcracks were filled by graphene. FTIR spectra displayed that all the characteristic absorption peaks were attributed to the epoxy resin cured with polyamide. The Tafel polarization curves showed that, as the graphene addition amount increased, the corrosive potential increased and the corrosive current decreased. ESI results proved that the addition of graphene into epoxy coatings could not only increase the impedance arc in Nyquist plots, but also increase the impedance modulus at low frequency. Finally, the enhanced anticorrosion mechanism was proposed and discussed.

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PEEK modified PLA shape memory blends: towards enhanced mechanical and deformation properties
Lan ZHANG, Zhaohua LIN, Qiang ZHOU, Suqian MA, Yunhong LIANG, Zhihui ZHANG
Front. Mater. Sci.    2020, 14 (2): 177-187.
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Polylactic acid (PLA) is one of the most promising shape memory polymers with outstanding biocompatibility, while poly(ether ether ketone) (PEEK) is a special engineering plastic with excellent mechanical performance. In this work, PEEK was selected to modify PLA, and a series of PLA blended with different PEEK contents (PLA/PEEK blends) were obtained. The effects of PEEK on thermodynamic, mechanical and shape memory properties of PLA/PEEK blends were investigated. The results showed that the thermal stability of the PLA/PEEK blend was improved with the PEEK content increase. The tensile strength reached the highest value of 20.6 MPa when the PEEK content was 10%. While the best shape memory performance occurred with the PEEK content of 15%, the shape recovery time was less than 2 s, and the shape fixation/recovery ratio was more than 99%. Furthermore, the programmable mimetic flower opening process was achieved by using PLA/PEEK blends with different PEEK content ratios. The above results indicated that the blend of an appropriate proportion of PEEK had positive effects on mechanical and deformation performances of PLA.

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Investigation of post-thermal annealing-induced enhancement in photovoltaic performance for squaraine-based organic solar cells
Rui ZHU, Feiyang LIU, Zixing WANG, Bin WEI, Guo CHEN
Front. Mater. Sci.    2020, 14 (1): 81-88.
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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.

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Study on quality of resistance spot welded aluminum alloys under various electrode pressures
San-san AO, Zhen LUO, Xin-xin TANG, Lin-shu ZHOU, Shu-xian YUAN, Rui WANG, Kai-lei SONG, Xing-zheng BU, Xiao-yi LI, Zhi-qing XUE
Front Mater Sci Chin    2009, 3 (1): 98-101.
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The electrode force is one of the main parameters in resistance spot welding (RSW). It is very important to guarantee the quality of aluminum alloys and determine whether the electrode pressure is stable or adjustable in the welding process. With the drive set of a servo-motor, we conduct the RSW tests and tensile shear tests on the 5052 aluminum alloy sheets. Results of these tests show that all variable pressure curves are suitable for spot welding, and all have their own rules in affecting the tensile strength of the spot welded joints.

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A simple and controllable nanostructure comprising non-conductive poly(vinylidene fluoride) and graphene nanosheets for supercapacitor
Jing SUN, Ling-Hao HE, Qiao-Ling ZHAO, Li-Fang CAI, Rui SONG, Yong-Mei HAO, Zhi MA, Wei HUANG
Front Mater Sci    2012, 6 (2): 149-159.
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An?effective?method?was?used?to produce stable and homogeneous colloidal suspensions of highly reduced graphene oxide (RGO) in N,N-dimethylformamide (DMF) without the assistance of dispersing agents. According to the results of general characterization, relatively pure graphene sheets with the morphology of single layer or few-layer structure were obtained. Then nanocomposite powders of RGO and poly(vinylidene fluoride) (PVDF) were prepared by vacuum filtration of the mixed dispersions of both components. The nanocomposites exhibit a high-frequency capacitative response with small equivalent series resistance (ESR) at 0.4 Ω, a nearly rectangular cyclic voltammogram and possess a rapid current response as electrodes for supercapacitor in 5 mol/L KOH electrolyte. Furthermore, after 600 galvanostatic charge/discharge cycles, the supercapacitor still performs a very high stability and efficiency of capacitance.

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Cited: Crossref(3) WebOfScience(3)
Numerical simulation of humping phenomenon in high speed gas metal arc welding
Ji CHEN, Chuan-Song WU
Front Mater Sci    2011, 5 (2): 90-97.
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It is of great significance to obtain a thorough understanding of the physical mechanisms responsible for humping bead phenomenon in high speed gas metal arc welding (GMAW) in order to raise welding efficiency. Experiments were conducted to observe the weld pool behaviors in high speed GMAW, and it was found that both the severely deformed weld pool surface and strong backward flowing play a dominant role in humping bead formation. In this study, a mathematical model is developed to quantitatively analyze the forming mechanism of humping beads for high speed GMAW through considering both the momentum and heat content distribution of the backward flowing molten metal inside the weld pool. The transient development of temperature profiles in the weld pool with severe deformation demonstrates the humping bead forming process under some welding conditions. The predicted and measured humping bead dimensions are in agreement.

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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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One-step gas-phase construction of carbon-coated Fe3O4 nanoparticle/carbon nanotube composite with enhanced electrochemical energy storage
Yun ZHAO, Linan YANG, Canliang MA
Front. Mater. Sci.    2020, 14 (2): 145-154.
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Carbon nanotubes (CNTs) as superior support materials for functional nanoparticles (NPs) have been widely demonstrated. Nevertheless, the homogeneous loading of these NPs is still frustrated due to the inert surface of CNTs. In this work, a facile gas-phase pyrolysis strategy that the mixture of ferrocene and CNTs are confined in an isolated reactor with rising temperature is developed to fabricate a carbon-coated Fe3O4 nanoparticle/carbon nanotube (Fe3O4@C/CNT) composite. It is found the ultra-small Fe3O4 NPs (<10 nm) enclosed in a thin carbon layer are uniformly anchored on the surface of CNTs. These structural benefits result in the excellent lithium-ion storage performances of the Fe3O4@C/CNT composite. It delivers a stable reversible capacity of 861 mA·h·g−1 at the current density of 100 mA·g−1 after 100 cycles. The capacity retention reaches as high as 54.5% even at 6000 mA·g−1. The kinetic analysis indicates that the featured structural modification improves the surface condition of the CNT matrix, and contributes to greatly decreased interface impendence and faster charge transfer. In addition, the post-morphology observation of the tested sample further confirms the robustness of the Fe3O4@C/CNT configuration.

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Host-mediated biofilm forming promotes post-graphene pathogen expansion via graphene micron-sheet
Kun YANG, Jinghuan TIAN, Wei QU, Bo LUAN, Ke LIU, Jun LIU, Likui WANG, Junhui JI, Wei ZHANG
Front. Mater. Sci.    2020, 14 (2): 221-231.
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Graphene is a potential candidate for applications in biomedical field. It is inevitable that graphene is in contact with the ubiquitous bacterial environment. More attention has been paid to the antimicrobial activity of graphene derivatives (graphene oxide, reduced graphene oxide) than the interaction between graphene and bacteria. Herein, we explore interaction between graphene micron-sheet and bacteria from micro (gene expression) and macro (colonies) perspectives. Results demonstrate that graphene micron-sheet accelerates the biofilm forming thus promoting pathogen expansion toward both Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus. The graphene micron-sheet acts as a “habitat” for increasing bacterial attachment and biofilm forming. For E. coli, graphene micron-sheet, firstly changes the integrity of periplasmic and outer membrane components, then makes membrane-associated and cell division genes increased, and finally promotes bacterial proliferation; For S. aureus, graphene micron-sheet can accelerate biofilm forming and develop bacterial expansion owing to the regulation of the quorum-sensing system and global regulatory proteins. The work can shed new light on the range of possible mode of actions, developing a better understanding of the capabilities of graphene micron-structures.

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Synthesis of sillenite-type Bi36Fe2O57 and elemental bismuth with visible-light photocatalytic activity for water treatment
Chuan DENG, Xianxian WEI, Ruixiang LIU, Yajie DU, Lei PAN, Xiang ZHONG, Jianhua SONG
Front. Mater. Sci.    2018, 12 (4): 415-425.
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With Fe(NO3)3·9H2O and Bi(NO3)3·5H2O as raw materials, different sillenite-type compounds and elemental bismuth were prepared by a facile one-pot solvothermal method using H2O, C2H5OH, (CH2OH)2 and C3H8O3 as solvents, respectively. The structure, morphology, elemental compositions and properties of samples were examined by XRD, SEM, TEM, ICP, XPS, N2 adsorption and desorption, UV-vis DRS and PL. The photocatalytic activities of different samples were evaluated by the photodegradation of RhB under visible-light irradiation (l>400 nm), and results show that Bi36Fe2O57 prepared using C2H5OH as the solvent owns the optimum performance. In order to explore the reaction mechanism, an additional experiment was designed to investigate the main active species during the photodegradation process via dissolving different trapping agents in the reaction solution before light irradiation. The results show that superoxide radical anions play a major role in this system since the RhB degradation was significantly suppressed after the addition of benzoquinone.

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Optimized optical design of thin-film transistor arrays for high transmittance and excellent chromaticity
Chengzhi LUO, Shiyu LONG, Guanghui LIU, COOPER, Min ZHANG, Fei AI
Front. Mater. Sci.    2020, 14 (1): 89-95.
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Transmittance and chromaticity are essential requirements for optical performance of thin-film transistor (TFT) arrays. However, it is still a challenge to get high transmittance and excellent chromaticity at the same time. In this paper, optimized optical design by using antireflection film theory and optical phase modulation is demonstrated in low temperature poly-silicon (LTPS) TFT arrays. To realize high transmittance, the refractive index difference of adjacent films is modified by using silicon oxynitride (SiOxNy) with adjustable refractive index. To realize excellent chromaticity, the thicknesses of multilayer films are precisely regulated for antireflection of certain wavelength light. The results show that the transmittance and chromaticity have been improved by about 6% and 18‰, respectively, at the same time, which is a big step forward for high optical performance of TFT arrays. The device characteristics of the TFT arrays with the optimal design, such as threshold voltage and electron mobility, are comparable to those of conventional TFT arrays. The optimized optical design results in enhanced power-conversion efficiencies and perfects the multilayer film design on the basic theory, which has great practicability to be applied in TFT arrays.

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Enhancement of red emission assigned to inversion defects in ZnAl2O4:Cr3+ hollow spheres
Dong ZHANG, Jingxin CHEN, Chunyu DU, Bingjun ZHU, Qingru WANG, Qiang SHI, Shouxin CUI, Wenjun WANG
Front. Mater. Sci.    2020, 14 (1): 73-80.
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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.

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One-step synthesis and self-assembly behavior of thermo-responsive star-shaped β-cyclodextrin--(P(MEO 2MA-co-PEGMA))21 copolymers
Lulu WEI, Beibei LU, Lei LI, Jianning WU, Zhiyong LIU, Xuhong GUO
Front. Mater. Sci.    2017, 11 (3): 223-232.
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A novel β-cyclodextrin–poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-poly(ethylene glycol) methacrylate (abbreviated as: β-CD–(P(MEO2MA-co-PEGMA))21) was prepared by using the one-step strategy, and then the star-shaped copolymers were used in the atom transfer radical polymerization (ATRP). The structure of star-shaped β-CD–(P(MEO2MA-co-PEGMA))21 copolymers were studied by FTIR, 1H NMR and gel permeation chromatography (GPC). The star-shaped copolymers could self-assembled into micelles in aqueous solution owing to the outer amphiphilic β-CD as a core and the hydrophilic P(MEO2MA-co-PEGMA) segments as a shell. These thermo-responsive star-shaped copolymers micelles exhibited lower critical solution temperature (LCST) in water, which could be finely tuned by changing the feed ratio of MEO2MA to PEGMA. The LCST of star-shaped β-CD–(P(MEO2MA-co-PEGMA))21 copolymer micelles were increased from 35°C to 58°C with the increasing content of PEGMA. The results were investigated by DLS and TEM. When the temperature was higher than corresponding LCSTs, the micelles started to associate and form spherical nanoparticles. Therefore, β-CD–(P(MEO2MA-co-PEGMA))21 star-shaped copolymer micelles could be potentially applied in nano-carrier, nano-reactor, smart materials and biomedical fields.

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Preparation of P(St-NMA) microsphere inks and their application in photonic crystal patterns with brilliant structural colors
Guojin LIU, Pengshuai HAN, Liqin CHAI, Peng LU, Yuping HE, Lan ZHOU
Front. Mater. Sci.    2020, 14 (1): 62-72.
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Patterned photonic crystals with structural colors on textile substrates have attracted a special attention due to the great advantages in application, which currently become a research hot-spot. This study utilized an ink-jet printing technology to prepare high-quality photonic crystal patterns with structural colors on polyester substrates. The self-assembly temperature of poly(styrene-N-methylol acrylamide) (P(St-NMA)) microspheres set to construct photonic crystals were deeply optimized. Moreover, the structural colors of prepared photonic crystal patterns were characterized and evaluated. When the mass fraction of P(St-NMA) microspheres was 1.0 wt.%, the pH value ranged from 5 to 7, and the surface tension was in the range of 63.79 to 71.20 mN/m, inks could present the best print performance. At 60 °C, prepared P(St-NMA) microsphere inks were good for printing to obtain patterned photonic crystals with regular arrangement and beautiful structural colors. Specifically, photonic crystals with different colors could be constructed by regulating the diameter of microspheres in inks, and prepared structural colors exhibited distinct iridescent phenomenon. The present results could provide a theoretical basis for the industrial realization of patterned photonic crystals by ink-jet printing technology.

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Facile synthesis of asymmetric patchy Janus Ag/Cu particles and study of their antifungal activity
Sudipta BISWAS, Satadru PRAMANIK, Suman MANDAL, Sudeshna SARKAR, Sujata CHAUDHURI, Swati DE
Front. Mater. Sci.    2020, 14 (1): 24-32.
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Asymmetric patchy Ag/Cu Janus nanoparticles (NPs) were synthesized via a “seed-mediated” approach. This is the first report of synthesis of nanometer sized metal-based Janus NPs without using complicated methods. Selective adsorption of the surfactant onto the seed NPs leads to the formation of Janus type structure. Subsequently the reduction potential of Ag+/Ag0 and Cu2+/Cu0 systems directs the formation of the “patch”. The patchy Janus NPs show significant antifungal activity towards a potent rice pathogen thus offering the prospect of future application in crop protection.

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