Deposition-environment-dependent structural and magnetic property modification of [111]-oriented epitaxial CoFe2O4 films

We examined the magnetic, structural, and chemical properties of CoFe₂O₄ films deposited on Al₂O₃ substrates using RF-magnetron sputtering under Ar and Ar + O₂ environments. Perpendicular magnetic anisotropy with large magnetization was observed in the case of the film deposited under the Ar + O₂ environment. However, no significant anisotropy appeared in the film deposited under the Ar environment. Interestingly, depth-dependent X-ray photoelectron spectra showed nearly identical stoichiometric ratios of Co/Fe and oxygen vacancies regardless of the deposition environment. Structurally, high-quality crystallinity with in-plane compressive strain, and lower surface and interfacial roughness were induced in the film deposited under the Ar + O₂ environment. Cross-sectional transmission electron microscopy and X-ray reflectivity measurements showed that oxygen not only suppressed the deposition rate but also increased the electron density of the film, resulting in better crystallinity. Hence, the presence of oxygen during deposition should be considered as one of the essential parameters for improving the structural and magnetic properties of ferrite films.     

白藜芦醇丙烯酸酯的合成及抗氧化活性研究

以白藜芦醇为先导化合物,合成了白藜芦醇丙烯酸酯,以获得具有更好抗氧化活性的白藜芦醇衍生物。以白藜芦醇和丙烯酰氯为原料,酯化法得到白藜芦醇丙烯酸酯。以维生素C为阳性对照,研究白藜芦醇丙烯酸酯对2,2-联苯-1-苯基肼(DPPH)自由基的清除活性和抗氧化活性。用NMR和HRLC-MS对白藜芦醇丙烯酸酯进行了表征。目标产物白藜芦醇丙烯酸酯收率为30.2%。白藜芦醇丙烯酸酯的抗氧化活性高于白藜芦醇,但低于维生素C。合成得到了白藜芦醇丙烯酸酯,其反应路线简单易行,条件温和,产物抗氧化活性较先导化合物有所提高。     

氧化石墨烯改性碳纤维复合材料抗冲击行为研究

使用单层纳米氧化石墨烯（NGO）粒子对环氧树脂进行改性处理，采用真空辅助树脂传递模塑成型工艺制备了[±45/0/90]_2S铺层角度下的纯树脂及单层NGO改性碳纤维复合材料（CFRP）层合板。通过落锤冲击试验、超声C扫描检测、冲击后压缩试验等对纯树脂及单层NGO改性CFRP进行实验研究。结果表明，纯树脂及单层NGO改性CFRP在损伤阻抗及损伤容限实验中均存在拐点现象，且拐点出现在相同深度位置，其中纯树脂CFRP拐点位置为0.51 mm，单层NGO改性CFRP拐点位置为0.43 mm；相对于纯树脂CFRP，单层NGO改性CFRP可以显著提高复合材料的抗冲击性能及冲击后的压缩性能；通过对冲击后凹坑深度及凹坑面积进行数据模拟，可以用拟合公式实现对复合材料的损伤预测。     

改性纳米碳酸钙用于硅酮胶挤出性研究

采用碳化法合成纳米碳酸钙,在反应过程中,调整反应起始温度合成不同晶型大小的纳米碳酸钙。通过透射电镜（TEM）、激光粒度仪对碳酸钙的物相、形貌、粒度进行分析,将改性纳米碳酸钙应用于硅酮胶基料制备及挤出性研究,分析改性纳米碳酸钙的颗粒大小、分散性、流变性能及表面改性剂对挤出性的影响。结果表明：粒径介于50~90 nm,屈服值介于66.4~148.9 Pa,黏度介于0.5~0.75 mPa·s,硬脂酸钠与LH-2、LH-3两种包覆剂进行复配改性的纳米碳酸钙用于硅酮胶基料具有较好的挤出性能。     

超疏水表面在金属防护中应用的研究进展

超疏水表面由于具有独特的微纳米粗糙结构和低表面能性质,能形成空气垫物理屏障层,减小材料表面与水或其他腐蚀介质之间的接触面积,因此被广泛应用于金属的腐蚀防护。首先简单介绍了超疏水表面的相关理论,主要包括Young氏方程、Wenzel模型和Cassie-Baxter模型。然后,归纳总结了三种制备超疏水表面的有效途径:在低表面能物质上构建微纳米级粗糙结构;先构建出具有微纳米级的粗糙结构,再对表面进行低表面能修饰;一步法完成低表面能修饰和微纳米级粗糙结构的构建。在此基础上,详细地综述了常见的超疏水表面(薄膜或涂层)在金属防护中的应用。进一步介绍了通过在超疏水体系中引入缓蚀剂的方式,构建具有主动防护功能的超疏水表面,并介绍了此种超疏水表面在金属防护中的应用。最后指出了目前的超疏水表面在制备工艺以及耐久性等方面存在的问题,并对其在金属防护领域的应用前景和发展方向作出了展望。     

纳米纤维素的疏水改性及应用研究进展

纳米纤维素作为一种性能优越的可再生纳米材料，应用前景极为广阔。然而，由于纳米纤维素结构上富含羟基，使其具有极强的亲水性，严重影响了纳米纤维素的疏水性能，并且在一定程度上限制了其在复合材料领域的应用。综述了纳米纤维素疏水改性的研究进展，从物理吸附、表面化学修饰（甲硅烷化、烷酰化、酯化等）、聚合物接枝共聚3个方面简述了目前应用较为广泛的疏水化改性方法，并对疏水纳米纤维素在包装材料、造纸、水净化等方面的应用现状进行了总结。最后对疏水改性纳米纤维素的未来发展进行了展望，旨在为疏水纳米纤维素的研究和应用提供参考。     

Synergistic reinforcement of surface modification on improving the bonding of veneering ceramics to zirconia

Veneering ceramics should be strongly bonded to zirconia core in order to achieve successfully long-term clinical practice. Indeed, to pursue the high zirconia core–veneering ceramic bonding is still a concerned issue. In this regard, this study was to treat zirconia surface using a 3?wt% Si₃N₄ solution in 4?M NaOH and to investigate the effect of soaking time (5, 10, and 20 days) on the surface properties of zirconia and shear bond strength between zirconia and veneering ceramics. The residual veneering ceramics on zirconia surfaces and failure modes were also examined after fracture. The results showed that the phase composition of zirconia before and after surface modification was not changed. The elemental mapping and depth profiling consistently revealed the soaking-time-dependent Si content on the zirconia surface. The surface roughness of zirconia was significantly (P?<?0.05) increased with the increasing soaking time. When zirconia was treated for 10 days, the shear bond strength value of 27.4?MPa was significantly (P?<?0.05) higher than the control (18.6?MPa), associated with greater remaining amounts of veneering ceramics on the zirconia surface. The failure mode of the treated zirconia was almost the mixed failure. On the basis of the data, surface modification using Si₃N₄ in NaOH solution for zirconia core could be a simple and effective method for enhancing the veneering ceramic–zirconia bonding.     

AlF3-modified LiCoPO4 for an advanced cathode towards high energy lithium-ion battery

Surface-interface reaction between the electrode and electrolyte plays a key role in lithium-ion storage properties, especially for high voltage cathode such as LiCoPO₄ and Ni-riched cathode. Generally, surface modification is an effective method to improve the electrochemical performance of electrode materials. Herein, in order to revise the LiCoPO₄ cathode with desirable properties, uniform AlF₃-modified LiCoPO₄ (LiCoPO₄@AlF₃) cathode materials in nano-sized distribution are synthesized. XRD result indicates that there is no structural transformation observed after AlF₃ coating. TEM characterization and XPS analysis reveal that the surface of LiCoPO₄ particle is coated by a nano-sized uniform AlF₃ layer. Further, the electrochemical results indicate that AlF₃ layer significantly improves the cycling and rate performances of LiCoPO₄ cathode within the voltage range of 3.0–5.0 V. After a series of optimization, 4 mol% AlF₃-coated LiCoPO₄ material exhibits the best properties including an initial discharge capacity of 159 mA h g^?1 at 0.1 C with 91% capacity retention after 50 cycles, especially a discharge capacity of 90 mA h g^?1 can be obtained at 1 C rate. CV curves indicate that the polarization of cathode is reduced by AlF₃ layer and EIS curves reveal that AlF₃ layer relieves the increase of resistance to facilitate Li-ion transfer at the interface between electrode and electrolyte during the cycling process. The enhanced electrochemical performances are attributed to that the AlF₃ layer can stabilize the interface between the cathode and electrolyte, form steady SEI film and suppress the electrolyte continuous decomposition at 5 V high voltages. This feasible strategy and novel characteristics of LiCoPO₄@AlF₃ could promise the prospective applications in the stat-art of special lithium-ion battery with high energy and/or power density.     

Hyperbranched Polyethylenimine Modified Waste Fiberboard Activated Carbon for Enhanced Adsorption of Hexavalent Chromium

The objective of this work is to prepare a hyperbranched polyethylenimine (HBPEI) grafted activated carbon obtained from waste fiberboard for effectively removing Cr(VI) from aqueous solution. The waste fiberboard activated carbon (WFAC) was modified by HBPEI and cross-linked with glutaraldehyde (GA). The optimal modified conditions were as follows: HBPEI molecular weight 10,000 g/mol, HBPEI/WFAC (w/w) 0.5, GA concentration 0.25%, reaction time 60 min. Both pristine WFAC and HBPEI–WFAC were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), Scanning electronic microscopy (SEM), and Roman spectra. XPS data showed the obvious increase in nitrogen (from 0.72% to 6.65%) after modification. The results of FTIR and XPS suggested that HBPEI was chemically bonded onto the WFAC by the glutaraldehyde (GA) between the amine groups of WFAC and that of HBPEI. HBPEI was also probably grafted onto WFAC through the intermolecular interaction between the carboxylate groups of WFAC and the amine groups of HBPEI. However, the BET surface area of modified WFAC declined slightly (about 200 m²/g). The I_D/I_G of modified WFAC decreased from 0.92 to 0.82, which indicated that the modification process had no significant effect on the graphitization of activated carbon. The adsorption property onto HBPEI–WFAC and the factors containing contact time, pH value, and Cr(VI) concentration were also investigated. Analysis of the Cr(VI) adsorption data was well simulated by the pseudo-second-order kinetic model and Langmuir adsorption isotherm model, and maximum Cr(VI) uptake of HBPEI–WFAC was 500 mg/g.     

Surface sedimentation and adherence of Nano‐SiO2 to improve thermal stability and flame resistance of melamine‐formaldehyde foam via sol‐gel method

Melamine‐formaldehyde foam possesses intrinsic flame retardance; however, relative poor thermal stability and a certain amount of heat release rate restrict its applications in heated environment to a degree. In the present research, sol‐gel method has been adopted to precipitate nano‐SiO₂ particles on the surface of the melamine‐formaldehyde foam's fibers to construct a protective inorganic gel layer. Taking advantages of the shielding effects of the gel layer, the thermal‐oxygen degradation of the foam can be greatly retarded during heating; hence, the thermal stability is remarkably improved, and the flame retardance is further enhanced. In addition, introducing a small amount of membrane‐forming agent in the sol‐gel system can make the depositional nano‐SiO₂ particles well adhered to avoid dusting.