Hydrothermal and entropy generation specifications of a hybrid ferronanofluid in microchannel heat sink embedded in CPUs

The objective of this numerical work is to evaluate the first law and second law performances of a hybrid nanofluid flowing through a liquid-cooled microchannel heatsink.The water-based hybrid nanofluid includes the Fe_3O_4 and carbon nanotubes(CNTs) nanoparticles.The heatsink includes a microchannel configuration for the flow field to gain heat from a processor placed on the bottom of the heatsink.The effects of Fe_3O_4 concentration(φFe_3O_4),CNT concentration(φ_(CNT)) and Reynolds number(Re) on the convective heat transfer coefficient,CPU surface temperature,thermal resistance,pumping power,as well as the rate of entropy generation due to the heat transfer and fluid friction is examined.The results indicated higher values of convective heat transfer coefficient,pumping power,and frictional entropy generation rate for higher values of Re,φFe_3O_4 and φ_(CNT).By increasing Re,φFe_3O_4 and φ_(CNT),the CPU surface temperature and the thermal resistance decrease,and the temperature distribution at the CPU surface became more uniform.To achieve the maximum performance of the studied heatsink,applying the hybrid nanofluid with low φFe_3O_4 and φ_(CNT) was suggested,while the minimum entropy generation was achieved with the application of nanofluid with high φFe_3O_4 and φ_(CNT).     

Synthesis of Fe3O4 and Pt nanoparticles on reduced graphene oxide and their use as a recyclable catalyst

A bifunctional Fe(3)O(4)-Pt/reduced graphene oxide (rGO) composite, i.e. Fe(3)O(4) nanoparticles (~4.8 nm in size) and Pt nanoparticles (~5 nm in size) loaded on a rGO surface, has been synthesized. It shows great catalytic performance for the reduction of methylene blue. Recycling of the composite can be achieved by simply applying an external magnetic field. In addition, the Fe(3)O(4)-Pt/rGO composite exhibits a higher catalytic activity and selectivity for aqueous-phase aerobic oxidation of benzyl alcohol than does the FeO(x)-Pt on carbon nanotubes (i.e. FeO(x)-Pt/CNT composite). Moreover, the approach for the synthesis of Fe(3)O(4)-Pt/rGO composite is simple, and can be widely employed to produce other rGO-based composites with special properties. Our work indicates that the rGO-based bifunctional composite has great potential for practical applications in various fields, such as catalytic reaction, electrochemical sensing, clean energy, etc.     

Highly selective fluorescent chemosensor for Zn2+ derived from inorganic-organic hybrid magnetic core/shell Fe3O4@SiO2 nanoparticles

ABSTRACT: Magnetic nanoparticles with attractive optical properties have been proposed for applications in such areas as separation and magnetic resonance imaging. In this paper, a simple and novel fluorescent sensor of Zn2+ was designed with 3,5-di-tert-butyl-2-hydroxybenzaldehyde [DTH] covalently grafted onto the surface of magnetic core/shell Fe3O4@SiO2 nanoparticles [NPs] (DTH-Fe3O4@SiO2 NPs) using the silanol hydrolysis approach. The DTH-Fe3O4@SiO2 inorganic-organic hybrid material was characterized by transmission electron microscopy, dynamic light scattering, X-ray power diffraction, diffuse reflectance infrared Fourier transform, UV-visible absorption and emission spectrometry. The compound DTH exhibited fluorescence response towards Zn2+ and Mg2+ ions, but the DTH-Fe3O4@SiO2 NPs only effectively recognized Zn2+ ion by significant fluorescent enhancement in the presence of various ions, which is due to the restriction of the N-C rotation of DTH-Fe3O4@SiO2 NPs and the formation of the rigid plane with conjugation when the DTH-Fe3O4@SiO2 is coordinated with Zn2+. Moreover, this DTH-Fe3O4@SiO2 fluorescent chemosensor also displayed superparamagnetic properties, and thus, it can be recycled by magnetic attraction.     

微波水热法制备纳米Fe3O4粉体

通过微波水热法制备了纳米Fe3O4颗粒,并对其进行了Ostwald熟化处理。研究了油酸和氢氧化钠含量对纳米Fe3O4粒径大小以及分散性的影响。利用XRD、TEM等方式对所制备颗粒的结构、形貌进行了表征,结果表明,所制备的纳米Fe3O4粒子属于反尖晶石结构,通过微波加热未经熟化的纳米Fe3O4粒子结晶度较低,平均粒径为6nm。经过在180℃下熟化8h后,转化为结晶度较高,分散性较好,平均粒径为7nm的纳米Fe3O4颗粒。     

酞菁铜-Fe3O4纳米复合粒子复合机理及其性能的研究

制备了酞菁铜（ＣｕＰｃ）－Ｆｅ３Ｏ４纳米复合粒子,分析了ＣｕＰｃ与Ｆｅ３Ｏ４纳米粒子的复合过程,提出了其复合机理。研究并建立了ＣｕＰｃ－Ｆｅ３Ｏ４纳米复合粒子的结构模型,研究了复合粒子的抗氧化性和热性。结果表明,ＣｕＰｃ与Ｆｅ３Ｏ４纳米粒子之间形成了化学键。在复合过程中,首先一部分ＣｕＰｃ与Ｆｅ３Ｏ４纳米粒子表面的氧离子形成化学键;然后Ｆｅ３Ｏ４纳米粒子发生聚集,形成聚集体;最后相当一部分ＣｕＰＣ     

分散剂对纳米四氧化三铁磁流体稳定性的影响

通过球磨手段,经表面活性剂表面处理颗粒,制备稳定分散纳米四氧化三铁磁性液体。选择表面活性剂GD-01、GD-02和GD-03,研究了溶液pH、球磨时间和表面活性剂用量对磁性液体分散性的影响,采用红外光谱分析仪（FT-IR）和高分辨透射电子显微镜（HRTEM）表征磁性液体中的颗粒。结果表明： GD-02的最佳pH为4.5,GD-01和GD-03的最佳pH为2.5,最佳球磨时间皆为5 h,最佳表面活性剂为GD-02,其最佳用量为0.5 g左右,此时颗粒表面形成稳定的吸附双电层结构,通过静电位阻和空间位阻作用,阻止颗粒团聚,制得分散性能很好的纳米磁性液体。     

Growth of carbon nanotube forests on metallic thin films

Growing carbon nanotube (CNT) forests on metals for integrated circuits interconnections or active layers applications is currently a challenge. CNT forests easily develop on insulators but their growth on metallic substrates is subject to interdiffusion and wettability effects that hamper the formation of the catalyst nanoparticles. This paper reports the successful growth of dense CNT forests on some metallic layers (Mo, Ta, W, and Ir) in comparison to other metallic films (Au, Cu, and Ti) over which CNTs are hardly achieved. The CNT forests are grown by thermal decomposition of C₂H₂ diluted in NH₃ and characterized by Raman spectroscopy and scanning electron microscopy. Stabilizing Al thin films placed between the metallic substrates and the Fe catalyst promote the formation of Fe nanoparticles. Metallic substrates, thickness of the Al stabilizer, and temperature and raise time during nanoparticles formation are all instrumental parameters in the growth and final structure of the CNT forests.     

壳聚糖修饰磁性纳米粒子对BSA的吸附性能

采用化学共沉淀法制备磁性Fe3O4纳米粒子,以（3-氯丙基）三甲氧基硅烷为偶联剂将壳聚糖共价键合到磁性Fe3O4纳米粒子的表面,通过红外光谱（FTIR）、X射线衍射（XRD）、扫描电子显微镜（SEM）及热重分析（TGA）对其进行了表征。主要研究了不同影响因素（吸附时间、pH值、牛血清白蛋白浓度）下壳聚糖修饰的磁性纳米粒子对牛血清白蛋白（BSA）的吸附性能。结果得到壳聚糖修饰的磁性Fe3O4纳米粒子粒径为20 nm左右,壳聚糖在磁性Fe3O4纳米粒子表面的接枝率为15.40%。研究表明：在不同条件下,与未修饰的磁性Fe3O4纳米粒子相比,经壳聚糖修饰的Fe3O4纳米粒子对BSA均表现出较强的吸附能力。     

三种表面活性剂对Fe3O4纳米颗粒的形貌影响

选用十六烷基三甲基溴化铵(CTAB)、聚乙烯吡咯烷酮(PVP)、十二烷基磺酸钠(SDS)3种表面活性剂,研究了这3类不同表面活性剂和不同添加量对Fe3O4纳米颗粒的形貌调控作用,利用透射电镜(TEM)对样品进行表征分析,并给出了机理解释。结果表明:1)3种不同的表面活性剂的加入都获得球形或近球形的纳米颗粒。根据TEM及沉积时间的综合分析,3种活性剂的平均粒径比较:SDS相似文献   

微乳液法制备Fe3O4/TiO2磁性纳米粒子

采用多元醇还原法制备出平均粒径为6.0 nm的Fe3O4磁性纳米粒子,以此磁性纳米粒子为核,在OP-10/正丁醇/环己烷/浓氨水反向微乳体系中制备出Fe3O4/TiO2磁性纳米复合粒子,通过XRD,TEM,VSM对复合粒子进行性能表征。结果表明,采用微乳液法能够制备出Fe3O4/TiO2磁性纳米复合粒子,并且包覆后比饱和磁化强度有所下降,但矫顽力仍趋近于0,显示超顺磁性。     

苯乙烯丙烯酸正丁酯共聚物/Fe3O4复合材料的制备与表征

采用原位聚合法制备了苯乙烯丙烯酸正丁酯共聚物（PSb）/四氧化三铁（Fe3O4）纳米复合材料,并通过傅里叶变换红外光谱仪、透射电子显微镜、X射线衍射仪、综合物理特性测量系统对该复合材料的结构与性能进行了表征。结果表明：Fe3O4纳米粒子直径约9 nm,同时能较均匀地分散在PSb中且无明显团聚;该复合材料具有良好的超顺磁性;XRD图谱中Fe3O4特征峰随着复合材料中Fe3O4含量的增加而逐渐增强;同时Fe3O4纳米粒子的加入提高了PSb的热稳定性。     

Fe_3O_4/介孔碳复合体的合成及其处理罗丹明B废水的应用

以介孔SBA-15为硬模板,利用硝酸铁和蔗糖一步浸渍的方法,通过纳米刻蚀合成了Fe3O4与介孔碳纳米粒子复合体（Fe3O4/介孔碳复合体）,对复合体进行吸附有机染料罗丹明B的磁性分离研究,实验表明,Fe3O4/介孔碳复合体有较好的吸附分离性能。     

潜在的T2类造影剂Fe3O4@BSA纳米粒子的合成及性能研究

制备了Fe_3O_4@BSA磁性纳米功能材料,包裹在Fe_3O_4纳米粒子表面的牛血清白蛋白(BSA)主要起到分散剂和稳定剂的作用。通过傅里叶变换红外光谱、X射线衍射、透射电子显微镜及热重分析对合成的Fe_3O_4@BSA纳米粒子进行了表征和分析。结果表明,制备的Fe_3O_4@BSA纳米粒子中BSA质量分数约为18.9%。体外成像结果表明,随着Fe_3O_4@BSA纳米粒子浓度的增加,T2成像信号增强,具有明显的阴性造影效果。于0.5 T外磁场下,测得Fe_3O_4@BSA纳米粒子的横向弛豫率(transverse relaxivity,r2)为148.18 L/(mmol·s)。结果表明,Fe_3O_4@BSA纳米粒子能够作为一种潜在的T2类磁共振成像造影剂。     

磁微粒子Fe_3O_4纯化CdS纳米晶的实验研究

以L-半胱氨酸、醋酸镉为原料,在磁微粒子Fe3O4存在下,通过水热法合成出CdS纳米晶与磁微粒子连接混合体,利用磁微粒子的磁性对合成的CdS纳米晶进行分离纯化,然后加入聚乙烯吡咯烷酮(PVP)、3-巯基丙酸使磁微粒子与硫化镉纳米晶分离。对产品进行了详尽的XRD、SEM、HRTEM及EDS能谱表征分析,并测试了纯化前后样品的荧光激发谱与荧光发射谱,荧光光谱显示获得预期的纯化效果。     

Static magnetic field-assisted synthesis of Fe_3O_4 nanoparticles and their adsorption of Mn(Ⅱ) in aqueous solution

A facile method for synthesis of the magnetic Fe_3O_4 nanoparticles was introduced.Magnetic nanoparticles were prepared via co-precipitation method with(PMF) and without(AMF) 0.15 T static magnetic field.The effects of magnetic field on the properties of magnetic nanoparticles were studied by XRD,TEM,SEM,VSM and BET.The results showed that the magnetic field in the co-precipitation reaction process did not result in the phase change of the Fe_3O_4 nanoparticles but improved the crystallinity.The morphology of Fe_3O_4 nanoparticles was varied from random spherical particles to rod-like cluster structure.The VSM results indicated that the saturation magnetization value of the Fe_3O_4 nanoparticles was significantly improved by the magnetic field.The BET of Fe_3O_4nanoparticles prepared with the magnetic field was larger than the control by 23.5%.The batch adsorption experiments of Mn(Ⅱ) on the PMF and AMF Fe_3O_4 nanoparticles showed that the Mn(II) equilibrium capacity was increased with the pH value increased.At pH 8,the Mn(Ⅱ) adsorption capacity for the PMF and AMF Fe_3O_4 was reached at 36.81 and 28.36 mg·g~(-1),respectively.The pseudo-second-order model fitted better the kinetic models and the Freundlich model fitted isotherm model well for both PMF and AMF Fe_3O_4.The results suggested that magnetic nanoparticles prepared by the magnetic field presented a fairly good potential as an adsorbent for an efficient removal of Mn(Ⅱ) from aqueous solution.     

疏水改性核壳结构颗粒对Pickering乳液的稳定作用

为了探究固体颗粒对乳液的稳定作用,采用双亲染料分子罗丹明B对核壳结构的Fe_3O_4@SiO_2纳米颗粒进行疏水改性,并将改性后的纳米颗粒作为稳定剂制备Pickering乳液。通过Zeta电位、FTIR、XRD、SEM、接触角测量、光学显微镜、电导率仪对Fe_3O_4@SiO_2纳米颗粒以及Pickering乳液的结构、形貌和性能进行表征与分析,结果表明:制备的纳米颗粒粒径小,约为150 nm,为单分散球形核壳结构;罗丹明B成功修饰到Fe_3O_4@SiO_2纳米颗粒表面,改性后颗粒接触角由30°增加至120°;随乳化剂颗粒质量浓度的增加,制备的乳液液滴的粒径减小。另外,所得Pickering乳液具有良好的磁场响应性,可通过外加磁场实现对乳液稳定性的可逆调控,且此过程可重复3次以上。     

聚乙烯亚胺功能化Fe3O4纳米粒子的制备

以油酸包覆的Fe3O4磁性纳米粒子为原料,3,4-二羟苯基丙酸(DHCA)为表面改性剂,四氢呋喃(THF)为溶剂制备出DHCA功能化的Fe3O4纳米粒子。将制备得到的功能化Fe3O4纳米粒子偶联聚乙烯亚胺(PEI),得到稳定分散的聚乙烯亚胺功能化Fe3O4磁性复合纳米粒子。利用FTIR、TEM、VSM、Zeta电位对磁性粒子组分、形貌、粒径、磁学性能和电位性能进行表征。该法简便,反应条件温和,所制备的PEI功能化Fe3O4纳米粒子具有良好的超顺磁性和分散性。     

Fe3O4/凹凸棒土磁性纳米复合材料的制备与表征

采用超声共沉淀法制备了Fe3O4-凹凸棒土(AT)磁性纳米复合材料,经红外光谱(FTIR),X射线衍射(XRD),场发射扫描电镜(FESEM),比表面积(BET)和振动样品磁强计(VSM)等方法进行表征.结果表明:Fe3O4纳米粒子较好地吸附在AT表面,并且表现出优良的吸附性能和顺磁性.     

Core-shell Fe3O4@SiO2 nanoparticles synthesized with well-dispersed hydrophilic Fe3O4 seeds

Silica coated magnetite (Fe3O4@SiO2) core-shell nanoparticles (NPs) with controlled silica shell thicknesses were prepared by a modified St?ber method using 20 nm hydrophilic Fe3O4 NPs as seeds. The core-shell NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), and UV-Vis adsorption spectra (UV-Vis). The results imply that NPs consist of a crystalline magnetite core and an amorphous silica shell. The silica shell thickness can be controlled from 12.5 nm to 45 nm by varying the experimental parameters. The reaction time, the ratio of TEOS/Fe3O4, and the concentration of hydrophilic Fe3O4 seeds were found to be very influential in the control of silica shell thickness. These well-dispersed core-shell Fe3O4@SiO2 NPs show superparamagnetic properties at room temperature.     

正交试验优化核壳型Fe3O4@SiO2磁性复合微球的制备工艺

采用共沉淀法和溶胶-凝胶法制备了磁性Fe3O4纳米粒子及核壳型Fe3O4@SiO2复合微球,利用红外光谱(FTIR)技术测定了微球表面基团,证明了SiO2确实在Fe3O4纳米粒子的表面形成了包覆层。通过正交试验设计,利用激光粒度仪测量的微球粒径为指标,考察TEOS与磁性微球的体积比、反应温度、反应时间和乙醇浓度四因素对微球粒径的影响。结果表明TEOS与磁性微球的体积比为2、反应温度为80℃、反应时间为4 h,乙醇浓度为80%是制备大粒径Fe3O4@SiO2磁性复合微球的适宜条件。