多孔羰基铁/CoFe2O4/聚苯胺复合材料的制备及吸波机理

通过金属点蚀技术制备了表面多孔形貌的羰基铁粉（PCIP）,并采用共沉淀及原位聚合方法,将CoFe₂O₄与聚苯胺（PANI）负载于多孔羰基铁表面,得到具有电磁吸收性能的PCIP/CoFe₂O₄/PANI复合材料.通过扫描电子显微镜（SEM）、X射线衍射仪（XRD）、傅里叶变换红外光谱仪（FTIR）、热重分析仪（TGA）及矢量网络分析仪（VNA）等对复合材料的形貌、成分和吸波性能进行了研究.结果表明,CoFe₂O₄/PANI团聚于PCIP表面,显著提升了复合材料电损耗能力,促进了低频电磁波的1/4波长干涉相消.当苯胺添加量为0.5 mL,复合材料在频率为5.7 GHz时,反射损耗达到-22.9 dB,低频吸波性能得到大幅提升.利用1/4波长干涉相消理论及电磁波界面反射模型对复合材料低频吸波性能提升的内在原因进行了分析.     

多孔羰基铁/SiO2/聚吡咯核壳结构复合材料的制备及电磁特性

首先对羰基铁进行点腐蚀得到多孔羰基铁,然后采用St?ber法和原位聚合法将SiO_2和导电高分子聚吡咯包覆在多孔羰基铁表面,制备多孔羰基铁/SiO_2/聚吡咯电磁复合吸波材料。采用XRD、SEM、TEM、FT-IR对样品结构、微观形貌进行了表征,在网络分析仪中采用同轴法测试样品电磁参数,并根据传输线理论研究了2~18 GHz微波频段内吡咯含量及涂层厚度对样品吸波性能的影响。实验结果表明:制备的多孔羰基铁/SiO_2/聚吡咯复合电磁吸波材料具有核壳结构;随着吡咯加入量的增加,吸波材料吸收峰逐渐向低频方向移动;当涂层厚度为3.5 mm、吡咯加入量为6%(w/w)时,在9.44~17.56 GHz范围内反射率均低于-10 d B,频带宽度为8.12 GHz,损耗反射率达到-23 d B。良好的吸波性能归因于复合物有效的阻抗匹配特性及多重界面极化效应,多孔羰基铁/SiO_2/聚吡咯是一种轻质、宽频、强吸收的吸波材料。     

海胆状氧化锌/羰基铁粉核壳结构复合粒子的抗氧化及吸波性能

针对羰基铁粉吸收剂在温度较高时易被氧化的问题,采用水热法制备了氧化锌包覆羰基铁粉核壳结构复合粒子,并分别将羰基铁粉和氧化锌/羰基铁粉核壳粒子与石蜡混合,制备复合材料。结果表明,氧化锌纳米棒致密的包覆在羰基铁粉颗粒表面形成海胆状核壳结构复合粒子,正是这种结构将羰基铁粉颗粒与空气隔绝,使得复合粒子的抗氧化性能得到显著改善。与羰基铁粉复合吸波材料相比,氧化锌/羰基铁粉核壳粒子的复合材料吸收峰稍向低频移动,反射损耗小于-5dB的带宽几乎保持不变,在不改变电磁吸波性能的前提下,提高了羰基铁粉粒子的使用温度。     

聚芳醚酮基复合吸波材料的制备及性能

以磁性多孔碳(WPC/MNPs-80)作为吸波剂材料, 通过溶液共混方式将其与聚芳醚酮复合, 制备了聚芳醚酮基复合吸波材料(6F-PAEK-Crosslink@WPC/MNPs-80). 为了通过溶液共混的方式制备复合材料并避免成膜过程中吸波剂的沉降问题, 设计合成了含有氨基与六氟异丙基的可溶性可交联型聚芳醚酮(6F-PAEK-NH₂). 结果表明, 在交联剂作用下形成的交联结构不仅避免了吸波剂粒子沉降, 而且还赋予了材料优异的耐热性能和力学性能. 此外, 6F-PAEK-Crosslink@WPC/MNPs-80还具有优异的吸波性能, 当复合膜厚度为1.4 mm时, 最大反射损耗达到了-33 dB, 损耗超过-10 dB的频带宽度达到4.8 GHz; 当复合膜厚度为1.8 mm时, 最大反射损耗为-44.5 dB, 损耗超过-10 dB的频带宽度达到3.1 GHz.因此, 6F-PAEK-Crosslink@WPC/MNPs-80是一种综合性能优异的电磁波吸收材料.     

La1-xSrxMn1-yFeyO3微波吸收特性研究

采用溶胶-凝胶法制备La1-xSrxMn1-yFeyO3（x=0．15，0．20，0．23；y=0．10，0．12，0．14，0．16），用HP8722型微波网络矢量分析仪测定样品在频率2-18GHz的电磁波吸收特性。发现Sr和Fe含量的改变都会影响体系的吸波性能，经测试得到x=0．2，y=0．14时的吸波特性最好。对于La1-xSr0.2Mn0.86Fe0.14O3，在涂层厚度为2mm时，有两个吸收峰，最大峰值达到了37dB，10dB以上的带宽达到了6．2GHz，在2-12．5GHz频率段微波吸收主要以介电损耗为主，在12．5GHz附近介电损耗和磁损耗发生突变，在12．5-18GHz频率段微波主要以磁损耗为主，电阻率在室温时处在半导体范围内，对吸波有利。     

海胆状氧化锌/羰基铁粉核壳结构复合粒子的抗氧化及吸波性能

针对羰基铁粉吸收剂在温度较高时易被氧化的问题,采用水热法制备了氧化锌包覆羰基铁粉核壳结构复合粒子,并分别将羰基铁粉和氧化锌/羰基铁粉核壳粒子与石蜡混合,制备复合材料。结果表明,氧化锌纳米棒致密的包覆在羰基铁粉颗粒表面形成海胆状核壳结构复合粒子,正是这种结构将羰基铁粉颗粒与空气隔绝,使得复合粒子的抗氧化性能得到显著改善。与羰基铁粉复合吸波材料相比,氧化锌/羰基铁粉核壳粒子的复合材料吸收峰稍向低频移动,反射损耗小于-5 d B的带宽几乎保持不变,在不改变电磁吸波性能的前提下,提高了羰基铁粉粒子的使用温度。     

碳纤维表面羰基铁的原位生长及吸波性能

以Fe(CO)5为前驱体,通过金属有机化学气相沉积(MOCVD),在碳纤维(CF)表面构筑厚度为纳米级的羰基铁(CI)壳层,通过改变沉积温度,调控核壳粉体的形貌结构和吸波性能。用X射线衍射仪、扫描电子显微镜和矢量网络分析仪对粉末的结构及电磁性能进行表征并对其吸波性能进行研究。结果表明:随着沉积温度升高(210~240℃),沉积到CF表面的羰基铁颗粒互相“吞并-融合”,此时CF-CI形成了完整的薄膜包覆型核壳结构;沉积温度太高时(270℃)会造成CF表面羰基铁壳层形貌的恶化。通过调节沉积温度,在纳米尺度上可以有效调控CI壳层的形貌,从而调节CF-CI核壳粒子的电磁性能。以核壳形貌及吸波性能为考察指标,最终确定最佳的沉积温度为240℃。以沉积温度为240℃时所获样品的电磁参数,模拟计算出涂层厚度为0.9 mm时,小于-10 dB的吸波带宽最大为4.6 GHz(13.4~18 GHz);涂层厚度为2.0 mm时,反射率达到最小值为-21.5 dB;厚度为0.9~3.9 mm时,在2~18 GHz均能实现吸波强度低于-10 dB。     

ZnO花状微球负载NaYF4:Yb,Tm复合物的制备及电磁性能EI北大核心CSCD

采用微波辅助溶剂热-超声浸渍两步法制备了ZnO花状微球负载NaYF4:Yb,Tm(ZnO/NaYF4:Yb,Tm)复合材料。通过对样品的形貌、组成、静磁与电磁特性的表征,讨论了NaYF4:Yb,Tm纳米晶负载量以及煅烧温度对复合材料吸波性能的影响,同时,揭示了该复合材料的吸波机制。结果显示,电磁波在ZnO分级花状结构中的多重反射可以提高材料对电磁波的吸收效率。同时,NaYF4:Yb,Tm的引入有利于界面极化、缺陷极化的产生。得益于上述优势和异质结构的协同作用,当NaYF4:Yb,Tm负载量为0.15mmol时,经500℃煅烧处理所得ZnO/NaYF4:Yb,Tm复合材料展示出优异的吸波特性,当匹配厚度为2.0mm时,对应有效吸收带宽为4.89GHz,其最大吸收为-39.38dB。     

稀土氧化物对Ni-Zn铁氧体/泡沫铝吸波性能的影响

为研究掺杂稀土氧化物对Ni-Zn铁氧体/泡沫铝材料吸波性能,在泡沫铝表面涂覆了单一 Ni-zn铁氧体(记作CFe)和掺杂质量分数为1%的稀土氧化物的Ni-Zn铁氧体复合粉(记作CFe'),利用CJB 2038-94"雷达吸波材料反射率测试方法"中的雷达截面(RCS)法对材料微波反射率进行了测量,扫描电镜(SEM)和X射线衍射仪(xRD)对吸波剂的形貌和物相进行了分析.结果表明,在12～18 GHz频段内,泡沫铝表面涂敷单一的铁氧体其吸收量为1.8 dB,加人稀土氧化物后,其吸波值由1.8 dB增至2.65 dB,在26.5～40 GHz频段内时,添加稀土氧化物后,吸收量有较大的提高,从11 dB增加到15 dB,10 dB带宽扩展近6倍.因此掺杂稀土氧化物是提高吸波材料性能的一种途径.     

ZnO纳米颗粒锚定的亚微米碳纤维的制备及其吸波性能

使用静电纺丝技术结合水热法制备了表面锚定ZnO纳米颗粒的亚微米碳纤维（ZnO/SDCFs）复合物,并详细研究了反应溶液的pH值对复合物的结构、组成、电磁特性和吸波性能的影响。结果显示,随着pH值的升高,ZnO的含量增加,介电常数、介电损耗以及电磁衰减能力均下降,但阻抗匹配程度提高。相比于纯碳纤维,所有ZnO/SDCFs复合物的吸波性能均得到不同程度的加强。其中,pH值等于8时所制备的ZnO/SDCFs-8复合物拥有最好的吸波性能,主要归因于电磁衰减能力和阻抗匹配间的更好平衡。当ZnO/SDCFs-8的填充量仅为2.5%（质量分数）、厚度为1.7 mm时,相应吸波涂层的最小反射损耗达到-44.1 dB,低于-10 dB的有效吸收带宽为6.1 GHz,频率范围为11.9~18 GHz;当厚度为3.0 mm时,有效吸收带宽可提高到11.8 GHz（6.2~18 GHz）。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.