【作者】 谢瑞刚；

【导师】 顾宏伟；

【作者基本信息】 苏州大学 ， 应用化学， 2015， 博士

【摘要】 金属纳米材料由于具有催化活性高,生物相容性好,抗菌性能好等诸多优点备受研究者的强烈关注。金属纳米材料的合成方法很多,其中液相合成法依旧是主要的合成方法。一般分为油相法和水相法两类。近年来,氢气用于纳米金属的合成已经取得一些进展。从铂纳米立方体,四面体到枝状纳米晶,氢气都被证明是一种有效清洁的还原剂。基于这一点,我们尝试以氢气作为主要还原剂,在常压下,液相合成了一些新型纳米材料。主要研究工作可以分为以下几个方面:(1)在纯油胺溶液中,常压低温下,合成了铂树突状纳米立方体。对材料合成的过程跟踪分析发现,动态组成的油胺和十八胺是调节铂纳米树突成立方体的关键。氢气还原诱发铂前驱体分解成核,快速形成晶种,在油胺的保护下生长并催化油胺加氢,使得纳米铂的表面不断更新,因此,这种方法制备的纳米铂材料表面比较干净。从材料的空间构型看,此种方法制备的铂纳米材料空间孔洞非常丰富,是催化剂的首选。随后,对不饱和烃和硝基苯的加氢反应上,显示了出色的催化性能。对甲醇的电氧化反应,立方纳米铂树突的催化活性达到了铂纳米粒子的5.3倍。(2)通过两步法,在纯油胺溶液中制备了Au@Pt系列纳米材料,外层的铂先是包覆在金粒子上,然后在外层的铂表面再长上树枝状的铂条。整个过程来说,外层的铂同样参与了油胺的氢化,结果是铂条表面更新带来整个催化剂的有效活性面积的变化。与商业的JM-Pt/C相比,制备的Au@Pt纳米材料在甲醇电催化和甲酸电催化方面都表现出来更好的催化性能。对甲酸的氧化上主要是脱水历程,其催化活性是商业铂碳的2倍以上。(3)利用顺式和反式1,2-环己烷二酸作为修饰剂,在油胺体系中,制备了空心纳米钯球。无碱条件下,两种纳米催化剂对苯乙酮的加氢显示出不同的选择性。顺式二酸修饰的纳米钯球倾向于生成苯乙醇,反式二酸修饰的二酸偏重于生成乙苯,添加NH3·H2O,可以实现选择性的转变,使顺式二酸修饰的催化剂选择性转向了乙苯。(4)使用邻苯二胺进行修饰铂纳米可以得到海绵状的纳米铂,使用R(+)-α-甲基苄胺和S(-)-α-甲基苄胺修饰的纳米金银可以得到手性纳米线和纳米链。这些材料都有潜在的催化应用前景。纳米铂在氢气氛围下,生长快速,在Pt NPs上沿着八个角生长速度最快,而在Fe Pt rods和Fe Pt NWs表面生长成双向外延生长,但在Au NWs上却是单向外延生长。即使是PVP包裹的Pd NWs和Ag NWs,在油相中,氢气还原下,纳米铂依旧可以还原生长在表面,形成异质结构。UV/O3处理的Pd NWs可有效去除材料表面的PVP,但是在处理过程中会出现断裂现象。(5)邻卤苯胺是重要的化工中间体,通常由邻卤硝基苯选择性加氢制备,但由于副反应较多,脱卤严重。所以寻求合适的催化体系一直都吸引着许多研究者。Fe(CO)5诱发成核制备的Pt NPs和适当的弱碱(Na HCO3和NH3·H2O)构成的催化体系用于邻卤硝基苯制邻卤苯胺。低温常压下即可实现加氢过程,产率达到99%以上,并且催化剂重现性好。更多还原

【Abstract】 Metal nano materials have attracted many researchers’ attention intensively due to the high catalytic activity, good biological combination,antibacterial performance and so on. There are many synthetic methods for metal nano materials, wherein liquid phase synthesis method is still the main synthesis method. Liquid phase synthesis method is generally divided into two types: oil phase method and aqueous phase method.In recent years, some progress has been made in the synthesis of metal materials with hydrogen.From platinum nano cube and tetrahedron to dendritic nanocrystals, hydrogen has been proven to be an effective clean reductant. For this reason, we synthesized a number of novel nanomaterials with the liquid-phase synthesis at atmospheric pressure and low temperatures in a hydrogen atmosphere.The main research work can be divided into the following areas:(1) Pt dendritic nanocubes were synthesized in pure oleylamine at low temperature and atmospheric pressure. According to the tracking analysis in the process of material synthesis, the dynamic composition of oleylamine and octadecylamine is the key factor for Pt dendritic nanocubes. The platinum precursor was induced to decomposition, nucleation and grow into Pt seeds by hydrogen. The surface of platinum nanocrystals have been continuously updated in the process of the catalytic hydrogenation of oleylamine oleylamine. Thus the surface of as-sythesized platinum nanocrystals is relatively clean. Pt dendritic nanocubes is the preferred catalyst for the porous configuration of the nanocrystals. Subsequently, Pt dendritic nanocubes showed excellent catalytic performance in the hydrogenation of unsaturated hydrocarbons and nitrobenzene. For methanol electro-oxidation reaction, the catalytic activity of platinum dendrites cubic nanometer was 5.3 times greater than platinum nanoparticles.(2) A series of Au@Pt was prepared in pure oleylamine by two-step method in a hydrogen atmosphere. The outer layer with platinum appeared when the surface of gold particles was surrounded platinum.Then the dendritic platinum strips grew on the outer layer. The outer platinum strips catalyzed hydrogenation of oleylamine. The ECSA(electrochemical surface area) of the Au@Pt nanocrystals changed with the renewal process of the platinum surface. Compared with the commercial JM-Pt/C, Au@Pt exhibited better electrocatalytic activity in the oxidation of formic acid and ethanol. The oxidation of formic acid is mainly dehydration process, and the catalytic activity of the prepared Au@Pt nanocrystals was 2 times than the commercial JM-Pt/C for the oxidation of formic acid.(3) The porous Palladium nanospheres were prepared in the pure oleylamine with trans-1,2-cyclohexanedicarboxylic acid and cis-1,2-cyclohexanedicarboxylic acid as the modifying agent. Under alkali conditions, the two catalysts for the hydrogenation of acetophenone show different selectivity. The catalyst modified with cis-1,2-cyclohexanedicarboxylic acid tends to generate phenethyl alcohol and the other catalyst puts emphasis up on ethylbenzene. when NH3·H2O was used, the catalyst selectivity was changed, that is to say the catalyst modified with cis-1,2-cyclohexanedicarboxylic acid tends to generate ethylbenzene.(4) Spongy platinum nanoparticles were synthesized when o-phenylenediamine was added to the oleylamine solution in a hydrogen atmosphere. Silver nanochains were produced with(R)-(+)-1-Phenylethylamine and(S)-(-)-1-Phenylethylamine as the modifying agent. Chiral Au nanowires were prepared when(R)-(+)-1-Phenylethylamine was used. These materials have the potential catalytic applications. Platinum nanocrystals grew fast especially along the 8 pods of Pt NPs. Polyhedral truncated cubic platinum and truncated cubic platinum changed to cubic platinum when the platinum precursor was added to pure oleylamine in a hydrogen atmosphere. Finally,Platinum overgrew on each corner of the cubic platinum. Epitaxial grew of Platinum nanostrips on the suface of Fe Pt rods, Fe Pt NWs and Au NWs. Even when Pd NWs and Ag NWs wered capped by PVP(polyvinylpyrrolidone), Platinum nanostrips also grew on the surface of Pd NWs and Ag NWs. Treatment was used to remove excess PVP on the surface of Pd NWs. PVP-capped Pd NWs broke in the process of UV/O3 treatment.(5) O-halogen aniline is an important chemical intermediate and usually prepared from selective hydrogenation of o-halogen nitrobenzene. But dehalogenation and side effects are the serious problems during the reaction. So the suitable catalyst system has been attracting many researchers. The catalytic system could solve this problem, which is made up of appropriate weak base(Na HCO3 and NH3·H2O) and Pt NPs induced nucleation by Fe(CO)5. The advantage of this system is good catalyst repeatability at a low temperature and atmospheric pressure.更多还原