金团簇掺杂镍原子的量子化学研究

利用基于密度泛函理论的量子化学从头计算方法,计算了金掺杂镍原子团簇AunNi2(n=1~4)的稳定结构和对应的电子态,部分稳定结构具有较高的自旋多重性.比较研究AunNi2和Aun的稳定性,结果表明Au-Ni相互作用较强,掺入两个Ni原子提高了纯金团簇的稳定性,而且团簇体积越大,这种影响越小,计算结果还再现了封闭结构高稳定性质的振荡性.     

Nano-Sized NiO Immobilized on Au/CNT for Benzyl Alcohol Oxidation: Influences of Hybrid Structure and Interface

Tiny gold nanoparticles were successfully anchored on carbon nanotubes (CNT) with NiO decoration by a two-step synthesis. Characterizations suggested that Ni species in an oxidative state preferred to be highly dispersed on CNT. During the synthesis, in situ reduction by NaBH₄ and thermal treatment in oxidation atmosphere were consequently carried out, causing the formation of Au-Ni-O_x interfaces and bimetal hybrid structure depending on the Ni/Au atomic ratios. With an appropriate Ni/Au atomic ratio of 8:1, Ni atoms migrated into the sub-layers of Au particles and induced the lattice contraction of Au particles, whilst a higher Ni/Au atomic ratio led to the accumulation of NiO fractions surrounding Au particles. Both contributed to the well-defined Au-Ni-O_x interface and accelerated reaction rates. Nickel species acted as structure promoters with essential Au-Ni-O_x hybrid structure as well as the active oxygen supplier, accounting for the enhanced activity for benzyl alcohol oxidation. However, the over-layer of unsaturated gold sites easily occured under a high Ni/Au ratio, resulting in a lower reaction rate. With an Au/Ni atomic ratio of 8:1, the specific rate of AuNi₈/CNT reached 185 μmol/g/s at only 50 °C in O₂ at ordinary pressure.     

Au-Ni异质结纳米晶的尺寸调控

系统研究了贵金属引导还原法制备Au-Ni异质结纳米晶中的尺寸控制规律, 并通过TEM、紫外-可见光谱对样品进行了表征. 研究表明: 在240 ℃条件下, Au-Ni异质结的合成过程中, 减少Au前驱体用量, 并不能减小异质结中Au端颗粒的尺寸, 此时其尺寸保持不变而Ni端颗粒的尺寸明显增大; 在反应体系中引入适量的双十二烷基二甲基溴化铵(DDAB)会使异质结Au端颗粒尺寸相应减小, 同时Ni端颗粒尺寸保持不变, 进而实现异质结两端颗粒尺寸的选择性调控. 要实现Au、Ni端颗粒尺寸的同时减小需降低反应温度, 但一定范围内的升高温度则不会产生明显作用. 以上研究不单提供了纳米异质结的调控方法, 也为进一步研究Au-Ni双金属纳米晶的催化等性能打下了材料基础.