摘 要

同金、银一样，铜因其在可见光区具有局域等离子共振效应而使其具有独特的光电性能，铜也是CO氧化、对硝基苯酚还原等重要反应的催化剂。已有的研究表明，形貌和尺寸均匀一致的单分散纳米铜能明显增强其等离子共振效应，以｛100｝面为暴露面的铜纳米晶体具有最好的催化性能。

本课题旨在在水相体系中采用种子生长法合成以｛100｝面为包围面的Pd@Cu核-壳纳米立方体。探讨了纳米立方钯种子、封端剂十六烷基胺（HDA）、还原剂抗坏血酸（L-AA）的用量等工艺参数对铜的形貌和尺寸的影响，通过对不同反应时间合成的纳米铜的形貌分析，探索了纳米铜立方的形成过程和机制，研究了不同尺寸的纳米铜与其等离子共振峰的位置关系，并进行了纳米铜催化对硝基苯酚还原实验。

研究结果表明：由于Cu与Pd的晶格失配率较高（7.1 %），Cu首先在Pd种子的一两个活性位点异相形核，并通过局部外延长大。改变Pd种子的用量能合成尺寸为45-106 nm的Pd@Cu核-壳纳米立方体，太少的种子会导致Cu的自形核过程使其形貌不均匀，过多的种子又会使Cu壳太薄使其立方体发育不完整。HDA除了能定向吸附在Cu的｛100｝面从而促进了立方体的形成外，它还能通过调节溶液的pH值来改变L-AA的还原能力,通过反应速率动力学的控制来决定Cu的形貌，加入太多或太少的HDA或L-AA均会因反应速率不合适而不利于Pd@Cu核-壳纳米立方体的形成。随着Pd@Cu核-壳纳米立方体的尺寸由45 nm增大到106 nm，共等离子共振峰位置从578 nm红移至622 nm，纳米铜对对硝基苯酚还原具有一定的催化作用。

关键词：Pd@Cu核-壳纳米立方体；种子生长法；局域等离子共振吸收；对硝基苯酚还原

Abstract

Copper (Cu) nanocrystals (NCs), like Ag and Au, possess unique optical and electric properties owing to localized surface plasmon resonances (LSPR) in the visible and the near-infrared ( NIR) frequencies. Cu can also catalyze reactions such as catalytic oxidation of CO and catalytic reduction of p-nitrophenol. The previous studies demonstrated that uniform size and shape induced a strong LSPR signal at a specific wavelength and nanocubes of Cu encosed by {100} facets exhibited superior catalytic activity than the Cu polyhedrons.

In this paper, we presented a facile synthesis of Pd@Cu core-shell nanocubes enclosed by {100} facets in aqueous solutions. The effect of the amount of Pd nanocubes as seeds, hexadecylamine (HDA) as capping agents and ascorbic acid (L-AA) as reductants on the shapes and sizes of Cu nanoparticles were investigated. To explore the formation process and mechanism of Pd@Cu core-shell nanocubes, TEM images from a set of samples under the same reaction condition at different time points were taken . Optical and catalytic properties of Pd@Cu core-shell nanocubes were also examined.

The results indicated that Cu perferably nucleates on one and two of the side faces of a Pd nanocube and then grow through localized epitaxial growth due to a large lattice mismatch between Pd and Cu (7.1 %). Pd@Cu core-shell nanocubes with tunable edge lengths over the range from 45 to 106 nm could been synthesized in aqueous solutions by using the various amount of Pd seeds. Less seeds would permit spontaneous nucleation of Cu and too many seeds would lead to the runtish thin Cu shells, both of which were unfavorable to the formation of Cu nanocubes. HDA can suppress the growth of {100} facets by absorbing on the facets and consequently promote the formation of Cu nanocubes enclosed by {100} facets. It can also changed the reducibility of L-AA by increasing the solution pH and sequentially facilitate cubic Cu shell growth by a kinetical mechanism. When the edge length of nanobues was increased from 45 to 106 nm, the LSPR peak was red-shifted from 578 to 622 nm. Pd@Cu core-shell nanocubes show reasonable catalytic performance toward 4-nitrophenol reduction.

Key Words：Pd@Cu core-shell nanocubes ; Seed-mediated growth ; localized surface plasmon resonances (LSPR) ; 4-nitrophenol reduction

目录

第1章 绪论 1

1.1课题研究背景 1

1.2国内外研究现状 1

1.3课题研究内容 2

1.4预期目标 2

1.5研究方法 3

第2章 Pd@Cu核-壳纳米立方体的制备及其性能测试 4

2.1实验药品及仪器 4

2.1.1实验试剂 4

2.1.2实验仪器 4

2.2 Pd@Cu 核-壳纳米立方体的制备 5

2.2.1 单次实验具体操作步骤 5

2.2.2 对照实验组具体操作步骤 6

2.3 Pd@Cu 核-壳纳米立方体的结构与光学性能表征 7

2.3.1 场发射扫描电镜（FESEM） 7

2.3.2 透射电镜（TEM） 7

2.3.3 X射线衍射（XRD） 8

2.3.4 紫外-可见吸收光谱（UV-vis） 8

2.4 Pd@Cu核-壳纳米立方体催化性能测试 8

第3章 结果与讨论 10

3.1纳米铜立方体合成与钯种子用量之间的关系 10

3.2纳米铜立方体合成与反应时间之间的关系 18

3.3纳米铜立方体合成与还原剂用量之间的关系 21

3.4纳米铜立方体合成与封端剂用量之间的关系 22

3.5纳米铜立方体催化性能研究 26

第4章 结论 35

参考文献 36

致 谢 37

第1章 绪论

1.1课题研究背景

铜是一种丰富而廉价的金属。普通的铜金属材料延展性好，导热性和导电性高，常用在电气、轻工、机械制造、建筑工业、国防工业等领域^[1]。当铜颗粒的尺寸为纳米级时，其性能更加优越^[1]。

纳米铜是紫褐色或紫黑色的粉末，纳米铜中的铜原子和普通铜中的铜原子相同，但是纳米铜颗粒很小，呈现的化学性质较普通铜更为活泼^[1][2]，故一般存放在惰性气体或有机溶剂中^[3]。纳米铜由于具有比表面大、表面活性中心数目多、颗粒极细且软、具有高自扩散系数等优点，使其在透明导电电极、透明导电薄膜、传感器、生物医药、催化剂等方面具有重要应用^[2][4]。

①.利用其等离子共振活性可取代金、银应用于表面增强拉曼光谱仪、荧光、抗肿瘤光热疗法、生物传感器、图像、催化剂等多个领域。缺点：但由于纳米铜在可见光区直到波长小于580 nm范围内等离子共振激发与带间跃迁重叠，导致它的共振吸收较弱。通过对铜纳米晶的形貌进行控制，使形貌和尺寸均匀，或者通过铜的取向生长，使其共振峰移至红外光区来避免与带间跃迁重叠，能提高其共振强度^[1]。