可控制备磁性四氧化三铁-金纳米复合颗粒及其催化性能研究

doi:10.15541/jim20170394

摘要/Abstract

摘要：

随着纳米催化剂的不断发展, 基于纳米金的多功能复合材料以其高效的催化性能而受到广泛关注。本研究采用简单可控的原位还原法, 制备了一种粒径均一、分散性良好、可快速磁分离且具有高催化活性与催化稳定性的磁性四氧化三铁-金纳米复合颗粒。首先用有机硅源-巯丙基三乙氧基硅烷(MPTES)水解得到的有机硅层来包覆粒径约100 nm的亲水四氧化三铁(Fe₃O₄)纳米颗粒, 再通过有机硅层表面的巯基来锚定原位还原生成的尺寸可控的金纳米颗粒(2 nm或6 nm), 得到内核为四氧化三铁、壳层为金纳米颗粒均匀修饰有机硅层的磁性氧化硅复合颗粒。利用透射电子显微镜(TEM)、动态光散射仪(DLS)和振动样品磁强计(VSM)等对所合成材料进行系统表征, 结果表明: 合成的磁性氧化硅复合颗粒核壳结构明显, 分散性良好, 粒径约为150 nm; 饱和磁强度为32.1 A•m²/kg, 具有良好的超顺磁特性。将其应用于4-硝基苯酚的催化还原, 转化频率(TOF)值高达70 s^-1, 远高于文献报道值, 五次循环反应后的转化率依然高达98%, 证实其具备高催化活性及良好的循环催化性能。

关键词: 原位还原, 磁性四氧化三铁-金纳米复合颗粒, 超顺磁性, 高催化活性, 循环性能

Abstract:

With the rapid development of nanocatalysts, gold-based nanocomposites have attracted more and more attention due to their excellent catalytic capability. In this study, a novel kind of gold-based magnetic nanocomposite with uniform size, high dispersity, magnetic separability, highly catalytic efficiency, and stability was facilely fabricated via a controllable in-situ reducing approach. Firstly, magnetic nanocomposites were synthesized through coating 100 nm-sized hydrophobic Fe₃O₄ nanoparticles with organosilica shell formed by the hydrolysis of mercaptopropyltriethoxysilane (MPTES). Then, size-controllable gold nanoparticles (2 nm or 6 nm) formed via in situ reduction was anchored onto the organosilica shell via Au-S covalent bonding, so that gold-based magnetic nanocomposites consisted of Fe₃O₄ nanoparticles as core and gold nanoparticles decorated organosilica as shell were obtained. Various techniques, such as Transmission Electron Microscope (TEM), Dynamic Light Scattering (DLS) and Vibrating Sample Magnetometer (VSM) were employed to characterize the as-synthesized samples. It is demonstrated that the as-prepared nanocomposite is highly-dispersed, core-shell structured and superparamagnetic with diameter of ~150 nm. The saturation magnetization was measured to be 32.1 Am²/kg. Furthermore, the turnover frequency (TOF) of MCN-Au (2 nm) is calculated to be 70 s^-1 towards the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). More importantly, the conversion rate maintains 98% after 5 cycling usage, verifying its highly catalytic capability and reusability.

Key words: in situ reduction, gold-based nanocomposite, superparamagnetic, highly catalytic capability, reusability

中图分类号:

TQ174

李永生, 陈玲. 可控制备磁性四氧化三铁-金纳米复合颗粒及其催化性能研究[J]. 无机材料学报, 2018, 33(2): 221-228.

LI Yong-Sheng, CHEN Ling. Controlled Synthesis of Gold-based Magnetic Nanocomposites and Their Catalytic Performance[J]. Journal of Inorganic Materials, 2018, 33(2): 221-228.

图/表 10

图1 MCN-Au复合颗粒的制备示意图

Fig. 1 Schematic illustration for preparation of the MCN-Au

图2 (a) Fe3O4, (b) MCN, (c~e) MCN-Au (2 nm)的透射电镜照片; (f) MCN-Au (2 nm)上负载Au NPs的粒径分布

Fig. 2 TEM images of (a) Fe3O4 particles, (b) MCN nanospheres, (c-e) MCN-Au (2 nm); (f) Size distribution of Au NPs on MCN-Au (2 nm)

图3 (a~c) MCN-Au (6 nm)的透射电镜照片; (d) MCN-Au (6 nm)上负载的Au NPs的粒径分布

Fig. 3 TEM images of (a-c) MCN-Au (6 nm); (d) Diameter distribution of Au NPs on MCN-Au (6 nm)

图4 (a) Fe3O4, (b) MCN, (c) MCN-Au (2 nm), (d) MCN-Au (6 nm)的扫描电镜照片; 不同粒子在水相中的动态光散射(DLS)粒径分布曲线

Fig. 4 SEM images of (a) Fe3O4 nanoparticles, (b) MCN, (c) MCN-Au (2 nm), (d) MCN-Au (6 nm); (e) Diameter distribution curves of different particles

图5 (a) MCN-Au (2 nm)的STEM照片; (b1)金元素、(b2)铁元素和(b3)硫元素的EDS元素面扫描图谱; (c) MCN-Au (2 nm)的能谱图

Fig. 5 STEM image of MCN-Au (2 nm) nanocomposites (a); scanning mapping of Au elements (b1), Fe elements (b2) and S elements (b3). Scale bar is 100 nm; (c) EDS pattern of MCN- Au (2 nm)

图6 (a) Fe3O4, (b) MCN, (c) MCN-Au (2 nm)和(d) MCN-Au (6 nm)的XRD图谱

Fig. 6 Wide-angle XRD patterns of (a) Fe3O4 nanoparticles, (b) MCN, (c) MCN-Au (2 nm) and (d) MCN-Au (6 nm)

图7 MCN-Au (2 nm) (黑色曲线)和MCN-Au (6 nm) (红色曲线)在水溶液中的紫外吸收光谱谱图

Fig. 7 UV-Vis spectra of (a) MCN-Au (2 nm) (black curve) and (b) MCN-Au (6 nm) (red curve) The insets are the digital photos of MCN-Au (2 nm) and MCN-Au (6 nm)

图8 Fe3O4纳米粒子, MCN, MCN-Au (2 nm)和MCN-Au (6 nm)的室温磁滞洄线

Fig. 8 Room-temperature magnetization hysteresis loops of the Fe3O4 nanoparticles, MCN, MCN-Au (2 nm), and MCN-Au (6 nm) The inset is a photograph of the MCN-Au (2 nm) under an external magnetic field

图9 MCN-Au(2 nm)催化4-NP的UV-Vis谱图(每隔20 s测试一次)

Fig. 9 UV-Vis spectra of the reduction of 4-NP in aqueous solution recorded every 20 s using MCN-Au (2 nm) as a catalyst

图10 在4-NP催化还原实验中MCN-Au的(a)Ct/C0和(b)ln(Ct/C0)与反应时间的曲线关系; (c)MCN-Au (2 nm)和(d)MCN-Au (6 nm)的循环使用性能测试

Fig. 10 Curves of (a) Ct/C0 and (b) ln(Ct/C0) versus the reaction time for the reduction of 4-NP over MCN-Au; the reusability of the (c) MCN-Au (2 nm) and (d) MCN-Au (6 nm)

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