摘要
采用高灵敏度的表面增强拉曼光谱(SERS)技术,结合不同长度的探针分子,通过电化学调控研究了Fe电极在离子液体中的表面增强因子、零电荷电位、界面吸附及界面双电层结构.利用壳层隔绝纳米粒子增强拉曼光谱(SHINERS)技术提高表面吸附物种的拉曼信号,降低高浓度本体的信号干扰,研究了1-丁基-3-甲基咪唑四氟硼酸盐([BMIm]BF4)离子液体本身在Au@SiO2修饰的Fe电极表面的吸附行为.结果表明,[BMIm]BF4在Au@SiO2修饰的Fe电极表面的吸附行为随电位变化而变化.在-1.3 V以正区间,咪唑阳离子以垂直吸附为主,随电位负移逐渐倾斜甚至平躺吸附于电极表面;当电位负至-2.3 V,咪唑阳离子还原成卡宾.再分别以不同分子长度的硫氰根(SCN-)和4-氰基吡啶(4-CNPy)为探针分子,发现SCN-在[BMIm]BF4中以N端吸附在纯Fe电极上,三键频率随电位变化的速率,即Stark系数为17 cm-1/V;4-CNPy以吡啶环上的N垂直吸附于Fe电极上,频率保持不变,即Stark系数接近零.以上结果表明,在离子液体中电极界面双电层与水体系的差别较大,电位主要分布在电极紧密层中,几乎无分散层存在.此外,还计算了[BMIm]BF4中Fe电极的增强因子约为1.5×102.
The surface enhanced factor, potential zero charge （pzc）, surface adsorption and structures of electrostatic double layer were electrochemically investigated at ionic liquids/Fe electrode interfaces through high sensitive surface enhanced Raman spectroscopy （SERS） combined with probe molecules of various lengths. In order to improve the intensity of Raman signals from adsorbed species and decrease the influences from the bulk ionic liquids, Au@SiO2 nanoparticles were spread over the Fe electrode, that is, shell-isolated nanoparticles-enhanced Raman spectroscopy （SHINERS） was employed. Based on the SHINERS technology, the adsorption behaviors of 1-butyl-3-methylimidazolium tetrafluoroborate （[BMIm]BF4） on a Au@SiO2 modified Fe electrode were investigated. It was found that the adsorption behaviors depended on the applied potentials. When the potentials were positive than -1.3 V [vs. a Pt quasireference electrode （PQRE）], [BMIm]BF4 was adsorbed with the imidazolium ring nearly perpendicular to the surface. While it kept tilted or even parallel as the potentials negative to -1.3 V. At a extremely negative potential （-2.3 V）, the imidazolium cation was reduced to carbene. In addi- tion, SCN^- and4-cyanopyridine （4-CNPy） with different molecular lengths were employed as probes. Electrochemical Stark effects of C-=N stretching band was measured to monitor the double structures at ionic liquids/Fe electrode interfaces. It was resulted that SCN^- and 4-CNPy were adsorbed through N atom and N atom of pyridine ring, respectively. The results revealed that the C≡N stretching band of SCN^- was shifted to low frequency with the negative moved potentials. The electrochemical Stark coefficient was about 17 cm^-1/V. However, the C≡N stretching band of 4-CNPy nearly kept constant, that is, Stark coefficient was 0 cm^-1/V. It was suggested that there were big differences comparing with aqueous systems. The surface electric field was mainly distributed in the compact layer of ionic liquids/Fe electrode interface. Moreover, through the calculation based on the SERS of SCN , the surface enhancement factor of rough Fe electrode in [BMIm]BF4 was about 1.5×10^2.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2013年第7期1059-1063,共5页
Acta Chimica Sinica
基金
国家自然科学基金(Nos.21073128
21033007
21173155)
江苏省自然科学基金(No.BK2012187)资助~~
关键词
表面增强拉曼光谱
界面
离子液体
Fe电极
吸附
surface enhanced Raman spectroscopy （SERS）
interface
ionic liquids
Fe electrode
adsorption
