纳米银/石墨烯复合SERS基底的制备及对铀(Ⅵ)的拉曼光谱研究

Design and Fabrication of Silver Nanoparticles/Graphen Complex Substrate and Its Application for Detecting Uranium(Ⅵ)

铀是核工业中一种重要的核燃料,研究其在水溶液中的浓度和种态信息具有重要意义。铀(Ⅵ)在水溶液中最稳定的存在形式UO_2^(2+),其标准Raman散射峰为871cm^(-1)。然而利用表面增强拉曼散射(SERS)技术检测铀(Ⅵ)时,铀(Ⅵ)与SERS基底的直接相互作用,使得铀(Ⅵ)的Raman峰存在很大程度的偏移,甚至偏移到710cm^(-1)。使用不同的SERS基底,其偏移程度也不同,无法反映溶液中铀(Ⅵ)的真实Raman信息,为解析溶液中铀(Ⅵ)的种态带来了很大困难。通过抗坏血酸活化银纳米粒子(AgNPs),在硅衬底上自组装AgNPs阵列,得到SERS基底。利用石墨烯介质隔层的化学惰性和完整性,通过悬空自助转移法在该自组装AgNPs SERS基底表面转移单层石墨烯,制备了纳米银/石墨烯复合SERS基底。并表征了该复合SERS基底的形貌,AgNPs粒子紧密连接在一起,形成纳米链结构,纳米链均匀地分布于衬底表面,单层石墨烯紧密覆盖于AgNPs表面,且石墨烯的亚纳米级厚度没有改变AgNPs的形貌。将这两类SERS基底用于检测硝酸铀酰,对于未覆盖石墨烯的AgNPs基底,UO_2^(2+)的对称伸缩振动峰为719cm^(-1),基底与UO_2^(2+)的相互作用导致谱峰宽化,并向低波数移动。而在覆盖了石墨烯的G-AgNPs复合SERS基底表面,UO_2^(2+)的对称伸缩振动峰为771cm^(-1),回移了52cm^(-1),这种大幅度的回移表明石墨烯隔层在一定程度上隔绝了UO_2^(2+)与AgNPs的相互作用。

Uranium is one of the important nuclear materials to nuclear industry.Because of the direct disposal of spent fuel,there is still a huge possibility that uranium migrates into the groundwater,causing water contamination.It is of great importance to understand the concentration and their species distribution in aqueous solutions.Surface-Enhanced Raman Scattering（SERS）technique has been widely used for the detection of uranium（Ⅵ）.However,the interactions between uranium（Ⅵ）and SERS substrate cause the symmetric stretching vibration peak of uranium（Ⅵ）shift to low wave number direction,which is unfavorable for confirming the species of uranium（Ⅵ）in aqueous solution.For instance,the normal Raman bands of uranyl in nitric acid solution are 871cm^（-1）,which belongs to the symmetric stretching mode of UO_2^（2＋）.However,it moves to 710cm^（-1） on the surface of silver nanorods SERS substrtate.What＇s more,different SERS substrate causes different number of shift.Graphene has advantages of inertness and integrity as well as 2-dimensional thickness.In this paper,graphene-isolated SERS substrate which is silver nanoparticles（AgNPs）/graphene complex substrate,was designed to prevent the interaction between SERS substrate and it was analyzed by using the inert graphene layer.First of all,according to our previous work,AgNPs SERS substrate was fabricated on silicon wafer by using an ascorbic acid-actived self-assembly method.Then,AgNPs/graphene complex substrate was prepared by transfering monolayer graphene onto the self-assembly AgNPs substrate.The morphology of complex substrate was obtained by SEM.Some AgNPs link together closely to form nanochain structures.Nanochain structures were distributed evenly on the surface of silicon wafer.The 2-dimensional thickness of graphene did not affect the morphology of AgNPs.When using the complex substrate to detect uranyl nitrate（5×10^-4 mol·L^-1）,the Raman peak that appeared around 771cm^（-1） is considered to be the symmetric stretching mode of UO_2^（2＋）,shifting back about 52cm^（-1） to high wave number direction when compared with AgNPs substrate,which was about^719cm^（-1）.The result indicates that graphene layer isolates the interaction between AgNPs substrate and uranyl in some degree.