多孔硅制备及其在重金属离子检测中的应用研究

【作者】 李绍元；

【导师】 马文会；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2014， 博士

【摘要】 近年来,随着经济的快速发展,水体重金属污染问题日益严重,直接影响着人类生存,危及人民生活与健康。水体环境中重金属离子浓度的检测无论是对环境安全还是人类健康都有着十分重要的意义。本论文综合利用纳米技术和有机合成技术,以纳米多孔硅(PS)材料作为研究对象,运用其光致发光(PL)特性及可调控的化学性状,将对重金属离子具有特异性螯合能力的有机功能基团修饰到多孔硅表面,以实现多孔硅基荧光传感器、多孔硅有机无机纳米复合材料对特定重金属离子的选择性检测和富集。研究内容主要包括以下几个方面：采用双槽电化学腐蚀方法制备多孔硅,系统考查了不同掺杂浓度硅片、不同制备参数(腐蚀液配比、腐蚀时间、腐蚀电流密度)对多孔硅形貌结构以及光致发光性能的影响。根据不同制备条件下样品的孔道结构及孔隙率对多孔硅表面层“龟裂”行为的影响,提出解释多孔硅表面层龟裂行为的模型；多孔硅制备参数对其PL发光强度及发光峰位有一定影响,通过引入量化指标孔隙率(P)作为“纽带”,建立制备参数对多孔硅PL发光峰位九λ之间的定量影响关系：λPL/nm=620.3-0.595P, R=0.905。采用金属纳米颗粒辅助刻蚀法(MACE)制备多孔硅纳米线,研究了制备参数对多孔硅纳米线形貌结构以及光致发光性能的影响。在一步MACE刻蚀法制备硅纳米线的过程中,通过对硅片进行预氧化处理,可以有效地在中等掺杂硅纳米线中引入多孔甚至介孔结构,根据实验现象,提出相应模型对氧化硅基底制备多孔硅纳米线的形成机理进行解释。通过在HF/AgNO3腐蚀体系中引入氧化物种H2O2,可以有效地在中等掺杂和低掺杂硅纳米线中引入大量多孔结构,当H2O2浓度为0.1M时,能获得大量垂直交错的腐蚀孔道,利用“自电泳驱动”模型对其形成过程进行解释。通过对不同制备方法和制备条件下获得的多孔硅样品光致发光性能进行比较后,选取具有PL发光性能较强且稳定性能较好的多孔硅,研究含不同金属离子(Cd2+、Co2+、Cr3+、Mn2+、Ni2+、Pb2+、Zn2+、Cu2+)溶液浸泡对其发光特性及表面化学性状的影响。研究结果表明,与其他金属离子不同,具有较正氧化还原电位的Cu2+能在多孔硅表面发生浸渍沉积,并使得多孔硅表面发生氧化,导致SiHx物种减少,使得多孔硅PL发光减弱甚至淬灭。利用多孔硅的这一荧光选择特性,建立起多孔硅PL发光强度与溶液中Cu2+浓度之间的线性关系,以便实现多孔硅荧光传感器对水溶液中铜离子的选择性快速定性及定量检测。研究结果表明在铜离子浓度为5×10-7～50×10-7M范围内,多孔硅PL强度与铜离子浓度存在如下线性关系：IPL=1269.6-15[Ccu2+]。采用电化学三电极体系,将带有氨基、硫脲基团的有机功能分子修饰到多孔硅表面,以功能化的多孔硅作为电化学传感器分别实现对Ag+、Pb2+重金属离子的检测。在较优条件下,实验结果显示,在10-3～10-7mol/L浓度范围内,溶液中Ag+离子浓度与Ag+-APTES-PS电极表面Ag+还原电位峰强之间呈现线性关系：Ipc(μA cm-2)=118.28+15.15×1gCag+(CAg+/mol L-1)(R2=0.97173)。采用三步共价偶联反应将氨基硫脲衍生物(TSCD)嫁接到多孔硅表面,结果表明,在扫描范围为-0.5-0.8V之间,TSCD-PSE表现出对Pb2+离子表现出选择性响应特性,在1×10-6M至1×10。M范围内,Pb0氧化峰强随富集溶液中Pb2+离子浓度呈现规律性变化趋势：I=-156exp(-1562[Pb2+])-260exp(-105[Pb2+])+446(R2=0.998)。在多孔硅表面引入Si-OH基团,并采用多步有机共价偶联技术,将具有刺激响应的苯并咪唑二硫衍生物(BDT)“接枝”到多孔硅表面,研究其对不同重金属离子(Cd2+、Cu2+、Hg2+、Pb2+、Co2+)的预富集能力,并在谷胱甘肽(GSH)存在的条件下,研究PS-BDT及PS-BDT-M2+材料的刺激响应行为。实验结果表明BDT对Cd2+表现出较好的选择富集特性(富集效率>95%)。采用高斯09量子化学计算软件对5种BDT-M2+配合物进行键长、前线轨道能量差以及反应过程中能量降低程度等分析,其结果表明BDT配体对不同金属离子显示出选择性配位特点,配位能力排序为：Cu2+>Pb2+>Cd2+>Hg2+>Co2+；在不同金属离子M2+与BDT形成配合物的情况下,GSH的加入会与BDT-M2+配合物形成新的S-S键,导致MBI-M2+基团脱落进入GSH溶液。然而计算结果表明,只有MBI-Cd2+在其脱落之后与GSHD化合物间存在较弱的相互作用,其他四种MBI-M2+分子都与GSHD具有较强的螯合作用,使得被BDT吸附的Cu2+、Pb2+、Hg2+、Co2+离子不能完全在GSH的作用下进入溶液,从而使BDT修饰的多孔硅复合材料表现出对Cd2+具有一定的选择富集特性。更多还原

【Abstract】 Recently, heavy metal pollution has becomes increasingly serious with the rapidly growing economy, which has directly affects ours living environment and threaten people’s life and health. Thus, the method with the advantage of fast and effective detection of metal ions concentration in solution must be expected, which is very important significance for human health and environmental safety.In this paper, nano-technology and organic synthesis technology have been jointly exploited. A fluorescent sensor was proposed based on fluorescence quenching feature of porous silicon, and the electrochemical metal ions sensors were developed using the organic group functionalized porous silicon, which shows selective preconcentration or detection for some metal ions. The main research contents are as follows.Porous silicon (PS) was prepared by anodizing highly doped p-type silicon in the solution of H2O/ethanol/HF. The effects of key fabrication parameters (HF concentration, etching time and current density) on the nanostructure of PS were carefully investigated. According to the experimental results, a more full-fledged model was developed to explain the crack behaviors on PS surface. The PL spectra blue shift of the sample with higher porosity is confirmed by HRTEM results that the higher porosity results in smaller Si nanocrystals. A linear model (λPL/nm=620.3-0.595P, R=0.905) was established to describe the correlation between PL peak positions and porosity of PS.Porous silicon nanowires (PSNWs) were fabricated by the metal-assisted chemical etching (MACE) method, the effects of fabrication parameters on the nanostructure and photoluminescence of silicon nanowires (SiNWs) were investigated. The simple pre-oxidization process is firstly used to treat the starting silicon wafer, and then PSNWs are successfully fabricated from the moderately doped wafer by one-step MACE technology in HF/AgNO3system. According to the experiment results, a model was proposed to explain the formation mechanism of porous SiNWs by etching the oxidized starting silicon. PSNWs were also fabricated by the’one-pot procedure’(MACE method in the HF/H2O2/AgNO3system. The experimental results indicate that porous structure can be introduced by the addition of H2O2. When H2O2concentration is0.1mol/L, numerous almost perpendicular pore channels can be observed in the etched silicon. A self-electrophoresis mode driven by H2O2reduction is proposed to explain the PSNWs formation.The porous silicon sample with strong and stable PL emission was selseted by comparing the PL properties of porous silicon fabricated under different conditions. The effects of various metal ions species (Cd2+、Co2+、Cr3+、Mn2+、Ni2+、Pb2+、Zn2+、Cu2+) on PL and surface chemisity of PS were studied. The results indicate that the copper ions with higher redox potential can deposite on PS surface, which leads the surface oxidization and reduction of SiHx group and causes the quenching of PL. The relationship between the PL intensity and copper ions concentration was established, the PL intensity of PS is decreased as the description of the equation of IPL=1269.6-15[CCu2+] when copper ions concentration is between5×10-7～50×10-7M.3-aminopropyltriethoxysilanes (APTES) and thiosemicarbazide derivative (TSCD) modified porous silicon electrode (PSE) has been respectively used for the detection of Ag+and Pb2+in aqueous solution. Under the optimal experimental conditions, the cathode peak currents of APTES-PSE were increased with Ag+concentrations over the range from1×10-3mol L-1to1×10-7mol L-1and the linear equation of｜Ipc｜(μA cm-2)=118.28+15.15×1gCAg+(CAg+/mol L-1)(R2=0.97173) was established. A multi-step graft route was designed for anchoring TSCD groups on porous silicon (PS) surface. The results display that the anodic peak current density increase with the increasing Pb2+concentration over the range of1×10-6mol L-1～1×10-3mol L-1and which has a good fitting with a second order exponential function, I=-156exp(-1562[Pb2+])-260exp(-105[Pb2+])+446(R2=0.998).The cleavable groups (benzimidazoledithi, BDT) were grafted on the PS surface by a stepwise covalent process. The pre-enrichment efficiency of BDT-PS was investigated at the different pH for the different metal species (Cd2+、Cu2+、Hg2+、Pb2+and Co2+). The results show that the BDT-PS has sensitive pre-enrichment for Cd ions (enrichment efficiency>95%). The bond length, the gaps of HOMO and LOMO and energy decrease before and after the chelation of coordination compounds (BDT-M2+) were calculated by Gaussian09. The results indicate that the ligand BDT has sensitive chelating ability for different metal ions (Cu2+>Pb2+>Cd2+>Hg2+>Co2+). The disulfide bonds in un-chelated BDT can be cleaved by glutathione (GSH) and leading the2-mercaptobenzimidazole (MBI) loss. The new disulfide bonds would form with the addition of GSH and the MBI-M2+was replaced by glutathione derivative (GSHD). But, compared with MBI-Cu2+、MBI-Pb2+、 MBI-Hg2+and MBI-Co2+, only MBI-Cd2+has a poor chelating with the resulting GSHD and can enter into GSH solution, which leads the BDT-PS shows a sensitive pre-enrichment proprety for Cd2+.更多还原