【作者】 李颖颖；

【导师】 丁轶；

【作者基本信息】 山东大学 ， 物理化学， 2010， 硕士

【摘要】 本论文利用去合金化法合成了纳米多孔银,并通过腐蚀条件的探索对纳米多孔银的合成机理进行了研究。鉴于纳米多孔银的特殊结构和简便制备方法,本文接下来以纳米多孔银为模板,进一步合成了中空纳米多孔Pt/Ag、Pd/Ag双金属功能材料和多孔AgCI/Ag纳米复合材料。通过透射电子显微镜(TEM),X-射线衍射(XRD),高分辨透射电镜(HRTEM),能量分散X-射线分析(EDS),电子衍射(SAED)分别对材料形貌、晶体结构、材料组分进行分析。通过电化学、光催化测试研究了它们的催化性能。旨在发展简便、无有机试剂参与、温和的合成方法合成新结构材料,并探索它们在催化方面的应用价值。1.去合金化法制备纳米多孔银及其制备条件的研究选择性腐蚀制备纳米多孔材料要点是在于协调较活泼金属溶解速率与较惰性金属扩散速率。30℃下,用约50μm厚的Ag23Al77合金在1M NaOH中腐蚀72h可以得到拥有均匀三维双连续孔壁结构的纳米多孔银结构,孔径尺寸约为40nm。温度升高或腐蚀溶液浓度增大都会影响最终材料的形貌。在HCl溶液中,同样的银铝合金片腐蚀也可以得到海绵状的三维双连续孔壁纳米多孔银结构,但多孔结构表面相对粗糙。研究证实Cl-的存在对于银的表面扩散具有明显的加速作用。2.中空纳米多孔Pt/Ag、Pd/Ag双金属材料的制备及其电催化性质研究以去合金化法制备的纳米多孔银同时为物理和化学模板,通过简单的置换反应制备了中空的纳米多孔双金属材料。其中以40nm纳米多孔银为物理模板(制备方法同上)和还原剂分别与H2PtCl6,K2PdCl4溶液进行置换反应。通过电镜观察证实纳米多孔结构的孔壁被掏空,形成了中空纳米多孔双金属结构。其中Pt/Ag材料的管壁表面比较光滑,管径大概为45 nm,壁厚约7 nm,而Pd/Ag材料的管壁上有直径约为4 nm的小孔,管径约40 nm,壁厚约5nm。XRD及电子衍射数据证实两种材料都为合金。在电催化性能测试中,我们发现Pt/Ag材料具有良好的甲醇电氧化性能和抗CO中毒能力。这种纳米结构独特的催化性能、简便环保的制备方法、显著的结构优势为其在非均相催化剂和燃料电池技术中显示了潜在的应用价值。3.海绵状纳米多孔AgCl/Ag复合材料的制备及其可见光催化性能的研究多孔AgCl/Ag纳米复合材料由简便的两步路径合成。其中包括去合金化法制备纳米多孔银及其随后的与H2O2和HCl混合溶液的氯化反应。电镜分析显示AgCl/Ag继承了纳米多孔银的均匀的拥有三维双连续孔壁多孔结构,孔壁尺寸约为600 nm。紫外漫反射数据显示该材料有明显的可见光响应现象,实验研究证实这一响应源自于材料中残余的Ag。在以甲基橙溶液降解为测试系统的材料可见光催化性能测试中,在420 nm波长以上光源的照射下,多孔AgCl/Ag的降解速率为0.75mg/min·gcat,明显优于体相AgCl。这种多孔结构的复合光催化材料及其简便制备方法在环境科学中显示了广阔的应用前景。更多还原

【Abstract】 Nanoporous silver (NPS) was fabricated by a simple dealloying method, and its formation mechanism was studied by corrosion condition controlling experiences. Based on the significative structure of NPS and its facile fabricating method, we further fabricated tubular nanoporous Pt/Ag, Pd/Ag bimetallic materials and porous AgCl/Ag nanocomposite. By means of TEM(Transmission Electron Microscopy), HRTEM(High Resolution Transmission Electron Microscopy), XRD(X-ray Diffraction), SAED(Select Area Electron Diffraction), EDS(Energy Dispersive X-Ray Spectrum) the surface morphology, crystal structure of these materials have been studied. Catalytic properties of these materials were explored by employing the electrochemical and photocatalytic test system. This paper was focusing on the developing of facile and environmental friendly fabrication method for effective catalytic material structure.1. Preparation of NPS by dealloying and the fabrication conditions study.The key point for the fabrication of nanoporous material by dealloying is to balance the dissolution speed of the more active element and the diffusion speed of the more inert element. Typically, NPS with sponge like uniform nanoporous surface can be fabricated by etching a piece of 50μm Ag23Al77 alloy in 1 M NaOH for 72 h at 30℃. The final morphology of the material was deeply related on the concentration/temperature of the corrosion solution and the corrosion time. Etching the same AgAl alloy in the HC1 solution can also obtain the nanoporous skeleton with bicontinuous pore ligaments companied with a rough surface. It is verified by the controlling experiments that the existence of Cl- can markedly accelerate the diffusion speed of Ag.2. Preparation and electrocatalytic performance of nanotubular porous platinum-group bimetallic nanocompositesDealloying was used to synthesize nanoporous metals to act as sacrificial templates, and followed by reacting with H2PtCl6 and K2PdCl4 solution precursors. Electron spectroscopy study revealed that the ligaments of the initial porous sturcture were completely hollow and the nanotubular porous bimetallic structures have been successively fabricated. The shell surface of the Pt/Ag material was smooth and seamless with tube diameter and shell thickness around 45 nm and 7nm respectively. The tube diameter and shell thickness of Pd/Ag material were around 40 nm and 5 nm respectively, and it has small holes with diameter of～4 nm on the shell. Crystal structure study approve the both of the two material were alloy. During the electrochemical test, Pt/Ag material exhibits high catalytic activity and CO-tolerance toward methanol oxidation. These nanostructures have obvious structural advantages in terms of unique catalytic properties, simple and clean processing, and saving precious metals, which suggest their great potential for use in heterogeneous catalysis and fuel cell technologies.3. Fabrication of porous AgCl/Ag nanocomposites and its visible light catalysis.Porous AgCl/Ag nanocomposites were fabricated with a facile two-step route, which involves the formation of nanoporous silver (NPS) by dealloying AgAl alloys, and a subsequent surface chlorination in a mixed solution containing H2O2 and HCl. Morphology study revealed a porous AgCl/Ag composite nanostructure that inherited the bicontinuous spongy morphology of NPS precursors with interconnected pore channels and solid ligaments. The existence of Ag in the structure was found to contribute greatly to enhanced absorption in the visible light region. In a test system for the degradation of methylic orange (MO) dye, it was found that porous AgCl/Ag nanocomposites performed very well as efficient and stable visible light catalysts. Under non-optimized conditions, the MO dye degradation rate can reach as high as 0.75 mg/min·gcat with 420 nm irradiation. It is believed that porous AgCl/Ag and similar structures will be promising nanostructured visible light photocatalysts useful for environmental science and technology.更多还原