Anodic Alumina Membranes: From Electrochemical Growth to Use as Template for Fabrication of Nanostructured Electrodes

The great success of anodic alumina membranes is due to their morphological features coupled to both thermal and chemical stability. The electrochemical fabrication allows accurate control of the porous structure: in fact, the membrane morphological characteristics (pore length, pore diameter and cell density) can be controlled by adjusting the anodizing parameters (bath, temperature, voltage and time). This article deals with both the fabrication and use of anodic alumina membranes. In particular, we will show the specific role of the addition of aluminum ions to phosphoric acid-based anodizing solution in modifying the morphology of anodic alumina membranes. Anodic alumina membranes were obtained at −1 °C in aqueous solutions of 0.4 M H3PO4 added with different amounts of Al(OH)3. For sake of completeness, the formation of PAA in pure 0.4 M H3PO4 in otherwise identical conditions was also investigated. We found that the presence of Al(OH)3 in solution highly affects the morphology of the porous layer. In particular, at high Al(OH)3 concentration (close to saturation) more compact porous layers were formed with narrow pores separated by thick oxide. The increase in the electric charge from 20 to 160 C cm−2 also contributes to modifying the morphology of porous oxide. The obtained anodic alumina membranes were used as a template to fabricate a regular array of PdCo alloy nanowires that is a valid alternative to Pt for hydrogen evolution reaction. The PdCo alloy was obtained by electrodeposition and we found that the composition of the nanowires depends on the concentration of two metals in the deposition solution.

Synthesis and Characterization of Tin and Germanium Based Semiconductor Nanocrystals

<p>Inorganic nanomaterials are being actively researched due to their unique physical and chemical properties. These materials can be used for a wide variety of applications and technologies which have stimulated research into the discovery, understanding and control of the morphology of materials at the nanoscale. Biologists have recently integrated biomaterials with semiconductor nanoparticles to expand their applications to include biosensing, bioimaging and therapeutic strategies. Since the water solubility of semiconductor nanoparticles is crucial for bioapplications, the fabrication of water-soluble semiconductor nanocrystals with tailored properties has become more significant. This thesis is focused on the solution phase synthesis of nanoparticles and nanowires containing the element tin. This includes tin nanoparticles, tingermanium alloy nanowires, tin sulphide nanoparticles and tin telluride nanoparticles. The aim of this research was to synthesize nanocrystals with tightly controlled size and shape for various applications,in particular for bioapplications. The properties, potential applications and crystal structure of target materials have been discussed in Chapter 1. The target materials synthesized by using chemical reaction in the presence of surfactant were characterized primarily by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX) and Selected Area Electron Diffraction (SAED). Powder X-ray Diffraction (XRD), Scanning Transmission Electron Microscopy (STEM), Scanning Electron Microscopy (SEM), Ultraviolet-Visible Microscopy Absorption (UV-VIS), Fourier Transform Infrared (FTIR), Photoluminescence (PL) and Diffuse Reflectance were also used extensively (Chapter 2). The third chapter of this thesis focuses on the the development of a facile and cheap route for the synthesis of tin nanoparticles by reducing a tin precursor in an organic solvent. The low-melting tin nanoparticles have been considered as a good catalyst for the growth of semiconductor nanowires. The fourth chapter in this thesis focuses on the development of a convenient synthesis of tin germanium alloy nanowires via solution-liquid-solid growth (SLS). Tin germanium alloy nanowires were synthesized through a self-catalyzed process in which the wires were grown from in situ made Sn droplets and Ge(Ph)₃Cl. The factors affecting morphology were ascertained and the growth direction, composition, local crystal structure and possible growth mechanism have been investigated. The fifth chapter in this thesis focuses on the development of a novel one-pot synthesis of water-soluble SnS nanoparticles. The synthesis of SnS nanoparticles involves the reaction of inorganic starting materials SnBr₂ and Na₂S in the presence of various ethanolamine derivatives in ethylene glycol. Optical studies of as synthesized SnS nanoparticle show size dependent effects in both absorbance and reflectivity. The sixth chapter in this thesis focuses on the development of a facile direct synthesis of water dispersible SnTe nanoparticles. The optical properties of prepared SnTe nanoparticles were determined. The final chapter in this thesis summarizes the main findings of this study and draws out recommendations for future work. In this study, some novel contributions have been made to produce facile one-pot synthesis of tin germanium nanowires and water soluble, size controlled tin chalcogenides nanoparticles. The main future work for tin germanium alloy naowires is to develop the method to produce nanowires without seed nanoparticles for optoelectronics applications. Further work is also needed to optimize the water synthesis of SnTe nanoparticles.</p>

Synthesis and Characterization of Tin and Germanium Based Semiconductor Nanocrystals

<p>Inorganic nanomaterials are being actively researched due to their unique physical and chemical properties. These materials can be used for a wide variety of applications and technologies which have stimulated research into the discovery, understanding and control of the morphology of materials at the nanoscale. Biologists have recently integrated biomaterials with semiconductor nanoparticles to expand their applications to include biosensing, bioimaging and therapeutic strategies. Since the water solubility of semiconductor nanoparticles is crucial for bioapplications, the fabrication of water-soluble semiconductor nanocrystals with tailored properties has become more significant. This thesis is focused on the solution phase synthesis of nanoparticles and nanowires containing the element tin. This includes tin nanoparticles, tingermanium alloy nanowires, tin sulphide nanoparticles and tin telluride nanoparticles. The aim of this research was to synthesize nanocrystals with tightly controlled size and shape for various applications,in particular for bioapplications. The properties, potential applications and crystal structure of target materials have been discussed in Chapter 1. The target materials synthesized by using chemical reaction in the presence of surfactant were characterized primarily by Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX) and Selected Area Electron Diffraction (SAED). Powder X-ray Diffraction (XRD), Scanning Transmission Electron Microscopy (STEM), Scanning Electron Microscopy (SEM), Ultraviolet-Visible Microscopy Absorption (UV-VIS), Fourier Transform Infrared (FTIR), Photoluminescence (PL) and Diffuse Reflectance were also used extensively (Chapter 2). The third chapter of this thesis focuses on the the development of a facile and cheap route for the synthesis of tin nanoparticles by reducing a tin precursor in an organic solvent. The low-melting tin nanoparticles have been considered as a good catalyst for the growth of semiconductor nanowires. The fourth chapter in this thesis focuses on the development of a convenient synthesis of tin germanium alloy nanowires via solution-liquid-solid growth (SLS). Tin germanium alloy nanowires were synthesized through a self-catalyzed process in which the wires were grown from in situ made Sn droplets and Ge(Ph)₃Cl. The factors affecting morphology were ascertained and the growth direction, composition, local crystal structure and possible growth mechanism have been investigated. The fifth chapter in this thesis focuses on the development of a novel one-pot synthesis of water-soluble SnS nanoparticles. The synthesis of SnS nanoparticles involves the reaction of inorganic starting materials SnBr₂ and Na₂S in the presence of various ethanolamine derivatives in ethylene glycol. Optical studies of as synthesized SnS nanoparticle show size dependent effects in both absorbance and reflectivity. The sixth chapter in this thesis focuses on the development of a facile direct synthesis of water dispersible SnTe nanoparticles. The optical properties of prepared SnTe nanoparticles were determined. The final chapter in this thesis summarizes the main findings of this study and draws out recommendations for future work. In this study, some novel contributions have been made to produce facile one-pot synthesis of tin germanium nanowires and water soluble, size controlled tin chalcogenides nanoparticles. The main future work for tin germanium alloy naowires is to develop the method to produce nanowires without seed nanoparticles for optoelectronics applications. Further work is also needed to optimize the water synthesis of SnTe nanoparticles.</p>

Subnanometer high-entropy alloy nanowires enable remarkable hydrogen oxidation catalysis

High-entropy alloys (HEAs) with unique physicochemical properties have attracted tremendous attention in many fields, yet the precise control on dimension and morphology at atomic level remains formidable challenges. Herein, we synthesize unique PtRuNiCoFeMo HEA subnanometer nanowires (SNWs) for alkaline hydrogen oxidation reaction (HOR). The mass and specific activities of HEA SNWs/C reach 6.75 A mgPt+Ru−1 and 8.96 mA cm−2, respectively, which are 2.8/2.6, 4.1/2.4, and 19.8/18.7 times higher than those of HEA NPs/C, commercial PtRu/C and Pt/C, respectively. It can even display enhanced resistance to CO poisoning during HOR in the presence of 1000 ppm CO. Density functional theory calculations reveal that the strong interactions between different metal sites in HEA SNWs can greatly regulate the binding strength of proton and hydroxyl, and therefore enhances the HOR activity. This work not only provides a viable synthetic route for the fabrication of Pt-based HEA subnano/nano materials, but also promotes the fundamental researches on catalysis and beyond.