Synthesis of nanostructured metals using Template-Assisted Electrodeposition

Name – Udit Kumar

Roll no. – 163110065

Course - Electrochemical Materials Science (MM 717)

Table of Contents

1. Introduction2. Electrodeposition Technique3. Types of Template Deposition4. Different Types of Templates and Their importance5. Anodic Alumina Templates6. Metallic nanowires and nanotubes by anodic alumina template-assisted

electrodeposition7. Conclusions

References

Introduction

Template-assisted electrodeposition is an important technique for synthesizingmetallic nanomaterials with controlled shape and size. Arrays of nanostructuredmaterials with specific arrangements can be prepared by this method, employingeither an active or restrictive template as a cathode in an electrochemical cell. Anoverview of the template-assisted electrodeposition process to synthesize metallicnanostructures is presented in this report. In the report topics related to abovementioned title such as - Types of template deposition, Different Types ofTemplates and Their importance , Anodic Alumina Template (As it is a widely usedand important template), Metallic nanowires and nanotubes by anodic aluminatemplate-assisted electrodeposition etc. has been touched.

Electrodeposition TechniqueIt is based on simple electrolytic cell principle. In the figure 1 basic elements ofelectrodeposition technique has been shown

Fig: 1 Schematic diagram of electrodeposition technique.

The nucleation of nanostructures on the electrode substrate duringelectrodeposition is influenced by the crystal structure of the substrate, specificfree surface energy, adhesion energy, lattice orientation of the electrode surface,

and crystallographic lattice mismatch at the nucleus-substrate interface boundary.The final size distribution of the electrodeposits, however, strongly depends on thekinetics of the nucleation and growth [1].

The electrodeposition process involves the formation of either an instantaneous ora progressive nucleation. In the case of instantaneous nucleation, all the nucleiform instantaneously on the electrode substrate, and subsequently grow with thetime of electrodeposition. In contrast, the number of nuclei that are formed is afunction of time of electrodeposition in the progressive nucleation. These nucleigradually grow and overlap, and therefore, the progressive nucleation processexhibits zones of reduced nucleation rate around the growing stable nuclei. Theelectrodeposition method consists of an electrochemical cell and accessories forapplying controlled current at a certain voltage [3].The cathode substrate on whichelectrodeposition of the nanostructure takes place can be made of eithernonmetallic or metallic materials. Using the surface of the cathode as a template,various desired nanostructures or morphologies can be synthesized broadlydivided into two groups:

1. active template- assisted2. restrictive template-based electrodeposition

Types of Template Deposition

Active Template-Assisted Electrodeposition

The formation of nanostructures in active template-based synthesis results fromgrowth of the nuclei that invariably nucleate at the holes and defects of theelectrode substrate.

Weak substrate-deposit interaction leading to preferential silver deposition at stepedges and other surface defects. The active template-assisted deposition includesnumerous other techniques. Nickel nanoparticles with a narrow size distributionhave been electrodeposited on a graphite surface using the hydrogen co-evolutionmethod. The electrodeposition of metal at large over-potential invariably results ininstantaneous nucleation, which is non-selective, mostly due to the formation of alarge number of nuclei on defect-free terraces as well as at defects such as stepedges on the surfaces. The nuclei density is expected to be of the order of 109cm^2. The dependence of the number of nuclei on time was investigated6 in a widerange of voltage intervals using different glassy carbon electrodes. The data for thesteady-state nucleation rate were interpreted on the basis of both classical andatomistic concepts of nucleation phenomena

Fig: 2 A schematic diagram forsynthesis of nanoparticle arraysthrough active template-assistedsynthesis [1].

Restrictive Template-Based Electrodeposition

Another template-assisted synthesis of mostly metal nanowires involves thedeposition of metal into the cylindrical pores or channels of an inert, nonconductivenonporous electrode material. Track-etch membranes, porous alumina, and othernonporous structures including conductive polymers, metals, semiconductors,carbons, and other solid materials have been used as templates to preparenanometer-sized particles, fibrils, rods, and tubules [7].

Anodic Alumina Templates

Porous anodic aluminum oxide (AAO) attracted a remark- able interest due to thepioneer work of Masuda and Fukuda [4]. Self-organized Nano-porous structurewith hex- agonal ordered morphology can be obtained on a highly pure Al surfacevia electrochemical anodization in acidic medium [4,7]. AAO is extensively applied

Fig: 3 A schematic electrodearrangement for the synthesis ofnanowires though restrictivetemplate-assistedelectrodeposition

in the fields of biosensor and bio filtration and as a Nano template for thefabrication of secondary nanostructured materials. AAO templates have manyadvantages over the poly- carbonate membranes like high pore density, thermalstability, cost effectiveness and versatility. Pore diameter, length, inter-porespacing, and pore ordering can be easily tailored by tuning the anodizingparameters such as volt- age, time, electrolytes, pH value, and temperature [6]

Preparation of AAO templates

Al foils were cut into 4.5 × 4.5 cm2 pieces. Before anodization, Al foils wereannealed at 500°C for 5 h in air to remove the mechanical stresses. Subsequently,the foils were etched in 1.0 M NaOH at room temperature until bubbles over thesurface of the foils were observed, followed by a rise in DI water many times anddried by air at high pressure. Al foils were used for anodization without any pre-treatment of electro-polishing. A simple, homemade, two-electrode system, withAl foil as a working electrode and a Pt foil as a counter electrode, was used for anelectrochemical anodization. A circular shape surface of the Al foil was exposed tothe electrolyte. Anodization was conducted in 0.4 M aqueous H2SO4 electrolyte atconstant voltage of 26 V for 23 h using a DC power source at 0°C. The anodizationinduced highly ordered Nano pores with hexagonal morphology over the exposedsurface of Al foil to the electrolyte. The templates were washed with DI water anddried using air at high pressure before deposition of Co-Ni binary alloy nanowires.[4,6,7].

Schematic diagram for co-deposition process of Co-Ni binary nanowires in nanopores of AAO template. (a)AAOtemplate with circular shape,(b) filling of nanopores started from Co-Ni binary nanowires at the bottom of AAO byexposing circular area to the Co and Ni precursor solution, (c) complete filling of the alumina nanopores from Co-Ni binary nanowires, (d) dissolution of alumina in NaOH to get Co-Ni binary nanowires [6]

Metallic nanowires and nanotubes by anodic alumina template-assisted electrodeposition

Since the discovery of carbon nanotubes, tubular nanostructures have attractedmuch more interest from researchers for their intriguing electronic, catalytic,optical, and magnetic properties. Among the synthesis methods, template-basedsynthesis earlier work by Martin et al [8], is an important synthetic strategy tofabricate nanotube arrays. Magnetic metallic nanotubes, such as Fe, Co [6] ,Ni andCo–Cu alloy nanotubes have been fabricated by electrodeposition in anodicaluminum oxide (AAO) template, but these methods commonly need somestrategies of AAO channels modification, multistep template replication and highcurrent. It is still a challenge to prepare alloy nanotube arrays by an easy one-stepway.

ConclusionsTemplate based Nano-structure synthesis is powerful technique and widely used inthe field of electrodeposition, as per the mass production I would say it is yet notan industrial technique. On the matter of fact of Nano wires as a reinforcing agentsis also recently adopted commercially. AAO template has shown promise in thisfield as it is easy to make. I haven’t talked about polymer based template which isalso an important technique and also widely researched, but it has its fair share ofcons.

References

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[2] J.C. Hulteen and C.R. Martin, “A General Template- Based Method for the Preparation ofNanomaterials,” Journal of Materials Chemistry, 7 (1997), pp. 1075–1087.

[3] A. Huczko, “Template-Based Synthesis of Nanomateri- als,” Applied Physics A, 70 (2000),pp. 365–376.

[4] Masuda, H., Fukuda, K., Chaikin, P. M., Register, R. A., Adamson, D. H., MasudaH.Fredrickson, G. H. (1995). Ordered metal nanohole arrays made by a two-step replicationof honeycomb structures of anodic alumina. Science (New York, N.Y.), 268(5216), 1466–8.http://doi.org/10.1126/science.268.5216.1466

[5] Chi Lu, & Zhi Chen. (2011). AAO Review -Reprint.pdf. Retrieved fromwww.aspbs.com/enn

[6] Ali, G., & Maqbool, M. (2013). Fabrication of cobalt-nickel binary nanowires in a highlyordered alumina template via AC electrodeposition, 1–8.

[7] Yanagishita, T., Nishio, K., & Masuda, H. (2005). Fabrication of metal nanohole arrayswith high aspect ratios using two-step replication of anodic porous alumina. AdvancedMaterials, 17(18), 2241–2243. http://doi.org/10.1002/adma.200500249

[8] Cepak, V. M., & Martin, C. R. (1999). Preparation of Polymeric Micro- and NanostructuresUsing a Template-Based Deposition Method. Chemistry of Materials, 11(5), 1363–1367.http://doi.org/10.1021/cm9811500