Metal and Metal-oxide Nanoparticle Synthesis by Laser Ablation of Aqueous Aerosols
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Metal and Metal-oxide Nanoparticle Synthesis by Laser Ablation of Aqueous Aerosols Kristofer L. Gleason1, John W. Keto2, Desiderio Kovar3, and Michael F. Becker1 1
Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, TX, U.S.A.
2
Department of Physics, University of Texas at Austin, Austin, TX, U.S.A.
3
Department of Mechanical Engineering, University of Texas at Austin, Austin, TX, U.S.A.
ABSTRACT We present a scalable, continuous manufacturing method of nanoparticle production based on laser ablation of an aerosol generated from an aqueous precursor solution. A Collison nebulizer is used to generate a mist of ~10 ȝm diameter water droplets containing dissolved transition metal salts, suspended in 1 atmosphere of buffer gas. Water from the droplets quickly evaporates, leaving solid particles ~2 ȝm in diameter for a typical solution concentration. These microparticles are then ablated by a pulsed KrF excimer laser (10 ns, Ȝ = 248 nm, 2 J/cm2 at focus). Ablation results in plasma breakdown of the microparticle and photothermal decomposition of the precursor material. Following ablation, nanoparticles 5-20 nm in diameter are formed and collected. For AgNO3 ablated in He gas, metal Ag nanoparticles were produced. For Cu(NO3)2 ablated in He, crystalline Cu2O nanoparticles were produced. For Ni(NO3)2 ablated in He, crystalline NiO nanoparticles were produced. A combination of AgNO3 and Cu(NO3)2 ablated in a reducing atmosphere of 10% H2 and 90% He yielded Ag-Cu alloy nanoparticles. In contrast to conventional wet-chemical synthesis processes, our nanoparticles are formed ‘bare,’ without surfactants or organic material contaminating the surface. Owing to their small size and high free surface area, nanoparticles produced by this process are ideally suited for applications that include catalysis and facilitated transport membranes. INTRODUCTION Nanoparticle synthesis is routinely accomplished by wet chemical techniques [1]. However, these protocols require use of a surfactant or polymer capping agent to stabilize particles from agglomeration. For applications requiring a clean particle surface, more elaborate synthesis routes are necessary. For example, spray pyrolysis [2] produces particles by thermal decomposition of an aqueous aerosol of precursor compounds flowing through a tube furnace. A residence time of several seconds is usually required for complete reaction. During this time, particles are subject to Brownian coagulation, which limits the minimum particle size. In the laser ablation of microparticle aerosol (LAMA) technique developed by our lab [3], nanoparticles are formed quickly via a laser driven shock process, and much shorter residence times are possible. We routinely produce Ag nanoparticles with 7 nm mean diameters, and a narrow size distribution. However, the technique requires feedstock material in the form of a micron-sized powder aerosol, adding substantially to the cost of production. In the present work, we introduce a new laser ablation technique that uti
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