Solution-mediated strategies for synthesizing metal oxides, borates and phosphides using nanocrystals as reactive precursors

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Title: Solution-mediated strategies for synthesizing metal oxides, borates and phosphides using nanocrystals as reactive precursors
Author: Henkes, Amanda Erin
Abstract: Because of their high surface area (and hence , increased reactivity ) nanocrystals can be used as reactive precursors in the low -temperature synthesis of solid state materials . When nanocrystals are used as reactants , the temperatures needed for diffusion between them can be significantly lower than for bulk -scale reactions ?often at temperatures attainable using solution -based techniques . In the following work , two synthetic strategies are defined and developed for accessing metal oxides , borates and phosphides using nanocrystalline precursors and solution -mediated techniques . Broadly , the strategies involve either 1 ) the formation of a nano -sized precursor in solution which is post -annealed after isolation to form a target metal oxide or borate or 2 ) the solution -mediated diffusion of phosphorus into a nanocrystalline metal to form target metal phosphides . To form multi -metal oxides using the first strategy , metal oxide nanoparticle precursors are mixed in stoichiometric ratios in solution to form a nanocomposite . After isolation , the nanocomposite is annealed in air at 700 -800 ?C to form target ternary metal oxides , including Y2Ti2O7 , Eu2Ti2O7 , NiTiO3 , Zn2SnO4 and CuInO2 . As a variation of this method , rare earth borate nanoparticle precursors can be formed in solution by the reaction of RE3+ with NaBH4 . After isolation , annealing in air at 700 -800 ?C crystallizes a range of REBO3 and Al3RE (BO3 )4 powders . Using solution -based techniques , metal phosphides can be formed by the reaction of pre -formed metal nanocrystals with trioctylphosphine (TOP ) , which acts as a mild phosphorus -source , at 300 -370 ?C . A range of transition metal phosphide nanocrystals are accessible using this strategy , including the polyphosphides PdP2 , AgP2 and Au2P3 . Furthermore , shape and size of the metal phosphide product can be influenced by the shape and size of the metal precursor , allowing for the templated -design of nanostructured metal phosphides . The utility of this technique is not limited to the nano -regime . Bulk -scale metal powders , wires , foils , thin films and nanostructured metals can be converted to metal phosphides using analogous reactions with hot TOP . The two -fold purpose of this work is to extend these solution -mediated nanocrystal -based synthetic strategies to new classes of materials , and to compliment the existing library of low -temperature methods for making solid state materials .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2674
Date: 2009-05-15

Citation

Solution-mediated strategies for synthesizing metal oxides, borates and phosphides using nanocrystals as reactive precursors. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2674 .

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