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A Critical Assessment of the Specific Role of Microwave Irradiation in the Synthesis of ZnO Micro‐ and Nanostructured Materials
Author(s) -
Baghbanzadeh Mostafa,
Škapin Srečo D.,
Orel Zorica Crnjak,
Kappe C. Oliver
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201103548
Subject(s) - materials science , crystallite , microwave , ethylene glycol , hydrothermal circulation , chemical engineering , solvent , zinc nitrate , nanomaterials , nanoparticle , hydrothermal synthesis , zinc , nanotechnology , organic chemistry , chemistry , physics , quantum mechanics , engineering , metallurgy
A rapid, microwave‐assisted hydrothermal method has been developed to access ultrafine ZnO hexagonal microrods of about 3–4 μm in length and 200–300 nm in width by using a 1:5 zinc nitrate/urea precursor system. The size and morphology of these ZnO materials can be influenced by subtle changes in precursor concentration, solvent system, and reaction temperature. Optimized conditions involve the use of a 1:3 water/ethylene glycol solvent system and 10 min microwave heating at 150 °C in a dedicated single‐mode microwave reactor with internal temperature control. Carefully executed control experiments ensuring identical heating and cooling profiles, stirring rates, and reactor geometries have demonstrated that for these preparations of ZnO microrods no differences between conventional and microwave dielectric heating are observed. The resulting ZnO microrods exhibited the same crystal phase, primary crystallite size, shape, and size distribution regardless of the heating mode. Similar results were obtained for the ultrafast preparation of ZnO nanoparticles with diameters of approximately 20 nm, synthesized by means of a nonaqueous sol–gel process at 200 °C from a Zn(acac) 2 (acac=acetylacetonate) precursor in benzyl alcohol. The specific role of microwave irradiation in enhancing these nanomaterial syntheses can thus be attributed to a purely thermal effect as a result of higher reaction temperatures, more rapid heating, and a better control of process parameters.