Effect of complexing agent on hydrothermal growth of ZnO crystals

In this study, three multidentate ligands-diethylenetriaminepentaacetate (DTPA), ethylenediaminetetraacetate (EDTA) and tetraethylenepentamine (tetren)-were investigated in the hydrothermal growth of crystals of zinc oxide (ZnO). Aqueous solutions containing zinc-ligand complexes and KOH were hydrothermally reacted and the products examined. Reactants were placed in teflon-lined stainless steel autoclaves and heated to a temperature of 200degrees C, generating pressures of approximately 15 atm. Optical microscopy and scanning electron microscopy on the resulting products revealed crystals with needle and plate habits, with needle lengths up to approximately 1 mm for EDTA and plate dimensions up to 100 Am for DTPA. When only complexing agent was varied at high pH, needles were observed for all samples, with EDTA yielding the longest (300 mum) and tetren yielding the shortest (20 mum); results were analyzed by considering complex formation constants, qualitative ligand polarity and complex strain. A variable pH study with 2 aminocarboxylic ligands, EDTA and DTPA, yielded mostly needles and dendritic formations for EDTA over the studied pH range (6-14), and plates or needles for DTPA. Results of variable pH products were analyzed by considering concentrations of all zinc-ligand and zinc-hydroxy species as a function of pH. (C) 2004 Elsevier B.V. All rights reserved.