Ethylene diamine tetra-acetic acid (EDTA) doped silica gels were made by the sol-gel process for the potential application as a filter for heavy metal ions in wastewater. The behavior of the organic molecule in the matrix was studied by investigating the percentage of EDTA leached out with a variation in the timing of addition of the EDTA molecule into the starting silica gel solution. Leach tests using water as the medium were performed for 2, 12 and 24 hours in order to determine the amount of EDTA trapped in the pores or in the matrix. A minimum amount of EDTA leached from the gels was detected in the samples to which EDTA was added 4 hours after initial hydrolysis of TEOS. This result was correlated to having a greater percentage of pore volume in the range of 15-20 Å, which was further substantiated with density measurements. The physical changes in the silica matrix altering the pore volume distribution were attributed to the addition of the water into which the EDTA molecule was initially dissolved.
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Oka, K.S., Mackenzie, J.D. Leaching Behavior of Edta in a Silica Sol-Gel Matrix. MRS Online Proceedings Library 346, 323–328 (1994). https://doi.org/10.1557/PROC-346-323