Rapid Photoelectrochemical Method for in Situ Determination of Effective Diffusion Coefficient of Organic Compounds

An in situ method for the rapid determination of diffusion coefficients of organic compounds was proposed and experimentally validated. The method is based on a photoelectrochemical oxidative degradation principle, using a nanoparticulate TiO2 thin-film electrode. The photocurrent that originated from the photoelectrocatalytic mineralization of the organic compound under diffusion-controlled conditions is measured and utilized to quantify the diffusion coefficient according to il = nFADCb/δ. It was found that, under optimized conditions, the thickness of the diffusion layer, δ, is a constant, independent of concentration and the chemical structure of the organic compound. The δ value can be experimentally determined with the organic compounds whose diffusion coefficient values are known. For this study, a mean δ value of 4.46 × 10-2 cm was obtained by employing a group of representative organic compounds including oxalic acid, succinic acid, benzoic acid, and glucose. The obtained δ value was then successfully applied to determine the diffusion coefficients of different organic compounds including glutaric acid, phthalic acid, malonic acid, catechol, and glycerol.