Quantification of hydroxyl radicals on cementitious materials by fluorescence spectrophotometry as a method to assess the photocatalytic activity

The production of hydroxyl radicals (OH center dot) by several photocatalytic cementitious materials was quantified by an adaptation of Terephthalic acid (TA) as probe method for fluorescence spectrometry (TA-FL method) for construction materials. Six different materials were evaluated for OH center dot using the method developed, and the photocatalytic activity was compared with the NOx degradation rate, obtaining a positive relationship between both parameters even though the rate of NOx degradation was significantly larger than that of the OH center dot detected. The difference could not be attributed exclusively to the contribution of O-center dot(2)-. Thus, it has been postulated that most of the NOx degradation takes place through the holes, trapped in the surface of the photocatalyst, in equilibrium with OH center dot in the bulk solution, which still makes the quantification of OH center dot as an effective indicator of the photocatalytic performance of cementitious materials. (C) 2015 Elsevier Ltd. All rights reserved.