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

The production of hydroxyl radicals (OH) 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 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 detected. The difference could not be attributed exclusively to the contribution of O2−. 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 in the bulk solution, which still makes the quantification of OH as an effective indicator of the photocatalytic performance of cementitious materials.