Study of NOx abatement by calcium alumniate cements modified by TiO2

Abstract

Different percentages of TiO2 (1 to 10 wt.%) were incorporated into two different Calcium Aluminate Cements (iron rich – d-CAC – and iron lean – w-CAC–) which were cured under two curing conditions. The mild hydrothermal curing condition 2 was chosen so as to resemble the natural ageing of aluminate cements in which hydrated hexagonal phases are converted into more stable cubic ones. Fresh and hardened state properties were studied. NOx removal under UV illumination was assessed in TiO2-bearing mortar samples. NO conversion values were higher in w-CAC than in d-CAC. Retention of NO2 in w-CAC samples was also more successful than in d-CAC samples due to the presence of ferrite in the latter ones. The presence of ferrite in d-CAC was established by XRD, SEM and EDAX. The interaction of ferrite phases with TiO2 was monitored in both types of mortars and different behaviours were observed. In the d-CAC, the incorporation of TiO2 results in the appearance of two new iron containing phases: namely pseudobrookite and in a lesser extent ilmenite, at the expense of brownmillerite. These new phases yielded in an improve photocatalytic efficiency of d-CAC in the visible region of spectrum, as proved by Methyl Orange degradation tests.