Influence of mixing methods on the NOx reduction capability and electrical properties of photocatalytic cementitious systems

Nitrogen oxides (NOx), regarded as toxic air pollutants, are a group of highly reactive and hazardous gases encompassing compounds ranging from nitrous to nitric acid. Especially in crowded cities, the release of these gases from the industrial organizations and vehicles has reached serious levels. To eliminate the adverse effects of these gases, titanium dioxide (TiO2) is used worldwide as a photocatalyst due to its high efficiency in oxidization of NOx. Incorporating TiO2 into cement-based composites gives them photocatalytic capability: uniform and stable dispersion of TiO2 throughout the matrix is an undisputable requirement for improved photocatalytic efficiency. The main purpose of this study is to investigate the effects of different mixing techniques and surfactant materials on the dispersion of high dosage nano-TiO2 particles (5% of total weight of binder materials) throughout cement-based materials, with the goal of producing cost-effective cementitious systems, more feasible mixing methods, and ensuring proper dispersion of nano-TiO2. Five different mixing methods were proposed to achieve uniform distribution of the nano-TiO2. They were each implemented using different mixing procedures, equipment and surfactants. The performance of each mixing method was evaluated based on photocatalytic performance, electrical impedance (EI), compressive strength and microstructural analysis. Test results showed evidence of the significantly positive effect of polyacrylic acid (PAA) on the dispersion of nano-TiO2. In general, the highest dispersion occurred with ultrasonication and binary utilization of polycarboxylate ether-based plasticizer (PCE) and PAA. The EI test was a highly effective evaluation method for homogeneous distribution of conductive nano particles throughout the matrix. Results also showed a significant relationship between electrical performance and nitric oxide (NO) degradation of composites, and electrical properties of composites are able to provide a reliable estimate of the photocatalytic efficiency of them.