Improved photocatalytic nitrogen oxides removal using recycled glass-nano-TiO₂ composites with NaOH pre-treatment

The use of waste glasses as aggregates in cementitious materials provides a viable recycling option to alleviate the burden on landfills in Hong Kong. More interestingly, the light-transmitting properties of glass are beneficial to augment the TiO₂-mediated photocatalytic activity. This study attempted to take full advantage of glass aggregate (GA) by attaching nano TiO₂ particles on its surface. NaOH etching was employed to pre-treat the surface of GA in order to increase its surface area before TiO₂ particles were attached. The experimental results showed that the treatment of NaOH etching effectively induced cracks and pores on the initially smooth surface of GA. As a result, a higher amount of nano TiO₂ particles (0.0434 g per 50 g of GA) were attached/absorbed on the surface of the treated GA compared to the untreated analogue (0.0224 g per 50 g of GA) when immersed in 10 g L⁻¹ TiO₂ solutions. More importantly, the higher TiO₂ absorption ability of the treated GA translated into a higher photocatalytic NO_x removal activity. Compared with the untreated GA-TiO₂ composites, the NaOH etched GA-TiO₂ composites (immersed in 1 g L⁻¹ TiO₂ solutions) experienced an approximately 60% increase in the photocatalytic NO_x removal efficiency. The overall findings revealed that compared with the sand-TiO₂ composites, the NaOH etching treated GA-TiO₂ composites not only garnered the beneficial effect from the light-transmitting of glass but also had the beneficial etching effect of NaOH treatment. Therefore, the developed NaOH etched GA-TiO₂ composites hold great potential for applications in cementitious photocatalytic materials.