Real-time monitoring of nanoscale TiO₂ concentration by spectrophotometry: implications of agglomeration due to natural organic matter and multivalent ions

The study of the environmental fate of nanoscale TiO₂ (n-TiO₂) is a major recent research focus which requires a rapid and accurate on-site concentration determination method. Inductively coupled plasma mass spectroscopy (ICP-MS) has been the most widely used method for determining the concentration of n-TiO₂ in environmental samples; however, poses many challenges, such as hazardous hydrofluoric acid pre-treatment and clear limitations in mobile on-site measurement and monitoring. This study demonstrates that industrial wastewater containing natural organic matter (NOM) can present a major challenge to the analysis of n-TiO₂ by ICP-MS, and introduces a spectrophotometry technique that can be used as an alternative. The results suggest that spectrophotometry methods can be more accurate than slurry nebulization ICP-MS for measuring the concentrations of n-TiO₂ in wastewater containing NOM under low salt conditions. Furthermore, this study demonstrates the use of a portable flow-through spectrophotometer for use in applications of wastewater treatment and environmental monitoring with real-time feedback of n-TiO₂ concentrations. The ability to detect and monitor n-TiO₂ will greatly assist in improving the understanding of hazards and risks that emerging nanomaterials pose to the environment and the public health.