This study aims to develop an analytical method for detecting inorganic engineering nanoparticles in the effluent of nanoparticle factories. The centrifugation, filtration, and dialysis technology have been adopted to take out all particles in the industrial wastewater from nanoparticle factories as a wastewater surrogate which still reserves the water chemistry properties including pH, ions, inorganic and organic matters, to establish nanomaterial detection methods. Dialysis technology showed the best performance to remove particles in the industrial wastewater. However, centrifugation and dialysis technology were time-consuming and costly. Filtration with 0.1 µm filter was applied to prepare the wastewater surrogate.
The particle size of nanoscale-Ag particles (nano-Ag) determined by DLS was 79.86 nm (PdI=0.206). The pHzpc of Ag nanoparticles was near pH 1. The zeta potential decreased with increasing pH. The particle size and polydispersant index of Ag nanoparticles keep stable in DI-water and wastewater surrogate at 4oC and 25oC. The concentration of dissolved Ag ions from Ag nanoparticles at 25oC is higher than that at 4oC. The preservation for nanoparticle samples was suggested to keep at 4oC without light. Microscale SiO2 (micro-SiO2) particles interfered the DLS measurement of Ag nanoparticles when SiO2/Ag concentration ratio was higher than 100. The Ag nanoparticles aggregated at pHzpc (pH 1). The effect of salt and humic acid in wastewater surrogate on DLS measurement of Ag nanoparticles was insignificant. The influences of three main aqueous parameters, pH, electrolyte, and humic acid, on nanomaterials in water were discussed. The obvious aggregation and sedimentation behaviors were found when the aqueous pH value was close to the pHzpc of Ag nanopartilces (~pH 1). The critical aggragation concentration (CAC) value of Ag nanoparticles was approximately 500 and 200 meq/L for NaCl and CaCl2, respectively. Humic acid did not cause the aggregation and sedimentation of Ag nanoparticles.
To remove microscale particles, the centrifugation with 4060 G for 2 min was effective to separate nano-Ag particles from micro-SiO2/nano-Ag and nano-TiO2/nano-Ag, and the recoveries were 64% and 40%, respectively. The other technology was applied to separate different sizes of nanoparticles is hydrodynamic chromatography (HDC). HDC can separate different sizes of Ag nanoparticles in water, wastewater surrogate, and wastewater. The larger size of nanoparticles has the shorter retention time. We can measure the particle size by the particlee-retention time from the calibration curve built by the well-known size of nanoparticles in the tested medium. With the cooperation of ICPMS, the concentration of the separated nanoparticles of the separated nanopatticles, by HDC can be measured.
Inorganic nanoparticles, dynamic light scattering (DLS), wastewater surrogate, centrifugation, hydrodynamic chromatography (HDC), aggregation, sedimentation, stability