Because of their unique chemical and physical properties, metallic nanoparticles and plastics are widely applied in consumer and industrial products. The increasing production and widespread usage of nanoparticles and plastics resulted in their increasing release into the environment during the production, application, recycling and disposal, and the released plastic debris will gradually degrade into tiny,
“secondary” microplastics (< 5 mm) and even nanoplastics (<1000 nm). Because of their high surface areas, nanoparticles and nanoplastics would adsorb various hazardous coexisting pollutants, and then bioaccumulate and transport through food chain, and therefore enhanced their exposure and risk to ecosystem and human health.Therefore, to exactly understand the distribution of nanoparticles and nanoplastics, and then assess the environmental risks of nanoparticles and nanoplastics to environment and organisms, accurate analysis and characterization of nanoparticles and nanoplastics in the environment is of great importance.
This dissertation focuses on analysis and characterization of Ag-containing nanoparticles and nanoplastics. First, by coupling disc-based solid phase extraction (SPE) with inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM),UV-vis spectroscopy,and size-exclusion chromatography coupled with ICP-MS (SEC-ICP-MS) techniques, we have developed a method for preconcentration, characterization and quantification of trace Ag-containing nanoparticles in environmental waters. Then, we presented the first use of surface enhanced Raman spectroscopy (SERS) to identify trace nanoplastics in environmental waters.
In the first part, we summarized the category, source and release pathways of metallic nanoparticles, and then reviewed the update methods used for extraction, separation, analysis and characterization of metallic nanoparticles. In additional, the source of nanoplastics in environment is briefly introduced, and then the current development of separation, determination and characterization of nanoplastics are summarized.
In the second part, we report the novel application of disc-based solid phase extraction (SPE) for separation and preconcentration of nanoparticulate Ag (NAg) in a large volume of water samples (1 L). Starting from real water samples, namely, river water, lake water, as well as the effluent and influent of wastewater treatment plant (WWTP), semi-automated enrichment of NAg from 1 L of samples was achieved within ~30 min using the disc-based SPE system, which consists of a syringe pump and a syringe filter holder to embed the filter membrane. While polyvinylidene fluoride (PVDF) membrane can selectively intercept NAg in the presence of Ag+ ,aqueous solution of 2% (m/v) FL-70 (a surfactant) was found to efficiently elute NAg without disturbing their sizes and shapes. Analysis of NAg was performed following optimization of filter membrane and elution conditions with an enrichment factor of 1000. Additionally, transmission electron microscopy (TEM), UV-vis spectroscopy, and size-exclusion chromatography coupled with ICP-MS (SEC-ICP-MS) analysis showed that no size and/or shape changes occurred after extraction, making this method attractive for practical applications. Furthermore, feasibility of the protocol was verified by applying it to extract NAg in four real waters with recoveries of 62.2–80.2% at 0.056–0.58 g/L spiked levels. This work will facilitate robust studies of trace NAg transformation and their hazard assessments in the environment.
In the third part, the first use of surface enhanced Raman spectroscopy (SERS) to identify trace nanoplastics (1–999 nm size range) is presented. When nanoplastics are surrounded by SERS-active silver nanoparticles (AgNPs), a set of Raman spectra with chemical information can be obtained via SERS mapping. This map shows the potential distribution of the nanoplastics on a silicon wafer, allowing a more detailed analysis of the nanoplastics to be quickly performed. This new method can identify previously undetectable plastic particles as small as ~50 nm, demonstrating the power of SERS to probe nanoplastics and study their formation. Our work is thus an important step in nanoplastic research.