Spatially Resolved Dissolution and Speciation Changes of ZnO Nanorods during Short-Term in Situ Incubation in a Simulated Wastewater Environment

Abstract

Zinc oxide engineered nanomaterials (ZnO ENMs) are used in a variety of applications worldwide due to their optoelectronic and antibacterial properties with potential contaminant risk to the environment following their disposal. One of the main potential pathways for ZnO nanomaterials to reach the environment is via urban wastewater treatment plants. So far there is no technique that can provide spatiotemporal nanoscale information about the rates and mechanisms by which the individual nanoparticles transform. Fundamental knowledge of how the surface chemistry of individual particles change, and the heterogeneity of transformations within the system, will reveal the critical physicochemical properties determining environmental damage and deactivation. We applied a methodology based on spatially resolved in situ X-ray fluorescence microscopy (XFM), allowing observation of real-time dissolution and morphological and chemical evolution of synthetic template-grown ZnO nanorods (∼725 nm length, ∼140 nm diameter). Core−shell ZnO-ZnS nanostructures were formed rapidly within 1 h, and significant amounts of ZnS species were generated, with a corresponding depletion of ZnO after 3 h. Diffuse nanoparticles of ZnS, Zn 3 (PO 4 ) 2 , and Zn adsorbed to Fe-oxyhydroxides were also imaged in some nonsterically impeded regions after 3 h. The formation of diffuse nanoparticles was affected by ongoing ZnO dissolution (quantified by inductively coupled plasma mass spectrometry) and the humic acid content in the simulated sludge. Complementary ex situ X-ray absorption spectroscopy and scanning electron microscopy confirmed a significant decrease in the ZnO contribution over time. Application of time-resolved XFM enables predictions about the rates at which ZnO nanomaterials transform during their first stages of the wastewater treatment process.

Revealing Nanomechanical Domains and Their Transient Behavior in Mixed‐Halide Perovskite Films

“…nXRF experiments were performed at the Hard X‐ray Nanoprobe at the I14 beamline at Diamond Light Source Ltd., Didcot, UK as described previously. [ 59,60 ] Briefly, horizontal mirrors shaped an X‐ray beam from an undulator source onto a secondary source. The beam then passed over a Si monochromator which selected the chosen beam energy of 20 keV.…”

The Hard X-ray Nanoprobe beamline at Diamond Light Source

“…Early beamline publications (McCulloch et al, 2019;Gomez-Gonzalez et al, 2019;Morrell et al, 2019;Walker et al, 2018) highlight some of the XRF, nano-XANES and nano-XRD capabilities. Fig.…”

“…Fig. 6 shows nano-XANES maps acquired on ZnO nanorods which were incubated in situ in a simulated sludge solution (Gomez-Gonzalez et al, 2019). In this experiment, a spectro-microscopy methodology for speciation analysis was followed, based on multiple 2D XRF maps acquired around and across the Zn K-edge.…”

Nanoscale Chemical Imaging of Nanoparticles under Real‐World Wastewater Treatment Conditions

“…Similar speciation analysis confirmed the initial ZnO nature of the "as-synthesized" nanorods. [19] [Right] Pie charts with the average of all individual (pixel-by-pixel) percentages were also generated, [37] © 2021 The Authors. Advanced Sustainable Systems published by Wiley-VCH GmbH region, a ≈93% contribution of ZnS was obtained (Figure 1a, pie chart, right).…”

“…We recently showed that dynamic ZnO ENMs transformations in a model simplified aquatic media, humic acid, can be mapped chemically using in situ X-ray fluorescence microscopy (XFM) using hard X-ray nanoprobes. [19] Micro-and nano-X-ray beams at synchrotron facilities combine a high-brilliance source with low emittance, providing superb energy resolution (≈0.5 eV) and tunability, as well as a high penetration capacity into the analyte, making them ideal characterization techniques for in operando imaging at the (sub)micrometric scale. [20,21] Micro-X-ray absorption and fluorescence spectromicroscopy have been applied in the hard X-ray range to quantify the Zn accumulation within biological and environmental samples, such as cells, [22,23] plants, [24][25][26] and soil sediments.…”