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

Abstract

Nanostructures of zinc oxide (ZnO) are at the forefront of application-driven nanotechnology because of their unique optical, piezoelectric, semiconducting, and antibacterial properties. Understanding nanomaterial transformations within wastewater treatmentplants is an important step to better predict their potential impact on the environment. Here, spatially resolved, in situ nano-X-ray fluorescence micro scopy is applied to directly observe nanometer-scale dissolution, morphological, and chemical evolution of individual and aggregated ZnO nanorods in complex "real-world" conditions: influent water and primary sludge collected from a municipal wastewater system. A complete transformation of isolated ZnO nanorods into ZnS occurs after only 1 hour in influent water, but larger aggregates of the ZnO nanorods transform only partially, with small contributions of ZnS and Zn-phosphate (Zn 3 (PO 4 ) 2 ) species, after 3 hours. Transformation of aggregates of the ZnO nanorods toward mixed ZnS, Zn adsorbed to Fe-oxyhydroxides, and a large contribution of Zn 3 (PO 4 ) 2 phases are observed during their incubation in primary sludge for 3 hours. Discrete, isolated ZnO regions are imaged with unprecedented spatial resolution, revealing their incipient transformation toward Zn 3 (PO 4 ) 2 . Passivation by transformation(s) into mixtures of less soluble phases may influence the subsequent bioreactivity of these nanomaterials. This work emphasizes the importance of imaging the nanoscale chemistry of mixtures of nanoparticles in highly complex, heterogeneous semi-solid matrices for improved prediction of their impacts on treatment processes, and potential environmental toxicity following release.

Toward Understanding the Environmental Risks of Combined Microplastics/Nanomaterials Exposures: Unveiling ZnO Transformations after Adsorption onto Polystyrene Microplastics in Environmental Solutions

“…Between 3 to 5 clusters grouping spectroscopically similar pixels were calculated by MANTiS, and their normalised XANES spectra were exported. Linear combination fitting (LCF) analyses of the normalised XANES region were performed by Athena from the Demeter software suite, [ 31 ] comparing against the standard spectra of the expected Zn‐species previously described in wastewater systems, as follow: bulk ZnO, ZnO ENMs (80–200 nm, US‐Nano), ZnS, Zn 3 (PO 4 ) 2 , [ 22 ] ZnCl 2 and a Copper Zinc Iron oxide (CuZnFe 2 O 4 ) nanopowder (<100 nm, Merk). The LCF of the Zn spectra was carried out starting from the best fit with one component, and the number of components ' n ' was increased as long as the normalised sum of the squared residuals (NSSR = ∑(data i − fit i ) 2 /∑(data i ) 2 ) of best n + 1‐component fit was at least 10% lower than the NSSR of the best n ‐component fit and if no component accounted for less than 5% of total Zn.…”

Chemical Limits on X-ray Nanobeam Studies in Water

“…While X-rays typically offer lower spatial resolution than electrons do, their penetrating power seems to allow application to complex environments and operating conditions . This is part of the motivation for recently investing in modern nanofocus instruments at most of the world’s synchrotrons, − enabling operando experiments with a variety of nanobeam techniques. − In particular, BCDI has been increasingly applied to problems in heterogeneous catalysis, electrocatalysis, − and complex electrochemical energy conversion systems. − The BCDI method requires extremely high flux densities when applied to small and industrially relevant nanoparticles, and the recently constructed fourth-generation synchrotron sources are expected to enable this by providing brighter and higher-quality X-ray beams. , …”

“…Figure 5. Numerical solution to the full model(17) under conditions corresponding to the NanoMAX beamline, MAX IV, with 7 × 10 10 s −1 photons at 8.5 keV, focused to a circular spot of 50 nm radius. In lieu of reliable diffusion coefficients, the H 2 O value (2.3 × 10 −5 cm 2 s −1 ) was used for OH • , and the H 2 value (5 × 10 −5 cm 2 s −1 ) was used for H • .…”

Chemical limits on X-ray nanobeam studies in water

“…10 This is part of the motivation for recently investing in modern nanofocus instruments at most of the world's synchrotrons, [11][12][13][14][15] enabling operando experiments with a variety of nanobeam techniques. [16][17][18][19][20][21] In particular, BCDI has been increasingly applied to problems in heterogeneous catalysis, 22 electrocatalysis, [23][24][25] and complex electrochemical energy conversion systems. [26][27][28][29] The BCDI method requires extremely high flux densities when applied to small and industrially relevant nanoparticles, 30 and the recently constructed 4:th generation synchrotron sources are expected to enable this by providing brighter and higher-quality X-ray beams.…”