A High Resolution Study of Dynamic Changes of Ce2O3 and CeO2 Nanoparticles in Complex Environmental Media

Unexpected nanoscale CeO2 structural transformations induced by ecologically relevant phosphate species

In the present study, the dissolution and microstructural transformation of CeO2 nanoparticles (NPs) in a phosphate-containing milieu were investigated. The dissolution behaviour of 2 nm and 5 nm CeO2 NPs in phosphate buffer solutions was found to differ markedly from that observed in 0.01 M NaClO4. Through synchrotron X-ray diffraction analysis and X-ray absorption spectroscopy, the interaction between CeO2 NPs and phosphate species was examined, revealing the transformation of the oxide into sodium-cerium double phosphate, with cerium predominantly existing in the Ce(IV) state. According to scanning and transmission electron microscopy observations, thus formed Na-Ce(IV) phosphate consists of spindle-like aggregates of nanocrystalline rods, presumably formed during phosphate anions sorption on the initial CeO2 surface. Pair distribution function analysis revealed that Na-Ce(IV) phosphate has a three-dimensional framework crystal structure, similar to NaTh2(PO4)3, as reported earlier, with large channels along the c-axis containing disordered sodium atoms. This study represents the first detailed analysis of phosphate-induced speciation and microstructural transformation of CeO2 NPs, resulting in the formation of Ce(IV) phosphate. Similar processes may occur in natural ecosystems upon the introduction of CeO2 NPs.

Aβ42 and ROS dual-targeted multifunctional nanocomposite for combination therapy of Alzheimer's disease

Amyloid-β (Aβ) readily misfolds into neurotoxic aggregates, generating high levels of reactive oxygen species (ROS), leading to progressive oxidative damage and ultimately cell death. Therefore, simultaneous inhibition of Aβ aggregation and scavenging of ROS may be a promising therapeutic strategy to alleviate Alzheimer's disease pathology. Based on the previously developed antibody 1F12 that targets all forms of Aβ42, we developed an Aβ42 and ROS dual-targeting nanocomposite using biodegradable mesoporous silica nanoparticles as carriers to load ultra-small cerium oxide nanocrystals (bMSNs@Ce-1F12). By modifying the brain-targeted rabies virus glycoprotein 29 (RVG29-bMSNs@Ce-1F12), this intelligent nanocomposite can efficiently target brain Aβ-rich regions. Combined with peripheral and central nervous system treatments, RVG29-bMSNs@Ce-1F12 can significantly alleviate AD symptoms by inhibiting Aβ42 misfolding, accelerating Aβ42 clearance, and scavenging ROS. Furthermore, this synergistic effect of ROS scavenging and Aβ clearance exhibited by this Aβ42 and ROS dual-targeted strategy also reduced the burden of hyperphosphorylated tau, alleviated glial cell activation, and ultimately improved cognitive function in APP/PS1 mice. Our findings indicate that RVG29-bMSNs@Ce-1F12 is a promising nanodrug that can facilitate multi-target treatment of AD.

Insights on the Dynamics and Toxicity of Nanoparticles in Environmental Matrices

The manufacturing rate of nanoparticles (10–100 nm) is steadily increasing due to their extensive applications in the fabrication of nanoproducts related to pharmaceuticals, cosmetics, medical devices, paints and pigments, energy storage etc. An increase in research related to nanotechnology is also a cause for the production and disposal of nanomaterials at the lab scale. As a result, contamination of environmental matrices with nanoparticles becomes inevitable, and the understanding of the risk of nanoecotoxicology is getting larger attention. In this context, focusing on the environmental hazards is essential. Hence, this manuscript aims to review the toxic effects of nanoparticles on soil, water, aquatic, and terrestrial organisms. The effects of toxicity on vertebrates, invertebrates, and plants and the source of exposure, environmental and biological dynamics, and the adverse effects of some nanoparticles are discussed.

Current Methods and Prospects for Analysis and Characterization of Nanomaterials in the Environment

Analysis and characterization of naturally occurring and engineered nanomaterials in the environment are critical for understanding their environmental behaviors and defining real exposure scenarios for environmental risk assessment. However, this is challenging primarily due to the low concentration, structural heterogeneity, and dynamic transformation of nanomaterials in complex environmental matrices. In this critical review, we first summarize sample pretreatment methods developed for separation and preconcentration of nanomaterials from environmental samples, including natural waters, wastewater, soils, sediments, and biological media. Then, we review the state-of-the-art microscopic, spectroscopic, mass spectrometric, electrochemical, and size-fractionation methods for determination of mass and number abundance, as well as the morphological, compositional, and structural properties of nanomaterials, with discussion on their advantages and limitations. Despite recent advances in detecting and characterizing nanomaterials in the environment, challenges remain to improve the analytical sensitivity and resolution and to expand the method applications. It is important to develop methods for simultaneous determination of multifaceted nanomaterial properties for in situ analysis and characterization of nanomaterials under dynamic environmental conditions and for detection of nanoscale contaminants of emerging concern (e.g., nanoplastics and biological nanoparticles), which will greatly facilitate the standardization of nanomaterial analysis and characterization methods for environmental samples.

Redox Active Cerium Oxide Nanoparticles: Current Status and Burning Issues

Research on cerium oxide nanoparticles (nanoceria) has captivated the scientific community due to their unique physical and chemical properties, such as redox activity and oxygen buffering capacity, which made them available for many technical applications, including biomedical applications. The redox mimetic antioxidant properties of nanoceria have been effective in the treatment of many diseases caused by reactive oxygen species (ROS) and reactive nitrogen species. The mechanism of ROS scavenging activity of nanoceria is still elusive, and its redox activity is controversial due to mixed reports in the literature showing pro-oxidant and antioxidant activity. In light of its current research interest, it is critical to understand the behavior of nanoceria in the biological environment and provide answers to some of the critical and open issues. This review critically analyzes the status of research on the application of nanoceria to treat diseases caused by ROS. It reviews the proposed mechanism of action and shows the effect of surface coatings on its redox activity. It also discusses some of the crucial issues in deciphering the mechanism and redox activity of nanoceria and suggests areas of future research.

Deciphering the effects of CeO2 nanoparticles on Escherichia coli in the presence of ferrous and sulfide ions: Physicochemical transformation-induced toxicity and detoxification mechanisms

The physicochemical transformations as well as the redox reaction-induced toxicity changes of ceria nanoparticles (CeO₂ NPs) in reducing conditions is extremely lacking. Herein, the behaviors, chemical modifications and toxicity of CeO₂ NPs in the presence of reduction-active ions (namely Fe²⁺ and S^2-) were investigated, with a particular emphasis on the cytotoxicity mechanism associated with their physicochemical transformations. The presence of Fe²⁺ and S^2- differently altered the surface properties and toxicity of CeO₂ NPs. Redox reactions with Fe²⁺ led to form small aggregates, boosted the reduction of Ce^IVO₂ and enhanced dissolved Ce³⁺ concentration. Moreover, CeO₂ NPs possessed a high affinity for Escherichia coli (E. coli) and induced the generation of •OH abiotically after reaction with Fe²⁺, provoking serious disruption of cell membranes and causing high toxicity to E. coli. In contrast, the amending of S^2- protected E. coli from direct contact with CeO₂ NPs by creating new Ce₂S₃ precipitated on the surface, accelerating the aggregation of NPs and reducing the concentration of dissolved Ce³⁺. This study suggested that the chemical interactions between the reactive surfaces of CeO₂ and reduction-active ions highly determined the stability and cytotoxicity of CeO₂ NPs, which provides fundamental insights into the environmental risks of CeO₂ NPs.

Surface Properties and Environmental Transformations Controlling the Bioaccumulation and Toxicity of Cerium Oxide Nanoparticles: A Critical Review

Increasing production and utilization of cerium oxide nanoparticles (CNPs) in recent years have raised wide concerns about their toxicity. Numerous studies have been conducted to reveal the toxicity of CNPs, but the results are sometimes contradictory. In this review, the most important factors in mediating CNPs toxicity are discussed, including (1) the roles of physicochemical properties (size, morphology, agglomeration condition, surface charge, coating and surface valence state) on CNPs toxicity; (2) the phase transfer and transformation process of CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S^2-, and ferrous ions. The physicochemical properties play key roles in the interactions of CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused by reactions with (in)organic ligands in both environmental and biological systems would further alter their fate, transport, and toxicity potential. Thus, the toxicity mechanisms are proposed based on the physical damage of direct adsorption of CNPs onto the cell membrane and chemical inhibition (including oxidative stress and interaction of CNPs with biomacromolecules). Finally, the current knowledge gaps and further research needs in identifying the toxicological risk factors of CNPs under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide new insights into cost-effectiveness of control options and management practices to prevent environmental risks from CNPs exposure.

Biochar-assisted transformation of engineered-cerium oxide nanoparticles: Effect on wheat growth, photosynthetic traits and cerium accumulation

The extensive use of nano-fabricated products in daily life is releasing a large volume of engineered nanoparticles (ENPs) in the environment having unknown consequences. Meanwhile, little efforts have been paid to immobilize and prevent the entry of these emerging contaminants in the food chain through plant uptake. Herein, we investigated the biochar role in cerium oxide nanoparticles (CeO₂NPs) bioaccumulation and subsequent translocation in wheat (Triticum aestivum L.) as well as impact on growth, photosynthesis and gas-exchange related physiological parameters. Results indicated that CeO₂NPs up to 500 mg L^-1 level promoted the plant growth by triggering photosynthesis, transpiration and stomatal conductance. Higher NPs concentration (2000 mg CeO₂NPs L^-1) has negatively affected the plant growth and photosynthesis related processes. Conversely, biochar amendment with CeO₂NPs considerably reduced (~9 folds) the plants accumulated contents of Ce even at 2000 mg L^-1 exposure level of CeO₂NPs through surface complexation process and alleviated the phyto-toxic effects of NPs on plant growth. XPS and FTIR analysis confirmed the role of biochar-mediated carboxylate and hydroxyl groups bonding with CeO₂NPs. These findings provides an inside mechanistic understanding about biochar interaction with nano-pollutants to inhibit their bioavailability to plant body.

Metal (Cd, Cr, Ni, Pb) removal from environmentally relevant waters using polyvinylpyrrolidone-coated magnetite nanoparticles

Water pollution is a major global challenge given the increasing growth in industry and human population, and certain metals can be highly toxic and contribute to this significantly. In this study, polyvinylpyrrolidone-coated magnetic nanoparticles (PVP–Fe₃O₄ NPs) were used to remove metals (Cd, Cr, Ni, and Pb) from synthetic soft water and sea water in the presence and absence of fulvic acid. Nanoparticle (NP) suspensions were added to water media at a range of metal concentrations (0.1–100 mg L⁻¹). Removal at different time points (1.5, 3, 6, 12, 24 hours) was also evaluated. Results showed that 167 mg L⁻¹ PVP–Fe₃O₄ NPs could remove nearly 100% of four metals at 0.1 mg L⁻¹ and more than 80% at 1 mg L⁻¹. The removal decreased as the initial metal concentration increased, although essentially 100% of the Pb was removed under all conditions. The kinetic adsorption fitted well to the pseudo-second-order model and in general, the majority of metal adsorption occurred within the first 1.5 hours. These NPs are a reliable method to remove metals under a wide range of environmentally relevant conditions. Our previous research showed the NPs effectively removed oil from waters, so these NPs offer the possibility of combined in situ remediation of oil and metals.

PVP–Fe₃O₄ NPs synthesized with no organic solvents, low toxicity reactants and low temperature/energy requirements could remove Cd, Cr, Ni, Pb efficiently in the different synthetic water media under environmentally relevant conditions.

Antioxidant properties of ALD grown nanoceria films with tunable valency

Herein, we provide the first account of a method to control cerium oxide's mixed valence states (as Ce³⁺ to Ce⁴⁺ ratio) in ultra-thin films formed via atomic layer deposition (ALD). It is determined that modulation of Ce³⁺/Ce⁴⁺ ratio occurs with respect to film thickness and is analogous to the change in surface chemistry observed for cerium oxide nanoparticles with varying particle diameter. The influence of film thickness on enzyme-mimetic radical scavenging is also characterized. Higher film thicknesses show 9-fold increase in catalytic activity. In vitro biocompatibility (apoptosis < 4%) and electrochemical biosensing (lowest concentration: 18 ppt) studies were performed to demonstrate the potential of ALD-grown nanoceria films for biomedical applications.

Phase Segregation, Transition, or New Phase Formation of Plutonium Dioxide: The Roles of Transition Metals

As impurities are virtually impossible to exclude from Pu oxides in realistic environments, understanding the roles of impurities is crucial for the applications and designs of Pu oxides. Here we perform a systematic first-principles DFT + U calculation to find the trends of transition-metal (TM) behaviors in PuO₂ in terms of energetics, atomic properties, oxidation states, and electronic structures. The results show that group IV-B elements Ti, Zr, and Hf are energetically and electronically favorable in PuO₂ and render the possibilities of forming Pu-TM-O ternary phases. In contrast, the remaining TMs tend to destabilize PuO₂ and whether phase segregation or transition occurs largely depends on the redox conditions: oxidation one induces segregation, whereas reduction one facilitates the transition from PuO₂ to Pu₂O₃. On the basis of the correlations between the properties of TMs and their relative stabilities in PuO₂, we conclude that the degree of electron match between TMs and Pu plays the decisive role in the stability, as established for the cases of tetravalent elements, whereas some electron-mismatched but energetically stable TMs such as III-B and V-B elements could drive the valence transition of Pu, resulting in the phase instability of PuO₂.

Investigation of the rheological behavior of activated sludge in response to CeO2 nanoparticles and potential mechanism

With the rapid development of CeO₂ nanoparticles (NPs), the released CeO₂ NPs entering into wastewater treatment plants might bring the challenges for sludge pumping and mixing. In this study, we firstly elucidated the rheological behavior of 4.0 wt% sludge at various concentrations of CeO₂ NPs. With the increase of CeO₂ NPs to 5 mg/L, the shear stress at any given shear rate was reduced and the limiting viscosity was also decreased, indicating the sludge became more flowability. The dynamic sweep tests further demonstrated the decreased elastic behavior and weakened internal structure in response to low concentrations of CeO₂ NPs (≤ 5 mg/L). However, 20 mg/L CeO₂ NPs had negative effects on the rheological evolution of sludge, namely, better solid-like property and higher elastic structure. These results were mainly attributed to the combination of the decreased β-D-glucopyranose polysaccharides which support the rigid structure of sludge and the dramatically increased protein content (especially in 20 mg/L CeO₂ NPs). These results can potentially provide novel information for the efficient design of sludge treatment when coped with CeO₂ NPs. Graphical abstract ᅟ.

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects-An updated review

The present review covers developments in studies of nanomaterials (NMs) in the environment since our much cited review in 2008. We discuss novel insights into fate and behavior, metrology, transformations, bioavailability, toxicity mechanisms, and environmental impacts, with a focus on terrestrial and aquatic systems. Overall, the findings were that: 1) despite substantial developments, critical gaps remain, in large part due to the lack of analytical, modeling, and field capabilities, and also due to the breadth and complexity of the area; 2) a key knowledge gap is the lack of data on environmental concentrations and dosimetry generally; 3) substantial evidence shows that there are nanospecific effects (different from the effects of both ions and larger particles) on the environment in terms of fate, bioavailability, and toxicity, but this is not consistent for all NMs, species, and relevant processes; 4) a paradigm is emerging that NMs are less toxic than equivalent dissolved materials but more toxic than the corresponding bulk materials; and 5) translation of incompletely understood science into regulation and policy continues to be challenging. There is a developing consensus that NMs may pose a relatively low environmental risk, but because of uncertainty and lack of data in many areas, definitive conclusions cannot be drawn. In addition, this emerging consensus will likely change rapidly with qualitative changes in the technology and increased future discharges. Environ Toxicol Chem 2018;37:2029-2063. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.