Hydrophobic Surface Coating Can Reduce Toxicity of Zinc Oxide Nanoparticles to the Marine Copepod Tigriopus japonicus.

Coated zinc oxide nanoparticles (ZnO-NPs) are more commonly applied in commercial products but current risk assessments mostly focus on bare ZnO-NPs. To investigate the impacts of surface coatings, this study examined acute and chronic toxicities of six chemicals, including bare ZnO-NPs, ZnO-NPs with three silane coatings of different hydrophobicity, zinc oxide bulk particles (ZnO-BKs), and zinc ions (Zn-IONs), toward a marine copepod, Tigriopus japonicus. In acute tests, bare ZnO-NPs and hydrophobic ZnO-NPs were less toxic than hydrophilic ZnO-NPs. Analyses of the copepod's antioxidant gene expression suggested that such differences were governed by hydrodynamic size and ion dissolution of the particles, which affected zinc bioaccumulation in copepods. Conversely, all test particles, except the least toxic hydrophobic ZnO-NPs, shared similar chronic toxicity as Zn-IONs because they mostly dissolved into zinc ions at low test concentrations. The metadata analysis, together with our test results, further suggested that the toxicity of coated metal-associated nanoparticles could be predicted by the hydrophobicity and density of their surface coatings. This study evidenced the influence of surface coatings on the physicochemical properties, toxicity, and toxic mechanisms of ZnO-NPs and provided insights into the toxicity prediction of coated nanoparticles from their coating properties to improve their future risk assessment and management.

Graphene-oxide-wrapped ZnMn2O4 as a high performance lithium-ion battery anode.

Cation distribution between tetrahedral and octahedral sites within the ZnMn2O4 spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameters can easily be tuned, from 5%-19%, depending on the annealing temperature. The upper limit of inversion is found for T = 400 °C as confirmed by x-ray powder diffraction and Raman spectroscopy. Excellent battery behavior is found for samples annealed at lower temperatures; after 500 cycles the specific capacity for as-prepared ZnMn2O4 is 909 mAh g-1, while ZnMn2O4 heat-treated at 300 °C is 1179 mAh g-1, which amounts to 101% of its initial capacity. Despite the excellent performance of a sample processed at 300 °C at lower charge/discharge rates (100 mAh g-1), a drop in the specific capacity is observed with rate increase. This issue is solved by graphene-oxide wrapping: the specific capacity obtained after the 400th cycle for graphene-oxide-wrapped ZnMn2O4 heat-treated at 300 °C is 799 mAh g-1 at a charge/discharge rate 0.5 A g-1, which is higher by a factor of 6 compared to samples without graphene -oxide wrapping.

Transmission electron microscopy artifacts in characterization of the nanomaterial-cell interactions.

We investigated transmission electron microscopy artifacts obtained using standard sample preparation protocols applied to the investigation of Escherichia coli cells exposed to common nanomaterials, such as TiO2, Ag, ZnO, and MgO. While the common protocols for some nanomaterials result only in known issues of nanomaterial-independent generation of anomalous deposits due to fixation and staining, for others, there are reactions between the nanomaterial and chemicals used for post-fixation or staining. Only in the case of TiO2 do we observe only the known issues of nanomaterial-independent generation of anomalous deposits due to exceptional chemical stability of this material. For the other three nanomaterials, different artifacts are observed. For each of those, we identify causes of the observed problems and suggest alternative sample preparation protocols to avoid artifacts arising from the sample preparation, which is essential for correct interpretation of the obtained images and drawing correct conclusions on cell-nanomaterial interactions. Finally, we propose modified sample preparation and characterization protocols for comprehensive and conclusive investigations of nanomaterial-cell interactions using electron microscopy and for obtaining clear and unambiguous revelation whether the nanomaterials studied penetrate the cells or accumulate at the cell membranes. In only the case of MgO and ZnO, the unambiguous presence of Zn and Mg could be observed inside the cells.

Toxicity of metal oxide nanoparticles: mechanisms, characterization, and avoiding experimental artefacts.

Metal oxide nanomaterials are widely used in practical applications and represent a class of nanomaterials with the highest global annual production. Many of those, such as TiO2 and ZnO, are generally considered non-toxic due to the lack of toxicity of the bulk material. However, these materials typically exhibit toxicity to bacteria and fungi, and there have been emerging concerns about their ecotoxicity effects. The understanding of the toxicity mechanisms is incomplete, with different studies often reporting contradictory results. The relationship between the material properties and toxicity appears to be complex and diifficult to understand, which is partly due to incomplete characterization of the nanomaterial, and possibly due to experimental artefacts in the characterization of the nanomaterial and/or its interactions with living organisms. This review discusses the comprehensive characterization of metal oxide nanomaterials and the mechanisms of their toxicity.

In situ synthesis of TiO2(B) nanotube/nanoparticle composite anode materials for lithium ion batteries.

Titania nanotubes were prepared by a simple hydrothermal route. Their electrochemical performance has been examined in detail and compared to TiO2(B) nanoparticles, TiO2 anatase and P25 titania nanoparticles. The cycling and rate performance of TiO2 nanotubes is superior to both types of nanoparticles, and it can be further improved by an in situ titanium precursor treatment, which results in the formation of TiO2 nanoparticles on/between the nanotubes. The obtained specific capacity after 200 cycles at 0.2 A g(-1) charge/discharge rate remained above 130 mAh g(-1). The enhanced lithium storage properties of these samples can be attributed to their unique morphology and crystal structure.

Mechanisms of antibacterial activity of MgO: non-ROS mediated toxicity of MgO nanoparticles towards Escherichia coli.

The toxicity of metal oxide nanomaterials and their antimicrobial activity is attracting increasing attention. Among these materials, MgO is particularly interesting as a low cost, environmentally-friendly material. The toxicity of MgO, similar to other metal oxide nanomaterials, is commonly attributed to the production of reactive oxygen species (ROS). We investigated the toxicity of three different MgO nanoparticle samples, and clearly demonstrated robust toxicity towards Escherichia coli bacterial cells in the absence of ROS production for two MgO nanoparticle samples. Proteomics data also clearly demonstrate the absence of oxidative stress and indicate that the primary mechanism of cell death is related to the cell membrane damage, which does not appear to be due to lipid peroxidation.

Antibacterial and photocatalytic activity of TiO2 and ZnO nanomaterials in phosphate buffer and saline solution.

We studied antibacterial and photocatalytic activity of anatase TiO2 and ZnO in phosphate buffer and saline solution. We found that the different anions in the suspension medium (chloride and phosphate) significantly affected the following suspension properties: the stability of nanoparticle suspension, the release of metal ions from the nanoparticles, and the production of the reactive oxygen species by the nanoparticles. As a result, antibacterial activity and photocatalytic dye degradation were also affected. However, the effect of the suspension medium was different for ZnO and TiO2. Obtained results are discussed.

Iron-Based Oxygen Scavengers on Mesoporous Silica Nanospheres.

Iron-based materials are among the most commonly used oxygen scavengers. Here, we investigated the mesoporous silica nanosphere (MSN)-supported iron-based scavengers, such as FeOx nanoparticles and different atomic layer deposition (ALD) coatings (FeOx and Fe). We found that the scavenger performance is a result of a complex interplay between available Brunauer-Emmett-Teller surface area and the scavenger composition, with the combination of infiltrated nanoparticles and Fe-ALD coating resulting in the best performance. When the glucose-based treatment of MSN is used to further enhance oxygen scavenging capacity, Fe-ALD coating yields the best performance, with a high oxygen adsorption capacity of 126.8 mL/g. ALD deposition of Fe represents a versatile method to introduce Fe-based oxygen scavengers onto different supports, and it can facilitate the integration of scavengers with different types of packaging, as the deposition can be performed at a low temperature of 150 °C.

Photocatalytic degradation of different types of microplastics by TiOx/ZnO tetrapod photocatalysts.

We investigated the use of titania coated ZnO tetrapods for photocatalytic degradation of two common types of microplastics, namely polyethylene (PE) microparticles and polyester (PES) microfibers. We found that the plastics morphology affects the rate of degradation, and that the use of electron scavengers is needed to maintain the reactivity of the photocatalysts over a prolonged period of time. Complete mass loss of PE and PES is achieved under UV illumination for 480 h and 624 h, respectively. In addition to pristine microplastics, the degradation of environmental microplastics sample (consisting primarily of polypropylene) was also demonstrated, though in this case longer degradation time (∼816 h) was needed to achieve complete mass loss of the samples.

Interactive effects of temperature and salinity on toxicity of zinc oxide nanoparticles towards the marine mussel Xenostrobus securis.

Growing application of zinc oxide nanoparticles (ZnO-NPs) in global market has led to the concern over their potential environmental impacts. Filter feeders like mussels are prone to nanoparticles due to their superior filter-feeding ability. Temperature and salinity of coastal and estuarine seawaters often vary seasonally and spatially, and their changes may jointly influence physicochemical properties of ZnO-NPs and thus their toxicity. This study, therefore, aimed to investigate the interactive effect of temperatures (15, 25 and 30 °C) and salinities (12 and 32 PSU) on physicochemical properties and sublethal toxicity of ZnO-NPs towards a marine mussel Xenostrobus securis, and to compare that with the toxicity caused by Zn2+ ions (zinc sulphate heptahydrate). The results revealed increased particle agglomeration but decreased zinc ion release of ZnO-NPs at the highest temperature and salinity condition (30 °C and 32 PSU). After exposure, ZnO-NPs significantly reduced survival, byssal attachment rate and filtration rate of the mussels at high temperature and salinity (30 °C and 32 PSU). Glutathione S-transferase and superoxide dismutase activities in the mussels were suppressed at 30 °C. These aligned with the augmented zinc accumulation with increasing temperature and salinity which could likely be attributable to increased particle agglomeration of ZnO-NP and enhanced intrinsic filtration rate of the mussels under these conditions. Together with the observed lower toxic potency of Zn2+ compared to ZnO-NPs, our results suggested that the mussels might accumulate more zinc through particle filtration under higher temperature and salinity, eventually resulting in elevated toxicity of ZnO-NPs. Overall, this study demonstrated the necessity to consider the interactive effect of environmental factors such as temperature and salinity during the toxicity assessment of nanoparticles.

Effect of Passivating Molecules and Antisolvents on Lifetime of Green Dion-Jacobson Perovskite Light-Emitting Diodes.

We investigated the influence of two passivating molecules containing a P═O group on the performance of quasi-2D Dion-Jacobson halide perovskite light-emitting diodes, namely, triphenylphosphine oxide (TPPO) and diphenyl-4-triphenylsilylphenyl phosphine oxide (TSPO1). We found that both passivating molecules lead to increased efficiency compared to control devices, while they had opposite effects on device lifetime, with a decrease observed for TPPO and an increase observed for TSPO1. The two passivating molecules resulted in differences in energy-level alignment, electron injection, film morphology and crystallinity, and ion migration during operation. While TPPO resulted in improved photoluminescence decay times, overall higher maximum external quantum efficiency (EQE) and device lifetime were obtained for TSPO1 compared to TPPO (14.4% vs 12.4% EQE, 341 min vs 42 min T50).

Dual Surface Modifications of NiOx/Perovskite Interface for Enhancement of Device Stability.

Various phosphonic acid based self-assembled monolayers (SAMs) have been commonly used for interface modifications in inverted perovskite solar cells. This typically results in significant enhancement of the hole extraction and consequent increase in the power conversion efficiency. However, the surface coverage and packing density of SAM molecules can vary, depending on the chosen SAM material and underlying oxide layer. In addition, different SAM molecules have diverse effects on the interfacial energy level alignment and perovskite film growth, resulting in complex relationships between surface modification, efficiency, and lifetime. Here we show that ethanolamine surface modification combined with [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) results in significant improvement in device stability compared to devices with 2PACz modification only. The significantly smaller size of ethanolamine enables it to fill any gaps in 2PACz coverage and provide improved interfacial defect passivation, while its different chemical structure enables it to provide complementary effects to 2PACz passivation. Consequently, the perovskite films are more stable under illumination (slower photoinduced segregation), and the devices exhibit significant stability enhancement. Despite similar power conversion efficiencies (PCE) between 2PACz only and combined ethanolamine-2PACz modification (PCE of champion devices ∼21.6-22.0% for rigid and ∼20.2-21.0% for flexible devices), the T80 lifetime under simulated solar illumination in ambient is improved more than 15 times for both rigid and flexible devices.

Encapsulation and Stability Testing of Perovskite Solar Cells for Real Life Applications.

With the progress in the development of perovskite solar cells, increased efforts have been devoted to enhancing their stability. With more devices being able to survive harsher stability testing conditions, such as damp heat or outdoor testing, there is increased interest in encapsulation techniques suitable for this type of tests, since both device architecture compatible with increased stability and effective encapsulation are necessary for those testing conditions. A variety of encapsulation techniques and materials have been reported to date for devices with different architectures and tested under different conditions. In this Perspective, we will discuss important factors affecting the encapsulation effectiveness and focus on the devices, which have been subjected to outdoor testing or damp heat testing. In addition to encapsulation requirements for these testing conditions, we will also discuss device requirements. Finally, we discuss possible methods for accelerating the testing of encapsulation and device stability and discuss the future outlook and important issues, which need to be addressed for further advancement of the stability of perovskite solar cells.

Contrasting toxicity of polystyrene nanoplastics to the rotifer Brachionus koreanus in the presence of zinc oxide nanoparticles and zinc ions.

Emerging contaminants such as nanoplastics and nanoparticles likely experience similar environmental behaviours, fate and effects but our knowledge of their combined toxicity is scanty. This study, therefore, investigated the joint toxicity of polystyrene nanoplastics (PNPs) and zinc oxide nanoparticles (ZnO-NPs) to an ecologically important rotifer Brachionus koreanus, and compared with the joint toxicity of PNPs and Zn ions (Zn-IONs from ZnSO4·7H2O). With increasing concentration, ZnO-NPs formed significant agglomeration with PNPs for up to 1.3 times of the original hydrodynamic size of ZnO-NPs, alongside doubling in their sedimentation and thereby losing 58% of their released Zn ions. In contrast, the availability of Zn-IONs was less affected by the agglomeration and sedimentation of PNPs, with only a loss of 18% of Zn ions at the highest concentration of PNPs. Consequently, as suggested by Concentration Addition and Independent Action models and the Model Deviation Ratios, ZnO-NPs and PNPs exerted an antagonistic interaction whereas Zn-IONs and PNPs exhibited an additive effect. We also advocate the use of the Nonparametric Response Surface method, which is more useful to predict the toxicity of chemical mixtures with interacting effects. Our findings suggested a potential difference between particle-particle and particle-ion interactions, especially at higher test concentrations, which may eventually affect their toxicity. We, therefore, call for a more systematic evaluation of commonly coexisting chemical mixtures which consist of nanoplastics and manufactured nanomaterials.

Interfacial stabilization for inverted perovskite solar cells with long-term stability.

Perovskite solar cells (PSCs) commonly exhibit significant performance degradation due to ion migration through the top charge transport layer and ultimately metal electrode corrosion. Here, we demonstrate an interfacial management strategy using a boron chloride subphthalocyanine (Cl6SubPc)/fullerene electron-transport layer, which not only passivates the interfacial defects in the perovskite, but also suppresses halide diffusion as evidenced by multiple techniques, including visual element mapping by electron energy loss spectroscopy. As a result, we obtain inverted PSCs with an efficiency of 22.0% (21.3% certified), shelf life of 7000 h, T80 of 816 h under damp heat stress (compared to less than 20 h without Cl6SubPc), and initial performance retention of 98% after 2000 h at 80 °C in inert environment, 90% after 2034 h of illumination and maximum power point tracking in ambient for encapsulated devices and 95% after 1272 h outdoor testing ISOS-O-1. Our strategy and results pave a new way to move PSCs forward to their potential commercialization solidly.

Very-low-bandgap metallopolyynes of platinum with a cyclopentadithiophenone ring for organic solar cells absorbing down to the near-infrared spectral region.

Two solution-processable metallopolyynes of platinum functionalized with the electron-deficient 4H-cyclopenta[2,1-b:3,4-b']dithiophen-4-one spacer and their model molecular complexes were synthesized and developed for the applications of polymer solar cells. These metallated polymers possess extremely low bandgaps of 1.44-1.53 eV which extend toward the near-infrared (NIR) range of the solar spectrum, and represent the lowest optical bandgap yet reported for platinum(II) metallopolyynes to date. The structural flexibility, processibility, and good photovoltaic performance make cyclopentadithiophenone-containing polymers prominent candidates for NIR photovoltaic applications.

In vivo toxicities of nine engineered nano metal oxides to the marine diatom Skeletonema costatum and rotifer Brachionus koreanus.

This study compared in vivo acute toxicities of nine engineered nano metal oxides to the marine diatom Skeletonema costatum and rotifer Brachionus koreanus. The sequence of their toxicities to S. costatum, based on growth inhibition, was: nano zinc oxide (nZnO) > nTiO2 (rutile) > nMgO > Annealed nMgO > nTiO2 (anatase) > Î³-nAl2O3 > nIn2O3 > α-nAl2O3 > nSnO2. Similarly, nZnO was also the most toxic to B. koreanus, but the other nano metal oxides were non-lethal. nMgO and nZnO were confirmed to trigger reactive oxygen species (ROS) mediated toxicity to the two marine organisms, while nTiO2 (both anatase and rutile forms) likely induced oxidative stress as shown by their acellular ROS production. nZnO may also cause damage in the endocrine system of B. koreanus, as indicated by the increased transcription of retinoid X receptor. Annealed nMgO reduces its toxicity via removal of O2- and impurities from its surface.

Unraveling the Crystallization Kinetics of 2D Perovskites with Sandwich-Type Structure for High-Performance Photovoltaics.

2D perovskite solar cells with high stability and high efficiency have attracted significant attention. A systematical static and dynamic structure investigation is carried out to show the details of 2D morphology evolution. A dual additive approach is used, where the synergy between an alkali metal cation and a polar solvent leads to high-quality 2D perovskite films with sandwich-type structures and vertical phase segregation. Such novel structure can induce high-quality 2D slab growth and reduce internal and surface defects, resulting in a high device efficiency of 16.48% with enhanced continuous illumination stability and improved moisture (55-60%) and thermal (85 °C) tolerances. Transient absorption spectra reveal the carrier migration from low n to high n species with different kinetics. An [PbI6 ]4- octagon coalescence transformation mechanism coupled with metal and organic cations wrapped is proposed. By solvent vapor annealing, a recrystallization and reorientation of the 2D perovskite slabs occurs to form an ideal structure with improved device performance and stability.

Side-Chain Engineering of Donor-Acceptor Conjugated Small Molecules As Dopant-Free Hole-Transport Materials for Efficient Normal Planar Perovskite Solar Cells.

Simultaneously improving efficiency and stability, which are particularly crucial factors for the commercialization of perovskite solar cells (PSCs), remains a major challenge. For high-efficiency normal PSCs, the development of stable dopant-free hole-transport materials (HTMs) seems imperative. Here, we developed potential donor-acceptor small molecules (BTTI) as HTMs for normal planar PSCs. Through tailoring its alkyl side-chain length as BTTI-C6, BTTI-C8, and BTTI-C12, our results show that upon shortening the side chain of BTTI, the hole mobility, film-forming capability, and resultant device performance were remarkably improved, with the device conversion efficiencies of 19.69% for BTTI-C6, 18.89% for BTTI-C8, and 17.49% for BTTI-C12. Meanwhile, compared to those made with the routine doped Spiro-OMeTAD, devices based on our dopant-free HTMs exhibited significantly improved stability. This work paves the way to the development of effective dopant-free HTMs for high-performance PSCs.

Novel Molecular Doping Mechanism for n-Doping of SnO2 via Triphenylphosphine Oxide and Its Effect on Perovskite Solar Cells.

Molecular doping of inorganic semiconductors is a rising topic in the field of organic/inorganic hybrid electronics. However, it is difficult to find dopant molecules which simultaneously exhibit strong reducibility and stability in ambient atmosphere, which are needed for n-type doping of oxide semiconductors. Herein, successful n-type doping of SnO2 is demonstrated by a simple, air-robust, and cost-effective triphenylphosphine oxide molecule. Strikingly, it is discovered that electrons are transferred from the R3P+ O- σ-bond to the peripheral tin atoms other than the directly interacted ones at the surface. That means those electrons are delocalized. The course is verified by multi-photophysical characterizations. This doping effect accounts for the enhancement of conductivity and the decline of work function of SnO2 , which enlarges the built-in field from 0.01 to 0.07 eV and decreases the energy barrier from 0.55 to 0.39 eV at the SnO2 /perovskite interface enabling an increase in the conversion efficiency of perovskite solar cells from 19.01% to 20.69%.