Multivalent magnetic nanoaggregates with unified antibacterial activity
and selective uptake of heavy metals and organic pollutants

Journal of Molecular Liquids

Covalently functionalized magnetite (Fe3O4) nanoaggregates carrying an imidazolium-derivative (1-hexadecyl-
3-vinyl imidazolium bromide, HDVI) and L-cysteine (L-Cys) as surface ligands act as bimodal water-treatment
particulate agents (HDVI@L-Cys@PAA@Fe3O4) with high antibacterial efficacy and specific surface adsorption
properties. For covalent conjugation of HDVI the polyacrylic acid (PAA)-coated magnetite nanocrystals (PAA@
Fe3O4) were functionalized with L-cysteine via carbodiimide coupling (L-Cys@PAA@Fe3O4) having terminal
-SH groups that were used for thiol-ene click chemistry. The carefully performed series of water-remediation
tests with magnetically separable HDVI@L-Cys@PAA@Fe3O4 nanoaggregates demonstrated their high efficiency
in the concomitant removal transition metal ions and organic pollutant without losing the antibacterial effect.
Time-dependent adsorption experiments showed high degree (>90%) of trapping and removal activity. Antibacterial
action of the HDVI@L-Cys@PAA@Fe3O4 nanoaggregates originates from the amphiphilic structure of HDVI
groups capable of penetrating the bacterial cell walls. The presence of surface-bound ligands and conversion efficiency
of carbodiimide and click chemistry protocol was verified by FT-IR, elemental and thermogravimetric
analysis. The phase, composition morphology and surface charge of nanoaggregates were examined by XRD,
SEM/TEM and zeta potential studies, respectively. The experimental findings reported here represent a conceptual
advancement in the state-of-the-art magnetic beads developed for water purification or remediation purposes.
Our results evidently demonstrate that nanoaggregates are highly effective in unifying bactericidal
activity against different microorganism with heavy metal and organic pollutant removal properties.

https://doi.org/10.1016/j.molliq.2020.114002

Controlled growth of Cu and CuO_x thin films from subvalent copper precursors

Dalton Transactions

A new Cu(I) precursor, [(COD)Cu(TFB-TFEA)] (COD = 1,5-cyclooctadiene and TFB-TFEA = N-(4,4,4-trifluorobut-1-en-3-on)-6,6,6-trifluoroethylamine) with high volatility and a clean thermal decomposition pattern was tested for thermal and plasma-assisted chemical vapor deposition (CVD). The heteroleptic configuration based on an anionic and a chelating neutral ligand unified both reactivity and sufficient stability resulting in an intrinsic molecular control over the composition of the resulting CVD deposits. The electronic influence of the ligand on the metal site was studied by 1D and 2D NMR spectroscopy, while EI mass spectrometry revealed the ligand elimination cascade. Thermal and plasma CVD experiments demonstrated the suitability of the copper compound for an atom-efficient (high molecule-to-material yield) deposition of copper(0) and copper(I) oxide films that could be converted into crystalline copper(II) oxide upon heat treatment at 500 °C.

https://doi.org/10.1039/D0DT02570D

Career progression through professional engagement: The impact of MRS student-led activities

MRS Bulletin: Society News

Professional organizations focusing on strong member–society interactions play a crucial role in the broader career development of its members and volunteers. In this context, the mission of the Materials Research Society (MRS) to promote communication among the global community of materials researchers is both an opportunity and responsibility. During the past several decades, MRS has addressed this challenge with utmost priority and authenticity, evident in its worldwide visibility. In addition to the large set of activities involving key players from universities, national laboratories, government, and policymakers, long-term engagement of students and young professionals plays a central role in the core values of MRS.

https://doi.org/10.1557/mrs.2020.99

Lead(II) Propionate Additive and a Dopant-Free Polymer Hole Transport Material for CsPbI₂Br Perovskite Solar Cells

ACS Energy Letters

All-inorganic perovskites (CsPbI₃ and CsPbI₂Br), owing to their greater thermal stability compared to organic–inorganic hybrid perovskites, are becoming popular in perovskite photovoltaics, but the problem that remains with CsPbI₂Br (or CsPbI₃) is the humidity-assisted phase transformation. Herein, we report on the formation of CsPbI₂Br α-phase and improvement of its phase stability under ambient atmosphere (20–30% relative humidity) by Pb(II) propionate additive in the CsPbI₂Br precursor. Solar cells employing a CsPbI₂Br film with an optimum concentration of the additive (1 mol %) and a donor–acceptor type polymer (synthesized by us) as dopant-free hole transport material that has a better energy level matching with CsPbI₂Br (compared to other polymers like P3HT, PTAA, and asy-PBTBDT) work with a champion power conversion cell efficiency of 14.58%. A continuous increase in the open-circuit voltage, reaching 1.36 V for 5 mol % Pb(II) propionate, indicates a remarkable defect-passivation effect by the additive.

https://doi.org/10.1021/acsenergylett.0c00244

Antibacterial Ag containing core‐shell polyvinyl alcohol‐poly (lactic acid) nanofibers for biomedical applications

Polymer engineering and science

Core‐shell‐structured polyvinyl alcohol (PVA)‐poly (lactic acid) (PLA) nanofibers combining the hydrophilic trait of PVA and the biocompatibility of PLA were produced using coaxial electrospinning. This allowed the incorporation of AgNO₃ in the PVA core of the distinct fibers as shown through transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) showed relatively uniform and bead‐free fibers with smooth surfaces. Ag‐containing fibers show significantly decreased diameters compared with Ag‐free samples as a result of the increased conductivity of the spinning solutions with increasing amounts of AgNO₃. In a postsynthetic treatment, the AgNO₃ was reduced forming silver nanoparticles (Ag NPs). Ag NPs of 45 to 90 nm size were located in the PVA core but also on the surface of the core‐shell fibers and as individual, agglomerated, and polymer‐coated particles of 100‐200 nm. Powder X‐ray diffraction (PXRD), energy dispersive X‐ray spectroscopy (EDX), and UV‐vis absorption spectroscopy confirmed the increasing amounts of Ag in the core‐shell fibers when using increasing amounts of AgNO₃ in the spinning solutions. The antibacterial activity of the nanofiber mats against two prokaryotes Escherichia coli (Gram‐negative) and Staphylococcus aureus (Gram‐positive) increased with increasing amounts of Ag, as expected and produces inhibition zones of 1 to 2 mm.

https://doi.org/10.1002/pen.25375

High-performance supercapacitors based on S-doped polyaniline nanotubes decorated with Ni(OH)₂ nanosponge and onion-like carbons derived from used car tyres

Electrochimica Acta

High performance supercapacitors are designed based on hierarchical Ni(OH)₂ nanosponges anchored on sulfur-enriched polyaniline (PANI) nanotubes and waste tyre-derived onion-like carbons (OLC) as counter electrode materials. The rational strategy of grafting mesoporous thin sheets of Ni(OH)₂ on PANI produces unique composite nanoarchitectures that shows superior potential in supercapacitors validated by higher electrochemical stability. The designed asymmetric supercapacitor configuration with OLC as anode exhibits excellent specific capacitance of 622 F g⁻¹ at higher current density of 2 A g⁻¹ with an exceptional capacity retention greater than 97% achieved upon 10,000 continuous charge-discharge cycles. The asymmetric device delivers the remarkable energy and power density of 70 Wh kg⁻¹ and 136 kW kg⁻¹, respectively, whereas the symmetric device delivers the maximum energy density of 23 Wh kg⁻¹ and power density of 292 kW kg⁻¹. Further, it is demonstrated that Ni(OH)₂@PANI composite-based all solid-state flexible asymmetric supercapacitor construction with OLC exhibits high specific capacitance value of 166 F g⁻¹ at a higher current density of 5 A g⁻¹. The prolonged cycle stability may be attributed to the synergistic effect of 3D-nanosponge-like Ni(OH)₂ on PANI nanotubes surface, stabilizing the volume changes upon cycling. The OLC derived from the pyrolysis of waste-tyres offers high energy density and better rate capability.

https://doi.org/10.1016/j.electacta.2020.136111

Cation-Deficient TiO₂(B) Nanowires with Protons Charge Compensation for Regulating Reversible Magnesium Storage

Nano Energy

Magnesium battery is a recently emerging energy storage system that has attracted considerable attention. However, its development is limited by the lack of proper electrode materials for reversible Mg²⁺ intercalation/de-intercalation with satisfied capacity. Here, we firstly report easy synthesis of Ti-deficient bronze titanium dioxide nanowires by topology transformation of H-titanate precursor. It’s found OH⁻ anions substitution of O²⁻ supports the formation of Ti vacancies in TiO₂(B) with a high concentration, denoted as (Ti_0.91O_1.64(OH)_0.36), and can be utilized as a robust host for Mg-ion storage. Both the theoretical and experimental study revealed that Ti-deficient TiO₂(B) exhibits much improved electronic properties with unpaired electrons. Density functional theory (DFT) calculations also reveal Ti vacancies provide more feasible binding sites for Mg-ion. More importantly, it’s surprisingly found the presence of protons enables a suitable binding energy for Mg-ion intercalation and extraction. As a result, such material displays discharge and charge capacities of 217.3 and 165.3 mA h g^-1 at 0.02 A g^-1, representing the highest value among the reported Ti-based electrode materials as well as a high initial Columbic efficiency up to 76.1%. This study gives a new and in-depth view on how cation-deficient structure regulates and promotes the reversible energy storage.

https://doi.org/10.1016/j.nanoen.2020.104716

Electrospun SrNb₂O₆ photoanodes from single-source precursors for photoelectrochemical water splitting

Solar Energy Materials and Solar Cells

Electrospinning of SrNb₂O₆ nanofibers from a single bimetallic alkoxide precursor [SrNb₂(OⁱPr)₁₂(HOⁱPr)] and the application of resulting oxide nanofiber meshes as potential photoanode material for solar water splitting is reported. Direct formation of single phase SrNb₂O₆ nanofibers from the precursor gel was favored by the tailored Sr:Nb ratio (1:2) and preordering of cations through Sr–O(R)-Nb units present in the molecular precursor. X-ray diffraction and photoelectron spectroscopy confirmed the chemical composition and formation of SrNb₂O₆ phase. A minor amount of orthorhombic SrNb₆O₁₆ phase was observed, when small excess of alkali metal was present during the precursor synthesis. The optical bandgap of photoelectrodes, produced by doctor blading and spin coating of the nanofibers, revealed bandgap energies between 3.25 and 3.43 eV, owing to different microstructure of the photoelectrodes. The measurement of photoelectrochemical properties in basic conditions showed photocurrent density values at 1.23 eV ranging from 0.06 mA/cm² to 0.16 mA/cm². A maximum value of 0.6 mA/cm² was obtained for spin-coated nanofiber photoelectrodes.

https://doi.org/10.1016/j.solmat.2020.110485

Atomic scale growth of GdFeO₃ perovskite thin films

Thin Solid Films

Thin films of multiferroic gadolinium orthoferrite (GdFeO₃) are of significant interest due to intrinsic coupling of magnetic and ferroelectric order in their monolithic bimetallic structures relevant for potential applications in magneto-optical data storage devices. Formation of this composition in stoichiometric pure form is challenging due to facile formation of the thermodynamically preferred garnet phase (Gd₃Fe₅O₁₂) that mostly coexists as a minor phase in gadolinium orthoferrite films. We report herein the selective epitaxial growth of GdFeO₃ films by atomic layer deposition of a single bimetallic precursor [GdFe(O^tBu)₆(C₅H₅N)₂] containing Gd:Fe in the required stoichiometric ratio, and using ozone as co-reactant. Intact vaporisation of [GdFe(O^tBu)₆(C₅H₅N)₂] in the gas phase and its clean conversion into the complex oxide phase as validated by mass spectral studies and thermogravimetry demonstrate the potential of the Gd-Fe compound as an efficient single-source precursor. Epitaxial growth of GdFeO₃ on SrTiO₃ substrates was confirmed by X-ray diffraction analysis, whereas the presence of Fe³⁺ and Gd³⁺ without any traces of N species from the ligands was verified by X- ray photoelectron spectroscopy. Magnetic properties of the resulting perovskite films studied by superconducting quantum interference device measurements revealed the superposition of two independent magnetic contributions due to paramagnetic (Gd³⁺) and ferromagnetic (Fe³⁺) sublattices in GdFeO₃.

https://doi.org/10.1016/j.tsf.2020.137848

Electrochemical Gas Sensor Integrated with Vanadium Monoxide Nanowires for Monitoring Low Concentrations of Ammonia Emission

Journal of the Electrochemical Society

An electrochemical sensor for the detection of extremely low concentration of ammonia (1 part per billion, ppb) was fabricated by integrating vanadium monoxide (VO_x; x = 0.8–1.2) nanowires on the platinum electrodes. The nanowire-based sensor responds at room temperature non-linearly to a staircase sequence of ammonia from 1 ppb to 100 ppb. The rise and fall time of the nanowire sensor was found to be 10 s and 9 s, respectively. While the immobilization of VO nanowires increased the electrochemical surface area, the defect rich and ionic nature of the VO surface (V²⁺O²⁻) facilitated the chemical interaction and adsorption of polar ammonia molecules as evident in the room temperature response of the VO@Pt amperometric electrochemical sensor. The availability of metal centered d-electrons and the semiconductor nature of vanadium monoxide lowered the interfacial resistance of the nanowire-modified sensor enabling the lower detection limit of ammonia. The sensor seems to respond to CH₄, H₂S and C₃H₆ as well although the NH₃ response is nearly six-fold compared to these common interfering compounds. The results pave the way for a low-cost alternative paper-based sensor to monitor ammonia emissions primarily from confined animal feeding operations (CAFOs).

https://iopscience.iop.org/article/10.1149/1945-7111/ab7114/meta

Structure-Decomposition relationships of homoleptic and heteroleptic vanadium(IV) alkoxides for defined gas phase depositions of VO₂ and V₂O₃ thin films

Materials Today: Proceedings

A facile high yield synthesis of a novel non-oxo heteroleptic vanadium(IV) alkoxide with chelating asymmetric fluorinated ß-heteroarylacetamides (2,2,2-trifluoro-N-(pyridine-2-yl)acetamide (H-PyTFA) (1)) with the general formula [V(O^tBu)₂(PyTFA)₂] (4) as precursor for nanostructured vanadium oxides films deposited by chemical vapor deposition (CVD) is presented here. Single crystal X-ray analysis, electron paramagnetic resonance (EPR) spectroscopy and mass spectrometry (EI-MS) revealed the unambiguous structural and electronic features of the monomeric octahedral complex 4. Comparative thermogravimetric studies with homoleptic monomeric vanadium(IV) tert–butoxide [V(O^tBu)₄] (2) and trimeric [V₃(μ-OEt)₄(OEt)₈] (3) displayed the strong influence of the alkyl function in vanadium(IV) alkoxides and chelating ligands on volatility, stability and thermal decomposition pathways to different oxide phases and morphologies. We demonstrated a controlled two-step thermal decomposition of heteroleptic vanadium(IV) alkoxide (4) which offer new opportunities for a versatile growth by the enlarged ‘CVD window’ between sublimation temperature and decomposition temperature and selective self-limited growth originated from the ‘Energy trap’ between the first and second decomposition steps. Preliminary CVD experiments proofed the successful conversion of the heteroleptic precursor 4 into vanadium dioxide with ribbon-like morphology on silicon, which revealed the impact of molecular precursor engineering on crystal growth kinetics.

Evaluation of Magnetite Nanoparticle-Based Toxicity on Embryo–Larvae Stages of Zebrafish (Danio rerio)

ACS Applied Nanomaterials

Iron oxide nanoparticles (NPs) are extensively used in various biomedical applications due to their suitability as carriers of diagnostic and therapeutic agents. Herein, we report on the evaluation of concentration-dependent toxicity studies of iron oxide (magnetite) NPs in zebrafish (Danio rerio). In order to follow the update of iron oxide NPs in animal model, particles were functionalized by conjugating a fluorescent dye (Congo Red) that serve as an efficient probe to track the uptake and accumulations of nanoparticles from the early life stages of Zebrafish. As in vivo model organism to study the diffusion an in vivo toxicity, zebrafish (ZF) embryos and larvae were treated with different concentrations of CR@Fe3O4 conjugates (100-800 µg/mL) during 4–96 hours post fertilization (hpf). Monitoring of mortality, hatching rate, and whole-embryo cellular death showed that incubation of low concentrations of the NPs did not exhibit adverse developmental toxicity during embryonic and larval stages of zebrafish. Minimal toxic effects were observed at high concentration (800 µg/mL) of CR@Fe3O4, causing mortality and delay in hatching cycles. However, CR@Fe3O4 exhibited higher toxic effect on zebrafish larvae suggesting higher bioavailability of the NPs on the tested animal stage. This study provides investigation on developmental toxicity in zebrafish caused by Fe3O4 NPs and provides an innovative insight of CR@Fe3O4 NPs serving as an optical probe to study the potential nanotoxicological effects of NPs in in vivo systems.

https://pubs.acs.org/doi/10.1021/acsanm.9b02330

Smart Fortified PHBV-CS Biopolymer with ZnO–Ag Nanocomposites for Enhanced Shelf Life of Food Packaging

ACS Applied Materials and Interfaces

Thymus vulgaris leaf extract was used as a stabilizer and reducing agent in the green, facile, and biomimetic hydrothermal decomposition reaction for the fabrication of zinc oxide–silver nanocomposites (ZnO–Ag NCs). The nanocomposite (NC) as an active agent was integrated into poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-chitosan (PHBV-CS) in a highly precise ratio of solvent mixture by ultrasonication without the aid of any coupling agent to fabricate the novel degradable biopolymer (BP) nanocomposite via solvent casting method to enhance the mechanical properties and antimicrobial activity and with the lowest immigration rate to improve the shelf life of poultry items. The ZnO–Ag NCs as a nanoactive agent in the food packaging preserved food safety by controlling its spoilage. The morphology, physical, mechanical, barrier, antibacterial, and migration properties of the nanocrystals were assessed via several characterization methods to show the enhancement of the prepared polymer in various aspects of properties. The NCs BP were used for potential sensory evaluation of chicken breast refrigerated over a period of 15 days. The data demonstrated that these bio-based nanocomposites show great antimicrobial activity that offers perspectives for the replacement of traditional petrochemical-based polymers currently used for food packaging of poultry items.

https://pubs.acs.org/doi/abs/10.1021/acsami.9b15724

Reversible Covalent Assembly of Nanoparticles through On-Surface Diels–Alder Reaction

Langmuir

We demonstrate here a controlled assembly of individual nanoscale building blocks into defined architectures based on chemospecific covalent bonding interactions. For this purpose, α-Fe₂O₃, γ-Fe₂O₃, and SiO₂ nanoparticles decorated with surface-conjugated organic ligands were used for performing on-surface Diels–Alder reactions. Driven through their chemical affinity and surface-grafted complementary functionalities, nanoparticles underwent click-reactions to produce covalently organized nanostructures. An advantage of using the Diels–Alder reaction is its reversible nature, which was used to click and unclick the nanoparticles on demand. The efficiency and chemical specificity of this approach opens up another synthetic access to unify materials with complementary properties, where the thermoresponsive nature of particle assemblies imparts to them a fully reversible character. The covalent conjugation strategies demonstrated in this work potentially allow the use of a diverse range of particles and ligands for their applications in different disciplines such as medicine, optics, or photonics. The nanoparticles morphology and crystalline nature were investigated by TEM and XRD analysis, while the presence of surface attached groups was verified by NMR, FTIR, UV–vis, and ζ potential measurements.

https://pubs.acs.org/doi/abs/10.1021/acs.langmuir.9b02261

Femto to microsecond dynamics of excited electrons in a quadruple cation perovskite

ACS Energy Letters

Quadruple cation mixed halide perovskite, GA0.014Cs0.043MA0.13FA0.73Pb(I0.815Br0.185)3, single crystals were grown for the first time using an inverse temperature crystallization process. Solar cell devices in n-i-p stack configuration using thin films of the same materials showed power conversion efficiency above 20%. Complementary time resolved spectroscopy confirmed that polycrystalline thin films and single crystals identically composed exhibit similar carrier dynamics in picosecond range. Cooling of excited carriers and bandgap renormalization occur on the same timescale of 200 – 300 fs. The radiative recombination rate (1.2×10-9 cm3/s) is comparable to values reported for GaAs semiconductor. At low excitation density, a long carrier lifetime of 3.2 µs was recorded possibly due to the passivation of recombination centers. This study clarifies discrepancies about lifetime of hot carriers, impact of radiative recombination, and role of recombination centers on solar cell performance. The quadruple cation perovskites displayed short time dynamics with slow recombination of charge carriers.

https://pubs.acs.org/doi/abs/10.1021/acsenergylett.9b02684