Janus-like Structure Research Articles

Janus-like Structure and Resonance Level Actualized Ultralow Lattice Thermal Conductivity and Enhanced ZTave in Mg3(Sb, Bi)2-Based Zintls.

Grain boundary (GB) engineering includes grain size and GB segregation. Grain size has been proven to affect the electrical properties of Mg3(Sb, Bi)2 at low temperatures. However, the formation mechanism of GB segregation and what kind of GB segregation is beneficial to the performance are still unclear. Here, the Ga/Bi cosegregation at GBs and Mg segregation within grains optimize the transport of electrons and phonons simultaneously. Ga/Bi cosegregation promotes the formation of Janus-like structures due to the diverse ordering tendencies of liquid Mg3Sb2 and Mg3Bi2 and the absence of a solid solution of Ga/Bi. The Janus-like structure significantly reduces the room-temperature lattice thermal conductivity by introducing diverse microdefects. Meanwhile, a coherent interface between the nano Mg segregation region and the matrix is formed, which reduces the thermal conductivity without affecting the carrier transport. Furthermore, the band structure calculations show that Ga doping introduces the resonance level, increasing the Seebeck coefficient. Finally, the lattice thermal conductivity reaches ∼0.4 W m-1 K-1, and a high average ZT of 1.21 between 323 and ∼773 K is achieved for Mg3.2Y0.02Ga0.03Sb1.5Bi0.5. This work provides guidance for improving the thermoelectric performance via designing cosegregation.

One-step sputtering of MoSSe metastable phase as thin film and predicted thermodynamic stability by computational methods

We present the fabrication of a MoS2−xSex thin film from a co-sputtering process using MoS2 and MoSe2 commercial targets with 99.9% purity. The sputtering of the MoS2 and MoSe2 was carried out using a straight and low-cost magnetron radio frequency sputtering recipe to achieve a MoS2−xSex phase with x = 1 and sharp interface formation as confirmed by Raman spectroscopy, time-of-flight secondary ion mass spectroscopy, and cross-sectional scanning electron microscopy. The sulfur and selenium atoms prefer to distribute randomly at the octahedral geometry of molybdenum inside the MoS2−xSex thin film, indicated by a blue shift in the A1g and E1g vibrational modes at 355 cm−1 and 255 cm−1, respectively. This work is complemented by computing the thermodynamic stability of a MoS2−xSex phase whereby density functional theory up to a maximum selenium concentration of 33.33 at.% in both a Janus-like and random distribution. Although the Janus-like and the random structures are in the same metastable state, the Janus-like structure is hindered by an energy barrier below selenium concentrations of 8 at.%. This research highlights the potential of transition metal dichalcogenides in mixed phases and the need for further exploration employing low-energy, large-scale methods to improve the materials’ fabrication and target latent applications of such structures.

Nanoceria and hybrid silver–ceria nanoparticles fabricated by liquid-mediated laser ablation as antimicrobial agents

In this study, cerium oxide and hybrid silver–ceria nanoparticles (NPs) have been fabricated, characterized and tested for antimicrobial efficacy for applications in the fields of biotechnology and environmental object disinfection/protection. For the preparation of CeO2 and the hybrid silver–ceria NPs, two approaches based on an eco-friendly laser ablation in solution method have been developed. Ceria NPs were synthesized by pulsed laser ablation of a ceria pressed tablet in distilled water. The size distribution of the formed NPs was bimodal, with average diameters of 2.5 and 7.6 nm. The cubic crystalline structure of the NPs (space group Fm-3 m) was confirmed by X-ray diffraction data, as well as Raman and optical absorption spectroscopy. The sequential laser ablation of silver and ceria targets in water allows for the preparation of hybrid CeO2–Ag NPs having a core–shell, decorated and Janus-like structure. Laser ablation of Ag in a CeO2 colloidal solution offers new opportunities to tune the structure and morphology, and to enhance the antimicrobial properties of the resulting NPs. The interaction of ceria and silver in a composite resulted in an improved antimicrobial activity, as tested towards Escherichia coli, Staphylococcus aureus bacteria and Candida albicans fungi, demonstrating the great potential of the hybrid silver–ceria NPs in biocatalytic and antimicrobial applications.

Selective denitrification of simulated oily wastewater by oxidation using Janus-structured carbon nanotubes

The intense industrial development has resulted in several consequences for human and environmental health, including the increased discharge of oily products in water bodies. Oily products are widely used in industry, often bearing an associated high cost. Finding alternatives to treat oily wastewater aiming at recovering oily and water phases is an approach allowing recovery of products of economic interest. In this work, Janus-like carbon nanotubes (CNTs) were synthesized by varying the feed time of acetonitrile and ethylene, respectively, as nitrogen/carbon and carbon precursors in a chemical vapor deposition (CVD) approach. The CVD approach allowed the synthesis of completely undoped, completely doped and partially doped CNTs with a Janus structure. The CNTs were then tested as catalysts for the selective oxidation of 4-nitrophenol (4-NP) contained in a simulated oily wastewater (2,2,4-trimethylpentane/water (O/W) = 1:9, volume basis) by catalytic wet peroxide oxidation (CWPO). The CWPO experiments were conducted for 24 h, 80 °C, 2.5 g L−1 of catalyst, and the stoichiometric concentration of H2O2 (3.6 g L−1) for the degradation of 4-NP (1 g L−1). The same conditions were kept for experiments conducted under a biphasic system. The catalysts bearing a Janus-like structure were demonstrated to be more effective in CWPO experiments in aqueous-only and biphasic systems for the abatement of 4-NP.

Growth pathways of Cu shells on Au and AuCu seeds: interdiffusion, shape transformations, strained shells and patchy surfaces.

The growth of AuCu nanoparticles obtained by depositing Cu atoms on starting seeds of pure Au and on mixed AuCu seeds is studied by molecular dynamics simulations. Depending on the shape of the seed, its composition and the growth temperature, different growth pathways are observed, in which several types of structural transformations take place. The final growth structures comprise Au@Cu core@shell arrangements as well as Janus-like structures with patchy surfaces. The results of the growth simulations are rationalized in terms of the activation of different diffusion processes, both on the surface and inside the growing clusters. These diffusion processes regulate structural transitions between different motifs and the occurrence of dewetting phenomena. The simulation results show that depositon of Cu atoms on pure Au or mixed AuCu seed can be an effective tool for producing clusters with uncommon surface atom arrangements of potential interest for catalysis.

Phase behavior and dynamics in a colloid-polymer mixture under spherical confinement.

From studies via molecular dynamics simulations, we report results on structure and dynamics in mixtures of active colloids and passive polymers that are confined inside a spherical container with a repulsive boundary. All interactions in the fully passive limit are chosen in such a way that in equilibrium coexistence between colloid-rich and polymer-rich phases occurs. For most part of the studies the chosen compositions give rise to Janus-like structure: nearly one side of the sphere is occupied by the colloids and the rest by the polymers. This partially wet situation mimics approximately a neutral wall in the fully passive scenario. Following the introduction of a velocity-aligning activity to the colloids, the shape of the polymer-rich domain changes to that of an ellipsoid, around the long axis of which the colloid-rich domain attains a macroscopic angular momentum. In the steady state, the orientation of this axis evolves via diffusion, magnitude of which depends upon the strength of activity, but only weakly.

Ultrastrong bonding, on-demand debonding, and easy re-bonding of non-sticking materials enabled by reversibly interlocked macromolecular networks-based Janus-like adhesive.

Simultaneously gluing hydrophobic and hydrophilic materials is a highly desired but intractable task. Herein, we developed a facile strategy using reversibly interlocked macromolecular networks (ILNs) as an adhesive. As shown by the proof-of-concept assembly of glass/ILNs/fluoropolymer (i.e., a simplified version of a photovoltaic module), the sandwiched ILNs were stratified after hot-pressing owing to temporary decrosslinking enabled by the built-in reversible covalent bonds. The fragmented component networks were enriched near their respective thermodynamically favored substrates to form a Janus-like structure. Strong elaborate interfacial bespoke chemical bonds and mechanical interlocking were thus established accompanied by the reconstruction of ILNs after cooling, which cooperated with the robust cohesion of the core part of the ILNs resulting from topological entanglements and led to a record-high peeling strength of 64.86 N cm-1. Also, the ILN-based Janus-like adhesive possessed reversible recyclability, adhesivity and on-demand de-bondability. The molecular design detailed in this study serves as a guide for developing a high-performance smart adhesive that firmly bonds non-sticking materials. Compared with existing Janus adhesives, our ILNs-based adhesive not only shows extremely useful reversibility but also greatly simplifies the adhesion process with no surface treatment required.

Structural and electrical properties of nanocolumnar W-Mo thin films with a Janus-like structure

A Janus-like structure is obtained in W-Mo thin films with a clear separation between both metals. Thin films are deposited on glass and silicon substrates by magnetron co-sputtering using glancing angle deposition technique with two tilted targets (oblique angle α = 80°). Films (two thickness series of 300 nm and 1 μm) are prepared with the same pressure (0.33 Pa) and tungsten target current (IW = 140 mA) but with various molybdenum target currents (from 10 to 200 mA). The effect of Mo target current and thickness on the films microstructure and electrical response is investigated using scanning and transmission electron microscopy, X-ray diffraction and van der Pauw method. Porous and columnar W-Mo thin films with inclined columns are obtained due to the shadowing effect. Playing on the Mo target current allows controlling the architecture of the films until obtaining columns perpendicular to the substrate surface and equivalent W and Mo atomic concentrations. X-ray diffraction shows a significant thickness effect on the films microstructure with dominance of α or β phases of W for 1 μm or 300 nm, respectively. From transmission electron microscopy, W and Mo are pointed out in distinct sides of the columns and a finer structural analysis supports the clear separation between W and Mo. This two components design is repeated for all columns in the film proving that W-Mo thin films exhibit a Janus-like structure.

Fabrication of kinetically stable micropolymofoam particles and the spontaneous induction of morphological transformation

We report fabrication of low-density polymeric microparticles (micropolymofoam particles [μPFPs]) using the piezoelectric inkjet method. After ejecting a polymer solution prepared by dissolving polymers in a volatile organic solvent, microdroplets are periodically generated through an inkjet nozzle in the air. Rapid evaporation of the solvent as it falls through the air leads to a highly porous surface and internal morphology. Optical microscope observation confirms that the inside of the μPFPs is filled with air. Notably, the use of more than two different polymers results in kinetically stable particles, in which the heterogeneous polymer chains are randomly entangled. Shape transformation of the kinetically stable μPFPs occurs upon adding a swelling solvent, spontaneously changing their geometry from porous and rugged-shaped to a Janus-like structure with a clear phase boundary. This transformation is directly monitored using an optical microscope. The surface free energy calculation reveals that particles are transformed to adopt a thermodynamically stable structure; this is achieved by imparting fluidity to the randomly entangled polymer chains, which is energetically unfavorable. In addition, porosity control can be possible by selectively removing one polymer phase of kinetically stable particles comprising two different polymers. Furthermore, the developed inkjet method can be applied for producing composite particles encapsulated with functional nanoparticles and coating or patterning them directly onto a substrate.

Adsorption of rapeseed proteins at oil/water interfaces. Janus-like napins dominate the interface

Plants offer a vast variety of protein extracts, typically containing multiple species of proteins that can serve as building blocks of soft materials, like emulsions. However, the role of each protein species concerning the formation of emulsions and interfaces with diverse rheological properties is still unknown. Therefore, deciphering the role of the individual proteins in an extract is highly relevant, since it determines the optimal level of purification, and hence the sustainability aspects of the extract. Here, we will show that when oil/water emulsions were prepared with a rapeseed protein extract containing napins and cruciferins (in a mass ratio of 1:1), only napins adsorbed at the interface exhibiting a soft solid-like rheological behavior. The dominance of napins at the interface was ascribed to their small size (radius r = 1.7 nm) and its unique Janus-like structure, as 45% of the amino acids are hydrophobic and primarily located at one side of the protein. Cruciferins with a bigger size (r = 4.4 nm) and a more homogeneous distribution of the hydrophobic domains couldn’t reach the interface, but they appear to just weakly interact with the adsorbed layer of napins.

The synthesis of Fe-Ag and Fe-Cu bimetallic nanoparticles by electrical explosion of wires

In the present study, we obtained antibacterial Fe-Cu and Fe-Ag bimetallic nanoparticles by electrical explosion of two twisted wires. This method allows obtaining nanoparticles of a given composition and morphology. As-synthesized nanoparticles were characterized by electron microscopy, X-ray diffraction, micro electrophoresis techniques and magnet technique. In result we observed the formation of nanoparticles with Janus-like structure with distinct separation of components inside the particle. These nanoparticles have a strong antibacterial activity against two bacteria strains. The high antimicrobial activity of the nanoparticles is due to the prolonged ion release in media. Taking into account the possibility of easy magnetic separation of the novel bimetallic demonstrate the potential for their use as promising new generation antibacterial agents for advanced antimicrobial water treatment technologies.

Site- and Spatial-Selective Integration of Non-noble Metal Ions into Quantum Dots for Robust Hydrogen Photogeneration

Summary Artificial photosystems consisting of semiconductor quantum dots (QDs) and non-noble metal ions (e.g., Fe2+, Co2+, Ni2+) show intrinsic advantages in efficient and cost-effective hydrogen (H2) evolution. However, well-controlled integration of these metal ions into ultra-small QDs is a major challenge. Here, we present a two-step strategy to realize site- and spatial-selective integration of earth-abundant Fe2+ ions in CdSe QDs; i.e., CdSe QDs are modified with a thin and anisotropic ZnS shell, and partial Zn2+ ions are selectively substituted by Fe2+ via cation exchange. The anisotropic ZnS layer not only passivates CdSe core but also works as an ideal medium to intimately anchor Fe2+. The multifunctional CdSe/Zn1−xFexS QD exhibits extraordinary activity and stability toward H2 photogeneration. Specifically, more than 880 mL (∼39,300 μmol) H2 gas is produced from 6 mL of aqueous solution during a consecutive 172 h (>1 week) experiment, thus achieving a turnover number of >600,000 per QD.

Surface Activity of Soft Polymer Colloids.

We investigate the behavior of polymer colloids at the interface between two immiscible liquids using molecular dynamics simulations. We study several colloid morphologies with various degrees of amphiphilicity, that is, purely solvophobic homogeneous and Janus particles and amphiphilic Janus and core-shell particles. Regardless of the specific morphology, the polymer colloids irreversibly anchor at the liquid-liquid interface, accompanied by a marked reduction of the interfacial tension, γ. Purely solvophobic particles lower γ because they reduce the interfacial area shared by the two immiscible liquids, whereas amphiphilic colloids have an additional enthalpic contribution. At the liquid-liquid interface, the solvophobic particles deform into oblate ellipsoids to maximize the occluded area at the interface. In contrast, amphiphilic Janus colloids orient their solvophobic/solvophilic parts toward the preferred liquids and form a prolate particle shape. The amphiphilic core-shell particles undergo a morphological transition to a prolate Janus-like structure as they anchor at the interface. We rationalize the deformation of the polymer colloids by considering a simple model system of spheroidal particles pinned at the liquid-liquid interface. We systematically compute the interfacial free energy for the various colloids as a function of their asphericity and find excellent qualitative agreement with the simulation findings. Our results show that solvophobic homoparticles can be almost as efficient surface-active agents as amphiphilic Janus colloids.

Fabrication of Fe-Cu composites from electroexplosive bimetallic nanoparticles by spark plasma sintering

The electrical explosion of two intertwined wires made of copper and iron makes it possible to synthesize Janus-like bimetallic nanoparticles comprised of Cu and Fe where the average nanoparticles size is 89 nm. We used spark plasma sintering (SPS) to fabricate a 3D composite material that included 47 wt% of Fe, and 53 wt% of Cu. It had even component distribution, relative density of 92.93% and microhardness of 265.1 HV. The microhardness of the fabricated composite is significantly higher than the values estimated according to the rule of mixtures. The properties of the Fe-53Cu 3D material suggest that the fine-grain structure is maintained after bimetallic nanoparticles that have Janus-like structure have been subjected to SPS.

Nanocomposite thin films based on Au-Ag nanoparticles embedded in a CuO matrix for localized surface plasmon resonance sensing

Nanocomposite thin films, composed of monometallic Au and Ag, and bimetallic AuAg nanoparticles, dispersed in a CuO matrix were prepared, characterised and tested for Localized Surface Plasmon Resonance (LSPR) sensing. The films were deposited by reactive magnetron sputtering, followed by a post-deposition thermal annealing to modify the size and shape of the nanoparticles distribution within the oxide matrix. Regarding the main results of the monometallic systems, the Au:CuO films showed LSPR bands from 800 nm to 650 nm, which reveal a progressive narrowing and a continuous blue-shift with increasing temperature (400–700 °C). The Ag:CuO films evidenced plasmonic bands at about 400 nm for temperatures of 500 °C and above. The bimetallic system, Au-Ag:CuO, showed LSPR bands in the range between those of the corresponding monometallic systems, due to the presence of Ag enriched AuAg alloy nanoparticles, taking part of Janus-like structures in some cases. In terms of LSPR sensing, Au:CuO films revealed the highest values of refractive index sensitivity since the nanoparticles are more exposed to the surrounding environment.

Formation of strong L10-FePd/α-Fe nanocomposite magnets by visualizing efficient exchange coupling.

Conceptual nanocomposite magnets (NCMs) composed of exchange-coupled hard/soft magnetic phases have been expected to show excellent magnetic performance based on simultaneous high coercivity (Hc) and high saturation magnetization (Ms). In our previous works, however, the Hc was considerably lower than its theoretical value (Ha), which prevented us from improving the performance of NCMs. Here, we show that the Hc of isolated particulate L10-FePd/α-Fe NCMs is dominated by their phase segregation into core/shell-like structures versus Janus-like structures. Using first-order reversal curve (FORC) analysis, we clearly distinguished a microscopically undetectable difference in the phase-segregation structure in the NCMs, finding both efficient and inefficient exchange coupling. The nanostructurally controlled NCMs dominated by core/shell-like structure with efficient exchange coupling showed the largest energy product ((BH)max = 17.5 MGOe) in the Fe–Pd system and the highest Hc/Ha value (26.5%) among all NCM powders.

Electrospun Janus-like pellicle displays coinstantaneous tri-function of aeolotropic conduction, magnetism and luminescence.

A new Janus-like pellicle with top-bottom structure, functionalized by conductive aeolotropism, magnetism and luminescence (defined as a CML Janus-like pellicle), is conceived and constructed via electrospinning by combining microcosmic with macroscopic partitions. [PANI/PMMA]//[Eu(BA)3phen/PMMA] and [Fe3O4/PMMA]//[Tb(BA)3phen/PMMA] Janus-like microribbons are selected as building units to construct a conductive aeolotropism-luminescence layer (CL layer) and magnetism-luminescence layer (ML layer), and the two layers are combined to form a CML Janus-like pellicle. Macroscopic partition is achieved by designing the Janus-like structure of the pellicle, while Janus-like microribbons are used for the microcosmic partition by separating rare earth luminescent compounds from dark-colored magnetic Fe3O4 NPs and conductive PANI. The CML Janus-like pellicle has stronger luminescence compared to the contrast samples. The magnetism of the CML Janus-like pellicle can be adjusted by changing the doping amount of Fe3O4 NPs. The CML Janus-like pellicle can achieve a strong and variable conductive aeolotropism via changing the doping amount of PANI and the highest conductive aeolotropism ratio can reach ca. 108 times when the PANI content is 70%. Microcosmic and macroscopic partitions are simultaneously integrated into the CML Janus-like pellicle, which results in almost no detrimental mutual influences between the two layers, and the overall performances of the CML Janus-like pellicle are greatly improved.

Preparation of QDs@SiO2/Polystyrene Composite Particles for Cancer Cells Detection

We report a sandwich immunoassay strategy for specific isolation and detection of cancer cells. Prostate cancer LNCaP cells overexpressing PSMA (Prostate-specific membrane antigen) were used as the model target to evaluate the performance of immunoassay. Inorganic/polymer nanocomposites with Janus-like structure and enhanced fluorescence properties were synthesized and applied for immobilization of QDs and the antibodies. PSMA antibodies were covalently conjugated to the QDs@SiO2/PS Janus-like composite nanoparticles to construct the fluorescent probes. Magnetic probes conjugated with polyclonal antibodies were used to capture and isolate the cancer cells. Results indicated high potential of the unique nanoprobes in specific isolation and detection of cancer cells.

Atomic Co/Ni dual sites and Co/Ni alloy nanoparticles in N-doped porous Janus-like carbon frameworks for bifunctional oxygen electrocatalysis

Single-atom electrocatalysts have attracted board interest in the recent years as they combine the advantages of heterogeneous and homogeneous electrocatalysts. Nevertheless, single-atom electrocatalysts with single metal component cannot further satisfy the demand of catalytic properties. This work developed atomic Co/Ni dual sites in N-doped porous carbon Janus-like frameworks through epitaxial growth of cobalt based MOFs on nickel complexes. Structural characterization and atomic-scale transmission electron microscopy revealed the homogeneously dispersed active sites of Co-Ni alloy and single Co/Ni atoms. Electrochemical data strongly demonstrated the advantages of integrating Co-MOF and Ni complex with different topological structures to form a Janus-like structure. The resultant catalysts afforded onset potential of 0.93 V and half-wave potential of 0.84 V for oxygen reduction reaction in alkaline media, and 0.86 V and 0.73 V in acid media, which is better than single noble-metal-free catalysts, even close to commercial Pt/C. Besides, the catalysts also exhibited good oxygen evolution reaction performance (a current density of 10 mA cm−2 at a potential of 1.59 V) and overvoltage between ORR and OER is 0.78 V. Density functional theory calculations indicated the high electrocatalytic activities are originated from the synergetic effect of atomic Co/Ni-N-C bonds and microstructure of the prepared materials. This work paves a new avenue for the development of multiatomic electrocatalysts for energy conversion.

Novel ZnO/NiO Janus-like nanofibers for effective photocatalytic degradation

In recent years, Janus materials have become a research hotspot in the field of materials science; however, fabricating inorganic Janus-like nanofibers (NFs) is still a challenge. Herein, we report novel ZnO/NiO Janus-like NFs with efficient photocatalytic performance via an electrospinning method followed by calcination treatment. The morphology, structure, chemical composition and crystallinity of ZnO/NiO Janus-like NFs were studied in detail via SEM, TEM, HRTEM, EDS, FT-IR, XPS and XRD, indicating that the NFs had a perfect Janus-like structure composed of ZnO and NiO. A series of photocatalytic experiments were carried out in aqueous organic dye solutions under 365 nm UV radiation for 1 h, with the degradation rate of malachite green able to reach 96%, proving that the NFs have great potential in the field of organic dye degradation. Furthermore, a reasonable catalytic mechanism for the ZnO/NiO Janus-like NFs was proposed, which was discussed from the view of electron–hole pairs and p-n junctions. In short, the method in our work is expected to become a new way of effectively preparing functional inorganic Janus-like NFs.