Evaluation of Electronic-Ionic Transport Properties of a Mg/Zr-Modified LiNi0.5Mn1.5O4 Cathode for Li-Ion Batteries

There is an enormous drive for moving toward cathode material research in LIBs due to the proposal of zero-emission electric vehicles together with the restriction of cathode materials in design. LiNi0.5Mn1.5O4 (LNMO) attracts great research interests as high-voltage Co-free cathodes in LIBs. However, a more extensive study is required for LNMO due to its poor electrochemical performance, especially at high temperature, because of the instability of the LNMO interface. Herein, we design structural modifications using Mg and Zr to alleviate the above-mentioned drawbacks by limiting Mn dissolution and tailoring interstitial sites (which are shown by structural and electrochemical characterizations). This strategy enhances the cycle life up to 1000 cycles at both 25 and 50 °C. In addition, a thorough characterization by impedance spectroscopy is applied to give an insight into the electronic and ionic transport properties and the intricate phase transitions occurring upon oxidation and reduction.

Markedly Improved Catalytic Dehydration of Sorbitol to Isosorbide by Sol-Gel Sulfated Zirconia: A Quantitative Structure-Reactivity Study

Isosorbide, a bicyclic C6 diol, has considerable value as a precursor for the production of bio-derived polymers. Current production of isosorbide from sorbitol utilizes homogeneous acid, commonly H2SO4, creating harmful waste and complicating separation. Thus, a heterogeneous acid catalyst capable of producing isosorbide from sorbitol in high yield under mild conditions would be desirable. Reported here is a quantitative investigation of the liquid-phase dehydration of neat sorbitol over sulfated zirconia (SZ) solid acid catalysts produced via sol-gel synthesis. The catalyst preparation allows for precise surface area control (morphology) and tunable catalytic activity. The S/Zr ratio (0.1-2.0) and calcination temperature (425-625 °C) were varied to evaluate their effects on morphology, acidity, and reaction kinetics and, as a result, to optimize the catalytic system for this transformation. With the optimal SZ catalyst, complete conversion of sorbitol occurred in <2 h under mild conditions to give isosorbide in 76% yield. Overall, the quantitative kinetics and structure-reactivity studies provided valuable insights into the parameters that govern product yields and SZ catalyst activity, central among these being the relative proportion of acid site types and Brønsted surface density.

Unveiling the Mechanism of the in Situ Formation of 3D Fiber Macroassemblies with Controlled Properties

Electrospinning technique is well-known for the generation of different fibers. While it is a "simple" technique, it lies in the fact that the fibers are typically produced in the form of densely packed two-dimensional (2D) mats with limited thickness, shape, and porosity. The highly demanded three-dimensional (3D) fiber assemblies have been explored by time-consuming postprocessing and/or complex setup modifications. Here, we use a classic electrospinning setup to directly produce 3D fiber macrostructures only by modulating the spinning solution. Increasing solution conductivity modifies electrodynamic jet behavior and fiber assembling process; both are observed in situ using a high-speed camera. More viscous solutions render thicker fibers that own enhanced mechanical stiffness as examined by finite element analysis. We reveal the correlation between the universal solution parameters and the dimensionality of fiber assemblies, thereof, enlightening the design of more "3D spinnable" solutions that are compatible with any commercial electrospinning equipment. After a calcination step, ultralightweight ceramic fiber assemblies are generated. These inexpensive materials can clean up exceptionally large fractions of oil spillages and provide high-performance thermal insulation. This work would drive the development and scale-up production of next-generation 3D fiber materials for engineering, biomedical, and environmental applications.

Mild Sol-Gel Conditions and High Dielectric Contrast: A Facile Processing toward Large-Scale Hybrid Photonic Crystals for Sensing and Photocatalysis

Solution processing of highly performing photonic crystals has been a towering ambition for making them technologically relevant in applications requiring mass and large-area production. It would indeed represent a paradigm changer for the fabrication of sensors and for light management nanostructures meant for photonics and advanced photocatalytic systems. On the other hand, solution-processed structures often suffer from low dielectric contrast and poor optical quality or require complex deposition procedures due to the intrinsic properties of components treatable from solution. This work reports on a low-temperature sol-gel route between the alkoxides of Si and Ti and poly(acrylic acid), leading to stable polymer-inorganic hybrid materials with tunable refractive index and, in the case of titania hybrid, photoactive properties. Alternating thin films of the two hybrids allows planar photonic crystals with high optical quality and dielectric contrast as large as 0.64. Moreover, low-temperature treatments also allow coupling the titania hybrids with several temperature-sensitive materials including dielectric and semiconducting polymers to fabricate photonic structures. These findings open new perspectives in several fields; preliminary results demonstrate that the hybrid structures are suitable for sensing and the enhancement of the catalytic activity of photoactive media and light emission control.

Gel-Print-Grow: A New Way of 3D Printing Metal-Organic Frameworks

3D printing offers an attractive means of forming structured metal-organic frameworks (MOFs), as this technique imparts digital geometric tuning to fit any process column. However, 3D-printed MOF structures are usually formed by suspending presynthesized particles into an ink for further processing. This leads to poor rheological properties as MOFs do not bind with inert binders. Herein, we address this problem by coordinating the MOF secondarily by 3D printing its gelated precursors. Specifically, we produced a printable sol-gel containing ∼70 wt % of HKUST-1 precursors and optimized the in situ growth conditions by varying the desolvation temperature and activation solvent. Analysis of the so-called gel-print-grow monoliths' properties as a function of the coordination variables revealed that desolvating at 120 °C produced fully formed MOF particles with comparable diffractive indices to the parent powder regardless of the activation solvent used. Assessment of the samples' textural properties revealed that washing in acetone or methanol produced the highest surface areas, pore volumes, and CO₂ adsorption capacities, however, washing with methanol produced binder swelling and collapse of the printed structure, thereby indicating that washing with acetone was more effective overall. This study represents a promising way of 3D printing MOFs and a breakthrough in additive manufacturing, since the simple, high-throughput, framework detailed herein-whereby the synthesis temperature and washing solvent are varied to optimize MOF coordination-could easily be applied to other crystallites. As such, it is anticipated that this new and exciting method will provide new paths to shape engineer MOFs for applications in energy-intensive fields and beyond.

Microplotter-Printed On-Chip Combinatorial Library of Ink-Derived Multiple Metal Oxides as an "Electronic Olfaction" Unit

Information about the surrounding atmosphere at a real timescale significantly relies on available gas sensors to be efficiently combined into multisensor arrays as electronic olfaction units. However, the array's performance is challenged by the ability to provide orthogonal responses from the employed sensors at a reasonable cost. This issue becomes more demanded when the arrays are designed under an on-chip paradigm to meet a number of emerging calls either in the internet-of-things industry or in situ noninvasive diagnostics of human breath, to name a few, for small-sized low-powered detectors. The recent advances in additive manufacturing provide a solid top-down background to develop such chip-based gas-analytical systems under low-cost technology protocols. Here, we employ hydrolytically active heteroligand complexes of metals as ink components for microplotter patterning a multioxide combinatorial library of chemiresistive type at a single chip equipped with multiple electrodes. To primarily test the performance of such a multisensor array, various semiconducting oxides of the p- and n-conductance origins based on pristine and mixed nanocrystalline MnO_x, TiO₂, ZrO₂, CeO₂, ZnO, Cr₂O₃, Co₃O₄, and SnO₂ thin films, of up to 70 nm thick, have been printed over hundred μm areas and their micronanostructure and fabrication conditions are thoroughly assessed. The developed multioxide library is shown to deliver at a range of operating temperatures, up to 400 °C, highly sensitive and highly selective vector signals to different, but chemically akin, alcohol vapors (methanol, ethanol, isopropanol, and n-butanol) as examples at low ppm concentrations when mixed with air. The suggested approach provides us a promising way to achieve cost-effective and well-performed electronic olfaction devices matured from the diverse chemiresistive responses of the printed nanocrystalline oxides.

Sol-Gel Synthesis of Spherical Mesoporous High-Entropy Oxides

High-entropy oxides (HEOs) have attracted increasing interest owing to their unique structures and fascinating physicochemical properties. Spherical mesoporous HEOs further inherit the advantages of spherical mesoporous materials including high surface area and tunable pore size. However, it is still a huge challenge to construct HEOs with uniform spheres and a mesoporous framework. Herein, a wet-chemistry sol-gel strategy is demonstrated for the synthesis of spherical mesoporous HEOs (e.g., Ni-Co-Cr-Fe-Mn oxide) with high specific surface area (42-143 m²/g), large pore size (5.5-8.3 nm), unique spherical morphology (∼55 nm), and spinel structure without any impure crystal phase using polyphenol as a polymerizable ligand. The metal/polyphenol-formaldehyde resin colloidal spheres are first synthesized via a sol-gel process. Because of their abundant catechol groups and strong chelating ability with different metal species, polyphenols can not only accommodate five different metal ions in their networks but also be well polymerized by formaldehyde to form colloidal spheres. After calcination, the metal species aggregate together to form HEOs, while the organic resin is fully decomposed to produce mesopores. Because of the open framework with accessible mesopores, they could be used as a peroxymonosulfate catalyst for degradation of organic pollutants and a nanoplatform for efficient detection of DNA. This work demonstrates a straightforward sol-gel strategy for design and synthesis of spherical mesoporous high-entropy materials, which would promote the exploration of new properties of high-entropy materials and extend their application.

Eutectic Synthesis of the P2-Type NaxFe1/2Mn1/2O2 Cathode with Improved Cell Design for Sodium-Ion Batteries

An engaging area of research in sodium-ion batteries (SIBs) has been focusing on discovery, design, and synthesis of high-capacity cathode materials in order to boost energy density to levels close enough to that of state-of-the-art lithium-ion batteries. Of particular interest, P2-type layered oxide, Na_2/3Fe_1/2Mn_1/2O₂, has been researched as a potential cathode in SIBs based on its high theoretical capacity of 260 mA h/g and use of noncritical materials. However, the reported synthesis methods are not only complex and energy-demanding but also often yield inhomogeneous and impure materials with capacities less than 200 mA h/g under impractical test conditions. Here, we report a novel synthesis route using low-temperature eutectic reaction to produce highly homogeneous, crystalline, and impurity-free P2-Na_xFe_1/2Mn_1/2O₂ with enhanced Na-ion diffusivity and kinetics. The overall electrochemical performances of the Na-ion cells have been improved by pairing the P2-cathode with presodiated hard carbon anodes, leading to reversible capacities in the range of 180 mA h/g. This new approach is a contribution toward the simplification of synthesis and scalability of sodium-based cathodes with high crystallinity and fine-tuned morphology and the realization of a sodium-ion battery system with lower cost and improved electrochemical performance.

Monitoring the Crystal Structure and the Electrochemical Properties of Na3(VO)2(PO4)2F through Fe3+ Substitution

We here present the synthesis of a new material, Na₃(VO)Fe(PO₄)₂F₂, by the sol-gel method. Its atomic and electronic structural descriptions are determined by a combination of several diffraction and spectroscopy techniques such as synchrotron X-ray powder diffraction and synchrotron X-ray absorption spectroscopy at V and Fe K edges, ⁵⁷Fe Mössbauer, and ³¹P solid-state nuclear magnetic resonance spectroscopy. The crystal structure of this newly obtained phase is similar to that of Na₃(VO)₂(PO₄)₂F, with a random distribution of Fe³⁺ ions over vanadium sites. Even though Fe³⁺ and V⁴⁺ ions situate on the same crystallographic position, their local environment can be studied separately using ⁵⁷Fe Mössbauer and X-ray absorption spectroscopy at Fe and V K edges, respectively. The Fe³⁺ ion resides in a symmetric octahedral environment, while the octahedral site of V⁴⁺ is greatly distorted due to the presence of the vanadyl bond. No electrochemical activity of the Fe⁴⁺/Fe³⁺ redox couple is detected, at least up to 5 V, whereas the reduction of Fe³⁺ to Fe²⁺ has been observed at ∼1.5 V versus Na⁺/Na through the insertion of 0.5 Na⁺ into Na₃(VO)Fe(PO₄)₂F₂. Comparing to Na₃(VO)₂(PO₄)₂F, the electrochemical profile of Na₃(VO)Fe(PO₄)₂F₂ in the same cycling condition shows a smaller polarization which could be due to a slight improvement in Na⁺ diffusion process thanks to the presence of Fe³⁺ in the framework. Furthermore, the desodiation mechanism occurring upon charging is investigated by operando synchrotron X-ray diffraction and operando synchrotron X-ray absorption at V K edge.

Versatile and Scalable Strategy To Grow Sol-Gel Derived 2H-MoS2 Thin Films with Superior Electronic Properties: A Memristive Case

Transition metal dichalcogenides, such as molybdenum disulfide (MoS₂), show peculiar chemical/physical properties that enable their use in applications ranging from micro- and nano-optoelectronics to surface catalysis, gas and light detection, and energy harvesting/production. One main limitation to fully harness the potential of MoS₂ is given by the lack of scalable and low environmental impact synthesis of MoS₂ films with high uniformity, hence setting a significant challenge for industrial applications. In this work, we develop a versatile and scalable sol-gel-derived MoS₂ film fabrication by spin coating deposition of an aqueous sol on different technologically relevant, flexible substrates with annealing at low temperatures (300 °C) and without the need of sulfurization and/or supply of hydrogen as compared to cutting-edge techniques. The electronic and physical properties of the MoS₂ thin films were extensively investigated by means of surface spectroscopy and structural characterization techniques. Spatially homogenous nanocrystalline 2H-MoS₂ thin films were obtained exhibiting high chemical purity and excellent electronic properties such as an energy band gap of 1.35 eV in agreement with the 2H phase of the MoS₂, and a density of states that corresponds to the n-type character expected for high-quality 2H-MoS₂. The potential use of sol-gel-grown MoS₂ as the candidate material for electronic applications was tested via electrical characterization and demonstrated via the reversible switching in resistivity typical for memristors with a measured ON-OFF ratio ≥10². The obtained results highlight that the novel low-cost fabrication method has a great potential to promote the use of high-quality MoS₂ in technological and industrial-relevant scalable applications.

High Throughput Synthesis of Multifunctional Oxide Nanostructures within Nanoreactors Defined by Beam Pen Lithography

Reliably obtaining nanostructures of complex oxides over large area with nanoscale resolution and well-controlled shape, spacing, and pattern symmetry remains a major challenge. In this article, millions of nanowells have been routinely generated by beam pen lithography. Each attoliter volume nanowell functions as a "nanoreactor", inside which oxide nanostructures are synthesized from their sol-gel precursors. Importantly, these nanometer scale entities are in single crystalline or textured forms and epitaxial to the underlying substrates, which promises functionalities including ferroelectricity, ferromagnetism, and multiferroicity. This method provides a general solution which allows one to rapidly screen structural parameters of oxide nanostructures comprising of three or more elements for prominent properties.

Metal-Semiconductor Hybrid Aerogels: Evolution of Optoelectronic Properties in a Low-Dimensional CdSe/Ag Nanoparticle Assembly

Hybrid nanomaterials composed of metal-semiconductor components exhibit unique properties in comparison to their individual counterparts, making them of great interest for optoelectronic applications. Theoretical and experimental studies suggest that interfacial interactions of individual components are of paramount importance to produce hybrid electronic states. The direct cross-linking of nanoparticles (NPs) via controlled removal of the surfactant ligands provides a route to tune interfacial interactions in a manner that has not been thoroughly investigated. Herein, we report the synthesis of CdSe/Ag heteronanostructures (aerogels) via oxidation induced self-assembly of thiol-coated NPs and the evolution of optical properties as a function of composition. Three hybrid systems were investigated, where the first and second excitonic energies of CdSe were matched with plasmonic energy of Au or Ag NPs and Ag hollow NPs. Physical characterization of the aerogels suggests the presence of an interconnected network of hexagonal CdSe and cubic Ag NPs. The optical properties of hybrids were systematically examined through UV-vis, photoluminescence (PL), and time-resolved (TR) PL spectroscopic studies that indicate the generation of alternate radiative decay pathways. A new emission (640 nm) from CdSe/Ag aerogels emerged at Ag loading as low as 0.27%, whereas absorption band tailing and PL quenching effects were observed at higher Ag and Au loading, respectively. The TRPL decay time of the new emission (∼600 ns) is markedly different from those of the band-edge (1.83 ± 0.03 ns) and trap-state (1190 ± 120 ns) emission maxima of phase pure CdSe, supporting the existence of alternate radiative relaxation pathways in sol-gel derived CdSe/Ag hybrids.

Mesochanneled hierarchically porous aluminosiloxane aerogel microspheres as a stable support for pH-responsive controlled drug release

The molecular-scale self-assembly of a 3D aluminosiloxane (Al-O-Si) hybrid gel network was successfully performed via the cocondensation of hydrolyzed alumina (AlOOH) and (3-aminopropyl)trimethoxysilane (APS). It was transformed into a microspherical aerogel framework of Al-O-Si containing mesochannels with tunable hierarchically bimodal meso/macroporosities by a subcritical drying technique. Good homogeneity of AlOOH and APS brought during the synthesis guaranteed a uniform distribution of two metal oxides in a single body. A systematic characterization of the aerogel support was carried out using FTIR, SEM, TEM, nitrogen adsorption/desorption analysis, WAXS, SAXS, and ξ-potential measurement in order to explore the material for drug uptake and release. The drug loading and release capacity and chemical stability of an aluminosiloxane aerogel were studied using two nonsteroidal antiinflammatory drugs, ibuprofen and aspirin. A comprehensive evaluation of the aluminosiloxane aerogel with ordered mesoporous MCM-41 was also performed. Aerogel supports showed a high drug loading capacity and a pH-responsive controlled-release property compared to MCM-41. Meanwhile, kinetic modeling studies indicate that the drug releases with a zero-order profile following the Korsmeyer-Peppas model. The biocompatibility of aluminosiloxane aerogels was established via ex vivo and in vivo studies. We also outline the use of aluminosiloxane aerogel as a support for a possible 3D matrix for an osteoconductive structure for bone tissue engineering.