Showing papers in "Chemistry of Materials in 2014"
TL;DR: This review examines the reaction mechanisms, the substrates and catalysts used in the reaction, and the subsequent implementation of the thiol-Michael reaction in materials science.
Abstract: The key attribute of the thiol-Michael addition reaction that makes it a prized tool in materials science is its modular “click” nature, which allows for the implementation of this highly efficient, “green” reaction in applications that vary from small molecule synthesis to in situ polymer modifications in biological systems to the surface functionalization of material coatings. Over the past few decades, interest in the thiol-Michael addition reaction has increased dramatically, as is evidenced by the number of studies that have been dedicated to elucidating different aspects of the reaction that range from an in-depth analysis aimed at understanding the mechanistic pathways of the reaction to synthetic studies that have examined modifying molecular structures with the aim of yielding highly efficient thiol-Michael reaction monomers. This review examines the reaction mechanisms, the substrates and catalysts used in the reaction, and the subsequent implementation of the thiol-Michael reaction in materials...
1,102 citations
TL;DR: This work reports on the fabrication of ∼1 × 1 cm2 Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC 2 films, in aqueous HF or NH4HF2, and opens the door for the use of MXenes in electronic, photonic, and sensing applications.
Abstract: Since the discovery of graphene, the quest for two-dimensional (2D) materials has intensified greatly. Recently, a new family of 2D transition metal carbides and carbonitrides (MXenes) was discovered that is both conducting and hydrophilic, an uncommon combination. To date MXenes have been produced as powders, flakes, and colloidal solutions. Herein, we report on the fabrication of ∼1 × 1 cm2 Ti3C2 films by selective etching of Al, from sputter-deposited epitaxial Ti3AlC2 films, in aqueous HF or NH4HF2. Films that were about 19 nm thick, etched with NH4HF2, transmit ∼90% of the light in the visible-to-infrared range and exhibit metallic conductivity down to ∼100 K. Below 100 K, the films’ resistivity increases with decreasing temperature and they exhibit negative magnetoresistance—both observations consistent with a weak localization phenomenon characteristic of many 2D defective solids. This advance opens the door for the use of MXenes in electronic, photonic, and sensing applications.
1,015 citations
TL;DR: In this paper, side chains in conjugated polymers have been used to tune a polymer's physical properties, including absorption, emission, energy level, molecular packing, and charge transport.
Abstract: Side chains in conjugated polymers have been primarily utilized as solubilizing groups. However, these side chains have roles that are far beyond. We advocate using side chain engineering to tune a polymer’s physical properties, including absorption, emission, energy level, molecular packing, and charge transport. To date, numerous flexible substituents suitable for constructing side chains have been reported. In this Perspective article, we advocate that the side chain engineering approach can advance better designs for next-generation conjugated polymers.
894 citations
TL;DR: Two types of carbon dots exhibiting respective excitationindependent blue emission and excitation dependent full-color emissions have been synthesized via a mild one-pot process from chlo....
Abstract: Two types of carbon dots (C dots) exhibiting respective excitation-independent blue emission and excitation-dependent full-color emissions have been synthesized via a mild one-pot process from chlo...
767 citations
TL;DR: This Perspective describes recent breakthroughs in mesoporous silica nanoparticle design and focuses on the requirements for an efficient stimuli-responsive and thus controllable release of cargo into cancer cells and design principles for smart and autonomous nanocarrier systems.
Abstract: Nanosized mesoporous silica particles with high colloidal stability attract growing attention as drug delivery systems for targeted cancer treatment and as bioimaging devices. This Perspective describes recent breakthroughs in mesoporous silica nanoparticle design to demonstrate their high potential as multifunctional drug delivery nanocarriers. These types of nanoparticles can feature a well-defined and tunable porosity at the nanometer scale, high loading capacity, and multiple functionality for targeting and entering different types of cells. We focus on the requirements for an efficient stimuli-responsive and thus controllable release of cargo into cancer cells and discuss design principles for smart and autonomous nanocarrier systems. Mesoporous silica nanoparticles are viewed as a promising and flexible platform for numerous biomedical applications.
760 citations
TL;DR: In this paper, the authors showed that the use of tannic acid is fundamental in the synthesis of silver seeds, with an unprecedented (nanometric resolution) narrow size distribution that becomes even narrower, by size focusing, during the growth process.
Abstract: Highly monodisperse sodium citrate-coated spherical silver nanoparticles (Ag NPs) with controlled sizes ranging from 10 to 200 nm have been synthesized by following a kinetically controlled seeded-growth approach via the reduction of silver nitrate by the combination of two chemical reducing agents: sodium citrate and tannic acid. The use of traces of tannic acid is fundamental in the synthesis of silver seeds, with an unprecedented (nanometric resolution) narrow size distribution that becomes even narrower, by size focusing, during the growth process. The homogeneous growth of Ag seeds is kinetically controlled by adjusting reaction parameters: concentrations of reducing agents, temperature, silver precursor to seed ratio, and pH. This method produces long-term stable aqueous colloidal dispersions of Ag NPs with narrow size distributions, relatively high concentrations (up to 6 × 1012 NPs/mL), and, more important, readily accessible surfaces. This was proved by studying the catalytic properties of as-syn...
668 citations
TL;DR: In this paper, the shape change of MoS2 domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges.
Abstract: Atmospheric-pressure chemical vapor deposition (CVD) is used to grow monolayer MoS2 two-dimensional crystals at elevated temperatures on silicon substrates with a 300 nm oxide layer. Our CVD reaction is hydrogen free, with the sulfur precursor placed in a furnace separate from the MoO3 precursor to individually control their heating profiles and provide greater flexibility in the growth recipe. We intentionally establish a sharp gradient of MoO3 precursor concentration on the growth substrate to explore its sensitivity to the resultant MoS2 domain growth within a relatively uniform temperature range. We find that the shape of MoS2 domains is highly dependent upon the spatial location on the silicon substrate, with variation from triangular to hexagonal geometries. The shape change of domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges. These results improve our understanding of the factors that influence the...
637 citations
TL;DR: In this paper, the major design constraints that motivate continued research in the field of solar-driven water splitting are summarized, and key device components that are now available for use in demonstration systems and prototypes.
Abstract: Through decades of sustained effort, researchers have made substantial progress on developing technologies for solar-driven water splitting. Nevertheless, more basic research is needed before prototype devices with a chance for commercial success can be demonstrated. In this Perspective, we summarize the major design constraints that motivate continued research in the field of solar-driven water splitting. Additionally, we discuss key device components that are now available for use in demonstration systems and prototypes. Finally, we highlight research areas where breakthroughs will be critical for continued progress toward commercial viability for solar-driven water-splitting devices.
626 citations
TL;DR: Capping agents are frequently used in colloidal synthesis to inhibit nanoparticle overgrowth and aggregation as well as to control the structural characteristics of the resulted nanoparticles in a precise manner as discussed by the authors.
Abstract: Capping agents are frequently used in colloidal synthesis to inhibit nanoparticle overgrowth and aggregation as well as to control the structural characteristics of the resulted nanoparticles in a precise manner. Study of the effect of the residual capping agents on particle surface has unveiled various adverse and favorable behaviors in catalytic applications. In essence, while the capping agents usually act as a physical barrier to restrict the free access of reactants to catalytic nanoparticles, they can also be utilized to promote catalytic performance of nanocrystals. Due to the complexity of these effects, a general survey of capping agents in nanocatalysis is therefore necessary. This short review starts from a brief introduction of common capping agents in nanoparticle synthesis and their adverse impact on heterogeneous catalysis. Next, representative progresses in capping agent removal and surfactant-free synthesis for obtaining surface-clean nanocatalysts are summarized. Lastly, we discuss the r...
624 citations
TL;DR: In this article, a solvent-evaporation-assisted intercalation method was introduced to fabricate the hybrid of alternating molybdenum disulfide (MoS2) sheets and reduced graphene oxide layers, in which the nanosize of the MoS2 nanosheets can be effectively controlled by leveraging the confinement effect within the two-dimensional graphene layers.
Abstract: Since the electrocatalytic activity of layered molybdenum disulfide (MoS2) for hydrogen evolution reaction (HER) closely depends on its exposed edges, the morphology and size of the material are critically important. Herein, we introduce a novel solvent-evaporation-assisted intercalation method to fabricate the hybrid of alternating MoS2 sheets and reduced graphene oxide layers, in which the nanosize of the MoS2 nanosheets can be effectively controlled by leveraging the confinement effect within the two-dimensional graphene layers. Significantly, the resulting MoS2/reduced graphene oxide (RGO) composite shows excellent catalytic activity for HER characterized by higher current densities and lower onset potentials than the conventional pre-exfoliated RGO supported MoS2 nanosheets. Further experiments on the effect of oxidation degree of graphene, the crystallinity of MoS2, and the exposed active site density on the HER performance of the MoS2/RGO composites show that there is an optimum condition for the c...
612 citations
TL;DR: In this article, three diamine monomers were selected for cross-linking graphene oxide (GO) to prepare composite graphene oxide-framework (GOF) membranes through filtration using a pressure assisted self-assembly technique.
Abstract: Three diamine monomers (ethylenediamine, butylenediamine, and p-phenylenediamine) were selected for cross-linking graphene oxide (GO) to prepare composite graphene oxide-framework (GOF) membranes through filtration using a pressure-assisted self-assembly technique. The membranes were applied to separate an ethanol–water mixture by pervaporation. Unmodified GO comprised only hydrogen bonds and π–π interactions, but after cross-linking it with a diamine, attenuated total reflectance–Fourier transform infrared and X-ray photoelectron spectroscopy demonstrated that the diamine was chemically bonded both to GO and the membrane support. Moreover, GO hydrophilicity was substantially altered; water contact angle increased from 24.4° to 80.6° (from cross-linking with an aliphatic structure of diamine to cross-linking with an aromatic structure). Results of X-ray diffraction showed that d-spacing in GOF layers varied from 10.4 to 8.7 A. For GOFs presoaked in 90 wt % ethanol–water, covalent bonds between the layer a...
TL;DR: In this article, the physical structure and morphology of conjugated polymers are discussed, and the key properties that make organic materials ideal for bioelectronics applications are highlighted, and a few recent devices that show either unique features or exceptionally high performance.
Abstract: In this Perspective, we make the case that the biological applications of organic semiconductor devices are significant. Indeed, we argue that this is an arena where organic materials have an advantage compared to traditional electronic materials, such as silicon. By discussing the physical structure and morphology of conjugated polymers, we are able to emphasize the key properties that make organic materials ideal for bioelectronics applications. We highlight a few recent devices that show either unique features or exceptionally high performance. On the basis of these examples, we discuss the future trajectory of this emerging field, note areas where further research is needed, and suggest possible applications in the short term.
TL;DR: In this article, the authors identify six ways in which a UiO-66 sample may deviate from what may be considered "ideal" for the material: symmetry forbidden reflections may appear in its PXRD pattern, and the material can be affected by alterations to the synthesisconditions.
Abstract: .Themostdramatic way that a sample may deviate from ideality is thatit may have a significantly lower thermal stability than expected,an issue which has not been previously reported. Figure 1(discussed in depth later) demonstrates the surprisingly widevariation in the thermal stabilities of three UiO-66 samplessynthesized at different temperatures, highlighting how severelythe material can be affected by alterations to the synthesisconditions.In addition to poor thermal stability, we identify six ways inwhich a UiO-66 sample may deviate from what may beconsidered “ideal” for the material: (1) Symmetry forbiddenreflections may appear in its PXRD pattern,
TL;DR: In this paper, Chen et al. reported a photovoltaic polymer (named as PTB7-Th, see Scheme 1a) by incorporating the 2-(2ethylhexyl)-thienyl group into the benzo[1,2-b:4,5-b′]dithiophene (BDT) unit.
Abstract: R polymer solar cells (PSCs) have been the subject of extensive study because of their potential applicability in lightweight, flexible, colorful and/or transparent large-area devices. To improve photovoltaic performance of PSCs, tremendous efforts have been devoted to designing, synthesizing and optimizing photovoltaic polymers with superior photovoltaic properties, such as suitable molecular energy levels, broad absorption band, high hole mobility, and so on. Since the first introduction of 2-alkylthienyl as the conjugated side groups in the benzo[1,2-b:4,5-b′]dithiophene (BDT) units, the alkylthienyl substituted BDT (BDT-T) units have been widely used to construct novel photovoltaic polymers and thereby the power conversion efficiencies (PCEs) have been boosted to several new heights in the field of PSCs. For instance, Chen et al. lately reported a photovoltaic polymer (named as PTB7-Th, see Scheme 1a) with superior photovoltaic properties by incorporating the 2-(2ethylhexyl)-thienyl group into the BDT unit of the well-known photovoltaic polymer, PTB7.
TL;DR: In this paper, the authors review the recent developments in nonlinear optical (NLO) phenomena such as second harmonic and difference frequency generation (SHG and DFG), which are effective at producing a coherent laser beam in difficult to reach frequency regions of the electromagnetic spectrum.
Abstract: Materials chemistry and the pursuit of new compounds through exploratory synthesis are having a strong impact in many technological fields. The field of nonlinear optics is directly impacted by the availability of enabling materials with high performance. Nonlinear optical (NLO) phenomena such as second harmonic and difference frequency generation (SHG and DFG, respectively) are effective at producing a coherent laser beam in difficult to reach frequency regions of the electromagnetic spectrum. Such regions include the infrared (IR), far-infrared, and terahertz frequencies. High performance NLO crystals are critical for applications utilizing these coherent light sources, and new materials are continuously sought for better conversion efficiency and performance. The class of metal chalcogenides is the most promising source of potential NLO materials with desirable properties particularly in the IR region where most classes of materials face various fundamental challenges. We review the recent developments...
TL;DR: In this paper, a series of nitrogen-containing polymer and carbon spheres were obtained by the sol-gel method by one-pot hydrothermal synthesis in the presence of resorcinol/formaldehyde as carbon precursors and ethylenediamine (EDA) as both a base catalyst and nitrogen precursor, followed by carbonization in nitrogen and activation with CO2.
Abstract: A series of nitrogen-containing polymer and carbon spheres were obtained by the sol–gel method. In particular, the nitrogen-rich carbon spheres were prepared by one-pot hydrothermal synthesis in the presence of resorcinol/formaldehyde as carbon precursors and ethylenediamine (EDA) as both a base catalyst and nitrogen precursor, followed by carbonization in nitrogen and activation with CO2. The introduction of EDA to the sol–gel system resulted in structurally bonded nitrogen-containing carbon spheres. The nitrogen doping level and the particle size can be tuned by varying the EDA amount in the reaction mixture. The maximum nitrogen doping level of 7.2 wt % in carbon spheres could be achieved without sacrificing the spherical morphology. The diameter of these carbon spheres (CS) can be tuned in the rage of 50–1200 nm by varying the EDA amount. N2 adsorption analysis showed that the aforementioned activated carbon spheres exhibited high surface area reaching up to1224 m2/g. Ultra high CO2 adsorption capacit...
TL;DR: In this article, the authors outline synthetic strategies of hierarchical SnO2 nanostructures in terms of the dimension and facet control of their constituting building blocks, creation of porous and hollow structures, as well as their modification by doping and loading with other elements.
Abstract: Complex three-dimensional hierarchical structures assembled from well-defined low-dimensional nanosized building blocks are an interesting class of nanomaterials with a rich variety of tunable physicochemical properties. Tin dioxide (SnO2) is an important n-type wide-bandgap semiconductor with wide applications in transparent conductive films, gas sensors, lithium-ion batteries, and solar cells. In this review, we outline synthetic strategies of hierarchical SnO2 nanostructures in terms of the dimension and the facet control of their constituting building blocks, creation of porous and hollow structures, as well as their modification by doping and loading with other elements. The design of hierarchical SnO2 nanostructures with an improved performance in lithium-ion batteries, sensitized solar cells, and gas-sensing applications is reviewed.
TL;DR: In this article, a nearly cubic NH2CH═NH2PbI3 (FAPbI 3) perovskite was synthesized for the mesoscopic solar cells.
Abstract: A new nearly cubic NH2CH═NH2PbI3 (FAPbI3) perovskite was synthesized for the mesoscopic solar cells. The measured band gap of bulk FAPbI3 is 1.43 eV and it is therefore potentially superior than the CH3NH3PbI3 (MAPbI3) as the light harvester. A homogeneous FAPbI3 perovskite layer was deposited on the TiO2 surface by utilizing the in situ dipping technology. As a result, a high efficiency of 7.5% was achieved using P3HT as the hole transport material. The nearly cubic crystal structure and appropriate band gap render this new FAPbI3 perovskite extremely attractive for next generation high-efficiency low-cost solar cells.
TL;DR: In this article, the thermal properties of CH3NH3PbX3 (X = I or Cl) perovskite using thermogravimetric analysis were examined.
Abstract: Recently organic–inorganic hybrid perovskites have attracted attention as light harvesting materials in mesoscopic cells. While a considerable number of deposition and formation methods have been reported for the perovskite crystalline material, most involve an annealing step. As such, the thermal behavior of this material and its individual components is of crucial interest. Here, we examine the thermal properties of the CH3NH3PbX3 (X = I or Cl) perovskite using thermogravimetric analysis. The role of the precursors is exposed, and the effect of the formation of excess organic species is investigated. The sublimation behavior of the organic component is intensively scrutinized. Furthermore, differential scanning calorimetry is employed to probe the crystal phase structure, revealing subtle differences depending on the deposition method.
TL;DR: In this article, the authors constructed a database of metal-organic frameworks (MOF) structures that are derived from experimental data but are immediately suitable for molecular simulations, and performed grand canonical Monte Carlo simulations of methane adsorption on all structures in the database.
Abstract: Experimentally refined crystal structures for metal–organic frameworks (MOFs) often include solvent molecules and partially occupied or disordered atoms. This creates a major impediment to applying high-throughput computational screening to MOFs. To address this problem, we have constructed a database of MOF structures that are derived from experimental data but are immediately suitable for molecular simulations. The computation-ready, experimental (CoRE) MOF database contains over 4700 porous structures with publically available atomic coordinates. Important physical and chemical properties including the surface area and pore dimensions are reported for these structures. To demonstrate the utility of the database, we performed grand canonical Monte Carlo simulations of methane adsorption on all structures in the CoRE MOF database. We investigated the structural properties of the CoRE MOFs that govern methane storage capacity and found that these relationships agree well with those derived recently from a...
TL;DR: A comprehensive review of metal-organic frameworks for hydrocarbon separations can be found in this article, with a focus on the potential relevance for separating various industrial alkane-, alkene-, and aromatic-containing mixtures.
Abstract: New materials capable of separating mixtures of saturated, unsaturated, and aromatic hydrocarbons can enable more efficient industrial processes and cleaner energy. Outstanding challenges in hydrocarbon separations stem from the similar structures, properties, and reactivities of the molecules comprising many of these mixtures. With high surface areas, tunable pore geometries, and adjustable surface functionality, metal–organic frameworks hold tremendous promise for effecting previously difficult or impossible separations. In this review, we provide a comprehensive account of the metal–organic frameworks that have been investigated for hydrocarbon separations within the context of their potential relevance for separating various industrial alkane-, alkene-, and aromatic-containing mixtures.
TL;DR: In this paper, the authors reported the facile synthesis of hydrophobic, flexible, and ultralightweight nanocellulose sponges using a novel and efficient silylation process in water.
Abstract: In this work, we report the facile synthesis of hydrophobic, flexible, and ultralightweight (ρsponge ≤ 17.3 mg/cm3) nanocellulose sponges using a novel and efficient silylation process in water. These functional materials with high porosity (≥99%) are easily engineered by freeze-drying water suspensions of nanofibrillated cellulose (NFC), a natural nanomaterial isolated from renewable resources, in the presence of methyltrimethoxysilane sols of various concentrations. Microscopic and solid state nuclear magnetic resonance analyses reveal that the sponges are composed of a three-dimensional cellulosic network of thin sheets and nanofilaments, covered by polysiloxanes. Compared with conventional inorganic porous materials, the silylated NFC sponges display an unprecedented flexibility with a maximal shape recovery corresponding to 96% of the original thickness after 50% compression strain. The sponges also combine both hydrophobic and oleophilic properties and prove to be very efficient in removing dodecane...
TL;DR: In this paper, a cross-linked polysulfide containing the phosphine exhibited repeated autonomous self-healing resulting in restoration of tensile strength as a result of the dynamic exchange of disulfide bonds.
Abstract: Tri-n-butylphosphine (TBP) has been shown to effectively catalyze an air-insensitive disulfide metathesis reaction under alkaline conditions at room temperature. A cross-linked polysulfide containing the phosphine exhibited repeated autonomous self-healing resulting in restoration of tensile strength as a result of the dynamic exchange of disulfide bonds. Interestingly, the cross-linked polysulfide can also be reshaped and reprocessed at room temperature via the TBP-mediated reshuffling of the macromolecular networks. The mechanical properties and self-healing ability of polymeric specimens made from chopped samples remain surprisingly constant. In sharp contrast, control specimens without the phosphine catalyst or S–S bonds are neither self-healable nor reprocessable.
TL;DR: The concept of a nucleation function is introduced, and approximated with a Gaussian form in this article, and the height and width of the nucleation functions are systematically varied by conditions that influence the colloidal stability of the small, primary nanocrystals participating in aggregative growth.
Abstract: The aggregative growth and oriented attachment of nanocrystals and nanoparticles are reviewed, and they are contrasted to classical LaMer nucleation and growth, and to Ostwald ripening. Kinetic and mechanistic models are presented, and experiments directly observing aggregative growth and oriented attachment are summarized. Aggregative growth is described as a nonclassical nucleation and growth process. The concept of a nucleation function is introduced, and approximated with a Gaussian form. The height (Γmax) and width (Δtn) of the nucleation function are systematically varied by conditions that influence the colloidal stability of the small, primary nanocrystals participating in aggregative growth. The nucleation parameters Γmax and Δtn correlate with the final nanocrystal mean size and size distribution, affording a potential means of achieving nucleation control in nanocrystal synthesis.
TL;DR: In this article, the authors illustrate progress over the past two decades on self-assembly in materials chemistry through research on systems where function is directly linked to noncovalent interactions among molecules.
Abstract: Organic materials naturally lend themselves to the crafting of structure and function using the strategies of self-assembly and supramolecular chemistry employed so effectively by biological systems. This perspective illustrates progress over the past two decades on self-assembly in materials chemistry through research on systems where function is directly linked to noncovalent interactions among molecules. The genesis of this approach in chemistry of materials involves the design of relatively simple structures using hydrogen bonding, π–π stacking, metal–ligand interactions, electrostatic forces, strong dipole–dipole association, hydrophobic forces, and steric repulsion. Gradually many new and exciting opportunities have emerged, such as supramolecular nanostructures that assemble into functional bulk materials and supramolecular polymers in which the motif of covalent connections among monomers is imitated by creating one-dimensional assemblies of an arbitrarily large set of molecules in both compositio...
TL;DR: In this article, the authors summarize the significant advances on the synthesis of mesoporous TiO2 in terms of rationally controlling the hydrolysis and condensation rates of titanium precursors to enable the cooperative assembly and/or successful infiltration via the templating methods.
Abstract: Mesoporous TiO2 has gained increasing interest because of its outstanding properties and promising applications in a wide range of fields. In this Perspective, we summarize the significant advances on the synthesis of mesoporous TiO2 in terms of rationally controlling the hydrolysis and condensation rates of titanium precursors to enable the cooperative assembly and/or successful infiltration via the templating methods. The rational designs and fundamentals for preparing mesoporous TiO2 are presented in the context of improving the conversion efficiencies of solar energy (e.g., maximizing the UV and/or visible light adsorption, minimizing the recombination of photogenerated electron–hole pairs, and optimizing the mass and charge transport) and enhancing the performances of lithium-ion batteries. New trends and ongoing challenges in this field are also highlighted and proposed.
TL;DR: In this paper, the synergy of conjugated backbones and flexible side chains in organic semiconducting materials has been discussed, which might significantly facilitate the understanding of the roles of flexible chains in structure-property relations.
Abstract: In the past couple of years, remarkable progress has been made in solution-processable organic semiconducting materials for optoelectronics. The development of novel π-conjugated backbones has always been the central issue in this field. In contrast, flexible side chains are less developed and usually used only as solubilizing groups. In this Perspective, we highlight the effects of the flexible chains in organic semiconductors, including the influences of length, odd–even effect, substitution position, terminal groups, branching position, and chirality of alkyl chains, as well as some significant features of oligo(ethylene glycol) and fluoroalkyl chains. Although the roles of flexible chains in organic semiconducting materials are complex and differ when corresponding conjugated skeleton changes, in this Perspective, we emphasize the synergy of conjugated backbones and flexible side chains, which might significantly facilitate the understanding of the roles of flexible chains in structure–property relati...
TL;DR: In this article, chemically cross-linked CNC aerogels were prepared based on hydrazone cross-linking of hydrazide and aldehyde-functionalized CNCs.
Abstract: Cellulose nanocrystals (CNCs) are entering the marketplace as new high-strength nanoadditives from renewable resources. These high aspect ratio particles have potential applications as rheological modifiers, reinforcing agents in composites, coatings, and porous materials. In this work, chemically cross-linked CNC aerogels were prepared based on hydrazone cross-linking of hydrazide and aldehyde-functionalized CNCs. The resulting aerogels were ultralightweight (5.6 mg/cm3) and highly porous (99.6%) with a bimodal pore distribution (mesopores 1 μm). Chemically cross-linked CNC aerogels showed enhanced mechanical properties and shape recovery ability, particularly in water, compared to previous reports of physically cross-linked CNC aerogels. Specifically, the aerogel shape recovered more than 85% after 80% compression, even after 20 compress and release cycles. These CNC aerogels can absorb significant amounts of both water (160 ± 10 g/g of aerogel) and dodecane (72 ± 5 g/g of aerogel...
TL;DR: In this article, a hierarchical ZnxCo3-xO4 nanostructures constructed with small secondary nanoneedles grown on primary rhombus-shaped pillar arrays were used for water oxidation.
Abstract: The design and fabrication of efficient and inexpensive electrodes for use in the oxygen evolution reaction (OER) is essential for energy-conversion technologies. In this study, high OER performance is achieved using novel hierarchical ZnxCo3–xO4 nanostructures constructed with small secondary nanoneedles grown on primary rhombus-shaped pillar arrays. The nanostructures have large roughness factor, high porosity, and high active-site density. Only a small overpotential of ∼0.32 V is needed for a current density of 10 mA/cm2 with a Tafel slope of 51 mV/decade. The nanostructures are also found to perform significantly better than pure Co3O4 and a commercial Ir/C catalyst and to perform similarly to the best OER catalysts that have been reported for alkaline media. These merits combined with the satisfactory stability of the nanostructures indicate that they are promising electrodes for water oxidation.
TL;DR: Li-substituted layered P2-Na 0.80[Li 0.12Ni 0.22Mn 0.66] O2 is investigated as an advanced cathode material for Na-ion batteries as mentioned in this paper.
Abstract: Li-substituted layered P2–Na0.80[Li0.12Ni0.22Mn0.66]O2 is investigated as an advanced cathode material for Na-ion batteries. Both neutron diffraction and nuclear magnetic resonance (NMR) spectroscopy are used to elucidate the local structure, and they reveal that most of the Li ions are located in transition metal (TM) sites, preferably surrounded by Mn ions. To characterize structural changes occurring upon electrochemical cycling, in situ synchrotron X-ray diffraction is conducted. It is clearly demonstrated that no significant phase transformation is observed up to 4.4 V charge for this material, unlike Li-free P2-type Na cathodes. The presence of monovalent Li ions in the TM layers allows more Na ions to reside in the prismatic sites, stabilizing the overall charge balance of the compound. Consequently, more Na ions remain in the compound upon charge, the P2 structure is retained in the high voltage region, and the phase transformation is delayed. Ex situ NMR is conducted on samples at different state...