Toxic Metal Sequestration Exploiting a Unprecedented Low-Molecular-Weight Hydrogel-to-Metallogel Transformation

We report herein the development of a unique low-molecular-weight gelator-induced technique for environmental remediation. The motive of this work is wastewater purification using a gel-based toxic heavy metal sequestration. The essence of this technique was to bring two different functionalities, one capable of multiple coordination and another with gel-forming ability, arranged in tandem within a single ligand molecule. Naturally, the success of the approach depends on whether the two tandem-arrayed functionalities are indeed working in tandem. Our results show that the ligand molecule is an excellent example of concomitant hydrogelator and metallogelator. The most interesting aspects of this study involve the toxic metal sequestration of Pb, Cd, and Hg which was further studied in detail with spectroscopic, microscopic, and diffraction techniques. We also report here a rare property of pure organic hydrogel-to-metallogel transformation which could open up a new avenue on wastewater purification. In essence, the hydrogels can be envisaged as a unique class of metal-free zeolite analogue for environmental remediation not by just absorbance but through absorbance cum coordination, which are further corroborated by the inductively coupled plasma-optical emission spectroscopy results.

Synthesis of hafnium nanoparticles and hafnium nanoparticle films by gas condensation and energetic deposition

In this work we study the fabrication and characterization of hafnium nanoparticles and hafnium nanoparticle thin films. Hafnium nanoparticles were grown in vacuum by magnetron-sputtering inert-gas condensation. The as deposited nanoparticles have a hexagonal close-packed crystal structure, they possess truncated hexagonal biprism shape and are prone to surface oxidation when exposed to ambient air forming core-shell Hf/HfO₂ structures. Hafnium nanoparticle thin films were formed through energetic nanoparticle deposition. This technique allows for the control of the energy of charged nanoparticles during vacuum deposition. The structural and nanomechanical properties of the nanoparticle thin films were investigated as a function of the kinetic energy of the nanoparticles. The results reveal that by proper adjustment of the nanoparticle energy, hexagonal close-packed porous nanoparticle thin films with good mechanical properties can be formed, without any additional treatment. It is shown that these films can be patterned on the substrate in sub-micrometer dimensions using conventional lithography while their porosity can be well controlled. The fabrication and experimental characterization of hafnium nanoparticles is reported for the first time in the literature.

Systematic design of superaerophobic nanotube-array electrode comprised of transition-metal sulfides for overall water splitting

Great attention has been focused on the design of electrocatalysts to enable electrochemical water splitting—a technology that allows energy derived from renewable resources to be stored in readily accessible and non-polluting chemical fuels. Herein we report a bifunctional nanotube-array electrode for water splitting in alkaline electrolyte. The electrode requires the overpotentials of 58 mV and 184 mV for hydrogen and oxygen evolution reactions respectively, meanwhile maintaining remarkable long-term durability. The prominent performance is due to the systematic optimization of chemical composition and geometric structure principally—that is, abundant electrocatalytic active sites, excellent conductivity of metallic 1T’ MoS₂, synergistic effects among iron, cobalt, nickel ions, and the superaerophobicity of electrode surface for fast mass transfer. The electrode is also demonstrated to function as anode and cathode, simultaneously, delivering 10 mA cm⁻² at a cell voltage of 1.429 V. Our results demonstrate substantial improvement in the design of high-efficiency electrodes for water electrolysis.

Water splitting by nanostructured, abundant catalysts provides a renewable means to make carbon neutral fuels, but the ideal material morphology and composition remain uncertain. Here, the authors prepare superaerophobic, multi-metallic sulfide nanotube arrays as bifunctional water splitting catalysts.

Poly(vinyl alcohol)-Assisted Fabrication of Hollow Carbon Spheres/Reduced Graphene Oxide Nanocomposites for High-Performance Lithium-Ion Battery Anodes

Three-dimensional hollow carbon spheres/reduced graphene oxide (DHCSs/RGO) nanocomposites with high-level heteroatom doping and hierarchical pores are fabricated via a versatile method. Poly(vinyl alcohol) (PVA) that serves as a dispersant and nucleating agent is used as the nonremoval template for synthesizing melamine resin (MR) spheres with abundant heteroatoms, which are subsequently composited with graphene oxide (GO). Use of PVA and implementation of freezing treatment prevent agglomeration of MR spheres within the GO network. Molten KOH is used to achieve the one-step carbonization/activation/reduction for the synthesis of DHCSs/RGO. DHCSs/RGO annealed at 700 °C shows superior discharge capacity of 1395 mA h/g at 0.1 A/g and 606 mA h/g at 5 A/g as well as excellent retentive capacity of 755 mA h/g after 600 cycles at a current density of 2 A/g. An extra CO₂ activation leads to further enhancement of electrochemical performance with outstanding discharge capacity of 1709 mA h/g at 0.1 A/g and 835 mA h/g at 2 A/g after 600 cycles. This work may improve our understanding of the synthesis of graphene-like nanocomposites with hollow and porous carbon architectures and fabrication of high-performance functional devices.

Interfacial Engineering of Hierarchical Transition Metal Oxide Heterostructures for Highly Sensitive Sensing of Hydrogen Peroxide

Hydrogen peroxide (H₂ O₂ ) is a major messenger molecule in cellular signal transduction. Direct detection of H₂ O₂ in complex environments provides the capability to illuminate its various biological functions. With this in mind, a novel electrochemical approach is here proposed by integrating a series of CoO nanostructures on CuO backbone at electrode interfaces. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction, and X-ray photoelectron spectroscopy demonstrate successful formation of core-shell CuO-CoO hetero-nanostructures. Theoretical calculations further confirm energy-favorable adsorption of H₂ O₂ on surface sites of CuO-CoO heterostructures. Contributing to the efficient electron transfer path and enhanced capture of H₂ O₂ in the unique leaf-like CuO-CoO hierarchical 3D interface, an optimal biosensor-based CuO-CoO-2.5 h electrode exhibits an ultrahigh sensitivity (6349 µA m m^-1 cm^-2 ), excellent selectivity, and a wide detection range for H₂ O₂ , and is capable of monitoring endogenous H₂ O₂ derived from human lung carcinoma cells A549. The synergistic effects for enhanced H₂ O₂ adsorption in integrated CuO-CoO nanostructures and performance of the sensor suggest a potential for exploring pathological and physiological roles of reactive oxygen species like H₂ O₂ in biological systems.

Hierarchically Porous Zirconia Monolith Fabricated from Bacterial Cellulose and Preceramic Polymer

A hierarchically porous zirconia (ZrO₂) monolith was successfully fabricated by using bacterial cellulose (BC) as a biotemplate and preceramic polymer as a zirconium resource, via freeze-drying and two-step calcination process. Images of scanning electron microscopy showed that the ZrO₂ monolith well-replicated a three-dimensional reticulated structure of pristine BC and possessed good morphology stability till 1100 °C in air. Results of N₂ adsorption/desorption and mercury porosimetry analysis revealed the hierarchically porous structure and large specific area (9.7 m²·g^-1) of the ZrO₂ monolith, respectively. Patterns of X-ray powder diffraction indicated that the monoclinic phase and tetragonal phase coexisted in the ZrO₂ monolith with the former as the main phase. In addition, the ZrO₂ monolith possessed low bulk density (0.13 g·cm^-3) and good mechanical strength. These properties suggest that the as-prepared ZrO₂ monolith has a great potential to serve as an ideal catalyst or catalyst support.

The Effect of Different Porogens on Porous PMMA Microspheres by Seed Swelling Polymerization and Its Application in High-Performance Liquid Chromatography

Monodisperse cross-linked porous poly (methyl methacrylate) (PMMA) microspheres (~2.5 μm in diameter) were prepared by using an improved two-step seed swelling polymerization method with monodisperse micron-grade PMMA microspheres seeds. The porous PMMA microspheres with diverse surface morphology and pore structure were obtained by tuning porogen systems. The monodisperse porous PMMA microspheres, which were prepared using toluene:dibutylphthalate (DBP) = 1:1 (v/v) as a porogen system, had the smallest pore size and the largest specific surface area. Then, the monodisperse porous PMMA microspheres were subjected to high-performance liquid chromatography. The liquid chromatographic column filler successfully realized complete separation of arginine, glycine and glutamic acid, and the separation effect was good. The porous PMMA microspheres provide a new material for the separation of amino acids by liquid chromatography.

Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste

Nature can efficiently recognize specific ions by exerting second-sphere interactions onto well-folded protein scaffolds. However, a considerable challenge remains to artificially manipulate such affinity, while being cost-effective in managing immense amounts of water samples. Here, we propose an effective approach to regulate uranyl capture performance by creating bio-inspired nano-traps, illustrated by constructing chelating moieties into porous frameworks, where the binding motif’s coordinative interaction towards uranyl is enhanced by introducing an assistant group, reminiscent of biological systems. Representatively, the porous framework bearing 2-aminobenzamidoxime is exceptional in sequestering high uranium concentrations with sufficient capacities (530 mg g⁻¹) and trace quantities, including uranium in real seawater (4.36 mg g⁻¹, triple the benchmark). Using a combination of spectroscopic, crystallographic, and theory calculation studies, it is revealed that the amino substituent assists in lowering the charge on uranyl in the complex and serves as a hydrogen bond acceptor, boosting the overall uranyl affinity of amidoxime.

Uranium extraction is important for both uranium recovery and nuclear waste management. Here, inspired by the high sensitivity of proteins towards specific metal ions, Ma and colleagues demonstrate that introducing secondary coordination spheres into amidoxime-functionalized porous polymers can enhance their uranyl chelating abilities.

Hierarchical SnS2/SnO2 nanoheterojunctions with increased active-sites and charge transfer for ultrasensitive NO2 detection

SnS2 nanosheets with unique properties are excellent candidate materials for fabricating high-performance NO2 gas sensors. However, serious restacking and aggregation during sensor fabrication have greatly impacted the sensing response. In this study, flower-like hierarchical SnS2 was prepared by a simple microwave method and partially thermally oxidized to form hierarchical SnS2/SnO2 nanocomposites to further improve the sensing performance at low operating temperature. The fabricated SnS2/SnO2 sensor exhibited ultrahigh response (resistance ratio = 51.1) toward 1 ppm NO2 at 100 °C, roughly 10.2 times higher than that of pure SnS2 nanoflowers. The excellent and enhanced NO2 sensing performances of hierarchical SnS2/SnO2 nanocomposites were attributed to the novel hierarchical structure of SnS2 and the nanoheterojunction between SnS2 and the ultrafine SnO2 nanoparticles. The SnS2/SnO2 sensors also exhibited excellent selectivity and reliable repeatability. The simple fabrication of high performance sensing materials may facilitate the large-scale production of NO2 gas sensors.

On the structural stability of guanosine-based supramolecular hydrogels

Supramolecular hydrogels formed from the self-assembly of low molecular weight derivatives are very attractive systems, because of their potential applications in nano- and bio-technology. In this paper, the stable and transparent hydrogels observed in binary mixtures of guanosine derivatives (G), namely guanosine 5'-monophosphate (GMP) and guanosine (Gua), dissolved in water (at volume fractions larger than 0.95), were investigated by microscopy techniques and Small Angle X-ray Scattering (SAXS). The results confirm the presence of G-quadruplexes, chiral cylindrical rods obtained by the regular stacking of self-assembled planar cyclic guanosine quartets. However, the addition of Gua determines the formation of very stable hydrogels able to trap large amounts of water (up to a volume fraction of 0.99) and characterised by an unusual anisotropic order. A modified lateral helix-to-helix interaction pattern, tuned by Gua, is suggested to be responsible for the supramolecular gelation and the stability of the hydrogels during swelling.

Structural Engineering of 2D Nanomaterials for Energy Storage and Catalysis

Research on 2D nanomaterials is rising to an unprecedented height and will continue to remain a very important topic in materials science. In parallel with the discovery of new candidate materials and exploration of their unique characteristics, there are intensive interests to rationally control and tune the properties of 2D nanomaterials in a predictable manner. Considerable attention is focused on modifying these materials structurally or engineering them into designed architectures to meet requirements for specific applications. Recent advances in such structural engineering strategies have demonstrated their ability to overcome current material limitations, showing great promise for promoting device performance to a new level in many energy-related applications. Existing in many forms, these strategies can be categorized based on how they intrinsically or extrinsically alter the pristine structure. Achieved through various synthetic routes and practiced in a range of different material systems, they usually share common descriptors that predestine them to be effective in certain circumstances. Therefore, understanding the underlying mechanism of these strategies to provide fundamental insights into structural design and property tailoring is of critical importance. Here, the most recent development of structural engineering of 2D nanomaterials and their significant effects in energy storage and catalysis technologies are addressed.

Polydopamine nanocoated whole-cell asymmetric biocatalysts

Our whole-cell biocatalyst with a polydopamine nanocoating shows high catalytic activity (5 times better productivity than the native cell) and reusability (84% of the initial yield after 5 batches, 8 times higher than the native cell) in asymmetric reduction. It also integrates with titania, silica, and magnetic nanoparticles for multi-functionalization.

High-Rota Synthesis of Single-/Double-/Multi-Unit-Cell Ti-HSZ Nanosheets To Catalyze Epoxidation of Large Cycloalkenes Efficiently

This work first reports high-efficiency epoxidation of large cycloalkenes (carbon number ≥ 7) with tert-butyl hydroperoxide (TBHP) over single-/double-/multi-unit-cell nanosheet-constructed hierarchical zeolite, which is synthesized by one-step hydrothermal crystallization using piperidine as the structure-directing agent of the microporous structure. The excellent catalytic property of the material is ascribed to its unique structural characteristic. Plenty of surface titanols or silanols on the surface of MWW nanosheets are beneficial for the formation of transition-state intermediates; a large number of intercrystalline mesopores in the shell of the material not only facilitate the formation of the intermediate for TBHP but also have nearly no hindrance for the diffusion and mass transfer of bulky cycloalkene to the above intermediates; the 12-MR side cups penetrating into the crystals from the external surface are exposed as much as possible to the reaction system because of the single-/double-/multi-unit-cell MWW nanosheet, serving as the primary reaction space for the epoxidation of bulky cyclic alkene and oxidants and providing enough space for the transition state of Ti-OO^tBu and bulky cycloalkane. Moreover, an efficient calcination-free catalytic reaction-regeneration method is developed to overcome the challenge for the recyclability of microporous Ti-zeolite in the catalytic epoxidation of bulky cycloalkenes.

Amino-functionalized hierarchical porous SiO2-AlOOH composite nanosheets with enhanced adsorption performance

Hierarchical porous SiO₂-AlOOH composite nanosheets (HPSA) with a three-dimensional (3D) structure were prepared from two-dimensional (2D) layered mineral kaolinite (A1₂Si₂O₅(OH)₄) via a template-free structural reorganization method. The obtained material was subjected to homogeneous and effective amino-functionalization by grafting it with (3-aminopropyl) triethoxysilane. Owing to the enhanced 3D hierarchical meso-macroporous structure containing highly dispersed protonated amino groups (NH₃⁺), the as-prepared amino-functionalized HPSA (NH₂-HPSA) showed unique adsorption performance towards the congo red anionic dye. It provides feasibilities to fabricate other functional hierarchical porous materials from clay minerals, which can offer potential applications in adsorption, separation, catalysis and other environmental remediation fields.

MOF-Derived Ultrathin Cobalt Phosphide Nanosheets as Efficient Bifunctional Hydrogen Evolution Reaction and Oxygen Evolution Reaction Electrocatalysts

The development of a highly efficient and stable bifunctional electrocatalyst for water splitting is still a challenging issue in obtaining clean and sustainable chemical fuels. Herein, a novel bifunctional catalyst consisting of 2D transition-metal phosphide nanosheets with abundant reactive sites templated by Co-centered metal-organic framework nanosheets, denoted as CoP-NS/C, has been developed through a facile one-step low-temperature phosphidation process. The as-prepared CoP-NS/C has large specific surface area and ultrathin nanosheets morphology providing rich catalytic active sites. It shows excellent electrocatalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic and alkaline media, with the Tafel slopes of 59 and 64 mV/dec and a current density of 10 mA/cm² at the overpotentials of 140 and 292 mV, respectively, which are remarkably superior to those of CoP/C, CoP particles, and comparable to those of commercial noble-metal catalysts. In addition, the CoP-NS/C also shows good durability after a long-term test.

Influence of particle size and dielectric environment on the dispersion behaviour and surface plasmon in nickel nanoparticles

Nickel nanoparticles (NPs) are promising candidates for various applications, including biomedical ones, as they have good magnetic properties as well as high thermal conductivity. We used well-characterized Ni NPs of average Scherrer sizes from 1.31 nm to 22.23 nm and investigated the effects of the primary particle size, size distribution and dielectric environments, and of separately adding non-ionic polyvinylpyrrolidone (PVP), cationic cetyltrimethylammonium bromide (CTAB) and anionic ethylenediaminetetraacetic acid (EDTA) in ethanol, on their stability and agglomeration behaviour using atomic force microscopy (AFM), particle size analysis and zeta potential study through dynamic light scattering (DLS) combined with UV-visible spectroscopy data. The dominant influence of surfactants, additives, particles size and shape on the surface plasmon resonance (SPR) was found. SPR is considerably sensitive to the dielectric environment in addition to size and shape. Moreover, increasing the concentration of PVP led to an enhanced SPR intensity and a shift in its position towards higher wavelength. 1.31 nm NPs with EDTA as an additive yielded the best dispersibility and also showed superparamagnetic behaviour at 300 K, indicating their favourable application potentials.

Mesoporous nanoplate multi-directional assembled Bi2WO6 for high efficient photocatalytic oxidation of NO

Herein, a mesoporous nanoplate multi-directional assembled Bi₂WO₆ architecture was successfully prepared and applied for the photocatalytic removal of NOx pollutants at low concentrations under visible light and simulated solar light irradiation. Bi₂WO₆-180-C synthesized at a hydrothermal temperature of 180 °C with calcination exhibited an excellent conversion efficiency in the photocatalytic oxidation of gaseous NO. The crystallinity, morphology, specific surface area, pore environment, light absorption, and separation of photogenerated electrons and holes were investigated by various techniques; the excellent photocatalytic performance of Bi₂WO₆-180-C was attributed to its special hierarchical mesoporous structure with an appropriate pore size and interconnected porous network, which imparted good gas permeability and fast mass transfer of reaction intermediates and final products of NO oxidation. Furthermore, hierarchical mesoporous Bi₂WO₆ showed excellent photocatalytic durability and reusability.

Yolk-Shell Nanostructures: Design, Synthesis, and Biomedical Applications

Yolk-shell nanostructures (YSNs) composed of a core within a hollow cavity surrounded by a porous outer shell have received tremendous research interest owing to their unique structural features, fascinating physicochemical properties, and widespread potential applications. Here, a comprehensive overview of the design, synthesis, and biomedical applications of YSNs is presented. The synthetic strategies toward YSNs are divided into four categories, including hard-templating, soft-templating, self-templating, and multimethod combination synthesis. For the hard- or soft-templating strategies, different types of rigid or vesicle templates are used for making YSNs. For the self-templating strategy, a number of unconventional synthetic methods without additional templates are introduced. For the multimethod combination strategy, various methods are applied together to produce YSNs that cannot be obtained directly by only a single method. The biomedical applications of YSNs including biosensing, bioimaging, drug/gene delivery, and cancer therapy are discussed in detail. Moreover, the potential superiority of YSNs for these applications is also highlighted. Finally, some perspectives on the future research and development of YSNs are provided.

Embedding MnO@Mn3 O4 Nanoparticles in an N-Doped-Carbon Framework Derived from Mn-Organic Clusters for Efficient Lithium Storage

The first synthesis of MnO@Mn₃ O₄ nanoparticles embedded in an N-doped porous carbon framework (MnO@Mn₃ O₄ /NPCF) through pyrolysis of mixed-valent Mn₈ clusters is reported. The unique features of MnO@Mn₃ O₄ /NPCF are derived from the distinct interfacial structure of the Mn₈ clusters, implying a new methodological strategy for hybrids. The characteristics of MnO@Mn₃ O₄ are determined by conducting high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron energy loss spectroscopy (EELS) valence-state analyses. Due to the combined advantages of MnO@Mn₃ O₄ , the uniform distribution, and the NPCF, MnO@Mn₃ O₄ /NPCF displays unprecedented lithium-storage performance (1500 mA h g^-1 at 0.2 A g^-1 over 270 cycles). Quantitative analysis reveals that capacitance and diffusion mechanisms account for Li⁺ storage, wherein the former dominates. First-principles calculations highlight the strong affiliation of MnO@Mn₃ O₄ and the NPCF, which favor structural stability. Meanwhile, defects of the NPCF decrease the diffusion energy barrier, thus enhancing the Li⁺ pseudocapacitive process, reversible capacity, and long cycling performance. This work presents a new methodology to construct composites for energy storage and conversion.

Multiscale Phase Separations for Hierarchically Ordered Macro/Mesostructured Metal Oxides

Porous architectures play an important role in various applications of inorganic materials. Several attempts to develop mesoporous materials with controlled macrostructures have been reported, but they usually require complicated multiple-step procedures, which limits their versatility and suitability for mass production. Here, a simple approach for controlling the macrostructures of mesoporous materials, without templates for the macropores, is reported. The controlled solvent evaporation induces both macrophase separation via spinodal decomposition and mesophase separation via block copolymer self-assembly, leading to the formation of hierarchically porous metal oxides with periodic macro/mesostructures. In addition, using this method, macrostructures of mesoporous metal oxides are controlled into spheres and mesoporous powders containing isolated macropores. Nanocomputed tomography, focused ion beam milling, and electron microscopy confirm well-defined macrostructures containing mesopores. Among the various porous structures, hierarchically macro/mesoporous metal oxide is employed as an anode material in lithium-ion batteries. The present approach could provide a broad and easily accessible platform for the manufacturing of mesoporous inorganic materials with different macrostructures.

2D/2D FeOCl/graphite oxide heterojunction with enhanced catalytic performance as a photo-Fenton catalyst

A novel 2D/2D FeOCl/graphite oxide heterojunction has been successfully prepared for the first time and shows remarkable enhanced photo-Fenton catalytic activity and stability.

Photochemistry and photophysics of MOFs: steps towards MOF-based sensing enhancements

In combination with porosity and tunability, light harvesting, energy transfer, and photocatalysis, are facets crucial for engineering of MOF-based sensors.

Nitrogen and sulfur co-doped carbon nanospheres for highly efficient oxidation of ethylbenzene

A facile synthesis of well-distributed N and S co-doped carbon spheres and their enhanced activity towards the selective oxidation of ethylbenzene.

Controllable synthesis 3D hierarchical structured MnO2@NiCo2O4 and its morphology-dependent activity

The α-MnO₂@NiCo₂O₄ hierarchical structure with the nanowire- and nanosheet-like morphology was controlled synthesized under different solvents and alkalis. The α-MnO₂@NiCo₂O₄ heterogeneous structure exhibits a remarkably enhanced activity in the DME combustion reaction.

Exploring the dicationic gemini surfactant for the generation of mesopores: a step towards the construction of a hierarchical metal–organic framework

The dicationic gemini surfactant cooperatively self-assembles with the Cu-BTC precursors to form a hierarchical microporous–mesoporous metal–organic framework.

Rationally designed hierarchical nickel nanoparticles-based magnetic yolk-like nanospindles for enhanced catalysis and protein adsorption

Herein, we demonstrate a mild route to construct spindle-like hybrid composites (FeO_x@SiO₂@C–Ni) that integrate the magnetic cores with high density metallic nickel NPs in yolk–shell structures, which exhibited excellent performance in catalysis and protein adsorption.

Salt-mediated synthesis of bimetallic networks with structural defects and their enhanced catalytic performances

Bimetallic alloys with abundant of structural defects and enhanced catalytic performances were prepared tailoring by salts.