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Electrocatalysts with dramatically enhanced water splitting efficiency, derived from controlled structures, phase transitions, functional activation

Development of a multifunctional and reusable air filter as a capture-and-disinfection system to kill pathogens in a single-pass air flow.

Developing sensing approaches that can exploit visible light for the detection of low-concentration hydrogen at room temperatures has become increasingly important for the safe use of hydrogen in many applications. In this study, heterostructures composed of monolayer MoS2 and Pd nanoclusters (Pd/MoS2) acting as photo- and hydrogen-sensitizers are successfully fabricated in a facile and scalable manner. The uniform deposition of morphologically isotropic Pd nanoclusters (11.5 ± 2.2 nm) on monolayer MoS2 produces a plethora of active heterojunctions, effectively suppressing charge carrier recombination under light illumination. The dual photo- and hydrogen-sensitizing functionality of Pd/MoS2 can enable its use as an active sensing layer in optoelectronic hydrogen sensors. Gas-sensing examinations reveal that the sensing performance of Pd/MoS2 is enhanced three-fold under visible light illumination (17% for 140 ppm of H2) in comparison with dark light (5% for 140 ppm of H2). Photoactivation is also found to enable excellent sensing reversibility and reproducibility in the obtained sensor. As a proof-of-concept, the integration of Pd nanoclusters and monolayer MoS2 can open a new avenue for light-induced hydrogen gas sensing at room temperature.

Integration of two metal constituents into core–shell structures is an efficient strategy to prepare advanced materials for a variety of applications. The controllable synthesis of targeted bimetallic core–shell nanostructures is an important yet challenging task. Herein, bimetallic nanoparticles comprising a gold multipod nanoparticle (GMN) core and distinctive Pd shell (GMN@Pd NPs) are successfully synthesized in a facile and controllable manner. Epitaxial or islanded growth of Pd on the GMNs can be readily achieved using appropriate stabilizing agents. The controllable growth mode of the Pd layers, coupled with the unique topologies of GMNs, are advantageous for enhancing the density of active interfacial surfaces in the composites. Particularly, I-GMN@Pd NPs show substantially enhanced ORR activity compared with monometallic counterparts and excellent durability and better tolerance to the crossover effect than that of Pt/C, rendering the materials highly desirable for practical use.

Oxygen evolution reaction (OER) is considered a major challenge in the production of efficient electrochemical water splitting devices. To overcome the challenge, the development of inexpensive electrochemical catalysts with high energy conversion efficiencies is vital. Nanohybrids composed of noble metal nanoparticles and transition metal hydroxides often possess catalytically active sites that are beneficial for OER performance. In this study, we report a successful synthesis of Ni(OH)2 nanoflowers with a high degree of crystallinity and uniformity. The as-prepared Ni(OH)2 nanoflowers are employed as templates for effective and controllable loading of Au nanodots to obtain Ni(OH)2@Au nanohybrids. An examination of the OER activity reveals that Ni(OH)2@Au nanohybrids exhibit a considerably lower overpotential (η) value (390 mV) at a current density of 5 mA cm–2 and a smaller Tafel slope (120 mV dec–1) than those of Ni(OH)2 nanoflowers (540 mV and 324 mV dec–1, respectively). The OER enhancement effect is mainly attributed to the decoration of Au nanodots, inducing charge transfer from Ni to Au and thereby stabilizing the Ni species at high oxidation levels. Moreover, the uniform loading of Au nanodots on the anisotropic Ni(OH)2 nanoflowers provides more active interfacial surfaces, which are expedient to OER.

COVID-19 has drawn great attention on the necessity for establishing pathogen-free indoor air. This paper offers an insight into the potential application of a multi-purpose filter to remove fine particulates and disinfect pathogens using melamine sponge with a copper-organic framework. In-situ growth dip coating method was applied to coat Cu-based coordination polymer particle (Cu-CPP) on melamine sponge (MS). The integration of Cu-CPPs with high crystallinity and highly active surface area (1,318.1 m2/g) enabled Cu-CPP/MS to have an excellent capture rate (99.66%) and an instant disinfection rate of 99.54% for Escherichia coli. Electrostatic attraction seemed to play a crucial role in capturing negative-charged pathogens effectively by positive charges on Cu-CPP arising from unbalanced copper ions in Cu-CPP. Disinfection of pathogens was mainly attributed to catalytically active Cu2+ sites. Organic ligand played an important role in bridging and maintaining Cu2+ ions within the framework. This study highlights the design of a new capture-and-disinfection (CDS) air filter system for pathogens using Cu-CPP/MS. It can be applied as a substitute for conventional high-efficiency particulate air (HEPA) filters. Electronic Supplementary Material Supplementary material is available for this article at 10.1007/s11814-021-1000-4 and is accessible for authorized users.

Despite recent advances toward understanding metallosupramolecular platforms, structural classification remains a challenge because of the high multiplicity and diversity originating from the variety of three-dimensional binding modes of metal ions and multifunctional ligands. In this review, multilevel coordination-driven assembly and its potential implementation in the analysis of a variety of structurally complicated metallosupramolecules are demonstrated. The classification of coordination-driven structures with their respective hierarchy levels is summarized based on the ability of each structural unit to construct ordered molecular platforms. Multilevel assembly is composed of (i) primary, (ii) secondary, (iii) tertiary, or higher-order assembly. The coordination-driven binding modes should differ by levels in a complex. In particular, tertiary assembly involves the use of predefined, well-organized secondary supramolecules as basic modules to build discrete or polymeric structures. Using the suggested concept, coordination-driven metallosupramolecular platforms can be readily classified depending on their respective hierarchical structures. We expect that this simple analytical approach will provide researchers with a more effective understanding of coordination-driven assembly and facilitate the design of new complexes for specialized applications.

Inorganic hybrid materials with anisotropic noble-metal nanoparticle cores and cagelike transition-metal chalcogenide shells are promising candidates for a wide variety of applications. Herein, we report an effective fabrication method for gold multipod nanoparticle (GMN) core–cobalt sulfide shell (GMN@CoxSy) nanostructures. The unique cagelike morphology is successfully acquired within nanohybrids (GMN@CoxSy nanocages). The cobalt-based metal–organic frameworks can act as versatile sacrificial templates to the desired hybrid nanomaterials through solution-based etching approaches without any undesirable reshaping of GMNs, which are embedded within. Examination of the electrocatalytic oxygen evolution reaction (OER) of the prepared nanohybrids reveals that a type of GMN@CoxSy nanohybrid shows a substantially lower overpotential (η) value (345 mV) compared with those of GMNs (617 mV) and CoxSy nanomaterials (418 mV) at a current density of 10 mA cm–2. The enhanced OER performance is mainly attributed to th...

Developing sensing approaches that can exploit visible light for the detection of low-concentration hydrogen at room temperatures has become increasingly important for the safe use of hydrogen in many applications. In this study, heterostructures composed of monolayer MoS

Water splitting is one of the efficient ways to produce hydrogen with zero carbon dioxide emission. Thus far, Pt has been regarded as a highly reactive catalyst for the hydrogen evolution reaction (HER); however, the high cost and rarity of Pt significantly hinder its commercial use. Herein, we successfully developed an HER catalyst composed of NiSx (x = 1 or 2) on stainless steel (NiSx/SUS) using electrodeposition and sulfurization techniques. Notably, the electrochemical active surface area(ECSA) of NiSx/SUS was improved more than two orders of magnitude, resulting in a considerable improvement in the electrochemical charge transfer and HER activity in comparison with stainless steel (SUS). The long-term HER examination by linear scan voltammetry (LSV) confirmed that NiSx/SUS was stable up to 2000 cycles.

Metallosupramolecule-based polymeric platforms with high degrees of hierarchy and tailorable functionalities are of great interests because of their unique morphologies and potential applications. Herein, the controllable synthesis of a highly-ordered polymeric structure, {[M,P-Co8 (PDA)6 (HIP)3 (DMF)5 (H2 O)]3 -[Co(DMF)(H2 O)2 ]} (1) (PDA=2,6-pyridinedicarboxylate, HIP=5-hydroxyisophthalate, DMF=dimethylformamide) with unique topology is reported. The solid-state structure of 1 reveals that it is alternately and periodically assembled from racemic supramolecular monomers to form a zigzag-shaped polymeric strand. Discrete racemic supramolecules (2) with topologies similar to those of monomeric species of 1 are also controllably synthesized in a separate reaction. Formation of intermolecular hydrogen bonds between supramolecules associated with hydroxyl groups of HIPs are critical for the unique solid-state packing geometries of 1 and 2.

Coordination polymer particles (CPPs) with a high degree of porosity and multi-functional reaction sites are promising for diverse applications. The integration of open sites favorable for the post-modification of CPPs presents a unique opportunity for the rational design of inorganic materials with target-oriented functions. Herein, we report a shape-controllable synthetic protocol for zinc-based coordination polymer nanocubes (Zn-CPNs). In the synthesis, 2,6-bis[(4-carboxyanilino)carbonyl] pyridine ([N3]) ligand is employed as an efficient shape-directing modulator to control the size and shape of Zn-CPNs. More importantly, the [N3] ligand provides metal binding sites suitable for the decoration of other functional metals such as copper ions. The copper-modified Zn-CPNs (Cu_Zn-CPNs) show good activities in a heterogeneous catalytic reaction.

Two-dimensional quantum dots (2D QDs) comprising PtS2 with low Pt loading (0.002 wt.%) distributed on a distinctive CVD-grown titanium carbide substrate (PtS2/TiC) was successfully synthesized and employed for a hydrogen evolution reaction (HER). Notably, despite the low loading of the former component, PtS2/TiC showed excellent HER activity with a superior overpotential (55 mV at 10 mA/cm−2) to that of commercial Pt/C (50 mV at 10 mA/cm−2). The Faraday efficiency of PtS2/TiC was found to be 92.5 %, revealing the superior properties of hydrogen production. The In-situ Raman spectra reveal the important role of S atoms in PtS2 as the active sites for HER, as evidenced by S H bonding formation at 2532 cm-1 during the HER process. This study provides a fundamental understanding essential for the design of more efficient catalysts in the field of electrochemical applications.

A glassy carbon electrode (GCE) was successfully functionalized with amine groups ( NH2) through the electrooxidation of carbamic acid, to produce an aminated GCE. The aminated GCE could be effectively used to detect current changes during the urease-catalyzed decomposition of urea. The silk fibroin (SF) scaffolds were used to place urease near the surface of the aminated GCE (urease/SF/aminated GCE). The prepared electrode was employed for electrochemical urea sensing utilizing cyclic voltammetry and amperometry techniques. The fabricated sensing platform displayed rapid detection response and high sensitivity of 112.3 μA mM−1 cm−2 with a linear correlation between current and urea concentrations (0.3–2.7 mM). Values for limit of detection (LOD) and limit of quantification (LOQ) were estimated to be 0.163 mM and 0.394 mM, respectively. The reproducible sensing responses recorded using the urease/SF/aminated GCE comprising replaceable SF discs (generated and functionalized with urease in the same batch) assure the suitability of the present platform for application in urea sensing devices.

Advanced hybrid nanomaterials tailored with unique morphologies and multiple functions can be synthesized by the controllable integration of two or more well-designed components. The distinctively shaped metal cores with well-defined coordination polymer shells can lead to synergistic structural properties in the resultant hybrid materials. Herein, we report a facile synthetic strategy for gold multipod nanoparticle (GMN) core-zeolitic imidazolate framework (ZIF-67) shell (GMN@ZIF-67) nanohybrids. Because of the structural anisotropy, which is crucial for heterogeneous seed-induced nucleation, and uniqueness of GMNs, their combination with ZIF-67 gives characteristic core-shell materials. The synthetic process can be readily achieved without using surfactants or capping reagents. Thus, it is potentially an environmentally friendly route to expedient nanohybrids. The material properties (i.e., surface area, size, and shape) of the resultant GMN@ZIF-67 nanohybrids can be readily controlled by simply varying the relative amount of GMNs and ZIF-67 precursors used.

Metal–organic frameworks (MOFs) with compositional multiplicity show unique topologies as well as enhanced chemical and physical properties. The construction of mixed-metal frameworks containing more than one type of metal element can provide further structural versatility and diversity. The combination of transition- and alkali-metal elements in a framework can result in interesting materials with substantial advantages. Herein, we report a synthetic strategy for the mixed transition- and alkali-metal frameworks [Na2Co(PDA)2] (1, PDA = 2,6-pyridinedicarboxylate) and [K2Co(PDA)2] (2). The solid-state structures of these frameworks show that two PDA ligands chelate to a cobalt ion to form a Co(PDA)22– species, which in turn undergoes further assembly mediated by alkali-metal cations (Na+ or K+) to give mixed-metal framework structures. The {[KCo(PDA)2]–·[NH2(CH3)2]+} framework (3) is also prepared by a change in stoichiometry. The multiple coordination of alkali metal atoms to the carboxylate oxygen atoms of the PDA ligands of the Co(PDA)22– species generates unique three-dimensional architectures. As 2 and 3 react with NaOH, the coordinated K+ exchanges readily with Na+ in aqueous solution, and finally 1 crystallizes. The strong ionic character and small size of Na+ account for the facile transformations of 2 and 3. Temperature-dependent magnetization studies reveal that 1 exhibits distinct magnetic susceptibility relative to those of 2 and 3.

Highly-ordered heteronanostructures can be synthesized by overgrowth of a secondary material on the as-prepared seed nanocrystal. The unique morphology of seed nanocrystals directs the shape of the secondary structure, which is exploited to develop structure-controlled composite nanomaterials. Herein, we report a facile and controllable synthetic strategy toward noble star-shaped bimetallic nanostructures. Gold multipod nanoparticle (GMN) core-platinum shell nanoparticles (GMN@Pt NPs) are successfully synthesized through the overgrowth of Pt on the surface of GMN seeds. Due to the structural uniqueness of GMNs, GMN@Pt NPs show bimetallic core-shell geometries, which have surface roughness and star-shaped multi-branches with sharp edges and tips. The island nucleation and growth of individual Pt particles to form a shell provide larger surface areas and plenty of defects on the bimetallic nanocrystals. GMN@Pt NPs with optimized Pt shells show much higher catalytic activities in 4-nitrophenol reduction and ethanol electrooxidation than those of GMNs or Pt nanoparticles, mainly due to the synergistic effects of the bicomponent nanosystem.

Effective incorporation of multiple types of ligands in a given coordination structure provides structural complexity and functional diversity to the resultant coordination-driven assembly. One of the most widely used synthetic approaches is the utilization of the molecular symmetry principle to combine multiple ligands and specific metallic centers in a preferred manner. The variation of metal ions can be helpful to understand the importance of symmetry for the generation of structurally hierarchical supramolecular platforms. We describe the synthesis and characterization of isostructural supramolecular helicates, [M8 (PDA)6 (AIP)3 (DMF)6-x (H2 O)x ] (M=Ni (1), Co (2), and Mn (3); PDA=2,6-pyridinedicarboxylate; AIP=5-aminoisophthalate; x=0 for 1, and x=4 for 2 and 3). The effect of metal variation on the formation of supramolecular helicates and their solid-state crystal packing are discussed. Despite the disparity in the ionic radii and distinct coordination-geometry preferences of Co2+ , Ni2+ , and Mn2+ , all metal centers engaged in the assembly with the heteroleptic ligands in the same manner to form isostructural supramolecular helicates.

A cobalt (Co) supramolecular triple-stranded helicate, [Co8(PDA)6(Br-PTA)3(DMF)4(H2O)2] (1) (PDA = 2,6-pyridinedicarboxylate, Br-PTA = 5-bromoisophthalate, DMF = dimethylformamide), is successfully synthesized and fully characterized. The solid-state structure of 1 shows that four cobalt atoms are coordinated by three PDA ligands to form a tetranuclear cobalt cluster with three extension points and the ditopic Br-PTA ligands interlink two basic assembly units. In crystal packing, the bromo group is surrounded by the cavity-like tetranuclear cobalt cluster, which acts as a metallocavitand, to generate a unique cage-like crystal packing geometry. The isomorphous molecular cage, which exhibits a similar crystal-packing geometry as observed in 1, is also successfully isolated. This is an unusual example of a highly symmetric cage-like crystal packing architecture, resulting from the interaction among metallocavitands of in situ generated supramolecular modules.

Raspberry-like gold nanoparticles (Au RLNPs) synthesized through reduction of HAuCl4 by using Brij35 surfactant and NaOH show high catalytic activity in the reduction of 4-nitrophenol and ethanol electrooxidation. The enhanced catalytic activity of Au RLNPs is mainly due to their high surface roughness. However, Au RLNPs are easily changed to spherical or aggregated nanoparticles by treatment with acids, thiols, and cationic surfactants (e.g., CTAB), making it difficult to sustain the catalytic activity. To improve the stability and applicability in a wide range of environments without degrading the original Au RLNP morphology, silica-coated Au RLNPs (Au RLNP@SiO2 NPs) were successfully synthesized through a sol–gel process using poly(vinylpyrrolidone) (PVP) as a primer. In comparison with Au RLNPs and other Au nanoparticles, Au RLNP@SiO2 NPs are more easily recovered and recycled in repeated catalytic reactions.

Uniform nanostructured nickel-based coordination polymer particles with multilayered morphologies (mL-NiCPPs) were successfully fabricated through a two-step heating process. To increase the surface area by reducing the size of mL-NiCPPs, pyridine and acetic acid were added as size modulators during the growth process. The resultant coordination polymer nanoparticles were then calcinated at a controlled temperature in order to produce nickel oxide nanostructures (mL-NiOs), which have a regular multilayered morphology and a high degree of crystallinity. Moreover, the mL-NiOs had a relatively high BET specific surface area (112 m2 g−1) and a well-defined pore size (10 nm), hence exhibited significant potential for use in a variety of applications. The synthesized mL-NiOs were successfully deposited onto indium tin oxide (ITO) serving as an efficient matrix for the immobilization of urease (Ur), which was used for urea detection. The prepared bioelectrode (Ur/NiO/ITO/glass) was employed for urea sensing using cyclic voltammetry (CV). The prepared electrodes showed a high sensitivity and a linear dependence of the current on the urea concentration.

We report a strategy to achieve a discrete cage molecule featuring a high level of structural hierarchy through a multiple-assembly process. A cobalt (Co) supramolecular triple-stranded helicate (Co-TSH)-based discrete molecular cage (1) is successfully synthesized and fully characterized. The solid-state structure of 1 shows that it is composed of six triple-stranded helicates interconnected by four linking cobalt species. This is an unusual example of a highly symmetric cage architecture resulting from the coordination-driven assembly of metallosupramolecular modules. The molecular cage 1 shows much higher CO2 uptake properties and selectivity compared with the separate supramolecular modules (Co-TSH, complex 2) and other molecular platforms.

Nano- (or micro-scale) metal-organic frameworks (NMOFs), also known as coordination polymer particles (CPPs), have received much attention because of their structural diversities and tunable properties. Besides the direct use, NMOFs can be alternatively used as sacrificial templates/precursors for the preparation of a wide range of hybrid inorganic nanomaterials in straightforward and controllable manners. Distinct advantages of using NMOF templates are correlated to their structural and functional tailorability at molecular levels that is rarely acquired in any other conventional template/precursor. In addition, NMOF-derived inorganic nanomaterials with distinct chemical and physical properties are inferred to dramatically expand the scope of their utilization in many fields. In this review, we aim to provide readers with a comprehensive summary of recent progress in terms of synthetic approaches for the production of diverse inorganic hybrid nanostructures from as-synthesized NMOFs and their promising applications.