Metal Ion Precursors Research Articles

Decoupling Intrinsic Metal Ion Reduction Rates from Structural Outcomes in Multimetallic Nanoparticles.

Simultaneously controlling both stoichiometry and atom arrangement during the synthesis of multimetallic nanoparticles is often challenging, especially when the desired metal precursors exhibit large differences in their intrinsic reduction kinetics. In such cases, traditional synthetic methods often lead to the formation of exclusively phase-segregated structures. In this study, we demonstrate that the relative reduction kinetics of the metal precursors can be manipulated independently of their intrinsic differences in reduction rates by modulating the instantaneous concentrations of the metal cation precursors. We achieve this control by adjusting the precursor addition rate, which decouples chemical ordering outcomes from differences in precursor reduction kinetics. To guide these experiments, we describe a quantitative model to determine how metal ion reduction rates evolve with variations in the precursor addition rate and thereby predict optimal conditions for the synthesis of multimetallic nanoparticles with precise structural and compositional outcomes. We demonstrate the efficacy of this model experimentally by synthesizing both core@shell and alloyed nanoparticles with stoichiometric control using the same metal ion precursors in two different bimetallic systems (Au-Pd and Au-Pt) as well as in a quinary metal system (Co, Ni, Cu, Pd, and Pt). This approach enables the design of nanoparticle architectures independent of intrinsic differences in metal ion reduction potentials of the constituent metals while maintaining both stoichiometric and structural control.

Why Colloidal Syntheses of Bimetallic Nanoparticles Cannot be Generalized.

Introducing one general synthesis to form bimetallic nanoparticles (NPs) could accelerate the discovery of NPs for promising energy applications. Although colloidal syntheses can provide precise structural and morphological control of bimetallic NPs, the complex chemical nature of multicomponent syntheses challenges the realization of such synthetic simplicity. Common synthetic issues are frequently ascribed to the variation in metal ion precursor reactivities and complex chemical interactions between the different metal surfaces and capping agents employed. However, no systematic studies have shown how these factors compete to ultimately assign the factor limiting the mixing and formation of bimetallic NPs. Here, we provide a parametric investigation of how the intrinsic standard reduction potentials (E0red) of the metal ions and cocapping agents influence the formation of bimetallic AuCu, AuPd, and PdCu NPs. Using a combination of in situ X-ray total scattering along with transmission electron microscopy and nuclear magnetic resonance spectroscopy, we illustrate the multifunctional role of the cocapping agents through interactions with both the metal ion precursors and NP surfaces to stabilize metastable structures. Additionally, we demonstrate how system-specific side reactions and the local metal ion coordination environment can be used to selectively tune the formation kinetics, structure, and morphology of bimetallic NPs. Ultimately, these insights show that the chemical interactions rather than the intrinsic E0red are responsible for the formation of bimetallic NPs. Broadly, these insights should aid the synthetic design of tailored multimetallic NPs.

Electroless Deposition of Noble Metals on Rod-Shape Plant Viruses in Various Aqueous Metal Precursor Solutions.

The challenge of synthesizing noble metal nanostructures sustainably has encouraged researchers to explore biological routes for nanostructure production, such as biotemplating. Plant viruses with rod-shape morphology, such as tobacco mosaic virus (TMV) and barley stripe mosaic virus (BSMV), offer promising biotemplates to produce metal nanorods. TMV and BSMV can be incubated in aqueous metal precursor solutions to mineralize metals on the coat proteins (CPs) of the viruses. Previous studies have primarily examined palladium (Pd) mineralization on TMV and BSMV using Na2PdCl4 as the Pd precursor. There is limited scientific literature on the effect of using alternative Pd precursor solutions besides Na2PdCl4 such as K2PdCl4 and PdCl2 to mineralize Pd on TMV and BSMV. Past attempts at mineralizing other noble metals such as platinum (Pt) and gold (Au) required an initial layer of Pd to be deposited on the TMV and BSMV biotemplates. In this study, we aimed to expand the understanding of using alternative Pd precursor solutions to mineralize Pd on TMV and BSMV. Additionally, the deposition of Pt and Au onto TMV and BSMV without the need for an initial Pd mineralization layer was achieved using alternative Pt and Au precursors, including K2PtCl4 and AuCl3, respectively. Pd, Pt, and Au were successfully deposited on TMV and BSMV by incubation in aqueous solutions of Na2PdCl4, K2PdCl4, PdCl2, K2PtCl4, and AuCl3. Kinetic studies were also conducted using ultraviolet-visible (UV-vis) spectroscopy to examine the rates at which Pd, Pt, and Au precursor ions were reduced during the mineralization process, mimicking their adsorption onto TMV and BSMV CPs. BSMV adsorbed noble metal precursor ions faster than TMV as determined by UV-vis spectroscopy. While palladium nanorods (PdNRs) offer high electrical conductivity desirable for electronic applications, Pd-coated TMV and BSMV may face limitations due to their organic cores, potentially compromising conductivity. To address this, one approach is to convert the organic core into conductive amorphous carbon through thermal annealing. In this study, in situ transmission electron microscopy was utilized to thermally anneal Pd-TMV2Cys, thereby transforming them into PdNRs with amorphous carbon cores.

Colorimetric sensor to monitor the temperature with in situ synthesized silver nanoparticles embedded in carboxymethyl cellulose metallogel

A colorimetric sensing platform based on carboxymethyl cellulose-silver nanoparticles (CMC-AgNPs) metallogel was proposed to monitor the temperature history and quality of perishable products stored at low temperature. The carboxymethyl cellulose (CMC) metallogel, fabricated in the presence of Ag+, incorporates ionic crosslinking of biopolymers, complexation between reactants, and subsequent in situ synthesis of AgNPs, which are designed to lead the color transition of metallogel from colorless to dark brown depending on temperature and time. The mechanical and structural properties of metallogels and AgNPs were characterized by rheology, XRD, and FT-IR. Color changes associated with temperature, time, and metal ion precursors were examined by UV–visible spectroscopy and colorimetry. The longer the exposure time to thermal stress condition such as room temperature (25 °C) or high temperature (60 °C), the deeper the color of metallogel. The CMC-AgNPs metallogel-based sensor provides an efficient, safe way to track temperature history and assess perishable products’ quality, crucial for the safe distribution of food, vaccines, and medicines. This cost-effective and reliable visual sensor minimizes spoilage and health risks by enabling accurate temperature monitoring without the need for complicated equipment.

Novel melatonin-producing Bacillus safensis EH143 mitigates salt and cadmium stress in soybean.

Recently, microorganism and exogenous melatonin application has been recognized as an efficient biological tool for enhancing salt tolerance and heavy metal detoxification in agriculture crops. Thus, the goal of this study was to isolate and evaluate a novel melatonin-producing plant growth promoting bacterium. With high-throughput whole genome sequencing, phytohormone measurements, expression profiling, and biochemical analysis, we can identify a novel PGPB that produces melatonin and unravel how it promotes soybean growth and development and protects against salt and Cd stress. We identify the melatonin synthesis pathway (tryptophan→tryptamine→serotonin melatonin) of the halotolerant (NaCl > 800 mM) and heavy metal-resistant (Cd >3 mM) rhizobacterium Bacillus safensis EH143 and use it to treat soybean plants subjected to Cd and NaCl stresses. Results show that EH143 will highly bioaccumulate heavy metals and significantly improve P and Ca2+ uptake and the K+/Na+ (93%↑under salt stress) ratio while reducing Cd uptake (49% under Cd stress) in shoots. This activity was supported by the expression of the ion regulator HKT1, MYPB67, and the calcium sensors CDPK5 and CaMK1 which ultimately led to increased plant growth. EH143 significantly decreased ABA content in shoots by 13%, 20%, and 34% and increased SA biosynthesis in shoots by 14.8%, 31%, and 48.2% in control, salt, and Cd-treated plants, upregulating CYP707A1 and CYP707A2 and PAL1 and ICS, respectively. The melatonin content significantly decreased along with a reduced expression of ASMT3 following treatment with EH143; moreover, reduced expression of peroxidase (POD) and superoxide dismutase (SOD) by 134.5% and 39% under salt+Cd stress, respectively and increased level of total amino acids were observed. Whole-genome sequencing and annotation of EH143 revealed the presence of the melatonin precursor tryptophan synthase (trpA, trpB, trpS), metal and other ion regulators (Cd: cadA, potassium: KtrA and KtrB, phosphate: glpT, calcium: yloB, the sodium/glucose cotransporter: sgIT, and the magnesium transporter: mgtE), and enzyme activators (including the siderophore transport proteins yfiZ and yfhA, the SOD sodA, the catalase katA1, and the glutathione regulator KefG) that may be involved in programming the plant metabolic system. As a consequence, EH143 treatment significantly reduced the contents of lipid peroxidation (O2-, MDA, and H2O2) up to 69%, 46%, and 29% in plants under salt+Cd stress, respectively. These findings suggest that EH143 could be a potent biofertilizer to alleviate NaCl and Cd toxicity in crops and serve as an alternative substitute for exogenous melatonin application.

Generalized Synthesis of Highly-Dispersed, Ultrafine Transition Metal Nanoparticles on Silica Spheres for Enhanced Optical Absorption.

Robust synthesis of ultrafine metal nanoparticles (ufMNPs) below 5nm with clean surfaces and strong optical absorption in the visible spectral range is challenging due to their instability originating from large surface-to-volume ratios. This work reports a general strategy involving two sequential steps: i) loading metal precursor ions onto the surface of silica nanospheres (SiOx NSs) by forming a uniform coating of metal oxyhydroxide [MOy(OH)z] through preferred surface acid-base reactions and ii) thermally reducing MOy(OH)z in forming gas at elevated temperatures to form ufMNPs evenly dispersed on the surface of SiOx NSs. The capability of this synthesis strategy is verified by loading ufMNPs of various transition metals and bimetallic combinations onto the SiOx NSs. The ufMNPs exhibit strong optical absorption enhanced by the optical scattering resonances in the SiOx NSs, which generate intense electric fields near the surface of the SiOx NSs. The SiOx NSs also support stabilizing the ufMNPs, which do not need additional organic capping reagents. The successful synthesis of SiOx-NS-supported ufMNPs with clean surfaces and enhanced optical absorption is promising for exploring the photocatalytic properties of ufMNPs.

Construction of strain responsive Ti-containing carboxymethyl cellulose hydrogel with transitional coordination precursor

Due to marvelous sensitivity and flexibility, conductive hydrogels are popularly used as strain sensors in intelligent skin and wearable electronic devices fields. However, hydrogel tends to be destroyed after long-term use or in accident, leading to performance degradation. Herein, we developed an environmental-friendly Ti-containing conductive hydrogel. The hydrogel network was constructed via a simple two-step method with coordination reaction and amidation reaction based on a metal ion precursor from transitional coordination. The synergies of reversible metal coordination bonds and dynamic hydrogen bonds endowed the hydrogel with excellent self-healing properties (3 h, 93.66 %), tensile properties (136.46 kPa), compression properties (1.122 MPa), and anti-fatigue performance. At the same time, the hydrogel showed excellent self-adhesion, even underwater. Due to Ti4+, electrical conductivity of the hydrogel was visibly enhanced (σ = 25.64 mS·cm−1), which resulted in fast response (TS [time sensitivity] = 24.78 s−1) and short recovery time (153 ms). As a flexible strain sensor, the hydrogel with stable conductivity and high sensitivity could precisely detect and distinguish a series of human motions, even different letter pronunciations. These remarkable features make it a promising application in the fields of intelligent skin and wearable electronic devices.

Effect of Precursor Solution on Sedimentation of Alkaline-earth Phosphates at Different Temperatures

Kinetic study of sedimentation of alkaline-earth phosphates-magnesium phosphate (MP), calcium phosphate (CP), strontium phosphate (SP) and barium phosphate (BP) precipitates was carried out by varying reactant concentration approach involving turn-wise variation of precursor metal ions (Mg2+, Ca2+, Sr2+ and Ba2+) and phosphate ion (PO43-) concentrations, and monitoring the settling of the precipitate formed in a precipitate sedimentation measurement apparatus. A pseudo-rate order equation, associated with the approach of varying reactant concentration, was linearized, and the dependence of precipitate sedimentation on precursor concentration, established therewith. Whereas MP precipitate gave positive order-sedimentation increased with increase in concentrations of precursor solutions, orders of CP, SP and BP precipitates were negative-sedimentation decreased with increase in concentrations of precursor solutions. Inter-particle attraction and repulsion associated with high solid concentration, volume of precipitate particles formed as well as chemical interactions of precipitate with the mother solution might have caused these effects.

Electroless Deposition of Base Metals at the Liquid/Liquid Interface of Ionic Liquids

Metal nanostructures can be formed at the electrochemical liquid/liquid interface, so-called ITIES. Our group has presented a method to form metal nanostructures at the liquid/liquid interface between ionic liquid (IL) and water (W) [1-10]. This IL/W method utilizes the spatial selectivity of the reaction site only at the liquid/liquid interface, which is achieved by the separation of metal precursor ions dissolved in the W phase and reducing agent in the IL phase. The metal reduction reaction is regarded as the electron transfer across the IL/W interface, which enables us to analyze the reaction process with liquid-liquid electrochemistry at the IL/W interface [11]. Moreover, the usage of ILs (not molecular oils) leads to the formation of 1-dimensional (1D) nanostructures despite the inherent 2D geometry of the liquid/liquid interface, as a result of the structure-forming ability of ILs at the air [12-14], liquid [14-16], and solid [17-19] interfaces. By using this IL/W method, we have successfully prepared 1D nanostructures of noble metals such as Au [1,6], Ag [7], Pt [3], and Pd [5,6], and also their composites with polymer [2] and nanocarbons [8-10].In this presentation, we would like to introduce our very recent efforts to develop a sister method that uses another liquid/liquid interface between IL and oil (O). Wet chemical techniques for the metal nanostructure formation in general, including our IL/W method described above, involve water and therefore cannot escape from the limitation of metal elements to noble ones. In contrast, the IL/O method [20-22] is water-free and therefore can be used even for base metals, expanding the applicability and versatility of wet chemistry for metal nanostructure formation. In the presentation, we introduce our water-free liquid/liquid interface method, the electrochemical measurements of the electron and ion transfers across the interface, and the obtained nanostructures of base metals such as zinc, aluminum, and magnesium. References Nishi, T. Kakinami, T. Sakka, Chem. Commun., 51 (2015) 13638. Nishi, I. Yajima, K. Amano, T. Sakka, Langmuir, 34 (2018) 2441. Zhang, N. Nishi, K. Amano, T. Sakka, Electrochim. Acta, 282 (2018) 886. Takagi, N. Nishi, T. Sakka, Chem. Lett., 48 (2019) 589. Zhang, N. Nishi, T. Sakka, ACS Appl. Mater. Interfaces, 11 (2019) 23731. Zhang, N. Nishi, T. Sakka, Electrochim. Acta, 325 (2019) 134919. Zhang, N. Nishi, T. Sakka, Colloids Surf. A, 597 (2020) 124747. Zhang, N. Nishi, I. Koya, T. Sakka, Chem. Mater., 32 (2020) 6374. Koya, T. Sakka, N. Nishi, Langmuir, 37 (2021) 9553. Koya, Y. Yokoyama, T. Sakka, N. Nishi, Chem. Lett., 51 (2022) 643. Kakiuchi and N. Nishi, Electrochemistry, 74 (2006) 942. Nishi, Y. Yasui, T. Uruga, H. Tanida, T. Yamada, S. Nakayama, H. Matsuoka, T. Kakiuchi, J. Chem. Phys., 132 (2010) 164705. Nishi, T. Uruga, H. Tanida, T. Kakiuchi, Langmuir, 27 (2011) 7531. Nishi, T. Uruga, H. Tanida, J. Electroanal. Chem., 759 (2015) 129. Katakura, K. Amano, T. Sakka, W. Bu, B. Lin, M. Schlossman, N. Nishi, J. Phys. Chem. B, 124 (2020) 6412. Ishii, T. Sakka, N. Nishi, Phys. Chem. Chem. Phys., 23 (2021) 22367. Nishi, J. Uchiyashiki, Y. Ikeda, S. Katakura, T. Oda, M. Hino, N. Yamada, J. Phys. Chem. C, 123 (2019) 9223. Nishi, T. Yamazawa, T. Sakka, H. Hotta, K. Hanaoka, H. Takahashi, Langmuir, 36 (2020) 10397. Nishi, J. Uchiyashiki, T. Oda, M. Hino, N. Yamada, Bull. Chem. Soc. Jpn., 94 (2021) 2914. Kuroyama, N. Nishi, T. Sakka, J. Electroanal. Chem., 881 (2021) 114959. Nishi, Y. Kuroyama, N. Yoshida, Y. Yokoyama, T. Sakka, ChemElectroChem, 10 (2023) e202201000. Yoshida, Y. Yokoyama, T. Sakka, N. Nishi, to be submitted.

Aqueous Solution-Gel Deposition of Copper-Based Photo-Electrodes for Multipurpose Photo-Electrochemical Systems

Efficient valorization of solar energy is expected to contribute significantly to a sustainable supply of energy and fuel sources, as well as the reduction of atmospheric pollution. To this end, photo-electrochemical systems show encouraging potential by converting light into chemical energy. These devices rely on semiconducting photoanodes and/or -cathodes that absorb light efficiently and generate electron-hole pairs with sufficient energy for initiating redox reactions. Several copper-based oxides exhibit appropriate band edges for both photo-electrochemical water splitting and CO2 reduction [1]. This, in combination with their bandgap values, low toxicity, and earth-abundance, has recently increased the attention for copper-based photo-electrodes for multipurpose photo-electrochemical systems. Substantial photocorrosion of CuO and Cu2O is the main issue restricting their application as functional photo-electrodes. In contrast, copper-based ternary oxides are found to be significantly less susceptible to photocorrosion. The citrate-based aqueous solution-gel method has proven to be a versatile approach for the formulation of stable aqueous metal ion precursor solutions, and the subsequent synthesis of (doped) multi-metal oxides by this method has been demonstrated numerously. [2,3] Still, due to the flexible redox chemistry of copper, the solution-gel synthesis of phase-pure copper-based ternary oxides remains challenging. This work describes the synthesis of copper-based photo-electrode materials by focusing on copper ferrite (CFO), copper tungstate (CWO), copper niobate (CNO), and copper bismuth oxide (CBO). The formulation of the respective precursor solutions is described, and their thermal decomposition is investigated. Thin-film photo-electrodes are deposited on transparent conductive substrates by spin coating. The phase purity of the resulting copper-based oxides is determined by X-ray diffraction and Raman spectroscopy. Using UV-Vis spectroscopy, the optical bandgap of the oxide semiconductors is calculated. Furthermore, the photo-electrodes are subjected to linear sweep voltammetry in dark and under illumination to evaluate their photo-electrochemical performance. [1] Wang et al. “Insights into the development of Cu-based photocathodes for carbon dioxide conversion” Green Chem. (2021) 23, 3207[2] Van den Rul et al. “Aqueous Solution-Based Synthesis of Nanostructured Metal Oxides” in “Handbook of Nanoceramics and Their Based Nanodevices” (2009) Ed. T-Y Tseng and H. S. Nalwa[3] Marchal et al. “Precursor Design Strategies for the Low-Temperature Synthesis of Functional Oxides: It’s All in the Chemistry” Chem. Eur. J. (2020) 26, 9070 This work has received funding from the Belgian federal government through the ETF project T-REX and from the VLAIO network “Flanders Innovation & Entrepreneurship” through the Catalisti Moonshot project SYN-CAT. Part of this work was financially supported by TNO in the framework of the “Energy Conversion and Storage” Early Research Program.

Lewis acidic Fe3+-driven catalytic active Ni3+ formation in Fe-free metal–organic framework for enhanced electrochemical glucose sensing

Manipulating metal valence states and porosity in the metal–organic framework (MOF) by alloying has been a unique tool for creating high-valent metal sites and pore environments in a structure that are inaccessible by other methods, favorable for accelerating the catalytic activity towards sensing applications. Herein, we report Fe3+-driven formation of catalytic active Ni3+ species in the amine-crafted benzene-dicarboxylate (BDC-NH2)-based MOF as a high-performance electrocatalyst for glucose sensing. This work took the benefit of different bonding stability between BDC-NH2 ligand, and Fe3+ and Ni2+ metal precursor ions in the heterometallic NixFe(1-x)-BDC-NH2 MOF. The FeCl3 that interacts weakly with ligand, oxidizes the Ni2+ precursor to Ni3+-based MOF owing to its Lewis acidic behavior and was subsequently removed from the structure supported by Ni atoms, during solvothermal synthesis. This enables to create mesopores within a highly stable Ni-MOF structure with optimal feed composition of Ni0.7Fe0.3-BDC-NH2. The Ni3+-based Ni0.7Fe0.3-BDC-NH2 demonstrates superior catalytic properties towards glucose sensing with a high sensitivity of 13,435 µA mM−1 cm−2 compared to the parent Ni2+-based Ni-BDC-NH2 (10897 μA mM−1cm−2), along with low detection limit (0.9 μM), short response time (≤5 s), excellent selectivity, and higher stability. This presented approach for fabricating high-valent nickel species, with a controlled quantity of Fe3+ integrated into the structure allowing pore engineering of MOFs, opens new avenues for designing high-performing MOF catalysts with porous framework for sensing applications.

Rapid Joule Heating Synthesis of Oxide-Socketed High-Entropy Alloy Nanoparticles as CO2 Conversion Catalysts.

The unorthodox surface chemistry of high-entropy alloy nanoparticles (HEA-NPs), with numerous interelemental synergies, helps catalyze a variety of essential chemical processes, such as the conversion of CO2 to CO, as a sustainable path to environmental remediation. However, the risk of agglomeration and phase separation in HEA-NPs during high-temperature operations are lasting issues that impede their practical viability. Herein, we present HEA-NP catalysts that are tightly sunk in an oxide overlayer for promoting the catalytic conversion of CO2 with exceptional stability and performance. We demonstrated the controlled formation of conformal oxide overlayers on carbon nanofiber surfaces via a simple sol-gel method, which facilitated a large uptake of metal precursor ions and helped to decrease the reaction temperature required for nanoparticle formation. During the rapid thermal shock synthesis process, the oxide overlayer would also impede nanoparticle growth, resulting in uniformly distributed small HEA-NPs (2.37 ± 0.78 nm). Moreover, these HEA-NPs were firmly socketed in the reducible oxide overlayer, enabling an ultrastable catalytic performance involving >50% CO2 conversion with >97% selectivity to CO for >300 h without extensive agglomeration. Altogether, we establish the rational design principles for the thermal shock synthesis of high-entropy alloy nanoparticles and offer a helpful mechanistic perspective on how the oxide overlayer impacts the nanoparticle synthesis behavior, providing a general platform for the designed synthesis of ultrastable and high-performance catalysts that could be utilized for various industrially and environmentally relevant chemical processes.

Facile MOF Support Improvement in Synergy with Light Acceleration for Efficient Nanoalloy-Catalyzed H2 Production from Formic Acid

Hydrogen (H2) generation and storage are actively investigated to provide a green source of energy, and formic acid (HCOOH), a major product obtained from the biomass, is regarded as a productive source of H2. Therefore, improvements in heterogeneous catalysts are called for. Here, a novel type of catalyst support is proposed involving simple addition of the mixture of metal ion precursors to core-shell ZIF-8@ZIF-67, followed by reduction with NaBH4, with performances surpassing those obtained using nanocatalysts in ZIF-8 or ZIF-67. The nanocatalysts PdxAg were optimized with ZIF-8@Pd2Ag1@ZIF-67 under visible-light illumination for selective HCOOH dehydrogenation involving a turnover frequency value of 430 h-1 under light irradiation at 353 K. These results also reveal the crucial roles of the Pd sites electronically promoted in the presence of visible light by the Ag plasmon resonance and the advantageous core-shell MOF structure. In order to examine the potential of extending this catalyst improvement principle to other catalytic reactions, 4-nitrophenol reduction, a benchmarking model of catalytic reaction, was tested, and the results also confirmed the superiority of the performance of ZIF-8@Pd2Ag1@ZIF-67 over Pd2Ag1@ZIF-8 and Pd2Ag1@ZIF-67, confirming the interest in the novel catalyst design.

Covalent Triazine Framework Encapsulated Ultrafine PdAu Alloy Nanoclusters as Additive-Free Catalysts for Efficient Hydrogen Production from Formic Acid

Dehydrogenation of formic acid (FA) represents a promising route for clean hydrogen production, the economic viability of which, however, is largely hindered by the catalyst inefficiency. Here, ultrafine Au–Pd bimetallic nanoclusters (NCs) confined within the cavities of bipyridyl covalent triazine frameworks (CTFs) are constructed via a metal-nitrogen coordination reduction strategy, which is enabled by the chelation between bidentate nitrogen sites of the bipyridine ligands and metal ion precursors. The resulting CTF-confined PdAu NCs exhibit a high initial turnover frequency up to 12,368 h–1 (333 K) toward the dehydrogenation of FA without any additives. The experimental and theoretical studies disclose that the pyridinic nitrogen sites of CTF not only facilitate the formation of monodisperse small-sized metal NCs via the anchoring and the pore confinement effect but also serve as a proton buffer which can store excess protons and thus suppress the recombination of adsorbed formate and hydrogen on the PdAu alloy surface. These findings would have significant implications for designing high-performance hydrogen production catalysts.

Guiding Metal Organic Framework Morphology via Monolayer Artificial Defect-Induced Preferential Facet Selection.

Guiding metal organic framework (MOF) morphology, especially without the need for chemical additives, still remains a challenge. For the first time, we report a unique surface guiding approach in controlling the crystal morphology formation of zeolitic imidazole framework-8 (ZIF-8) and HKUST-1 MOFs on disrupted alkanethiol self-assembled monolayer (SAM)-covered Au substrates. Selective molecule removal is applied to generate diverse SAM matrices rich in artificial molecular defects in a monolayer to direct the dynamic crystal growth process. When a 11-mercaptoundecanol alkanethiol monolayer is ruptured, the hydroxyl tail groups of surface residue molecules act as nucleating sites by coordination with precursor metal ions. Meanwhile, the exposed alkane chain backbones stabilize a particular facet of MOF nuclei in the dynamic growth by slowing down their crystal growth rates along a specific direction. The competitive formation between the [110] and [100] planes of ZIF-8 ultimately regulates the crystal shapes from rhombic dodecahedron, truncated rhombic dodecahedron, and truncated cube to cube. Similarly, changeable morphologies of HKUST-1 crystals are also achieved from cube and tetrakaidekahedron to octahedron, originating from the competitive selection between the [100] and [111] planes. In addition to the artificial matrix preferred orientation of initial nucleation, parameters such as temperature also play a crucial role in the resulting crystal morphology. Standing on the additive-free MOF crystal morphology growth control, porous architectures prepared in this approach can act as templates for ligand-free metal (Au, Ag, and Cu) nanocluster synthesis. The nanocluster-embedded MOF structures represent distinct crystal morphology-dependent optical properties, and interestingly, their fluorescence emission can be highly enhanced by facet-induced nanocluster packing alignments. These findings not only provide a unique thought on MOF crystal morphology guidance but also pave a new route for the accompanied property investigation and further application.

Polyethylenimine as a Non-Innocent Ligand for Hexacyanoferrates Immobilization

To understand how polyethyleneimine (PEI), as a ligand, affects structure and properties of the transition metals hexacyanoferrates (HCFs) immobilized in cross-linked PEI matrix, we have synthesized Cu(II), Zn(II), and Fe(III) HCFs via successive ion-exchange reactions with metal salts and K4[FeII(CN)6] or K3[FeIII(CN)6]. The structure and properties of the obtained materials in comparison with the crystalline HCF analogs were investigated with FT-IR, Mössbauer, and UV-Vis spectroscopy. Complete reduction of Fe(III) to Fe(II) by PEI in HCF(III) was confirmed. When synthesis was performed at pH favoring binding of precursor metal ions by PEI, cyano-bridged hybrids rather than polymer-HCFs composites were formed. Although the obtained hybrids did not demonstrate sorption activity toward cesium ions, known for crystalline HCFs, they are of interest for the other applications. SQUID measurements revealed a significant difference in magnetic properties of PEI-HCFs hybrids in comparison with crystalline HCFs. Due to the Fe(III) to Fe(II) reduction in HCF ions, Cu(II) and Fe(III) HCFs(III) lost the molecular magnets properties in PEI matrix, but magnetic ordering, including ferromagnet-antiferromagnet interactions, was observed in all hybrids over the broad temperature range.

Single Step Metal Nanoparticle Fabrication Using Atmospheric Pressure Plasma Jets

The interaction of atmospheric pressure plasma discharges with liquid or vapour phases is a hot-topic in plasma science and technology. Synthesis and processing of nanomaterials using atmospheric pressure plasma jets attracts more attention because of its simplicity and cost effectiveness. The plasma containing reactive electrons and active chemical species activates physical processes and reduction reaction of metal salts which leads to the formation of metal nanoparticles. Among the unique features of atmospheric pressure plasmas, the chemical non-equilibrium environment produces highly reactive radicals and ions from the precursors as well as inside the plasma. Thus the energy transfer could be initiated with high energy electrons and excited species from plasma and could be achieved by the reactions with reactive species of the precursors. Plasma compliments the production of nanomaterials in vapour phase or from aerosols and in solutions of the precursors. The interface between plasmas and vapors can be employed for rapid, simultaneous reduction and deposition of metal nanoparticles from metal salts, for instance gold nanoparticles from chloroauric acid (HAuCl4).We have employed an atmospheric pressure plasma jet setup operating with a mixture of He and Ar gases to produce gold nanocrystals onto a silicon wafer substrate. In this study, it reveals an easy and reliable synthesis mechanism of gold nanoparticles from chloroauric acid using atmospheric pressure plasma jet working with a high voltage source. A solution of the precursor in water acts as the feed solution for the process which is introduced to plasma in the form of microdroplets and metal nanoparticles were formed inside the plasma from the vapours containing the precursor molecules. Since the plasma-liquid/vapour chemistry allows the lead of accelerated reactions and instantly reduce the metal ions to metal atoms skipping the intermediate steps in the reduction process. The nanoparticles were collected on to a Si wafer substrate downstream of the plasma jet and characterized via scanning electron microscopy, Raman spectroscopy, transition electron microscopy etc. The polygonal nanoparticles sized 40-100 nm were obtained and they do not tend to agglomerate or fuse onto the substrate. Due to the low volatility of the precursor solution and the presence of comparatively larger microdroplets inside the plasma the nanoparticles tend to deposit in a pattern like galaxies on the silicon wafer substrate. These results would lead to the development of low cost and mobile, user-friendly atmospheric pressure plasma devices for the synthesis of nanoparticles without any toxic chemicals for the reduction of metal salt.The challenge in this process is in creating a vapour-plasma interface directly. This problem has been solved by incorporating a vaporizer directly to plasma. The vaporizer would introduce a new phase which would be a combination of gaseous plasma and plasma-liquid interface. To ease the transportation and diffusion of precursor molecules at the interface an inert gas has been introduced to the vaporizer as a carrier. At the interface, high energy electrons are introduced to the vapors containing the precursor metal ions and these wet electrons play the key role as initiators for the reduction process inside the plasma. Nanoparticles are formed inside the plasma by simple reduction mechanism carried out by short-lived reducing species formed at the interface. From the qualitative analysis carried our during the process implies the formation of short-lived reducing agents like hydrogen peroxide (H2O2) which is known as a reducing agent for chloroaurate ions in water medium. The size and shape of the nanoparticles are controlled by the residence time of the particles inside the plasma and the population density of the metal ions. Whereas the purity in turn the reduction rate of metal ions are dependent upon the feed gas flow as well as the applied voltage, i.e. plasma power.Concisely, atmospheric pressure plasma jets are outstanding choice for the synthesis of gold nanoparticles from chloroauric acid without any external reducing agents. The synthesized gold nanoparticles are promising for different applications because of its geometry and shape. Because of its polygonal geometries the particles are plasmonic active surfaces, the functional for highly specific sensing applications and nanoelectronics devices. However, the low-temperature plasma-vapour interphases containing droplets, the evaporation may add new complexities such as quantitative analysis of non-equilibrium chemistry to plasma chemistry which is yet to be understood and developed.

Controlling Electronic Energy Structure of Near-IR-Responsive Ag(In,Ga)(S,Se)2 Quantum Dots for In Vivo Bioimaging

[Introduction] Since cancer is a leading cause of death worldwide, early diagnostic and treatment observation using biosensors becomes urgent. To date, the development of the biosensors is limited to the utilization of fluorescent probes such as organic dyes or fluorescent proteins, which suffer from various weakness[1]. Therefore, new probes that are more photostable than current organic fluorophores are needed.Semiconductor called quantum dots (QDs) of a few nanometers in size exhibit unique photochemical properties different from their bulk materials, owing to the quantum size effect. Binary QDs composed of group II−VI or IV−VI semiconductors, such as CdS, CdSe, and PbS, have been intensively investigated because of intense PL, high quantum yield, resistance to photo-bleaching, and broad excitation with narrow emission bands, which made them ideal for high contrast optical imaging of biological systems. However, notable toxicity associated with Cd and Pb causes serious limitations in practical use. Recently, mixed-cation QDs, such as ZnAgInS[2], AgInGaS[3], and AgInGaSe[4], have been an environmentally friendly alternative to conventional binary QDs. Their photochemical properties were controlled through the composition of QDs as well as their particle size. Controlling the composition of QDs containing multinary chalcogen elements, that is, mixed-anion QDs, is also expected to be another strategy to tune their physicochemical properties, but the method to prepare such QDs showing intense PL has not been developed well.In this study, we report the strategy to prepare Ag(In, Ga)(S, Se)2 (AIGSSe) QDs, of tunable photochemical properties, such as energy gap (Eg) and photoluminescence peak, with the ratio of Se/S in the particles. [Experimental] AIGSSe QDs were synthesized by a solution-phase synthesis method. A mixture of AgOAc, In(acac)3, and Ga(acac)3 was used as a metal ion precursor, and that of thiourea and selenourea was used as a chalcogen precursor. These were added to a test tube with a mixture solvent of oleylamine and dodecane thiol, in which the ratio of Se/(Se+S) varied from 0 to 1.0. The solution was heated at 100~250 °C, and then formed QDs were isolated by adding methanol. The resulting wet precipitates were washed several times with ethanol, followed by dissolving in chloroform. Thus-obtained AIGSSe QDs were surface-coated by GaSx shell to improve PL property. Furthermore, these QDs were incorporated into unilamellar liposomes of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) to make them dissolved in aqueous solution before being injected into the back of a mouse, and their PL intensity was measured. [Results and Discussion] The absorption onset was red-shifted from 580 nm to 830 nm with an increase in the Se/(S+Se) ratio in preparation, indicating that the Eg of QDs was decreased from 1.9 to 1.5 eV with an increase in the Se/(Se+S) ratio from 0 to 1.0 in QDs. Thus-obtained AIGSSe QDs exhibited broad PL peaks with relatively weak intensities. However, the surface coating of AIGSSe QDs with GaSx shell (AIGSSe@GaSx) remarkably enhanced the intensity of PL peak. The PL quantum yield (QY) of AIGSSe QDs varied in the range of 2~43%, but QDs with each Se/(S+Se) ratio exhibited increased QY after surface coating with GaSx shell. Especially, AIGSSe@GaSx with Se/(S+Se) = 0 had the highest QY value as much as 50%. The PL peak wavelength was red-shifted from 580 nm to 785 nm with a decrease in the Eg of AIGSSe core, the FWHM of PL peak being varied in the range of 0.147 ~ 0.357 eV.TEM measurement revealed that the AIGSSe@GaSx QDs were spherical, and their average size was almost constant at ca. 4 nm with narrow size distribution, regardless of Se/(Se+S) in preparation. AIGSSe@GaSx QDs with Se/(Se+S) = 0.50 exhibited a sharp PL peak at 785 nm in first biological window, which was suitable for in vivo imaging. These QDs were encapsulated with DSPC liposomes so that the QDs were dispersed in aqueous solution. Thus-obtained AIGSSe@GaSx QD-DSPC liposomes maintained a sharp band-edge PL peak even in an aqueous dispersion, in which the PLQY was slightly decreased from 25% in chloroform to 21% in aqueous dispersions but was high enough to be used as a near-IR PL probe. We successfully detected PL emission from the QDs through the skin of a mouse, and the PL intensity was proportional to the concentration of injected QDs. [References] [1] T. Jin, et al., J Mater Chem B, 2020, 8, 10686.[2] T. Kameyama, et al., J. Phys. Chem. C, 2018, 122, 13705.[3] T. Kameyama, et al., ACS Appl. Mater. Interfaces, 2018, 10, 42844.[4] T. Kameyama, et al., ACS Appl. Nano Mater., 2020, 3, 3275.

In Situ Liquid Phase TEM of Nanoparticle Formation and Diffusion in a Phase-Separated Medium.

Colloidal nanoparticles are synthesized in a complex reaction mixture that has an inhomogeneous chemical environment induced by local phase separation of the medium. Nanoparticle syntheses based on micelles, emulsions, flow of different fluids, injection of ionic precursors in organic solvents, and mixing the metal organic phase of precursors with an aqueous phase of reducing agents are well established. However, the formation mechanism of nanoparticles in the phase-separated medium is not well understood because of the complexity originating from the presence of phase boundaries as well as nonuniform chemical species, concentrations, and viscosity in different phases. Herein, we investigate the formation mechanism and diffusion of silver nanoparticles in a phase-separated medium by using liquid phase transmission electron microscopy and many-body dissipative particle dynamics simulations. A quantitative analysis of the individual growth trajectories reveals that a large portion of silver nanoparticles nucleate and grow rapidly at the phase boundaries, where metal ion precursors and reducing agents from the two separated phases react to form monomers. The results suggest that the motion of the silver nanoparticles at the interfaces is highly affected by the interaction with polymers and exhibits superdiffusive dynamics because of the polymer relaxation.

Silver‐Ion‐Selective Gelation of Simple Pyridine‐Naphthalimide Conjugates with Multiple Applications: Sensing, Drug Delivery, Dye Adsorption and Ion Conductivity

AbstractNaphthalimide‐based compounds 1–4, which show excellent gelation from semi aqueous solvents in the presence of Ag+ ions over a series of other metal ions have been synthesized. While compounds 1–3 form gel in the presence of Ag+ ion in DMF‐H2O (1 : 1, v/v), compound 4, devoid of pyridine, acts as non gelator under identical conditions. The gels reveal rock and fibrous like morphologies and show good viscoelastic response as established from rheological study. Ag‐gels of 1–3 exhibit excellent ion conduction property along with other attributes in material chemistry. Ion transport properties within the gels are analyzed by evaluating the different electrical parameters viz. ion conductivity, ion diffusivity and concentration of mobile ions at different temperatures using impedance spectroscopy. Despite identical concentration of metal ion precursor within the gels, a strong gelator‐dependent conduction property is observed. Furthermore, the Ag‐gels as soft functional materials discriminate L‐ cysteine from other amino acids and show good response in drug delivery and dye adsorption from wastewater.