Island-in-Sea Structured Pt3Fe Nanoparticles-in-Fe Single Atoms Loaded in Carbon Materials as Superior Electrocatalysts toward Alkaline HER and Acidic ORR.

In this work, Pt3Fe nanoparticles (Pt3Fe NPs) with the ordered internal structure and Pt-rich shells surrounded by plenty of Fe single atoms (Fe SAs) as active species (Pt3Fe NP-in-Fe SA) loaded in the carbon materials are successfully fabricated, which are abbreviated as island-in-sea structured (IISS) Pt3Fe NP-in-Fe SA catalysts. Moreover, the synergistic effect of O-bridging between Pt3Fe NPs and Fe SAs, and the ordered internal structured Pt3Fe NPs with Pt-rich shells of an optimal thickness contributes to the achievement of the local acidic environments on the surfaces of Pt3Fe NPs in the alkaline hydrogen evolution reaction (HER) and the enhancement of the desorption rate of *OH intermediate in the acidic oxygen reduction reaction (ORR). In addition, the electronic interactions between Pt3Fe NPs and dispersed Fe SAs cannot only provide efficient electrons transfer, but also prevent the aggregation and dissolution of Pt3Fe NPs. Furthermore, the overpotential and the half wave potential of the as-prepared IISS Pt3Fe NP-in-Fe SA catalysts toward the alkaline HER and toward the acidic ORR are 8 mV at a current density of 10 mA cm-2 and 0.933 V, respectively, which is 29 lower and 86 mV higher than those (37 mV and 0.847 V) of commercial Pt/C catalysts.

Ethanol Oxidation via 12-Electron Pathway on Spiky Au@AuPd Nanoparticles Assisted by Near-Infrared Light.

In this work, ethanol oxidation reaction (EOR) via 12-electron (C1-12e) pathway on spiky Au@AuPd nanoparticles (NPs) with ultrathin AuPd alloy shells is achieved in alkaline media with the assistance of the near-infrared (NIR) light. It is found that OH radicals can be produced from the OHads species adsorbed on the surfaces of Pd atoms led by surface plasmon resonance (SPR) effect of spiky Au@AuPd NPs under the irradiation of NIR light. Moreover, OH radicals play the key role for the achievement of EOR proceeded by the desirable C1-12e pathway because OH radicals can directly break the C-C bonds of ethanol. Accordingly, the electrocatalytic performance of spiky Au@AuPd NPs toward EOR under NIR light is greatly improved. For instance, their mass activity can be up to 33.2 A mgpd -1 in the 0.5 m KOH solution containing 0.5 m ethanol, which is about 158 times higher than that of commercial Pd/C catalysts (0.21 A mgpd -1 ) and is better than those of the state-of-the-art Pd-based catalysts reported in literature thus far, to the best of our knowledge. Moreover, their highest mass activity can be further improved to 118.3 A mgpd -1 in the 1.5 m KOH solution containing 1.25 m ethanol.

Controlled Iodine Phase Transfer of Covalent Organic Framework Membranes for Instant but Sustained Disinfection.

Freestanding membranes of CuCl2-implanted TpPa covalent organic frameworks (COFs) were mechanochemically produced. The resulting membrane had a high I2 adsorption capacity (566.78 g·mol-1) in cyclohexane, which corresponds to 2.2I2 per unit cell with 1.3I2 immobilized on 3Cl- ions (60%) and 0.9 on 3N atoms (40%). Upon being placed in aqueous media, the membrane released 61.1% of its loaded I2 mainly by its Cl- ions within 10 min and the remaining 38.9% mainly from its N atoms within about 5 h. Thanks to that, the COF membranes loaded with 1.5 mg of I2 could be repetitively utilized to kill about 108 CFU/mL E. coli in 0.5-3 min at least five times, after which the membranes could retain their bactericidal activity for 4 h against 108 CFU/mL E. coli. This highlights the promising application of I2-loaded TpPa-CuCl2 COF membranes for instant and sustained disinfection.

Dimensional and Optoelectronic Tuning of Lead-free Perovskite Cs3 Bi2 I9-n Brn Single Crystals for Enhanced Hard X-ray Detection.

Inorganic Bi-based perovskites have shown great potential in X-ray detection for their large absorption to X-rays, diverse low-dimensional structures, and eco-friendliness without toxic metals. However, they suffer from poor carrier transport properties compared to Pb-based perovskites. Here, we propose a mixed-halogen strategy to tune the structural dimensions and optoelectronic properties of Cs3 Bi2 I9-n Brn (0≤n≤9). Ten centimeter-sized single crystals are successfully grown by the Bridgman technique. Upon doping bromine to zero-dimensional Cs3 Bi2 I9 , the crystal transforms into a two-dimensional structure as the bromine content reaches Cs3 Bi2 I8 Br. Correspondingly, the optoelectronic properties are adjusted. Among these crystals, Cs3 Bi2 I8 Br exhibits negligible ion migration, moderate resistivity, and the best carrier transport capability. The sensitivities in 100 keV hard X-ray detection are 1.33×104 and 1.74×104  µC Gyair -1 cm-2 at room temperature and 75 °C, respectively, which are the highest among all reported bismuth perovskites. Moreover, the lowest detection limit of 28.6 nGyair s-1 and ultralow dark current drift of 9.12×10-9  nA cm-1 s-1 V-1 are obtained owing to the high ionic activation energy. Our work demonstrates that Br incorporation is an effective strategy to enhance the X-ray detection performance by tuning the dimensional and optoelectronic properties.

Fe-Ni Alloy Nanoclusters Anchored on Carbon Aerogels as High-Efficiency Oxygen Electrocatalysts in Rechargeable Zn-Air Batteries.

In this work, Fe-Ni alloy nanoclusters (Fe-Ni ANCs) anchored on N, S co-doped carbon aerogel (Fe-Ni ANC@NSCA catalysts) are successfully prepared by the optimal pyrolysis of polyaniline (PANI) aerogels derived from the freeze-drying of PANI hydrogel obtained by the polymerization of aniline monomers in the co-presence of tannic acid (TA), Fe3+ , and Ni2+ ions. In addition, the optimal molar ratio of the TA, Fe3+ , and Ni2+ ions for synthesis of Fe-Ni ANC@NSCA catalysts are 1:2:5, which can guarantee the formation of carbon aerogel composed of quasi-2D porous carbon sheets and the formation of high-density Fe-Ni ANCs with an ultrasmall size between 2 to 2.8 nm. These Fe-Ni ANCs consisting of N4 -Fe-O-Ni-N4 moiety are proposed as a new type of active species for the first time, to the best of the authors' knowledge. Thanks to their unique features, the Fe-Ni ANC@NSCA catalysts show excellent performance in oxygen reduction reaction with a half-wave potential (E1/2 ) of 0.891 V and oxygen evolution reaction (260 mV @ 10 mA cm-2 ) in alkaline media as bifunctional catalysts, which are better than the state-of-the-art commercial Pt/C catalysts and RuO2 catalysts. Moreover, Zn-air battery assembled with the Fe-Ni ANC@NSCA catalysts also shows a remarkable performance and exceptionally high stability over 500 h at 5 mA cm-2 .

Synthesis of Uniform Gold Nanorods with Large Width to Realize Ultralow SERS Detection.

In this work, we successfully demonstrate high-yield synthesis of high-quality gold nanorods (Au NRs) with width ranging from 6.5 nm to 175 nm by introducing heptanol molecules as secondary templating agents during cetyltrimethylammonium bromide-templated, seeded growth method. The results show that an appropriate concentration of heptanol molecules not only alter the micellization behavior of CTAB in water, but also help silver ions impact the symmetry-breaking efficiency of additional Au-NP seeds in addition to enhancing the utilization of gold precursors. Moreover, the generality and versatility of the present strategy for synthesis of Au NRs with flexible controlled dimensions are further demonstrated by successful synthesis of Au NRs with the assistance of other fatty alcohols with properly long alkyl chains. Furthermore, when arrays of vertically aligned Au NRs with large width (AVA-Au120×90 NRs) are used as SERS substrates, they can achieve the ultralow limit of detection for crystal violet (10-16  M) with good reliability and reproducibility, and the rapid detection and identification of residual harmful substances.

Passively Q-switched mid-infrared laser pulse generation with gold nanospheres as a saturable absorber.

High-quality gold (Au) nanospheres (Au-NPs) with a diameter of 52 nm were prepared by the seeded growth method. The mid-infrared (MIR) nonlinear saturable absorption properties were measured by a balanced twin-detector measurement technique. With the as-prepared Au-NPs saturable absorber (SA), an efficient passively Q-switched laser was realized at 2.95 µm for the first time, to the best of our knowledge. Under an absorbed pump power of 4.0 W, a maximum output power of 268 mW was obtained with the shortest pulse width of 734 ns and repetition rate of 91 kHz, corresponding to the pulse energy up to 2.95 µJ. The results indicate that Au-NPs are promising candidates as SAs for MIR laser pulse generation.

Realizing enhanced luminescence of silver nanocluster-peptide soft hydrogels by PEI reinforcement.

Metal nanoclusters (NCs) are a new type of fluorescent nanomaterial composed of several to several tens of metal ions or atoms with a wide range of applications in the fields of catalysis, optics, and biomedicine. However, fluorescence quenching when existing as individuals in aqueous solutions greatly limits their applications. In this study, six-core Ag(i) NCs (Ag6-NCs) were interacted with peptides (DD-5) in water to form soft hydrogels with the aggregation-induced emission (AIE) of Ag6-NCs. The introduction of polyethyleneimine (PEI) into the Ag6-NCs/DD-5 hydrogel succeeded in further enhancing the fluorescence intensity. This dual-AIE behavior of the Ag6-NCs/DD-5/PEI hydrogels is mainly ascribed to the strong hydrogen bonding among the carboxyl groups of Ag6, those of DD-5 and the amino groups of PEI, which effectively restricted intramolecular vibration of the capping ligands on the Ag6-NCs. Moreover, the addition of PEI can effectively promote the gelation speed of Ag6-NCs/DD-5 and act as a physical cross-linker, leading to an increase of the mechanical strength of the hydrogel. This work opens a new pathway for the fabrication of smart composite materials with multiple functions, which show a variety of applications such as chemical/biosensing and bioimaging.

Revitalizing the Frens Method To Synthesize Uniform, Quasi-Spherical Gold Nanoparticles with Deliberately Regulated Sizes from 2 to 330 nm.

In this work, we have successfully developed a new and consistent model to describe the growth of gold nanoparticles (Au NPs) via citrate reduction of auric acid (HAuCl4) by carefully assessing the temporal evolution of the NP sizes and surface charges by means of dynamic light scattering (DLS) and zeta-potential measurements. The new model demonstrates that the nucleation and growth of the Au NPs occur exclusively in the particles of the complexes of Au(+) ions and sodium acetone dicarboxylate (SAD) derived from the citrate/HAuCl4 redox reaction, which proceeds as described by the classic LaMer model. Concomitant with the Au NP growing therein, the Au(+)/SAD complex particles undergo reversible agglomeration with the reaction time, which may result in an abnormal color change of the reaction media but have little impact on the Au NP growth. Built on the new model, we have successfully produced monodisperse quasi-spherical Au NPs with sizes precisely regulated from 2 to 330 nm via simple citrate reduction in a one-pot manner. To date, highly uniform Au NPs with sizes spanning such a large size range could not be formed otherwise even via deliberately controlled seeded growth methods.

Formation of Hybrid Perovskite Tin Iodide Single Crystals by Top-Seeded Solution Growth.

Hybrid perovskites have generated a great deal of interest because of their potential in photovoltaic applications. However, the toxicity of lead means that there is interest in finding a nontoxic substitute. Bulk single crystals of both cubic CH3NH3 SnI3 and CH(NH2)2 SnI3 were obtained by using the top-seeded solution growth method under an ambient atmosphere. Structural refinement, band gap, thermal properties, and XPS measurements of CH3NH3 SnI3 and CH(NH2)2 SnI3 single crystals are also reported in detail. These results should pave the way for further applications of CH3NH3 SnI3 and CH(NH2)2 SnI3.

Effect of latent heat in boiling water on the synthesis of gold nanoparticles of different sizes by using the Turkevich method.

The Turkevich method, involving the reduction of HAuCl4 with citrate in boiling water, allows the facile production of monodisperse, quasispherical gold nanoparticles (AuNPs). Although, it is well-known that the size of the AuNPs obtained with the same recipe vary slightly (as little as approximately 4 nm), but noticeably, from one report to another, it has rarely been studied. The present work demonstrates that this size variation can be reconciled by the small, but noticeable, effect that the latent heat in boiling water has on the size of the AuNPs obtained by using the Turkevich method. The increase in latent heat during water boiling caused an approximately 3 nm reduction in the size of the as-prepared AuNPs; this reduction in size is mainly a result of accelerated nucleation driven by the extra heat. It was further demonstrated that, the heating temperature can be utilized as an additional measure to adjust the growth rate of AuNPs during the reduction of HAuCl4 with citrate in boiling water. Therefore, the latent heat of boiling solvents may provide one way to control nucleation and growth in the synthesis of monodisperse nanoparticles.

Directed self-assembly of gold nanoparticles into plasmonic chains.

The plasmonic behavior of metals at the nanoscale is not only appealing for fundamental studies, but also very useful for the development of innovative photonic devices. The past few decades have witnessed great progress in colloidal synthesis of monodisperse metal nanoparticles with defined shapes. This has significantly fueled up the research of directing the metal nanoparticles to self-assemble into tailored extended structures, especially low dimensional ones, for a better control and manipulation of the interactions of the metal nanoparticles with light. In parallel, theories for a better description of nanoplasmonics have been increasingly developed and improved. Thus, the present review is focused on the overview of current experimental and theoretical developments in the directed self-assembly of metal nanoparticles with tailored plasmonic properties, which, hopefully, will provide useful guidelines for future research studies and applications of nanoplasmonics.

High yield seedless synthesis of high-quality gold nanocrystals with various shapes.

In this Article, high-quality gold nanocrystals (Au NCs) with various shapes including concave cubic, trisoctahedral, cubic, rod-like, and quasi-spherical have been successfully produced in high yield via adding a trace amount of NaBH4 solution into growth solutions mainly composed of HAuCl4, ascorbic acid, and surfactants. The sizes and shapes of as-prepared Au NCs can be tuned by the compositions of the growth solutions and the amount of NaBH4 added. The electrocatalytic performance of differently shaped Au NCs for methanol oxidation was studied; as-prepared trisoctahedral or concave cubic Au NCs are more highly active electrocatalysts for methanol oxidation due to the presence of high-index facets on their surface.

Synthesis of monodisperse, quasi-spherical silver nanoparticles with sizes defined by the nature of silver precursors.

Monodisperse, quasi-spherical silver nanoparticles (Ag NPs) with controlled sizes have been produced directly in water via adding the aqueous solutions of the mixtures of AgNO3 and sodium citrate to boiling aqueous solutions of ascorbic acid (AA). Different compounds, including NaCl, NaBr, KI, Na2SO4, Na2CO3, Na2S, and Na3PO4, are added to the AgNO3/citrate mixture solutions to form new silver compounds with fairly low solubility in water, which are used as precursors instead of soluble Ag(+) ions to synthesize Ag NPs via AA/citrate reduction. This enables us not only to produce monodisperse, quasi-spherical Ag NPs but also to tune the sizes of the resulting NPs from 16 to 30 nm according to the potential of new silver precursors as well as the concentrations of anions.

Synthesis of polyaniline-coated carbon nanotubes and study on their pH-sensitive conductivity.

We report the synthesis of polyaniline-coated-carbon nanotubes (PANI-c-CNTs) composites by using water-soluble CNTs with phenyl sulfonate groups as templates. A series of characterizations including transmission electron microscopy (TEM), Fourier-Transform Infrared Spectroscopy (FTIR) and UV-vis spectroscopy were conducted to investigate the formation of PANI coating on the surfaces of the CNTs. The thickness of PANI coating in the PANI-c-CNTs composites was controlled by adjusting concentrations of aniline and CNTs. The conductivities of PANI-c-CNTs composites were measured by using conductive atomic force microscopy (c-AFM). It was found that the conductivities of PANI-c-CNTs composites were remarkably affected after doping and dedoping process of PANI coating by different pH solution. Therefore, our preliminary result indicates that as-prepared PANI-c-CNTs composites may be used as gas sensor such as HCl and NH3 vapor.

Simple synthesis of monodisperse, quasi-spherical, citrate-stabilized silver nanocrystals in water.

Monodisperse, quasi-spherical silver nanocrystals (Ag NCs) have been produced directly in water via adding the aqueous solution of a mixture of AgNO3, sodium citrate, and KI into the boiling aqueous solutions of ascorbic acid (AA). The AA is used to significantly accelerate reduction of AgNO3 in order to promote a very fast nucleation, and the KI is used to tailor the growth of the Ag NCs into a quasi-spherical shape via its preferential adsorption on the NC {111} facets. The major role of citrate is to stabilize the newly formed NCs, whereas it has a minor contribution to reduction of AgNO3. The synergy of the effects of AA, citrate, and KI can significantly narrow the size distributions of the Ag NCs obtained so and transform the NC shapes to be truly quasi-spherical.

Preparation of porous hollow polyaniline microspheres and study on their in vitro release behavior.

We report the synthesis of porous hollow polyaniline (PANI) microspheres loaded with Acid Red 8 dye (200-600 nm diameters under different reaction conditions) by using spherically mesoporous aggregates of Fe3O4 particles as soft templates and ammonium persulfate (APS) as the oxidant at 2.5 degrees C. Since the as-prepared spherical aggregates of Fe3O4 particles are readily dissolved in acidic aqueous solution, these spherical aggregates can be treated as soft template for the fabrication of hollow spheres. This process is therefore more convenient than other reported methods which require the post-treatment to remove the templates under strict conditions. The influence of the synthetic conditions on the formation and size of PANI microspheres was investigated. The morphology was confirmed by transmission electron microscopy (TEM). The chemical and electronic structures of the PANI microspheres were also studied by FTIR and UV-Vis spectrometry, respectively. The experimental in vitro release showed that these porous hollow PANI microspheres provided a controlled release of the entrapped dye, which was regulated by pH. Furthermore, the releasing behavior was qualitatively explained based on effective dissociation constant as a function of the pH.

The enhancement in the performance of ultra-small core-shell Au@AuPt nanoparticles toward HER and ORR by surface engineering.

In this work, ultra-small core-shell (USCS) Au38.4@Au4.1Pt57.5 nanoparticles (NPs) with an optimal Pt-to-Au ratio were successfully prepared by the optimal etching treatment of USCS Au@AuPt NPs by Fe(III) ions to remove some exposed Au atoms on their outermost surfaces. The as-prepared USCS Au38.4@Au4.1Pt57.5 NPs with Fe(III)-etching treatment for 2 h loaded on carbon black as catalysts (USCS2h Au38.4@Au4.1Pt57.5-NP/C catalysts) exhibit superior electrocatalytic activity and durability for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in acidic media. For instance, the overpotential of USCS2h Au38.4@Au4.1Pt57.5-NP/C catalysts toward the HER is 13 mV at a current density of -10 mA cm-2 (η10 = 13 mV), which is much better than that of commercial Pt/C catalysts (η10 = 31 mV). Moreover, their mass activity (63.8 A mgPt-1) is about 16.4 times larger than that of commercial Pt/C catalysts (3.9 A mgPt-1). In addition, they also present better long-term stability. Furthermore, they also show an improved activity toward the ORR in terms of the half-wave potential (E1/2) (0.89 V vs. RHE), which is more positive by about 38 mV than commercial Pt/C catalysts (0.852 V). In addition, they also show a higher kinetic current density (14.22 mA cm-2 at 0.85 V) and better long-term durability. This etching-treatment strategy can be extended to further improve the catalytic performance of ultra-small Au-based bimetallic or multi-metallic NPs by surface engineering.

Synthetic Principles of Spiky Au Nanoparticles.

In this work, the synthetic principles of spiky Au nanoparticles (spiky Au NPs) with an average number of spikes of less than or equal to six and controlled core sizes by using Au nanorods as seeds (Au-NR seeds) are summarized on the basis of the results of a series of control experiments. In addition, one empirical equation that can roughly estimate the number of spiky Au NPs is proposed, demonstrated by the results of the products prepared from different aspect ratios of Au-NRs as seeds and non-Au-NR seeds. Moreover, the synthetic principles of spiky Au NPs are further demonstrated by taking the successful synthesis of a serials of spiky Au21×7 NPs. Furthermore, the as-prepared spiky Au@Au11.8Pd88.2 NPs with ultrathin AuPd shells, which are derived from spiky Au21×7 NPs with the smallest cores, can bear excellent catalytic activity (say, E1/2 = 0.947 V) and durability toward the oxygen reduction reaction (ORR) in alkaline conditions, compared with commercial Pt/C catalysts (E1/2 = 0.883 V).

Rapid seeded growth of monodisperse, quasi-spherical, citrate-stabilized gold nanoparticles via H2O2 reduction.

In this report, we demonstrate a rapid and simple seeded growth method for synthesizing monodisperse, quasi-spherical, citrate-stabilized Au nanoparticles (Au NPs) via H(2)O(2) reduction of HAuCl(4). Au NPs with diameter ranging from 30 to 230 nm can be synthesized by simply adding 12 nm citrate stabilized Au NP seeds to an aqueous solution of H(2)O(2) and HAuCl(4) under ambient conditions. The diameter of the resulting Au NPs can be quantitatively controlled by the molar ratio of HAuCl(4) to the Au seeds. The standard deviation of the Au NP sizes is less than 10%, and the ellipticity (ratio of major to minor axes) of the NPs is less than 1.1. Compared to existing ones, the present seeded growth approach is implemented within 1 min under ambient condition, and no unfavorable additives are involved because H(2)O(2) can readily decompose into H(2)O during storage or via boiling.