Effect of the Titanium Dioxide Shell on the Plasmon Properties of Silver Nanoparticles

The results of the synthesis of Ag—TiO₂ nanostructures were presented. The optical properties of silver nanoparticles and Ag—TiO₂ structures were studied. The size and shape of Ag—TiO₂ nanostructures were determined. The electron density in silver, the damping constant of plasma oscillations, and the ratio between the masses of the Ag core and the TiO₂ shell were determined from the absorption spectra of Ag and Ag—TiO₂ solutions. It was shown that the semiconductor shell of titanium dioxide leads to a decrease in the electron density in silver nanoparticles and the damping constant of plasma oscillations.     

Photogenic MnO2/Ag metal nanocomposites and their dye adsorbing activities

• Manganese dioxide/silver (MnO₂/Ag) nanoparticles were fabricated by using KMnO₄-NaBH₄ redox reaction at room temperature. The optical and structural properties of MnO₂/Ag were determined using UV–visible and Fourier transform infrared spectroscopies. The morphology was established with scanning and transmission electron microcopies, and X-ray diffraction. MnO₂/Ag showed excellent adsorbing activity to the removal of Congo red. The various kinetic models were used to determine the rate of dye removal. Congo red adsorption onto MnO₂Ag proceeds through the pseudo-second-order kinetic model. Langmuir adsorption capacity (Q⁰_max = 97.1 mg/g), and sorption intensity (n = 1.6) were estimated with Langmuir and Freundlich adsorption isotherm models for 250 mg/L Congo red. Elovich model suggest the adsorption of Congo red with the MnO₂Ag proceeds through the film diffusion. The positive values of enthalpy changes (ΔH⁰), entropy changes (ΔS⁰), and negative Gibbs free energy changes (ΔG⁰) showed that the Congo red adsorption process was endothermic, spontaneous, and chemisorption process followed with physical mechanism. The results showed that the removal efficiency decreases from 98% to 89% after the six consecutive experiments.

     

Coaxial Carbon/MnO2 Hollow Nanofibers as Sulfur Hosts for High‐Performance Lithium‐Sulfur Batteries

Lithium‐sulfur (Li‐S) batteries have recently attracted a large amount of attention as promising candidates for next‐generation high‐power energy storage devices because of their high theoretical capacity and energy density. However, the shuttle effect of polysulfides and poor conductivity of sulfur are still vital issues that constrain their specific capacity and cyclic stability. Here, we design coaxial MnO₂‐graphitic carbon hollow nanofibers as sulfur hosts for high‐performance lithium‐sulfur batteries. The hollow C/MnO₂ coaxial nanofibers are synthesized via electrospinning and carbonization of the carbon nanofibers (CNFs), followed by an in situ redox reaction to grow MnO₂ nanosheets on the surface of CNFs. The inner graphitic carbon layer not only maintains intimate contact with sulfur and outer MnO₂ shell to significantly increase the overall electrical conductivity but also acts as a protective layer to prevent dissolution of polysulfides. The outer MnO₂ nanosheets restrain the shuttle effect greatly through chemisorption and redox reaction. Therefore, the robust S@C/MnO₂ nanofiber cathode delivers an extraordinary rate capability and excellent cycling stability with a capacity decay rate of 0.044 and 0.051 % per cycle after 1000 cycles at 1.0 C and 2.0 C, respectively. Our present work brings forward a new facile and efficient strategy for the functionalization of inorganic metal oxide on graphitic carbons as sulfur hosts for high performance Li‐S batteries.     

Synthesis and Characterization of Copolymercore-Silvershell Composite Microspheres

Composite microspheres composed of monodispersed poly（St-co-MAA） latices with diameter about 260 nm as core and Ag nanocrystals as shell were prepared by an in situ reduction method. The shell thickness could be controlled in the range of 15--45 nm by this coating process. The structure and the composition of the core-shell microspheres were characterized by transmission electron microscopy （TEM）, X-ray diffractometry （XRD）, X-ray photoelectron spectroscopy （XPS）, and thermogravimetric analysis （TG）. The formation of the composite microspheres is explained by the nucleation of silver on the surface of the latices followed by growth of the silver shell.     

Electrochemical formation and reduction of silver oxides in alkaline media

The anodic oxidation of silver electrodes in NaOH solution and the reduction of the silver oxides formed were studied by potential step chronoamperometry. Oxidation of Ag to Ag₂O is a diffusion-controlled reaction, the diffusion control being established in the solid phase. Oxidation of Ag₂O to AgO proceeds via a nucleation and growth-controlled process. The amount of AgO decreased with increasing step height. The current—time curves for this reaction have been analysed with the Kolmogoroff—Avrami equation. Reduction of AgO to Ag₂O occurs initially on the outside of the electrode, and the rate of the reaction is limited by diffusion of ions across the thickening layer of Ag₂O. Reduction of Ag₂O to Ag proceeds via a nucleation and growth reaction.     

The chemical identity of “[Ag(py)2]MnO4” organic solvent soluble oxidizing agent and new synthetic routes for the preparation of [Ag(py)n]XO4 (X = Mn,Cl, and Re,n = 2–4) complexes

Abstract

A widely used oxidizing agent in organic chemistry with an assumed structure of “[Ag(py)₂]MnO₄” and its perchlorate and perrhenate analogues are studied. Their synthesis in pure form is challenging. In order to clarify the chemical nature of the known compounds and find routes to new derivatives, a systematic study is presented for the synthesis of [Ag(py)_n]XO₄ (X?=?Mn, Cl, and Re, n?=?2–4) complexes. Ten complexes including four new derivatives, [Ag(py)₄]MnO₄, [Ag(py)₄]MnO₄·4[Ag(py)₂]MnO₄, [Ag(py)₂]ClO₄·0.5 py, and [Ag(py)₂]ReO₄, are synthesized and characterized. The chemical identity of “Ag(py)₂MnO₄” is also clarified. A novel route to prepare [Ag(py)₂]MnO₄ is developed. The reaction of AgXO₄ salts with neat pyridine followed by various crystallization techniques is used to prepare [Ag(py)₂]XO₄, [Ag(py)₄]XO₄, [Ag(py)₄]XO₄·4[Ag(py)₂]XO₄, and [Ag(py)₂]XO₄·0.5py (X?=?Cl, Mn) complexes. The solid phase structure of [Ag(py)₂]MnO₄·0.5py is determined (a?=?19.410 Å, b?=?7.788 Å, c?=?21.177 Å, β?=?104.20°, C2/c (15), Z?=?4 (3a)). [Ag(py)₂]⁺ cations in the crystal form dimeric units where silver ions are connected by oxygen atoms of two MnO₄^– anions. The Ag…Ag distance is indicative of argentophilic interactions. The pyridine ring π…π interactions contribute to the stability of the crystal lattice.     

Synthesis of mixed silver halide nanocrystals in reversed micelles

The specifics of the synthesis of silver halide nanocrystals of mixed composition and the core-shell structures in reversed micelles were experimentally studied. It was shown that homogeneous AgBr _x I_{1 ? x} nanocrystals of ～5 nm in size with the iodide concentration up to 70%, as well as the core-shell structures AgI/AgBr and AgBr/AgI, can be synthesized by the micellar synthesis. It was found that the relation of the crystalline structures of the core and shell materials plays an important role in the shell formation. The shell of γ-AgI alone is formed on the AgBr nanocrystals with a close lattice type, whereas β-AgI with the hexagonal lattice forms an individual phase of nanoparticles, rather than the shell.     

The Pt-free 1T/2H-MoS2/CdS/MnOx hollow core-shell nanocomposites toward overall water splitting via HER/OER synergy of 1T-MoS2/MnOx

Hydrogen evolution reaction/Oxygen evolution reaction (HER/OER) synergy would be the most important issue for overall water splitting. The Pt-free 1T/2H-MoS₂/CdS/MnO_x hollow core–shell nanocomposites are fabricated via a continuous hydrothermal–chemical method; therefore, the OER co-catalysts MnO_x and CdS shell are deposited on the surface of SiO₂ nanosphere templates continuously via hydrothermal–chemical method. Subsequently, the SiO₂ templates are etched via chemical method and the 2H-MoS₂/CdS hollow core–shell heterojunction and 1T-MoS₂ HER co-catalyst are introduced via one-step hydrothermal method. Evaluated by photocatalytic performance, the 1T/2H-MoS₂/CdS/MnO_x exhibits an enhanced HER performance of about ~50 folds than that of single CdS hollow nanosphere, and achieves a decent overall water splitting performance of about ~1668.00(H₂)/824.61(O₂) μmol/g?h, which can be mainly ascribed to the well HER/OER synergy and formation of hollow core–shell structure. Therefore, the 1T-MoS₂ with quick electron transport and decent solid/liquid interface can promote the photogenerated electron diffusing, the MnO_x with mixed Mn³⁺/Mn⁴⁺ ions can activate the hole-related species for OH^? oxidation and promote H₂O₂ decomposition, the 2H–MoS₂/CdS heterojunction can separate the charge carrier and meet the potential to achieve overall water splitting. Additionally, the 1T/2H-MoS₂ with decent lattice matching can improve the charge carrier transport, the 1T-MoS₂ with sufficient specific surface areas can increase active sites and the hollow core–shell structure can increase solar efficiency which is also beneficial for enhancing the overall water splitting performance and stability.     

Polymer particles with dendrimer@SiO2-Ag hierarchical shell and their application in catalytic column

Polymer particles with dendrimer@SiO₂–Ag hierarchical shell were prepared, and their application in the catalytic column for the reduction of 4-nitrophenol (4-NP) was also investigated. The PS microspheres with the carboxyl group were used as the supports for the immobilization of dendrimer@SiO₂–Ag shell. The polyamidoamine (PAMAM) dendrimer was grafted on the surface of PS microsphere through repetitive Michael addition reaction of methyl acrylate (MA) and amidation of the obtained esters with a large excess of ethylenediamine (EDA) successively. The silver nanoparticles formed inside the PAMAM shell. Then, the silver nanoparticles, which were used as center of nucleation, were coated with SiO₂ shell through improved Stöber method. Moreover, the more silver nanoparticles were dispersed on the surface of SiO₂ shell. The contents of silver element were measured using inductively coupled plasma (ICP-MS). The obtained PS@PAMAM@SiO₂–Ag nanoparticles were packed in stainless steel column, which has been used effectively for the catalytic reduction of 4-NP. Under column pressures, the rigid SiO₂ shell plays a better role in immobilization of silver nanoparticles than the soft PAMAM shell. This technique for packing catalytic nanoparticles in column improves the efficiency of application with metal catalysts as well as reduces the tedious separation processes in catalytic reaction.     

One-pot synthesis, optical property and self-assembly of monodisperse silver nanospheres

High-quality spherical silver (Ag) nanocrystals have been synthesized by using a one-pot approach, in which pre-synthesis of organometallic precursors is not required. This reaction involves the thermolysis of a mixed solution of silver acetate and n-dodecanethiol in a non-coordinating organic solvent. The size of the as-obtained Ag nanospheres can be controlled by adjusting the reaction time, reaction temperature and the amount of silver acetate added. The growth and nucleation process of the resultant Ag nanospheres have been studied by employing UV-vis absorption spectra and transmission electron microscopy (TEM) images. Furthermore, these Ag nanospheres have good self-assembly behaviors, and they are easily self-assembled into two- or three-dimensional superlattice structures due to the bundling and interdigitation of thiolate molecules adsorbed on Ag nanospheres. This one-pot synthetic procedure is simple and highly reproducible, which may be extended to prepare other noble-metal nanocrystals.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of lead. selenium,tellurium and chromium

Monovalent-thallium can be successfully used for the back titration of KMnO₄ in the course of estimating Pb⁺², Sc⁺⁴, Te⁺⁴ and Cr⁺³.Reduction of KMnO4 with Tl+ in alkaline solution yields MnO₄^-2 which then passes to MnO₂. he end-points are attained late, but in presence of telluric acid the end-point at MnO₂ stage corresonds to the theoretical value. Reduction at the MnO₄^-2 stage can be checked in presence of Ba⁺² ns and good results obtained with 1–1.5N NaOH.     

Silver Complexes with Cyanoguanidine: Preparation and Crystal Structures of [Ag(cgn)2]F and [Ag(cgn)2][BF4]

The silver cyanoguanidine complexes [Ag(cgn)₂]F ( 1 ), [Ag(cgn)₂][BF₄] ( 2 ), [Ag(cgn)₂][ClO₄] ( 3 ) and [Ag(cgn)][NO₃] ( 4 ) were obtained from aqueous solutions of the corresponding silver salts and cyanoguanidine. The crystal structures of 1 and 2 have been determined by single crystal X‐ray diffraction. 1 : Space group P1¯, Z = 2, cell constants at —65 °C: a =618.18(3), b = 761.49(8), c = 971.2(1) pm; α = 93.56(1), β = 97.439(8), γ = 97.376(9)β; R₁ = 0.0218 2 : Space group P1¯, Z = 2, cell constants at —65 °C: a = 549.79(9), b = 958.17(17), c = 1121.04(12) pm; α = 90.026(13), β = 102.520(11), γ = 95.937(14)°; R₁ = 0.0283.     

Synthesis of SiO2/Y2O3:Eu core-shell materials and hollow spheres

The SiO₂/Y₂O₃:Eu core-shell materials and hollow spheres were first synthesized by a template-mediated method. X-ray diffraction patterns indicated that the broadened diffraction peaks result from nanocrystals of Y₂O₃:Eu shells and hollow spheres. X-ray photoelectron spectra showed that the Y₂O₃:Eu shells are linked with silica cores by Si-O-Y chemical bond. SEM and TEM observations showed that the size of SiO₂/Y₂O₃:Eu core-shell structure is in the range of 140-180 nm, and the thickness of Y₂O₃:Eu hollow spherical shell is about 20-40 nm. The photoluminescence spectra of SiO₂/Y₂O₃:Eu core-shell materials and Y₂O₃:Eu hollow spheres have better red luminescent properties, and the broadened emission bands came from the size effects of nanocrystals composed of Y₂O₃:Eu shell.     

A redox-hydrothermal route to β-MnO2 hollow octahedra

Beta-Manganese dioxides' (β-MnO₂) hollow octahedra have been prepared by a synergetic redox reaction using cuprous chloride (CuCl) and hydrochloric acid (HCl) as reductants and potassium permanganate (KMnO₄) as oxidant through a hydrothermal route. During the process, the self-generated chlorine (Cl₂) gas bubbles and HCl's etching appear to be necessary for the formation of MnO₂ hollow structure. The catalytic efficiency of the prepared β-MnO₂ hollow octahedra was high which has been demonstrated by the catalytic oxidation of methylene blue (MB) dye in the presence of hydrogen peroxide (H₂O₂) under natural light.     

Enhanced specific energy of silver-doped MnO2/graphene oxide electrodes as facile fabrication symmetric supercapacitor device

The present work is about the preparation of silver (Ag)-doped manganese oxide (MnO₂)/graphene oxide (GO) composite thin films are deposited by a facile and binder-free successive ionic layer adsorption and reaction (SILAR) method for the first time. The Brunauer-Emmett-Teller (BET) study revealed the nanosheets of MnO₂–Ag3/GO exhibit high specific surface area of 192 m² g^?1. The tailored flower-like morphology and interconnected nanosheets of MnO₂–Ag3/GO electrodes achieved high electrochemical performance. The maximum specific capacitance (Cs) of 877 F g^?1 at the scan rate of 5 mV s^?1 is obtained for MnO₂–Ag3/GO electrode tested in 1 M sodium sulfate (Na₂SO₄) electrolyte with capacity retention of 94.57% after 5000 cycling stability. The MnO₂–Ag3/GO composite-based flexible solid state symmetric supercapacitor (FSS-SSC) device delivered Cs as 164 F g^?1 with specific energy of 57 Wh kg^?1 at specific power of 1.6 kW kg^?1 and capacitive retention of 94% after 10,000 cycles.     

Synthesis of β-ketophosphonates with electron rich β-aryl groups as useful organophosphorus reagents in lignans synthesis

Investigation of the oxidation reaction of electron rich alkoxy substituted β-aryl β-hydroxyphosphonates to corresponding β-ketophosphonates, which may be utilized in syntheses of lignans with various oxidizing agents (PCC, PDC, SIBX, CAN, Oxone^®, KMNO₄/SiO₂, KMnO₄/MS 4 Å, KMnO₄/CuSO₄, KMnO₄/CuSO₄/Al₂O₃, MnO₂, CrO₃/SiO₂, H₂O₂/salen) is described. The effect of oxidants and reaction conditions on the reaction efficiency and yield was also investigated.     

Seed‐Mediated Growth of Silver Nanocubes in Aqueous Solution with Tunable Size and Their Conversion to Au Nanocages with Efficient Photothermal Property

Two seed‐mediated approaches for the growth of silver nanocubes in aqueous solution have been developed. Addition of a silver‐seed solution to a mixture of cetyltrimethylammonium chloride (CTAC), silver trifluoroacetate, and ascorbic acid and heating the solution at 60 °C for 1.5 h produces uniform Ag nanocubes with tunable sizes from 23 to 60 nm by simply adjusting the volume of silver‐seed solution introduced. Alternatively, the silver‐seed solution can be injected into a mixture of cetyltrimethylammonium bromide (CTAB), silver nitrate, copper sulfate, and ascorbic acid and heated to 80 °C for 2 h to generate 46 nm silver nanocubes. Plate‐like Ag nanocrystals exposing {111} surfaces can be synthesized by reducing Ag(NH₃)₂⁺ with ascorbic acid in a CTAC solution. Relatively large Ag nanocubes were converted to cuboctahedral Au/Ag and Au nanocages and nanoframes with empty {111} faces through a galvanic replacement reaction. The nanocages showed a progressive plasmonic band red‐shift with increasing Au content. The nanocages exhibited high and stable photothermal efficiency with solution temperatures quickly reaching beyond 100 °C when irradiated with an 808 nm laser for large heat and water vapor generation.     

Synthesis of binary polyelectrolyte/inorganic composite capsules of micron size

Different approaches for the synthesis of binary polyelectrolyte/inorganic layered composite capsules of micron size are described. As the polyelectrolyte part of the composite, a poly(styrene sulfonate)/poly(allylamine hydrochloride) complex was taken; the inorganic component was composed of magnetic nanoparticles (Fe₃O₄, CoFe₂O₄, MnFe₂O₄, ZnFe₂O₄), insulator nanoparticles (rare-earth fluorides) or metal nanoparticles (Ag). An inner inorganic layer was formed inside the hollow polyelectrolyte capsule via chemical or photochemical reaction in a spatially restricted capsule volume. The inorganic nanophase synthesized was characterized by transmission electron microscopy, scanning electron microscopy, and wide angle X-ray scattering techniques and weakly crystallized particles 6–9 nm in diameter were detected, presumably attached to the inner side of the capsule shell. Polyelectrolyte capsules filled with ferrite (magnetite) particles possess substantial magnetic activity and are easily manipulated in water solution by an external magnetic field.     

MnO2/graphene oxide: A highly efficient catalyst for imine synthesis from alcohols and amines

α‐MnO₂ nanocrystals supported on graphene oxide (α‐MnO₂/GO) was prepared through a soft chemical route and evaluated for the first time as a novel, eco‐friendly and efficient catalyst in the coupling reaction of alcohols and amines to imines. The well‐organized α‐MnO₂/GO was characterized using various techniques. The results show that MnO₂ nanocrystals are highly dispersed on the GO sheets and interconnected with each other, leading to large available surface area, which greatly enhances the catalytic performance of conventional MnO₂. Under mild conditions, the catalyst exhibits excellent catalytic activity and selectivity with O₂ serving as terminal oxidant. Various imines can be smoothly obtained in good to excellent yield. Importantly, the catalyst is easily recovered and can be reused six times with no significant loss of activity.     

Solubility‐Parameter‐Guided Solvent Selection to Initiate Ostwald Ripening for Interior Space‐Tunable Structures with Architecture‐Dependent Electrochemical Performance

Despite significant advancement in preparing various hollow structures by Ostwald ripening, one common problem is the intractable uncontrollability of initiating Ostwald ripening due to the complexity of the reaction processes. Here, a new strategy on Hansen solubility parameter (HSP)‐guided solvent selection to initiate Ostwald ripening is proposed. Based on this comprehensive principle for solvent optimization, N,N‐dimethylformamide (DMF) was screened out, achieving accurate synthesis of interior space‐tunable MoSe₂ spherical structures (solid, core–shell, yolk‐shell and hollow spheres). The resultant MoSe₂ structures exhibit architecture‐dependent electrochemical performances towards hydrogen evolution reaction and sodium‐ion batteries. This pre‐solvent selection strategy can effectively provide researchers great possibility in efficiently synthesizing various hollow structures. This work paves a new pathway for deeply understanding Ostwald ripening.