Thermal and pH Dual Responsive Copolymer and Silver Nanoparticle Composite for Catalytic Application

N‐Isopropylacrylamide and vinyl imidazole copolymer, P(NIPAM‐co‐VI), was synthesized by free radical emulsion polymerization. Then, the copolymer and silver nanoparticle composite, P(NIPAM‐co‐VI)‐Ag, was prepared by in situ reduction of AgNO₃ with NaBH₄. Due to the coexistence of thermal‐responsive PNIPAM and pH‐responsive PVI, P(NIPAM‐co‐VI) and P(NIPAM‐co‐VI)‐Ag exhibited both thermal and pH responsibility, their size would change while altering the temperature or pH of the circumvent. Their thermal and pH dual responsive properties were studied by dynamic light scattering (DLS). P(NIPAM‐co‐VI)‐Ag could be stably dispersed in water at a pH range from 3.0 to 9.3, which is favorable to use P(NIPAM‐co‐VI)‐Ag as a catalyst in the reduction reaction of p‐nitrophenol. The reaction rate constant (k_app) increased with the decrease of pH or the increase of VI content in the copolymer.     

Mn Oxide‐Silver Composite Nanowires for Improved Thermal Stability,SERS and Electrical Conductivity

Redox transformation reaction between aqueous AgNO₃ and Mn(CH₃COO)₂ at low temperature (～80 °C) has been adopted for industrial‐scale production of uniform Ag–MnOOH composite nanowires for the first time. Varying amounts of incorporated Ag in the composite retain the 1D morphology of the composite. Nanowires upon annealing evolve Ag–MnO₂ nanocomposites, once again with the retention of the parental morphology. Just 4 % of silver incorporation in the composite demonstrates metal‐like conducting performance from the corresponding semiconducting material. Transition of MnO₂ to Mn₂O₃ to Mn₃O₄ takes place upon heat treatment in relation to successive increase in Ag concentrations in the nanowires. The composites offer resistance to the observed oxide transformation. This is evidenced from the progressive increase in transition temperature. In situ Raman, ex situ thermal and XRD analysis corroborate the fact. The composite with 12 % Ag offers resistance to the transformation of MnO₂, which is also verified from laser heating. Importantly, Ag nanoparticle incorporation is proved to offer a thermally stable and better surface enhanced Raman scattering (SERS) platform than the individual components. Both the Ag–MnOOH and Ag–MnO₂ nanocomposites with 8 atomic % Ag show the best SERS enhancement (enhancement factor ～10¹⁰). The observed enhancement relates to charge transfer as well as electromagnetic effects.     

Electrodeposition of Silver Nanoparticles on MWCNT Film Electrodes for Hydrogen Peroxide Sensing

Silver （Ag） nanoparticles were directly electrodeposited on multi-walled carbon nanotubes （MWCNT） in AgNO3/LiNO3 containing EDTA （ethylenediaminetetraacetic acid）. The structure and nature of the resulting Ag/MWNT composite were characterized by field emission scanning electron microscopy （FE-SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）, and the distribution shape of Ag nanoparticles was found to be dependent on the presence of EDTA. The modified electrode showed excellent electrocatalytic activity to redox reaction of hydrogen peroxide and the mechanism of hydrogen peroxide was partly reversible procession with oxidation and reduction peaks at 0.77 and -0.83 V, respectively. The oxidation and reduction peak currents were linearly related to hydrogen peroxide concentration in the range of 1×10^-6-3×10^-4 and 1 ×10^-8-7× 10^-4 mol·L^-1 with correlation coefficients of 0.996 and 0.986, and 3s-detection limit of 9 × 10^-7 and 7 × 10^-9 mol·L^-1.     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

Polyacrylamide/reduced graphene oxide-Ag nanocomposite as highly efficient antibacterial transparent film

In this study, preparation and characterization of polyacrylamide/reduced graphene oxide-Ag (PAM/rGO-Ag) nanocomposites as a new nanocomposite film were investigated. First, PAM/GO nanocomposite was synthesized by in situ polymerization strategy. Afterward, highly stable and uniformly distributed silver nanoparticles (Ag NPs) have been obtained with PAM/GO nanocomposite as nanoreactors via in situ reduction of silver nitrate (AgNO₃) using sodium borohydride (NaBH₄) as reducing agent. In addition, the prepared PAM/rGO-Ag nanocomposite was thermally annealed in order to achieve high-performance nanocomposite film with antimicrobial activities. The prepared nanocomposite was characterized by XRD, FT-IR, SEM, TEM and TGA. The obtained results demonstrate that the silver nanoparticles were well decorated and dispersed on the graphene oxide nanosheets. In fact, the GO nanosheets and polyacrylamide chains act as a support and stabilize the Ag nanoparticles. Moreover, antimicrobial activities of the films were also examined, and the films containing well-dispersed and stabilized Ag nanoparticles showed outstanding antibacterial activity.     

Preparation and characterization of Ag‐deposited aminosilane‐modified silicate by chemical reduction method

Nanocomposites based on silver (Ag) and organically modified silicate (Ormosil) were prepared by an in situ reduction method, in which silver nitrate, tetraethoxysilane and N‐[3‐(trimethoxysilyl)propyl]diethylenetriamine (ATS) acted as precursor, linker, and colloidal suspension stabilizer, respectively. The objective of the study was to produce silver nanoparticles through AgNO₃ chemical reduction in a continuous media, in which aminosilanes act as superficial modifiers of Ag nanoparticles, inhibiting their growth and preventing aggregation. The physical properties of the Ormosil/Ag composites were examined using NMR, electron spin resonance, scanning electron microscope, transmission electron microscope, and thermal gravimetric analysis spectroscopy, the results of which indicated that Ag was incorporated in the Ormosil matrix after impregnation. The Ag content and surface morphology of the Ormosil/Ag composites depended on the initial concentration of AgNO₃. The antibacterial effects of the Ormosil/Ag composites were assessed by the zone of inhibition and plate‐counting methods, and an excellent antibacterial performance was discovered. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Structure and morphology controllable synthesis of Ag/carbon hybrid with ionic liquid as soft-template and their catalytic properties

Ag/carbon hybrids were fabricated by the redox of glucose and silver nitrate (AgNO₃) in the presence of imidazolium ionic liquid ([C₁₄mim]BF₄) under hydrothermal condition. Monodisperse carbon hollow sub-microspheres encapsulating Ag nanoparticles and Ag/carbon cables were selectively prepared by varying the concentration of ionic liquid. Other reaction parameters, such as reaction temperature, reaction time and the mole ratio of silver nitrate to glucose, play important roles in controlling the structures of the products. The products were characterized by XRD, TEM (HRTEM), SEM, energy-dispersive X-ray spectroscopy (EDX), FTIR spectroscopy and a Raman spectrometer. The possible formation mechanism was proposed. The catalytic property of the hybrid in the oxidation of 1-butanol by H₂O₂ was also investigated.     

A Surfactant‐Encapsulating Polyoxometalate Nanowire Assembly as a New Carrier for Nanoscale Noble‐Metal Catalysts

The loading of noble‐metal nanoparticles (NMNPs) onto various carriers to obtain stable and highly efficient catalysts is currently an important strategy in the development of noble metal (NM)‐based catalytic reactions and their applications. We herein report a nanowire supramolecular assembly constructed from the surfactant‐encapsulating polyoxometalates (SEPs) CTAB‐PW₁₂, which can act as new carriers for NMNPs. In this case, the Ag NPs are loaded onto the SEP nanowire assembly with a narrow size distribution from 5 to 20 nm in diameter; the average size is approximately 10 nm. The Ag NPs on the nanowire assemblies are well stabilized and the over agglomeration of Ag NPs is avoided owing to the existence of well‐arranged polyoxometalate (POM) units in the SEP assembly and the hydrophobic surfactant on the surface of the nanowire assembly. Furthermore, the loading amount of the Ag NPs can be adjusted by controlling the concentration of the AgNO₃ aqueous solution. The resultant Ag/CTAB‐PW₁₂ composite materials exhibit high activity and good stability for the catalytic reduction of 4‐nitrophenol (4‐NP) with NaBH₄ in isopropanol/H₂O solution. The NMNPs‐loaded SEP nanoassembly may represent a new composite catalyst system for application in NM‐based catalysis.     

Effect of Chemical Charging/Discharging on Plasmonic Behavior of Silver Metal Nanoparticles Prepared using Citrate‐Stabilized Cadmium Selenide Quantum Dots

The thermodynamics and kinetics of the chemical and electrochemical charging of a catalyst surface are very important to understand its applicability as a catalyst material, particularly in redox catalysis. Through the present study, we hereby communicate the results obtained from our detailed investigations related to the effect of chemical charging on the plasmonic behavior of silver metal nanoparticles (Ag MNPs) as redox catalysts. Two different batches of Ag MNPs were prepared through thermally assisted chemical reduction of silver ions. The difference in these batches was the use or not of citrate‐capped cadmium selenide quantum dots (Q‐CdSe) for the reduction of solution‐phase silver ions to their colloidal plasmonic phase. The charge on the surfaces of the Ag MNPs was varied by the chemical electron injection method by using BH₄^? ions from a NaBH₄ solution. The processes of charging and discharging were monitored by using UV/Vis absorption spectroscopy. The impact of the concentration of the reductant on the charging and discharging processes was also investigated. The Ag MNPs were also tested for their voltammetric response, wherein it was observed that it was more difficult to oxidize the Ag MNPs prepared with Q‐CdSe seeds than to oxidize Ag MNPs prepared without Q‐CdSe particles. Our results demonstrate that Q‐CdSe seeds not only enhance the redox catalytic activity of Ag MNPs but also provide stability towards polarization of their plasmonic behavior.     

Li4Ti5O12/(Ag+C)电极材料的固相合成及电化学性能

以Li₂CO₃,TiO₂为原料,葡萄糖为碳源,采用固相煅烧工艺合成了亚微米级的Li₄Ti₅O₁₂/C复合负极材料。并将之与AgNO₃复合,采用固相方法制备出了Ag表面修饰的Li₄Ti₅O₁₂/(Ag+C)复合材料。采用XRD、SEM和TEM测试方法对材料的微结构进行了表征。结果表明,C的存在对Ag单质在Li₄Ti₅O₁₂/C颗粒表面的大量形成起到了积极的促进作用,从而很大程度地提高了Li₄Ti₅O₁₂/C的电导率,因此有效地改善了其电化学性能。在1C倍率下,Li₄Ti₅O₁₂/(Ag+C)复合材料的首次放电容量达到了164 mAh·g^-1。     

High catalytic activity of a new Ag phosphorus ylide complex supported on montmorillonite: synthesis,characterization, and application for room temperature nitro reduction

In this work, the phosphorus ylide, [PPh₃CHC(O)CH₂Cl], was reacted with AgNO₃ to give the [Ag{C(H)PPh₃C(O)CH₂Cl}₂]⁺NO₃ ^? as the product. Then, it was supported on the modified montmorillonite nanoclay to prepare a new catalyst for the reduction reaction. The structure and morphology of the nanoclay catalyst were characterized by FT-IR, X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray analysis and transmission electron microscopy techniques; also, the content of silver was obtained by inductively coupled plasma analyzer. This composition was exploited to study its catalytic activity in the reduction in aromatic nitro compounds; it displayed the high catalytic activity. Factors such as catalyst amount, solvent, temperature and reaction time were all systematically investigated to elucidate their effects on the yield of catalytic reduction in nitroarenes. This catalytic system exhibited high activity toward aromatic nitro compounds under mild conditions. The catalyst was reused five times without any significant loss in its catalytic activity.     

Ag/PANI/Fe_2O_3复合纳米粒子的合成与催化性能

借助于PANI的还原性质,PANI/Fe2O3复合载体与AgNO3发生表面氧化还原反应,合成了Ag/PANI/Fe2O3复合纳米粒子。TEM和XRD结果表明,立方晶系纳米银的平均粒径10nm。FTIR结果表明,Ag与PANI及Fe2O3复合载体之间不存在化学键合作用,但由于PANI与Ag之间的电子相互作用,Ag/PANI/Fe2O3复合纳米粒子的FTIR吸收峰发生蓝移。Ag/PANI/Fe2O3复合纳米粒子对于间硝基苯磺酸钠的硼氢化钠还原反应表现出良好的催化活性,30min内间硝基苯磺酸钠的转化率达到86.77%。     

Method for Visible Light‐Induced Photocatalytic Degradation of Methylparaben in Water Using Nanostructured Ag/AgBr@m‐WO3

An efficient method of photocatalytic degradation of methylparaben in water using Ag nanoparticles (NPs) loaded AgBr‐mesoporous‐WO₃ composite photocatalyst (Ag/AgBr@m‐WO₃), under visible light is presented. In this process, quantification of methylparaben in water was carried out by high‐performance liquid chromatography (HPLC) and the HPLC results showed a significant reduction of methylparaben in water due to the enhanced of photocatalytic degradation efficiency of Ag/AgBr@m‐WO₃. For the material synthesis, highly ordered mesoporous‐WO₃ (m‐WO₃) was initially synthesized by sol–gel method and AgBr nanoparticles (NPs) were subsequently introduced in the pores of m‐WO₃, and finally, the Ag nanoparticles were introduced by light irradiation. The enhanced photocatalytic degradation of methylparaben in water is attributed to the formation of surface plasmonic resonance (SPR) due to the introduction of Ag NPs on the surface of the catalyst. Also, the formation of heterojunction between AgBr and mesoporous‐WO₃ in Ag/AgBr@m‐WO₃ significantly inhibited the recombination of light‐induced electron‐hole pairs in the semiconductor composite. The morphological and optical characterizations of the synthesized photocatalysts (Ag/AgBr@m‐WO₃) were carried out using SEM, TEM, XDR, N₂ adsorption–desorption, UV‐VIS diffuse reflectance spectroscopy (DRS). Also, the photocatalytic studies using radical scavengers were carried out and the results indicated that ${\text{O}}_2^{·-}$ is the main reactive species.     

Silver supported on Co3O4 modified carbon as electrocatalyst for oxygen reduction reaction in alkaline media

The electroreduction of oxygen was firstly studied on Ag/Co₃O₄–C in alkaline media prepared by depositing Ag on Co₃O₄ modified carbon (Co₃O₄–C). The Ag/Co₃O₄–C composite not only displayed relatively large electrochemical active surface area (ESA), high catalytic activity towards oxygen reduction reaction (ORR), but also exhibited good methanol tolerance and stability in alkaline media. Ag/Co₃O₄–C could be a valuable catalyst for ORR and be applied to alkaline fuel cells and metal–air batteries.     

N-Heterocycle (tetrazole)-stabilized pseudocyclic λ3-iodane: Synthesis and reactivity

An N-heterocycle (tetrazole)-stabilized pseudocyclic λ³-iodane was synthesized and its thermal stability and redox activity were studied. Simultaneous thermogravimetric analysis and differential scanning calorimetry revealed that the polyvalent iodine compound started to degrade at 127 °C and showed a notable exothermic decomposition peak at 147 °C, which was markedly more pronounced than the parent tetrazole with monovalent iodine. The reduction potential was determined by cyclic voltammetry to be ?0.38 V vs AgNO₃|Ag in dimethyl sulfoxide at a scan rate of 0.02 V/s. The oxidative power of the polyvalent iodine compound was demonstrated by conducting oxidation of thioanisole to sulfoxide and oxidative dimerization of thiobenzamide to 3,5-diphenyl-1,2,4-thiadiazole.     

Synthesis of Zwitterionic Cobaltocenium Borate and Borata‐alkene Derivatives from a Borole‐Radical Anion

Chemical single‐electron reduction of 1‐mesityl‐2,3,4,5‐tetraphenylborole ( 3 ) gave a stable radical anion [CoCp*₂][ 3 ] as shown in earlier investigations. Herein, we present the reaction of [CoCp*₂][ 3 ] with the 2,2,6,6‐tetramethylpiperidine‐N‐oxyl radical (TEMPO), a common radical trap. Instead of radical recombination, the reaction proceeds through a redox pathway involving oxidation of the borole radical anion combined with reduction of TEMPO. This electron‐transfer process is accompanied by a deprotonation reaction of the cobaltocenium counterion by the base TEMPO^? to give TEMPO‐H and a neutral cobalt(I) fulvene complex ( 7 ). The latter was not observed directly during the reaction, because it instantaneously reacts as a nucleophile attacking at the boron center of the in situ generated borole 3 to give the borate 6 . However, 7 was synthesized independently by deprotonation of [CoCp*₂][PF₆]. In addition, the obtained zwitterionic cobaltocenium borate 6 undergoes a photolytic rearrangement to form the borata‐alkene derivative 9 that thermally transforms to the chiral cobaltocenium borate 12 . Our investigations are based on spectroscopic evidence, X‐ray crystallography, elemental analysis, as well as DFT calculations.     

Preparation and antibacterial activity of electrospun chitosan/poly(ethylene oxide) membranes containing silver nanoparticles

Fairly uniform chitosan (CS)/poly(ethylene oxide) (PEO) ultrafine fibers containing silver nanoparticles (AgNPs) were successfully prepared by electrospinning of CS/PEO solutions containing Ag/CS colloids by means of in situ chemical reduction of Ag ions. The presence of AgNPs in the electrospun ultrafine fibers was confirmed by X-ray diffraction patterns. The AgNPs were evenly distributed in CS/PEO ultrafine fibers with the size less than 5 nm observed under a transmission electron microscope. X-ray photoelectron spectroscopy suggested that the existence of Ag―O bond in the composite ultrafine fibers led to the tight combination between Ag and CS. Evaluation of antimicrobial activities of the electrospun Ag/CS/PEO fibrous membranes against Escherichia coli showed that the AgNPs in the ultrafine fibers significantly enhanced the inactivation of bacteria.     

Doping Sumanene with Both Chalcogens and Phosphorus(V): One‐Step Synthesis,Coordination, and Selective Response Toward AgI

Heterasumanenes 4 – 6 containing chalcogen (S, Se, and Te) and phosphorus atoms have been synthesized in a one‐pot reaction from trichalcogenasumanenes 1 – 3 by replacing one chalcogen atom with a P=S unit. The P=S unit makes 4 – 6 almost planar and shrinks the HOMO–LUMO gap as compared to 1 – 3 . The bonding between Ag⁺ and S atom on P=S brings about a distinct change to the optical properties of 4 – 6 ; 4 in particular shows a selective fluorescence response toward Ag⁺ with LOD of 0.21 μm . Compounds 4 – 6 form complexes with AgNO₃ to be ( 4 )₂?AgNO₃, ( 5 )₂?AgNO₃, and ( 6 )₂?(AgNO₃)₃. In complexes, the coordination between Ag⁺ and P=S is observed, which leads to shrinkage of C?P and C?X (X=S, Se, Te) bond lengths. As a result, 4 , 5 , and 6 are all bowl‐shaped in complexes with bowl‐depths reaching to 0.66 Å, 0.42 Å, and 0.40 Å, respectively. There are Ag?Te dative bonds between Ag⁺ and Te atom on telluorophene in ( 6 )₂?(AgNO₃)₃.     

Doping Sumanene with Both Chalcogens and Phosphorus(V): One‐Step Synthesis,Coordination, and Selective Response Toward AgI

Heterasumanenes 4 – 6 containing chalcogen (S, Se, and Te) and phosphorus atoms have been synthesized in a one‐pot reaction from trichalcogenasumanenes 1 – 3 by replacing one chalcogen atom with a P=S unit. The P=S unit makes 4 – 6 almost planar and shrinks the HOMO–LUMO gap as compared to 1 – 3 . The bonding between Ag⁺ and S atom on P=S brings about a distinct change to the optical properties of 4 – 6 ; 4 in particular shows a selective fluorescence response toward Ag⁺ with LOD of 0.21 μm . Compounds 4 – 6 form complexes with AgNO₃ to be ( 4 )₂?AgNO₃, ( 5 )₂?AgNO₃, and ( 6 )₂?(AgNO₃)₃. In complexes, the coordination between Ag⁺ and P=S is observed, which leads to shrinkage of C?P and C?X (X=S, Se, Te) bond lengths. As a result, 4 , 5 , and 6 are all bowl‐shaped in complexes with bowl‐depths reaching to 0.66 Å, 0.42 Å, and 0.40 Å, respectively. There are Ag?Te dative bonds between Ag⁺ and Te atom on telluorophene in ( 6 )₂?(AgNO₃)₃.     

The enhancement of oxygen flux on Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) hollow fibers using silver surface modification

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) hollow fibers were fabricated using a phase inversion/sintering method. As oxygen permeation of BSCF hollow fibers is controlled by the rate surface exchange kinetics, catalytic Ag particles were coated on both inner and outer surfaces using chemical deposition method, as verified by SEM and EDX. The Ag coated BSCF membranes showed up to 100% increase in oxygen permeation at 700 °C, and improvements lower than 10% were measured at 950 °C as compared with unmodified membranes. It was found that Ag catalyst surface loading was non-homogenous and concentrated on the perovskite grain boundaries. As a result, lighter Ag surface loading delivered improved oxygen flux while oxygen flux reached a maximum even though in the presence of excess catalyst loading. The catalytic activity of Ag was beneficial in enhancing surface reaction kinetics up to 850 °C attributed to the spillover effect. Above this temperature, the increase in oxygen permeation rate was marginally diminished due to the reduction of the spillover effect.