Redox Sorption and Recovery of Silver Ions as Silver Nanocrystals on Poly(aniline‐co‐5‐sulfo‐2‐anisidine) Nanosorbents

Poly[aniline(AN)‐co‐5‐sulfo‐2‐anisidine(SA)] nanograins with rough and porous structure demonstrate ultrastrong adsorption and highly efficient recovery of silver ions. The effects of five key factors—AN/SA ratio, Ag^I concentration, sorption time, ultrasonic treatment, and coexisting ions—on Ag^I adsorbability were optimized, and AN/SA (50/50) copolymer nanograins were found to exhibit much stronger Ag^I adsorption than polyaniline and all other reported sorbents. The maximal Ag^I sorption capacity of up to 2034 mg g^?1 (18.86 mmol g^?1) is the highest thus far and also much higher than the maximal Hg‐ion sorption capacity (10.28 mmol g^?1). Especially at ≤2 mM Ag^I, the nanosorbents exhibit ≥99.98 % adsorptivity, and thus achieve almost complete Ag^I sorption. The sorption fits the Langmuir isotherm well and follows pseudo‐second‐order kinetics. Studies by IR, UV/Vis, X‐ray diffraction, polarizing microscopy, centrifugation, thermogravimetry, and conductivity techniques showed that Ag^I sorption occurs by a redox mechanism mainly involving reduction of Ag^I to separable silver nanocrystals, chelation between Ag^I and ? NH? /? N?/? NH₂/ ? SO₃H/? OCH₃, and ion exchange between Ag^I and H⁺ on ? SO₃^?H⁺. Competitive sorption of Ag^I with coexisting Hg, Pb, Cu, Fe, Al, K, and Na ions was systematically investigated. In particular, the copolymer nanoparticles bearing many functional groups on their rough and porous surface can be directly used to recover and separate precious silver nanocrystals from practical Ag^I wastewaters containing Fe, Al, K, and Na ions from Kodak Studio. The nanograins have great application potential in the noble metals industry, resource reuse, wastewater treatment, and functional hybrid nanocomposites.     

A novel route to in‐situ incorporation of silver nanoparticles into supramolecular hydrogel networks

A novel strategy was developed for the in situ incorporation of silver nanoparticles into the supramolecular hydrogel networks, in which colloidally stable silver hydrosols were firstly prepared in the presence of an amphiphilic block copolymer of poly(oxyethylene)‐poly(oxypropylene)‐poly(oxyethylene) and then mixed with aqueous solution of α‐cyclodextrin. The analyses from rheology, X‐ray diffraction, and scanning electron microscopy confirmed the formation of the supramolecular‐structured hydrogels hybridized with silver nanoparticles. In particular, the colloidal stability of the resultant silver hydrosol and its gelation kinetics in the presence of α‐cyclodextrin as well as the viscoelastic properties of the resultant hybrid hydrogel were investigated under various concentrations of the used block copolymer. It was found that the used block copolymer could act not only as the effective reducing and stabilizing agents for the preparation of the silver hydrosol but also as the effective guest molecule for the supramolecular self‐assembly with α‐cyclodextrin. In addition, the effects of silver nanoparticles on the gelation process and the hydrogel strength were also studied. Such a hybrid hydrogel material could show a good catalytic activity for the reduction of methylene blue dye by sodium borohydride. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 740–749, 2009     

PdAg2 nanoparticles in aqueous solution: Preparation, characterization, and catalytic properties

The reduction of a heterobimetallic complex, Pd(OOCMe)₄Ag₂(HOOCMe)₄, with hydrogen or sodium borohydride in an aqueous solution produces PdAg₂ nanoparticles of an alloy or intermetallic type. It is shown that the catalytic activity of the particles in the reduction of methyl viologen with hydrogen is lower than that of palladium nanoparticles of the same size. Therewith, ??borohydride?? nanoparticles manifest a higher catalytic activity than do ??hydrogen?? ones. Unlike silver nanoparticles, PdAg₂ nanoparticles do not catalyze the decomposition of hydrazine.     

AgPt nanoparticles supported on magnetic graphene oxide nanosheets for catalytic reduction of 4‐nitrophenol: Studies of kinetics and mechanism

Ag_x Pt_100−x (x  = 0, 25, 50, 75 and 100) nanoparticles were grown on the surface of magnetic graphene oxide nanosheets (Fe₃O₄@GO) for the first time. The as‐prepared nanocomposites were characterized using various techniques such as Fourier transform infrared spectroscopy, powder X‐ray diffraction, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller surface area analysis, vibrating sample magnetometry and thermogravimetric analysis. The Fe₃O₄@GO‐Ag_x Pt_100−x catalysts were applied in the reduction of 4‐nitrophenol (4‐NP) to 4‐aminophenol using sodium borohydride (NaBH₄). The synthesized nanocomposites exhibited excellent catalytic performance in the reduction of 4‐NP with high recyclability for five consecutive runs. The Fe₃O₄@GO‐Ag₇₅Pt₂₅ nanocomposite exhibited the best catalytic activity with a rate constant as high as 140.6 × 10⁻³ s⁻¹. The obtained kinetic data were modelled with the Langmuir–Hinshelwood equation. The energy of activation and thermodynamic parameters including enthalpy, entropy of activation and activation Gibbs free energy were calculated.     

Facile preparation of metal nanoparticle‐coated polystyrene beads by catechol conjugated polymer

A universal method to modify polystyrene beads (PSBs) is proposed, using the 2‐chloro‐3′,4′‐dihydroxyacetophenone (CCDP) quaternized to poly(ethylene glycol)‐g‐poly(dimethylaminethyl methacrylate) [PEG‐g‐PDMA, QC‐PEG]. In the study, CCDP of QC‐PEG is adhered onto PSBs under alkali condition, where polyvinyl pyrrolidone (PVP) has been added as stabilizer. The surface modified PSBs with QC‐PEG (QC‐PSBs) have been functionalized, by depositing silver nanoparticles (Ag‐PSBs) as antimicrobial, iron oxide nanoparticles (Fe‐PSBs) as magnet, and TiO₂ nanoparticles (Ti‐PSBs) as photo‐catalyst. Modification and functionalization of the obtained PSBs have been rectified by microscopy and spectroscopy investigations, including scanning electron microscope, X‐ray photoelectron microscope, and UV–vis spectrometer. The functionalized Ag‐PSBs show outstanding antimicrobial activities against gram‐positive and gram‐negative bacteria, due to their containing silver nanoparticles; while significant photo‐catalytic behavior was found against methylene blue, after depositing TiO₂ nanoparticles. The proposed universal modified PSBs will make a strong contribution in different fields, as a functional material. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly Efficient Visible Light Plasmonic Photocatalyst Ag@Ag(Br,I)

The new plasmonic photocatalyst Ag@Ag(Br,I) was synthesized by the ion‐exchange process between the silver bromide and potassium iodide, then by reducing some Ag⁺ ions in the surface region of Ag(Br,I) particles to Ag⁰ species. Ag nanoparticles are formed from Ag(Br,I) by the light‐induced chemical reduction reaction. The Ag@Ag(Br,I) particles have irregular shapes with their sizes varying from 83 nm to 1 μm. The as‐grown plasmonic photocatalyst shows strong absorption in the visible light region because of the plasmon resonance of Ag nanoparticles. The ability of this compound to reduce Cr^VI under visible light was compared with those of other reference photocatalyst. The plasmonic photocatalyst is shown to be highly efficient under visible light. The stability of the photocatalyst was examined by X‐ray diffraction and X‐ray photoelectron spectroscopy. The XRD pattern and XPS spectra prove the stability of the plasmonic photocatalyst Ag@Ag(Br,I).     

Catalysis of the Reduction of Silver Ions by Ag2S Nanoparticles

Silver sulfide nanoparticles were found to catalyze the reduction of Ag⁺ ions by sodium sulfite and hydroquinone. The change in the absorption spectrum of the reaction mixtures was studied. New bands were found to arise at 403, 415, and 426 nm depending on the reaction conditions. These bands were identified as plasmon bands of metallic silver nanoparticles. The kinetics of this process was determined under various conditions and Ag₂S nanoparticles were found to be a highly active catalyst.     

In situ formation of silver nanoparticles within an amphiphilic graft copolymer film

Silver nanoparticles were prepared by UV irradiation from silver salts, such as AgBF₄ or AgNO₃, when dissolved in an amphiphilic film of poly((oxyethylene)₉ methacrylate)‐graft‐poly((dimethyl siloxane)_n methacrylate), POEM‐g‐mPDMS. The in situ formation of silver nanoparticles in the graft copolymer film was confirmed by transmission electron microscopy (TEM), UV‐visible spectroscopy, and wide angle X‐ray scattering (WAXS). The results demonstrated that the use of AgBF₄ yielded silver nanoparticles with a smaller size (～5 nm) and narrower particle distribution when compared with AgNO₃. The formation of silver nanoparticles was explained in terms of the interaction strength of the silver ions with the ether oxygens of POEM, as revealed by differential scanning calorimetry (DSC) and X‐ray photoelectron spectroscopy (XPS). It was thus concluded that a stronger interaction of silver ions with the ether oxygens results in a more stable formation of silver nanoparticles, which produces uniform and small‐sized nanoparticles. DSC and small angle X‐ray scattering (SAXS) data also showed the selective incorporation and in situ reduction of the silver ions within the hydrophilic POEM domains. Excellent mechanical properties of the nanocomposite films (3–5 × 10⁵ dyn/cm²) were observed, mostly because of the confinement of silver nanoparticles in the POEM chains as well as interfaces created by the microphase separation of the graft copolymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1283–1290, 2007     

Colloidal copper and peculiarities of its reaction with silver ions in aqueous solution

Interactions between colloidal copper and silver ions lead to the formation of silver nanoparticles. The reaction proceeds through the intermediate stage of the formation of a copper-silver contact pair. The formation of bimetallic Ag_coreCu_shell nanoparticles is observed in the presence of the “seeding” silver nanoparticles and upon the simultaneous radiochemical reduction of Ag⁺ and Cu²⁺ ions.     

Size effects of PtcoreAgshell and AgcorePtshell nanoparticles on their catalytic activity in aqueous solutions

Platinum colloids in an aqueous solution catalyze the reduction of silver ions by hydrogen to form Pt-Ag core-shell bimetallic nanoparticles. In the presence of the silver nanoparticles, Pt^II ions are reduced by hydrogen to form Ag_corePt_shell nanoparticles. The effect of the structure and composition of the nanoparticles on the ability of platinum to catalyze the one-electron reduction of methyl viologen by hydrogen in an aqueous solution was studied. For the Pt_coreAg_shell nanoparticles, an induction period preceding the start of the reaction was found. The thicker the silver shell on platinum, the longer the lag time of the reaction, which is probably due to a decrease in the rate of hydrogen transfer to the platinum core. For the Ag_corePt_shell nanoparticles, the size effect was revealed: at the shell thickness less than 1 nm (～4 atomic layers of platinum), platinum loses the ability to catalyze the reaction. The mechanism of the catalytic process is discussed.     

Ultrafine Au and Ag Nanoparticles Synthesized from Self‐Assembled Peptide Fibers and Their Excellent Catalytic Activity

The self‐assembly of an amphiphilic peptide molecule to form nanofibers facilitated by Ag⁺ ions was investigated. Ultrafine AgNPs (NPs=nanoparticles) with an average size of 1.67 nm were synthesized in situ along the fibers due to the weak reducibility of the ‐SH group on the peptide molecule. By adding NaBH₄ to the peptide solution, ultrafine AgNPs and AuNPs were synthesized with an average size of 1.35 and 1.18 nm, respectively. The AuNPs, AgNPs, and AgNPs/nanofibers all exhibited excellent catalytic activity toward the reduction of 4‐nitrophenol, with turnover frequency (TOF) values of 720, 188, and 96 h^?1, respectively. Three dyes were selected for catalytic degradation by the prepared nanoparticles and the nanoparticles showed selective catalysis activity toward the different dyes. It was a surprising discovery that the ultrafine AuNPs in this work had an extremely high catalytic activity toward methylene blue, with a reaction rate constant of 0.21 s^?1 and a TOF value of 1899 h^?1.     

Green Biosynthesis of Silver Nanoparticles Using ‘Polygonum Hydropiper’ and Study its Catalytic Degradation of Methylene Blue

The green synthesis of silver nanoparticles with the small size and high stability paved the way to improve and protect the environment by decreasing the use of toxic chemicals and eliminating biological risks in biomedical applications. Plant mediated synthesis of silver nanoparticles is gaining more importance owing its simplicity, rapid rate of synthesis of nanoparticles and eco-friendliness. In this study, focus on biosynthesis of silver nanoparticles using Polygonum hydropiper extract and its catalytic degradation of hazardous dye, methylene blue has been highlighted. The rapid reduction of silver (Ag) ions was monitored using UV-Visible spectrophotometer and showed formation of silver nanoparticles within less than one hour with maximum absorption of silver nanoparticles at 430 nm. The major functional groups present in the synthesis responsible for the formation of silver nanoparticles. It was identified by using Fourier Transform Infrared spectrophotometer (FTIR). Field Electron Scanning Microscope (FESEM) was used to characterise the nanoparticles synthesized using P.hydropiper. The morphology of silver nanoparticles was predominantly spherical and aggregated into irregular structure with average diameter of 60 nm. In addition, this report emphasizes the effect of the silver nanoparticles on the degradation rate of hazardous dyes by sodium borohydride (NaBH₄). The efficiency of silver nanoparticles as a promising candidate for the catalysis of organic dyes by NaBH₄ through the electron transfer process is established in the present study.     

Smart synthesis of silver nanoparticles supported in porous polybenzoxazine nanocomposites via a main-chain type benzoxazine resin

Novel silver nanoparticles immobilized on macroporous polybenzoxazine nanocomposites were prepared as catalysts for catalytic reduction reaction.     

Preparation of raspberry-like polypyrrole composites with applications in catalysis

Raspberry-like composites were prepared by coating the silver/polypyrrole core/shell composites onto the surface of silica spheres via oxidation polymerization of pyrrole monomer with [Ag(NH₃)₂]⁺ ions as oxidants. The whole process allowed the absence of stabilizers, which greatly improved the quality of the conducting polymer composites. The morphology of the resulting composites was investigated, which can be described as raspberry-like; also, the structure and composition of the composites were characterized in detail. A possible formation mechanism was proposed. The present synthetic strategy substantially extended the scope of metal/conducting polymer composite synthesis. The raspberry-like composites exhibited excellent catalytic properties in the reduction of methylene blue dye with the reducing agent of sodium borohydride.     

A High-Performance Catalytic and Recyclability of Phyto-Synthesized Silver Nanoparticles Embedded in Natural Polymer

The present work deals with phytogenic synthesis of Ag NPs in the natural polymer alginate as support material using Aglaia elaeagnoidea leaf extract as a reducing, capping, and stabilizing agent. Ag nanoparticles embedded in alginate were characterized using UV–Vis absorption spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy techniques and selected area electron diffraction techniques. The formation of AgNPs embedded in the polymer was in spherical shape with an average size of 12 nm range has been noticed. The prepared embedded nanoparticles in polymer were evaluated as a solid heterogeneous catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) and methylene blue to leuco methylene blue in the liquid phase using sodium borohydride (NaBH₄) as reducing agent. The silver nanoparticles embedded polymer exhibited extraordinary catalytic efficacy in reduction of 4-NP to 4-AP and the rate constant is 0.5054 min^?1 at ambient conditions. The catalyst was recycled and reused up to 10 cycles without significant loss of catalytic activity. The preparation of Ag–CA composite was facile, stable, efficient, eco-friendly, easy to recycle, non-toxic, and cost effective for commercial application.     

Synthesis of Copper-Silver Bicomponent Nanoparticles in the Presence of Nitrilotrimethylenephosphonic Acid

Synthesis of stable mixed nanoparticles (SMNs) by chemical co-reduction of copper and silver complexonates with sodium borohydride in an open system with the access of air oxygen was studied for the first time the. Variation of the Cu²⁺ to Ag⁺ molar ratio within 1: (0.05–0.5) enabled targeted formation of differently structured nanoparticles (core-shell type), Cu_coreAg_shell and Ag_coreCu_shell. It was found that, by choosing appropriate synthesis conditions, it is possible to produce oxidation-resistant copper particles protected by a shell of a precious metal or to involve the copper complex of nitrilotrimethylenephosphonic acid in silver reduction. The resulting SMNs may become widely used for obtaining various functional materials.

     

Metallogels Derived from Silver Coordination Polymers of C3‐Symmetric Tris(pyridylamide) Tripodal Ligands: Synthesis of Ag Nanoparticles and Catalysis

By applying a recently developed crystal engineering rationale, four C₃ symmetric tris(pyridylamide) ligands namely 1,3,5‐tris(nicotinamidomethyl)‐2,4,6‐triethylbenzene, 1,3,5‐tris(isonicotinamidomethyl)‐2,4,6‐triethylbenzene, 1,3,5‐tris(nicotinamidomethyl)‐2,4,6‐trimethylbenzene, and 1,3,5‐tris(isonicotinamidomethyl)‐2,4,6‐trimethylbenzene, which contain potential hydrogen‐bonding sites, were designed and synthesized for generating Ag^I coordination polymers and coordination‐polymer‐based gels. The coordination polymers thus obtained were characterized by single‐crystal X‐ray diffraction. The silver metallogels were characterized by transmission electron microscopy (TEM) and dynamic rheology. Upon exposure to visible light, these silver metallogels produced silver nanoparticles (AgNPs), which were characterized by TEM, powder X‐ray diffraction, energy dispersive X‐ray and X‐ray photoelectron spectroscopy. These NPs were found to be effectively catalyzed the reduction of 4‐nitrophenolate to 4‐aminophenolate without the use of any exogenous reducing agent.     

One‐step Hydrothermal Synthesis and Assembly of Copper and Silver Nanoparticles to Aggregates in Glyoxal Reduction System

A simple hydrothermal process has been developed for the synthesis and assembly of copper and silver nanoparticles to aggregates. The reduction of Cu²⁺ and Ag⁺ ions to the zerovalent metal was performed by glyoxal in the absence of any external agent. The produced glyoxylic acid (GA) in the redox process stabi‐ lized metallic copper and silver particles and rendered them oxidation resistant for several months and dispersible in polar organic solvents and water. Detailed nanostructures of synthesized products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The results demonstrated that assembly of nanoparticles to aggregates and their regularity were dependent on the reaction conditions such as temperature and concentration of the starting material. The Ostwald ripening process was proposed to explain the formation of copper nanoparticles by TEM observation at several times during the reaction. The existence of the surface stabilizing agent was identified by Fourier Transform infrared spectroscopy (FT‐IR) and thermogravimetric analyses (TGA).     

Vanadium supported on spinel cobalt ferrite nanoparticles as an efficient and magnetically recoverable catalyst for oxidative degradation of methylene blue

Vanadium supported on spinel cobalt ferrite nanoparticles was synthesized and characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray analysis and transmission electron microscopy. For the first time, the prepared material was used for the catalytic degradation of methylene blue as an organic dye in the presence of hydrogen peroxide as a green oxidant and NaHCO₃ as a co‐reagent at room temperature. The dependency of removal percentage on various parameters such as amount of catalyst, pH, reaction time and temperature and the effect of radical scavenging agents were studied. Finally, recoverability and reusability of the vanadium supported on spinel cobalt ferrite nanoparticles were investigated.     

Synthesis of gold/polydopamine composite surfaces on glass substrates for localized surface plasmon resonance and catalysis

Composite materials of polydopamine (PDA) and gold nanoparticles on glass substrates (Au/PDA@slide) were obtained via a simple chemical process. First, PDA films (PDA@slide) were formed by immersing slides in 20 mg ml⁻¹ dopamine aqueous solution at pH = 8.5 for 1 h. Then, PDA@slide was dipped in 0.02 M chloroauric acid (HAuCl₄) aqueous solution for a certain time, Au/PDA@slide being formed. Gold nanoparticles were obtained by the reductive properties of PDA. The morphology and chemical composition of the composite material were characterized using scanning electron microscopy, X‐ray diffraction and X‐ray photoelectron spectroscopy. The catalytic properties of Au/PDA@slide were evaluated using the reduction of 4‐nitrophenol (4‐NP) in the presence of sodium borohydride (NaBH₄) aqueous solution at room temperature. The catalytic activity of the optimal Au/PDA@slide was so satisfactory that the reduction of 4‐NP was completed within 10 min. Moreover, the Au/PDA@slide composite material was stable up to five cycles without significant loss of its catalytic activity. In addition, Au/PDA@slide also exhibited photocatalytic ability, photodegrading 2.5 ml of 17.5 mg l⁻¹ methyl orange in 100 min. By measuring the UV–visible absorption bands of Au/PDA@slide, it was proved that the condition of the strongest surface plasmon resonance of Au/PDA@slide was the optimal condition for catalytic reduction of 4‐NP.