Encapsulated Ag Nanoparticles Research Articles

Probing variation of the structure and electrical conductivity of functionalized PVA based composite films doped with silver nanoparticles and irradiated by gamma rays

Polyvinyl alcohol/sulfuric acid/ethanol films doped with nano-silver particles are prepared using in-situ chemical reduction method. The as-prepared films are irradiated with gamma rays at dose range 0–50 kGy. The elemental analysis of as-prepared samples using energy dispersive x-ray spectroscopy (EDXS) showed presence of oxygen and silver peaks which refers to the probable formation of silver oxide nano-particle (Ag2O NPs) phase. Moreover, scanning electron microscope (SEM) analysis confirmed that the inserted Ag nanoparticles have regular and uniformly distributed pores within the PVA network. X-ray diffraction (XRD) measurements indicated that of Ag2O and Ag nanoparticles are embedded in the PVA matrix in cubic face-centered structure. Structural variations due to gamma irradiation are also probed by high-resolution transmission electron microscopy (HR-TEM) which displayed that the diameter of encapsulated Ag nanoparticles increases from ∼15 nm up to 34 nm against irradiation dose. The measured dc electrical conductivity results indicated that the thermal activation energy decreased from 0.95 eV to 0.56 eV as a sequence of irradiation dose in the range 0–50 kGy The evaluation of the frequency exponent factor, s, derived from the measured ac conductivity data indicated that correlated barrier hopping (CBH) is the most probable conduction mechanism for the present films. The measured dielectric constants and Cole-Cole diagrams are employed in the analysis of the dependence of the dielectric constant on the irradiation dose.

In situ TEM nanomechanical study on enhanced toughness of graphene-nanoparticle nanocomposite

Although theoretical studies and experimental research have shown outstanding mechanical properties of graphene, its brittleness and low toughness restrict its widespread industrial use. Here, we conducted a study to examine the impact of encapsulated Ag nanoparticles on the mechanical properties of graphene through in situ nanomechanical testing in an aberration-corrected transmission electron microscope (TEM). The presence of Ag nanoparticles was found to decrease crack propagation speed, enabling the TEM observation of crack deflection around the nanoparticles at nanoscale, as well as real-time measurement of the concomitant increase in stress. Using our nanomechanical testing data, we were able to quantitatively estimate the stress intensity factor, which serves as a measurement of fracture toughness for graphene, and then compared our results with previously reported values. We further discuss the role of nanoparticles in the propagation of cracks and their potential to enhance the toughness of materials. These findings have practical implications for the development of high-performance graphene composite materials.

Formation of SiO2-Encapsulated Ag Nanoparticles on SiO2 Nanofibers and Their Application as Robust, Flexible Pressure Sensor Working under High Temperatures

Lightweight, flexible pressure sensors working under high temperatures have intrigued great research interest owing to their potential in firefighting, aerospace technology, and automotive and petroleum industries. Here, we propose a strategy to prepare SiO2 shell-coated Ag nanoparticles on SiO2 nanofiber membranes (SNFs), which prohibit nanoparticle migration and fusion. The reduction treatment of the nanofiber membrane promotes the in situ reduction of AgNO3 into Ag seeds, which further grow as Ag nanoparticles in the following wet-chemical treatment. Then, a protective silica layer is fabricated on the Ag nanoparticles, which effectively prevents the nanoparticles’ migration and fusion; we propose that metal–support interaction (MSI) may help to form the silica coatings on the Ag nanoparticles. The as-formed Ag nanoparticles with a SiO2 coating layer are sinter-resistant and show much higher thermal stability than bare Ag nanoparticles on the nanofibers. The as-assembled pressure sensors using these SNFs as active materials can continuously work at 350 °C without performance decay. After annealing the SNF at 600 °C for 2 h, the SNF can still maintain its performance as a pressure sensor. The high-sensitivity, high-temperature-resistant, and robust SNF may provide a platform for unconventional pressure sensor construction. The strategies used in this study may bring insights into both the design and application of these sinter-resistant nanostructures.

Mineral Content and Antiurolithiatic Analysis of Horse Gram Flour

Macrotyloma Uniflorum is commonly known as horse gram. It is found in India, Africa, Australia, and Srilanka. It is reported to have pharmaceutical applications like antioxidant, anticancer, and anti-diabetic. The present paper provides the information about the utility of horse gram as a cheap source of mineral content with anti-urolithiatic property. The phytochemical analyses were also carried out to determine the presence of secondary metabolites. Horse gram powder contains macro nutrients and micro nutrients. Calcium is the major mineral content followed by potassium. The studies suggest that the utilized natural biomass could be tapped as a source of mineral and carbohydrates. Horse gram seed powder comprises of highest carbohydrate content followed by phenol, sterol, terpenoid, and protein. Bio encapsulated Ag nano particles showed highest dissolution of struvite stones as compared to aqueous and ethanol extracts. Hence it could be suggested as a major ingredient in functional food.

Facile encapsulating Ag nanoparticles into a Tetrathiafulvalene-based Zr-MOF for enhanced Photocatalysis

A facile and efficient synthetic strategy was used to prepare a silver nanoparticles-doped MOF (Ag NPs@Zr-TTFTB, TTFTB = tetrathiafulvalene tetrabenzoate) catalyst. Considering the stability of Zr6 cluster-based MOFs and the confinement of small Ag NPs (below 5 nm), title hybrids can be used for the photocatalytic degradation of sulfamethoxazole (SMZ). The prepared Ag NPs@Zr-TTFTB were found to efficiently remove SMZ (k = 0.009 min−1) and remain active in the wide range of pH values (3.0 ~ 9.0) and four cycles. The leaching amount of Ag and Zr under different pH values were only accounted for 0.18% ~ 0.61% and 0.01% ~ 0.05% of used Ag NPs@Zr-TTFTB, respectively, which indicated its excellent stability. Studies on the catalytic mechanism revealed that the proposed heterostructure of Ag NPs and Zr-TTFTB led to the electron transfer and the generation of active oxygen species, resulting in its remarkable photocatalytic activities.

Antibacterial ultrafiltration membrane with silver nanoparticle impregnation by interfacial polymerization for ballast water

AbstractInterfacial polymerization technology was employed to immobilize silver (Ag) nanoparticles on the surface of commercial polyethersulfone (PES) membrane to develop antibacterial and antifouling ultrafiltration membrane. Ag nanoparticles were prepared from the reduction of silver nitrate (AgNO3) by sodium borohydride in the presence of polyethyleneimine (PEI) as the stabilizer. The encapsulated Ag nanoparticles in the PEI solution were embedded into the PEI membrane when trimesoyl chloride solution was used to crosslink the PEI solution with the PES membrane, forming Ag‐polyamide (PA) networks through the interfacial polymerization reaction. Experimental results showed that the membrane prepared with 50 mmol/L of AgNO3 and 20 mmol/L of PEI had the optimized antibacterial effect against Escherichia coli. Bacterial concentration and species were also investigated. Exiguobacterium aestuarii and Staphylococcus aureus which are gram‐positive bacteria, needed significantly more time for the Ag‐PA/PES membrane to kill the bacteria completely when compared to E.coli and Vibrio coralliilyticus which are gram‐negative bacteria. This study showed that Ag nanoparticles impregnated in membrane surfaces were 100% effective in killing various types of marine bacteria and bacteria in the seawater collected off Sentosa Island in Singapore. These membranes exhibit excellent antibacterial and antifouling properties which can be used to kill bacteria in ballast water and seawater.

Facile and effective repair of Pt/Nafion IPMC actuator by dip-coating of PVP@AgNPs

Ionic polymer metal composite (IPMC) always takes big risks of electrode cracking and peeling, which lead to energy wasting, waterloss, and uneven electric field distribution, thus hamper its commercial applications. To address this issue, we propose a facile and effective technique to repair the electrode fatigue by coating polyvinylpyrrolidone (PVP) encapsulated Ag nanoparticles (PVP@AgNPs) on the long-term used IPMC surface. To improve the electrochemical stability, the silver nanoparticles (Ag NPs) with a diameter of ∼34 nm are encapsulated by a 1.3 nm thick PVP film, thus forming a shell–core structure to resist corrosion from the electrolyte solution. Physiochemical investigations reveal that, PVP@AgNPs closely attach to the interior and exterior surfaces of the original Pt nanograin electrode, thus refreshing its electronic conductivity; the repaired IPMC actuator exhibits better electromechanical properties compared to its precursor actuator: 7.62 folds in displacement output, 9.38 folds in force output, and 9.73 folds in stable working time.

Magnetic multi-functional SBA-15 supported silver nanocomposites: Synthesis, characterization and application

A novel magnetic multi-functional nanocomposites, MagS-Ag, is developed via a facile route. The material is composed of dense-silica-film-coated Fe3O4, SBA-15 as supporters, and encapsulated Ag nanoparticles. The synthesis strategy involves Fe3O4 covered with inert silica films through an improved dense liquid silica coating (DLSC) method, and SBA-15 supported silver ammonia precursor, followed by ultrasonic mixing in toluene and thermal reduction in an inert atmosphere. The as-synthesized MagS-Ag was characterized to validate the preferable physical and chemical properties. With these properties, MagS-Ag exhibits outstanding capabilities in catalytic reduction of 4-nitrophenol (4-NP) and capture of elemental mercury (Hg0) from coal-fired flue gas. The spent materials can be easily separated/collected by a magnetic field, and regenerated after five application cycles without any considerable performance deterioration. Overall, MagS-Ag with a combination of ease preparation, low cost and excellent recycle capability has a great potential for a broad application in respective fields.

Core-shell ZnO@Cu2O encapsulated Ag NPs nanocomposites for photooxidation-adsorption of iodide anions under visible light

Iodide anion (I−) is one of the most-problematic radioactive nuclides in used nuclear fuel due to its intrinsic characteristics of a high toxicity and environmental mobility. Therefore, effective and selective elimination of I− from nuclear contaminated solution is highly beneficial for the pollution remediation purposes in the development of nuclear power, but is of significant challenge owing to the extreme conditions of the high acidity, strong ionizing radiation field and high concentration of competing anions. Herein, a novel core–shell ZnO@Cu2O (ZC) encapsulated Ag nanoparticles (Ag NPs) nanocomposites have been fabricated via a facile one step self-assembly process and an environmentally friendly technique. The as-fabricated ZnO@Ag@Cu2O (ZAC) nanocomposites were characterized and applied to capture of I− from aqueous solution. Adsorption studies revealed that the ternary nanocomposites showed fast removal kinetics, high photooxidation-adsorption capacity (up to 217.4 mg g−1 at pH = 3 for ZAC-2), satisfactory selectivity and high acidity resistance. Furthermore, the nanocomposites also exhibited a good reusability, as no significant change in the uptake capacity was observed even after five adsorption-regeneration cycles. Inspired by the superior features, a possible mechanism (chemical adsorption coupled with photooxidations) was proposed based on XRD, XPS and Raman spectra analysis for the pre- and post-adsorbed samples as well as the detailed adsorption experimental evidence.

Encapsulating Ag nanoparticles into ZIF-8 as an efficient strategy to boost uranium photoreduction without sacrificial agents

Hot electrons generated over Ag nanoparticles were transferred to ZIF-8 to efficiently reduce adsorbed U(vi). The coherence between adsorption sites and electron acceptors directly contributes to the excellent U(vi) enrichment performance.

Tuning the efficiency of CoFe2O4@rGO composite by encapsulating Ag nanoparticles for the photocatalytic degradation of methyl violet dye and energy storage systems

Photocatalytic activity of the Ag NPs/CoFe2O4@rGO composite.

Simple Electrochemical Synthesis of Polyethylenimine-Encapsulated Ag Nanoparticles from Solid AgCl Applied in Catalytic Reduction of H2O2

We report a simple and environmentally friendly synthesis of polyethylenimine (PEI)-encapsulated Ag nanoparticles (AgNPs) by a direct electroreduction of solid AgCl. The AgNPs, characterized by field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS), revealed that AgNPs diameters (100–500 nm) depended on the loading of the AgCl precursor. Using cyclic voltammetry (CV), it was confirmed that the AgNPs had a catalytic effect on the electrochemical reduction of H2O2. The obtained AgNPs were subsequently used to construct an electrochemical H2O2 sensor exhibiting a low detection limit (1.66 μM) and a wide linear response range, with real-life tests indicating an insensitivity to common interferents and confirming the potential use of the developed technique in diverse applications.

Nonenzymatic Glucose Sensing and Magnetic Property Based On the Composite Formed by Encapsulating Ag Nanoparticles in Cluster-Based Co-MOF.

Utilizing the oxygen-bridged 5,5'-oxidiisophthalic acid (H4L) linker, one Co(II)-based 3D porous MOF {[Co5(L)2(OH)2(OH2)2(H2O)4]·2DMF·H2O}n (1) with pentanuclear [Co5(μ3-OH)2(μ2-OH2)2]8+ cluster was prepared. The glassy carbon electrode was modified by 1, and the obtained electrode revealed electrocatalytic performance for glucose oxidation. The porous MOF matrix is beneficial for dispersing Ag nanoparticles evenly in the interior cages or channels, so Ag@1 composite composed of both Ag nanoparticles and MOF was further prepared through deposition-reduction method to enhance electrocatalytic activity. The result demonstrates that the glucose oxidation by Ag@1 was greatly increased with low detection limit (1.32 μM) and good selectivity and sensitivity (0.135 μA μM-1), which promote the application of MOF-template porous composites as advanced electrochemical sensor materials. Furthermore, 1 shows an interesting magnetic spin-glass slow dynamics for the existing of peculiar pentanuclear Co(II) clusters.

Core-shell Ag@In2O3 hollow hetero-nanostructures for selective ethanol detection in air

By applying the Ag@carbon nanospheres as self-sacrificial templates, Ag@In2O3 core-shell nanospheres (Ag@In2O3 CSNs) have been successfully prepared via the aging and subsequent annealing process. The formation and sensing performances of this Ag@In2O3 CSNs based sensor are systematically evaluated and analyzed in detail. Compared to pristine In2O3 nanospheres with solid and hollow inner structures, the as-prepared Ag@In2O3 CSNs exhibit the best response (∼72.56 to 50 ppm), especially in terms of the outstanding reusability as well as the excellent anti-interference to other biomarkers in human breath. Such virtues are owing to the unique structure (porous shell and internal voids) and the catalytic effect of encapsulated Ag nanoparticles, which provides considerable active centers and diffusion channels for ethanol. The investigation in this research may shed light on the fabrication of a novel In2O3-based nanocomposite for ethanol gas sensor detection.

A Facile Method for Controlled Fabrication of Hybrid Silver Nanoparticle-Poly(-caprolactone) Fibrous Constructs with Antimicrobial Properties.

Infection is one of the major factors affecting wound healing. The use of polymeric fibrous constructs or scaffolds with encapsulated biologically active components has shown great potential in topical wound care as wound dressings to expedite wound healing process; however, there is a limitation in precise control over the release of active components. Therefore, in this study, the authors developed a facile method for controlled fabrication of poly(-caprolactone) (PCL) microfibrous constructs with silver (Ag) nanoparticles as antibacterial agent by single capillary electrospinning. By optimizing spinning parameters, the PCL microfibrous constructs were fabricated. The encapsulation of Ag nanoparticles within the PCL microfibers was confirmed using microstructural analysis. The encapsulation efficacy and release profile of Ag was evaluated in vitro. The diffusion study further revealed the controlled release and optimal bioavailability of Ag during the experimental period. in vitro assessment of antibacterial activity of electrospun hybrid constructs showed a high antibacterial activity and an inhibitory effect on the growth of both staphylococcus aureus and escherichia coli bacteria when compared to PCL and their efficiency of antibacterial activity also varied with respect to the percent of encapsulated Ag nanoparticles. This kind of Ag nanoparticles-loaded PCL microfibrous constructs may be considered for wound care applications.

Selectively encapsulating Ag nanoparticles on the surface of two-dimensional graphene for surface-enhanced Raman scattering

Abstract For preparation of surface-enhanced Raman scattering (SERS) substrate with high stability, reproducibility, and sensitivity performances, graphene/Ag nanoparticles were chosen to make further improvement by introducing molecularly imprinted polymer (MIP) film to protect Ag nanoparticles. The thickness of the resulting ultra-thin MIP layer is 2 nm on the surface of Ag nanoparticles. The preparation of two-dimensional/core-shell structure SERS substrate (G/Ag@MIP) possesses high SERS activity toward the probe of bovine serum albumin (BSA) target molecule, which exhibits a 10 −12 M detection limit. The G/Ag@MIP shows good selectivity and recycle rate in the detecting process. These results show that the hybrid material as a SERS sensor is potential for medical diagnosis in life sciences.

Core-shell metal-organic frameworks and metal functionalization to access highest efficiency in catalytic carboxylation

A core-shell metal-organic frameworks (MOF@MOF) based on the Zr-MOFs assembly from core-structure UiO-66 combined with shell-structure UiO-67-BPY were explored. The synthesized materials were characterized via XRD, FTIR, SEM, TEM, and surface area analysis, etc. indicating the presence of a core-shell structure of UiO-66@UiO-67-BPY. Furthermore, incorporation of the bipyridinic (BPY) group in the linker used to construct the shell layer (UiO-67-BPY) could coordinate with active metal species and thus create an advantage for site-selective metal incorporation in the core-shell structure. Silver (Ag) was selected for the selective metal incorporation and an excellent Ag-dispersion via coordination with the bipyridinic groups in the UiO-67-BPY layer of the core-shell material was obtained. The synthesized material (UiO-66@UiO-67-BPY-Ag) was successfully applied as a heterogeneous catalyst for the CO2 fixation via carboxylation of terminal alkynes. The catalytic material showed excellent yields using at a low Ag-loading under mild reaction condition (50 °C, 1 bar). Moreover, the catalyst can be recycled for at least 5 times maintaining a stable catalytic performance. Interestingly, the high catalytic activity of the synthesized material demonstrated clearly the beneficial advantage of the metalated core-shell structure over the reported routes to synthesize silver catalysts such as encapsulated Ag nanoparticles (AgNP@MOF) or Ag-bidentately coordinated on traditional MOFs applying the same reaction model.

Multiple Silver Nanoparticles Anchored Hollow Mesoporous Silica Nanospheres by Polyacrylic Acid Aggregate Templating Approach for Catalytic Reduction of p-Nitrophenol.

Anchoring metal cores inside porous shells can endow metal catalyst with high selectivity and stability. Herein, multiple silver nanoparticles were successfully anchored in hollow mesoporous silica nanospheres (Ag@HMSNs) through a facile one-pot method. Polyacrylic acid aggregates self-assembled in water/ethanol solvent were used as core templates and Ag nanoparticles captors, and hexadecyl trimethoxysilane (C16TMS) was used as the pore-making agent. The hollow cavity, encapsulated multiple Ag nanoparticles, and mesoporous silica shell of the Ag@HMSNs were confirmed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and nitrogen sorption analysis. Just as expected, Ag nanoparticles (2-5 nm) were encapsulated in the cavity of hollow mesoporous silica nanospheres with the size of about 200 nm. The fabricated Ag@HMSNs showed excellent performance for catalytic reduction of p-nitrophenol (4-NP). Also, catalytic activity of the Ag@HMSNs for 4-NP reduction was increased with the addition amount of the pore-making agents and surface areas. The superior catalytic performance was attributed to the unique structural features of Ag@HMSNs architecture, in which the mesoporous shell provided readily accessible pathway for fast transport of reactants to the encapsulated Ag nanoparticles.

Hollow ZSM-5 zeolite encapsulated Ag nanoparticles for SO2-resistant selective catalytic oxidation of ammonia to nitrogen

Hollow ZSM-5 encapsulating Ag particles (Ag/ZSM-5-OH) have been successfully synthesized, characterized and tested in NH3-SCO reaction. In comparison with Ag/Al2O3 and Ag/ZSM-5-OH, Ag/ZSM-5 catalyst displayed the lowest T100 (110 °C), much higher TOF and the lowest Ea. Although fresh Ag/ZSM-5-OH catalyst showed the relatively low NH3 conversion, its reaction cycles stability was significant higher than that of Ag/Al2O3 and Ag/ZSM-5 catalysts. The hollow structure of ZSM-5 zeolite could prevent sintering and/or leaching of Ag particles during NH3 oxidation process. Zeolite membrane formed during dissolution-recrystallization process in the surface of hollow ZSM-5 could offer good separation properties for SO2. So SO2 did not diffuse into the hollow structure to be poisoned Ag catalyst, finally induced the outstanding SO2/H2O resistance.

Self-assembly of Gradient Copolymer Synthesized by Spontaneous Batch RAFT Emulsion Polymerization and Its Application on Encapsulating Ag Nanoparticles

The gradient copolymers of acrylic acid and trifluoroethyl methacrylate (coded as P(TFEMA-grad-AA)) were synthesized via reversible addition-fragmentation transfer (RAFT) emulsifier-free emulsion polymerization. The spontaneous batch feeding approach was used to control the gradient chain sequence. Transmission electron microscopy (TEM) analysis revealed that the P(TFEMA-grad-AA) can self-assemble to form spherical micelles, rodlike micelles or vesicles in selective solvents. Morphological transition of the P(TFEMA-grad-AA) micelles was sensitive to the water content of the dioxane/water mixed solvent. More interestingly, Ag nanoparticles (NPs) were encapsulated by the P(TFEMA-grad-AA) micelles during the self-assembly process. The gradient chain sequence made the Ag NPs easily enter the core of the micelles, even when P(TFEMA-grad-AA) had less hydrophobic fluoro-units and more hydrophilic units. TEM images with energy dispersive spectrometer indicated that the nanocomposite micelles consisted of a Ag NPs core and a gradient copolymer shell.