Immobilization Of Silver Nanoparticles Research Articles

Stretchable silver@CNT-poly(vinyl alcohol) films with efficient electromagnetic shielding prepared by polydopamine functionalization

The design of CNT/polymer composite shields is reduced to resolve the issue of CNTs agglomeration which has been tackled by complex and harsh chemical treatments damaging their electrical conductivity and limiting shielding capability. Herein, CNTs were coated with polydopamine (PDA) by exploiting the in-situ spontaneous polymerization of PDA on organic/inorganic surfaces. The PDA functional layer not only resulted in improved CNT dispersion after 2 h-coating time but also served as a platform for subsequent immobilization of silver nanoparticles by the catechol and nitrogen-containing groups of PDA. The well-dispersed CNT and the incorporation of extra silver particles conductive phase resulted in flexible and highly conductive Ag@PDA@CNT-poly(vinyl alcohol) (PVA) films with significantly improved shielding effectiveness of 42.75 dB with respect to pristine CNTs (21 dB). The size of silver particles controlled by PDA polymerization time, the formation of an efficient conductive network and conduction/interfacial polarization-induced loss mechanisms were reasoned to be responsible for dictating the films shielding performance. Such low-key and green approach could be instrumental to developing other metal/CNT polymer films as next-generation lightweight shields for flexible electronics.

Bactericidal activity of immobilized silver nanoparticles on silica substrates with different sizes.

Hybrid particles with immobilized silver nanoparticles (AgNPs) receive a lot of attention due to their excellent antibacterial activity with the prevention of inherent aggregation of AgNPs. In this study, serial sized silica substrate particles (231, 401, and 605nm) and their corresponding hybrid particles with AgNPs (~ 30nm) are prepared, with detailed bactericidal images of the corresponding particles at various times. Their bactericidal activity is elucidated for both Gram-positive Streptococcus agalactiae and Gram-negative Escherichia coli CN13, which show the size of 0.8μm × 0.9μm and 1.3μm × 1.8μm, respectively. There is a large difference in the bactericidal activity between the smallest (231nm, 3-log10 reduction) and larger (401 and 605nm, 6-log10 reduction) silica substrates, whereas there is hardly a difference between the latter. Their effective total surface area (ETSA) is considered important for their bactericidal activity, based on the nearly equal large ETSA of the well-dispersed two larger silica substrates and the much smaller ETSA of the agglomerated smallest substrates. Submicron-sized pits appear on the bacterial membrane by direct contact with the hybrid particles, implicating the importance of ETSA. Still, further research is needed with much different silica substrate sizes to fully elucidate the impact of the silica substrate on the bactericidal activity of immobilized AgNPs.

Mussel-Inspired Ag NPs Immobilized on Melamine Sponge for Reduction of 4-Nitrophenol, Antibacterial Applications and Its Superhydrophobic Derivative for Oil-Water Separation.

A functional material integrated with a variety of functions is highly desired in wastewater treatment. In this research, a mussel-inspired method of immobilizing silver nanoparticles on the skeleton of a melamine sponge is proposed and applied for water remediation. Ag NPs were reduced in situ and grown on a polydopamine-modified melamine sponge. The catalytic reduction of 4-nitrophenol (4-NP) in the presence of the obtained MS-PDA-Ag was evaluated, and the results demonstrated that the MS-PDA-Ag presented high catalytic reduction activity. In addition, the monolithic MS-PDA-Ag presents excellent reusability with no remarkable decrease in catalytic efficiency after multiple reuses. Owing to the immobilized Ag NPs, the MS-PDA-Ag can also effectively inhibit the growth of bacteria against both gram-positive and gram-negative species, making it possible for bacteria elimination in polluted water. To further explore the possibility of utilizing the MS-PDA-Ag for versatile applications, a superhydrophobic derivative (S-MS-PDA-Ag) was prepared by coating a low-surface-energy substance (octadecanethiol) on the surface of MS-PDA-Ag. The obtained S-MS-PDA-Ag presents the capacities of oil/organics adsorption and water repellence, which can separate the insoluble oil/organics from water. The melamine sponge immobilized with Ag NPs demonstrates prominent catalytic reduction of 4-NP, antibacterial activity and the superhydrophobic derivative presents the capacity of insoluble oil/organics separation from oil-water mixtures, exhibiting high potential in the remediation of polluted water.

Fabrication of Ag nanoparticles supported on amino-functionalized peeled-watermelon structured silica-coated nano-Fe3O4 with enhanced catalytic activity for reduction of 4-nitrophenol

In this work, novel silver nanoparticles supported on amino-functionalized peeled-watermelon-like silica-coated magnetic catalysts (Fe3O4@SiO2-NH2-Ag) were successfully synthesized for the catalytic reduction of 4-nitrophenol (4-NP) in wastewater. The Fe3O4 nanoparticles were further coated with silica forming a structure similar to peeled watermelon to improve the stability of magnetic Fe3O4 and inhibit their aggregation. Furthermore, surface modification of Fe3O4@SiO2 particles with amino groups was used for the immobilization of silver nanoparticles. As a result, the Fe3O4@SiO2-NH2-Ag (10%) exhibits excellent catalytic activity to reduce 4-NP, which obtained the first-best reaction rate constant of 0.026 s−1. Besides, the Fe3O4@SiO2-NH2-Ag could be easily recovered under an external magnetic field and was reused for 25 catalytic cycles without a significant decline in catalytic activity. The related catalytic mechanism of the reaction was discussed. Overall, the excellent magnetic recyclable nature and immortal catalytic activity make Fe3O4@SiO2-NH2-Ag a very promising material for practical use.

Immobilization of Silver Nanoparticles on the Surface of Cellulose Nanofibers Using High-Pressure Wet-Type Jet Mill

Composite material immobilized silver nanoparticles (NPs) on the surface of cellulose nanofibers (CNF) was prepared using a high-pressure wet-type jet mill. A mixture both containing an aqueous silver nitrate solution and a CNF suspension was prepared as a raw starting material. The mixture was pulverized with the high-pressure wet-type jet mill at a pressure of 100 or 200 MPa. An X-ray diffraction pattern of the obtained sample revealed the presence of not only cellulose type I crystallites but also silver metal crystallites. According to observation by field-emission scanning electron microscopy, it was found that many silver NPs were immobilized on the surface of CNF. Note that almost all the silver NPs were well dispersed on the surface of CNF. It was cleared that the silver NPs had a spherical in shape with an average particle size of about 3 nm by the transmission electron microscope observation. The average size of the silver NPs slightly increased with the number of jet milling cycles, however, the change in the discharge pressure of the high-pressure wet-type jet mill did not affect the NPs size. The silver content in the composite materials increased with increasing both the number of jet milling cycles and the discharge pressure. The silver NPs were deposited by using the thermal energy released in the jet milling process, and their grain growth was then inhibited because the suspension was cooled immediately through the cooling tube. Therefore, it was assumed that silver NPs with a narrow size distribution could be immobilized on the surface of CNF.

High strength antibacterial membranes consisted of nanofibrous chitosan immobilized silver nanoparticles

AbstractChitosan (CS) has biocompatibility and biodegradability, but the bulk CS hydrogel/membranes with its poor strength and limited antibacterial property could not satisfy the practical application. Here green dissolving/regeneration and in situ reduction strategy was combined to construct high strength antibacterial CS membranes. First nanofibrous CS hydrogels were constructed through dissolving CS in LiOH/KOH/urea aqueous system via freezing–thawing process followed regeneration. Then, Ag NPs were immobilized along CS nanofibers through in situ reductions of Ag + by the NH2 group of CS. The obtained NCM‐Ag composite dry membranes are easy for storing and can quick switch to nanofibrous hydrogels as absorbing water. Size of Ag NPs can be controlled to very small until 2 nm by concentration and limited space network. Fourier transform infrared spectroscopy and X‐ray photoelectron spectrometer indicated the forceful grasp ability of CS nanofibers to Ag NPs for a stable binding, mechanical property was enhanced over 100Mpa as the nanofibrous structure and chain linked by Ag coordination. The NCM‐Ag membranes had excellent antibacterial activities against both Staphylococcus aureus and Escherichia coli. Moreover, such nanofibrous CS membrane exhibited good adhesive ability to tissues. Combining all these properties, NCM‐Ag membranes would be potential as antibacterial adhesion barrier to accelerate wound healing.

Polydopamine-coated chitosan hydrogel beads for synthesis and immobilization of silver nanoparticles to simultaneously enhance antimicrobial activity and adsorption kinetics

Polydopamine-coated chitosan hydrogel beads for synthesis and immobilization of silver nanoparticles to simultaneously enhance antimicrobial activity and adsorption kinetics

Immobilization of Silver Nanoparticles on Chitosan-Coated Silica-Gel-Beads and the Antibacterial Activity

Silver nanoparticles (Ag0) have attracted the most attention due to their broad antimicrobial application and outstanding activity. The silver nanoparticles are usually in colloidal form, then immobilization the colloid onto solid support is still interesting to explore. In this work, a new method for silver colloidal nanoparticle immobilization on silica gel beads (SiG), which was then symbolized as Ag0-[chi-SiG] was conducted and characterized successfully. The finding proved that SiG must be coated with three chitosan film layers to give stable support for silver nanoparticles. This coating method caused the chitosan completely covered SiG, and the chitosan film provides coordination bonding for silver ions. The most appropriate solvent for silver ion impregnation on the surface of chi-SiG is methanol compared to other solvents. Tungsten lamp as the photo-irradiation, which is low cost and environmentally friendly has been proven effective for silver ion reduction, as shown by silver metal colloid UV-Vis surface plasmon resonance at 400-700 nm. Ag0-[chi-SiG] showed the antibacterial properties of inhibiting the growth Staphylococcus aureus and Escherichia coli; then it provides the potential application for antibacterial filter material. According to the weight comparison between antibacterial standard and Ag content, then Ag0-[chi-SiG] has two and five times higher of exhibiting zone for each bacteria.

Green synthesized Ag-TiO2 for degradation of organic dye through visible light driven photo-reactor and its kinetics

Abstract This study reports a green approach for the modification of titanium dioxide (TiO2) nanoparticles with immobilization of silver nanoparticles. One of the natural sources i.e., Mangifera indica leaf extract was utilized as reducing and capping agent for the fabrication of Ag-TiO2 nanocatalyst. Further, the surface morphology and band-gap energy of prepared Ag-TiO2 were analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and UV–Vis spectroscopy. Also, it was characterized by X-ray Powder Diffraction (XRD) which provides the information regarding the crystallinity of the Ag-TiO2. Subsequently, photo activity of Ag-TiO2 was investigated for the degradation of methylene blue (MB) dye wastewater through visible light driven photoreactor. The Ag-TiO2 provided highest (68%) of photo-degradation efficiency within 110 min for 7.81 × 10−5 mol/L initial MB concentration at pH 8 by using 0.19 g/L photocatalyst. Further, addition of 10 mM H2O2 boost up the MB photodegradation to 74%. The kinetic study confirmed the MB degradation followed first order rate of reaction.

Immobilized Ag-nanoparticles (iNPs) for environmental applications: Elucidation of immobilized silver-induced inhibition mechanism of Escherichia coli

Although silver nanoparticles (AgNPs) appear to be promising for certain medical/pharmaceutical applications, they present significant disadvantages when it comes to environmental applications due to the need for recovery of the metal (Ag) which is considered hazardous for the environment. The present study examines the antimicrobial properties and mechanism of action of immobilized (on Al2O3) silver nanoparticles’ (1 wt% Ag-iNPs) regarding the treatment of E. coli microbial solutions. Antimicrobial experiments were conducted in semi-batch mode using a three-phase continuous flow stirred tank reactor. Every treated sample was taken from the outlet of the reactor for the time intervals of 0, 5 and 25 min. To ensure that the bactericidal property of Ag-iNPs is not attributed to the dissolution of surface silver (as free Ag+), a suitable Ag+ scavenger was used as already described in our earlier studies. Regarding the molecular analysis performed under this study, the regulation of key enzymes involved in bactericidal activity of E. coli, was examined, after their treatment either with immobilized silver nanoparticles (Ag-iNPs) or AgNO3. Specifically, 50 mL sample for each case was centrifuged (10 min at 10,000 rpm) and the pellet (≈109 cells) was immediately subjected to total RNA extraction. For real-time RT-qPCR analyses, 1 μg of total RNA was converted into cDNA. It was found that PldA gene, which encodes outer membrane’s phospholipase A (OMPLA), was up-regulated after 5 and 25 min of treatment with Ag-iNPs. OMPLA’s activation appears to be the initial step of Ag-iNPs bactericidal mechanism that ultimately leads to the creation of holes on the outer membrane (OM), irreversibly disturbing the cells’ respiration cycle. In addition, after treatment with Ag-iNPs, Blue copper oxidase CueO (encoded by cueO gene) was found to be over-produced and appears to play a key-role in the oxidative transfer of silver from the surface of Ag-iNPs to the cell. This leads to the Ag-induced displacement of copper from its native protein sites such as CusS/CusR, a fact that causes the release of labile copper and ROS inside the cell. In addition, TEM analysis of bacteria treated with Ag-iNPs revealed severe morphological changes (“holes”) on bacterial outer membrane, indicating that there is an intermediate step in the proposed antimicrobial mechanism which takes place on the surface of Ag-iNPs.

In-situ synthesis and immobilization of silver nanoparticles on microfibrillated cellulose for long-term antibacterial applications

In-situ synthesis and immobilization of silver nanoparticles on microfibrillated cellulose for long-term antibacterial applications

Silver nanoparticles supported on P, Se-codoped g-C3N4 nanosheet as a novel heterogeneous catalyst for reduction of nitroaromatics to their corresponding amines

P, Se-codoped g-C3N4 (PSeCN) nanosheet was in situ prepared by facile thermal polymerization of melamine, phosphonitrilic chloride trimer, and selenium black powder as the precursors. It was found as a suitable support for the immobilization of silver nanoparticles (Ag NPs). The prepared nanocatalyst was fully characterized via standard analysis methods including EDX, ICP-OES, XRD, FT-IR, SEM, TEM, and BET. This PSeCN/Ag nanocatalyst with a higher specific surface area compared with CN, showed excellent catalytic activity towards the reduction of several nitroaromatic compounds using sodium borohydride (NaBH4) in short reaction times with high efficiency and good selectivity in water as a green solvent. Significantly, the above-mentioned nanocomposite could be reused six times without appreciable loss of its catalytic activity.

Immobilization of Silver Nanoparticles on the Surface of Cellulose Nanofibers Using High-Pressure Wet-Type Jet Mill

Immobilization of Silver Nanoparticles on the Surface of Cellulose Nanofibers Using High-Pressure Wet-Type Jet Mill

One-pot synthesis of silver nanoparticle deposited cellulose nanocrystals with high colloidal stability for bacterial contaminated water purification

Cellulose nanocrystals (CNCs) have been utilized as a scaffold to immobilize silver nanoparticles (AgNPs) for their potential application as an antibacterial agent and bactericidal filler. However, the present implemented strategies involve synthesis by multi-step and utilize environment non-friendly reducing agents for the deposition of AgNPs on CNCs. Furthermore, the long-time aqueous dispersion stability of prepared AgNPs hybrids is another issue of concern for their efficient utilization as an antibacterial filler. We have developed an environmentally benign one-pot method using a biocompatible polyvinyl+pyrolidone (PVP) as a reducing agent to deposit AgNPs on CNCs. The developed method exhibited the uniform in-situ deposition of AgNPs on CNCs. The formed (CNC-PVP-Ag) nanohybrid displayed excellent long time aqueous colloidal stability (8 months), antibacterial and anti-biofouling activities (12.5 µg/mL and 25 µg/mL for E. coli and S. aureus) which is 4 and 2 times lower than AgNPs (w/o CNCs) prepared by the identical process as of CNC-PVP-Ag. As water-borne microbial contaminations are a global water quality concern, the excellent antibacterial and anti-biofouling activity of CNC-PVP-Ag was applied for water purification. An efficient bacterial filtration performance (100% reduction of Escherichia coli viability) was achieved after two filtration cycles.

Poly(vinyl alcohol)-based composite film with Ag-immobilized TEMPO-oxidized nano-tea cellulose for improving photocatalytic performance

In the present study, we report a simple and eco-friendly method for the synthesis and immobilization of silver nanoparticles (AgNPs) onto functional films using green tea extract as a reducing and capping agent. The freestanding flexible immobilized AgNPs composite was obtained from a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated tea cellulose (TTC) process. Scanning electron microscopy analysis revealed the homogeneous coating of the AgNPs on the surface of the TTC nanofibers. Ag-TTC-poly(vinyl alcohol) (PVA) composite film was prepared through a simple solvent casting method, which displayed higher antioxidant activity than the TTC-PVA film, and the rate of release of Ag was reduced owing to the immobilized AgNPs. The photocatalytic performance of Ag-TTC-PVA composite film was evaluated along with the investigations of the optical transparency, morphology, and thermal properties. Ag-TTC-PVA composite film showed enhanced photocatalytic property than TTC-PVA film. This study presents a simple approach for the green synthesis of materials with controlled leakage based on Ag-TTC-PVA composite film, which has good potential application prospects in the development for the photocatalytic degradation of certain toxic dyes, thereby paving the way for waste treatment.

Photothermal Sweeping Gas Membrane Distillation and Reverse Electrodialysis for light-to-heat-to-power conversion

Water and energy are two intimately interconnected issues of strategic relevance for a sustainable industrial development. Herein, we integrated light-harvesting/self-heating membranes and salinity gradient technology with the aim to implement the innovative concept of light-to-heat-to-power conversion.Novel photothermal membranes, prepared by immobilizing silver nanoparticles (AgNPs) on the top layer of microporous polyvinylidene fluoride (PVDF) matrix, were tested – for the first time – in a Sweep Gas Membrane Distillation (SGMD) unit applied to the desalination of synthetic seawater solution (0.5M NaCl). As a result of the ability of noble metal nanofillers to act as localized thermoplasmonic nano-heaters at membrane-feed interface for efficient water evaporation, an increase of transmembrane flux under UV radiation by about 10-fold with respect to unloaded PVDF membrane was observed.The SGMD retentate, consisting in hypersaline brine (progressively concentrated up to 4M NaCl and rejected at about 40°C) was fed to a Reverse Electrodialysis unit with the aim to harvest electrochemical energy. The maximum power density, measured for a retentate concentration increasing from 1M to 4M, raised from 0.13 to 0.9 W/m2MP (MP: RED membrane pair). Overall, the proposed integrated membrane system allowed to extract about 10% of the energy not employed for water evaporation.

Substrate-Independent, Regenerable Anti-Biofouling Coating for Polymeric Membranes.

Biofouling is a common but significant issue in the membrane process as it reduces permeate flux, increases energy costs, and shortens the life span of membranes. As an effective antibacterial agent, a small amount of silver nanoparticles (AgNPs) immobilized on membrane surfaces will alleviate the membrane from biofouling. However, loading AgNPs on the membrane surface remains a challenge due to the low loading efficiency or the lack of bonding stability between AgNPs and the membrane surface. In this study, a substrate-independent method is reported to immobilize silver nanoparticles on polymeric membrane surfaces by firstly modifying the membrane surface with functional groups and then forming silver nanoparticles in situ. The obtained membranes had good anti-biofouling properties as demonstrated from disk diffusion and anti-biofouling tests. The silver nanoparticles were stably immobilized on the membrane surfaces and easily regenerated. This method is applicable to various polymeric micro-, ultra-, nano-filtration and reverse osmosis (RO) membranes.

Antiviral application of colloidal and immobilized silver nanoparticles

This study explored the application of colloidal and immobilized silver nanoparticles (AgNPs) for inactivation of bacteriophages. Coliphages that are commonly used as indicators for enteric viruses, were used in this study. Colloidal AgNPs were synthesized via a chemical reduction approach using sodium borohydride as reducing agent and trisodium citrate as stabilizing agent. AgNP-immobilized glass substrate was prepared by immobilizing AgNPs on amine-functionalized glass substrate by post-immobilization method. The AgNP-immobilized glass substrate was also tested so as to minimize the release of AgNPs in the treated water. The characterization of AgNPs and the AgNP-immobilized glass surface was done using field emission gun-transmission electron microscopy and scanning electron microscopy. Studies conducted with varying concentrations of colloidal AgNPs displayed good antiviral activity for MS2 and T4 bacteriophage. Colloidal AgNPs at a dose of 60 μg ml−1 could completely inactivate MS2 and T4 bacteriophage within 30 and 50 min with an initial concentration of 103 PFU ml−1. Contaminated water (100 ml) in an unstirred batch reactor with an initial bacteriophage concentration of 103 PFU ml−1 could be inactivated by the AgNP-immobilized glass substrate (1 cm × 1 cm, containing 3.7 μg cm−2 silver) suspended centrally in the batch reactor. Complete 3-Log bacteriophage inactivation was achieved within 70 and 80 min for MS2 and T4 bacteriophage, respectively, while the aqueous silver concentration was less than 25 μg l−1. This is significantly lower than the recommended standard for silver in drinking water (i.e. 100 μg l−1, US EPA). Thus, AgNP-immobilized glass may have good potential for generating virus-free drinking water.

A sandwich-like chitosan-based antibacterial nanocomposite film with reduced graphene oxide immobilized silver nanoparticles

Bacterial breeding is the main cause of food perishability, which is harmful to human health. Silver nanoparticles (AgNPs) are one of the most widely used antimicrobial agents, but they are easy to release and cause cumulative toxicity. In this work, with corn stalk as green reductant and GO as template, a simple electrostatic self-assembled sandwich-like chitosan (CS) wrapped rGO@AgNPs nanocomposite film (CS/rGO@AgNPs) was synthesized to achieve stabilizing and controlled-release of AgNPs. The results showed that the the CS/rGO@AgNPs film continued releasing AgNPs for up to 14 days, and the final release amount of silver nanoparticles was only about 1.9 %. More importantly, the nanocomposite film showed durable antibacterial effect and good antibacterial activity against E. coli and S. aureus, and they showed no toxicity to cells. Hence, the nanocomposite film has potential application as an effective and safe packaging material to prolong the shelf life of food products.

Hematite/Polystyrene Raspberry‐Like Microcomposites as Stable Support for Silver Nanoparticle Immobilization

AbstractAmong the methods utilized for the preparation of raspberry‐like microcomposites, due to its simplicity and universality, the electrostatically‐driven deposition of nanoparticles at the surface of microparticles is especially attractive. This process, leading to the formation of a single nanoparticle monolayer, is widely reported. On the other hand, no data concerning the electrostatically‐driven formation of nanoparticle bilayers at the surface of microparticles are reported. To fill this gap, the detailed investigation of the formation of silver/hematite nanoparticle bilayers at the surface of polystyrene microparticles is reported. First, the hematite/polystyrene raspberry‐like microcomposites are obtained by immobilization of hematite nanoparticles under an electrostatically‐driven process. The stability of hematite/polystyrene microcomposites at elevated temperatures up to 323 K is monitored using microelectrophoresis. No significant changes in the hematite nanoparticle layer coverage are observed after prolonged time of incubation. This proves the irreversible character of nanoparticle immobilization. Next, the hematite/polystyrene microcomposites are utilized as the interfaces for immobilization of negatively charged silver nanoparticles. This process is quantitatively described using electrokinetic measurements. The changes in the hydrodynamic diameter of microcomposites are also determined. Finally, the validity of the electrokinetic model used in this work for predicting the zeta potential of the silver/hematite/polystyrene microcomposites is confirmed.