Adsorption Of AgNPs Research Articles

Atmospheric pressure plasma deposition of silver nanoparticles on bark fabric for bacterial growth inhibition

Plasma technology that operates at atmospheric pressure is increasingly used for surface modification of heat-sensitive materials to confer antibacterial properties. In this study, atmospheric pressure plasma jet (APPJ) system was used to deposit silver nanoparticles (AgNPs) for antibacterial application into bark fabric used in the Cordillera Region, Philippines. Plasma was produced by applying 15 kV to silver electrodes while the argon and oxygen gases were allowed to flow at 15 and 5 liters per minute (LPM), respectively. Characterization of plasma by optical emission spectroscopy (OES) suggests the formation of active plasma species. The observed surface roughness which consequently enhanced the adsorption of AgNPs was confirmed by scanning electron microscopy (SEM) and wavelength dispersive x-ray fluorescence (WDXRF) analyses. Fourier transform infrared spectroscopy - attenuated total reflectance (FTIR-ATR) results further revealed the removal of surface impurities as indicated by the production of carbon dioxide. Qualitative and quantitative antibacterial assays proved the efficiency of the samples in inhibiting the growth of bacteria namely Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. The antibacterial efficiency of the samples proportionally increased with longer plasma treatment time. Atmospheric pressure plasma jet could serve as a promising deposition technique with potential application in the production of antibacterial fabrics.

Insights into the lower trophic transfer of silver ions than silver containing nanoparticles along an aquatic food chain

Silver nanoparticles (AgNPs) released into the environment are subject to environmental transformation processes before accumulating in aquatic organisms and transferring along the food chain. Lack of understanding on how environmental transformation affects trophic transfer of AgNPs hinders accurate prediction of the environmental risks of these widely present nanomaterials. Here we discover that pristine AgNPs as well as their sulfidation products (Ag2S-NPs) and dissolution products (Ag+) tend to be accumulated in Daphnia magna and subsequently transferred to zebrafish. In D. magna, Ag+ exhibits the highest bioaccumulation potential whereas Ag2S-NPs show the lowest bioaccumulation. Surprisingly, the biomagnification factor of Ag+ along the D. magna-zebrafish food chain appears to be significantly lower relative to AgNPs and Ag2S-NPs, likely due to the limited release of Ag from D. magna to zebrafish during digestion. Moreover, AgNPs and their transformation products mainly accumulate in the internal organs, particularly intestine, of zebrafish. Adsorption of AgNPs on the surface of the intestinal cell membrane mitigates depuration of AgNPs and, at least in part, leads to the larger biomagnification factor of AgNPs, relative to their transformation products. This research highlights the necessity of considering environmental transformation processes of nanomaterials in assessing their bioavailability and risk.

Silver Nanoparticles Induce Time- and Tissue-Specific Genotoxicity in Oreochromis niloticus: Utilizing the Adsorptive Capacities of Fruit Peels to Minimize Genotoxicity.

Fish were exposed to a sub-lethal concentration of silver nanoparticles with and without orange and banana peels water treatment for 24, 48, and 96h. The adsorption of AgNPs on both peels was recognized by scanning electron microscopic, energy dispersive X-ray spectroscopy, and laser ablation imaging. The % of DNA damage in liver and muscle tissues (comet assay) showed significant elevations in all studied groups with the maximum level in liver tissues after 24h. DNA damage was markedly decreased after 48, and 96h signifying the presence of an effective repairing mechanism. Micronucleus and nine nuclear anomalies were recorded in the peripheral blood cells. All anomalies were observed in all studied groups with a maximum induction rate after 96h. of exposure. Based on the % of DNA damage and the frequencies of nuclear anomalies, water treatment with orange and banana peel succeeded to reduce AgNPs-induced genotoxic damage.

Nucleation and growth mechanism of Cu-Zn/AgNPs composite coatings at different concentrations of silver nanoparticles (AgNPs) in solution

Atomic force microscopy (AFM), X-ray Diffraction (XRD), and electrochemical techniques (voltammetry and chronoamperometry) were used to evaluate the influence of the concentration of silver nanoparticles (AgNPs) on the electrodeposition and nucleation mode of Cu-Zn/AgNPs composite coatings. The voltammetry analysis display three reduction processes during the formation of the Cu-Zn/AgNPs metal composite. The first process (peakPCI) appears in the potential range of -0.5 to -1.2 V vs. saturated calomel electrode (SCE) and corresponds to the reduction of Cu(II) to Cu(0). The second and the third processes, peak PCII and PCIII, respectively are located in the range of -1.4 to -1.6 V vs. SCE and are associated with the deposition of various crystalline phases of the Cu-Zn alloy. The potential of the PCI peak is shifted in the negative direction by increasing the concentration of AgNPs in the electrolytic solution. This effect is related to the adsorption of AgNPs on the substrate surface. From the chronoamperometry study, it was possible to disclose a process of nucleation and growth of phases in the potential region where the peak PCI is formed. This nucleation process may be explained in terms of a combination of an adsorption process and a diffusion-controlled three-dimensional crystal nucleation and growth mechanism (3D−dc(PcI)). In the potential range where the PCII and PCIII peaks appear, a second nucleation process take place. This nucleation process involves three mechanisms: an adsorption process and two three-dimensional (3D) mechanisms of the kinetics of nucleation and diffusion-controlled growth of bimetallic phases (3Ddc−bimetal) that correspond to the nucleation of various phases of the alloys. On the other hand, a decrease in the nucleation kinetics parameters (density of active sites formed (N0) and the nucleation rate (A)) is observed with the increasing concentration of the AgNPs in the electrolytic solution. XRD analysis confirmed the formation of various crystalline structures of the Cu-Zn alloy at -1.50 V vs. SCE. Furthermore, AFM showed that the morphology and size of the formed metal clusters strongly depend on the content of the AgNPs in the bath.

Polyacrylamide hydrogels doped with different shapes of silver nanoparticles: Antibacterial and mechanical properties

The incorporation of nanoparticles into a hydrogel matrix enables the development of innovative smart materials with enhanced biophysical properties. In this proof-of-concept study, we encapsulated different shapes (spherical, triangular and rod) of silver nanoparticles (AgNPs) within a hydrogel matrix of polyacrylamide (PAA) and N-methylenebisacrylamide (MBA) (PAA-MBA) to investigate whether these hydrogels exhibited shape-dependent antimicrobial and mechanical properties. We examined the mechanism of adsorption of different shapes of AgNPs using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Results showed that the adsorption of AgNPs was primarily occurring on the surface/outer pores of the PAA-MBA hydrogel and that rod AgNPs demonstrated a relatively slower adsorption within the hydrogel matrix. The mechanical properties of AgNP-doped hydrogels were evaluated using rheology and atomic force microscopy (AFM) quantitative imaging. We observed a higher storage and Young’s modulus which proved that the incorporation of the various shapes of AgNPs increased the mechanical properties of the hydrogels with no significant differences between the different shapes. While both spherical and triangular AgNP-doped hydrogels showed strong antimicrobial activity, the hydrogel with the rod AgNPs had a relatively lower antimicrobial activity. Overall, our preliminary results demonstrated that nanocomposite hydrogels were promising materials for applications in the future development of wound dressings.

Synthesis of Hydroxyapatite-Ag Composite as Antimicrobial Agent.

Innovative and improved antimicrobial agents by nanotechnology are developed to control and mitigation of resistant microorganisms. Nanoparticles of metals or oxide metals be able to be toxic to bacteria, demonstrating biocidal behaviors at low concentrations. The integration of silver nanoparticles in ceramic matrices has enhanced the antimicrobial performance, resulting in the search for new composites with improved bactericidal properties. The aim of this study was to prepare and characterize hydroxyapatite-silver nanocomposite and evaluate its antimicrobial properties against various Gram-positive and negative bacteria related to drug-resistance infections. Hydroxyapatite nanopowders were produced by sol-gel and silver nanoparticles were synthesized by reduction of Ag+ions with the simple addition of gallic acid. Hydroxyapatite-silver composite (HAp-AgNPs) was prepared by adsorption of AgNPs at several concentrations. The results of UV–visible spectroscopy, dynamic light scattering, and transmission scanning electron microscopy revealed the existence of AgNPs with diameters around 6 nm. Scanning electron microscopy and energy dispersive X-ray spectroscopy corroborated the presence of silver disseminated over the surface of hydroxyapatite nanopowders. All HAp-AgNPs composites demonstrated excellent antibacterial effect even at lower silver concentration. HAp-AgNPs composites have a higher possibility for medical applications focused no the control of microorganisms with drug-resistance.

Facile Bacterial Cellulose Nanofibrillation for the Development of a Plasmonic Paper Sensor.

In this present work, a plasmonic sensor is developed through an extremely cheap cellulose-based source, widely known as a food product, nata de coco (NDC). Capturing its interesting features, such as innate surface roughness from naturally grown cellulose during its fermentation period, the engineering and modulation of NDC fibril size and properties were attempted through a high-pressure homogenization (HPH) treatment to obtain highly dense nanofibrils. After the transformation into a thin, paper-sheet form through a casting process, the homogenized bacterial cellulose (HBC) resulting from HPH was compared with the normally agitated bacterial cellulose (BC) pulp and decorated with silver nanoparticles (AgNPs) to produce plasmonic papers, for further application as surface-enhanced Raman scattering (SERS) substrate. As demonstrated in the measurement of Rhodamine 6G (R6G) molecule, the plasmonic HBC paper sheet provided more prominent SERS signals than the plasmonic BC due to its high surface roughness and improved textural properties from the nanofibrillation process favoring better adsorption of AgNPs and effective SERS hotspots generation. The plasmonic HBC obtained a 2 order higher estimated SERS enhancement factor over the plasmonic BC with a limit of detection of approximately 92 fM. Results denote that the proposed approach provides a new, green-synthesis route toward the exploration of biodegradable sources integrated into an inexpensive and simple nanostructuring process for the production of flexible, paper-based, plasmonic sensors.

Synthesis and biochemical characterization of silver nanoparticles grafted chitosan (Chi-Ag-NPs): in vitro studies on antioxidant and antibacterial applications

Metal-based nanoparticles with potential antioxidant and antimicrobial properties have led to their incorporation of biomaterials for human health care importance. The present investigation is to study on the silver nanoparticles grafted chitosan (Chi-Ag-NPs) composite materials due to their potential applications. Chi-Ag-NPs were synthesized by chemical reduction of silver nitrate salts and biodegradable chitosan. The obtained Chi-Ag-NPs were characterised for Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Transmission electron microscopy (TEM), X-ray powder diffraction, antioxidant and antibacterial properties. UV–visible spectra showed the configuration proficiency of Ag-NPs and chitosan. FTIR spectra indicated that the functional groups of chitosan have particular interactions with Ag-NPs. Particle size and TEM analyses showed that Chi-Ag-NPs were equivalently dispersed in matrix with an average size of 10–230 nm. The surface morphological structures of chitosan has played important role in influencing the adsorption of Ag-NPs. Chi-Ag-NPs were tested for their bioactive properties and results exhibited higher antioxidant and antibacterial activities by the addition of Ag-NPs. Chi-Ag-NPs composites were non-toxic to L929 fibroblast cells. The present investigation suggested that chitosan will be a good source for the preparation of bionanocomposite materials and also could be useful in different industrial and biomedical applications.

Adsorption of Bovine Serum Albumin on Silver Nanoparticle Layer Deposited on Mercaptohexylpyridinium‐Coated Quartz Crystal Microbalance with Dissipation Gold Electrode: Studied by Electrochemical Quartz Crystal Microbalance with Dissipation

Increasing use of silver nanoparticles (AgNPs) in different consumer products provokes interest in understanding interactions of AgNPs with biological molecules, e.g., proteins. The adsorption of AgNPs and bovine serum albumin (BSA) onto self‐assembled monolayer of mercaptohexylpyridinium (MHP) on gold surface is described. A quartz crystal microbalance coupled with electrochemical measurements are used to study interactions between AgNPs and BSA. It is found that AgNPs adsorbed on MHP can be considered as highly elastic (stiff) film as the dissipation ΔD ≈ 0. Measurements of the mass loss and the increase in dissipation in parallel with the electrochemical oxidation/reduction of AgNPs shows that albumin adsorption on AgNPs highly diminish electrochemical Ag/AgCl conversion. The formation of a less rigid Ag layer than the original MHP‐AgNPs film is also indicated. The 3D assemblies of nanostructures observed with scanning electron microscopy (SEM) reveal clustering of particles after the redox process.

Duplex-specific nuclease assisted miRNA assay based on gold and silver nanoparticles co-decorated on electrode interface

miRNAs are small non-coding RNAs for gene regulation, which serve as promising biomarkers for the diagnosis of certain diseases. In this contribution, we have proposed a convenient electrochemical biosensing strategy based on the interaction between DNA modified gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs). In principle, citrate capped AuNPs and AgNPs can be co-decorated on the electrode successively. However, with the modification of DNA on AuNPs surface, a strong negative layer is formed. AuNPs@DNA modified electrode could then inhibit subsequent adsorption of AgNPs due to the electrostatic repulsion and steric hindrance effect. As a result, electrochemical response from AgNPs is significantly decreased. On the other hand, in the presence of target miRNA, DNA on AuNPs hybridizes with miRNA and can thus be cyclically digested by duplex-specific nuclease (DSN). Without the shield of DNA, AgNPs can be relaunched at the AuNPs modified electrode. By analyzing the silver stripping peak, highly sensitive detection of miRNA can be achieved. This biosensor exhibits the limit of detection as low as 0.62 fM and a broad linear range from 1 fM to 1 pM. It may hold great potential utility for miRNA assay in the applications of biomedical researches and early clinical diagnosis.

Adsorption Characteristics of Ag Nanoparticles on Cellulose Nanofibrils with Different Chemical Compositions.

The adsorption characteristics of silver nanoparticles (AgNPs) on cellulose nanofibrils (CNFs) were investigated herein with different chemical compositions. Pure cellulose nanofibers (PCNFs), lignocellulose nanofibers (LCNFs) with different lignin contents (LCNF-20% and LCNF-31%), and holocellulose nanofibers (HCNFs) with hemicellulose were used in this study. Furthermore, CNFs and silver nitrate were mixed and reacted at different temperatures, and NaBH4 was used as the reducing agent. First, the effect of temperature on the adsorption of AgNPs on PCNF was studied. At an optimal temperature (45 °C), the effect of the chemical composition of CNF was studied. The overall properties were analyzed using UV-vis spectroscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The AgNPs were found to be spherical under all conditions with average diameter of 5.3 nm (PCNF), 5.6 nm (HCNF), 6.3 nm (LCNF-20%) and 6.6 nm (LCNF-31%). The amount of AgNPs adsorbed on the CNF was observed to vary, based on the chemical composition of the CNF. The adsorption amount of AgNPs was observed to increase in the order of LCNF-20% > PCNF > LCNF-31% > HCNF. The results indicated that phenolic hydroxyl groups present in LCNF significantly affected the adsorption of AgNPs.

Detection of creatinine using silver nanoparticles on a poly(pyrrole) thin film-based surface plasmon resonance sensor

Surface plasmon resonance (SPR) technique is a great tool to investigate the binding of analyte to functionalized surfaces and the immobilization of biomolecules. Creatinine is one of the biomarkers for monitoring renal functions and making a diagnosis of kidney disease. Elevated creatinine levels in the human body signifies impaired kidney disease. In this work, we developed a new strategy for creatinine detection using starch stabilized silver nanoparticles (starch-AgNPs) on poly(pyrrole) (PPy) thin film using the SPR technique. The assay exhibited the obvious change from yellow to orange color of AgNPs solution in the presence of creatinine, showing good sensitivity due to the localized plasmon effect of AgNPs. Based on this effect, the change of SPR reflectivity in the Kretschmann configuration was enhanced by the adsorption of AgNPs in the presence of creatinine on the PPy film. The SPR reflectivity upon the injection of the mixed solution on the PPy thin film increased with increasing creatinine concentration in the linear range from 10 to 1000 μM. As a comparison, performances of the creatinine sensor with three SPR sensor systems, i.e. only PPy film, PPy film with AgNPs, and PPy film with aggregated AgNPs, were studied. The SPR sensor with aggregated AgNPs was improved approximately four times compared with the substrate without aggregated AgNPs, and the limit of the detection was 0.19 μM. The proposed method is potentially useful for clinical applications.

Silver nanoparticles inhibit denitrification by altering the viability and metabolic activity of Pseudomonas stutzeri

The environmental toxicity of silver nanoparticles (AgNPs) is currently the focus of intensive research. However, the mechanisms underlying the cytotoxic effects of AgNPs on denitrifying microbes have yet to be explicitly demonstrated. Herein, Pseudomonas stutzeri was used to explore the effects of AgNPs on denitrification and cytotoxicity. The denitrification efficiency decreased from 94.91% in the AgNP-free treatment to 87.66%, 60.51% and 36.10% with treatments of 3.125, 6.25 and 12.5 mg/L AgNPs, respectively. The inhibition and delay in the denitrification process from treatment with AgNPs likely occurred through alteration of the viability and metabolic activity of P. stutzeri. Flow cytometry analysis indicated that the early apoptotic rates of P. stutzeri were 8.72%, 30.60%, and 48.60% with treatments of 3.125, 6.25, and 12.5 mg/L AgNPs, respectively. Results for scanning electron microscope (SEM) imaging, ζ-potential analysis, lactate dehydrogenase (LDH) release and malondialdehyde (MDA) production assays demonstrated adsorption of AgNPs on the cell surface, which altered membrane potential and mediated lipid peroxidation; these events eventually resulted in the aberration of cell morphology. Transmission electron microscopy (TEM) images and measurements of Ag content distribution by ICP-MS indicated that AgNPs were easily internalized by P. stutzeri, which increased the accumulation of reactive oxygen species (ROS). Furthermore, the presence of AgNPs also greatly inhibited expression of genes napA, nirS, cnorB, and nosZ, thereby reducing the activities of nitrate reductase (NAR) and nitrite reductase (NIR). These findings will help further our understanding of the mechanism underlying AgNPs cytotoxicity, and provide the means to evaluate the negative effect of nanoparticles in the environment.

Removal of silver nanoparticles in aqueous solution by activated sludge: Mechanism and characteristics

The increasing production and use of silver nanoparticles (AgNPs) have attracted more and more attention due to their environmental and health risks. Municipal sewage biological treatment unit has been playing an important role in the removal of AgNPs. This study investigated the mechanism and characteristics of AgNPs and their removal from aqueous solution by activated sludge. Results from Scanning Electron Microscope and Energy Dispersive Spectrometer (SEM/EDS) showed that mixed AgNPs were immobilized by activated sludge. It was shown by X-ray photoelectron spectroscopy (XPS) that the fixed AgNPs had an oxidation state of +1. It was inferred by fourier transform infra-red (FTIR) spectra that AgNPs were adsorbed by activated sludge via binding with its primary amino (R-NH2) radical groups on the surface. These results revealed that the major mechanism for the removal of AgNPs by activated sludge was adsorption. The experiment data were in agreement with the Langmuir and Redlich-Peterson isotherms. The maximum adsorption capacity ranged from 12–32 mg g−1 at temperatures of 10–30 °C. Thermodynamic experiment showed that the adsorption of AgNPs by activated sludge was a spontaneous and endothermic reaction. The adsorption kinetics data were in good agreement with the pseudo-second-order model. The factor results indicated that the adsorption of AgNPs onto activated sludge was influenced by electrostatic repulsion, agglomeration, and the process of oxidation and sulfurization.

Heteroaggregation and dissolution of silver nanoparticles by iron oxide colloids under environmentally relevant conditions

Electrostatic interactions governed the adsorption of AgNPs by iron oxide colloids under environmentally relevant conditions.

Interactions Between Silver Nanoparticles/Silver Ions and Liposomes: Evaluation of the Potential Passive Diffusion of Silver and Effects of Speciation.

Silver nanoparticles, used mainly for their antibacterial properties, are among the most common manufactured nanomaterials. How they interact with aquatic organisms, especially how they cross biological membranes, remains uncertain. Free Ag+ ions, released from these nanoparticles, are known to play an important role in their overall bioavailability. In this project, we have studied the uptake of dissolved and nanoparticulate silver by liposomes. These unilamellar vesicles, composed of phospholipids, have long been used as models for natural biological membranes, notably to study the potential uptake of solutes by passive diffusion through the phospholipid bilayer. The liposomes were synthesized using extrusion techniques and were exposed over time to dissolved silver under different conditions where Ag+, AgS2O3-, or AgCl0 were the dominant species. Similar experiments were conducted with the complexes HgCl 2 0 and Cd(DDC) 2 0 , both of which are hydrophobic and known to diffuse passively through biological membranes. The uptake kinetics of Ag+, HgCl 2 0 , and Cd(DDC) 2 0 show no increase in internalized concentrations over time, unlike AgS2O3- and AgCl0, which appear to pass through the phospholipid bilayer. These results are in contradiction with our initial hypothesis that lipophilic Hg and Cd complexes would be able to cross the membrane, whereas silver would not. Encapsulated tritiated water inside the liposomes was shown to rapidly diffuse through the lipid bilayer, suggesting a high permeability. We hypothesize that monovalent anions or complexes as well as small neutral complexes with a strong dipole can diffuse through our model membrane. Finally, liposomes were exposed to 5-nm polyvinylpyrrolidone-coated silver nanoparticles over time. No significant uptake of nanoparticulate silver was observed. Neither disruption of the membrane nor invagination of nanoparticles into the liposomes was observed. This suggests that the main risk caused by AgNPs for nonendocytotic biological cells would be the elevation of the free silver concentration near the membrane surface due to adsorption of AgNPs and subsequent oxidation/dissolution.

Simultaneous adsorption of silver nanoparticles and silver ions on large pore mesoporous silica

Large pore mesoporous silica was synthesized using citric acid as template and modified with mercaptopropyl trimethoxysilane. The MP-Silica exhibited a surface area of 474 m2 g−1 with an average pore diameter of 11 nm (pore diameter ranging from 2 to 30 nm). The material was used in the adsorption of silver ions, AgNPs and simultaneous adsorption of these silver species was also observed. The adsorption of silver ions occurred rapidly and followed a pseudo-second order kinetic model. The adsorption equilibrium of silver ions could be described with a Langmuir isotherm and the maximum adsorption capacity was found to be 114.9 mg g−1. In the mixture of AgNPs and silver ions, the adsorption of AgNPs followed a pseudo-second order kinetic model and took place more slowly compared to silver ions due to their larger size. The MP-Silica exhibited a maximum adsorption capacity of 91.9 mg AgNPs g−1 in the mixture. The adsorption of silver species on MP-Silica occurred through chemisorption via the coordination of these species with thiol groups on the surface. The removal of silver species from wastewater samples and consumer products by MP-Silica was demonstrated.

Nanocomposite films based on chitosan–poly(vinyl alcohol) and silver nanoparticles with high antibacterial and antioxidant activities

Abstract The present study focused on the synthesis of chitosan–silver nanocomposite films (CSNFs) due to their potential application in various domains including wound dressing, packaging and water purification. Silver nanoparticles (Ag NPs) were generated in-situ by using UV-irradiation and chitosan (CS) as both reductant and stabilizer. FTIR spectra revealed that the primary amine and amide groups of chitosan have specific interactions with nanoparticles surface. The diameter of AgNPs ranged from 170 to 200 nm as determined by DLS and TEM observation. Furthermore, CSNFs were tested for their biological activities and results showed higher antioxidant and antibacterial activities than chitosan film, which increased with AgNPs amount, suggesting that surface structures of chitosan strongly influence the adsorption of AgNPs and the antimicrobial activities. These observations indicate that nanocomposite films have potential applications as anti-infectious wound dressing. Many studies reported the toxicity of AgNPs and their health and environmental risks. For that purpose, cytotoxicity of CS–AgNPs was performed by MTT assay on Chinese hamster ovary R(CHO-K1) cell lines. Results showed that CS–AgNPs have no-cytotoxicity effect, which suggests the possibility of CS–AgNPs uses in foods and biomedical applications.

Antibacterial thermoplastic polyurethane electrospun fiber mats prepared by 3-aminopropyltriethoxysilane-assisted adsorption of Ag nanoparticles

Antibacterial thermoplastic polyurethane (TPU) electrospun fiber mats were prepared by adsorption of Ag nanoparticles (Ag NPs) onto TPU/3-aminopropyltriethoxysilane (APS) co-electrospun fiber mats from silver sol. The use of APS can functionalize TPU fibers with amino groups, facilitating the adsorption of Ag NPs. The effects of pH of silver sol and APS content on Ag NP adsorption and antibacterial activity were investigated. Ag NP adsorption was evidenced by TEM, XPS and TGA. Significant Ag NP adsorption occurred at pH = 3−5. The main driving force for Ag NP adsorption is electrostatic interaction between ―NH3 + of the fibers and ―COO− derived from the ―COOH group capped on the surfaces of Ag NPs. The antibacterial activity of the Ag NP-decorated TPU/APS fiber mats was investigated using both gram-negative Escherichia coli and gram-positive Bacillus subtilis. The antibacterial rate increases with increasing APS content up to 5% where the antibacterial rates against both types of bacteria are over 99.9%.

Removal of silver nanoparticles by mussel-inspired Fe3O4@ polydopamine core-shell microspheres and its use as efficient catalyst for methylene blue reduction

The removal of silver nanoparticles (AgNPs) from water is highly needed because of their increasing use and potential risk to the environment due to their toxic effects. Catalysis over AgNPs has received significant attention because of their highly catalytic performance. However, their use in practical applications is limited due to high cost and limited resources. Here, we present for the first time that the mussel-inspired Fe3O4@polydopamine (Fe3O4@PDA) nanocomposite can be used for efficient removal and recovery of AgNPs. Adsorption of AgNPs over Fe3O4@PDA was confirmed by TEM, FT-IR, XRD, TGA and magnetic property. The adsorption efficiency of AgNPs by Fe3O4@PDA was investigated as a function of pH, contact time, ionic strength and concentration of AgNPs. The kinetic data were well fitted to a pseudo-second order kinetic model. The isotherm data were well described by Langmuir model with a maximum adsorption capacity of 169.5 mg/g, which was higher than those by other adsorbents. Notably, the obtained AgNPs-Fe3O4@PDA exhibited highly catalytic activity for methylene blue reduction by NaBH4 with a rate constant of 1.44 × 10−3/s, which was much higher than those by other AgNPs catalysts. The AgNPs-Fe3O4@PDA promised good recyclability for at least 8 cycles and acid resistant with good stability.