A gentle method to graft thiol-functional groups onto silica gel for adsorption of silver ions and immobilization of silver nanoparticles

Magnetic covalent organic framework for the adsorption of silver nanoparticles and recycled as surface-enhanced Raman substrate and high-efficiency catalysts for 4-nitrophenol degradation

A magnetic covalent organic framework Fe₃O₄@BM was prepared with melamine and 4-4'-biphenyldialdehyde as monomers and used as adsorbent for Ag NP removal. Fe₃O₄@BM was characterized by zeta potential analysis, transform infrared spectrometry, X-ray diffraction, thermogravimetric analysis, contact angle, and N₂ adsorption-desorption. Fe₃O₄@BM possessed plentiful amino groups, positive potential, and rapid separation performance, making it a promising adsorbent for silver nanoparticles. The adsorption process followed the pseudo-second-order kinetic equation and Langmuir isotherm model. The maximum adsorption capacity of Ag NPs calculated by the Langmuir isotherm model was 544.9 mg/g. The adsorption product Fe₃O₄@BM@Ag could be recycled and efficiently catalyze the degradation of 4-nitrophenol within 6 min. Meanwhile, the recycled Fe₃O₄@BM@Ag could also be used as a surface-enhanced Raman substrate for DTNB detection, and the limit of detection of DTNB reached as low as 10^-7 mol/L. This work prepared a promising adsorbent Fe₃O₄@BM for Ag NP adsorption and provided a sustainable approach for the recycling of the adsorption product Fe₃O₄@BM@Ag.

Imidazolium-Modified Silica Gel for Highly Selective Preconcentration of Ag(I) from the Nitric Acid Medium

The ion-exchange behavior of an organomineral material with an imidazolium (1-methyl-3-(prop-2-yn-1-yl)-1H-imidazol-3-ium bromide)-modified silica gel was studied for the extraction of Ag(I) from nitric acid media. The extraction from multicomponent systems containing Fe(III), Co(II), Ni(II), Cu(II), Pb(II), and Mn(II) in 100- and 1000-fold molar excesses with respect to Ag(I) was shown to occur with high selectivity. Based on the data of X-ray diffraction and X-ray fluorescence spectroscopy for samples of modified silica gel, a mixed ion exchange–adsorption mechanism for the extraction of Ag(I) was proposed. The effect of the phase contact time and the concentration of nitric acid on the distribution coefficient of Ag(I) was studied. The selectivity factors of the extraction of Ag(I) from multicomponent systems containing foreign cations in 100- and 1000-fold molar excesses under steady-state and dynamic concentration conditions were calculated.

Transport of tetracycline in saturated porous media: combined functions of inorganic ligands and solution pH

To date, there is still very little knowledge about the combined effects of typical inorganic ligands and solution pH values on mobility characteristics of tetracycline (TC) through saturated aquifer media. In this work, three typical inorganic ligands (i.e., phosphate, silicate, and iodate) were employed in the transport experiments. Generally, all the ligands promoted TC mobility over the pH range of 5.0-9.0 owing to the enhanced electrostatic repulsion between sand grains and TC anionic forms (i.e., TC^- and TC^2-) as well as the competitive deposition between ligands and antibiotic molecules for attachment sites. Furthermore, the transport-enhancement effects of ligands on TC intensively depended on ligand type and followed the sequence of phosphate > silicate > iodate. This phenomenon was ascribed to their different molecular sizes and binding abilities to sand grains. Interestingly, the differences in extents of enhanced effects of various inorganic ligands on TC transport varied with background solution pH due to pH-induced different extents of deposition site competition effects. Moreover, the two-site nonequilibrium model (which accounts for an equilibrium site and a kinetic site) as well as adsorption and kinetic studies were performed to help interpret the controlling mechanisms for the synergistic effects of inorganic ligands and solution pH on TC transport in saturated quartz sand. The findings of our study clearly demonstrate that inorganic ligands may be critical factors in assessing the fate and transport of antibiotics in groundwater systems.

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

Supported nanoparticles are commonly applied in heterogeneous catalysis. The catalytic performance of these solid catalysts is, for a given support, dependent on the nanoparticle size, shape, and composition, thus necessitating synthesis techniques that allow for preparing these materials with fine control over those properties. Such control can be exploited to deconvolute their effects on the catalyst's performance, which is the basis for knowledge-driven catalyst design. In this regard, bottom-up synthesis procedures based on colloidal chemistry or atomic layer deposition (ALD) have proven successful in achieving the desired level of control for a variety of fundamental studies. This review aims to give an account of recent progress made in the two aforementioned synthesis techniques for the application of controlled catalytic materials in gas-phase catalysis. For each technique, the focus goes to mono- and bimetallic materials, as well as to recent efforts in enhancing their performance by embedding colloidal templates in porous oxide phases or by the deposition of oxide overlayers via ALD. As a recent extension to the latter, the concept of area-selective ALD for advanced atomic-scale catalyst design is discussed.

Two Novel BODIPY-Functional Magnetite Fluorescent Nano-Sensors for Detecting of Cr(VI) Ions in Aqueous Solutions

In this study, we developed two different very sensitive magnetite fluorescent Fe₃O₄@SiO₂-TPED-BODIPY and Fe₃O₄@SiO₂-TMPTA-BODIPY nano-sensors for the selective detection of Cr(VI) ions. The Cr(VI) metal ions sensing is based on the fluorescent quenching of BODIPY functionalized with Fe₃O₄@SiO₂-TPED and Fe₃O₄@SiO₂-TMPTA nanoparticles in the ethanol-water environment. Characterization of the newly synthesized fluorescent BODIPY compound was performed on a ¹H and ¹³C-NMR spectrometer. The morphology, chemical and physical properties of the sensing nano-sensors were studied by transmission thermogravimetric analysis (TGA), X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscopy (SEM), FT-IR spectroscopy, and transmission electron microscopy (TEM). UV-visible and fluorescent spectroscopy were used to characterize BODIPY functionalized magnetite fluorescent nano-sensors. Characterization measurements revealed that the mean particle diameter of magnetite fluorescent Fe₃O₄@SiO₂-TPED-BODIPY and Fe₃O₄@SiO₂-TMPTA-BODIPY nano-sensors was 18.5 and 19 nm, respectively. The magnetite fluorescent Fe₃O₄@SiO₂-TPED-BODIPY and Fe₃O₄@SiO₂-TMPTA-BODIPY nano-sensors (0.1 gL^-1 in EtOH/H₂O, v/v (3/7)) showed fluorescence quenching responses towards Cr(VI) ions in the medium at pH:1. The fluorescence quenches of the magnetite fluorescent Fe₃O₄@SiO₂-TPED-BODIPY and Fe₃O₄@SiO₂-TMPTA-BODIPY nano-sensors by Cr(VI) were completed in first 5 and 3 min. Respectively. These features provide potential uses of BODIPY functionalized magnetite fluorescent nano-sensors (Fe₃O₄@SiO₂-TPED-BODIPY and Fe₃O₄@SiO₂-TMPTA-BODIPY) as a new class of non-toxic sensors for environmental applications. Graphical Abstract.

Polyethylenimine modified potassium tungsten oxide adsorbent for highly efficient Ag+ removal and valuable Ag0 recovery

Elemental Ag⁰ is well known for its remarkable catalytic and antibacterial properties, thus the regeneration of valuable Ag⁰ metal from Ag⁺ wastewater is of great significance. In this study, a novel polyethylenimine (PEI) modified potassium tungsten oxide (N-K₂W₄O₁₃) adsorbent was prepared for Ag⁺ removal and reduction to Ag⁰ using glutaraldehyde as crosslinking agent. XPS and FT-IR spectra verified PEI successfully anchored on the surface O and W atoms of K₂W₄O₁₃ through aldehyde bridges. The content of PEI in N-K₂W₄O₁₃ was calculated as 8.74wt% by TG curve. A heterogeneous PEI coating was observed in the SEM and TEM images. The N-K₂W₄O₁₃ exhibited larger Ag⁺ uptake (48.25mg/g) than the raw K₂W₄O₁₃ (42.50mg/g) though required a longer equilibrium time. This was due to the combined results of strong chelation and weak electrostatic repulsion that meanwhile occurring on the positive-charged surface of N-K₂W₄O₁₃. The maximum Ag⁺ uptake on N-K₂W₄O₁₃ was 72.5mg/g, which was larger than many of the reported adsorbents. Furthermore, the prepared N-K₂W₄O₁₃ displayed good anti-interference toward background ions (Na⁺, K⁺) and hold a stable Ag⁺ removal (>95%) after five runs of recycling tests. The mechanism studies elucidated that NH/N groups from the PEI modified N-K₂W₄O₁₃ mainly accounted for the Ag⁺ adsorption and Ag⁰ recovery in the adsorption-reduction process. Ion-exchange between Ag⁺ and K⁺ from the N-K₂W₄O₁₃ lattice also occurred. This work provided a facile method to synthesize a promising adsorbent for Ag⁺ wastewater remediation and valuable Ag⁰ recovery.

Morphology-controlled copper nanowire synthesis and magnetic field assisted self-assembly

Morphology, dimensions, crystalline structure and compositions of nanomaterials are very critical in determining their unique characteristics. Here we report how the reducing agent concentration affects the surface morphology of copper nanowires and establish the optimized reaction conditions to synthesize high aspect ratio nanowires with a smooth surface. Also, reported is the magnetic field assisted technique to control the orientational and positional ordering of cupronickel nanowires (Cu/Ni NWs) on a large-scale area. A combination of magnetic field, surface derivatization and photolithographic techniques allowed self-assembly of Cu/Ni NWs into channels. The channel resistance as a function of the applied magnetic field during fabrication shows an anomalous decrease owing to the positional end-to-end alignment of NWs. Magnetic field and areal NW density dependence of NW sheet resistance in channels is presented and analyzed using scaling theoretical models.

Kinetic, Isotherm, and Thermodynamic Studies for Ag(I) Adsorption Using Carboxymethyl Functionalized Poly(glycidyl methacrylate)

Industrial wastewater contains large amounts of silver ions. Here, a new adsorbent was synthesized by functionalizing poly(glycidyl methacrylate) with carboxymethyl groups. The adsorbent was used to recover Ag(I) in wastewater. Fourier transform infrared spectroscopy, zeta potential, scanning electron microscopy, and X-ray photoelectron spectroscopy were used to characterize the adsorbent. The experimental parameters affecting the adsorption are solution pH, contact time, and initial silver ion concentration. The optimum pH for adsorption of Ag(I) is pH 4. The maximum adsorption capacity at pH 4 is 157.05 mg/g, and the adsorption reaches equilibrium at 300 min. The kinetics and isotherms of the adsorption process were described by pseudo second-order, Langmuir and D-R models, respectively. The adsorption process was a single layer chemical adsorption, exothermic, feasible, and spontaneous. The adsorption mechanism is electrostatic or chelation. The adsorbent selectively absorbed Ag(I) from coexisting ions (Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺). Finally, the removal rate of silver ions decreased from 79.29% to 65.01% after four repetitive experiments, which proved that the adsorbent had good reusability. The adsorbent has great potential benefit in removing Ag(I).

A selective and sensitive nanosensor for fluorescent detection of specific IgEs to purified allergens in human serum

Food allergies are increasingly recognized as a major healthcare concern. In order to sensitively and specifically detect allergies from blood samples of at-risk allergic patients, an effective magnetic fluorescence sensing platform (EMFP) was constructed. The EMFP incorporated hollow mesoporous silica nanospheres (HMNs) to amplify signal from the target IgE in addition to magnetic nanoparticles (MNPs) to capture and separate the target IgE. The application of EMFP to immunoassays indicated a detection limit of 0.0159 ng mL⁻¹ for low concentration specific immunoglobulin E (sIgE) against purified shellfish Metapenaeus ensis (Meta. E.) allergens, which is 15 fold more sensitive than the commercially available Food and Drug Administration-approved analyzers. Notably, EMFP was specific for the targeted sIgE even with interference by other sIgEs. In addition, the detection time is only 75 min, considerably faster than current commercial ELISA kits for IgE assays. Together, these results demonstrated that EMFP has excellent sensitivity and selectivity for the rapid detection of sIgE. The method thus exhibits potential toward the rapid monitoring of sIgE against Meta. E. allergens in clinical application.

The effective magnetic fluorescence sensing platform was employed to amplify signal and capture target IgE in one step.

Silver Nanoparticle Generators: Silicon Dioxide Microspheres

A green and simple approach has been developed to synthesize un-coated Ag nanoparticles (AgNPs) in situ on the surface of thiol-group-functionalized silica dioxide microspheres (TSMs) in the aqueous solution. As soon as the Ag⁺ ions attach onto the surface of TSMs, nucleation and growth of AgNPs can spontaneously complete within one minute without other reducing agents or capping agents. The main reason is that the self-assembled silane-layer formed by mercaptosilane molecules could reduce the Ag⁰ formation energy, transport electrons efficiently, improve the nucleation density, and protect AgNPs against oxidation. Thus, the supported AgNPs show excellent chemical/photochemical stability in air and solution. Meanwhile, the size of as-prepared AgNPs could be controlled by tuning the concentration of Ag⁺ ions. This process provides a general route to generate bare AgNPs on the surface of silica dioxide in situ, which might be extended to other materials and is promising in developing novel methodologies for making supported noble metal NPs with desired structure and properties.

Fabrication of ZIF-8@SiO2 Micro/Nano Hierarchical Superhydrophobic Surface on AZ31 Magnesium Alloy with Impressive Corrosion Resistance and Abrasion Resistance

Superhydrophobic coatings are highly promising for protecting material surfaces and for wide applications. In this study, superhydrophobic composites, comprising a rhombic-dodecahedral zeolitic imidazolate framework (ZIF-8@SiO₂), have been manufactured onto AZ31 magnesium alloy via chemical etching and dip-coating methods to enhance stability and corrosion resistance. Herein, we report on a simple strategy to modify hydrophobic hexadecyltrimethoxysilan (HDTMS) on ZIF-8@SiO₂ to significantly improve the property of repelling water. We show that various liquids can be stable on its surface and maintain a contact angle higher than 150°. The morphologies and chemical composition were characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FI-IR). In addition, the anticorrosion and antiattrition properties of the film were assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization and HT, respectively. Such a coating shows promising potential as a material for large-scale fabrication.

Antimicrobial Properties of Biofunctionalized Silver Nanoparticles on Clinical Isolates of Streptococcus mutans and Its Serotypes

(1) Background: Streptococcus mutans (S. mutans) is the principal pathogen involved in the formation of dental caries. Other systemic diseases have also been associated with specific S. mutans serotypes (c, e, f, and k). Silver nanoparticles (SNP) have been demonstrated to have good antibacterial effects against S. mutans; therefore, limited studies have evaluated the antimicrobial activity of biofunctionalized SNP on S. mutans serotypes. The purpose of this work was to prepare and characterize coated SNP using two different organic components and to evaluate the antimicrobial activity of SNP in clinical isolates of S. mutans strains and serotypes; (2) Methods: SNP with bovine serum albumin (BSA) or chitosan (CS) coatings were prepared and the physical, chemical and microbiological properties of SNP were evaluated; (3) Results: Both types of coated SNP showed antimicrobial activity against S. mutans bacteria and serotypes. Better inhibition was associated with smaller particles and BSA coatings; however, no significant differences were found between the different serotypes, indicating a similar sensitivity to the coated SNP; (4) Conclusion: This study concludes that BSA and CS coated SNP had good antimicrobial activity against S. mutans strains and the four serotypes, and this study suggest the widespread use of SNP as an antimicrobial agent for the inhibition of S. mutans bacteria.

C,N-bipyrazole receptor grafted onto a porous silica surface as a novel adsorbent based polymer hybrid

A simple heterogeneous synthesis of pure adsorbent based polymer hybrid made by condensing a functionalized C,N-bipyrazole with a 3-glycidoxypropyl-trimethoxysilane silylant agent, previously anchored on a silica surface was developed. The formed material (SG2P) was characterized through elemental analysis, FT-IR spectroscopy, (13)C NMR of solid state, scanning electron microscope (SEM), and was studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and B.J.H. pore sizes. The new material exhibits good thermal stability determined by thermogravimetry curves and good chemical stability was examined in various acidic and buffer solutions (pH 1-7). The binding and adsorption abilities of SG2P were investigated for Hg(2+), Cd(2+), Pb(2+), Zn(2+), K(+), Na(+) and Li(+) cations and compared to the results of classical liquid-liquid extraction with the unbound C,N-bipyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SG2P exhibits a high selectivity toward Hg(2+) ion with no complexation being observed towards zinc and alkali metals. The extracted and the complexing cation percentages were determined by atomic absorption measurements.

Mesoporous organosilica nanoparticles containing superacid and click functionalities leading to cooperativity in biocidal coatings

A superior degree of functionality in materials can be expected, if two or more operational entities are related in a cooperative form. It is obvious that, for this purpose, one is seeking materials with complex design comprising bi- or multiple functional groups complementing each other. In the current paper, it is demonstrated that periodically ordered mesoporous organosilicas (PMOs) based on co-condensation of sol-gel precursors with bridging phenyl derivatives RF1,2C6H3[Si(O(iso)Pr)3]2 allow for rich opportunities in providing high-surface area materials with such a special chemical architecture. PMOs containing high density of thiol (≅ RF1) and sulfonic acid units (≅ RF2) were prepared as mesoporous nanoparticles via an aerosol-assisted gas-phase method and were tested for biocidal applications. Each of the mentioned organic groups fulfills several tasks at once. The selective functionalization of thiols located at the surface of the particles using click chemistry leads to durable grafting on different substrates like glass or stainless steel, and the intraparticle -SH groups are important regarding the uptake of metal ions like Ag(+) and for immobilization of Ag(0) nanoparticles inside the pores as an enduring reservoir for antibacterial force. The superacidic sulfonic acid groups exhibit a strong and instantaneous biocidal acitivity, and they are important for adjusting the Ag(+) release rate. Biological studies involving inhibitory investigation tests (MIC), fluorescence microscopy (life/dead staining), and bacterial adhesion tests with Pseudomonas aeruginosa show that the organobifunctional materials present much better performance against biofilm formation compared to materials containing only one of the above-mentioned groups.

Development of negatively charged particulate surfaces through a dry plasma-assisted approach

A completely dry method has been introduced for the development of negatively charged oxidized sulfur-terminated particles.

The Effect of Hydrothermal Treatment on Silver Nanoparticles Stabilized by Chitosan and Its Possible Application to Produce Mesoporous Silver Powder

Aggregation state of silver nanoparticles dispersed in an aqueous solution greatly varies with storage and treatment conditions. In this study, silver nanoparticles synthesized in chitosan solution by a chemical reduction method were hydrothermally treated at different temperatures. The variation in the aggregation state of silver nanoparticles in the solution was observed by UV-Vis spectroscopy and field emission transmission electron microscopy. Results indicated that a phase transition occurred while silver nanoparticles were hydrothermally treated for 5 h at 100 and 120∘C; however, they aggregated and completely precipitated at 150∘C. Mesoporous silver powder obtained by hydrothermal treatment at 150∘C was characterized by using X-ray diffraction technique, BET analyzer, and scanning electron spectroscope.