Recycling functional colloids and nanoparticles

Composites of Montmorillonite and Titania Nanoparticles Prepared by Inverse Microemulsion Method: Physico-Chemical Characterization

TiO₂/montmorillonite composites were synthesized using inverse micellar route for the preparation of titania nanoparticles (4-6 nm diameter) in 1-hexanol and for the dispersion of one of the clay components. Two series of composites were obtained: one derived from cetyltrimethylammonium organomontmorillonite (CTA-Mt), exfoliated in 1-hexanol, and the other from sodium form of montmorillonite (Na-Mt) dispersed by formation of an inverse microemulsion in 1-hexanol. The TiO₂ content ranged from 16 to 64 wt.%. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopy/energy dispersive X-ray spectroscopy, thermal analysis, and N₂ adsorption-desorption isotherms. The Na-Mt-derived component was shown to undergo transformation to CTA-Mt, as indicated by basal spacing of 17.5 nm, due to the interaction with the CTABr surfactant in inverse microemulsion. It was also better dispersed and intermixed with TiO₂ nanoparticles. As a result, the TiO₂/Na-Mt series displayed superior textural properties, with specific surface area up to 256 m²g^-1 and pore volume up to 0.247 cm³g^-1 compared with 208 m²g^-1 and 0.231 cm³g^-1, respectively, for the TiO₂/CTA-Mt counterpart. Members of both series were uniformly mesoporous, with the dominant pore size around 5 nm, i.e., comparable with the dimensions of titania nanoparticles. The advantage of the adopted synthesis method is discussed in the context of other preparative procedures used for manufacturing of titania-clay composites.

Surfactant stabilized gold nanomaterials for environmental sensing applications - A review

Surfactant stabilized Gold (Au) nanomaterials (NMs) have been documented extensively in recent years for numerous sensing applications in the academic literature. Despite the crucial role these surfactants play in the sensing applications, the comprehensive reviews that highlights the fundamentals associated with these assemblies and impact of these surfactants on the properties and sensing mechanisms are still quite scare. This review is an attempt in organizing the vast literature associated with this domain by providing critical insights into the fundamentals, preparation methodologies and sensing mechanisms of these surfactant stabilized Au NMs. For the simplification, the surfactants are divided into the typical and advanced surfactants and the Au NMs are classified into Au nanoparticles (NPs) and Au nanoclusters (NCs) depending upon the complexity in structure and size of the NMs respectively. The preparative methodologies are also elaborated for enhancing the understanding of the readers regarding such assemblies. The case studies regarding surfactant stabilized Au NMs were further divided into colorimetric sensors, surface plasmonic resonance (SPR) based sensors, luminescence-based sensors, and electrochemical/electrical sensors depending upon the property utilized by the sensor for the sensing of an analyte. Future perspectives are also discussed in detail for the researchers looking for further progress in that particular research domain.

Shape- and size-dependent desorption kinetics and surface acidity of nano-SnO2

With the decrease of particle size, Ed and ln A increase, and Ed octahedron > Ed sphere and ln A octahedron > ln A sphere.

Novel analytical expressions for determining van der Waals interaction between a particle and air-water interface: Unexpected stronger van der Waals force than capillary force

HYPOTHESIS

Analytical expressions for calculating Hamaker constant (HC) and van der Waals (VDW) energy/force for interaction of a particle with a solid water interface has been reported for over eighty years. This work further developed novel analytical expressions and numerical approaches for determining HC and VDW interaction energy/force for the particle approaching and penetrating air-water interface (AWI), respectively.

METHODS

The expressions of HC and VDW interaction energy/force before penetrating were developed through analysis of the variation in free energy of the interaction system with bringing the particle from infinity to the vicinity of the AWI. The surface element integration (SEI) technique was modified to calculate VDW energy/force after penetrating.

FINDINGS

We explain why repulsive VDW energy exists inhibiting the particle from approaching the AWI. We found very significant VDW repulsion for a particle at a concave AWI after penetration, which can even exceed the capillary force and cause strong retention in water films on a solid surface and at air-water-solid interface line. The methods and findings of this work are critical to quantification and understanding of a variety of engineered processes such as particle manipulation (e.g., bubble flotation, Pickering emulsion, and particle laden interfaces).

Titania-Clay Mineral Composites for Environmental Catalysis and Photocatalysis

The use of titania-based composite materials in the field of heterogeneous catalysis and photocatalysis has a long and rich history. Hybrid structures combining titania nanoparticles with clay minerals have been extensively investigated for nearly four decades. The attractiveness of clay minerals as components of functional materials stems primarily from their compositional versatility and the possibility of using silicate lamellae as prefabricated building blocks ready to be fitted into the desired nanoconstruction. This review focuses on the evolution over the years of synthetic strategies employed for the manufacturing of titania–clay mineral composites with particular attention to the role of the adopted preparative approach in shaping the physical and chemical characteristics of the materials and enabling, ultimately, tuning of their catalytic and/or photocatalytic performance.

Promising opportunities and potential risk of nanoparticle on the society

The ever-promising opportunities and the uses of NP in our life are increasing but their present and future potential risks on the animals, plants and microorganisms are not well discussed elsewhere. In this review, the authors have systematically discussed the toxic effect of the uses of NP on animals, plants and microorganisms including human health. They have also discussed about the bioaccumulation of these NP in the food chain. Finally, they have provided some possible suggestions for the uses of NP to reduce the detrimental effect on the environment.

Tunable Molybdenum Disulfide-Enabled Fiber Mats for High-Efficiency Removal of Mercury from Water

The application of molybdenum disulfide (MoS₂) for water decontamination is expanded toward a novel approach for mercury removal using nanofibrous mats coated with MoS₂. A bottom-up synthesis method for growing MoS₂ on carbon nanofibers was employed to maximize the nanocomposite decontamination potential while minimizing the release of the nanomaterial to treated water. First, a co-polymer of polyacrylonitrile and polystyrene was electrospun as nanofibrous mats and pretreated to form pristine carbon fibers. Next, three solvothermal methods of controlled in situ MoS₂ growth of different morphologies were achieved on the surface of the fibers using three different sets of precursors. Finally, these MoS₂-enabled fibers were extensively characterized and evaluated for their mercuric removal efficiency. Two mercury removal mechanisms, including reduction-oxidation reactions and physicochemical adsorption, were elucidated. The two nanocomposites with the fastest (0.436 min^-1 mg^-1) and highest mercury removal (6258.7 mg g^-1) were then further optimized through intercalation with poly(vinylpyrrolidone), which increased the MoS₂ interlayer distance from 0.68 nm to more than 0.90 nm. The final, optimal fabrication technique (evaluated according to mercuric capacity, kinetics, and nanocomposite stability) demonstrated five times higher adsorption than the second-best method and obtained 70% of the theoretical mercury adsorption capacity of MoS₂. Overall, results from this study indicate an alternative, advanced material to increase the efficiency of aqueous mercury removal while also providing the basis for other novel environmental applications such as selective sensing, disinfection, and photocatalysis.

Gold Recycling at Laboratory Scale: From Nanowaste to Nanospheres

The market for products based on nanotechnology, and with it the use of nanomaterials and the generation of nanowaste, increases day by day. Among the vast variety of nanomaterials available, gold nanoparticles (AuNPs) are among the most studied and applied in commercial products. This current situation requires both the development of recovery methods to reduce the amount of nanowaste produced, and new synthetic methods that allow the reuse of recovered gold for new nanomaterial production, keeping in mind both economical and ecological considerations. In this work, a methodology to recover gold from aqueous laboratory nanowaste and transform it into an aqueous HAuCl₄ solution was developed, using extremely simple procedures and readily available chemical reagents (NaCl, HCl, H₂ O₂ ) and allowing the recovery of more than 99 % of the original gold. The experiments were performed by using both simulated and real laboratory nanowastes, and practically the same results were obtained. Moreover, the subsequent use of the obtained aqueous HAuCl₄ solution from the recovered gold to produce spherical AuNPs through a seed-mediated approach was demonstrated. Thus, this work presents for the first time a complete recycling cycle from nanowaste to the reagent and back to the nanomaterial.

Simple and green technique for sequestration and concentration of silver nanoparticles by polysaccharides immobilized on glass beads in aqueous media

BACKGROUND

Engineered nanoparticles have unique properties compared to bulk materials and their commercial uses growing rapidly. They represent a potential risk for environment and health and could be eventually released in water. Silver nanoparticles (Ag NP) are applied in various products and are well-known for their antibacterial properties. Nowadays, pre-concentration and separation methods for Ag NP possess some limitations. Here, we present a simple, green method to sequestrate and concentrate Ag NP from different aqueous media.

RESULTS

Supported polysaccharides on glass beads synthesized in water by a single step reaction show high sequestration capacity of citrate-coated Ag NP in aqueous media. Supported polysaccharides were characterized by infrared spectroscopy, scanning electron microscopy (SEM) and elemental analysis. Sequestration of 83.0 % of Ag NP was attained from a 20 μg.L(-1) aqueous solution with supported chitosan in water whereas supported 2-hydroxyethylcellulose (HEC) reached 64.0 % in synthetic seawater in 2 h. The influence of polymer/glass beads ratio and molecular weight of polysaccharides was also studied. The effect of the salinity and humic acids on sequestration of Ag NP was investigated. Supported polymers have shown high performance for sequestration of ionic silver. Sequestration of 82.5 % and 80.8 % were obtained from a 60 μg.L(-1) silver ion (as nitrate salt) with supported HEC and chitosan, respectively. Sequestrated Ag NP was characterized with transmission electron microscopy (TEM) where images showed Ag NP with unchanged size and shape.

CONCLUSIONS

This sequestration method, involving green synthesis, allows efficient concentration and characterization of Ag NP from different aqueous media. This simple and fast method is a potential sustainable technique for elimination of Ag NP and ionic silver from waste waters and waters at different salinities.

Urokinase-coated chitosan nanoparticles for thrombolytic therapy: preparation and pharmacodynamics in vivo

Blood reperfusion of affected limbs is the most effective therapy for peripheral vascular thrombotic disease, restoring nutrition and blood flow to threatened tissues. Because it is more cost-effective than other thrombolytics, urokinase (UK) is widely used to treat venous thrombosis in China. However, its use is limited because of the risk of UK-related hemorrhagic complications. UK-coated nanoparticles (NPs) may decrease adverse effects while simultaneously increasing thrombolytic benefits. The aim of this study was to combine the sustained-release properties of NPs with the clinical benefits of catheter-directed thrombolysis (CDT) to create a promising new therapy. NPs were prepared via self-assembled chitosan and tripolyphosphate, introduced into a thrombosis model in New Zealand white rabbits, and the ratio of the residual thrombus cross-sectional area to the vascular cross-sectional area was calculated. The NPs had a drug-bearing efficiency of 14.5 ± 1.3%, an encapsulation efficiency of 94.8 ± 2.1% while the particle size of UK-coated NPs was 236 nm. Transmission electron microscopy results showed that the shape of the NPs were spherical and regular. Whether delivered by intravenation or catheter, UK-coated NPs produced a significant increase in the thrombolytic effect compared with free UK and confirmed the superiority of CDT for improving clot lysis over drug-induced systemic thrombolysis. The intravenous NPs caused an abnormal increase in fibrinogen. In conclusion, a water-soluble UK-WCS-NP suspension with good encapsulation efficiency was easily prepared UK-WCS-NPs were capable of maintaining UK activity, provided sustained-release of UK and exhibited better thrombolytic function than free UK.

Forced desorption of nanoparticles from an oil-water interface

While nanoparticle adsorption to fluid interfaces has been studied from a fundamental standpoint and exploited in application, the reverse process, that is, desorption and disassembly, remains relatively unexplored. Here we demonstrate the forced desorption of gold nanoparticles capped with amphiphilic ligands from an oil-water interface. A monolayer of nanoparticles is allowed to spontaneously form by adsorption from an aqueous suspension onto a drop of oil and is subsequently compressed by decreasing the drop volume. The surface pressure is monitored by pendant drop tensiometry throughout the process. Upon compression, the nanoparticles are mechanically forced out of the interface into the aqueous phase. An optical method is developed to measure the nanoparticle area density in situ. We show that desorption occurs at a coverage that corresponds to close packing of the ligand-capped particles, suggesting that ligand-induced repulsion plays a crucial role in this process.