Precise seed-mediated growth and size-controlled synthesis of palladium nanoparticles using a green chemistry approach

Nanotechnology-General Aspects: A Chemical Reduction Approach to the Synthesis of Nanoparticles

The role of nanotechnology is increasingly important in our society. Through it, scientists are acquiring the ability to understand the structure and properties of materials and manipulate them at the scale of atoms and molecules. Nanomaterials are at the forefront of the rapidly growing field of nanotechnology. The synthesis of nanostructured materials, especially metallic nanoparticles, has attracted tremendous interest over the past decade due to their unique properties, making these materials excellent and indispensable in many areas of human activity. These special properties can be attributed to the small size and large specific surface area of nanoparticles, which are very different from those of bulk materials. Nanoparticles of different sizes and shapes are needed for many applications, so a variety of protocols are required to produce monodisperse nanoparticles with controlled morphology. The purpose of this review is firstly to introduce the reader to the basic aspects related to the field of nanotechnology and, secondly, to discuss metallic nanoparticles in greater detail. This article explains the basic concepts of nanotechnology, introduces methods for synthesizing nanoparticles, and describes their types, properties, and possible applications. Of many methods proposed for the synthesis of metal nanoparticles, a chemical reduction is usually preferred because it is easy to perform, cost-effective, efficient, and also allows control of the structural parameters through optimization of the synthesis conditions. Therefore, a chemical reduction method is discussed in more detail-each factor needed for the synthesis of nanoparticles by chemical reduction is described in detail, i.e., metal precursors, solvents, reducing agents, and stabilizers. The methods that are used to characterize nanomaterials are described. Finally, based on the available literature collection, it is shown how changing the synthesis parameters/methods affects the final characteristics of nanoparticles.

Novel Polyelectrolyte Complex Membranes Containing Carboxymethyl Cellulose-Gelatin for Pervaporation Dehydration of Azeotropic Bioethanol for Biofuel

Polyelectrolyte complex membranes (PECMs) were prepared by combining sodium carboxymethyl cellulose (NaCMC) and gelatin (Ge) with variations in the Ge content in the NaCMC matrix. Characterization methods, such as infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), contact angle analysis (CA), and universal testing machines (UTM) were used to investigate the physicochemical studies of the prepared membranes. The pervaporation characteristics of membranes with Ge content were investigated using an azeotropic mixture of water and bioethanol. The obtained data revealed that the membrane with 15 mass% of Ge (M-3) showed a maximum flux of 7.8403 × 10^-2 kg/m²·h with separation selectivity of 2917 at 30 °C. In particular, the total and water flux of PECMs are shown as very close to each other indicating that the fabricated membranes could be employed to successfully break the azeotropic point of water-bioethanol mixtures. Using temperature-dependent permeation and diffusion data, the Arrhenius activation parameters were calculated, and the obtained values of water permeation (E_pw) were considerably smaller than bioethanol permeation (E_pE). Developed membranes showed the positive heat of sorption (ΔH_s), suggesting that Henry's sorption mode is predominant.

A Novel Palladium-Based Heterogeneous Catalyst for Tandem Annulation: A Strategy for Direct Synthesis of Acridones

In order to develop an efficient, rapid, and modular cascade strategy for the direct synthesis of acridones, palladium supported on sulfated alumina and microwave activation are employed. Multifunctional heterogeneous palladium catalysts were prepared in order to carry out the sequential annulation via a Buchwald–Hartwig amination followed by an intramolecular annulation in a one-pot process. This new protocol represents the first report on a catalytic tandem synthesis of acridone derivatives from commercially available starting materials, under ligand-free conditions. The scope of the present methodology is extended to the generation of a library of functionalized acridones, showing high functional group compatibility, in moderate to excellent yields. The applicability of this novel transformation was demonstrated by the concise total synthesis of the natural product arborinine.

Tailoring noble metal nanoparticle designs to enable sensitive lateral flow immunoassay

Lateral flow immunoassay (LFIA) with gold nanoparticles (AuNPs) as signal reporters is a popular point-of-care diagnostic technique. However, given the weak absorbance of traditional 20-40 nm spherical AuNPs, their sensitivity is low, which greatly limits the wide application of AuNP-based LFIA. With the rapid advances in materials science and nanotechnology, the synthesis of noble metal nanoparticles (NMNPs) has enhanced physicochemical properties such as optical, plasmonic, catalytic, and multifunctional activity by simply engineering their physical parameters, including the size, shape, composition, and external structure. Using these engineered NMNPs as an alternative to traditional AuNPs, the sensitivity of LFIA has been significantly improved, thereby greatly expanding the working range and application scenarios of LFIA, particularly in trace analysis. Therefore, in this review, we will focus on the design of engineered NMNPs and their demonstration in improving LFIA. We highlight the strategies available for tailoring NMNP designs, the effect of NMNP engineering on their performance, and the working principle of each engineering design for enhancing LFIA. Finally, current challenges and future improvements in this field are briefly discussed.

Influence of Polysaccharides' Molecular Structure on the Antibacterial Activity and Cytotoxicity of Green Synthesized Composites Based on Silver Nanoparticles and Carboxymethyl-Cellulose

In this paper we report on the influence of polysaccharides' molecular structure on the antibacterial activity and cytotoxicity of composites based on silver nanoparticles (AgNPs) immobilized into carboxymethyl-cellulose (CMC). These composites were green synthesized from the reduction of silver ions into aqueous solutions of the polysaccharide, using CMC with different degree of substitution (DS) and molecular weight (Mw). The composites were characterized by transmission electron microscopy (TEM), as well as infrared (ATR-FTIR), ultraviolet (UV-Vis), Raman, and X-ray photo-electron (XPS) spectroscopic techniques. The antibacterial activity was evaluated with minimum inhibitory concentration against Enterococcus faecalis. The cytotoxicity of composites was assessed against human gingival fibroblast. Experimental evidence suggests that particle size distribution and morphology of AgNPs change according to the quantity of silver precursor added to the reaction, as well as the DS and Mw of CMC used for composites preparation. This is related to the dispersion of silver precursor into aqueous solutions of the polysaccharide and the formation of Ag-O coordination bonds among AgNPs and COO^- moieties of CMC. Moreover, these coordination bonds modify the ability of nanoparticles to produce and release Ag⁺ into aqueous dispersion, adjusting their antibacterial activity and the induction of cytotoxicity into the tested biological environments.

Nanomagnet-Silica Nanoparticles Decorated with Au@Pd for Enhanced Peroxidase-Like Activity and Colorimetric Glucose Sensing

Nanomagnet-silica shell (Fe₃O₄@SiO₂) decorated with Au@Pd nanoparticles (NPs) were synthesized successfully. The characterization of Fe₃O₄@SiO₂-NH₂-Au@PdNPs was achieved using several spectroscopic and microscopic techniques. The quantitative surface analysis was confirmed using X-ray photoelectron spectroscopy. The Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs exhibited excellent peroxidase-like activity by effectively catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂. The absorption peaks at 370 and 652 nm confirmed the peroxidase-like activity of the Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs. The Michaelis-Menten constant (K_m) of 0.350 and 0.090 mM showed strong affinity toward H₂O₂ and TMB at Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs. The mechanism of the peroxidase-like activity was found to proceed via an electron transfer process. A simple colorimetric sensor based on glucose oxidase and Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs showed excellent selectivity and sensitivity towards the detection of glucose. The fabricated glucose biosensor exhibited a wide linear response toward glucose from 0.010 to 60.0 μM with an limit of detection of 60.0 nM and limit of quantification of 200 nM. The colorimetric biosensor based on Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs as a peroxidase mimic was also successfully applied for the determination of glucose concentrations in serum samples. The synthesized Fe₃O₄@SiO₂-NH₂-Au@Pd_0.30NPs nanozymes exhibited excellent potential as an alternative to horseradish peroxidase for low-cost glucose monitoring.

Ascorbic Acid-Assisted Polyol Synthesis of Iron and Fe/GO, Fe/h-BN Composites for Pb2+ Removal from Wastewaters

Iron powders and Fe/graphene oxide and Fe/boron nitride composites were synthesized by means of a polyol synthesis method. The effect of NaOH/Fe and ascorbic acid/Fe ratios on the characteristics of synthesized products were evaluated. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, low-temperature nitrogen adsorption and Raman-spectroscopy. Ascorbic acid-assisted polyol synthesis resulted in the 10-fold decrease of the iron particles' size and almost 2-fold increase of lead removal efficiency. The deposition of iron on the surface of graphene oxide lead to the formation of small 20-30 nm sized particles as well as bigger 200-300 nm sized particles, while the reduction in presence of boron nitride resulted in the 100-200 nm sized particles. The difference is attributed to the surface state of graphene oxide and boron nitride. Adsorption properties of the obtained materials were studied in the process of Pb²⁺ ion removal from wastewater.

Dechlorination of Excess Trichloroethene by Bimetallic and Sulfidated Nanoscale Zero-Valent Iron

Nanoscale zerovalent iron (nZVI) likely finds its application in source zone remediation. Two approaches to modify nZVI have been reported: bimetal (Fe-Me) and sulfidated nZVI (S-nZVI). However, previous research has primarily focused on enhancing particle reactivity with these two modifications under more plume-like conditions. In this study, we systematically compared the trichloroethene (TCE) dechlorination pathway, rate, and electron selectivity of Fe-Me (Me: Pd, Ni, Cu, and Ag), S-nZVI, and nZVI with excess TCE simulating source zone conditions. TCE dechlorination on Fe-Me was primarily via hydrogenolysis while that on S-nZVI and nZVI was mainly via β-elimination. The surface-area normalized TCE reduction rate ( k^'_SA) of Fe-Pd, S-nZVI, Fe-Ni, Fe-Cu, and Fe-Ag were ∼6800-, 190-, 130-, 20-, and 8-fold greater than nZVI. All bimetallic modification enhanced the competing hydrogen evolution reaction (HER) while sulfidation inhibited HER. Fe-Cu and Fe-Ag negligibly enhanced electron utilization efficiency (ε_e) while Fe-Pd, Fe-Ni, and S-nZVI dramatically increased ε_e from 2% to ∼100%, 69%, and 72%, respectively. Adsorbed atomic hydrogen was identified to be responsible for the TCE dechlorination on Fe-Me but not on S-nZVI. The enhanced dechlorination rate along with the reduced HER of S-nZVI can be explained by that FeS conducting major electrons mediated TCE dechlorination while Fe oxides conducting minor electrons mediated HER.

Silver nanoparticle production by the fungus Fusarium oxysporum: nanoparticle characterisation and analysis of antifungal activity against pathogenic yeasts

The microbial synthesis of nanoparticles is a green chemistry approach that combines nanotechnology and microbial biotechnology. The aim of this study was to obtain silver nanoparticles (SNPs) using aqueous extract from the filamentous fungus Fusarium oxysporum as an alternative to chemical procedures and to evaluate its antifungal activity. SNPs production increased in a concentration-dependent way up to 1 mM silver nitrate until 30 days of reaction. Monodispersed and spherical SNPs were predominantly produced. After 60 days, it was possible to observe degenerated SNPs with in additional needle morphology. The SNPs showed a high antifungal activity against Candida and Cryptococcus , with minimum inhibitory concentration values ≤ 1.68 µg/mL for both genera. Morphological alterations of Cryptococcus neoformans treated with SNPs were observed such as disruption of the cell wall and cytoplasmic membrane and lost of the cytoplasm content. This work revealed that SNPs can be easily produced by F. oxysporum aqueous extracts and may be a feasible, low-cost, environmentally friendly method for generating stable and uniformly sized SNPs. Finally, we have demonstrated that these SNPs are active against pathogenic fungi, such as Candida and Cryptococcus .

Aggregation and stabilization of multiwalled carbon nanotubes in aqueous suspensions: influences of carboxymethyl cellulose, starch and humic acid

Aggregation and stability of multiwalled carbon nanotubes in aqueous solutions were investigated with two polysaccharide stabilizers (carboxymethyl cellulose and a water soluble starch) and a natural organic matter (leonardite humic acid).

Silver/polysaccharide-based nanofibrous materials synthesized from green chemistry approach

In this contribution a novel green chemistry approach for the synthesis of nanofibrous materials based on blends of carboxymethyl-cellulose (CMC)-silver nanoparticles (AgNPs) composite and polyvinyl-alcohol (PVA) is proposed. These nanofibrous materials were obtained from the electrospinning of blends of aqueous solutions of CMC-AgNPs composite and PVA, which were prepared at different CMC/PVA weight ratios in order to electrospin nanofibers applying a constant tension of 15kV. The synthesized materials were characterized by means of transmission electron microscopy, scanning electron microscopy; as well as Fourier-transform infrared, ultraviolet and Raman spectroscopic techniques. Experimental evidence suggests that the diameter of the nanofibers is thinner than any other reported in the literature regarding the electrospinning of CMC. This feature is related to the interactions of AgNPs with carboxyl functional groups of the CMC, which diminish those between the later and acetyl groups of PVA.

Rapid, one-pot procedure to synthesise103Pd:Pd@Au nanoparticles en route for radiosensitisation and radiotherapeutic applications

Radioactive gold–palladium nanoparticles for radiotherapy.

Growth of branched gold nanoparticles on solid surfaces and their use as surface-enhanced Raman scattering substrates

Branched gold nanoparticles were synthesized directly on solid surfaces (silicon, glass, ITO) in high yield. They revealed strong SERS activity for the detection of R6G with an enhancement factor estimated as greater than 8 orders of magnitude.

Preparation of biocompatible magnetite-carboxymethyl cellulose nanocomposite: characterization of nanocomposite by FTIR, XRD, FESEM and TEM

The preparation and characterization of magnetite-carboxymethyl cellulose nano-composite (M-CMC) material is described. Magnetite nano-particles were synthesized by a modified co-precipitation method using ferrous chloride tetrahydrate and ferric chloride hexahydrate in ammonium hydroxide solution. The M-CMC nano-composite particles were synthesized by embedding the magnetite nanoparticles inside carboxymethyl cellulose (CMC) using a freshly prepared mixture of Fe3O4 with CMC precursor. Morphology, particle size, and structural properties of magnetite-carboxymethyl cellulose nano-composite was accomplished using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) and field emission scanning electron microscopy (FESEM) analysis. As a result, magnetite nano-particles with an average size of 35nm were obtained. The biocompatible Fe3O4-carboxymethyl cellulose nano-composite particles obtained from the natural CMC polymers have a potential range of application in biomedical field.

Totally Ecofriendly Synthesis of Silver Nanoparticles from Aqueous Dissolutions of Polysaccharides

In this contribution, a totally ecofriendly synthesis of silver nanoparticles from aqueous dissolution of polysaccharides is reported. The synthesis of nanoparticles was performed using aqueous dissolutions of silver nitrate (AgNO3) and carboxymethyl-cellulose (CMC) as both reducing and stabilization agent and using different AgNO3 : CMC weight ratios. Resultant yellowish to reddish dispersions were characterized by means of transmission electron microscopy and their related techniques, such as bright field and Z-contrast imaging and electron diffraction, as well as ultraviolet-visible and infrared spectroscopic techniques. The experimental evidence suggests that the morphology and particle size distribution of the silver nanoparticles depend on the AgNO3 : CMC weight ratio. This feature seems to be related to the stabilization given by the CMC matrix, which, according to our experimental findings, is steric in nature. Regarding such experimental evidence, a synthesis mechanism in which CMC acts as stabilizer and reducing agent is proposed.

Iron-Based Nanoparticles for Toxic Organic Degradation: Silica Platform and Green Synthesis

Iron and iron oxide nanoparticles (NPs) are finding wide applications for the remediation of various toxic chloro-organic compounds (such as trichloroethylene, TCE), via reductive and oxidative processes. In this study, Fe NPs (30-50 nm) are synthesized by reduction from ferric ions immobilized (by ion exchange) on a platform (two types of sulfonated silica particles), in order to prevent the NP agglomeration. Next, the Fe NPs are oxidized and their effectiveness for the oxidative dechlorination of TCE via the heterogeneous decomposition of hydrogen peroxide to OH• on the surface of the iron oxide NPs was demonstrated. For the reductive approach, the use of ascorbic acid as a "green" reducing agent in conjunction with a secondary metal (Pd) inhibits NP oxidation and agglomeration through surface adsorbed species. The Fe/Pd NPs have been successfully applied for the dechlorination of TCE (k(SA), surface-area normalized reaction rate, = 8.1 ×10(-4) L/m(2)h).

Size and composition control of Pt-In nanoparticles prepared by seed-mediated growth using bimetallic seeds

A two-step method has been developed for precise size and composition control of bimetallic Pt-In nanoparticles. Very small (1.62 nm) PtIn seed nanoparticles with 1:1 metal ratio were prepared in the absence of capping agents followed by growth of Pt on their surface in the presence of oleyl amine as reducing and stabilizing agent. Nanoparticles with bulk compositions of Pt(4)In, Pt(3)In, and Pt(2)In could be synthesized with average diameter smaller than 3 nm. TEM, EDX, and XPS provided evidence for homogeneous growth without separate nucleation of pure platinum nanoparticles in the reaction solution. Pt(3)In nanoparticles were deposited onto SiO(2) surface by incipient wetness impregnation. Temperature-induced changes in the particle surface were monitored by in situ IR spectroscopy and CO adsorption. It was found that surface alloy composition of the particles could be tuned by using oxidizing or reducing atmospheres.

Green Synthesis of Robust, Biocompatible Silver Nanoparticles Using Garlic Extract

This paper details a facile approach for the synthesis of stable and monodisperse silver nanoparticles performed at ambient/low temperature where Allium sativum (garlic) extract functions as the silver salt reducing agent during nanoparticle synthesis as well as the post-synthesis stabilizing ligands. Varying the synthesis conditions provides control of particle size, size-distribution, and kinetics of particle formation. Infrared spectroscopy, energy dispersive x-ray chemical analysis, and high performance liquid chromatography indicated that the carbohydrates present in the garlic extract are the most likely nanoparticle stabilizing chemistry. The synthesized silver nanoparticles also demonstrate potential for biomeical applications, owing to the 1) enhanced stability in biological media, 2) resistance to oxidation by the addition of H2O2, 3) ease and scalability of synthesis, and 4) lack of harsh chemicals required for synthesis. Cytotoxicity assays indicated no decrease in cellular proliferation for vascular smooth muscle cells and 3T3 fibroblasts at a concentration of 25 μg/ml, confirming that garlic extract prepared silver nanoparticles are ideal candidates for future experimentation and implementation into biomedical applications.

Nanostructured membranes for enzyme catalysis and green synthesis of nanoparticles

Macroporous membranes functionalized with ionizable macromolecules provide promising applications in high capacity toxic metal capture, nanoparticle syntheses, and catalysis. Our low-pressure membrane approach has good reaction and separation selectivities, which are tunable by varying pH, ionic strength, or pressure. The sustainable green chemistry approach under ambient conditions and the evaluation of a reactive poly(acrylic acid) (PAA)-modified polyvinylidene fluoride (PVDF) membrane is described. Two distinct membrane types were obtained through different methods: 1) a stacked membrane through layer-by-layer assembly for the incorporation of enzymes (catalase and glucose oxidase), providing tunable product yields and 2) Fe/Pd nanoparticles for degradation of pollutants, obtained through an in situ green synthesis. Bioreactor-nanodomain interactions and mixed matrix nanocomposite membranes provide remarkable versatility compared to conventional membranes.

Time-dependent effect in green synthesis of silver nanoparticles

The application of “green” chemistry rules to nanoscience and nanotechnology is very important in the preparation of various nanomaterials. In this work, we successfully developed an eco-friendly chemistry method for preparing silver nanoparticles (Ag-NPs) in natural polymeric media. The colloidal Ag-NPs were synthesized in an aqueous solution using silver nitrate, gelatin, and glucose as a silver precursor, stabilizer, and reducing agent, respectively. The properties of synthesized colloidal Ag-NPs were studied at different reaction times. The ultraviolet-visible (UV-vis) spectra were in excellent agreement with the obtained nanostructure studies performed by transmission electron microscopy (TEM) and their size distributions. The prepared samples were also characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The use of eco-friendly reagents, such as gelatin and glucose, provides green and economic attributes to this work.

Seed-mediated growth of palladium nanocrystals: the effect of pseudo-halide thiocyanate ions

In synthesis in a solution phase, adsorbates such as halides can interact selectively with different metal crystal facets and affect the final morphology of nanocrystals. Pseudo-halide thiocyanate ions (SCN-) can also adsorb on the metal surface, but they have never been used for the synthesis of shape-controlled colloidal metal nanocrystals. In this study, we first investigated the effect of SCN- on the morphology of palladium nanocrystals through a seed-mediated growth method. The presence of 1 µM SCN- in the growth solutions could lead to the formation of palladium polyhedra: truncated rhombic dodecahedra enclosed by twelve {110}, eight {111} and six {100} facets. The products were nanocubes enclosed with six {100} facets if cetyltrimethylammonium bromide (CTAB) was the only capping agent. Meanwhile, the mechanism of the effect of SCN- on the morphology of Pd nanocrystals is discussed.

Size-controlled synthesis of Pd nanocrystals using a specific multifunctional peptide

Here we report a peptide-mediated synthesis of Pd NCs in aqueous solution with controllable size in the sub-10 nanometre regime. The specific multifunctional peptide Q7 selected using the phage display technique can bind to the Pd NC surface and act as a stabilizer to mediate Pd crystal nucleation and growth. At the nucleation stage, Q7 bound to and helped stabilize the different-sized small Pd NC nuclei achieved using different concentrations of the external reducing agent, NaBH4. At the growth stage, Q7 played the dual role of binding to and reducing the precursor onto the existing nuclei, which led to the further controllable growth of the Pd NCs. By using the variable sizes of nuclei as seeds, and by introducing different amounts of precursors Pd NCs with tunable sizes from 2.6 to 6.6 nm were achieved with good size distribution.

Colloidal Inorganic Nanocrystal Based Nanocomposites: Functional Materials for Micro and Nanofabrication

The unique size- and shape-dependent electronic properties of nanocrystals (NCs) make them extremely attractive as novel structural building blocks for constructing a new generation of innovative materials and solid-state devices. Recent advances in material chemistry has allowed the synthesis of colloidal NCs with a wide range of compositions, with a precise control on size, shape and uniformity as well as specific surface chemistry. By incorporating such nanostructures in polymers, mesoscopic materials can be achieved and their properties engineered by choosing NCs differing in size and/or composition, properly tuning the interaction between NCs and surrounding environment. In this contribution, different approaches will be presented as effective opportunities for conveying colloidal NC properties to nanocomposite materials for micro and nanofabrication. Patterning of such nanocomposites either by conventional lithographic techniques and emerging patterning tools, such as ink jet printing and nanoimprint lithography, will be illustrated, pointing out their technological impact on developing new optoelectronic and sensing devices.

Biocatalytic growth of gold agglomerates on an electrode for aptamer-based electrochemical detection

Here we describe the biocatalytic growth of high-density gold agglomerates on a gold electrode surface to form a carrier for aptamer probe immobilization. The present approach provides a simple strategy to promote the seed-mediated deposition of Au from AuCl(4)(-) onto surface-attached 12 nm diameter Au nanoparticles (AuNPs) in the presence of reductive coenzyme and surfactant. The growth process was studied by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). This nanostructured platform is effective and prospective toward the aptamer probe immobilization. For the nice performance of enhanced substrate, the aptamer-sensing interface showed excellent applicability under the investigations such as alternating current voltammetry (ACV) and surface-enhanced Resonance Raman scattering (SERRS) spectra.

Aqueous - Phase Synthesis of PAA in PVDF Membrane Pores for Nanoparticle Synthesis and Dichlorobiphenyl Degradation

This paper deals with bimetallic (Fe/Pd) nanoparticle synthesis inside the membrane pores and application for catalytic dechlorination of toxic organic compounds form aqueous streams. Membranes have been used as platforms for nanoparticle synthesis in order to reduce the agglomeration, encountered in solution phase synthesis which leads to a dramatic loss of reactivity. The membrane support, polyvinylidene fluoride (PVDF) was modified by in situ polymerization of acrylic acid in aqueous phase. Subsequent steps included ion exchange with Fe(2+), reduction to Fe(0) with sodium borohydride and Pd deposition. Various techniques, such as STEM, EDX, FTIR and permeability measurements, were used for membrane characterization and showed that bimetallic (Fe/Pd) nanoparticles with an average size of 20-30 nm have been incorporated inside of the PAA-coated membrane pores. The Fe/Pd-modified membranes showed a high reactivity toward a model compound, 2, 2'-dichlorobyphenyl and a strong dependence of degradation on Pd (hydrogenation catalyst) content. The use of convective flow substantially reduces the degradation time: 43% conversion of dichlorobiphenyl to biphenyl can be achieved in less than 40 s residence time. Another important aspect is the ability to regenerate and reuse the Fe/Pd bimetallic systems by washing with a solution of sodium borohydride, because the iron becomes inactivated (corroded) as the dechlorination reaction proceeds.

Size-selective fractionation of nanoparticles at an application scale using CO2 gas-expanded liquids

Size-based fractionation of nanoparticles remains a non-trivial task for the preparation of well-defined nanomaterials for certain applications and fundamental studies. Typical fractionation techniques prove to be inefficient for large nanoparticle quantities due to several factors including the expense of equipment, throughput constraints, and the amount of organic solvent waste produced. Through the use of the pressure-tunable physico-chemical properties of CO2-expanded liquids, a rapid, precise, and environmentally sustainable size-selective fractionation of ligand-stabilized nanoparticles is possible through simple variations in applied CO2 pressure. An apparatus capable of fractionating large quantities of nanoparticles into distinct fractions with the ability to control mean diameters and size distributions has been developed. This apparatus consists of three vertically mounted pressure vessels connected in series with needle valves. This process, at current design scales, operated at room temperature, and CO2 pressures between 0 and 50 bar, results in a batch size-selective fractionation of a concentrated nanoparticle dispersion. This paper presents this new apparatus and the separation results of various single pass fractionations as well as recursive fractionations.