Concentration Of Reducing Agent Research Articles

Temperature Dependent Growth Kinetics of Pd Nanocrystals: Insights from Liquid Cell Transmission Electron Microscopy.

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

Co-P-B/Ti foil as an efficient catalyst for hydrogen production from the hydrolysis of NaBH4 solution

Sodium borohydride (NaBH4) can hydrolyze to generate hydrogen (H2) with the proper catalysts for the fast-growing hydrogen economy. Developing more highly active, cost-effective and stable catalysts is considered to be a promising strategy. Herein, Co-P-B thin film supported on titanium foil (Co-P-B/Ti foil) was fabricated via chemical deposition at room temperature and applied to catalyze H2 production from hydrolysis NaBH4 solution. The catalytic properties of Co-P-B/Ti foil for NaBH4 hydrolysis were studied by adjusting reducing agent concentration, response time, and depositional pH value. The optimized Co-P-B/Ti foil thin film catalyst showed an enhanced catalytic performance. The highest hydrogen generation rate was obtained to be 5529.7 mL·min-1·g-1, and the apparent activation energy was 48.4 kJ·mol-1, which was superior to most of reported catalysts. One reason might be due to the special morphology, increasing the surface area of the catalyst and providing more active sites on the catalyst surface. Another reason might be the mutual effect of the Co, P and B elements. Moreover, the optimized Co-P-B/Ti foil thin film catalyst displayed good recycling ability toward the hydrolysis of NaBH4 solution after 5 cycles.

Study on the performance of coal gangue ceramsite steel fiber high strength concrete

Our study aims to use coal gangue ceramsite (CGC) as coarse aggregate and add an appropriate volume fraction of steel fiber to prepare high strength concrete with lighter weight and meeting pumping requirements. The effects of (w/b) ratio, CGC content, the volume fraction of steel fiber, and water reducing agent content on the properties of coal gangue ceramsite steel fiber concrete (CGCSFC) were analyzed by orthogonal test, range analysis, and variance analysis. The optimal mix proportion of CGCSFC was obtained by using the efficacy coefficient method combined with the AHP-CRITIC method. The results showed that the crushing value of CGC was 37.26 % lower than that of coal gangue (CG). The reason for the increase in the strength of CGC was that there were few micro-cracks in CGC and the increase in quartz content. The (w/b) ratio had the most significant effect on the compressive strength of CGCSFC. CGCSFCs with compressive strength of 60–90 MPa and slump of 140–220 mm were prepared. The dry apparent density of CGCSFC with the same strength grade was 18.2–19.4 % lower than that of normal concrete (NC), and the specific strength was increased by 19.7–36.3 %. The average calculation error of Bowromi modified formula considering CGC content and the volume fraction of steel fiber is 3.82 %.

Defect-controlled fabrication of reduced graphene oxide/ZnO/PMMA-based solid-state optical limiting filters with SA/RSA switching property

A solid-state optical limiting filter was fabricated by noncovalently functionalizing a graphene-based nanocomposite with a polymer. Graphene oxide was reduced by varying reducing agent concentration and functionalized with metal oxide nanoparticles to enhance electronic transitions and third-order nonlinear optical characteristics. The nanocomposite was dispersed over the PMMA polymer framework, and thin films with μm-scale thickness were fabricated using the dip coating method. XRD analysis confirmed the wurtzite crystal structure of ZnO nanoparticles and the amorphous nature of PMMA. The carbon structural integrity was analyzed using Raman spectra. Linear optical studies revealed a redshift in the π-π* transition peak in rGO, suggesting enhanced conjugation. Third-order nonlinear refraction and absorption properties were assessed using the Z-scan technique, revealing a switching behavior in nonlinear absorption at different input intensities. An increase in the relative concentration of sp2 domains enhanced the nonlinear absorption. Optical limiting potential, determined using open aperture Z-scan data, yielded a threshold value of 0.066 GW/cm2. This study aims to develop a solid-state optical filter with a high laser damage threshold by adjusting the reduction rate, tuning defect levels, and analyzing its effect on the optical limiting potential.

Preparation and electromagnetic wave absorption of compressible graphene aerogels

In this study, a developed easy-operation method was adopted to generate ultralight and compressible graphene aerogels by using graphene oxide and ammonia. By changing the process parameters, such as reduction temperature, reducing agent content and ammonia concentration, the variation laws of the density and pore size of aerogels were obtained, which aided in realizing the controllable preparation of aerogel structures. The prepared graphene aerogel has good compressive performance, and its density can reach 5.26 mg/cm3. Although it was repeatedly compressed 200 times under a load that was 4000 times as large as its own weight, it maintained its structural integrity and mechanical properties. An ideal model of three-dimensional graphene aerogel was constructed, and the electromagnetic wave absorption performance was simulated using the Computer Simulation Technology (CST) Microwave Studio software. The results showed that when the thickness, pore size and height of the sheet were 1.4, 5 and 14 mm, respectively, an optimal electromagnetic wave absorption effect of −31.08 dB could be obtained. Furthermore, the effects of thickness, pore size and height of the sheet on the electromagnetic wave absorption performance are revealed, which provide a reference for the structural design of aerogels with both compressibility and electromagnetic wave absorption performance.

Antimicrobial Properties of Carboxymethyl Cellulose/Starch/N'N Methylenebisacrylamide Membranes Endowed by Ultrasound and Their Potential Application in Antimicrobial Packaging.

Cellulose is used widely in antimicrobial packaging due to its abundance in nature, biodegradability, renewability, non-toxicity, and low cost. However, how efficiently and rapidly it imparts high antimicrobial activity to cellulose-based packaging materials remains a challenge. In this work, Ag NPs were deposited on the surface of carboxymethyl cellulose/starch/N'N Methylenebisacrylamide film using ultrasonic radiation. Morphology and structure analysis of as-prepared films were conducted, and the antibacterial effects under different ultrasonic times and reductant contents were investigated. These results showed that Ag NPs were distributed uniformly on the film surface under an ultrasonic time of 45 min. The size of Ag NPs changes as the reducing agent content decreases. The composite film demonstrated a slightly better antibacterial effect against E. coli than against S. aureus. Therefore, this work can provide valuable insights for the research on antimicrobial packaging.

Growth and properties of tantalum carbide coatings on graphite by TRD technique

The tantalum carbide-coated graphite material exhibits remarkable chemical stability, corrosion resistance, and heat shock resistance, enabling it to demonstrate excellent stability during the growth of wide bandgap semiconductors. Its application significantly enhances the quality of third-generation semiconductor crystals. Nevertheless, the high cost of this material hinders its widespread utilization in the field of wide bandgap semiconductors. To address this challenge, this study employs the Thermo-reaction deposition and diffusion (TRD) technique to successfully fabricate a tantalum carbide coating on the surface of graphite. Through thermodynamic analysis, this article validate the thermodynamic feasibility of preparing tantalum carbide coatings using the TRD process. To achieve a dense and uniform TaC coating on the graphite surface, we systematically investigate the effects of reducing agent content, reaction temperature, and reaction time on the microstructure of the coating. Experimental research has found that a molar ratio of B4C to Ta2O5 of 1:0.64 optimizes the coating uniformity. Deviations from this ratio, either higher or lower, can lead to coating inhomogeneity or even failure in coating formation. Additionally, this article determine that a reaction temperature range of 1200–1400 °C, coupled with a reaction time not exceeding 6 h, represents the most suitable conditions for preparing TaC coatings on the graphite surface. Finally, to evaluate the practical performance of the coated graphite, this article simulate the corrosive environment encountered during the physical vapor transport method for growing aluminum nitride single crystals. The results demonstrate a significant improvement in the corrosion resistance of the coated graphite. This enhancement is primarily attributed to the formation of a dense TaC coating on the graphite surface, which exhibits remarkable stability at elevated temperatures.

Bio-fabrication of silver nanoparticles using Commelina erecta, L.: a mechanistic approach on synthesis, optimization, antibacterial, and antioxidant potential.

The ongoing exploration of economical, sustainable, and environment-friendly methods for synthesizing monodisperse colloidal metal nanoparticles is growing day by day due to their potential application in various fields. The use of plant derivatives in nanoparticle synthesis and their suitability as sustainable catalysts have emerged as significant areas of research. In this study, silver nanoparticles were synthesized using an aqueous extract obtained from the commonly found weed Commelina erecta, L. Extensive study is conducted to optimize various synthesis parameters such as pH, reducing agent concentration, silver nitrate concentration, and temperature. The plant extract utilized in the synthesis process contained variety of antioxidants, including malic acid, phenol, benzoic acid, and catechol, which played a crucial role in both reduction and capping during the synthesis process, thereby making them suitable for biomedical applications. The optimized synthesis process yielded silver nanoparticles with a particle size of 16.2 ± 3.1nm. These nanoparticles exhibited excellent stability and demonstrated remarkable antibacterial activity compared to the standard antibacterial agent, streptomycin. In addition, the silver nanoparticles displayed promising antioxidant activity attributed to the presence of antioxidant functional groups on their surface. This study reports, for the first time, the synthesis of silver nanoparticles using antioxidant compounds present in C. erecta, L. plant extract. The antioxidant compounds identified through GC-MS belong to phenols, phenolic acids, and carboxylic acid groups. Furthermore, the exceptional antimicrobial and antioxidant properties exhibited by the synthesized silver nanoparticles offer new possibilities for their potential applications.

SYNTHESIS AND CHARACTERIZATION OF SELENIUM NANOPARTICLES STABILIZED WITH DIDECYLDIMETHYLAMMONIUM CHLORIDE

As part of this work, a synthesis procedure was developed and the characteristic of selenium nanoparticles stabilized with didecyldimethylammonium chloride (DDAC) was carried out. Nanoparticles were obtained by chemical reduction in an aqueous medium. Selenous acid was used as a selenium-containing precursor, ascorbic acid was used as a reducing agent, and didecyldimethylammonium chloride was used as a stabilizer. To determine the optimal parameters for the synthesis of selenium nanoparticles stabilized with didecyldimethylammonium chloride, a multifactorial experiment was carried out. The input parameters were the concentration of selenous acid, the concentration of didecyldimethylammonium chloride (DDAC) and the concentration of ascorbic acid. The average hydrodynamic radius of selenium particles, which was determined by the method of dynamic light scattering, was considered as an output parameter. The optimal parameters for the synthesis of selenium nanoparticles (R from 15 to 25 nm) have been established: reducing agent concentration – from 1.076 mol/l to 2.118 mol/l, stabilizer concentration – from 0.006 mol/l to 0.085 mol/l, precursor concentration – from 0.004 mol /l to 0.236 mol/l. At the next stage of research, the effect of solution pH on the average hydrodynamic radius of selenium nanoparticles was determined. It was shown that in the pH range from 1.81 to 2.21, the average hydrodynamic radius of selenium nanoparticles does not change significantly, which indicates the aggregative stability of selenium nanoparticles in this range. In the pH range from 2.21 to 4.56, there is a sharp increase in the average hydrodynamic radius from 21 to 497 nm. At pH ˃ 7.96, coagulation of selenium particles is observed.

Research of the workability, mechanical and hydration mechanism of coal gangue-construction solid waste backfilling materials

In order to effectively address the issues of coal gangue emissions and the accumulation of construction solid waste, a combined treatment of coal gangue and construction solid waste can be implemented. In this study, a composite backfilling material was designed, with coal gangue and construction solid waste as the main aggregates. Through laboratory experiments, the time-dependent flow performance, mechanical properties, and microstructure of the material were analyzed under different proportions of factors including fly ash content, substitution rate of construction solid waste, mass concentration, and water reducing agent content. The research results indicate the following: The effects of reducing agent content, mass concentration, fly ash content, and substitution rate of construction solid waste on flow performance increased in that order. The addition of construction solid waste is negatively correlated with the strength of filling materials. The appropriate substitution ratios for FA, construction solid waste, mass concentration, and reducing agent were determined to be 21 %, 50 %, 80 %, and 0.6 %, respectively. The CH component in the material exhibited a trend of initially increasing and then decreasing, providing a large amount of reactants for secondary hydration reactions and strengthening the internal structure of the material. In the middle stage of hydration, FA and activators played an important role in the later stage by providing raw materials for secondary hydration, enriching the internal composition of the structure, and enhancing the backfilling performance of the backfilling material. This study can achieve the recycling and utilization of coal gangue and construction solid waste, and enhance the stability and bearing capacity of backfilling materials.

Radiochemical Oxygen Depletion Depends on Chemical Environment and Dose-Rate: Implications for FLASH Effect

FLASH (dose rates > 40 Gy/s) radiotherapy (RT) protects normal tissues from radiation damage, compared with conventional RT (∼Gy/min). Radiation-chemical oxygen depletion (ROD) has been the leading and most-studied mechanism to explain FLASH. Previous studies have reported low ROD values of ∼0.35 µM/Gy, however, they do not accurately model (utilizing water or oxidized substrates such as albumin) the intracellular environment. It has been proposed that the intracellular environment may support higher ROD values due to its specific chemical makeup. As chemical reducing agents, which play a critical role in the cell, may promote ROD, we measured ROD for several well-known cellular reducing agents. Precision polarographic oxygen sensors were used to measure ROD over a ∼100-0 µM oxygen concentration range in solutions containing various types of intracellular reducing agents, either alone or combined with glycerol (1M; to simulate the intracellular hydroxyl-radical-scavenging capacity). A Cs irradiator and a research proton beamline were used for radiation beam generation over a 10,000-fold (0.0085 to 100 Gy/s) dose rate range. Reagents were grouped generally into primary free-radical scavengers (glycerol & lysozyme) and reducing agents (cysteamine, cysteine, glutathione, dextrin-conjugated linoleic acid, NAD(P)H, ascorbate and uric acid). Reducing agents at 1 mM significantly altered ROD values. ROD, at 0.1 Gy/s varied from greater than 1 µM/Gy for NADPH to less than 0.1 µM/Gy for uric acid. Even higher RODs were found at lower dose rates and/or higher reducing agent concentrations. Although most greatly increased ROD, ascorbate and uric acid decreased ROD and additionally imposed an oxygen dependence of ROD at low oxygen concentrations. Interestingly, all agents having high rates of ROD at low dose rates show a decrease at FLASH dose rates and this seems to be a proportional response (i.e., the greater the ROD at low dose rate, the greater the inhibition by FLASH). At FLASH dose rates our data for a simple mixture of glycerol and glutathione showed the same trend as recent studies that, in general, FLASH had ∼25% lower ROD rates than conventional demonstrating agreement between polarographic sensors and optical phosphorescence decay methods. ROD was greatly augmented by some intracellular reducing agents but others effectively reversed this effect. Ascorbate had its greatest impact at low oxygen concentrations. ROD decreased with increasing dose rate and in all cases was less than 1 µM/Gy at 100 Gy/s, potentially posing a fundamental limit of max ROD for FLASH.

Controlled synthesis of gold nanorods and integrated with titanium dioxide for enhancing visible light‐driven antioxidant activity

AbstractIn this work, gold nanorods (AuNRs) with well‐controlled aspect ratios were prepared using a modified seed‐growth method and covered by TiO2 layers through the hydrothermal reaction to improve stability. Integrating TiO2 with plasmonic rod‐like gold nanoparticles could enhance their photo activity by the local surface plasmon resonance (LSPR) effect. AuNRs aspect ratios were controlled by varying the amount of seed solution, reducing agents, surfactant (CTAB), and titanium (IV) but oxide. The optical properties of formed AuNRs can be tuned in the spectral range from 400 to 900 nm by adjusting the ratio between seed solution and reducing agent concentration. Besides, the absorption of the UV‐light function of TiO2 and the antioxidant properties of gold nanoparticles were also integrated to prepare a kind of multifunctional material. The obtained AuNRs/TiO2 were then determined by ultraviolet‐visible spectroscopy (UV‐Vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy (HR‐TEM), selected area electron diffraction (SAED), and energy‐dispersive X‐ray spectroscopy (EDS). Microscopic images (TEM, SEM) revealed that the average particle size of the AuNRs decorated in the titanium dioxide ranged from 20 to 60 nm, depending on the experimental parameters. Furthermore, HRTEM, EDS, and SAED results provided more precise information insight into the formed gold nanocrystals. The AuNRs/TiO2 exhibited superior antioxidant activity by reducing free 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radicals at different concentrations. The results indicated that AuNRs/TiO2 improves antioxidant and optical absorption activities. The antioxidation effect was proved more excellent than solely used of spherical, rod‐liked gold nanoparticles or TiO2 nanoparticles. This novel design of AuNRs/TiO2 may open a new avenue for facilitating multifunctional nanoparticles in cosmetic applications.

Synergistic effects of gold nanoparticles enhanced the sensitivity of enzyme-linked immunosorbent assay for latex allergens

Hevea brasiliensis rubber elongation factor (Hev b1), a non-glycosylated protein, is a notable allergen in natural latex products. This study aims to assess enzyme-linked immunosorbent assay (ELISA) combined with gold nanoparticles (AuNPs) as a Hev b1 detection substrate. AuNP synthesis precursor and reducing agent concentrations were optimized using factorial design and multiple linear regression (MLR). The optimized conditions yielded spherical AuNPs with an average particle size of 73 ± 23 nm. This substrate enhanced detection sensitivity by around 50% compared to the limit of detection of the bare substrate, in the linear range of 0.25–1.75 μg/mL. Additionally, the heightened absorbance intensity observed during Hev b1 ELISA signifies both augmented surface immobilization of the analyte and optical induction arising from the aggregation of suitably small AuNPs (<80 nm) into dimer clusters, supported by discrete dipole approximation (DDA). Overall, the findings highlighted the synergistic effects of AuNPs in enhancing the performance of ELISA for Hev b1 detection.

Synergistic photocatalytic performance of Fe@Fe2O3 core-shell nanostructures supported on g-C3N4 nanosheets for RhB and phenol decolorization: Fabrication, characterization, and mechanistic insights

In this study, Fe@Fe2O3 core-shell nanoparticles were synthesized and adsorbed onto g-C3N4 nanosheets through a chemical adsorption process. The resulting Fe@Fe2O3/g-C3N4 nanocomposites exhibited a unique morphology and were characterized by a narrow dispersion of Fe@Fe2O3 nanostructures uniformly distributed on the g-C3N4 nanosheets. The impact of varying reaction parameters, such as reaction time and reducing agent concentration, on the reactivity and properties of iron was investigated. The enhanced photoactivity of Fe@Fe2O3/g-C3N4 nanocomposites for RhB and phenol was explored, and it was found that the heterojunction formed between Fe2O3 and g-C3N4 facilitated efficient charge partition, thereby reducing electron-hole recombination, and promoting the separation of photogenerated charges. Mechanistic insights into the degradation process of the pollutant RhB were gained using Fe@Fe2O3/g-C3N4 nanocomposites, and it was found that the holes (h+) and superoxide radicals (O2−) were the main active species involved in the degradation of RhB. The study highlights the potential of Fe@Fe2O3/g-C3N4 nanocomposites to eliminate contaminants.

Influence of reducing agent concentration on the luminescence and photophysical processes constant rates of silver clusters in silica-based glass

Series of silica-based glasses doped with antimony was synthesized to host luminescent silver clusters formed via Na+-Ag+ low-temperature ion exchange and heat treatment. Spectroscopic study reveals that increase in antimony concentration affects emission spectra, quantum yields, and fluorescence lifetimes. Photophysical processes rate constants, including radiative and nonradiative transitions and intersystem crossing, were estimated based on experimental spectroscopic characterization. Correlation between photophysical processes rate constants and increase in concentration of antimony was demonstrated.

Synthesis of amino talc-like clay-supported Au nanoparticles with outstanding catalytic activity for 4-nitrophenol reduction

Studies on synthesizing gold nanoparticle-based catalysts to reduce the amount of gold and improve the catalytic activity at the same time are still crucial. The reduction reaction of 4-nitrophenol (a toxic compound) to 4-aminophenol (a non-toxic compound and essential material for the pharmaceutical industries) is a standard reaction for analyzing the catalytic activity of AuNPs. A capping agent is indispensable for producing stable and size-controlled gold nanoparticles (AuNPs) and in maintaining the catalytic activity of the AuNPs. However, some previous studies reported that capping agents reduced the catalytic activity of AuNPs through a surface-blocking phenomenon. Moreover, introducing a framework for capped AuNPs could be another consideration to increase the dispersion of AuNPs in an aqueous medium, eventually improving the catalytic activity of the AuNPs. Amino talc-like clay, a relatively non-toxic and well-dispersed layered material in aqueous solution, has been used as a framework for AuNPs. The present study reports the AuNP synthesis using delaminated amino talc-like clay (DAC) as a framework that brings about gold nanoparticles with superior catalytic activity to other supports. Moreover, the effect of the reducing agent concentration, Mn addition and pH conditions are discussed in determining this excellent property. DAC shows a promising role as a AuNP framework which increases the catalytic activity by improving the dispersion and stability of the material in the colloidal system. The pH-dependent stacking structure arrangement of the DAC support was a determining factor of Kapp for the 4-nitrophenol reduction reaction by DAC stabilized AuNPs. Under acidic conditions, the stacking structure of DAC was destroyed, providing more open space for the AuNPs attached to the clay surface, which increased the Kapp value. On the contrary, under basic conditions, the stacking structure of DAC was re-arranged, closing the surface space of the AuNPs attached to the interlayer clay, which decreased the Kapp value. Moreover, the DAC stabilizer provided a partially capped AuNP structure in neutral and acidic aqueous solutions, which prevented the catalytically active surface blocking phenomenon occurring in the ordinary capping type. Mn addition during the synthesis process controlled the production of small-size gold nanoparticles and increased the catalytic activity of the material.

Tunable Reversal of Circular Dichroism in the Seed-Mediated Growth of Bichiral Plasmonic Nanoparticles.

Plasmonic nanoparticles with an intrinsic chiral structure have emerged as a promising chiral platform for applications in biosensing, medicine, catalysis, separation, and photonics. Quantitative understanding of the correlation between nanoparticle structure and optical chirality becomes increasingly important but still represents a significantly challenging task. Here we demonstrate that tunable signal reversal of circular dichroism in the seed-mediated chiral growth of plasmonic nanoparticles can be achieved through the hybridization of bichiral centers without inverting the geometric chirality. Both experimental and theoretical results demonstrated the opposite sign of circular dichroism of two different bichiral geometries. Chiral molecules were found to not only contribute to the chirality transfer from molecules to nanoparticles but also manipulate the structural evolution of nanoparticles that synergistically drive the formation of two different chiral centers. By deliberately adjusting the concentration of chiral molecules and other synthetic parameters, such as the reducing agent concentration, the capping surfactant concentration, and the amount of Au precursor, we have been able to fine-tune the circular dichroism reversal of bichiral Au nanoparticles. We further demonstrate that the structure of chiral molecules and the crystal structure of Au seeds play crucial roles in the formation of Au nanoparticles with bichiral centers. The insights gained from this work not only shed light on the underlying mechanisms dictating the intriguing geometric and chirality evolution of bichiral plasmonic nanoparticles but also provide an important knowledge framework that guides the rational design of bichiral plasmonic nanostructures toward chiroptical applications.

Analysis of Platinum Distribution within a Nafion 212 Membrane during Electroless Deposition

Ionic polymer metal composite (IPMC) is an electrically-responsive material made of perfluorinated sulfonic acid (PFSA) ionomers electroless plated with noble metal, such as platinum. Recently, interest in thin IPMC has been rising because of its potential applications in micro-electromechanical systems. However, little effort has been made so far on studying metal electroless deposition within thin PFSA membranes (thinner than 100 um). In this paper we study the platinum distribution within a thin Nafion membrane (Nafion 212, 50 µm-thick) using standard manufacturing recipe. We compare the obtained distribution with the distribution reported in literature based on thick Nafion membrane (Nafion 117, 180 µm-thick). We show that in Nafion 212 the maximum Pt concentration is situated in the bulk of the membrane, while in Nafion 117 the maximum peak is situated at the liquid-membrane boundary, suggesting a different rate determining deposition mechanism. Electroless deposition of platinum in Nafion 212 Ionic polymer metal composite (IPMC) is rising interest in the microelectromechanical system (MEMS) since smaller and thinner IPMC substrates would expand the applications. IPMCs are mostly made of a perfluorinated sulfonic acid ionomers (PFSA) membrane, such as commercially-available Nafion, coated with platinum. The prevalent way of manufacturing IPMC relies on the chemical reduction of platinum on the surface of the PFSA membrane, i.e. electroless deposition (1). Most of the reports on IPMC manufacturing rely on Nafion 117 (thickness of 0.180 mm, equivalent weight 1100 g/mol) while Nafion 212 has been poorly studied (thickness 0.050 mm, equivalent weight 1100 g/mol). This contribution aims at filling this gap.Materials and methodsA PFSA membrane (Nafion 212 membrane) has been coated with platinum using the standard recipe already describe elsewhere (1). An immersion-reduction step was performed in an immersion bath composed of tetraammineplatinum chloride (Pt(NH3)4Cl2, 0.2%), and reduction baths made of sodium borohydride (NaBH4, 5%). After the first immersion (30 min and 2 hours, respectively), the samples were immerged in the reduction bath until the end of the precipitation. Samples were then frozen in liquid nitrogen and cut, and analyzed with electrons dispersive x-ray spectroscopy (EDS) and processing of scanning electron microscopy (SEM) images (Fig 1a).Figure 1. a) EDS detection of platinum (yellow) overlapped with SEM picture of the cross-section of IPMC. Platinum distribution and Rayleigh fit for single reduction step (NaBH4) of platinum in a Nafion 212 membrane, after 30 minutes (b) and 2 hours (c) of immersion.Results and discussionThe distribution of platinum within Nafion 117 has already been studied by Millet et al. (2). The Pt distributions thereby reported strongly differs from the profiles we obtained (Fig 2). In the aforementioned profiles, the maximum Pt concentration is located at the liquid-substrate boundary of the Nafion membrane (2), whereas the Pt distribution in Nafion 212 reaches the maximum inside the Nafion membrane, between 0.5 µm and 1 µm below the surface (Fig 1b 1c).As reported by Millet et al., two limiting types of kinetics may be encountered in a dynamic exchange process, such that the deposition rate-determining mechanism is either diffusion in the liquid-film boundary (F-mechanism), or diffusion in the membrane (M-mechanism).The position of the peaks in our experimental data suggests that the mechanism determining the Pt precipitation rate inside Nafion 212 is diffusion inside the membrane while using Nafion 117 with the same reducing agent concentration leads to a precipitation rate determined by diffusion at the liquid/film boundary. It has been proven experimentally that ionic conductivity and water uptake of Nafion 212 is higher than for Nafion 117 (3). Thus we can hypothesize that the different behavior of thinner Nafion could explain the different empirical Pt distribution obtained using same reducing agent concentration. We could obtain a good fit of the Pt distribution (R2=0.919 and R2=0.945) within Nafion 212 with the Rayleigh distribution for immersion time of 30 minutes and 2 hours respectively (Eq 1.):f(x,σ 2) = (x/σ 2) exp(-x/2σ 2) [1]The scale parameter σ was found to be 4.19 and 4.58 for the sample immerged for 30 minutes and 2 hours, respectively. Further investigation of the precipitation mechanism inside Nafion 212 membrane and estimations of the phenomenological equations of mass transport correlated to Rayleigh distribution is reserved for future work.References K. Kim, M. Shahinpoor, Smart Mater. Struct., 12, 1, p. 65 (2003).P. Millet, R. Durand, E. Dartyge, G. Tourillon, and A. Fontaine J. Electrochem. Soc., 140, 5, pp. 1373-1380 (1993).A. Kusoglu, A.Z. Weber Chem. Rev. 117, 3 pp. 987-1104 (2017). Figure 1

New Green Approaches in Nanoparticles Synthesis: An Overview.

Nanotechnology is constantly expanding, with nanomaterials being more and more used in common commercial products that define our modern life. Among all types of nanomaterials, nanoparticles (NPs) occupy an important place, considering the great amount that is produced nowadays and the diversity of their applications. Conventional techniques applied to synthesize NPs have some issues that impede them from being appreciated as safe for the environment and health. The alternative to these might be the use of living organisms or biological extracts that can be involved in the green approach synthesis of NPs, a process that is free of harmful chemicals, cost-effective and a low energy consumer. Several factors, including biological reducing agent concentration, initial precursor salt concentration, agitation, reaction time, pH, temperature and light, can influence the characteristics of biologically synthesized NPs. The interdependence between these reaction parameters was not explored, being the main impediment in the implementation of the biological method on an industrial scale. Our aim is to present a brief review that focuses on the current knowledge regarding how the aforementioned factors can control the size and shape of green-synthesized NPs. We also provide an overview of the biomolecules that were found to be suitable for NP synthesis. This work is meant to be a support for researchers who intend to develop new green approaches for the synthesis of NPs.

Green synthesis of well-dissolved high-stable silver nanoparticles using hydroxypropylmethyl cellulose as a protective agent

This paper presented the synthesis of Ag nanoparticles (Ag NPs) by the chemical reduction method which is simple and environmentally friendly. Silver nitrate, hydroxypropylmethyl cellulose (HPMC), and glucose were used as silver precursors, protective agents, and reducing agents, respectively. The effects of AgNO3 concentration, glucose concentration, HPMC content, reaction time, and reaction temperature on the formation of Ag NPs were investigated. The properties of Ag NPs were analyzed by transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectroscopy, and X-ray diffraction (XRD). The results indicated that when the HPMC content was 0.01%, AgNO3 concentration was 0.05 M and glucose reducing agent concentration was 0.4%, the best reaction occurred in 9 hours at 90oC. The Ag NPs prepared under HPMC protection possessed a face-centered cubic crystal structure (FCC), a spherical shape having average sizes in the range of 8 ‒ 12 nm. The Ag colloidal solution had a suitable zeta potential (-37.21 mV) to maintain the stability and to avoid the agglomeration of Ag NPs. In addition,the paper proposed a method to indirectly determine the Ag NPs content through the separation of Ag NPs from the colloidal solution by coagulation, using the electrolyte Al(NO3)3.9H2O.