Concentration Of KBr Research Articles

Optimized production of antimicrobial compounds by endophytic Aspergillus niger CBMAI 2766

Fungi can adapt their metabolism to different cultivation conditions, which may accompany changes in secondary metabolites, but few cost-effective approaches were presented. Therefore, Aspergillus niger CBMAI 2766 was studied aiming at the obtention of antibacterial compounds using KBr, an innocuous and inexpensive salt. The addition of this salt to culture medium was an interesting strategy for obtention of natural products at higher concentrations, as observed by the increased extract mass that favored the isolation of biologically active compounds. Furthermore, an experimental design with temperature, pH, and KBr concentration was performed to maximize the obtained products. Seven compounds were isolated: the phenylalanine derivatives Aspernigrin A 1 and Pestalamide B 2, the polyketides RF-3192C 3, Foncesinone A 6 and Aurasperone A 7, and the bicoumarins Orlandin 4 and Kotanin 5. The bactericidal activity of 5 against Gram-positive bacteria was observed for the first time in this study. Furthermore, antimicrobial activities of the isolated metabolites 3–7 were described in the literature. In summary, the employed experimental design showed that 34 °C and 10 g.L−1 KBr were optimal conditions for producing the bioactive compounds 5-7, employing this inexpensive salt as medium modifier. Thus, indicating that this proposal presents potential for enhancing antimicrobials production.

Size optimization of IrOx nanoparticles synthesized by Br mediation for enhanced PEM water electrolysis

We have creatively developed a hydrothermal approach to synthesize ultra-small IrOx nanoparticles with precise size control at 1.6 nm by carefully modulating KBr concentrations. Br ions are adsorbed onto the surface of IrOx and modulate the free energy through adsorption, thereby controlling the nanoparticle size to achieve ultra-small IrOx. The tailored IrOx nanoparticles are aimed to be high-performance electrocatalysts for efficient oxygen evolution reaction. The optimized nanoparticles exhibited an ultra-low overpotential of 230 mV to reach 10 mA/cm2 for oxygen evolution reaction in acid and showed negligible degradation after 50 h operation at 10 mA/cm2. When assembled in a proton exchange membrane electrolyzer, the catalyst enabled the device to reach 1 A/cm2 at only 1.69 V with excellent durability over 100 h at 1 A/cm2. Through detailed cost accounting, it was determined that 1 kg of hydrogen could be produced for a remarkably low, significantly below prevailing cost targets. This work not only develops an effective strategy to enhance oxygen evolution reaction efficiency by tailoring IrO2 particle size, but also shows the great potential for scalable application in industrial water electrolysis.

The electrosynthesis of ethylene oxide in a tandem recycle flow reactor system

In this work an electrochemical tandem recycle reactor was developed for the selective electro-oxidation of ethylene into ethylene oxide with a concentrated product outflow, resulting in an more sustainable pathway towards EO as opposed to the partial oxidation process. The system consisted of (i) a cation exchange membrane equipped module operating at a constant setpoint of 133.3 mA/cm2 and (ii) an anion exchange membrane unit in sequence, with a variable setpoint to regulate the pH. An excess of ethylene was supplied to the porous anode of the cation exchange module, which subsequently reacted with evolved bromine into 2-bromoethanol. As a result the anolyte acidified, which in turn promoted a selective bromine production. The anion exchange module also contributed to the Br2 production, converted 2-bromoethanol into ethylene oxide and neutralized the anolyte. The system underwent equal charge experiments in varied anolyte concentrations with a (i) Ni gauze cathode and an IrO2 coated Ti anode in the cation exchange module and (ii) graphite electrodes in the anion exchange unit. For experiments of 6 up to 10 h, Faradaic efficiencies towards ethylene oxide of 80.2 ± 6% and 46.7 ± 4.5% were sustained in 0.5 M and 3 M KBr anolyte respectively. The reduced selectivity in augmented KBr concentrations was predominantly caused by organochemical thermodynamics, which provoked an increased 1,2-dibromoethane production. The highest ethylene oxide production was achieved in a 0.5 M KBr condition, i.e. 10 g/L, which is ten times higher than the maximum reported figure in literature. In terms of stability, pretreated anodes, i.e. baked at 450 °C in air prior to testing, showed no degradation before and after testing on SEM-EDS analyses, whereas untreated structures were susceptible to corrosion.

SEM Studies of Polyaniline Thin Films Doped with Different Concentrations of KBr & C6H3N3O7

Polyaniline has been the oldest among all the conducting polymers. The unique properties of conducting polymers not only provide great scope for their applications but also have led to the development of new models to explain their observed properties. Polyaniline has rapidly become the subject of considerable interest for physicists, chemists and material scientists. In this paper we have carried out the Scanning Electron Microscopy characteristics of Polyaniline thin films doped with different concentrations (15% & 30%) of the dopants like Potassium Bromide and Picric Acid. The films has been prepared by using Vacuum Evaporation Technique and then characterized for SEM studies by using Scanning Electron Microscopy unit. The SEM study reveals that the grain size increases with the increase in the concentration of the above said dopants which in turn increases the crystallinity of the material. This behavior ensures its application in the optoelectronic devices.

Morphology Control of TiO2 Nanorods Using KBr Salt for Enhancing the Photocatalytic Activity of TiO2 and MoS2/TiO2 Heterostructures.

In this study, the effect of KBr salt on the growth of TiO2 nanorods (NRs) was systematically studied. The addition of KBr with different concentrations provides a controllable growth of TiO2 NRs using hydrothermal method. The results revealed that the presence of KBr molecules affects the growth rate by suppressing the growth in the lateral direction and allowing for axial growth. This results in affecting the morphology by decreasing the diameter of the nanorods, and increasing the free space between them. Enhancing the free spaces between the adjacent nanorods gives rise to remarkable increase in the internal surface area, with more exposure side surface. To obtain benefit from the enlargement in the inner surface area, TiO2 NRs were used for the preparation of MoS2/TiO2 heterostructures. To study the influence of the morphology on their activity, TiO2 NRs samples with different KBr concentrations as well as the MoS2/TiO2 heterostructures were evaluated towards the photocatalytic degradation of Rhodamine B dyes.

Halogen ion-modified silver nanoparticles for ultrasensitive surface-enhanced Raman spectroscopy detection of polycyclic aromatic hydrocarbons.

Rapid ultrasensitive detection of trace polycyclic aromatic hydrocarbons (PAHs) is essential and significant for pollution control due to their hazard, persistence, and the wide distribution in the environment. Therefore, rapid detection of PAHs is critical for controlling pollution and protecting the ecology. Considering the advantages of surface-enhanced Raman spectroscopy (SERS), a simple and reliable SERS method was proposed in this work for detecting PAHs in water. Three chemicals, namely NaCl, KBr, and KI, were chosen to modify Ag nanoparticles (NPs) for phenanthrene (Phe) detection, and Ag NPs modified with KBr (Ag-Br NPs) showed the best SERS response. The mixing sequence and the concentration of KBr were optimized. The addition order of mixing KBr and Ag NPs before Phe solution was the best sequence, and the optimal concentration of KBr was 20 mM. Under optimal conditions, the limits of quantification for Phe, pyrene (Pyr), and anthracene (Ant) were 10-6 M, 10-7 M, and 10-7 M, respectively. Mixed PAHs (Phe, Pyr, and Ant) in spiked water samples were identified and quantified successfully. The proposed method has good application prospects in environmental pollution monitoring.

Removal of phenol from wastewater by electrochemical bromination in a flow reactor.

Electrochemical methods have been widely applied in the treatment of phenol wastewater for the past few years. However, conventional electrochemical advanced oxidation processes (EAOPs) generally encounter the problem of electrode passivation and the energy consumption required for mineralization is high. In this work, we reported the treatment of phenol wastewater by electrochemical bromination method in a flow electrolysis cell. The Ti/Sb-SnO2/PbO2 electrode was prepared and used as anode. The experiments were carried out under different initial pH, KBr concentrations, current densities, and volumetric flow rates. The generated 2,4,6-tribromophenol (TBP) could be easily separated from the electrode surface and electrolyte. The brominated intermediates were identified by GC/MS. The removal efficiencies for phenol and COD were 100% and 82.7%, respectively, under the best operational conditions (current density of 40mAcm-2, KBr concentration of 0.074mol L-1, initial pH of 1.0, and volumetric flow rate of 114mLmin-1). Furthermore, our electrochemical bromination method offered a high apparent current efficiency (ACE) of 276.6% and a low energy consumption (EC) of 4.54 × 10-3 kWh gCOD-1 after 40min of electrolysis time, indicating that this process was suitable for phenol wastewater treatment.

Synthesis of silver nanorings via a facile one-pot method

We herein report a new polyol-based method for the synthesis of silver nanorings. The effects of the molecular weight of polyvinylpyrrolidone (PVP), the concentration of KBr, the reaction time, and stirring speed on the final morphologies of these silver nanorings were studied. The structures of these silver nanorings were characterized by scanning electron microscope (SEM) and UV–Vis spectrophotometer. In addition, the conditions for the growth of the silver nanorings were optimized, and the growth mechanism of these silver nanorings was explored. The results show that the formation and the morphology of silver nanorings are closely related to the molecular weight of PVP, the KBr concentration, the reaction time, and the stirring speed. Herein, the silver nanorings were obtained with a ring-diameter of ~10 μm and wire diameters in the range of 20–40 nm. This family of silver nanorings with well-defined ring structures has great potential for applications in nanoscale photonics, plasma devices, and optical manipulation.

Development of a non-invasive method for monitoring variations in salt concentrations of seawater using nuclear technique and Monte Carlo simulation

In the oil production industry, water is used as a fluid injected into the well to raise the oil when the well is depressurized. Water thus produced presents variations in the concentrations of dissolved salts, as there is a mixture of different types of water, related to its origin (such as connate water, sea water). Because it is reused in oil production, water needs to be monitored to maintain the standard suitable for its use as it can be hypersaline, contributing to the encrustation of pipes and contamination of underground water reservoirs. In this study, a noninvasive method was developed to determine the salt concentration in seawater. The method uses a detection system that contains a NaI(Tl) detector, a241Am source, and a sample holder to measure the mass attenuation coefficient of saltwater samples. For validation, the same setup was also simulated using the MCNPX code. Saltwater samples with different concentrations of NaCl and KBr were used as a proxy for seawater. The mass attenuation coefficients for the simulation exhibited the smallest relative errors (up to 6.2%), and the experimental ones exhibited the highest relative errors (up to 25%) when compared with theoretical values.

Activated carbon electrode with promising specific capacitance based on potassium bromide redox additive electrolyte for supercapacitor application

Halogenated Bromide (Br −) was subsequently dosed to aqueous electrolyte solution to enforce the capacitance features of activated carbon (AC) electrodes in electric double-layer supercapacitor devices for electrical energy storage. Physicochemical properties for AC with sodium sulfate (Na2SO4) and KBr redox additive were assessed by different characterization tools such as XRD, SEM, EDS, surface roughness, and BET techniques. Cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spectroscopy (EIS), and the stability after 1000 cycles have been used to monitor the electrochemical behaviors of the prepared electrodes. The presence of halogen atom exhibited large faradaic resembling battery like-type in charge–discharge curves. In the aqueous solution, the investigated electrode showed a high specific capacitance of 957.8 F g−1 at a specific current of 0.46 A g−1 using a certain concentration of KBr added to Na2SO4. The single AC electrode showed specific energy of 133 Wh kg−1 and specific power of 859.6 W kg−1. Besides, the AC electrode displayed excellent long-term stability in Na2SO4@KBr electrolyte, preserving retention capacitance of 174%. AC/AC symmetric supercapacitor cell demonstrated excellent electrochemical performance, including specific energy of 57.15 Wh kg−1, specific capacitance of 127 F g−1, specific power of 5262 W kg−1 at a specific current of 3.8 A g−1, and 82.8% capacitance retention after 10,000 cycles.

Viscometric and Densimetric Study of Water–PEG–KBr Systems

The dynamic viscosity and density of a water–PEG–KBr system are measured in the ranges of 293.15–323.15 K and 0–0.001 mol parts. Polyethylene glycol samples with average molecular weights of 1000, 1500, 3000, 4000, and 6000 g/mol are used. The concentration of KBr is 0.01 mol parts. The activation parameters of viscous flow (Gibbs energy, enthalpy, and entropy) and the partial molar volume of PEG in a solution are calculated using experimental data in the specified range of temperatures and concentrations. It is shown that the activation parameters of viscous flow grow along with concentration and molar weight. It is found that the partial molar volume of PEG in a solution falls as the concentration rises, and the partial molar volume per monomer does not change, depending on the average molecular weight of PEG. A simple way of determining the hydration number of a polymer molecule is described, based on which the hydration number of a PEG macromolecule in a solution is calculated. It is found that the hydration number of a PEG macromolecule falls as the temperature rises and grows along with the molecular weight.

Synthesis of Citrate-Coated Penta-twinned Palladium Nanorods and Ultrathin Nanowires with a Tunable Aspect Ratio.

Green and scalable methodologies for the preparation of metal nanoparticles with fine control of shape and size are of high interest in many areas including catalysis, nanomedicine, and nanodiagnostics. In this contribution, we describe a new synthetic method for the production of palladium (Pd) penta-twinned nanowires and nanorods utilizing sodium citrate, formic acid, ascorbic acid, and potassium bromide (KBr) in water, without the use of surfactants or polymers. The synthesis is green, fast, and without the need of complex setups. Interestingly, a microwave-assisted scale-up process has been developed. The combination of a synthetic protocol for seeds and the seed-mediated growth process allows us to synthesize nanorods and nanowires by modulating the concentration of KBr. The synthesized nanomaterials have been physicochemically characterized. High-resolution transmission electron microscopy shows that the nanorods and nanowires have a penta-twinned structure enclosed by {100} lateral facets. Moreover, the absence of sticky molecules or toxic byproducts guarantees the biocompatibility of the nanomaterials, while leaving the surface clean to perform enzymatic activities.

On the organic solvent free preparation of ultrafiltration and nanofiltration membranes using polyelectrolyte complexation in an all aqueous phase inversion process

Sustainable polymeric membrane fabrication aims for processes without the use of hazardous organic solvents or crosslinkers. One promising alternative method represents the fabrication of polyelectrolyte complex (PEC) membranes based on aqueous phase separation. We present the fabrication of PEC membranes from salt dilution induced phase separation. The complexation of the polyanion PSS and polycation PDADMAC is suppressed by an overcritical KBr concentration. The overcritical liquid polymer solution is cast and subsequently immersed in deionized water. The concentration gradient leads to salt diffusion out of, and water into the liquid polymer solution until the composition enters the demixing gap. Further salt dilution induces polyelectrolyte precipitation in the two phase region and forms the final porous PEC membrane. The presented approach shows similarities to the established non-solvent induced phase separation (NIPS), so high potential for the transfer of existing expertise. Most notably, the influence of simultaneous demixing of polyions is observed for different polyanion/polycation ratios in the liquid polymer solution. Three monomer ratios lead to membranes with different morphologies and separation properties in the range of ultrafiltration and nanofiltration. The presented method can be applied with commercially available polyelectrolytes and is easy to implement. This method is a promising approach to eliminating the use of organic solvents and realizing a sustainable alternative to the state of the art polymeric membrane fabrication processes.

Measurements of the Electric Conductivity of MWCNT Suspension Electrodes with Varying Potassium Bromide Electrolyte Ionic Strength

Suspension electrodes are under intense investigation due to their use in electrochemical systems such as redox flow batteries, capacitive deionization cells and flow supercapacitors. They provide novel functionalities not available with static electrodes, such as spatial power-energy decoupling for flow hybrid batteries, and continuous water desalination by capacitive deionization cells. Yet their electric conductivity is low relative to static electrodes made of the same material. It was previously found that suspension electrodes employing multi-walled carbon nanotubes (MWCNTs) demonstrate among the highest electric conductivities in deionized water, yet the effect of electrolyte ionic strength on their electric conductivity of was not elucidated. We here measure the electric conductivity of MWCNTs suspensions in a KBr electrolyte under flow using two- and four-electrode setups with alternative and direct current (DC) techniques. Only the two-electrode DC technique measured solely electronic conductivity, while all the other techniques measured the combined ionic and electronic conductivity. The electronic conductivity increased with MWCNT concentration in accordance with percolation theory power law. It increased also with electrolyte concentration by one to two orders of magnitude, with the critical exponent value transitioning from ∼2 to ∼1 with the increasing KBr concentration, which was explained in terms of the Derjaguin-Landau-Verwey-Overbeek theory.

Preparation and characterization of water-based magnetorheological fluid using wormlike surfactant micelles

Magnetorheological fluids (MRFs) are smart materials whose rheological properties can be controlled via external magnetic field. One of the most important challenges of MRFs is their sedimentation problem. In this paper, worm-like micelles (WLMs) has been used to improve the properties of water based MRFs. Cetyltrimethyl ammonium bromide (CTAB) was used as a dispersant in the presence of KBr. The steady state and dynamic rheological measurements were performed to study the effect of CTAB concentration on the properties and the internal structure of the fluids. The static light scattering (SLS) and cryo-scanning electron microscope were done to study the structure of WLMs. The magnetorheological properties was studied under external magnetic field up to 76 kA/m. The stability of the suspensions was investigated by sedimentation test. The WLMs are formed in water at CTAB and KBr concentration of 0.2 M and 0.1 M respectively. It was found that MRFs with improved stability and yield stress can be obtained using WLMs in water.

The ionic resistance and chemical stability of polycrystalline K-β″ alumina in aqueous solutions at room temperature

Interfaces between alkali metal solid state electrolytes and aqueous solutions are often unstable. In particular, the use of β/β″ alumina superionic conductors is generally limited to conditions absent of liquid water due to their well-known sensitivity to water vapor. However, the degradation mechanism upon exposure to aqueous solutions is not well understood. Using impedance spectroscopy, infrared spectroscopy, and chemical analysis, we studied the mechanism of ionic impedance rise for K+-ion-conducting, polycrystalline K-β″ alumina membranes in room temperature aqueous solutions. By using a non-blocking Fe2+/Fe3+ couple in a symmetric aqueous impedance cell with different concentrations of LiOH, NaOH, KOH, CsOH, and KBr, we find that the rate of resistance rise of the membrane is highly dependent on the pH and K+ concentration in the solution. We find the rate decreases from ~50–200 Ω cm2 h−1 in neutral pH solutions to ~0.1–1 Ω cm2 h−1 in alkaline solutions or solutions with high K+ concentrations. Characterization results are consistent with ion exchange of K+ for hydrated protons as the mechanism of resistance rise.

Dioxidomolybdenum(VI) and dioxidouranium(VI) complexes as functional mimic of haloperoxidases catalytic activity in presence of H2O2–KBr–HClO4

The stable dibasic tetradentate ligand 1,4-bis-(2-hydroxy-3,5-dimethylbenzyl)piperazine (H2pip-2,4-dmp, I) prepared by reacting 2,4-dimethylphenol with piperazine in the presence of formaldehyde reacts with [MoVIO2(acac)2] and [UVIO2(CH3COO)2] in equimolar ratio to give neutral hexa-coordinated [MoVIO2(pip-2,4-dmp)] (1) and hepta-coordinated [UVIO2(pip-2,4-dmp)(MeOH)] (2), respectively. After characterizing these complexes by spectroscopic (IR, UV/Vis, 1H and 13C NMR) data, elemental and thermal analyses (and single crystal X-ray diffraction study of uranium complex), they are used as catalysts to study the oxidative bromination of thymol. Such catalytic reactions are observed by many model vanadium complexes and are considered as a functional mimic of haloperoxidases. The catalytic oxidation resulted in the formation of three products namely, 2-bromothymol, 4-bromothymol and 2,4-dibromothymol. The optimized reaction conditions are obtained considering concentration of KBr, HClO4, and oxidant for the maximum yield of brominated products. Under the optimized reaction conditions, the product selectivity for both the prepared complexes is investigated. They are found to be competent homogeneous catalysts to afford the products in good yield.

Comparison of KBr and NaCl effects on the glass transition temperature of hydrated layer-by-layer assemblies.

The influence of assembly and post-assembly conditions on the glass transition temperature of free-standing poly(diallyldimethyl ammonium) (PDADMA)/poly(4-styrene sulfonate) (PSS) layer-by-layer (LbL) films assembled in 0.5M NaCl and 0.5M KBr are explored using modulated differential scanning calorimetry. Upon completion, PDADMA/PSS LbL assemblies are hydrated using solutions containing various concentrations of KBr. The data indicate that water provides the primary driving force for changes in the glass transition temperature of completed films rather than the post-assembly salt type. However, upon changing the assembly salt conditions from NaCl to KBr, the glass transition temperature shows a decrease of nearly 20 °C. Additionally, the composition of the films upon analysis with 1H NMR spectroscopy and neutron activation analysis indicates an elevated number of extrinsic binding sites within the film structure when KBr is the assembly salt. This shows a clear link between the assembly conditions and the internal structure and, therefore, the thermal properties of PDADMA/PSS LbL assemblies.

QCM-D Investigation of Swelling Behavior of Layer-by-Layer Thin Films upon Exposure to Monovalent Ions.

Polyelectrolyte multilayers and layer-by-layer assemblies are susceptible to structural changes in response to ionic environment. By altering the salt type and ionic strength, structural changes can be induced by disruption of intrinsically bound ion pairs within the multilayer network via electrostatic screening. Notably, high salt concentrations have been used for the purposes of salt-annealing and self-healing of LbL assemblies with KBr, in particular, yielding a remarkably rapid response. However, to date, the structural and swelling effects of various monovalent ion species on the behavior of LbL assemblies remain unclear, including a quantitative view of ion content in the LbL assembly and thickness changes over a wide concentration window. Here, we investigate the effects of various concentrations of KBr (0 to 1.6 M) on the swelling and de-swelling of LbL assemblies formed from poly(diallyldimethylammonium) polycation (PDADMA) and poly(styrene sulfonate) polyanion (PSS) in 0.5 M NaCl using quartz-crystal microbalance with dissipation (QCM-D) monitoring as compared to KCl, NaBr, and NaCl. The ion content after salt exchange is quantified using neutron activation analysis (NAA). Our results demonstrate that Br- ions have a much greater effect on the structure of as-prepared thin films than Cl- at ionic strengths above assembly conditions, which is possibly caused by the more chaotropic nature of Br-. It is also found that the anion in general dominates the swelling response as compared to the cation because of the excess PDADMA in the multilayer. Four response regimes are identified that delineate swelling due to electrostatic repulsion, slight contraction, swelling due to doping, and film destruction as ionic strength increases. This understanding is critical if such materials are to be used in applications requiring submersion in chemically dynamic environments such as sensors, coatings on biomedical implants, and filtration membranes.

Photoinduced formation of silver nanoparticles in a new Na_2O/K_2O/CaO/CaF_2/Al_2O_3/ZnO/SiO_2 photo thermal refractive glass: evidence of Ag - AgBr core shell structures

Photo thermal refractive glasses of the type Na2O-SiO2-Al2O3-K2O-CaO-CaF2-ZnO doped with CeO2, Ag2O, SnO2, Sb2O3 were prepared using different concentrations of KBr. A UV irradiation followed by a thermal treatment leads to the formation of Ag-nanoparticles, indicated by the appearance of a plasmon resonance peak. This optical resonance position shifts with increasing KBr concentrations to higher wavelengths caused by the formation of an AgBr shell. The Mie theory with the aid of the optical dispersion of AgBr together with the measured dispersion of the used glasses was successfully applied to describe the optical relation of particle size and AgBr core shell thickness within the given glass. The results were compared with UV-vis-NIR spectroscopy.