Potassium Ferrocyanide Research Articles

Modification Of a Screen-Printed Carbon Electrode with Nanoporous Gold by Electrodeposition and Dealloying of a Gold-Copper Alloy

In this study, a three-dimensional structure of nanoporous gold (NPG) was made by selectively corroding copper (Cu) from gold-copper (Au-Cu) alloys using a two-step electrochemical method. Given its large surface area and interconnected porous network, nanoporous gold is a suitable material for the advancement of electrochemical sensors. The screen-printed carbon electrode (SPCE) modified with nanoporous gold (NPG/SPCE) was fabricated by electrodepositing a gold-copper alloy from gold ion (Au3+) and copper ion (Cu2+) solution via cyclic voltammetry (CV) by scanning from -0.3 V to -0.8 V for 80 cycles. The copper is then removed via a dealloying process in 3M HNO3 using the cyclic voltammogram (CV) method by scanning potential from 0 V to +1.0 V for 100 cycles at 100 mV/s. The morphology, elemental composition, and electrochemical active surface area (ECSA) of NPG/SPCE electrodes were characterized using FESEM, EDX, and CV analysis, respectively. The electrochemical performance of the NPG/SPCE was compared with bare SPCE in a 10 mM potassium ferrocyanide (K4FeCN6) solution using cyclic voltammetry. The morphological study using FESEM revealed that the NPG/SPCE had an average pore diameter of 53 nm. The quantification of elements using EDX shows that 84 % of the copper in the electrodeposited gold-copper alloy electrode was successfully removed by the dealloying process. The higher number of cycles during the dealloying process led to producing NPG with higher ECSA electrodes. The ECSA of NPG/SPCE is 12 times greater than that of bare or unmodified SPCE in an equivalent geometrical area. NPG/SPCE has a much better electron transfer surface than bare SPCE due to its high surface area and gold surface properties, making it a potential sensing material for biosensing applications.

Inkjet-based facile fabrication of a copper ferrocyanide-embedded magnetic alginate microadsorbent for highly enhanced cesium removal

For the first time, simple and facile fabrication of a magnetic alginate microadsorbent via piezoelectric inkjet technology was developed for the selective removal of 137Cs via magnetic separation. Through the ejection of an alginate solution containing potassium ferrocyanide and magnetic nanoparticles (MNPs) into a Cu2+ solution via an inkjet device, the fabrication of a copper ferrocyanide-embedded magnetic alginate microadsorbent (CuFC-MAM) with an average size of 39.38 μm was easily achieved in a one-pot fabrication process; here, the Cu2+ ions acted as both a cross-linker for the gelation of alginate and a Cu source for the in situ synthesis of CuFC with potassium ferrocyanide. The Cs adsorption behavior of CuFC-MAM was effectively fitted by the pseudo-second-order kinetic model and Langmuir isotherm. Owing to the increased specific surface area of CuFC-MAM, its pseudo-second-order rate constant and maximum adsorption capacity were 76.54 and 1.486 times greater than those of CuFC-embedded magnetic alginate macroadsorbents fabricated without inkjet devices. Compared with other Cs adsorbents, CuFC-MAM presented the highest maximum capacity and Kd value; these results were attributed to the high content of CuFC in CuFC-MAM (50.15%). In addition, our CuFC-MAM exhibited an excellent removal efficiency of radioactive Cs, exceeding 99% from seawater.

Comprehensive investigation of zinc and tin-based metal oxides for advanced electrochemical detection of organophosphate pesticides

Different metal oxide (MO) nanomaterials, such as ZnO, SnO2, and nanocomposites of ZnO:SnO2 with various ratios of (1:9), (2:8), and (3:7) were prepared and coated on glassy carbon electrode (GCE). These MOs were tested as sensing material for organophosphate (OP) pesticides detection. Among all MOs, ZnO:SnO2 (1:9) coated GCE increases redox peak current at different buffer solutions with varying pH compared to bare GCE. Moreover, among these pH values, ZnO:SnO2 (1:9) coated GCE significantly enhanced the redox peak at pH 6.2, emphasizing optimal electrochemical conditions for the given pesticides. The morphological, elemental composition, metal ions-functional group interation, and crystallinity of different MO nanocomposites were examined using field-emission scanning electron microscopy (FESEM), fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectrum (EDX), and X-ray diffraction (XRD), respectively. The modified GCE with ZnO:SnO2 (1:9) showed an excellent performance during the electrochemial sensing of the diazinon (DiZn) pesticide. Therefore, detailed study was carried out for the sensing of DiZn. Furthermore, the electrochemical behavior of the ZnO:SnO2 (1:9) coated GCE was evaluated using cyclic voltammetry (CV) with 0.5 mL (5 mM) potassium ferrocyanide, resulting in a pronounced increase in anodic and cathodic peak potentials (Epa = 0.423 V, Epc = 0.1945 V) and currents (Ipa = 9.867 × 10-5 mA, Ipc = -7.993 × 10-5 mA). In addition, electrochemical impedance spectroscopy (EIS) demonstrated a reduction in charge transfer resistance for the coated ZnO:SnO2 (1:9) GCE. Differential pulse voltammetry (DPV) further showed a linear relationship between current and pesticide concentration, with a high correlation coefficient (R2 = 0.996), low limit of detection (LOD = 0.0133 mM) and low limit of quantification (LOQ = 0.0405 mM). Real samples, including tap and seawater, were analyzed to validate the method’s applicability. Additionally, chronoamperometry with a step potential of 1.2 V indicated high sensitivity for DiZn detection, with a sensitivity of 0.23 mA mM−1 cm−2. Finally, the stability of the ZnO:SnO2 (1:9) coated GCE was confirmed through recyclability tests over three cycles using CV and DPV techniques, ensuring its robustness for practical applications in pesticide detection.

Fabrication and performance assessment of coin cell supercapacitors with multiwalled carbon nanotube-supported mixed metal oxide nanocomposites and redox additive electrolyte

In the realm of supercapacitor applications, the fabrication of coin cell supercapacitors with superior performances played a crucial role. In this work, an asymmetrical type coin supercapacitor was fabricated with multiwalled carbon nanotube supported mixed metal oxide (CuO/CoO@MWCNT - CCM) nanocomposites (NCs) and potassium ferrocyanide incorporated KOH based redox additive electrolyte (RAE). The synergistic effect and the enhanced conductivity by the mixed metal oxides and MWCNT, respectively, were acted as the performance enhancer for electrode performances. On the other hand, RAE with optimized concentration provided additional redox active sites for superior performances. The combined effect of CCM NCs and RAE, were responsible for the superior performances. CCM NCs were prepared by one-pot hydrothermal technique and characterized. Working electrodes with CCM NCs were fabricated by doctor blade method and evaluated in KOH and RAE. It exhibited 1838.55 Fg−1 of specific capacitance (Csp) in RAE. Assembled asymmetrical supercapacitors with CCM NCs modified working electrode and activated carbon based anode, delivered 123.91 Fg−1 of Csp at 2.75 Ag−1 in RAE. The assembled supercapacitors delivered the highest energy density of 27.53 Wh kg−1 and power density of 1875 W kg−1 in RAE with an impressive 82.89 % of cyclic retention after 5000 GCD cycles. Finally, an asymmetric coin cell supercapacitor (CR2302) was fabricated with CCM NCs and RAE. The fabricated coin cell delivered the charge and discharge capacities of 157.72 and 55.99 mAh g−1, respectively in KOH, whereas these values were significantly improved 172.46 and 126.2 mAh g−1 respectively, in RAE. It proved that the fabricated coin cell supercapacitors performed well in terms of maximum charge and discharge performances in RAE compared to conventional KOH.

Current Mirror Improved Potentiostat (CMIPot) for a Three Electrode Electrochemical Cell.

This work presents a novel compact CMOS potentiostat-designed circuit for an electrochemical cell. The proposed topology functions as a circuit interface, controlling the polarization of voltage signals at the sensor electrodes and facilitating current measurement during the oxidation-reduction process of an analyzed solution. The potentiostat, designed for CMOS technology, comprises a two-stage amplifier, two current mirror blocks coupled to this amplifier, and a CMOS push-pull output stage. The electrochemical method of cyclic voltammetry is employed, operating within a voltage range of ±0.8 V and scan rates of 10 mV/s, 25 mV/s, 100 mV/s, and 250 mV/s. The circuit is capable of reading currents ranging from 10 µA to 500 µA. Experimental results were obtained using a potassium ferrocyanide K3[Fe(CN)6] redox solution with concentrations of 10, 15, and 20 mmol/L, and their corresponding voltammograms were evaluated. The experimental results from a discrete circuit demonstrate that the proposed potentiostat topology produces outcomes consistent with those of classical topologies presented in the literature and industrial equipment.

Fast Reaction of the Prussian Blue Based Nanozyme "Artificial Peroxidase" with the Substrates: Pre-Steady-State Kinetic Approach.

This letter introduces the pre-steady-state kinetic approach, which is traditional for evaluation of elementary constants in molecular (enzyme) catalysis, for nanozymes. Apparently, the most active peroxidase-mimicking nanozyme based on catalytically synthesized Prussian Blue nanoparticles has been chosen. The elementary constants (k1) for the nanozymes' reduction by an electron-donor substrate (being the fastest stage according to steady-state kinetic data) have been determined by means of stopped-flow spectroscopy. These constants have been found to be dependent on both the size of the nanozyme and the reducing substrate redox potential. For the smallest nanozymes (32 nm in diameter), log(k1) linearly decays with an increase of the substrate redox potential (cotangent value ≈125 mV). On the contrary, for the largest nanozymes with a diameter above 150 nm, k1 is almost independent of it. Moreover, for the substrate with the lowest redox potential (K4[Fe(CN)6]), the rate constant under discussion (k1) is almost independent of the nanozymes' size. Perhaps, the rate of the intrananozyme electron transfer causing bleaching becomes comparative or even lower than that of the nanoparticle interaction with the fastest substrate. Anyway, the elementary constant of nanozyme reduction with potassium ferrocyanide (k1) reaches the value of 1 × 1010 M-1 s-1, which is 3-4 orders of magnitude faster than for enzymes peroxidases. The obtained results obviously demonstrate that the pre-steady-state kinetic approach is able to discover novel advantages of nanozymes from both fundamental and practical points of view.

THE FABRICATION OF MIP BASED ELECTROCHEMICAL SENSOR FOR THE DETERMINATION OF DOBUTAMINE

Objective: Dobutamine (DBT), one of the most common synthetic catecholamines, is important in the renal, cardiovascular, hormonal, and central nervous systems. In our study, it is proposed to produce the first MIP-based electrochemical sensor for DBT analysis. MIP(DBT)/GCE was developed by electropolymerization of 4-aminobenzoic acid (4-ABA) in the presence of DBT. Analytical performance and validation evaluation were performed on both standard solution and commercial serum samples. Material and Method: DBT was supplied by the Vem pharmaceutical company. For the preparation of 5 mM [Fe(CN)6]3-/4- solution, known amounts of potassium ferricyanide ([K3Fe(CN)6]) and potassium ferrocyanide (K4[Fe(CN)6].3H2O mixed in 0.1 M KCl solution. The 4-ABA was used to create the polymeric film in the presence of DBT. Electrochemical measurements were actualized in IVIUM compactStat.h potentiostat (Eindhoven, The Netherlands) using a three-electrode system consisting of Pt wire, Ag/AgCl reference electrode, and glassy carbon electrode (GCE). Result and Discussion: The MIP(DBT)/GCE sensor was applied to standard solution and commercial serum samples. When DBT concentrations were plotted against ΔI values, a linear response between 1×10-13 and 1×10-12 M was obtained in both environments. LOD results were found to be 0.087×10-13 M and 0.033×10-13 M in standard solution and commercial human serum, respectively. Recovery% and RSD% were found to be 99.68-100.32% and 1.38-1.66%, respectively.

Sustainable graphitic carbon derived from oil palm frond biomass for supercapacitor application: Effect of redox additive and artificial neural network‑based modeling approach

One-step pyrolyzed graphitic carbon (GC) derived from oil palm frond biomass was synthesized at different durations (1, 3, and 5 h) without utilizing of activating agent. The optimum GC-5 h exhibited a honeycomb-like structure (1.9 nm), high carbon content (84 %), graphitic peak at 2θ ∼ 24.2°, and wide pore size (2.17 nm) suitable to accommodate solvated electrolyte ions. Symmetric supercapacitor (SSC) cells with three redox additives (hydroquinone (HQ), ammonium monovanadate (AM), and potassium ferrocyanide (PF)) in H2SO4 electrolyte are tested. The GC-5 h SSC shows a CS of 595F/g in 0.01 M HQ/H2SO4 electrolyte at a current density of 3 A/g. The cell exhibits an energy density (ED) of 22 Wh kg−1 and a power density (PD) of 2,400 W kg−1. It demonstrates a capacitance retention of 93 % after 10,000 cycles. To develop the intricate interactions between the electrode structure, active operating circumstances, and electrochemical performance of the SSC, an artificial neural network (ANN) approach was applied herein. The model uses the Levenberg-Marquart training method, incorporating the Tanh and Purelin activation functions. The data demonstrate that the constructed ANN model can predict the SSC with values that nearly match the experimental data with an MSE of 6.8122 × 10−5 and R of 0.9989.

Comparison of Approaches for Assessing Linearity of Impedance Measurements

There are two experimental methods available to assess the linearity of electrochemical impedance measurements. Observation of current as a function of potential, known as Lissajous plots, provides an instantaneous visual representation of the data.1 Deviation from an elliptical shape suggests a perturbation amplitude that is too large, resulting in nonlinear impedance data. A second approach is to measure, along with the fundamental, the higher harmonics of the measurement signal. Under potentiostatic control, the harmonics of current that exceed the noise level suggest nonlinear behavior. These harmonics may be expressed in terms of a frequency-dependent total harmonic distortion, THD, written as the ratio between the sum of the root mean square of the harmonic magnitude and fundamental frequency magnitude for electrochemical applications.The impedance was measured for a model system consisting of a Pt disk immersed in an electrolyte containing 0.01 M potassium ferricyanide, 0.01 M potassium ferrocyanide, and 1 M KCl. Measurements were performed using a Gamry Reference 3000 with THD measurement enabled and disabled. Low-frequency (10 mHz) Lissajous plots were recorded to facilitate comparison of the two methods for assessing linearity. The impedance measurements with THD enabled or disabled were in good agreement, including the frequency-dependent stochastic error structure, the shapes of Lissajous curves, and the values of the impedance. Both the low-frequency THD and the low-frequency Lissajous plots gave similar sensitivity to nonlinear behavior. Perturbation amplitudes of 1, 5, and 10 mV rms yielded elliptical Lissajous plots with THD values on the order of the background noise. Interestingly, the THD for the 10 mV perturbation was slightly above the background noise with a value of 0.01 (or 1 % of the fundamental). Perturbation amplitudes of 20, 60, and 100 mV rms yielded both non-elliptical Lissajous plots and low-frequency THD values much larger than the background noise.The regression of the measurement model 2 to the imaginary part of the impedance was applied to assess the consistency of the measured data to the Kramers-Kronig relations.3 Data measured at amplitudes of 1, 5, 10, and 20 mV rms were found to be consistent with the Kramers-Kronig relations, and data collected with amplitudes of 60 or 100 mV rms were found to be inconsistent with the Kramers-Kronig relations. As the measurement with a 20 mV rms amplitude was found to be nonlinear by observation of non-elliptical Lissajous plots and a THD of 4.2% at a frequency of 10 mHz, the post-measurement analysis of consistency with the Kramers-Kronig relations was found to be less sensitive than experimental observation of Lissajous plots and calculation of THD. Comparison of Lissajous plots to THD values suggests that experiments with THD less than 1% of the fundamental may be considered to be linear.

Innovative potassium hexacyanoferrate intercalated into layered double hydroxide adsorbent for efficient cesium removal from seawater

Effective radioactive wastewater treatment technology is essential to ensure the sustainable development of nuclear energy. Here, the potassium ferrocyanide (HCF) intercalating with layered double hydroxide (LDH) (HCF@LDH) was successfully synthesized by coprecipitation method for selective cesium (Cs) removal from seawater. Characteristics of the adsorbent, and adsorption performance under different environmental conditions including Cs+ ion selectivity, and underlying adsorption mechanism were systematically investigated. The experimental results demonstrated that the adsorption capacity of HCF@LDH was 52.08 mg/g and it effectively removed 100 % of Cs+ from up to 200 mg/L Cs solution within 1 h under an optimal pH of 6.0–10.0. Moreover, the adsorbent displayed high selectivity towards Cs+ even in seawater and more than 90 % of Cs+ was removed from seawater and the highest cesium removal capacity from seawater was 44.64 mg/g. Both the Langmuir isotherm model (R2 = 0.997) and the pseudo-second-order kinetic model (R2 = 0.999) provided a good fit for the adsorption data signifying the adsorption process is homogeneous and formed monolayer through chemisorption. Furthermore, the reusability analysis exhibited this adsorbent was recycled and reused for at least 5 cycles without losing its original adsorption performance. The physicochemical analysis of the HCF@LDH proved that K4Fe (CN)6 successfully intercalated onto LDH and cation exchange between K+ and Cs+ played an important role in effective Cs adsorption. More specifically, the interstitial spaces of the hexacyanoferrate crystals facilitate the cation exchange process. The findings of this study demonstrate that HCF@LDH is a unique, highly effective, and selective adsorbent for Cs+ from complex seawater.

Biochemical and Structural Characterization of a Novel Psychrophilic Laccase (Multicopper Oxidase) Discovered from Oenococcus oeni 229 (ENOLAB 4002).

Recently, prokaryotic laccases from lactic acid bacteria (LAB), which can degrade biogenic amines, were discovered. A laccase enzyme has been cloned from Oenococcus oeni, a very important LAB in winemaking, and it has been expressed in Escherichia coli. This enzyme has similar characteristics to those previously isolated from LAB as the ability to oxidize canonical substrates such as 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,6-dimethoxyphenol (2,6-DMP), and potassium ferrocyanide K4[Fe(CN6)], and non-conventional substrates as biogenic amines. However, it presents some distinctiveness, the most characteristic being its psychrophilic behaviour, not seen before among these enzymes. Psychrophilic enzymes capable of efficient catalysis at low temperatures are of great interest due to their potential applications in various biotechnological processes. In this study, we report the discovery and characterization of a new psychrophilic laccase, a multicopper oxidase (MCO), from the bacterium Oenococcus oeni. The psychrophilic laccase gene, designated as LcOe 229, was identified through the genomic analysis of O. oeni, a Gram-positive bacterium commonly found in wine fermentation. The gene was successfully cloned and heterologously expressed in Escherichia coli, and the recombinant enzyme was purified to homogeneity. Biochemical characterization of the psychrophilic laccase revealed its optimal activity at low temperatures, with a peak at 10 °C. To our knowledge, this is the lowest optimum temperature described so far for laccases. Furthermore, the psychrophilic laccase demonstrated remarkable stability and activity at low pH (optimum pH 2.5 for ABTS), suggesting its potential for diverse biotechnological applications. The kinetic properties of LcOe 229 were determined, revealing a high catalytic efficiency (kcat/Km) for several substrates at low temperatures. This exceptional cold adaptation of LcOe 229 indicates its potential as a biocatalyst in cold environments or applications requiring low-temperature processes. The crystal structure of the psychrophilic laccase was determined using X-ray crystallography demonstrating structural features similar to other LAB laccases, such as an extended N-terminal and an extended C-terminal end, with the latter containing a disulphide bond. Also, the structure shows two Met residues at the entrance of the T1Cu site, common in LAB laccases, which we suggest could be involved in substrate binding, thus expanding the substrate-binding pocket for laccases. A structural comparison of LcOe 229 with Antarctic laccases has not revealed specific features assigned to cold-active laccases versus mesophilic. Thus, further investigation of this psychrophilic laccase and its engineering could lead to enhanced cold-active enzymes with improved properties for future biotechnological applications. Overall, the discovery of this novel psychrophilic laccase from O. oeni expands our understanding of cold-adapted enzymes and presents new opportunities for their industrial applications in cold environments.

Rapid, low-cost determination of Hg2+, Cu2+, and Fe3+ using a cellulose paper-based sensor and UV–vis method with silver nanoparticles synthesized with S. mammosum

As water effluents are often highly contaminated with metals, having a quick and cost-effective method of analysis is crucial. This study used the supernatant derived from the green synthesis of silver nanoparticles (AgNPs) with Solanum mammosum to detect mercury, copper, and iron with a low-cost cellulose paper-based sensor and a rapid colorimetric method applying ultraviolet–visible spectroscopy (UV–Vis). AgNPs in two precursor concentrations using silver nitrate, 1 mM (17.4 ± 9 nm) and 50 mM (and 22 ± 8.1 nm), were utilized to assess the efficacy of the analysis and removal of Hg2+, Cu2+, and Fe3+ from contaminated water. Cellulose paper-based sensor showed limits of detection (LODs) for Hg2+ of 2.46 and 123 μM using AgNPs at concentrations of 1 and 50 mM, respectively. For Cu2+, the LODs were 55 and 2750 μM, and for Fe3+, the LODs were 49 and 2470 μM using the respective concentrations. To differentiate and detect the cations with the naked eye, a potassium iodide and potassium ferrocyanide (1:1) aqueous solution was used, producing a yellow, pink, and blue color for Hg2+, Cu2+, and Fe3+, respectively. Additionally, the titration curves of Hg2+, Fe3+, and Cu2+ were examined by UV–Vis using the supernatant liquid. The LODs for the UV–Vis method using AgNPs at a concentration of 1 mM were 1.50 μM for Hg2+, 10.7 μM for Cu2+, and 4.33 μM for Fe3+, while the LODs for AgNPs at 50 mM were 5.75, 27.6, and 15 μM for Hg2+, Cu2+, and Fe3+, respectively. Furthermore, these nanoparticles were utilized to assess the efficacy of the removal of Hg2+, Cu2+, and Fe3+ from contaminated water. Removal efficiency with the solid 50 mM AgNPs was analyzed via flame absorption spectrophotometry; values over 95% were obtained for the three ions. The results underscore the effectiveness of a green synthesis approach to generating AgNPs, enabling efficient and economical cation analysis and water decontamination.

Adsorptive flotation of cesium radionuclides from aqueous solutions using rice straw agriculture waste as a low-cost and eco-friendly adsorbent

ABSTRACT The removal of caesium radionuclides from an aqueous solution by flotation using rice straw (RS) agricultural waste as a low-cost and eco-friendly adsorbent in the presence of potassium ferrocyanide (KFC) was investigated. The influence of many adsorption parameters and flotation was evaluated on the removal efficiency of 137Cs. The adsorption results demonstrated that the concerned radionuclide was efficiently removed in the presence of 2 × 10−4 mol/L KFC using 10 g/L RS at pH ≥ 7. The double exponential kinetic model and the Freundlich model were the best models for fitting the adsorption kinetic and isotherm data, respectively. The maximum adsorption capacity of RS, calculated from the Langmuir model, was 280.405 mg/g. after being transferred to the flotation cell, 137Cs loaded onto ferrocyanide-modified rice straw (FMRS) was successfully floated at pH 7 using 3 × 10−4 mol/L cetyltrimethylammonium bromide (CTAB) surfactant in the presence of 4% ethanol. Removal percentages of 56% and > 99.5% were achieved for 137Cs-loaded FMRS within 5 min using sodium dodecyl sulphate (SDS) and CTAB, respectively. The results obtained in this investigation indicate the efficiency of the suggested strategy and hence its applicability for the removal of 137Cs+ from radioactive liquid wastes.

Exploring the potential of surface-modified alginate beads for catalytic removal of environmental pollutants and hydrogen gas generation

In this study, hydrogel beads were fabricated using alginate (Algt) polymer containing dispersed nickel phthalocyanine (NTC) nanomaterial. The viscous solution of Algt and NTC was poured dropwise into a divalent Ca2+ ions, resulting in the formation of hydrogel beads known as NTC@Algt-BDs. The surface of the NTC@Algt-BDs was further modified by coating them with different types of metal ions, yielding metal-coated M+/NTC@Algt-BDs. The adsorbed metal ions i.e., Cu+2, Ag+, Ni+2, Co+2, and Fe+3 were subsequently reduced to zero-valent metal nanoparticles (M0) by NaBH4. The prepared beads were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Initially, M0/NTC@Algt-BDs were examined for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Among them, Cu0/NTC@Algt-BDs catalyst exhibited the highest reduction rate and therefore, investigated for reduction of different nitrophenols (NPs) and dyes, including 2-nitrophenol (2-NP), 2,6-dinitrophenol (2,6-DNP), methyl orange (MO), potassium ferrocyanide (PFC), congo red (CR), and acridine orange (ArO). The highest reduction rates of 2.019 and 1.394 min−1 were observed for MO and 2-NP, respectively. Furthermore, the fabricated catalysts were employed for the efficient production of H2 gas by NaBH4 methanolysis. Among which the Ag0/NTC@Algt-BDs catalyst showed excellent catalytic production of H2 gas, exhibiting the lowest activation energy (Ea) of 25.169 kJ/mol at ambient temperature. Furthermore, the impact of NaBH4 amount, and catalyst dosage on the reduction of 2-NP and H2 gas production was conducted whereas the effect of temperature on methanolysis of NaBH4 for evolution of H2 gas was studied. The amount of H2 gas was confirmed by GC-TCD system. Additionally, the recyclability of the catalyst was investigated, as it garnered significant research interest.

Palladium-Catalyzed Cyanations of Aryl Imidazolylsulfonates with K4[Fe(CN)6]: A Pragmatic Approach to Benzonitriles from Phenols

AbstractA general Pd-catalyzed approach for the conversion of phenols into benzonitriles via aryl imidazolylsulfonates with a non-toxic cyanide source, potassium ferrocyanide, has been developed. Salient features of this method include low palladium precatalyst loadings (as low as 1.0 mol% total Pd), mild reaction conditions, and environmentally benign by-products compared to other (pseudo)halide aryl electrophiles. The initial scope of the reaction on a range of phenolic precursors is demonstrated including a one-pot, two-step approach to convert phenols directly into benzonitriles.

Enhanced Citric Acid Production through Aspergillus niger: Insights from Fermentation Studies Using Sugarcane Molasses.

The production of citric acid, a vital agricultural commodity utilized across various industries such as food, beverages, pharmaceuticals, agriculture, detergents, and cosmetics, predominantly relies on microbial fermentation, with Aspergillus niger accounting for approximately 90% of global production. In this study, we aimed to optimize the key factors influencing citric acid production, with a focus on strains, fermentation techniques, and carbon sources, particularly sugarcane molasses. A. niger, sourced from the Botany department/Biotechnology laboratories at Govt. College of Science, Lahore, was employed for citric acid production. The process involved inoculum preparation through spore collection from 3 to 5 days of cultured PDA slants. The fermentation medium, comprising cane molasses with a 15% sugar concentration, was meticulously prepared and optimized for various factors, including magnesium sulfate, potassium ferrocyanide, time of addition of potassium ferrocyanide, ammonium oxalate, and calcium chloride. Our optimization results shed light on the significant impact of different factors on citric acid production. For instance, the addition of 0.4 g/L magnesium sulfate led to a maximum yield of 75%, while 2 g/L potassium ferrocyanide, added at 24 h, achieved a yield of 78%. Remarkably, ammonium oxalate, at a concentration of 10 g/L, resulted in a notable 77% yield. Conversely, the addition of calcium chloride exhibited negligible effects on citric acid production, with the control group yielding more at 78%. Our study underscores the potential for optimizing factors to enhance citric acid production by A. niger in submerged fermentation. These findings highlight the pivotal role of magnesium sulfate, potassium ferrocyanide, and ammonium oxalate in augmenting citric acid yields while emphasizing the minimal impact of calcium chloride. Ultimately, these insights contribute to advancing our understanding of microbial citric acid biosynthesis, providing valuable implications for industrial applications and future research endeavors.

Effect of Potassium Ferrocyanide on CMP Performance of Ruthenium in H2O2-based Slurries

As feature size of integrated circuits develops to 7 nm, ruthenium is considered the preferred material to replace traditional Ta/TaN barrier layers. Ruthenium can be electroplated without the need for copper seed crystal layers. However, the removal of the ruthenium barrier layer during the polishing process must be addressed. Therefore, this article studies the promoting effect of potassium ferrocyanide (K4Fe(CN)6) and hydrogen peroxide (H2O2) containing silicon slurries on the rate of ruthenium chemical mechanical polishing. Experiments have shown that the polishing rate of ruthenium is significantly improved by the combined action of K4Fe(CN)6 and H2O2. The stronger hydroxyl radicals is the main factor in achieving a high Ru polishing rate, which accelerates the dissolution and removal of Ru layers by converting the hard Ru layer into softer RuO2 and RuO3 oxide layers. The dependencies of the chemical properties (such as electrochemical impedance spectroscopy and surface morphology) proved that the CMP mechanism using Fenton reaction principally performs chemical oxidation and etching dominant CMP simultaneously. This study is expected to provide ideas and insights for the development and design of a new alkaline polishing solution for ruthenium, which is beneficial for the wider application of ruthenium in the field of integrated circuits.

Label-Free Ratiometric Homogeneous Electrochemical Strategy Based on Exonuclease III-Aided Signal Amplification for Facile and Rapid Detection of miR-378.

MiR-378 is abnormally expressed in various cancers, such as hepatocellular carcinoma, renal cell carcinoma, and nonsmall cell lung cancer. Here, we developed a label- and immobilization-free ratiometric homogeneous electrochemical strategy based on exonuclease III (Exo III) for the facile and rapid determination of miR-378. Two 3'-protruding hairpin DNA probes (HPs) are designed in this strategy. Doxorubicin (DOX) and potassium ferrocyanide (Fe2+) were used as label-free probes to produce a response signal (IDOX) and a reference signal (IFe2+) in the solution phase. When no target was present in the solution, the HP was stable, most of the DOX was intercalated in the stem of the HP, and the diffusion rate of DOX was significantly reduced, resulting in reduced electrochemical signal response. When miR-378 was present, double-cycle signal amplification triggered by Exo III cleavage was initiated, ultimately disrupting the hairpin structures of HP1 and HP2 and releasing a large amount of DOX into the solution, yielding a stronger electrochemical signal, which was low to 50 pM. This detection possesses excellent selectivity, demonstrating high application potential in biological systems, and offers simple and low-cost electrochemical detection for miR-378.

The Fast Quantification of Vitamin B12 in Milk Powder by High-Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry.

This study presents a new technique for determining vitamin B12 in milk powder using high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS). We used ultrasonics with potassium ferrocyanide and zinc acetate solutions to extract the samples. 59Co was employed as the analytical target for cyanocobalamin. It was separated using a Phenomenex Luna 5 μm C18 (250 × 4.6 mm) chromatographic column with a mobile phase consisting of 1.6 mmol/L EDTA and 0.4 mmol/L KH2PO4 in a 60% v/v methanol solution (pH = 4.0). The sample has an excellent separating degree for free cobalt and cyanocobalamin, and isocratic elution can be finished within 4.0 min. To eliminate the matrix interference due to the presence of milk powder, we applied collision mode (KED). The linear range of cyanocobalamine ranged from 1.0 μg/L to 20 μg/L, with correlation coefficients (r2) of 0.9994. The limit of detection (LOD) was 0.63 μg/kg, and the limit of quantitation (LOQ) was 2.11 μg/kg. The mean recoveries were in the range of 87.4-103.6%. The accuracy and precision of the developed method are well suited for the fast quantification of the trace vitamin B12 in milk powder.

Unambiguous identification of asymmetric and symmetric synapses using volume electron microscopy.

The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into two primary morphological types: Gray's type I and type II, corresponding to Colonnier's asymmetric (AS) and symmetric (SS) synapses, respectively. AS and SS have a thick and thin postsynaptic density, respectively. In the cerebral cortex, since most AS are excitatory (glutamatergic), and SS are inhibitory (GABAergic), determining the distribution, size, density, and proportion of the two major cortical types of synapses is critical, not only to better understand synaptic organization in terms of connectivity, but also from a functional perspective. However, several technical challenges complicate the study of synapses. Potassium ferrocyanide has been utilized in recent volume electron microscope studies to enhance electron density in cellular membranes. However, identifying synaptic junctions, especially SS, becomes more challenging as the postsynaptic densities become thinner with increasing concentrations of potassium ferrocyanide. Here we describe a protocol employing Focused Ion Beam Milling and Scanning Electron Microscopy for studying brain tissue. The focus is on the unequivocal identification of AS and SS types. To validate SS observed using this protocol as GABAergic, experiments with immunocytochemistry for the vesicular GABA transporter were conducted on fixed mouse brain tissue sections. This material was processed with different concentrations of potassium ferrocyanide, aiming to determine its optimal concentration. We demonstrate that using a low concentration of potassium ferrocyanide (0.1%) improves membrane visualization while allowing unequivocal identification of synapses as AS or SS.