Saturated KCl Research Articles

Fabrication of a molecularly imprinted poly(methyl methacrylate) decorated graphite electrode for detection of aloe emodin in Aloe vera

In this work, the authors represent a comprehensive approach for the development and validation of a novel graphite-supported molecularly imprinted poly(methyl methacrylate) electrode for the selective and sensitive detection of aloe emodin (AE) in aloe-based cosmetic products. The electrocatalytic activity of the electrode was evaluated using cyclic voltammetry and differential pulse voltammetry techniques in phosphate buffer saline. Surface morphology, structural characteristics, and imprinting endorsement were investigated using field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, and UV-Vis spectroscopy. Under the optimal conditions, the electrode showed an oxidative differential pulse voltammetry peak at -0.2931±0.011 V (vs. Ag/AgCl, saturated KCl). The current was increased linearly with increasing concentrations of AE from 0.0005 to 350 µM, with a low detection limit of 0.0003 µM. The voltammetric analysis has been validated by reverse-phase high-performance liquid chromatography (RP-HPLC) methods. A partial least square regression model was developed to correlate the results obtained from the proposed system with the reference values obtained by RP-HPLC. The model showed a high prediction accuracy of 95.95 % for the detection of AE in cosmetic samples. The developed electrode provides a low-cost, rapid, easy, and convenient method for the detection of AE in cosmetic products, offering potential benefits for quality control and safety assessment in the cosmetic industry.

Characterization of Electrochemically Active Bacteria Utilizing Redox Response in Microbial Electrolysis Cell

This study focuses on micro-electrochemical screening to select microbial strains capable of directly transfer electrons to the working electrode dependent on specific enzymatic machinery. The main objective of this work is to select and identify promising strains for allow the bioelectrolysis production of hydrogen. To achieve this goal, microbial composites (artificial biofilms), have been developed using Escherichia coli CGE1 from LCPME. CNRS Fransh, Pseudomonas putrifisciens (CIP 69.13) (CIP, Collection Institut Pasteur, Fransh). Shewanella oneidensis MR-1 (ATCC 700550), and Thiobacillus denitrificans, from (ATCC, American Type Culture Collection), each one enclosed in a matrix carbon nanotubes and protamine matrix, forming an artificial biofilm on buckypaper. Cyclic Voltammetry (CV) measurements were performed over a potential range of +0.4 to -0.7V at 5mV/s under 30°C, using a saturated KCl Ag/AgCl reference electrode and a stainless-steel grid counter electrode. For E. coli and P. putrifisciens, the measurement focused on the oxidation of 20mM glucose, while the former bacteria were growth with and without O2. For S. oneidensis and T. denitrificans the focus was on the reduction of fumarate and 20 mM of NaNOH3+, respectively. As results, E. coli and P. putrifisciens species show no notable electrochemical activity, with no signal of glucose oxidation, due to the absence of type C cytochromes in the cytoplasmic membrane, unlike S. oneidensis and T. denitrificans, that demonstrate a direct electron transfer.

Over-Time Stability Evaluation of Fluorinated Self-Assembled Monolayer on Commercial Indium Tin Oxide Electrode on PET Substrate

Motivation: Self-Assembled Monolayer (SAM) modified electrode has a key role in electrochemical biosensor applications to achieve desired sensing properties such as selective interaction with target protein and anti-fouling properties of non-specific protein. However, the degradation of SAM layer on the electrode can cause the electrochemical response to drift over time. This causes adversary effect on the designed biosensor such as limited shelf life and inconsistent electrochemical signal reading between electrodes. For that matter, it is important to understand the signal drift behaviour and ultimately obtain a SAM-modified electrode with good stability over time. In this study, we observed the signal drift of SAM-modified indium tin oxide electrode on PET substrate (ITO-PET). Three-electrode electrochemical impedance spectroscopy (EIS) measurement was carried to evaluate the electrochemical properties of the ITO-PET substrate over time. Materials and Methods: Commercial ITO-PET (Adafruit, NY, USA) was used as electrode and was modified using Perfluoro-octyltriethoxysilane (Sigma Aldrich, St. Louis, MO, USA) self-assembled monolayer. The ITO-PET substrate was modified by using room temperature RCA-1 silanization process as shown in Figure 1. The modified electrode was rinsed in ethanol and DI water and stored in dark condition with temperature of 5oC. The Electrochemical Impedance Spectroscopy measurements were carried by using Solartron SI1260 impedance analyser tandem with SI1287 potentiostat. with saturated KCl Ag/AgCl (RRPEAGCL2, Pine Research, NC, USA) electrode and Pt wire counter electrode (MW-1032; BASi, West Lafayette, IN, USA). Potassium Ferricyanide (K3Fe(CN)6) (Fischer Scientific, Fair Lawn, NJ, USA) with concentration of 10 mM in 1x PBS was used as redox probe. The EIS run was set at 0.31 Vdc and 10 mV Vac amplitude with frequency ranging from 0.1 – 10000 Hz. Results: We observed significant increase charge transfer resistance (Rct)increase of SAM-ITO sample (4498 ± 460 Ω.cm2) compared to the bare ITO sample (1348 ± 68 Ω.cm2). The signal also maintains its consistency after one week of storage in enclosed dry and dark environment at 5oC with 3% change in average Rct value (133 Ω.cm2). Ongoing work in this study includes the electrochemical signal evaluation of the ITO-SAM electrode exposed to protein such as casein and BSA. Figure 1

Synthesis of conjugated structural copolymer poly(3-hexylthiophene-random-benzoyl dithieno[3,2-b:2’,3’-d]pyrrole) by electrochemical method

Electrochemical copolymer synthesis of benzoyl dithieno[3,2-b:2’,3’-d]pyrrole and 3-hexylthiophene (3HT) promises to create new polymer with suitable improved HOMO and LUMO with the energy level of acceptor compounds such as Fullerene (C60) or the novel accepted organic compound in the heterojunction in organic solar cell. Electrochemical synthesis of copolymer (3-hexylthiophene-random-benzoylbdithieno[3,2-b:2’,3’-d]pyrrole by linear potential scanning method was studied and applied for synthesis of conjugated copolymer where three electrodes have been used for polymerisation including the working electrode of Indium Tin Oxide (ITO) substrate, the reference electrode of Ag/AgCl in saturated KCl and the counter electrode of platinum wire. The synthesised copolymer was characterised and evaluated through an electrochemical process, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and ultraviolet-visible spectroscopy (UV-Vis) measurements. The synthesised copolymer has a bandgap of 2.09 eV, HOMO and LUMO energy levels of -5.21 and -3.12 eV, respectively. The HOMO-LUMO of the synthesised conjugated copolymer is closed with the HOMO-LUMO of Fullerene; therefore, the conjugated copolymer is a potential material for the fabrication of organic solar cell.

Closed-loop cleaning treatment system — resource recovery of coal gangue

ABSTRACT Coal gangue (CG) is one of the main solid wastes emitted by coal mining. It causes severe damage to the environment. CG contains high levels of valuable elements (Al, Si) and has the potential for utilization and clean disposal. Here, an environment-friendly process for separating valuable components from CG was proposed: the closed-loop system of activation-leach-separation. The results show that the decarbonization rate was close to 100% under the optimum conditions of CG particle size of 0.075 mm to 0.15 mm and activated at 800°C for 120 min. Subsequently, it was transformed into a mixed-acid system with a hydrochloric acid (HCl) concentration of 4.5 mol/L, hydrofluoric acid (HF) volume fraction of 15%, and the liquid-solid ratio of 10:1, which achieved excellent separation efficiency. The residual rate of Al in the solution was only 0.7%, and the extraction rate of Si can reach 71.6%. Further, industrial-grade AlF3 products were also recovered. By adding saturated KCl solution and reacting at 33°C for 15 min, Si was further recovered in K2SiF6, and the yield was 85.83%. Particularly, the leaching solution maintained good extraction efficiency in the subsequent three cycles, the yield of K2SiF6 was 88.29%, confirming the feasibility of the closed-loop system. This treatment embodied the environmental-friendly properties of low acid consumption and low effluent discharge, providing a feasible method for clean treatment and resource utilization of CG.

Electroanalytical Determination of Trimetazidine in Pharmaceuticals and Synthetic Urine Using an Anodically Treated Boron-Doped Diamond (BDD) Electrode and Square Wave Voltammetry (SWV)

Trimetazidine dihydrochloride is an anti-ischemic agent widely used in the treatment of coronary artery disease, more specifically in the treatment of angina. Here is reported a simple and sensitive electroanalytical methodology for quantifying trimetazidine in pharmaceutical and synthetic urine samples using square-wave voltammetry. The influence of anodic and cathodic treatments on boron-doped diamond (BDD) was evaluated. The best results for trimetazidine were obtained using a BDD treated anodically at +3.0 V versus Ag(s)/AgCl(s)/Cl-(aq., saturated KCl) for 300 s in 0.1 mol L−1 H2SO4. The determination of trimetazidine was carried out in Britton-Robinson buffer at pH 3. Trimetazidine oxidation reveals two well-defined irreversible oxidation peaks. A calibration relationship was obtained from 0.35 mg L-1 to 2.6 mg L−1 (R2 = 0.997). Limits of detection and quantification for trimetazidine were 5.63 x 10−9 and 1.88 x 10−8 mol L−1, respectively. Recovery values were between 97 and 101 % and 96.8 and 99.8 % in pharmaceutical and synthetic urine.

Regulating Microstructure and Macroscopic Properties in Saturated Salt Solutions Containing Disordered Anions and Cations by Magnetic Field.

Saturated aqueous salt solutions have diverse applications in food production, mineral processing, pharmaceuticals, and environmental monitoring. However, the random and disordered arrangement of ions in these solutions poses limitations across different fields. In this study, we employ magnetic fields to regulate the disordered arrangement by a comprehensive methodology combining contact angle measurement, Raman spectroscopy, X-ray diffraction, and molecular dynamics simulations on saturated KCl solutions. Our findings reveal that weak magnetic fields impede the formation of K-Cl contact pairs and disrupt hydrogen bond networks, particularly DDAA and free OH types. However, they facilitate the interaction between water molecules and ions, leading to an increase in the number of K-O and Cl-H contact pairs, along with an expansion in ion hydration radius. These changes affect macroscopic properties, including the interaction with solid substrates and potential solubility increases. Our experimental and simulation results mutually validate each other, contributing to a theoretical framework for studying magnetic field-material interactions.

Gold Ultralow Loading on Nickel Foam for Nitrogen Electrochemical Reduction

Gold electroless deposition on nickel foam offers several advantages over traditional electrodeposition techniques. One of the main advantages is that it can produce uniform thickness coatings on complex shapes and geometries, such as porous and three-dimensional substrates like nickel foam. The resulting gold-nickel foam composite has high surface area and good electrical conductivity, making it suitable for various electrochemical applications, including catalysis, sensing, and energy storage.In this work we focused on the development of synthetic strategies to grow and optimize the surface coverage of gold on nickel foam and the evaluation of its suitability for the electrochemical reduction of nitrogen for ammonia synthesis.The gold electroless deposition on Ni Foam has been obtained by immersion in aqueous solution containing KAuCl4 and HCl, with or without stirring and addition of a surfactant agent (Isopropyl Alcohol). Depositions were performed by varying the immersion time from 30 seconds to 30 minutes. Scanning electron microscopy (SEM) has been employed to compare different deposition conditions and to optimize the morphology of the nanofilms, allowing higher catalytic activity. The electrochemical performance of the gold deposited on nickel foam was evaluated in a standard two compartments electrochemical cell using a Pt wire as counter electrode (CE), a saturated calomel electrode (SCE, saturated KCl) as reference and 0.1 M Na2SO4 solution as electrolyte. Electrochemical active surface area (EASA) and linear sweep voltammetry (LSV) have been adopted to evaluate the active area and the overpotential toward hydrogen evolution reaction (HER). Chronoamperometry experiments were carried out at various potentials to evaluate the performance of the catalyst for the electroreduction of nitrogen and ammonia synthesis.The amount of ammonia produced was measured by the indophenol blue method.The maximum NH3 yield of 2.8x10-11 mol s-1 cm-2 was achieved at -0.045 V vs RHE. The maximum faradaic efficiency of 5.8% was achieved at more positive potential (0.015 V vs RHE) due to the HER.The results show that the gold on nickel foam exhibits excellent electrochemical stability and high conductivity.This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under grant agreement No 101006941. This project started on the 1st of November 2020 with a duration of 42 months.

Catholyte Modulation and Prussian Blue/Berlin Green Redox Mediator Enabling Efficient High‐Potential Mn2+/MnO2 Reaction for Aqueous Hybrid Batteries

The use of multielectron Mn2+/MnO2 cathode reaction achieves high‐energy aqueous acid–base asymmetric hybrid batteries. However, the ion crossover through the membrane and the accumulation of unreacted MnO2 lead to serve potential and capacity decay of the cathode during cycling. Herein, the catholyte modulation using the KCl additive and the design of a Prussian blue/Berlin green (PB/BG) redox mediator on the cathode current collector are developed to promote high‐potential Mn2+/MnO2 reaction. The addition of saturated KCl greatly suppresses the ion crossover to maintain the catholyte acidity, thus enabling high‐potential Mn2+/MnO2 reaction and stable high‐voltage discharge plateau of ≈2.2 V for the hybrid battery at a prolonged cycling. The reversible MnO2 deposition is effectively improved by the PB/BG redox mediator, which contributes to significant enhancements in the reversible capacity, rate capability, and cycling stability of the cathode. Importantly, the as‐assembled hybrid battery exhibits the highest energy density of ≈260 Wh kg−1 (based on the mass of the aqueous MnCl2 catholyte and a hydrogen storage anode material) among the previously reported Mn‐based acid–base asymmetric batteries.

Cathodic Polarization Behavior of Steel in Aqueous MgCl2 Solutions Containing Zn2+

So far, we have revealed that the dissolution rate of zinc is accelerated in relative high concentrations of MgCl2 in the corrosion process of galvanic couples consisting of zinc and steel. In this study, we investigated the cathodic polarization behavior of steel in MgCl2 solution containing Zn2+ and the effect of Zn2+ dissolved in the solution on the oxygen reduction reaction and hydrogen evolution reaction.The specimens used in the experiments were carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined into a 1.5×1.5×0.3 cm3. One side of the specimen was polished with SiC abrasive paper up to #2000 grit and degreased in acetone before being used for the experiment. The test solution was mixtures of 0.25 M MgCl2 + x mM ZnCl2 (x = 2.5, 5 mM, Mg/Zn molar ratio: 100, 50) at room temperature under a naturally aerated condition. As a comparison solution, 0.5 M NaCl + y mM ZnCl2 (x = 5, 10 mM, molar ratio of Na/Zn: 100, 50) with the same chloride ion concentrations were used. Cathodic polarization curves of steel were measured using a three-electrode method with a platinum wire as the counter electrode and an Ag/AgCl electrode (saturated KCl, SSE) as the reference electrode. The potential sweep rate was 0.5 mV/s. After the polarization test, the specimen surfaces were observed with a scanning electron microscope and analyzed for corrosion products formed during cathodic polarization with XRD and laser Raman spectroscopy.The cathodic polarization behavior of steel in MgCl2 solution without Zn2+ was investigated and compared with that of NaCl solution without Zn2+. Diffusion-limited currents of dissolved oxygen reduction (ORR) were observed at -0.6 V to -0.8 V in MgCl2 and NaCl solutions. Furthermore, cathodic polarization in MgCl2 and NaCl solutions showed an increase in current due to hydrogen evolution reaction (HER), and the cathodic current due to HER on steel was larger in the MgCl2 solution than in the NaCl solution. To investigate the difference in HER in both solutions, the steel surface was observed after constant polarization at -1.0 V for 20 min. Mg(OH)2 deposition was observed on the steel surface in the MgCl2 solution, but not in the NaCl solution. This indicates that the increase in pH due to ORR and HER is mitigated by the formation of Mg(OH)2 during cathodic polarization. Therefore, due to the pH buffering action of Mg2+ associated with the formation of Mg(OH)2, it can be considered that a larger HER current flowed in the MgCl2 solution than in the NaCl solution when compared at the same potential.On the other hand, cathodic polarization curves for steel in MgCl2 and NaCl solution containing Zn2+ were investigated. As a result, ORR and HER were observed at potentials down to -1 V in the MgCl2 and NaCl solutions containing Zn2+; the cathodic current due to ORR and HER in the MgCl2 and NaCl solutions containing Zn2+ was reduced compared to the solutions without Zn2+. The inhibition of ORR and HER can be attributed to the precipitation of Zn corrosion products.These results suggest that in solution environments containing Mg2+ and Zn2+, the promotion of HER by the effect of Mg2+ and the inhibition of HER and ORR by Zn corrosion products occur simultaneously.

Experimental Study on the Effects of Applied Electric Field on Liquid Infiltration into Hydrophobic Zeolite

A nanofluidic energy absorption system (NEAS) is composed of nanoporous material and functional liquid with high energy absorption density. Applying an electric field to adjust the energy absorption characteristics of a nanofluidic system will open broader prospects for its application. In the current work, ZSM-5 zeolite was adopted as the nanoporous material and water, a 25% KCl solution, and a saturated KCl solution were adopted as functional liquids to configure NEASs. Pressure-induced infiltration experiments were carried out to study the infiltration and defiltration characteristics of the NEASs under the action of an applied electric field. The results show that the introduction of an applied electric field can weaken the hydrogen bonds between molecules, thus reducing the equivalent surface tension and contact angle, changing the infiltrability of liquid molecules into the nanopores, and reducing the infiltration pressure of the system. In an electrolyte solution/zeolite system, the anions and cations move close to the two plate electrodes under the action of an external electric field, and the fluid properties in the central zone of the pressure chamber are close to the water/zeolite system. For both an ultra-low conductivity liquid and an electrolyte solution/zeolite system, applying an electric field can effectively improve the relative outflow rate of liquid, thus improving the reusability of the system.

Electrochemical Detection of Aloe Emodin using Platinum Electrode Based Voltammetry Technique

In this work, a noble metal based platinum (Pt) electrode has been explored to detect one of the important phytochemical Aloe Emodin (AE) in Liliaceae family. A sensitive three-electrode system was equipped to assess the electrochemical behavior of AE using Pt electrode as a working electrode along with silver/silver chloride (saturated KCl) and a steel as a reference electrode and a counter electrode, respectively. The redox response of Pt electrode against AE was analyzed using cyclic voltammetry (CV) at a scan rate ranging from 0.01 Vs-1 to 0.4 Vs-1 that showed well-defined reversible peaks in phosphate buffer saline (PBS at pH 6.0). Under optimized experimental condition, DPV peak currents were linear over concentration range 1 µM -150 µM with R2 value of 0.987 In addition, the sensitivity of the electrode was excellent with sensitivity factor of 1.3 A/M and the limit of detection (LOD) was obtained 0.2 µM. Principal component analysis (PCA) was performed on the response data to demonstrate diverse discrimination of different concentration of AE. The developed sensor showed excellent repeatability and can be successfully used to detect AE in Aloe.

Pectinose electrochemical quantitative analysis method using functional metal materials

ABSTRACT As a soluble dietary fiber, pectin has the functions of lowering cholesterol, reducing weight and improving human immunity. However, nowadays, many studies have been reported on the extraction of pectin, but few on its quantitative analysis. In this paper, graphene modified copper foam and copper sheet were used as working electrodes, respectively. Pt electrode as counter electrode and Ag/AgCl (saturated KCl solution) electrode was used as reference electrode to build electrochemical detection system. The electrochemical responses to pectinose solution were measured by voltammetry (CV) and chronoamperometry (i-t). The detection data were analyzed to develop pectinose quantitative analysis model. Results indicated that the proposed method could determine pectinose concentration in solution, and graphene modified copper foam presented better responses. The sensitivity was 0.68851A cm−2 mmol/L, the detection limit was 0.24825 mol/L. This method presents some advantages including fast response, easy operation, and low cost. It provides a new method for pectinose quantitative detection.

Water sorption isotherms on lyophilized jabuticaba (Myrciaria cauliflora) peel: potential byproduct for the production of dehydrated foods.

In this work, water sorption profiles on lyophilized jabuticaba peel were evaluated using the BET, GAB, Halsey, Henderson, Oswin and Smith isotherm models. All water sorption studies were conducted using the static gravimetric method and saturated CH3COOK, K2CO3, NaBr, SnCl2, KCl and BaCl2 solutions at 20, 30 and 35°C. The best water sorption isotherm fits were determined with the GAB model at 20°C, Oswin model at 30°C and Halsey model at 35°C. The curve profiles of the isotherm models employed were classified as type III. The results revealed that lyophilized jabuticaba peel can be safely stored at 20, 30 or 35°C with the monitoring and control of relative humidity, equilibrium humidity and water activity. However, microbial action and undesirable enzymatic reactions may occur at 35°C when the relative humidity is above 22%. The present results are useful for defining suitable storage and production conditions of a novel jabuticaba peel-based process for the production of dehydrated foods.

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Robust O-Pd-Cl catalyst-electrolyte interfaces enhance CO tolerance of Pd/C catalyst for stable CO2 electroreduction

Carbon-supported Pd catalysts are highly active yet can be easily poisoned by the in-situ formed carbon monoxide (CO) during CO2 electrochemical reduction reaction (CO2RR). Herein, we introduce a novel approach to enhance the CO tolerance and activity of Pd/C catalyst by manipulating catalyst-electrolyte interfaces in saturated KCl electrolyte. During the CO2RR, the Cl- ions in electrolyte trigger the surface dynamic reconstruction of Pd/C catalyst with the formation of O-Pd-Cl species at catalyst-electrolyte interfaces. The reconstructed Pd/C catalysts can achieve nearly 100% of CO Faradaic efficiency and feature high stability and CO tolerance, which can maintain a better activity in the presence of over 2000 ppm and 23200 ppm of CO in H-type cell and flow cell, respectively. Meanwhile, using such highly concentrated electrolyte, the hydrogen evolution reaction is strongly suppressed. The experimental and theoretical results have confirmed that the O-Pd-Cl species mediated by Cl- ions enable the high activity, good CO resistance and long lifetime of the Pd/C catalyst. These findings may provide some inspirations into the design and fabrication of active yet stable Pd-based catalysts for CO2 electroreduction, and offer some insights into manipulation of the activity and stability for the Pd catalysts at catalyst-electrolyte interfaces.

Quantitative determination of d-psicose based on flexible copper film materials and electrochemical scanning methods

In this paper, a three-electrode electrochemical detection system was designed. Platinum electrode was used as the counter electrode, saturated KCl electrode as reference electrode, and copper film material as working electrode, respectively. Cyclic voltammetry (CV) and chronoamperometry (i-t) methods were used for d-psicose scanning. CV results indicated that d-psicose presented the oxidation–reduction reacting procedure on the surface of copper film electrode. Testing parameters optimization was conducted using CV scanning in different scanning rates. d-psicose quantitative determination model was developed by i-t scanning results. The sensitivity was9419.1A×cm-2·mol/L, the detection limit was1.04311×10-8mol/L. The proposed method has some advantages including high sensitivity, low detection line, and fast response speed. Negative control testing results by using glucose, sucrose, and NaCl solutions demonstrated that the proposed method had good selectivity.

Carbon Nanotubes-Based Fuel Cell for Cr(VI) Removal and Electricity Generation.

A fuel cell, an energy transducer, can convert chemical energy into electrical energy. In this work, graphite felt (GF) loaded with polypyrrole (PPy) and carboxylic carbon nanotubes (CNTs-COOH) was used as a cathode (GF/PPy/CNTs-COOH) in a double-chamber nonbiofuel cell (D-nBFC) to remove Cr(VI) efficiently. Therein, Na2S2O3 in an alkaline solution and Cr(VI) in a strongly acidic solution were employed as anode and cathode solutions, respectively. An agar salt bridge, consisting of saturated KCl solution, was used to transport ions between the anode and cathode. This system suggested that the removal efficiency of Cr(VI) could reach 99.6%. The maximum current, power, and power density could achieve 136.8 μA, 18.7 μW, and 20.8 mW/m2 at 90 min, respectively. Additionally, GF/PPy/CNTs-COOH also had good electrocatalytic stability and reusability after four cycles, which played an important role in the development of the D-nBFC system. Therefore, this study provides an environmentally friendly and efficient method to remove Cr(VI) and generate electricity simultaneously.

Single Particle Electrochemical Oxidation of Polyvinylpyrrolidone-Capped Silver Nanospheres, Nanocubes, and Nanoplates in Potassium Nitrate and Potassium Hydroxide Solutions

Single particle electrochemical oxidation of polyvinylpyrrolidone-capped silver nanoparticles at a microdisk electrode is investigated as a function of particle shape (spheres, cubes, and plates) in potassium nitrate and potassium hydroxide solutions. In potassium nitrate, extreme anodic potentials (≥1500 mV vs Ag/AgCl (3 M KCl)) are necessary to achieve oxidation, while lower anodic potentials are required in potassium hydroxide (≥900 mV vs Ag/AgCl (saturated KCl)). Upon oxidation, silver oxide is formed, readily catalyzing water oxidation, producing a spike-step current response. The spike duration for each particle is used to probe effects of particle shape on the oxidation mechanism, and is substantially shorter in nitrate solution at the large overpotentials than in hydroxide solution. The integration of current spikes indicates oxidation to a mixed-valence complex. In both electrolytes, the rate of silver oxidation strongly depends on silver content of the nanoparticles, rather than the shape-dependent variable–surface area. The step height, which reflects rate of water oxidation, also tracks the silver content more so than shape. The reactivity of less-protected citrate-capped particles toward silver oxidation is also compared with that of the polymer-capped particles under these anodic conditions in the nitrate and hydroxide solutions.

Preparing porous Cu/Pd electrode on nickel foam using hydrogen bubbles dynamic template for high-efficiency and high-stability removal of nitrate from water.

Electrochemical reduction is a promising technology to remove nitrate from water. The metallic composition and geometry of electrodes usually dominate the nitrate removal property. Based on nickel foam (NF), we prepared Cu/Pd bimetallic electrode using hydrogen bubbles dynamic template according to a two-step electrodeposition method (Pd after Cu). The micromorphology, crystal structure, and metallic composition were analyzed by using the field emission scanning electron microscope with energy dispersive spectroscopy (FESEM-EDS), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) instruments, respectively. 4.4mg of Cu and 1.4mg of Pd were detected on the prepared Cu/Pd electrode. The micromorphology of prepared Cu/Pd electrode showed a grape-bunch look with porous structure of two stage sizes (100-500nm and 200-300μm). 98% of the initial NO3--N (100mg/L) was removed under the potential of - 1.6V vs. Ag/AgCl saturated KCl after 24h of reaction when using 0.05mol/L of Na2SO4 or NaCl as electrolyte. But the concentration of produced NH4+-N was higher than 80mg/L when using Na2SO4 as electrolyte, which was close to 0mg/L when using NaCl as electrolyte. The cyclic voltammetry curves of 1000 cycles and the long-term continuous flow test of about 200h suggested that the prepared Cu/Pd electrode showed high stability for nitrate removal from water.