Ferricyanide Concentration Research Articles

An eco-friendly approach for bioelectricity production through microbial fuel cell using Musa acuminata as waste biomass

With the increasing population and industrialization, the demand of electricity is increasing day-by-day and high energy demands have adverse effects on fossil fuels consumption. The sustainable development goal (SDG) 7 focuses on green energy. Due to this, global attention is shifted from conventional sources to non conventional energy sources such as solar energy, wind energy, waste biomass, etc. This work explores the feasibility of a microbial fuel cell for bio-electricity production. The effect of different catholytes on bio electricity production is assessed. This research includes the fabrication of a H-shaped double chambered microbial fuel cell using two containers of 2 L each. Both the containers were connected with an agar salt bridge. The bioelectricity was produced from banana peel waste using potassium dichromate and potassium ferricyanide as catholyte and zinc rod and copper plate as electrodes. With potassium dichromate, the maximum value of voltage and current was found as 0.20 V and 0.112 mA respectively, while in case of potassium ferricyanide the maximum voltage and current obtained was 0.42 V and 0.55 mA respectively at 0.1 M concentration of catholyte. Substrates like glucose (10 % by weight) and sodium acetate (5 % by weight) was added in the banana peel slurry so as to make the microbial fuel cell more efficient. Further, impact of increase in potassium ferricyanide concentration from 0.1 to 0.5 M concentration on the generation of electricity was analysed and it was found that with increase in concentration of catholyte, voltage and current enhanced. The maximum voltage, current and power density found by increasing concentration of potassium ferricyanide from 0.1 to 0.5 M was 0.9 V, 3.36 mA and 1.055 W/m2. This study concludes that potassium ferricyanide is better oxidising agent than potassium dichromate. Microbial fuel cell can be a promising technology for bioelectricity production using banana peel waste.

Heat and mass transfer performance of ferricyanide/ferrocyanide thermocell and optimization analysis

Thermocell, as a device of thermoelectric conversion, can directly convert waste heat into electricity without moving parts and gas emissions. The overall numerical thermocell model is an effective tool used to study different processes and phenomena of heat and mass transfer. In this study, the mathematical model of Fe(CN)63−/4- thermocell was established and numerically analyzed. The influence of cell's size, temperature difference, electrolyte concentration, and electrode structure on the output power and efficiency of thermocell were studied under the multiple physical fields of temperature, velocity, concentration, and electrochemical reaction. The results revealed that higher cell's height, shorter cell's length, and higher concentrations tend to maximize electrical output power. At the cell's height of 10 mm, cell's length of 2 mm, the temperatures of the hot side and cold side of 310.55 K and 290.55 K respectively, and initial concentrations of ferrocyanide and ferricyanide of 400 moL/m³, yielded the maximum value of electrical output power of 6.75 μW. This research demonstrated that improving the performance of the thermocell depended not only on electrochemistry and materials, but also on design optimization. Combining the influence of temperature difference and electrolyte concentration, the optimization strategy including the size, temperature, concentration, and structure of thermocell was further proposed. The established thermocell model and the proposed optimization strategy can provide guidance for the designing of thermocells having higher output and conversion efficiency in the future.

Phase Behavior and Electrochemical Properties of Highly Asymmetric Redox Coacervates.

This work reports the phase behavior and electrochemical properties of liquid coacervates made of ferricyanide and poly(ethylenimine). In contrast to the typical polyanion/polycation pairs used in liquid coacervates, the ferricyanide/poly(ethylenimine) system is highly asymmetric because poly(ethylenimine) has approximately 170 charges per molecule, while ferricyanide has only 3. Two types of phase diagrams were measured and fitted with a theoretical model. In the first type of diagram, the stability of the coacervate was studied in the plane given by the concentration of poly(ethylenimine) versus the concentration of ferricyanide for a fixed concentration of added monovalent salt (NaCl). The second type of diagram involved the plane given by the concentration of poly(ethylenimine) vs the concentration of the added monovalent salt for a fixed poly(ethyleneimine)/ferricyanide ratio. Interestingly, these phase diagrams displayed qualitative similarities to those of symmetric polyanion/polycation systems, suggesting that coacervates formed by a polyelectrolyte and a small multivalent ion can be treated as a specific case of polyelectrolyte coacervate. The characterization of the electrochemical properties of the coacervate revealed that the addition of monovalent salt greatly enhances charge transport, presumably by breaking ion pairs between ferricyanide and poly(ethylenimine). This finding highlights the significant influence of added salt on the transport properties of coacervates. This study provides the first comprehensive characterization of the phase behavior and transport properties of asymmetric coacervates and places these results within the broader context of the better-known symmetric polyelectrolyte coacervates.

The Leaching of Palladium from Polymetallic Oxide Ores using Alkaline Ferricyanide Solutions

ABSTRACT The present study investigated a novel method of alkaline ferricyanide leaching to extract palladium (Pd) from a Western Australian disseminated platinum-group metal (PGM) oxide ore that bears Ni and Cu. While cyanide has been used to leach Pd, it is well known for its toxicity and large consumption in the presence of base metals. A more benign alternative, in the form of alkaline ferricyanide, is evaluated in this research to serve the combined role of lixiviant and oxidant. Various leaching parameters, such as ferricyanide concentration (1–30 g/L), dissolved oxygen level (up to 25 ppm), pH (10–12), and temperature (20–80°C), were investigated to evaluate Pd extraction. The Pd extraction was found to be the most sensitive to leach temperature with Pd extraction doubling when the temperature was raised from 20°C to 80°C. The highest Pd extraction of 76.1% was achieved at 10 g/L ferricyanide, pH 11, DO 15 ppm, 80°C, and 10% solids. The alkaline ferricyanide leaching system showed high selectivity for Pd over other metals (Pt, Co, Ni, Cu). The co-extractions of base metals (Co, Cu, and Ni) were all below 2%, and that of Pt was below 10% over the range of temperatures investigated. Although conventional cyanidation at a low cyanide consumption (1 kg/t) showed slightly better performance in Pd extraction, the ferricyanide leaching significantly improved the settleability and filterability of the leaching slurry considering the finely ground nature and high-clay content of the lateritic oxide ores. In contrast, the cyanidation leaching slurry was found to filter or settle poorly.

Using and Validation of a new Spectrophotometric method for determination of Vitamin C in Pharmaceutical samples

A new simple and rapid spectrophotometric method for determination the accurate amount of vitamin C containedin pharmaceutical samples has been developed. The ferric chloride is reduced by vitamin C and then reacts with potassium ferricyanide to create a dark blue solution of Prussian blue. The resulted color was observant at the absorption wavelength of 697nm. Optimum reaction conditions of Ferric chloride, Potassium Ferricyanide concentrations, reaction time, temperature and pH where investigated. Influence of potential interfering substances were also examined.Analyzes of commercial pharmaceutical samples showed good correlation with the valuesgiven by the manufacturers and the results obtained by a titration method with Iodine. The apparent molar absorptivity value is found to be 3.25 × 103. The results of analysis have been validated statistically, with good correlation coefficient (0.999). The proposed method has better LOD and LOQ values than many methods used to determine vitamin C in pharmaceutical forms.

A novel method for Ion Exchange Capacity characterization applied to Anion Exchange Membranes for Water Electrolysers

Hydrogen production from water electrolysis, hydrogen fuel cells and redox flow batteries are the right approach for the renewable energy sector because the electricity generated by solar, wind, photovoltaic, hydroelectric can be managed with a carbon-free approach. These technologies all have in common one fundamental component: the membrane. Different types of membranes have been developed for both cationic and anionic exchange, and recently, research activity focalized on improving their performances is very fervent. One fundamental characteristic of a membrane is its Ion Exchange Capacity (IEC), i.e. the density of charged functionalizing groups. Within our research project NEMESI, funded by EU-PNRR (ID: RSH2B_000002), and dedicated to Anion Exchange Membrane Water Electrolysis, we studied and validated a novel alternative method to measure IEC. The present titration methods have limitations for the need of dedicated hardware or qualitative inspection of their color-turning endpoint. The proposed method, based on the redox titration of potassium ferricyanide with ascorbic acid, allows a quantitative and independent assessment based on both potentiometric and spectrophotometric measurements, along with the usually adopted visual observation, as the yellow-colored ferricyanide is reduced to colorless ferrocyanide. Moreover, if compared to the classical Mohr titration with silver nitrate, the new method can be carried out at variable ferricyanide concentrations during the addition of the ascorbic acid, so a complete curve of the redox reaction can be constructed: the initial ferricyanide ion load of the membrane (IEC) can thus be derived in a more precise way than with a single-point evaluation. Only one Ag/AgCl reference electrode and a platinum working electrode are required without any power supply/potentiostat. The proposed method was validated using Anion Exchange Membranes with known IEC.

A Novel Gel Thermoelectric Chemical Cell for Harvesting Low-Grade Heat Energy.

The use of gel thermoelectric chemical cells to capture low-grade heat for conversion to electricity is an attractive approach. However, there are few studies on whether the distribution of redox species in the electrolyte has an effect on the performance of cells. Herein, this concern was discussed by constructing a novel gel thermoelectric chemical cell (Cu-C-cg). Using cellulose-like rice paper as a separator, a concentration gradient of electrolyte was carefully constructed, so that the concentration of potassium ferrocyanide gradually decreased from the hot electrode to the cold electrode while the concentration of potassium ferricyanide gradually increased. Through electrochemical measurement and analysis, it was found that the thermoelectric performance of this cell outperformed the cell without electrolyte concentration gradients. Meanwhile, this performance could be enhanced by the use of asymmetric electrodes composed of copper foil and carbon electrodes. After optimizing the conditions, the open-circuit voltage, output power, and Seebeck coefficient of the Cu-C-cg cell at 12 K temperature difference were 0.450 V, 183 μW, and 7.82 mV K-1 , respectively. This work not only provides a novel idea in gel-based cell design but also an excellent thermoelectric chemical cell.

Real-Time Convolutional Voltammetry Enhanced by Energetic (Hot) Electrons and Holes on a Surface Plasmon Waveguide Electrode.

Surface plasmon polaritons (SPPs) propagating along a waveguide working electrode are sensitive to changes in the local refractive index, which follow changes in the concentration of reduced and oxidized species near the working electrode. The real-time response of the output optical power from a waveguide working electrode is proportional to the time convolution of the electrochemical current density, precluding the need to compute the latter a posteriori via numerical integration. Convolutional voltammetry yields complementary results to conventional voltammetry and can be used to determine the diffusion constant, bulk concentration, and the number of transferred electrons of electroactive species. The theoretical optical response of a waveguide working electrode is derived and validated experimentally via chronoamperometry and cyclic voltammetry measurements under low power SPP excitation, for various concentrations of potassium ferricyanide in potassium nitrate electrolyte at various scan rates. Increasing the SPP power induces a regime where the SPPs no longer act solely as a probe of electrochemical activity, but also as a pump creating energetic electrons and holes via absorption in the working electrode. In this regime, the transfer of energetic carriers (electrons and holes) to the redox species dominates the electrochemical current density, which becomes significantly enhanced relative to equilibrium conditions (low SPP power). In this regime the output optical power remains proportional to the time convolution of the current density, even with the latter significantly enhanced by the transfer of energetic carriers.

Electrochemical Performance of Lithographically-Defined Micro-Electrodes for Integration and Device Applications

Small; lithographically-defined and closely-spaced metallic features of dimensions and separation in the micrometer range are of strong interest as working and counter electrodes in compact electrochemical sensing devices. Such micro-electrode systems can be integrated with microfluidics and optical biosensors, such as surface plasmon waveguide biosensors, to enable multi-modal sensing strategies. We investigate lithographically-defined gold and platinum micro-electrodes experimentally, via cyclic voltammetry (CV) measurements obtained at various scan rates and concentrations of potassium ferricyanide as the redox species, in potassium nitrate as the supporting electrolyte. The magnitude of the double-layer capacitance is estimated using the voltammograms. Concentration curves for potassium ferricyanide are extracted from our CV measurements as a function of scan rate, and could be used as calibration curves from which an unknown concentration of potassium ferricyanide in the range of 0.5–5 mM can be determined. A blind test was done to confirm the validity of the calibration curve. The diffusion coefficient of potassium ferricyanide is also extracted from our CV measurements by fitting to the Randles–Sevcik equation (D = 4.18 × 10−10 m2/s). Our CV measurements were compared with measurements obtained using macroscopic commercial electrodes, yielding good agreement and verifying that the shape of our CV curves do not depend on micro-electrode geometry (only on area). We also compare our CV measurements with theoretical curves computed using the Butler–Volmer equation, achieving essentially perfect agreement while extracting the rate constant at zero potential for our redox species (ko = 10−6 m/s). Finally, we demonstrate the importance of burn-in to stabilize electrodes from the effects of electromigration and grain reorganization before use in CV measurements, by comparing with results obtained with as-deposited electrodes. Burn-in (or equivalently, annealing) of lithographic microelectrodes before use is of general importance to electrochemical sensing devices

PH-dependence of signaling-state formation in Drosophila cryptochrome

Cryptochromes, FAD-dependent blue light photoreceptors, undergo a series of electron transfer reactions after light excitation. Time-resolved optical spectroscopy was employed to investigate the pH dependence of all light-dependent reactions in the cryptochrome from fruit flies. Signal state formation experiments on a time scale of seconds were found to be strongly pH dependent, and formation of both anionic and neutral FAD radicals could be detected, with reaction rates increasing by a factor of ~2.5 from basic to neutral pH values. Additionally, the influence of the amino acid His378 was investigated in further detail: Two protein variants, DmCry H378A and H378Q, showed significantly reduced rate constants for signal state formation, which again differed at neutral and alkaline pH values. Hence, His378 was identified as an amino acid responsible for the pronounced pH dependence; however, this amino acid can be excluded as a proton donor for the protonation of the anionic FAD radical. Other conserved amino acids appear to alter the overall polarity of the binding pocket and thus to be responsible for the pronounced pH dependence. Furthermore, the influence of pH and other experimental parameters, such as temperature, glycerol or ferricyanide concentrations, on the intermediately formed FAD–tryptophan radical pair was explored, which deprotonates on a microsecond time scale with a clear pH dependence, and subsequently recombines within milliseconds. Surprisingly, the latter reaction showed no pH dependence; potential reasons are discussed. All results are reviewed in terms of the photoreceptor and potential magnetoreceptor functions of Drosophila cryptochrome.

Electrochemical detection characteristics of the composite films of boron‐doped nanocrystalline diamond and amorphous carbon prepared using the coaxial arc plasma deposition method

In this study, we applied coaxial arc plasma deposition in vacuum and without substrate heating to prepare composite films of boron‐doped nanocrystalline diamond and amorphous carbon (B‐doped NCD/a‐C) exhibiting electrochemical characteristics similar to those exhibited by the conductive polycrystalline diamond electrodes. Furthermore, we confirmed that the deposited films can be used to determine the current density owing to various concentrations of potassium ferricyanide (K3[Fe(CN6)]). Moreover, the concentration of K3[Fe(CN6)] and its current density were strongly correlated. Based on these experimental results, the deposited films were highly valuable as electrodes for electrochemical sensors. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Fabrication of Photocurable Hyaluronic Acid Coated Microneedle Sensor for Glucose Monitoring

Introduction Microneedle (MN) has been developed to diagnose and detect the biomarkers which are related to various diseases such as diabetes mellitus (DB) and caner. The biomarkers could be extracted from interstitial fluid (ISF) in the human body by using MN with a minimally-invasive and pain-free manner. In particular, glucose sensing has widely been investigated due to increase of DB patients who suffered inconvenience of frequent monitoring of glucose levels. MN-based sensors targeting ISF glucose monitoring was introduced and showed the possibility to replace the existing blood-based glucose sensing technologies [1-3]. We hypothesized that the coating of a MN surface with swellable material such as hydrogel could increase detection sensitivity and time for stabilization. Thus, we developed a swellable hydrogel coated MN sensor which could extract the glucose from ISF with swelling for a short time. Methacrylated hyaluronic acid (MeHA), photo-crosslinkable hydrogel, was utilized to absorb ISF containing biomarkers for electrochemical reaction with the metallized surface of a MN. Cyclic voltammetry (CV) with a model redox species, ferricyanide, were performed to characterize the MeHA-coated MN sensors for the detection of glucose. Experimental Methods To fabricate the MeHA coated MN sensor, 3×3 SU-8 MN array was transfer molded on the 1 cm × 2 cm of the glass wafer. The female PDMS mold which was patterned MN shapes were filled with SU-8 in a vacuum condition and the mold was gently transferred on the glass wafer. After UV curing, the MN electrode was prepared by the Ti-gold sputtering. MeHA was synthesized by modifying from the hydroxyl groups to the methyl group in basic condition. Dimethylformamide, methacrylic anhydride, and sodium chloride were mixed in the 2% of hyaluronic acid solution while a solution was controlled in basic condition. The precursor was washed three times by ethanol and was freeze-dried to obtain the MeHA sponges. Then, the MeHA sponges were dissolved into the deionized water which was contained 0.05% of the photoinitiator for preparing the MeHA solution. The MeHA solution was poured on the surface of gold-sputtered SU-8 MN arrays and the swellable MN sensor was fabricated after drying. Before measuring the glucose, potassium ferricyanide (K3[Fe(CN)6]) which was the standard redox solution to conduct CV was used as an alternative of the biomarker. The MeHA coated MN electrode was used as a working electrode and a Pt mesh electrode was used as a counter electrode. The MN sensor was immersed into the potassium ferricyanide solution and the CV was conducted while the concentration chose 10 mM, 10 μM, and 1 μM to confirm sensitivity and detection limit of the three-electrode system with MeHA coated MN sensor. Results and Discussion The 3×3 array of SU-8 MNs fabricated on a glass wafer had the height of 640 μm and the aspect ratio of 1.6. The MeHA was successfully synthesized and the MeHA film had a swelling ratio of 450% after 10 sec swelling in the phosphate buffered saline. By using the three-electrode system including the MeHA uniform coated MN electrode, in vitro sensing tests were performed with various concentrations of potassium ferricyanide. As the results of the CV analysis, when the concentration of potassium ferricyanide was 10 mM, the anodic and cathodic peak currents of the measured I-V curve were 135 and 144 μA, respectively. Although the peaks were observed from the CV plots, it was hard to measure the exact value of peak currents when the concentration of potassium ferricyanide, 10 μM, and 1 μM. Nevertheless, the current peaks of 10 μM was slightly higher than the peaks of the 1 μM sample. Since the peak current was increased in proportion to the level of potassium ferricyanide, it was concluded that the MeHA coated MN sensor system could be used to measure the biomarker. These results also support that the biomarkers could be extracted from the ISF by the swelling behavior of the MeHA coated on the surface of MNs. Summary The MeHA coated MN sensor was fabricated with simple molding techniques and various photocurable materials such as SU-8 2010 and MeHA. The ferricyanide could be extracted by using the swelling behavior of the MeHA. As the results of in vitro test, the various concentration of potassium ferricyanide solution was measured with the three-electrode system including MeHA coated MN sensor and the detection limit was observed at least 1 μM. Reference 1. Sharma, Sanjiv, et al. "A pilot study in humans of microneedle sensor arrays for continuous glucose monitoring." (2018).2. Caliò, A., et al. "Polymeric microneedles based enzymatic electrodes for electrochemical biosensing of glucose and lactic acid." Sensors and Actuators B: Chemical 236 (2016): 343-349.3. Ribet, Federico, Göran Stemme, and Niclas Roxhed. "Real-time intradermal continuous glucose monitoring using a minimally invasive microneedle-based system." Biomedical microdevices 20.4 (2018): 101.

Lucina pectinata oxyhemoglobin (II-III) heterodimer pH susceptibility

Lucina pectinata live in high concentrations of hydrogen sulfide (H2S) and contains one hemoglobin, Hemoglobin I (HbI), transporting H2S and two hemoglobins, Hemoglobin II (HbII) and Hemoglobin (HbIII), transferring dioxygen to symbionts. HbII and HbIII contain B10 tyrosine (Tyr) and E7 glutamine (Gln) in the heme pocket generating an efficient hydrogen bonding network with the (HbII-HbIII)-O2 species, leading to very low ligand dissociation rates. The results indicate that the oxy-hemeprotein is susceptible to pH from 4 to 9, at acidic conditions, and as a function of the potassium ferricyanide concentration, 100% of the met-aquo derivative is produced. Without a strong oxidant, pH 5 generates a small concentration of the met-aquo complex. The process is accelerated by the presence of salts, as indicated by the crystallization structures and UV–Vis spectra. The results suggest that acidic pH generates conformational changes associated with B10 and E7 heme pocket amino acids, weakening the (HbII-HbIII)-O2 hydrogen bond network. The observation is supported by X-ray crystallography, since at pH 4 and 5, the heme-Fe tends to oxidize, while at pH 7, the oxy-heterodimer is present. Conformational changes also are observed at higher pH by the presence of a 605 nm transition associated with the iron heme-Tyr interaction. Therefore, pH is one crucial factor regulating the (HbII-HbIII)-O2 complex hydrogen-bonding network. Thus, it can be proposed that the hydrogen bonding adjustments between the heme bound O2 and the Tyr and Gln amino acids contribute to oxygen dissociation from the (HbII-HbIII)-O2 system.

A Compact Low-Power Current-to-Digital Readout Circuit for Amperometric Electrochemical Sensors.

This paper introduces a novel compact low-power amperometric instrumentation design with current-to-digital output for electrochemical sensors. By incorporating the double layer capacitance of an electrochemical sensor's impedance model, our new design can maintain performance while dramatically reducing circuit complexity and size. Electrochemical experiments with potassium ferricyanide, show that the circuit output is in good agreement with results obtained using commercial amperometric instrumentation. A high level of linearity (R2 = 0.991) between the circuit output and the concentration of potassium ferricyanide was also demonstrated. Furthermore, we show that a CMOS implementation of the presented architecture could save 25.3% of area, and 47.6% of power compared to a traditional amperometric instrumentation structure. Thus, this new circuit structure is ideally suited for portable/wireless electrochemical sensing applications.

A multi-technique approach towards the mechanistic investigation of the electrodeposition of Prussian blue over carbon nanotubes film

A detailed and multi-technique study on the kinetics and mechanism of the electrodeposition of Prussian blue (PB) over iron filled-carbon nanotubes (CNTs) thin films is presented here. PB is electrochemically synthesized through a heterogeneous reaction between iron species encapsulated into CNTs and ferricyanide ion in aqueous solution. The reaction was followed by a combination of in-situ or ex-situ measurements through UV–Vis spectroscopy, cyclic voltammetry, Raman spectroscopy and scanning electron microscopy. The analysis of the evolution of a new parameter that we called coverage ratio as well as an innovative way to associate the data extracted from cyclic voltammetry with the electrochemical reaction, are introduced by the first time. Similar response vs. time profiles are obtained from absorbance, charge, current, band intensity in Raman spectra, particle size, and coverage ratio, yet providing different aspects of the growth mechanism. Electrochemical data demonstrates an initial mixed control process related to the iron releases from the CNTs cavities and nucleation, followed by a diffusion limited regime on the growth of PB. Spectroscopic data indicates pseudo-first order kinetics, dependent on ferricyanide concentration, and the rate limited by the iron releases from the CNTs. Both particle size of PB and coverage ratio show a progressive nucleation of PB corroborating the proposed mechanism. Raman data also confirm the PB growth rate over the CNTs walls and evidence of PB/CNT interactions during voltammetric cycles. This multi-technique approach gives insights on different aspects of PB electrodeposition and can be extended to a wide class of different materials.

Silver dissolution in a novel leaching system: Reaction kinetics study

Effective silver recovery is usually restricted by either environmental pollution or high recovery costs. To tackle the issues, this study introduces a novel method for the effective recovery of silver by utilizing the alkaline sodium thiosulfate-potassium ferricyanide leaching system. The reaction kinetics of silver dissolution in this system was investigated via the rotating disk electrode technology. The influences of important parameters, including the rotation speed, sodium thiosulfate concentration, potassium ferricyanide concentration, and temperature, on the silver dissolution rate were systematically investigated. The activation energy was measured to be 17.96 kJ·mol-1 when the silver dissolution was controlled by a diffusion process. When the silver dissolution was in the region of mixed control, the reaction orders of ferricyanide and thiosulfate were found to be 0.57 and 0.19, respectively, and the reaction orders of ferricyanide and thiosulfate were 0.55 and 0.22, respectively, when the silver dissolution was controlled by surface reaction. This study has great potential for the development of an environmentally friendly silver recovery process from end--of-life products.

Equilibrium and kinetic studies of ferricyanide adsorption from aqueous solution by activated red mud

In this study, activated red mud (ARM) was used as a new adsorbent for the removal of ferricyanide anions from aqueous solution. Based on the percentage of ferricyanide removal and ferricyanide adsorption capacity, optimum conditions were evaluated using the response surface method (RSM) and central composite design (CCD). In optimum conditions (pH = 5.6, adsorbent dosage of 2.59 g, ferricyanide concentration of 60 ppm and contact time of 60 min), the percentage of ferricyanide removal and ferricyanide adsorption capacity were obtained as 79.6% and 1.8 mg/g, respectively. The kinetics and equilibrium studies were evaluated by considering the effective parameters including pH and ferricyanide concentration. Kinetic studies were evaluated by kinetic models of pseudo first-order, pseudo-second-order (four different linearized forms), Elovich and intraparticle diffusion. The results of the kinetic study indicated that the mechanism of ferricyanide adsorption onto the ARM adsorbent is a chemisorption interaction by a fast ferricyanide adsorption onto ARM and subsequently the slow diffusion of ferricyanide ions into the ARM inner adsorption sites. The equilibrium studies showed that the adsorption process followed the Langmuir model in which ferricyanide adsorption onto ARM was homogeneous with monolayer adsorption. The results indicated that the activation process of red mud improved adsorbent efficiency and increased the adsorption capacity.

Heterotrophic nitrogen removal in Bacillus sp. K5: involvement of a novel hydroxylamine oxidase.

An aerobic denitrifying bacterium isolated from a bio-trickling filter treating NOx, Bacillus sp. K5, is able to convert ammonium to nitrite, in which hydroxylamine oxidase (HAO) plays a critical role. In the present study, the performance for simultaneous nitrification and denitrification was investigated with batch experiments and an HAO was purified by an anion-exchange and gel-filtration chromatography from strain K5. The purified HAO's molecular mass was determined by SDS-PAGE and its activity by measuring the change in the concentration of ferricyanide, the electron acceptor. Results showed that as much as 87.8 mg L-1 ammonium-N was removed without nitrite accumulation within 24 hours in the sodium citrate medium at C/N of 15. The HAO isolated from the strain K5 was approximately 71 KDa. With hydroxylamine (NH2OH) as a substrate and potassium ferricyanide as an electron acceptor, the enzyme was capable of oxidizing NH2OH to nitrite in vitro when the pH varied from 7 to 9 and temperature ranged from 25 °C to 40 °C. This is the first time that an HAO has been purified from the Bacillus genus, and the findings revealed that it is distinctive in its molecular mass and enzyme properties.

Toxicity detection in water containing heavy metal ions with a self-powered microbial fuel cell-based biosensor

In this work, a self-powered microbial fuel cell (MFC)-based biosensor was developed for detecting toxicity in water containing heavy metal ions. Experimental conditions containing concentration of potassium ferricyanide, load resistor and glucose concentration were optimized. Six heavy metal ions (2mg/L, Cu2+, Hg2+, Zn2+, Cd2+, Pb2+ and Cr3+) were tested by this biosensor and the inhibition ratios obtained were 12.56%, 13.99%, 8.81%, 9.29%, 5.59% and 1.95%, respectively. The inhibition ratios of 28.13% was also obtained for detecting the laboratory wastewater containing several heavy metal ions. The experimental results exhibited the feasibility and potential of the self-powered biosensor in detecting toxicities in water containing heavy metal ions.

Growth Mechanism of Dendritic Hematite via Hydrolysis of Ferricyanide

The detailed process of the hydrolysis of ferricyanide into dendritic α-Fe2O3 (hematite) crystals with snowflake-like, feather-like, and leaf-like morphologies has been investigated. [Fe(CN)6]3– anions were found to polymerize into large, disordered soft matter aggregates at an early stage. The nucleation of hematite crystals took place near the surface of these aggregates via further hydrolysis. After the crystals grew to a certain size, branches started to appear. When the concentration of ferricyanide was low (i.e. 2 mM to 3.8 mM), growth was preferentially along the six equivalent ⟨1120⟩ directions, resulting in a flat snowflake-like shape, while high concentrations (i.e. 9 mM to 500 mM) of ferricyanide led to the growth of selective directions along the ⟨1011⟩ zone axes, forming a feather-like or leaf-like morphology. Highly selective adsorption and surface hydrolysis of [Fe(CN)6]3– anions on α-Fe2O3 crystals was found to be a crucial process in the formation of these novel morphologies. It was fou...