Metal Ions In Aqueous Solution Research Articles

Cyclic Voltammetric studies of calcium acetate salt with Methylene blue (MB) Using Gold Electrode

Cyclic Voltammetric studies of calcium acetate salt [Ca(CH3COO)2] in absence or presence of Methylene blue (MB) were performed to predict and analyze the behavior of complexation between the ligand and metal ion in aqueous solution. From these studies, the values of solvation and kinetic parameters [Ep (peak potential), Ip(peak current), ΔEp (peak potential difference), E½ (half wave potential), D(Diffusion coefficient), Ks (electron transfer rate constant), Г(surface coverage) and Qa (quantity of electricity)] were evaluated. In addition, the effect of different concentration and a scan rate of above the calculated quantities were studied. In case of presence MB, the stability constants and Gibbs free energies were performed.

Manifestations of Weak O-H···F Hydrogen Bonding in M(H2O) n(B12F12) Salt Hydrates: Unusually Sharp Fourier Transform Infrared ν(OH) Bands and Latent Porosity (M = Mg-Ba, Co, Ni, Zn).

Eight M(H2O) n(Z) salt hydrates were characterized by single-crystal X-ray diffraction (Z2- = B12F122-): M = Ca, Sr, n = 7; M = Mg, Co, Ni, Zn, n = 6; M = Ba, n = 4, 5. Weak O-H···F hydrogen bonding between the M(H2O) n2+ cations and Z2- resulted in room-temperature Fourier transform infrared (FTIR) spectra having sharp ν(OH) bands, with full widths at half max of 10-30 cm-1, which are much more narrow than ν(OH) bands in room temperature FTIR spectra of most salt hydrates. Clearly resolved νasym(OH/OD) and νsym(OH/OD) bands with Δν(OH) as small as 17 cm-1 and Δν(OD) as small as 11 cm-1 were observed (Δν(OX) = νasym(OX) - νsym(OX)). The isomorphic hexahydrates ( R3̅) have two fac-(H2O)3 sets of H2O ligands and nearly octahedral coordination spheres. They exhibited four resolvable ν(OH) bands, one νasym(OH)/νsym(OH) pair for H2O ligands with longer O(H)···F distances and one νasym(OH)/νsym(OH) pair for H2O ligands with shorter O(H)···F distances. The ν(OH) bands for the three H2O molecules with shorter, slightly stronger O(H)···F hydrogen bonds were broader, more intense, and red-shifted by ca. 25 cm-1 relative to the bands for the three other H2O molecules, the first time that such small differences in relatively weak O(H)···F hydrogen bonds in the same crystalline hexahydrate have resulted in observable IR spectroscopic differences at room temperature. For the first time room temperature ν(OH) values for salt hexahydrates showed the monotonic progression Mg2+ > Co2+ > Ni2+ > Zn2+, essentially the same progression as the p Ka values for these metal ions in aqueous solution. A further manifestation of the weak O-H···F hydrogen bonding in these hydrates is the latent porosity exhibited by Ba(H2O)5,8(Z), Sr(H2O) n,m(Z), and Ca(H2O)4,6(Z). Finally, the H2O/D2O exchange reaction Co(D2O)6(Z) → Co(H2O)6(Z) was ca. 50% complete in 1 h at 50 °C in N2/17 Torr H2O( g).

Preparation of air-stable magnetic g-C3N4@Fe0-graphene composite by new reduction method for simultaneous and synergistic conversion of organic dyes and heavy metal ions in aqueous solution

Although composites that consist of graphite phase carbon nitride (g-C3N4)/nanoscale zero valent iron had already been proved to be effective for conversion of organic pollutants and heavy metal ions from wastewater, however, nano Fe0 is prone to be oxidized in air. In order to prevent the oxidation and increase the stability of the aforementioned composite, this research provides a facile and economical g-C3N4@Fe0-rGO synthesis method with high photocatalytic activity for removal of RhB and Cr(VI) simultaneously under visible light. Characterization results show that dispersibility and stability of nano Fe0 were significantly increased in g-C3N4@Fe0-rGO. Moreover, g-C3N4@Fe0-rGO exhibits synergetic effects among each component of the composite, resulting in facilitating the photogenerated charges separation, enhancing the surface activity of nano Fe0, possessing the magnetic property for facile recycling. In addition, due to the formation of iron-carbon microbatteries between graphene and nano Fe0, g-C3N4@Fe0-rGO demonstrates superior activity in removal of RhB and Cr(VI). And g-C3N4@Fe0-rGO retained excellent stability without apparent loss in catalytic activity after 5 cycles. The photocatalytic tests and quenching tests reveal that nano Fe0 and ⋅OH are main factor for RhB and Cr(VI) removal. Insights into the mechanism of the enhanced reduction of Cr(VI) and photodegradation of RhB at the same time were proposed. This study is expected to provide a novel synthesis method for the design of efficient, visible light driven, and recyclable photocatalysts for environmental remediation of both organic dyes and heavy metal ions.

An Advanced Hand-Held Microfiber-Based Sensor for Ultrasensitive Lead Ion Detection.

This study demonstrated a l-glutathione-modified nonadiabatic microfiber sensor to detect a trace level of heavy metal ions in aqueous solution. The sensor showed an exclusively selective response to Pb2+ among other metal ions and a measured detection limit of 5 μg/L, lower than the maximum allowable limit of Pb2+ in drinking water by the World Health Organization. Moreover, a novel compact all-fiber-based interrogation scheme was proposed to promote the development of a portable hand-held system for on-site measurement. The presented scheme does not require costly and bulky laboratory equipment but operates based on the reflected optical power of two fiber Bragg gratings (FBG), measured using photodetectors independently.

Anthracene Based AIE Active Probe for Colorimetric and Fluorimetric Detection of Cu2+ Ions

Abstract A novel aggregation induced emission (AIE) active anthracene based dihydroquinazolinone derivative (probe 1) has been synthesized and characterized by means of spectroscopic methods. The photophysical properties of this probe have been investigated in solvents of different polarity display that fluorescence states are of intramolecular charge transfer (ICT) character. Probe 1 show clear AIE behavior in water/THF mixture on reaching water fraction 95%. The AIE behavior of probe 1 have been exploited for the detection of metal ions in aqueous solution which reveals high selectivity and sensitivity towards Cu2+ ions by colorimetrically and function as a chemosensor in a remarkable turn-off fluorescence manner. Further, the experimental results were investigated by computational means by optimizing the ground state geometries of probe 1 and probe 1-Cu complex using density functional theory (DFT) at B3LYP/6-31G∗∗ and B3LYP/6-31G∗∗(LANL2DZ) levels of theory. Intra-molecular charge transfer was observed in probe 1 while ligand to metal charge transfer (LMCT) for probe 1-Cu complex.

“Green” synthesis of nanoparticles of precious metals: antimicrobial and catalytic properties

The paper presents the use of agricultural products, namely grape skins, in the “green” synthesis of monometallic (Au, Ag) and bimetallic (Au-Ag) nanoparticles (NPs) from aqueous solutions of metal ions of the corresponding precursors. At present, there exist urgent problems of utilization of waste from the agro-industrial complex, rational use of nature and transition to the use of environment-friendly and energy-efficient technologies. Therefore, there is a tendency to use “green” technologies in obtaining nanomaterials that are considered environment-friendly and resource-saving. The study has proved the efficiency of using food waste (grape skins) as a reducing and stabilizing agent in forming nanoparticles of precious metals of mono- and bimetallic structures. Biological raw materials were extracted in an aqueous medium under a short-term effect of low-temperature plasma discharges. On the basis of the complex analysis of the extract composition, it was proved that the hydroxyl, carbonyl and carboxyl functional groups of the organic compounds of the grape skin extract are responsible for the recovery of the metal ions and stabilization of the resulting NPs. The research has proved that mono- and bimetallic NPs are formed with the following peaks: for Ag 0 (λ max =440 nm), Au 0 (λ max =540 nm), and Ag-Au (λ max =510 nm). The size and stability of the nanoparticles obtained by the “green” synthesis were assessed in comparison with the same parameters for the plasmochemical method of nanoparticles’ formation. The study has revealed antibacterial, catalytic and anti-corrosion properties of the synthesized nanoparticles. The resulting monometallic (Au, Ag) and bimetallic (Au–Ag) nanoparticles show excellent catalytic activity while recovering p-nitrophenol (4-NPh) to p-aminophenol (4-APh) in the presence of NaBH 4 . The synthesized NPs demonstrate their antibacterial activity against gram-positive and gram-negative bacteria. The findings allow to expand the practical application of metal nanoparticles in various industries and enhance the processing and reuse of non-liquid waste

Biosorption of iron by heavy-metal tolerant Micrococcus sp.

The presence of metal ions in aqueous solutions represents, nowadays a major environmental problem. The present study investigates the potential adsorption capacity of Micrococcus sp. for the removal of iron (III) ions from aqueous solution. The adsorbent was characterized using FTIR analysis, in order to reveal the presence of functional groups. Batch adsorption experiments were carried out to evaluate the effect of process parameters such as pH, contact time, initial iron concentration, temperature and adsorbent dosage on removal capacity. The optimum removal of iron (III) ions was obtained at pH 6 with 94.2%, adsorbent dose of 0.5g with 92.5% and equilibrium time of 30 min with 88.6%. Kinetic data were successfully described with pseudo-first order, pseudo-second order and elovich models. The results show that the biosorption process of Fe (III) followed pseudo second order with R2= 0.999. The equilibrium data was further tested using Langmuir, Freundlich and Temkin models, and was found to follow the Langmuir isotherm (R2= 0.978).Thermodynamic parameters such as ∆Go, ∆Ho and ∆So were evaluated and it has been found that the biosorption process was feasible, spontaneous and exothermic in nature.Keywords: Bacteria, Biosorption, Iron, Isotherm, Kinetic

Formation of multilayer through layer-by-layer assembly of starch-based polyanion with divalent metal ion

The layer-by-layer (LbL) assembly between metal ion and starch-based anion driven by electrostatic interaction was investigated. Multilayer films were obtained from starch-based derivative containing carboxyl groups (SC) with copper or lead ions. It was found that the concentration of metal ion in aqueous solution decreased with increasing the layers. X-ray photoelectron spectroscopy exhibited the content of Cu(II) was higher when the surface was copper-ion-layer than that composed of SC. The surface of the film was smooth and no obvious fault plane was observed on its cross-section, which also indicated that the LbL assembly between starch-based polyanion and metal ion was carried out. Sodium alginate was adopted as another polyanion to conduct the LbL assembly. Part of metal ion was replaced with rhodamine B to fabricate composite multilayer. During such an assembly, the concentration of copper ion in aqueous solution decreased with increasing the layers as well. These phenomena suggested that the LbL assembly between polysaccharide-based polyanion and metal ion was feasible.

Removal of lead by exopolysaccharides from Paenibacillus peoriae strainTS7 isolated from rhizosphere of durum wheat

Abstract This work aimed to study the removal of heavy metal ions in aqueous solution by extracellular polysaccharides (EPS) extracted from bacterial strain coded TS7. The 16S ribosomal RNA gene sequencing allowed us to identify this strain as Paenibacillus peoriae . The EPS were defined by GLC-MS and 1 H NMR as a homopolysaccharides of fructose. The effect of contact time, initial metal ions concentration, mass of the polysaccharide and pH on the metal uptake were investigated by employing batch adsorption technique. The results showed that the maximum removal percentage was achieved at 180 min with an initial lead concentration of 100 ppm and the mass of 0.5 g L −1 EPS at pH 6.8. The maximal metal uptake ( q max ) value in Dubinin–Radushkevich (D–R) adsorption isotherm of EPS was found 277.54 mg g −1 . The adsorption surface of the metal at surface of TS7 EPS was confirmed through scanning electron microscopy. Besides, FT-IR analysis indicated that some functional groups of TS7 EPS may play an important role in lead biosorption.

The role of solvent charge donation in the stabilization of metal ions in aqueous solution

Abstract

Electroinduced drift of solvated ions in salt solution of Ce and Ni

This paper shows the selective drift of cationic aqua complexes of chloride salts of metal ions in aqueous solutions under the exposure an asymmetric electric field (100 Hz, 750/150 V). The spatial distribution of $$\hbox {Ce}^{3+}$$ and $$\hbox {Ni}^{2+}$$ cations was demonstrated, and the maximum cation separation coefficients in the longitudinal section of the inter-electrode space were calculated for the stationary and circulating solution for different exposure durations of the electric field and solution circulation rates. A decrease in the relative concentration of cations was observed when moving from top down of the experimental cell, while the direction of cation drift along the sectional plane was independent of the distance from electrodes, the solution circulation rate, and nature of metal. It was established that while the solution moved from the grounded electrode to the potential electrode along the bottom and top parts of the sections, there was a decrease of concentrations of both cations in the central part of the cell and an increase near the electrodes. On the basis of the obtained data, the optimal points of sampling and drop were determined. The calculated maximum separation coefficients of $$\hbox {Ce}^{3+}$$ and $$\hbox {Ni}^{2+}$$ ions were $$1.200\pm 0.108$$ and $$1.036\pm 0.025$$ , for the stationary and circulating solution at a rate of $$7 \hbox { L}\cdot \hbox {h}^{-1}$$ , respectively. SYNOPSIS Drift of $$\hbox {Ce}^{3+}$$ and $$\hbox {Ni}^{2+}$$ ions in aqueous solution may be subjected to asymmetric electric field. As a result, the spatial distribution and, consequently, separation coefficients of the cations are determined by the distance from the electrodes, solution circulation rate, metal nature, duration of the electric field exposure, and rates of the solution circulation.

Nanocomposites CoPt-x/Diatomite-C as oxygen reversible electrocatalysts for zinc-air batteries: Diatomite boosted the catalytic activity and durability

The exploration of oxygen reversible electrocatalysts to boost oxygen reduction reaction and oxygen evolution reaction is critical for the development of high-performance aqueous Zn-air batteries. Since diatomite with porous structure can adsorb metal ions in aqueous solution, herein, we prepare the nanocomposite CoPt-x/Diatomite-C for both oxygen reduction and evolution reactions, and diatomite is found significantly promotes the electrocatalytic activity and durability. With the presence of diatomite, CoPt-1/Diatomite-C shows a lower Tafel slope (63 mV dec−1 at high potential range), larger diffusion-limited current density (4.94 mA cm−2) and superior durability for ORR. Particularly, the specific and mass activities of CoPt-1/Diatomite-C for ORR are 0.74 mA cm−2 and 286 mA mg−1, respectively, which are 2.5 and 3.0 times higher than that of CoPt-1/C without diatomite; For OER, the overpotential of CoPt-9/Diatomite-C decreases nearly 30 mV at 10 mA cm−2, while the Tafel slope also reduces 16 mV dec−1 versus CoPt-9/C catalyst. Moreover, a rechargeable Zn-air battery with these composites as air-cathode is self-assembled, and diatomite boosts the battery performance with desirable properties. CoPt-9/Diatomite-C displays the optimal performance, with a power density of 140 mW cm−2, a specific capacity of 616 mA h g−1 at 10 mA cm−2 and an exceedingly robust cycling life. This work provides a viable and cost-effective strategy for fabricating oxygen reversible electrocatalysts for metal-air battery applications.

INDIUM EXTRACTION FROM SOLUTIONS WITH MODIFIED ALUMINOSILICATES

The aim of this work was to study the adsorption of indium from aqueous solutions on modified highly dispersed aluminosilicates for the recovery of indium from technological solutions. The adsorption isotherms of indium, iron and zinc from multi component solutions on modified by di(2-ethylhexyl) phosphoric acid montmorillonite were obtained. It was shown that adsorption processes can be reliably described by models of Langmuir and Freundlich (R2 = 0.96–0.99). The shape of the isotherms is determined both by the surface properties of the sorbent and forms of presence of metal ions in aqueous solutions. The highest value of Langmuir constant Kads = 422.65 for reagent "Metоsol" was obtained for ions of indium, which indicates the preferential affinity of the sorbing mineral to this element, since the corresponding figures for the ions Fe2+ (1.09) and Zn2+ (0.78) are close to unity. At sorption of metal ions from model solution in the range of acidity of 1-20 g/dm3 of H2SO4 the extraction of indium remains unchanged at ~70 %, and iron – is reduced from 39 to 15% of the initial content. With the further increase of acidity to 100 g/dm3 of H2SO4, the recovery of indium is reduced to 40 %; iron down to 14 %. In the examined range of concentration of sulfuric acid the extraction of zinc is from 6.0 to 7.5 percent. The value of the static exchange capacity for the studied metals are mmol/g: 0.39–0.23 of indium; 0.11–0.04 of iron(III); 0.05–0.04 of zinc. A rank of affinity of reagent "Metоsol" to extract the metal ions from solution with pre-reduced iron(III) was In3+ > Fe2+ > Zn2+ which determines the feasibility of its use for the selective adsorption of indium from the complex composition of technological solutions of zinc production.

Colorimetric determination of Hg(II) sensor based on magnetic nanocomposite (Fe3O4@ZIF-67) acting as peroxidase mimics

An extremely sensitive colorimetric sensor has been developed for selective determination of Hg2+ in aqueous solution based on magnetic nanocomposite (Fe3O4@ZIF-67), which results in an effective intrinsic peroxidase mimicking activities and makes the composites oxidize the 3, 3′, 5, 5′- tetramethyl benzidine (TMB) in the presence of hydrogen peroxide (H2O2) to produce a blue coloured solution. Significantly, the oxidation of TMB was retarded or prevented in the presence of antiradical biomolecules Glutathione (GSH) because of its strong cation restoration property. When Hg2+ is added, the strong affinity of mercury ions with thiol groups of GSH provokes the oxidation of the substrates, which helps the solution turn into blue colour. The absorbance intensity was proportional to the concentration of Hg2+ in the wide range of 0–30 nM and detection limit was successfully as low as 0.36 nM. The resultant nanocomposite based peroxidase mimicking activity applied as a versatile platform in the colorimetric detection of Hg2+ was established the other co-existing metal ions in aqueous solutions. Finally the sensor was applied to detect Hg2+ in real water sample with satisfactory recovery results. Interestingly, the proposed colorimetric sensing platform held great potential in the application of mercury contamination in industrial sewage.

Combined Approach To Remove and Fast Detect Heavy Metals in Water Based on PES–TiO2 Electrospun Mats and Porphyrin Chemosensors

Hybrid poly(ether sulfones) (PES)–TiO2 electrospun mats are used as selective filters to remove lead and zinc ions from water. Presence of TiO2 is functional to trigger fiber’s surface charge that allows for better performances in terms of ionic adsorption with respect to bare PES mats. Temperature increase promotes a speed up of ion removal. Ability of electrospun mats to retain adsorbed ions is proven by washing procedures, which confirm the lack of released Pb2+ in solution, even after sonication. To detect presence of metal ions in aqueous solutions, water-soluble porphyrins are used as chemosensors, which are able to provide fast, in-field, and real-time analysis. In particular, cationic H2T4 metalation, occurring both in solution or at transparent glass surface, allows for a straightforward spectrophotometric (UV–vis) detection of metal ions in solution.

Removal of Pb<sup>2+</sup>, Cu<sup>2+</sup>, Ni<sup>2+</sup>, Cd<sup>2+</sup> from Wastewater using Fly Ash Based Geopolymer as an Adsorbent

This work aims to evaluate the effectiveness of fly ash based geopolymer powder as an adsorbent for heavy metals in aqueous solution. The structure of synthesized geopolymer was found to be highly amorphous due to the dissolution of fly ash phase. Moreover, the fly ash geopolymer powder has higher surface area compares to original fly ash with specific surface area of 85.01 m²/g and 0.83 m2/g, respectively. For this reason, the geopolymer powder has much higher removal efficiency compared to the original fly ash powder. The removal efficiency was affected by contact time, geopolymer amount, heavy metal initial concentration, pH, and temperature. The four heavy metals were chosen (Pb2+, Cu2+, Ni2+, Cd2+) for adsorption test. The highest heavy metal removal capacity was obtained at pH 5. The geopolymer powder adsorbed metal cations in the order of Pb2+>Cu2+>Cd2+>Ni2+. In addition, Langmuir model is more suitable for fly ash geopolymer powder adsorption of heavy metal ions in aqueous solution than Freundlich model. The results showed that the fly ash geopolymer powder has high efficiency for removal metal which could be employed excellent alternative for wastewater treatment.

Formaldehyde Controlling the Synthesis of Multishelled SiO2/FexOy Hollow Porous Spheres

A concise and facile sol-gel method to prepare multiple magnetic SiO2/Fe xO y hollow porous spheres was developed. A series of SiO2/Fe xO y hollow porous spheres consisting of single shell, yolk-shell, double shells, and triple shells could be obtained by simply adjusting the formaldehyde amount, as Fe(acac)3 was used as the shell-forming promoter. As the formaldehyde amount increases, the morphology of the as-prepared hollow spheres changed from single-shelled, yolk-shelled, double-shelled, to triple-shelled and then turned back. The spheres possess a large specific surface area (∼966 m2/g), uniform mesopores (∼4.5 nm), and large pore volume (1.37 cm3/g). Moreover, the yolk-shelled spheres have been successfully used in in situ adsorbing and reducing heavy metal ions in aqueous solution; the results suggested that it was an efficient adsorbent and convenient to concentrate from water.

Multifunctional Ln-MOF Luminescent Probe for Efficient Sensing of Fe3+, Ce3+, and Acetone.

A new series of five three-dimensional Ln(III) metal-organic frameworks (MOFs) formulated as [Ln4(μ6-L)2(μ-HCOO)(μ3-OH)3(μ3-O)(DMF)2(H2O)4] n {Ln3+ = Tb3+ (1), Eu3+ (2), Gd3+ (3), Dy3+ (4), and Er3+ (5)} was successfully obtained via a solvothermal reaction between the corresponding lanthanide(III) nitrates and 2-(6-carboxypyridin-3-yl)terephthalic acid (H3L). All of the obtained compounds were fully characterized, and their structures were established by single-crystal X-ray diffraction. All products are isostructural and possess porous 3D networks of the fluorite topological type, which are driven by the cubane-like [Ln4(μ3-OH)3(μ3-O)(μ-HCOO)]6+ blocks and μ6-L3- spacers. Luminescent and sensing properties of 1-5 were investigated in detail, revealing a unique capability of Tb-MOF (1) for sensing acetone and metal(III) cations (Fe3+ or Ce3+) with high efficiency and selectivity. Apart from a facile recyclability after sensing experiments, the obtained Tb-MOF material features a remarkable stability in a diversity of environments such as common solvents, aqueous solutions of metal ions, and solutions with a broad pH range from 4 to 11. In addition, compound 1 represents a very rare example of the versatile Ln-MOF probe capable of sensing Ce3+ or Fe3+ cations or acetone molecules.

A previously undescribed hexapeptide His-Arg-Phe-Leu-Arg-His-NH2 from amphibian skin secretion shows CO2 and metal biding affinities

A previously undescribed six residues long peptide His-Arg-Phe-Leu-Arg-His was identified and purified from the skin secretion of the amphibian Phyllomedusa centralis. A synthetic analogue carboxyamidated HRFLRH-NH2 showed structural changes induced by CO2 and metal ions in aqueous solution when analyzed by NMR. The present work reports NMR structures for the carboxyamidated hexapeptide in the presence CO2, Zn2+ and Cd2+, suggesting possible affinity regions on the polypeptide chain for each ligand. The NMR structures were optimized by DFT to identify probable biding sites of these species in the polypeptide structure. To our best knowledge, this is the first time that a putative CO2 binding site is described on a peptide structure obtained in aqueous conditions, at room temperature.

Novel Carbon Paper@Magnesium Silicate Composite Porous Films: Design, Fabrication, and Adsorption Behavior for Heavy Metal Ions in Aqueous Solution.

It is of great and increasing interest to explore porous adsorption films to reduce heavy metal ions in aqueous solution. Here, we for the first time fabricated carbon paper@magnesium silicate (CP@MS) composite films for the high-efficiency removal of Zn2+ and Cu2+ by a solid-phase transformation from hydromagnesite-coated CP (CP@MCH) precursor film in a hydrothermal route and detailedly examined adsorption process for Zn2+ and Cu2+ as well as the adsorption mechanism. The suitable initial pH range is beyond 4.0 for the adsorption of the CP@MS to remove Zn2+ under the investigated conditions, and the adsorption capacity is mainly up to the pore size of the porous film. The composite film exhibits excellent adsorption capacity for both of Zn2+ and Cu2+ with the corresponding maximum adsorption quantity of 198.0 mg g-1 for Zn2+ and 113.5 mg g-1 for Cu2+, which are advantageous over most of those reported in the literature. Furthermore, the adsorption behavior of the CP@MS film follows the pseudo-second-order kinetic model and the Langmuir adsorption equation for Zn2+ with the cation-exchange mechanism. Particularly, the CP@MS film shows promising practical applications for the removal of heavy metal ions in water by an adsorption-filtration system.