Adsorption Of Nitrate Ions Research Articles

Preparation and utilization of wheat straw anionic sorbent for the removal of nitrate from aqueous solution

In order to reduce the impact of eutrophication caused by agricultural residues (i.e., excess nitrate) in aqueous solution, economic and effective anionic sorbents are required. In this article, we prepared anionic sorbent using wheat straw. Its structural characteristics and adsorption properties for nitrate removal from aqueous solution were investigated. The results indicate that the yield of the prepared anionic sorbent, the total exchange capacity, and the maximum adsorption capacity were 350%, 2.57 mEq/g, and 2.08 mmol/g, respectively. The Freundlich isotherm mode is more suitable than the Langmuir mode and the adsorption process accords with the first order reaction kinetic rate equation. When multiple anions (SO 4 2−, H 2PO 4−, NO 3−, and NO 2−) were present, the isotherm mode of prepared anionic sorbent for nitrate was consistent with Freundlich mode; however, the capacity of nitrate adsorption was reduced by 50%. In alkaline solutions, about 90% of adsorbed nitrate ions could be desorbed from prepared anionic sorbent. The results of this study confirmed that the wheat straw anionic sorbent can be used as an excellent nitrate sorbent that removes nitrate from aqueous solutions.

The effect of acid treatment of carbon cloth on the adsorption of nitrite and nitrate ions

The effects of functional groups on the adsorption efficiency of nitrate and nitrite from water by carbon cloth were investigated. The carbon cloth was treated by sulfuric acid and used for the adsorption of nitrate and nitrite from water samples at nearly neutral solutions. The concentrations of ions in the solution were monitored using in situ UV spectroscopy. Acid treatment caused a significant increase in the adsorption rate of ions and the adsorption capacity of the adsorbent.

Adsorption of Nitrate Ions onto Sepiolite and Surfactant-Modified Sepiolite

The adsorption of nitrate ions onto clay minerals has not been given much attention, possibly because clay surfaces are negatively charged. In order to increase the positive charge on the surface, sepiolite was modified in the present studies by treatment with dodecylethyldimethylammonium (DEDMA) bromide. After such modification, it was found that the maximum amount of nitrate ion adsorbed occurred at a pH value of 2.0. The chemical composition of natural sepiolite was determined by EDX methods and surface characterization of both natural and modified sepiolite samples was undertaken using FT-IR spectroscopic techniques. The adsorption of nitrate ions onto these adsorbents was determined by ion chromatography. The kinetic parameters of the adsorption process were calculated and it was shown that the reaction kinetic data could be fitted using the pseudo-second-order rate model. The calculated results indicate that both natural and surfactant-modified sepiolite are effective sorbents for the removal of anionic contaminants; however, the surfactant-modified sepiolite (453 mmol/kg) was more effective than the unmodified sepiolite (408 mmol/kg) in this respect. The adsorption data obtained were well described by the Freundlich adsorption isotherm.

Adsorption of ammonium and nitrate ions by poly(N‐isopropylacrylamide) gel and poly(N‐isopropylacrylamide‐co‐chlorophyllin) gel in different states

AbstractThe adsorption of ammonium and nitrate by temperature‐stimulus‐responsive poly(N‐isopropylacrylamide) (NIPA) gel and poly(N‐isopropylacrylamide‐co‐chlorophyllin) (NIPA‐CH) gel in different states was investigated. Both the NIPA gel and NIPA‐CH gel could adsorb ammonium and nitrate in a swollen state (swollen gel) and a swelling state (swelling gel), and they adsorbed ammonium more than nitrate. When the gels were shrinking (shrinking gel), they could adsorb a little ammonium from solution, but when the gels were in a shrunken state (shrunken gel), they hardly adsorbed ammonium. The adsorption of both ammonium and nitrate increased for the swelling NIPA gel in comparison with the swollen gel. The NIPA‐CH gel was the opposite in this respect. The difference in the amounts of adsorption of ammonium and nitrate by the swollen and swelling NIPA‐CH gels was more significant than that of the NIPA gels. It was suggested that ions such as ammonium and nitrate could not diffuse into the gels freely. The adsorption of ammonium and nitrate was affected not only by the phase transitions of the gels but also by the electrical charges. The experimental results for the adsorption of ammonium and nitrate during the volume changes of the gels imply that if the gels are applied to the immobilization of microorganisms, they may improve mass transfer between the immobilization matrix and bulk liquid under cyclic temperature changes and promote reactions of the immobilized microorganisms, especially the nitrification of nitrifying bacteria immobilized by the NIPA‐CH gel. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2367–2372, 2005

Characterization of adsorption gels prepared from plant biomaterials

The adsorption of Pb(II), Cu(II), Cd(II), and Zn(II) by new biomaterial gels synthesized in cross-linked reactions from agricultural wastes such as lemon, yuzu (Citrus junos), and coffee was investigated. Experimental data of adsorption equilibrium from the heavy metal solutions correlate well with Freundlich isotherm equations. The adsorption mechanism involved acid ion-exchange reactions between the heavy metal and the carboxylic acid of pectic acid in the lemon and yuzu gels, improving the amounts of Pb(II), Cu(II), Cd(II), and Zn(II) adsorbed onto the lemon and yuzu gels by approximately 5- and 6-fold, respectively. The maximum adsorption capacities of the yuzu and lemon gels for Pb(II) and Cu(II) were high. Among the biomaterial gels investigated, the lemon gel possessed the highest complexation ability with these heavy metals. In addition, the adsorption of nitrate ion (NO3−) was especially strong by the Pb(II)-adsorbed lemon gel, as shown by IR absorption spectrophotometry. These results indicate that lemon and yuzu gels can function, as new “green chemistry” adsorbents, which can be generated from recycled wastes, involve zero emissions, and provide effective recovery of precious resources.

Development of a novel electrochemical cell for slab optical waveguide spectroscopy for in situ observation of methylene blue and anions on an electrode/electrolyte interface

A new spectroelectrochemical cell for slab optical waveguide (SOWG) spectroscopy was developed in order to observe in situ an electrode/electrolyte interface for bulk electrolysis. The new SOWG spectroelectrochemical cell has been evaluated by simultaneous electrochemical-absorption experiments of methylene blue (MB) using cyclic voltammetry (CV) and SOWG spectrometry. CV was performed in the SOWG spectroelectrochemical cell using indium tin oxide (ITO) coated glass as the working electrode, platinum wire as the counter electrode and a silver/silver chloride electrode (Ag/AgCl) as the reference electrode. Based on the CV and SOWG spectrometric data, it was found that the SOWG spectra showed the MB spectra on the electrode surface selectively and that SOWG with the cell would be useful as a tool for in situ study of an electrode/electrolyte interface. Using this cell, the effects of the supporting electrolytes, NaNO 3, KNO 3, CH 3COONa, and CH 3COOK on the absorbance of MB were examined at the potential of +0.8 V versus Ag/AgCl. The decrease in MB absorbance by nitrate ions was greater than that of acetate ions. Therefore the competitive adsorption of nitrate ions was stronger than that of acetate ions. Thus, the decrease in absorbance of MB in the presence of anions demonstrates the competitive adsorption of anions. These results show that the extent of specific adsorption of electrolytes was observed by measuring the SOWG absorbance intensity of MB.

Electrocatalytic Reduction of Nitrate on Activated Rhodium Electrode Surfaces

Electrodeposited rhodium films on titanium substrates have been electrochemically activated to produce a high area surface with a specific activity for nitrate electroreduction directly to N2. The activation process involves oxidation/reduction cycles in an alkaline, KCl electrolyte containing nitrate ions. Surfaces of up to 230 times the geometric area are achieved, together with a surface morphological modification. While the active surface, once formed, is intrinsically unstable during long-term nitrate reduction, its activity can be maintained in situ by an electrochemical cycling procedure. The high area rhodium has the form of a nano-structured ‘sponge’, with a surface area of ca. 19 m2 g−1. The morphological modification is evidenced by a change in the hydrogen UPD structure, changes in the surface redox behaviour associated with OH adsorption, and a reduction in the activation energy for nitrate reduction from ca. 47 to 20 kJ mol−1. The reduction in activation energy, however, is accompanied by a decrease in the pre-exponential factor, and this apparent compensation effect results in similar rate constants on the activated and unactivated surfaces. The enhancement in the catalyst's activity for nitrate reduction results from an increase in the relative activity of nitrate reduction over water reduction. The activated catalyst sustains steady state nitrate reduction at an increased over-potential before the reaction to N2 decays, and hydrogen evolution and reduction to ammonia take place. The presence of nitrate ions is essential for the formation of the active surface, and specifically adsorbed nitrate ions and reductive intermediates are present at the surface when it is reformed. A mechanism for the elementary surface reaction steps involved in nitrate reduction, and the apparent ‘habit’ growth of the active surface phase in the nitrate containing solution is discussed.

Basic study for gas cleaning using discharge and electrophoresis

A NO x removal method using discharge plasma and electrophoresis for exhaust control was studied. The 65–50% of NO was oxidized to NO 2 or HNO 3 by the discharge plasma with specific input energy of 45 J/l. The electrophoresis was carried out to concentrate the NO 2 or HNO 3 adsorbed on the adsorbents. As a result, 80% of the adsorbed nitrate ions were found in the anode region. A combination of molecular sieve pellets of 13X and glass fiber cloth was tested for the collection of nitrate ions. The ability of simultaneous concentration of nitrate ions and sulfate ions using electrophoresis was examined.

Underpotential Deposition and Adsorption of Lead on Gold Polycrystalline Electrodes: I. XPS and TOF-SIMS Investigations in 0.1 M NaCl Electrolytes

The composition of lead chloride complex ions adsorbed during the underpotential deposition of lead on a polycrystalline gold electrode in was studied by X‐ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS). Gold electrodes were emersed at 0.3, −0.29, and −0.42 V vs. saturated calomel electrode. Then, either before or after rinsing, the surface concentrations of various species were analyzed using the two vacuum spectroscopic techniques. An adsorbed species with the stoichiometry of was present on the polycrystalline gold electrode just before the underpotential deposition (UPD) region at +0.3 V. The ejection of some adsorbed and Pb(II) occurred during the UPD Pb discharge process. A mechanism of Pb(II) adsorption and UPD is proposed which is consistent with a parallel electrochemical study. [J. Electrochem. Soc., 146, 2555 (1999)] Strong adsorption of nitrate ions was detected. © 1999 The Electrochemical Society. All rights reserved.

SNIFTIRS studies of the electrochemical double layer

Abstract In-situ IR reflection spectroscopy has been used to probe the structure of the double layer on an Au(111) electrode in solutions containing specifically adsorbed nitrate ions. The adsorbed nitrate ion is found to be bonded to the gold surface through one of its oxygen atoms. Both adsorbed nitrate ions, as well as those in the solution are found to possess C 2 v symmetry. Nitrate ions in the double layer form contact ion-pairs with hydronium ions, possibly with an extra water molecule incorporated in the ion-pair moiety. The extent of ion-pairing is found to depend on the applied potential. An indication of the onset of water chemisorption on the gold surface is also found with the present technique. On the basis of combined ATR and SNIFTIRS (subtractively normalized interfacial Fourier transform IR spectroscopy) experiments it is shown that the width of the deconvoluted nitrate band can be used to estimate the vicinity of the potential of zero charge (pzc). It was found that the pzc in 0.01 M HNO 3 is close to that observed in 0.01 M HClO 4 , and that it shifts by ca. −100 mV per pH unit due to the specific adsorption of nitrate.

On the adsorption and reduction of NO 3− ions at Au and Pt electrodes studied by in situ FTIR spectroscopy

The adsorption of nitrate ions on gold and platinum electrodes in acid solution has been studied in acidic solution using in situ FURS. It is found that nitrate is adsorbed probably with a two-fold coordination on gold electrodes as suggested by the adsórbate potential-dependent spectral feature centered between 1440 and 1460 cm −1. In addition, partial reduction of the nitrate ions at more negative potentials (ca. 0.05 V) generates nitrite ions in solution. These ions are co-adsorbed with nitrate ions in the double layer region of potentials. The nitrite ions seem to be adsorbed O-down with a one-fold or two-fold coordination. Platinum electrodes are found to be much more active catalytically to nitrate reduction than gold electrodes. The reduction of nitrate ions at potentials below 0.8 V generates an adsorbed product presenting a potential-dependent band at 1540 to 1580 cm −1 which has been identified as adsorbed NO.

Fourier transform infrared study of the adsorption and coadsorption of nitric oxide, nitrogen dioxide and ammonia on TiO 2 anatase

The adsorption and coadsorption of NO, NO 2 and NH 3 on TiO 2 anatase has been studied by Fourier-transform infrared (FT-IR) spectroscopy. Upon NO adsorption, nitrosyl species adsorbed on two different Lewis sites are observed, together with N 2O produced via the reduction of NO by Ti 3+, and NO 3- formed by oxidation of NO by Ti 4+. Adsorption of NO 2 produces several distinct adsorbed nitrate ions with different thermal stabilities. NH 3 molecularly coordinated on two different Lewis sites is observed upon NH 3 adsorption. Nitrosyls are not formed by contacting the NH 3-covered surface of TiO 2 with gaseous NO. Coadsorption of NH 3 with NO and NO 2 causes only a few perturbations, attributed to changes in the coordination of nitrates and of NH 3 species. No evidence is found for the reaction of NO x with NH 3 to 523 K, in line with the poor catalytic activity of TiO 2 in the Selective Catalytic Reduction (SCR) of NOx by NH 3.

The electroreduction of fluoropentamminocobalt(III) cation in the presence of specifically adsorbed nitrate anions

The kinetics of electroreduction of Co(NH 3) 5F 2+ cation have been studied at a Hg electrode in solutions of NaNO 3 + NaF with an ionic strength of 0.2 M. The acceleration of the reduction due to adsorption of nitrate ions could not be rationalized on the basis of the change in the average potential on the outer Helmholtz plane. Under most conditions, the acceleration was less than that predicted by the classical theory, the magnitude of the difference increasing with the extent of adsorption and with shift in electrode potential in the positive direction. The results obtained can be explained in terms of changes in the potential profiles near the electrode caused by adsorbed anions with consideration of discreteness-of-charge effects.

The effects of counter ion nature on the adsorption of nitrate ion at the mercury/solution interface

The adsorption of nitrate ion at mercury has been studied from two systems at constant ionic strength, namely, xM NaNO3 + (0.2 − x) M NaF and x M KNO3 + (0.2 − x) M KF. The surface excess due to adsorbed nitrate ions was determined from differential capacity data using a modified version of the Hurwitz–Parsons analysis which takes into consideration variation in ionic activity coefficients with solution composition. The amount of adsorbed nitrate ion at a given electrode charge density and bulk nitrate ion concentration is shown to depend markedly on both ionic strength and the nature of the counter ion at the outer Helmholtz plane; when the charge in the diffuse layer is positive, an increase in ionic strength results in more anion adsorption and vice versa. A change in the cation from Na+ to K+ also results in increased anion adsorption. The effects observed are discussed in terms of the Stern–Grahame–Levine model for ionic adsorption which is based on an electrostatic description of the charged interface with consideration of discreteness-of-charge effects.

XPS study of the interactions between aluminium metal and nitrate ions

Thin oxide films formed on aluminium in different nitrate solutions have been examined by the X-ray photoelectron spectroscopy (XPS). It has been shown that the adsorption of nitrate ions on the oxidized surface of aluminium is followed by their reduction inside the oxide film. The mechanism of this reduction process is discussed on the basis of the XPS data.

Adsorption of inorganic anions on a mercury electrode from solutions in formamide II. Adsorption of chloride and nitrate ions

Adsorption of inorganic anions on a mercury electrode from solutions in formamide II. Adsorption of chloride and nitrate ions

Ionic adsorption at the mercury—solution interface from solutions of lithium nitrate in dimethyl sulphoxide

The specific adsorption of nitrate ions at the mercury/dimethylsulphoxide interface has been determined from measurements of interfacial capacitance and corresponding activity coefficients in the system Hg/LiNO 3 in DMSO. The standard free energy of adsorption was found to be a linear function of electrode charge. The data were fitted to a virial isotherm and charge saturation was not approached. The second virial coefficient ( B ) was found to be larger than that for the comparable aqueous value and to be significantly charge dependent. The Esin and Markov coefficients were larger than the corresponding aqueous values and suggest that nitrate ions are more strongly adsorbed from this solvent than from water. No evidence for the specific adsorption of the cation was found.

Adsorption of inorganic anions on a mercury electrode from solutions in formamide II. Adsorption of chloride and nitrate ions

Specific adsorption of chloride and nitrate ions on a mercury electrode from solutions of the respective potassium salts in formamide has been studied by measurements of the double layer capacity and the interfacial tension as a function of concentration. Specific adsorption of nitrate although weak is confirmed by comparison of the results with the diffuse layer theory. Chloride is more strongly adsorbed but its behavior, as in aqueous solutions, is more complex than that of the corresponding iodide system. The results are examined in terms of a low-coverage approximation to Frumkin's isotherm at constant charge on the metal, with allowance for the variation of the diffuse layer potential, and also at constant potential across the double layer. The adsorption of chloride obeys neither form of isotherm whereas the adsorption of iodide can be described by both. Adsorbed chloride ions produce an unusually large potential difference across the inner region of the double layer which is consistent with a mean dielectric constant of 3 compared with a value of 7 calculated for the iodide system.

Ionic adsorption at the mercury-solution interface from solutions of lithium nitrate in dimethyl sulphoxide

Summary The specific adsorption of nitrate ions at the mercury/dimethylsulphoxide interface has been determined from measurements of interfacial capacitance and corresponding activity coefficients in the system Hg/LiNO3 in DMSO. The standard free energy of adsorption was found to be a linear function of electrode charge. The data were fitted to a virial isotherm and charge saturation was not approached. The second virial coefficient (B) was found to be larger than that for the comparable aqueous value and to be significantly charge dependent. The Esin and Markov coefficients were larger than the corresponding aqueous values and suggest that nitrate ions are more strongly adsorbed from this solvent than from water. No evidence for the specific adsorption of the cation was found.

THE INFLUENCE OF METAL SALTS ON THE ζ-POTENTIAL OF DEGUMMED SILK FIBRE

The ζ-potential at the interfaces between degummed silk fibre and the aqueous solutions containing a number of trivalent metal nitrates was measured by means of the streaming potential method. The trivalent metals used were Al, Ga, In, Cr, Fe, Rh, Sc, Y, La, Sm, Tb, Er and Yb.At pH 5.0, generally, the negative ζ-potential decreases with increasing concentration of metal salt. In the cases of Al, Ga, In, Cr, Fe, Rh and Sc, it reverses its sign at concentrations in the region of 10-6-10-4M and then approaches a limiting positive value which differs for each metal salt: the sequence for the reversal of charge concentrations is Fe Ga>Rh. In the cases of Al, In, Cr and Sc, with increasing concentration of metal salt, the ζ-potential decreases and nearly becomes zero at concentrations in the region of 10-6-10-5M. At higher concentrations it rises slightly. In other cases, the ζ-potential decreases with increasing concentration of metal salt and reaches a negative value. The decrease in the ζ-potential is due to the adsorption of nitrate ions: this was discussed by measuring the ζ-potential for potassium nitrate.